Activation of TRPV1-Expressing Renal Sensory Nerves of Rats with N-Oleoyldopamine Attenuates High-Fat-Diet-Induced Impairment of Renal Function.

Enhanced renal sympathetic nerve activity (RSNA) contributes to obesity-induced renal disease, while the role of afferent renal nerve activity (ARNA) is not fully understood. The present study tested the hypothesis that activating the transient receptor potential vanilloid 1 (TRPV1) channel in afferent renal nerves suppresses RSNA and prevents renal dysfunction and hypertension in obese rats. N-oleoyldopamine (OLDA, 1 ng/kg, daily) was administrated intrathecally (T8-L3) via an indwelled catheter to chronically activate, TRPV1-positive afferent renal nerves in rats fed a chow diet or high-fat diet (HFD) for 8 weeks. HFD intake significantly increased the body weight, impaired glucose and insulin tolerance, decreased creatinine clearance, and elevated systolic blood pressure in rats compared with the levels of the chow-fed rats (all p < 0.05). An intrathecal OLDA treatment for 8 weeks did not affect the fasting glucose level, glucose tolerance, and insulin tolerance in rats fed either chow or HFD. As expected, the chronic OLDA treatment significantly increased the levels of plasma calcitonin gene-related peptide and substance P and ARNA in the HFD-fed rats (all p < 0.05). Interestingly, the OLDA treatment decreased the urinary norepinephrine level and RSNA in rats fed HFD (both p < 0.05). Importantly, the OLDA treatment attenuated HFD-induced decreases in creatinine clearance and urinary Na+ excretion and increases in the plasma urea level, urinary albumin level, and systolic blood pressure at the end of an 8-week treatment (all p < 0.05). Taken together, the intrathecal administration of OLDA ameliorates the enhancement of RSNA, renal dysfunction, and hypertension in obese rats. These findings shed light on the roles of TRPV1-positive renal afferent nerves in obesity-related renal dysfunction and hypertension.

Ablation of TRPV1-positive nerves exacerbates salt-induced hypertension and tissue injury in rats after renal ischemia-reperfusion via infiltration of macrophages.

Background: High-salt intake after renal ischemia/reperfusion (I/R) injury leads to hypertension and further renal injury, but the mechanisms are largely unknown. This study tested the hypothesis that degeneration of transient receptor potential vanilloid 1 (TRPV1)-positive nerves exacerbates salt-induced hypertension and renal injury after I/R via enhancing renal macrophage infiltration.Methods: Large dose of capsaicin (CAP, 100 mg/kg, subcutaneously) was used to degenerate rat TRPV1-positive nerves. Then, rats were subjected to renal I/R injury and fed with a low-salt (0.4% NaCl) diet for 5 weeks after I/R, followed by a high-salt (4% NaCl) diet for 4 weeks during which macrophages were depleted using liposome-encapsulated clodronate (LC, 1.3 ml/kg/week, intravenously).Results: The protein level of TRPV1 in the kidney was downregulated by renal I/R injury and was further decreased by CAP treatment. LC treatment did not affect the protein levels of renal TRPV1. After renal I/R injury, high-salt diet significantly increased renal macrophage infiltration, inflammatory cytokines (tumor necrosis factor-alpha and interleukin 1 beta), systolic blood pressure, the urine/water intake ratio, plasma creatine and urea levels, urinary 8-isoprostane, and renal collagen deposition. Interestingly, CAP treatment further increased these parameters. These increases were abolished by depleting macrophages with LC treatment.Conclusions: These data suggest that degenerating TRPV1-positive nerves exacerbates salt-induced hypertension and tissue injury in rats after renal I/R injury via macrophages-mediated renal inflammation.

Knockout of TRPA1 exacerbates angiotensin II-induced kidney injury.

