Structural and physicochemical requirements of endotoxins for the activation of arachidonic acid metabolism in mouse peritoneal macrophages in vitro.

Lipopolysaccharides of different wild-type and mutant gram-negative bacteria, as well as synthetic and bacterial free lipid A, were studied for their ability to activate arachidonic acid metabolism in mouse peritoneal macrophages in vitro. It was found that lipopolysaccharides of deep-rough mutants of Salmonella minnesota and Escherichia coli (Re to Rc chemotypes) stimulated macrophages to release significant amounts of leukotriene C4 (LTC4) and prostaglandin E2 (PGE2). Lipopolysaccharides of wild-type strains (S. abortus equi, S. friedenau) only induced PGE2 and not LTC4 formation. Unexpectedly, free bacterial and synthetic E. coli lipid A were only weak inducers of LTC4 and PGE2 production. Deacylated Re-mutant lipopolysaccharide preparations were inactive. However, co-incubation of macrophages with both deacylated lipopolysaccharide and lipid A lead to the release of significant amounts of LTC4 and PGE2, similar to those obtained with Re-mutant lipopolysaccharide. The significance of the lipid A portion of lipopolysaccharide for the induction of LTC4 was indicated by demonstrating that peritoneal macrophages of endotoxin-low-responder mice or of mice rendered tolerant to endotoxin did not respond with the release of arachidonic acid metabolites on stimulation with Re-mutant lipopolysaccharide and that polymyxin B prevented the Re-lipopolysaccharide-induced LTC4 and PGE2 release. Physical measurements showed that the phase-transition temperatures of both free lipid A and S-form lipopolysaccharide were above 37 degrees C while those of R-mutant lipopolysaccharides were significantly lower (30-35 degrees C). Thus, with the materials investigated, an inverse relationship between the phase-transition temperature and the capacity to elicit LTC4 production was revealed.

Chemical structure and biologic activity of bacterial and synthetic lipid A.

The chemical structure of the lipid A component of enterobacterial lipopolysaccharide (LPS) is now known in some detail. For example, lipid A of Escherichia coli consists of a beta(1----6)-linked D-glucosamine disaccharide that carries four (R)-3-hydroxytetradecanoyl groups in positions 2, 3, 2', and 3' and two phosphoryl residues in positions 1 and 4'. The hydroxy fatty acids at positions 2' and 3' are acylated at their 3-hydroxyl groups by dodecanoic acid and tetradecanoic acid, respectively. The hydroxyl groups in positions 4 and 6' are free, the latter serving as the attachment site for the polysaccharide component in intact LPS. On the basis of this structure, E. coli-type lipid A and partial structures thereof have been chemically synthesized (group of T. Shiba, Osaka University, Osaka, Japan) and analyzed for endotoxic activity. In all in vivo and in vitro test systems employed (including lethal toxicity, pyrogenicity, local Shwartzman reactivity, B lymphocyte mitogenicity, macrophage activation, and serologic cross-reactivity with lipid A antiserum), synthetic lipid A has activity identical to that of E. coli lipid A. These findings support the structural proposal for lipid A and prove the previous hypothesis that the endotoxic principle is embedded in lipid A.

Formation and metabolism of leukotriene C4 in macrophages exposed to bacterial lipopolysaccharide.

Lipopolysaccharide (10 micrograms/ml) was found to stimulate resident mouse peritoneal macrophages to produce leukotriene C4 (36 +/- 1.3 ng/10(6) cells, SEM, n = 20) within 16 h. Spontaneous synthesis in control cultures without lipopolysaccharide was less than 1.6 ng/10(6) cells. Leukotriene C4 was characterized by reversed-phase high-performance liquid chromatography, ultraviolet spectrometry and radioimmunoassay. When the macrophages, prelabeled with [3H]arachidonic acid, were treated with lipopolysaccharide radioactivity was incorporated into leukotriene C4. The amount produced varied with the method of macrophage preparation and incubation conditions and was dependent on the amount of lipopolysaccharide added (0.5-60 micrograms/ml), on cell counts and on the incubation time (4-16 h). The released leukotriene C4 was converted to a compound identified as a C6-cysteinylleukotriene, indicating metabolism of the leukotriene by the macrophages. Parallel determinations of prostaglandins E2 and F2 alpha by radioimmunoassay demonstrated that leukotriene C4 and prostaglandin E2 are formed by mouse peritoneal macrophages to a similar degree.

Newer aspects of the chemical structure and biological activity of bacterial endotoxins.

