TYROSINE PREVENTS CAPSAICIN-INDUCED PROTEIN-SYNTHESIS INHIBITION IN CULTURED-CELLS

Our previous studies have shown that capsaicin competitively inhibits the fixation of tyrosine on its specific tRNA catalysed by the tyrosyl -tRNA synthetase in a cell-free system. These results suggested a prob able protective effect of tyrosine versus capsaicin cytotoxicity. The experiments were performed on Vero cells originating from monkey kidne y and on primocultures of hippocampal astrocytes. Firstly, the toxicit y of capsaicin was determined on these cells by assessing the protein synthesis followed by [H-3]L-leucine incorporation after 24 h of incub ation with different concentrations of capsaicin (17, 34, 68, 136, 340 and 680 mu M). The concentration required to inhibit 50% of the prote in synthesis (IC50) was found to be 97 mu M. Then, both cell types wer e cultured with capsaicin at IC50 concentration and supplemented with different concentrations of the amino acid (ratio [capsaicin]/[tyrosin e]: 1:1, 1:2, 1:4 and 1:8). The inhibition of protein synthesis induce d by capsaicin was prevented in a concentration-dependent manner by ty rosine. The inhibition was completely prevented by a tyrosine concentr ation four times higher than capsaicin concentration. Provided that th is competitive action of tyrosine on the molecular mode of action of c apsaicin is confirmed in other cells such as neurones, it could be spe culated that capsaicin could disturb the synthesis of the catecholamin es, neurotransmitters of the central nervous system deriving from tyro sine. (C) 1997 Elsevier Science Ireland Ltd.