Modulation Of Platelet-Activating-Factor Production By Incorporation Of Naturally Occurring 1-O-Alkylglycerols In Phospholipids Of Human Leukemic Monocyte-Like Thp-1 Cells
European journal of biochemistry(1997)
摘要
1-O-Alkylglycerols (alkyl-Gro), naturally occurring compounds abundant in shark liver oil, protect patients from radiotherapy side-effects. However, the protection mechanism is not well understood. It might be mediated by alkyl-Gro incorporation into pools of platelet-activating factor (PAF) precursor and subsequent modification of PAF biosynthesis. Using a H-3-labelled or unlabelled natural alkyl-Gro mixture, in which prominent alkyl chains were C18:1(9) (54-65%), C16:1(7) (5-15.5%), and C16:0 (5-10%), we investigated the incorporation of alkyl-aro into phospholipids of human leukemic monocyte-like THP-1 cells. Incubation of cells for 24 h with [H-3]alkyl-Gro (10 mu M) resulted in their incorporation into 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (1097+/-25.1 pmol/2x10(6) cells) and into 1-alkyl-2-acyl-sn-glycero-3-phosphoethanolamine (640.4+/-12.5 pmol/2x10(6) cells) with a total yield of 6.5%. Such incorporation induced production of 1-O-[H-3]alkyl-2-acetyl-sn-glycero-3-phosocholine ([H-3]PAF), which was increased after stimulation by the calcium ionophore A23187. HPLC analysis of the [H-3]PAF molecular species indicated that the three major [H-3]alkyl-Gro were used for [H-3]PAF synthesis in ratios similar to that of the mixture. Total production of biologically active PAF, as measured by the platelet-aggregation bioassay, was also increased by alkyl-Gro incorporation in resting (+20%) and in A23187-stimulated (+59%) THP-1 cells. HPLC analysis of the [H-3]PAF produced in the presence of [H-3]acetate, confirmed that levels of PAE but not of its l-acyl analog, were increased by alkyl-Gro incorporation in resting and stimulated cells. However, the rise in [H-3]acetyl-PAF, which resulted mainly from C16:0 PAF, was reduced by about 50% in the presence of the PAF-receptor antagonist SR 27417, providing evidence that stimulation of total PAF synthesis was caused by the increase in the precursor pool and autocrine amplification of PAF-induced PAF production. Thus, the supplementation of THP-1 cells in culture with naturally occurring alkyl-Gro led to the incorporation of alkyl-aro into ether-containing phospholipids, which were subsequently used for PAF synthesis. Furthermore, alkyl-Gro incorporation resulted in a significant rise in PAF production by THP-1 cells under resting and stimulated conditions. These results may be of importance for modulating PAF production in several pathophysiological conditions, such as peroxysome deficiencies, that are associated with a lack of ether lipid synthesis.
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关键词
alkylglycerol,platelet-activating factor,platelet aggregation,phospholipid
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