Allyl isothiocyanate increases carbohydrate oxidation through enhancing insulin secretion by TRPV1

Abstract

The transient receptor potential (TRP) V1 is a cation channel belonging to the TRP channel family and it has been reported to be involved in energy metabolism, especially glucose metabolism. While, we have previously shown that intragastric administration of allyl isothiocyanate (AITC) enhanced glucose metabolism via TRPV1, the underlying mechanism has not been elucidated. In this study, we examined the relationship between insulin secretion and the increase in carbohydrate oxidation due to AITC. Intragastric administration of AITC elevated blood insulin levels in mice and AITC directly enhanced insulin secretion from isolated islets. These observations were not reproduced in TRPV1 knockout mice. Furthermore, AITC did not increase carbohydrate oxidation in streptozotocin-treated mice. These results suggest that intragastric administration of AITC could induce insulin secretion from islets via TRPV1 and that enhancement of insulin secretion was related to the increased carbohydrate oxidation due to AITC.     

Intragastric administration of AMG517, a TRPV1 antagonist,enhanced activity-dependent energy metabolism via capsaicin-sensitive sensory nerves in mice

ABSTRACT

Transient receptor potential vanilloid 1 (TRPV1), a nociceptive cation channel, is known to play roles in regulating the energy metabolism (EM) of the whole body. We previously reported that TRPV1 antagonists such as AMG517 enhanced EM in mice, however, these mechanisms remain unclear. The aim of this study was to explore the mechanisms underlying the enhancement of EM by AMG517, a selective TRPV1 antagonist, in mice. Respiratory gas analysis indicated that intragastric administration of AMG517 enhanced EM along with increasing locomotor activity in mice. Next, to clarify the possible involvement with afferent sensory nerves, including the vagus, we desensitized the capsaicin-sensitive sensory nerves of mice by systemic capsaicin treatment. In the desensitized mice, intragastric administration of AMG517 did not change EM and locomotor activity. Therefore, this study indicated that intragastric administration of AMG517 enhanced EM and increased locomotor activity via capsaicin-sensitive sensory nerves, including vagal afferents in mice.     

Pore dilation occurs in TRPA1 but not in TRPM8 channels

Pain-related sensitization and synaptic plasticity in the central nucleus of the amygdala (CeA) depend on the endogenous activation of NMDA receptors and phosphorylation of the NR1 subunit through a PKA-dependent mechanism. Functional NMDA receptors are heteromeric assemblies of NR1 with NR2A-D or NR3A, B subunits. NMDA receptors composed of NR1 and NR2B subunits have been implicated in neuroplasticity and are present in the CeA. Here we used a selective NR2B antagonist (Ro-256981) to determine the contribution of NR2B-containing NMDA receptors to pain-related sensitization of CeA neurons. Extracellular single-unit recordings were made from CeA neurons in anesthetized adult male rats before and during the development of an acute arthritis. Arthritis was induced in one knee joint by intraarticular injections of kaolin and carrageenan. Brief (15 s) mechanical stimuli of innocuous (100–500 g/30 mm²) and noxious (1000–2000 g/30 mm²) intensity were applied to the knee and other parts of the body. In agreement with our previous studies, all CeA neurons developed increased background and evoked activity after arthritis induction. Ro-256981 (1, 10 and 100 μM; 15 min each) was administered into the CeA by microdialysis 5–6 h postinduction of arthritis. Ro-256981 concentration-dependently decreased evoked responses, but not background activity. This pattern of effect is different from that of an NMDA receptor antagonist (AP5) in our previous studies. AP5 (100 μM – 5 mM) inhibited background activity and evoked responses. The differential effects of AP5 and Ro-256981 may suggest that NMDA receptors containing the NR2B subunit are important but not sole contributors to pain-related changes of CeA neurons.     

Diallyl sulfides in garlic activate both TRPA1 and TRPV1

We searched for novel agonists of TRP receptors especially for TRPA1 and TRPV1 in foods. We focused attention on garlic compounds, diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS). In TRPA1 or TRPV1 heterogeneously expressed CHO cells, all of those compounds increased [Ca²⁺]_i in concentration-dependent manner. The EC₅₀ values of DADS and DATS were similar to that of allyl isothiocyanate (AITC) and that of DAS was 170-fold larger than that of AITC. Maximum responses of these sulfides were equal to that of AITC. The EC₅₀ values of these compounds for TRPV1 were around 100 μM against that of capsaicin (CAP), 25.6 nM and maximum responses of garlic compounds were half to that of CAP. The Ca²⁺ responses were significantly suppressed by co-application of antagonist. We conclude that DAS, DADS, and DATS are agonist of both TRPA1 and TRPV1 but with high affinity for TRPA1.     

