The effect of metformin therapy on cardiac function and survival in volume-overload model of heart failure in rats Short title: Metformin therapy in volume-overload heart failure in rats A c c e p t e d M a n u s c r i p t Licenced copy. Copying is not permitted, except with prior permission and as allowed by law.© 2011 The Authors Journal compilation © 2011 Portland Press Limited 2 Abstract Aims: Advanced heart failure (HF) is associated with altered substrate metabolism. Whether modification of substrate use improves the course of HF remains unknown. Antihyperglycemic drug metformin (MET) affects substrate metabolism and its use might be associated with improved outcome in diabetic HF. The aim of the study was to examine whether MET would improve cardiac function and survival also in non-diabetic HF. Methods: Volume overload HF was induced in male Wistar rats by creating aorto-caval fistula (ACF). Animals were randomized to placebo/MET (300mg/kg/day, 0.5% in food) groups and underwent assessment of metabolism, cardiovascular and mitochondrial functions (n=6-12/group) in advanced HF stage (21 st week). A separate cohort served for survival analysis (n=10-90/group). Results: The ACF group had marked cardiac hypertrophy, increased LVEDP and lung weight confirming decompensated HF, increased circulating free fatty acids (FFA), intraabdominal fat depletion, lower glycogen synthesis in the skeletal muscle (diaphragm), lower myocardial triglyceride content and attenuated myocardial 14 C-glucose and 14 C-palmitate oxidation, but preserved mitochondrial respiratory function, glucose tolerance and insulin sensitivity. MET therapy normalized serum FFA, decreased myocardial glucose oxidation, increased myocardial palmitate oxidation, but it had no effect on myocardial gene expression, AMPK signalling, ATP level, mitochondrial respiration, cardiac morphology, function and long-term survival despite reaching therapeutic serum level (2.2 ± 0.7 μg/ml). Conclusion: MET-induced enhancement of myocardial fatty acid oxidation had neutral effect on cardiac function and survival. Recently reported cardioprotective effects of MET may not be universal to all forms of HF and may require AMPK activation or ATP depletion. No increase in mortality on MET supports its safe use in diabetic HF.
IntroductionAdvanced heart failure (HF) is characterized not only by a depression of heart mechanical performance but also by altered myocardial metabolism -attenuated expression of fatty acid oxidation genes [1,2] and by diminished oxidation of long chain fatty acids [1,[3][4][5], which may contribute to diminished metabolic flexibility and to energetic deficiency that further promotes worsening of HF [6]. Targeting energetic substrate metabolism might thus serve as a target for novel therapeutic approaches to HF [7,8]. Metformin (MET), a widely used antihyperglycemic drug with insulin-sensitizing properties, could be a suitable candidate for metabolic HF therapy. MET lowers serum glucose by inhibiting liver gluconeogenesis, lowers circulating free...