Protein Binding of NADH on Chemical Preconditioning

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Abstract
: Chemical preconditioning, an emerging neuroprotective strategy described in recent years, results in preserved energy metabolism during hypoxia via yet unknown mechanisms. The hypoxic increase of NADH content is attenuated by preconditioning. The goal of the present study was to investigate whether attenuation of the hypoxic NADH increase is due to a shift between free and protein‐bound NADH. NADH in solution has a fluorescence maximum at 469.2 nm. In untreated mouse hippocampal slices, λcontrol onset is 456.2 ± 5.3 nm in CA1 (mean ± SD ; p < 0.01 vs. solution) and 454.6 ± 6.1 nm in CA3 [p < 0.01 vs. solution, not significant (NS) to λcontrol onset in CA1]. In slices prepared from animals pretreated in vivo with 20 mg/kg 3‐nitropropionate, λpreconditioning onset is 439.2 ± 5.0 nm (p < 0.001 vs. control) in CA1 and 434.2 ± 6.4 nm in CA3 (p < 0.001 vs. control ; NS to λpreconditioning onset in CA1). In controls, the fluorescence maximum shifts to λcontrol hypoxia 458.2 ± 1.3 nm in CA1 (NS vs. onset) and 456.0 ± 3.6 nm in CA3 (NS vs. onset). On preconditioning with 3‐nitropropionate, λpreconditioning hypoxia shifts to 446.4 ± 4.3 nm in CA1 (p < 0.03 vs. onset) and 438.6 ± 6.9 nm in CA3 (p < 0.03 vs. onset). Posthypoxic decay of free and protein‐bound NADH is diminished after preconditioning. We conclude that the free NADH level is reduced on an increase of hypoxic tolerance by chemical preconditioning. Reduction of free NADH content is maintained during hypoxia after preconditioning.