Hydroxyl radical is produced via the Fenton reaction in submitochondrial particles under oxidative stress: implications for diseases associated with iron accumulation.

Mitochondrial dysfunction and reactive oxygen species (ROS) are often implicated in diseases involving oxidative stress and elevated iron. As mitochondria produce ATP by oxidative phosphorylation, ROS by-products are generated from the electron transport chain. Although superoxide and hydrogen peroxide have been thoroughly investigated, little evidence documents hydroxyl radical (HO()) production in mitochondria. In order to determine whether HO() is generated under oxidative stress conditions by a Fenton-type mechanism, bovine heart submitochondrial particles were examined for HO() in the presence and absence of iron ligands, antioxidant enzymes and HO() scavengers. HO() was measured as 2,3- and 2,5-dihydroxybenzoic acid (DHBA), using HPLC with electrochemical detection. The iron ligand desferrioxamine significantly decreased DHBAs, indicating that HO() generation required iron redox-cycling. In addition, results from exogenous SOD and catalase, exogenous hydrogen peroxide, and HO()-scavenger studies support a Fenton-type reaction mechanism. The results indicate that increased HO() levels occur in mitochondria under oxidative stress and that the HO(*) levels can be modulated with antioxidant enzymes and iron ligands. Our findings together with reports on iron accumulation in degenerative diseases highlight the importance of developing mitochondrial-targeted antioxidants for the therapeutic intervention of diseases associated with mitochondrial dysfunction and oxidative stress.