Pinoline and N-acetylserotonin reduce glutamate-induced lipid peroxidation in retinal homogenates

Glutamate is a neurotransmitter associated with oxidative retinal disorders. Pinoline (PIN) and N-acetylserotonin (NAS) are newly identified neural protectors. We investigated the glutamate-induced lipid peroxidation (LPO) and the protective effects of PIN and NAS in the retina. Porcine retinal homogenates were treated with different concentrations of glutamate. The malondialdehyde (MDA) level per unit weight of protein was quantified spectro-photometrically as an index of LPO. The glutamate concentration that induced a significant increase in retinal MDA was determined. The glutamate-treated retinal homogenate was then co-incubated with 5 different concentrations (0, 35.7, 71.5, 143 and 286 microM) of PIN, NAS or their combinations (concentration corresponding to 25, 50 and 75% of protection). Glutamate induced a significant dose-dependent increase in retinal MDA (p<0.0001). Co-incubation with PIN or NAS significantly suppressed the glutamate-induced MDA (p<0.01) in a dose-dependent manner (p<0.0001). The concentrations to inhibit 50% of LPO were 132.8 and 98.6 microM for PIN and NAS, respectively. In summary, elevated glutamate induced retinal LPO. Both PIN and NAS suppressed the glutamate-induced LPO and a synergic protection was evident after incubation in PIN/NAS mixtures.