Thesis (Ph.D.)--Chulalongkorn University, 2011

This study aimed to determine antioxidant activities of Tamarindus indica seed coat extracts and evaluate its protective activities against hydrogen peroxide (H2O2)-induced oxidative stress in human foreskin fibroblast CCD-1064Sk cells. The roasted seed coat of tamarind was extracted with various solvent systems: 70% ethanol (TSCE-E), ethyl acetate (TSCE-EA), 70% ethanol followed by partition with chloroform and then ethyl acetate (TSCE-EEA), and boiling-water followed by partition with ethyl acetate (TSCE-W). The highest phenolic content was observed in TSCE-W which revealed the free radical scavenging activities in cell-free system. TSCE-W possessed the highest DPPH● and ABTS●+ scavenging activities. TSCE-W was also exhibited superoxide anion radical, hydroxyl radical, H2O2, and nitric oxide scavenging activities, including reducing power and anti-lipid peroxidation activities comparable with other TSCEs. In cell-based assay, TSCE-W up to 1 mg/mL did not show cytoxicity against CCD-1064Sk cells as determined by various standard assays: MTT, neutral red, Hoechst 33342 staining and trypan blue dye exclusion assay. Cells treated with TSCE-W alone at the non-toxic concentration did not generate reactive oxygen species (ROS) and lipid peroxidation. Additionally, TSCE-W significantly increased intracellular glutathione (GSH) level and the activity of superoxide dismutase (SOD) and catalase (CAT). TSCE-W reduced the generation of ROS and lipid peroxidation as well as increased intracellular GSH level in H2O2-treated cells. The antioxidant mechanism of TSCE-W via protein expression was performed using Western blot analysis. The result showed that treatment of TSCE-W before H2O2 exposure for 3 h significantly up-regulated the protein expression of antioxidant enzymes including copper, zinc superoxide dismutase (Cu,ZnSOD), glutathione peroxidase (GPx), and glutathione-S-transferase (GST) as compared with vehicle control. Treatment of TSCE-W prior to H2O2 exposure for 6 h maintained the protein expression of Cu,ZnSOD, GPx, and CAT comparable with vehicle control. The results suggest that an inexpensive and simple boiling-water extraction of TSCE-W may provide a good source of natural antioxidant. TSCE-W protected oxidative stress in cells by the regulation of antioxidant enzymes expression, TSCE-W potentially useful for health food additives and cosmeceuticals.