Oxidative Status and Thiol/Disulfide Homeostasis Are Changed During 75 g Oral Glucose Tolerance Test over a Five-Hour...

Oral glucose loading may affect oxidative status during oral glucose tolerance test (OGTT). We aimed to investigate how oxidant and antioxidant markers and thiol/disulfide parameters change during OGTT.

OGTT was performed to 42 volunteers who were considered risk of type 2 diabetes and were divided into three groups (normoglycemic, prediabetes, diabetes) according glucose levels during OGTT. Glucose, insulin, c-peptide, total antioxidant status (TAS), total oxidant status (TOS), total thiol and native thiol were investigated with auto-anaylzer for five-hours period.

Decrease of TAS and increase of TOS levels began with the increase in glucose and insulin levels. The increase of TAS started at third hour and reached the highest levels at fifth hour. OSI levels were higher at fourth hour than fasting and first hours in normoglycemic and diabetes groups. In the prediabetic group, TAS were higher than the other groups, TOS peak was at the second hour (p < 0.05). Native thiol and total thiol levels showed variable course during OGTT, both parameters increased at the end of the process (p < 0.05). Disulfide levels showed an increase trend but it was not statistically different in normoglycemic and diabetes groups. In prediabetes group, second hour disulfide level was lower than fasting state and disulfide was significantly increased at third, fourth and fifth hours and fifth hour disulfide level was also higher than fasting.

Oxidative stress parameters and thiol/disulfide balance were found to deteriorate within five-hours after glucose loading in all groups. These results indicates that oxidative stress occurs during OGTT.