Optical Assessment of Nociceptive TRP Channel Function at the Peripheral Nerve Terminal.

Free nerve endings are key structures in sensory transduction of noxious stimuli. In spite of this, little is known about their functional organization. Transient receptor potential (TRP) channels have emerged as key molecular identities in the sensory transduction of pain-producing stimuli, yet the vast majority of our knowledge about sensory TRP channel function is limited to data obtained from in vitro models which do not necessarily reflect physiological conditions. In recent years, the development of novel optical methods such as genetically encoded calcium indicators and photo-modulation of ion channel activity by pharmacological tools has provided an invaluable opportunity to directly assess nociceptive TRP channel function at the nerve terminal.

Amelioration from the ocular irritant Capsaicin: development and assessment of a Capsazepine in situ gel system for ocular delivery.

BACKGROUND: Defense personnel utilize capsaicin-based ocular sprays as non-lethal agents for law implementation during instances of mob violence. This study involves the capsaicin antagonist Capsazepine and the investigation of whether Capsazepine's antagonistic approach can be favorably utilized for defense utilization to block capsaicin-initiated pain and inflammation via the ocular pathway. RESEARCH DESIGN AND METHODS: Ocular capsazepine in situ gels were prepared with polymers Pluronic F-127 and Chitosan; optimized formulation was quantified in ocular tissues chromatographically and by in vivo live ocular imaging; anti-inflammatory efficacy was determined by eye irritation testing, corneal and retinal imaging, ocular prostaglandin estimation, and by viability and proliferation testing using human ocular cell lines, etc. RESULTS: A physicochemically stable Capsazepine in situ gel was formulated which showed little ocular irritation, considerable transcorneal permeation; was precisely quantified in ocular tissues by gas chromatography and in vivo live ocular imaging; showed anti-inflammatory properties against capsaicin by eye imaging experiments, prostaglandin declination and showed acceptable cytocompatibility when studied using human ocular cell lines. CONCLUSIONS: The fabricated in situ Capsazepine gel system might be promising for ocular delivery as it appears a pharmacologically potent and safe development, suitable for utilization in the ocular clinical therapy, provided there is additional research to substantiate it.

Assessment of Pharmacology, Safety, and Metabolic activity of Capsaicin Feeding in Mice.

Capsaicin (CAP) activates transient receptor potential vanilloid subfamily 1 (TRPV1) to counter high-fat diet (HFD)-induced obesity. Several studies suggest that CAP induces the browning of white adipocytes in vitro or inguinal white adipose tissue (iWAT) in vivo. However, there is a lack of data on the dose-response for CAP to inhibit HFD-induced obesity. Therefore, we first performed experiments to correlate the effect of various doses of CAP to prevent HFD-induced weight gain in wild-type (WT) mice. Next, we performed a subchronic safety study in WT mice fed a normal chow diet (NCD ± CAP, 0.01% in NCD) or HFD ± CAP (0.01% in HFD) for eight months. We analyzed the expression of adipogenic and thermogenic genes and proteins in the iWAT from these mice, conducted histological studies of vital organs, measured the inflammatory cytokines in plasma and iWAT, and evaluated liver and kidney functions. The dose-response study showed that CAP, at doses above 0.001% in HFD, countered HFD-induced obesity in mice. However, no difference in the anti-obesity effect of CAP was observed at doses above 0.003% in HFD. Also, CAP, above 0.001%, enhanced the expression of sirtuin-1 and thermogenic uncoupling protein 1 (UCP-1) in the iWAT. Safety analyses suggest that CAP did not cause inflammation. However, HFD elevated plasma alanine aminotransferase and creatinine, caused iWAT hypertrophy and hepatic steatosis, and CAP reversed these. Our data suggest that CAP antagonizes HFD-induced metabolic stress and inflammation, while it does not cause any systemic toxicities and is well tolerated by mice.

Acute administration of capsaicin increases resting energy expenditure in young obese subjects without affecting energy intake, appetite, and circulating levels of orexigenic/anorexigenic peptides.

