PAF-Degrading Acetylhydrolase Is Preferentially Associated With Dense LDL and VHDL-1 in Human Plasma

Abstract

In human plasma, platelet activating factor (PAF)-degrading acetylhydrolase (acetylhydrolase) is principally transported in association with LDLs and HDLs; this enzyme hydrolyzes PAF and short-chain forms of oxidized phosphatidylcholine, transforming them into lyso-PAF and lysophosphatidylcholine, respectively. We have examined the distribution, catalytic characteristics, and transfer of acetylhydrolase activity among plasma lipoprotein subspecies separated by isopycnic density gradient ultracentrifugation; the possibility that the plasma enzyme may be partially derived from adherent monocytes has also been evaluated. In normolipidemic subjects with Lp(a) levels < 0.1 mg/mL, acetylhydrolase was associated preferentially with small, dense LDL particles (LDL-5; d = 1.050 to 1.063 g/mL) and with the very-high-density lipoprotein-1 subfraction (VHDL-1; d = 1.156 to 1.179 g/mL), representing 23.9 +/- 1.7% and 20.6 +/- 3.2%, respectively, of total plasma activity. The apparent Km values for PAF of the enzyme associated with such lipoproteins were 89.7 +/- 23.4 and 34.8 +/- 4.5 mumol/L for LDL-5 and VHDL-1, respectively: indeed, the Km value for LDL-5 was some 10-fold higher than that of the light LDL-1, LDL-2, and LDL-3 subspecies, whereas the Km of VHDL-1 was some twofold greater than those of the HDL-2 and HDL-3 subspecies. Furthermore, when expressed on the basis of unit plasma volume, the Vmax of the acetylhydrolase associated with LDL-5 was some 150-fold greater than that in LDL-1 (d = 1.019 to 1.023 g/mL). No significant differences in the pH dependence of enzyme activity or in sensitivity to protease inactivation, sulfydryl reagents, the serine protease inhibitor Pefabloc, or the PAF antagonist CV 3988 could be detected between apo B-containing and apo A-I-containing lipoprotein particle subspecies. Incubation of LDL-1 (Km = 8.4 +/- 2.6 mumol/L) and LDL-2 (d = 1.023 to 1.029 g/mL; Km = 8.4 +/- 3.3 mumol/L) subspecies with LDL-5, in which acetylhydrolase had been inactivated by pretreatment with Pefabloc, demonstrated preferential transfer of acetylhydrolase to LDL-5. Acetylhydrolase transferred to LDL-5 from the light LDL subspecies exhibited a Km of 9.4 +/- 2.2 mumol/L, a value characteristic of the particle donors. Finally, acetylhydrolase (Km = 23.4 +/- 7.6 mumol/L) released by adherent human monocytes in culture was found to bind preferentially to small, dense LDL subspecies upon incubation of Pefabloc-inactivated plasma with monocyte supernatant.(ABSTRACT TRUNCATED AT 400 WORDS)

Atividade da enzima acetil-hidrolase do fator ativador de plaquetas (PAF-AH) em pacientes com diabete melito tipo 1

“…The cause of this increase is perhaps related to the elevation of LDL levels that accompanies aging 43 , since a significant correlation between LDL levels and PAF-AH activity occurs 42,[44][45][46][47] . Data from the literature corroborate the correlation of PAF-AH activity with HDL and LDL found in our sample 16,17 .…”

“…Theoretically, this enzyme may promote atherogenesis if the products it releases from LDL phospholipids have a deleterious effect on arterial walls 14 , or it may be protective if, when hydrolyzing PAF, it reduces the inflammatory and thrombotic tendency of the blood 15 . Plasma PAF-AH is mainly associated with LDL (preferentially subfraction 5); however, a small amount (< 20% of the enzyme activity) is associated with HDL (preferentially subfraction 1) 16,17 .…”

Platelet-Activating Factor Acetylhydrolases: Broad Substrate Specificity and Lipoprotein Binding Does Not Modulate the Catalytic Properties of the Plasma Enzyme

“…The distribution of pPAF-AH among LDL density subfractions was also investigated after fractionation by the D 2 O-density gradient ultracentrifugation procedure as described in Materials and Methods. The highest PAF-AH activity was detected in the dense LDL fractions (d ) 1.043-1.046 g/mL) (Figure 3), which is similar to the previous findings (9).…”

The effect of moxonidine on plasma lipid profile and on LDL subclass distribution

“…Lipoprotein mass in each subfraction was calculated as the sum of the concentrations of the individual components (cholesterol, triglyceride, phospholipid and protein) and allowed the determination of the percent chemical composition. 16 …”

“…The lag time, the maximal rate of conjugated dienes formation, and the total amount of dienes formed were calculated as previously described. 16 The relative electrophoretic mobility (REM) of the oxidised subfractions was determined by agarose gel electrophoresis on agarose gels [Lipo + Lp(a), Sebia].…”