Capsaicin pretreatment attenuates LPS-induced hypothermia through TRPV1-independent mechanisms in chicken

Transient receptor potential vanilloid 1 (TRPV1)-independent actions of capsaicin on cellular excitability and ion transport

Capsaicin is a naturally occurring alkaloid derived from chili pepper that is responsible for its hot pungent taste. Capsaicin is known to exert multiple pharmacological actions, including analgesia, anticancer, anti-inflammatory, antiobesity, and antioxidant effects. The transient receptor potential vanilloid subfamily member 1 (TRPV1) is the main receptor mediating the majority of the capsaicin effects. However, numerous studies suggest that the TRPV1 receptor is not the only target for capsaicin. An increasing number of studies indicates that capsaicin, at low to mid µM ranges, not only indirectly through TRPV1-mediated Ca²⁺ increases, but also directly modulates the functions of voltage-gated Na⁺ , K⁺ , and Ca²⁺ channels, as well as ligand-gated ion channels and other ion transporters and enzymes involved in cellular excitability. These TRPV1-independent effects are mediated by alterations of the biophysical properties of the lipid membrane and subsequent modulation of the functional properties of ion channels and by direct binding of capsaicin to the channels. The present study, for the first time, systematically categorizes this diverse range of non-TRPV1 targets and discusses cellular and molecular mechanisms mediating TRPV1-independent effects of capsaicin in excitable, as well as nonexcitable cells.

Effect of ornithokinin on feeding behavior, cloacal temperature, voluntary activity and crop emptying rate in chicks

Bradykinin is a well-studied bioactive peptide associated with several physiological functions, including vasodilation and inflammation, in mammals. However, its avian homolog, ornithokinin, has received less research attention in birds. Therefore this study aimed to investigate the effect of intraperitoneal (IP) and intracerebroventricular (ICV) injections of ornithokinin on feeding behavior, cloacal temperature, voluntary activity, crop emptying rate, and blood constituents in chicks (Gallus gallus). We also investigated the effect of lipopolysaccharide (LPS), a cell wall component of gram-negative bacteria, on ornithokinin-associated gene expression was also investigated to determine whether activation of the ornithokinin system is induced by bacterial infection. Both IP and ICV injections of ornithokinin significantly decreased feed intake, cloacal temperature, voluntary activity, and crop emptying rate in chicks, but they did not affect the plasma concentration of corticosterone. Additionally, LPS significantly increased the expression of ornithokinin B2 receptor mRNA in several organs. Hence, ornithokinin is associated with a range of physiological responses in chicks and may be related to their response to bacterial infection.

Effect of lithium chloride on food intake, cloacal temperature, voluntary activity, and crop-emptying rate in chicks

Infections frequently accompany with non-specific symptoms such as anorexia and hyperthermia. In addition, there may be unpleasant sensations such as visceral discomfort during infection. Lipopolysaccharide (LPS), a Gram-negative bacteria cell wall component, is known to induce the unpleasant sensation of conditioned taste aversion in mammals. However, the relationship between unpleasant sensations and changes in behavior and physiological conditions has not been investigated extensively in birds. Lithium chloride (LiCl) is a compound that induces unpleasant sensations, including visceral discomfort, although its effects on behavior and physiological conditions have also not been investigated extensively in birds. Thus, the present study was aimed to investigate the effect of an intraperitoneal (IP) injection of LiCl on conditioned visual aversion, food intake, cloacal temperature, voluntary activity, crop-emptying rate, and blood constituents in chicks (Gallus gallus). We also examined the effect of IP injections of LPS and zymosan, a cell wall component of fungus, on conditioned visual aversion formation. First, IP injection of LiCl was confirmed to induce conditioned visual aversion in chicks. An IP injection of LiCl significantly decreased food intake, voluntary activity, and crop-emptying rate but did not affect the temperature. In addition, the injection of LiCl significantly increased plasma corticosterone concentration, indicating that LiCl serves as a stressor in chicks. Finally, IP injections of LPS and zymosan were found to induce conditioned visual aversion in chicks. Collectively, these results suggest that LiCl induces conditioned aversion, anorexia, hypoactivity, and inhibition of crop-emptying in chicks. In addition, LPS and zymosan would induce unpleasant sensations in chicks.

