Characterization of Green and Yellow Papaya for Antioxidation and Glucose Uptake Stimulatory Activity in HepG2 Liver Cells

Abstract

Abstract Objectives The long-term objective of present research is to evaluate papaya for anti-diabetic properties. The current objectives were (1) To determine polyphenolic contents and antioxidation activity of leaves, skin, pulp, and seeds of green and yellow papaya and (2) to evaluate their effects on glucose uptake in HepG2 liver cells. Methods The leaves, skin, pulp, and seeds samples were freeze dried and then extracted in water or 80% Methanol. The total phenolic contents of each extracted sample was determined using the Folin- Ciocalteu method. The antioxidation activity in each sample was determined using 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and Ferric ion reducing antioxidation power (FRAP) assays. Effect of each fraction on glucose uptake was determined using a fluorescent-tagged NBD-Glucose derivative. Results The concertation of polyphenols was highest in both water and methanol extracts of seeds from yellow papaya compared to that in seeds from green papaya. Leaves and skin fractions contained modest concentration of polyphenols whereas pulp contained the lowest concentration of polyphenols. FRAP assay indicates that both water and methanol extracts of leaves, skin, pulp, and seeds from yellow papaya exhibited higher antioxidation activity compared to that of green papaya. A similar antioxidation activity pattern was observed by DPPH assay. Leaves and skin from both green and yellow papaya showed modest to high antioxidation activity whereas pulp from both green and yellow papaya contained a low antioxidation activity. In contrast, green papaya extracts significantly stimulated glucose uptake in HepG2 liver cells compared to that of yellow papaya extracts. Both water and methanol extract of pulp from green papaya showed the greatest stimulation of glucose uptake followed by leaves and skin. Conclusions Although the seeds from yellow papaya contained highest concentration of polyphenols and exhibited highest antioxidation activity, pulp from green papaya showed significantly higher stimulation of glucose uptake in liver cells. Our data indicates that polyphenolic content and/or antioxidation activity in papaya may not be related to their glucose uptake stimulatory activity in liver cells. This study concludes that regular consumption of green papaya may be beneficial for preventing diabetes. Funding Sources Capacity Building Grant, USDA.