Recent advances in understanding of vanilloid receptors: a therapeutic target for treatment of pain and inflammation in skin

Discovery of Nonpungent Transient Receptor Potential Vanilloid 1 (TRPV1) Agonist as Strong Topical Analgesic

Paradoxically, some TRPV1 agonists are, at the organismal level, both nonpungent and clinically useful as topical analgesics. Here, we describe the scaled-up synthesis and characterization in mouse models of a novel, nonpungent vanilloid. Potent analgesic activity was observed in models of neuropathic pain, and the compound blocked capsaicin induced allodynia, showing dermal accumulation with little transdermal absorption. Finally, it displayed much weaker systemic toxicity compared to capsaicin and was negative in assays of genotoxicity.

Capsaicin and Its Role in Chronic Diseases

A significant number of experimental and clinical studies published in peer-reviewed journals have demonstrated promising pharmacological properties of capsaicin in relieving signs and symptoms of non-communicable diseases (chronic diseases). This chapter provides an overview made from basic and clinical research studies of the potential therapeutic effects of capsaicin, loaded in different application forms, such as solution and cream, on chronic diseases (e.g. arthritis, chronic pain, functional gastrointestinal disorders and cancer). In addition to the anti-inflammatory and analgesic properties of capsaicin largely recognized via, mainly, interaction with the TRPV1, the effects of capsaicin on different cell signalling pathways will be further discussed here. The analgesic, anti-inflammatory or apoptotic effects of capsaicin show promising results in arthritis, neuropathic pain, gastrointestinal disorders or cancer, since evidence demonstrates that the oral or local application of capsaicin reduce inflammation and pain in rheumatoid arthritis, promotes gastric protection against ulcer and induces apoptosis of the tumour cells. Sadly, these results have been paralleled by conflicting studies, which indicate that high concentrations of capsaicin are likely to evoke deleterious effects, thus suggesting that capsaicin activates different pathways at different concentrations in both human and rodent tissues. Thus, to establish effective capsaicin doses for chronic conditions, which can be benefited from capsaicin therapeutic effects, is a real challenge that must be pursued.

The carbonate analogues of 5'-halogenated resiniferatoxin as TRPV1 ligands

A series of carbonate analogues of 5'-halogenated RTX have been investigated in order to examine the effect of the carbonate group as a linker and the role of halogens in the reversal of activity from agonism to antagonism for rat and human TRPV1 heterologously expressed in Chinese hamster ovary cells. The carbonate analogues showed similar activities to the corresponding RTX derivatives in rat TRPV1 but lower potency in human TRPV1. 5-Halogenation converted the agonists to partial agonists or full antagonists and the extent of antagonism reflected the order of I>Br>Cl>F, with a somewhat greater extent of antagonism for the derivatives of the 4-amino RTX surrogates compared to the corresponding derivatives of RTX itself. The carbonate analogues of I-RTX (60) and 5-bromo-4-amino-RTX (66) were potent and full antagonists with Ki(ant)=2.23 and 2.46 nM, respectively, for rat TRPV1, which were ca. 5-fold more potent than I-RTX (2) under our conditions. The conformational analysis of the I-RTX-carbonate (60) indicated that its bent conformation was similar to that of I-RTX, consistent with compound 60 and I-RTX showing comparable potent antagonism.

Capsaicin sensitizes TRAIL-induced apoptosis through Sp1-mediated DR5 up-regulation: involvement of Ca(2+) influx

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various malignant cells, several cancers including human hepatocellular carcinoma (HCC) exhibit potent resistance to TRAIL-induced cell death. The aim of this study is to evaluate the anti-cancer potential of capsaicin in TRAIL-induced cancer cell death. As indicated by assays that measure phosphatidylserine exposure, mitochondrial activity and activation of caspases, capsaicin potentiated TRAIL-resistant cells to lead to cell death. In addition, we found that capsaicin induces the cell surface expression of TRAIL receptor DR5, but not DR4 through the activation Sp1 on its promoter region. Furthermore, we investigated that capsaicin-induced DR5 expression and apoptosis are inhibited by calcium chelator or inhibitors for calmodulin-dependent protein kinase. Taken together, our data suggest that capsaicin sensitizes TRAIL-mediated HCC cell apoptosis by DR5 up-regulation via calcium influx-dependent Sp1 activation.