Cutaneous TRPV4 Channels Activate Warmth-Defense Responses in Young and Adult Birds

Transient receptor potential vanilloid 4 (TRPV4) channels are sensitive to warm ambient temperatures (Tas), triggering heat loss responses in adult rats in a Tas range of ∼26–30°C. In birds, however, the thermoregulatory role of TRPV4 has never been shown. Here, we hypothesized that stimulation of TRPV4 induces thermolytic responses for body temperature (Tb) maintenance in birds, and that this function is already present in early life, when the Ta range for TRPV4 activation does not represent a warm condition for these animals. We first demonstrated the presence of TRPV4 in the dorsal and ventral skin of chickens (Gallus gallus domesticus) by immunohistochemistry. Then, we evaluated the effects of the TRPV4 agonist, RN1747, and the TRPV4 antagonists, HC067047 and GSK2193874, on Tb and thermoeffectors at different Tas in 5-day-old chicks and 60-day-old adult chickens. For the chicks, RN1747 transiently reduced Tb both in thermoneutrality (31°C) and in a cold Ta for this phase (26°C), which relied on huddling behavior inhibition. The TRPV4 antagonists alone did not affect Tb or thermoeffectors but blocked the Tb decrease and huddling inhibition promoted by RN1747. For the adults, TRPV4 antagonism increased Tb when animals were exposed to 28°C (suprathermoneutral condition for adults), but not to 19°C. In contrast, RN1747 decreased Tb by reducing metabolic rate and activating thermal tachypnea at 19°C, a Ta below the activation range of TRPV4. Our results indicate that peripheral TRPV4 receptors are functional in early life, but may be inhibited at that time when the range of activation (∼26–30°C) represents cold Ta for chicks, and become physiologically relevant for Tb maintenance when the activation Ta range for TRPV4 becomes suprathermoneutral for adult chickens.

Central and peripheral effects of L-citrulline on thermal physiology and nitric oxide regeneration in broilers

The mechanism that mediates L-citrulline (L-Cit) hypothermia is poorly understood, and the involvement of nitric oxide signaling has not been fully elucidated. Therefore, this study aimed to determine L-Cit's influence on body temperature and to ascertain the central and peripheral mechanisms associated with this response. Chicks responded to intracerebroventricular (ICV) injection of L-Cit with high and low body temperatures (P < 0.05) depending on the dose tested, for both the surface and rectal temperatures. Peripheral (i.p.) L-Cit injection did not affect body temperature responses. Nitric oxide (NO) concentration and NO synthase (NOS) were influenced with varying doses of L-Cit. Hypothalamic NO was increased at 4 µg L-Cit whereas, plasma iNOS was elevated at 2µg L-Cit treatment. However, i.p. L-Cit did not change the NO content, rather it induced higher (P < 0.05) plasma tNOS and iNOS activity, and further upregulated iNOS and nNOS gene expression in the hypothalamus. In addition, ICV L-Cit potentiated a pro- versus anti-inflammatory milieu with the induction of IL-8, IL-10, and TGFβ (P < 0.05), which may be related to the changes in body temperature. Following ICV L-Cit administration, it was observed that L-Cit caused dose variable changes in the ultrastructure of hypothalamic neurons. The lowest dose was associated with a higher number of dead or degenerating neurons, whereas the highest L-Cit dose had fewer neuronal numbers with larger sizes. Therefore, this study shows that central and peripheral L-Cit administration imposes changes in body temperature, nitric oxide production, and inflammatory responses, in a dose-dependent manner.

