How do Ca2+ and 5-aminolevulinic acid-derived oxyradicals promote injury to isolated mitochondria?
The biosynthetic heme precursor 5-aminolevulinic acid (5-ALA) is a generator of oxygen radicals in vitro and possibly in vivo during pathologic situations of 5-ALA overload, for example, acute intermittent porphyria and saturnism. It has been observed that 5-ALA induces, in isolated rat liver mitochondria, permeabilization of the inner mitochondrial membrane (a phenomenon called permeability transition) as verified by the elimination of the transmembrane electrical potential, Ca2+ release, mitochondrial swelling, and increase in state-4 respiratory rate. The damaging process is primarily attributed to .OH radicals as elucidated by the protection by catalase, superoxide dismutase, and the Fe(II) chelator o-phenanthroline. Ruthenium red, EGTA, and dithiothretol (DTT) have been observed to prevent the action of 5-ALA-generated oxyradicals, suggesting the participation of both Ca2+ and the oxidation of critical thiol membrane proteins in the process of permeability transition. 5-ALA-induced polymerization of thiol membrane proteins has also been demonstrated by SDS-PAGE electrophoresis of the mitochondrial suspensions, a process similar to that observed in mitochondria treated with tert-butyI hydroperoxide. EGTA addition, in contrast with DTT or antioxidants, restores the previously eliminated electrical potential. Furthermore, EGTA prevents the 5-ALA-mediated polimeryzation of thiol proteins. These observations suggest that Ca2+ participates in a later stage of the permeability transition, after the oxidation of the thiol proteins. The effects of 5-ALA-derived oxyradicals in isolated mitochondria could be used as a tool for more general studies of oxidative stress, such as the mitochondrial injury that follows processes of ischemia and reperfusion or xenobiotic poisoning.
Hermes-Lima
M
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Institute of Biochemistry, K. B. Storey Laboratory, Carleton University, Ottawa, Canada.
D000622:Aminolevulinic Acid / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002374:Catalase / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D017665:Hydroxyl Radical / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress; D010618:Phenanthrolines / Q000494:pharmacology; D051381:Rats; D013482:Superoxide Dismutase / Q000494:pharmacology
D005609:Free Radicals; D007502:Iron Chelating Agents; D010618:Phenanthrolines; D017665:Hydroxyl Radical; D000622:Aminolevulinic Acid; D002374:Catalase; D013482:Superoxide Dismutase; D002118:Calcium; D004229:Dithiothreitol; C025205:1,10-phenanthroline