MODULATION OF PLATELET-ACTIVATING-FACTOR PRODUCTION BY INCORPORATION OF NATURALLY-OCCURRING 1-O-ALKYLGLYCEROLS IN PHOSPHOLIPIDS OF HUMAN LEUKEMIC MONOCYTE-LIKE THP-1 CELLS
A. Hichami et al., 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, 250(2), 1997, pp. 242-248
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 whi
ch 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 inc
orporation into 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (1097+/-2
5.1 pmol/2x10(6) cells) and into 1-alkyl-2-acyl-sn-glycero-3-phosphoet
hanolamine (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 stimulat
ion by the calcium ionophore A23187. HPLC analysis of the [H-3]PAF mol
ecular 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. Tota
l production of biologically active PAF, as measured by the platelet-a
ggregation bioassay, was also increased by alkyl-Gro incorporation in
resting (+20%) and in A23187-stimulated (+59%) THP-1 cells. HPLC analy
sis of the [H-3]PAF produced in the presence of [H-3]acetate, confirme
d that levels of PAE but not of its l-acyl analog, were increased by a
lkyl-Gro incorporation in resting and stimulated cells. However, the r
ise in [H-3]acetyl-PAF, which resulted mainly from C16:0 PAF, was redu
ced by about 50% in the presence of the PAF-receptor antagonist SR 274
17, providing evidence that stimulation of total PAF synthesis was cau
sed by the increase in the precursor pool and autocrine amplification
of PAF-induced PAF production. Thus, the supplementation of THP-1 cell
s in culture with naturally occurring alkyl-Gro led to the incorporati
on of alkyl-aro into ether-containing phospholipids, which were subseq
uently used for PAF synthesis. Furthermore, alkyl-Gro incorporation re
sulted in a significant rise in PAF production by THP-1 cells under re
sting and stimulated conditions. These results may be of importance fo
r modulating PAF production in several pathophysiological conditions,
such as peroxysome deficiencies, that are associated with a lack of et
her lipid synthesis.