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Vitamin C (vitC) deficiency has been associated with an increased risk of cardiovascular disease; while several putative mechanistic links have been proposed, functional evidence supporting a causal relationship is scarce. In this study, we investigated how vitC deficiency affects coronary artery vasomotor function and the development of coronary atherosclerotic plaques in guinea pigs subjected to chronic dyslipidemia by a high-fat diet regime. Female Hartley guinea pigs were fed either a control (low-fat diet and sufficient vitC) (N = 8) or a high-fat diet with either sufficient (N = 8) or deficient (N = 10) vitC for 32 weeks. Guinea pigs subjected to the high-fat diet developed significant atherosclerotic plaques in their coronary arteries, with no quantitative effect of vitC deficiency. In isolated coronary arteries, vasomotor responses to potassium, carbachol, nitric oxide, or bradykinin were studied in a wire myograph. Carbachol, bradykinin, and nitric oxide mediated relaxation in the coronary arteries of the control group. While vasorelaxation to carbachol and nitric oxide was preserved in the two high-fat diet groups, bradykinin-induced vasorelaxation was abolished. Interestingly, bradykinin induced a significant contraction in coronary arteries from vitC-deficient guinea pigs (p < 0.05). The bradykinin-induced contraction was unaffected by L-NAME but significantly inhibited by both indomethacin and vitC, suggesting that, during vitC deficiency, increased release of arachidonic acid metabolites and vascular oxidative stress are involved in the constrictor effects mediated by bradykinin. In conclusion, the present study shows supporting evidence that poor vitC status negatively affects coronary artery function.

Oxidative stress is directly linked to non-alcoholic fatty liver disease (NAFLD) and the progression to steaotohepatitis (NASH). Thus, a beneficial role of antioxidants in delaying disease progression and/or accelerating recovery may be expected, as corroborated by recommendations of, e.g., vitamin E supplementation to patients. This study investigated the effect of vitamin C deficiency—often resulting from poor diets low in fruits and vegetables and high in fat—combined with/without a change to a low fat diet on NAFLD/NASH phenotype and hepatic transcriptome in the guinea pig NASH model. Vitamin C deficiency per se did not accelerate disease induction. How-ever, the results showed an effect of the diet change on the resolution of hepatic histopathological hallmarks (steatosis, inflammation, and ballooning) (p < 0.05 or less) and indicated a positive effect of a high vitamin C intake when combined with a low fat diet. Our data show that a diet change is important in NASH regression and suggest that a poor vitamin C status delays the reversion to-wards a healthy hepatic transcriptome and phenotype. In conclusion, the findings support a beneficial role of adequate vitamin C intake in the regression of NASH and may indicate that vitamin C supplementation in addition to lifestyle modifications could accelerate recovery in NASH patients with poor vitamin C status.

The glucagon-like peptide-1 receptor (GLP1R) is expressed in the renal vasculature and known to be downregulated under hypertensive conditions in rats and humans. However, little is known about the regulation in other types of renal pathology involving vascular changes. This study investigates the expression of the GLP1R in renal vasculature after glomerular injury in the nephrotoxic nephritis mouse model, high cholesterol, and atherosclerosis in the Ldlr-/- mouse on Western diet, and ex vivo injury in an organ culture model. The immunohistochemical signal of the GLP1R was significantly decreased in arteries from mice with nephrotoxic nephritis after 42 days compared to 7 days and saline control (P < 0.05). Histological evaluation of kidneys from Ldlr-/- mice on Western diet showed a decreased GLP1R specific immunohistochemical signal (P < 0.05). The dilatory response to liraglutide was decreased in Western diet fed Ldlr-/- mice compared to C57Bl/6J controls (P < 0.05). Organ culture significantly decreased the immunohistochemical signal of the GLP1R (P <0.05) and the expression of Glp1r mRNA (P < 0.005) compared to fresh. Organ cultured vessels showed vascular smooth muscle cell remodelling as Acta2 expression was decreased (P < 0.005) and Ednrb was increased (P < 0.05). In conclusion, nephrotoxic nephritis and hypercholesterolaemia led to decreased GLP1R specific immunohistochemical signal. Ex vivo vascular injury in the organ culture model leads to a decrease in expression of GLP1R expressionand contractile VSMC specific markers and increase in expression of dedifferentiation markers suggestive of an inverse relationship between phenotypic switch of the VSMC and the expression of the GLP1R; however, the causal relationship remains elusive.