Dietary L-citrulline influences body temperature and inflammatory responses during nitric oxide synthase inhibition and endotoxin challenge in chickens

Recent studies have revealed the role of L-citrulline (L-CIT) in thermoregulation, but very little is known about the mechanisms involved. In this study, nitric oxide synthase inhibition and endotoxin-induced fever were used to investigate the effects of L-CIT on body temperature and inflammatory responses. In experiment 1, NW-nitro-L-arginine methyl ester (L-NAME, 150 mg/kg BW), was i. p. injected into chicks fed with basal (CON) or L-CIT diets for 14 days. In experiment 2, Lipopolysaccharide (LPS, 2 mg/kg BW) was i. p. injected following 21d feeding with CON or L-CIT diets. In experiment 3, chickens were injected with either L-NAME, LPS, or L-NAME + LPS following 26 days feeding with CON or L-CIT diets. The rectal (RT), ear (ET), and core body temperature (CBT) of chickens were examined. Results showed that L-NAME effectively decreased the RT, ET, CBT, and plasma NO concentration. In contrast, LPS increased NO levels and initiated hyperthermia by increasing RT, ET, CBT, and PGE2 levels. L-CIT diet reduced the mean CBT in experiment 1 and diminished the NO level, PGE2 level, and mean RT in experiment 3. Co-administration of L-CIT + LPS upregulated IL-6 expression, whereas, LPS injection alone induced IL-10, IL-1β, and TLR4 gene expressions. Therefore, this study reveals that L-CIT-induced hypothermia was related to NO inhibition and a decrease in PGE2 concentration. Conversely, LPS induced hyperthermia was associated with an increase in both NO and PGE2 concentrations.

Regulated hypothermia in response to endotoxin in birds

KEY POINTS

The costs associated with immune and thermal responses may exceed the benefits to the host during severe inflammation. In this case, regulated hypothermia instead of fever can occur in rodents as a beneficial strategy to conserve energy for vital functions with consequent tissue protection and hypoxia prevention. We tested the hypothesis that this phenomenon is not exclusive to mammals, but extends to the other endothermic group, birds. A decrease in metabolic rate without any failure in mitochondrial respiration, nor oxygen delivery, is the main evidence supporting the regulated nature of endotoxin-induced hypothermia in chicks. Thermolytic mechanisms such as tachypnea and cutaneous vasodilatation can also be recruited to facilitate body temperature decrease under lipopolysaccharide treatment, especially in the cold. Our findings bring a new perspective for evolutionary medicine studies on energy trade-off in host defence because regulated hypothermia may be a phenomenon spread among vertebrates facing a severe immune challenge.

ABSTRACT

A switch from fever to regulated hypothermia can occur in mammals under circumstances of reduced physiological fitness (e.g. sepsis) to direct energy to defend vital systems. Birds in which the cost to resist a pathogen is additive to the highest metabolic rate and body temperature (T_b ) among vertebrates may also benefit from regulated hypothermia during systemic inflammation. Here, we show that the decrease in T_b observed during an immune challenge in birds is a regulated hypothermia, and not a result of metabolic failure. We investigated O₂ consumption (thermogenesis index), ventilation (respiratory heat loss), skin temperature (sensible heat loss) and muscle mitochondrial respiration (thermogenic tissue) during T_b fall in chicken chicks challenged with endotoxin [lipopolysaccharide (LPS)]. Chicks injected with LPS were also tested regarding the capacity to raise O₂ consumption to meet an increased demand driven by 2,4-dinitrophenol. LPS decreased T_b and the metabolic rate of chicks without affecting muscle uncoupled, coupled and non-coupled mitochondrial respiration. LPS-challenged chicks were indeed capable of increasing metabolic rate in response to 2,4-dinitrophenol, indicating no O₂ delivery limitation. Additionally, chicks did not attempt to prevent T_b from falling during hypothermia but, instead, activated cutaneous and respiratory thermolytic mechanisms, providing an additional cooling force. These data provide the first evidence of the regulated nature of the hypothermic response to endotoxin in birds. Therefore, it changes the current understanding of bird's thermoregulation during severe inflammation, indicating that regulated hypothermia is either a convergent trait for endotherms or a conserved response among vertebrates, which adds a new perspective for evolutionary medicine research.

