Bioavailability of a Capsaicin Lipid Multi-particulate Formulation in Rats

Background and Objective

Because of the stomach-burning sensation it induces, capsaicin has been used at relatively low doses as a nutritional supplement, which has limited its bioavailability. The objective of this study was to investigate the serum bioavailability of capsaicin supplementation with or without a lipid multi-particulate (LMP) formulation.

Methods

Thirty-five rats were divided into five groups and administered capsaicin at either 0.2 or 1 mg/kg with or without the LMP formulation. Capsaicin bioavailability was assessed based on the area under the concentation–time curve (AUC), the time to peak concentration (T_max), and the peak serum concentration (C_max).

Results

For each formulation, the capsaicin C_max was reached at 90 min and decreased thereafter. Serum capsaicin concentrations were greater in rats administered the higher dose of capsaicin (1 mg/kg) in the LMP formulation at all measurement times (P  ≤ 0.05). The AUC showed a significant increase, about 20%, when capsaicin was administered in the LMP formulation at the high dose (P  = 0.002). The T_max for oral capsaicin was similar whether or not administration was via the LMP formulation (P  = 0.163). However, the C_max of capsaicin increased in a dose-dependent manner (P  < 0.05). Although the LMP formulation of the high dose of capsaicin resulted in a numerically higher C_max, it was not statistically significantly higher (P  = 0.068).

Conclusions

The present work demonstrated that administration of capsaicin via the LMP formulation significantly impacted the pharmacokinetic parameters and the serum bioavailability of orally administered 1 mg/kg capsaicin in rats. The bioavailability of capsaicin in humans may also be increased by using the LMP formulation.

Capsaicin-loaded solid lipid nanoparticles: design, biodistribution, in silico modeling and in vitro cytotoxicity evaluation

Lower doses of capsaicin (8-methyl-N-vanillyl-6-nonenamide) have the potential to serve as an anticancer drug, however, due to its pungency, irritant effect, poor water solubility and high distribution volume often linked to various off-target effects, its therapeutic use is limited. This study aimed to determine the biodistribution and anticancer efficacy of capsaicin loaded solid lipid nanoparticles (SLNs) in human hepatocellular carcinoma in vitro. In this study, SLNs of stearic acid loaded with capsaicin was formulated by the solvent evaporation-emulsification technique and were instantly characterized for their encapsulation efficiency, morphology, loading capacity, stability, particle size, charge and in vitro drug release profile. Synthesized SLNs were predominantly spherical, 80 nm diameter particles that proved to be biocompatible with good stability in aqueous conditions. In vivo biodistribution studies of the formulated SLNs showed that 48 h after injection in the lateral tail vein, up to 15% of the cells in the liver, 1.04% of the cells in the spleen, 3.05% of the cells in the kidneys, 3.76% of the cells in the heart, 1.31% of the cells in the lungs and 0% of the cells in the brain of rats were determined. Molecular docking studies against the identified targets in HepG2 cells showed that the capsaicin is able to bind Abelson tyrosine-protein kinase, c-Src kinase, p38 MAP kinase and VEGF-receptor. Molecular dynamic simulation showed that capsaicin-VEGF receptor complex is highly stable at 50 nano seconds. The IC₅₀ of capsaicin loaded SLNs in HepG2 cells in vitro was 21.36 μg × ml^-1. These findings suggest that capsaicin loaded SLNs are stable in circulation for a period up to 3 d, providing a controlled release of loaded capsaicin and enhanced anticancer activity.

Nonpungent N-AVAM Capsaicin Analogues and Cancer Therapy

Capsaicin displays robust growth-inhibitory activity in multiple human cancers. However, the feasibility of capsaicin as a clinically relevant anticancer drug is hampered by its adverse side effects. This concern has led to extensive research focused on the isolation and synthesis of second-generation nonpungent capsaicin analogues with potent antineoplastic activity. A major class of nonpungent capsaicin-like compounds belongs to the N-acyl-vanillylamide (N-AVAM) derivatives of capsaicin (hereafter referred as N-AVAM capsaicin analogues). This perspective discusses the isolation of N-AVAM capsaicin analogues from natural sources as well as their synthesis by chemical and enzymatic methods. The perspective describes the pharmacokinetic properties and anticancer activity of N-AVAM capsaicin analogues. The signaling pathways underlying the growth-inhibitory effects of N-AVAM capsaicin analogues have also been highlighted. It is hoped that the insights obtained in this perspective will facilitate the synthesis of a second generation of N-AVAM capsaicin analogues with improved stability and growth-suppressive activity in human cancer.

Differences of the tumour cell glycocalyx affect binding of capsaicin-loaded chitosan nanocapsules

The glycocalyx regulates the interaction of mammalian cells with extracellular molecules, such as cytokines. However, it is unknown to which extend the glycocalyx of distinct cancer cells control the binding and uptake of nanoparticles. In the present study, exome sequencing data of cancer patients and analysis of distinct melanoma and bladder cancer cell lines suggested differences in cancer cell-exposed glycocalyx components such as heparan sulphate. Our data indicate that glycocalyx differences affected the binding of cationic chitosan nanocapsules (Chi-NCs). The pronounced glycocalyx of bladder cancer cells enhanced the internalisation of nanoencapsulated capsaicin. Consequently, capsaicin induced apoptosis in the cancer cells, but not in the less glycosylated benign urothelial cells. Moreover, we measured counterion condensation on highly negatively charged heparan sulphate chains. Counterion condensation triggered a cooperative binding of Chi-NCs, characterised by a weak binding rate at low Chi-NC doses and a strongly increased binding rate at high Chi-NC concentrations. Our results indicate that the glycocalyx of tumour cells controls the binding and biological activity of nanoparticles. This has to be considered for the design of tumour cell directed nanocarriers to improve the delivery of cytotoxic drugs. Differential nanoparticle binding may also be useful to discriminate tumour cells from healthy cells.

Inhibitory effect of Capsicum chinense and Piper nigrum fruits, capsaicin and piperine on aflatoxins production in Aspergillus parasiticus by downregulating the expression of aflD, aflM, aflR, and aflS genes of aflatoxins biosynthetic pathway

Aflatoxins produced by Aspergillus parasiticus are toxic and carcinogenic metabolites. The biosynthesis of this mycotoxins is a complex process and involves at least 30 genes clustered within an approximately 82 kB gene cluster. In the present study, the effect of Capsicum chinense and Piper nigrum fruits on Aspergillus parasiticus growth and aflatoxin production were studied in relation to the expression of aflD, aflM, aflR, and aflS four; key genes of aflatoxins biosynthesis pathway. GC-EIMS analysis identified capsaicin (66,107 µg g^-1) and piperine (1,138 µg g^-1) as the most abundant compounds in C. chinense and P. nigrum fruits, respectively. The antifungal and anti-aflatoxigenic assays showed that C. chinense, P. nigrum, capsaicin, and piperine inhibited A. parasiticus growth and aflatoxins production in a dose-dependent manner. The piperine at 300 µg mL^-1 produced higher radial growth inhibition (89%) and aflatoxin production inhibition (69%). The expression of aflatoxin biosynthetic genes was evaluated by quantitative real-time PCR (qRT-PCR) and revealed that aflatoxin inhibition occurring via downregulating the aflS and aflR, and subsequently aflD and aflM genes. These results will improve our understanding of the mechanism of aflatoxin regulation by C. chinense, P. nigrum, capsaicin, and piperine, and provides a reference for further study.

Capsaicin metabolites and GSH-associated detoxification and biotransformation pathways in human liver microsomes revealed by LC-HRMS/MS with data-mining tools

Capsaicin (CAP) is a principal pungent ingredient in hot peppers, it is also employed as a common food additive, an efficient pharmaceutical component, or even a riot control agent. CAP exerts various pharmacological activities as well as associated adverse physiological responses and causes moderate toxicity if overused. A full screening and identification of CAP metabolites in combination with its main detoxification pathways are crucial for the clear demonstration on its pharmacological and toxicological significance. Here, we employed a post-acquisition data-mining metabolic screening approach to rapidly find and identify a broad range of CAP metabolites generated from in vitro human liver microsomes, based on an ultra-performance liquid chromatography-quadrupole orbitrap high resolution tandem mass spectrometric method. First, we collected full scan MS and MS/MS data sets by a data-dependent acquisition method in positive ion mode, and then we employed a modified mass defect filter and a diagnostic ion filter to screen and identify all the probable CAP metabolites, combining with information including retention time, accurate mass, characteristic fragments, and relevant drug biotransformation patterns. In comparison with the stable isotope-labeled CAP involved biotransformation products, we confirmed 19 functionalized metabolites and 13 glutathione (GSH) conjugates of CAP, in which 13 metabolites are reported for the first time. We then briefly depicted an overview metabolic pathway of CAP from the GSH detoxification viewpoint, revealed that various metabolites of CAP can be generated from single or multiple biotransformation and metabolic reactions. Both CAP and its reactive metabolites produced relevant GSH conjugates, which indicates a wide and important detoxification value of GSH conjugation way.

