Serum cytokines in thyrotoxicosis

Area of Science:

• Endocrinology
• Bone Biology
• Immunology

Background:

• Thyroid hormone overproduction is linked to increased bone resorption.
• Elevated serum interleukin-6 (IL-6) observed in thyrotoxicosis, but its cause (hormone excess vs. inflammation) is unclear.
• Graves' disease (GD) and toxic nodular goiter (TNG) involve thyroid hormone excess and potential autoimmune inflammation.

Purpose of the Study:

• To investigate whether osteotropic cytokines, specifically IL-6 and IL-8, mediate bone resorption in hyperthyroidism.
• To differentiate the effects of thyroid hormone excess from autoimmune inflammation on cytokine levels.
• To assess changes in IL-6 and IL-8 following treatment for hyperthyroidism.

Main Methods:

• Longitudinal study of 34 hyperthyroid patients (GD, TNG, thyroid carcinoma on TSH suppression) and 12 controls.
• Measurements included serum free T4, T3, IL-6, IL-8, IL-1beta, TNF-alpha, IL-11, bone-specific alkaline phosphatase (b-ALP), and urinary deoxypyridinoline (Udpd).
• Measurements taken at baseline and for 6 months after carbimazole treatment.

Main Results:

• Untreated GD and TNG patients showed significantly elevated IL-6 and IL-8 compared to controls.
• These cytokine levels decreased to control levels after treatment.
• Thyroid carcinoma patients on TSH suppressive therapy also had elevated IL-6 and IL-8.
• IL-6 and IL-8 levels correlated with serum T3 and free T4, but not with bone resorption markers (Udpd, b-ALP).
• IL-1beta, IL-11, and TNF-alpha were not elevated.

Conclusions:

• Elevated IL-6 and IL-8 in hyperthyroidism are primarily due to thyroid hormone excess, not autoimmune inflammation.
• These cytokines likely originate from bone osteoblasts, despite lack of correlation with acute bone turnover markers.
• Thyroid hormone excess directly influences cytokine production, contributing to bone resorption.