INDUCTION OF EARLY GENE-EXPRESSION IN MURINE MACROPHAGES BY SYNTHETICLIPID-A ANALOGS WITH DIFFERING ENDOTOXIC POTENTIALS

Numerous lipid A analogs have been synthesized in an attempt to dissoc iate endotoxic activities from beneficial immunomodulatory activities. In the present study, we have evaluated select lipid A analogs in mac rophages for their ability to induce a panel of lipopolysaccharide (LP S)-inducible genes to gain insights into the molecular mechanisms whic h underlie endotoxicity. We evaluated three monosaccharide lipid A ana logs: SDZ MRL 953, an agonist with an improved therapeutic margin over endotoxin; SDZ 281.288, a more toxic analog; and SDZ 880.431, an anal og with proven LPS-inhibitory activity. In addition, three disaccharid e lipid A analogs (i.e., lipid IV(A), SDZ 880.611, and SDZ 880.924) th at differ in acylation and phosphorylation patterns were also examined and compared with synthetic lipid A. With the exception of SDZ 880.43 1, each of these structurally diverse analogs was able to induce the c omplete panel of LPS-inducible genes, specifically genes which encode tumor necrosis factor alpha (TNF-alpha), interleukin-1beta, 75-kDa typ e 2 TNF receptor (D7), IP-10, D3, and D8. These results underscore tha t macrophage stimulation by lipid A analogs is permissive to considera ble structural diversity. Structures with favorable therapeutic indice s (SDZ MRL 953, SDZ 880.611, and SDZ 880.924) were not different from structures with poor therapeutic indices (lipid A, lipid IV(A), and SD Z 281.288) with regard to gene induction. Nonetheless, the nontoxic SD Z MRL 953 was approximately 1,000-fold less potent than synthetic lipi d A at inducing TNF-alpha secretion, and perhaps this contributes to t he lack of toxicity exhibited by this compound. The ability of compoun d SDZ 880.431 to inhibit TNF-alpha secretion induced by both SDZ MRL 9 53 and smooth LPS suggests that the monosaccharide and smooth LPS shar e a receptor or a portion thereof. A pattern of protein tyrosine phosp horylation similar to that induced by LPS was stimulated by the monosa ccharides SDZ MRL 953 and SDZ 281.288 and disaccharides lipid IV(A), S DZ 880.924, and SDZ 880.611, providing evidence for a common signallin g pathway.