Hope D. Anderson

Resveratrol prevents the development of pathological cardiac hypertrophy and contractile dysfunction in the SHR without lowering blood pressure.

BACKGROUND Cardiac hypertrophy is a compensatory enlargement of the heart in response to stress such as hypertension. It is beneficial in reducing stress placed on the heart. However, when the stress is of a chronic nature, it becomes pathological and leads to cardiac dysfunction and heart failure. Current treatments for hypertension and heart failure have proven beneficial but are not highly specific and associated with side effects. Accordingly, there is an important need for alternative strategies to provide safe and effective treatment. METHODS Ten-week-old male spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats were treated with resveratrol (2.5 mg/kg/day) for a period of 10 weeks. Systolic blood pressure, and cardiac structure and function were measured in all groups at different time points of resveratrol treatment. Oxidative stress was also determined in all groups after 10 weeks of resveratrol treatment. RESULTS SHRs were characterized with high blood pressure and concentric hypertrophy from 15 weeks of age. Cardiac functional abnormalities were also evident in SHR from 15 weeks onwards. Resveratrol treatment significantly prevented the development of concentric hypertrophy, and systolic and diastolic dysfunction in SHR without lowering blood pressure. Resveratrol also significantly reduced the oxidative stress levels of cardiac tissue in SHR. CONCLUSIONS Resveratrol treatment was beneficial in preventing the development of concentric hypertrophy and cardiac dysfunction in SHR. The cardioprotective effect of resveratrol in SHR may be partially mediated by a reduction in oxidative stress. Thus, resveratrol may have potential in preventing cardiac impairment in patients with essential hypertension.

Astrocyte-induced cortical vasodilation is mediated by D-serine and endothelial nitric oxide synthase

Astrocytes play a critical role in neurovascular coupling by providing a physical linkage from synapses to arterioles and releasing vaso-active gliotransmitters. We identified a gliotransmitter pathway by which astrocytes influence arteriole lumen diameter. Astrocytes synthesize and release NMDA receptor coagonist, D-serine, in response to neurotransmitter input. Mouse cortical slice astrocyte activation by metabotropic glutamate receptors or photolysis of caged Ca2+ produced dilation of penetrating arterioles in a manner attenuated by scavenging D-serine with D-amino acid oxidase, deleting the enzyme responsible for D-serine synthesis (serine racemase) or blocking NMDA receptor glycine coagonist sites with 5,7-dichlorokynurenic acid. We also found that dilatory responses were dramatically reduced by inhibition or elimination of endothelial nitric oxide synthase and that the vasodilatory effect of endothelial nitric oxide synthase is likely mediated by suppressing levels of the vasoconstrictor arachidonic acid metabolite, 20-hydroxy arachidonic acid. Our results provide evidence that D-serine coactivation of NMDA receptors and endothelial nitric oxide synthase is involved in astrocyte-mediated neurovascular coupling.

Resveratrol and Small Artery Compliance and Remodeling in the Spontaneously Hypertensive Rat

BACKGROUND Small arteries from the spontaneously hypertensive rat (SHR) exhibit abnormal stiffness and geometry. This study investigated the effects of resveratrol, a polyphenol found in foods such as red grapes, on small arteries in SHR. METHODS Wistar-Kyoto (WKY) rats and SHR were treated with resveratrol (2.5 mg/kg/day) for 10 weeks. Mesenteric small artery segments (third-order branches) were mounted in a pressure myograph, and vascular geometry and mechanical properties were calculated from lumen and media dimensions measured at incremental intraluminal pressures. Systolic blood pressure was measured by tail-cuff plethysmography. RESULTS Increased compliance and reduced wall component stiffness were observed in SHR arteries vs. WKY arteries. Though resveratrol did not prevent lowering of wall component stiffness, it did attenuate, at least in part, the increased compliance of SHR arteries. In contrast, resveratrol increased compliance and reduced wall component stiffness in WKY arteries. SHR arteries exhibited remodeling that consisted of narrowed lumens, thickened media widths, and augmented media-to-lumen ratios. Resveratrol partially attenuated the remodeling process and also abolished exaggerated ERK signaling and expression of proliferating cell nuclear antigen (a marker of proliferation) in SHR arteries. The latter effects might be related to the ability of resveratrol to alleviate oxidative stress in SHR and enhance protein kinase G (PKG) activity. Elevated blood pressure in 20-week-old SHR was unaffected by resveratrol. CONCLUSIONS The ability of resveratrol to limit the increase in compliance of SHR arteries is likely related to inhibitory effects on remodeling and pro-growth ERK signaling rather than blood pressure or arterial wall component stiffness.