Macrophage-mediated inflammation plays a critical role in hypertensive kidney disease. Here, we investigated the role of transient receptor potential ankyrin 1 (TRPA1), a sensor of inflammation, in angiotensin II (ANG II)-induced renal injury. Subcutaneous infusion of ANG II (600 ng·min-1·kg-1) for 28 days was used to induce hypertension and renal injury in mice. The results showed that ANG II-induced hypertensive mice have decreased renal Trpa1 expression (P < 0.01), whereas ANG II receptor type 1a-deficient hypotensive mice have increased renal Trpa1 expression (P < 0.05) compared with their normotensive counterparts. ANG II induced similar elevations of systolic blood pressure in Trpa1-/- and wild-type (WT) mice but led to higher levels of blood urea nitrogen (P < 0.05), serum creatinine (P < 0.05), and renal fibrosis (P < 0.01) in Trpa1-/- mice than WT mice. Similarly, ANG II increased both CD68+/inducible nitric oxide synthase+ M1 and CD68+/arginase 1+ M2 macrophages in the kidneys of both Trpa1-/- and WT mice (all P < 0.01), with higher extents in Trpa1-/- mice (both P < 0.01). Compared with WT mice, Trpa1-/- mice had significantly increased expression levels of inflammatory cytokines and their receptors in the kidney. Cultured murine macrophages were stimulated with phorbol 12-myristate 13-acetate, which downregulated gene expression of TRPA1 (P < 0.01). A TRPA1 agonist, cinnamaldehyde, significantly inhibited phorbol 12-myristate 13-acetate-stimulated expression of IL-1ß and chemokine (C-C motif) ligand 2 in macrophages, which were attenuated by pretreatment with a TRPA1 antagonist, HC030031. Furthermore, activation of TRPA1 with cinnamaldehyde induced apoptosis of macrophages. These findings suggest that TRPA1 may play a protective role in ANG II-induced renal injury, likely through inhibiting macrophage-mediated inflammation.

Activation of TRPV1 Prevents Salt-Induced Kidney Damage and Hypertension After Renal Ischemia-Reperfusion Injury in Rats.

BACKGROUND/AIMS: High-salt intake after recovery from renal ischemia-reperfusion (I/R) injury leads to hypertension with severe renal damage. Transient receptor potential vanilloid type 1 (TRPV1) channels have been involved in the regulation of inflammation and oxidative stress following ischemic organ injury. We tested the hypothesis that activation of TRPV1 conveys preconditioning protection to the kidney subjected to I/R. METHODS: TRPV1 was activated or down-regulated by subcutaneous injection of a low (1mg/kg) or high (100mg/kg) dose of capsaicin, respectively, 3 hours before ischemia. Rats were fed a 0.4% NaCl diet for 5 weeks after I/R followed by a 4% NaCl diet for 4 more weeks in 4 groups: sham, I/R, I/R+high-dose capsaicin (HCap), and I/R+low-dose capsaicin (LCap). RESULTS: Renal TRPV1 expression was decreased in I/R rats (P< 0.05) and further reduced in I/R+HCap group (P< 0.05) but unchanged in I/R+LCap rats compared with the sham group. Blood pressure were elevated in I/R rats (P< 0.05) and further increased in I/R+HCap group (P< 0.05) but unchanged in I/R+LCap rats compared with sham. Renal function was impaired in I/R rats (P< 0.05) and further deteriorated in I/R+HCap group (P< 0.05) but unchanged in I/R+LCap group. Renal inflammatory responses, oxidative stress, and renal collagen deposition were augmented in I/R rats (all P< 0.05) and further intensified in I/R+HCap group (all P< 0.05) but unchanged in I/R+LCap group. CONCLUSION: Activation of TRPV1 plays an anti-inflammatory and anti-oxidative stress role in preventing renal tissue damage and salt-induced hypertension after I/R injury, indicating that TRPV1 conveys preconditioning protection that may have therapeutic implication.

Transient receptor potential vanilloid in blood pressure regulation.

