Adrenal sympathetic efferent nerve and catecholamine secretion excitation caused by capsaicin in rats

Differential engagement of inhibitory and excitatory cardiopulmonary reflexes by capsaicin and phenylbiguanide in C57BL/6 mice

The Bezold-Jarisch reflex is a powerful inhibitory reflex initiated by activation of cardiopulmonary vagal nerves during myocardial ischemia, hemorrhage, and orthostatic stress leading to bradycardia, vasodilation, hypotension, and vasovagal syncope. This clinically relevant reflex has been studied by measuring heart rate (HR) and mean arterial pressure (MAP) responses to injections of a variety of chemical compounds. We hypothesized that reflex responses to different compounds vary due to differential activation of vagal afferent subtypes and/or variable coactivation of excitatory afferents. HR and MAP responses to intravenous injections of the transient receptor potential vanilloid-1 (TRPV1) agonist capsaicin and the serotonin 5-HT3 receptor agonist phenylbiguanide (PBG) were measured in anesthetized C57BL/6 mice before and after bilateral cervical vagotomy. Capsaicin and PBG evoked rapid dose-dependent decreases in HR and MAP followed by increases in HR and MAP above baseline. Bezold-Jarisch reflex responses were abolished after vagotomy, whereas the delayed tachycardic and pressor responses to capsaicin and PBG were differentially enhanced. The relative magnitude of bradycardic versus depressor responses (↓HR/↓MAP) in vagus-intact mice was greater with capsaicin. In contrast, after vagotomy, the magnitude of excitatory tachycardic versus pressor responses (↑HR/↑MAP) was greater with PBG. Although capsaicin-induced increases in MAP and HR postvagotomy were strongly attenuated or abolished after administration of the ganglionic blocker hexamethonium, PBG-induced increases in MAP and HR were mildly attenuated and unchanged, respectively. We conclude that responses to capsaicin and PBG differ in mice, with implications for delineating the role of endogenous agonists of TRPV1 and 5-HT3 receptors in evoking cardiopulmonary reflexes in pathophysiological states.

Capsicum annuum L. and its bioactive constituents: A critical review of a traditional culinary spice in terms of its modern pharmacological potentials with toxicological issues

Capsicum annuum L., commonly known as chili pepper, is used as an important spice globally and as a crude drug in many traditional medicine systems. The fruits of C. annuum have been used as a tonic, antiseptic, and stimulating agent, to treat dyspepsia, appetites, and flatulence, and to improve digestion and circulation. The article aims to critically review the phytochemical and pharmacological properties of C. annuum and its major compounds. Capsaicin, dihydrocapsaicin, and some carotenoids are reported as the major active compounds with several pharmacological potentials especially as anticancer and cardioprotectant. The anticancer effect of capsaicinoids is mainly mediated through mechanisms involving the interaction of Ca²⁺ -dependent activation of the MAPK pathway, suppression of NOX-dependent reactive oxygen species generation, and p53-mediated activation of mitochondrial apoptosis in cancer cells. Similarly, the cardioprotective effects of capsaicinoids are mediated through their interaction with cellular transient receptor potential vanilloid 1 channel, and restoration of calcitonin gene-related peptide via Ca²⁺ -dependent release of neuropeptides and suppression of bradykinin. In conclusion, this comprehensive review presents detailed information about the traditional uses, phytochemistry, and pharmacology of major bioactive principles of C. annuum with special emphasis on anticancer, cardioprotective effects, and plausible toxic adversities along with food safety.

TRP Channels as Molecular Targets to Relieve Endocrine-Related Diseases

Transient receptor potential (TRP) channels are polymodal channels capable of sensing environmental stimuli, which are widely expressed on the plasma membrane of cells and play an essential role in the physiological or pathological processes of cells as sensors. TRPs often form functional homo- or heterotetramers that act as cation channels to flow Na⁺ and Ca²⁺, change membrane potential and [Ca²⁺]_i (cytosolic [Ca²⁺]), and change protein expression levels, channel attributes, and regulatory factors. Under normal circumstances, various TRP channels respond to intracellular and extracellular stimuli such as temperature, pH, osmotic pressure, chemicals, cytokines, and cell damage and depletion of Ca²⁺ reserves. As cation transport channels and physical and chemical stimulation receptors, TRPs play an important role in regulating secretion, interfering with cell proliferation, and affecting neural activity in these glands and their adenocarcinoma cells. Many studies have proved that TRPs are widely distributed in the pancreas, adrenal gland, and other glands. This article reviews the specific regulatory mechanisms of various TRP channels in some common glands (pancreas, salivary gland, lacrimal gland, adrenal gland, mammary gland, gallbladder, and sweat gland).

Estimation of Dietary Capsaicinoid Exposure in Korea and Assessment of Its Health Effects

The consumption of capsaicinoids, the active components in chili peppers, has been associated with both positive and negative health effects, and the level of capsaicinoid exposure may be an important determinant. Dietary capsaicinoid exposure was estimated using a previously developed database for capsaicinoid content and a 24-h dietary recall dataset obtained from the Korea National Health and Nutrition Examination Survey. The estimated consumption level was evaluated to determine its potential effects on weight reduction and gastrointestinal distress. The estimated daily mean capsaicinoid intake was 3.25 mg (2.17 mg capsaicin), and most Koreans consumed 1–30 mg of capsaicinoids (0.67–20 mg capsaicin) in a day. No adverse effect of capsaicin consumption was reported other than abdominal pain. For long-term repeated consumption, 30 mg may be the maximum tolerable dose. However, the effects on body weight or energy balance were inconsistent in 4–12 week clinical studies conducted with various capsaicin doses (2–135 mg), which was likely due to the complex interplay between capsaicin dose, study length, and participant characteristics. Therefore, the capsaicin consumption of most Koreans was below the levels that may cause adverse effects. However, more long-term studies for the dose range of 2–20 mg are required to further characterize capsaicin’s health benefits in Koreans.