Intestinal absorption of black chokeberry cyanidin 3-glycosides is promoted by capsaicin and capsiate in a rat ligated small intestinal loop model

Recent studies have shown that aronia (black chokeberry) and haskap fruits (contain anthocyanins) have beneficial health effects in animals and humans. However, some reports have shown that anthocyanin is poorly absorbed in the small intestine. In this study, we compared the intestinal absorption of aronia and haskap anthocyanins by using rats with a ligated small intestinal loop and cannulated portal vein. Our results clearly showed that the intestinal absorption of aronia anthocyanins was significantly lower than that of haskap anthocyanins, suggesting that the intestinal absorption of anthocyanins is influenced by the glycoside type (galactoside or glucoside). In addition, we also examined the effects of capsaicin and capsiate on intestinal anthocyanin absorption. The amount of aronia anthocyanins in portal blood was much higher when they were co-administered with capsaicin or capsiate. Our study is the first to show that the intestinal absorption of aronia anthocyanins is promoted by capsaicin and capsiate.

CAPSAICIN: ITS BIOLOGICAL ACTIVITIES AND IN SILICO TARGET FISHING

Capsicum annuum L. is a rich source of capsaicin, an alkaloid, which is a very pungent compound. Due to ever growing need of capsaicin, an extensive research on its efficient cultivation as well as chemical synthesis is underway. Owing to the pungent nature of capsaicin, its analogous molecules without pungent effect are being explored. The objective of this descriptive review is to comprehensively present the updates on the bioactivities of capsaicin. Additionally, the in silico target fishing approach has been used to identify the possible protein targets of capsaicin. This article will definitely provide future perspectives of research on capsaicin.

Developmental Toxicity Study of Pure trans-Capsaicin in Rats and Rabbits

Human environmental and dietary exposure to trans-capsaicin—the pungent ingredient in chili peppers—is ubiquitous. Moreover, based on the highly selective agonism of trans-capsaicin for TRPV1 receptors, drug products containing high concentrations of trans-capsaicin are under development as analgesics. For instance, a high-concentration (8% w/ w) pure trans-capsaicin dermal patch (designated NGX-4010) is in advanced clinical evaluation for the management of neuropathic pain of peripheral origin. Our objective was to investigate effects of trans-capsaicin on embryo/fetal development, consequent to maternal exposure, from implantation to closure of the hard palate. trans-Capsaicin was delivered systemically by means of either a patch [NGX-4010 (25, 37.5, or 50 cm2)] to pregnant Sprague-Dawley rats on days of presumed gestation (DGs) 7 through 17, or via a 10% w/ v capsaicin liquid formulation (CLF), at dosages of 3, 6.5 or 13 μl/cm2 applied to a 200-cm2 area on the back on DGs 7 though 19 to timed-mated New Zealand white rabbits. In rats, the maternal no-observable-effect level (NOEL) was less than 25 cm2 but no cesarean-sectioning or litter parameters were affected by application of NGX-4010 at patch sizes as high as 50 cm2. The only test article–related observations were delays in skeletal ossification, evident as significant reductions in the average number of metatarsals and ossified hindlimb and forelimb phalanges that occurred in the 50 cm2 NGX-4010 dose group. Although the values for ossified metatarsals were outside the historical control range, ossified hindlimb and forelimb phalanges were within historical control ranges. No other gross external, soft tissue, or skeletal fetal alterations (malformations or variations) were caused by application of the NGX-4010. In rabbits, the maternal NOEL was less than 3 μl/cm2 CLF (or 0.3 mg/cm2 trans-capsaicin) per 200 cm2, but no cesarean-sectioning or litter parameters were affected. No fetal alterations (malformations or variations) were caused by dosages of CLF as high as 13 μl/cm2 (or 1.3 mg/cm2 trans-capsaicin). Taken together, these data suggest that trans-capsaicin should not be considered a developmental toxicant.

Capsaicin 8 % Patch: A Review in Peripheral Neuropathic Pain

The capsaicin 8 % patch (QUTENZA®) is an adhesive patch containing a high concentration (8 % w/w) of synthetic capsaicin, a selective agonist of transient receptor potential vanilloid 1 channel. It is approved for treatment of peripheral neuropathic pain in adults either alone or in combination with other medicinal products for pain in the EU; it is only approved to treat postherpetic neuralgia (PHN) in the USA. In patients with painful diabetic peripheral neuropathy (PDPN), a single 30-min application of the capsaicin 8 % patch significantly improved pain relief and sleep quality compared with placebo in a 12-week double-blind trial. In a 52-week, randomized trial, up to seven consecutive 30-min treatments with the capsaicin 8 % patch (≤7 treatments each at least 8 weeks apart) plus standard of care therapy was associated with sustained pain relief and no negative neurological safety consequences compared with standard of care. In two randomized trials, a single 60-min application of the capsaicin 8 % patch reduced pain scores significantly more than a low-concentration (0.04 %) capsaicin control patch in patients with PHN. Capsaicin 8 % patch treatment was noninferior to pregabalin (optimized dosage) in a randomized trial in patients with nondiabetic peripheral neuropathic pain. Results in two trials in patients with HIV-AN were equivocal, with a significant improvement in pain intensity observed in one trial, but not in the other. The capsaicin 8 % patch was associated with expected, transient, capsaicin-related application-site adverse events such as erythema and pain.

Development of Organogel-Derived Capsaicin Nanoemulsion with Improved Bioaccessibility and Reduced Gastric Mucosa Irritation

Capsaicin (CAP) is the major active component in chili peppers with health-promoting benefits. However, the low bioavailability and irritating quality of CAP greatly limit its applications in functional foods. The objective of this study was to develop a food-grade nanoemulsion to increase the dissolution and bioaccessibility of CAP and to alleviate its irritating effects. To achieve this goal, CAP was first dissolved in medium-chain triacylglycerol (MCT), followed by the addition of sucrose stearate S-370 as organogelator to develop CAP-loaded organogel. The oil-in-water (O/W) emulsion was formed using organogel as the oil phase and Tween 80 as the emulsifier. After ultrasonication treatment, droplet sizes of emulsion were decreased to 168 nm with enhanced dissolution rate and bioaccessibility. In vivo study further confirmed the reduced rat gastric mucosa irritation caused by CAP. The organogel-derived nanoemulsion was proved to be an effective delivery system for CAP-based functional food products.

In vitro and in vivo evaluation of capsaicin-loaded microemulsion for enhanced oral bioavailability

BACKGROUND

Capsaicin, as a food additive, has attracted worldwide concern owing to its pungency and multiple pharmacological effects. However, poor water solubility and low bioavailability have limited its application. This study aims to develop a capsaicin-loaded microemulsion to enhance the oral bioavailability of the anti-neuropathic-pain component, capsaicin, which is poorly water soluble.

RESULTS

In this study, the microemulsion consisting of Cremophor EL, ethanol, medium-chain triglycerides (oil phase) and water (external phase) was prepared and characterized (particle size, morphology, stability and encapsulation efficiency). The gastric mucosa irritation test of formulated capsaicin was performed in rats to evaluate its oral feasibility, followed by the pharmacokinetic study in vivo. Under these conditions, the encapsulated capsaicin revealed a faster capsaicin release in vitro coupled with a greater absorption in vivo when compared to the free capsaicin. The oral bioavailability of the formulated capsaicin-loaded microemulsions was 2.64-fold faster than that of free capsaicin. No significant irritation was observed on the mucosa from the pathological section of capsaicin-loaded microemulsion treated stomach.

CONCLUSION

These results indicate that the developed microemulsion represents a safe and orally effective carrier for poorly soluble substances. The formulation could be used for clinical trials and expand the application of capsaicin.

Preparation, characterization, and pharmacokinetics study of capsaicin via hydroxypropyl-beta-cyclodextrin encapsulation

CONTEXT

Capsaicin (CAP) is an effective drug in the treatment of pain and cancer. However, its practical administration has been limited due to poor aqueous solubility and bioavailability, as well as strong gastrointestinal irritation.

OBJECTIVE

The objective of this study is to improve the solubility and oral bioavailability of CAP by reducing irritation via hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex formulation, in vitro and in vivo analysis.

MATERIALS AND METHODS

The complex (CAP-HP-β-CD) was developed via the magnetic stirring method and characterized using ultraviolet (UV) absorption spectrometry, infrared radiation (IR) spectroscopy, and differential scanning calorimetry (DSC). Rats were treated with CAP (90 mg × kg(-1)) or CAP-HP-β-CD (corresponding to 90 mg × kg(-1) CAP) by gavage, and all the plasma samples were analyzed with high performance liquid chromatography (HPLC).

RESULTS

The results of UV, IR, and DSC showed that an acceptable CAP-HP-β-CD (encapsulation efficiency, 75.83%; drug loading, 7.44%) was formulated. In vitro release study of CAP-HP-β-CD revealed that the cumulative release of CAP from HP-β-CD encapsulation was obviously enhanced (above 80% increases). Similarly, the in vivo pharmacokinetics parameters also increased, Cmax (from 737.94 to 1117.57 ng × mL(-1)), AUC0- (from 5285.9 to 7409.8 ng × h × mL(-1)) or relative bioavailability (139.38%). The gastric irritation bioassay further showed that the CAP-HP-β-CD was far better than free CAP.

DISCUSSION AND CONCLUSION

CAP exhibited significant aqueous solubility and oral bioavailability, as well as minimal irritation effect after forming inclusion complex with HP-β-CD. Therefore, these findings could provide an equally important alternative option for the clinical use of CAP.

