Enzymic oxidation of capsaicin

Cytochrome P450-mediated carbon-carbon bond formation in drug metabolism

Cytochrome P450 (CYPs) enzymes are essential for the metabolism of numerous drug compounds and are capable of catalyzing many types of biotransformation reactions. One of the more unusual reactions catalyzed by CYPs is carbon-carbon (C-C) bond formation, which is critical in organic synthesis but found less commonly in nature. This review focuses on examples of C-C bond formation that occur during drug metabolism and highlights the mechanism for the formation of novel drug metabolites that result from these reactions. The different roles that mammalian CYPs can play in C-C bond formations are also discussed in detail. Ultimately, an understanding of the range of xenobiotics that undergo C-C bond formation and the mechanisms by which they do so can further facilitate metabolite identification and drug design efforts.

Quantification of capsaicinoids in chillies by solid-phase extraction coupled with voltammetry

Capsaicinoids were extracted from a range of spices and chillies using methanol, prior to concentrating the compounds using solid-phase extraction cartridges and water/methanol (50:50% v/v) as the solvent, followed by elution with acetonitrile. The primary extraction procedure, involving only sonication of the spices in methanol, gave results comparable to a procedure that used a combination of sonication, stirring and centrifuging. The voltammetric quantification of the capsaicinoids, at approximately +0.5 V vs. ferrocene^0/+ that were transferred from methanol/water into acetonitrile/water via solid phase extraction, was carried out in microcentrifuge tubes. Linear calibration curves for voltammetry measurements were obtained from low ppm up to at least 1400 ppm of capsaicinoids, with concentrations being detected in the different source extracts (paprika, tabasco sauce, cayenne pepper, and fresh chillies) from approximately 17 to 430 ppm, which corresponded to values of between approximately 130 and 4000 ppm, respectively, present in the original samples.

Analyses of Synthetic N-Acyl Dopamine Derivatives Revealing Different Structural Requirements for Their Anti-inflammatory and Transient-Receptor-Potential-Channel-of-the-Vanilloid-Receptor-Subfamily-Subtype-1 (TRPV1)-Activating Properties

We studied the chemical entities within N-octanoyl dopamine (NOD) responsible for the activation of transient-receptor-potential channels of the vanilloid-receptor subtype 1 (TRPV1) and inhibition of inflammation. The potency of NOD in activating TRPV1 was significantly higher compared with those of variants in which the ortho-dihydroxy groups were acetylated, one of the hydroxy groups was omitted ( N-octanoyl tyramine), or the ester functionality consisted of a bulky fatty acid ( N-pivaloyl dopamine). Shortening of the amide linker (ΔNOD) slightly increased its potency, which was further increased when the carbonyl and amide groups (ΔNODR) were interchanged. With the exception of ΔNOD, the presence of an intact catechol structure was obligatory for the inhibition of VCAM-1 and the induction of HO-1 expression. Because TRPV1 activation and the inhibition of inflammation by N-acyl dopamines require different structural entities, our findings provide a framework for the rational design of TRPV1 agonists with improved anti-inflammatory properties.

Interdisciplinary review for correlation between the plant origin capsaicinoids, non-steroidal antiinflammatory drugs, gastrointestinal mucosal damage and prevention in animals and human beings

BACKGROUND

The plant origin capsaicinoids (capsaicin, dihydrocapsaicin, norcapsaicin, dihydrocapsaicin, homocapsaicin, homodihydrocapsaicin) are well known and used as nutritional additive agents in the every day nutritional practice from the last 9,500 years; however, we had have a very little scientifically based knowledge on their chemistry, physiology and pharmacology in animal observations, and in humans up to the mid-twentieth century. Our knowledge about their chemistry, physiology, pharmacology entered to be scientifically based evidence from the year 1980, dominantly in animal observations. The human observations with capsaicin (capsaicinoids), in terms of good clinical practice, have been started only in the last 10-year period (from 1997) in randomized, prospective, multiclinical studies. The name of "capsaicin" used only in the physiological and pharmacological research both in animal experiments and in human observation. The "capsaicin" (as a "chemically" used natural compound) modifies the so-called capsaicin-sensitive afferent nerves depending on their applied doses.

