Effects of Metformin on Collagen Glycation and Diastolic Dysfunction in Diabetic Myocardium

BACKGROUND: Collagen accumulation in the myocardial interstitium of diabetic animals is considered to promote diastolic stiffness through advanced glycosylation. Because in vitro data suggest that metformin can modify glycosylation, this study was undertaken in a canine diabetic model 4 months in duration. METHODS AND RESULTS: Untreated diabetics (group II) and diabetics treated with metformin alone (group III) or with insulin (group IV) were compared in the basal state and during volume infusion. Basal hemoglobin A(1c), heart rate, aortic pressure, and ejection fraction were comparable. Left ventricular end-diastolic pressure was significantly increased in the untreated diabetics of group II, associated with a reduced end-diastolic volume. By contrast these parameters in the metformin-treated diabetics of group III were comparable with those in the normals of group I. Similarly in group IV end-diastolic volume was higher than that in group II, but filling pressure, although lower, was not significantly so. Calculation of left ventricular chamber stiffness in the basal state indicated a higher level for group II compared with controls and the treatment groups. During the systemic infusion of dextran, the untreated diabetics of group II had the largest end-diastolic pressure increase and the smallest rise of end-diastolic volume of the treatment groups, consistent with a significantly greater chamber stiffness. Myocardial collagen concentration was increased in group II with an interstitial distribution on morphological exam. Levels of collagen-linked advanced glycosylation end products isolated from the left ventricular were significantly greater in group II than in group I. Treatment with metformin prevented the increment observed in the untreated diabetic but had no effect on the elevated collagen concentration. CONCLUSIONS: Untreated diabetics exhibited increased diastolic chamber stiffness associated with collagen-linked glycation in myocardium compared with control animals. Chronic metformin use prevented the abnormalities of function and composition.