Reactive oxygen species (ROS) is considered a double-edged sword. The slightly elevated level of ROS helps in wound healing by inhibiting microbial infection. In contrast, excessive ROS levels in the wound site show deleterious effects on wound healing by extending the inflammation phase. Understanding the ROS-mediated molecular and biomolecular mechanisms and their effect on cellular homeostasis and inflammation thus substantially improves the possibility of exogenously augmenting and manipulating wound healing with the emerging antioxidant therapeutics. This review comprehensively delves into the relationship between ROS and critical phases of wound healing and the processes underpinning antioxidant therapies. The manuscript also discusses cutting-edge antioxidant therapeutics that act via ROS scavenging to enhance chronic wound healing.
Reactive oxygen species (ROS) is considered a double-edged sword. The slightly elevated level of ROS helps in wound healing by inhibiting microbial infection. In contrast, excessive ROS levels in the wound site show deleterious effects on wound healing by extending the inflammation phase. Understanding the ROS-mediated molecular and biomolecular mechanisms and their effect on cellular homeostasis and inflammation thus substantially improves the possibility of exogenously augmenting and manipulating wound healing with the emerging antioxidant therapeutics. This review comprehensively delves into the relationship between ROS and critical phases of wound healing and the processes underpinning antioxidant therapies. The manuscript also discusses cutting-edge antioxidant therapeutics that act via ROS scavenging to enhance chronic wound healing.
The skin is the body’s
outermost layer, protecting it from
toxic elements and serving various essential functions. When skin
is damaged, a multistep process begins that offers at least some restoration
of the afflicted skin. Wound healing is a well-known process in which
the wound recovers through three overlapping phases: inflammation,
proliferation, and remodeling.[1] The wounded
vascular system forms a platelet plug shortly after an injury or damage
to temporarily stop blood loss from the wound. In addition, the inflammatory
phase attracts a variety of immune cells, which generate pro-inflammatory
cytokines and enzymes to speed up the healing process.The slightly
elevated ROS produced during wound healing plays an
essential role in avoiding bacteria and other microbial infections.[2] ROS also plays a crucial role in intracellular
signaling. The production of elevated level of different ROS at the
wound site from the different cells are known as a respiratory burst.
The production of a higher level of hydroxyl radicals (OH•), superoxide (O–2), hydrogen peroxide
(H2O2), iron, and copper ions causes significant
damage to the cells.[3] Oxidative stress
caused due to a rise in ROS levels induces tissue damage and cell
death.[4] Antioxidant therapies can considerably
reduce the elevated level of ROS produced during the wound healing
phases, making them a viable treatment option for nonhealing wounds.
This review delves into the relationship between ROS and essential
phases of wound healing and the processes underpinning antioxidant
therapies. We also spoke about some of the most cutting-edge, innovative
antioxidant therapies for quick wound healing.
Link between the Free Radicals in Cellular Homeostasis
during Wound Healing
Adenosine triphosphate (ATP) synthesis
during mitochondrial oxidative
phosphorylation requires oxygen as a substrate for energy production
in the cells. Moreover, rapid wound healing also needs a great deal
of energy. As a result, ROS and its derivatives may play an essential
part in wound healing. The ROS family includes oxygen derivatives
such as OH•, peroxide, superoxide anion, hydrogen
peroxide (H2O2), etc. In mitochondria during
ATP production, endogenous ROS species are generated due to enzymatic
activity. During nonhealing wounds, these ROS are produced in a considerabe
amount. Further, these elevated ROS scavenges electrons from neighboring
molecules or cells through oxidation and causes cellular damage. According
to research, a small amount of ROS keeps cells in equilibrium and
elevated levels of ROS show deleterious effects on wound healing.Generally, cell function and homeostasis are maintained when the
ROS level remains constant at the baseline level. Increased production
of ROS activates pro-apoptotic proteins, resulting in cell death and
necrosis.[5] ROS also acts in charge of vasoconstriction
and vasorelaxation. Furthermore, nitric oxide (NO) is a ROS that naturally
combines with various molecules (e.g., oxygen, transition metals,
s-nitrosothiols, other ROS, and ONOO–) to function
as an antioxidant. Many cells, including fibroblasts, keratinocytes,
platelets, endothelial cells, and macrophages, employ these radicals
during wound healing.[6] The role of a moderate
level of ROS in various phases of wound healing through cellular interactions
are depicted in Figure .
Figure 1
ROS and their role in the various process of wound healing.
ROS and their role in the various process of wound healing.Oxygen stimulates re-epithelialization, wound healing,
keratinocyte
differentiation, fibroblast proliferation, and migration, angiogenesis,
collagen production, and wound contraction during tissue regeneration.
Optimal oxygenation of cells and tissues is essential for tissue regeneration
and wound healing. Choi et al. prepared oxygen-releasing polymeric
microspheres and embedded them in alginate-based hydrogels. Double
emulsion was used to incorporate H2O2 into PLGA
to make oxygen-releasing microspheres (ORMs). The alginate-based hydrogel
was implanted with H2O2–PLGA microspheres
to generate an oxygen-releasing sponge (ORHS). In vivo research tested the ORHS for wound healing safety and effectiveness.
Experiments demonstrated that oxygen produced from ORM and ORHS promotes
cell growth and wound healing. The ORM may give oxygen to cells and
tissues that need it, while the ORHS can heal wounds by enhancing
angiogenesis with oxygen. Oxygen-releasing polymeric microspheres
and hydrogel scaffolds offers immense promise for tissue engineering
applications requiring oxygen.[7]The
earliest step in battling invading pathogens and boosting cellular
signal transduction pathways in response to skin injury starts with
the increased ROS generation.[8] Nuclear
factor E2 p45-related factor 2 (Nrf2) supports wound healing in damaged
and inflammatory tissue.[9] This shows that
moderate level of epithelial ROS works as a sensor for Nrf2 expression.
ROS build-up prevents wound infections.[10] NO- and H2S-driven signals may also modulate the Nrf2
transcription factor.[11]Nrf2/Keap1
protects against ROS, electrophilic, and proteotoxic
stress.[12] Nrf2 reduces cellular stress
and restores redox equilibrium by regulating the expression of over
1000 genes, including HMOX1, TRX, GSR, Gclc, Gclm, SOD1, and catalase.[13] Nrf2 signaling also governs essential cellular
processes such as apoptosis, autophagy, angiogenesis, proliferation,
and cell migration.[14] Nrf2 targets antioxidant
enzymes, detoxifying enzymes, proteases, chaperones, inflammatory
factors, and growth factors.[15] NO, siRNA,
bee venom, and other active substances are Nrf2 activators that enhance
wound healing.[8]Low levels of caNrf2
in keratinocytes protect mice against UVB-induced
cell death.[16] More robust expression of
caNrf2, reflecting endogenous Nrf2 activation by chemical activators,
induced skin abnormalities, including moderate inflammation, hyperkeratosis,
sebaceous gland enlargement, and epidermal barrier function deficiencies.[17] However, these animals had quicker wound closure
due to increased re-epithelialization. While caNrf2 expression promoted
wound healing, keratinocyte migration and proliferation in the wound
epidermis were unaffected. CaNrf2 promoted hair follicle and sebaceous
gland growth in the wound periphery.[10] Instead,
caNRF2 increased hair follicle bulge, junctional zone, and upper isthmus
stem cells. All of these processes were previously shown to contribute
to wound re-epithelialization.[18] The extra
pool of cells formed near the wound edge, possibly by stem cell growth,
appears to serve as a reserve of cells to move into and repopulate
the wound. Nrf2-mediated epigen expression may stimulate stem cell
growth. This epidermal growth factor family member, encoded by Nrf2,[17] promotes hair follicle stem cell proliferation
in vivo.[19] Faster wound closure in caNrf2-transgenic
animals needed significant Nrf2 activation since mice expressing lower
amounts of the transgene failed to demonstrate differences despite
a minor increase in Nrf2 target gene expression.[10] These observations suggest that Nrf2 activation may promote
wound re-epithelialization and that the degree of activation may be
significant when assessing its efficacy.Effect of Nrf2’s
on fibroblasts have also been studied.
