Recent progress in micro and nano-encapsulation of bioactive derivatives of the Brazilian genus Pterodon.

In the last few decades, utilization of medicinal plants by the pharmaceutical industry has led to the identification of many new bioactive compounds. The genus Pterodon, native of the Brazilian Flora, is known for the therapeutic properties attributed to its species, which are widely used in popular medicine for their anti-inflammatory, anti-rheumatic, tonic, and depurative properties. The intrinsic low water solubility of the plant derivatives from the genus, including diterpenes with vouacapane skeletons that are partially associated with the pharmacological activities, impairs the bioavailability of these bioactive compounds. Recent studies have aimed to encapsulate Pterodon products to improve their water solubility, achieve stability, increase their efficacy, and allow clinical applications. The purpose of this paper is to review recent research on the use of nanotechnology for the development of new products from plant derivatives of the Pterodon genus in different types of micro- and nanocarriers. Therapeutic properties of their different products are also presented. Finally, an update about the current and future applications of encapsulated formulations is provided.

Introduction

The use of plants for medicinal purposes for the treatment of various diseases has occurred for thousands of years and the wide structural variability of molecules with biological activity has been appreciated more recently [1-3]. The World Health Organization (WHO) suggests that developing countries, comprising around 80% of the world population, depend on traditional medicine for primary health care [4,5].

In recent years, the search for new natural products has escalated. The number of publications for the term “Natural Products” on Pubmed increased from 452 items in 2000 to more than 5000 in 2021. In addition, plants are of great importance in traditional medicine, cosmetics, and homeopathy, although their use goes far beyond the new drugs approved by regulatory agencies such as the US Food and Drug Administration (FDA) or the Brazilian Health Regulatory Agency (ANVISA) [6]. Plant-derived natural compounds are responsible, directly or indirectly, for approximately one-quarter of the drugs currently available in the world [7].

Synthesis of chemical entities from plants of medicinal importance has been a valuable resource for the development of new drugs [8]. Since these new bioactive compounds can be used either directly as therapeutic agents or as prototypes for the development of new analogs with improved efficacy or reduced toxicity [9-11]. Examples of commercially available plant-derived drugs include salicin (analgesic agent) extracted from Salix spp. and later the development of its derivative, the aspirin [12]. Quinine and artemisinin and its derivatives (antimalarial), isolated from Cinchona officinalis and Artemisia annua, respectively [13,14]; digoxin (muscle relaxant) isolated from Digitalis lanata, used for more than 200 years [15,16]; codeine and morphine (analgesic) isolated from opium (Papaver somniferum) [17,18]. An antiviral and antitumoral agent, podophyllotoxin, was isolated from Podophyllum peltatum [19,20].

The search for new compounds with biological activity is motivated by unmet therapeutic needs. Brazil is a particularly rich source of plants that have undiscovered bioactive compounds having wide biodiversity. However, the use of naturally derived molecules as a source of new medicines also presents some challenges. The isolation, characterization, and purification processes can be costly and time-consuming. In addition, the lipophilicity of the compounds can impair their use in vivo [21]. This helps to explain why among the 1562 drugs approved by FDA from 1981 to 2014, 21% were natural product derivatives. However, only 4% were used without alteration [6].

The trees of the genus Pterodon are native to, and have an extensive presence in, Brazil. Their extracts and oils contain bioactive compounds, subject to ethnopharmacological use mainly as anti-rheumatic, pain relief or to treat throat infections and respiratory disorders such as bronchitis [22-24]. The main compounds present in this genus are isoflavones and triterpenes found in the wood [25]; alkaloids, saponins, glycosides, and steroids in the bark [26-29]; sesquiterpenes, isoflavones, and saponins in the leaves [30-33]; terpenoids of furanoditerpenes type, sesquiterpenes, diterpene vouacapanic skeleton in fruit oil [34-40].

Some studies suggest that biological activities of the species of the genus Pterodon are directly related to the furan diterpene and sesquiterpene contents [41-43]. Pterodon-derived products include oleoresin, an essential oil that can be extracted by cold-pressing and hydro-distillation with no use of solvents [34,40,44,45]. Biological activities have been ascribed to diterpenes from the fruit, especially the vouacapan skeleton, 6α, 7β-dihydroxy-vouacapan-17β-oic acid extracted by the Soxhlet method, using solvents like petroleum ether [46] hexane [47,48], ethanol [49]. Cold extraction using dichloromethane [39,50] and hexane [23,42] were also reported to produce Pterodon extracts.

These extracts are complex mixtures of chemicals that might have associated biological properties. A study that evaluated the anti-nociceptive and anti-inflammatory effect, in addition to the suppression of B and T lymphocyte response and nitric oxide production, suggested the therapeutic potential of the genus in controlling exacerbated cellular and humoral immune response in autoimmune diseases and chronic inflammatory processes [51,52]. In another study, antinociceptive activity was attributed to geranylgeraniol and the diterpene 6α,7β-dihydroxyivouacapan-17 α-methyl-oate isolated from the crude seed extract [50]. Analysis of the hydroethanolic extract also demonstrated anti-nociceptive activity in acute and chronic pain models [53].

The oleoresins extracted from the fruit include a blend of lipophilic molecules, including the volatile and non-volatile fractions, while their essential oils are made up of volatile lipophilic substances with antispasmodic and anti-inflammatory actions [41,45,54,55]. However, their therapeutic use is still limited by poor water solubility, which results in low bioavailability and impairs clinical application. To overcome these problems, formulations using micro- and nanotechnology-based systems are being developed (Fig. 1) [56].