Capsaicin Analogue Supplementation Does Not Improve 10 km Running Time-Trial Performance in Male Amateur Athletes: A Randomized, Crossover, Double-Blind and Placebo-Controlled Study

Background: To investigate the acute effects of a capsaicin analogue supplement on 10 km time-trial performance and physiological responses in amateur athletes. Methods: Twenty-one participants (age = 29.3 ± 5.5 years, weight 74.2 ± 11.3 kg, height 176.0 ± 0.0 cm, fat mass 12.7 ± 3.8%, V˙O_2max 62.7 ± 8.4 mL·k⁻¹·min⁻¹), completed two randomized, double-blind trials: capsaicin analogue condition (Capsiate (CAP) = 24 mg) or a placebo (PLA) condition. The participants consumed two doses of 12 mg of CAP or PLA capsule 45 min before and immediately at the start of each trial. The time required to complete 10 km, lactate concentration, maximum heart rate (HR_peak), and rating of perceived exertion (RPE) were recorded. Results: The 10 km time-trial performance (CAP = 45.07 ± 6.41 min vs. PLA = 45.13 ± 6.73, p = 0.828) was not statistically significantly different between conditions. No statistically significant differences between conditions were detected for lactate concentration (p = 0.507), HR_peak (p = 0.897) and RPE (p = 0.517). Conclusion: Two doses of a 12 mg Capsaicin analogue supplement did not improve performance and physiological responses in a 10 km running time-trial in amateur athletes.

Effects of oral stimulation with capsaicin on salivary secretion and neural activities in the autonomic system and the brain

BACKGROUND/PURPOSE

Although it has been reported that capsaicin ingestion has effects of protecting stomach mucosa and promoting energy consumption, physiological responses to oral stimulation with capsaicin has not been elucidated. Therefore, we investigated the effect of oral capsaicin stimulation on oral health and mental conditions by measuring changes in salivation, autonomic nervous activity and electroencephalogram (EEG).

MATERIALS AND METHODS

Eighteen healthy adults participated in this study. The stimulus concentrations of capsaicin and five basic taste solutions were determined based on the measured threshold of each stimulus in each subject. The weight of secreted saliva and the changes in concentrations of salivary secretory immunoglobulin A (SIgA) induced by capsaicin and taste stimuli were measured. Salivary α-amylase activity and heart rate variability (HRV) were measured as indicators of autonomic nervous activity. From EEG, psychological condition was analyzed by measuring the powers of theta, alpha, and beta bands.

RESULTS

The salivary secretion rate was significantly increased by stimulation with capsaicin, NaCl, and citric acid compared with deionized water, and capsaicin demonstrated the most potent effect among tested stimuli. The secreted amount of SIgA per minute was elevated by capsaicin stimulation. Salivary α-amylase activity and HRV analysis demonstrated an elevation of sympathetic nervous activity induced by capsaicin. EEG analysis showed a significant increase in beta band power.

CONCLUSION

These results suggest that oral stimulation with capsaicin may be effective in improving oral conditions by increasing salivary flow and SIgA secretion, and in enhancing physical and mental conditions as indicated by sympathetic nerve and EEG changes.

Adaptive thermogenesis by dietary n-3 polyunsaturated fatty acids: Emerging evidence and mechanisms

Brown/beige fat plays a crucial role in maintaining energy homeostasis through non-shivering thermogenesis in response to cold temperature and excess nutrition (adaptive thermogenesis). Although numerous molecular and genetic regulators have been identified, relatively little information is available regarding thermogenic dietary molecules. Recently, a growing body of evidence suggests that high consumption of n-3 polyunsaturated fatty acids (PUFA) or activation of GPR120, a membrane receptor of n-3 PUFA, stimulate adaptive thermogenesis. In this review, we summarize the emerging evidence that n-3 PUFA promote brown/beige fat formation and highlight the potential mechanisms whereby n-3 PUFA require GPR120 as a signaling platform or act independently. Human clinical trials are revisited in the context of energy expenditure. Additionally, we explore some future perspective that n-3 PUFA intake might be a useful strategy to boost or sustain metabolic activities of brown/beige fat at different lifecycle stages of pregnancy and senescence. Given that a high ratio of n-6/n-3 PUFA intake is associated with the development of obesity and type 2 diabetes, understanding the impact of n-6/n-3 ratio on energy expenditure and adaptive thermogenesis will inform the implementation of a novel nutritional strategy for preventing obesity.

Supra-pharmacological concentration of capsaicin stimulates brown adipogenesis through induction of endoplasmic reticulum stress

We previously showed that brown (pre)adipocytes express Trpv1, a capsaicin receptor, and that capsaicin stimulates differentiation of brown preadipocytes in the late stages of brown adipogenesis. The present study revealed that treatment with 100 μM capsaicin stimulates brown adipogenesis by inducing endoplasmic reticulum (ER) stress. Treatment with capsaicin (100 μM) during brown adipogenesis enhanced lipid accumulation and the expression of Ucp1, a gene selectively expressed in brown adipocytes. Capsaicin treatment also caused an increase in the cytosolic calcium concentration even when extracellular calcium was removed. I-RTX, a Trpv1 inhibitor, did not modulate the increase in cytosolic calcium concentration, lipid accumulation or Ucp1 expression. Previous studies revealed that the release of calcium from the ER induces ER stress, leading to the conversion of X-box binding protein 1 (Xbp1) pre-mRNA to spliced Xbp1 (sXbp1) as well as the up-regulation of Chop expression. Capsaicin treatment increased the expression of sXbp1 and Chop in brown preadipocytes and did not enhance lipid accumulation or Ucp1 expression in Xbp1 knockdown cells. The present results describe a novel mechanism of brown adipogenesis regulation via ER stress that is induced by a supra-pharmacological concentration of capsaicin.