Anti-obesity effects of capsaicin and the underlying mechanisms: a review

The mechanisms of anti-obesity effects of capsaicin in cell models, rodent models and human subjects were reviewed.

TRPV1 mediates astrocyte activation and interleukin-1β release induced by hypoxic ischemia (HI)

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is a serious birth complication with high incidence in both advanced and developing countries. Children surviving from HIE often have severe long-term sequela including cerebral palsy, epilepsy, and cognitive disabilities. The severity of HIE in infants is tightly associated with increased IL-1β expression and astrocyte activation which was regulated by transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel in the TRP family.

METHODS

Neonatal hypoxic ischemia (HI) and oxygen-glucose deprivation (OGD) were used to simulate HIE in vivo and in vitro. Primarily cultured astrocytes were used for investigating the expression of glial fibrillary acidic protein (GFAP), IL-1β, Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and activation of the nucleotide-binding, oligomerization domain (NOD)-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome by using Western blot, q-PCR, and immunofluorescence. Brain atrophy, infarct size, and neurobehavioral disorders were evaluated by Nissl staining, 2,3,5-triphenyltetrazolium chloride monohydrate (TTC) staining and neurobehavioral tests (geotaxis reflex, cliff aversion reaction, and grip test) individually.

RESULTS

Astrocytes were overactivated after neonatal HI and OGD challenge. The number of activated astrocytes, the expression level of IL-1β, brain atrophy, and shrinking infarct size were all downregulated in TRPV1 KO mice. TRPV1 deficiency in astrocytes attenuated the expression of GFAP and IL-1β by reducing phosphorylation of JAK2 and STAT3. Meanwhile, IL-1β release was significantly reduced in TRPV1 deficiency astrocytes by inhibiting activation of NLRP3 inflammasome. Additionally, neonatal HI-induced neurobehavioral disorders were significantly improved in the TRPV1 KO mice.

CONCLUSIONS

TRPV1 promotes activation of astrocytes and release of astrocyte-derived IL-1β mainly via JAK2-STAT3 signaling and activation of the NLRP3 inflammasome. Our findings provide mechanistic insights into TRPV1-mediated brain damage and neurobehavioral disorders caused by neonatal HI and potentially identify astrocytic TRPV1 as a novel therapeutic target for treating HIE in the subacute stages (24 h).

Forsythiaside attenuates Escherichia coli lipopolysaccharide-induced liver acute inflammatory response in chicken

This study investigated the effects of forsythiaside on the acute inflammatory response induced by Escherichia coli lipopolysaccharide (LPS) in liver of broiler chickens. Fifteen-day-old chickens were randomly assigned to three groups (n = 20 for each group, orally treated with 0, 30, or 60 mg/kg BW of forsythiaside) for 7 days. At 21 days of age, the chickens were intravenously injected with either LPS (200 μg/kg BW) or sterile saline (200 μg/kg BW, control group). All the chickens were humanely euthanized by cervical dislocation 2 h after the LPS injection. The results showed that the injection of LPS induced some indexes, including total proteins, nitric oxide (NO), interleukin-1beta (IL-1β), interleukin-6 (IL-6), and interleukin-17 (IL-17) production ( P < 0.05) and increased the mRNA expression of LPS-induced tumor necrosis factor-alpha (LITAF), IL-1β, IL-17, IL-6, and inducible nitric oxide synthase (iNOS) ( P < 0.05). Forsythiaside supplementation alleviated the LPS-induced inflammatory response by inhibiting the production of total proteins, NO, LITAF, IL-1β, IL-17, and IL-6 and down-regulating the mRNA expression of pro-inflammatory cytokines and iNOS. In conclusion, forsythiaside is a potential treatment for LPS-induced liver acute inflammation in chicken.