PURPOSE OF REVIEW: The involvement of neurohormonal factors in the pathogenesis of hypertension has been extensively studied. However, the mechanisms underlying the role of the transient receptor potential vanilloid type 1 (TRPV1) channels in hypertension are still largely unknown. This review presents some of the most recent findings regarding the potential mechanisms of TRPV1 in mediating blood pressure, the pathophysiology of hypertension, and its related disorders. RECENT FINDINGS: TRPV1 may be activated by exogenous vanilloid or endo-vanilloid compounds and its function modulated by vasoactive mediators. TRPV1 also interacts with various physiological and pathophysiological systems involved in salt and water homeostasis and cardiovascular homeostasis. Impairment of TRPV1 signaling may contribute to the pathogenesis of diseases such as hypertension, heart failure, atherosclerosis, diabetes, obesity, myocardial ischemia, and stroke. SUMMARY: Accumulating evidence implicates TRPV1 as serving a key role in cardiovascular health by regulating cardiovascular function and protecting against cardiovascular injury. Given the large prevalence of hypertension and its related disorders, the possible involvement of TRPV1 makes it a potential target of therapy for cardiovascular disease. Future study of TRPV1 may enhance our understanding of several cardiovascular diseases and may unveil novel pharmacological strategies for treating hypertension.

Role of the transient receptor potential vanilloid type 1 channel in renal inflammation induced by lipopolysaccharide in mice.

To determine the role of the transient receptor potential vanilloid type 1 (TRPV1) channel in the regulation of renal inflammation, lipopolysaccharide (LPS, 3 mg/kg) was intraperitoneally injected into wild-type (WT) and TRPV1-null mutant (TRPV1(-/-)) mice. The kidney and serum were collected 6 or 24 h after LPS injection for morphological analysis and proinflammatory cytokine assay. LPS injection led to a similar degree of transient hypotension and bradycardia in WT and TRPV1(-/-) mice determined by a telemetry system. LPS administration caused parenchymal red blood cell congestion and fading of intact glomerular structure in TRPV1(-/-) compared with WT mice. Serum creatinine levels were higher 24 h after LPS injection in TRPV1(-/-) than in WT mice. Neutrophil and macrophage infiltration in the kidneys was greater 6 h for the former and 24 h for both after LPS injection in TRPV1(-/-) than in WT mice. Serum cytokine levels including tumor necrosis factor (TNF)-α, IL-1ß, and IL-6 were higher 6 h after LPS injection in TRPV1(-/-) compared with WT mice. Likewise, renal chemokine levels including keratinocyte-derived chemokines and macrophage inflammatory protein were higher 6 h after LPS injection in TRPV1(-/-) than in WT mice. Renal VCAM-1 and ICAM-1 expression was further elevated 6 h for the former and 24 h for the latter after LPS injection in TRPV1(-/-) than in WT mice. Renal nuclear factor-κB (NF-κB) activity was further increased 6 h after LPS injection in TRPV1(-/-) compared with WT mice. Pharmacological blockade TRPV1 in WT mice showed aggravated renal and serum inflammatory responses resembling that of TRPV1(-/-) mice. Thus TRPV1 gene ablation exacerbates LPS-induced renal tissue and function injury, including aggravated renal neutrophil and macrophage infiltration, chemokine and adhesion molecule levels, and glomerular hypercellularity accompanying with further increased serum creatinine and cytokine levels. These results indicate that TRPV1 is activated during LPS challenge, which may constitute a protect mechanism against LPS-induced renal injury via reducing renal inflammatory responses.

Cellular biophysical dynamics and ion channel activities detected by AFM-based nanorobotic manipulator in insulinoma ß-cells.

Distinct biochemical, electrochemical and electromechanical coupling processes of pancreatic ß-cells may well underlie different response patterns of insulin release from glucose and capsaicin stimulation. Intracellular Ca(2+) levels increased rapidly and dose-dependently upon glucose stimulation, accompanied with about threefold rapid increases in cellular stiffness. Subsequently, cellular stiffness diminished rapidly and settled at a value about twofold of the baseline. Capsaicin caused a similar transient increase in intracellular Ca(2+) changes. However, cellular stiffness increased gradually to about twofold until leveling off. The current study characterizes for the first time the biophysical properties underlying glucose-induced biphasic responses of insulin secretion, distinctive from the slow and single-phased stiffness response to capsaicin despite similar changes in intracellular Ca(2+) levels. The integrated AFM nanorobotics and optical investigation enables the fine dissection of mechano-property from ion channel activities in response to specific and non-specific agonist stimulation, providing novel biomechanical markers for the insulin secretion process. FROM THE CLINICAL EDITOR: This study characterizes the biophysical properties underlying glucose-induced biphasic responses of insulin secretion. Integrated AFM nanorobotics and optical investigations provided novel biomechanical markers for the insulin secretion process.

