Serum paraoxonase activity before and after treatment of thyrotoxicosis.
OBJECTIVE
Antioxidant effects of paraoxonase, a high density lipoprotein (HDL)-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. The purpose of this study was to evaluate serum paraoxonase activity in patients with hyperthyroidism before and after treatment with methimazole (MMI).


METHODS
Twenty-four hyperthyroid patients (15 women and nine men, aged 43.0 +/- 12.9 years) and 23 age- and sex-matched healthy controls were studied. Serum paraoxonase activity, lipid, lipoprotein and apolipoprotein levels were measured in fasting samples. Patients were treated with MMI 20-30 mg daily for the first month, and 5-10 mg daily thereafter, and re-evaluated after 6-9 months of treatment.


RESULTS
Significantly lower serum paraoxonase activity was present in hyperthyroid patients before treatment compared with the controls (43.4 +/- 21.9 vs. 72.6 +/- 41.2 U/ml, P < 0.005). After a mean follow-up of 7.3 months, 15 patients became euthyroid (treated) and nine were still hyperthyroid. After follow-up, serum paraoxonase activity had increased to 62.2 +/- 37.4 U/ml in those who became euthyroid (P < 0.05 compared with baseline). In patients who were still hyperthyroid serum paraoxonase was unchanged from baseline, at 43.2 +/- 23.2 U/ml.


CONCLUSIONS
Serum paraoxonase is reduced in patients with hyperthyroidism and reverts to normal after euthyroidism is attained. Reduced serum paraoxonase activity in thyrotoxicosis might predispose lipids to oxidation.
Raiszadeh
Farbod
F
Endocrine Research Centre, Shaheed Beheshti University of Medical Sciences, Tehran, Iran.
Solati
Mehrdad
M
Etemadi
Arash
A
Azizi
Fereidoun
F
D000293:Adolescent; D000328:Adult; D000368:Aged; D013956:Antithyroid Agents / Q000627:therapeutic use*; D043303:Aryldialkylphosphatase / Q000097:blood*; D016022:Case-Control Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood* / Q000188:drug therapy; D008297:Male; D008713:Methimazole / Q000627:therapeutic use*; D008875:Middle Aged
D013956:Antithyroid Agents; D008713:Methimazole; D043303:Aryldialkylphosphatase