Platelet-activating factor acetylhydrolase and transacetylase activities in human aorta and mammary artery

Abstract

Platelet-activating factor (PAF), the potent phospholipid mediator of inflammation, is involved in atherosclerosis. Platelet-activating factor-acetylhydrolase (PAF-AH), the enzyme that inactivates PAF bioactivity, possesses both acetylhydrolase and transacetylase activities. In the present study, we measured acetylhydrolase and transacetylase activities in human atherogenic aorta and nonatherogenic mammary arteries. Immunohistochemistry analysis showed PAF-AH expression in the intima and the media of the aorta and in the media of mammary arteries. Acetylhydrolase and transacetylase activities were (mean +/- SE, n = 38): acetylhydrolase of aorta, 2.8 +/- 0.5 pmol/min/mg of tissue; transacetylase of aorta, 3.3 +/- 0.7 pmol/min/mg of tissue; acetylhydrolase of mammary artery, 1.4 +/- 0.3 pmol/min/mg of tissue (P < 0.004 as compared with acetylhydrolase of aorta); transacetylase of mammary artery, 0.8 +/- 0.2 pmol/min/mg of tissue (P < 0.03 as compared with acetylhydrolase of mammary artery). Lyso-PAF accumulation and an increase in PAF bioactivity were observed in the aorta of some patients. Reverse-phase HPLC and electrospray ionization mass spectrometry analysis revealed that 1-O-hexadecyl-2 acetyl-sn glycero-3-phosphocholine accounted for 60% of the PAF bioactivity and 1-O-hexadecyl-2-butanoyl-sn-glycerol-3-phosphocholine for 40% of the PAF bioactivity. The nonatherogenic properties of mammary arteries may in part be due to low PAF formation regulated by PAF-AH activity. In atherogenic aortas, an imbalance between PAF-AH and transacetylase activity, as well as lyso-PAF accumulation, may lead to unregulated PAF formation and to progression of atherosclerosis.

Fig. 1.

Immunohistochemical analysis of atherogenic aortas. A: CD68 expression in macrophages located in the intima; original magnification × 200. B: Staining with anti-CD3 showing the absence of T cells and serving as a blank; original magnification × 200. C: PAF-acetylhydrolase (PAF-AH) cytoplasmic expression in macrophages; original magnification × 200. D: PAF-AH expression in smooth muscle cells (SMCs); original magnification × 400. E: PAF receptor (PAF-R) expression in monocyte-macrophages in the intima; original magnification × 200. F: PAF-R expression in SMCs; original magnification × 400.

Fig. 2.

Immunohistochemical analysis of nonatherogenic mammary arteries. A: Strong expression of PAF-AH in the media; original magnification × 400. B: Weak expression of PAF-R in the media; original magnification × 400. C: Staining with anti-CD68 showing the absence of macrophages and serving as a blank; original magnification × 200.

Fig. 3.

A: Bar graph showing the distribution of PAF bioactivity in arteries of patients. B: Bar graph showing the distribution of lyso-PAF in arteries of patients.

Fig. 4.

Correlation between transacetylase activity and lyso-PAF in human arteries. The 95% confidence interval is shown by the dashed line. Transacetylase activity was expressed in pmol/min/mg of tissue and lyso-PAF in pg/mg tissue. r, Pearson correlation coefficient.

Fig. 5.

A: Graphs show the PAF bioactivity in each HPLC fraction of aortic samples; arrows indicate the retention times of synthetic radiolabeled standards. B: PAF bioactive material, which was recovered from reverse-phase HPLC with the retention time of C16:0 PAF, was dissolved in methanol-ammonium acetate (10 mM; 70:30), introduced into the mass spectrometry ion source, and analyzed by positive-ion flow injection electrospray ionization mass spectrometry (ESI-MS). C: PAF bioactive material, which was recovered from reverse-phase HPLC with the retention time of butanoyl-PAF, was dissolved in methanol-ammonium acetate (10 mM; 70:30), introduced into the mass spectrometry ion source, and analyzed by the positive-ion flow injection ESI-MS. D: Lipids extracted from the reverse-phase HPLC fraction with the retention time of lyso-PAF were dissolved in methanol-ammonium acetate (10 mM; 70:30), introduced into the mass spectrometry ion source, and analyzed by positive-ion flow injection ESI-MS.