ACUTE DILATORY AND NEGATIVE INOTROPIC EFFECTS OF HOMOCYSTEINE ARE INHIBITED BY AN ADENOSINE BLOCKER

Metabolic Therapy of Heart Failure: Is There a Future for B Vitamins?

Heart failure (HF) is a plague of the aging population in industrialized countries that continues to cause many deaths despite intensive research into more effective treatments. Although the therapeutic arsenal to face heart failure has been expanding, the relatively short life expectancy of HF patients is pushing towards novel therapeutic strategies. Heart failure is associated with drastic metabolic disorders, including severe myocardial mitochondrial dysfunction and systemic nutrient deprivation secondary to severe cardiac dysfunction. To date, no effective therapy has been developed to restore the cardiac energy metabolism of the failing myocardium, mainly due to the metabolic complexity and intertwining of the involved processes. Recent years have witnessed a growing scientific interest in natural molecules that play a pivotal role in energy metabolism with promising therapeutic effects against heart failure. Among these molecules, B vitamins are a class of water soluble vitamins that are directly involved in energy metabolism and are of particular interest since they are intimately linked to energy metabolism and HF patients are often B vitamin deficient. This review aims at assessing the value of B vitamin supplementation in the treatment of heart failure.

Homocysteine ameliorates the endothelium-independent hypoxic vasoconstriction via the suppression of phosphatidylinositol 3-kinase/Akt pathway in porcine coronary arteries

OBJECTIVE

Endothelium-independent coronary vasoconstriction induced by continuous hypoxia contributes to the development of ischemic heart diseases. Acute elevation of homocysteine (Hcy) has a potent of vasodilation. The present study aims to investigate the role of Hcy in endothelium-independent hypoxic coronary vasoconstriction and its underlying mechanisms.

METHODS AND RESULTS

Vessel tension of isolated porcine coronary arteries was measured by organ chamber study and the protein expression were detected by western blot. A sustained contraction of porcine coronary artery was induced when exposed to prolonged hypoxia for more than 15 min, which was significantly reduced by Hcy in a dose-dependent manner but not affected by cysteine or N-acetyl-l-cysteine. Phosphorylated myosin light chain (MLC-p) at Ser19 was decreased when exposure to hypoxia for 15 min, and could be reversed by prolonged hypoxia for 30 and 60 min. The recovery of MLC-p at Ser19 by hypoxia for more than 30 min could be abolished by Hcy. The protein levels of phosphorylated Akt at Ser473 and phosphorylated P85 at Tyr508 were decreased by Hcy in normoxia, and were also reduced exposure to hypoxia for 15 min and then augmented by prolonged hypoxia for more than 30 min, which could be prevented by Hcy. The protein level of P110α was not affected by Hcy or prolonged hypoxia.

CONCLUSIONS

This study demonstrates that Hcy can ameliorate the endothelium-independent hypoxic coronary vasoconstriction, in which the inhibition of PI3K/Akt signaling pathway may be involved.

The effects of homocysteine-related compounds on cardiac contractility, coronary flow, and oxidative stress markers in isolated rat heart

Research on the effects of homocysteine on the vascular wall, especially in endothelial and smooth muscle cells, has indicated that increased homocysteine levels lead to cellular stress and cell damage. Considering the adverse effects of homocysteine on vascular function and the role of oxidative stress in these mechanisms, the aim of this study was to estimate the influence of different homocysteine isoforms on cardiac contractility, coronary flow, and oxidative stress markers in isolated rat heart. The hearts of male Wistar albino rats (n = 36, age 8 weeks, body mass 180-200 g), were excised and retrogradely perfused according to the Langendorff technique at a constant perfusion pressure (70 cmH(2)O) and administered with three isoforms of 10 μM homocysteine [DL-Hcy, DL-Hcy thiolactone-hydrochloride (TLHC) and L-Hcy TLHC). After the insertion and placement of the sensor in the left ventricle, the parameters of heart function: maximum rate of pressure development in the left ventricle (dP/dt max), minimum rate of pressure development in the left ventricle (dP/dt min), systolic left ventricular pressure (SLVP), diastolic left ventricular pressure (DLVP), mean blood pressure (MBP) and heart rate (HR)] were continuously registered. Flowmetry was used to evaluate the coronary flow. Markers of oxidative stress: index of lipid peroxidation measured as TBARS, nitric oxide measured through nitrites (NO(2)(-)), superoxide anion radical (O(2)(-)), and hydrogen peroxide (H(2)O(2)) in the coronary venous effluent were assessed spectrophotometrically. Our results showed that administration of Hcy compounds in concentration of 10 μM induced depression of cardiac contractility, manifested by a decrease in dp/dt max after administration of any Hcy compound, decrease in dp/dt min after administration of L-Hcy TLHC, decrease in SLVP after administration of DL-Hcy TLHC and DL-Hcy, and the drop in CF after administration of any Hcy compound. Regarding the effects of Hcy on oxidative stress parameters, only L-Hcy TLHC significantly affected O(2)(-) release. L-Hcy TLHC showed a cardiotoxic effect by affecting heart contractility, but surprisingly, it decreased the release of O(2)(-).

Role of adenosine antagonism in the cardio-renal syndrome: Pathophysiology and therapeutic potential

The adversarial relationship between the heart and the kidney in heart failure results from normal homeostatic mechanisms which become inappropriate in the setting of heart failure. The cardio-renal syndrome represents the sum total of this adversarial relation and is clinically manifest as worsening renal function limiting diuresis in spite of volume overload. Tubuloglomerular feedback is a major pathophysiologic component of this syndrome. Adenosine, acting via A1 receptors, plays a major role in tubuloglomerular feedback in the normal state and in cardio-renal syndrome. Preclinical studies and initial human studies suggest that adenosine antagonism increases diuresis and preserves glomerular filtration in the setting of decompensated heart failure. Considering the ubiquitous distribution of adenosine receptors in the body, it is crucial to tailor this therapeutic agent to avoid side effects, especially neurotoxicity. Larger studies are presently underway to understand the therapeutic potential of this novel class of agents.