Efeitos da hipercolesterolemia genetica e estatinas sobre a função mitocondrial / Effects of genetic hypercholesteromy and statins on mitochondrial functions

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Recent results from our group demonstrated that hypercholesterolemic LDL receptor knockout (LDLR-/-) mice mitochondria possess a lower antioxidant capacity due to a large consumption of reducing equivalents from NADPH to sustain high rates of lipogenesis (Oliveira et al., FASEB J.; 19: 278-280; 2005). In this work, LDLR-/- mice oxidative stress was further characterized by showing a lower mitochondrial GSH/GSSG ratio and a higher liver content of protein carbonyls as compared to control mice. No differences in the activity of the antioxidant enzyme system glutathione reductase/peroxidase was observed. Exogenous catalase prevented the spontaneous oxidation of endogenous NAD(p)H in mitochondria isolated from LDLR-/- mice, indicating that this oxidation is mediated by mitochondrial generated H IND. 2 O IND. 2 . The higher rate of H IND. 2 O IND. 2 release in LDLK/- mitochondria was also prevented by the presence of exogenous isocitrate and rotenone, which maintain NADP fully reduced. Our hypothesis that high rates of lipogenesis decreases NADPH/NADP+ ratio due to a decreased content of NADP-linked substrates is supported by observations that oxygen consumption supported by endogenous substrates was lower in LDLR-/- mice than in control mitochondria, but was similar in the presence of exogenous isocitrate. Indeed, endogenous mitochondriallevels of isocitrate were significantly lower in LDLK-/- mice. ln the second part ofthis work, we used statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) in an attempt to Correct the oxidative stress observed in LDLK-/- mice, but we found that the drug treatment worsened this defect. We report here that liver mitochondria isolated from hypercholesterolemic LDL receptor knockout mice treated during 15 days with therapeutic doses (100 mg/kg, p.o.) of lovastatin presented a higher susceptibility to develop membrane permeability transition (MPT). In experiments in vitro, lovastatin induced MPT in a dose-dependent manner (10-80 mu M) by a mechanism sensitive to cyclosporin A (cyclophilin inhibitor), dithiothreitol (reducing agent), ADP (adenine nucleotide carrier inhibitor), catalase ( H IND. 2 O IND. 2 reductant) and EGTA (calcium chelator). In agreement with the inhibition of the mitochondrial swelling by dithiothreitol, lovastatin also decreased the content of total mitochondrial membrane protein thiol groups. Simvastatin had similar effects on mitochondria; however, pravastatin, a hydrophilic statin, had a weaker effect in inducing MPT. These results demonstrate that statins can act directly on mitochondria either in vivo or in vitro inducing permeability transition, which is a process involved in cell death

ASSUNTO(S)

hydroxymethylglutaryl-coa reductase inhibitors hypercholesterolemy mitochondria mitocondria inibidores de hidroximetilglutaril-coa redutases hipercolesterolemia

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