Interferon-inducing, pyrogenic and proclotting enzyme of horseshoe crab activation activities of chemically synthesized lipid A analogues

Activity of monosaccharide lipid A analogues in human monocytic cells as agonists or antagonists of bacterial lipopolysaccharide

The lipid A portion of bacterial lipopolysaccharide (LPS) plays a central role in the production of endotoxic mediators. Different responses between human and murine macrophages to lipid A-like structures have been indicated. We investigated a series of structurally related monosaccharide lipid A analogues for their potency to activate human macrophage U937 cells and peripheral blood mononuclear cells for production of tumor necrosis factor-alpha and interleukin-6 compared with their potency to activate murine macrophage RAW264.7 cells. Two of the analogues were found to have sufficient potency to activate the human cells as well as the murine cells. These analogues comprise D-glucosamine, phosphoryl groups, and acyl groups of defined carbon chain lengths (C(14) and C(12)) in a ratio of 1:1:3. This ratio of molecular constituents is proportional to that of the complete disaccharide structure of lipid A (2:2:6). Other analogues with two or four C(14) acyl groups and with three acyl groups but including a C(10) or a C(16) acyl group, which are active to murine cells, showed no LPS-agonistic activity, but did show LPS-antagonistic activity, to human cells. An LPS-antagonistic analogue in the murine cells also showed antagonistic activity in human cells. These results reveal that lipid A analogues recognized as being LPS agonists by human macrophages have common structural features in monosaccharide and disaccharide structures which are more strict than those required for recognition by murine macrophages and that broad lipid A-like structures are recognized as being LPS antagonists by human cells but are recognized by murine cells as being either LPS agonists or antagonists.

Relationship of structure and biological activity of monosaccharide lipid A analogues to induction of nitric oxide production by murine macrophage RAW264.7 cells

Lipid A is the active center of bacterial lipopolysaccharide (LPS), which exhibits diverse biological activities via the production of various mediators. We investigated the production of nitric oxide (NO), one of the mediators, by a murine macrophage cell line, RAW264. 7, upon stimulation with a series of monosaccharide lipid A analogues to elucidate the relationship of structure and activity in NO production. The production of other representative mediators, such as tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6), was also investigated to compare the structural requirements for the production of these cytokines with those for the production of NO. Structure-activity relationships in NO production correlated well with those in the production of TNF-alpha and IL-6. Among the lipid A analogues possessing different numbers of acyl groups on a 4-O-phosphono-D-glucosamine backbone, compounds like GLA-60 that possess three tetradecanoyl (C14) groups exhibited stronger activities in the production of the mediators than compounds possessing four or two C14 groups. Time course study of the production of these mediators showed that production of NO started and peaked later than those of TNF-alpha and IL-6. Neither neutralization of TNF-alpha activity by antibody nor suppression of TNF-alpha production by pentoxifylline showed a significant suppressive effect on production of NO and IL-6 upon stimulation with LPS or lipid A analogues. Neutralization of IL-6 activity by antibody showed no significant suppressive effect on production of NO and TNF-alpha. A monosaccharide lipid A analogue (GLA-58) which exhibited no detectable agonistic activity showed a suppressive effect on the production of all three mediators upon stimulation with LPS or lipid A analogues. These results indicate that signals for NO production by LPS agonists in murine macrophages are transduced in good correlation with those for production of TNF-alpha and IL-6, although they are not transduced via production of those cytokines.

The activity of lipid A and core components of bacterial lipopolysaccharides in the prevention of the hypersensitive response in pepper

Pre-treatment of leaves of pepper (Capsicum annuum) with lipopolysaccharide (LPS) preparations from enteric bacteria and Xanthomonas campestris could prevent the hypersensitive response caused by an avirulent X. campestris strain. By use of a range of deep-rough mutants, the minimal structure in Salmonella LPS responsible for the elicitation of this effect was determined to be lipid A attached to a disaccharide of 2-keto-3-deoxyoctulosonate; lipid A alone and the free core oligosaccharide from a Salmonella Ra mutant were not effective. For Xanthomonas, the core oligosaccharide alone had activity although lipid A was not effective. The results suggest that pepper cells can recognize different structures within bacterial LPS to trigger alterations in plant response to avirulent pathogens.