Knockout of Trpa1 accelerates age-related cardiac fibrosis and dysfunction.

Age-related cardiac fibrosis contributes to the development of heart failure with preserved ejection fraction which lacks ideal treatment. Transient receptor potential ankyrin 1 (TRPA1) is an oxidative stress sensor and could attenuate age-related pathologies in invertebrates. The present study aimed to test whether TRPA1 plays a role in age-related cardiac remodeling and dysfunction. The cardiac function and pathology of 12-week-old (young) and 52-week-old (older) Trpa1-/- mice and wild-type (WT) littermates were evaluated by echocardiography and histologic analyses. The expression levels of 84 fibrosis-related genes in the heart were measured by quantitative polymerase chain reaction array. Young Trpa1-/- and WT mice had similar left ventricular wall thickness, volume, and systolic and diastolic function. Older Trpa1-/- mice had significantly increased left ventricular internal diameter and volume and impaired systolic (lower left ventricular ejection fraction) and diastolic (higher E/A ratio and isovolumetric relaxation time) functions compared with older WT mice (P<0.05 or P<0.01). Importantly, older Trpa1-/- mice had enhanced cardiac fibrosis than older WT mice (P<0.05) while the two strains had similar degree of cardiac hypertrophy. Among the 84 fibrosis-related genes, Acta2, Inhbe, Ifng, and Ccl11 were significantly upregulated, while Timp3, Stat6, and Ilk were significantly downregulated in the heart of older Trpa1-/- mice compared with older WT mice. Taken together, we found that knocking out Trpa1 accelerated age-related myocardial fibrosis, ventricular dilation, and cardiac dysfunction. These findings suggest that TRPA1 may become a therapeutic target for preventing and/or treating cardiac fibrosis and heart failure with preserved ejection fraction in the elderly.

Activation of TRPV1 improves natriuresis and salt sensitivity in high-fat diet fed mice.

Western diet (WD) intake increases morbidity of obesity and salt-sensitive hypertension albeit mechanisms are largely unknown. We investigated the role of transient receptor potential vanilloid 1 (TRPV1) in WD intake-induced hypertension. TRPV1-/- and wild-type (WT) mice were fed a normal (CON) or Western diet (WD) for 16-18 weeks. Mean arterial pressure (MAP) after normal sodium glucose (NSG) loading with or without L-NAME (a NO synthase inhibitor) or N-oleoyldopamine (OLDA, a TRPV1agonist) was not different between the two strains on CON.WT or TRPV1-/- mice fed WD had increased MAP after NSG, with a greater magnitude in TRPV1-/- mice. OLDA decreased while L-NAME increased MAP in WT-WD but not in TRPV1-/--WD mice. The urinary nitrates plus nitrites excretion (UNOx), an indicator of renal NO production, was increased in both strains on CON after NSG. TRPV1 ablation with WD intake abolished NSG-induced increment in UNOx. OLDA further increased while L-NAME prevented NSG-induced increment in UNOx in WT-WD mice. Urinary sodium excretion was increased in both strains on CON and in WT-WD mice but not in TRPV1-/--WD mice after NSG. OLDA further increased while L-NAME prevented NSG-induced increases in sodium excretion in WT-WD but not in TRPV1-/--WD mice. Thus, TRPV1 ablation increases salt sensitivity during WD intake possibly via impaired renal NO production and sodium excretion. Activation of TRPV1 enhances renal NO production and sodium excretion, resulting in prevention of increased salt sensitivity during WD intake.

Protective effect of TRPV1 against renal fibrosis via inhibition of TGF-ß/Smad signaling in DOCA-salt hypertension.

