Alterations in rats in vivo of the chemical structure of lipopolysaccharide from Salmonella abortus equi

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Abstract
A biosynthetically double‐labelled lipopolysaccharide (LPS) from Salmonella abortus equi was used to study possible in vivo degradation of LPS in rats. The preparation designated rLPS‐I was labelled with 3H in the fatty acids and 14C in the sugars. Three days after its intravenous injection the concentration of the two isotopes in the liver was analysed directly by combustion of liver tissue in a sample oxidizer. It was found that compared to the starting LPS, less 3H activity was present than 14C, indicating that partial deacylation had occurred. Reisolation and purification of radioactive material present in the liver revealed that all radioactivity was present in a macromolecular form. Analysis showed that the ratio of the two isotopes was identical to that determined in the starting liver tissue. To exclude the possibility that the loss of 3H might have been due to isotopic dilution the above experiments were repeated with a second LPS preparation (rLPS‐II) labelled with 14C in the fatty acids and 3H in glucosamine. Isotopic analysis confirmed that here too a lower content of fatty acids in the LPS was present in the liver. A large‐scale (20 rats) reisolation of non‐radioactive LPS of S. abortus equi from rat livers three days after injection was carried out. Chemical analysis revealed the presence of 3‐deoxy‐d‐manno‐octulosonic acid, heptose, galactose, mannose and rhamnose in a molar ratio similar to that of the original LPS. However a significant reduction in the amount of abequose was found. Fatty acid analysis showed a significant reduction in the content of 3‐hydroxytetradecanoic, dodecanoic and hexadecanoic acids, while 2‐hydroxytetradecanoic acid was virtually absent. Only the relative amount of tetradecanoic acid was comparable to that of the starting LPS. Biological activity tests on the reisolated material showed a reduced antigenic activity. However, pyrogenicity, lethal toxicity, local Shwartzman‐inducing properties and Limulus lysate gelating activity were comparable to the starting S. abortus equi LPS.