QSAR and docking studies on capsazepine derivatives for immunomodulatory and anti-inflammatory activity

Capsazepine, an antagonist of capsaicin, is discovered by the structure and activity relationship. In previous studies it has been found that capsazepine has potency for immunomodulation and anti-inflammatory activity and emerging as a favourable target in quest for efficacious and safe anti-inflammatory drug. Thus, a 2D quantitative structural activity relationship (QSAR) model against target tumor necrosis factor-α (TNF-α) was developed using multiple linear regression method (MLR) with good internal prediction (r2 = 0.8779) and external prediction (r2pred = 0.5865) using Discovery Studio v3.5 (Accelrys, USA). The predicted activity was further validated by in vitro experiment. Capsazepine was tested in lipopolysaccharide (LPS) induced inflammation in peritoneal mouse macrophages. Anti-inflammatory profile of capsazepine was assessed by its potency to inhibit the production of inflammatory mediator TNF-α. The in vitro experiment indicated that capsazepine is an efficient anti-inflammatory agent. Since, the developed QSAR model showed significant correlations between chemical structure and anti-inflammatory activity, it was successfully applied in the screening of forty-four virtual derivatives of capsazepine, which finally afforded six potent derivatives, CPZ-29, CPZ-30, CPZ-33, CPZ-34, CPZ-35 and CPZ-36. To gain more insights into the molecular mechanism of action of capsazepine and its derivatives, molecular docking and in silico absorption, distribution, metabolism, excretion and toxicity (ADMET) studies were performed. The results of QSAR, molecular docking, in silico ADMET screening and in vitro experimental studies provide guideline and mechanistic scope for the identification of more potent anti-inflammatory & immunomodulatory drug.

Preparation of a capsaicin-loaded nanoemulsion for improving skin penetration

Capsaicin o/w nanoemulsions with enhanced skin permeation were successfully prepared by controlling the ratios of the surfactant mixtures, oleoresin capsicum as the oil phase, and aqueous phase. Oleoresin capsicum contains 22.67 mg/g of capsaicin, which is an active and oil-soluble ingredient. Nonionic surfactants, Tween 80 and Span 80, were used to optimize the weight ratio of surfactant mixtures (85.98:14.02) by calculating the hydrophile-lipophile balance (HLB) value. The optimal processing conditions for stable nanoemulsions were investigated by using a ternary phase diagram. The mean droplet size of nanoemulsions ranged from 20 to 62 nm. Skin permeation studies were performed using a Franz diffusion cell. The permeation profiles and confocal laser scanning microscopy (CLSM) images supported that capsaicin nanoemulsion could well permeate all skin layers from the stratum corneum to the dermis. The selected nanoemulsions showed great potential as transdermal delivery carriers for enhancing the permeation of core materials.

Properties of capsaicinoids for the control of fungi and oomycetes pathogenic to pepper

Capsaicinoids are pungent compounds found in pepper (Capsicum spp.) fruits. Capsaicin showed antimicrobial activity in plate assays against seven isolates of five species of fungi and nine isolates of two species of oomycetes. The general trend was that oomycetes were more inhibited than fungi. Assays of capsaicin biosynthetic precursors suggest that the lateral chain of capsaicinoids has more inhibitory activity than the phenolic part. In planta tests of capsaicinoids (capsaicin and N-vanillylnonanamide) applied to the roots demonstrated that these compounds conferred protection against the pathogenic fungus Verticillium dahliae and induced both chitinase activity and expression of several defence-related genes, such as CASC1, CACHI2 and CABGLU. N-Vanillylnonanamide infiltrated into cotyledons confers systemic protection to the upper leaves of pepper against the fungal pathogen Botrytis cinerea. In wild-type tomato plants such cotyledon infiltration has no protective effect, but is effective in the Never-ripe tomato mutant impaired in ethylene response. A similar effect was observed in tomato after salicylic acid infiltration.

Pharmacokinetic characteristics of capsaicin-loaded nanoemulsions fabricated with alginate and chitosan

Nanotechnologies are being employed to enhance the stability and oral bioavailability of lipophilic substances, such as capsaicin. This study aimed to examine the pharmacokinetic properties of the formulated capsaicin-loaded nanoemulsions. A pharmacokinetic study was carried out using double-layer nanoemulsions fabricated with alginate and chitosan polymers and triple-layer nanoemulsions fabricated with chitosan/alginate polymers. Capsaicin nanoemulsions and capsaicin control (oleoresin capsicum) were administered to the rat at a dose of 10 mg/kg. A statistically significant difference was found in the area under the curve from time zero to time infinity (AUCinf) among formulations (p < 0.01). In comparison to the control group, the relative bioavailability of formulated nanoemulsions was up to 131.7. The AUCinf increased in a nano-size-dependent manner; as nano size decreased, AUCinf increased. IN comparison to the double-layer nanoemulsions, the triple-layer nanoemulsion showed a significantly increased volume of distribution, resulting in the increased clearance and decreased AUCinf. It was concluded that the formulated nanoemulsions could significantly enhance the bioavailabilty of capsaicin.

[Optimization of preparation process of floating sustained-release pellets of capsaicin based on nanometer CaCO3 by central composite design-response surface method]

OBJECTIVE

To prepare floating sustained-release pellets of capsaicin based on nanometer CaCO3.

METHOD

The floating sustained-release pellets were prepared by the dropping method with sodium alginate as matrix. The effects of the concentration of sodium alginate, the ratio of capsaicin to sodium alginate and the ratio of nanometer CaCO3 to sodium alginate on pellets were detected in the single-factor test. On that basis, central composite design-response surface method were used to optimize the formula, with the floating capacity, drug-loading rate and in vitro drug release property of pellets as indicators.

RESULT

In the optimal formula, CaCl2 accounted for 1.87%, the ratio of nanometer CaCO3 to sodium alginate was 2.16:1, and the ratio of capsaicin to sodium alginate was 2.36: 1, respectively. Capsaicin sustained-release pellets prepared under the conditions featured round granule, even particle size. It could float on artificial gastric fluid for over 15 hours, showing good sustained-release effect. Its accumulative drug-release percent of pellets in vitro at 12 h were 89.93%.

CONCLUSION

The floating sustained-release pellets of capsaicin show good floating capacity and sustained-release effect after being optimized with central composite design-response surface method.

Topical capsaicin for pain management: therapeutic potential and mechanisms of action of the new high-concentration capsaicin 8% patch

Topical capsaicin formulations are used for pain management. Safety and modest efficacy of low-concentration capsaicin formulations, which require repeated daily self-administration, are supported by meta-analyses of numerous studies. A high-concentration capsaicin 8% patch (Qutenza™) was recently approved in the EU and USA. A single 60-min application in patients with neuropathic pain produced effective pain relief for up to 12 weeks. Advantages of the high-concentration capsaicin patch include longer duration of effect, patient compliance, and low risk for systemic effects or drug-drug interactions. The mechanism of action of topical capsaicin has been ascribed to depletion of substance P. However, experimental and clinical studies show that depletion of substance P from nociceptors is only a correlate of capsaicin treatment and has little, if any, causative role in pain relief. Rather, topical capsaicin acts in the skin to attenuate cutaneous hypersensitivity and reduce pain by a process best described as 'defunctionalization' of nociceptor fibres. Defunctionalization is due to a number of effects that include temporary loss of membrane potential, inability to transport neurotrophic factors leading to altered phenotype, and reversible retraction of epidermal and dermal nerve fibre terminals. Peripheral neuropathic hypersensitivity is mediated by diverse mechanisms, including altered expression of the capsaicin receptor TRPV1 or other key ion channels in affected or intact adjacent peripheral nociceptive nerve fibres, aberrant re-innervation, and collateral sprouting, all of which are defunctionalized by topical capsaicin. Evidence suggests that the utility of topical capsaicin may extend beyond painful peripheral neuropathies.

Tissue distribution & elimination of capsaicin, piperine & curcumin following oral intake in rats

BACKGROUND & OBJECTIVES

Curcumin, capsaicin and piperine--the bioactive compounds present in spices--turmeric (Curcuma longa), red pepper (Capsicum annuum) and black pepper (Piper nigrum) respectively, have a considerable portion of structural homology. Tissue distribution and elimination of these three structurally similar bioactive compounds was examined following their oral intake in rats.

METHODS

Separate sets of animals (150-160 g) were orally administered the three spice principles at dosages of 30 mg (capsaicin), 170 mg (piperine) and 500 mg (curcumin) / kg body weight. The tissue concentrations of administered spice compounds were determined by HPLC.

RESULTS

Maximum distribution of 24.4 per cent of administered capsaicin was seen at 1 h, while no intact capsaicin was detectable after 4 days. Absorption of capsaicin was about 94 per cent and very rapid relative to other two compounds. A maximum of 10.8 per cent of administered piperine was seen in tissues at 6 h. Absorption of the administered piperine was about 96 per cent. Curcumin concentration was maximum in the intestine at 1 h; maximum in blood at 6 h and remained at significantly higher level even at 24 h. About 63.5 per cent of the curcumin dose was absorbed. Only a small portion of the administered dose of capsaicin (< 0.1%) and curcumin (0.173 %) was excreted in urine, whereas piperine was not detectable in urine. Enhanced bioavailability of curcumin was evidenced when the same was orally administered concomitant with piperine. Intestinal absorption of curcumin was relatively higher when administered concomitantly with piperine, and it stayed significantly longer in the body tissues. Intact curcumin was detected in brain at 24, 48 and 96 h with a maximum at 48 h.