Fig. 1.

Worldwide importance of medicinal plants and their progress towards micro and nano-encapsulation.

Particulate nanocarriers can be used to facilitate the dispersion of lipophilic compounds in water, the encapsulation of hydro and/or lipophilic compounds, protection of the encapsulated compound against degradation, modification of the drug pharmacokinetics, increase in therapeutic efficiency, [57-61]. Recently, studies have shown the promising capacity of micro and nanostructured systems as a delivery platform for vegetable derivatives extracted from the species of the genus Pterodon, implying the possible extension of this approach to other bioactive molecules from the same genus.

Pterodon genus

The plants of the genus Pterodon (family Leguminosae/Fabaceae) are native to Brazil and popularly known as “Sucupira-branca” or “Faveiro”, classified into four species: P. emarginatus Vogel (synonymy Sweetia inornata Mohlenbr.; Acosmium inornatum (Mohlenbr.) Yakovlev; P. polygalaeflorus (Benth)); P. pubescens (Benth.) Benth; P. abruptus (Moric.) Benth. (synonymy Commilobium abruptum Moric.); P. apparicioi Pedersoli, where the last two are endemic [53,62]. The genus Pterodon comprises aromatic trees growing 6–18 m tall and may have alternating or opposite leaflets. Their flowers may be pink or violet with cryptosmara type fruits with well-developed wings, or not. Present in several Brazilian phytogeographic domains, the species are widely distributed in the various North regions (Rondônia e Tocantins), Northeast (Bahia, Ceará, Maranhão e Piauí), Midwest (Distrito Federal, Goiás, Mato Grosso do Sul e Mato Grosso), and Southeast (Minas Gerais e São Paulo) [24, 62].

The literature reports that oils and extracts obtained from fruit or seeds of Pterodon genus have a large array of active compounds and are recognized for their therapeutic properties, being widely used in popular medicine [24,49]. Furthermore, a growing scientific interest is observed not only in biological applications and activities, but also in a search for a renewable source of the sample, the seeds, and fruit of Pterodon species, in which the supply of drug, extracts or fractions would not be limiting. Moreover, use of native materials is sustainable and may improve ecological conservation efforts.

Phytochemicals

Phytochemical investigations on the extracts and oil of the fruits and seeds of the Pterodon species revealed the presence of compounds such as saponins, phenolics, and terpenes [63,64]. There are several papers referring also to the isolation of di- and sesquiterpenes such as specific compounds of interest within this genus, according to their displayed effects and probably related to biological activities [46,65]. Since the various substances in the class of terpenes are derived from mevalonic acid, their molecular structures are composed of variations of isoprene units (Fig. 2a). Diterpenes contain four isoprene units in their basic structure and may be linear (i.e., geranylgeraniol) (Fig. 2b) or cyclic with vouacapanic structure (also referred to as furan diterpenes) (Fig. 2c) [66].

Fig. 2.

Chemical structure of (a) isoprene and isolated diterpenes from Pterodon sp. (b) linear structure of Geranylgeraniol and (c) cyclic structure of vouacapane compounds. Dashed lines indicate where the four isoprene units are joined.

Other constituents, still of the terpene class, that have been identified as major components in the genus include the sesquiterpenes, with potential antioxidant activities and anti-inflammatory properties [36,45, 53,67]. Compounds from the essential oils of P. polygalaeflorus seeds, with a basic structure of three isoprene units such as β-elemene, β-caryophyllene, and α-humulene (Fig. 3) are associated with anti-nociceptive, anti-inflammatory, and antispasmodic effects [41,55,68].

Fig. 3.

Chemical structure of some of the main sesquiterpene compounds isolated from the essential oil seeds and fruits of the genus Pterodon.

Therapeutic properties

Although the biological effects of this genus are accepted, there is a lack of analytical methodologies to isolate and quantify furan diterpenes compared to sesquiterpenes. In this scenario, there remains a need to better understand the effects of this complex mixtures. Hydroalcoholic extracts from seeds of Pterodon pubescens show an anti-arthritic effect related dependent on the presence of furan diterpenoids and sesquiterpenes [69-71]. Further biological activities were presented for oleaginous extracts obtained from Pterodon: antinociceptive [50,51,63,72], anti-inflammatory [23,37,42,73], antileishmanial [31] and antimicrobial [30,74]. Some of the bioactive molecules such as β-caryophyllene and β-elemene are reported as major constituents in the essential oils of P. emarginatus comprising ~35% and 17%, respectively, depending on the plant collection site [34,40,75]. Possible therapeutic targets of these compounds seem associated with suppression of pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) and cell adhesion molecules (MCP-1) [76-78].

In the 1960s, studies of the genus Pterodon started when Mors and colleagues demonstrated the chemoprophylactic efficacy of the P. pubescens fruit essential oil against Shistosoma mansoni cercariae [79]. Later, geranylgeraniol and 14,15-epoxigeranylgeraniol were isolated from the fruits of P. pubescens crude oil and the latter demonstrated prophylactic action against the trematode that causes schistosomiasis, by inhibiting the penetration of cercariae into the skin [80].

Subsequently, studies revealed other activities such as the analgesic effect of oleaginous extracts obtained from Pterodon species [81-83]. Vouacapan derivatives 6α-7β-dihydroxyvouacapan-17β-oate [81], 6α, 7β-Diacetoxyvouacapane [39] and 6α-7β-Dihydroxyvouacapan-17β-oic acid (DHVA) [43] were previously associated with this activity via activation of the catecholaminergic system or the involvement of central and peripheral opioidergic mechanisms [72,81]. Oral administration of different doses of DHVA (50 and 100 mg/kg) inhibited the second phase of nociceptive behavior of the formalin test, which is dependent on peripheral inflammation and changes in central processing [43,84]. However, there is no evidence that DHVA has any central anti-nociceptive activities. Other than the vouacapan derivatives, linear diterpenes geranylgeraniol and farnesol seem also to contribute to their analgesic actions, through modulation of inflammation [82].

