Hormone-replacement therapy increases serum paraoxonase arylesterase activity in diabetic postmenopausal women

The paraoxonase (PON1) enzyme is associated with high-density lipoproteins (HDL) in the blood and is low in patients with type 2 diabetes. Hormone-replacement therapy (HRT) can increase HDL cholesterol levels, but its effect on serum PON1 arylesterase activity is uncertain. The aim of the present study was to determine the effect of 6 months' HRT with conjugated equine estrogen and medroxyprogesterone acetate on serum PON1 arylesterase activity in postmenopausal women with type 2 diabetes. Serum PON1 activity was measured immediately before and at the end of the second arm of a randomized, placebo-controlled, crossover with washout study originally designed to test the effect of HRT on plasma lipids in diabetic postmenopausal women. Baseline serum PON1 arylesterase activity was significantly (P <.001) lower in the postmenopausal diabetic women (149 +/- 38 micromol/mL/min; n = 47) than values in healthy postmenopausal women (173 +/- 32 micromol/mL/min; n = 51). Serum PON1 activity increased (10%) significantly (P =.009) in diabetic women treated with HRT compared with placebo. A significant (P =.02) interaction between baseline PON1 activity and treatment indicated a greater increase in PON1 activity during HRT in women with lower baseline activities. At baseline, serum PON1 arylesterase activity was correlated significantly with plasma HDL cholesterol levels in diabetic women (r = 0.333, P =.01, n = 47), and the increase in serum PON1 activity was correlated significantly with the change in plasma HDL cholesterol during HRT (r = 0.659, P =.0001, n = 28). These data suggest that serum PON1 activity is abnormally low in postmenopausal women with type 2 diabetes and increases during HRT, particularly in women with lower baseline levels and in those who show a concomitant increase in HDL cholesterol.