Resveratrol prevents norepinephrine induced hypertrophy in adult rat cardiomyocytes, by activating NO-AMPK pathway

Increased adrenergic drive is a major factor influencing the development of pathological cardiac hypertrophy, a stage which precedes overt heart failure. We examined the effect of resveratrol, a polyphenol (found predominantly in grapes), in preventing norepinephrine induced hypertrophy of adult cardiomyocyte, and the role of nitric oxide (NO) and adenosine monophosphate kinase (AMPK) in the effects of resveratrol. Cardiomyocytes isolated from adult rats were pretreated, or not, with resveratrol and then exposed to norepinephrine for 24h. In other experiments cardiomyocytes were also treated with different pharmacological inhibitors of NO synthase, AMPK and sirtuin for elucidating the signaling pathways underlying the effect of resveratrol. In order to validate the role of these signaling molecules in the in vivo settings, we also examined hearts from resveratrol treated spontaneously hypertensive rats (SHR), a genetic model of essential hypertension. Cardiomyocyte hypertrophy was determined by morphometry and (3)H-phenylalanine incorporation assay. NO levels and AMPK activity were measured using a specific assay kit and western blot analysis respectively. In vitro, resveratrol prevented the norepinephrine-induced increase in cardiomyocytes size and protein synthesis. Pharmacological inhibition of NO-AMPK signaling abolished the anti-hypertrophic action of resveratrol. Consistent with the in vitro findings, the anti-hypertrophic effect of resveratrol in the SHR model was associated with increases in NO and AMPK activity. This study demonstrates that NO-AMPK signaling is linked to the anti-hypertrophic effect of resveratrol in adult cardiomyocytes in vitro, and in the SHR model in vivo.

Suppression of Cardiac Myocyte Hypertrophy by Conjugated Linoleic Acid ROLE OF PEROXISOME PROLIFERATOR-ACTIVATED RECEPTORS α AND γ

Conjugated linoleic acid (CLA) refers to a naturally occurring mixture of positional and geometric isomers of linoleic acid. Evidence suggests that CLA is a dietary constituent and nutraceutical with anti-cancer, insulin-sensitizing, immunomodulatory, weight-partitioning, and cardioprotective properties. The aim of this study was to evaluate the effects of intervention with CLA on cardiac hypertrophy. In vitro, CLA prevented indicators of cardiomyocyte hypertrophy elicited by endothelin-1, including cell size augmentation, protein synthesis, and fetal gene activation. Similar anti-hypertrophic effects of CLA were observed in hypertrophy induced by angiotensin II, fibroblast growth factor, and mechanical strain. CLA may inhibit hypertrophy through activation of peroxisome proliferator-activated receptors (PPARs). CLA stimulated PPAR activity in cardiomyocytes, and the anti-hypertrophic effects of CLA were blocked by genetic and pharmacological inhibitors of PPAR isoforms α and γ. CLA may disrupt hypertrophic signaling by stimulating diacylglycerol kinase ζ, which decreases availability of diacylglycerol and thereby inhibits the protein kinase Cϵ pathway. In vivo, dietary CLA supplementation significantly reduced blood pressure and cardiac hypertrophy in spontaneously hypertensive heart failure rats. These data suggest that dietary supplementation with CLA may be a viable strategy to prevent pathological cardiac hypertrophy, a major risk factor for heart failure.

