Serum arylesterase/diazoxonase activity and genetic polymorphisms in patients with type 2 diabetes

Human serum paraoxonase (PON1) is associated with high-density lipoprotein (HDL) and inhibits the oxidation of low-density lipoprotein (LDL) in vitro, suggesting that PON1 protects against atherosclerosis. We detected 3 polymorphisms of the PON1 gene and investigated PON1 enzyme activities as paraoxonase (PON), arylesterase (ARYL) and diazoxonase (DIAZ), and serum PON1 concentration in 106 patients with type 2 diabetes and 161 control subjects. All 3 enzyme activities and specific activities of PON1 in diabetic patients were significantly lower than those in controls, while there was no difference in serum PON1 concentration between the patient and control groups. The specific activities of PON, ARYL, and DIAZ in patients were 6.82 +/- 3.14 nmol x min(-1) x U(-1) (mean +/- SD, U; unit for serum PON1 concentration), 4.77 +/- 0.17 micromol x min(-1) x U(-1), and 193 +/- 92 nmol x min(-1) x U(-1), respectively, whereas those in controls were 9.33 +/- 3.92 nmol x min(-1) x U(-1), 5.36 +/- 0.14 micromol x min(-1) x U(-1), and 242 +/- 103 nmol x min(-1) x U(-1), respectively. There was no significant difference in the allelic frequencies of -108C/T, 55L/M, or 192Q/R between the patient and control groups. When each enzyme activity was compared between the patient and control groups in each genotype subgroup, all activities were lower in the patient group. The PON and ARYL activities were lower in patients with retinopathy or nephropathy than in those without such complications, and the ARYL activity was also lower in patients with neuropathy. In conclusion, all specific enzyme activities of PON1 were lower in patients with type 2 diabetes independent of the -108C/T, 55L/M, or 192Q/R polymorphism, and this impaired PON1 function may be involved in development of diabetic microangiopathy.