The association between serum paraoxonase-1 activity, thyroid hormones and lipids profile in patients with primary hyperthyroidism

Introduction: Changes in serum lipid concentrations occur frequently in disorders of thyroid function. Antioxidant effects of paraoxonase, a high density lipoprotein -associated enzyme that inhibits low- density lipoprotein cholesterol (LDL-C) oxidation in human serum, have been reported. Patients with thyroid dysfunction are more susceptible to oxidative stress, and may show enhanced LDL-C oxidation. Aim of work: To find out possible relationship between thyroid hormones, lipids profile levels and serum paraoxonase-1 (PON-1) activity in patients with hyperthyroidism. Materials and Methods: The study included 35 hyperthyroid patients (group A) and 35 healthy subjects served as control group (group B). All subjects were subjected to thorough history and clinical examination, laboratory investigations including: thyroid stimulating hormone (TSH), free triiodothyronine (free T3), free thyroxine (free T4), liver and kidney function tests, complete blood picture, fasting and 2 hours post prandial blood glucose, chest X-ray and Doppler ultrasound of thyroid gland. In addition to measurement of total cholesterol (total-C), high-density lipoprotein cholesterol (HDL-C), (LDL-C), triglyceride (TG) and serum PON-1 activity. Results: Serum PON-1 activity, TSH, total-C and LDL-C values were significantly low in hyperthyroid patients compared to controls. Serum PON-1 activity was significantly negatively correlated with free T3 and free T4 levels and significantly positively correlated with total-C and TSH levels in hyperthyroid patients. Free T3 and free T4 were significantly negatively correlated with total-C, LDL-C and HDL-C levels, and significantly positively correlated with triglycerides while ,TSH levels were significantly positively correlated with total-C, LDL-C and HDL-C levels and significantly negatively correlated with triglycerides in hyperthyroid patients. Conclusion: In hyperthyroidism, PON-1 activity decreased, which is known as an important antioxidant enzyme with cardioprotective effects by protecting LDL and HDL from oxidation. So, this may be associated with increased cardiovascular risk of coronary heart disease in those subjects. Keywords: Paraoxonase-1 activity, oxidative stress, hyperthyroidism, lipids profile levels.