Physiological responses to central and peripheral injection of polyinosinic-polycytidylic acid in chicks

1. The purpose of the present study was to determine if intracerebroventricular (ICV) and intraperitoneal (IP) injection of polyinosinic-polycytidylic acid (poly I:C), a viral mimetic that binds to toll-like receptor-3 (TLR3), affects food intake, voluntary activity, cloacal temperature, plasma corticosterone (CORT) and glucose concentrations, and crop emptying rate in chicks (Gallus gallus). 2. Both ICV and IP injection of poly I:C significantly decreased food intake. 3. IP but not ICV injection of poly I:C significantly suppressed voluntary activity, whereas ICV injection decreased time spent sitting. Both ICV and IP injection of poly I:C significantly increased plasma CORT and glucose concentration. Neither ICV nor IP injection of poly I:C significantly affected cloacal temperature. 4. In addition, ICV injection of poly I:C significantly reduced crop emptying rate, whereas IP injection had no effect. 5. These results suggested that central TLR3 is related to anorexia, stress response and retardation of crop emptying while peripheral TLR3 is related to anorexia, change in behaviour and stress responses during viral infection in chicks.

The identification, characterization, and function of two TREMs genes in Chinese Yangzhou goose (Anas cygnoides)

Triggering receptor expressed on myeloid cells (TREM) is a cell-surface receptor primarily expressed on macrophages. Here, two novel TREM genes, AcTREM1 and AcTREM2, were identified from Anas cygnoides. AcTREM1 cDNA contained a putative signal peptide, two IG domains, and a transmembrane domain. The deduced AcTREM2 sequence also contained a signal peptide, an IG domain, and a transmembrane domain. qRT-PCR, fluorescence in situ hybridization, and immunofluorescence experiments showed that AcTREM1 and AcTREM2 were mainly expressed in the liver and spleen, and both genes and proteins were mainly distributed in cytoplasm. AcTREM1 expression in the liver and spleen was significantly upregulated following lipopolysaccharide (LPS) challenge at an early stage of infection and then decreased at a later stage. Changes in AcTREM2 expression were reciprocal to those of AcTREM1 in the liver and spleen after LPS challenge. Our results indicate that AcTREM1 and AcTREM2 participate in the antibacterial immunity of A. cygnoides.

Nitric oxide and fever: immune-to-brain signaling vs. thermogenesis in chicks

Nitric oxide (NO) plays a role in thermogenesis but does not mediate immune-to-brain febrigenic signaling in rats. There are suggestions of a different situation in birds, but the underlying evidence is not compelling. The present study was designed to clarify this matter in 5-day-old chicks challenged with a low or high dose of bacterial LPS. The lower LPS dose (2 μg/kg im) induced fever at 3–5 h postinjection, whereas 100 μg/kg im decreased core body temperature (Tc) (at 1 h) followed by fever (at 4 or 5 h). Plasma nitrate levels increased 4 h after LPS injection, but they were not correlated with the magnitude of fever. The NO synthase inhibitor ( NG-nitro-l-arginine methyl ester, l-NAME; 50 mg/kg im) attenuated the fever induced by either dose of LPS and enhanced the magnitude of the Tc reduction induced by the high dose in chicks at 31–32°C. These effects were associated with suppression of metabolic rate, at least in the case of the high LPS dose. Conversely, the effects of l-NAME on Tc disappeared in chicks maintained at 35–36°C, suggesting that febrigenic signaling was essentially unaffected. Accordingly, the LPS-induced rise in the brain level of PGE2 was not affected by l-NAME. Moreover, l-NAME augmented LPS-induced huddling, which is indicative of compensatory mechanisms to run fever in the face of attenuated thermogenesis. Therefore, as in rats, systemic inhibition of NO synthesis attenuates LPS-induced fever in chicks by affecting thermoeffector activity and not by interfering with immune-to-brain signaling. This may constitute a conserved effect of NO in endotherms.

