Identification and quantification of the oxidized protein profile in the Zucker diabetic fatty rat supplemented with green tea

Angela D Myracle, Purdue University

Abstract

Green tea (GT) is a beverage that is consumed throughout the world. GT is a source of catechins, which may have health benefits that could be beneficial to individuals that are obese and/or have type 2 diabetes (T2DM). Oral consumption of GT has been shown to have modest effects on reducing body weight, food intake and blood glucose. A study was conducted to evaluate if long term supplementation with GT formulated with ascorbic acid to increase the bioavailability of catechins would improve the glucose tolerance and counteract the effects of oxidative stress in Zucker diabetic fatty (ZDF) rats. This approach was chosen since the bioavailability of GT is very low and the catechins are very labile in alkaline environments. ZDF rats were supplemented daily for six weeks with one of the following: (1) water (control), (2) ascorbic acid (AA) (17mg/kg/day), (3) GT (85 mg/kg/day) or (4) GT+AA combination. Data collected included glucose tolerance tests (GTT), insulin, daily weight, dual energy x-ray absorptiometery (DEXA) and food consumption. None of the supplement groups reduced blood glucose or improved insulin sensitivity. There was a modest reduction seen in the GT and GT+AA treated for fat mass and for total food consumption. Urinary isoprostane measures at six weeks indicated a trend toward reduction in OS in the AA, GT and GT+AA supplement groups compared to the control, however there was no statistical significance. The hyperglycemia of Diabetes mellitus (DM) results in increased levels of oxidative stress which is thought to contribute to the secondary complications of the disease. The green tea catechins have antioxidant activity. In this study we also evaluated the efficacy of long term supplementation with formulated GT in counteracting the effects of oxidative stress in Zucker diabetic fatty (ZDF) rats. Antioxidants neutralize reactive oxygen species (ROS) thereby reducing oxidative stress (OS). Complications such as nephropathy result from OS damage to tissues. Although, GT and GT+AA were not effective in significantly reducing hyperglycemia in ZDF rats, the antioxidant capacity of the catechins may offer some protection against the oxidative damage of hyperglycemia Proteomics techniques were utilized to examine the hypothesis that antioxidants (catechins and ascorbic acid) can reduce OS and reduce the amount of oxidized proteins in diabetic ZDF rats. Plasma was labeled with biotin hydrazide to tag the oxidized proteins and affinity purified to remove the abundant and nonoxidized proteins. Oxidized proteins were quantified by isobaric tags for relative and absolute quantification (iTRAQ) and identified with matrix assisted laser ionization desorption (MALDI). One hundred twenty oxidized proteins were identified and quantified. This study marks the first attempt to examine the oxidized plasma proteome and to investigate if antioxidant supplementation protects proteins from oxidative damage. To date, methodology to test for the efficacy of antioxidants is very limited and only provides general information about the increase or decrease that is promoted by the antioxidant. The studies done for this dissertation help fill a gap in knowledge concerning antioxidant function in vivo and provide a new technique that may be useful to address the efficacy of antioxidants.

Degree

Ph.D.

Advisors

Burgess, Purdue University.

Subject Area

Nutrition

COinS