Protective effect of l-cysteine and glutathione on the modulated suckling rat brain Na +,K +-ATPase and Mg 2+-ATPase activities induced by the in vitro galactosaemia

Abstract

Galactosaemia is an inborn error of galactose (Gal) metabolism characterized by irreversible brain damage. The aim of this study was to evaluate whether the antioxidants l-cysteine (Cys) and the reduced glutathione (GSH) could reverse the alterations of brain total antioxidant status (TAS) and the modulated activities of the enzymes Na +,K +-ATPase and Mg 2+-ATPase in in vitro galactosaemia. Mixture A (mix. A: galactose-1-phosphate (Gal-1-P, 2 mM) plus galactitol (Galtol, 2 mM) plus Gal (4 mM) = classical galactosaemia) or Mixture B (mix. B: Galtol (2 mM) plus Gal (1 mM) = galactokinase deficiency galactosaemia) were preincubated in the presence or absence of Cys (0.83 mM) or GSH (0.83 mM) with whole brain homogenates of suckling rats at 37 °C for 1 h. TAS and the enzyme activities were determined spectrophotometrically. The preincubation of brain homogenates with mix. A or mix. B resulted in a decrease of TAS to 30% ( P<0.01), while the presence of Cys or GSH increased TAS to 20% ( P<0.01) and 60% ( P<0.001), respectively. The antioxidants reversed the inhibited Na +,K +-ATPase by mix. A or mix. B and the stimulated Mg 2+-ATPase by mix. B to control values, whereas no effect was observed on the enormously activated Mg 2+-ATPase by mix. A. Conclusions: (a) Gal and its derivatives may produce free radicals in the suckling rat brain, reported for first time, (b) Na +,K +-ATPase inhibition and Mg 2+-ATPase activation are probably due to the oxidative stress from the above compounds, (c) Cys or GSH could play a protective role reversing the inhibited Na +,K +-ATPase toward normal in in vitro galactosaemia and (d) the addition of the above antioxidants may reduce the consequences of brain Mg 2+-ATPase activation by Gal and Galtol in galactokinase deficiency galactosaemia.