Receptor activity and conformational analysis of 5'-halogenated resiniferatoxin analogs as TRPV1 ligands

A series of 5'-halogenated resiniferatoxin analogs have been investigated in order to examine the effect of halogenation in the A-region on their binding and the functional pattern of agonism/antagonism for rat TRPV1 heterologously expressed in Chinese hamster ovary cells. Halogenation at the 5-position in the A-region of RTX and of 4-amino RTX shifted the agonism of parent compounds toward antagonism. The extent of antagonism was greater as the size of the halogen increased (I > Br > Cl > F) while the binding affinities were similar, as previously observed for our potent agonists. In this series, 5-bromo-4-amino RTX (39) showed very potent antagonism with K(i) (ant) = 2.81 nM, which was thus 4.5-fold more potent than 5'-iodo RTX, previously reported as a potent TRPV1 antagonist. Molecular modeling analyses with selected agonists and the corresponding halogenated antagonists revealed a striking conformational difference. The 3-methoxy of the A-region in the agonists remained free to interact with the receptor whereas in the case of the antagonists, the compounds assumed a bent conformation, permitting the 3-methoxy to instead form an internal hydrogen bond with the C4-hydroxyl of the diterpene.

Capsaicin displays anti-proliferative activity against human small cell lung cancer in cell culture and nude mice models via the E2F pathway

Background

Small cell lung cancer (SCLC) is characterized by rapid progression and low survival rates. Therefore, novel therapeutic agents are urgently needed for this disease. Capsaicin, the active ingredient of chilli peppers, displays anti-proliferative activity in prostate and epidermoid cancer in vitro. However, the anti-proliferative activity of capsaicin has not been studied in human SCLCs. The present manuscript fills this void of knowledge and explores the anti-proliferative effect of capsaicin in SCLC in vitro and in vivo.

Methodology/Principal Findings

BrdU assays and PCNA ELISAs showed that capsaicin displays robust anti-proliferative activity in four human SCLC cell lines. Furthermore, capsaicin potently suppressed the growth of H69 human SCLC tumors in vivo as ascertained by CAM assays and nude mice models. The second part of our study attempted to provide insight into molecular mechanisms underlying the anti-proliferative activity of capsaicin. We found that the anti-proliferative activity of capsaicin is correlated with a decrease in the expression of E2F-responsive proliferative genes like cyclin E, thymidylate synthase, cdc25A and cdc6, both at mRNA and protein levels. The transcription factor E2F4 mediated the anti-proliferative activity of capsaicin. Ablation of E2F4 levels by siRNA methodology suppressed capsaicin-induced G1 arrest. ChIP assays demonstrated that capsaicin caused the recruitment of E2F4 and p130 on E2F-responsive proliferative promoters, thereby inhibiting cell proliferation.

Conclusions/Significance

Our findings suggest that the anti-proliferative effects of capsaicin could be useful in the therapy of human SCLCs.

Non-vanillyl resiniferatoxin analogues as potent and metabolically stable transient receptor potential vanilloid 1 agonists

A series of non-vanillyl resiniferatoxin analogues, having 4-methylsulfonylaminophenyl and fluorophenyl moieties as vanillyl surrogates, have been investigated as ligands for rat TRPV1 heterologously expressed in Chinese hamster ovary cells. Although lacking the metabolically problematic 4-hydroxy substituent on the A-region phenyl ring, the compounds retained substantial agonist potency. Indeed, the 3-methoxy-4-methylsulfonylaminophenyl analog (1) was modestly (2.5-fold) more potent than RTX, with an EC(50)=0.106 nM. Further, it resembled RTX in its kinetics and pattern of stimulation of the levels of intracellular calcium in individual cells, as revealed by imaging. Compound 1 displayed modestly enhanced in vitro stability in rat liver microsomes and in plasma, suggesting that it might be a pharmacokinetically more favorable surrogate of resiniferatoxin. Molecular modeling analyses with selected analogues provide evidence that the conformational differences could affect their binding affinities, especially for the ester versus amide at the B-region.

TRP channels as novel players in the pathogenesis and therapy of itch

Itch (pruritus) is a sensory phenomenon characterized by a (usually) negative affective component and the initiation of a special behavioral act, i.e. scratching. Older studies predominantly have interpreted itch as a type of pain. Recent neurophysiological findings, however, have provided compelling evidence that itch (although it indeed has intimate connections to pain) rather needs to be understood as a separate sensory modality. Therefore, a novel pruriceptive system has been proposed, within which itch-inducing peripheral mediators (pruritogens), itch-selective receptors (pruriceptors), sensory afferents and spinal cord neurons, and defined, itch-processing central nervous system regions display complex, layered responses to itch. In this review, we begin with a current overview on the neurophysiology of pruritus, and distinguish it from that of pain. We then focus on the functional characteristics of the large family of transient receptor potential (TRP) channels in skin-coupled sensory mechanisms, including itch and pain. In particular, we argue that - due to their expression patterns, activation mechanisms, regulatory roles, and pharmacological sensitivities - certain thermosensitive TRP channels are key players in pruritus pathogenesis. We close by proposing a novel, TRP-centered concept of pruritus pathogenesis and sketch important future experimental directions towards the therapeutic targeting of TRP channels in the clinical management of itch.