AIMS

The specific action of capsaicin (capsaicinoids) on sensory afferent nerves modifying gastrointestinal (GI) function (under very specific conditions) offers a possibility for the production of an orally applicable drug or for other drug combinations, which can be used in the human medical therapy. The production of new drug is based on the critical interdisciplinary review of the results obtained with capsaicinoids.

MATERIALS AND METHODS

This paper gives an interdisciplinary and critical overview on the chemical, physiological, pharmacological and toxicological actions of the natural origin capsaicinoids (from the point of drug production) under conditions of acute, subacute and chronic administration in animal experiments and human observations, toxicology, pharmacokinetics). This interdisciplinary review covers the following main chapters: (1) physiological and pharmacological research tool by capsaicin in the animals and human beings, (2) capsaicin research in animals (including the acute, subacute toxicology and chronic toxicology metabolism, genotoxicology), (3) capsaicin observation with capsaicin in human beings.

CONCLUSION

(1) The capsaicin used in the physiological and pharmacological observations (in animals and human beings) chemically represents different chemical compounds, which can be obtained from the plants (paprika, chilli, etc.), (2) capsaicinoids are able to modify the capsaicin-sensitive afferent nerves, which have principle roles in the defence of different organs (including the gastrointestinal tract [against the different chemicals, heat, strech, chemical millieu-induced damage], (3) the application of capsaicin (capsaicinoids) can be repeated for the beneficial effects on the gastrointestinal tract as those in animal experiments. After this interdisciplinary and critical review, this paper demonstrates the well-planned research pathways of the discoveries of capsaicinoids from plant chemistry, via physiology, pharmacology and toxicology in animal experiments and human observations.

Final report on the safety assessment of capsicum annuum extract, capsicum annuum fruit extract, capsicum annuum resin, capsicum annuum fruit powder, capsicum frutescens fruit, capsicum frutescens fruit extract, capsicum frutescens resin, and capsaicin