Activation of serotonin receptor 2 by glucosylsphingosine can be enhanced by TRPA1 but not TRPV1: Implication of a novel glucosylsphingosine-mediated itch pathway

Glucosylsphingosine (GS) is an endogenous sphingolipid that specifically accumulates in the skin of patients with atopic dermatitis (AD). Notably, it was recently found that GS can induce itch sensation by activating serotonin receptor 2A and TRPV4 ion channels. However, it is still uncertain whether other molecules are involved in GS-induced itch sensation. Therefore, by using the calcium imaging technique, we investigated whether serotonin receptor 2 – specifically 2A and 2B – can interact with TRPV1 and TRPA1, because these are representative ion channels in the transmission of itch. As a result, it was found that GS did not activate TRPV1 or TRPA1 per se. Moreover, cells expressing both serotonin receptor 2 and TRPV1 did not show any changes in calcium responses. However, enhanced calcium responses were observed in cells expressing serotonin receptor 2 and TRPA1, suggesting a possible interaction between these two molecules. Similar synergistic effects were also observed in cells expressing serotonin receptor 2 and TRPA1, but not TRPV1. Furthermore, a phospholipase C inhibitor (U73122) and a store-operated calcium entry blocker (SKF96365) significantly reduced GS-induced responses in cells expressing both serotonin receptor 2 and TRPA1, but not with pre-treatment with a Gβγ-complex blocker (gallein). Therefore, we propose a putative novel pathway for GS-induced itch sensation, such that serotonin receptor 2 could be coupled to TRPA1 but not TRPV1 in sensory neurons.     

TRPV1 and TRPA1 Mediate Peripheral Nitric Oxide-Induced Nociception in Mice

Nitric oxide (NO) can induce acute pain in humans and plays an important role in pain sensitization caused by inflammation and injury in animal models. There is evidence that NO acts both in the central nervous system via a cyclic GMP pathway and in the periphery on sensory neurons through unknown mechanisms. It has recently been suggested that TRPV1 and TRPA1, two polymodal ion channels that sense noxious stimuli impinging on peripheral nociceptors, are activated by NO in heterologous systems. Here, we investigate the relevance of this activation. We demonstrate that NO donors directly activate TRPV1 and TRPA1 in isolated inside-out patch recordings. Cultured primary sensory neurons display both TRPV1- and TRPA1-dependent responses to NO donors. BH4, an essential co-factor for NO production, causes activation of a subset of DRG neurons as assayed by calcium imaging, and this activation is at least partly dependent on nitric oxide synthase activity. We show that BH4-induced calcium influx is ablated in DRG neurons from TRPA1/TRPV1 double knockout mice, suggesting that production of endogenous levels of NO can activate these ion channels. In behavioral assays, peripheral NO-induced nociception is compromised when TRPV1 and TRPA1 are both ablated. These results provide genetic evidence that the peripheral nociceptive action of NO is mediated by both TRPV1 and TRPA1.     

Central but not systemic administration of ghrelin induces wakefulness in mice

Ghrelin is a brain-gut peptide hormone widely known for its orexigenic and growth hormone-releasing activities. Findings from our and other laboratories indicate a role of ghrelin in sleep regulation. The effects of exogenous ghrelin on sleep-wake activity in mice are, however, unknown. The aim of the present study was to determine the sleep-modulating effects of ghrelin after central and systemic administrations in mice. Sleep-wake activity after intracerebroventricular (i.c.v.) administration of 0.2, 1 and 5 μg ghrelin and intraperitoneal injections of 40, 100, and 400 μg/kg ghrelin prior to light onset were determined in C57BL/6 mice. In addition, body temperature, motor activity and 1-hour food intake was measured after the systemic injections. Sleep effects of systemic ghrelin (40 and 400 μg/kg) injected before dark onset were also determined. I.c.v. injection of ghrelin increased wakefulness and suppressed non-rapid-eye-movement sleep and electroencephalographic slow-wave activity in the first hour after injections. Rapid-eye-movement sleep was decreased for 2-4 hours after each dose of ghrelin. Sytemic administration of ghrelin did not induce changes in sleep-wake activity in mice at dark or light onset. Motor activity and body temperature remained unaltered and food intake was significantly increased after systemic injections of ghrelin given prior the light period. These findings indicate that the activation of central, but not peripheral, ghrelin-sensitive mechanisms elicits arousal in mice. The results are consistent with the hypothesis that the activation of the hypothalamic neuronal circuit formed by ghrelin, orexin, and neuropeptide Y neurons triggers behavioral sequence characterized by increased wakefulness, motor activity and feeding in nocturnal rodents.     

