PLASMA CHOLESTERYL ESTER TRANSFER PROTEIN-ACTIVITY IN HYPERTHYROIDISMAND HYPOTHYROIDISM

Thyroid dysfunction is associated with multiple changes in lipoprotein metabolism, and we have determined the effects of thyroid dysfunction on plasma cholesteryl ester transfer protein (CETP) activity. CETP is a plasma protein that mediates the exchange of cholesteryl ester and triglyceride between plasma lipoproteins and plays an important role i n high-density lipoprotein metabolism and in the reverse cholesterol t ransport pathway. Plasma CETP activity was assayed in 18 hyperthyroid and in 17 hypothyroid patients, before and after treatment, by measuri ng the transfer of cholesteryl esters from exogenous radiolabeled high -density lipoprotein to apolipoprotein B-containing lipoproteins. Plas ma CETP activity was increased in hyperthyroid patients, compared with their matched controls (22.11 +/- 8.92% transferred/5 mu L.4 h vs. 16 .75 +/- 6.48, P < 0.05), whereas in hypothyroid patients, plasma CETP activity was decreased (11.14 +/- 4.84% transferred/5 mu L.4 h vs. 17. 26 +/- 7.13, P < 0.01). Plasma CETP activity decreased after treatment of thyrotoxicosis, although a significant change was observed, mainly in the severely thyrotoxic patients with free T-4 > 100 pmol/L (n = 1 1, 25.61 +/- 8.12% transferred/5 mu L.4 h vs. 21.71 plus/similar to 7. 84, P < 0.05). In the hypothyroid patients, there was a significant in crease in plasma CETP activity after thyroxine replacement (11.14 +/- 4.84% transferred/5 mu L.4 h vs. 15.46 +/- 6.71, P < 0.01). There was a strong positive correlation between log(free T-4) and plasma CETP ac tivity (r = 0.51, P < 0.001). In summary, both hyper and hypothyroidis m are associated with significant changes in plasma CETP activity, and these changes are corrected when the patients have been rendered euth yroid.