title: Long term stability of paraoxonase-1 and high-density lipoprotein in human serum.
abstract: 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°C, -70°C and -196°C. It was found that the stability of the PON1 activity is constant during 12 months of storage at -70°C and -196°C. Storage at -20°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°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°C) is not necessary.
authors.affiliation: Laboratory for Health Protection Research, National Institute of Public Health and the Environment, PO Box 1, Bilthoven, BA 3720, The Netherlands.
authors.forename: Piet K
authors.initials: PK
authors.lastname: Beekhof
authors.forename: Maryana
authors.initials: M
authors.lastname: Gorshunska
authors.forename: Eugène H J M
authors.initials: EH
authors.lastname: Jansen
mesh_terms: D043303:Aryldialkylphosphatase / Q000737:chemistry / Q000378:metabolism*; D015925:Cryopreservation; D006801:Humans; D008075:Lipoproteins, HDL / Q000737:chemistry / Q000378:metabolism*; D055550:Protein Stability; D044967:Serum / Q000737:chemistry*; D013696:Temperature
chemical_list: D008075:Lipoproteins, HDL; D043303:Aryldialkylphosphatase