The hexane and methanol extracts of the fruits and seeds of Pterodon polygalaeflorus showed larvicidal activity against Aedes aegypti [47]. In this study, hexane extracts showed the best activity, which could be related to furanic diterpenes such as methyl 6α,7β-dihydroxyvouacapan-17β-oate, 6β-hydroxyvouacapan-7β, 17β-lactone, 6α-acetoxyvouacapane and DHVA [47,85]. Studies of antiproliferative activities in tumor cells of crude extracts of Pterodon seeds also were performed [39,49,86]. Furan diterpene rich fractions were able to induce DNA fragmentation, cell cycle arrest in the G1 phase, change in cyclin D1 and E2-expressing levels, increased cytochrome C release, and apoptosis induction in tumor cells [87,88].

The bioactive molecules of the genus Pterodon present in extracts, fractions, as well as the isolated compounds of the species are mostly substances with large hydrocarbon chains of low polarity with enormous structural diversity (Figs. 2 and 3), features that can limit bioavailability. To circumvent this problem, development of pharmaceutical nanotechnology-based formulations has been carried out [89]. Delivery systems from bioactive natural products are considered promising to increase therapeutic efficacy, mask the flavor of plant-derived product and protect it from possible degradation [90-92].

Nanotechnology as a drug delivery strategy for encapsulating derivatives from the genus Pterodon

Nanotechnology is the manipulation and control of matter on the nanoscale dimension using scientific knowledge [93]. It can be applied in several areas since it is a multidisciplinary field, including industrial and biomedical applications [94-96]. One significant challenge in developing pharmaceutical products is low water solubility and limited cellular permeability. This limitation can be overcome using nanosystems, exemplified by such marketed products as the liposomal formulations encapsulating the antitumor drugs daunorubicin and cytarabine (Vyxeos®), doxorubicin (Doxil®), vincristine sulfate (Marqibo®), irinotecan (Onivyde®) or antifungal amphotericin (AmBisome®, Abelcet®, Amphotec®), as well as the polymer-based nanoparticles for encapsulating triptorelin (Trelstar™), certolizumab pegol (Cimzia®) and estradiol (Estrasorb®) formulations indicated to treat prostate cancer, moderate vasomotor symptoms and autoimmune inflammatory diseases, respectively [97,98].

Liposomes and polymer-based nanoparticles are the most advanced in terms of clinical translation, cancer therapy being the main application, which may reflect both the levels of funding in the area as well as the suitability of nanocarriers for the drug delivery of antineoplastic. In addition to the encapsulation of drug molecules, research has shown that lipid-based nanoparticles are interesting strategies for the encapsulation of oligonucleotides (RNA, mRNA, siRNA, and DNA) for the treatment and prevention of various diseases [99,100]. Recently, there was FDA approval for Onpattro®, consisting of siRNA encapsulated in lipid nanoparticles for the treatment of polyneuropathy in adults with hereditary transthyretin-mediated amyloidosis [101,102]. Given the current situation regarding the SARS-CoV-2 pandemic scenario, the successful development and fast-tracking of nanotechnology-based vaccines as the delivery vehicle of messenger RNA (mRNA) and DNA have shown notable implications for the future of nanotechnology-enabled for drug and gene delivery. The safety and efficacy data of these nanosystems already available on the market can supply the foundation for the clinical translation on future therapeutic applications. Although each formulation has its challenges to face and overcome [103].

As a drug transport and delivery system, nanocarriers in medicine are colloidal systems that contain an encapsulated active pharmaceutical ingredient (API), integrated into the particle core, or matrix, conjugated on the nanoparticle surface [104]. They can be used as a platform for the diagnosis, prevention, and/or treatment of several diseases [105-107]. Different systems can be used to encapsulate bioactive compounds. Due to their small size and the large surface area, leading to improved pharmacokinetics and site-specific delivery, nanoscale particles have shown promising drug delivery properties [104, 108]. In general, their applications aim to increase a drug’s therapeutic index and safety profile, lowering the required doses used to achieve effective therapy. They, also, can be used to protect unstable substances in the face of early degradation or against possible instabilities in the biological environment. Furthermore, sustained drug release and increased cellular uptake are often associated with the use of nanosystems [89,109].

Nanostructured systems can be categorized as metallic, lipid, or polymeric [110]. Metallic nanoparticles have a core composed of alkali and noble metals [61,111]. They can be classified as hard-nanoparticles whose central core is hardened and may limit drug-loading/appending capacity to the particle’s surface. Soft-nanoparticles refer to those materials whose central core is efficient for drug-loading and provide structural flexibility [112]. The polymeric and lipidic nanoparticles have flexible cores which can deform temporarily by stress or contact with surfaces [113]. Polymer-based nanoparticles are colloidal particles such as nanocapsules, and nanospheres where the drug can be encapsulated or adsorbed to the polymer [114,115]. While lipid-based systems consist of a lipidic dispersion stabilized by surfactants (phospholipids, proteins, polysaccharides or minerals) and can be represented by liposomes, nano, or microemulsions, nanostructured lipid carriers [116].