Quantification of the endotoxin-neutralizing capacity of serum and plasma

A new procedure for quantifying the endotoxin-neutralizing capacity (ENC) of plasma or serum is described. Serially diluted samples were preincubated with endotoxin (lipopolysaccharide; LPS) and the sample dilution producing 50% inhibition of Tachypleus amebocyte lysate activation was measured by a Limulus peptide C enzyme-linked immunosorbent assay. The assay was not subject to interference from plasma or serum at a 500-fold dilution. The ENC of fresh sera from 120 healthy human donors, determined with Salmonella abortus LPS, had a median value of 7.7 kEU/ml (95% confidence limits 3-24 kEU/ml). Values for heparinized fresh plasma were close to those for the corresponding sera. Serum ENC varied greatly with different types of LPS. Neutralization of LPS by serum was rapid, heat-labile, and fully reversed by acidification. Addition of 2 mM EDTA to the serum diluent or pretreatment of LPS with 0.5% deoxycholate enhanced the ENC of serum about 25-fold or 10-fold respectively. The neutralization of LPS by polymyxin B or lysozyme could be demonstrated by the ENC assay, while that by human serum albumin, fibronectin or anti-LPS immunoglobulins was only detected in the presence of 2 mM EDTA. The kinetic changes of LPS and ENC during rabbit endotoxemia were also determined. The ENC assay may be used to study the significance of plasma ENC in Gram-negative infections and to identify the components contributing to plasma ENC.

Expression of endotoxic activities by synthetic monosaccharide lipid A analogs with alkyl-branched acyl substituents

Synthetic monosaccharide lipid A analogs with alkyl-branched acyl substituents instead of the usual ester-branched acyl substituents were investigated for their biological activities. The activities were compared with those of a representative synthetic monosaccharide lipid A analog with an ester branch (GLA-60) and synthetic complete lipid A (506) to estimate the role of the attaching mode of the branched side chains for expression of endotoxic activities. Among the analogs with alkyl branches, GLA-146 and GLA-147, which have C12 and C14 alkyl side chains, respectively, showed strong endotoxic activities. These analogs exhibited comparable or stronger activities than those of GLA-60 in murine macrophage activation activities to induce mediators such as tumor necrosis factors, interleukin 6, and nitric oxide and in mitogenic activity towards murine spleen cells; however, these activities were weaker than the respective activities of 506. With respect to lethal toxicity to galactosamine-sensitized mice, the analogs showed stronger activity than that of GLA-60 and activity closer to that of 506. With respect to adjuvant activity, no significant activity was observed in the analogs, while the activities of GLA-60 and 506 were strong. When lipopolysaccharide-resistant C3H/HeJ mice were used, the activities described above were not observed either for the analogs under investigation nor for GLA-60 and 506. These findings indicate that the ester type of branch in lipid A and its analogs does not play an indispensable role in the expression of various endotoxic activities. However, it may play some role in the expression of adjuvant activity and in lowering the level of toxicity.

Multistep regulation mechanisms for tolerance induction to lipopolysaccharide lethality in the tumor-necrosis-factor-alpha-mediated pathway. Application of non-toxic monosaccharide lipid A analogues for elucidation of mechanisms

Lipid A is the active principle of lipopolysaccharide (LPS). Synthetic lipid A analogues with monosaccharide backbones, GLA-60, GLA-69 and GLA-58, which exhibit potent, weak and scarce agonistic activities of LPS, respectively, induced tolerance against LPS lethality in galactosamine-(GalN)-sensitized mice while none of them were pyrogenic in rabbits. The tolerance-inducing mechanisms were investigated focusing on the regulation of tumor-necrosis-factor-alpha(TNF-alpha)-mediated lethal pathway of LPS. Induction of serum TNF-alpha in LPS-challenged mice was suppressed by prior administration of these analogues as well as LPS. Prior treatment of murine macrophages with the substances suppressed LPS-stimulated TNF-alpha production in the culture supernatant and TNF-alpha mRNA expression in the cells as well. Lethal toxicity of TNF-alpha in GalN-sensitized mice was effectively suppressed by prior treatment with LPS, GLA-60 and GLA-69 but not by GLA-58. This protective effect was suggested to be mediated by endogenous TNF-alpha, which was induced by prior treatment with the effective substances, because either neutralization of endogenously induced TNF-alpha activity with an antibody or deletion of its induction by using LPS-resistant C3H/HeJ mice reduced the protective effect, and a detectable amount of TNF-alpha was produced by stimulating macrophages with the effective substances but not with GLA-58. These results indicated that multiple regulation steps (one is prior to and the others are following TNF-alpha production) are participating in the tolerance induction by LPS and some lipid A analogues and that GLA-58 is a characteristic compound which induces the tolerance by only blocking the step prior to TNF-alpha production.