Involvement of TRPV1 Channels in Energy Homeostasis

The ion channel TRPV1 is involved in a wide range of processes including nociception, thermosensation and, more recently discovered, energy homeostasis. Tightly controlling energy homeostasis is important to maintain a healthy body weight, or to aid in weight loss by expending more energy than energy intake. TRPV1 may be involved in energy homeostasis, both in the control of food intake and energy expenditure. In the periphery, it is possible that TRPV1 can impact on appetite through control of appetite hormone levels or via modulation of gastrointestinal vagal afferent signaling. Further, TRPV1 may increase energy expenditure via heat production. Dietary supplementation with TRPV1 agonists, such as capsaicin, has yielded conflicting results with some studies indicating a reduction in food intake and increase in energy expenditure, and other studies indicating the converse. Nonetheless, it is increasingly apparent that TRPV1 may be dysregulated in obesity and contributing to the development of this disease. The mechanisms behind this dysregulation are currently unknown but interactions with other systems, such as the endocannabinoid systems, could be altered and therefore play a role in this dysregulation. Further, TRPV1 channels appear to be involved in pancreatic insulin secretion. Therefore, given its plausible involvement in regulation of energy and glucose homeostasis and its dysregulation in obesity, TRPV1 may be a target for weight loss therapy and diabetes. However, further research is required too fully elucidate TRPV1s role in these processes. The review provides an overview of current knowledge in this field and potential areas for development.

Involvement of thermosensitive TRP channels in energy metabolism

To date, 11 thermosensitive transient receptor potential (thermo-TRP) channels have been identified. Recent studies have characterized the mechanism of thermosensing by thermo-TRPs and the physiological role of thermo-TRPs in energy metabolism. In this review, we highlight the role of various thermo-TRPs in energy metabolism and hormone secretion. In the pancreas, TRPM2 and other TRPs regulate insulin secretion. TRPV2 expressed in brown adipocytes contributes to differentiation and/or thermogenesis. Sensory nerves that express TRPV1 promote increased energy expenditure by activating sympathetic nerves and adrenaline secretion. Here, we first show that capsaicin-induced adrenaline secretion is completely impaired in TRPV1 knockout mice. The thermogenic effects of TRPV1 agonists are attributable to brown adipose tissue (BAT) activation in mice and humans. Moreover, TRPA1- and TRPM8-expressing sensory nerves also contribute to potentiation of BAT thermogenesis and energy expenditure in mice. Together, thermo-TRPs are promising targets for combating obesity and metabolic disorders.

Dietary Factors Promoting Brown and Beige Fat Development and Thermogenesis

Brown adipose tissue (BAT) is a specialized fat tissue that has a high capacity to dissociate cellular respiration from ATP utilization, resulting in the release of stored energy as heat. Adult humans possess a substantial amount of BAT in the form of constitutively active brown fat or inducible beige fat. BAT activity in humans is inversely correlated with adiposity, blood glucose concentrations, and insulin sensitivity; this suggests that strategies aimed at BAT-mediated bioenergetics are an attractive therapeutic target in combating the continuing epidemic of obesity and diabetes. Despite advances in knowledge regarding the developmental lineage and transcriptional regulators of brown and beige adipocytes, our current understanding of environmental modifiers of BAT thermogenesis, such as diet, is limited. In this review, we consolidated the latest research on dietary molecules that may serve to promote BAT thermogenesis. Here, we summarized the thermogenic function of selected phytochemicals (e.g., capsaicin, resveratrol, curcumin, green tea, and berberine), dietary fatty acids (e.g., fish oil and conjugated linoleic acids), and all-trans retinoic acid, a vitamin A metabolite. We also delineated the proposed mechanisms whereby these dietary molecules promote BAT activity and/or browning of white adipose tissue. Characterizing thermogenic dietary factors may offer novel insight into revising nutritional intervention strategies aimed at obesity and diabetes prevention and management.

Nutrition Supplements to Stimulate Lipolysis: A Review in Relation to Endurance Exercise Capacity

Athletes make great efforts to increase their endurance capacity in many ways. Using nutrition supplements for stimulating lipolysis is one such strategy to improve endurance performance. These supplements contain certain ingredients that affect fat metabolism; furthermore, in combination with endurance training, they tend to have additive effects. A large body of scientific evidence shows that nutrition supplements increase fat metabolism; however, the usefulness of lipolytic supplements as ergogenic functional foods remains controversial. The present review will describe the effectiveness of lipolytic supplements in fat metabolism and as an ergogenic aid for increasing endurance exercise capacity. There are a number of lipolytic supplements available on the market, but this review focuses on natural ingredients such as caffeine, green tea extract, L-carnitine, Garcinia cambogia (hydroxycitric acid), capsaicin, ginseng, taurine, silk peptides and octacosanol, all of which have shown scientific evidence of enhancing fat metabolism associated with improving endurance performance. We excluded some other supplements owing to lack of data on fat metabolism or endurance capacity. Based on the data in this review, we suggest that a caffeine and green tea extract improves endurance performance and enhances fat oxidation. Regarding other supplements, the data on their practical implications needs to be gathered, especially for athletes.

POTENTIAL ADMINISTRATION OF LIPOIC ACID AND COENZYME Q AGAINST ADIPOGENSIS: TARGET FOR WEIGHT REDUCTION

Background:

Body overweight and obesity were considered as a risk factor for many systemic diseases as diabetic hypertension, cardiovascular diseases, and some cancers. The lipoic acid and Co Q are considered as coenzymes needed for enhancement metabolic rate. The goal of this study is to evaluate the anti-obese effect of lipoic acid alone or combined with Co-Q in rats.