They can also be classified as passive or active targeting depending on how they target the desired tissue. In passive targeting, drug-loaded nanocarriers remain sufficiently long in circulation to accumulate in a desired tissue contingent on properties like size, pH, temperature, and charge [117,118]. Drug accumulation in areas with leaky vasculature i. e., tumors, is also exploited for passively targeting [119,120]. The aim is to get selective delivery of drugs into the site of action and low systemic toxicity. Alternatively, in the active targeting (or ligand-based targeting), a biological marker is attached to the nanocarrier surface to be recognized by receptors expressed in the target cell surfaces [119,121]. This strategy is expected not only to improve the affinity and precision of the nanocarriers to the target cells/tissue but also to increase cell uptake [122,123]. Active targeting can lead to better therapeutic effects. Some studies demonstrated that folate receptor–targeted liposomes loaded with antitumor drugs inhibited tumor growth [124,125]. Liposomal formulations showed greater efficacy in MDA-MB-231 and 4T1 mouse models of metastatic breast cancer compared to individual components or current conventional formulations. Highlighting the efficiency of using active targeting for recognition, retention, and cell uptake after accumulation in the target region [126-129]. The development of receptor-targeted systems could, therefore, significantly improve the delivery efficiency of drug-loaded nanocarriers.

For the administration of bioactive compounds from plants, nanosystems have been studied [130]. However, encapsulation of compounds and derivatives from the genus Pterodon has produced twenty-three (23) types of formulations that have been reported in the literature. As shown in Fig. 4, nanoemulsions and microemulsions are the most prevalent, followed by polymeric particulate systems, magnetic/metallic, and nanoparticles nanostructured lipid carriers.

Fig. 4.

Percentage distribution profile of nanostructured systems based on species of the genus Pterodon.

Throughout the literature, different combinations of drugs/bioactive ingredients of Pterodon spp. loaded in drug-delivery systems can be found and are listed in Table 1.

Table 1

Drug-delivery systems based on Pterodon spp. bioactive products and applications.

Pterodon spp.	Plants extracts/vouacapan derivative	Delivery system	Preparation methods	Drug-Delivery properties	Biological activities	References
P. emarginatus	Oil obtained through the cold pressing of fruits	NE	Emulsification - low energy method	Optimized formulation: 125.1 ± 0.5 nm, PI: 0.175 ± 0.014; dose 250 ppm induces mortality level of 100%; no toxicity for mammals	Larvicidal on Aedes aegypti	[45]
P. emarginatus	Essential oil from fruits	NE	Phase inversion emulsification	Optimized formulation: 128.0 ± 6.2 nm, PI: 0.250; Dose 150 μg/mL induces mortality	Larvicidal on Aedes aegypti	[131]
P. emarginatus	Oleoresin from fruit	NE	Phase inversion emulsification - with some modifications	Size distribution: < 180 nm, PI: < 0.200; Thermosensitive substances may be efficiently encapsulated by this technique; New perspectives for biological evaluation	Still uninvestigated	[132]
P. emarginatus	Oleoresin from fruit	NE	Emulsification - low energy method	More stable formulation: 151.0 ± 2.3, PI: < 0.3; Doses 500 mg/L, decrease in cell viability; Low toxic effects on environment	Larvicidal on Culex quinquefasciatus	[133]
P. emarginatus	Oil obtained through the cold pressing of fruits	NE	Hot high-pressure homogenization	Size distribution: 150 nm, PI: < 0.2 Formulation stability for 90 days	Antioxidant activity	[134]
P. emarginatus	Essential oil from fruits	NE	Phase inversion emulsification - with some modifications	Size distribution: 116.8 ± 0.3606 nm, PI 0.187 ± 0.008	Anthelmintic	[135]
P. emarginatus	Essential oil from fruits	NE	Emulsification - low energy method	Optimized formulation: 130 nm, PI < 0.20; Physical stability in temperature from 25 °C to 80 °C; Formulation classified as non-irritant	Still uninvestigated	[40]
P. emarginatus	Oleoresin from fruit	NE	Phase inversion emulsification - with some modifications	Particle size: < 180 nm; narrow size distribution (PI from 0.136); stable at room temperature	Leishmanicidal	[136]
P. pubescens	Hexanic fruit extracts and Supercritical fluid extract	NE	High shear homogenization	Low particle size (< 200 nm) and narrow distribution PI: < 0.2; Better selectivity index	Leishmanicidal	[137]
P. pubescens	Hexanic fruit extract	NE	High shear homogenization	Optimized formulation: < 200 nm a very narrow size distribution (PI from 0.11)	Anti-rheumatic/anti-arthritic	[138]
P. pubescens	Hexanic fruit extract	NE	High shear homogenization	Unimodal distribution profile; PI: < 0.3; Good stability throughout the study	Anti-inflammatory	[139]
P. emarginatus	Oil obtained through the cold pressing of fruits	ME	Reverse-phase methods	Size distribution: 56.8 ± 6.07 nm; Narrow size distribution (PI < 0.2); Stability at 5 and 25 °C for 30-day	Anti-inflammatory	[140]
P. pubescens	Hexanic fruit extract	NE	High shear homogenization	Size distribution: 16.33 ± 0.30–26.63 ± 0.21 nm; Narrow size distribution (PI < 0.3); Encapsulation efficiency > 90%; Good stability	Still uninvestigated	[141]
P. pubescens	Ethanolic fruit extract	NE	High shear homogenization	Spherical-shaped nanosized structure; Predominantly elastic characteristic; Good stability	Antiarthritic	[142]
P. pubescens	Oleaginous fractions from alcohol extract of the fruit	MC	Phase separation (coacervation)	Size distribution: 0.468–0.903 μm depending on the type of chitosan used in preparing the formulation; Modified oleaginous fractions release profile	Still uninvestigated	[90]
P. pubescens	Crude extract seeds and isomers 6α-hydroxy-7β-acetoxy-vouacapan-17β-oate methyl ester and 6α-acetoxy-7β-hydroxy-vouacapan-17β-oate methyl ester	MC	Spray drying	Good encapsulation efficiency and Its stability can be modified leading to increase shelf lifetime of formulation	Anti-nociceptive	[143]
P. emarginatus	Essential oil from fruits	MC	Spray drying	Size distribution: 1.250 μm; System capable of conserving and protecting essential oil from degradation and evaporation	Still uninvestigated	[44]
P. pubescens	Ethanol fruit extract	Nanofibers	Electrospinning	Size distribution: 1.91 ± 0.71 μm; Controlled release profile; Non-cytotoxic behavior in vitro	Wound healing	[144]
P. emarginatus	Resin extracted from the seed	Maghemite NP	Co-precipitation	Size distribution: 84 nm monodisperse size profile; expand applications due to semiconducting properties	Still uninvestigated	[145]
P. emarginatus	Aqueous extract from the seeds/leaves	Metallic NP	Green synthesis	NP in the size range 59–66 nm; predominantly spherical in shape; moderate stability (PI: 0.3)	Antimicrobial	[146,147]
P. pubescens	Oil obtained from hexanic fruit extract	NLC	Melt emulsification	Optimized formulation: 94.47 ± 2.05 nm, PI: 0.197 ± 0.003; The chemical profile of the oil remained unchanged after preparation method	Antitumoral	[148]
Unidentified	Essential oil from fruits	NLC	Hot high-pressure homogenization	Optimized formulation: 148.1 ± 0.1 nm, PI: 0.274 ± 0.029 after preparation; showed no cytotoxic effect against Caco-2 cell line	Still uninvestigated	[149]

