C-Jun N-terminal kinase inhibition and α-tocopherol protect midbrain dopaminergic neurons from interferon-γ/lipopolysaccharide-induced injury without affecting nitric oxide production

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Abstract
Interferon-γ (IFN-γ)/lipopolysaccharide (LPS) induces delayed dopaminergic neuron loss in midbrain slice cultures, because of nitric oxide production resulting from p38 mitogen-activated protein kinase (p38 MAPK)-dependent induction of inducible nitric oxide synthase (iNOS). In this study, we show that inhibition of c-Jun N-terminal kinase (JNK), but not of extracellular signal-regulated kinase, protects dopaminergic neurons from IFN-γ/LPS-induced degeneration. In contrast to a p38 MAPK inhibitor, SB203580, however, a JNK inhibitor, anthra[1,9-cd]pyrazol-6(2H)-one (SP600125), did not suppress IFN-γ/LPS-induced iNOS expression and nitric oxide production. Involvement of NADPH oxidase-derived superoxide production in dopaminergic neurodegeneration was not obvious, in that superoxide dismutase/catalase or manganese 3-methoxy-N,N′-bis(salicylidene)ethylenediamine chloride (EUK-134), a superoxide dismutase/catalase mimetic, did not afford neuroprotection. Moreover, the NADPH oxidase inhibitors apocynin and diphenylene iodonium were protective against IFN-γ/LPS cytotoxicity only at concentrations that suppressed nitric oxide production. Notably, α-tocopherol effectively prevented IFN-γ/LPS-induced dopaminergic neuron degeneration, without affecting iNOS induction and nitric oxide production. These results underscore the neuroprotective potential of JNK inhibitor and α-tocopherol, in the sense that both agents could rescue dopaminergic neurons under inflammatory conditions associated with robust increases in nitric oxide production.