Impaired capsaicin-induced relaxation in diabetic mesenteric arteries

TRPV1: A novel target for the therapy of diabetes and diabetic complications

BACKGROUND

Diabetes mellitus is a chronic metabolic disease characterized by abnormally elevated blood glucose levels. Type II diabetes accounts for approximately 90% of all cases. Several drugs are available for hyperglycemia treatment. However, the current therapies for managing high blood glucose do not prevent or reverse the disease progression, which may result in complications and adverse effects, including diabetic neuropathy, retinopathy, and nephropathy. Hence, developing safer and more effective methods for lowering blood glucose levels is imperative. Transient receptor potential vanilloid-1 (TRPV1) is a significant member of the transient receptor potential family. It is present in numerous body tissues and organs and performs vital physiological functions.

PURPOSE

This review aimed to develop new targeted TRPV1 hypoglycemic drugs by systematically summarizing the mechanism of action of the TRPV1-based signaling pathway in preventing and treating diabetes and its complications.

METHODS

Literature searches were performed in the PubMed, Web of Science, Google Scholar, Medline, and Scopus databases for 10 years from 2013 to 2023. The search terms included "diabetes," "TRPV1," "diabetic complications," and "capsaicin."

RESULTS

TRPV1 is an essential potential target for treating diabetes mellitus and its complications. It reduces hepatic glucose production and food intake and promotes thermogenesis, metabolism, and insulin secretion. Activation of TRPV1 ameliorates diabetic nephropathy, retinopathy, myocardial infarction, vascular endothelial dysfunction, gastroparesis, and bladder dysfunction. Suppression of TRPV1 improves diabetes-related osteoporosis. However, the therapeutic effects of activating or suppressing TRPV1 may vary when treating diabetic neuropathy and periodontitis.

CONCLUSION

This review demonstrates that TRPV1 is a potential therapeutic target for diabetes and its complications. Additionally, it provides a theoretical basis for developing new hypoglycemic drugs that target TRPV1.

Does sex influence near-infrared spectroscopy-derived indicators of microvascular reactivity and the response to acute dietary capsaicin

Endothelial dysfunction is associated with cardiovascular disease development, nitric oxide (NO) deficiencies, and may be limb or sex-specific. Prior in vitro work indicated that the transient receptor potential vanilloid channel-1 (TRPV₁) is expressed in human arteries and the TRPV₁ agonist capsaicin alters vasodilation in an endothelium-dependent manner; however, it is unknown if this translates in vivo or is limb or sex-dependent. Therefore, we sought to determine if there was limb or sex-specificity in the effect of capsaicin on microvascular function using near-infrared spectroscopy (NIRS)-derived tissue oxygen saturation (StO₂) reperfusion slope. In a blinded placebo-controlled crossover design, 45 young males (M: n = 25) and females (F: n = 20), the reperfusion slopes of the forearm and quadriceps were assessed, and a urine sample obtained to assay for nitrate/nitrite (NOx) concentrations and antioxidant capacity after acutely ingesting placebo or capsaicin. Under placebo, females had greater reperfusion rates in both the forearm (M: 0.44 ± 0.24 vs. F: 0.98 ± 0.46 %/sec; p = 0.002, d = -1.50) and quadricep (M: 0.86 ± 0.31 vs. F: 1.17 ± 0.43 %/sec; p = 0.010, d = -0.85). Capsaicin decreased microvascular responsiveness in the forearm of females (placebo: 0.98 ± 0.45 vs. capsaicin: 0.84 ± 0.45 %/sec) as compared to males (placebo: 0.45 ± 0.24 vs. capsaicin: 0.38 ± 0.16 %/sec, interaction p < 0.001, η² = 0.475). There was a sex*treatment interaction for NOx concentrations, where males increased (placebo: 21.13 ± 12.83 vs. capsaicin: 23.82 ± 13.34 μM), while females decreased (placebo: 22.78 ± 14.40 vs. capsaicin: 14.43 ± 10.01 μM; p = 0.037, η² = 0.042). Using NIRS to assess microvascular function, there is apparent limb and sex-specificity, and, for the first-time, document that acute oral capsaicin alters reperfusion slope in a sexually divergent manner.