Abbreviations: PI: polydispersity index; MC: microcapsules; NP: nanoparticles; NLC: nanostructured lipid carriers; ME: microemulsions; NE: nanoemulsions.

Micro and nanoemulsions

Nanoemulsions are colloidal thermodynamically unstable dispersions of oil in water (O/W) or water in oil (W/O) stabilized by an interfacial film of surfactant molecules and sometimes co-surfactants [150-152]. Microemulsions can be differentiated as a colloidal thermodynamically stable dispersion. These nanosystems have the advantage of transporting high loads of lipophilic substances and also protect the encapsulated bioactives from hydrolysis, oxidation, or enzymatic degradation [153]. The main interest for using drug delivery systems based on microemulsions or nanoemulsions is to increase bioactive bioavailability [154,155]. This incorporation can be accomplished through several methods, classified into two primary categories: high-energy and low-energy methods (Fig. 5). Nanoemulsions require the input of some external energy to convert the separate immiscible components into a dispersion. High-energy methods supply intense forces that disrupt and intermingle the oil and water phases resulting in tiny droplets with high kinetic energy. Mechanical devices such as ultrasonication or high-pressure homogenizers are generally used for nanoemulsion preparations [151,156]. Nanoemulsions formulated through high-energy methods can therefore achieve high stability and small particle size. In contrast, low-energy methods take advantage of the intrinsic physicochemical properties of formulation components that require a little addition of external energy to generate droplets. Phase inversion emulsification (emulsification methods) and self-emulsification are examples of low-energy approaches for the formation of micro and nanoemulsions. In principle, the process consists of mixing two liquid phases, one oily phase containing hydrophilic surfactant (plus drug) and an aqueous phase. When these two liquids are brought into contact, the surfactant molecules rapidly diffuse from the oily phase to the aqueous phase, which causes turbulence creating nano-sized emulsion droplets [154]. Currently, there is a focus on producing nano or microemulsions using low-energy methods once they are considered energetically efficient. In addition, it has a simple implementation and does not require sophisticated and expensive equipment [157].

Fig. 5.

Schematic illustration of the high-energy and low-energy methods for obtaining micro and nano-emulsion.

Once the thermodynamic instability of nanoemulsions is dependent on the preparation method, its optimization appears to be of fundamental importance for the development of successful delivery systems [156] and can lead to safer and more environmentally friendly practices.

Nanoemulsion is also an alternative for the delivery of hydrophobic compounds [158]. In order to increase the pharmacological efficacy of oily extracts from the genus Pterodon, several nanoemulsions (NE) have been developed. Among them, NE of the essential oil extracted from P. emarginatus. In this context, a study proposed the development of NE (O/W) with essential oils from P. emarginatus [131]. NE with the best results were prepared with essential oil and polysorbate 80 (1:1) in concentrations of 0.25% (wt/wt), using a simple organic solvent-free, low-energy method. NE containing essential oil from P. emarginatus fruits were able to induce mortality in Aedes aegypti larvae. This larvicidal activity may be associated with β-caryophyllene, the main compound corresponding to 25.8% of the relative percentage in the oil. Valentim et al. [135] evaluated the in vitro antiparasitic activity of NE containing essential oil of P. emarginatus against monogenic parasites of the type Anacanthorus spathulatus, Notozothecium janauachensis, and Mymarothecium boegeri that usually infect the fish Colossoma macropomum. The in vitro results showed that NE containing the essential oils at concentrations from 100 to 600 mg/L had 100% antiparasitic activity. As the main constituents present in the essential oil of P. emarginatus are the compounds β-elemene, β-caryophyllene, and α-humulene, we can imply that they are responsible for biological activity. Recently, NE loaded P. emarginatus essential oil demonstrated high kinetic stability and was non-irritating, estimated by HET-CAM [40]. The results of this study can serve as a lead in determining in vivo therapeutic properties of this nanoformulation.

