Activation of paraoxonase 1 is associated with HDL remodeling ex vivo.

BACKGROUND

We hypothesize that during high density lipoprotein (HDL) remodeling PON1 reaches an optimal distribution in HDL subclasses by which it achieves maximum activity. We conducted this study to gain insight on PON1 fate and activation during short-term HDL remodeling ex vivo.

METHODS

Serum from 8 healthy volunteers was either frozen at -80°C (time 0) or incubated under sterile conditions for up to 48h at 37°C or at 4°C. Aliquots were taken at 3, 6, 9, 24 and 48 h and immediately frozen at -80°C. PON1 activities were measured, as well as PON1 and apolipoprotein distributions in HDL subclasses by gradient gel electrophoresis.

RESULTS

The first novel finding in our study is the evidence provided for a significant activation of both lactonase and arylesterase activities of PON1 that ensues in a very short time frame of incubation of serum ex vivo at 37°C. All subjects studied displayed these changes, the activation was apparent in <3h, peaked at 6h and amounted to >20%. This is associated with a temperature and time-dependent redistribution of PON1 activity in HDL subclasses, with an increase in activity in both very large HDL2 and small HDL3 in the first phase (3-9h), followed by a progressive transfer of PON1 to very large HDL2 as the particles mature. These changes are paralleled by the appearance of weak, but apparent PON1 activity at subspecies that correspond to sdLDL. During the first phase of PON1 activation and shifts, a parallel shift of apoE can be evidenced: at 3-9h, apoE increases in sdLDL, after that time it is lost from HDL and also from sdLDL and stays in VLDL at the origin of the run. ApoA-I shifts towards larger particles, which parallels the change in PON1. As HDL matures there is a progressive shift of apoA-II towards larger HDL. Low levels of apoA-IV at the initiation of the incubation are followed by time dependent quick disappearance of apoA-IV in HDL which parallels the changes in PON1, apoE and A-II.

CONCLUSION

Short, ex vivo incubation of serum leads to quick activation of PON1 associated with transfers to HDL3c, large HDL and sdLDL. The process is blocked by CETP and LCAT inhibitors. The data suggest that HDL maturation optimizes PON1 activity. These findings may be of interest for future studies aimed at modulating PON-1 activity for its cardioprotective effects and suggest a new mechanism whereby CETP inhibitors failed in clinical trials.