A putative mitochondrial mechanism for antioxidative cytoprotection by 17beta-estradiol

Abstract

It has been demonstrated that estrogens are potent antioxidants and protect against H 2O 2-mediated depletion of intracellular ATP in human lens epithelial cells (HLE-B3) [Invest. Ophthalmol. Vis. Sci. 44 (2003) 2067]. To investigate the mechanism by which 17β-estradiol (17β-E 2) protects against oxidative stress, HLE-B3 cells were exposed to insult with H 2O 2 at physiological (50 μ m) and moderately supra- physiological (100 μ m) levels over a time course of several hours, with and without pretreatment with 17β-E 2. The ability of 17β-E 2 to prevent H 2O 2-induced injury to several oxidant susceptible components of the cellular ATP generating machinery, including abundances of mitochondrial gene transcripts encoding respiratory chain subunits and cytochrome c, the glycolytic pathway enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the energy-shuttling creatine kinase (CK) system, and mitochondrial membrane potential (Δ Ψ m), a measure of mitochondrial membrane integrity, were determined 3 hr after oxidative insult. Northern blot analysis revealed H 2O 2-induced reductions in mitochondrial transcripts for nicotinamide adenine dinucleotide dehydrogenase (NADH) subunits 4 and 5 and cytochrome c. H 2O 2 also inactivated GAPDH but did not alter CK activity. Pretreatment and simultaneous addition of 17β-E 2 with H 2O 2 did not prevent the reductions in mitochondrial transcript levels and GAPDH activity. 17β-Estradiol did moderate the collapse of mitochondrial membrane potential (Δ Ψ m) in response to H 2O 2 as demonstrated by JC-1 staining and fluorescence microscopy. Although the precise mode of action responsible for protection by estradiols against oxidative stress remains to be determined, these results indicate that the hormone stabilizes the mitochondrial membrane, thereby preserving the driving force for oxidative ATP synthesis.