The amber-colored oleoresin from P. emarginatus has been widely investigated, where the main components include the volatile essential oils made up of a mixture of terpenoids, e.g., the diterpenes with vouacapan skeleton and the non-volatile components [132]. Recent studies have focused on the development of NE for carrying this oleoresin (NE P. emarginatus oleoresin) for larvicidal applications against Aedes aegypti and Culex quinquefasciatus, the main vector of dengue and lymphatic filariasis, respectively [45,133]. The NE were developed using a simple low-energy method with or without heating in solvent-free conditions, remaining stable during storage at room temperature when protected from light [45,132,133]. The formulations proposed in these studies for encapsulation of oleoresin showed activities (at 250–12.5 ppm, relative to oleoresin) against A. aegypti having a possible mechanism through the reversible inhibition of acetylcholinesterase [45]. Larvicidal activity against Culex quinquefasciatus, indicated morphological changes. However, unlike the larvicidal mechanism of action presented for A. aegypti, NE P. emarginatus oleoresin does not seem to inhibit acetylcholinesterase in C. quinquefasciatus larvae, and further studies are needed to evaluate possible mechanisms of action. In addition to evaluating the activity of a new product, it is essential to assess toxicological profiles, in this case, ecotoxicological risks. Exposing NE P. emarginatus oleoresin to an aquatic ecosystem using Chlorella vulgaris as a biological indicator, showed this formulation is potentially ecofriendly and non-toxic [133].

Recently, NE prepared with oleoresin from the fruits of P. emarginatus showed antioxidant and chemoprotective activity, at 10 μg/mL, against ultraviolet (UV) radiation to human keratinocytes. These activities were related to the presence of phenolic compounds and terpenes present in the extracts of P. emarginatus. In parallel to the antioxidant effects, the NE managed to modulate the inflammatory profile of epithelial cells. A reduction in the levels of pro-inflammatory cytokines, IL-6 and IL-8, was observed in keratinocytes after UV irradiation [134]. Despite the high energy emulsification method and heating (at 65 °C) used to produce the nanoformulation, the oil activity was preserved.

The anti-inflammatory effects of P. emarginatus oleoresin from fruits Kawakami et al. [136] was evaluated with the topical use of NE oleoresin at 20% (wt/wt) in combination with intraperitoneal (i.p.) meglumine antimoniate in the treatment of lesions caused by Leishmania (Leishmania) amazonensis. The results demonstrated the effectiveness of the proposed combination in reducing the parasitic burden and the levels of cytokines (IFN-γ and IL-10) in the lesion. In a study reported by Santos et al. [137] extracts from the fruits of P. pubescens presented antileishmanial activity and the nanoemulsions from the optimized extracts were proposed to increase the activity and reduce possible toxicities. The extraction method influenced the pharmacological activities of the extracts (IC50: 40.7 ± 2.9 μg/mL for hexane extract and IC50: 33, 8 ± 4,6 μg/mL for supercritical fluid extract). Although both extracts have high cytotoxicity, supercritical extracts were more effective, showing superior inhibition against L. amazonensis promastigotes and amastigotes than extracts obtained by conventional methods. This fact is attributed to the high content of the geranylgeraniol derivative in supercritical extracts. Nanoemulsions showed a better index of selectivity and significant activity against parasite amastigotes Leishmania amazonensis (IC50: 2.7 ± 0.1 μg/mL for hexane extract nanoemulsion and IC50: 1.9 ± 0.3 μg/mL for supercritical fluid extract nanoemulsion). The findings of this study show that the developed NE promotes a drastic decrease in the IC50 and increase in the selectivity index [137]. In the search for an efficient topical application system, the incorporation of hyaluronic acid in NE with P. pubescens fruit extract-loaded was also evaluated and showed an improvement of rheological properties. The addition of the cross-linked biomaterial resulted in increased viscosity and stability, which might facilitate topical applications [141].

Nanoemulsions containing optimized P. pubescens ethanolic extracts of the fruits were developed by Hoscheid et al. [138]. To assess their efficiency and safety, another study by the same group [139], evaluated the anti-inflammatory activities of NE in a model of carrageenan-induced peritonitis. The NE containing ethanolic extracts of P. pubescens showed a significant inhibitory effect on leukocyte migration, even after 1 year of storage, indicating potential use in anti-inflammatory therapies, as well as in the treatment of arthritis [142]. The anti-inflammatory potential of the oil extracted from the fruits of P. emarginatus and encapsulated in microemulsions was evaluated in the ear edema model induced by the topical application of croton oil [140]. Both the oil extracted and the proposed microemulsion system showed anti-inflammatory potential. However, the microemulsion was more efficient, possibly due to dermal or transdermal permeability improvements [159].

Fundamental differences between micro and nanoemulsion surround the free energy of the system, giving them distinct characteristics in preparation, formulation and stability [160]. However, the use of microemulsions for bioactive compound delivery can be limited by the high concentrations of surfactants, since these agents, at certain levels, might be irritatants [161,162]. On the other hand, nanoemulsions can be potential alternatives in this case since lower concentrations of surfactant are needed when compared to microemulsions [163].