Skin fibroblasts produce cytokines and growth factors, deposit ECM,
and constrict wounds.[20] Activating Nrf2
in fibroblasts causes senescence in both in vitro and in vivo conditions.
Nrf2-mediated deposition of an altered matrisome with high quantities
of senescence-promoting factor plasminogen activator inhibitor-1 drove
this (PAI-1, serpine1). Accelerated senescence was found in both caNrf2-expressing
cells and wild-type fibroblasts treated with the Nrf2 activator tert-butylhydroquinone.[21] Senescent
cells offer key biochemical signals to surrounding cells through a
growth-promoting secretome called the senescence-associated secretory
phenotype (SASP). Senescent cells aid in wound healing.[22] caNrf2 fibroblasts secrete factors that promote
keratinocyte growth.[21] Mice expressing
caNrf2 in fibroblasts had quicker wound closure due to increased keratinocyte
proliferation in the wound epidermis.
ROS and Its Direct Connection with Inflammation
in Wound Healing
According to the previously reported studies,
ROS aid in various
stages of tissue repair. ROS is a secondary messenger for various
immunocytes and nonlymphoid cells involved in wound healing. They
have a remarkable ability to modulate angiogenesis and blood perfusion
in the wound healing domain.[8] Furthermore,
they have evolved into a critical coordinator in deploying lymphoid
cells to the site of interest (i.e., wound regions) and effective
tissue recovery. A moderate level of ROS generation is essential for
fighting microbes and cell survival signaling. Furthermore, both increased
and decreased ROS levels can cause oxidative damage, which can delay
the healing process of chronic wounds.[23,24]Inflammation
plays a critical role in the initiation of wound healing.[25] An elevated and prolonged ROS production at
the wound site leads to chronic inflammation. Deregulation of the
inflammatory phase and chronic response cause tissue damage.[26] Fascinatingly, re-establishing the ROS equilibrium
can significantly improve the damaged skin condition. Excess ROS in
injured skin tissue activates transcription factors such as activator
protein 1 (AP-1), mitogen-activated protein kinase (MAPK), nuclear
factor kappa B (NF-κB), and nuclear factor erythroid-derived
2-like 2 (Nrf2).[3,27,28] Among these transcription factors, Nrf2 controls the transcription
of the antioxidant gene by binding to the antioxidant response element
(ARE) to increase the transcription of its target genes.[29,30] Nrf2 is primarily involved in defending against high levels of endogenous
ROS build-up, which aids in wound healing. According to reports, Nrf2
overexpression can significantly protect cells against cellular damage
induced by oxidative stress. Furthermore, studies have shown that
Nrf2 overexpression is critical for controlling the re-epithelialization
process.[30,31]In contrast, NF-κB and AP-1
activation increased the number
of matrices metalloproteins (MMPs) in dermal fibroblasts, leading
to extracellular matrix protein breakdown (ECM), which leads to the
delay in the wound healing process. However, the published studies
indicate Nrf2’s beneficial function in healing chronic wounds.[31,32] In diabetic wounds, persistent pro-inflammatory macrophages and
dysregulation of the wound healing inflammatory phase link to persistent
nod-like receptor (NLR)-3-containing inflammasome activity.[33] NLR family pyrin domain-containing 3 (NLRP3)
demonstrates innate immune responses after sensing damage-associated
molecular patterns (DAMPs) and pathogen-associated molecular patterns
(PAMPs) via NLR receptors. When activated by DAMPs and PAMPs, NLRP3
interacts with the apoptosis-associated spike-like protein (ASC).
Following that, ASC interacts with procaspase-1 to generate NLRP3
inflammasomes. Thus, the created complex promotes proteolytic cleavage,
which aids in expressing interleukins (IL-1 and IL-18), which are
responsible for various inflammatory and immunological activities
(Figure ). Inflammasomes
have multiple features, including an autoimmune impact, antibacterial
activity, and autoinflammatory reactions.
Figure 2
Mitochondria dysfunction
mediated activation of the inflammasome.
Damaged mitochondria secrete molecular patterns identified by the
cytosolic and membrane receptors such as toll-like receptors (TLR)
9. NLRP3 inflammasomes get activated by interacting with various responses,
including DAMPs. Further, the NLRP3 forms caspase activation and recruitment
domain (CARD) with ASC and CASP1 called inflammasomes. Caspase-1 stimulates
the inflammasome complex for activation, and the activated inflammasomes
help convert the pro-IL-1β and pro-IL-18 into matured forms.
Mitochondrial DNA (mtDNA) formyl proteins, ATP, and mitochondria ROS
also help to start the NLRP3 inflammasomes directly or indirectly
by receptor-mediated (FPR1, P2RX7). TLR9 specifically interacts with
the mitochondrial DNA motifs and activates the signaling cascades
resulting in a pro-inflammatory cytokine response. TLR-9, toll-like
receptor-9; CARD, caspase activation, and recruitment domain; CASP1,
caspase-1; DAMPs, danger-associated molecular patterns; IL, interleukin;
mtDNA, mitochondrial DNA; mtROS, mitochondrial reactive oxygen species;
FPR1, formyl peptide receptor 1; P2RX7, P2X purinoceptor.
Mitochondria dysfunction
mediated activation of the inflammasome.
Damaged mitochondria secrete molecular patterns identified by the
cytosolic and membrane receptors such as toll-like receptors (TLR)
9. NLRP3 inflammasomes get activated by interacting with various responses,
including DAMPs. Further, the NLRP3 forms caspase activation and recruitment
domain (CARD) with ASC and CASP1 called inflammasomes. Caspase-1 stimulates
the inflammasome complex for activation, and the activated inflammasomes
help convert the pro-IL-1β and pro-IL-18 into matured forms.
Mitochondrial DNA (mtDNA) formyl proteins, ATP, and mitochondria ROS
also help to start the NLRP3 inflammasomes directly or indirectly
by receptor-mediated (FPR1, P2RX7). TLR9 specifically interacts with
the mitochondrial DNA motifs and activates the signaling cascades
resulting in a pro-inflammatory cytokine response. TLR-9, toll-like
receptor-9; CARD, caspase activation, and recruitment domain; CASP1,
caspase-1; DAMPs, danger-associated molecular patterns; IL, interleukin;
mtDNA, mitochondrial DNA; mtROS, mitochondrial reactive oxygen species;
FPR1, formyl peptide receptor 1; P2RX7, P2X purinoceptor.
