Modulated serum activities and concentrations of paraoxonase in high density lipoprotein deficiency states.

Paraoxonase is a high density lipoprotein (HDL) associated enzyme with a hypothesised role in the protection of low density lipoproteins (LDL) from oxidative stress. The present study examined paraoxonase in several genetically distinct HDL deficiency states. Despite reduction or even absence of detectable HDL, enzyme activity was present in sera from A-I-Pisa, A-I-Helsinki, A-I-Milano and Tangier patients. Both enzyme activities and peptide concentrations were modulated (reduced) but specific activities were broadly similar to controls, suggesting an impact on peptide concentration rather than an inhibition of enzyme activity. Despite the absence of HDL in A-I-Pisa and Tangier subjects, there was no association of paraoxonase with very low density lipoproteins or LDL. Paraoxonase function is maintained in HDL deficient states. It implies that certain HDL-associated anti-atherogenic processes may not be entirely compromised by HDL deficiency. This has important implications for the cardiovascular risk associated with modulated HDL concentrations.

Quantification of human serum paraoxonase by enzyme-linked immunoassay: population differences in protein concentrations.

Paraoxonase is a serum protein bound to high-density lipoproteins (HDLs). The physiological function of the enzyme is unknown, but a role in lipid metabolism has been postulated. To date, studies of the protein have had to rely on measurements of enzyme activity with various substrates. We have developed a highly specific, competitive e.l.i.s.a. using a previously characterized monoclonal antibody. The assay can detect 20 ng of paraoxonase with a working range of 75-600 ng. Intra- and interassay coefficients of variation were 6.5 and 7.9% respectively. Serum concentrations of paraoxonase in healthy subjects from Geneva and Manchester ranged from 25 to 118 micrograms/ml. There were significant differences in mean concentrations between the two groups (Geneva, 79.3 +/- 18.7 micrograms/ml; Manchester, 59.9 +/- 24.1 micrograms/ml: P < 0.001), differences also apparent when subjects were compared according to paraoxonase phenotype. These appeared to be largely a consequence of differences in apolipoprotein A-I concentrations between the two populations, suggesting that HDL particle number may be important in determining serum levels of paraoxonase. Paraoxonase specific activities were also significantly different between the two groups of subjects (Geneva, 2.08 +/- 0.96 units/mg; Manchester, 3.08 +/- 1.73 units/mg: P < 0.001), which may reflect differences in HDL particle composition. The e.l.i.s.a. should furnish the necessary complement to studies of paraoxonase enzymic activity and has already provided evidence for differences with respect to serum levels of the protein both between populations and between phenotypes within populations.