Polymeric particles

Polymeric particles have been extensively researched as delivery systems. Data in the literature have shown that such systems can modify pharmacokinetics and improve the therapeutic index of many drugs [164]. Some of the advantages of using polymeric systems include easy production, the facility to obtain a solid form that is more stable and marketable, controlled and sustained drug release, ability to modify surfaces with ligands for targeted drug delivery [165]. Differences between micro and nanoparticles relate to their size in micrometers and nanometers, respectively. For structural organization, they can be classified as spheres and capsules. The spheres are formed by a polymeric matrix, where the lipophilic and/or hydrophilic drug can be retained (solubilized or dispersed). The capsules are vesicular systems in which a polymeric wall surrounds the oily liquid core. In this case, the lipophilic drug is usually dissolved in the core, but may also be adsorbed to the polymeric surface [166,167].

Countless synthetic or natural polymers can be used for the development of polymeric nanoparticles. The release profile of the compound can be modulated according to its hydro and lipophilic properties and the nature of the polymers used in the development of the systems [168, 169]. Natural polymers, such as polysaccharides e.g., chitosan, dextran, are well known for their benefits in biodegradability and their negligible toxicity. On the other side, customizable degradation rates and physical and mechanical characteristics benefit synthetic polymers compared to natural polymers. The polymers most commonly used in the production of these carriers are aliphatic polyesters such as polyglycolic acid (PGA), polylactic acid (PLA), poly-lactic-co-glycolic acid (PLGA), and poly--ε-caprolactone (PCL) due to biocompatibility and biodegradability [170, 171].

In order to produce microcapsules, the most common techniques used for encapsulation of oils are spray-drying and coacervation [172, 173]. Spray-drying is well-established to produce microparticles by atomizing the liquid suspension into a fine spray-dried by a stream of hot air. This method provides stable dehydrated products in the form of fine powders [174]. The principle behind the coacervation process involves the precipitation of polymers around of active compound, thus encapsulating it. With specific environmental influence (ionic strength, pH, or temperature variation), the liquid phase separates from the polymer-rich (coacervate) phase, forming microspheres or core-shell structured microcapsules [174,175]. This method offers an advantage for encapsulating heat-sensitive compounds. However, depending on the polymer used, a high amount of organic solvent might be required, requiring subsequent evaporation from the product [176,177]. In some cases, the encapsulation by the spray-drying process may be preferred to the coacervation method, as no organic solvents are needed within the preparation and is associated with low process costs allowing large-scale production in a continuous mode [177]. Different polymeric systems were developed from natural or synthetic polymers for the encapsulation of phytochemicals or plant extracts of Pterodon species (Fig. 6), in search of potential therapeutic interventions for future use in many diseases.

Fig. 6.

Schematic illustration of the use of different polymer systems for encapsulation of phytochemicals or plant extracts of Pterodon species.

The first study to develop polymeric particulate systems employing derivatives of the genus Pterodon was reported by Servat et al. [143]. Microcapsules were produced by spray-drying of the biopolymers maltodextrin and gum arabic and the crude extract or vouacapan mixture (6α-hydroxy-7β-acetoxy-vouacapan-17β-oate methyl ester and 6α-acetoxy-7β-hydroxy-vouacapan-17β-oate methyl). Antinociceptive activity after i.p. administration of microcapsules with the crude extract or the vouacapan mixture was confirmed. Subsequently, a study by Alves et al. [44] evaluated the influence of different spray-drying parameters (as dryer inlet and flow injection) and excipient proportions on the production and the stability of microcapsule produced with P. emarginatus essential oil. Thus, the proposed system produced microcapsules around 5 μm with encapsulation efficiency higher than 90% and increased stability, in addition to solving the inconvenience of poor water solubility [44,143]. In another study, Reinas et al. [90] microcapsules with oleaginous fractions were obtained from an alcohol extract from the fruits of P. pubescens using alginate/chitosan polymers of different molecular weights. Diameters of the microcapsules were between 0.4 and 1.0 μm. The best formulation prepared with alginate and low-molecular-weight chitosan presented high encapsulation efficiency of about 99,5% for vouacapanes methyl 6α-acetoxy-7β-hydroxyvouacapan-17β-oate and methyl 6α-hydroxy-7β-acetoxyvouacapan-17β-oate. Furthermore, in vitro release profile of the vouacapanes-loaded microcapsules was close to 75% (acid pH) after 24 h. Recently, PCL-based nanofibers associated with the ethanolic extracts from P. pubescens fruits were developed and showed potential in vitro activity in wound-healing assays. The extract could inhibit acute inflammatory actions attributed to the presence of voaucapans, limiting the phases of pain response and edema formation [144].

Magnetic and metallic nanoparticles

Among the various nanosystems, magnetic iron oxide nanoparticles stand out for their high surface area and specific properties related to their magnetism [178,179]. Various methods have been reported for the synthesis of iron oxide magnetite (Fe3O4) or maghemite (γ-Fe2O3) nano-particles. The most common include sol-gel synthesis, co-precipitation, micro-emulsion, and hydrothermal synthesis. However, co-precipitation has advantages of low cost, high product purity, and organic solvent-free conditions, presenting great potential for applications in several technological areas [180].