Capsaicin Alleviates Vascular Endothelial Dysfunction and Cardiomyopathy via TRPV1/eNOS Pathway in Diabetic Rats

Background

Endothelial dysfunction and cardiomyopathy are considered to be important vascular complications associated with diabetes. This study was designed to investigate whether capsaicin (CAP), a selective TRPV1 agonist, could prevent diabetes-induced endothelial dysfunction and cardiomyopathy.

Methods

Male Sprague Dawley rats aged 8 weeks were injected intraperitoneally with streptozotocin (STZ, 50 mg/kg) to establish the diabetes model. The diabetic rats were randomly divided into the untreated diabetes group (DM, 10/group) and diabetes plus CAP treatment group (DM+CAP, 10/group); meanwhile, the nondiabetic healthy rats were used as normal controls (10/group). DM+CAP group were treated with CAP by gavage for 8 weeks. The cultured mouse vascular endothelial cells were exposed to different concentrations of glucose in the presence or absence of CAP treatment. The TRPV1 inhibitor capsazepine (CPZ) and eNOS inhibitor L-NAME were used in vivo and in vitro experiment.

Results

CAP treatment significantly decreased the serum total cholesterol (TC) and total triglyceride (TG) and ameliorated the pathogenesis and fibrosis in the heart, while did not significantly improve plasma glucose level and the body weights of diabetic rats. In addition, CAP enhanced the expression of TRPV1 and eNOS in the heart and normalized the vascular permeability under diabetic state. Similarly, CAP treatment also increased nitric oxide and reduced reactive oxygen species. The same results were observed in cultured mouse vascular endothelial cells by CAP treatment. These beneficial effects of CAP were abolished by either CPZ or L-NAME.

Conclusions

CAP might protect against hyperglycemia-induced endothelial dysfunction and diabetic cardiomyopathy through TRPV1/eNOS pathway.

Neuropeptides, Inflammation, Biofilms, and diabetic Foot Ulcers

A diabetic foot ulcer (DFU) is a serious complication in patients with diabetes mellitus (DM). A DFU is the most common cause of non-traumatic limb amputation, and patients with DFUs have increased mortality rates within 5 years after amputation. DFUs also increase the risk of cardiovascular and cerebrovascular diseases; therefore, with the increasing incidence and prevalence of diabetic foot wounds, DFUs are gradually becoming a major public health problem. The pathophysiology of DFUs is complicated and remains unclear. In recent years, many studies have demonstrated that the pathophysiology of DFUs is especially associated with neuropeptides, inflammation, and biofilms. Neuropeptides, especially substance P (SP) and calcitonin gene-related peptide (CGRP), play an important role in wound healing. SP and CGRP accelerate the healing of cutaneous wounds by promoting neovascularization, inhibiting the release of certain proinflammatory chemokines, regulating macrophage polarization, and so on. However, the expression of SP and CGRP was downregulated in DM and DFUs. DFUs are characterized by a sustained inflammatory phase. Immune cells such as neutrophils and macrophages are involved in the sustained inflammatory phase in DFUs by extracellular traps (NETs) and dysregulated macrophage polarization, which delays wound healing. Furthermore, DFUs are at increased risk of biofilm formation. Biofilms disturb wound healing by inducing a chronic inflammatory response, inhibiting macrophage phagocytosis and keratinocyte proliferation migration, and transferring antimicrobial resistance genes. To understand the relationships among neuropeptides, inflammation, biofilms, and DFUs, this review highlights the recent scientific advances that provide possible pathophysiological insights into the delayed healing of DFUs.