To investigate the effects of the transient receptor potential vanilloid type 1 (TRPV1) channel on renal extracellular matrix (ECM) protein expression including collagen deposition and the transforming growth factor ß (TGF-ß)/Smad signaling pathway during salt-dependent hypertension, wild-type (WT) and TRPV1-null (TRPV1⁻/⁻) mutant mice were uninephrectomized and given deoxycorticosterone acetate (DOCA)-salt for 4 wks. TRPV1 gene ablation exaggerated DOCA-salt-induced impairment of renal function as evidenced by increased albumin excretion (µg/24 h) compared with WT mice (83.7 ± 7.1 versus 28.3 ± 4.8, P < 0.05), but had no apparent effect on mean arterial pressure (mmHg) as determined by radiotelemetry (141 ± 4 versus 138 ± 3, P > 0.05). Morphological analysis showed that DOCA-salt-induced glomerulosclerosis, tubular injury and macrophage infiltration (cells/mm²) were increased in TRPV1⁻/⁻ compared with WT mice (0.74 ± 0.08 versus 0.34 ± 0.04; 3.14 ± 0.26 versus 2.00 ± 0.31; 68 ± 5 versus 40 ± 4, P < 0.05). Immunostaining studies showed that DOCA-salt treatment decreased nephrin but increased collagen type I and IV as well as phosphorylated Smad2/3 staining in kidneys of TRPV1⁻/⁻ compared with WT mice. Hydroxyproline assay and Western blot showed that DOCA-salt treatment increased collagen content (µg/mg dry tissue) and fibronectin protein expression (%ß-actin arbitrary units) in the kidney of TRPV1⁻/⁻ compared with WT mice (26.7 ± 2.7 versus 17.4 ± 1.8; 0.93 ± 0.07 versus 0.65 ± 0.08, P < 0.05). Acceleration of renal ECM protein deposition in DOCA-salt-treated TRPV1⁻/⁻ mice was accompanied by increased TGF-ß1, as well as phosphorylation of Smad2/3 protein expression (%ß-actin arbitrary units) compared with DOCA-salt-treated WT mice (0.61 ± 0.07 versus 0.32 ± 0.05; 0.57 ± 0.07 versus 0.25 ± 0.05; 0.71 ± 0.08 versus 0.40 ± 0.06, P < 0.05). These results show that exaggerated renal functional and structural injuries are accompanied by increased production of ECM protein and activation of the TGF-ß/Smad2/3 signaling pathway. These data suggest that activation of TRPV1 attenuates the progression of renal fibrosis possibly via suppression of the TGF-ß and its downstream regulatory signaling pathway.

Enhanced salt sensitivity following shRNA silencing of neuronal TRPV1 in rat spinal cord.

AIM: To investigate the effects of selective knockdown of TRPV1 channels in the lower thoracic and upper lumbar segments of spinal cord, dorsal root ganglia (DRG) and mesenteric arteries on rat blood pressure responses to high salt intake. METHODS: TRPV1 short-hairpin RNA (shRNA) was delivered using intrathecal injection (6 µg · kg(-1) · d(-1), for 3 d). Levels of TRPV1 and tyrosine hydroxylase expression were determined by Western blot analysis. Systolic blood pressure and mean arterial pressure (MAP) were examined using tail-cuff and direct arterial measurement, respectively. RESULTS: In rats injected with control shRNA, high-salt diet (HS) caused higher systolic blood pressure compared with normal-salt diet (NS) (HS:149 ± 4 mmHg; NS:126 ± 2 mmHg, P<0.05). Intrathecal injection of TRPV1 shRNA significantly increased the systolic blood pressure in both HS rats and NS rats (HS:169 ± 3 mmHg; NS:139 ± 2 mmHg). The increases was greater in HS rats than in NS rats (HS: 13.9% ± 1.8%; NS: 9.8 ± 0.7, P<0.05). After TRPV1 shRNA treatment, TRPV1 expression in the dorsal horn and DRG of T8-L3 segments and in mesenteric arteries was knocked down to a greater extent in HS rats compared with NS rats. Blockade of α1-adrenoceptors abolished the TRPV1 shRNA-induced pressor effects. In rats injected with TRPV1 shRNA, level of tyrosine hydroxylase in mesenteric arteries was increased to a greater extent in HS rats compared with NS rats. CONCLUSION: Selective knockdown of TRPV1 expression in the lower thoracic and upper lumbar segments of spinal cord, DRG, and mesenteric arteries enhanced the prohypertensive effects of high salt intake, suggesting that TRPV1 channels in these sites protect against increased salt sensitivity, possibly via suppression of sympatho-excitatory responses.