CONCLUSIONS

Considerable difference exists in the bioavailability of the three test compounds. Curcumin could be traced in the brain following its administration. Bioavailability of curcumin can be improved by co-administration with piperine.

NGX-4010, a high-concentration capsaicin dermal patch for lasting relief of peripheral neuropathic pain

NeurogesX Inc is developing NGX-4010, a rapid-delivery dermal patch application system that contains high-concentration trans-capsaicin, for the treatment of peripheral neuropathic pain. Capsaicin evokes a lasting and reversible refractory state in primary sensory neurons involved in the generation and maintenance of neuropathic pain. NGX-4010 can be applied to the painful skin area up to a total surface area of 1120 cm2. In phase I clinical trials, NGX-4010 increased the threshold for warmth detection, reduced epidermal sensory nerve fiber density and was well tolerated. In phase II trials, NGX-4010 was effective in reducing pain in patients with post-herpetic neuralgia (PHN), HIV-associated distal sensory neuropathy (HIV-DSP) and painful diabetic neuropathy (PDN). Data from phase III trials in patients with PHN demonstrated that significantly more pain relief was achieved by NGX-4010 (30 to 32% reduction from baseline) compared with a low-concentration capsaicin active control (20 to 24% reduction); however, only one of two studies involving patients with HIV-DSP met the primary endpoint. NGX-4010 appears to have the potential to be an effective adjunctive or a stand-alone therapy for PHN, as well as potentially for HIV-DSP and PDN. NGX-4010 has been granted approval by the European Commission and an NDA has been accepted for filing by the FDA.

Pharmacokinetic and the effect of capsaicin in Capsicum frutescens on decreasing plasma glucose level

BACKGROUND

The active substance found in Capsicum frutescens (capsicum) that gives hot and spicy flavor is capsaicin, and it seems to have many pharmacological effects.

OBJECTIVE

The present research was conducted to study the effect of capsicum on plasma glucose level and to correlate its action with the pharmacokinetic properties of capsaicin in capsicum.

MATERIAL AND METHOD

The crossover study was performed in 12 healthy volunteers by performing the OGTT while receiving placebo or 5 grams of capsicum. The insulin secretion and capsaicin level in plasma were measured using the HPLC method.

RESULTS

The results of the OGTT showed that plasma glucose levels in volunteers who received capsicum were significantly lower than those in the placebo group at 30 and 45 minutes (p < 0.05). Furthermore, plasma insulin levels were significantly higher at 60, 75, 105, and 120 minutes (p < 0.05). When comparing before and after capsicum intake, the results showed the insulin levels were maintained The pharmacokinetic parameters of capsaicin shown as C(max), T(max), AUC(0-t), T1/2 are 2.47 +/- 0.13 ng/ml, 47.08 +/- 1.99 min, 103.6 +/- 11.3 ng x min/ml, and 24.87 +/- 4.97 min, respectively.

CONCLUSION

In conclusion, the present study found that 5 grams of capsicum presented capsaicin levels that were associated with a decrease in plasma glucose levels and the maintenance of insulin levels. The present result might have clinical implications in the management of type 2 diabetes.

Effect of HPbetaCD on solubility and transdermal delivery of capsaicin through rat skin

We evaluated the ability of hydroxypropyl-beta-cyclodextrin (HPbetaCD) to influence the percutaneous absorption of capsaicin (CP) through isolated rat skin. Phase solubility analysis and phase distribution studies suggested the potential of HPbetaCD as a solubilizer and permeation enhancer for CP. In vitro permeation studies showed the trend that, the penetration flux (J(s)) of CP increased with the increasing concentration of HPbetaCD from 0 to 2.20% (w/v), and then decreased dramatically when the concentration of HPbetaCD kept on increasing up to 15% (w/v). 2.20% (w/v) of HPbetaCD provided both just adequate solubilization and preferred J(s) for the permeation of CP (0.075%, w/v). Similar change patterns of the permeation parameters were also observed in the hydrogels, but the J(s) of CP was reduced significantly along with the increasing concentration of Carbopol U21. Histological analysis showed an invasive action of HPbetaCD on the stratum corneum (SC) of rat skin, which could only reduce the lag time (T(L)) but could not increase the J(s) of CP. On the other hand, the complexation of HPbetaCD with CP could attenuate this invasive action. It is inferred that excess of HPbetaCD could not only disturb the percutaneous absorption of CP but also disrupt the structure of SC.

Use of spray-cooling technology for development of microencapsulated capsicum oleoresin for the growing pig as an alternative to in-feed antibiotics: A study of release using in vitro models1

The aim of this study was to develop sustained release microspheres of capsicum oleoresin as an alternative to in-feed additives. Two spray-cooling technologies, a fluidized air bed using a spray nozzle system and a vibrating nozzle system placed on top of a cooling tower, were used to microencapsulate 20% of capsicum oleoresin in a hydrogenated, rapeseed oil matrix. Microencapsulation was intended to reduce the irritating effect of capsicum oleoresin and to control its release kinetics during consumption by the animal. Particles produced by the fluidized air bed process (batch F1) ranged from 180 to 1,000 microm in size. The impact of particle size on release of capsaicin, the main active compound of capsicum oleoresin, was studied after sieving batch F1 to obtain 4 formulations: F1a (180 to 250 microm), F1b (250 to 500 microm), F1c (500 to 710 microm), and F1d (710 to 1,000 microm). The vibrating nozzle system can produce a monodispersive particle size distribution. In this study, particles of 500 to 710 microm were made (batch F2). The release kinetics of the formulations was estimated in a flow-through cell dissolution apparatus (CFC). The time to achieve a 90% dissolution value (T90%) of capsaicin for subbatches of F1 increased with the increase in particle size (P < 0.05), with the greatest value of 165.5 +/- 13.2 min for F1d. The kinetics of dissolution of F2 was slower than all F1 subbatches, with a T90% of 422.7 +/- 30.0 min. Nevertheless, because CFC systems are ill suited for experiments with solid feed and thus limit their predictive values, follow-up studies were performed on F1c and F2 using an in vitro dynamic model that simulated more closely the digestive environment. For both formulations a lower quantity of capsaicin dialyzed was recorded under fed condition vs. fasting condition with 46.9% +/- 1.0 vs. 74.7% +/- 2.7 for F1c and 32.4% +/- 1.4 vs. 44.2% +/- 2.6 for F2, respectively. This suggests a possible interaction between capsaicin and the feed matrix. Moreover, 40.4 +/- 3.9% of the total capsaicin intake in F2 form was dialyzed after 8 h of digestion when feed had been granulated vs. 32.4 +/- 1.4% when feed had not been granulated, which suggests that the feed granulation process could lead to a partial degradation of the microspheres and to a limitation of the sustained release effect. This study demonstrates the potential and the limitations of spray-cooling technology to encapsulate feed additives.

Administration of ciprofloxacin and capsaicin in rats to achieve higher maximal serum concentrations

To test if capsaicin could improve the bioavailability of ciprofloxacin (1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid, CAS 85721-33-1, Bay q 3939) in rats, 0.01, 0.1, 0.5 and 1% capsaicin ((E)-N-[(4-hydroxy-3-methoxyphenyl)methyl]-8-methyl-6-nonenamide, trans-8-methyl-N-vanillyl-6-nonenamide, CAS 404-86-4) dissolved in ethanol and mixed with 20 mg/kg of ciprofloxacin were orally administered to groups of 10 rats each. Control groups were dosed with capsaicin-free, ethanol-containing or ethanol-free ciprofloxacin. Reference intravenous pharmacokinetics of ciprofloxacin was also established. The results revealed that capsaicin increased ciprofloxacin bioavailability by approximately 70% in groups receiving preparations containing capsaicin at a rate of 0.01, 0.1 and 0.5%. Higher concentrations failed to further increase bioavailability. However, capsaicin appears to have little or no impact on the rate of absorption or clearance of ciprofloxacin. Considering that 0.01% or 0.1% capsaicin are unlikely to upset the gastrointestinal tract, it may be worth attempting to study if a similar effect occurs in man, and to evaluate if the addition of capsaicin can be used as a method to increase the area under the curve/minimum inhibitory concentration rate, a key variable to improve clinical efficacy of ciprofloxacin.