The GLP-1 receptor (GLP-1R) in the kidney is expressed exclusively in vascular smooth muscle cells in arteries and arterioles. Downstream effects of the activation of the renal vascular GLP-1R are elusive but may involve regulation of the renin-angiotensin-aldosterone system (RAAS). The expression of Ren1 in the mouse renal vasculature was investigated by in situ hybridization after a single subcutaneous dose of liraglutide, semaglutide and after repeated injections of liraglutide. Single and repeated exposure to GLP-1R agonists induced expression of Ren1 in the renal vascular smooth muscle cell compartment compared with vehicle injected controls (p <.0001) for both semaglutide and liraglutide. The present data show a robust induction of Ren1 expression in the vascular smooth muscle cells of the kidney after single and repeated GLP-1R activation and this renin recruitment may be involved in the effects of GLP-1R agonist treatment on kidney disease.

Recent clinical intervention studies have shown that the GLP1 analogue liraglutide lowers cardiovascular risk, but the underlying mechanism has not yet been fully elucidated. This study investigated effects of liraglutide on endothelial function in the Ldlr-/- mouse model. Mice (n=12/group) were fed western diet or chow for 12 weeks followed by four weeks of treatment with liraglutide (1mg/kg/day) or vehicle subcutaneously. Weight loss, blood lipid content, plaque burden, vasomotor function of the aorta, and gene expression pattern in aorta and brachiocephalic artery were monitored. Liraglutide treatment significantly induced weight loss (p<0.0001), decreased blood triglycerides (p<0.0001), and total cholesterol (p<0.0001) in western diet-fed mice but did not decrease plaque burden. Liraglutide also improved endothelium-mediated dilation of the distal thoracis aorta (p= 0.0067), but it did not affect phenylephrine or sodium nitroprusside responses. Fluidigm analyses of 96 genes showed significantly altered expression of seven genes related to inflammation, vascular smooth muscle cells and extracellular matrix composition in liraglutide-treated animals. We conclude that treatment with liraglutide decreased endothelial dysfunction, and that this could be linked to decreased inflammation or regulation of vascular remodelling.

Although commonly associated with obesity, non-alcoholic fatty liver disease (NAFLD) is also present in the lean population representing a unique disease phenotype. Affecting 25% of the world's population, NAFLD is associated with increased mortality especially when progressed to non-alcoholic steatohepatitis (NASH). However, no approved pharmacological treatments exist. Current research focuses mainly on NASH associated with obesity, leaving the effectiveness of promising treatments in lean NASH virtually unknown. This study therefore aimed to evaluate the effect of liraglutide (glucagon-like peptide 1 analogue) and dietary intervention, alone and in combination, in guinea pigs with non-obese NASH. After 20 weeks of high-fat feeding (20% fat, 15% sucrose, 0.35% cholesterol), 40 female guinea pigs were block-randomized based on weight into four groups receiving one of four treatments for 4 weeks: continued high-fat diet (HF, control), high-fat diet and liraglutide treatment (HFL), chow diet (4% fat, 0% sucrose, 0% cholesterol; HFC) or chow diet and liraglutide treatment (HFCL). High-fat feeding induced NASH with severe fibrosis. Liraglutide decreased inflammation (p < 0.05) and hepatocyte ballooning (p < 0.05), while increasing hepatic α-tocopherol (p = 0.0154). Dietary intervention did not improve liver histopathology significantly, but decreased liver weight (p = 0.004), plasma total cholesterol (p = 0.0175), LDL-cholesterol (p = 0.0063), VLDL-cholesterol (p = 0.0034), hepatic cholesterol (p < 0.0001) and increased hepatic vitamin C (p = 0.0099). Combined liraglutide and dietary intervention induced a rapid weight loss, necessitating periodical liraglutide dose adjustment/discontinuation, limiting the strength of the findings from this group. Collectively, this pre-clinical study supports the beneficial effect of liraglutide on NASH and extends this notion to lean NASH.