Although capsaicin has been reported to reduce energy intake and increase energy expenditure in an adult (normal weight or overweight) population, thus resulting in a net negative energy balance and weight loss, these beneficial effects have not been investigated in young obese subjects. We hypothesize that capsaicin acutely administered in young obese subjects exerts the same effects on energy balance and that these effects are mediated by changes in gastrointestinal peptides regulating appetite. Thus, the aim of the present study was to evaluate the acute effects of capsaicin (2 mg) or placebo on energy intake, hunger, and satiety in obese adolescents and young adults (female-male ratio: 4:6, age: 21.0 ± 5.8 years; body mass index: 41.5 ± 4.3 kg/m2) provided an ad libitum dinner. Furthermore, circulating levels of some orexigenic (ghrelin) and anorexigenic (glucagon-like peptide 1 and peptide YY) peptides were measured after a meal completely consumed (lunch), together with the evaluation of hunger and satiety and assessment of resting energy expenditure (REE) through indirect computerized calorimetry. When compared to placebo, capsaicin did not significantly change either energy intake or hunger/satiety 6 hours after its administration (dinner). No differences in circulating levels of ghrelin, glucagon-like peptide 1, and peptide YY and in hunger/satiety were found in the 3 hours immediately after food ingestion among obese subjects treated with capsaicin or placebo (lunch). By contrast, the meal significantly increased REE in the capsaicin- but not placebo-treated group (capsaicin: from 1957.2 ± 455.1 kcal/d up to 2342.3 ± 562.1 kcal/d, P < .05; placebo: from 2060.1 ± 483.4 kcal/d up to 2296.0 ± 484.5 kcal/d). The pre-post meal difference in REE after capsaicin administration was significantly higher than that observed after placebo (385.1 ± 164.4 kcal/d vs 235.9 ± 166.1 kcal/d, P < .05). In conclusion, although capsaicin does not exert hypophagic effects, these preliminary data demonstrate its ability as a metabolic activator in young obese subjects.

Dihydrocapsiate improved age-associated impairments in mice by increasing energy expenditure.

Metabolic dysfunction is associated with aging and results in age-associated chronic diseases, including type 2 diabetes mellitus, cardiovascular disease, and stroke. Hence, there has been a focus on increasing energy expenditure in aged populations to protect them from age-associated diseases. Dihydrocapsiate (DCT) is a compound that belongs to the capsinoid family. Capsinoids are capsaicin analogs that are found in nonpungent peppers and increase whole body energy expenditure. However, their effect on energy expenditure has been reported only in young populations, and to date the effectiveness of DCT in increasing energy expenditure in aged populations has not been investigated. In this study, we investigated whether DCT supplementation in aged mice improves age-associated impairments. We obtained 5-wk-old and 1-yr-old male C57BL/6J mice and randomly assigned the aged mice to two groups, resulting in a total of three groups: 1) young mice, 2) old mice, and 3) old mice supplemented with 0.3% DCT. After 12 wk of supplementation, blood and tissue samples were collected and analyzed. DCT significantly suppressed age-associated fat accumulation, adipocyte hypertrophy, and liver steatosis. In addition, the DCT treatment dramatically suppressed age-associated increases in hepatic inflammation, immune cell infiltration, and oxidative stress. DCT exerted these suppression effects by increasing energy expenditure linked to upregulation of both the oxidative phosphorylation gene program and fatty acid oxidation in skeletal muscle. These results indicate that DCT efficiently improves age-associated impairments, including liver steatosis and inflammation, in part by increasing energy expenditure via activation of the fat oxidation pathway in skeletal muscle.

Low-cost functional plasticity of TRPV1 supports heat tolerance in squirrels and camels.

The ability to sense heat is crucial for survival. Increased heat tolerance may prove beneficial by conferring the ability to inhabit otherwise prohibitive ecological niches. This phenomenon is widespread and is found in both large and small animals. For example, ground squirrels and camels can tolerate temperatures more than 40 °C better than many other mammalian species, yet a molecular mechanism subserving this ability is unclear. Transient receptor potential vanilloid 1 (TRPV1) is a polymodal ion channel involved in the detection of noxious thermal and chemical stimuli by primary afferents of the somatosensory system. Here, we show that thirteen-lined ground squirrels (Ictidomys tridecemlineatus) and Bactrian camels (Camelus ferus) express TRPV1 orthologs with dramatically reduced temperature sensitivity. The loss of sensitivity is restricted to temperature and does not affect capsaicin or acid responses, thereby maintaining a role for TRPV1 as a detector of noxious chemical cues. We show that heat sensitivity can be reengineered in both TRPV1 orthologs by a single amino acid substitution in the N-terminal ankyrin-repeat domain. Conversely, reciprocal mutations suppress heat sensitivity of rat TRPV1, supporting functional conservation of the residues. Our studies suggest that squirrels and camels co-opt a common molecular strategy to adapt to hot environments by suppressing the efficiency of TRPV1-mediated heat detection at the level of somatosensory neurons. Such adaptation is possible because of the remarkable functional flexibility of the TRPV1 molecule, which can undergo profound tuning at the minimal cost of a single amino acid change.

