Effects of genistein on Leber’s hereditary optic neuropathy (LHON) mitochondrial metabolism.

Leber's hereditary optic neuropathy (LHON), a maternally inherited form of central vision loss, is caused by pathogenic point mutations in mitochondrial-encoded subunits of complex I, the first site of the mitochondrial respiratory chain. The most frequent LHON-associated mutations are the homoplasmic m. 11778 G>A in MTND4 gene, the m. 14484 T>C in MTND6 and the m.3460 G>A in ND1 gene [1-2]. One of the open problems in LHON is the variable penetrance: mtDNA mutations are necessary but not sufficient to induce the clinical phenotype. In fact, approximately 50% of males and only 10% of females harboring a primary mtDNA mutation develop the disease. Proposed modifiers include, secondary mtDNA mutations, mtDNA haplogroup, nuclear encoded genes, tobacco and alcohol consumption, and the exposure to toxic compounds [3-4]. By using the cell model of trans-mitochondrial cybrids we recently showed that estrogens ameliorate mitochondrial function, increase cell viability and prevent oxidative stress damage in LHON [5]. Thus, different exposure to estrogens between males and females may account for the still unexplained male prevalence. Aim of the present study was to compare the anti-oxidative effects of estrogens and phytoestrogens (i.e genistein, one of the soy isoflavones) on LHON metabolism by using the cybrid cells model. Cybrids were incubated in glucose-free, galactose supplemented medium, forcing the cells to rely mainly on the mitochondrial respiratory chain to produce ATP. Results show that, contrary to control cybrids, in each cell line harboring one of the three most frequent LHON pathogenic mutations, ROS increase, mitochondrial network is altered and there is an high percentage of cell death. Genistein (0.1 µM), similar to estrogens, prevents the alterations induced by galactose on cell growth, ROS production and mitochondrial network. Furthermore genistein activates ERK1 and ERK2 MAP kinases thus up-regulating Mn-SOD antioxidant enzyme. The effects of genistein are antagonised by ERs specific inhibitor (ICI 182780), demonstrating the involvement of estrogen-receptors as mechanism of protection of LHON cybrids from oxidative stress. Our results open new therapeutic approaches for LHON. 1. Carelli V et al. (2004) - Prog Retin Eye Res, 23: 53–89. 2. Man PY et al. (2009) - J Med Genet, 46: 145–58. 3. Phasukkijwatana N et al. (2010) - Hum Genet 2010, 128: 39–49. 4. Kirkman MA et al. (2009) - Brain, 132: 2317–26. 5. Giordano C, Montopoli M et al. (2011) – Brain, 134:220-34.