Biomolecular Links of Oxidative Stress with
Wound Healing
Due to ROS’s limited half-life, it is
challenging to determine
their concentration in vivo. Recently, efforts were made to determine
the ROS concentration in the murine wound models at the wound site
using electrochemical techniques. The study findings indicated a low
concentration of H2O2 in the wound (range from
100 to 250 μM). The early wound healing phase (day 2 following
damage) had a greater concentration of H2O2 than
the later wound healing phase. In addition, the dihydroethidium staining
experiment reveals the presence of superoxide as well as H2O2 near the wound margins.[34] Another study found that superoxide levels peaked 2 days postwounding
in the inflammatory phase.[35] Superoxide
ion generation was reduced 3-fold in the mice with the missing Rac2
gene compared to the control animals. In these mice, a shallow level
of superoxide production at the wound site leads to compromised wound
closure. Thus, these findings suggest that a modest level of ROS is
essential for the normal wound healing process.Most studies
used indirect measurement of lipids, deoxyribonucleic
acid (DNA), and oxidative protein products to determine ROS concentrations
at the wound site.[36] Immunohistochemistry
was also used to assess the formation of 4-hydroxy-2-nonenal (4-HNE)
due to lipid peroxidation. Co-immunostaining reveals 4-HNE as the
primary lipid peroxidation product in neutrophils. Further, a respiratory
burst of these inflammatory cells produces superoxide, which increases
superoxide generation and exaggerates lipid peroxidation.[35]Malondialdehyde (MDA) is a byproduct of
lipid peroxidation caused
by various oxidative stressors.[37] Elevated
levels of the free radicals promote over production of MDA.[38] These elevated levels of MDA promote pro-inflammatory
molecules. This might lead to increased lymphocyte activation, which
worsens diabetic problems.[39] Musalmah et
al. tested the antioxidant activity of α-tocopherol on the plasma
MDA levels and its role in normal and diabetic wound closure rate
in the rats. The results showed that α-tocopherol decreased
plasma malondialdehyde, enhanced glutathione peroxidase activity,
and sped wound healing in rats.[40]Gupta et al. found that compared to control animals, significant
MDA levels are present in the damaged wounds. Surprisingly, no significant
variation in MDA levels was seen in this investigation in both chronic
and acute wound fluids.[41] Another fatty
acid peroxidation product is 8-isoprostanes, found in greater concentrations
in the fluid of chronic wounds than in acute human wounds.[42] These findings show that oxidative stress plays
a significant role in chronic ulcers, causing the inflammatory phase
to continue.[43] Also, the considerable rise
in the allantoin to the uric acid proportion in chronic wounds strengthens
the hypothesis. This ratio is the indication of oxidative stress.[44]Another possible measure for understanding
oxidative stress is
to measure the oxidized protein level at the wound site in preclinical
animal models. The Oxyblot (protein standard) revealed a considerable
increase in oxidized protein levels in chronic wounds compared to
healthy skin. Importantly, oxidized proteins were found in more significant
quantities in male mice than in female mice.[45] The rise in oxidative protein levels may contribute to more inflammation
and worse wound health in the male mice.[46] However, reactive protein concentrations were higher in acute wound
fluids than in chronic wound fluids. More research is needed to flesh
out the findings. Another oxidative protein marker that the immunohistochemistry
assay can detect is nitrotyrosine. Reactive molecules bind to the
protein’s tyrosine residues, resulting in the formation of
3-nitrotyrosine.Wound healing is governed by various hormones,
growth factors,
and cytokines.[47] Recent research has found
that ROS and NO are also essential regulators of wound healing.[27] In general, ROS protects against invading pathogens.
In addition, a modest level of ROS also participates in intracellular
signaling pathways.[48] For example, injecting
H2O2 in small amounts into a wound enhances
wound angiogenesis.[34] On the other hand,
surplus levels of ROS will be detrimental to wound healing due to
their high reactivity.[13]
Mechanistic Look at Antioxidants and Their Role
in Controlling Oxidative Stress
According to research and
clinical data, antioxidants, and anti-inflammatory
approaches have shown potential effects in the treatment of wounds.
Currently, among all available antioxidant techniques, mitochondrial-targeted
antioxidants have piqued the interest of researchers. Most notably,
peptides used to target mitochondria have shown enormous promise.
Elamipretide, for example, has a solid ability to alleviate mitochondrial
dysfunction and abnormal inflammatory effects via stimulation of nucleotide-attached
oligomerization domain (NOD)-like receptors (e.g., NLRP3), inflammasome,
inhibition of the NF-κB signaling pathway, and so on.[23] The presence of exceptionally high levels of
ROS in tissues (for example, skin) promotes the activation of specific
types of transcription factors such as Nrf2, AP-1, NF-κB, and
MAPK pathways.Overactivation of the NF-κB pathway, on
the other hand, impedes
wound healing in type 2 diabetes patients. Some pioneering studies
indicated that miR-146a and SIRT1 treatment targets and limits the
previously active NF-κB pathway. However, Nrf2 is the primary
controller of the antioxidant gene that regulates the transcription
of cytoprotective genes by binding to the critical ARE and initiating
the transcription via its target genes.[29,30] Furthermore,
studies show that antioxidants have a role in the stimulating Nrf2/Kelch-like
ECH-associated protein-1 (KEAP1) pathway, particularly in the healing
of diabetic wounds.These findings imply that addressing Nrf2
and KEAP1 can be effective
with gene therapy and molecular wound repair in diabetes patients
(Figure A,B).
Figure 3
Two major pathways
in antioxidant therapy “Nrf2 pathway
and the NFκB pathway”. (A) Under unstressed events, KEAP1
interrelates with Nrf2 and actin cytoskeleton to retain Nrf2 in dormant
form and thus encourage both ubiquitination and deprivation of Nrf2.
In addition, oxidative stress not only separates Nrf2 from KEAP1 but
also translocates it to the nucleus. In the nucleus, Nrf2 heterodimerizes
with Maf. It produces Nrf2-Maf heterodimer, which further attaches
to ARE to form metabolic genes. For instance, NQO1, heme oxygenase-1
(HO-1), GSTs, GCL, and manganese superoxide dismutase (MnSOD) produce
antioxidant effects. Additionally, oxidative stress is controlled
via the activation of the Nrf2 pathway. In addition, the levels of
KEAP1 are lowered by the siKEAP1 after loading them into RISC and
by eliminating complementary mRNA of the KEAP1. Furthermore, Nrf2
activators, for instance, SF, CA, DMF, RTA408, and genistein, also
induce the Nrf2 pathway and improve oxidative stress. (B) In resting
conditions, NFκB dimers develop a complex with IkB protein in
the cytoplasm. TNF-α, an inflammatory signal, encourages phosphorylation
of IkB protein due to the involvement of IKK, which leads to ubiquitination
and ultimately degradation of IkB. In addition, after moving active
NFκB into the nucleus, it stimulates target genes such as TNF-α,
NADPH oxidase (NOX)-2, cyclooxygenase-2 (COX-2), inducible nitric
oxide synthase (iNOS), IL-6, and IL-1b causing both oxidative stresses
as well as inflammation. Moreover, oxidative stress is controlled
by hindering the NFκB pathway. Furthermore, MiR-146a shows aptitude
toward targeting, inhibiting TRAF6, impeding the stimulation of IKK,
and the NFκB pathway. Finally, SIRT1 activators, such as SRT1720,
resveratrol, and berberine, overcome attaching of NFκB to inflammation-initiating
gene promoters and their transcriptional events via stimulating SIRT1.
RISC, RNA-induced silencing complex; TRAF6, tumor necrosis factor
receptor-associated factor 6; ARE, antioxidant response element.