The endothelin type B receptor (ETB or EDNRB) is highly plastic and is upregulated in smooth muscle cells (SMCs) by arterial injury and following organ culture in vitro. We hypothesized that this transcriptional plasticity may arise, in part, because EDNRB is controlled by a balance of transcriptional inputs from myocardin-related transcription factors (MRTFs) and ternary complex factors (TCFs). We found significant positive correlations between the TCFs ELK3 and FLI1 versus EDNRB in human arteries. The MRTF MKL2 also correlated with EDNRB. Overexpression of ELK3, FLI1, and MKL2 in human coronary artery SMCs promoted expression of EDNRB, and the effect of MKL2 was antagonized by myocardin (MYOCD), which also correlated negatively with EDNRB at the tissue level. Silencing of MKL2 reduced basal EDNRB expression, but depolymerization of actin using latrun-culin B (LatB) or overexpression of constitutively active cofilin, as well as treatment with the Rho-associated kinase (ROCK) inhibitor Y27632, increased EDNRB in a MEK/ERK-dependent fashion. Tran-script-specific primers indicated that the second EDNRB transcript (EDNRB_2) was targeted, but this promoter was largely unresponsive to LatB and was inhibited rather than stimulated by MKL2 and FLI1, suggesting distant control elements or an indirect effect. LatB also reduced expression of endothelin-1, but supplementation experiments argued that this was not the cause of EDNRB induction. EDNRB finally changed in parallel with ELK3 and FLI1 in rat and human carotid artery lesions. These studies implicate the actin cytoskeleton and ELK3, FLI1, and MKL2 in the transcriptional control of EDNRB and increase our understanding of the plasticity of this receptor.

OBJECTIVES: The purinergic system has not been investigated in detail following ischemia/reperfusion (I/R) injury in the heart. In the present study we focus on both release and response to extracellular adenosine triphosphate (ATP). Pannexin (Panx) channels have been shown to be involved in ATP release from myocytes and can activate P2X1 and P2Y2 receptors on the coronary artery.DESIGN: We applied a well characterized I/R model in rats, with 24 hours of reperfusion. Panx expression in the myocardial tissue was measured with quantitative polymerase chain reaction (qPCR) and flow cytometry. ATP release was detected in situ using luminescence and the vascular response to nucleotides determined in a wire myograph.RESULTS: Here we show that Panx expression is increased after experimental myocardial I/R, leading to an increase in extracellular ATP release, which could be inhibited by probenecid. Functional studies revealed that the P2Y2 receptor dependent contraction is reduced in the coronary artery after I/R, which might be a response to the increased ATP levels.CONCLUSION: We therefore, conclude that the regulation of the arterial purinergic system minimizes coronary contractions following ischemia.

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Vitamin C (vitC) deficiency is associated with increased cardiovascular disease risk, but its specific interplay with arteriolar function is unclear. This study investigates the effect of vitC deficiency in guinea pigs on plasma biopterin status and the vasomotor responses in coronary arteries exposed to vasoconstrictor/-dilator agents. Dunkin Hartley female guinea pigs (n = 32) were randomized to high (1500 mg/kg diet) or low (0 to 50 mg/kg diet) vitC for 10-12 weeks. At euthanasia, coronary artery segments were dissected and mounted in a wire-myograph. Vasomotor responses to potassium, carbachol, sodium nitroprusside (SNP), U46619, sarafotoxin 6c (S6c) and endothelin-1 (ET-1) were recorded. Plasma vitC and tetrahydrobiopterin were measured by HPLC. Plasma vitC status reflected the diets with deficient animals displaying reduced tetrahydrobiopterin. Vasoconstrictor responses to carbachol were significantly decreased in vitC deficient coronary arteries independent of their general vasoconstrictor/vasodilator capacity (p < 0.001). Moreover, in vitC deficient animals, carbachol-induced vasodilator responses correlated with coronary artery diameter (p < 0.001). Inhibition of cyclooxygenases with indomethacin increased carbachol-induced vasoconstriction, suggesting an augmented carbachol-induced release of vasodilator prostanoids. Atropine abolished carbachol-induced vasomotion, supporting a specific muscarinic receptor effect. Arterial responses to SNP, potassium, S6c, U46619 and ET-1 were unaffected by vitC status. The study shows that vitC deficiency decreases tetrahydrobiopterin concentrations and muscarinic receptor mediated contraction in coronary arteries. This attenuated vasoconstrictor response may be linked to altered production of vasoactive arachidonic acid metabolites and reduced muscarinic receptor expression/signaling.

