Neuroprotective potential of Polygonum minus (daun kesum) extracts against glutamate-induced toxicity

Leong, Chi Fung (2024) Neuroprotective potential of Polygonum minus (daun kesum) extracts against glutamate-induced toxicity. Masters thesis, Sunway University.

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Abstract

Glutamate-induced neurotoxicity, stemming from dysregulation of the glutamate neurotransmitter within the central nervous system, is implicated in various neurodegenerative diseases. Given the limited efficacy of current treatments, researchers are exploring natural products with neuroprotective properties as potential preventive or therapeutic options. Natural antioxidants, recognized for their ability to counter neurodegenerative conditions, have been extensively studied. Polygonum minus, a commonly used herb and culinary ingredient in Southeast Asia, has shown promise in vitro and in vivo for its antioxidant-related neuroprotective effects. However, its specific potential against glutamate-induced toxicity remains poorly understood. This study aimed to assess the neuroprotective effects of P. minus leaves extracts, both ethanolic and essential oil, against glutamate-induced toxicity in HT22 mouse hippocampal cells. Glu-induced toxicity was evaluated across various concentrations (1mM to 10 mM) using cell viability and apoptotic assays. Glu displayed a dose-dependent cytotoxicity on HT22. Specifically, 4 mM and 5 mM reduced viability and induced apoptosis in HT22 cells. To assess the neuroprotective effects of P. minus extracts, co-treatment of P. minus EtOH (0.1 to 25 µg/mL) and P. minus EO (0.1 to 50 µg/mL) with Glu (4 and 5 mM) for 24 hours was conducted via cell viability assays. Co-treatment of P. minus EtOH with Glu did not exhibit a protective effect on HT22 cell viability, whereas co-treatment of P. minus EO (50 µg/mL) with Glu (4 mM and 5mM) prevented the decrease in the viability of HT22 cells induced by Glu toxicity. Therefore, we focused on the neuroprotective effects of P. minus EO (50 µg/mL) against Glu treatment for our subsequent work. To understand the neuroprotective actions of P. minus EO, calcium (Ca2+) influx, mitochondrial function, and apoptotic analyses were performed using biochemical assays and Hoechst 33342 staining. Co-treatment of P. minus EO at 50 µg/mL with 4 mM Glu reduced the intracellular Ca2+ influx, reactive oxygen species (ROS), and potentially increased mitochondrial membrane potential (MMP) levels in HT22 cells compared to the 4 mM Glu alone group. In apoptotic assays, P. minus EO at 50 µg/mL with Glu (4 and 5 mM) reduced the activated caspases levels as compared to the Glu-treated cells. The percentage of apoptotic cells was also reduced compared to the 4 mM Glu alone group. Additionally, P. minus EO exhibited modulatory effects in Glu-induced apoptotic cell death mechanisms in HT22 cells. Co-treatment of P. minus EO at 50 µg/mL with 4 mM Glu significantly reduced the activation of p44/42 MAPK proteins, while potentially decreasing Bax and the Bax/Bcl-2 ratio compared to the Glu-treated cells. These results suggest that P. minus EO may provide antioxidant-associated neuroprotection against glutamate-induced apoptosis in HT22 cells. Further investigations are warranted to elucidate the precise neuroprotective mechanisms of P. minus extracts against glutamate-induced toxicity.

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