Insight into the metabolic shifts in Graves' hyperthyroidism: a study of acylcarnitine and lipid profiles.

Objective: Graves' disease increases metabolism and leads to net lipid degradation. Circulating acylcarnitines reflect lipid metabolism and the state of fatty acid oxidation in individuals. The aim of this study was to explore the lipid and acylcarnitine profiles in patients with Graves' disease.

Methods: Seven lipids/apolipoproteins and 23 acylcarnitines were analysed in 100 newly diagnosed Graves' disease patients and validated in another 51 patients. Both groups were age- and sex-matched with healthy subjects.

Results: The hyperthyroid Graves' disease patients (n = 88) from the main cohort (78 females, median age 42 (17-67) years) had significantly (P < 0.05) higher levels of medium- and long-chain acylcarnitines, and lower levels of short-chain acylcarnitines, compared with healthy subjects. Factor analysis showed that medium- and long-chain acylcarnitines explained most of the differences between the two groups. Serum levels of the five lipids/apolipoproteins were significantly lower in the hyperthyroid Graves' disease patients compared with healthy subjects. Patients (n = 21) treated with antithyroid drugs for 6 weeks had acylcarnitine levels closer to healthy subjects, compared with 79 treatment-naïve hyperthyroid patients. The main findings were confirmed in the validation group.

Conclusion: Increased levels of medium- and long-chain acylcarnitines in patients with newly diagnosed Graves' disease may reflect accelerated catabolism. Lower levels of short-chain acylcarnitines point to Graves' disease being a catabolic condition, with a shift in energy source from carbohydrates to fat.