Studies on the in vitro absorption of spice principles – Curcumin, capsaicin and piperine in rat intestines

A comparative evaluation of the absorbability of three structurally similar and physiologically active spice principles in an in vitro system consisting of everted rat intestinal sacs was made. When everted sacs of rat intestines were incubated with 50-1000 microg of curcumin in 10 ml incubation medium, absorption of the spice principle was maximum at 100 microg concentration. The amount of absorbed curcumin present in the serosal fluid was negligible. This and the comparatively lower recovery of the original compound suggested that curcumin to some extent undergoes a modification during absorption. For similar concentrations of added piperine, about 44-63% of piperine disappeared from the mucosal side. Absorption of piperine which was maximum at 800 microg per 10 ml was about 63%. The absolute amounts of piperine absorbed in this in vitro system exceeded the amounts of curcumin. The absorbed piperine could be traced in both the serosal fluid and in the intestinal tissue, indicating that piperine did not undergo any metabolic change during the process of absorption. 7-12% of the absorbed piperine was found in the serosal fluid. When everted sacs of rat intestines were incubated with 10-500 microg of capsaicin, a maximum of 82-88% absorption could be seen in the lower concentrations, and the amount of absorbed capsaicin did not proportionately increase at higher concentrations. A relatively higher percentage of the absorbed capsaicin could be seen in the serosal fluid as compared to curcumin or piperine. When these spice active principles were associated with mixed micelles, their in vitro intestinal absorption was relatively higher. Curcumin absorption in everted intestinal sac increased from 48.7% to 56.1% when the same was present in micelles. In the case of capsaicin and piperine, increase in absorption was 27.8-44.4% and 43.4-57.4%, respectively, when they were present in micelles as compared to its native form.

Intestinal chemo- and mechano-sensitivity: selective modification of small intestinal sensitivity by lipids

BACKGROUND

Intestinal chemo-nociception is a recently described mechanism of perception of intraluminal stimuli that might involve pathways independent from mechano-nociception.

AIM

To investigate whether intraluminal lipids not only modify mechano-sensitivity, but also influence chemo-sensitivity.

METHOD

Nineteen healthy volunteers ingested an orojejunal tube assembly for mechanical and chemical stimulation of the proximal jejunum. Volume-controlled distension of a jejunal balloon and capsaicin perfusion were performed during simultaneous infusion of saline or a 10% lipid emulsion. A standard questionnaire evaluated quality and intensity of symptoms induced by intestinal stimulation.

RESULTS

Balloon volumes to induce perception thresholds were significantly reduced during lipid perfusion (P < 0.05), while balloon pressures remained unaltered (P > 0.05). Saline infusion (2.5 mL/min) did not alter thresholds of perception. Lipid infusion also increased intensity of perception during given distension volumes (P < 0.05). Lipid infusion did neither affect perception quality induced by capsaicin, nor perception thresholds, nor intensity of perception during capsaicin perfusion (P > 0.05). The quality of sensations induced by capsaicin perfusion was similar to sensations during distension, except of sensation of warmth, that was almost exclusively reported during capsaicin perfusion.

CONCLUSIONS

Intraluminal lipids selectively modify intestinal mechano-perception and do not alter chemo-perception. Intestinal chemo-nociception and mechano-nociception are two mechanisms of intestinal perception that involve distinct sensory pathways.

Toxicity studies with pure trans-capsaicin delivered to dogs via intravenous administration

Previous toxicology and pharmacology studies have reported variable acute cardiac effects of capsaicin, primarily involving hypotension and bradycardia. However, these studies have suffered from two important limitations. First, the capsaicin tested has been derived from pepper plant extracts, which is likely to display varying degrees of purity and possibly diverse impurity profiles. Second, post-dosing follow-up was generally limited to three or fewer days. Therefore, the objective of the studies reported here was to test the cardiac and other target organ toxicity potential of pure, synthetic trans-capsaicin (the only naturally occurring stereoisomer of capsaicin) when delivered via intravenous administration to dogs either acutely or for 14 days. Taken together, results from these two studies indicate that pure trans--capsaicin--even when delivered directly into the systemic circulation at high dose levels--is rapidly eliminated, induces transient tachycardia and hypertension, does not alter the duration of cardiac action potentials, and causes only very minimal organ toxicities. The different toxicity profiles of pure trans-capsaicin reported here and chili pepper extracts previously reported suggest that the purity and source of capsaicin should be an important consideration for toxicological evaluations.

Effects of capsaicin on P-gp function and expression in Caco-2 cells

Capsaicin is the pungent component of hot chilli, a popular spice in many populations. The aim of the present study was to evaluate the chronicity and reversibility of the modulating effect of capsaicin on both the P-gp expression and activity in the Caco-2 cell monolayers. Capsaicin at concentrations ranging from 10 to 100 microM, which were found to be non-cytotoxic towards the Caco-2 cells, were observed to inhibit P-gp mediated efflux transport of [3H]-digoxin in the cells. The acute inhibitory effect was dependent on the capsaicin concentration and duration of exposure, with abolishment of polarity of [3H]-digoxin transport attained at 50 microM of capsaicin. In contrast, longer term (48 and 72 h) co-incubation of the Caco-2 cells with capsaicin (50 and 100 microM) increased P-gp activity through an up-regulation of cellular P-gp protein and MDR1 mRNA levels. The up-regulated protein was functionally active, as demonstrated by higher degree of [3H]-digoxin efflux across the cell monolayers, but the induction was readily reversed by the removal of the spice from the culture medium. The induction of P-gp protein and mRNA levels was also influenced by capsaicin concentration and duration of exposure, with higher expression levels, in particular of the mRNA, seen at higher spice concentrations over prolonged period of incubation. Our data suggest that caution should be exercised when capsaicin is to be consumed with drugs that are P-gp substrates. In particular, the oral bioavailability of these drugs may be influenced by the P-gp status of populations that rely heavily on hot chilli in their diets.

[Preparation and in vitro evaluations of topically applied capsaicin transfersomes]

OBJECTIVE

Capsaicin transfersomes were prepared and its quality specifications were evaluated.

METHOD

Capsaicin transfersomes were prepared by high shear dispersing machine and evaluated on the entrapment efficiency, drugs release rate and in vitro skin permeation.

RESULT

Capsaicin transfersomes is composed of single unilamellar vesicles, with average size of 150.6 nm. Capsaicin entrapment efficiency achieved 96.7% while concentration of lecithin used was 8%. cumulative release amount of capsaicin was in direct proportion to the ethanol concentration in the medium. The in vitro rate cumulative penetration rate of capsaicin was higher in transfersomes than in cream and suspension in rats. Adomen skin cumulative penetration rate in vitro of capsaicin transfersomes in mouse was significantly higher than that from rat and men. In the same way,cumulative penetration rate in vitro of capsaicin transfersomes through abdomen skin epidermal membrance was significantly higher than that with derma and full skin in men.

CONCLUSION

Entrapment efficiency of capsaicin transfersomes reached 96.7%, meeting the criterion of China pharmacopia( > 80%), skin penetration of capsaicin was enhanced by a capsaicin transfersomes preparation and was affected by diverse characters and levels of skin.

[Preparation and in vitro and in vivo evaluations of topically applied capsaicin transfersomes]

AIM

To prepare capsaicin transfersomes and evaluate them in vitro and in vivo.

METHODS

Capsaicin transfersomes were prepared by high shear dispersing machine and evaluated by entrapment efficiency, release rate, in vitro skin permeation and distribution in different tissues in vivo.

RESULTS

Capsaicin transfersomes were composed of single unilamellar vesicles with an average diameter of 150.6 nm. Capsaicin entrapment efficiency increased distinctly with increasing of concentration of lecithin and entrapment efficiency is 96.7% while concentration of lecithin to 8%. Cumulative release amount of capsaicin is in direct proportion to the ethanol concentration in the receptor medium. In vitro capsaicin cumulative penetration amount showed higher levels in transfersomes than cream and suspension in rat abdominal skin. Abdominal skin cumulative penetration amount in vitro of capsaicin transfersomes in mouse was significantly higher than that from rat and men. In the same way, abdominal skin epidermal membrane cumulative penetration amount in vitro of capsaicin transfersomes was significantly higher than that from derma and full skin in human abdominal skin. The capsaicin tissue distribution of capsaicin injection by multiple celiac injections in rats is different: bone > plasma > skin > muscle. There is a similar result by multiple thigh topical application of capsaicin transfersomes: bone > skin > plasma > muscle.

CONCLUSION

Entrapment efficiency of capsaicin transfersomes reached the criterion of China Pharmacopoeia (> 80%) and capsaicin skin penetration can be increased by capsaicin transfersomes. It should be noted that the diverse characters and levels of skin may probably affect the permeating capability of capsaicin. Capsaicin tissue distribution in bone and muscle is similar and is different in plasma and skin by multiple injections and topical skin apply.

Nitric-oxide mediated effects of transdermal capsaicin patches on the ischemic threshold in patients with stable coronary disease

BACKGROUND

Capsaicin has been shown to exert direct vasodilating effects through increased calcitonin gene-related peptide (CGRP) release. However, no data exist on its effect following systemic administration in humans.

METHODS

Twelve male patients with stable coronary disease and a persistently positive exercise were selected for study. According to a double blind, placebo-controlled, cross-over study, patients were randomized to placebo or 3 g oleic capsaicin-containing patches, on 2 different days and with a 2-day interval between treatments. Patients performed treadmill exercise testing according to the Bruce protocol. Time to 1 mm ST segment depression and to peak exercise, maximal ST segment depression, and the number of ECG leads showing diagnostic changes were also measured. Blood samples for nitric oxide (NO) and CGRP were drawn at baseline, 2, 6, and 24 hours after exercise.

RESULTS

On placebo, all patients had a positive ECG during exercise test. Only 1 patient experienced angina, on both treatments. With capsaicin, 1 patient had a negative exercise, while 8 patients significantly increased time to 1 mm ST depression from 328 +/- 167 to 401 +/- 174 seconds (P = 0.01). Of the remaining patients, 1 did not show any changes and 2 showed a worse ischemic threshold when on capsaicin. CGRP levels were not significantly different between placebo and capsaicin treatment. Conversely, when on capsaicin, NO significantly increased at 6 hours.