Naturally occurring hypothermia is more advantageous than fever in severe forms of lipopolysaccharide- and Escherichia coli-induced systemic inflammation

The natural switch from fever to hypothermia observed in the most severe cases of systemic inflammation is a phenomenon that continues to puzzle clinicians and scientists. The present study was the first to evaluate in direct experiments how the development of hypothermia vs. fever during severe forms of systemic inflammation impacts the pathophysiology of this malady and mortality rates in rats. Following administration of bacterial lipopolysaccharide (LPS; 5 or 18 mg/kg) or of a clinical Escherichia coli isolate (5 × 10(9) or 1 × 10(10) CFU/kg), hypothermia developed in rats exposed to a mildly cool environment, but not in rats exposed to a warm environment; only fever was revealed in the warm environment. Development of hypothermia instead of fever suppressed endotoxemia in E. coli-infected rats, but not in LPS-injected rats. The infiltration of the lungs by neutrophils was similarly suppressed in E. coli-infected rats of the hypothermic group. These potentially beneficial effects came with costs, as hypothermia increased bacterial burden in the liver. Furthermore, the hypotensive responses to LPS or E. coli were exaggerated in rats of the hypothermic group. This exaggeration, however, occurred independently of changes in inflammatory cytokines and prostaglandins. Despite possible costs, development of hypothermia lessened abdominal organ dysfunction and reduced overall mortality rates in both the E. coli and LPS models. By demonstrating that naturally occurring hypothermia is more advantageous than fever in severe forms of aseptic (LPS-induced) or septic (E. coli-induced) systemic inflammation, this study provides new grounds for the management of this deadly condition.

Capsaicin sensitizes TRAIL-induced apoptosis through Sp1-mediated DR5 up-regulation: involvement of Ca(2+) influx

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various malignant cells, several cancers including human hepatocellular carcinoma (HCC) exhibit potent resistance to TRAIL-induced cell death. The aim of this study is to evaluate the anti-cancer potential of capsaicin in TRAIL-induced cancer cell death. As indicated by assays that measure phosphatidylserine exposure, mitochondrial activity and activation of caspases, capsaicin potentiated TRAIL-resistant cells to lead to cell death. In addition, we found that capsaicin induces the cell surface expression of TRAIL receptor DR5, but not DR4 through the activation Sp1 on its promoter region. Furthermore, we investigated that capsaicin-induced DR5 expression and apoptosis are inhibited by calcium chelator or inhibitors for calmodulin-dependent protein kinase. Taken together, our data suggest that capsaicin sensitizes TRAIL-mediated HCC cell apoptosis by DR5 up-regulation via calcium influx-dependent Sp1 activation.

Thermoregulatory phenotype of the Trpv1 knockout mouse: thermoeffector dysbalance with hyperkinesis

This study aimed at determining the thermoregulatory phenotype of mice lacking transient receptor potential vanilloid-1 (TRPV1) channels. We used Trpv1 knockout (KO) mice and their genetically unaltered littermates to study diurnal variations in deep body temperature (T(b)) and thermoeffector activities under basal conditions, as well as thermoregulatory responses to severe heat and cold. Only subtle alterations were found in the basal T(b) of Trpv1 KO mice or in their T(b) responses to thermal challenges. The main thermoregulatory abnormality of Trpv1 KO mice was a different pattern of thermoeffectors used to regulate T(b). On the autonomic side, Trpv1 KO mice were hypometabolic (had a lower oxygen consumption) and hypervasoconstricted (had a lower tail skin temperature). In agreement with the enhanced skin vasoconstriction, Trpv1 KO mice had a higher thermoneutral zone. On the behavioral side, Trpv1 KO mice preferred a lower ambient temperature and expressed a higher locomotor activity. Experiments with pharmacological TRPV1 agonists (resiniferatoxin and anandamide) and a TRPV1 antagonist (AMG0347) confirmed that TRPV1 channels located outside the brain tonically inhibit locomotor activity. With age (observed for up to 14 months), the body mass of Trpv1 KO mice exceeded that of controls, sometimes approaching 60 g. In summary, Trpv1 KO mice possess a distinct thermoregulatory phenotype, which is coupled with a predisposition to age-associated overweight and includes hypometabolism, enhanced skin vasoconstriction, decreased thermopreferendum, and hyperkinesis. The latter may be one of the primary deficiencies in Trpv1 KO mice. We propose that TRPV1-mediated signals from the periphery tonically suppress the general locomotor activity.

