Capsiate improves glucose metabolism by improving insulin sensitivity better than capsaicin in diabetic rats

Red peppers and red pepper paste are reported to have anti-obesity, analgesic and anti-inflammatory effects in animals and humans due to the capsaicin in red pepper. We investigated whether consuming capsaicin and capsiate, a nonpungent capsaicin analogue, modifies glucose-stimulated insulin secretion, pancreatic β-cell survival and insulin sensitivity in 90% pancreatectomized (Px) diabetic rats, a moderate and non-obese type 2 diabetic animal model. Px diabetic rats were divided into 3 treatment groups: 1) capsaicin (Px-CPA), 2) capsiate (Px-CPI) or 3) dextrose (Px-CON) and provided high fat diets (40 energy % fat) containing assigned components (0.025% capsaicin, capsiate, or dextrose) for 8 weeks. Both capsaicin and capsiate reduced body weight gain, visceral fat accumulation, serum leptin levels and improved glucose tolerance without modulating energy intake in diabetic rats. In comparison to the control, both capsaicin and capsiate potentiated first and second and phase insulin secretion during hyperglycemic clamp. Both also increased β-cell mass by increasing proliferation and decreasing apoptosis of β-cells by potentiating insulin/IGF-1 signaling. However, only capsiate enhanced hepatic insulin sensitivity during euglycemic hyperinuslinemic clamp. Capsiate reduced hepatic glucose output and increased triglyceride accumulation in the hyperinsulinemic state and capsiate alone significantly increased glycogen storage. This was related to enhanced pAkt→PEPCK and pAMPK signaling. Capsaicin and capsiate reduced triglyceride storage through activating pAMPK. In conclusion, capsaicin and capsiate improve glucose homeostasis but they differently enhance insulin sensitivity in the liver, insulin secretion patterns, and islet morphometry in diabetic rats. Capsiate has better anti-diabetic actions than capsaicin.     

Upregulation of uncoupling proteins by oral administration of capsiate, a nonpungent capsaicin analog.

Capsiate is a nonpungent capsaicin analog, a recently identified principle of the nonpungent red pepper cultivar CH-19 Sweet. In the present study, we report that 2-wk treatment of capsiate increased metabolic rate and promoted fat oxidation at rest, suggesting that capsiate may prevent obesity. To explain these effects, at least in part, we examined uncoupling proteins (UCPs) and thyroid hormones. UCPs and thyroid hormones play important roles in energy expenditure, the maintenance of body weight, and thermoregulation. Two-week treatment of capsiate increased the levels of UCP1 protein and mRNA in brown adipose tissue and UCP2 mRNA in white adipose tissue. This dose of capsiate did not change serum triiodothyronine or thyroxine levels. A single dose of capsiate temporarily raised both UCP1 mRNA in brown adipose tissue and UCP3 mRNA in skeletal muscle. These results suggest that UCP1 and UCP2 may contribute to the promotion of energy metabolism by capsiate, but that thyroid hormones do not.     

Proteomic analysis of liver proteins in rats fed with a high-fat diet in response to capsaicin treatments

Consumption of spicy foods has been reported to convey thermogenic properties. Thus, ingredients in these foods could be considered as potential agents for prevention of a positive energy balance and obesity. Capsaicin in particular is one of the main capsaicinoids, which is a pungent principle of red pepper, and is also utilized as a medicine. In this study, 2-dimensional gel electrophoresis (2-DE) was carried out to identify differential expression of liver proteins in rats fed with a high-fat diet (HFD) in response to capsaicin treatments. In addition, immunoblot analysis of some liver proteins was performed for validation of proteomic analysis and suggestions of a molecular action of capsaicin. Results of animal experiments revealed that weight gain of rats in the HFD + Cap group was decreased by 8% compared to the HFD control group. In our search for potential proteins associated with thermo-genesis and lipid metabolism, we analyzed differential expression patterns in rat liver using 2-DE. Proteomic analysis of liver samples demonstrated that approximately 120 spots were differentially expressed from a total of 950 matched spots, of which 23 spots have been identified by peptide mass finger printing using MALDI-TOF mass spectrometry. Protein levels of UCP2 and FAS were decreased, whereas those of p-AMPK, p-ACC, and CPT-1 were increased by capsaicin administration. These data suggest that the effect of capsaicin on energy expenditure and fatty acid oxidation in rat liver might be mediated through activation of the AMPK-ACC-malonyl-CoA metabolic signaling pathway.     