CONCLUSIONS

Transdermal capsaicin may improve ischemic threshold in patients with stable coronary disease, probably through arteriolar vasodilation. Increased capsaicin-induced NO availability could represent the principal mechanism of action.

Electrically-Assisted Skin Permeation of Two Synthetic Capsaicin Derivatives, Sodium Nonivamide Acetate and Sodium Nonivamide Propionate, via Rate-Controlling Polyethylene Membranes

The objective of this study was to examine the transdermal delivery of sodium nonivamide acetate (SNA) using iontophoresis and electroporation with ultra high molecular weight polyethylene membranes (Solupor) to achieve controlled transdermal drug delivery. A derivative of SNA, sodium nonivamide propionate (SNP), was also used as a model drug in this investigation. Iontophoresis increased the transdermal permeation of SNA as compared to passive diffusion. Most Solupor membranes were rate-limiting for the iontophoretic permeation of SNA except for Solupor 8P07, which showed negligible resistance to SNA delivery. The tortuosity (Gurley number), pore size, and the current density-induced attachments on the surface of the Solupor membranes may have been important for their rate-controlling effect. The trends for inhibiting or controlling SNA permeation were similar for both iontophoretic and electroporation applications. The higher molecular size and lower hydrophilicity of SNP compared to SNA resulted in lower permeation of SNP using electrically-assisted methods. Moreover, the various types of Solupor membranes showed similar trends for both SNA and SNP. This present study indicates that Solupor membranes act as rate-limiting membranes for controlling the release and skin permeation of both SNA and SNP by electrically-assisted methods.

Effects of vehicle on the uptake and elimination kinetics of capsaicinoids in human skin in vivo

While the physiologic and molecular effects of capsaicinoids have been extensively studied in various model systems by a variety of administration routes, little is known about the uptake and elimination kinetic profiles in human skin following topical exposure. The present study evaluated the uptake and elimination kinetics of capsaicinoids in human stratum corneum following a single topical exposure to 3% solutions containing 55% capsaicin, 35% dihydrocapsaicin, and 10% other analogues prepared in three vehicles: mineral oil (MO), propylene glycol (PG), and isopropyl alcohol (IPA). Capsaicinoid solutions were evaluated simultaneously in a random application pattern on the volar forearms of 12 subjects using a small, single 150-microg dose. Capsaicin and dihydrocapsaicin were recovered from human skin using commercial adhesive discs to harvest stratum corneum from treated sites. Capsaicinoids were extracted from the stratum corneum-adhesive discs and quantified by liquid chromatography/mass spectroscopy (LC/MS). Both capsaicinoids were detected in stratum corneum 1 min after application with all vehicles and achieved a pseudo-steady state shortly thereafter. IPA delivered three times greater capsaicin and dihydrocapsaicin into the human stratum corneum than PG or MO at all time points investigated. The Cmax of capsaicin in IPA, PG, and MO was 16.1, 6.2, and 6.5 microg, respectively. The dihydrocapsaicin content was 60% of capsaicin with all vehicles. The estimated T(half) of capsaicin and dihydrocapsaicin in the three vehicles was similar (24 h). Thus, maximal cutaneous capsaicinoid concentrations were achieved quickly in the human stratum corneum and were concentration and vehicle dependent. In contrast, capsaicinoid half-life was long and vehicle independent.

Direct interaction of adenosine with the TRPV1 channel protein

Vanilloid receptor 1 (TRPV1), a nonspecific cation channel expressed primarily in small sensory neurons, mediates inflammatory thermal pain sensation. The function and expression of TRPV1 are enhanced during inflammation and certain neuropathies, leading to sustained hyperalgesia. Activation of TRPV1 in the spinal cord and periphery promotes release of adenosine, which produces analgesia by activating A(1) and A(2A) adenosine receptor (AR) on central and peripheral neurons. This study provides evidence of a direct interaction of AR analogs with TRPV1. Adenosine analogs inhibit TRPV1-mediated Ca(2+) entry in human embryonic kidney (HEK293) cells stably expressing TRPV1 (HEK/TRPV1) and DRG neurons. This inhibition was independent of A(2A)AR activation. Specific binding of [(3)H]resiniferatoxin (RTX) in plasma membrane preparations was inhibited by CGS21680, an A(2A)AR agonist. Similar degrees of inhibition were observed with both agonists and antagonists of ARs. Adenosine analogs inhibited [(3)H]RTX binding to affinity-purified TRPV1, indicative of a direct interaction of these ligands with the receptor. Furthermore, specific capsaicin-sensitive binding of [(3)H]CGS21680 was observed in Xenopus oocyte membranes expressing TRPV1. Capsaicin-induced inward currents in DRG neurons were inhibited by adenosine and agonist and antagonist of A(2A)AR at nanomolar concentrations. Increasing the concentrations of capsaicin reversed the inhibitory response to capsaicin, suggesting a competitive inhibition at TRPV1. Finally, exposure of HEK/TRPV1 cells to capsaicin induced an approximately 2.4-fold increase in proapoptotic cells that was abolished by adenosine analogs. Together, these data suggest that adenosine could serve as an endogenous inhibitor of TRPV1 activity by directly interacting with the receptor protein.

Gender differences in regional cutaneous microcirculatory responses to capsaicin

Vascular responsiveness between healthy male and female subjects to capsaicin, an agent promoting neuropeptide release, was compared. Changes in skin perfusion were measured non-invasively using laser Doppler imaging. Topical application of a 3% solution of capsaicin to the dorsum of the hand resulted in vasodilatation in nine of 10 male subjects, but in less than half of the female subjects. Responses to capsaicin at the shin were smaller but did not show gender differences. Fingertip temperature was significantly lower in females compared with males and this correlated (r = 0.54, P < 0.01) with the maximum response to capsaicin. These effects were specific to capsaicin as endothelium-dependent and -independent vasodilator mechanisms, assessed non-invasively by iontophoresis of acetylcholine and sodium nitroprusside, respectively, showed no gender differences. These findings suggest a specific anomaly in capsaicin-sensitive vasodilator mechanisms in some subjects, perhaps indicative of subclinical expression of Raynaud's phenomenon.

A novel capsaicin derivative VOA induced relaxation in rat mesenteric and aortic arteries: involvement of CGRP, NO, cGMP, and endothelium-dependent activities

The vasorelaxant effects of N-[4-O-[2-methoxy, phenoxyethylaminobutyl]-3-methoxy benzyl]-nonamide (VOA), a novel capsaicin derivative, and associated releasing activities of nitric oxide (NO) and calcitonin gene-related peptide (CGRP) were investigated in this study. Systemic administration of VOA decreased blood pressure and heart rate in a dose-dependent manner in both normotensive as well as spontaneously hypertensive rats. Nw-nitro-L-arginine methyl ester (L-NAME), glibenclamide, and capsazepine inhibited VOA-induced hypotension. In phenylephrine-precontracted rat aortic rings and mesenteric arteries with intact endothelium, VOA caused a concentration-dependent relaxation. This relaxation was reduced after endothelium was removed or pretreated with L-NAME, methylene blue, 1 H-[1,2,4]oxidazolol [4,3-a] quinoxalin-1-one, tetraethylammonium, glibenclamide, CGRP (8-37), or capsazepine, respectively. In endothelially denuded vessel rings, tetraethylammonium, glibenclamide, CGRP (8-37), and capsazepine also reduced VOA-induced relaxation. In high potassium (80 mmol/L)-precontracted rat aortic rings with intact endothelium, VOA failed to induce relaxation. VOA induced a concentration-dependent increase of CGRP-like enzyme immunoreactivity, which was also significantly inhibited by capsazepine. In human umbilical vein endothelial cells, VOA increased NO release and guanosine-3', 5'-cyclic monophosphate level, which were significantly inhibited by L-NAME. The Western blot analysis on human umbilical vein endothelial cells indicated that VOA increased the expression of endothelium nitric oxide synthase. In conclusion, VOA might exert its relaxation effects in rat vascular smooth muscle through the CGRP/KATP channel and the NO/ cGMP pathway.

Genotoxicity studies with pure trans-capsaicin

Both positive and negative effects have been found in classical genetic toxicology assays with capsaicin. However, the capsaicin tested in most studies has been derived from pepper plant extracts, which is likely to display varying degrees of purity and possibly diverse impurity profiles. Therefore, the objective of the series of studies reported here was to test the genotoxic potential of pure, synthetic trans-capsaicin (the only naturally occurring geometric isomer of capsaicin), using four genotoxicity assays widely used to evaluate drug substances. These included the Ames, mouse lymphoma cell mutation, mouse in vivo bone marrow micronucleus and chromosomal aberration in human peripheral blood lymphocytes (HPBL) assays. In the Ames assay, pure trans-capsaicin was not mutagenic to Salmonella typhimurium or Escherichia coli when dissolved in dimethylsulfoxide and tested at concentrations extending into the toxic range. trans-Capsaicin was weakly mutagenic in mouse lymphoma L5178Y cells, in the presence of S9 mix, when dissolved in dimethylsulfoxide and tested at concentrations extending into the toxic range. Limited evidence for very weak activity was also obtained in the absence of S9 mix. trans-Capsaicin did not induce micronuclei in bone marrow cells when tested to the maximum tolerated dose of 800 mg/kg per day in male and 200 mg/kg per day in female CD-1 mice using a 0 h plus 24 h oral dosing and 48 h sampling regimen. Finally, trans-capsaicin did not induce structural or numerical chromosomal aberrations when evaluated for its ability to induce clastogenicity in blood lymphocytes. Taken together, these data suggest that the genotoxic potential of pure trans-capsaicin is very low, especially as the clinical significance of weak mutagenicity in the mouse lymphoma assay for catechol-moiety containing compounds is unclear. Moreover, the different genotoxicity profiles of pure trans-capsaicin and purified chili pepper extracts suggest that the purity and source of capsaicin should always be an important consideration for toxicological evaluations.

