Increased adipose tissue secretion of interleukin-6, but not of leptin, plasminogen activator inhibitor-1 or tumour necrosis factor alpha, in Graves' hyperthyroidism

Department of Medicine, Karolinska Institutet, Huddinge University Hospital, Sweden.

OBJECTIVE: This study was designed to investigate adipose tissue secretion of interleukin-6 (IL-6), leptin, tumour necrosis factor alpha (TNF-alpha) and plasminogen activator inhibitor-1 (PAI-1) in Graves' hyperthyroidism. DESIGN: We studied 10 patients before and during (after 8 weeks) anti-thyroid treatment for Graves' hyperthyroidism and 16 healthy, euthyroid control subjects. METHODS: Plasma levels of thyroid hormones and serum/plasma levels of IL-6, leptin, TNF-alpha and PAI-1 were analysed. Subcutaneous fat biopsies were taken for subsequent measurement of IL-6, leptin, TNF-alpha and PAI-1 protein secretion. RESULTS: In patients with Graves' disease, the anti-thyroid treatment resulted in significant reductions of plasma thyroxine and triiodothyronine levels. No differences in serum concentration or adipose tissue secretion of leptin or TNF-alpha were observed either before, as compared with during, anti-thyroid treatment, or in comparison with euthyroid controls. In contrast, plasma PAI-1 activity, but not adipose tissue secretion of PAI-1, was increased both in Graves' disease before as compared with during anti-thyroid treatment (P=0.01) and in thyrotoxic patients compared with euthyroid controls (P=0.0001). Finally, adipose secretion of IL-6 was increased both before (8-fold, P=0.001) and during (6-fold, P<0.0001) treatment as compared with control subjects. Accordingly, serum concentration of IL-6 was also increased by about 50% in thyrotoxic patients as compared with healthy controls (P=0.03). CONCLUSIONS: In Graves' hyperthyroidism regardless of thyroid status, adipose tissue secretion of IL-6, but not of leptin, TNF-alpha or PAI-1, is markedly increased in comparison with euthyroid controls. This suggests that autoimmune thyroidal disorder may regulate adipose tissue release of IL-6.

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