Comparative Analysis of Oxidative Metabolism in Liver in Different Experimental Models of Hypothyroidism: Low Iodine Diet and Anti-Thyroid drug (Methimazole)

Objectives: On the concept of oxidative stress in hypothyroidism, which still remains ambiguous and controversial, the article emphasizes the issue of the impact of the experimental conditions on the validity of the data obtained in different methods of modeling thyroid dysfunction. Materials and Methods: Experiments were conducted on 112 white nonlinear male rats. Thyroid hormones and biomarkers of oxidative metabolism in the liver tissue were determined in rats kept for 3 months on a low-iodine diet (LID) and in rats with methimazole (MMI)-induced hypothyroidism (2,5 mg/100 g of body weight for 3 weeks). Results: In LID-rats (n=96) total serum T4 amounted 43, total T3 in liver tissue - 73% of the level found in euthyroid animal, p=0.0121 and p=0.0051, respectively), whereas in MMI-rats (n=96) both total and free serum T4 were 67% of control (p=0.0002 for both total and free T4). In LID-rats cytochrome oxidase (CcOX) activity in liver tissue was 68.5, concentration of malondialdehyde (MDA) - 58% of euthyroids (p value - 0.0202 and 0.0127, respectively), while protein carbonyls (PC) level was 116% of the control (p=0.0411). In MMI-rats liver malate dehydrogenase (MDH) activity decreased up to 70.9, but succinate dehydrogenase (SDH) activity and MDA concentration increased up to 163.6 and 154% of the level in euthyroid animals respectively (p˂0.05). Conclusion: LID-model led to the more pronounced inhibition of thyroid function, than that the MMI-hypothyroidism model used. LID-model was accompanied by a decrease in the intensity of oxidative metabolism in liver tissue, whereas MMI-hypothyroidism - by activation of the succinate oxidation pathway and an increase in the concentration of secondary lipid peroxidation products in the liver of experimental animals. The results suggest that the conflicting data obtained from studies of oxidative metabolism in hypothyroidism, among other assumptions, may be due to the different approaches used by researchers to model thyroid dysfunction.