Chemical Warfare Agents Chemical Warfare Agents: Their Past and Continuing Threat and Evolving Therapies Part II of II

Chemical warfare agents are ideal weapons for terrorists and for use in military operations against both civilian populations and troops. Thus, there have been efforts by the United States in cooperation with other concerned nations to develop animal models to understand the pathophysiology of the injuries induced by these agents, and to develop suitable animal models for testing of pre-and post-exposure protectants and therapies. Sulfur mustard remains the most significant chemical warfare agent that produces cutaneous injuries. Institution of standard recommendations prior to threatened exposure or after exposure are something that we need to be aware of in the world we live in. In addition, pre-and post-exposure therapies now being studied offer hope for moderating the mortality and morbidity that can result from chemical exposure.

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)

Capsaicin induced apoptosis of B16-F10 melanoma cells through down-regulation of Bcl-2

Capsaicin (8-methyl-N-vanillyl-6-nonenamide), a pungent ingredient of hot chili peppers, has been reported to possess substantial anticarcinogenic and antimutagenic activities. In the present study, we investigated the effect of capsaicin on induction of apoptosis in highly metastatic B16-F10 murine melanoma cells. Capsaicin inhibited growth of B16-F10 cells in a concentration-dependent manner. Proapoptotic effect of capsaicin was evidenced by nuclear condensation, internucleosomal DNA fragmentation, in situ terminal nick-end labeling of fragmented DNA (TUNEL), and an increased sub G1 fraction. Treatment of B16-F10 cells with capsaicin caused release of mitochondrial cytochrome c, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase in a dose-dependent manner. Furthermore, Bcl-2 expression in the B16-F10 cells was slightly down-regulated by capsaicin treatment. In contrast, there were no alterations in the levels of Bax in capsaicin-treated cells. Collectively, these findings indicate that capsaicin-induces apoptosis of B16-F10 melanoma cells via down-regulation the Bcl-2.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Neurophysiological, neuroimmunological, and neuroendocrine basis of pruritus

Pruritus (itch) can be defined as an unpleasant cutaneous sensation associated with the immediate desire to scratch. Recent findings have identified potential classes of endogenous "itch mediators" and establish a modern concept for the pathophysiology of pruritus. First, there in no universal peripheral itch mediator, but disease-specific sets of involved mediators. Second, numerous mediators of skin cells can activate and sensitize pruritic nerve endings, and even modulate their growth. Our knowledge of itch processing in the spinal cord and the involved centers in the central nervous system is rapidly growing. This review summarizes the current information about the significance of neuron-skin interactions, ion channels, neuropeptides, proteases, cannabinoids, opioids, kinins, cytokines, biogenic amines, neurotransmitters, and their receptors in the pathobiology of pruritus. A deeper understanding of these circuits is required for the development of novel antipruritic strategies.

Frontiers in pruritus research: scratching the brain for more effective itch therapy

This Review highlights selected frontiers in pruritus research and focuses on recently attained insights into the neurophysiological, neuroimmunological, and neuroendocrine mechanisms underlying skin-derived itch (pruritogenic pruritus), which may affect future antipruritic strategies. Special attention is paid to newly identified itch-specific neuronal pathways in the spinothalamic tract that are distinct from pain pathways and to CNS regions that process peripheral pruritogenic stimuli. In addition, the relation between itch and pain is discussed, with emphasis on how the intimate contacts between these closely related yet distinct sensory phenomena may be exploited therapeutically. Furthermore, newly identified or unduly neglected intracutaneous itch mediators (e.g., endovanilloids, proteases, cannabinoids, opioids, neurotrophins, and cytokines) and relevant receptors (e.g., vanilloid receptor channels and proteinase-activated, cannabinoid, opioid, cytokine, and new histamine receptors) are discussed. In summarizing promising new avenues for managing itch more effectively, we advocate therapeutic approaches that strive for the combination of peripherally active antiinflammatory agents with drugs that counteract chronic central itch sensitization.

Activation of transient receptor potential vanilloid 1 (TRPV1) by resiniferatoxin

Transient receptor potential vanilloid 1 (TRPV1) is a Ca(2+) permeable non-selective cation channel activated by physical and chemical stimuli. Resiniferatoxin (RTX), an ultrapotent agonist of TRPV1, is under investigation for treatment of urinary bladder hyper-reflexia and chronic pain conditions. Here, we have determined the characteristics of RTX-induced responses in cells expressing native and cloned rat TRPV1. Whole-cell currents increase with repeated application of submaximal concentrations of RTX until a maximal response is attained and do not deactivate even after prolonged washout. Interestingly, the rate of activation and block by capsazepine of RTX-induced currents are significantly slower than for capsaicin-induced currents. RTX-induced whole-cell currents are outwardly rectifying, but to a lesser extent than capsaicin-induced currents. RTX-induced single channel currents exhibit multiple conductance states and outward rectification. The open probability (P(o)) of RTX-induced currents is higher at all potentials as compared to capsaicin-induced currents, which showed a strong voltage-dependent decrease at negative potentials. Single-channel kinetic analyses reveal that open-time distribution of RTX-induced currents can be fitted with three exponential components at negative and positive potentials. The areas of distribution of the longer open time constants are significantly larger than capsaicin-induced currents. The closed-time distribution of RTX-induced currents can be fitted with three exponential components as compared to capsaicin-induced currents, which require four exponential components. Current-clamp experiments reveal that low concentrations of RTX caused a slow and sustained depolarization beyond threshold while generating few action potentials. Concentrations of capsaicin required for the same extent of depolarization generated a significantly greater number of action potentials. These properties of RTX may play a role in its clinical usefulness.

