Riikka Malin

Polymorphism in high density lipoprotein paraoxonase gene and risk of acute myocardial infarction in men: prospective nested case-control study

Increased lipid peroxidation is associated with accelerated progression of atherosclerosis.1 Paraoxonase (paraoxonase/arylesterase) is an antioxidative enzyme in high density lipoproteins, which protect against coronary disease2 3 It eliminates organophosphorus pesticides but also the products of lipid peroxidation2 4 The mutation at position 54 of the paraoxonase gene in which methionine is substituted by leucine (Met54Leu) has an effect on paraoxonase, increasing its activity; people who have the methionine allele show decreased paraoxonase activity.4 Only a few studies have looked at the association of the Met54Leu polymorphism with coronary disease,2 5 and the findings are inconclusive. Thus we carried out a prospective study of the role of this polymorphism on the risk of acute myocardial infarction in healthy men from eastern Finland. Our prospective nested case-control study was carried out among participants in the Kuopio ischaemic heart disease risk factor study We examined 2682 (83%) of 3235 invited men aged 42, 48, 54 or 60 during 1984-9. Blood samples were collected and risk factors assessed at baseline. A DNA sample was available for this study for 1137 men who were free of coronary disease. We registered and verified all myocardial infarctions—definite or possible—between the baseline examinations and the end of 1995.3 The mean follow up time was 8.5 years, and in patients who had had multiple infarctions we considered only the first. The cases were all 55 men (among the 1137) who had had an infarction by 1995. The controls were drawn from the remaining members of the same cohort. Two controls for each case (110 men) were matched …

Paraoxonase genotype modifies the effect of pravastatin on high-density lipoprotein cholesterol

Paraoxonase (PON) is an enzyme carried by high-density lipoprotein cholesterol (HDL-C). Two gene polymorphisms leading to amino acid substitutions of methionine for leucine at position 55 (M/L55) and arginine for glutamine at position 192 (R/Q192) modulate the activity of the enzyme and possibly also lipid and apolipoprotein concentrations. Our purpose was to examine the effect of the PON genotype on HDL-C and apolipoprotein AI (apo AI) responses to pravastatin treatment. Fifty-one mildly hypercholesterolemic male subjects (mean age 35 +/- 4 years) were enrolled by this prospective, randomized, double-blind study. Lipid concentrations were measured at baseline and after 6 months of pravastatin (n = 25) or placebo (n = 26) therapy. Low active (MM, ML or QQ) and high active (LL or RQ, RR) PON genotype groups were related to lipid and apolipoprotein concentration changes. Pravastatin increased the apo AI concentration 12% (P = 0.017, RANOVA) and tended to increase the HDL-C concentration (P = 0.095, RANOVA) in R allele carriers but not in QQ homozygotes. Significant predictors of the change in apo AI concentration during pravastatin treatment were R/Q192 genotype (P = 0.002), apo AI concentration at baseline (P = 0.002) and M/L55 genotype (P = 0.042). Correspondingly, R/Q192 (P = 0.009) and M/L55 (P = 0.050) genotypes were the statistically significant determinants of HDL-C concentration change. The PON genotype thus modifies the effect of pravastatin on serum HDL-C and apo AI concentrations. This could partly explain the contradictory results obtained from previous studies on the effects of statins on the serum HDL-C concentration.

Paraoxonase producing PON1 gene M/L55 polymorphism is related to autopsy-verified artery-wall atherosclerosis

Paraoxonase (PON) is an antioxidative enzyme, which eliminates lipid peroxides. PON has two common polymorphisms (M/L55 and R/Q192) that influence PON concentration and activity. We studied whether the M/L55 or R/Q192 genotype relates with the severity of atherosclerosis of the abdominal aorta, and the mesenteric and common iliac arteries in 123 consecutive autopsy cases (90 males and 33 females, aged 18-93 years). The severity of atherosclerosis in the arteries was evaluated, and the percentage of stenosis was measured. The intimal thickness in the internal elastic lamina (IEL) of the coeliac (CA), superior mesenteric (SMA) and inferior mesenteric (IMA) arteries were measured by light-microscopy. The LL homozygous men had more atherosclerotic plaques and complicated lesions in the common iliac arteries (56.8%) than the M allele carriers (28.3%, P=0.007). In logistic regression analysis, age (P<0.001) and the PON M/L55 genotype (P=0.015) were associated significantly with the severity of atherosclerosis in the common iliac arteries independent of smoking status, R/Q192 genotype, hypertension, diabetes mellitus, BMI and sex. The mean intima of the IMA was significantly thicker (P=0.035) and the number of stenotic lesions in SMAs significantly higher (P=0.008) in the LL homozygous men than M allele carriers. In turn, the R/Q192 genotype was not statistically significantly associated with plaque type, intimal thickness in the IEL or with the number of stenotic lesions. This study demonstrates that PON L55 homozygosity is an independent risk factor for autopsy-verified atherosclerosis in Finns.

Lipid peroxidation is increased in paraoxonase L55 homozygotes compared with M-allele carriers

Human serum paraoxonase (PON) is an antioxidative enzyme, which circulates on high-density lipoproteins and appears to use oxidized phospholipids as physiological substrates. PON M/L55 substitution changes the ability of PON to prevent lipid oxidation. Urinary 8-iso-PGF2α (one of F2-isoprostanes) may represent a non-invasive in vivo index of free radical generation and we propose that PON might influence the biosynthesis of 8-iso-PGF2α in the vasculature. We studied the urinary excretion of 8-iso-PGF2α and related it to PON M/L55 genotypes in patients with type 2 diabetes mellitus (n = 55) and non-diabetic control subjects (n = 55). Urinary 8-iso-PGF2α was determined by competitive ELISA and the PON genotype by a PCR based restriction enzyme digestion method. LL homozygotes were compared to M-allele carriers (ML heterozygotes and MM homozygotes). The urinary excretion of 8-iso-PGF2α among non-diabetic non-smoking LL homozygotes was 3995.5 ± 3352.8 ng/24-hour and among M-allele carriers 1689.8 ± 1051.3 ng/24-hour (p = 0.017, ANCOVA; gender, hypertension, total cholesterol, triglycerides and LDL cholesterol as covariates). The excretion of 8-iso-PGF2α, was increased in type 2 diabetes mellitus compared to non-diabetic control subjects. PON may thus protect against oxidative stress by destroying some biologically active lipids. Excretion of 8-iso-PGF2α is increased in type 2 diabetes, which may reflect oxidant injury.

The Met54Leu polymorphism of paraoxonase (PON) enzyme gene is not a genetic risk factor for non‐insulin‐dependent diabetes mellitus in Finns

To the Editor: Paraoxonase (PON) is an an tioxidative enzyme associated with high-density lipoproteins, which protect against coronary heart disease (CHD) (1). The two alleles of the PON gene arise from a mutation of A to T within codon 54, which causes the substitution of methionine (M) to leucine (L). Met54Leu genotypes of PON have been associated with differences in the plasma concentrations and activities of the PON enzyme and there are highly significant decreases in enzyme activity when passing from the Lto the M-allele (2). Serum PON activity is decreased in both insulin-dependent and non-insulin-dependent diabetes melfitus (NIDDM), particularly when peripheral neuropathy is present (3). These findings have led to the hypothesis that PON protects low-density lipoprotein from lipid peroxidation whicfi also impedes the peroxidation of nerve membranes associated with diabetic heuropathy (4). Therefore, our aim was to elucidate the Met54Leu genotype distribution in Finland and to investigate whether there are differences in PON allele distributions between patients with NIDDM and their non-diabetic controls.