Nanomechanical analysis of insulinoma cells after glucose and capsaicin stimulation using atomic force microscopy.

AIM: Glucose stimulates insulin secretion from pancreatic islet ß cells by altering ion channel activity and membrane potential in the ß cells. TRPV1 channel is expressed in the ß cells and capsaicin induces insulin secretion similarly to glucose. This study aims to investigate the biophysical properties of the ß cells upon stimulation of membrane channels using an atomic force microscopic (AFM) nanoindentation system. METHODS: ATCC insulinoma cell line was used. Cell stiffness, a marker of reorganization of cell membrane and cytoskeleton due to ion channel activation, was measured in real time using an integrated AFM nanoindentation system. Cell height that represented structural changes was simultaneously recorded along with cell stiffness. RESULTS: After administration of glucose (16, 20 and 40 mmol/L), the cell stiffness was markedly increased in a dose-dependent manner, whereas cell height was changed in an opposite way. Lower concentrations of capsaicin (1.67 × 10(-9) and 1.67 × 10(-8) mol/L) increased the cell stiffness without altering cell height. In contrast, higher concentrations of capsaicin (1.67 × 10(-6) and 1.67 × 10(-7) mol/L) had no effect on the cell physical properties. CONCLUSION: A unique bio-nanomechanical signature was identified for characterizing biophysical properties of insulinoma cells upon general or specific activation of membrane channels. This study may deepen our understanding of stimulus-secretion coupling of pancreatic islet cells that leads to insulin secretion.

Knockout of Trpa1 Exacerbates Renal Ischemia-Reperfusion Injury With Classical Activation of Macrophages.

BACKGROUND: Classically activated macrophages contribute to the development of renal ischemia-reperfusion injury (IRI). This study aimed to investigate the role of transient receptor potential ankyrin 1 (Trpa1), a regulator of macrophage activation, in IRI-induced acute kidney injury (AKI) by using the Trpa1 gene knockout (Trpa1-/-) mouse model. METHODS: Male 8-week-old Trpa1-/- mice and wild-type (WT) littermates were subjected to renal ischemia for 35 minutes by clamping bilateral renal pedicles under isoflurane anesthesia, and blood and tissue samples were collected 24 hours after reperfusion and analyzed with histological and molecular measurements. RESULTS: Following IRI, Trpa1-/- mice developed more deteriorated biochemical and morphological signs of AKI when comparing with WT mice. More classically activated M1 macrophages were found in the kidneys of Trpa1-/- mice comparing with WT mice after IRI, while the counts of alternatively activated M2 macrophages in the kidney were similar between the 2 strains after IRI. Furthermore, significantly higher expression levels of proinflammatory markers including interleukin-1 beta and tumor necrosis factor alpha were detected in the kidney of Trpa1-/- mice compared with WT mice after IRI. The levels of TRPA1 protein in the kidney of WT mice were also decreased after IRI. CONCLUSIONS: Our results show that ablation of Trpa1 exacerbates infiltration of classically activated macrophages, renal inflammation, and renal injury in mice after IRI. These findings suggest that activation of TRPA1 may protect against IRI-induced AKI via regulation of macrophage-mediated inflammatory pathway.

Ablation of TRPV1 Abolishes Salicylate-Induced Sympathetic Activity Suppression and Exacerbates Salicylate-Induced Renal Dysfunction in Diet-Induced Obesity.

