Plasma and Lp(a)-associated PAF-acetylhydrolase activity in uremic patients undergoing different dialysis procedures.

UNLABELLED: Plasma and Lp(a)-associated PAF-acetylhydrolase activity in uremic patients undergoing different dialysis procedures.

BACKGROUND: Platelet-activating factor (PAF) is a potent inflammatory mediator associated with several physiopathological conditions, including renal diseases. PAF is degraded to the inactive metabolite lyso-PAF by PAF-acetylhydrolase (PAF-AH), which is considered as a potent anti-inflammatory and anti-atherogenic enzyme associated with lipoproteins. In this study, we evaluated the plasma- and lipoprotein(a) [Lp(a)]-associated PAF-AH activity in relationship to plasma lipid parameters and Lp(a) isoform size in patients with mild/moderate chronic renal failure (CRF), as well as in hemodialysis (HD) and chronic ambulatory peritoneal dialysis (CAPD) patients.

METHODS: We studied 74 patients undergoing maintenance HD, 44 patients undergoing CAPD, 56 patients with mild/moderate CRF, and 98 healthy subjects whose lipid profile, as well as plasma and high-density lipoprotein (HDL)-associated PAF-AH activity, was determined. Moreover, the effect of Lp(a) plasma levels on the distribution of PAF-AH among plasma lipoproteins, as well as the specific activity and kinetic properties of PAF-AH on two different Lp(a) isoforms, was measured in each studied group.

RESULTS: The plasma PAF-AH activity in all studied groups was significantly higher than in controls, and the increase was more profound in CAPD patients. The HDL-associated PAF-AH activity, expressed per milliliter of plasma, was similar among all studied groups; however, when it was expressed as either per milligrams of HDL cholesterol or per milligrams of plasma apolipoprotein (apo) AI, the PAF-AH activity was significantly higher in all patient groups compared with controls. All patient groups had significantly elevated plasma Lp(a) levels, which altered the distribution of PAF-AH among the plasma lipoproteins compared with that observed in subjects with very low plasma Lp(a) levels (<8 mg/dl). Additionally, in each studied group, the specific activity as well as the apparent Km and Vmax values of the 19K4 apo(a) isoform were significantly higher (P < 0.01) compared with the values of the 23K4 isoform. However, the specific activity, as well as the Km and Vmax values on either the 19K4 apo(a) isoform or the 23K4 isoform, was significantly higher in CAPD patients compared with the other three groups.

CONCLUSIONS: Plasma PAF-AH activity is increased in uremic patients. This elevation is more profound in CAPD patients, who also exhibit a more atherogenic lipid profile and more pronounced alterations in the specific activity and the kinetic constants of Lp(a)-associated PAF-AH.