Effects of resiniferatoxin desensitization of capsaicin-sensitive afferents on detrusor over-activity induced by intravesical capsaicin, acetic acid or ATP in conscious rats

Recent studies have provided evidence for a major role of urothelially released ATP acting on a subpopulation of pelvic afferent nerves in mechano-afferent transduction in the bladder. We investigated whether desensitization of capsaicin-sensitive nerve fibres by systemic resiniferatoxin (RTX)-pretreatment can counteract the detrusor over-activity induced by intravesical capsaicin, acetic acid or ATP. Cystometric investigations were performed on awake female Sprague-Dawley rats before and 24 h after injection of RTX (0.3 mg/kg s.c.) or vehicle. The effects of intravesically instilled ATP (0.1 or 1.0 mM), capsaicin (30 microM) or acetic acid (pH 4.0) were compared with those of intravesical saline. RTX, but not its vehicle, significantly increased threshold pressure, voiding interval, micturition volume and bladder capacity. In the vehicle-pretreated rats, intravesical instillation of capsaicin or acetic acid significantly decreased voiding interval, micturition volume, and bladder capacity. However, in the RTX-pretreated rats, neither capsaicin nor acetic acid affected any parameter. On the other hand, intravesical ATP (0.1 mM) significantly decreased voiding interval and micturition volume in both groups of animals. At 1.0 mM, ATP also increased basal pressure and decreased the pressure threshold for micturition in both groups. The present results support the view that increased extracellular ATP has a role in mechano-afferent transduction in the rat bladder and that ATP-induced facilitation of the micturition reflex is mediated, at least partly, by nerves other than capsaicin-sensitive afferent nerves.

In vitro topical application and in vivo pharmacodynamic evaluation of nonivamide hydrogels using Wistar rat as an animal model

Nonivamide, a so-called synthetic capsaicin, is a substitute for capsaicin which has a similar chemical structure and pharmacological activities as those of capsaicin. The purposes of this study were to explore the in vivo pharmacodynamic responses of nonivamide in hydrogels using Wistar rat as an animal model and to correlate the in vivo results with in vitro topical application. The incorporation of Pluronic F-127 polymer into hydrogels resulted in retarded release of nonivamide. Chitosan and carboxymethylcellulose hydrogels produced higher levels of in vitro nonivamide permeation and skin distribution. The in vivo effects of nonivamide on skin perturbation and vasodilation were found to differ depending on dose and duration after topical application. Quantification of transepidermal water loss was demonstrated to correlate with the measured in vitro skin distribution of nonivamide. The various doses of nonivamide in the hydrogels did not markedly influence erythematous reactions of skin as determined by colorimetric measurements. Hydrogel formulations of nonivamide delivered more drug to the skin and produced greater pharmacodynamic activities than did cream bases of capsaicin.

Effect of capsaicin and dimethyl sulfoxide on ion transport in the selected experimental models

The aim of the present work was to determine the changes in ion transport in the selected epithelium-lined organs under influence of mechanical stimuli, and also to assess similarities and differences in reactions to capsaicin and dimethyl sulfoxide (DMSO) between trachea and caecum of rabbit and the skin of frog in this experimental setup. The experiments were conducted on rabbit trachea and caecum, and the skin of frog, Rana esculenta L. The experiments consisted in measuring transepithelial electrical potential (PD in mV) with Ussing apparatus, modified to enable testing of the effects of mechanical stimulation of organs and defined pharmacological treatments. It was demonstrated that the addition of DMSO to the stimulating fluid decreased reversible hyperpolarization (dPD) after mechanical stimulation by at least 50% in all studied groups. On the other hand, action of capsaicin was dependent on the organ studied as well as on experimental conditions (e.g. type of incubation). Capsaicin decreased PD and reaction to mechanical stimulation in trachea incubated in Ringer solution supplemented with amiloride. On the other hand, it did not influence electrophysiological parameters of the trachea following its incubation with bumetanide. Capsaicin did not change electrical potential or reactivity of rabbit caecum incubated with both amiloride and bumetanide. The administration of capsaicin on frog skin incubated with bumetanide caused inhibition of the reaction to mechanical stimulation, whereas during incubation with amiloride no changes were recorded in PD and dPD of the skin. The present study demonstrated that capsaicin and DMSO could modify processes of ion transport dependent on mechanical stimulation.

Transdermal iontophoresis of sodium nonivamide acetate. V. Combined effect of physical enhancement methods

The effect of iontophoresis combined with treatment of other physical enhancement methods such as electroporation, low frequency ultrasound, and erbium:YAG (yttrium-aluminum-garnet) laser on the transdermal delivery of sodium nonivamide acetate (SNA) was examined in this present study. Iontophoresis increased the transdermal flux of SNA in vitro as compared to the passive diffusion without any enhancement. Furthermore, iontophoresis was always the most potent enhancement method for SNA permeation among the physical enhancement methods tested. Pulsing of high voltages (electroporation) followed by iontophoresis did not result in increased transport over iontophoresis alone. However, electroporation shortened the onset of transdermal iontophoretic delivery of SNA. Pretreatment of low frequency ultrasound (sonophoresis) alone on skin did not increase the skin permeation of SNA. The combination of iontophoresis and sonophoresis increased transdermal SNA transport more than each method by itself. The enhancement of drug transport across shunt routes and reduction of the threshold voltage in the presence of an electric field may contribute to this synergistic effect. Use of an erbium:YAG laser was a good method for enhancing transdermal absorption of SNA because it allows precise control of stratum corneum (SC) removal, and this ablation of SC could be reversible to the original normal status. The combination of laser treatment and iontophoresis also synergized the skin permeation of SNA, possibly due to a gradual drop in the electric resistance of the skin. The results in this present study point out that the choice of certain conditions with suitable physical enhancement methods can induce a synergistic effect on transdermal delivery of SNA during iontophoresis.

In vitro and in vivo evaluations of topically applied capsaicin and nonivamide from hydrogels

The purpose of this study was designed to investigate the in vitro and in vivo skin absorption of capsaicin and nonivamide from hydrogels. Various commercialized creams of capsaicin were also compared with hydrogels. Both skin stripping technique and Mexameter were applied to evaluate the level of capsaicin and nonivamide retained in stratum corneum (SC) and skin erythema in vivo. The partition of drug between skin and the hydrogel matrix was considered to play an important role in the permeation process. The in vitro permeation of capsaicin from hydrogels depends on the physicochemical nature and the concentration of the polymer used. The incorporation of nonionic Pluronic F-127 polymer into hydrogels resulted in a retarded release of capsaicin. On the other hand, the in vitro capsaicin permeation showed higher levels in cationic chitosan and anionic carboxymethyl cellulose (CMC) hydrogels than cream bases. The permeation of nonivamide was retarded at the late stage of in vitro application. The inter-subject variation was more significant in the in vivo study than in vitro skin permeation experiments. The cream induced in vivo skin erythema depending on the drug concentration, however, the dose-dependence was not observed in hydrogels. Nonivamide-treated skin showed stronger erythema than capsaicin-treated skin. The present study indicates that there is a moderate correlation between in vitro skin permeation and in vivo erythema responses of topically applied capsaicin and nonivamide. The correlation between drug amount in SC and skin erythema test in vivo was also observed.

Enhanced skin permeation of a new capsaicin derivative (DA-5018) from a binary vehicle system composed of isopropyl myristate and ethoxydiglycol

DA-5018, a recently synthesized capsaicin analog, appears to possess potent analgesic activity when administered topically. The objective of this study is to test the feasibility of the topical administration of this compound. Specifically, our goal was to identify vehicle system that permit a reasonable transdermal permeation of the compound in mice. Among the vehicles examined, isopropyl myristate (IPM) showed the largest in vitro permeability across the intact skin (83.6 +/- 5.42 microl/cm2/h). However, due to the limited solubility of DA-5018 in IPM (0.53 mg/ml), the maximal flux from the IPM medium remained at only 44.3 +/- 2.87 microg/cm2/hr. In order to increase the flux, addition of better solvents for DA-5018 was attempted, under the assumption that flux is the result of both solubility and permeability. Ethoxydiglycol (EG) and oleic acid (OA) were selected as examples of good solvents. The addition of EG or OA to IPM at a 1:1 volume ratio resulted in a comparable increase in the solubility of the compound (i.e., to 61.1 and 50.2 mg/ml for EG and OA, respectively). However, the addition of EG at a 1:1 volume ratio, for example, increased the flux 6.3 fold (i.e., 279 microg/cm2/hr), while OA, at a 1:1 volume ratio, decreased the flux 5 fold (i.e., 9.26 microg/cm2/hr). The mechanism of this discrepancy between EG and OA was investigated by measuring the permeabilty of DA-5018 across the stratum corneum-removed skin of the mouse, under the hypothesis that the viable skin layer may serve as a barrier for the permeation of lipophilic substances such as DA 5018. The permeability of DA-5018, from the medium of EG or OA, across the viable skin differed greatly for EG (0.41 microl/cm2/hr) and OA (0.086 microl/cm2/hr), suggesting that a higher permeability across the viable skin layer is needed for the second solvents. The maximum flux across the intact skin was achieved for DA-5018 when EG was added to IPM at a 1:1 volume ratio. Thus, the use of a binary system appears to be the bes approach for realizing the transdermal delivery of DA-5018 at a reasonable rate.

