Tournefolic acid B methyl ester attenuates glutamate-induced toxicity by blockade of ROS accumulation and abrogating the activation of caspases and JNK in rat cortical neurons

The effects of nine polyphenolic compounds on glutamate-mediated toxicity were investigated. The underlying mechanisms by which a polyphenolic compound confers its effect were also elucidated. Treatment of cortical neurons with 50 mum glutamate for 24 h decreased cell viability by 45.8 +/- 7.9%, and 50 mum of tournefolic acid B methyl ester attenuated glutamate-induced cell death by 46.8 +/- 17.8%. Glutamate increased the activity of caspase 35.2-fold, and to a similar extent for caspase 2, 6, 8 and 9. Tournefolic acid B methyl ester abrogated glutamate-induced activation of caspase 2, 3, 6 and 9 by about 70%, and to a lesser extent for caspase 8. Treatment with glutamate for 1 h elevated reactive oxygen species (ROS) by 208.3 +/- 21.3%. Tournefolic acid B methyl ester eliminated the glutamate-induced accumulation of ROS. Glutamate increased the phosphorylation of p54-c-jun N-terminal kinase (JNK) concomitantly with activation of the endogenous antioxidant defense system. Tournefolic acid B methyl ester at 50 mum diminished the activity of p54-JNK in control and glutamate-treated cells, coinciding with the abolishment of the glutamate-triggered antioxidant defense system. Therefore, tournefolic acid B methyl ester blocked the activation of the caspase cascade, eliminated ROS accumulation and abrogated the activation of JNK, thereby conferring a neuroprotective effect on glutamate-mediated neurotoxicity.