The possible role of thyroid hormones on the DNA damage of heart tissue in diabetic rats

Oxidative stress in diabetes mellitus may play an important role in development of diabetes related vascular complications. Production of ROS increases in diabetic patients, especially in the bad glycemic controlled ones and may lead damage to the structure of DNA. 8-OHdG are the changes of purine remnants which are induced with ROS. It is the important and sensitive marker of oxidative DNA damage and oxidative stress.It?s thought that there has been a sinergism between thyroid hormones and insulin. It was shown in diabetes that thyroid hormones caused changes in some key enzyme activities at the carbohydrate metabolism. In the studies done in rat tissues, it was reported that thyroid hormones may mediate some effects of insuline. Thyroid dysfunction may increase oxidative stress.In this study, we aimed to establish the potential role of thyroid hormones, in heart tissue DNA damage of diabetic rats. For that, we planned to use HPLC-ECD for detecting 8-OHdG which is the indicator of DNA damage, in the heart tissues of different groups.Groups are determined as follows; control group, diabetes group, diabetes + insulin group, hypothyroidism group, hypothyroidism + diabetes group, hypothyroidism + diabetes + insulin group, hypothyroidism + diabetes + insulin + t4 (5µg/kg) group, hypothyroidism + diabetes + insulin + t4 (2,5µg/kg) group.In our study, mean 8-OHdG value was found significantly higher in diabetes group than control group, value of the diabetes + insulin group was found significantly lower than the value of diabetes group while similar with control group in rat heart tissue. In hypothyroidism group, it was significantly higher than the values of control group and diabetes group.When hypothyroidism + diabetes group was treated by administration of insulin, it was seen that the oxidative damage wasn?t improved. In the high dose T4 treated group, 8-OHdG was significantly higher and there was no significantly difference between the low dose T4 treated group and control group. When compared the high dose T4 treated group with the low dose T4 treated group, it was seen that high dose group had higher 8-OHdG level.In conclusion; oxidative stress related DNA damage may develop in diabetes and hypothyroidism, single insulin may be effective in presence only diabetes, but if there are diabetes and hypothyroidism together, single insulin may not be effective and may need thyroid hormone in physiological dose. All these findings make think that insulin may not show the improvement effect on DNA damage in the presence of hypothyroidism in diabetes mellitus and with a great possibility, thyroid hormones may mediate some effects of insulin.