J. Biol. Chem., Vol. 265, Issue 16, 9159-9164, Jun, 1990
Highly purified lipid X is devoid of immunostimulatory activity. Isolation and characterization of immunostimulating contaminants in a batch of synthetic lipid X
H Aschauer, A Grob, J Hildebrandt, E Schuetze and P Stuetz
Sandoz Forschungsinstitut, Vienna, Austria.
Lipid X, an early precursor in the biosynthesis of lipid A has been
reported to directly induce cytokine release in macrophages but also to
inhibit endotoxin-induced tumor necrosis factor (TNF) induction. In this
report we provide evidence that these conflicting results could be due to
contaminants present in different batches of lipid X used. Thus, in an
apparently pure batch of crystalline lipid X as obtained by a published
procedure (Macher, I. (1987) Carbohydr. Res. 262, 79-84) small amounts of
N,O-acylated disaccharide-1-phosphates could be identified. Their isolation
was achieved by gel filtration on Sephadex LH-20 and further analysis of
fractions showing elevated limulus amebocyte lysate values by thin layer
chromatography and reverse-phase high performance liquid chromatography
(HPLC) in combination with bioassays. Identification of immunostimulatory
by-products was possible by testing HPLC-fractions for TNF-induction in
bone marrow-derived mouse macrophages. Applying these procedures a
disaccharide-1- phosphate, containing four 3(R)-hydroxymyristic acids at
positions 2, 3, 2', 3', was identified as the main immunostimulatory side
product. Two isomeric hydrolysis products of this compound with only three
3(R)- hydroxymyristic acid moieties attached to the
disaccharide-1-phosphate were also identified. Surprisingly, these
compounds behave quite differently in the TNF induction test. The
disaccharide-1-phosphate, acylated at positions 2, 2', 3', is a very potent
inducer of TNF- release whereas the corresponding isomer containing the
3(R)- hydroxymyristic acids in positions 2, 3, 2', does not induce TNF
release, but strongly inhibits TNF release as induced by the former
compound. Thus, contamination of "pure" lipid X with immunostimulatory or
immunoinhibitory impurities may explain the divergent pharmacological
profiles which were attributed to synthetic lipid X.