Capsiate, a nonpungent capsaicin analog, increases endurance swimming capacity of mice by stimulation of vanilloid receptors

We investigated the effect of capsiate, a nonpungent natural capsaicin analog, on the swimming capacity of mice in an adjustable-current water pool. Male BALB/c mice orally given capsiate (10 mg/kg) were able to keep swimming longer before exhaustion than the control mice. After 30 min of swimming, the residual glycogen in the gastrocnemius muscle was higher, the serum free fatty acid concentration tended to be higher, and the serum lactic acid concentration was significantly lower in the capsiate-administered mice. The value for the respiratory exchange ratio of the capsiate group was significantly lower during both resting and treadmill running. These physiological differences were abolished by administering the vanilloid receptor antagonist, capsazepin (0.17 mmol/kg, i.p.). The mice were not averse to the capsiate solution during a 4-h two-bottle choice test. These results suggest that the oral administration of capsiate enhanced fat oxidation and spared carbohydrate utilization, and consequently increased the endurance swimming capacity of the mice via stimulation of their vanilloid receptors. Practical application of capsiate is expected.     

Administration of capsiate, a non-pungent capsaicin analog, promotes energy metabolism and suppresses body fat accumulation in mice

We investigated the effects of a single oral administration of capsiate, which is found in the fruits of a non-pungent cultivar of pepper, CH-19 Sweet, and has the same structure as capsaicin except for replacement of NH by O in the alkyl chain, on the thermogenesis and fat accumulation in mice. The oxygen consumption and serum adrenalin concentration were higher in both the capsaicin (10 mg/kg-body weight) and capsiate (10 mg/kg-body weight) groups than those in the control group. We also examined the effects of 2 weeks of administration of capsaicin and capsiate on body fat accumulation. Eevery day for 2 weeks administration of capsiate (10, 50 mg/kg-body weight/day) markedly suppressed body fat accumulation as well as capsaicin (10 mg/kg-body weight/day). These results suggest that capsiate promotes energy metabolism and suppresses body fat accumulation as does capsaicin.     

One-procedure synthesis of capsiate from capsaicin by lipase-catalyzed dynamic transacylation

Capsiate has a structure similar to capsaicin but no oral pungency. Furthermore, capsiate displayed antioxidant activity and inhibited angiogenesis and vascular permeability, and therefore, showed potential as a medicine and food supplement. Capsaicin is now commercially available, however capsiate is scarcely present in natural foods. We investigated the direct enzymatic conversion of a capsaicinoid to a capsinoid. It was observed that the rate of lipase-catalyzed acylation of vanillyl alcohol with nonanoic acid was faster than that of hydrolysis of N-vanillylnonanamide to vanillyl amide and nonanoic acid in n-hexane at 70°C. As a result, we performed a one-procedure synthesis of capsiate from capsaicin via lipase-catalyzed transacylation.     

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.     

CH-19 Sweet,a Non-Pungent Cultivar of Red Pepper,Increased Body Temperature and Oxygen Consumption in Humans

We investigated the effect of CH-19 Sweet, a nonpungent cultivar of red pepper, on body temperature and oxygen consumption in humans. CH-19 Sweet was given to 11 healthy volunteers, and core body temperature, body surface temperature and oxygen consumption were measured. The control group ingested California-Wandar, which contained neither capsaicin nor capsiate. The core body temperature in the CH-19 Sweet group was significantly higher than that in the control group (P<0.01). The forehead temperature measured by infrared thermography in the CH-19 Sweet group was significantly higher than that in the control group. The body surface temperature was increased for about 20 min after consumption of CH-19 Sweet intake, and the neck temperature was significantly higher (P<0.001) than when the subjects consumed California-Wandar. We also measured respiratory gas by indirect calorimetry while subjects wore a face mask. A significant difference was detected in oxygen consumption between the two groups, and the value was significantly higher in the CH-19 Sweet group (P<0.03). These results suggest that CH-19 Sweet increased thermogenesis and energy consumption.     

