Validation of a paraoxon-based method for measurement of paraoxonase (PON-1) activity and establishment of RIs in horses.

The research validates an experimental method using paraoxon to measure the activity of an enzyme called paraoxonase-1 (PON-1) in horses. This validation was also purposed towards setting reference intervals (RIs) for this enzyme in healthy horses and foals.

Context and Aim

• Paraoxonase-1 (PON-1) is an enzyme known for its antioxidant properties and is considered as a ‘negative acute phase protein’.
• However, there had not been any existing information on the performance of a method using paraoxon for evaluating PON-1 levels in horse serum.
• The research was thus aimed at validating such a method for horses, and also to establish standard RIs in healthy horses and foals.

Methodology

• The study was carried out on horses and foals deemed healthy after a physical exam and routine biochemistry.
• The activity of PON-1 in the serum was tracked using an automated spectrophotometer and an enzymatic method that had been validated in other species.
• After analytical validation involving precision, accuracy, and interference studies, the RIs were ascertained using the Reference Value Advisor software.
• Any differences in the results due to sex, age, or breed were separately noted and statistically analysed.

Results

• 120 horses and 55 foals were determined to be healthy for the study.
• The method using paraoxon was found to have acceptable precision and accuracy, although it experienced interference from conditions like mild bilirubinemia, severe lipemia, and hemoglobinemia.
• The RIs noted in the entire population ranged from 38.1 to 80.8 U/mL.
• The Harris and Boyd test indicated that separate RIs should be implemented only for adult females, Warmblood adults, and Trotter adults.

Conclusions

• This study shows that the analytical performances of using the paraoxon-based method for measuring PON-1 levels in horses are satisfactory.
• The levels of PON-1 activity are lower in horses than in other domestic species.
• The findings call for further studies to understand whether healthy and sick horses can be correctly classified using this PON-1 assay.