Excessive ROS production causes oxidative stress, leading to cellular damage and potentially death. Polyphenols are plant-derived compounds widely regarded for their antioxidant activity. Their utilization presents an opportunity to investigate sustainable methods to improve human health. The goal of this thesis was to study the antioxidant activities of tart cherry pit (CP) extracts and elucidate the potential use of flavonoids in novel applications; as preventative care against ROS when polyphenol-rich tart cherry pits are applied to keratinocytes (HaCaT) and fibroblasts (NIH3T3), and as regulators of immunosuppressive myeloid-derived suppressor cells (MDSC).CPs are a byproduct of cherry processing that contribute to landfill waste accumulation negatively impacting the environment with their methane footprint. Until recently, the polyphenolic content of CPs had not been described. This study aimed to utilize if polyphenols present in extracts made from CPs would be effective antioxidants in skin cells. In this thesis, an untargeted mass spectrometry analysis was used to determine the polyphenols present in CPs. The antioxidant activity of CP extracts was evaluated in human skin cells exposed to H2O2 and LPS by assessing ROS production and investigating the pro- and anti-oxidant genes involved. The findings from this thesis show that CP extracts are safe and effective as antioxidants, suggesting their potential use in skincare. In addition, this study investigated the role of flavonoids, a class of polyphenols, in the regulation of myeloid derived suppressor cells (MDSCs) which through immunosuppression contribute to tumor progression and chronic inflammatory disease progression. Here, we first established a high-throughput protocol to stimulate immunosuppressive activity in MSC2, a model system for MDSCs, by promoting LPS-induced ROS. Next, we investigated the antioxidant effect of selected flavonoids in counteracting MSC2 immunosuppressive activity. The results from this thesis indicate that flavonoids effectively reduced LPS-induced ROS, suggesting their role in overcoming immunosuppression, paving a path for future studies on the application of flavonoids against immunosuppression. The findings in this thesis highlight the applicability of plant-based antioxidants in human health, emphasizing the importance of future investigation of uses for polyphenols.
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