Two major pathways
in antioxidant therapy “Nrf2 pathway
and the NFκB pathway”. (A) Under unstressed events, KEAP1
interrelates with Nrf2 and actin cytoskeleton to retain Nrf2 in dormant
form and thus encourage both ubiquitination and deprivation of Nrf2.
In addition, oxidative stress not only separates Nrf2 from KEAP1 but
also translocates it to the nucleus. In the nucleus, Nrf2 heterodimerizes
with Maf. It produces Nrf2-Maf heterodimer, which further attaches
to ARE to form metabolic genes. For instance, NQO1, heme oxygenase-1
(HO-1), GSTs, GCL, and manganese superoxide dismutase (MnSOD) produce
antioxidant effects. Additionally, oxidative stress is controlled
via the activation of the Nrf2 pathway. In addition, the levels of
KEAP1 are lowered by the siKEAP1 after loading them into RISC and
by eliminating complementary mRNA of the KEAP1. Furthermore, Nrf2
activators, for instance, SF, CA, DMF, RTA408, and genistein, also
induce the Nrf2 pathway and improve oxidative stress. (B) In resting
conditions, NFκB dimers develop a complex with IkB protein in
the cytoplasm. TNF-α, an inflammatory signal, encourages phosphorylation
of IkB protein due to the involvement of IKK, which leads to ubiquitination
and ultimately degradation of IkB. In addition, after moving active
NFκB into the nucleus, it stimulates target genes such as TNF-α,
NADPH oxidase (NOX)-2, cyclooxygenase-2 (COX-2), inducible nitric
oxide synthase (iNOS), IL-6, and IL-1b causing both oxidative stresses
as well as inflammation. Moreover, oxidative stress is controlled
by hindering the NFκB pathway. Furthermore, MiR-146a shows aptitude
toward targeting, inhibiting TRAF6, impeding the stimulation of IKK,
and the NFκB pathway. Finally, SIRT1 activators, such as SRT1720,
resveratrol, and berberine, overcome attaching of NFκB to inflammation-initiating
gene promoters and their transcriptional events via stimulating SIRT1.
RISC, RNA-induced silencing complex; TRAF6, tumor necrosis factor
receptor-associated factor 6; ARE, antioxidant response element.Most patients (diabetic and nondiabetic) with oxidative
stress-dependent
long-term wounds are treated with antibiotics, moisture dressing,
pressure off-loading, and surgical excision of the lesion.[49] Current research focuses on specific strategies
for improving the recovery speed of chronic wounds, such as using
collagen-derived tissue-engineered grafts, various growth factors
for topical use, and the engagement of different cells obtained through
bone marrow (e.g., endothelial/epithelial cells), etc. Precise regulation
of ROS expression using antioxidants and antioxidative enzymes can
also significantly reduce oxidative stress-induced cellular harm.[50]
Emerging Antioxidant Novel Therapeutics for
Combating the Oxidative Stress in Wound Healing
The elevated
levels of ROS in the wound are managed by antioxidants
such as phytochemicals, endogenous compounds, peptides, and polymers
are commonly employed. Several antioxidants effectively control the
oxidative stress in the wound and aid wound healing. A detailed overview
of the antioxidant phytochemicals in wound healing applications has
been explicitly discussed elsewhere.[51−56] This work examined the innovative antioxidant techniques used for
quick wound healing in recent years. Figure depicts several unique antioxidant treatment
methods for fast wound healing.
Figure 4
Emerging novel antioxidant therapeutic
approaches for rapid wound
healing.
Emerging novel antioxidant therapeutic
approaches for rapid wound
healing.
Leading Antioxidative Enzymes for Wound Healing
Antioxidant enzymes help with oxidative stress and diabetic wounds.
SOD, catalase, glutathione peroxidase, and heme oxygenase are antioxidant
enzymes.[57] Antioxidant enzymes have been
used in diabetic wound healing in recent years.
Superoxide Dismutase
Superoxide
dismutase is an antioxidant enzyme involved in oxidative stress. As
an endogenous factor capable of scavenging free radicals, SOD catalyzes
the breakdown of superoxide radicals into hydrogen peroxide which
is transformed into water and oxygen.[58] However, SOD is produced at insufficient levels in diabetic wound
healing, resulting in increased oxidative stress and poor wound healing.
In recent years, research have documented usage of SOD in diabetic
wound healing, with SOD-loaded hydrogels are successfully encouraging
the repair of chronic diabetic wounds.[59]In a murine model with full-thickness burns, intravenous Cu/Zn-SOD
at 10 mg/kg (poly(butyl ester) bound SOD) affected plasma thiobarbituric
acid reactive (TBAR) metabolite after prewound dosing.[60] At 3 h after burn, SOD-treated mice showed lower
plasma TBAR metabolite levels than saline-treated animals. SOD-treated
animals survived burns 7 days longer than control rats.
Glutathione Peroxidase (GPX)
GPX
proteins decrease H2O2 and organic peroxides
glutathione-dependently. Humans have eight GPX genes (GPX1–8).
GPX1–4 are selenoproteins with a selenocysteine (SeCys) residue
in the catalytic core.[61] Because GPX needs
glutathione as an electron donor, a wound lesion should reduce glutathione
levels and GPX activity.[62]GPX1 mRNA
is elevated in a wound lesion,[63] although
GPX1 protein levels are low in damaged skin.[64] Normal rat wounds have lower protein and GPX levels.[64] Immunocompromised rats had similar outcomes.[65] Alkylation or nitric oxide-dependent oxidation
of SeCys lowers GPX activity, but high H2O2 and
a SOD1 deficit convert SeCys to dehydroalanine, causing irreversible
inactivation and degradation.[66] GPX1 protein
levels are elevated between days 3 and 7 following a cutaneous injury,
according to another research.[67] Thus,
our existing evidence on GPX1 protein levels after injury is inconsistent,
and it is not apparent what explains the disparity.Some GPX
family members need selenium for SeCys biosynthesis and
translational inclusion.[68] Selenium reduces
GPX1 protein abundance. A quarter of trauma patients with skin wound
healing abnormalities had low serum selenium,[69] confirming GPX’s role in etiology. Selenium may convert macrophages
from M1, which creates ROS, to M2, which stimulates cell growth.[70] GPX1-deficient animals may convert macrophages
to M2. Selenium may work independently of GPX production and activity.
Selenium may be used to treat wound healing issues, albeit the process
requires further study.
Heme Oxygenases (HO)
HO degrades
heme to biliverdin, iron, and CO and fights oxidative damage. Biliverdin
reductase converts biliverdin to bilirubin. Appropriate quantities
of bilirubin operate as a powerful antioxidant in the blood.HO-1 is inducible by oxidative stress and hypoxia.[71] HO-1 mRNA and protein are elevated in wounds, suggesting
that HO-1 protects against ROS by producing bilirubin.[72] HO-1 knockout mice demonstrate delayed wound
healing due to poor re-epithelialization and angiogenesis.[73]HO-1 regulates diabetic wound healing,
according to studies. Hemin,
a potent inducer of HO-1, may expedite wound healing in diabetic rat
wounds by lowering inflammatory cytokines including TNF- and IL-6,
boosting antioxidants, and encouraging angiogenesis.[74] HO-1 inhibitor in-protoporphyrin IX (SnPPIX) worsened oxidative
stress and delayed wound closure in nondiabetic mice. Recent investigations
corroborate HO-1’s usefulness in diabetic wound healing.[75]
Antioxidant Peptides with Potential for Wound
Healing
A slew of research back up the idea that antioxidant
and antimicrobial peptides enhance wound healing in the skin through
various mechanisms, including neutralizing the oxidative species,
regulating cytokine production, cell migration, proliferation, and,
in some circumstances, angiogenesis.[76] For
example, by activating the epidermal growth factor in human skin,
these peptides cause the expression of human-defensin (hBD)-2 and
boost cytokine production in keratinocytes and cell migration.[77] The recent finding of the antioxidant peptides
in wound healing suggests that cathelicidins are essential in enhancing
the host defensive system. Cathelicidins are more abundant invertebrates
than amphibians. Some cathelicidins have recently exhibited possible
antioxidant action in wound healing activities. Gj-CATH3, derived
from Gekko Japonicus, is a significant example of a cathelicidin peptide.