Materials and Methods:

Ninety male albino rats (100-150g) were used in this study, divided into six groups (15 each). Group I: Normal rats fed normal diet. Group II: Rats fed high fat diet (HFD). Group III: Rats fed HFD were given lipoic acid (10 μg/kg b w/day) intra-gastric by stomach tube. Group IV: Rats fed HFD were given Co-Q (10 μg/kg b.w/day) intra-gastric. Group V: Rats fed HFD were given lipoic acid (50 mg/kg b w/day) and Co-Q (10 μg/kg b. w/day). Group VI: Rats were given orlistat intra-gastric (10 mg/kg b w/day) as positive control for 6 weeks. Serum was subjected for determination of lipid profile, liver function tests atherogenic factor and lipoprotein lipase.

Results:

It was found that treatment with lipoic acid or Co-Q or combined showed increase in the activity of lipoprotein lipase (P < 0.001) and reduction of atherogenic effect and obesity index (P <0.001). The effect of combined gives good results than orlistat or individual treatment.

Conclusion:

lipoic acid combined with Co-Q increase fat oxidation and prevent fat accumulation. The consumption of lipoic acid daily promotes fat oxidation and prevents its accumulation in visceral tissues. Further studies should be carried out to examine the mechanistic signals of these nutrients that helps in weight management.

Capsaicin: Current Understanding of Its Mechanisms and Therapy of Pain and Other Pre-Clinical and Clinical Uses

In this review, we discuss the importance of capsaicin to the current understanding of neuronal modulation of pain and explore the mechanisms of capsaicin-induced pain. We will focus on the analgesic effects of capsaicin and its clinical applicability in treating pain. Furthermore, we will draw attention to the rationale for other clinical therapeutic uses and implications of capsaicin in diseases such as obesity, diabetes, cardiovascular conditions, cancer, airway diseases, itch, gastric, and urological disorders.

Catecholamines Facilitate Fuel Expenditure and Protect Against Obesity via a Novel Network of the Gut-Brain Axis in Transcription Factor Skn-1-deficient Mice

Taste signals and nutrient stimuli sensed by the gastrointestinal tract are transmitted to the brain to regulate feeding behavior and energy homeostasis. This system is referred to as the gut-brain axis. Here we show that both brush cells and type II taste cells are eliminated in the gastrointestinal tract of transcription factor Skn-1 knockout (KO) mice. Despite unaltered food intake, Skn-1 KO mice have reduced body weight with lower body fat due to increased energy expenditure. In this model, 24-h urinary excretion of catecholamines was significantly elevated, accompanied by increased fatty acid β-oxidation and fuel dissipation in skeletal muscle and impaired insulin secretion driven by glucose. These results suggest the existence of brain-mediated energy homeostatic pathways originating from brush cells and type II taste cells in the gastrointestinal tract and ending in peripheral tissues, including the adrenal glands. The discovery of food-derived factors that regulate these cells may open new avenues the treatment of obesity and diabetes.

RESEARCH CONTEXT

Taste signals and nutrient stimuli sensed by the gastrointestinal tract are transmitted to the brain to regulate feeding behavior and energy homeostasis along the gut-brain axis. We propose the concept that taste-receiving cells in the oral cavity and/or food-borne chemicals-receiving brush cells in the gut are involved in regulation of the body weight and adiposity via the brain. The discovery of food-derived factors that regulate these cells may open new avenues for the treatment of obesity and diabetes.

Fish oil intake induces UCP1 upregulation in brown and white adipose tissue via the sympathetic nervous system

Brown adipose tissue (BAT) plays a central role in regulating energy homeostasis, and may provide novel strategies for the treatment of human obesity. BAT-mediated thermogenesis is regulated by mitochondrial uncoupling protein 1 (UCP1) in classical brown and ectopic beige adipocytes, and is controlled by sympathetic nervous system (SNS). Previous work indicated that fish oil intake reduces fat accumulation and induces UCP1 expression in BAT; however, the detailed mechanism of this effect remains unclear. In this study, we investigated the effect of fish oil on energy expenditure and the SNS. Fish oil intake increased oxygen consumption and rectal temperature, with concomitant upregulation of UCP1 and the β3 adrenergic receptor (β3AR), two markers of beige adipocytes, in the interscapular BAT and inguinal white adipose tissue (WAT). Additionally, fish oil intake increased the elimination of urinary catecholamines and the noradrenaline (NA) turnover rate in interscapular BAT and inguinal WAT. Furthermore, the effects of fish oil on SNS-mediated energy expenditure were abolished in transient receptor potential vanilloid 1 (TRPV1) knockout mice. In conclusion, fish oil intake can induce UCP1 expression in classical brown and beige adipocytes via the SNS, thereby attenuating fat accumulation and ameliorating lipid metabolism.

Acute effects of capsaicin on energy expenditure and fat oxidation in negative energy balance

Background

Addition of capsaicin (CAPS) to the diet has been shown to increase energy expenditure; therefore capsaicin is an interesting target for anti-obesity therapy.

Aim

We investigated the 24 h effects of CAPS on energy expenditure, substrate oxidation and blood pressure during 25% negative energy balance.

Methods

Subjects underwent four 36 h sessions in a respiration chamber for measurements of energy expenditure, substrate oxidation and blood pressure. They received 100% or 75% of their daily energy requirements in the conditions ‘100%CAPS’, ‘100%Control’, ‘75%CAPS’ and ‘75%Control’. CAPS was given at a dose of 2.56 mg (1.03 g of red chili pepper, 39,050 Scoville heat units (SHU)) with every meal.

Results

An induced negative energy balance of 25% was effectively a 20.5% negative energy balance due to adapting mechanisms. Diet-induced thermogenesis (DIT) and resting energy expenditure (REE) at 75%CAPS did not differ from DIT and REE at 100%Control, while at 75%Control these tended to be or were lower than at 100%Control (p = 0.05 and p = 0.02 respectively). Sleeping metabolic rate (SMR) at 75%CAPS did not differ from SMR at 100%CAPS, while SMR at 75%Control was lower than at 100%CAPS (p = 0.04). Fat oxidation at 75%CAPS was higher than at 100%Control (p = 0.03), while with 75%Control it did not differ from 100%Control. Respiratory quotient (RQ) was more decreased at 75%CAPS (p = 0.04) than at 75%Control (p = 0.05) when compared with 100%Control. Blood pressure did not differ between the four conditions.

