QUANTIFICATION OF HUMAN SERUM PARAOXONASE BY ENZYME-LINKED IMMUNOASSAY - POPULATION DIFFERENCES IN PROTEIN CONCENTRATIONS

Paraoxonase is a serum protein bound to high-density lipoproteins (HDL s). 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 subs trates. We have developed a highly specific, competitive e.l.i.s.a. us ing a previously characterized monoclonal antibody. The assay can dete ct 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. S erum concentrations of paraoxonase in healthy subjects from Geneva and Manchester ranged from 25 to 118 mu g/ml. There were significant diff erences in mean concentrations between the two groups (Geneva, 79.3+/- 18.7 mu g/ml; Manchester, 59.9+/-24.1 mu g/ml: P < 0.001), differences also apparent when subjects were compared according to paraoxonase ph enotype. These appeared to be largely a consequence of differences in apolipoprotein A-I concentrations between the two populations, suggest ing that HDL particle number may be important in determining serum lev els of paraoxonase. Paraoxonase specific activities were also signific antly different between the two groups of subjects (Geneva, 2.08+/-0.9 6 units/mg; Manchester, 3.08+/-1.73 units/mg: P < 0.001), which may re flect differences in HDL particle composition. The e.l.i.s.a. should f urnish the necessary complement to studies of paraoxonase enzymic acti vity and has already provided evidence for differences with respect to serum levels of the protein both between populations and between phen otypes within populations.