Assessment of Free Drug Concentration in Cyclodextrin Formulations Is Essential to Determine Drug Potency in Functional In Vitro Assays.

Cyclodextrins (CD) have the ability to form inclusion complexes with drugs and can be used as excipients to enhance solubility of poorly soluble drugs. To make accurate estimations of the potency of the drug, knowledge of the free drug concentration is important. The aim of this study was to evaluate the applicability of calculated free drug concentrations toward response measurements in a transient receptor potential vanilloid receptor-1 cell-based in vitro assay. This included accounting for potential competitive CD binding of 2 transient receptor potential vanilloid receptor-1 active entities: 1 antagonist, and 1 agonist (capsaicin). Solubility of the CD-drug complexes was measured, and the ligand to substrate affinity in CD formulations was determined according to the phase-solubility technique. The total concentration of antagonist, agonist, CD, and the binding constants between ligands and CD were used to calculate the free concentration of CD ligands. For capsaicin and 2 of the 3 investigated model drugs, the calculated free drug concentration was consistent with the experimental in vitro data while it was overestimated for one of the compounds. In conclusion, the suggested approach can be used to calculate free drug concentration and competitive binding in CD formulations for the application of cell-based drug functionality assays.

Assessment of human brown adipose tissue density during daily ingestion of thermogenic capsinoids using near-infrared time-resolved spectroscopy.

18F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDGPET/CT) is widely used as a standard method for evaluating human brown adipose tissue (BAT), a recognized therapeutic target of obesity. However, a longitudinal BAT study using FDG-PET/CT is lacking owing to limitations of the method. Near-infrared time-resolved spectroscopy (NIR(TRS)) is a technique for evaluating human BAT density noninvasively. This study aimed to test whether NIRTRS could detect changes in BAT density during or after long-term intervention. First, using FDG-PET/CT, we confirmed a significant increase (+48.8%, P < 0.05) in BAT activity in the supraclavicular region after 6-week treatment with thermogenic capsaicin analogs, capsinoids. Next, 20 volunteers were administered either capsinoids or placebo daily for 8 weeks in a double-blind design, and BAT density was measured using NIR(TRS) every 2 weeks during the 8-week treatment period and an 8-week period after stopping treatment. Consistent with FDG-PET/CT results, NIR(TRS) successfully detected an increase in BAT density during the 8-week treatment (+46.4%, P < 0.05), and a decrease in the 8-week follow-up period (-12.5%, P = 0.07), only in the capsinoid-treated, but not the placebo, group. Thus, NIR(TRS) can be applied for quantitative assessment of BAT in longitudinal intervention studies in humans.

Capsiate supplementation reduces oxidative cost of contraction in exercising mouse skeletal muscle in vivo.

Chronic administration of capsiate is known to accelerate whole-body basal energy metabolism, but the consequences in exercising skeletal muscle remain very poorly documented. In order to clarify this issue, the effect of 2-week daily administration of either vehicle (control) or purified capsiate (at 10- or 100-mg/kg body weight) on skeletal muscle function and energetics were investigated throughout a multidisciplinary approach combining in vivo and in vitro measurements in mice. Mechanical performance and energy metabolism were assessed strictly non-invasively in contracting gastrocnemius muscle using magnetic resonance (MR) imaging and 31-phosphorus MR spectroscopy (31P-MRS). Regardless of the dose, capsiate treatments markedly disturbed basal bioenergetics in vivo including intracellular pH alkalosis and decreased phosphocreatine content. Besides, capsiate administration did affect neither mitochondrial uncoupling protein-3 gene expression nor both basal and maximal oxygen consumption in isolated saponin-permeabilized fibers, but decreased by about twofold the Km of mitochondrial respiration for ADP. During a standardized in vivo fatiguing protocol (6-min of repeated maximal isometric contractions electrically induced at a frequency of 1.7 Hz), both capsiate treatments reduced oxidative cost of contraction by 30-40%, whereas force-generating capacity and fatigability were not changed. Moreover, the rate of phosphocreatine resynthesis during the post-electrostimulation recovery period remained unaffected by capsiate. Both capsiate treatments further promoted muscle mass gain, and the higher dose also reduced body weight gain and abdominal fat content. These findings demonstrate that, in addition to its anti-obesity effect, capsiate supplementation improves oxidative metabolism in exercising muscle, which strengthen this compound as a natural compound for improving health.