Tachykinins stimulate a subset of mouse taste cells

The tachykinins substance P (SP) and neurokinin A (NKA) are present in nociceptive sensory fibers expressing transient receptor potential cation channel, subfamily V, member 1 (TRPV1). These fibers are found extensively in and around the taste buds of several species. Tachykinins are released from nociceptive fibers by irritants such as capsaicin, the active compound found in chili peppers commonly associated with the sensation of spiciness. Using real-time Ca(2+)-imaging on isolated taste cells, it was observed that SP induces Ca(2+) -responses in a subset of taste cells at concentrations in the low nanomolar range. These responses were reversibly inhibited by blocking the SP receptor NK-1R. NKA also induced Ca(2+)-responses in a subset of taste cells, but only at concentrations in the high nanomolar range. These responses were only partially inhibited by blocking the NKA receptor NK-2R, and were also inhibited by blocking NK-1R indicating that NKA is only active in taste cells at concentrations that activate both receptors. In addition, it was determined that tachykinin signaling in taste cells requires Ca(2+)-release from endoplasmic reticulum stores. RT-PCR analysis further confirmed that mouse taste buds express NK-1R and NK-2R. Using Ca(2+)-imaging and single cell RT-PCR, it was determined that the majority of tachykinin-responsive taste cells were Type I (Glial-like) and umami-responsive Type II (Receptor) cells. Importantly, stimulating NK-1R had an additive effect on Ca(2+) responses evoked by umami stimuli in Type II (Receptor) cells. This data indicates that tachykinin release from nociceptive sensory fibers in and around taste buds may enhance umami and other taste modalities, providing a possible mechanism for the increased palatability of spicy foods.     

Involvement of Reactive Oxygen Species in Capsaicinoid-induced Apoptosis in Transformed Cells

Some varieties of sweet pepper accumulate non-pungent isosters of capsaicin, a type of compounds exemplified by capsiate. The only structural difference between capsaicin and capsiate is the link between the vanillyl and the acyl moieties, via an amide bond in the former and via an ester bond in the latter. By flow cytometry analyses we have determined that nor-dihydrocapsiate, a simplified analogue of capsiate, is a pro-oxidant compound that induces apoptosis in the Jurkat tumor cell line. The nuclear DNA fragmentation induced by nor-dihydrocapsiate is preceded by an increase in the production of reactive oxygen species and by a subsequent disruption of mitochondria transmembrane potential. Capsiate-induced apoptosis is initiated at the S phase of the cell cycle and is mediated by a caspase-3-dependent pathway. The accumulation of intracellular reactive oxygen species in capsiate-treated cells is greatly prevented by the presence of ferricyanide, suggesting that capsiates target a cellular redox system distinct from the one involved in the mitochondrial electron-chain transport. Methylation of the phenolic hydroxyl of nor-dihydrocapsiate completely abrogated the ability to induce reactive oxygen species and apoptosis, highlighting the relevance of the presence of a free phenolic hydroxyl for the pro-oxidant properties of capsaicinoids.     

Capsaicin Treatment Attenuates Cholangiocarcinoma Carcinogenesis

Capsaicin, the most abundant pungent molecule produced by pepper plants, represents an important ingredient in spicy foods consumed throughout the world. Studies have shown that capsaicin can relieve inflammation and has anti-proliferative effects on various human malignancies. Cholangiocarcinoma (CC) is a cancer disease with rising incidence. The prognosis remains dismal with little advance in treatment. The aim of the present study is to explore the anti-tumor activity of capsaicin in cultured human CC cell lines. Capsaicin effectively impaired cell proliferation, migration, invasion, epithelial to mesenchymal transition and growth of softagar colonies. Further, we show that capsaicin treatment of CC cells regulates the Hedgehog signaling pathway. Conclusion: Our results provide a basis for capsaicin to improve the prognosis of CCs in vivo and present new insights into the effectiveness and mode of action of capsaicin.     

Involvement of reactive oxygen species in capsaicinoid-induced apoptosis in transformed cells

Some varieties of sweet pepper accumulate non-pungent isosters of capsaicin, a type of compounds exemplified by capsiate. The only structural difference between capsaicin and capsiate is the link between the vanillyl and the acyl moieties, via an amide bond in the former and via an ester bond in the latter. By flow cytometry analyses we have determined that nor-dihydrocapsiate, a simplified analogue of capsiate, is a pro-oxidant compound that induces apoptosis in the Jurkat tumor cell line. The nuclear DNA fragmentation induced by nor-dihydrocapsiate is preceded by an increase in the production of reactive oxygen species and by a subsequent disruption of mitochondria transmembrane potential. Capsiate-induced apoptosis is initiated at the S phase of the cell cycle and is mediated by a caspase-3-dependent pathway. The accumulation of intracellular reactive oxygen species in capsiate-treated cells is greatly prevented by the presence of ferricyanide, suggesting that capsiates target a cellular redox system distinct from the one involved in the mitochondrial electron-chain transport. Methylation of the phenolic hydroxyl of nor-dihydrocapsiate completely abrogated the ability to induce reactive oxygen species and apoptosis, highlighting the relevance of the presence of a free phenolic hydroxyl for the pro-oxidant properties of capsaicinoids.     