The hypothermic response to bacterial lipopolysaccharide critically depends on brain CB1, but not CB2 or TRPV1, receptors

Hypothermia occurs in the most severe cases of systemic inflammation, but the mechanisms involved are poorly understood. This study evaluated whether the hypothermic response to bacterial lipopolysaccharide (LPS) is modulated by the endocannabinoid anandamide(AEA) and its receptors: cannabinoid-1 (CB1), cannabinoid-2 (CB2) and transient receptor potential vanilloid-1 (TRPV1). In rats exposed to an ambient temperature of 22◦C, a moderate dose of LPS (25 - 100 μg kg−1 I.V.) induced a fall in body temperature with a nadir at ∼100 minpostinjection. This response was not affected by desensitization of intra-abdominal TRPV1 receptors with resiniferatoxin (20 μg kg - 1 I.P.), by systemic TRPV1 antagonism with capsazepine(40mg kg−1 I.P.), or by systemic CB2 receptor antagonism with SR144528 (1.4 mg kg−1 I.P.).However, CB1 receptor antagonism by rimonabant (4.6mg kg−1 I.P.) or SLV319 (15mg kg−1 I.P.)blocked LPS hypothermia. The effect of rimonabant was further studied. Rimonabant blocked LPS hypothermia when administered I.C.V. at a dose (4.6 μg) that was too low to produce systemic effects. The blockade of LPS hypothermia by I.C.V. rimonabant was associated with suppression of the circulating level of tumour necrosis factor-α. In contrast to rimonabant,the I.C.V. administration of AEA (50 μg) enhanced LPS hypothermia. Importantly, I.C.V. AEAdid not evoke hypothermia in rats not treated with LPS, thus indicating that AEA modulates LPS-activated pathways in the brain rather than thermo effector pathways. In conclusion, the present study reveals a novel, critical role of brain CB1 receptors in LPS hypothermia. Brain CB1 receptors may constitute a new therapeutic target in systemic inflammation and sepsis.

Capsaicin sensitizes malignant glioma cells to TRAIL-mediated apoptosis via DR5 upregulation and survivin downregulation

Capsaicin, a pungent ingredient of red chili peppers, has been reported to possess antitumor activities. Here, we show that subtoxic doses of capsaicin effectively sensitize multiple malignant glioma cell lines to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Although TRAIL alone mediated partial proteolytic processing of procaspase-3 in glioma cells, cotreatment with capsaicin and TRAIL efficiently restored complete activation of caspases. We found that treatment of various gliomas with capsaicin significantly upregulated DR5, a death receptor of TRAIL, and downregulated the caspase inhibitor survivin. The induction of DR5 was mediated by CHOP/GADD153. The reduction in survivin protein level was associated with downregulation of cyclin B and Cdc2 expression, suggesting that inhibition of Cdc2 activity might contribute to capsaicin-induced survivin downregulation. Taken together, these results indicate that the activity of capsaicin toward DR5 and survivin contributes to the amplification of caspase cascades, thereby restoring TRAIL sensitivity in malignant glioma cells. Interestingly, normal astrocytes were resistant to combined treatment with capsaicin and TRAIL. Neither capsaicin-induced DR5 upregulation/survivin downregulation nor the partial processing of procaspase-3 by TRAIL was induced in astrocytes. Thus, a combined regimen using capsaicin and TRAIL may provide a safe and effective strategy for treating malignant gliomas.

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.