Avaliação do potencial biológico da Tabebuia aurea (Silva Manso) como fonte de moléculas bioativas para atividade antimicrobiana, antiedematogênica e antirradicalar / Biological potential assessment of Tabebuiaaurea (Silva Manso) as a source of bioactive molecules for antimicrobial, antiedematogenic and antiradical activity

RESUMO As espécies da família Bignoniaceae e do gênero Tabebuia são amplamente utilizadas na medicina tradicional e possuem um forte potencial terapêutico. Diante disso, objetivou-se avaliar o potencial biológico da Tabebuia aurea, determinando a atividade antimicrobiana; por meio do método da microdiluição em caldo, para a determinação da Concentração Inibitória Mínima (CIM); antiedematogênica, pelo ensaio de edema de orelha induzido por capsaicina; e antirradicalar, frente ao radical DPPH. Os extratos etanólicos de T. aurea não evidenciaram citotoxicidade, exceto o extrato etanólico da flor nas concentrações > 0,5 mg mL-1. O extrato etanólico da flor foi ativo com ação bactericida frente a S. epidermidis (CIM de 0,06 mg mL-1) enquanto o extrato etanólico da folha foi moderadamente ativo frente a S. epidermidis (CIM: 0,25 mg mL-1) e S. aureus (CIM: 0,50 mg mL-1) sugerindo ação bacteriostática para ambas as linhagens. Os dois extratos apresentaram ação antiedematogênica, com inibição do edema de 40,50% pelo extrato etanólico da flor e de 41,73% pelo extrato da folha. T. aurea não apresentou atividade antirradicalar. Os resultados comprovam o perfil antibacteriano e antiedematogênico com ausência de citotoxidade pela T. aurea. Sugere-se a continuação dos testes com frações e substâncias isoladas das flores e folhas da referida espécie vegetal, bem como de experimentos in vivo, como forma de agregar evidências visando à busca de novos fitoterápicos.

ABSTRACT The species of Bignoniaceae family and genus Tabebuia are widely used in the traditional medicine and have a great therapeutic potential. The aim of the current research was to evaluate the biological potential of the Tabebuia aurea, determining its antimicrobial activity by the microdilution broth method, to predict the anti-edematogenic Minimum Inhibitory Concentration (MIC) by ear edema assay induced by capsaicin; and the antiradical one, towards DPPH. The ethanol extracts of T. aureashowed no cytotoxicity, except for the flower ethanol extract in concentrations above > 0.5 mg mL-1. The ethanol extract of the flower was active, with bactericidal action, against S. epidermidis (MIC 0.06 mg ml-1) and the ethanol extract of moderately active recto S. epidermidis (CIM: 0.25 mg mL-1) and S. aureus (MIC: 0.50 mg mL-1) were bacteriostatic for both strains. Both extracts had antiedematogenic action on the inhibition of edema of 40.50% by the ethanol extract of the flower and 41.73% by leaf extract. T. aurea did not show antiradical activity. The results indicate the antibacterial and antiedematogenic profile with no cytotoxicity by the T. aurea. It suggests the continuation of tests with isolated fractions and substances of flowers and leaves of that plant species as well as in vivo trials, in order to enhance the evidences targeted on finding new herbal medicines.

Assessment of intraoral mucosal pain induced by the application of capsaicin.