Capsicum-derived ingredients function as skin-conditioning agents--miscellaneous, external analgesics, flavoring agents, or fragrance components in cosmetics. These ingredients are used in 19 cosmetic products at concentrations as high as 5%. Cosmetic-grade material may be extracted using hexane, ethanol, or vegetable oil and contain the full range of phytocompounds that are found in the Capsicum annuum or Capsicum frutescens plant (aka red chiles), including Capsaicin. Aflatoxin and N-nitroso compounds (N-nitrosodimethylamine and N-nitrosopyrrolidine) have been detected as contaminants. The ultraviolet (UV) absorption spectrum for Capsicum Annuum Fruit Extract indicates a small peak at approximately 275 nm, and a gradual increase in absorbance, beginning at approximately 400 nm. Capsicum and paprika are generally recognized as safe by the U.S. Food and Drug Administration for use in food. Hexane, chloroform, and ethyl acetate extracts of Capsicum Frutescens Fruit at 200 mg/kg resulted in death of all mice. In a short-term inhalation toxicity study using rats, no difference was found between vehicle control and a 7% Capsicum Oleoresin solution. In a 4-week feeding study, red chilli (Capsicum annuum) in the diet at concentrations up to 10% was relatively nontoxic in groups of male mice. In an 8-week feeding study using rats, intestinal exfoliation, cytoplasmic fatty vacuolation and centrilobular necrosis of hepatocytes, and aggregation of lymphocytes in the portal areas were seen at 10% Capsicum Frutescens Fruit, but not 2%. Rats fed 0.5 g/kg day-1 crude Capsicum Fruit Extract for 60 days exhibited no significant gross pathology at necropsy, but slight hyperemia of the liver and reddening of the gastric mucosa were observed. Weanling rats fed basal diets supplemented with whole red pepper at concentrations up to 5.0% for up to 8 weeks had no pathology of the large intestines, livers, and kidneys, but destruction of the taste buds and keratinization and erosion of the gastrointestinal (GI) tract were noted in groups fed 0.5% to 5.0% red pepper. The results of 9-and 12-month extension of this study showed normal large intestines and kidneys. In rabbits fed Capsicum Annuum Powder at 5 mg/kg day-1 in the diet daily for 12 months damage to the liver and spleen was noted. A rabbit skin irritation test of Capsicum Annuum Fruit Extract at concentrations ranging from 0.1% to 1.0% produced no irritation, but Capsicum Frutescens Fruit Extract induced concentration-dependent (at 25 to 500 microg/ml) cytotoxicity in a human buccal mucosa fibroblast cell line. An ethanol extract of red chili was mutagenic in Salmonella typhimurium TA98, but not in TA100, or in Escherichia coli. Other genotoxicity assays gave a similar pattern of mixed results. Adenocarcinoma of the abdomen was observed in 7/20 mice fed 100 mg red chilies per day for 12 months; no tumors were seen in control animals. Neoplastic changes in the liver and intestinal tumors were observed in rats fed red chili powder at 80 mg/kg day-1 for 30 days, intestinal and colon tumors were seen in rats fed red chili powder and 1,2-dimethyl hydrazine, but no tumors were observed in controls. In another study in rats, however, red chile pepper in the diet at the same dose decreased the number of tumors seen with 1,2-dimethylhydrazine. Other feeding studies evaluated the effect of red chili peppers on the incidence of stomach tumors produced by N-methyl-N'-nitro-N-nitrosoguanidine, finding that red pepper had a promoting effect. Capsicum Frutescens Fruit Extract promoted the carcinogenic effect of methyl(acetoxymethyl)nitrosamine (carcinogen) or benzene hexachloride (hepatocarcinogen) in inbred male and female Balb/c mice dosed orally (tongue application). Clinical findings include symptoms of cough, sneezing, and runny nose in chili factory workers. Human respiratory responses to Capsicum Oleoresin spray include burning of the throat, wheezing, dry cough, shortness of breath, gagging, gasping, inability to breathe or speak, and, rarely, cyanosis, apnea, and respiratory arrest. A trade name mixture containing 1% to 5% Capsicum Frutescens Fruit Extract induced very slight erythema in 1 of 10 volunteers patch tested for 48 h. Capsicum Frutescens Fruit Extract at 0.025% in a repeated-insult patch test using 103 subjects resulted in no clinically meaningful irritation or allergic contact dermatitis. One epidemiological study indicated that chili pepper consumption may be a strong risk factor for gastric cancer in populations with high intakes of chili pepper; however, other studies did not find this association. Capsaicin functions as an external analgesic, a fragrance ingredient, and as a skin-conditioning agent--miscellaneous in cosmetic products, but is not in current use. Capsaicin is not generally recognized as safe and effective by the U.S. Food and Drug Administration for fever blister and cold sore treatment, but is considered to be safe and