Ethanolic extract of Streblus asper leaves protects against glutamate-induced toxicity in HT22 hippocampal neuronal cells and extends lifespan of Caenorhabditis elegans

Background: Although such local herb as Streblus asper (family Moraceae) has long been recognized for traditional folk medicines and important ingredient of traditional longevity formula, its anti-neurodegeneration or anti-aging activity is little known. This study aimed to investigate the neuroprotective effect of S. asper leaf extracts (SA-EE) against toxicity of glutamate-mediated oxidative stress, a crucial factor contributing to the neuronal loss in age-associated neurodegenerative diseases and the underlying mechanism as well as to evaluate its longevity effect.

Methods: Using mouse hippocampal HT22 as a model for glutamate oxidative toxicity, we carried out MTT and LDH assays including Annexin V-FITC/propidium iodide staining to determine the SA-EE effect against glutamate-induced cell death. Antioxidant activities of SA-EE were evaluated using the radical scavenging and DCFH-DA assays. To elucidate the underlying mechanisms, SA-EE treated cells were analyzed for the expressions of mRNA and proteins interested by immunofluorescent staining, western blot analysis and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) techniques. The longevity effect of SA-EE was examined on C. elegans by lifespan assay.

Results: We demonstrate that a concentration-dependent reduction of glutamate-induced cytotoxicity was significant after SA-EE treatment as measured by MTT and LDH assays. Annexin V-FITC/propidium iodide and immunofluorescent staining showed that co-treatment of glutamate with SA-EE significantly reduced apoptotic-inducing factor (AIF)-dependent apoptotic cell death. DCFH-DA assay revealed that this extract was capable of dose dependently attenuating the ROS caused by glutamate. Western blot analysis and qRT-PCR showed that nuclear factor erythroid 2-related factor 2 (Nrf2) protein levels in the nucleus, as well as mRNA levels of antioxidant-related genes under Nrf2 regulation were significantly increased by SA-EE. Furthermore, this extract was capable of extending the lifespan of C. elegans.

Conclusions: SA-EE possesses both longevity effects and neuroprotective activity against glutamate-induced cell death, supporting its therapeutic potential for the treatment of age-associated neurodegenerative diseases.