Sodium salicylate (SA), a cyclooxygenase inhibitor, has been shown to increase insulin sensitivity and to suppress inflammation in obese patients and animal models. Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel expressed in afferent nerve fibers. Cyclooxygenase-derived prostaglandins are involved in the activation and sensitization of TRPV1. This study tested whether the metabolic and renal effects of SA were mediated by the TRPV1 channel. Wild-type (WT) and TRPV1-/- mice were fed a Western diet (WD) for 4 months and received SA infusion (120mg/kg/day) or vehicle for the last 4 weeks of WD feeding. SA treatment significantly increased blood pressure in WD-fed TRPV1-/- mice (p < 0.05) but not in WD-fed WT mice. Similarly, SA impaired renal blood flow in TRPV1-/- mice (p < 0.05) but not in WT mice. SA improved insulin and glucose tolerance in both WT and TRPV1-/- mice on WD (all p < 0.05). In addition, SA reduced renal p65 and urinary prostaglandin E2, prostaglandin F1α, and interleukin-6 in both WT and TRPV1-/- mice (all p < 0.05). SA decreased urine noradrenaline levels, increased afferent renal nerve activity, and improved baroreflex sensitivity in WT mice (all p < 0.05) but not in TRPV1-/- mice. Importantly, SA increased serum creatinine and urine kidney injury molecule-1 levels and decreased the glomerular filtration rate in obese WT mice (all p < 0.05), and these detrimental effects were significantly exacerbated in obese TRPV1-/- mice (all p < 0.05). Lastly, SA treatment increased urine albumin levels in TRPV1-/- mice (p < 0.05) but not in WT mice. Taken together, SA-elicited metabolic benefits and anti-inflammatory effects are independent of TRPV1, while SA-induced sympathetic suppression is dependent on TRPV1 channels. SA-induced renal dysfunction is dependent on intact TRPV1 channels. These findings suggest that SA needs to be cautiously used in patients with obesity or diabetes, as SA-induced renal dysfunction may be exacerbated due to impaired TRPV1 in obese and diabetic patients.

Relationship between blood pressure and kidney diseases in large randomized controlled trials: secondary analyses using SPRINT and ACCORD-BP trials.

Hypertension is a risk factor for acute kidney injury. In this study, we aimed to identify the optimal blood pressure (BP) targets for CKD and non-CKD patients. We analyzed the data of the Systolic Blood Pressure Intervention Trial (SPRINT) and the Action to Control Cardiovascular Risk in Diabetes Blood Pressure trial (ACCORD BP) to determine the nonlinear relationship between BP and renal disease development using the Generalized Additive Model (GAM). Optimal systolic BP/diastolic BP (SBP/DBP) with lowest renal risk were estimated using GAM. Logistic regression was employed to find odds ratios (ORs) of adverse renal outcomes by three BP groups (high/medium/low). Both study trials have demonstrated a "U"-shaped relationship between BP and renal outcomes. For non-CKD patients in SPRINT trial, risk of 30% reduction in eGFR among intensive group patients with DBP ≤ 70 mmHg was significantly higher than the group with DBP between 71 and 85 mmHg (OR = 2.31, 95% CI = 1.51-3.53). For non-CKD patients in ACCORD trial, risk of doubling of serum creatinine (SCr) or >20 mL/min decrease in eGFR among intensive group patients with DBP ≤ 70 mmHg was significantly higher than the group with DBP between 71 and 85 mmHg (OR = 1.49, 95% CI = 1.12-1.99). For CKD patients in SPRINT trial, there are no significant differences in renal outcomes by different SBP/DBP levels. Our analysis of both SPRINT and ACCORD datasets demonstrated that lower-than-optimal DBP may lead to poor renal outcomes in non-CKD patients. Healthcare providers should be cautious of too low DBP level in intensive BP management due to poor renal outcomes for non-CKD patients.

P2Y2 receptors mediate ATP-induced resensitization of TRPV1 expressed by kidney projecting sensory neurons.

The transient receptor potential vanilloid type 1 (TRPV1) channel is a ligand-gated cation channel expressed by sensory nerves. P2Y receptors are G protein-coupled receptors that are also expressed by TRPV1-positive sensory neurons. Therefore, we studied interactions between P2Y receptors and TRPV1 function on kidney projecting sensory neurons. Application of Fast Blue (FB) to nerves surrounding the renal artery retrogradely labeled neurons in dorsal root ganglia of rats. Whole cell recording was performed on FB-labeled neurons maintained in primary culture. Capsaicin was used to activate TRPV1. Four types of kidney projecting neurons were identified based on capsaicin responses: 1) desensitizing (35%), 2) nondesensitizing (29%), 3) silent (3%), and 4) insensitive (30%). Silent neurons responded to capsaicin only after ATP (100 microM) pretreatment. ATP reversed desensitization in desensitizing neurons. Insensitive neurons never responded to capsaicin. UTP, a P2Y purinoceptor 2 (P2Y(2))/P2Y(4) receptor agonist, reversed capsaicin-induced TRPV1 desensitization. 2-methyl-thio-ATP (2-Me-S-ATP), a P2Y(1) receptor agonist, did not change desensitization. MRS 2179 and pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), drugs that block P2Y(1) receptors, did not block ATP-induced resensitization of TRPV1. Suramin, a P2Y(2) receptor antagonist, blocked resensitization caused by UTP. Immunocytochemical studies showed that FB-labeled neurons coexpressed P2Y(2) receptors and TRPV1. We conclude that P2Y(2) receptor activation can maintain TRPV1 function perhaps during sustained episodes of activity of kidney projecting sensory neurons.