Axonal transport of VR1 capsaicin receptor mRNA in primary afferents and its participation in inflammation-induced increase in capsaicin sensitivity

Capsaicin receptors are expressed in primary sensory neurons and excited by heat and protons. We examined the inflammation-induced changes of the level of VR1 capsaicin receptor mRNA in sensory neurons and the sensitivity of primary afferents to capsaicin. Carrageenan treatment induced axonal transport of VR1 mRNA, but not that of preprotachykinin mRNA, from the dorsal root ganglia to central and peripheral axon terminals. The sensitivity of central terminals to capsaicin, which was estimated by measuring the capsaicin-evoked release of glutamate from the dorsal horn, was increased by peripheral inflammation, and such an increase was suppressed by inhibiting the RNA translation in the dorsal horn with cycloheximide and an intrathecal injection of VR1 antisense oligonucleotides. Thus, peripheral inflammation induces the axonal transport of VR1 mRNA, which may be involved in the hypersensitivity of primary afferents to capsaicin and the production of inflammatory hyperalgesia.

The effect of the base on the kinetics of action of the capsaicinoid nonivamide: evaluation with a hyperemic test

Because of their selective receptor-mediated action on cutaneous nociceptive C-fibers, the interest in capsaicinoids as topical analgetic drugs has been constantly growing over the past years. Knowledge of the pharmacokinetics seems particularly important for potential future clinical applications. Therefore, the aim of the present study was to investigate the influence of the type of preparation on the time course of action of the capsaicinoid nonivamide monitored by the axon-reflex-induced hyperemic action and area of erythema. Sixteen healthy subjects were included in the study. The hyperemic responses after application of nonivamide in an oil-in-water (O/W) emulsion and in a water-free ointment were assessed both by laser Doppler perfusion imaging and planimetry after 0, 15, 30, 45, 60, 120 and 240 min. They were compared with the reaction after application of the nicotinic ester nicoboxil and a combination of nonivamide and nicoboxil in the same preparations. Applied as a water-free ointment, nonivamide showed a slow onset of hyperemic action, reaching its maximum 45 min after application. When applied as an O/W emulsion, however, the increase in effect was high, reaching its maximum already after 30 min. Application of the nicoboxil preparations revealed a clearly lesser influence of the base regarding the onset of maximum effect. The combination of both substances showed an additive effect for both bases, and a maximum effect was found already after 15 min with both the water-free ointment and the O/W emulsion base. In conclusion, the results of the present study show that there appears to be a strong influence of the vehicle on the kinetics of action of capsaicinoids, and that the hyperemic test used in this paper is very useful for the quantitative determination of the pharmacokinetic properties of capsaicinoids. Moreover, the C-fiber-stimulating effect of capsaicinoids can, at least in part, be enhanced by combination with a nicotinic ester, even though these substances have no direct effect on the C-fibers.

Permeability of a capsaicin derivative, [14C]DA-5018 to blood-brain barrier corrected with HPLC method

In the present work, the transport mechanism of a capsaicin derivative, DA-5018, through blood-brain barrier (BBB) has been investigated to evaluate the feasibility of potential drug development. The result of pharmacokinetic parameters obtained from the intravenous injection of plasma volume marker, [3H]RSA and [14C]DA-5018, indicated that both AUC, area under the plasma concentration curve and VD, volume of distribution in brain of [3H]RSA agreed with those reported (1620 +/- 10 percentage injected dose minute per milliliter (%IDmin/ml) and 12.0 +/- 0.1 microliters/g, respectively). Elimination half-life and AUC of [14C]DA-5018 is corrected by the HPLC analysis, 19.6 +/- 1.2 min and 7.69 +/- 0.85% IDmin/ml, respectively. The metabolic rate of [14C] DA-5018 was very rapid. The blood-brain barrier permeability surface area (PS) product of [14C]DA-5018 was calculated to be 0.24 +/- 0.05 microliter/min/g. The result of internal carotid artery perfusion and capillary depletion suggested that [14C]DA-5018 pass through BBB with the time increasingly. Investigation of transport mechanism of [14C]DA-5018 using agonist and antagonist suggested that vanilloid (capsaicin) receptor did not exist in the BBB, and nutrient carrier system in the BBB has no effect on the transport of DA-5018. In conclusion, despite the fact that penetration of DA-5018 through BBB is significant, the intact drug found in the brain tissue is small because of a rapid metabolism. Therefore, for the central analgesic effect of DA-5018, the method to increase the metabolic stability in plasma and the brain permeability should be considered.

Pharmacokinetics of a non-narcotic analgesic, DA-5018, in rats

The pharmacokinetics of a non-narcotic analgesic, DA-5018, were compared after single intravenous (i.v.), subcutaneous (s.c.), and oral administrations, and after multiple (seven consecutive days) s.c. administration to rats. After i.v. administration of DA-5018, 1, 2, and 5 mg kg-1, the pharmacokinetic parameters of DA-5018 were independent of the dose ranges studied. After oral administration of DA-5018, absorption of the drug from gastrointestinal (GI) tract was fast, but the extent of absolute bioavailability (F) was low; the values were 23.2, 23.0, and 27.3% for 2, 5, and 10 mg kg-1, respectively. After single s.c. administration of DA-5018, absorption of the drug from the injected site was fast and the extent of absorption was fairly good; the F values were 74.5 and 71.8% for 2 and 5 mg kg-1, respectively. The lower F values after oral administration of DA-5018 to rats could be due to degradation of the drug in rat GI tract and/or considerable first-pass effect. After i.v., oral, and s.c. administration of DA-5018, the drug had a strong affinity to the rat tissues studied as reflected in the greater-than-unity tissue to plasma ratio. After i.v., oral, and s.c. administration of the drug, the biliary and urinary excretion of unchanged DA-5018 were negligible. There was no significant difference in the pharmacokinetics or tissue distribution of DA-5018 between single and multiple s.c. administration of the drug, 5 mg kg-1, to rats, indicating that there could be no tissue accumulation of the drug after multiple s.c. administration of the drug to rats.

Development and evaluation of transdermal patches of nonivamide and sodium nonivamide acetate

Transdermal patches were developed and evaluated for two synthetic derivatives of capsaicin, nonivamide (NVA) and sodium nonivamide acetate (SNA), by in vitro and in vivo skin permeation. The designed system was essentially based on natural rubber or polymeric Gelva dispersion. The characterization of physicochemical properties of the patches showed adequate adhesive force and low thickness which suggested these patch formulations possessed good quality. In the study of in vitro percutaneous experiment, the predicted therapeutic activities of patches were all higher than that of a commercially available plaster after the calculation of antinociceptive index. The highest in vitro penetration flux was found in the Gelva patch for NVA. The result of in vivo experiments revealed a high obverse correlation with that of in vitro experiments. The information of this present study is helpful for the further development of NVA and SNA transdermal drug delivery system.

Percutaneous absorption of vanilloids: in vivo and in vitro studies

The percutaneous absorption of three highly lipophilic analogs of capsaicin--vanillylnonanamide (VN), olvanil, and NE-21610--was measured in vivo in the CD:VAF rat, and in vitro through excised CD: VAF and SkH:Fz rat skin and human cadaver skin. Absorption and skin metabolism were monitored by radiolabel techniques. The rank order of penetration in all species was VN > olvanil > NE-21610, in accordance with that expected from their physical properties. Rat skin was more permeable than human skin by factors ranging from 4 to 8 for VN, 10 to 20 for olvanil, and approximately 10 to 100 for NE-21610. All three compounds were extensively metabolized during passage through fresh SkH:Fz rat skin, with the primary route of degradation for at least two of the compounds involving hydrolysis of the amide bond (the metabolites of NE-21610 were not identified). For the in vitro studies a range of receptor solutions was employed to determine a set of conditions that best mimicked in vivo absorption. The results with phosphate-buffered saline containing a preservative and 1-6% polyoxyethylene-20 oleyl ether (Oleth-20) were in good agreement with in vivo results for all three compounds for periods up to 24 h post-dose; after this time, in vivo absorption rates declined but in vitro rates remained relatively constant. Buffered saline or saline containing 0.5% bovine serum albumin led to marked underestimates of in vivo penetration for olvanil and NE-21610, whereas a 1:1 ethanol: water solution led to gross overestimates of the in vivo absorption rates for all three compounds.