effective as an external analgesic counterirritant. Ingested Capsaicin is rapidly absorbed from the stomach and small intestine in animal studies. Subcutaneous injection of Capsaicin in rats resulted in a rise in the blood concentration, reaching a maximum at 5 h; the highest tissue concentrations were in the kidney and lowest in the liver. In vitro percutaneous absorption of Capsaicin has been demonstrated in human, rat, mouse, rabbit, and pig skin. Enhancement of the skin permeation of naproxen (nonsteroidal anti-inflammatory agent) in the presence of Capsaicin has also been demonstrated. Pharmacological and physiological studies demonstrated that Capsaicin, which contains a vanillyl moiety, produces its sensory effects by activating a Ca2 +-permeable ion channel on sensory neurons. Capsaicin is a known activator of vanilloid receptor 1. Capsaicin-induced stimulation of prostaglandin biosynthesis has been shown using bull seminal vesicles and rheumatoid arthritis synoviocytes. Capsaicin inhibits protein synthesis in Vero kidney cells and human neuroblastoma SHSY-5Y cells in vitro, and inhibits growth of E. coli, Pseudomonas solanacearum, and Bacillus subtilis bacterial cultures, but not Saccharomyces cerevisiae. Oral LD50 values as low as 161.2 mg/kg (rats) and 118.8 mg/kg (mice) have been reported for Capsaicin in acute oral toxicity studies, with hemorrhage of the gastric fundus observed in some of the animals that died. Intravenous, intraperitoneal, and subcutaneous LD50 values were lower. In subchronic oral toxicity studies using mice, Capsaicin produced statistically significant differences in the growth rate and liver/body weight increases. Capsaicin is an ocular irritant in mice, rats, and rabbits. Dose-related edema was observed in animals receiving Capsaicin injections into the hindpaw (rats) or application to the ear (mice). In guinea pigs, dinitrochlorobenzene contact dermatitis was enhanced in the presence of Capsaicin, injected subcutaneously, whereas dermal application inhibited sensitization in mice. Immune system effects have been observed in neonatal rats injected subcutaneously with Capsaicin. Capsaicin produced mixed results in S. typhimurium micronucleus and sister-chromatid exchange genotoxicity assays. Positive results for Capsaicin were reported in DNA damage assays. Carcinogenic, cocarcinogenic, anticarcinogenic, antitumorigenic, tumor promotion, and anti-tumor promotion effects of Capsaicin have been reported in animal studies. Except for a significant reduction in crown-rump length in day 18 rats injected subcutaneously with Capsaicin (50 mg/kg) on gestation days 14, 16, 18, or 20, no reproductive or developmental toxicity was noted. In pregnant mice dosed subcutaneously with Capsaicin, depletion of substance P in the spinal cord and peripheral nerves of pregnant females and fetuses was noted. In clinical tests, nerve degeneration of intracutaneous nerve fibers and a decrease in pain sensation induced by heat and mechanical stimuli were evident in subjects injected intradermally with Capsaicin. An increase in mean inspiratory flow was reported for eight normal subjects who inhaled nebulized 10(-7) M Capsaicin. The results of provocative and predictive tests involving human subjects indicated that Capsaicin is a skin irritant. Overall, studies suggested that these ingredients can be irritating at low concentrations. Although the genotoxicity, carcinogenicity, and tumor promotion potential of Capsaicin have been demonstrated, so have opposite effects. Skin irritation and other tumor-promoting effects of Capsaicin appear to be mediated through interaction with the same vanilloid receptor. Given this mechanism of action and the observation that many tumor promoters are irritating to the skin, the Panel considered it likely that a potent tumor promoter may also be a moderate to severe skin irritant. Thus, a limitation on Capsaicin content that would significantly reduce its skin irritation potential is expected to, in effect, lessen any concerns relating to tumor promotion potential. Because Capsaicin enhanced the penetration of an anti-inflammatory agent through human skin, the Panel recommends that care should be exercised in using ingredients that contain Capsaicin in cosmetic products. The Panel advised industry that the total polychlorinated biphenyl (PCB)/pesticide contamination should be limited to not more than 40 ppm, with not more than 10 ppm for any specific residue, and agreed on the following limitations for other impurities: arsenic (3 mg/kg max), heavy metals (0.002% max), and lead (5 mg/kg max). Industry was also advised that aflatoxin should not be present in these ingredients (the Panel adopted < or =15 ppb as corresponding to "negative" aflatoxin content), and that ingredients derived from Capsicum annuum and Capsicum Frutescens Plant species should not be used in products where N-nitroso compounds may be formed. (ABSTRACT TRUNCATED)