In vitro investigations demonstrated that they had a high antioxidant
capacity. However, their application does not emerge because of the
high manufacturing cost and related toxicity.Cai et al. created
a plethora of analogues for the Gj-CATH3 short peptide to improve
cell sensitivity. 2,2′-Azinobis-3-ethylbenzthiazoline-6-sulfonic
acid (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay results
showed that the two analogues of the Gj-CATH3 such as Gj-CATH3-(38–42),
and Gj-CATH3-(33–42)-peptide had high antioxidant activity.
Cytotoxic and hemolytic experiments, on the other hand, revealed much-decreased
cell toxicity and hemolysis when compared to Gj-CATH3. Further in
vitro cell line investigations on HaCaT cells showed that cell proliferation
had improved significantly. On the other hand, preclinical trials
revealed robust wound healing activity and increased superoxide dismutase
(SOD) activity. Treatment with Gj-CATH3 derivatives such as Gj-CATH3-(38–42)-peptide
and Gj-CATH3-(33–42)-peptides resulted in much lower MDA concentrations
in the excisional wound model tissues. According to the authors, this
was the first study to look at the wound healing function of cathelicidins.
This study adds to the interest in the research of cathelicidins as
an alternative wound healing therapy.[78]Similarly, Cao et al. discovered cathelicidin-OA1 from Odorrana andersonii, an antioxidant cathelicidin. This peptide’s
functional investigation found that it lacked antibacterial, hemolytic,
and poisonous properties. However, cathelicidin-OA1 demonstrated considerable
antioxidant activity in the ABTS+ and DPPH tests. Furthermore,
in vitro tests on HaCaT and fibroblasts revealed enhanced cell proliferation
in a dose-dependent and time-dependent manner. Cathelicidin-OA1 was
used to treat full-thickness wounds in mice and displayed improved
wound healing.Furthermore, at lower concentrations, the study
found dose-dependent
wound healing activity. Histopathological findings revealed that the
peptide also enhanced tissue re-epithelialization and granulation
during the early stages of wound healing. Interestingly, granulation
tissue production dramatically decreases in the later stages of wound
healing. Compared to control and epidermal growth factor (EGF) treated
rats, cathelicidin-OA1 treated rats displayed vigorous wound healing
activity. Furthermore, wound healing aids by a transient increase
in tumor necrotic factor (TNF-α) production following a protein
therapy. This may aid in releasing growth factors and the recruitment
of cells at the wound site. Furthermore, increased expression of transforming
growth factor (TGF-β) leads to faster wound healing. Overall,
the suggested peptide aids in the recruitment of macrophages, consequently
increasing TNF-α and TGF-β production and, as a result,
the potential wound healing activity.[79]Wound infections cause inflammation and immunological responses,
which delay wound healing and cause increased tissue damage.[80] Furthermore, a disproportionate quantity of
ROS in infected wounds causes an imbalance in the antioxidant defense
system, impacting inflammatory responses, inhibiting angiogenesis,
and slowing wound regeneration.[81] However,
treating wounds with ROS scavenging material increased the therapeutic
effect with rapid wound healing. Dopamine-containing compounds with
intrinsic antibacterial and ROS scavenging action treat therapeutically
relevant infected wounds. Dopamine conjugation with catechols benefits
ROS scavenging[38] by enhancing dopamine’s
dose-dependent antioxidant capacity.Hussain et al. created
a dopamine-substituted multidomain peptide
(DAP) with various favorable wound healing properties. DAP contains
unique qualities such as antibacterial activity, ROS scavenging activity,
and firm skin adherence. DAP has the potential to produce sheets comprising
hydrogels with dopamine at the surface (Figure a). Adding multivalent ions or exposing hydrogel
to UV radiation improves the mechanical characteristics of the hydrogel.
Examination of DAP hydrogels for antimicrobial capabilities discovers
that DAP exhibits broad-spectrum antibacterial activities. This broad-spectrum
antibacterial action attributes to the DAP’s positively charged
lysine residues and sheet formation. The OH radical clearance test
analyzes the DAP’s ROS scavenging activity and discovers the
scavenging impact of the DAP is dose-dependent.
Figure 5
Antioxidant and wound
healing activity of DAP: (a) Chemical structure
and self-assembled structural alignment of DAP; (b) percentage cell
viability, mean fluorescence intensity, and live/dead assay for biocompatibility
estimation of DAP; (c) photographs of wound images and their respective
wound closure rates; (d) bacterial burden isolated from the infected
wound in different groups at days 2 and 4 and quantitative analysis
of the bacterial inhibition by various treatment at days 2 and 4;
(e) immunohistological evaluation of different treatment groups H&E,
IL-6, and TNF-α staining on day 6 and H&E, Masson’s
trichrome, and α-smooth muscle actin (α-SMA) staining
on day 14, wound re-epithelialization, number of a blood vessel per
area, and fraction of collagen volume in wounded tissue. Adapted with
the permissions from ref (82). Copyright 2021 American Chemical Society.
Antioxidant and wound
healing activity of DAP: (a) Chemical structure
and self-assembled structural alignment of DAP; (b) percentage cell
viability, mean fluorescence intensity, and live/dead assay for biocompatibility
estimation of DAP; (c) photographs of wound images and their respective
wound closure rates; (d) bacterial burden isolated from the infected
wound in different groups at days 2 and 4 and quantitative analysis
of the bacterial inhibition by various treatment at days 2 and 4;
(e) immunohistological evaluation of different treatment groups H&E,
IL-6, and TNF-α staining on day 6 and H&E, Masson’s
trichrome, and α-smooth muscle actin (α-SMA) staining
on day 14, wound re-epithelialization, number of a blood vessel per
area, and fraction of collagen volume in wounded tissue. Adapted with
the permissions from ref (82). Copyright 2021 American Chemical Society.Furthermore, at 2 mg/mL, DAP had the most incredible
scavenging
action. Compared to the hydrocolloid treatment, 3T3 fibroblast cells
treated with the DAP enhanced significant cell proliferation (Figure b). Effective wound
healing was seen when this DAP was administered to the wounds in a
full-thickness model of mice (Figure c). A brief inflammatory phase was also detected due
to the DAP’s natural antibacterial and antioxidant action (Figure d). On day 6 of therapy,
immunohistochemistry examination revealed significantly fewer pro-inflammatory
markers such as IL-6 and TNF-α. In the DAP-treated rats, substantial
blood vessel development and collagen deposition were observed (Figure e). This research
suggests that peptides with engineered antimicrobial and antioxidant
properties can scavenge ROS, reduce the bacterial burden at the wound
site, reduce wound closure time, promote granular tissue formation,
improve collagen synthesis, and rapid vascularization for rapid wound
healing.[82]Several studies have shown
that fish and their byproducts have
wound healing properties. The wound healing activity of the fish and
its products is primarily related to the antioxidant capacity of the
peptides found in them.[83] Potential antioxidant
peptides can aid wound healing by neutralizing ROS, acting as a chelator,
or decreasing lipid peroxidation.[84] However,
the in vivo antioxidant capacity of the many peptides is yet unknown.
