Comparative antioxidant properties of some GABAergic phenols and related compounds, determined for homogeneous and membrane systems.

Some phenols, like propofol, thymol and related compounds, have been shown to act on the GABA(A) receptor. Several compounds with GABAergic activity have displayed neuroprotective effects attributed mainly to the potentiation of GABA(A)-mediated inhibition of synaptic transmission. It has also been found that compounds containing a phenolic OH group can scavenge reactive oxygen species, as in the case of propofol, among others. Thus, the neuroprotective action mechanism of GABAergic phenols would involve both effects, their pharmacological activity on GABA(A) and their intrinsic antioxidant ability. In this context, the study of the antioxidant properties of phenolic compounds included in the present work will enable these capacities to be correlated with their eventual pharmacological activities. The assays chosen in this study included determination of antioxidant ability in homogeneous isotropic systems (DPPH reduction, FRAP and hydrogen peroxide scavenging) and in heterogeneous membrane systems (inhibition of lipid peroxidation of phospholipid SUVs). The comparative evaluation of the results showed some differences between the relative order of antioxidant potency among all assayed compounds determined by using both types of systems. This analysis supports the conclusion that the antioxidant values obtained in homogeneous non-membrane systems, for phenols or other lipophilic compounds, should be revised according to their capacity of interaction with membranes (i.e. Log P in membrane-buffer system) in order to obtain antioxidant potency values more approximate to those actually occurring in biological systems. These results are essential to understand the actual neuroprotective action mechanism exerted by phenolic compounds involving a pharmacological activity, an antioxidant effect or both actions exerted mutually.