Gram-negative bacteria express at their surface various amphiphiles among which the lipopolysaccharides (endotoxins, O-antigens) have been studied most intensively. Lipopolysaccharides consist of a heteropolysaccharide portion (O-specific chain and core) which is responsible for the O- (and R-) antigenic properties and a covalently bound lipid component, termed lipid A, which contains the endotoxic principle of lipopolysaccharides. The detailed chemical structure of a large number of O-chains and the general architecture of the core oligosaccharide has been established. Recent analyses of the enterobacterial inner core region indicate the presence of a linear trisaccharide of alpha 2.4-linked 3-deoxy-D-manno-2-octulosonic acid (KDO) residues of which only the reducing group is believed to be located in the main core chain. This KDO residue which provides the link between the polysaccharide and the lipid A component appears to be involved in a recently detected ubiquitous immunodeterminant expressed by lipopolysaccharides of various origin. The chemical structure of enterobacterial lipid A's is now known in some detail. Lipid A of Salmonella, Escherichia coli and Proteus consists of a beta 1.6-linked D-glucosamine disaccharide which carries four (R)-3-hydroxytetradecanoyl groups in positions 2, 3, 2' and 3' and two phosphoryl residues in positions 1 and 4'. Up to three of the hydroxy fatty acids (positions 2, 2' and 3') are, at their 3-hydroxyl groups, acylated by non-hydroxylated acyl residues, and to phosphoryl groups non-acylated, nitrogen-containing residues such as 4-amino-4-deoxy-L-arabinopyranose and phosphorylethanolamine may be bound. The hydroxyl group in position 4 of the glucosamine disaccharide is free and that in position 6' serves as the attachment site for KDO (i.e. the polysaccharide component) in lipopolysaccharide. Based on this structure lipid A analogues have been chemically synthesized and analysed for endotoxic activity in vivo and in vitro. In two test systems (pyrogenicity, local Shwartzman reaction) the synthetic part structures exhibited weak or no endotoxic activity, as did a precursor of lipid A biosynthesis which is structurally identical to one of the analogues. In many other systems, however, including lethal toxicity, B-lymphocyte mitogenicity, macrophage activation, induction of cross tolerance, expression of lipid A antigenicity, the synthetic materials were of comparable activity as bacterial free lipid A. These findings support the structural proposals made for lipid A and they prove the previous hypothesis that the endotoxic principle is embedded in lipid A.(ABSTRACT TRUNCATED AT 400 WORDS)

Endotoxic properties of chemically synthesized lipid A part structures. Comparison of synthetic lipid A precursor and synthetic analogues with biosynthetic lipid A precursor and free lipid A.

Synthetic lipid A part structures corresponding structurally to a biosynthetic lipid A disaccharide precursor have been analyzed for endotoxic activity in several systems in vivo and in vitro. It was found that a synthetic beta-1,6-linked D-glucosamine disaccharide, which carries four molar equivalents of (R)-3-hydroxytetradecanoyl residues in positions 2, 3, 2' and 3' and phosphoryl groups in positions 1 and 4' (preparation 406), exhibited lethal toxicity, B lymphocyte mitogenicity, the capacity to engender prostaglandin formation in macrophages and to induce endotoxic tolerance, as well as serological lipid A antigenicity. On a weight basis, preparation 406 was of comparable activity to lipid A precursor and bacterial free lipid A. Preparation 406, like lipid A precursor, lacked, however, the ability to induce the local Shwartzman phenomenon and both preparations were of moderate pyrogenicity. Two further synthetic analogues which contained only one phosphoryl group (preparation 404 at C-4', preparation 405 at C-1) showed comparable or diminished activity depending on the test system employed, except in the capacity to inactivate complement where they exhibited, in contrast to preparation 406, significant activity. The results show that the endotoxic principle of lipopolysaccharides, as postulated previously is embedded in the lipid A component. Our results also suggest initial conclusions on the structural requirements for the expression of endotoxin activities.

Enzymic synthesis of lignin precursors. Purification and properties of 4-coumarate:CoA ligase from cambial sap of spruce (Picea abies L.).

4-Coumarate:CoA ligase was purified from cambial sap of spruce (Picea abies). A 1627-fold purification of the enzyme with a yield of 37% was achieved by a six-step procedure including dye-ligand chromatography. Isozymes of the ligase were not detected. The enzyme has an Mr of about 63 000 and is a single polypeptide chain. Ferulic, 4-coumaric and caffeic acids are efficient substrates for the ligase. In contrast to some ligases from angiosperms, the ligase from spruce (gymnosperm) does not activate sinapic acid. The substrate specificity of the ligase is consistent with the lignin composition of spruce.

Enzymic synthesis of lignin precursors. Comparison of cinnamoyl-CoA reductase and cinnamyl alcohol:NADP+ dehydrogenase from spruce (Picea abies L.) and soybean (Glycine max L.).

Cambial sap of spruce (Picea abies) proved to be a good source for isolation of cinnamoyl-CoA reductase and cinnamyl alcohol:NADP+ dehydrogenase. Apparently homogeneous enzymes were obtained by a multistep procedure including dye-ligand chromatography and for the reductase also affinity chromatography on (coenzyme A)-agarose. An improved purification procedure for the reductase from soybean cell cultures is also reported. Molecular weights and subunit composition of reductase and dehydrogenase from spruce are very similar to those of the corresponding enzymes from soybean. Reduction of feruloyl-CoA to coniferaldehyde catalysed by the reductase is a freely reversible reaction with an equilibrium constant of 5.6 x 10(-4) M at pH 6.25. A strong dependence of the Michaelis constants on the type of buffer was found. For reductase the Km-value of feruloyl-CoA in phosphate buffer (5.2 microM) is about 14-times similar than in citrate buffer (73 microM). Pronounced differences in substrate specificities between the enzymes from spruce and soybean were found, which reflect the different lignin composition of gymnosperms and dicotyledenous angiosperms. From the kinetic constants of the enzymes it can be concluded that under physiological conditions feruloyl-CoA is the preferred substrate for the reductase from both sources whereas sinapoyl-CoA is a substrate only for the soybean reductase and sinapyldehyde a substrate only for the soybean dehydrogenase. 4-Coumaroyl-CoA is a poor substrate for the reductase from both spruce and soybean. This result is consistent with the low content of 4-coumaryl alcohol units in gymnosperm and angiosperm lignin.