Peculiarities of lipid and protein peroxidation in autoimmune thyroiditis with and without mild thyroid dysfunction

The aim of this study was to investigate lipid and protein peroxidation in autoimmune thyroiditis (AT) and subclinical hypothyroidism (SH), as well as to evaluate its correlation for arterial stiffness and relationship to replacement treatment. Methods. The study included 85 women; 32 of them had no thyroid pathology (group 1, controls) and 53 had AT and SH (group 2). Free-radical protein and lipid oxidation (FRO), serum antioxidant activity (AOA), arterial elasticity parameters were investigated. In addition, we compared different categories of the patients included in group 2: patients having euthyroidism ( n = 18) and subclinical hypothyroidism ( n = 35); AT patients with TSH less ( n = 26)and not less ( n = 27) than the median of group values (∼ 6 mU/ml). In 33 patients the dynamic changes of FRO were reevaluated after 6–8 months of thyroxine replacement. Results. AT patients demonstrated higher oxidative protein modification rate (OMB) which was confirmed by 75% elevation of OMB 363nm index ( p = 0,049) and greater activity of lipid peroxidation (LPO) confirmed by 11% elevation of luminescence intensity index Imax ( p = 0,035) but no increase in AOA, catalase and superoxide dismutase activity ( p > 0,05). Oxidative stress severity was positively associated with TSH; dyslipidaemia had a stronger influence on oxidative stress. The proportions of women with relative disparity between elevated malondialdehyde (MDA) and depressed antioxidant activity (AOA), were significantly higher in AT and SH groups ( р < 0,05). The most significant difference between oxidative stress parameters was found among patients having TSH less and not less then 6 mU/ml. The subgroup with higher TSH was found to have higher indexes of endogenous intoxication and LPO products values (the increase of EI254nm, EI274nm, EI294nm, triene conjugates by 18%; 19%; 29% и 38% respectively, p <0,05). Oxidative stress can affect arterial stiffness and vascular remodeling. Levothyroxine activates pro- and antioxidants but antioxidants are more significantly involved, and balance can be improved. Conclusion. AT is accompanied by FRO activation, АОА depression, their imbalance and oxidative stress development. Significant correlations are observed for TSH, dislipidaemia and FRO. Oxidative stress demonstrates detrimental effects on arterial functions which may be partly reversed by replacement therapy. Levothyroxine activates pro- and antioxidants with the predominant positive effect on AOA.