Role of paraoxonase-1 as a diagnostic marker for feline infectious peritonitis.

Feline infectious peritonitis (FIP) is characterised by the presence of systemic inflammation accompanied by oxidative stress. Paraoxonase-1 (PON-1) is a negative acute phase reactant produced by the liver. A paraoxon-based method has been validated to measure PON-1 activity in feline serum. The aim of this study was to investigate the usefulness of PON-1 activity as a biomarker to discriminate FIP from other diseases with similar clinical signs. Of 159 cats enrolled, 71 were healthy, 34 had FIP and 54 had another disease but presented with clinical signs that could be consistent with FIP. PON-1 activity was lower (P <0.0001) in cats with FIP (median, 26.55 U/L; range, 5.40-78.20 U/L) compared to healthy (median, 87.5 U/L; range, 46.60-215.50 U/L) and Non-FIP Sick group cats (median, 57.90 U/L; range, 3.80-122.60 U/L). Two receiver operating characteristic curves were used to determine the thresholds that maximised the performance of PON-1 activity in predicting FIP both from a screening and diagnostic point of view. A threshold of 78.30 U/L yielded a sensitivity of 100%, a specificity of 50.4%, and a negative likelihood ratio of 0.00 (screening curve). While a threshold of 24.90 U/L maximised specificity (94.4%), had a sensitivity of 44.1%, and increased the likelihood ratio to 7.94, making PON-1 activity a good confirmatory test for FIP (diagnostic curve). Using these thresholds, serum PON-1 activity showed good diagnostic performance in discriminating FIP affected cats from cats with other inflammatory conditions.

Paraoxonase activity as a tool for clinical monitoring of dogs treated for canine leishmaniasis.

This study was designed to determine if the activity of paraoxonase (PON1), an antioxidant enzyme that works as a negative acute phase reactant, is a better predictor for the clinical recovery of leishmaniotic dogs receiving standard treatments compared with inflammatory markers such as C reactive protein (CRP) and electrophoretic fractions. For this purpose we tested 20 healthy dogs (controls) and 39 leishmaniotic dogs classified as sick (group A, n=23) or severely sick (group B, n=16) and tested at admission and after 3, 7, 14, 21, 28, 35 and 42 days. At admission, CRP and electrophoresis were altered in both groups, while PON1 activity was abnormal only in group B. There were no differences related to the outcome (mortality, complications or time of recovery). PON1 activity normalized in about 2 weeks in dogs that had abnormal values at admission and a final positive outcome; CRP normalized in 4-6 weeks and electrophoretic fractions were still altered after 6 weeks. The results show that, at admission, inflammatory markers did not predict the outcome of leishmaniasis. PON1 activity decreased only in some dogs with systemic inflammation but not in those with mild leishmaniasis: when decreased, PON1 normalized earlier than other markers in dogs that responded to treatment. This finding most likely depends on the rapid decrease in oxidative phenomena. PON1 activity should therefore be tested on admission: if low values are recorded, severe inflammation may be suspected and PON1 measurement may be repeated during treatment to early identify responsive dogs.