The impact of levothyroxine sodium treatment on oxidative stress in Hashimoto’s thyroiditis

Abstract

Objective: Although several studies reported increased oxidative stress in Hashimoto's thyroiditis (HT), the effect of levothyroxine treatment on oxidative status is not studied extensively. Therefore, we conducted this study to investigate the effects of levothyroxine replacement on oxidative stress in HT. Design and methods: Thirty-six patients recently diagnosed with HT-related hypothyroidism and 36 healthy controls were included in the study. Levothyroxine replacement was started to patients with hypothyroidism, and had been followed-up for 6 months. Results: Mean basal serum total antioxidant status (TAS), total thiol, arylesterase, and paraoxonase 1 (PON1) levels were significantly lower, and serum total oxidant status (TOS) and oxidative stress index (OSI) were significantly higher in the patients with hypothyroid than the controls. In the hypothyroid group serum TAS, total thiol, arylesterase, and PON1 levels increased and serum TOS and OSI levels decreased significantly after levothyroxine treatment. Pretreatment serum TAS, total thiol, PON1, and arylesterase levels were positively correlated with free levothyroxine (fT 4 ) and negatively correlated with thyroid-stimulating hormone (TSH), antithyroid peroxidase (anti-TPO), and antithyroglobulin (anti-TG) levels. Also, pretreatment serum TOS and OSI levels were negatively correlated with fT 4 levels and positively correlated with TSH, anti-TPO, and anti-TG. We have also found that the fT 4 and anti-TPO levels are independent predictors of the oxidative stress parameters in stepwise multivariable linear regression analysis. Conclusion: This study suggests that levothyroxine replacement decreases oxidant status and increases antioxidant status following the 6 months of levothyroxine replacement in hypothyroidism that develops in accordance with the HT.

Serum paraoxonase‐1 activity is inversely related to free thyroxine in euthyroid subjects: The PREVEND Cohort Study

“…Inconsistent effects of thyroid function status on PON‐1 activity have been reported so far . The inverse relation of PON‐1 activity with free T 4 as shown in the current study suggests that low‐normal thyroid function could contribute to higher PON‐1 activity, although it should be emphasized that this relationship was modest.…”

“…In the present study, we only included euthyroid subjects using strict criteria, that is TSH, free T 4 and free T 3 each being within their respective reference range, as done in other reports . Moreover, we excluded subjects with positive antithyroid peroxidase autoantibodies to avoid possible confounding of latent thyroid autoimmunity on inflammatory and oxidative stress as much as possible …”

“…22 The effect of thyroid dysfunction on serum PON-1 activity has only been determined in a limited number of studies. [23][24][25][26][27] Remarkably, PON-1 activity was found to be impaired in both hypothyroidism and hyperthyroidism. 23 In addition, PON-1 activity was decreased in (subclinical) hypothyroidism in some, 24,25 but not in other studies.…”

“…[23][24][25][26][27] Remarkably, PON-1 activity was found to be impaired in both hypothyroidism and hyperthyroidism. 23 In addition, PON-1 activity was decreased in (subclinical) hypothyroidism in some, 24,25 but not in other studies. [26][27][28] No data are currently available concerning the association of serum PON-1 activity in the context of variations in thyroid hormone levels within the euthyroid range.…”

“…The effect of thyroid dysfunction on serum PON‐1 activity has only been determined in a limited number of studies . Remarkably, PON‐1 activity was found to be impaired in both hypothyroidism and hyperthyroidism .…”