Long term stability of paraoxonase-1 and high-density lipoprotein in human serum

Background: Paraoxonase-1 (PON1) is an enzyme with numerous functions and receives an increasing interest in clinical and epidemiological studies. Sometimes samples are stored for longer periods at a certain temperature. Therefore the stability of PON1 activity must be checked and retained upon storage for longer periods. Results: In this study the stability of PON1 activity has been tested in human serum samples during storage up to 12 months at 3 commonly used temperatures, -20 degrees C, -70 degrees C and -196 degrees C. It was found that the stability of the PON1 activity is constant during 12 months of storage at -70 degrees C and -196 degrees C. Storage at -20 degrees C resulted in a small but statistically significant decrease after 6 months to about 94% of its original value. Nonetheless, the rank order between the samples at T = 0 and 12 months remained the same. The same temperature dependence was found for the associated high-density lipoprotein. Conclusions: It can be concluded that -70 degrees C is the right temperature for storage to maintain the PON1 activity for at least one year. Storage at a lower temperature in liquid nitrogen (-196 degrees C) is not necessary.