Effects of short term hypothyroidism on the lipid transfer to HDL and other parameters related to lipoprotein metabolism in patients submitted to thyroidectomy for thyroid cancer.

BACKGROUND: Elevation of LDL-cholesterol is the hallmark of hypothyroidism dyslipidemia, but alterations on HDL plasma levels and metabolism are less understood. The aim of this study was to explore aspects of HDL metabolism and enzymes that act on HDL after a short period of overt hypothyroidism.

METHODS: Eighteen women (44±11 years, BMI 27.9±5.2kg/m2) were studied before total thyroidectomy for thyroid cancer, when they were in euthyroid state, and after thyroidectomy, in overt hypothyroidism for 3 weeks, following levothyroxine withdrawal for performance of whole body scan.

RESULTS: TSH and FT4 confirmed hypothyroidism; low thyroglobulin and radioiodine uptake indicated near absence of thyroid tissue. LDL-cholesterol (125±35 vs 167±40 mg/dL, p=0.0002), HDL-cholesterol (39±8 vs 46±10 mg/dL, p=0.0025), non-HDL cholesterol (149±38 vs 201±46 mg/dL, p<0.0001), unesterified cholesterol (53±10 vs 70±16 mg/dL, p=0.0003), apolipoprotein (apo) A-I (1.32±0.19 vs 1.44±0.22 g/L, p<0.04) and apo B (0.97±0.25 vs 1.31±0.28 g/L, p<0.0001) plasma concentrations were all higher in hypothyroidism compared to values in the euthyroid state, but triglycerides and Lp(a) were unchanged. There were no changes in HDL particle size and lipid composition, CETP and LCAT concentrations and in PON1 activity. Regarding the in vitro assay to estimate lipid transfer to HDL, there were no changes when comparing euthyroid to hypothyroid state, but when adjusted for HDL-C, the unesterified cholesterol (0.14±0.03 vs 0.11±0.02, p<0.0001), triglycerides (0.11±0.02vs 0.09±0.02, p<0.0001) phospholipids (0.44±0.09 vs 0.40±0.07, p=0.0205) and esterified cholesterol (0.14±0.03 vs 0.13±0.03, p=0.0043) transfer to HDL were all diminished in hypothyroidism.

CONCLUSION: In short-term hypothyroidism, HDL-cholesterol increased but this did not increase the capacity of the HDL fraction to receive lipids or the activity of PON-1, the anti-oxidation enzyme associated to HDL.