An analog of thyrotropin-releasing hormone (TRH) is neuroprotective against glutamate-induced toxicity in fetal rat hippocampal neurons in vitro

TRH has been found to be efficacious in treating certain neurodegenerative disorders such as epilepsy, Alzheimer's disease, neurotrauma and depression, however, its mechanism of action is poorly understood. Since glutamate (Glu) toxicity has been implicated in these disorders, we utilized primary enriched cultures of rat fetal (E 17) hippocampal neurons to test the hypothesis that an analog of TRH, 3-Methyl-Histidine TRH (3Me-H TRH), given concurrently with Glu would protect such neurons against cell damage and cell death. Cell viability was assessed via Trypan Blue exclusion cell counts, and neuronal damage was determined by assaying lactic acid dehydrogenase (LDH) released in the conditioned media. Fetal hippocampal neurons were cultured in neurobasal media for 7 days. On day 7, neurons (106/well) were treated with: control media, 10 μM 3Me-H TRH, 500 μM Glu or 500 μM Glu with either 10, 1, 0.1, 0.01 or 0.001 μM 3Me-H TRH. Both media and neurons were harvested 16 h after treatment. Prolonged exposure to 10 μM 3Me-H TRH was not toxic to the cells, whereas neurons exposed to 500 μM Glu resulted in maximal cell death. Notably, 10, 1 and 0.1 μM 3Me-H TRH, when co-treated with 500 μM Glu, protected fetal neurons against cell death in a concentration-dependent manner. These results provide support for an important neuroprotective effect of TRH/analogs against glutamate toxicity in primary hippocampal neuronal culture and implicate a potentially beneficial role of TRH/analogs in neurodegenerative diseases.