Down-Regulation of Tumor-Associated NADH Oxidase,tNOX (ENOX2), Enhances Capsaicin-Induced Inhibition of Gastric Cancer Cell Growth

Gastric cancer is a common human malignancy and a major contributor to cancer-related deaths worldwide. Unfortunately, the prognosis of most gastric cancer patients is poor because they are generally diagnosed at a late stage after the cancer has already metastasized. Most current research, therefore, emphasizes selective targeting of cancer cells by apoptosis-inducing agents. One such therapeutic agent is capsaicin, a component of chili peppers that has been shown to possess anti-growth activity against various cancer cell lines. Here, we examined the effect of capsaicin on SNU-1 and TMC-1 gastric cancer cells and found differing outcomes between the two cell lines. Our results show that capsaicin induced significant cytotoxicity with increases in oxidative stress, PARP cleavage, and apoptosis in sensitive SNU-1 cells. In contrast, TMC-1 cells were much less sensitive to capsaicin, exhibiting low cytotoxicity and very little apoptosis in response to capsaicin treatment. Capsaicin-induced apoptosis in SNU-1 cells was associated with down-regulation of tumor-associated NADH oxidase (tNOX) mRNA and protein. On the contrary, tNOX expression was scarcely affected by capsaicin in TMC-1 cells. We further showed that tNOX-knockdown sensitized TMC-1 cells to capsaicin-induced apoptosis and G1 phase accumulation, and led to decreased cell growth, demonstrating that tNOX is essential for cancer cell growth. Collectively, these results indicate that capsaicin induces divergent effects of the growth of gastric cancer cells that parallel its effects on tNOX expression, and demonstrate that forced tNOX down-regulation restored capsaicin-induced growth inhibition in TMC-1 cells.     

The effects of vanilloid analogues structurally related to capsaicin on the transient receptor potential vanilloid 1 channel

Transient receptor potential vanilloid 1 (TRPV1) is known as a receptor of capsaicin, a spicy ingredient of chili peppers. It is also sensitive to a variety of pungent compounds and is involved in nociception. Here, we focused on the structural characteristics of capsaicin, and investigated whether vanillylmanderic acid (VMA), vanillic acid (VAcid), vanillyl alcohol (VAlc), vanillyl butyl ether (VBE), and vanillin, containing a vanillyl skeleton similar to capsaicin, affected the TRPV1 activities. For detection of TRPV1 activity, intracellular Ca²⁺ concentration ([Ca²⁺]_i) was measured in HEK 293 cells heterologously expressing mouse TRPV1 (mTRPV1-HEK) and in mouse sensory neurons. Except for vanillin, four vanilloid analogues dose-dependently increased [Ca²⁺]_i in mTRPV1-HEK. The solutions that dissolved VMA, VAcid and vanillin at high concentrations were acidic, whereas those of VAlc and VBE were neutral. Neutralized VAcid evoked [Ca²⁺]_i increases but neutralized VMA did not. Mutation of capsaicin-sensing sites diminished [Ca²⁺]_i responses to VAcid, VAlc and VBE. VAcid, VMA, and vanillin suppressed the activation of TRPV1 induced by capsaicin. VAcid and VMA also inhibited the acid-induced TRPV1 activation. In sensory neurons, VMA diminished TRPV1 activation by capsaicin or acids. The present data indicate that these structural characteristics of chemical compounds on TRPV1 may provide strategies for the development of novel analgesic drugs targeting nociceptive TRPV1.     

Capsaicin Interaction with TRPV1 Channels in a Lipid Bilayer: Molecular Dynamics Simulation

