Preliminary validation study of Paraoxonase-1 in horses

Paraoxonase-1 (PON-1) is an anti-oxidant enzyme associated with high-density lipoproteins in blood. PON-1 is a negative acute-phase protein being its plasmatic activity reduced during inflammation due to consumption by oxidants. Considering the possible clinical usefulness of PON-1 as an early inflammatory marker this is a preliminary validation study in horses. Serum PON-1 activity was measured in 69 clinically healthy animals (31 adult female, 18 geldings, 11 stallions, 9 foals) using an enzymatic method adapted from other species. In order to preliminarily assess the possible utility of PON-1 as a marker of Systemic Inflammatory Response Syndrome (SIRS), blood from 6 sick foals, classified according to a validated SIRS scale, was analyzed. Intra- and inter-assay imprecision were assessed by repeated analysis of pooled samples and evaluation of coefficient of variations (CV). Accuracy was indirectly evaluated through linearity under dilution (LUD) and spiking recovery test (SRT). Results of the different groups of healthy horses were compared to each other with a Friedmann test with Bonferroni correction. The method is precise (inter- and inter-assay CVs <5%) and accurate (LUD and SRT fit the linear model). PON-1 activity was higher in foals and in adult females (mean ± SD: 63.7±15.5 and 60.8±10.1, respectively) than in geldings and adult males (52.5±10.2 and 47.2±7.7, respectively). In 3/6 SIRS foals PON-1 activity was lower than the lowest percentile of distribution of healthy foals. This study demonstrated that the method of measurement of PON-1 activity in horses is precise and accurate and PON-1 may be a marker of SIRS.