Serum Lipids and Apolipoproteins A-I, A-II, and B in Hyperthyroidism before and after Treatment

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Abstract
The serum concentrations of total cholesterol (TC), triglycerides (TG), high density lipoprotein-cholesterol (HDLc), low density lipoprotein-cholesterol (LDLc), and the apolipoproteins (apo) A-I, A-II, and B were measured in 33 hyperthyroid patients before and after treatment. The results were compared with those of healthy controls. Apo A-I, A-II, and B were assayed by immunonephelometry. The serum levels of TC (mean ± SD, 167 ± 36 mg/dl, HDLc (40.8 ± 12 mg/dl), and LDLc (108 ± 35 mg/dl) were decreased in the untreated hyperthyroid patients compared to both the values after treatment (TC: 215 ± 54 mg/dl; P < 0.001; HDLc: 52 ± 14 mg/dl; P < 0.001; LDLc: 146 ± 47 mg/dl; P < 0.001) and the control values (TC: 206 + 39 mg/dl; P < 0.001; HDLc: 47.4 ± 10 mg/dl; P < 0.01; LDLc: 145 ± 38 mg/dl; P < 0.001). TG levels were not statistically different before and after treatment. The apo A-I concentrations (116 ± 24 mg/dl) were lower before than after treatment (131 ± 28 mg/dl; P < 0.01), but they were not statistically different from those in the control group (115 ± 19 mg/dl). The apo A-II levels were identical in all groups (before treatment, 35 ± 7 mg/dl; after treatment, 37 ± 9 mg/dl; control group, 36 ± 9 mg/dl). The apo B levels were lower in the untreated hyperthyroid patients (86 ± 23 mg/dl) compared to those in controls (103 ± 19 mg/dl; P < 0.001) and patients after therapy (103 ± 25 mg/dl; P < 0.001). The increase in HDLc relative to the major HDL apo A-I and A-II during treatment for hyperthyroidism was associated with changes in body weight. The apo A-I to apo A-II and LDLc to apo B ratios, however, were significantly lower before compared to those after treatment, when the influence of increasing body weight during therapy was accounted for. This study emphasizes the important regulating role of thyroid hormones on lipid and apolipoprotein metabolism.