OBJECTIVE: To develop an objective method for assessing nociceptive behaviour in an animal model of capsaicin-induced intraoral pain. Changes in nociceptive responses were also examined after injury to the inferior alveolar nerve (IAN). DESIGN: Nociceptive responses evoked by the intraoral application of various doses of capsaicin were analyzed in lightly anaesthetized rats. The number of c-Fos protein-like immunoreactive (Fos-LI) neurons in the medullary dorsal horn (MDH) induced by the intraoral application of capsaicin was measured. Behavioural and c-Fos responses were also examined 14 days after injury to the IAN. RESULTS: Larger doses of intraoral capsaicin (1, 10 and 100µg) induced vigorous licking behaviour and c-Fos response in the MDH in a reproducible manner. The magnitudes of both behavioural activity and the c-Fos response from the 10 and 100µg doses of capsaicin were significantly greater than that by the 1µg dose. Injury to the IAN exaggerated the behavioural and c-Fos responses evoked by intraoral capsaicin. CONCLUSIONS: The intraoral application of capsaicin is a valid and reliable method for studying intraoral pain and hyperalgesia following nerve injury.

Capsaicin and sensory neurones: a historical perspective.

Capsaicin, the pungent ingredient of red pepper has become not only a "hot" topic in neuroscience but its new target-related unique actions have opened the door for the drug industry to introduce a new chapter of analgesics. After several lines of translational efforts with over 1,000 patents and clinical trials, the 8% capsaicin dermal patch reached the market and its long-lasting local analgesic effect in some severe neuropathic pain states is now well established. This introductory chapter outlines on one hand the historical background based on the author's 50 years of experience in this field and on the other hand emphasizes new scopes, fascinating perspectives in pharmaco-physiology, and molecular pharmacology of nociceptive sensory neurons. Evidence for the effect of capsaicin on C-polymodal nociceptors (CMH), C-mechanoinsensitive (CHMi), and silent C-nociceptors are listed and the features of the capsaicin-induced blocking effects of nociceptors are demonstrated. Common and different characteristics of nociceptor-blocking actions after systemic, perineural, local, intrathecal, and in vitro treatments are summarized. Evidence for the misleading conclusions drawn from neonatal capsaicin pretreatment is presented. Perspectives opened from cloning the capsaicin receptor "Transient Receptor Potential Vanilloid 1" (TRPV1) are outlined and potential molecular mechanisms behind the long-lasting functional, ultrastructural, and nerve terminal-damaging effects of capsaicin and other TRPV1 agonists are summarized. Neurogenic inflammation and the long-list of "capsaicin-sensitive" tissue responses are mediated by an unorthodox dual sensory-efferent function of peptidergic TRPV1-expressing nerve terminals which differ from the classical efferent and sensory nerve endings that have a unidirectional role in neuroregulation. Thermoregulatory effects of capsaicin are discussed in detail. It is suggested that since hyperthermia and burn risk due to enhanced noxious heat threshold are the major obstacles of some TRPV1 antagonists, they could be overcome. The special "multisteric" gating function of the TRPV1 cation channel provides the structural ground for blocking chemical activation of TRPV1 without affecting its responsiveness to physical stimuli. A new chapter of potential analgesics targeting nociceptors is now already supported for pain relief in persistent pathological pain states.

The effects of a co-application of menthol and capsaicin on nociceptive behaviors of the rat on the operant orofacial pain assessment device.

BACKGROUND: Transient receptor potential (TRP) cation channels are involved in the perception of hot and cold pain and are targets for pain relief in humans. We hypothesized that agonists of TRPV1 and TRPM8/TRPA1, capsaicin and menthol, would alter nociceptive behaviors in the rat, but their opposite effects on temperature detection would attenuate one another if combined. METHODS: Rats were tested on the Orofacial Pain Assessment Device (OPAD, Stoelting Co.) at three temperatures within a 17 min behavioral session (33°C, 21°C, 45°C). RESULTS: The lick/face ratio (L/F: reward licking events divided by the number of stimulus contacts. Each time there is a licking event a contact is being made.) is a measure of nociception on the OPAD and this was equally reduced at 45°C and 21°C suggesting they are both nociceptive and/or aversive to rats. However, rats consumed (licks) equal amounts at 33°C and 21°C but less at 45°C suggesting that heat is more nociceptive than cold at these temperatures in the orofacial pain model. When menthol and capsaicin were applied alone they both induced nociceptive behaviors like lower L/F ratios and licks. When applied together though, the licks at 21°C were equal to those at 33°C and both were significantly higher than at 45°C. CONCLUSIONS: This suggests that the cool temperature is less nociceptive when TRPM8/TRPA1 and TRPV1 are co-activated. These results suggest that co-activation of TRP channels can reduce certain nociceptive behaviors. These data demonstrate that the motivational aspects of nociception can be influenced selectively by TRP channel modulation and that certain aspects of pain can be dissociated and therefore targeted selectively in the clinic.

