Comparative study of taurine and tauropyrone: GABA receptor binding, mitochondrial processes and behaviour

Abstract

Taurine, a sulfur-containing amino acid, has high hydrophilicity and is poorly absorbed. Tauropyrone, a taurine-containing 1,4-dihydropyridine derivative, is suggested to have greater activity than taurine owing to improved physicochemical properties that facilitate delivery of the compound to target cells. The aim of this study was to determine whether the 1,4-dihydropyridine moiety in tauropyrone improves the pharmacological efficacy of taurine in vitro and in vivo. The effects of taurine and tauropyrone, as well as of the 1,4-dihydropyridine moiety were compared in in-vitro experiments to determine the binding to GABA receptors and influence on mitochondrial processes (isolated rat liver mitochondria), and in in-vivo tests to assess the influence on behavioural effects caused by the GABA-A receptor ligands, bicuculline, diazepam and ethanol. Unlike taurine, tauropyrone did not display binding activity for the GABA-A receptor, and only taurine (but not tauropyrone) at low doses (0.1, 1.0 and 10 mg/kg) antagonised the bicuculline-induced convulsion effect. Taurine and tauropyrone had no effect on diazepam myorelaxing action, and they both exerted a comparable 'anti-ethanol' effect (shortening of the ethanol-sleeping time). Taurine and tauropyrone did not influence processes of mitochondrial bioenergetics. The action of tauropyrone at the level of the GABA-A receptor differs qualitatively from that of taurine, probably because of its 1,4-dihydropyridine moiety, which may hinder access to the GABA-A receptor GABA site. Tauropyrone does not show improved pharmacological efficacy in in-vitro and in-vivo studies in comparison with taurine.