Background: Coronary artery remodelling and vasospasm is a complication of acute myocardial ischemia and reperfusion. The underlying mechanisms are complex, but the vasoconstrictor peptide endothelin-1 is suggested to have an important role. This study aimed to determine whether the expression of endothelin-1 and its receptors are regulated in the myocardium and in coronary arteries after experimental ischemia-reperfusion. Furthermore, we evaluated whether treatment with a specific MEK1/2 inhibitor, U0126, modified the expression and function of these proteins. Methods and findings: Sprague-Dawley rats were randomly divided into three groups: sham-operated, ischemiareperfusion with vehicle treatment and ischemia-reperfusion with U0126 treatment. Ischemia was induced by ligating the left anterior descending coronary artery for 30 minutes followed by reperfusion. U0126 was administered before ischemia and repeated 6 hours after start of reperfusion. The contractile properties of isolated coronary arteries to endothelin-1 and sarafotoxin 6c were evaluated using wire-myography. The gene expression of endothelin-1 and endothelin receptors were measured using qPCR. Distribution and localization of proteins (pERK1/2, prepro-endothelin-1, endothelin-1, and endothelin ETA and ETB receptors) were analysed by Western blot and immunohistochemistry. We found that pERK1/2 was significantly augmented in the ischemic area 3 hours after ischemia-reperfusion; this correlated with increased ETB receptor and ET-1 gene expressions in ischemic myocardium and in coronary arteries. ETB receptor-mediated vasoconstriction was observed to be increased in coronary arteries 24 hours after ischemia-reperfusion. Treatment with U0126 reduced pERK1/2, expression of ET-1 and ETB receptor, and ETB receptor-mediated vasoconstriction. Conclusions: These findings suggest that the MEK-ERK1/2 signaling pathway is important for regulating

Cerebral ischaemia results in enhanced endothelin B (ETB ) receptor-mediated contraction and receptor protein expression in the affected cerebrovascular smooth muscle cells (SMC). Organ culture of cerebral arteries is a method to induce similar alterations in ETB receptor expression. We hypothesize that rapid and sustained reduction in wall tension/stretch is a possible trigger mechanism for this vascular remodelling. Isolated rat middle cerebral artery (MCA) segments were incubated in a wire-myograph with or without mechanical stretch, prior to assessment of their contractile response to the selective ETB receptor agonist sarafotoxin 6c. The involvement of extracellular regulated kinase (ERK) 1/2 and focal adhesion kinase (FAK) were studied by their specific inhibitors U0126 and PF-228, respectively. Compared to their stretched counterparts, un-stretched MCA segments showed a significantly increased ETB receptor-mediated contractile response following 12 hr of incubation, which was attenuated by either U0126 or PF-228. The functionally increased ETB -mediated contractility could be attributed to two different mechanisms: 1) a difference in ETB receptor localization from primarily endothelial expression to SMC expression and 2) an increased calcium sensitivity of the SMCs due to an increased expression of the calcium channel transient receptor potential canonical 1. Collectively, our results present a possible mechanism linking lack of vessel wall stretch/tension to changes in ETB receptor-mediated contractility via triggering of an early mechanosensitive signalling pathway involving ERK1/2 and FAK signalling. A mechanism likely to be an initiating factor for the increased ETB receptor-mediated contractility found after cerebral ischaemia. This article is protected by copyright. All rights reserved.

Endothelins act via two receptor subtypes, endothelin receptor type A (ETA ) and type B (ETB ). Under physiological conditions in coronary arteries ETA receptors expressed in smooth muscle cells mediate vasoconstriction whereas ETB receptors mainly found in endothelial cells mediate vasorelaxation. However, under pathophysiological conditions ETB receptors may also be expressed in vascular smooth muscle cells mediating vasoconstriction. We aimed to investigate whether vasoconstrictor ETB receptors are upregulated in coronary arteries after experimental myocardial ischemia in rats.