Impaired mitochondrial respiratory functions and oxidative stress in streptozotocin-induced diabetic rats.
Bottom Line: These animals showed a persistent increase in reactive oxygen and nitrogen species (ROS and RNS, respectively) production.Mitochondrial matrix aconitase, a ROS sensitive enzyme, was markedly inhibited in the diabetic rat tissues.Increased expression of oxidative stress marker proteins Hsp-70 and HO-1 was also observed along with increased expression of nitric oxide synthase.
We have previously shown a tissue-specific increase in oxidative stress in the early stages of streptozotocin (STZ)-induced diabetic rats. In this study, we investigated oxidative stress-related long-term complications and mitochondrial dysfunctions in the different tissues of STZ-induced diabetic rats (>15 mM blood glucose for 8 weeks). These animals showed a persistent increase in reactive oxygen and nitrogen species (ROS and RNS, respectively) production. Oxidative protein carbonylation was also increased with the maximum effect observed in the pancreas of diabetic rats. The activities of mitochondrial respiratory enzymes ubiquinol: cytochrome c oxidoreductase (Complex III) and cytochrome c oxidase (Complex IV) were significantly decreased while that of NADH:ubiquinone oxidoreductase (Complex I) and succinate:ubiquinone oxidoreductase (Complex II) were moderately increased in diabetic rats, which was confirmed by the increased expression of the 70 kDa Complex II sub-unit. Mitochondrial matrix aconitase, a ROS sensitive enzyme, was markedly inhibited in the diabetic rat tissues. Increased expression of oxidative stress marker proteins Hsp-70 and HO-1 was also observed along with increased expression of nitric oxide synthase. These results suggest that mitochondrial respiratory complexes may play a critical role in ROS/RNS homeostasis and oxidative stress related changes in type 1 diabetes and may have implications in the etiology of diabetes and its complications.
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Mentions: In order to determine the increase in oxidative stress and whether the increased mitochondrial formation of NO in STZ-treated diabetic rats was due to mitochondrial NOS, we carried out immunoblot analysis of mitochondrial proteins from control and experimental rat tissues using iNOS antibody. Although not shown here, mitochondria from different rat tissues exhibited a maximum interaction with iNOS antibody when compared with nNOS or eNOS antibodies. As shown in Figure 7, the maximum induction in the level of mitochondrial NOS was observed in the pancreas (∼4 fold), followed by the liver (∼2.5 fold), kidney (1.5 fold) and brain (1.6 fold). An increased expression was also seen with other oxidative stress marker proteins, Hsp-70 and HO-1. An increased expression of the 70 kDa subunit of the mitochondrial Complex II was confirmation of an increased catalytic activity in the tissues from diabetic rats.