The effect of St. John's wort (Hypericum perforatum) extracts, hypericin and hyperforin against glutamate induced excitotoxicity in human retinal glial cells

The retina is the tissue that forms the innermost layer of the eye and converts light into nerve impulses. Müller cells are the main glial cells of the retina that are in close contact with both blood vessels and neurons. Thanks to this position, Müller cells can contribute to retinal homeostasis, retinal structure and function. One of the important functions of Müller glia is the uptake and recycling of neurotransmitters such as glutamate. Glutamate is one of the the main neurotransmitters of the central nervous system. Abnormal glutamate release causes overstimulation of glutamate receptors and can lead to damage known as the excitotoxicity. Excessive glutamate release causes oxidative stress which leads to Müller cell dysfunction. Müller cell dysfunstion affects the pathogenesis of retinal diseases such as diabetic retinopathy and glaucoma. Hypericum perforatum is a perennial herbaceous plant belongs to Hypericaceae family. Pharmacological and clinical studies demonstrated that Hypericum perforatum exerts antidepressant, anti-inflammatory, antimicrobial, anticancer, antioxidant and neuroprotective effect. In this study, cytotoxicity of Hypericum perforatum extracts, oil, hypericin and hyperforin on MIO-M1 retinal glial cells and SH-SY5Y neuronal cells were analyzed. The protective effect of extracts, oil, hypericin and hyperforin against glutamate excitotoxicity were determined. According to the cell viability analysis, the gliaprotective and neuroprotective activity were detected with oil treatment.