Influence of PON1 Polymorphisms on the Association between Serum Paraoxonase 1 and Homocysteinemia in a General Population

Factors Associated with Paraoxonase Genotypes and Activity in a Diverse, Young, Healthy Population: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

Background: Paraoxonase may mitigate oxidative damage and thus lower risk of macrovascular disease.

Methods: DNA samples from 2252 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study were genotyped for the L55M and Q192R polymorphisms of the PON1 (paraoxonase 1) gene, and paraoxonase activity was measured in serum.

Results: The 192R (67.4% vs 29.7%) and 55L (80.0% vs 63.8%) alleles were more common in blacks vs whites. The Q192R locus was the strongest correlate of paraoxonase activity (100.4 nmol/mL/min greater in the 192RR than the 192QQ genotype). After adjustment for the Q192R locus, the L55M locus (12.7 nmol/mL/min difference between 55LL and 55MM) and race (6.6 nmol/mL/min difference between blacks and whites) were correlated with paraoxonase activity (P ≤0.0001), as were concentrations of HDL cholesterol (23.9 nmol/mL/min difference between highest and lowest quintiles), triglycerides (12.6 nmol/mL/min difference between highest and lowest quintiles), LDL cholesterol (8.2 nmol/mL/min difference between highest and lowest quintiles), smoking status (6.3 nmol/mL/min difference between current smokers of ≥15 cigarettes/day and never smokers), and glucose concentrations at the highest quintile (6.5 nmol/mL/min difference between highest and lowest quintiles in nondiabetic participants). There was no cross-sectional or longitudinal association between paraoxonase enzyme activity and coronary artery calcification (CAC), an early marker of cardiovascular disease, or its progression over 5 years.

Conclusions: Paraoxonase may not play an important role during the early pathogenesis of cardiovascular disease. However, associations with lipids and glucose suggest that paraoxonase may modify or react to macrovascular disease pathogenesis.

Paraoxonase-1 concentrations in end-stage renal disease patients increase after hemodialysis: correlation with low molecular AGE adduct clearance

BACKGROUND

Hemorrhagic stroke and ischemic heart disease continue to be key problems in patients with end stage renal failure. Reduced serum paraoxonase (PON-1) activity has been described in these patients, which could contribute to the accelerated development of atherosclerosis. We hypothesized that retention of uremic toxins and or "middle molecules" including advanced glycation (AGE) free adducts and peptides could play a mechanistic role in decreasing PON-1 activity.

METHODS

We enrolled 22 ESRD patients undergoing hemodialysis in whom paired pre- and post-dialysis samples were studied along with 30 age-matched control subjects.

RESULTS

ESRD patients showed a 76% decrease in PON-1 activity. As expected, ESRD patients had an increase in lipoperoxides and advanced oxidation protein products (AOPP). Our patients had a 3-fold increase in serum AGEs and a striking 10-fold increase in low molecular weight (<10 kDa) AGEs. Post-dialysis samples in all patients displayed an increase in PON-1 activity, which ranged from 4 to 40% of the predialysis value. HDL-cholesterol, apoAI, free cholesterol (as a LCAT surrogate), HDL-subclasses and TG did not change significantly after dialysis. Changes in PON-1 activity display a good correlation (r=0.66, p<0.001) with rates in which creatinine and urea are cleared. Clearance of low molecular weight AGEs after hemodialysis explains 79% of the changes in PON-1 activity and are hence a much better predictor than creatinine changes (r=0.89, p<0.00). In vitro incubation of paraoxonase with serum ultrafiltrates show a time and concentration dependent inhibition of PON-1 by the ultrafiltrates, an inhibition that is up to 3 times higher (from 8 to 24%) when chronic renal failure patients are the source of the ultrafiltrate.

CONCLUSION

We showed that HD results in a significant, consistent increase in the activity of the antioxidant enzyme PON-1. The effect, correlates with the effectiveness of dialysis to clear creatinine and urea, and with the clearance of AGE adducts of low molecular weight. This effect was replicated in vitro, showing time and dose dependency. Our results suggest that another cause for the observed lower PON-1 concentrations in CRF are the retention of low-middle molecules and demonstrate a positive effect of hemodialysis in the delicate oxidant-antioxidant state of these patients, that should be weighted against other pro-oxidant effects that have also been shown to occur previously. If the hypothesis that AGEs are the main culprits is proved in further research, this opens a putative therapeutic avenue for AGE blockers in ESRD.