Conclusion

In an effectively 20.5% negative energy balance, consumption of 2.56 mg capsaicin per meal supports negative energy balance by counteracting the unfavorable negative energy balance effect of decrease in components of energy expenditure. Moreover, consumption of 2.56 mg capsaicin per meal promotes fat oxidation in negative energy balance and does not increase blood pressure significantly.

Trial Registration

Nederlands Trial Register; registration number NTR2944

A case of acute myocardial infarction due to the use of cayenne pepper pills

The use of weight loss pills containing cayenne pepper has ever been increasing. The main component of cayenne pepper pills is capsaicin. There are conflicting data about the effects of capsaicin on the cardiovascular system. In this paper, we present the case of a 41 year old male patient with no cardiovascular risk factors who took cayenne pepper pills to lose weight and developed acute myocardial infarction.

GABAB receptors in the NTS mediate the inhibitory effect of trigeminal nociceptive inputs on parasympathetic reflex vasodilation in the rat masseter muscle

The present study was designed to examine whether trigeminal nociceptive inputs are involved in the modulation of parasympathetic reflex vasodilation in the jaw muscles. This was accomplished by investigating the effects of noxious stimulation to the orofacial area with capsaicin, and by microinjecting GABAA and GABAB receptor agonists or antagonists into the nucleus of the solitary tract (NTS), on masseter hemodynamics in urethane-anesthetized rats. Electrical stimulation of the central cut end of the cervical vagus nerve (cVN) in sympathectomized animals bilaterally increased blood flow in the masseter muscle (MBF). Increases in MBF evoked by cVN stimulation were markedly reduced following injection of capsaicin into the anterior tongue in the distribution of the lingual nerve or lower lip, but not when injected into the skin of the dorsum of the foot. Intravenous administration of either phentolamine or propranolol had no effect on the inhibitory effects of capsaicin injection on the increases of MBF evoked by cVN stimulation, which were largely abolished by microinjecting the GABAB receptor agonist baclofen into the NTS. Microinjection of the GABAB receptor antagonist CGP-35348 into the NTS markedly attenuated the capsaicin-induced inhibition of MBF increase evoked by cVN stimulation, while microinjection of the GABAA receptor antagonist bicuculline did not. Our results indicate that trigeminal nociceptive inputs inhibit vagal-parasympathetic reflex vasodilation in the masseter muscle and suggest that the activation of GABAB rather than GABAA receptors underlies the observed inhibition in the NTS.

Acute myocardial infarction and coronary vasospasm associated with the ingestion of cayenne pepper pills in a 25-year-old male

Capsaicin, one of the major active components of cayenne pepper pills, is an over-the-counter substance with sympathomimetic activity used commonly by young individuals for weight loss. Here we report the case of a previously healthy young male who developed severe chest pain after using cayenne pepper pills for slimming and sustained an extensive inferior myocardial infarction. Electrocardiography combined with a bedside transthoracic echocardiogram confirmed the diagnosis of acute myocardial infarction. The patient denied using illicit substances, and he had no risk factors for coronary artery disease. His medication history revealed that he had recently started taking cayenne pepper pills for slimming. A subsequent coronary angiogram revealed patent coronary arteries, suggesting that the mechanism was vasospasm. We postulate that the patient developed acute coronary vasospasm and a myocardial infarction in the presence of this known sympathomimetic agent. This case highlights the potential danger of capsaicin, even when used by otherwise healthy individuals.

Hyperactive when young, hypoactive and overweight when aged: connecting the dots in the story about locomotor activity, body mass, and aging in Trpv1 knockout mice

We have recently found that, at a young age, transient receptor potential vanilloid-1 (Trpv1) knockout (⁻/⁻) mice have a higher locomotor activity than their wild-type littermates (⁺/⁺). We have also found that, with age, Trpv1^−/− mice become substantially heavier than Trpv1^+/+ controls, thus forming a paradoxical association between locomotor hyperactivity and overweight. The present study solves this contradiction. By using two experimental paradigms, we show that aged Trpv1^−/− mice have not an increased, but a decreased, locomotor activity, as compared to age-matched Trpv1^+/+ controls. We also confirm that aged Trpv1^−/− mice are overweight. We conclude that TRPV1 channels are involved in the regulation of both general locomotor activity and body mass in an age-dependent manner.

Capsaicinoids-induced changes of plasma glucose, free fatty acid and glycerol concentrations in rats

Red peppers are used as a spice for enhancing the palatability of foods. Two major capsaicinoids, dihydrocapsaicin (DHC) and capsaicin (CAP) are responsible for up to 90% of the total pungency of pepper fruits. These capsaicinoids are known to enhance energy metabolism and thermogenesis. However, there is a little information on the effects of capsaicinoids on the lipolysis and carbohydrate metabolism. We studied the effects of DHC and CAP on plasma glucose, free fatty acid (FFA) and glycerol concentrations in rats. Male six-week-old Sprague Dawley rats were divided into the DHC, CAP and control groups. Each capsaicinoid (dose = 3 mg/kg BW/day) was subcutaneously administered to rats for 10 days. DHC increased markedly plasma glucose, FFA and glycerol concentrations on day 1-10 by 14-35%, 61-103% and 108-174%, respectively, as compared with those of the control group. CAP increased relatively plasma glucose concentrations on day 1-3 by 15-17%, as compared with the control group. However, there were no significant differences in plasma glucose concentrations on day 7-10 among three groups. On the contrary, CAP did not change plasma FFA and glycerol concentrations on day 1-3. However, CAP increased markedly plasma FFA and glycerol concentrations on day 7-10 by 54-89% and 92-98%, respectively, as compared with the control group. DHC and CAP did not change the weights of white (perirenal and periepididymal) and brown (interscapular) adipose tissues. In conclusion, the effects of capsaicinoids on plasma glucose, FFA and glycerol concentrations were relatively higher in the DHC than in the CAP, and capsaicinoids did not change the weight of white and brown adipose tissues.

