Serum concentrations of adipocytokines in patients with hyperthyroidism and hypothyroidism before and after control of thyroid function

Abstract

Adipose tissue is a hormonally active system that produces and releases different bioactive substances. Leptin, adiponectin and resistin are some of the recently discovered adipocytokines that participate in the regulation of intermediate metabolism. The aim of this study was to evaluate the circulating levels of leptin, adiponectin and resistin in patients with thyroid dysfunction before and after normalization of thyroid function with appropriate therapy. We studied 20 patients with hyperthyroidism (16 women and 4 men; mean age 47.2 +/- 3.9 years) and 20 patients with hypothyroidism (17 women and 3 men; 51.5 +/- 4.1 years). A group of 20 euthyroid subjects served as control group. Patients were evaluated at the time of diagnosis and again after normalization of thyroid function with appropriate therapy. Serum concentrations of free T4 (FT4), total T3, TSH, insulin, leptin, adiponectin and resistin were measured in all subjects. Hyperthyroid patients showed significantly decreased leptin levels in comparison with controls (11.0 +/- 1.1 vs. 30.4 +/- 5.0 microg/l, P < 0.001). No significant differences in adiponectin levels between hyperthyroid and control groups were found (27.8 +/- 4.0 vs. 46.0 +/- 12.0 mg/l, NS). Patients with hyperthyroidism exhibited reduced resistin levels in comparison with euthyroid subjects (6.4 +/- 0.8 vs. 8.4 +/- 0.7 microg/l, P < 0.05). Normalization of circulating thyroid hormone was accompanied by a nonsignificant increase in leptin levels (12.9 +/- 1.7 microg/l, P < 0.01 vs. control) and no significant modification both in adiponectin (32.0 +/- 7.1 mg/l, NS) and resistin (5.4 +/- 0.7 microg/l, NS) levels. Adjustment of adipocytokine concentrations for body mass index (BMI) showed that treatment of hyperthyroidism induced a significant reduction in adjusted resistin concentrations (0.21 +/- 0.03 vs. 0.28 +/- 0.03 microg/l/BMI units, P < 0.05), with no changes in adjusted leptin and adiponectin. Hypothyroid patients showed significantly lower leptin levels compared with the controls (16.0 +/- 3.5 vs. 30.4 +/- 5.0 microg/l, P < 0.05). Adiponectin levels in patients with hypothyroidism (71.8 +/- 16.0 mg/l) were similar to those in the control group and were not modified with therapy. Resistin levels were significantly reduced among hypothyroid patients (5.8 +/- 1.0 microg/l, P < 0.05), and were not increased after levothyroxine therapy. A significant rise in BMI-corrected leptin levels was observed after replacement therapy, with no changes in adiponectin- and resistin-corrected values. The results suggest that (1) low serum leptin levels are present in both hyperthyroid and hypothyroid patients but are only increased after therapy in the latter; (2) resistin might be implicated in the insulin resistance state that accompanies thyrotoxicosis; and (3) inadequate secretion of adiponectin seems to have no role in metabolic changes associated with thyroid dysfunction.