Abstract
Left ventricular hypertrophy (LVH) is often associated with a change in myocardial energy substrate preference from fatty acids to glucose. A possible anti hypertrophic treatment strategy could aim at stimulating or restoring normal myocardial energy metabolism. Metformin, an adenosine monophosphate-activated protein kinase (AMPK) activator used in the management of glucose metabolism in diabetes, is also a fatty acid oxidation stimulator. The effect of metformin on the development of eccentric LVH and ventricular function in chronic left ventricular (LV) volume overload (VO) is unknown. This study was designed to study this question in a VO rat model caused by severe aortic valve regurgitation (AR). Male Wistar rats were divided in four groups (13-15 animals / group): Shams (S) treated or not (C) with metformin (M; 100 mg/kg/d PO) and severe ARreceiving or not metformin. Treatment was started one week before surgery and the animals were sacrificed 9 weeks later. As expected AR rats developed severe eccentric LVH during the course of the protocol. Metformin treatment did not influence the total heart weight. However, LV remodeling associated with the severe VO was severe in ARM than in ARC. Fractional shortening, a marker of systolic function, was significantly higher in ARM compared to ARC group. Metformin also increased the activity of enzymes associated with fatty acid oxidation while inhibiting phosphofructokinase, a glycolytic enzyme. A 2 month treatment with metformin reduced LV eccentric remodeling associated with severe VO and helped maintain a better systolic function.
Highlights
Chronic left ventricular volume overload (VO) causes severe left ventricular dilatation and eccentric hypertrophy (LVH)
We have previously demonstrated that LV volume overload caused by aortic valve regurgitation causes severe eccentric LVH and significantly impairs myocardial metabolism [7]
The weight of both left and right ventricles were markedly increased in aortic valve regurgitation (AR) animals but again metformin had no effect on the weight of both ventricles respectively
Summary
Chronic left ventricular volume overload (VO) causes severe left ventricular dilatation and eccentric hypertrophy (LVH). The normal myocardium has a preference for fatty acids as the main substrate for ATP formation. An increased reliance on glucose with an overall reduced oxidative metabolism is often observed [1,2,3]. Impaired myocardial energetics activate AMP-activated protein kinase (AMPK), leading to increased glucose uptake and glycolysis [4]. AMPK activation can stimulate fatty acid oxidation and block the mammalian target of rapamycin (mTOR) pro-hypertrophic pathway [5]. We have previously demonstrated that LV volume overload caused by aortic valve regurgitation causes severe eccentric LVH and significantly impairs myocardial metabolism [7]
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