International Postgraduate Research Conference (IPRC)

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Author: search.filters.author.Jayathilaka, N.Subject: search.filters.subject.Oxidative stress

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    Antioxidant Effect of Coconut Milk on Oxidative Damage in Commensal Lactobacilli in the Gastrointestinal Tract
    (International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Karunasiri, A.N.; Gunawardena, M.; Seneviratne, K.; Jayathilaka, N.
    Coconut milk (CM) is the aqueous extract of coconut endosperm which is rich in polyphenols. Coconut milk is commonly used in culinary applications in South Asia. In this study, protective effect of phenolic antioxidants (PA) extracted from CM was tested in lactobacilli which are the prominent probiotic forms in the human gut. These commensals help to maintain the immune and metabolic homeostasis. The intestinal environment can be altered by many factors that generate reactive oxygen species (ROS) resulting in oxidative stress. Enteric bacteria have been reported to mediate redox homeostasis through the regulation of ROS production. However, oxidative damage to the gut microbiota has been suggested to contribute to several diseases including intestinal and neurodegenerative disorders. Here, the activity of phenolic antioxidants extracted from CM on oxidative damage in Lactobacillus acedophillus, L. plantarum, L. lactis, L. casei and L. fermentum under aerobic conditions were evaluated based on the amount of products of macromolecular damage. The total polyphenol content of aqueous extract of CM was 8.21±0.13 mg/L as determined by the Folin Ciocalteu method. Bacterial cultures at optical density of 0.5 at 620 nm were incubated at 37°C under aerobic conditions to induce the oxidative damage. The cells were cultured overnight with a concentration series of PA (0, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 mg/mL) to assess the protective effect on oxidative damage. The concentration of PA was kept below the concentration that affect cell viability as determined by 2,3,5-triphenyltetrazolium chloride assay at 620 nm. Lipid peroxide levels (μg/mL) and protein carbonyl levels (nmol/mL) were detected with thiobarbituric acid and 2,4-DNPH respectively. Growth under aerobic conditions affected the cell viability and induced significant (P<0.05) damage to proteins and lipids in the lactobacilli under investigation. Treatment with increasing concentrations of PA from CM showed a corresponding increase in the cell viability and a corresponding decrease in the amount of lipid peroxides and protein carbonyls under aerobic conditions. Therefore, PA from CM protect gut microbiota from oxidative damages in lipid and proteins without affecting their viability.
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    Protective Effect of Coconut Cake Phenolic Antioxidants on Oxidative Stress Induced Macromolecular Damage in HEp-2 Cells.
    (In: Proceedings of the International Postgraduate Research Conference 2017 (IPRC – 2017), Faculty of Graduate Studies, University of Kelaniya, Sri Lanka., 2017) Karunasiri, M. G. A. N.; Seneviratne, K.N.; Jayathilaka, N.
    Coconut cake, a by-product of the coconut oil manufacturing is a rich source of phenolic antioxidants. The majority of research dealing with phenolic antioxidants is primarily focused on the extraction of phenolic substances from plant materials and assessment of antioxidant properties in chemical systems. However, such assays in chemical systems do not guarantee the antioxidant properties of phenolic substances in biological systems. In this study, inhibition of H2O2 induced oxidative damage on lipids and proteins by coconut cake phenolic antioxidants (CCPA) was studied in HEp-2 cells as the biological system. CCPA were extracted with 70 % ethanol and the total polyphenol content was measured by Folin Ciocalteu method. The CCPA content, calculated as gallic acid equivalents was 182.81 ± 28.73 mg/kg. The o-diphenols content, calculated as caffeic acid equivalent using a method reported by Gutfinger was 66.83 ± 16.50 mg/kg. Oxidative damage in HEp-2 cells was induced by adding H2O2in PBS for 1 hr. The maximum concentration of H2O2 that does not affect the cell viability (>99 %) was determined as 100 µM using Cell-Titer Glo Luminescent Cell Viability Assay. Formationof thiobarbituric acid reactive species (TBARS) due to lipid peroxidationin HEp-2 cells (0.010±0.000 µM/mL) compared to the control (0.007±0.000 µM/mL) without H2O2was inhibited with 0.5mg/mLCCPA (0.007±0.000µM/mL). Protein oxidation (3.05±0.06nmol/mL) compared to the control (2.14±0.06nmol/mL) without H2O2 as assessed by protein carbonyl formation assay with 2, 4-dinitophenylhydrazine was alsoinhibited by treating the HEp-2 cells with 0.5mg/mL CCPA (2.41±0.06 nmol/mL). Thus, CCPA caninhibit oxidative stress-induced macromolecular damage of lipids and proteins in biological systems.