Insulin resistance—associated cardiovascular disease: potential benefits of conjugated linoleic acid

Type 2 diabetes and associated cardiovascular disease have reached global epidemic proportions. Recent data from the World Health Organization Multinational Study of Vascular Disease in Diabetes indicate that cardiovascular disease is the leading cause of mortality (52% of deaths) in individuals with type 2 diabetes. Although insulin resistance plays a critical role in the pathogenesis of type 2 diabetes-related cardiovascular disease, other related risk factors often cluster in a single patient; the combination of insulin resistance and these risk factors is known as the metabolic syndrome. According to the World Health Organization definition, this constellation of risk factors includes hypertension, elevated plasma triacylglycerol, reduced HDL cholesterol, central obesity, and microalbuminuria. The Multiple Risk Factor Intervention Trial showed that, although diabetes or insulin resistance is an independent risk factor for cardiovascular disease mortality, these other components of the metabolic syndrome confer additive risk. Thus, to effectively address cardiovascular disease in persons with diabetes, intervention would ideally target all these factors. Conjugated linoleic acid could represent a candidate agent. The therapeutic potential of conjugated linoleic acid against insulin resistance-associated cardiovascular disease is discussed on the basis of the reported effects of conjugated linoleic acid on individual components of the metabolic syndrome.

Suppression of endothelin-1-induced cardiac myocyte hypertrophy by PPAR agonists: role of diacylglycerol kinase zeta

AIMS Ligand activation of peroxisome proliferator-activated receptors (PPARs) prevents cardiomyocyte hypertrophy, but the underlying signalling mechanisms remain unknown. We previously reported that the anti-hypertrophic effect of the dietary polyunsaturated fatty acid, conjugated linoleic acid (CLA), was associated with the upregulation of diacylglycerol (DAG) kinase (DGK). DGK catalyses phosphorylative conversion/attenuation of DAG, thereby modulating protein kinase C (PKC) and G-protein signalling. As the anti-hypertrophic effects of CLA were attenuated by inhibitors of PPARs, the present aim was to investigate the involvement of DGK in the anti-hypertrophic actions of bona fide selective PPAR agonists. METHODS AND RESULTS Endothelin-1 (ET1)-induced hypertrophy of neonatal, and then adult, Sprague-Dawley rat cardiomyocytes served as experimental paradigms. Expression of DGKζ, the predominant DGK isoform in myocytes, was stimulated by ligands of PPARγ (troglitazone) or PPARα (fenofibrate) and was accompanied by increased DGK activity. Troglitazone or fenofibrate prevented hypertrophic indicators elicited by ET1, including myocyte size augmentation, de novo protein synthesis, hypertrophic gene expression, and activation of the pro-hypertrophic signal, PKCε. shRNA knockdown of DGKζ abolished the growth-inhibitory effects of PPARs and restored all ET1-induced aspects of hypertrophy. Importantly, the involvement of DGK in the ability of troglitazone and fenofibrate to block ET1-induced hypertrophy and PKCε signalling was verified in adult rat myocytes. CONCLUSION Collectively, these findings show that the anti-hypertrophic actions of PPARs require DGKζ. Thus, within the cardiomyocyte, there exists a PPAR-DGK signalling axis that underpins the ability of PPAR ligands to inhibit ET1-dependent hypertrophy.

Reduced hemodynamic load aids low-dose resveratrol in reversing cardiovascular defects in hypertensive rats.

Cardiac hypertrophy and associated myocardial remodeling is one of the main complications of hypertension resulting in the development of heart failure. It is of great significance to explore novel treatments to reverse cardiac hypertrophy in hypertensives with or without affecting blood pressure. In the present study, we investigated whether low-dose resveratrol alone or in a combination with a blood pressure-lowering agent can reverse hypertension-induced cardiovascular dysfunction. Twenty-week-old male spontaneously hypertensive rats (SHRs) and Wistar–Kyoto rats were treated with resveratrol (2.5 mg kg−1 per day) and/or hydralazine (25 mg kg−1 per day) for 8 weeks. Blood pressure, cardiac structure and function, and electrocardiogram measurements were examined. Pressure myography of resistance arteries, histological examinations of heart tissues, oxidative stress and inflammatory measurements were also preformed to assess the efficacy of the treatment. Although resveratrol treatment alone was ineffective in reducing systolic blood pressure, diastolic blood pressure, diastolic dysfunction and vascular remodeling, it significantly prevented the systolic impairment and reduced myocardial fibrosis, and reduced oxidative stress and inflammation in hypertensive rats. Furthermore, a combination of resveratrol with hydralazine treatment significantly reduced blood pressure, improved systolic and diastolic function, decreased fibrosis and improved vascular geometry. In summary, low-dose resveratrol itself was unable to reduce systolic blood pressure, diastolic blood pressure, diastolic dysfunction and vascular remodeling. However, resveratrol alone alleviated cardiac fibrosis and some of the functional abnormalities in SHRs. And a combination of resveratrol with hydralazine was more effective than resveratrol or hydralazine alone in improving overall cardiovascular parameters.

