Effect of levothyroxine replacement therapy on paraoxonase-1 and carotid intima-media thickness in subclinical hypothyroidism

Background: Paraoxonase-1 (PON-1) may play an important role in atherosclerosis. Atherosclerosis is an inflammatory disease and C-reactive protein is a marker for inflammation. The aim of this study was to determine serum PON-1 activity and high-sensitivity C-reactive protein (hs-CRP) levels and assess carotid intima-media thickness, a marker of early atherosclerotic changes, in patients with subclinical hypothyroidism. Material/Methods: hs-CRP concentrations and PON-1 activity with respect to carotid intima-media thickness were evaluated in 38 subclinical hypothyroidism patients (normolipidemic, mean age: 49.79 +/- 10.04 years) before and after 3 months of stable euthyroidism and compared with those of 19 euthyroid normolipidemic healthy individuals (mean age: 49.95 +/- 8.12 years). Results: At baseline, the patients with subclinical hypothyroidism had similar levels of PON-1 activity and hs-CRP and a similar lipid profile as the controls; however, the carotid intima-media thickness was greater than in the controls. Levothyroxine treatment had no effect on serum PON-1 activity and hs-CRP level, but it resulted in a significant reduction in carotid intima-media thickness in the subclinical hypothyroidism patients. Conclusions: PON-1 activity and hs-CRP levels did not significantly differ between subclinical hypothyroid patients and controls. Although levothyroxine treatment might have the potential to reverse the progression of atherosclerosis in subclinical hypothyroid patients, PON-1 activity and hs-CRP levels were not affected by this treatment. The reduction in carotid intima-media thickness was independent of the decrease in serum lipid profile or other variables.