Cold stress increases reactive oxygen species formation via TRPA1 activation in A549 cells

Reactive oxygen species (ROS) are responsible for lung damage during inhalation of cold air. However, the mechanism of the ROS production induced by cold stress in the lung is still unclear. In this work, we measured the changes of ROS and the cytosolic Ca²⁺ concentration ([Ca²⁺]_c) in A549 cell. We observed that cold stress (from 20 to 5 °C) exposure of A549 cell resulted in an increase of ROS and [Ca²⁺]_c, which was completely attenuated by removing Ca²⁺ from medium. Further experiments showed that cold-sensing transient receptor potential subfamily member 1 (TRPA1) agonist (allyl isothiocyanate, AITC) increased the production of ROS and the level of [Ca²⁺]_c in A549 cell. Moreover, HC-030031, a TRPA1 selective antagonist, significantly inhibited the enhanced ROS and [Ca²⁺]_c induced by AITC or cold stimulation, respectively. Taken together, these data demonstrated that TRPA1 activation played an important role in the enhanced production of ROS induced by cold stress in A549 cell.     

Isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men

Human lipid intake contains various amounts of trans fatty acids. Refined vegetable and frying oils, rich in linoleic acid and/or alpha-linolenic acid, are the main dietary sources of trans-18:2 and trans-18:3 fatty acids. The aim of the present study was to compare the oxidation of linoleic acid, alpha-linolenic acid, and their major trans isomers in human volunteers. For that purpose, TG, each containing two molecules of [1-(13)C]linoleic acid, alpha-[1-(13)C]linolenic acid, [1-(13)C]-9cis,12trans-18:2, or [1-(13)C]-9cis,12cis,15trans-18:3, were synthesized. Eight healthy young men ingested labeled TG mixed with 30 g of olive oil. Total CO(2) production and (13)CO(2) excretion were determined over 48 h. The pattern of oxidation was similar for the four fatty acids, with a peak at 8 h and a return to baseline at 24 h. Cumulative oxidation over 8 h of linoleic acid, 9cis,12trans-18:2, alpha-linolenic acid, and 9cis,12cis,15trans-18:3 were, respectively, 14.0 +/- 4.1%, 24.7 +/- 6.7%, 23.6 +/- 3.3%, and 23.4 +/- 3.7% of the oral load, showing that isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men.     

The pungency of garlic: activation of TRPA1 and TRPV1 in response to allicin

Garlic's pungent flavor has made it a popular ingredient in cuisines around the world and throughout history. Garlic's health benefits have been elevated from folklore to clinical study. Although there is some controversy as to the efficacy of garlic, garlic products are one of the most popular herbal supplements in the U.S. Chemically complex, garlic contains different assortments of sulfur compounds depending on whether the cloves are intact, crushed, cooked, or raw. Raw garlic, when cut and placed on the tongue or lips, elicits painful burning and prickling sensations through unknown mechanisms. Here, we show that raw but not baked garlic activates TRPA1 and TRPV1, two temperature-activated ion channels that belong to the transient receptor potential (TRP) family. These thermoTRPs are present in the pain-sensing neurons that innervate the mouth. We further show that allicin, an unstable component of fresh garlic, is the chemical responsible for TRPA1 and TRPV1 activation and is therefore likely to cause garlic's pungency.     