Capsaicin and evodiamine ingestion does not augment energy expenditure and fat oxidation at rest or after moderately-intense exercise.

Capsaicin and evodiamine are 2 thermogenic agents recognized for their ability to stimulate the sympathetic nervous system. We hypothesized that both capsaicin and evodiamine would be effective at increasing thermogenesis and lipid oxidation during rest and exercise. In a randomized, cross-over design, 11 men ingested 500 mg of cayenne pepper (1.25 mg capsaicin), 500 mg evodiamine, or placebo at rest following 30 minutes of energy expenditure assessment using open-circuit spirometry. Energy expenditure was assessed again prior to commencing approximately 30 minutes of treadmill exercise at 65% peak oxygen consumption. Energy expenditure was assessed for another 30 minutes of the post-exercise period. Heart rate, blood pressure, core temperature, and venous blood samples were obtained 30 minutes before supplement ingestion, 1 hour after supplement ingestion, immediately post-exercise, and 45 minutes post-exercise. Serum markers of lipid oxidation (glycerol, free fatty acids, glucose, epinephrine, and norepinephrine) were determined spectrophotometrically with enzyme-linked immunosorbent assay. Two-way analyses of variance with repeated measures were performed for each dependent variable (P ≤ .05) with Supplement and Test as main effects. Statistical analyses revealed significant main effects for Test for hemodynamics, energy expenditure, serum catecholamines, and markers of fat oxidation immediately post-exercise (P < .05). No significant interactions between Supplement and Test were noted for any criterion variable (P > .05). These results suggest that acute ingestion of 500 mg of cayenne (1.25 mg capsaicin) or evodiamine is not effective at inducing thermogenesis and increasing fat oxidation at rest or during exercise in men.

Acute effect on satiety, resting energy expenditure, respiratory quotient, glucagon-like peptide-1, free fatty acids, and glycerol following consumption of a combination of bioactive food ingredients in overweight subjects.

OBJECTIVE: A combination of bioactive food ingredients (capsaicinoids, epigallocatechin gallate, piperin, and l-carnitine, CBFI) may promote satiety and thermogenesis. The study was conducted in order to assess whether there is any effect on satiety, resting energy expenditure (REE), respiratory quotient, glucagon-like peptide-1 (GLP-1), free fatty acids (FFA) and glycerol release, following a standardized mixed meal with or without single consumption of a CBFI. DESIGN: An 8-week randomized double-blind placebo-controlled trial. SETTING: Dietetic and Metabolic Unit, Azienda di Servizi alla Persona, University of Pavia and "Villa delle Querce" Clinical Rehabilitation Institute, Rome, Italy. PARTICIPANTS: Thirty-seven overweight adults (body mass index [BMI]: 25-35). INTERVENTION: Nineteen overweight subjects were included in the supplemented group (14 women, 5 men; age 46.4 ± 6.4; BMI: 30.5 ± 3.3) and 18 in the placebo group (13 women, 5 men; age 40.8 ± 11.5; BMI: 30.1 ± 2.6). Satiety was assessed using 100-mm visual analogue scales (VAS) and the area under the curve was calculated. RESULTS: All measured parameters increased significantly in comparison with baseline in response to meal, both with CBFI and with placebo. However, throughout the study day, the supplemented group experienced a significantly greater increase than the placebo group in their sensation of satiety following acute administration of the supplement. CONCLUSION: CBFI may therefore be of great value in the treatment of overweight patients by increasing satiety and stimulating thermogenesis.

Assessment of the biological similarity of three capsaicin analogs (Capsinoids) found in non-pungent chili pepper (CH-19 Sweet) fruits.