Protective activity of lipid A analogue GLA-60 against murine cytomegalovirus infection in mice

A chemically synthesized lipid A subunit analogue, GLA-60 (2-deoxy-4-O-phosphono-2-[(3R)-3-hydroxytetradecanamido]-3-O-[(3R) - 3-tetradecanoyloxytetradecanoyl]-D-glucose), has many of the activities of endotoxins but little, if any, toxicity. We investigated the protective activity of GLA-60 against murine cytomegalovirus (MCMV) infection in NMRI mice. Intraperitoneal administration of GLA-60 at 1 day before MCMV infection at doses of 1, 10, or 100 micrograms per mouse significantly reduced mortality. GLA-60 stimulated peritoneal natural killer (NK) cell and macrophage activities, and these activities were abolished by in vitro treatment with anti-asialo GM1 antibody and anti-Mac1 antibody, respectively. GLA-60 proved also protective against MCMV infection in mice in which either NK cells or macrophages were depleted by in vivo treatment with anti-asialo GM1 or anti-Mac1 antibody. The anti-MCMV activity of GLA-60 can at least be partially attributed to activation of NK cells and macrophages.

Effect of acyl substituents of synthetic lipid A-subunit analogues on their immunomodulating antiviral activity

A chemically synthesized lipid A-subunit analogue, GLA-60, 2-deoxy-4-O-phosphono-2-[(3R)-3-hydroxytetradecanamido]-3-O-[(3R)- 3- tetradecanoyloxytetradecanoyl]-D-glucose, has many of the activities of endotoxin but has little toxicity. Then, compounds with various lengths of acyl side chain of the acyloxyacyl group at the 3-O position of GLA-60 were synthesized and evaluated for interferon (IFN)-inducing activity, natural killer (NK) cell activation and antiviral activity. The compounds with acyl side chains between C8 and C15 exhibited significant antiviral activity (inhibition of pox tail lesion formation in vaccinia virus-infected mice), serum IFN-inducing activity and NK cell activation. However, the compound carrying a C2 or a C16 acyl side chain did not exhibit these activities. The compounds with a C13 or C14 acyl side chain showed strong protective against herpes simplex virus type 1 in cyclophosphamide-immunosuppressed mice.

Endotoxic properties of chemically synthesized lipid A analogs. Studies on six inflammatory reactions in vivo, and one reaction in vitro

Biological activities of two groups of synthesized lipid A analogs, the counterpart of biosynthetic precursor, Lehmann's Ia type, 406, and E. coli lipid A type, 506, as well as their non-phosphorylated, and mono-phosphorylated analogs were investigated. The activities employed included four bone marrow cell reactions in mice, mice skin reaction, leukocytes migration in rabbits' cornea, and hemagglutination. Compound 406 and 506 elicited bone marrow reactions in mice and hemagglutination of mouse RBC, although 406 failed to elicit hemorrhage and necrosis also in mice skin. Compound 406 did not elicit corneal reaction in rabbits. The results suggest that for elicitation of this reaction and mice skin reaction, acyloxyacyl structure is required. Cytotoxicity and thromboplastin production of four bone marrow reactions had been reported by us to be endotoxic reactions, since these had not been elicited by peptidoglycan of Lactobacillus and Staphylococcus (1981) and 300 series synthesized analogs (1984) which did not have endotoxic structures. From these results, it seems that these two marrow reactions and hemagglutination require, as does the limulus test, the lipid A part structure as is present in 406.

Antiherpes activity of chemically synthesized lipid A-subunit analogue GLA-60 in immunosuppressed mice

Intraperitoneal administration of 10 micrograms GLA-60, a chemically synthesized lipid A analogue, to mice one day after treatment with 200 mg/kg of cyclophosphamide (CY) significantly increased the number of macrophages, lymphocytes and polymorphonuclear leukocytes (PMNs) in the peritoneal cavity. The intrinsic antiviral activity of macrophages against herpes simplex virus type 1 (HSV-1) as well as natural killer (NK) activity against YAC-1 target cells was stimulated by administration of GLA-60 to CY-immunosuppressed mice. When the mice were administered GLA-60 prior to HSV-1 infection, virus growth was inhibited and the mortality rate of infected mice was reduced. Thus, GLA-60 is a potent immunomodulator achieving its antiviral action through enhancement of nonspecific host defense mechanisms. Combined treatment of GLA-60 with the antiviral agent acyclovir (ACV) resulted in greater protection against HSV-1 in the CY-immunosuppressed mice than did single treatment with either GLA-60 or ACV.

