Relationship between Thyroid Stimulating hormone and Antioxidant Status in Patients with Suspected Thyroid Dysfunction   A. M. S. M. Wickramarathne1,2*, R. Sivakanesan2, D. K. K. Nanayakkara3   1Post Graduate Institute of Science, University of Peradeniya 2Department of Biochemistry, Faculty of Medicine, University of Peradeniya 3 Nuclear Medicine Unit, Faculty of Medicine, University of Peradeniya Abstract Thyroid hormones are involved in the regulation of basal metabolic rate and in oxidative metabolism. The study was conducted on antioxidant status and thyroid stimulating hormone (TSH) of patients referred to the Nuclear Medicine unit to assess the thyroid function. Serum TSH level was measured using immuno-radiometric assay. Antioxidant status was estimated by serum Total Antioxidant Capacity (TAC) using Ferric Reducing Ability of Plasma, and the extent of protein oxidation was assessed by the serum protein thiol concentration using Ellman’s method. There was no significant correlation between TSH and TAC (P=0.103) or TSH and protein thiol (P=0.269). A significant positive correlation was observed between TSH and TAC (r=0.526, P=0.036) in hypothyroid patients. Serum TAC and protein thiol concentrations of females had a significant negative correlation (r= -0.263, P=0.015). The study thus concludes that, there is a significant positive correlation between TSH and TAC in hypothyroid patients. There were no significant differences in TAC and protein thiol concentrations between three thyroid groups. Introduction Thyroid hormones are involved in the regulation of basal metabolic rate and in oxidative metabolism. In hyperthyroid conditions metabolic activities are increased and thereby there is an increase in the total consumption of oxygen. These conditions can promote formation of reactive oxygen species (ROS) and other free radicals, resulting in oxidative stress and impairment of the antioxidant system (Abalovich et al., 2003). Hence a study was conducted with the objective of understanding the relationship between serum thyroid stimulating hormone (TSH) and serum antioxidant levels in patients with suspected thyroid dysfunction who were currently not on treatment. Results The study population (n=93) had a mean TSH of 5.4 ± 12.3 mU/L. Mean serum TAC was 719.1 ± 164.5 µmol/L and the mean serum protein thiol concentration was 517.7 ± 9.3 µmol/L. There was no significant correlation between TSH and TAC (P=0.103) or TSH and protein thiol (P=0.269). In the study population, 9 patients (9.7%) were hyperthyroid, 68 (73.1%) were euthyroid while 16 (17.2%) were hypothyroid. There was a significant positive correlation between TSH and TAC (r=0.526, P=0.036) in hypothyroid patients. No such correlation was observed in hyperthyroid or euthyroid patients. There was no significant difference in the mean TAC or protein concentrations between the three groups (Table 1). The protein thiol concentration was lowest in hyperthyroid patients and highest in hypothyroids even though the mean concentrations among the groups were not significantly different. (Table 1) Table 1. Mean values for Age, TSH, TAC and Protein thiol Majority of the study group (n=85, 91.4%) were females and 8 (8.6%) were males. Serum TAC and protein thiol concentrations of females had a significant negative correlation (r= -0.263, P=0.015). In contrast, no significant correlation was observed between TAC and protein thiol concentrations in males (r=0487, P=0.221). Discussion Mean TAC value seen in this study (719.1±164.5 µmol/L) is slightly lower than that of apparently healthy Chinese adults (1017 ± 206 µmol/L) Benzie and Strain (1996). Mean protein thiol concentration obtained in this study was higher than those seen in healthy controls (376 ± 64 µmol/L) in India (Suresh et al., 2010). This study showed a significantly negative correlation between mean TAC and protein thiol levels of females. In males there was no significant correlation. In a study done by Jansen and Ruskovska (2013), protein thiols of males have shown a negative but no significant correlation with the TAC (r = −0.008). Unlike in the present study, Rao and Prasad (2012) observed significant decrease in protein thiol levels in hyperthyroid and hypothyroid patients compared to euthyroid controls. Age (Years) TSH (mU/L) TAC (µmol/L) Protein thiol Hyperthyroid 53.3 ± 16.1 0.1222 ± 0.044 785.5 ± 151.7 496.5 ± 141.5 Euthyroid 44.6 ± 12.5 1.82 ± 1.060 706.6 ± 167.1 516.0 ± 79.5 Hypothyroid 40.0 ± 16.3 23.38 ± 22.39 734.9 ± 159.8 536.8 ± 97.4 Methodology Samples were collected from patients who were referred to the Nuclear Medicine unit, University of Peradeniya to assess the thyroid gland function from September to December 2013. Patients who were not on thyroxine or antithyroid drugs at the time of sample collection were selected for the study after obtaining their informed written consent. Ethical clearance for this study was obtained from Ethics Committee, Postgraduate Institute of Science. Serum TSH level was measured using immuno-radiometric assay method (IRMA). Oxidant stress was estimated by serum Total Antioxidant Capacity (TAC) and serum protein thiol concentration. TAC was estimated using Ferric Reducing Ability of Plasma, by reducing ferric- tripyridyltriazine (Fe3+-TPTZ) to form a blue colored ferrous-tripyridyltriazine (Fe2+- TPTZ) complex (Benzie and Strain, 1996). Protein thiol in serum was estimated using Ellman’s reagent (Koster et al., 1986). Conclusion There was no significant difference in TAC or protein thiol concentrations between the hypothyroids, euthyroids and hyperthyroids. A significant positive correlation was observed between TSH and TAC in hypothyroid patients. 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