Transient receptor potential vanilloid subtype 1 (TRPV1) is a heat-sensitive ion channel also involved in pain sensation, and is the receptor for capsaicin, the active ingredient of hot chili peppers. The recent structures of TRPV1 revealed putative ligand density within the S1 to S4 voltage-sensor-like domain of the protein. However, questions remain regarding the dynamic role of the lipid bilayer in ligand binding to TRPV1. Molecular dynamics simulations were used to explore behavior of capsaicin in a 1-palmitoyl-2-oleoyl phosphatidylcholine bilayer and with the target S1–S4 transmembrane helices of TRPV1. Equilibrium simulations reveal a preferred interfacial localization for capsaicin. We also observed a capsaicin molecule flipping from the extracellular to the intracellular leaflet, and subsequently able to access the intracellular TRPV1 binding site. Calculation of the potential of mean force (i.e., free energy profile) of capsaicin along the bilayer normal confirms that it prefers an interfacial localization. The free energy profile indicates that there is a nontrivial but surmountable barrier to the flipping of capsaicin between opposing leaflets of the bilayer. Molecular dynamics of the S1–S4 transmembrane helices of the TRPV1 in a lipid bilayer confirm that Y511, known to be crucial to capsaicin binding, has a distribution along the bilayer normal similar to that of the aromatic group of capsaicin. Simulations were conducted of the TRPV1 S1–S4 transmembrane helices in the presence of capsaicin placed in the aqueous phase, in the lipid, or docked to the protein. No stable interaction between ligand and protein was seen for simulations initiated with capsaicin in the bilayer. However, interactions were seen between TRPV1 and capsaicin starting from the cytosolic aqueous phase, and capsaicin remained stable in the majority of simulations from the docked pose. We discuss the significance of capsaicin flipping from the extracellular to the intracellular leaflet and mechanisms of binding site access by capsaicin.     

Apoptosis induction by dohevanil, a DHA substitutive analog of capsaicin, in MCF-7 cells

Capsaicin (8-methyl-N-vanillyl-6-nonenamide), a major pungent ingredient in a variety of red peppers of the genus Capsicum, is a type of vanilloid. It has been shown to induce apoptosis in many cell types. The effects of vanilloids on apoptosis induction are thought to be correlated with the length and degree of the unsaturation of the fatty acyl chains. In this study, we compared the effect of capsaicin and its docosahexaenoic acid (DHA, C22:6) analog (we named as dohevanil) on human breast cancer MCF-7 cells, which do not express caspase-3. Dohevanil, which was synthesized from DHA and vanillylamine, has longer and highly unsaturated fatty acyl chain than capsaicin. We showed that both vanilloids exhibit effects of growth inhibition and DNA fragmentation induction in MCF-7 cells. These effects of dohevanil were more potent than capsaicin. Because these effects were inhibited by z-VAD-fmk, a broad-spectrum caspase inhibitor, the vanilloids induced the apoptosis via caspase-dependent pathway not involving caspase-3. In conclusion, dohevanil has a more potent effect on apoptosis induction in MCF-7 cells than capsaicin.     

Chili und der Capsaicinrezeptor TRPV1

Some like it hot – and spicy: Chili and the capsaicin receptor TRPV1 Since many hundred years, many people like to eat chili pepper containing the pungent ingredient capsaicin that is responsible for making the food hot and spicy. Capsaicin activates transient receptor potential TRPV1 channels that are predominantly expressed in sensory neurons involved in pain sensation. TRPV1 is a noxious heat sensor and can also be activated by protons and several animal toxins. Thus, TRPV1 is a polymodal sensor of multiple noxious stimuli that cause pain. TRPV1 functions as a nocisensor that detects chemical and thermal stimuli and transduces this stimulation into sensory nerve impulses which leads to the perception of pain. Inhibition of TRPV1 reduces or abolishes pain sensation. A strong activation of TRPV1 induces a long-lasting refractory period of the pain-detecting system (desensitization) and may even lead to an irreversible loss of TRPV1-expressing sensory neurons. It still remains unclear why many people love hot and spicy food, accompanied by a burning sensation in the mouth.     

Capsaicin-induced activation of erythrocyte membrane sodium/potassium and calcium adenosine triphosphatases

Capsaicin is the pungent ingredient present in hot peppers of the genus Capsicum. Capsaicin's effect on sensory neurons has been well studied; however, its effect on non-neuronal cells is still not fully understood. This study was undertaken to evaluate the effect of capsaicin on erythrocyte membrane enzymes: Na+/K(+)-ATPase and Ca(2+)-ATPase. Treatment with capsaicin (0.01-100 microM) caused a transient increase in the activities of both enzymes; the effect declined at lower concentrations of capsaicin, and no significant effect was observed at 0.01 microM capsaicin. The effect of capsaicin was fast with a significant (p<0.01) activation of enzyme activity observed within minutes of incubation. The findings on the effect of capsaicin on human erythrocyte membrane enzymes Na+/K(+)-ATPase and Ca(2+)-ATPase signify the importance of the non-neuronal effects of capsaicin, and the need for evaluating the physiological impact of high capsaicin (capsicum) consumption in some regions of the world.     

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 K _m 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.