A hot new twist to hair biology: involvement of vanilloid receptor-1 (VR1/TRPV1) signaling in human hair growth control

The vanilloid receptor-1 (VR1, or transient receptor potential vanilloid-1 receptor, TRPV1) is activated by capsaicin, the key ingredient of hot peppers. TRPV1 was originally described on sensory neurons as a central integrator of various nociceptive stimuli. However, several human skin cell populations are also now recognized to express TRPV1, but with unknown function. Exploiting the human hair follicle (HF) as a prototypic epithelial-mesenchymal interaction system, we have characterized the HF expression of TRPV1 in situ and have examined TRPV1 signaling in organ-cultured human scalp HF and outer root sheath (ORS) keratinocytes in vitro. TRPV1 immunoreactivity was confined to distinct epithelial compartments of the human HF, mainly to the ORS and hair matrix. In organ culture, TRPV1 activation by capsaicin resulted in a dose-dependent and TRPV1-specific inhibition of hair shaft elongation, suppression of proliferation, induction of apoptosis, premature HF regression (catagen), and up-regulation of intrafollicular transforming growth factor-beta(2). Cultured human ORS keratinocytes also expressed functional TRPV1, whose stimulation inhibited proliferation, induced apoptosis, elevated intracellular calcium concentration, up-regulated known endogenous hair growth inhibitors (interleukin-1beta, transforming growth factor-beta(2)), and down-regulated known hair growth promoters (hepatocyte growth factor, insulin-like growth factor-I, stem cell factor). These findings strongly support TRPV1 as a significant novel player in human hair growth control, underscore the physiological importance of TRPV1 in human skin beyond nociception, and identify TRPV1 as a promising, novel target for pharmacological manipulations of epithelial growth disorders.

Assessment of pepper spray product potency in Asian and Caucasian forearm skin using transepidermal water loss, skin temperature and reflectance colorimetry

Historically, pepper spray product potency has been established using a taste test evaluation. A taste test is subjective and may not be appropriate for assessing pepper potency in skin. The current study evaluated chemically diverse pepper sprays in human forearm skin using three objective, noninvasive parameters: transepidermal water loss, skin surface temperature and erythema, as a means for assessing dermal pharmacology, toxicology and product potency. Five commercial pepper spray products containing various capsaicinoid analogs at various concentrations were evaluated in duplicate on volar forearms of six Caucasians and six Asians using a 10 min exposure. Mean surface skin temperature, transepidermal water loss results were highly variable and therefore did not demonstrate dose responsive behavior to increasing capsaicinoid concentrations. Erythema, as measured by increases in a* (reflected light in the red-to-green color spectrum) of the L*a*b* uniform color scale, was superior among parameters evaluated in discriminating pepper spray potency and correlated well with the relative and total capsaicinoid concentration in the products. Products containing greater than 16 mg ml(-1) capsaicinoid concentration produced greater erythema responses in Caucasians than Asians. Asians responded greater to the synthetic analog, nonivamide, than to mixtures of capsaicinoids, while Caucasians responded equally to both capsaicinoid analogs. Thus, pepper spray product potency in human skin reflects the total capsaicinoid concentration, the specific capsaicin analog(s) present, and the race of the individual exposed. The finding that the reflectance colorimeter a* scale can differentiate these parameters in skin will have a significant impact on evaluating the use and efficacy of pepper spray products in humans.

Effects of capsaicin on the sensorimotor function of the proximal stomach in humans

BACKGROUND

Capsaicin-sensitive afferents have been implicated in the control of visceral sensorimotor functions.

AIM

To study the effects of capsaicin on the sensorimotor function of the proximal stomach in humans.

METHODS

In 10 healthy subjects, a gastric barostat was used to study the effect of saline or capsaicin-containing red pepper sauce on the sensitivity to gastric distension and on gastric accommodation to a meal.

RESULTS

The administration of capsaicin was accompanied by a relaxation of the proximal stomach. After capsaicin, the compliance of the proximal stomach was increased and higher perception scores were reached for the same distending pressures. Dosing with capsaicin significantly decreased the pressures and corresponding wall tensions at the discomfort threshold. Gastric accommodation to a meal was not altered by capsaicin.

