Glenn Warr

LPS down-regulates the expression of chemokine receptor CCR2 in mice and abolishes macrophage infiltration in acute inflammation.

Interactions between chemokines and their specific receptors are important for leukocyte trafficking. The CC‐chemokine monocyte chemoattractant protein‐1 (MCP‐1) and its specific receptor CCR2 are essential in monocytic infiltration and have been associated with several inflammatory diseases. It has been reported that several endotoxin and proinflammatory cytokines inhibit CCR2 expression in vitro in human monocytes. We report here that lipopolysaccharides (LPS) down‐regulated CCR2 expression both in vitro and in vivo. Injection of LPS into mice dramatically reduced the expression of CCR2 on the surface of peripheral blood cells and completely blocked macrophage infiltration into the peritoneal cavity in response to thioglycollate elicitation. In addition, treatment of mice with LPS reduced their efficiency to clear Listeria monocytogenes infection. These results suggest that down‐regulation of CCR2 and blockage of monocyte infiltration may contribute to the inhibition of macrophage function in vivo by a low dose of LPS. J. Leukoc. Biol. 65: 265–269; 1999.

Prostacyclin agonists reduce early atherosclerosis in hyperlipidemic hamsters. Octimibate and BMY 42393 suppress monocyte chemotaxis, macrophage cholesteryl ester accumulation, scavenger receptor activity, and tumor necrosis factor production.

We determined the effects of two prostacyclin agonists (octimibate and BMY 42393) on the progression of the fatty streak in vivo and on macrophage function in vitro. Hamsters were fed chow plus 0.05% cholesterol and 10% coconut oil. Control hamsters were compared with animals receiving either octimibate (10 or 30 mg/kg per day) or BMY 42393 (30 mg/kg per day). After 10 weeks of treatment, octimibate decreased plasma total cholesterol and triglycerides by 43% and 32%, respectively. Neither agonist affected blood pressure or heart rate. Lesion-prone aortic arches were stained with hematoxylin and oil red O and examined en face. Compared with controls, octimibate and BMY 42393 on average decreased mononuclear cells attached to the luminal surface by 44% and reduced subendothelial macrophage-foam cell number by 56%, foam cell size by 38%, and fatty streak area by 63%. Since octimibate is a putative inhibitor of acyl coenzyme A cholesterol acyltransferase, we studied the effect of both agents on cholesteryl ester metabolism in murine macrophages. At 10 microM, octimibate and BMY 42393 decreased cholesteryl ester accumulation in macrophages by 90% and 41%, respectively. Octimibate inhibited cholesteryl ester synthesis by 96% and increased the rate of cholesteryl ester degradation by 52%. Both prostacyclin agonists reduced macrophage scavenger receptor-mediated uptake of acetylated low density lipoprotein by 24-66% and increased cyclic adenosine monophosphate levels. Octimibate and BMY 42393 inhibited the secretion of tumor necrosis factor by 80-88% when macrophages were activated with lipopolysaccharide. At 10 microM, both agents decreased human monocyte chemotaxis to N-formyl-methionyl-leucyl-phenylalanine by 64-79%. The in vitro results with octimibate and BMY 42393 are consistent with the low number of small foam cells quantified in vivo. We suggest that octimibate and BMY 42393 suppress monocyte-macrophage atherogenic activity and cytokine production and thus inhibit the development of early atherosclerosis.

Trichodimerol (BMS‐182123) inhibits lipopolysaccharide‐induced eicosanoid secretion in THP‐1 human monocytic cells

The fungal metabolite trichodimerol (BMS‐182123) has demonstrated inhibition of lipopolysaccharide (LPS) ‐stimulated tumor necrosis factor‐α (TNF‐α) secretion in various in vitro macrophage models (human and murine) including primary and tumor cell lines. When challenged with LPS, differentiated THP‐1 monocytic cells secrete elevated levels of the cyclooxygenase products prostaglandin E2 (PGE2), thromboxane B2, and prostaglandin F2α (PGF2α). Studies directed at elucidating the mechanism of action of BMS‐182123 as a TNF‐α inhibitor revealed that the compound has a profound inhibitory effect on prostanoid secretion in response to LPS challenge. The key enzymes in prostaglandin synthesis are the constitutive cyclooxygenase, prostaglandin H synthase‐1 (PGHS‐1), and the mitogen‐induced cyclooxygenase (PGHS‐2), which is induced upon LPS stimulation in THP‐1 cells. BMS‐182123 did not inhibit the cyclooxygenase activity of PGHS‐1 in an in vitro assay, suggesting that inhibition is due to a blockade in synthesis of cyclooxygenase enzyme. Western blot analysis of microsomal pellets from THP‐1 cells stimulated with LPS (with or without BMS‐182123 pretreatment) provided convincing evidence that the inhibition of prostaglandin synthesis is a result of suppressed synthesis of PGHS‐2 enzyme. Northern blot analysis of THP‐1 RNA demonstrated that BMS‐182123 inhibits the induction of PGHS‐2 at the level of transcription. J. Leukoc. Biol. 60: 271–277; 1996.

Lipopolysaccharide (LPS) alters phosphatidylcholine metabolism in elicited peritoneal macrophages.

We investigated the effects of LPS on mouse peritoneal macrophage phospholipids using radiolabeled precursors. LPS (200 ng/ml) stimulated incorporation of [32P] into all classes of phospholipids within 0.5 hr, and after 2 hr the increase was 60% greater than controls. Separation of the phospholipid classes by thin‐layer chromatography revealed a selective increase in incorporation of label into phosphatidylcholine (PC) (90% increase compared to approximately 50% in the other phospholipids). In macrophages labeled with [3H]‐choline, LPS stimulated both the incorporation of label into PC and the release of incorporated label into the medium. The time dependencies of stimulated [3H] release and [32P] incorporation were similar. These data are consistent with the hypothesis that LPS activates macrophages via a PC‐specific phospholipase‐dependent mechanism.

A Highly Conserved Intraspecies Homolog of the Saccharomyces cerevisiae Elongation Factor-3 Encoded by the HEF3 Gene

A paralog (intraspecies homolog) of the Saccharomyces cerevisiae YEF3 gene, encoding elongation factor‐3, has been sequenced in the course of the yeast genome project, and identified by database searching; this gene has been designated HEF3. Bioinformatic and Northern blot analysis indicate that the HEF3 gene is not expressed during vegetative growth. Deletion of the HEF3 gene reveals no growth defects, nor any defects in mating or sporulation. A high copy 2μ clone of HEF3 was constructed, and was shown to be unable to complement a null allele of yef3. Finally, an in vitro assay for ribosome‐stimulated ATPase activity was performed with isogenic HEF3 and Δhef3 strains; no difference in biochemical activity could be detected in these strains. From these results, we conclude that the HEF3 gene does not encode a functional homolog of YEF3.