Silveira et al. [145] proposed the development of maghemite nano-particles conjugated with sucupira seed resins produced by co-precipitation methods, without the need for expensive equipment or organic solvents. Molecular traces of iron oxide in the resins extracted from sucupira seeds expressed semiconductor characteristics. This system could be further investigated regarding more improved preparation methods and characterization [145]. In addition, the potential applications of maghemite nanoparticles directed against a specific target with the use of an external magnetic field combined with bioactive sucupira resin are of potential interest [181]. More studies are needed on the phytochemical characterization of the resins extracted from the sucupira seeds and the development of colloidal systems with ideal physicochemical characteristics for application in vivo [182,183]. Preparation of promising delivery systems phytochemicals-based or plant extracts have also been employed successfully to generate metal nanoparticles with enhanced antimicrobial property (Fig. 7) [184,185]. Within this context, recently Oliveira et al. [146] synthesized silver nanoparticles using aqueous extracts of P. emarginatus (AgNPs-PE). Similarly, Toledo et al. [147] demonstrated bactericidal and fungal activity of AgNPs-PE when associated with 1% gentamicin sulfate (AgNPs-PEG) and hyaluronic acid (AgNPs-PEG-AH2).

Fig. 7.

Schematic illustration of the association between plant extracts or phytochemicals and their possible biomedical application.

Nanostructured lipid carriers (NLCs)

NLCs are systems formed by mixing solid and liquid lipids (oils), generating a less structured lipid matrix with imperfections that lead to greater accommodation of bioactive compounds, stabilized in water solution by surfactants [186]. The NLCs have been developed to enhance the encapsulation efficiency and prevent the expulsion of the drug during storage, a condition that usually can occur with solid lipid nanoparticles [187]. Its advantages compared to other nanosystems include the absence of organic solvents for their production and the ability to modulate the release profile of the encapsulated bioactive compound [188]. Furthermore, lipid nanocarriers can be produced with natural lipids that have the advantage of inherent biological activity [189]. Developed as a promising alternative for liposomes and nano-emulsions, NLCs show advantageous features such as the use of low-cost excipients, ease of preparation, and high-scale production [190]. In this process, different methods have been developed and modified to produce NLCs under stable conditions, capable of reaching the specific target. In general, the most common methods used to manufacture these nanosystems can be divided into three different approaches. The first involves high-energy methods such as high shear homogenization and/or ultrasound techniques performed at elevated temperatures (hot homogenization) or below room temperature (cold homogenization). This approach has the advantage of being a highly effective dispersion technique for large-scale production. The cold homogenization further includes advantages as an absence of drug degradation by temperature or crystalline modification. The second approach involves low-energy methods, in which the commonly used technique is microemulsion formation. The advantage of this method is producing NLCs spherical and narrow in size [191]. The solvent emulsification-evaporation technique is a third approach for obtaining NLCs [191]. The technique consists of mixing an organic containing oil phase (liquid lipid + solid lipid) and drug dissolved in an organic solvent (water-immiscible) with an aqueous phase. This process allows the formation of nanodispersions, followed by evaporating the organic solvent causing precipitation of lipid nanoparticles in the aqueous phase. Through this method, small and monodisperse particles are obtained with high encapsulation efficiency [192]. However, the drawback of the method is the use of organic solvents, potentially leading to toxicity issues [191].

Outuki et al. [148] optimized the development of NLCs containing P. pubescens fruit oil that provided promising activities against human colon adenocarcinoma cell line (HT-29) in vitro. In this study, the NLCs formulation containing 5% Precirol® ATO 5, 0.5% P80H, 2.5% PEG-40H castor oil as an aqueous surfactant, and 2% P. pubescens oil presented the best physicochemical characteristics. The authors showed that NLC formulations encapsulating P. pubescens oil were more effective against HT-29 cells when compared to the free oil, associating the efficiency improvement with the higher cellular uptake of the NLCs. Therefore, a well-designed controlled release system may enhance target specificity, optimizing the activities of compounds perhaps implying further application in colorectal cancer therapy.

The essential oils from fruits of the genus Pterodon was also encapsulated in NLCs by [149]. The optimized NLCs in this study consisted of 0.5% (wt/vol) essential oil of Pterodon, 4.5% (wt/vol) of glycerol monostearate as a solid lipid, and 1.4% (wt/vol) polyethylene glycol succinate D-α-tocopherol as surfactant. Using Franz diffusion cells, the release kinetics followed first-order, where the variation in concentration over time depends only on the concentration of sucupira oil encapsulated in the NLCs. Additional bioavailability studies are still required, in addition to in vivo efficacy.

The development of Pterodon genus-derived bioactive-loaded NLC has been extensively investigated showing promising results as drug delivery systems for the treatment of various diseases (Fig. 8).

Fig. 8.

Schematic representation of the theoretical upside of developing plant (Pterodon genus) derived bioactive-loaded nanostructured lipid carriers.

Conclusion

The search for new therapeutic alternatives using flora provides a valuable outlet for new drug discovery in the pharmaceutical industry. However, many new drug molecules have poor water solubility. Overcoming such solubility and/or permeability barriers can be achieved using drug delivery systems such as nano- and micro- structured systems. In this review, we stress the capacity for particulate carriers to encapsulate vegetal derivatives, and detail how their use has shown promising biological activities. This serves to highlight the benefits of encapsulating extracts, oils, and bioactive compounds of the genus Pterodon in lipid, polymeric, and hybrid diverse particulate systems with desired performance and functionality. However, such approaches are mostly at the fundamental research stage still focused on the development of micro and nanostructured systems to overcome some potential challenges related to stability, solubility, and bioavailability. Therefore, there are currently no Pterodon genus-derived encapsulated formulations in clinical trials or commercially available. Although many different combinations of drug carriers and extracts, oils, and bioactive compounds of the genus Pterodon are currently being developed. Further related to the potential of Pterodon genus compounds, there is a relative dearth of information about their mechanisms of action and toxicities. Even though particulate carriers have been studied with respect to their application of the genus Pterodon, there is a requirement for more robust in vivo studies. These could provide a platform for further development of safe and effective therapies using these natural product extracts.