The KEAP1-Nrf2 signaling pathway was identified as one of the most
plausible explanations in several investigations for wound healing
activity of the antioxidant peptides.[85] This pathway plays a critical regulatory function in displaying
the cytoprotective impact on oxidative stress. Nrf2 plays an essential
role in the cellular antioxidant process; nevertheless, KEAP1 promotes
Nrf2 degradation.[86] As a result, antioxidant
peptides that can interact with KEAP1 and block the formation of the
Keasp1-Nrf2 complex can potentially boost antioxidant activity in
vivo.[87]Zhang et al. isolated a novel
antioxidant peptide after digesting
the snakehead with simulated gastrointestinal fluid. To study the
antioxidant potential of newly isolated peptides, antioxidant tests
such as DPPH and hydroxyl radical assays were performed. In the DPPH
experiment, a peptide having the sequences SDGSNIHFPN and PGMLGGSPPGLLGGSPP
had the best antioxidant potential among the four new peptides tested.
In silico molecular docking of peptides with KEAP1 indicated an acceptable
ligand binding efficacy. Furthermore, the cell viability findings
revealed cytoprotective activity against H2O2-treated cells. This study discovered that peptides could not only
operate as possible new antioxidants by stimulating the KEAP1-Nrf2
signaling but also be exploited as potential treatments for fast wound
healing.[88]
Nanomaterials That Trap Free Radicals for
Wound Healing
Many diseases, including cancer, inflammatory
disorders, and neurological problems, are caused by an imbalance in
free radical production in the human body.[89] Endogenous enzymes such as glutathione (GSH) peroxidase, superoxide
dismutase (SOD), catalase, and others have successfully reduced free
radical levels. Scavengers of free radicals may interact with free
radicals to interrupt the peroxidation chain events. However, significantly
high quantities of free radicals (e.g., O2-) can inhibit
their action. As the illness worsens, it cannot replenish an appropriate
amount of these enzymes. As a result, highly biocompatible synthetic
antioxidant materials are necessary to fight this problem. Polydopamine
(PDA) contains antioxidation characteristics such as melanin. PDA’s
antioxidant mechanism is currently being studied due to its intricacy.
The free-radical scavenging mechanism of PDA may be connected to the
redox chemistry of the polycatechol structure, lifetime of inner radical,
and rapid energy transfer. The catechol may quench free radicals by
giving hydrogen atoms on the phenolic hydroxyl group and reduce specific
molecules by electron transfer, generating a stable quinone structure
via the interaction of generated phenoxyl radicals and second quenching
free radicals.[90] PDA’s ROS-scavenging
capacity is frequently used in oxidative stress-induced disease treatment.
Polydopamine (PDA) nanoparticles (NPs) are well-known for scavenging
free radicals and are employed to neutralize a range of ROS types.[91]Jing et al. used a bottom-up strategy
to create innovative PDA 2D nanosheets (NSs) (PDA NSs). This non-enzymatic
NS exhibits outstanding free radical scavenging action against a broad
spectrum of free radicals, including O2–, ABTS+, and DPPH. Furthermore, PDA NSs demonstrated considerable
antioxidant activity against O2–free
radicals. Aside from that, PDA NSs have anti-inflammatory properties.
PDA NSs were administered to 14 mm full-thickness damaged rat models
to test if they may speed up wound healing. Before being investigated
for wound healing capabilities in animals, the NSs were tested for
biocompatibility on mouse fibroblasts (L-929). Wounds treated with
60 g/mL exhibited complete healing with no apparent scar on day 14.
Compared to the control group, histological evaluation of the treated
group demonstrated a substantial reduction in inflammatory cells and
an enhanced degree of collagen deposition at the wound site. As a
result, nanomaterials such as PDA NSs have the potential to speed
up wound healing and reduce scar formation.[92]2,2,6,6-Tetramethylpiperidinenoxyl (TEMPO) may grab unpaired
electrons
from other radicals by a single electron on nitroxide, and the redox
process switches between nitroxide, oxoammonium cation, and hydroxylamine.
The nitroxide/oxoammonium redox pair enhances catalysis through reversible
one-electron redox reaction and hydroxylamine functions as an antioxidant
hydrogen-atom donor. TEMPO conducts Fenton reactions and radical–radical
recombination as a membrane-permeable stable nitroxide radical.[93]TEMPO may cure different disorders, according
to studies.[94] Polynitroxyl albumin and
TEMPO lowered ROS levels
in a hepatic liver ischemia and reperfusion injury model, reducing
liver damage and inflammatory response symptoms, especially ICAM-1
and neutrophil accumulation.[95] TEMPO ameliorated
dehydroepiandrosterone-induced polycystic ovarian syndrome (PCOS)
by reducing oxidative stress in the stomach, reversing gut dysbiosis,
and altering the interaction between host metabolites and gut microbiota.
TEMPO therapy for PCOS is promising.[96] Calabrese
et al. studied TEMPO’s anti-inflammatory effect in osteoarthritis
(OA). TEMPO reduces inflammation, oxidative stress, nitrite production,
and pro-inflammatory mediators. TEMPO was predicted to be a novel
therapy for oxidative stress-induced inflammation.[97]Yin et al. prepared three forms of water-soluble
fullerenes and
assessed the ROS scavenging efficacy. The three fullerene materials
C60(C(COOH)2)2, C60(OH)22, and Gd@C82(OH)22 protect cells from
H2O2-induced oxidative damage, maintain mitochondrial
membrane potential, and inhibit intracellular ROS generation. The
ROS scavenging efficacies for the fullerene materials are as follows
Gd@C82(OH)22 ≥ C60(OH)22 > C60(C(COOH)2)2. Consistent
with their cytoprotective abilities, these derivatives can scavenge
the stable DPPH, ROS, O2•-, HO•, and inhibit lipid peroxidation in vitro. The differences
in free radical-scavenging abilities support the hypothesis that chemical
properties, such as surface chemistry-induced differences in electron
affinity, and physical properties, such as degree of aggregation,
influence the biological and biomedical activities of functionalized
fullerenes. This is the first report of fullerene compounds scavenging
all physiologically relevant ROS. The involvement of oxidative stress
and damage in many illnesses implies that fullerene derivatives may
be useful in vivo cytoprotective and therapeutic agents.[98] Thus, free radical trapping characteristics
of TEMPO and fullerene NPs are comparable and can be explored to treat
chronic wounds by regulating the ROS level at the wound site in the
future.[99]
Nanozymes (Antioxidant Enzymes Mimicking Nanomaterials)
for Wound Healing
The diabetic wound’s hyperglycemic
environment dramatically increases the likelihood of bacterial infections,
making wound healing a problematic task. Aside from bacterial infections,
ROS is another risk factor that slows wound healing. Furthermore,
accumulating ROS might cause an inflammatory reaction at the wound
site, slowing recovery. Cerium NPs (CeO2 NPs) have high
photolytic and antioxidant activity, making them excellent alternative
therapies for wound healing and other disorders.[100] Previous research on CeO2 has found that it
promotes cell proliferation and migration and neutralizes the ROS
level in chronic ulcers, hence expediting wound healing.[101] Furthermore, CeO2 NPs imitate SOD
and catalase (CAT) imitating activities.[102] Combining antioxidant CeO2 with the antibacterial substance,
on the other hand, will significantly reduce bacterial growth and
decrease the ROS load, which might potentially expedite wound healing.Ma et al. created a biocompatible nanocomposite by combining a
PEG-MoS2 and CeO2 (MoS2–CeO2) via simple electrostatic interactions with exceptional photothermal
antibacterial activity against both Gram-negative and Gram-positive
bacteria, as well as antioxidant activity for wound infection reduction
and wound repair (Figure a). The reversible transformational character of the Ce3+ and Ce4+ (biological antioxidant mimics) is offered
by the MoS2–CeO2 nanocomposite with exceptional
antioxidant activity (Figure b). The in vivo streptozotocin-diabetic rat wound model verified
wound healing at day 14 after NIR laser and nanocomposite therapy.
