PON1 enzyme activity assays for serum and heparinized plasma in horses and stability evaluation of the enzyme activity over different freeze-thaw cycles and mimic transportation

Consistent information and standardization procedures regarding the time of storage for frozen samples and the effects of storage time on enzyme activity are still missing in the literature. Thus, we evaluated the effects of different storage temperatures (−20 °C and − 80 °C), three repetitive freeze/thaw cycles, and 24-h mimic transportation on the activities of PON1 (paraoxonase and arylesterase), enzymes involved in the protection and detoxification processes of reactive molecules. PON1 enzymes' activity was validated on serum and heparinized plasma in horses. The results revealed that conditions and time of storage of blood samples for PON1 analyses altered the activities of both enzymes in both sample types, evidencing that these conditions can lead to protein degradation or general alteration. Specifically, paraoxonase and arylesterase activities significantly decreased among storage temperatures, with major effects detected at −20 °C. The repeated freeze/thaw cycles at −20 °C and 24-h mimic transport conditions also generated an expected degradation of the arylesterase in both serum and heparinized plasma while freeze/thaw cycles at −80 °C caused an increase of both arylesterase and paraoxonase activities on both sample types. In general, similar enzyme responses were detected between serum and heparinized plasma.