Activation of TRPV1 by dietary capsaicin improves endothelium-dependent vasorelaxation and prevents hypertension

Abstract

Some plant-based diets lower the cardiometabolic risks and prevalence of hypertension. New evidence implies a role for the transient receptor potential vanilloid 1 (TRPV1) cation channel in the pathogenesis of cardiometabolic diseases. Little is known about impact of chronic TRPV1 activation on the regulation of vascular function and blood pressure. Here we report that chronic TRPV1 activation by dietary capsaicin increases the phosphorylation of protein kinase A (PKA) and eNOS and thus production of nitric oxide (NO) in endothelial cells, which is calcium dependent. TRPV1 activation by capsaicin enhances endothelium-dependent relaxation in wild-type mice, an effect absent in TRPV1-deficient mice. Long-term stimulation of TRPV1 can activate PKA, which contributes to increased eNOS phosphorylation, improves vasorelaxation, and lowers blood pressure in genetically hypertensive rats. We conclude that TRPV1 activation by dietary capsaicin improves endothelial function. TRPV1-mediated increase in NO production may represent a promising target for therapeutic intervention of hypertension.

Figure 1. Location and Functional Characterization of TRPV1 Channels in Arteries

(A and B) TRPV1 mRNA was detected by RT-PCR, and TRPV1 protein level was detected by immunoblotting in mesenteric arteries (MA) and cultured endothelial cells (ECs) from WT but not from TRPV1^−/− mice. M, marker. (C) Representative immunofluorescence images of TRPV1 in ECs (left panel, bar denotes 50 μm) and in mesenteric arteries (MA) (right panel, bar denotes 100 μm) from WT (upper panel) and TRPV1^−/− mice (lower panel). DAPI denotes visualizing nuclei. Coexpression of CD31 (red) with TRPV1 (green) is shown. (D) Representative tracings, with inset summary data showing capsaicin (CAP) stimulated increases of [Ca²⁺]_i in ECs; **p < 0.01 versus capsaicin 1 nM, ^##p < 0.01 versus capsaicin 0.1 μM. Data are means ± SEM (six separate experiments). (E) Representative tracings, with inset summary data showing the inhibitory effects of specific TRPV1 antagonist 5′-iodo-resiniferatoxin (iRTX), the intracellular Ca²⁺ chelator, BAPTA-AM and TRPV1 deficiency (TRPV1^−/−) on capsaicin-induced Ca²⁺ entry in cultured ECs. **p < 0.01 versus control. Data are means ± SEM (six experiments). (F) TRPV1 protein expression in mesenteric arteries (MA) from WT mice fed with normal diet (ND) and normal diet plus capsaicin (NC) for 6 months; *p < 0.05 versus ND. Data are means ± SEM (three to six experiments). (G) TRPV1 expression in mesenteric arteries from TRPV1 transgenic mice (TRPV1-tg) and WT littermates; *p < 0.05 versus WT. Data are means ± SEM (three to six experiments).

Figure 2. Activation of TRPV1 Increases Intracellular Calcium and Enhances eNOS Activity in the Vasculature

(A) Colocalization of eNOS and TRPV1 in mesenteric arteries from WT (upper panel) and TRPV1-deficient mice (TRPV1^−/−, lower panel), which were detected by immunofluorescence staining for eNOS (red) and TRPV1 (green). Scale bar denotes 100 μm. Photomicrographs are representative of three samples performed for each combination. (B and C) Immunoblottings showing the effect of capsaicin (1 μM) on the levels of p-eNOS and eNOS in cultured ECs from WT and from TRPV1^−/− mice. *p < 0.05 versus control. Data are means ± SEM. Each n = 3. (D and E) Immunoblottings showing the effect of dietary capsaicin (0.01%) to WT and TRPV1^−/− mice for 6 months on levels of p-eNOS and eNOS in mesenteric arteries (MA); *p < 0.05 versus ND. ND, normal diet; NC, normal diet plus capsaicin. The pooled data are means ± SEM. Each n = 3. (F) Levels of p-eNOS and eNOS by immunoblotting and summary data showing inhibition of capsaicin-induced increase of p-eNOS by specific TRPV1 antagonist 5′-iodo-RTX (iRTX), or the intracellular Ca²⁺ chelator BAPTA-AM, or EGTA in cultured ECs from WT mice; **p < 0.01 versus control, ^##p < 0.01 versus capsaicin group. CAP, capsaicin. Data are means ± SEM. Each n = 3.

