Mitochondrial permeability transition pore opening inhibition by ecdysterone in heart mitochondria of aging rats

Nitric oxide reacts rapidly with superoxide to produce the potent oxidant peroxynitrite. In vivo mitochondria produce superoxide as well as NO. In heart mitochondria of aging rats the amount of NO and O2(-) are increased thus the levels of peroxynitrite produced may be increased too, in this reason mitochondria may be a major site of peroxynitrite formation. Oxidative stress induces cyclosporine A-sensitive mitochondrial efflux of calcium and proapoptotic factors through MPTP (mitochondrial permeability transition pore) opening in heart mitochondria which may contribute to tissue damage and mitochondrial dysfunction in aging rats. We tested the levels of NO and superoxide generation in mitochondria simultaneously with cyclosporine A-sensitive MPTP opening by Ca2+ and phenylarsine oxide (PAO) to determine whether downregulation of both NO and O2(-) generation in heart mitochondria by potent steroid antioxidant and free radical scavenger ecdysterone may protect heart mitochondria of aging rats again tissue damage. C27-phytosteroid hormone ecdysterone (10 mkg/100g, per os, 2 weeks) mimics action of its structural analog C27- steroid hormone calcitriol (1alpha,25-dihydroxyvitamin D3) and exert its cardio protection in aging heart mitochondria by inhibition of MPTP opening with effectivity of action of hormone melatonine (150 mkg/100g, 2 weeks [ V.F. Sagach et al. Fyziol. J (Ukr), 2006, 52(2), 3-15]). MPTP inhibition is dependent on paradoxycally high activation by ecdusterone of oxidative degradation of L-arginine by mtcNOS in mitochondria, by downregulation of superoxide generation and L-arginine degradation by arginase II and NO generation by mtiNOS in de novo and by NADP-dependent mtNR (nitrate reductase) in salvage pathways. These results suggest that MPTP opening may be directly influenced by ecdysterone signaling in mitochondria. The signaling pathway by which ecdysterone may coregulate the O2(-) and NO generation in heart mitochondria of aging rats may involve an outer mitochondrial membrane estrogen receptor coupled to mitochondrial PI3K/Akt/PKB activation results in superactivation and constitutive NO synthesis by mtcNOS.