Vascular Dysfunction in Diabetes and Obesity: Focus on TRP Channels

Transient receptor potential (TRP) superfamily consists of a diverse group of non-selective cation channels that has a wide tissue distribution and is involved in many physiological processes including sensory perception, secretion of hormones, vasoconstriction/vasorelaxation, and cell cycle modulation. In the blood vessels, TRP channels are present in endothelial cells, vascular smooth muscle cells, perivascular adipose tissue (PVAT) and perivascular sensory nerves, and these channels have been implicated in the regulation of vascular tone, vascular cell proliferation, vascular wall permeability and angiogenesis. Additionally, dysfunction of TRP channels is associated with cardiometabolic diseases, such as diabetes and obesity. Unfortunately, the prevalence of diabetes and obesity is rising worldwide, becoming an important public health problems. These conditions have been associated, highlighting that obesity is a risk factor for type 2 diabetes. As well, both cardiometabolic diseases have been linked to a common disorder, vascular dysfunction. In this review, we briefly consider general aspects of TRP channels, and we focus the attention on TRPC (canonical or classical), TRPV (vanilloid), TRPM (melastatin), and TRPML (mucolipin), which were shown to be involved in vascular alterations of diabetes and obesity or are potentially linked to vascular dysfunction. Therefore, elucidation of the functional and molecular mechanisms underlying the role of TRP channels in vascular dysfunction in diabetes and obesity is important for the prevention of vascular complications and end-organ damage, providing a further therapeutic target in the treatment of these metabolic diseases.

Dietary capsaicin-mediated attenuation of hypertension in a rat model of renovascular hypertension

Background: Capsaicin, a pungent component of chili pepper, has been reported to decrease blood pressure (BP) and to cause vasorelaxation via nitric oxide (NO) production. However, it is still unclear how dietary capsaicin effects on renovascular hypertension. To examine this, we observed the effects of dietary capsaicin on BP in 2-kidney, 1-clip renovascular hypertension (2K1C) rats, and investigated the participation of NO in the mechanism.Methods: Rats with 2K1C or sham-operated rats (SHAM) were treated with 0.006% capsaicin diet (CAP) or control diet (CTL) for 6 weeks. Systolic BP (SBP) was measured by tail-cuff method once a week. In the end, mean arterial BP (MAP) was measured in the rats under anesthesia. These observations were performed also in the rats taking a NO synthase (NOS) inhibitor (LN). After rats were euthanized, thoracic aortas were collected and used for western blot analyses to evaluate the phosphorylated ratio of endothelial NOS (eNOS), protein kinase A (PKA) and B (Akt), in order to explore a mechanism of the effects on BP by dietary capsaicin.Results: SBP and MAP in 2K1C rats were significantly higher than in SHAM rats when fed CTL, but not when fed CAP. Those in 2K1C-CAP rats were significantly lower than in 2K1C-CTL rats. LN suppressed the effect of dietary capsaicin. The ratios of phosphorylated (p-) eNOS/eNOS and p-Akt/Akt, but not p-PKA/PKA, were significantly increased in rats fed CAP compared with rats fed CTL.Conclusion: Dietary capsaicin may alleviate 2K1C renovascular hypertension, probably via enhancing phosphorylation of Akt and eNOS.Abbreviations: 2K1C: 2-kidney, 1-clip hypertension model; Akt: protein kinase B; Ang II: angiotensin II; ANOVA: measures analysis of variance; BP: blood pressure; EC: endothelial cell; eNOS: endothelial nitric oxide synthase; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; L-NAME, LN: Nω-Nitro-L-arginine methyl ester hydrochloride; MA: mesenteric arteries; MAP: mean arterial blood pressure; NO: nitric oxide; PKA: protein kinase A; PVDF: polyvinylidene difluoride; SBP: Systolic blood pressure; SHR: spontaneously hypertensive rats; SN: sympathetic nervous; TRPV1: transient receptor potential vanilloid type 1; WKY: Wistar Kyoto rats.

