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Mitochondrial superoxide and coenzyme Q in insulin-deficient rats: increased electron leak
Journal article   Open access   Peer reviewed

Mitochondrial superoxide and coenzyme Q in insulin-deficient rats: increased electron leak

Judith A Herlein, Brian D Fink, Dorlyne M Henry, Mark A Yorek, Lynn M Teesch and William I Sivitz
American journal of physiology. Regulatory, integrative and comparative physiology, Vol.301(6), pp.R1616-R1624
Integrative and Translational Physiology: Integrative Aspects of Energy Homeostasis and Metabolic Diseases
12/2011
DOI: 10.1152/ajpregu.00395.2011
PMCID: PMC3233854
PMID: 21940403
url
https://doi.org/10.1152/ajpregu.00395.2011View
Published (Version of record) Open Access

Abstract

Mitochondrial superoxide is important in the pathogeneses of diabetes and its complications. However, there is uncertainty regarding the intrinsic propensity of mitochondria to generate this radical. Studies to date suggest that superoxide production by mitochondria of insulin-sensitive target tissues of insulin-deficient rodents is reduced or unchanged. Moreover, little is known of the role of the Coenzyme Q (CoQ), whose semiquinone form reacts with molecular oxygen to generate superoxide. We measured reactive oxygen species (ROS) production, respiratory parameters, and CoQ content in mitochondria from gastrocnemius muscle of control and streptozotocin (STZ)-diabetic rats. CoQ content did not differ between mitochondria isolated from vehicle- or STZ-treated animals. CoQ also was unaffected by weight loss in the absence of diabetes (induced by caloric restriction). Under state 4 or state 3 conditions, both respiration and ROS release were reduced in diabetic mitochondria fueled with succinate, glutamate plus malate, or with all three substrates (continuous TCA cycle). However, H 2 O 2 and directly measured superoxide production were substantially increased in gastrocnemius mitochondria of diabetic rats when expressed per unit oxygen consumed. On the basis of substrate and inhibitor effects, the mechanism involved multiple electron transport sites. More limited results using heart mitochondria were similar. ROS per unit respiration was greater in muscle mitochondria from diabetic compared with control rats during state 3, as well as state 4, while the reduction in ROS per unit respiration on transition to state 3 was less for diabetic mitochondria. In summary, ROS production is, in fact, increased in mitochondria from insulin-deficient muscle when considered relative to electron transport. This is evident on multiple energy substrates and in different respiratory states. CoQ is not reduced in diabetic mitochondria or with weight loss due to food restriction. The implications of these findings are discussed.
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