Functional expression of TRPA1 channel,TRPV1 channel and TMEM100 in human odontoblasts

TRPA1 and TRPV1 channels respond to external stimulation as pain mediators and form a complex with a transmembrane protein TMEM100 in some tissues. However, their expression and interaction in dental pulp is unclear. To investigate the functional co-expression of TRPA1 channel, TRPV1 channel and TMEM100 in human odontoblasts (HODs), immunohistochemistry, immunofluorescence staining and Western blot were used to study their co-localization and expression in both native HODs and cultured HOD-like cells. Calcium imaging was used to detect the functional interaction between TRPA1 and TRPV1 channels. Immunohistochemistry and multiple immunofluorescence staining of tooth slices showed positive expression of TRPA1 channel, TRPV1 channel and TMEM100 mainly in the cell bodies of HODs, and TRPA1 channel presented more obvious immunofluorescence in the cell processes than TRPV1 channel and TMEM100. HALO software analysis showed that TRPA1 and TRPV1 channels were positively expressed in most TMEM100⁺ HODs and these three proteins were strongly correlated in HODs (P < 0.01). The protein expression levels of TRPA1 channel, TRPV1 channel and TMEM100 in HODs showed no significant difference (P?>?0.05). Double immunofluorescence staining of cultured HOD-like cells visually demonstrated that TRPA1 and TRPV1 channel were both highly co-localized with TMEM100 with similar expressive intensity. Calcium imaging showed that there was a functional interaction between TRPA1 and TRPV1 channels in HOD-like cells, and TRPA1 channel might play a greater role in this interaction. Overall, we concluded that TRPA1 channel, TRPV1 channel and TMEM100 could be functionally co-expressed in HODs.

     

Dendritic cells do not transduce inflammatory stimuli via the capsaicin receptor TRPV1

Inflammatory stimuli provide critical activation signals for dendritic cells (DC). Signaling through the capsaicin receptor TRPV1 is reported to initiate DC maturation and migration. We attempted to characterize TRPV1 channels in DC. Capsaicin or extracellular protons failed to elicit a change in intracellular [Ca(2+)] or membrane current in DC. In contrast, capsaicin evoked a sustained increase in [Ca(2+)] and large inwards currents in sensory neurons and TRPV1-expressing HEK293 cells. TRPV1 expression was confirmed by RT-PCR in sensory neurons, but was undetectable in DC. Interestingly, and in contrast to capsaicin, the inflammatory neuropeptide substance P evoked Ca(2+) transients in DC. Thus, our data do not support the hypothesis that DC express TRPV1 channels. Rather, signaling through TRPV1 in sensory nerves may modulate DC via neurogenic actions.     

Ciglitazone is not itself thermogenic but increases the potential for thermogenesis in lean mice

Chronic dietary administration of the oral hypoglycaemic ciglitazone (3 g/day for 14–28 days) to lean, non-diabetic CD1 mice resulted in increased brown adipose tissue mitochondrial GDP binding and a marked increase in the thermic effect of the beta-adrenoceptor agonist BRL 26830A. However, ciglitazone was not itself thermogenic after an acute dose, nor did it raise resting metabolic rate during chronic dietary dosing.     

Endurance training increases fatty acid turnover, but not fat oxidation, in young men.

We examined the effects of exercise intensity and a 10-wk cycle ergometer training program [5 days/wk, 1 h, 75% peak oxygen consumption (VO2 peak)] on plasma free fatty acid (FFA) flux, total fat oxidation, and whole body lipolysis in healthy male subjects (n = 10; age = 25.6 +/- 1.0 yr). Two pretraining trials (45 and 65% of VO2 peak) and two posttraining trials (same absolute workload, 65% of old VO2 peak; and same relative workload, 65% of new VO2 peak) were performed by using an infusion of [1-13C]palmitate and [1,1,2,3, 3-2H]glycerol. An additional nine subjects (age 25.4 +/- 0.8 yr) were treated similarly but were infused with [1,1,2,3,3-2H]glycerol and not [1-13C]palmitate. Subjects were studied postabsorptive for 90 min of rest and 1 h of cycling exercise. After training, subjects increased VO2 peak by 9.4 +/- 1.4%. Pretraining, plasma FFA kinetics were inversely related to exercise intensity with rates of appearance (Ra) and disappearance (Rd) being significantly higher at 45 than at 65% VO2 peak (Ra: 8.14 +/- 1.28 vs. 6.64 +/- 0.46, Rd: 8. 03 +/- 1.28 vs. 6.42 +/- 0.41 mol. kg-1. min-1) (P 相似文献   

Differential cytotoxicity and intracellular calcium-signalling following activation of the calcium-permeable ion channels TRPV1 and TRPA1

