Microwave-Assisted Extraction, In Vitro Antioxidant Activity, and Hepatoprotective Potential of Flavonoid-Rich Watermelon (Citrullus lanatus) Seed Extract in Acetaminophen-Induced Liver Damage in Wistar Rats

Abstract

Watermelon (Citrullus lanatus) seed are an underutilized agro-industrial by-product in Nigeria, which contains flavonoids with antioxidant properties. This study optimized microwave-assisted extraction (MAE) of flavonoids from watermelon seeds, evaluated the extract's in vitro antioxidant activity, and investigated its hepatoprotective effects against acetaminophen (APAP)-induced liver injury in Wistar rats. Eight MAE conditions were assessed in terms of solid-to-solvent ratio, microwave power and extraction time, and the total flavonoid content (TFC) was determined by the aluminium chloride colorimetric assay. The optimum flavonoid yield (8.03 mg/mL) was obtained at a 1:10 solid-to-solvent ratio, 60 microwave power, and 30 min extraction time. The optimized extract exhibited concentration-dependent antioxidant activity in DPPH radical scavenging, ferric reducing antioxidant power (FRAP) and Lipid peroxidation inhibition assays although lower than that of ascorbic acid. Acute oral toxicity testing following OECD guideline 425 established an LD50 of 2000 mg/kg. The results show that in APAP-treated rats, the extract dose-dependently ameliorated hepatic injury by reducing elevated ALT, AST, and ALP activities, improving lipid profile, restoring antioxidant defenses (CAT, SOD, and GSH), increasing haemoglobin levels, and lowering malondialdehyde concentrations. The highest extract dose (LD50 ×1/10) produced effects comparable to silymarin. The findings suggest that watermelon seed flavonoid extract has the potential to be used as a low-cost hepatoprotective agent and a functional ingredient derived from agricultural waste.