Die molekularen Mechanismen der Neurotoxizität der Immunsuppressiva Ciclosporin, Sirolimus und Everolimus

Abstract

Due to synergistic immunosuppressive activity and different spectra of side effects, combination of CsA with the m-TOR inhibitors sirolimus (Srl) or everolimus (RAD) improves immunosuppressive therapy. Metabonomic NMR-studies were combined with biochemical methods to reveal different aspects of the drugs neurotoxicity. Three in vitro cell systems were tested for immunosuppressant (ISS) toxicity.Because of their tumor origin C6-Glioma cells are an insufficient model system. Their metabolism differs widely from normal glia-cells.Primary astrocytes fit best for the biochemical methods but pharmacodynamic (PD) and pharmacokinetic (PK) effects were inappropriately regarded as revealed by comparison with in vivo results.Rat brain slices are best for the investigation of ISS-neurotoxicity. Their cell metabolism is comparable to in vivo metabolism of young rats. Srl synergistically enhanced the toxic effects of CsA (oxidative stress and inhibition of energy metabolism). RAD in contrast antagonized CsA-toxicity, showing the same pattern as the antioxidant Vitamin E.The in vivo part of this work demonstrated the importance of PD and PK effects in the drug-combinations. CsA entered into brain-mitochondria and inhibited mitochondrial energy production, which was compensated by enhanced cytosolic energy production. Srl did not enter brain mitochondria, but increased CsA in mitochondria and hence the toxic effects of CsA on mitochondrial energy metabolism. By inhibition of glycolysis Srl demolished the adaptation for CsA-induced energy failure. RAD distributed in competition to CsA into brain mitochondria, lowering CsA in mitochondria and CsA-toxic effects. Organ specific ISS-toxicity could be explained due to different concentrations. Rat kidney-concentrations of the ISS were up to ten times higher than in brain. Age- and sex-different expression levels of the P-Glycoprotein (P-gp) led to different ISS-brain-concentrations, with close relation to the observed toxic effects.