CONCLUSION

The acute administration of capsaicin decreases proximal gastric tone, inhibits phasic contractility of the proximal stomach and increases sensitivity to proximal gastric distension. These data suggest the involvement of vanilloid receptor 1 in the modulation of gastric sensorimotor function in humans.

Resiniferatoxin-induced loss of plasma membrane in vanilloid receptor expressing cells

Resiniferatoxin (RTX), a potent analog of capsaicin, was evaluated electrophysiologically in dorsal root ganglion (DRG) cells and cell lines ectopically expressing the vanilloid receptor type 1 (VR1) to determine if cell phenotype influenced RTXs neurotoxic properties. Furthermore, capsaicin and heat activation of VR1 were evaluated in these cells to determine if cellular damage was unique to RTX activation of the receptors. RTX application to DRG cells identified as type 1, 2 or 5, cell types known to express VR1, induced large inward currents. RTX did not induce currents in DRG cells that do not express the receptor (type 4 cells). In cell lines ectopically expressing VR1, RTX-induced similar currents. RTX produced no effect in non-transfected cells. After exposure to RTX both DRG cells and transfected cells failed to respond to subsequent applications of the agonist. In addition, whole cell capacitance was reduced up to 70%. The decrease in capacitance was associated with the loss of plasma membrane, as determined by confocal microscopy. Cell phenotype, other than VR1 expression, did not influence the response to RTX. Interestingly, capsaicin and heat activation of vanilloid receptors also decreased cell capacitance, but the loss of membrane was not as great as with RTX and responses to these stimuli were not lost after the initial exposure. The loss of cell membrane required elevated intracellular levels of Ca2+. From these data it was concluded that the loss of cell membrane was dependent on the presence of both VR1 and intracellular Ca2+ accumulation, but not on cell phenotype.

Neuropeptídeos na pele

Há evidências crescentes de que a inervação cutânea é capaz de modular uma variedade de fenômenos cutâneos agudos e crônicos, interagindo com as células da pele e seus componentes imunes. Essa forma de sinalização local entre tecido nervoso e tecido cutâneo ocorre especialmente por meio dos neuropeptídeos, uma numerosa família de neurotransmissores de natureza química comum e nomenclatura heterogênea presentes em todo o sistema nervoso e secretados pelas fibras nervosas cutâneas. São alvo desta revisão os neuropeptídeos substância P (SP), o peptídeo relacionado ao gene da calcitonina (CGRP), o peptídeo vasoativo intestinal (VIP), o peptídeo ativador da adenilato-ciclase pituitária (PACAP), o neuropeptídeo Y (NPY) e a somatostatina (SOM). Serão discutidas suas ações sobre as células da pele e sistema imune, bem como estudos recentes que sugerem a participação dos neuropeptídeos nas respostas inflamatórias cutâneas, nas reações de hipersensibilidade e em dermatoses humanas, notadamente na psoríase, dermatite atópica, hanseníase e alopecia.

Modulation of cutaneous inflammation by angiotensin-converting enzyme

Cutaneous neurogenic inflammation is a complex biological response of the host immune system to noxious stimuli. Present evidence suggests that zinc metalloproteases may play an important role in the regulation of neurogenic inflammation by controlling the local availability of neuropeptides, such as substance P (SP), that are capable of initiating or amplifying cutaneous inflammation after release from sensory nerves. To address the hypothesis that the dipeptidyl carboxypeptidase angiotensin-converting enzyme (ACE) is capable of modulating skin inflammation, we have analyzed murine allergic contact dermatitis (ACD) and irritant contact dermatitis (ICD) using wild-type C57BL/6J (ACE(+/+)) or genetically engineered mice with a heterozygous deletion of somatic ACE (ACE(+/-)). In 2,4-dinitro-1-fluorobenzene-sensitized ACE(+/-) mice, ACD was significantly augmented in comparison to ACE(+/+) controls as determined by the degree of ear swelling after exposure to hapten. Likewise, systemic treatment of ACE(+/+) mice with the ACE inhibitor captopril before sensitization or elicitation of ACD significantly augmented the ACD response. In contrast, local damage and neuropeptide depletion of sensory nerves following capsaicin, injection of a bradykinin B(2), or a SP receptor antagonist before sensitization significantly inhibited the augmented effector phase of ACD in mice with functionally absent ACE. However, in contrast to ACD, the response to the irritant croton oil was not significantly altered in ACE(+/-) compared with ACE(+/+) mice. Thus, ACE by degrading bradykinin and SP significantly controls cutaneous inflammatory responses to allergens but not to irritants, which may explain the frequently observed exacerbation of inflammatory skin disease in patients under medication with ACE inhibitors.

