The Antioxidant Effect of Lycium Fruit Extract on Hyperglycemia-Induced Oxidative Stress in Human Liver and Rat Muscle Cell Lines

This dissertation, "The Antioxidant Effect of Lycium Fruit Extract on Hyperglycemia-induced Oxidative Stress in Human Liver and Rat Muscle Cell Lines" by Ka-man, Chow, 鄒嘉敏, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: ABSTRACT of thesis entitled THE ANTIOXIDANT EFFECT OF LYCIUM FRUIT EXTRACT ON HYPERGLYCEMIA-INDUCED OXIDATIVE STRESS IN HUMAN LIVER AND RAT MUSCLE CELL LINES Submitted by CHOW KA MAN for the degree of Master of Philosophy at The University of Hong Kong in August 2005 At the cellular level, an environment that is high in glucose and free fatty acid (FFA) will lead to the formation of excess amount of reactive oxygen species (ROS). This increases the oxidative stress inside the cells and leads to hyperglycemia which is one of the factors in the development of overt diabetes and its complications. Studies in diabetic patients have also shown that oxidative stress is significantly increased in association with a reduction in some antioxidant enzyme activities when compared with normal subjects. This leads to the concept of antioxidant therapy in diabetic patients. Lycium fruit has long been used by Chinese herbalists for its anti-aging and hypoglycemic properties. Scientists have recently found that lycium fruit is rich in different kinds of antioxidants. The objective of this study is to investigate whether the aqueous extract of lycium fruit (LFE) can reduce the formation of ROS in association with enhanced activities of antioxidant enzymes that include superoxide dismutase (SOD) and catalase (CAT) in rat skeletal muscle (L6) and human liver cells (HepG2). Cells were first cultured in normal (5.5mM glucose) and hyperglycemic conditions (30mM and 60mM glucose) to develop an in-vitro model for the investigation of hyperglycemia-induced oxidative stress in L6 and HepG2. Both L6 and HepG2 responded with an increase in glucose uptake and an increase in ROS production in I associate with a decrease in SOD activity when cultured in high glucose conditions compared to normal controls. However, L6 showed a transient increase in CAT activity which then returned to normal when cultured for a longer period, whereas HepG2 showed a significant decrease in CAT activity when cultured for 12 hours. Cells were further cultured in normal and 30mM glucose with the supplementation of 0.5 to 4 mg/ml LFE to investigate the possible antioxidant effect of LFE. A significant reduction in the hyperglycemia-induced oxidative stress was observed in both L6 and HepG2, and the significant reduction in the intracellular ROS level might have been due to the ROS scavenging activity of LFE on the superoxide anion, hydroxyl radical and hydrogen peroxide. An increase in activities of the antioxidant enzymes with the supplementation of LFE was also observed. These results suggest that the aqueous extract of lycium fruit is effective in protecting the skeletal muscle and liver cells against the oxidative damage caused by hyperglycemia in-vitro. II DOI: 10.5353/th_b3618613 Subjects: Lycium chinense - Therapeutic use Oxidation, Physiological Hyperglycemia Liver - Physiology Rats - Physiology