Background:

Previous results from our laboratory suggest that heart mitochondrial dysfunction precedes myocardial failure associated with sustained hyperglycemia.

Purpose:

The aim of this study was to analyze the early events that take place in heart mitochondria in a type 1 diabetes mellitus (DM) model.

Methods:

Male Wistar rats were injected with streptozotocin (STZ; 60 mg/kg, ip.) to induce DM. They were euthanized 10 or 14 days later and the heart mitochondrial fraction was obtained.

Results:

State 3 O2 consumption in the presence of malate-glutamate (21%) or succinate (16%), and complex I-III (27%), II-III (24%) and IV (22%) activities were lower in diabetic animals 14 days after STZ injection. When animals were euthanized at day 10, only state 3 O2 consumption sustained by complex I substrates (23%) and its corresponding respiratory control (30%) were lower in rats injected with STZ, in agreement with reduced complex I-III activity (17%). These changes were accompanied by increased H2O2 (117%), NO (30%) and ONOO- (~225%) production rates, mtNOS expression (29%) and O2 - (~150%) and NO (~30%) steady-state concentrations, together with a decrease in Mn-SOD activity (15%) and mitochondrial [GSSG+GSH] (28%), without changes in PGC-1α expression.

Conclusion:

Complex I dysfunction and increased H2O2, NO and ONOO- production rates can be considered subcellular prodromal signals of the mitochondrial damage that precedes myocardial dysfunction in diabetes.