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 probable protective effect of tyrosine versus capsaicin cytotoxicity. The experiments were performed on Vero cells originating from monkey kidney and on primocultures of hippocampal astrocytes. Firstly, the toxicity of capsaicin was determined on these cells by assessing the protein synthesis followed by [3H]L-leucine incorporation after 24 h of incubation with different concentrations of capsaicin (17, 34, 68, 136, 340 and 680 microM). The concentration required to inhibit 50% of the protein synthesis (IC50) was found to be 97 microM. Then, both cell types were cultured with capsaicin at IC50 concentration and supplemented with different concentrations of the amino acid (ratio [capsaicin]/[tyrosine]: 1:1, 1:2, 1:4 and 1:8). The inhibition of protein synthesis induced by capsaicin was prevented in a concentration-dependent manner by tyrosine. The inhibition was completely prevented by a tyrosine concentration four times higher than capsaicin concentration. Provided that this competitive action of tyrosine on the molecular mode of action of capsaicin is confirmed in other cells such as neurones, it could be speculated that capsaicin could disturb the synthesis of the catecholamines, neurotransmitters of the central nervous system deriving from tyrosine.