Histopathological examination of the nanocomposite and the NIR laser-treated
groups revealed fewer inflammatory cells and fibroblast migration.
In addition, parallel alignment of dense collagen fibers was seen
in the nanocomposite and the NIR 808 nm laser-treated group.
Figure 6
Illustration
of MoS2–CeO2 nanocomposite
for wound healing: (a) synthetic scheme of MoS2–CeO2 nanocomposite; (b) MoS2–CeO2 nanocomposite antioxidant and antibacterial mechanism; (c) MoS2–CeO2 nanocomposite actions on various phases
of wound healing for promoting wound healing. Adapted with permission
from ref (103). Copyright
2021 John Wiley and Sons.
Illustration
of MoS2–CeO2 nanocomposite
for wound healing: (a) synthetic scheme of MoS2–CeO2 nanocomposite; (b) MoS2–CeO2 nanocomposite antioxidant and antibacterial mechanism; (c) MoS2–CeO2 nanocomposite actions on various phases
of wound healing for promoting wound healing. Adapted with permission
from ref (103). Copyright
2021 John Wiley and Sons.Surprisingly, collagen production at the wound
site was uneven
in the remaining groups. Collagen synthesis was high and stayed the
same in all treatment groups compared to the control group animals,
regardless of the treatment methods with or without the NIR laser.
Overall, the MoS2–CeO2 nanocomposite,
combined with the NIR 808 nm laser therapy, demonstrated remarkable
antibacterial, antioxidant, anti-inflammatory, and regenerative characteristics
for the quick healing of chronic wounds (Figure c). Finally, the findings revealed that MoS2–CeO2 nanocomposite might be deemed therapeutically
viable alternative treatments for treating chronic nonhealing wounds
with laser aid.[103] Similarly, platinum,
copper, and Prussian blue imitate endogenous antioxidant enzymes (e.g.,
peroxidase, catalase, etc.) and SOD-like action. These carriers can
be used to investigate wound healing activities.[104]
Antioxidant Biosurfactants Used in Wound Healing
Biosurfactants are molecules that resemble surfactants.[105] These biosurfactants are highly biocompatible,
environment-friendly, biodegradable, and stable across various pH
and temperature conditions. Biosurfactants are employed in cosmetic
and medicinal applications due to their inherent antioxidant, antibacterial,
and antifungal activity and their perfect physicochemical qualities.[106] Biosurfactants are classified into several
groups: flavolipids, lipopeptides, phospholipids, fatty acids, and
glycolipids.[107] Because of their antioxidant
and antibacterial capabilities, they were appealing carriers for testing
their wound healing potential.Lipopeptide biosurfactants, for
example, have potential physicochemical features such as antiwrinkle,
free radical scavenging, moisturizing, and antibacterial qualities.
They are found in dermatological products intended for cosmetic purposes.
Zouari et al. isolated an SPB1 lipopeptide biosurfactant (LBS) from Bacillus subtilis and assessed its antioxidant properties
using the DPPH assay. The wound healing ability of the SPB1 lipopeptide
was also studied in excisional rat wound models. Using the DPPH test,
the SPB1 free radical scavenging activity was 70.4% at 1 mg/mL with
an IC50 = 0.55 mg/mL. SPB1 LBS was then added into the
gel and administered topically to the wound site in rats every 2 days
for 13 days. Finally, data showed a considerable reduction in wound
area on day 13 compared to control, CICAFLORATM, and glycerol-treated
animals.Histopathological examinations indicated that the epithelial
layer
of the skin had been completely repaired. Furthermore, on day 13,
complete wound healing was seen in the animals treated with the 15
mg/mL SPB1 LBS-based gels compared to the 5 mg/mL SPB1 LBS-based gels.
Finally, the scientists stated that SPB1 LBS might be a possible wound
healing therapy. However, before contemplating this peptide as a potential
therapy for wound healing, its comprehensive biocompatibility, safety,
and toxicity tests are needed.[108]Similarly, Ohadi et al. isolated LBS from Acinetobacter Junii B6
and studied its antioxidant and wound healing properties. The antioxidant
capacity of the extracted lipopeptide biosurfactant was determined
using FRAP and DPPH tests. Not only that, but they also used kits
to test MDA, H2O2, and GSH. The DPPH test revealed
significant scavenging action, with an IC50 of 0.7 mg/mL.
The LBS’s ROS scavenging action was supported by the findings
of the MDA, H2O2, and GSH tests. The 5 mg/mL
LBS-loaded gels were used to treat the injured animals. On day 13,
the wound length was significantly shorter in the LBS-treated group
than in the control group. On day 13, histopathological examination
revealed a small lesion area, better re-epithelialization, and decreased
neutrophil inflammation in the LBS-treated mice compared to the control
animals. The significant wound healing action of the LBS isolated
from Acinetobacter Junii B6 is related to its intrinsic antioxidant
potential.[109]In continuation of
this study, Mehrabani et al. studied LBS’s
angiogenic and proliferative capabilities on human umbilical vein
endothelial cells (HUVECs). Treatment with 300 g/mL LBS increased
cell motility and vascular endothelial growth factor (VEGF) levels
in HUVECs.[110] Other biosurfactants produced
from Bacillus amyloliquefaciens, Pseudomonas
aeruginosa, Bacillus strains, and Lactobacillus casei have high antioxidant and antibacterial
activity.[111] However, the potential of
these biosurfactants’ wound healing action has not yet been
studied. Shortly, preclinical wound models can be used to investigate
the efficacy of these kinds of biosurfactants in wound healing.
Nanoparticle Engineered Nanofibers with Antioxidant
and Wound Healing Properties
Nanofibers are a nanomaterial
created as an intriguing material for healing wounds and restoring
damaged skin. Nanofibers are polymers that can be natural or manufactured
and have variable releasing characteristics and morphological alignment.[112] They are ideal drug delivery systems and employed
for oxygen transportation because of their extraordinary features,
including porous nature, strong biocompatibility, mechanical qualities,
and high surface to volume ratio.[113]Nanofibers must be adorned or loaded with antioxidant medicines or
NPs to treat clinical wounds. Several nanofibers have recently been
functionalized with potent antioxidants for wound healing applications.
