GABAergic effects of some foods extracts via inhibition of GABA transaminase (GABA-T)

Abstract

Objective: GABAergic system is a target for various groups of medications including sedatives, anxiolytics, muscle relaxants, antidepressants and antiepileptics. Several foods or food ingredients are able to affect the GABAergic system by the inhibition of the γ-aminobutyric acid (GABA) degrading enzymes including the GABA-transaminase and succinate semialdehyde dehydrogenase. The purpose of this study to investigate the inhibitory effects of tea (Camellia sinensis), coffee (Coffea arabica L.), peppermint (Mentha piperita L.), thyme (Thymus vulgaris L.), and cinnamon (Cinnamomum zeylanicum) on GABA degrading enzymes. Methods: The inhibition of the GABA-T by aqueous extracts of tea (Camellia sinensis), coffee (Coffea arabica L.), peppermint (Mentha piperita L.), cinnamon (Cinnamomum zeylanicum), and thyme (Thymus vulgaris L.) was investigated using a fluorometric microplate enzyme assay. Dose-dependent inhibition of the GABA-degrading enzymes was attained by all the food extracts tested. For determination of the IC50 values of the extracts (± 95 % CI), a linear regression was performed using Origin® (Origin® 2015G von Origin Lab Corporation, Northampton, MA 01060 USA). Results: The aqueous extract of black tea presented the strongest inhibitory activity with an IC50-value (half maximal inhibitory concentration) of 13.0 (11.0-15.3) µg/mL. The tested food extracts were successful in inhibiting the GABA-degrading enzymes even at low concentrations. Conclusion:In conclusion, the selected food extracts could serve as natural inhibitors for GABA-degrading enzymes thus, they could increase the GABA concentration in the brain.