Role of TRP Channels in Dinoflagellate Mechanotransduction

Transient receptor potential (TRP) ion channels are common components of mechanosensing pathways, mainly described in mammals and other multicellular organisms. To gain insight into the evolutionary origins of eukaryotic mechanosensory proteins, we investigated the involvement of TRP channels in mechanosensing in a unicellular eukaryotic protist, the dinoflagellate Lingulodinium polyedra. BLASTP analysis of the protein sequences predicted from the L. polyedra transcriptome revealed six sequences with high similarity to human TRPM2, TRPM8, TRPML2, TRPP1, and TRPP2; and characteristic TRP domains were identified in all sequences. In a phylogenetic tree including all mammalian TRP subfamilies and TRP channel sequences from unicellular and multicellular organisms, the L. polyedra sequences grouped with the TRPM, TPPML, and TRPP clades. In pharmacological experiments, we used the intrinsic bioluminescence of L. polyedra as a reporter of mechanoresponsivity. Capsaicin and RN1734, agonists of mammalian TRPV, and arachidonic acid, an agonist of mammalian TRPV, TRPA, TRPM, and Drosophila TRP, all stimulated bioluminescence in L. polyedra. Mechanical stimulation of bioluminescence, but not capsaicin-stimulated bioluminescence, was inhibited by gadolinium (Gd³⁺), a general inhibitor of mechanosensitive ion channels, and the phospholipase C (PLC) inhibitor U73122. These pharmacological results are consistent with the involvement of TRP-like channels in mechanosensing by L. polyedra. The TRP channels do not appear to be mechanoreceptors but rather are components of the mechanotransduction signaling pathway and may be activated via a PLC-dependent mechanism. The presence and function of TRP channels in a dinoflagellate emphasize the evolutionary conservation of both the channel structures and their functions.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Renoprotection: focus on TRPV1, TRPV4, TRPC6 and TRPM2

Members of the transient receptor potential (TRP) cation channel receptor family have unique sites of regulatory function in the kidney which enables them to promote regional vasodilatation and controlled Ca²⁺ influx into podocytes and tubular cells. Activated TRP vanilloid 1 receptor channels (TRPV1) have been found to elicit renoprotection in rodent models of acute kidney injury following ischaemia/reperfusion. Transient receptor potential cation channel, subfamily C, member 6 (TRPC6) in podocytes is involved in chronic proteinuric kidney disease, particularly in focal segmental glomerulosclerosis (FSGS). TRP vanilloid 4 receptor channels (TRPV4) are highly expressed in the kidney, where they induce Ca²⁺ influx into endothelial and tubular cells. TRP melastatin (TRPM2) non-selective cation channels are expressed in the cytoplasm and intracellular organelles, where their inhibition ameliorates ischaemic renal pathology. Although some of their basic properties have been recently identified, the renovascular role of TRPV1, TRPV4, TRPC6 and TRPM2 channels in disease states such as obesity, hypertension and diabetes is largely unknown. In this review, we discuss recent evidence for TRPV1, TRPV4, TRPC6 and TRPM2 serving as potential targets for acute and chronic renoprotection in chronic vascular and metabolic disease.

Dietary Capsaicin Protects Cardiometabolic Organs from Dysfunction

Chili peppers have a long history of use for flavoring, coloring, and preserving food, as well as for medical purposes. The increased use of chili peppers in food is very popular worldwide. Capsaicin is the major pungent bioactivator in chili peppers. The beneficial effects of capsaicin on cardiovascular function and metabolic regulation have been validated in experimental and population studies. The receptor for capsaicin is called the transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is ubiquitously distributed in the brain, sensory nerves, dorsal root ganglia, bladder, gut, and blood vessels. Activation of TRPV1 leads to increased intracellular calcium signaling and, subsequently, various physiological effects. TRPV1 is well known for its prominent roles in inflammation, oxidation stress, and pain sensation. Recently, TRPV1 was found to play critical roles in cardiovascular function and metabolic homeostasis. Experimental studies demonstrated that activation of TRPV1 by capsaicin could ameliorate obesity, diabetes, and hypertension. Additionally, TRPV1 activation preserved the function of cardiometabolic organs. Furthermore, population studies also confirmed the beneficial effects of capsaicin on human health. The habitual consumption of spicy foods was inversely associated with both total and certain causes of specific mortality after adjustment for other known or potential risk factors. The enjoyment of spicy flavors in food was associated with a lower prevalence of obesity, type 2 diabetes, and cardiovascular diseases. These results suggest that capsaicin and TRPV1 may be potential targets for the management of cardiometabolic vascular diseases and their related target organs dysfunction.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.