Impact of Graves' hyperthyroidism treatment on lipid profiles and cholesterol dynamics: a prospective observational study.

Background: The impact of Graves' hyperthyroidism treatment on lipid metabolism remains unclear. This prospective observational study aimed to clarify the changes in lipid profiles and associated metabolic pathways, including cholesterol synthesis, absorption, and low-density lipoprotein (LDL) receptor regulation, following treatment.

Methods: Seventeen patients newly diagnosed with Graves' hyperthyroidism were enrolled and followed for 6 months after achieving euthyroid status. Serum lipids (total cholesterol, LDL-cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides), apolipoproteins, non-cholesterol sterols (markers of cholesterol synthesis and absorption), proprotein convertase subtilisin/kexin type 9 (PCSK9), and lipoprotein lipase (LPL) levels were measured at baseline, at euthyroid status (Eu-0M), and 6 months after euthyroid status (Eu-6M).

Results: After treatment, serum total cholesterol, LDL-C, and HDL-C levels increased rapidly compared to baseline, while triglyceride levels showed a delayed but significant increase at Eu-6M. Levels of apolipoprotein (apo) AI, AII, B, and CIII increased significantly after treatment, whereas apo B-48 increased only at Eu-6M, and apo CII and apo E remained unchanged. Markers of cholesterol synthesis (lathosterol) and absorption (sitosterol, campesterol, and cholestanol) increased significantly after treatment, indicating enhanced cholesterol metabolism. Circulating PCSK9 levels increased significantly and remained elevated, while LPL levels did not change significantly.

Conclusion: Treatment of Graves' hyperthyroidism rapidly increases cholesterol levels through enhanced cholesterol synthesis and absorption, possibly mediated by increased circulating PCSK9.