Inhibitory effects of capsaicinoids on fatty acid desaturation in a rat liver cell line

The inhibitory effects of such vanillylamides as capsaicin and nine capsaicinoids on fatty acid desaturation in liver cells were investigated by using the cultured rat liver cell line, BRL-3A. When capsaicin was added to the medium, it had a relatively strong inhibitory effect on delta6 desaturation and clear inhibitory effects on delta5 and C24delta16 desaturation (delta16 desaturation of C24-polyunsaturated fatty acids). Capsaicinoids with side carbon chain lengths of C10:0 and C12:0 expressed the maximum inhibitory effects of the nine capsaicinoids on fatty acid desaturation in the BRL-3A cells. The inhibitory effects of the capsaicinoids were not correlated with their pungency.

Substance P

Substance P is considered to be an important neuropeptide in nociceptive processes. Although substance P was described more than 60 years ago, there is still controversy about its exact role in nociception. This article reviews the current knowledge about the function of substance P in pain. Special emphasis is put on how to use this knowledge in the development of new ways to treat pain.

Stimulation of dichlorofluorescin oxidation by capsaicin and analogues in RAW 264 monocyte/macrophages: lack of involvement of the vanilloid receptor

In studies into the oxidative burst in RAW 264 monocyte/macrophages, it was observed that capsaicin, a vanilloid receptor agonist, stimulated dichlorofluorescin (DCFH) oxidation in a concentration-dependent manner, which could be blocked by capsazepine, a vanilloid receptor antagonist. However, by use of a number of vanilloid agonists (including N-octyl-3-chloro-4-hydroxyphenylacetamide, 4m), we demonstrated that there was no relationship between vanilloid agonist potency and the capacity to stimulate DCFH oxidation. The oxidative burst stimulators Tween 20 and phorbol myristyl acetate (PMA) also stimulated reactive oxygen species generation, which again was inhibited by capsazepine. Use of the selective inhibitor diphenyliodonium iodide ruled out a role for plasma membrane NAD(P)H oxidase as the site of capsaicin- and 4m-stimulated DCFH oxidation. However, this DCFH oxidation was modulated by a number of inhibitors of mitochondrial respiration. Rotenone enhanced DCFH oxidation induced by capsaicin and 4m, whilst malonic acid and potassium cyanide inhibited this response. 2,4-Dinitrophenol, an inhibitor of oxidative phosphorylation, was without effect. The antioxidant trolox c inhibited DCFH oxidation stimulated by capsaicin, 4m, and PMA, whereas N-acetylcysteine, a precursor of glutathione, was without effect. Capsazepine inhibited DCFH oxidation in unstimulated cells and in cells treated with menadione, a redox-cycling quinone. Capsazepine was also a potent antioxidant when measured in a Fe3+ reduction assay. We concluded that DCFH oxidation stimulated by vanilloid analogues was not mediated via a vanilloid receptor, but rather by impairment of mitochondrial electron transport.

Topical medications for orofacial neuropathic pain: a review

BACKGROUND

The authors discuss the local pharmacotherapy for chronic orofacial neuropathic pain disorders such as neuropathies, neuromas and neuralgias.

METHODS

The authors conducted a systematic literature review on this topic. The focus of the review involved the two most commonly applied medications for neuropathic disorders--local anesthetics and capsaicin. Other compounds such as nonsteroidal anti-inflammatory drugs, sympathomimetic agents, anticonvulsants and N-methyl-D-aspartate receptor antagonists also were reviewed. The medication delivery and retention methods appropriate for oral and perioral disease and pain control are described in this article.

RESULTS

There are an ever-increasing number of agents that can be used to help patients with neuropathic-based oral and perioral pain problems. Moreover, a clear advancement in the delivery of these medications is the development of a vehicle-carrier agent (pluronic lecithin organogel) that can penetrate the mucosa and cutaneous tissues and carry the active medication with it to the treatment site. The major caveat underlying these treatment strategies is that except for patient testimony and a few studies, there are limited empirical data on the efficacy of most of these new formulations, and additional research is clearly needed.

CONCLUSIONS

Because of their rapid onset and low side-effect profile, topical medications offer a distinct advantage over systemic administration for those orofacial disorders that are regional, near the surface and chronic and that demonstrate some response such as pain relief to topical or subcutaneous anesthetics.

CLINICAL IMPLICATIONS

Practicing dentists now have some new tools they can use to help manage patients who have a chronic nerve pain disorder in and around the mouth.

The effects of capsaicin on reflux, gastric emptying and dyspepsia

AIMS

To evaluate capsaicin's effects on heartburn, dyspepsia, gastric acidity and emptying, and gastro-oesophageal reflux, and to test the hypothesis that capsaicin induces heartburn and exacerbates symptoms by sensitizing the oesophagus.