Figure 3. TRPV1-Mediated NO Production Is Associated with Calcium Influx

(A and B) Representative pictures and summary data showing quantification of capsaicin-induced NO production in ECs using a dye 4,5-diaminofluorescein diacetate (DAF-2DA), which is converted into the fluorescent DAF-2T in the presence of NO. RTX, resiniferatoxin; iRTX, 5′-iodo-resiniferatoxin. *p < 0.05 versus control, ^#p < 0.05 versus capsaicin group. Scale bar denotes 100 μm. (C and D) Representative tracings and summary data showing the effects of iRTX, BAPTA-AM, and EGTA on capsaicin-induced NO production in cultured ECs. **p < 0.01 versus capsaicin group (CAP). (E and F) Representative tracings and summary data showing concentration-dependent effect of capsaicin-induced increase of NO production in freshly isolated mesenteric arteries from WT mice. *p < 0.05, **p < 0.01 versus capsaicin (CAP) 1 nM, ^#p < 0.05 versus CAP 0.1 μM. (G and H) Representative tracings and summary data showing the effects of L-NAME on capsaicin-induced NO production in mesenteric arteries from WT mice; **p < 0.01 compared with control group. (I and J) Representative tracings and summary data showing capsaicin-induced NO production in mesenteric arteries from mice with different TRPV1 genotypes. *p < 0.05, **p < 0.01 versus WT; ^##p < 0.01 versus TRPV1^−/− mice; ^ΔΔp < 0.01 versus TRPV1 heterozygote mice (TRPV1^+/−). Data are means ± SEM (three to six experiments).

Figure 4. Effects of TRPV1 Activation on PKA Phosphorylation and Activity

(A) The effect of TRPV1 activation on PKA activity in cultured ECs. CAP, capsaicin; EGTA, ethylene glycol tetraacetic acid; iRTX, 5′-iodo-RTX; *p < 0.05, **p < 0.01 versus control. Data are means ± SEM. Each n = 6. (B) The effect of TRPV1 activation on PKA phosphorylation in cultured ECs. CAP, capsaicin; **p < 0.01 versus control. Data are means ± SEM. Each n = 3. (C) The effect of TRPV1 activation on eNOS phosphorylation in cultured ECs. CAP, capsaicin; **p < 0.01 versus control. Data are means ± SEM. Each n = 3. (D) The effect of PKA inhibitor KT5720 on capsaicin-induced increase of NO production in cultured ECs. CAP, capsaicin; *p < 0.05 versus control; #p < 0.05 versus CAP. Data are means ± SEM. Each n = 3–6. Scale bar denotes 100 μm. (E) The effect of TRPV1 activation on PKA phosphorylation in primary cultured aortic ECs from WT mice. *p < 0.05 versus control. Data are means ± SEM. Each n = 3. (F) Lack of effect of TRPV1 activation on PKA phosphorylation in primary cultured aortic ECs from TRPV1^−/− mice. Data are means ± SEM. Each n = 3. (G) The effect of chronic TRPV1 activation on PKA phosphorylation in mesenteric arteries (MA) from WT mice. ND, normal diet; NC, capsaicin diet; *p < 0.05 versus ND. Data are means ± SEM. Each n = 3. (H) Lack of effect of chronic TRPV1 activation on PKA phosphorylation in mesenteric arteries (MA) from TRPV1-deficient mice. ND, normal diet; NC, capsaicin diet. Data are means ± SEM. Each n = 3. (I) Effect of PKA inhibitor KT5720 (2 μM) on capsaicin-induced relaxation in freshly isolated mesenteric arteries from WT mice; values are expressed as means ± SEM (four to eight arterial rings); *p < 0.05, **p < 0.01 versus control. (J) Effect of PKA inhibitor KT5720 (2 μM) on capsaicin-induced relaxation in freshly isolated mesenteric arteries from TRPV1^−/− mice. Data are means ± SEM (four to eight arterial rings).