Intragastric administration of allyl isothiocyanate increases carbohydrate oxidation via TRPV1 but not TRPA1 in mice

The transient receptor potential (TRP) channel family is composed of a wide variety of cation-permeable channels activated polymodally by various stimuli and is implicated in a variety of cellular functions. Recent investigations have revealed that activation of TRP channels is involved not only in nociception and thermosensation but also in thermoregulation and energy metabolism. We investigated the effect of intragastric administration of TRP channel agonists on changes in energy substrate utilization of mice. Intragastric administration of allyl isothiocyanate (AITC; a typical TRPA1 agonist) markedly increased carbohydrate oxidation but did not affect oxygen consumption. To examine whether TRP channels mediate this increase in carbohydrate oxidation, we used TRPA1 and TRPV1 knockout (KO) mice. Intragastric administration of AITC increased carbohydrate oxidation in TRPA1 KO mice but not in TRPV1 KO mice. Furthermore, AITC dose-dependently increased intracellular calcium ion concentration in cells expressing TRPV1. These findings suggest that AITC might activate TRPV1 and that AITC increased carbohydrate oxidation via TRPV1.

Intragastric administration of capsiate, a transient receptor potential channel agonist, triggers thermogenic sympathetic responses

The sympathetic thermoregulatory system controls the magnitude of adaptive thermogenesis in correspondence with the environmental temperature or the state of energy intake and plays a key role in determining the resultant energy storage. However, the nature of the trigger initiating this reflex arc remains to be determined. Here, using capsiate, a digestion-vulnerable capsaicin analog, we examined the involvement of specific activation of transient receptor potential (TRP) channels within the gastrointestinal tract in the thermogenic sympathetic system by measuring the efferent activity of the postganglionic sympathetic nerve innervating brown adipose tissue (BAT) in anesthetized rats. Intragastric administration of capsiate resulted in a time- and dose-dependent increase in integrated BAT sympathetic nerve activity (SNA) over 180 min, which was characterized by an emergence of sporadic high-activity phases composed of low-frequency bursts. This increase in BAT SNA was abolished by blockade of TRP channels as well as of sympathetic ganglionic transmission and was inhibited by ablation of the gastrointestinal vagus nerve. The activation of SNA was delimited to BAT and did not occur in the heart or pancreas. These results point to a neural pathway enabling the selective activation of the central network regulating the BAT SNA in response to a specific stimulation of gastrointestinal TRP channels and offer important implications for understanding the dietary-dependent regulation of energy metabolism and control of obesity.

Effect of dihydrocapsiate on resting metabolic rate in humans

BACKGROUND

Dihydrocapsiate is a capsinoid found in chili peppers. Dihydrocapsiate is similar to capsaicin, which is known for its thermogenic properties.

OBJECTIVE

The objective was to determine the acute and chronic effect of dihydrocapsiate on resting metabolic rate (RMR).

DESIGN

Seventy-eight healthy subjects in a double-blind, parallel-arm trial were randomly assigned to 3 groups receiving 0 (placebo), 3, or 9 mg dihydrocapsiate/d for 28 d. After a 10-h overnight fast, RMR was measured by indirect calorimetry for 30 min before and 120 min after ingestion of dihydrocapsiate.

RESULTS

RMR was similar in the 3 groups before dosing on day 1 [1714 ± 41 kcal/d (0 mg), 1760 ± 41 kcal/d (3 mg), and 1694 ± 38 kcal/d (9 mg)] and after acute dosing (41 ± 17, 55 ± 17, and 3 ± 24 kcal/d for 3-mg, 9-mg, and placebo groups, respectively). When the chronic effect of dihydrocapsiate on RMR was calculated from the average 2-h RMR on day 28 minus the 30-min preingestion RMR at baseline, a borderline effect in subjects receiving 3 mg dihydrocapsiate/d compared with placebo was observed (61 ± 24 kcal/d compared with -1 ± 12 kcal/d, P = 0.054), whereas no significant increase in RMR in comparison with placebo was noted for the 9-mg/d dose (48 ± 23 kcal/d compared with -1 ± 12 kcal/d, P = 0.12). When data from both groups were combined, the thermic effect of dihydrocapsiate reached significance (53 ± 9 kcal/d compared with -1 ± 12 kcal/d in the placebo group, P = 0.04). Fat oxidation was unaffected by dihydrocapsiate.

CONCLUSION

After 1 mo of supplementation, dihydrocapsiate had a small thermogenic effect of ≈50 kcal/d, which is in the range of day-to-day RMR variability. This trial was registered at clinicaltrials.gov as NCT00999297.

Acute effects of dihydrocapsaicin and capsaicin on the distribution of white blood cells in rats

The acute effects of dihydrocapsaicin (DHC) and capsaicin (CAP) on the number of white blood cells (WBCs), neutrophils, eosinophils, basophils, monocytes, lymphocytes, T lymphocytes, B lymphocytes and NK cells, and serum corticosterone levels were studied in rats. Male 7-wk-old SD rats were divided into DHC (3.0 mg/kg BW), CAP (3.0 mg/kg BW) and control (CON) groups. The number of total WBCs was 1.30-1.42 times significantly higher in the DHC group than in the CON group at 6-12 h. The number of neutrophils was 1.62 times significantly higher in the DHC group than in the CON group at 12 h. The number of total WBCs and neutrophils, however, showed no significant changes between the CAP and CON groups. The number of lymphocytes was 0.61 and 0.70 times significantly lower in the DHC and CAP groups than in the CON group at 3 h. The number of T lymphocytes and B lymphocytes was 0.74 and 0.54 times lower in the DHC group than in the CON group, respectively. CAP, however, did not significantly change the number of T lymphocytes or B lymphocytes. No significant changes in the number of NK cells were observed among the three groups. CAP and DHC did not change the number of monocytes, eosinophils or basophils. No significant changes of the serum corticosterone levels were observed among the three groups. In conclusion, capsaicinoids decreased the number of acquired immunity cells, and increased the number of total WBCs and neutrophils without changing the number of monocytes, eosinophils or basophils. The magnitude of these effects was relatively higher in DHC than in CAP.

