Analysis of Neuroprotection by Taurine and Taurine Combinations in Primary Neuronal Cultures and in Neuronal Cell Lines Exposed to Glutamate Excitotoxicity and to Hypoxia/Re-oxygenation.

Ischemic stroke is one of the greatest contributors to death and long term disability in developed countries. Ischemia induced brain injury arises due to excessive release of glutamate and involves cell death due to apoptosis and endoplasmic reticulum (ER) stress responses. Despite major research efforts there are currently no effective treatments for stroke. Taurine, a free amino acid found in high concentrations in many invertebrate and vertebrate systems can provide protection against a range of neurological disorders. Here we demonstrate that taurine can combat ER stress responses induced by glutamate or by hypoxia/re-oxygenation in neuronal cell lines and primary neuronal cultures. Taurine decreased expression of ER stress markers GRP78, CHOP, Bim and caspase 12 in primary neuronal cultures exposed to hypoxia/re-oxygenation. In analyzing individual ER stress pathways we demonstrated that taurine treatment can result in reduced levels of cleaved ATF6 and decreased p-IRE1 levels. We hypothesized that because of the complex nature of stroke a combination therapy approach may be optimal. For this reason we proceeded to test combination therapies using taurine plus low dose administration of an additional drug: either granulocyte colony stimulating factor (G-CSF) or sulindac a non-steroidal anti-inflammatory drug with potent protective functions through signaling via ischemic preconditioning pathways. When primary neurons were pretreated with 25 mM taurine and 25 ng/mL G-CSF for I hour and then exposed to high levels of glutamate, the taurine/G-CSF combination increased the protective effect against glutamate toxicity to 88% cell survival compared to 75% cell survival from an individual treatment with taurine or G-CSF alone. Pre-exposure of PC12 cells to 5 mM taurine or 25 µM sulindac did not protect the cells from hypoxia/re-oxygenation stress whereas at these concentrations the combination of taurine plus sulindac provided significant protection. In summary we have demonstrated the protective effect of taurine in primary neuronal cultures against hypoxia with re-oxygenation through inhibition of ATF6 or p-IRE-1 pathway but not the PERK pathway of ER stress. Furthermore the combinations of taurine plus an additional drug (either G-CSF or sulindac) can show enhanced potency for protecting PC 12 cells from glutamate toxicity or hypoxia/re-oxygenation through inhibition of ER stress responses.

Beneficial effect of taurine on hypoxia- and glutamate-induced endoplasmic reticulum stress pathways in primary neuronal culture.

Stroke (hypoxia) is one of the leading causes of mortality in the developed countries, and it can induce excessive glutamate release and endoplasmic reticulum (ER) stress. Taurine, as a free amino acid, present in high concentrations in a range of organs in mammals, can provide protection against multiple neurological diseases. Here, we present a study to investigate the potential protective benefits of taurine against ER stress induced by glutamate and hypoxia/reoxygenation in primary cortical neuronal cultures. We found that taurine suppresses the up-regulation of caspase-12 and GADD153/CHOP induced by hypoxia/reoxygenation, suggesting that taurine may exert a protective function against hypoxia/reoxygenation by reducing the ER stress. Moreover, taurine can down-regulate the ratio of cleaved ATF6 and full length ATF6, and p-IRE1 expression, indicating that taurine inhibits the ER stress induced by hypoxia/reoxygenation and glutamate through suppressing ATF6 and IRE1 pathways.