Effects of a high-salt diet on TRPV-1-dependent renal nerve activity in Dahl salt-sensitive rats.

OBJECTIVE: To test the hypothesis that transient receptor potential vanilloid type 1 channel (TRPV1)-mediated increases in afferent renal nerve activity (ARNA) and release of substance P (SP) and calcitonin gene-related peptide (CGRP) from the renal pelvis are suppressed in Dahl salt-sensitive (DS), but not -resistant (DR), rats fed a high-salt (HS) diet. METHODS AND RESULTS: Male DS and DR rats were given a HS or low-salt (LS) diet for 3 weeks. Perfusion of capsaicin (CAP, 10(-6)M), a selective TRPV1 agonist, into the left renal pelvis increased ipsilateral ARNA in all groups, but with a smaller magnitude in DS-HS compared to other groups. CAP increased contralateral urine flow in all groups except DS-HS rats. CAP-induced release of SP and CGRP from the renal pelvis was less in DS-HS compared to other groups. Western blot showed that TRPV1 expression in the kidney decreased while expression of neurokinin 1 receptors increased in DS-HS compared to other groups. CONCLUSION: TRPV1-mediated increases in ARNA and release of SP and CGRP in the renal pelvis are impaired in DS rats fed a HS diet, which can likely be attributed to suppressed TRPV1 expression in the kidney and contributes to increased salt sensitivity.

Protective Effects of TRPV1 Activation Against Cardiac Ischemia/ Reperfusion Injury is Blunted by Diet-Induced Obesity.

BACKGROUND: Activation of Transient Receptor Potential Vanilloid Subtype 1 (TRPV1) channels protects the heart from Ischemia/Reperfusion (I/R) injury through releasing Calcitonin Gene-Related Peptide (CGRP) and Substance P (SP). The current study aimed to study the cardioprotective effects of TRPV1 in obesity. METHODS: TRPV1 gene knockout (TRPV1-/-) and Wild-Type (WT) mice were Fed a High-Fat Diet (HFD) or a control diet or for 20 weeks, and then the hearts were collected for I/R injury ex vivo. The hearts were mounted on a Langendorff apparatus and subjected to ischemia (30 min) and reperfusion (40 min) after incubated with capsaicin (10 nmol/L), CGRP (0.1 µmol/L) and SP (0.1 µmol/L). Then, Coronary Flow (CF), left ventricular peak positive dP/dt (+dP/dt), Left Ventricular Developed Pressure (LVDP) and Left Ventricular End-Diastolic Pressure (LVEDP) were measured. RESULTS: HFD intake remarkably reduced CF, +dP/dt and LVDP and elevated LVEDP in both strains (P<0.05). Treatment with capsaicin decreased infarct size, increased CF, +dP/dt and LVDP, and decreased LVEDP in WT mice on control diet (P<0.05), but did not do so in other three groups. Treatment with CGRP and SP decreased infarct size in both strains fed with control diet (P<0.05). In contrast, not all the parameters of cardiac postischemic recovery in HFD-fed WT and TRPV1-/- mice were improved by CGRP and SP. CONCLUSION: These results suggest that HFD intake impairs cardiac postischemic recovery. HFDinduced impairment of recovery is alleviated by CGRP in both strains and by SP only in TRPV1-/- mice, indicating that the effects of CGRP and SP are differentially regulated during HFD intake.