Figure 5. Chronic Activation of TRPV1 Enhances Endothelium-Dependent Relaxation

(A) Effect of endothelium denudation on capsaicin-induced relaxation in freshly isolated mesenteric arteries from WT mice; *p < 0.05 versus control. PE, phenylephrine. (B) Effect of TRPV1 deficiency (TRPV1^−/−) on capsaicin-induced relaxation in mesenteric arteries; *p < 0.05 versus WT mice. (C and D) Acetylcholine- and nitroglycerin-induced relaxation in the presence or absence of L-NAME (100 μM) in isolated mesenteric arteries from WT mice on normal diet (ND) or capsaicin diet (NC); *p < 0.05. (E and F) Acetylcholine- and nitroglycerin-induced relaxation in the presence or absence of L-NAME (100 μM) in isolated mesenteric arteries from TRPV1 transgenic mice (TRPV1-tg) and their WT littermates; **p < 0.01. (G and H) Acetylcholine- and nitroglycerin-induced relaxation in the presence or absence of L-NAME (100 μM) in isolated mesenteric arteries from TRPV1-deficient mice (TRPV1^−/−) on normal diet (ND) or capsaicin diet (NC). Data are means ± SEM (four to eight arterial rings).

Figure 6. Role of Perivascular Sensory Nerves in TRPV1-Mediated Relaxation

(A) Representative tracings showing inhibitory effect of L-NAME and CGRP receptor antagonist CGRP 8-37 on capsaicin-induced relaxation in mouse mesenteric arteries. (B) Effect of L-NAME (100 μM) on capsaicin-induced relaxation in freshly isolated mesenteric arteries from C57BL/6J mice; **p < 0.01. (C) Effect of CGRP 8-37 (3 μM) on capsaicin-induced relaxation in freshly isolated mesenteric arteries from C57BL/6J mice; *p < 0.05. (D) Effects of L-NAME (100 μM) and CGRP 8-37 (3 μM) on capsaicin-induced relaxation in freshly isolated mesenteric arteries from C57BL/6J mice; **p < 0.01. Data are means ± SEM (four to six experiments).

Figure 7. Effects of TRPV1 Activation on Blood Pressure and Vascular Relaxation in Spontaneous Hypertensive Rats

(A) The plasma concentration of capsaicin in rats administered intragastrically with a single dose of capsaicin (15 mg/kg body weight). (B–D) Identification of capsaicin in plasma: mass spectrometry of capsaicin, chromatogram of extracted plasma sample from capsaicin-treated rats, and chromatogram of authentic capsaicin. (E) The time course of capsaicin-induced reduction in SBP in SHR fed with normal diet (ND) or normal diet plus capsaicin (NC) for 7 months. SBP was determined using tail cuff method. *p < 0.05 versus ND. (F and G) Capsaicin-induced reduction of SBP and diastolic blood pressure (DBP) in SHR. Blood pressure was determined for 24 hr using radiotelemetry in SHR fed with normal diet (ND) or normal diet plus capsaicin (NC) for 7 months. (H) Acetylcholine-induced relaxation in the presence or absence of L-NAME (100 μM) in isolated mesenteric arteries from SHR fed without (ND) or with capsaicin (NC) for 7 months. *p < 0.05 versus ND group. (I) Nitroglycerin-induced relaxation in isolated mesenteric arteries from SHR fed without (ND) or with capsaicin (NC) for 7 months. (J) TRPV1 protein expression in mesenteric artery from SHR fed without (ND) or with capsaicin (NC) for 7 months. *p < 0.05 compared with ND group. (K) Levels of p-PKA and PKA protein in mesenteric arteries from SHR fed without (ND) or with capsaicin (NC) for 7 months. *p < 0.05 versus ND group. (L) Levels of p-eNOS and eNOS protein in mesenteric arteries from SHR fed without (ND) or with capsaicin (NC) for 7 months. *p < 0.05 compared with ND group. (M) Increased plasma nitrate/nitrite levels in SHR treated without (ND) or with capsaicin (NC) for 7 months.*p < 0.05 versus ND group. Data are means ± SEM.