Coactivation of NMDA receptors by glutamate and D-serine induces dilation of isolated middle cerebral arteries

N-methyl-d-aspartate (NMDA) receptors are glutamate-gated cation channels that mediate excitatory neurotransmission in the central nervous system. In addition to glutamate, NMDA receptors are also activated by coagonist binding of the gliotransmitter, d-serine. Neuronal NMDA receptors mediate activity-dependent blood flow regulation in the brain. Our objective was to determine whether NMDA receptors expressed by brain endothelial cells can induce vasodilation of isolated brain arteries. Adult mouse middle cerebral arteries (MCAs) were isolated, pressurized, and preconstricted with norepinephrine. N-methyl-d-aspartate receptor agonists, glutamate and NMDA, significantly dilated MCAs in a concentration-dependent manner in the presence of d-serine but not alone. Dilation was significantly inhibited by NMDA receptor antagonists, d-2-amino-5-phosphonopentanoate and 5,7-dichlorokynurenic acid, indicating a response dependent on NMDA receptor glutamate and d-serine binding sites, respectively. Vasodilation was inhibited by denuding the endothelium and by selective inhibition or genetic knockout of endothelial nitric oxide synthase (eNOS). We also found evidence for expression of the pan-NMDA receptor subunit, NR1, in mouse primary brain endothelial cells, and for the NMDA receptor subunit NR2C in cortical arteries in situ. Overall, we conclude that NMDA receptor coactivation by glutamate and d-serine increases lumen diameter in pressurized MCA in an endothelial and eNOS-dependent mechanism.

The intestinal bioavailability of vaccenic acid and activation of peroxisome proliferator‐activated receptor‐α and ‐γ in a rodent model of dyslipidemia and the metabolic syndrome

SCOPE Evidence suggests a neutral to beneficial role of certain trans fatty acids (TFA) from natural ruminant sources. Trans11-18:1 (vaccenic acid, VA), the most predominant ruminant TFA and a precursor to conjugated linoleic acid, has been shown to improve atherogenic dyslipidemia and symptoms of hepatic steatosis in animal models. The objective of this study was to assess the intestinal bioavailability of various VA sources including synthetic free fatty acid (FFA) and natural ruminant triglyceride forms, as well as the mechanistic pathways that mediate VAs bioactivity. METHODS AND RESULTS VA acts as a partial agonist to both peroxisome proliferator-activated receptors (PPAR)-α and PPAR-γ in vitro, with similar affinity compared to commonly known PPAR agonists. It was further confirmed that VA at 30 and 100 μM concentrations suppressed cardiomyocyte hypertrophy vitro in a PPAR-α- and PPAR-γ-dependent manner. In vivo, feeding of VA (1%, w/w) resulted in increased mRNA and protein expression of PPAR-γ in the mucosa of JCR:LA-cp rats, a model of the metabolic syndrome (p < 0.01 and p < 0.05, respectively) compared to control. In addition, VA from a triglyceride source had greater intestinal bioavailability in vivo compared to VA provided in an FFA form (p < 0.01). CONCLUSION The activation of PPAR-α- and PPAR-γ-dependent pathways provides a mechanistic explanation of how VA improves blood lipids and related metabolic disorders during conditions of hyperlipidemia. This report also supports the consideration of differential reporting of industrially produced versus natural TFA on food nutrient labels.