Defective Oxidative Metabolism of Heart Mitochondria from Genetically Diabetic Mice

Long chain saturated β-hydroxy fatty acid content and oxidative metabolism were studied in hearts of diabetic mice (C57BL/KsJ db/db) with a progressive cardiomy-opathy at intervals of 7, 10, 16, and 26 wk of age. Total β-hydroxy fatty acid (BHFA) content increases progressively with age in diabetic hearts with a mean value of 143.5 nmoi/g dry wt as compared with a mean of 59.6 nmol/g dry wt in control hearts. There was also a redistribution of BHFA in myocardium of diabetic mice when compared with controls, with a relative decrease in β-hydroxymyristate and an increase of β-hy-droxypalmitate. Oxidative phosphorylation studies using isolated mitochondria from diabetic mice demonstrated depressed state 3 oxidation rates with both palmityl carnitine and pyruvate as substrates. While mitochondrial NADH-oxidase activity was not statistically different from that of controls, there was a significant decrease in mitochondrial total NAD + NADH content in diabetic hearts. In addition, treatment of my-ocardfal tissue with lanthanum demonstrated an abnormal permeability of sarcolemmal, intercalated disc as well as mitochondrial membranes in myocytes of diabetic mice. The data indicate that deficiencies in total NAD + NADH content can account for the depressed state 3 oxidation of palmitylcarnitine and pyruvate in diabetic mice that in turn may explain the abnormal accumulation of BFHA. The latter could play a role in altering the permeability of cardiac cell membranes.