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 34 clinically healthy animals (25 adults – median age: 11 years – and 9 foals – median age 20 days) 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 5 SIRS horses, 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 foals and adults were compared with a Wilcoxon signed rank test. The method was precise (inter- and inter-assay CVs <5%) and accurate (LUD and SRT fit the linear model). PON-1 activity ranged between 56.4 to 67.5 U/L (median: 63.9) in adults and 61.8 to 71.9 U/L (median: 63.7) in foals and no significant differences were found between them. In 4/5 SIRS horses PON-1 activity was lower than in controls and after treatment increased over time. 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.