Solvents of different polarities (water, ethanol, ethyl acetate and hexane) were used for the extraction of antioxidants from the leaves and stems of the shoots of Barringtonia racemosa. The leaf water extracts had the highest polyphenol and ascorbic acid contents. Flavonoids and carotenoids were highest in the leaf ethyl acetate extracts. The leaf water extracts had the highest ferric reducing activities and scavenging activities against ABTS, DPPH and superoxide anion radicals. Antioxidant activities of these extracts were comparable to, if not higher than the antioxidants BHT, ascorbic acid, rutin and gallic acid. UHPLC analyses revealed the presence of gallic acid, protocatechuic acid, ellagic acid, quercetin and kaempferol in the leaves. Overall, the leaves contained more antioxidant compounds and higher antioxidant activities than the stems. This study demonstrates the polar nature of antioxidants in the shoots of B. racemosa. There is great potential for the plant as a natural source of antioxidants

The leaf extract ofTamarindus indicaL. (T. indica) had been reported to possess high phenolic content and showed high antioxidant activities. In this study, the effects of the antioxidant-rich leaf extract of theT. indicaon lipid peroxidation, antioxidant enzyme activities, H₂O₂-induced ROS production and gene expression patterns were investigated in liver HepG2 cells. Lipid peroxidation and ROS production were inhibited and the activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase was enhanced when the cells were treated with the antioxidant-rich leaf extract. cDNA microarray analysis revealed that 207 genes were significantly regulated by at least 1.5-fold (p< 0.05) in cells treated with the antioxidant-rich leaf extract. The expression ofKNG1, SERPINC1, SERPIND1, SERPINE1, FGG, FGA, MVK, DHCR24, CYP24A1,ALDH6A1, EPHX1andLEAP2were amongst the highly regulated. When the significantly regulated genes were analyzed using Ingenuity Pathway Analysis software, “Lipid Metabolism, Small Molecule Biochemistry, Hematological Disease” was the top biological network affected by the leaf extract, with a score of 36. The top predicted canonical pathway affected by the leaf extract was the coagulation system (P< 2.80 × 10⁻⁶) followed by the superpathway of cholesterol biosynthesis (P< 2.17 × 10⁻⁴), intrinsic prothrombin pathway (P< 2.92 × 10⁻⁴), Immune Protection/Antimicrobial Response (P< 2.28 × 10⁻³) and xenobiotic metabolism signaling (P< 2.41 × 10⁻³). The antioxidant-rich leaf extract ofT. indicaalso altered the expression of proteins that are involved in the Coagulation System and the Intrinsic Prothrombin Activation Pathway (KNG1, SERPINE1, FGG), Superpathway of Cholesterol Biosynthesis (MVK), Immune protection/antimicrobial response (IFNGR1, LEAP2, ANXA3 and MX1) and Xenobiotic Metabolism Signaling (ALDH6A1, ADH6). In conclusion, the antioxidant-rich leaf extract ofT. indicainhibited lipid peroxidation and ROS production, enhanced antioxidant enzyme activities and significantly regulated the expression of genes and proteins involved with consequential impact on the coagulation system, cholesterol biosynthesis, xenobiotic metabolism signaling and antimicrobial response.

Tamarindus indica L. (T. indica) or locally known as “asam jawa” belongs to the family Leguminosae. T. indica seeds as by-products from the fruits were previously reported to contain high polyphenolic content. However, identification of their bioactive polyphenols using recent technologies is less well researched but nonetheless important. Hence, it was the aim of this study to provide further information on the polyphenolic content and antioxidant activities as well as to identify and quantify its bioactive polyphenols. T. indica seeds were extracted with methanol and were then fractionated with different compositions of hexane, ethyl acetate and methanol. Polyphenolic contents were measured using Folin-Ciocalteu assay while antioxidant activities were measured using DPPH radical scavenging and ferric reducing (FRAP) activities. The cytotoxic activities of the crude extract and the active fraction were evaluated in HepG2 cells using MTT assay. The cells were then pre-treated with the IC₂₀ concentrations and induced with H₂O₂ before measuring their cellular antioxidant activities including FRAP, DPPH, lipid peroxidation, ROS generation and antioxidant enzymes, SOD, GPx and CAT. Analyses of polyphenols in the crude extract and its active fraction were done using UHPLC and NMR. Amongst the 7 isolated fractions, fraction F3 showed the highest polyphenolic content and antioxidant activities. When HepG2 cells were treated with fraction F3 or the crude extract, the former demonstrated higher antioxidant activities. F3 also showed stronger inhibition of lipid peroxidation and ROS generation, and enhanced activities of SOD, GPx and CAT of HepG2 cells following H₂O₂-induced oxidative damage. UHPLC analyses revealed the presence of catechin, procyanidin B2, caffeic acid, ferulic acid, chloramphenicol, myricetin, morin, quercetin, apigenin and kaempferol, in the crude seed extract of T. indica. UHPLC and NMR analyses identified the presence of caffeic acid in fraction F3. Our studies were the first to report caffeic acid as the active polyphenol isolated from T. indica seeds which likely contributed to the potent antioxidant defense system of HepG2 cells. Results from this study indicate that caffeic acid together with other polyphenols in T. indica seeds can enhance the antioxidant activities of treated HepG2 cells which can provide protection against oxidative damage.