The transient receptor potential vanilloid-1 channel in thermoregulation: a thermosensor it is not

The development of antagonists of the transient receptor potential vanilloid-1 (TRPV1) channel as pain therapeutics has revealed that these compounds cause hyperthermia in humans. This undesirable on-target side effect has triggered a surge of interest in the role of TRPV1 in thermoregulation and revived the hypothesis that TRPV1 channels serve as thermosensors. We review literature data on the distribution of TRPV1 channels in the body and on thermoregulatory responses to TRPV1 agonists and antagonists. We propose that two principal populations of TRPV1-expressing cells have connections with efferent thermoeffector pathways: 1) first-order sensory (polymodal), glutamatergic dorsal-root (and possibly nodose) ganglia neurons that innervate the abdominal viscera and 2) higher-order sensory, glutamatergic neurons presumably located in the median preoptic hypothalamic nucleus. We further hypothesize that all thermoregulatory responses to TRPV1 agonists and antagonists and thermoregulatory manifestations of TRPV1 desensitization stem from primary actions on these two neuronal populations. Agonists act primarily centrally on population 2; antagonists act primarily peripherally on population 1. We analyze what roles TRPV1 might play in thermoregulation and conclude that this channel does not serve as a thermosensor, at least not under physiological conditions. In the hypothalamus, TRPV1 channels are inactive at common brain temperatures. In the abdomen, TRPV1 channels are tonically activated, but not by temperature. However, tonic activation of visceral TRPV1 by nonthermal factors suppresses autonomic cold-defense effectors and, consequently, body temperature. Blockade of this activation by TRPV1 antagonists disinhibits thermoeffectors and causes hyperthermia. Strategies for creating hyperthermia-free TRPV1 antagonists are outlined. The potential physiological and pathological significance of TRPV1-mediated thermoregulatory effects is discussed.

Effect of capsinoids on energy metabolism in human subjects

Capsinoids are non-pungent compounds with molecular structures similar to capsaicin, which has accepted thermogenic properties. To assess the acute effect of a plant-derived preparation of capsinoids on energy metabolism, we determined RMR and non-protein respiratory quotient (NPRQ) after ingestion of different doses of the capsinoids. Thirteen healthy subjects received four doses of the capsinoids (1, 3, 6 and 12 mg) and placebo using a crossover, randomised, double-blind trial. After a 10 h overnight fast as inpatients, RMR was measured by indirect calorimetry for 45 min before and 120 min after ingesting capsinoids or placebo. Blood pressure and axillary temperature were measured before ( - 55 and - 5 min) and after (60 and 120 min) dosing. Before dosing, mean RMR was 6247 (se 92) kJ/d and NPRQ was 0.86 (se 0.01). At 120 min after dosing, metabolic rate and NPRQ remained similar across the four capsinoids and placebo doses. Capsinoids also had no influence on blood pressure or axillary temperature. Capsinoids provided in four doses did not affect metabolic rate and fuel partitioning in human subjects when measured 2 h after exposure. Longer exposure and higher capsinoids doses may be required to cause meaningful acute effects on energy metabolism.

Alterations of autonomic nervous activity and energy metabolism by capsaicin ingestion during aerobic exercise in healthy men

We investigated whether capsaicin ingestion (150 mg) enhances substrate oxidation associated with thermogenic sympathetic activity as an energy metabolic modulator without causing prolongation of the cardiac OT interval during aerobic exercise in humans. Ten healthy males [24.4 (4.3) y] volunteered for this study. The cardiac autonomic nervous activities evaluated by means of heart rate variability of power spectral analysis, energy metabolism, and ECG QT interval were continuously measured during 5-min rest and 30-min exercise at 50% of maximal ventilatory threshold (50% VT(max)) on a stationary ergometer with placebo or capsaicin oral administration chosen at random. The results indicated that there were no significant differences in heart rate during rest or exercise between the two trials. Autonomic nervous activity increased in the capsaicin tablet trial during exercise, but the difference did not reach statistical significance. Capsaicin, however, significantly induced a lower respiratory gas exchange ratio [0.92 (0.02) vs. 0.94 (0.02), means (SE), p < 0.05] and higher fat oxidation [0.17 (0.04) vs. 0.12 (0.04) g/min, means (SE), p < 0.05] during exercise. On the other hand, the data on the cardiac OT interval showed no significant difference, indicating that oral administration of capsaicin did not cause any adverse effect on cardiac depolarization-repolarization. In conclusion, it may be considered that capsaicin consumption 1 h before low intensity exercise (50% VT(max)) is a valuable supplement for the treatment of individuals with hyperlipidemia and/or obesity because it improves lipolysis without any adverse effects on the cardiac depolarization and repolarization process.

Hot receptors in the brain

Two major approaches have been employed for the development of novel drugs to treat chronic pain. The most traditional approach identifies molecules involved in pain as potential therapeutic targets and has focused mainly on the periphery and spinal cord. A more recent approach identifies molecules that are involved in long-term plasticity. Drugs developed through the latter approach are predicted to treat chronic, but not physiological or acute, pain. The TRPV1 (transient receptor potential vanilloid-1) receptor is involved in nociceptive processing, and is a candidate therapeutic target for pain. While most research on TRPV1 receptors has been conducted at the level of the spinal cord and peripheral structures, considerably less research has focused on supraspinal structures. This short paper summarizes progress made on TRPV1 receptors, and reviews research on the expression and function of TRPV1 receptors in supraspinal structures. We suggest that the TRPV1 receptor may be involved in pain processing in higher brain structures, such as the anterior cingulate cortex. In addition, some regions of the brain utilize the TRPV1 receptor for functions apparently unrelated to pain.

