O6 Cardiac mitochondrial dysfunction time course in Type 1 Diabetes

Abstract

Introduction: we have shown (Bombicino et al., 2016 and 2017) that 25 days of sustained hyperglycemia leads to generalized cardiac mitochondrial dysfunction that includes decreased tissue and mitochondrial O2 consumption, activities of complexes I-III, II- III and IV, of ATP production, of the ADP/O ratio and of Mn-SOD activity, accompanied by an increase in the production rates of H2O2, NO and ONOO-, and the triggering of mitochondrial biogenesis, although the “new” mitochondria show structural alterations. This dysfunction occurs in the absence of hypertrophy and changes in cardiac function at rest, but with cardiac compromise in the face of work overload, suggesting that mitochondrial dysfunction precedes myocardial failure in diabetic patients.

Objectives: to study the early events and analyze the temporal evolution of cardiac mitochondrial dysfunction in a model of type 1 diabetes.

Materials and methods: Diabetes was induced in male Wistar rats by a dose of streptozotocin (STZ, 60 mg/kg, ip). Blood glucose was determined at 72 h (C:127±5, DM:415±23 mg/dl). Animals were sacrificed 7, 10, or 14 days post-STZ injection (4, 7, or 11 days of hyperglycemia) and the hearts were removed. Mitochondrial functionality and biogenesis, the generation of reactive oxygen and nitrogen species and the redox state were determined.

Results: no changes were observed in mitochondrial O2 consumption or in the activity of respiratory complexes in the hearts of animals subjected to 4 days of hyperglycemia. However, if hyperglycemia lasts for 7 days, a reduction in O2 consumption is observed in state 3 sustained by malate-glutamate. (21%) and complex I activity (17%), without changes in ADP/O, accompanied by an increase in the production rates of H2O2 (117%), NO (30%) and ONOO- (225 %), a reduction in the activity of Mn-SOD (15%) and [GSSG+GSH] (28%). Steady-state [NO] and [O2-] are higher in the cardiac mitochondria of the diabetic group. Although the increase in [NO]ss was similar after 7 and 25 days of hyperglycemia (25-30%), the increase in [O2-]ss was greater after 25 days of hyperglycemia (350% at 25 days vs 150 % at 7 days), as well as the production speed of ONOO- (450% at 25 days vs 225% at 7 days). Contrary to what was observed after 25 days of hyperglycemia, mitochondrial biogenesis -assessed by the expression of PGC-1alpha and cardiac mitochondrial mass- is not triggered after 7 days of high blood glucose. When hyperglycemia is sustained for 11 days, not only does state 3 respiration supported by malate-glutamate decrease (21%) and the activity of complex I (27%), but also the activities of complexes II-III (24% ) and IV (22%) and breathing in state 3 using succinate (16%). This cardiac mitochondrial dysfunction deteriorates further if hyperglycemia is maintained for 25 days, observing generalized mitochondrial dysfunction (Bombicino et al. 2016 and 2017).

Conclusions: the analysis of the time course of cardiac mitochondrial dysfunction, triggered directly or indirectly by hyperglycemia, shows that complex I dysfunction and increased production rates of H2O2, NO and, consequently, ONOO, constitute prodromal signals. of mitochondrial dysfunction that precedes myocardial failure in diabetes.