METHODS

Eleven heartburn sufferers underwent two separate pH monitoring sessions and assessments of gastric emptying (13C-octanoic acid breath test), heartburn and dyspepsia (100 mm VAS) after a non-irritant meal. The meal consisted of a sausage biscuit with egg, cheese and 30 g raw onion, 8 oz chocolate milk and a peppermint patty. Thirty minutes prior to meal consumption, subjects were administered a placebo capsule. On visit 1, subjects consumed the meal containing 100 microl 13C-octanoic acid cooked in the egg, over 15 min. On visit 2, subjects consumed the meal plus 5 mg capsaicin in gelatin capsules.

RESULTS

Oesophageal and gastric pH profiles and gastric emptying were not different between meals. Capsaicin did not alter mean heartburn and dyspepsia scores (P > 0.05), but significantly decreased time to peak heartburn (120 min vs. 247 min; P < 0.003). Time to peak dyspepsia was not altered by capsaicin (P > 0.05).

CONCLUSION

Capsaicin enhances noxious postprandial heartburn, presumably by direct effects on sensory neurons.

Resiniferatoxin-type phorboid vanilloids display capsaicin-like selectivity at native vanilloid receptors on rat DRG neurons and at the cloned vanilloid receptor VR1

1 Although the cloned rat vanilloid receptor VR1 appears to account for both receptor binding and calcium uptake, the identification of vanilloids selective for one or the other response is of importance because these ligands may induce distinct patterns of biological activities. 2 Phorbol 12,13-didecanoate 20-homovanillate (PDDHV) evoked 45Ca(2+)-uptake by rat dorsal root ganglion neurons (expressing native vanilloid receptors) in culture with an EC50 of 70 nM but inhibited [3H]-resiniferatoxin (RTX) binding to rat dorsal root ganglion membranes with a much lower potency (Ki>10,000 nM). This difference in potencies represents a more than 100 fold selectivity for capsaicin-type pharmacology. 3 45Ca2+ influx by PDDHV was fully inhibited by the competitive vanilloid receptor antagonist capsazepine, consistent with the calcium uptake occurring via vanilloid receptors. 4 PDDHV induced calcium mobilization in CHO cells transfected with the cloned rat vanilloid receptor VR1 with an EC50 of 125 nM and inhibited [3H]-RTX binding to these cells with an estimated Ki of 10,000 nM. By contrast, PDDHV failed to evoke a measurable calcium response in non-transfected CHO cells, confirming its action through VR1. 5 We conclude that PDDHV is two orders of magnitude more potent for inducing calcium uptake than for inhibiting RTX binding at vanilloid receptors, making this novel vanilloid a ligand selective for capsaicin-type pharmacology. These results emphasize the importance of monitoring multiple endpoints for evaluation of vanilloid receptor structure-activity relations. Furthermore, PDDHV now provides a tool to explore the biological correlates of capsaicin-type vanilloid pharmacology.

The cloned rat vanilloid receptor VR1 mediates both R-type binding and C-type calcium response in dorsal root ganglion neurons

[(3)H]Resiniferatoxin (RTX) binding and calcium uptake by rat dorsal root ganglion (DRG) neurons show distinct structure-activity relations, suggestive of independent vanilloid receptor (VR) subtypes. We have now characterized ligand binding to rat VR1 expressed in human embryonic kidney (HEK293) and Chinese hamster ovary (CHO) cells and compared the structure-activity relations with those for calcium mobilization. Human embryonic kidney cells (HEK293/VR1 cells) and Chinese hamster ovary cells transfected with VR1 (CHO/VR1 cells) bound [(3)H]RTX with affinities of 84 and 103 pM, respectively, and positive cooperativity (Hill numbers were 2.1 and 1.8). These parameters are similar to those determined with rat DRG membranes expressing native VRs (a K(d) of 70 pM and a Hill number of 1.7). The typical vanilloid agonists olvanil and capsaicin inhibited [(3)H]RTX binding to HEK293/VR1 cells with K(i) values of 0.4 and 4.0 microM, respectively. The corresponding values in DRG membranes were 0.3 and 2.5 microM. HEK293/VR1 cells and DRG membranes also recognized the novel vanilloids isovelleral and scutigeral with similar K(i) values (18 and 20 microM in HEK293/VR1 cells; 24 and 21 microM in DRGs). The competitive vanilloid receptor antagonist capsazepine inhibited [(3)H]RTX binding to HEK293/VR1 cells with a K(i) value of 6.2 microM and binding to DRG membranes with a K(i) value of 8.6 microM. RTX and capsaicin induced calcium mobilization in HEK293/VR1 cells with EC(50) values of 4.1 and 82 nM, respectively. Thus, the relative potencies of RTX (more potent for binding) and capsaicin (more potent for calcium mobilization) are similar in DRG neurons and cells transfected with VR1. We conclude that VR1 can account for both the ligand binding and calcium uptake observed in rat DRG neurons.