Several members of the transient receptor channel (TRP) family can mediate a calcium-dependent cytotoxicity. In sensory neurons, vanilloids like capsaicin induce neurotoxicity by activating TRPV1. The closely related ion channel TRPA1 is also activated by irritants, but it is unclear if and how TRPA1 mediates cell death. In the present study we explored cytotoxicity and intracellular calcium signalling resulting from activation of TRPV1 and TRPA1, either heterologously expressed in HEK 293 cells or in native mouse dorsal root ganglion (DRG) neurons. While activation of TRPV1 by the vanilloids capsaicin, resiniferatoxin and anandamide results in calcium-dependent cell death, activation by protons and the oxidant chloramine-T failed to reduce cell viability. The TRPA1-agonists acrolein, carvacrol and capsazepine all induced cytotoxicity, but this effect is independent of TRPA1. Activation of both TRPA1 and TRPV1 triggers a strong influx of external calcium, but also a strong calcium-release from intracellular stores most likely including the endoplasmic reticulum (ER). Activation of TRPV1, but not TRPA1 also results in a strong increase of mitochondrial calcium both in HEK 293 cells and mouse DRG neurons. Our data demonstrate that activation of TRPV1, but not TRPA1 mediates a calcium-dependent cell death. While both receptors mediate a release of calcium from intracellular stores, only activation of TRPV1 seems to mediate a robust and probably lethal increase in mitochondrial calcium.     

Leptin increases FA oxidation in lean but not obese human skeletal muscle: evidence of peripheral leptin resistance

The adipocyte-derived hormone leptin has been shown to acutely increase fatty acid (FA) oxidation and decrease esterification in resting rodent skeletal muscle. However, the effects of leptin on human skeletal muscle FA metabolism are completely unknown. In these studies, we have utilized an isolated human skeletal muscle preparation combined with the pulse-chase technique to measure FA metabolism with and without leptin in lean and obese human skeletal muscle. Under basal conditions (in the absence of leptin), muscle from the obese demonstrated significantly elevated levels of total FA uptake (+72%, P = 0.038) and enhanced rates of FA esterification into triacylglycerol (+102%, P = 0.042) compared with lean subjects. In the presence of leptin, lean muscle had elevated rates of endogenous (+103%, P = 0.01) and exogenous (+150%, P = 0.03) palmitate oxidation. When the ratio of esterification to exogenous oxidation was examined, leptin reduced this ratio (-47%, P = 0.032), demonstrating the increased partitioning of FA toward oxidation and away from storage. Contrary to these findings in lean muscle, leptin had no effect on FA metabolism in skeletal muscle of the obese. This study provides the first evidence that leptin increases FA oxidation in skeletal muscle of lean, but not obese humans, thus demonstrating the development of leptin resistance in obese human skeletal muscle.     

Probiotic use decreases intestinal inflammation and increases bone density in healthy male but not female mice

Osteoporosis can result from intestinal inflammation, as is seen with inflammatory bowel disease. Probiotics, microorganisms that provide a health benefit to the host when ingested in adequate amounts, can have anti‐inflammatory properties and are currently being examined to treat inflammatory bowel disease. Here, we examined if treating healthy male mice with Lactobacillus reuteri ATCC PTA 6475 (a candidate probiotic with anti‐TNFα activity) could affect intestinal TNFα levels and enhance bone density. Adult male mice were given L. reuteri 6475 orally by gavage for 3×/week for 4 weeks. Examination of jejunal and ileal RNA profiles indicates that L. reuteri suppressed basal TNFα mRNA levels in the jejunum and ileum in male mice, but surprisingly not in female mice. Next, we examined bone responses. Micro‐computed tomography demonstrated that L. reuteri 6475 treatment increased male trabecular bone parameters (mineral density, bone volume fraction, trabecular number, and trabecular thickness) in the distal femur metaphyseal region as well as in the lumbar vertebrae. Cortical bone parameters were unaffected. Dynamic and static histomorphometry and serum remodeling parameters indicate that L. reuteri ingestion increases osteoblast serum markers and dynamic measures of bone formation in male mice. In contrast to male mice, L. reuteri had no effect on bone parameters in female mice. Taken together our studies indicate that femoral and vertebral bone formation increases in response to oral probiotic use, leading to increased trabecular bone volume in male mice. J. Cell. Physiol. 228: 1793–1798, 2013. © 2013 Wiley Periodicals, Inc.