For example, the curcumin-encapsulated zein-silk fibroin-chitosan
nanofiber has optimal physicochemical properties for wound healing[114] with good mechanical stability, biodegradability,
and biocompatibility. On the other hand, chitosan is a natural antioxidant,
anti-inflammatory, and antibacterial agent with remarkable wound-healing
capabilities. In an in vitro fibroblast cell culture investigation,
these nanofibers improved adhesion and cell proliferation while causing
little toxicity. This combination produced an outstanding mechanical
performance and antioxidant, biodegradability, biocompatibility, and
wound healing capabilities.Similarly, in another work, silver
nanoparticles were loaded into
hyaluronic acid and polygalacturonic acid nanofibers to obtain antioxidant
and anti-inflammatory capabilities to accelerate wound healing.[115] Silver nanoparticles aid in the scavenging
of ROS and reduce their concentration in the wound during wound healing.
They can also function as antibacterial agents by damaging their cell
membrane and interacting with their DNA simultaneously. Polygalacturonic
acid, on the other hand, aids in the stabilization of silver nanoparticles.
Furthermore, because of its hydrophilic nature, hyaluronic acid aids
in the reduction of wound exudate formation. Thus, their collaboration
results in effective nanofibers mat for wound healing applications.
The preclinical investigations for wound healing assessment of the
nanofiber mat on the rat wound model revealed quicker wound healing
when compared to the commercially available ointment formulations.
Cell-Based Therapeutics for Wound Healing
Exosomes, mesenchymal stem cells (MSCs), and growth factors provide
a glimmer of hope in wound healing treatments. MSCs, in general, promote
the migration and proliferation of critical cells to the wound bed
and regulate ECM-related proteins by generating fibronectin and collagen.[116] In particular, epidermal growth factors (EGF),
in particular, aids in EGF receptor activation and promote the migration
and proliferation of keratinocytes, endothelial cells, and fibroblasts
at the wound site.[117] However, EGF degrades
at the wound site due to protease activity and persistent wound infections.[118]Recently, bone marrow MSCs have sparked
interest in treating diabetic wound healing. They do, however, have
several limitations, such as limited viability and growth near the
wound bed. Mohanty and Pradhan created an EGF-curcumin bandage bioconjugate
and put it into MSCs (MSCs-EGF-Cur B) to address these constraints.
Furthermore, X-ray photoelectron spectroscopy (XPS) and Fourier transform
infrared spectroscopy (FTIR) studies establish the EGF conjugation
effectiveness. In contrast, FTIR was used to examine the chemical
integrity of the curcumin in the matrix. In addition, the TNFα
level was determined using an ELISA test, and the mouse embryonic
fibroblasts were subjected to an inflammatory assay. TNF-α levels
in EGF-Cur B treated cells were the same as in healthy control cells.
The lipopolysaccharide (LPS) treated group, on the other hand, saw
a considerable drop in TNF-α levels. EGF-Cur B treated MSCs
showed a significant increase in the MSC transcription factors compared
to the MSCs grown in standard conditions. The cell proliferation potential
of EGF-Cur B was significantly increased compared to curcumin B.Furthermore, for 12 days, a diabetic full-thickness rat model was
utilized to assess the effectiveness of the MSCs-EGF-Cur B, EGF-Cur
B, MSCs, and MSCs-Cur. Significant improvements in wound closure,
collagen production, granular tissue development, and angiogenesis
were reported in MSCs-EGF-Cur B treated rats. As a result, hybrid
systems containing growth factors, MSCs, and antioxidant chemicals
may offer the most excellent alternative treatments for treating difficult-to-heal
wounds by working on several processes.[119]
Exosome Laden Oxygen Releasing Antioxidant
and Antibacterial Cryogel (OxOBand)
Infections, oxidative
stress, decreased angiogenesis, and a low quantity of oxygen at the
wound are essential clinical features of nonhealing chronic wounds.[120] As a result, increasing angiogenesis, neutralizing
oxidative stress, supplying oxygen, and avoiding infections might
be a unique approach to managing chronic wounds and improving clinical
outcomes.Shiekh et al. created an exosome-loaded oxygen-releasing
antioxidant wound dressing (OxOBand) to aid chronic wound closure
and skin regeneration (Figure a). The OxOBand comprises polyurethane cryogels with high
porosity and regulated oxygen release capabilities and an exosome
as a supplement. The usage of OxOBand increases the pace of wound
healing closure boosts collagen production and enhances angiogenesis.
Exosomes employed in OxOBand aid in the migration of human fibroblasts
and keratinocytes. Exosomes also allow fibroblasts and keratinocytes
to have longer lives under hyperglycemic conditions.
Figure 7
(a) Schematic illustration
of OxOBand and their properties; (b)
study design for diabetic wound production and subsequent healing;
(c) representative images of the wound healing on different days;
(d) residual wound and % wound closure; (e) H&E staining of the
wounds (left) and higher magnification images (right) on day 14 after
treatment; (f) granulation tissue quantification results on day 14
after treatment; (g) quantitative epidermal thickness at the center
of the wound. Adapted with permission from ref (121). Copyright 2020 Elsevier.
(a) Schematic illustration
of OxOBand and their properties; (b)
study design for diabetic wound production and subsequent healing;
(c) representative images of the wound healing on different days;
(d) residual wound and % wound closure; (e) H&E staining of the
wounds (left) and higher magnification images (right) on day 14 after
treatment; (f) granulation tissue quantification results on day 14
after treatment; (g) quantitative epidermal thickness at the center
of the wound. Adapted with permission from ref (121). Copyright 2020 Elsevier.It dramatically decreased oxidative stress in diabetes
wounds after
14 days of wound progression compared to diabetic control wounds (Figure b–d). The
OxOBand dressings aided in developing epithelial cells and hair follicles,
much like healthy skin. The OxOBand therapy of clinically complex
diabetic wounds reduced ulceration and infection, increasing collagen
deposition, wound healing, and re-epithelialization (Figure e–g). Novel treatments,
such as the OxOBand therapy method, can help to open up new avenues
of therapeutic development for treating chronic wounds.[121]
Conclusions
Many studies demonstrate
the importance of ROS in wound healing.
On the one hand, a low amount of ROS aids in defense of wounds against
microbial infections and promotes vascularization by activating multiple
cellular signaling pathways. On the other hand, excessive production
of ROS impedes wound healing by creating oxidative stress and, as
a result, causing inflammation. If ROS detoxification is not performed
at the appropriate time, the wound frequently becomes nonhealing and
chronic, making treatment challenging. As a result, we require effective
ROS detoxifying agents and antibacterial and anti-inflammatory capabilities
that comprise medicines. We reviewed new therapeutics with remarkable
antioxidant, antimicrobial, and anti-inflammatory characteristics
to aid wound healing. As a result, in this review, we have included
many potential innovative treatment methods that essentially stimulate
wound healing by detoxifying ROS. This information expects researchers
to attempt to create and describe clinically relevant numerous innovative
systems with advanced features, such as antioxidant, anti-inflammatory,
and antibacterial capabilities, to improve wound healing.
Authors: Paul Hiebert; Mateusz S Wietecha; Michael Cangkrama; Eric Haertel; Eleni Mavrogonatou; Michael Stumpe; Heiko Steenbock; Serena Grossi; Hans-Dietmar Beer; Peter Angel; Jürgen Brinckmann; Dimitris Kletsas; Jörn Dengjel; Sabine Werner Journal: Dev Cell Date: 2018-07-16 Impact factor: 12.270