Obesity and thermogenesis related to the consumption of caffeine, ephedrine, capsaicin, and green tea

The global prevalence of obesity has increased considerably in the last decade. Tools for obesity management, including caffeine, ephedrine, capsaicin, and green tea have been proposed as strategies for weight loss and weight maintenance, since they may increase energy expenditure and have been proposed to counteract the decrease in metabolic rate that is present during weight loss. A combination of caffeine and ephedrine has shown to be effective in long-term weight management, likely due to different mechanisms that may operate synergistically, e.g., respectively inhibiting the phosphodiesterase-induced degradation of cAMP and enhancing the sympathetic release of catecholamines. However, adverse effects of ephedrine prevent the feasibility of this approach. Capsaicin has been shown to be effective, yet when it is used clinically it requires a strong compliance to a certain dosage, that has not been shown to be feasible yet. Also positive effects on body-weight management have been shown using green tea mixtures. Green tea, by containing both tea catechins and caffeine, may act through inhibition of catechol O-methyl-transferase, and inhibition of phosphodiesterase. Here, the mechanisms may also operate synergistically. In addition, tea catechins have antiangiogenic properties that may prevent development of overweight and obesity. Furthermore, the sympathetic nervous system is involved in the regulation of lipolysis, and the sympathetic innervation of white adipose tissue may play an important role in the regulation of total body fat in general.

Lack of integrative control of body temperature after capsaicin administration

BACKGROUND

Body temperature is usually regulated by opposing controls of heat production and heat loss. However, systemic administration of capsaicin, the pungent ingredient of hot peppers, facilitated heat production and heat loss simultaneously in rats. We recently found that the capsaicin-induced heat loss and heat production occur simultaneously and that the biphasic change in body temperature is a sum of transient heat loss and long-lasting heat production. Moreover, suppression of the heat loss response did not affect capsaicin-induced heat production and suppression of heat production did not affect capsaicin-induced heat loss. These observations suggest the independent peripheral mechanisms of capsaicin-induced thermal responses. Thus, the capsaicin-induced thermal responses apparently lack an integrated control.

METHODS

Male Wistar rats were maintained at an ambient temperature of 24 +/- 1 degrees C on a 12 h on-off lighting schedule at least for two weeks before the experiments. They were anesthetized with urethane (1.5 g/kg, i.p.) and placed on a heating pad, which was kept between 29 and 30 degrees C. Skin temperature(Ts) was measured with a small thermistor, which was taped to the dorsal surface of the rat's tail, to assess vasoactive changes indirectly. Colonic temperature(Tc) was measured with another thermistor inserted about 60 mm into the anus. O2 consumption was measured by the open-circuit method, and values were corrected for metabolic body size (kg0.75). Capsaicin (Sigma) was dissolved in a solution comprising 80% saline, 10% Tween 80, and 10% ethanol, and injected subcutaneously at a dose of 5 mg/kg. Each rat received a single injection of capsaicin because repeated administration of capsaicin renders an animal insensitive to the subsequent administration of capsaicin. Laminectomy was performed at the level of the first and second cervical vertebrae to expose the cervical spinal cord for sectioning. The brain was transected at 4-mm rostral from the interaural line with an L-shaped knife.

RESULTS

After administration of capsaicin, O2 consumption increased from 13.5 +/- 0.4 mL/min/kg0.75 at 0 min to a peak of 15.9 +/- 0.4 mL/min/kg0.75 at 71 min and gradually declined but remained higher than the basal value until the end of the 4-h observation period. Ts also immediately increased from 27.7 +/- 0.2 degrees C to 31.9 +/- 0.3 degrees C at 39 min, and it returned to the baseline level within 90 min after the capsaicin administration. Tc initially decreased from 37.1 +/- 0.1 degrees C to 36.8 +/- 0.2 degrees C at 43 min and then gradually increased over the baseline level and remained at 37.6 +/- 0.2 degrees C until the end of the experiment. In spinalized rats, the capsaicin-induced increases in O2 consumption was largely attenuated, while the basal O2 consumption was similar to that of control rats. The basal Ts of spinalized rats was 32.4 +/- 0.3 degrees C, which was higher than that of control rats. Capsaicin increased Ts by less than 1 degree C, and Tc did not change after the capsaicin administration. O2 consumption of decerebrated rats was statistically higher than that of control rats after the injection of capsaicin. However, capsaicin did not increase Ts, showing a lack of a vasodilatory response. Decerebration between the hypothalamus and midbrain prevented the capsaicin-induced heat loss but not the heat production response.

CONCLUSION

These results show that the capsaicin-induced heat production and heat loss are controlled separately by the brainstem and by the forebrain, respectively, and suggest that the body temperature regulation is performed without an integrative center.

Responses of adrenal function to stimulation of lumbar and thoracic interspinous tissues in the rat

In urethane-anesthetized Wistar rats, the responses of adrenal sympathetic nerve activity and catecholamine secretion were measured following chemical stimulation of lumbar and thoracic interspinous tissues. Injection of normal saline into the lower lumbar or lower thoracic interspinous tissues produced no changes in adrenal sympathetic nerve activity or catecholamine secretion. On the other hand, the injection of capsaicin produced protracted increases in adrenal nerve activity and catecholamine secretion both in CNS-intact animals and in animals acutely spinalized at the Cl-2 level. Repetitive electrical stimulation of the medial branch of a lumbar primary dorsal ramus, the nerve which provides sensation to the lumbar interspinous tissues, produced A- and C-reflex discharges, mediated at the spinal and supraspinal levels, in the adrenal sympathetic nerve.