CH-19 Sweet is a newly found chili pepper breed bearing much less pungent fruits. Because CH-19 Sweet fruits were found to contain three analogs (capsinoids) of capsaicin, a major component of pungency of hot peppers (the analogs are capsiate or CST, dihydrocapsiate or DCT, and nordihydrocapsiate or NDCT), we assessed in this study the bio-potencies of these three capsinoids by comparing them with capsaicin. The three capsinoids bound to transient potential vanilloid 1 (TRPV1) receptors expressed in cultured cells and activated Ca(2+) influx in a concentration-dependent manner with similar magnitudes. In contrast to capsaicin, capsinoids at the same concentration induced virtually no nociceptive responses when applied to the eyes or the oral cavities of mice. Intravenous administration of capsaicin or 20-fold increased doses of each capsinoid to rats induced significant increases in plasma catecholamine levels. Orally administered, each capsinoid enhanced oxygen consumption in mice. Based on the present results, capsaicin and these three capsinoids should have similar bio-potency, though capsinoids do not generate pungency or sensory irritation.

Behavioral assessment and identification of a molecular marker in a salicylate-induced tinnitus in rats.

Tinnitus is a non-observable phantom sensation. As such, it is a difficult condition to investigate and, to date, no effective treatment has been developed. To approach this phantom sensation, we aimed to develop a rat behavioral model of tinnitus using salicylate, an active component of aspirin known to induce tinnitus. We also aimed to establish a molecular marker of tinnitus by assessing the expression of transient receptor potential cation channel superfamily V-1 (TRPV1) in the rat auditory pathway during salicylate-induced tinnitus. Animals were trained to perform "an active avoidance task": animals were conditioned by electrical footshock to move to the other side of the conditioning box when hearing a sound. Animals received a single injection of saline or salicylate (400 mg/kg i.p.) and false positive responses were measured 2 h after injection as the number of movements during a silent period. The number of responses in salicylate-treated animals was highest when the conditioned stimulus was 60 dB sound pressure level (SPL) and 16 kHz. This indicates that animals could feel tinnitus 2 h after salicylate injection, equivalent to that induced by 60 dB SPL and 16 kHz. By means of real-time PCR and western blot analysis, TRPV1 expression was significantly upregulated in spiral ganglion cells 2 h after salicylate injection and this upregulation together with the increase in the number of false positive responses was significantly suppressed by capsazepine (10 mg/kg i.p.), a specific antagonist of TRPV1. This suggests that salicylate could induce tinnitus through activation of TRPV1 in the rat auditory pathway.

Enhanced energy expenditure and fat oxidation in humans with high BMI scores by the ingestion of novel and non-pungent capsaicin analogues (capsinoids).

The biochemical and physiological indices were monitored in 44 subjects after 4-week capsinoids (capsaicin analogues with low pungency) intake. The subjects were randomly assigned to 3 groups: CSNs3 (3 mg/kg of capsinoids), CSNs10 (10 mg/kg of capsinoids) and the control (placebo). Measurements were performed in the morning on overnight-fasted subjects. The oxygen consumption (VO(2)), resting energy expenditure (REE) and fat oxidation increased slightly compared to pre-administration values without any adverse effects, although the increase was not significant. The increase in fat oxidation was positively and significantly correlated with the body mass index (BMI). A meta-analysis was therefore conducted on a subgroup consisting of subjects with BMI >or= 25 (n=28). As a result, not only VO(2) increased significantly (p<0.05) in the CSNs10 group, but also REE in the CSNs10 group and fat oxidation in the CSNs3 and CSNs10 groups tended to increase (p<0.1). Consequently, a capsinoids intake would be able to enhance the energy expenditure and fat burning in humans, particularly those with high BMI.

Assessment of oral trigeminal sensitivity in humans.

The aim of this prospective study was to establish a clinical test for the assessment of oral trigeminal sensitivity. Capsaicin-impregnated filter paper strips (five concentrations: 0.0001-1%) were used to measure trigeminal thresholds. The strips were placed on the anterior tongue for 10 s. Subjects were asked to report the onset of any sensory perception, quality and duration of sensory perception. Thresholds were estimated in two ways: (1) threshold (THR1) related to sensory perception and (2) intensity related threshold (THR2). The test was applied to 63 healthy subjects (mean age 40 years; 34 women, 29 men). For whole-mouth testing with capsaicin, a small but significant correlation was found between THR1 and THR2 (r (63) = 0.41). Coefficients of correlation between test and re-test were r (30) = 0.60 for THR1 and r (30) = 0.78 THR2. Neither THR1 nor THR2 indicated either side or sex-related differences. Age-related differences were only found in THR2 scores, which were lower in young subjects (<40 years). Reliable assessment of intraoral trigeminal sensitivity appears to be possible using the presently described technique.