Evaluation of the antioxidant potential and HT-29 cytotoxicity of crude ethanolic peel extract from locally-grown pomelo (Citrus maxima)

Abstract

Colorectal cancer is the third most common cancer worldwide. While treatments are available, they often have limitations and can be expensive, particularly for low-income Filipinos. This rationale encouraged the researchers to explore natural products as potential and sustainable treatment alternatives. Citrus maxima or pomelo, is native to Southeast Asian countries, including the Philippines. The peels of pomelo that are often discarded as waste are rich in bioactive compounds that can serve as therapeutic agents through their antioxidant, anti-inflammatory, and cytotoxic properties. This study investigated the antioxidant potential and cytotoxic activity of pomelo peel extract on the HT-29 colorectal adenocarcinoma cell line. The extract was prepared through maceration in 80% ethanol, followed by liquid-liquid extraction (LLE) with water and hexane, from which the polar partition was obtained. DPPH antioxidant assay, total flavonoid content (TFC), total phenolic content (TPC), and cytotoxicity assays were performed. The pomelo peel extract showed a moisture content of 75.39%, with the extraction process resulting in an overall extraction yield of 4.84% (w/w). Results showed a TFC of 17.29 ± 1.21 mg quercetin equivalent (QE)/g, TPC of 107.36 ± 0.73 mg gallic acid equivalent (GAE)/g, and an IC₅₀ of 5.958 mg/mL for the DPPH assay. In the cytotoxicity assay, the HT-29 cells exhibited a dose-dependent response to the pomelo peel extract, with an IC₅₀ value of 0.8752 mg/mL. Furthermore, varying concentrations of the pomelo peel extract combined with regulated cell death (RCD) inhibitors—Ferrostatin-1 (Fer-1, ferroptosis), Necrostatin-1 (Nec-1s, necroptosis), and ZVAD-FMK (apoptosis/pyroptosis)—showed no impact on the cell viability. This demonstrates the pomelo peel extract’s antioxidant and cytotoxic potential for colorectal cancer; however, the specific cell death pathway remains unclear. Therefore, additional replicates and time-dependent treatments with the extract and inhibitors are recommended to further elucidate the mechanisms involved and clarify the pathway dynamics