Reducing and oxidizing agents sensitize heat-activated vanilloid receptor (TRPV1) current

We have previously reported that the reducing agent dithiothreitol (DTT) strongly increases thermally induced activity of the transient receptor potential vanilloid receptor-1 (TRPV1) channel. Here, we show that exposure to oxidizing agents also enhances the heat-induced activation of TRPV1. The actions of sulfhydryl modifiers on heat-evoked whole-cell membrane currents were examined in TRPV1-transfected human embryonic kidney 293T cells. The sensitizing effects of the membrane-permeable oxidizing agents diamide (1 mM), chloramine-T (1 mM), and the copper-o-complex (100:400 microM) were not reversed by washout, consistent with the stable nature of covalently modified sulfhydryl groups. In contrast, the membrane-impermeable cysteine-specific oxidant 5,5'-dithio-bis-(2-nitrobenzoic acid) (0.5 mM) was ineffective. The alkylating agent N-ethylmaleimide (1 mM) strongly and irreversibly affected heat-evoked responses in a manner that depended on DTT pretreatment. Extracellular application of the membrane-impermeable reducing agent glutathione (10 mM) mimicked the effects of 10 mM DTT in potentiating the heat-induced and voltage-induced membrane currents. Using site-directed mutagenesis, we identified Cys621 as the residue responsible for the extracellular modulation of TRPV1 by reducing agents. These data suggest that the vanilloid receptor is targeted by redox-active substances that directly modulate channel activity at sites located extracellularly as well as within the cytoplasmic domains. The results obtained demonstrate that an optimal redox state is crucial for the proper functioning of the TRPV1 channel and both its reduced and oxidized states can result in an increase in responsiveness to thermal stimuli.

Peroxidase-catalyzed oxidation of capsaicinoids: steady-state and transient-state kinetic studies

Capsaicinoids are the pungent compounds in Capsicum fruits (i.e., "hot" peppers). Peroxidases catalyze capsaicinoid oxidation and may play a central role in their metabolism. However, key kinetic aspects of peroxidase-catalyzed capsaicinoid oxidation remain unresolved. Using transient-state methods, we evaluated horseradish peroxidase compound I and II reduction by two prominent capsaicinoids (25 degrees C, pH 7.0). We determined rate constants approaching 2 x 10(7) and 5 x 10(5)M(-1)s(-1) for compound I and compound II reduction, respectively. We also determined k(app) values for steady-state capsaicinoid oxidation approaching 8 x 10(5)M(-1)s(-1) (25 degrees C, pH 7.0). Accounting for stoichiometry, these are in excellent agreement with constants for compound II reduction, suggesting that this reaction governs capsaicinoid-dependent peroxidase turnover. Ascorbate rapidly reduced capsaicinoid radicals, assisting in the determination of the kinetic constants reported. Because ascorbate accumulates in Capsicum fruits, it may also be an important determinant for capsaicinoid content and preservation in Capsicum fruits and related products.

Capsaicin, a double-edged sword: toxicity, metabolism, and chemopreventive potential

Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is a primary pungent and irritating principle present in chilies and red peppers which are widely used as spices. Because of its selective effects on the functions of a defined subpopulation of sensory neurons, capsaicin is currently used as a versatile tool for the study of pain mechanisms and also for pharmacotherapy to treat several pain disorders. Considering the frequent consumption of capsaicin as a food additive and its current medicinal use, correct assessment of hazardous effects of this compound is important. Mutagenic and carcinogenic activities of capsaicin and chili extracts have been studied, but results are conflicting. Mammalian metabolism of capsaicin has been also reported. Capsaicin appears to interact with xenobiotic metabolizing enzymes, particularly microsomal cytochrome P450-dependent monooxygenases which are involved in activation as well as detoxification of various chemical carcinogens and mutagens. Recent studies have shown that hepatic cytochrome P450 2E1 catalyzes the conversion of capsaicin to reactive species such as the phenoxy radical intermediate capable of covalently binding to the active site of the enzyme as well as tissue macromolecules. While covalent modification of protein and nucleic acids leads to toxicity including necrosis, mutagenesis, and carcinogenesis, suicidal inhibition of microsomal cytochrome P450 may prohibit further activation of capsaicin and also of other toxic xenobiotics. Results from recent studies indicate that capsaicin possesses the chemoprotective activity against some chemical carcinogens and mutagens.