The prevention and treatment of cutaneous injury secondary to chemical warfare agents. Application of these finding to other dermatologic conditions and wound healing

Chemical warfare agents are easily and inexpensively produced and are therefore potentially accessible to even underdeveloped nations and are a threat to civilian populations as well as advancing troops. Sulfur mustard is by far the most significant chemical warfare agent that produces cutaneous injury. Significant advances over the past few years have been made in understanding the pathophysiology of the lesions produced by sulfur mustard, as well as development of barrier creams and pre and post exposure therapies to moderate the damage and accelerate healing. Not only have these advances improved our understanding of the sulfur mustard injury and the care of the patients, these are potentially numerous applications for these findings in other dermatologic conditions including the treatment of chronic wounds.

Dialdehyde sesquiterpenes and other terpenoids as vanilloids

Selected naturally occurring unsaturated dialdehyde sesquiterpenes and related bioactive terpenoids were assayed for vanilloid-like activity. Out of the 25 compounds tested, eight inhibited completely the specific binding of [3H]resiniferatoxin by rat spinal cord membranes: binding affinities ranged from 0.6 microM for cinnamodial to 19.0 microM for hebelomic acid F. These values were comparable to the binding affinity of capsaicin (2.7 microM). With the exception of four ligands, compounds that inhibited resiniferatoxin binding to rat spinal cord membranes were also pungent on the human tongue where they showed cross-tachyphylaxis with capsaicin. As expected from their reactive nature, these compounds possess additional sites of action, as reflected in the complex behavior of the stimulation of calcium influx by cinnamodial and cinnamosmolide at high concentrations. This observation might explain the unexpectedly weak membrane depolarization by cinnamodial compared to capsaicin. We conclude that a range of sesquiterpene dialdehydes and related terpenoids, both pungent and non-pungent, may function as vanilloids. These compounds may represent a new chemical lead for the development of vanilloid drugs, structurally unrelated to either capsaicin or resiniferatoxin.

Specific vanilloid responses in C6 rat glioma cells

Capsaicin and its ultrapotent analog resiniferatoxin (RTX) act through specific vanilloid receptors on sensory neurons. Here, we describe specific vanilloid responses in rat C6 glioma cells. Capsaicin and RTX stimulated 45Ca uptake in a similar fashion to that found for cultured rat dorsal root ganglion neurons (DRGs); this response was antagonized by the antagonists capsazepine and ruthenium red. As in DRGs, pretreatment of C6 cells with capsaicin or RTX produced desensitization to subsequent stimulation of 45Ca uptake. The potency for desensitization by RTX in the C6 cells corresponded to that for 45Ca uptake, whereas in DRGs it occurred at significantly lower concentrations corresponding to that for the high affinity [3H]RTX binding site. Consistent with this difference, in C6 cells we were unable to detect [3H]RTX binding. These characteristics suggest the presence of C-type but not R-type vanilloid receptors on C6 cells. After 2 day treatment, capsaicin but not RTX inhibited the proliferation and altered the differentiation of the cells and produced apoptosis. In the long term experiments, capsazepine, instead of antagonizing the effect of capsaicin, acted as an agonist. Moreover, capsazepine displayed these effects with higher potency than that of capsaicin. The different potencies and structure activity relations suggest a distinct mechanism for these long-term vanilloid effects. Our finding that C6 cells can respond directly to capsaicin necessitates a reevaluation of the in vivo pathway of response to vanilloids, and highlights the importance of the neuron-glial network.

Characterization of Functional Vanilloid Receptors Expressed by Mast Cells

Capsaicin and its ultrapotent analog resiniferatoxin (RTX) act through specific vanilloid receptors on sensory neurons. The C-type receptor is coupled to 45Ca uptake, whereas the R-type is detectable by [3H]RTX binding. We describe here specific vanilloid responses in murine mast cells (MCs). In the MC lines and in bone marrow-derived mast cells, capsaicin and RTX induced45Ca uptake similarly to that observed for cultured rat dorsal root ganglion neurons (DRGs). This response was antagonized by the antagonists capsazepine and ruthenium red. As in DRGs, pretreatment of MCs with capsaicin or RTX induced desensitization to subsequent stimulation of 45Ca uptake. The potency for desensitization by RTX in the MCs corresponded to that for 45Ca uptake, whereas in DRGs it occurred at significantly lower concentrations corresponding to that for the high-affinity [3H]RTX binding site. Consistent with this difference, in MCs we were unable to detect [3H]RTX binding. Vanilloids were noncytotoxic to the MCs, in contrast to the DRGs. Although vanilloids did not cause degranulation in MCs, in the P815 clone capsaicin evoked selective interleukin-4 release. We conclude that certain MCs possess vanilloid receptors, but only the C-type that functions as a channel. Our finding that MCs can respond directly to capsaicin necessitates a reevaluation of the in vivo pathway of inflammation in response to vanilloids.