Structural requirements of lipid A for endotoxicity and other biological activities

For the past ten years, several groups were engaged in synthetic studies of lipid A, namely the lipid portion of bacterial lipopolysaccharides (LPS) that has been assumed to be the bioactive center of LPS, but has not been unanimously approved. Among them, Shiba, Kusumoto, and colleagues, Osaka, Japan have synthesized most energetically and successfully a variety of counterparts of lipid As, biosynthetic lipid A precursors, and their analogs. The endotoxic and related bioactivities of these synthetic compounds were studied by Japanese and German groups, including ours. In 1985, one of the compounds, having an acylation and phosphorylation pattern in beta(1-6)-D-glucosamine disaccharide which was proposed for Escherichia coli F515 lipid A was found to be exhibit full endotoxic and related bioactivities identical to those of the bacterial product. The study was extended by synthesis and examination of bioactivities of variously acylated D-glucosamine di- and monosaccharide phosphates, which correspond to structural components of lipid As, and their analogs or derivatives. Thus, structural requirements have been fairly well elucidated. In this article, first we will review the progress of synthetic and biological studies, with particular emphasis on chemical structure--bioactivities relationships of lipid As, and then we will discuss possible usefulness of some less or nontoxic lipid A-related synthetic compounds in clinical and preventive medicine.

Enhancement of nonspecific resistance to viral infection by chemically synthesized lipid A-subunit analogs with different backbone structures and acyl groups

Protection against vaccinia virus infection and induction of interferon (IFN) were investigated in Propionibacterium acnes-primed mice following treatment with chemically synthesized lipid A-subunit derivatives. The antiviral activity was based on the reduction of numbers of tail lesions in mice injected intravenously with the test compounds 1 day before virus infection. GLA-27, a 4-O-phosphono-D-glucosamine carrying 3-O-tetradecanoyl (C14) and N-3-tetradecanoyloxytetradecanoyl [C14-O-(C14)] groups, offered significant antiviral activity. Chemical modifications at the C1 position of GLA-27, e.g. phosphorylation, replacement of OH by an SH, did not cause a significant change in antiviral activity. GLA-57 carrying an N-3-dodecanoyloxytetradecanoyl group showed stronger activity than GLA-27, but GLA-58 carrying an N-3-hexadecanoyloxytetradecanoyl group did not exhibit significant activity. GLA-59 carrying 3-O-3-hydroxytetradecanoyl and N-C14-O-(C14) groups was more active than GLA-27 and GLA-57. GLA-60 possessing the same fatty acid substituents as GLA-59 but in the reversed order was the most active of all compounds tested. This suggests that the nature and position of the acyl substituents are important for achieving the antiviral effects. The (R) isomers of GLA-59 and GLA-60 possessed stronger IFN-inducing activity than the (S) isomers, but no significant difference in antiviral activity was seen between the isomers.

Antiviral and immunomodulating activities of chemically synthesized lipid A-subunit analogues GLA-27 and GLA-60

Biological and antiviral activities of chemically synthesized lipid A-subunit analogues, GLA-27 and GLA-60, were investigated with respect to defense mechanisms such as macrophage and natural killer (NK) cell activation and interferon (IFN)-inducing activity. GLA-27, a 4-O-phosphono-D-glucosamine derivative carrying 3-O-tetradecanoyl (C14) and 2-N-3-tetradecanoyloxytetradecanoyl (C14-O-(C14] group, and GLA-60, a similar analogue carrying 3-O-linked C14-O-(C14) and 2-N-linked 3-hydroxytetradecanoyl (C14-OH) groups, strongly inhibited the formation of pox tail lesions and the growth of vaccinia virus at the tail lesion sites in infected mice. The antiviral activity of GLA-60 was about 1000-fold higher than that of muramyldipeptide (MDP), a representative immunomodulator. GLA-27 and GLA-60 had stronger immunomodulating activity than MDP in macrophage activation, NK cell activation and IFN-inducing activity, although it was weaker than natural lipid A. Toxic manifestations such as pyrogenicity, local Schwartzman reaction and lethality were far less pronounced for GLA-27 and GLA-60 than for natural lipid A.

Immunopharmacological activities of chemically synthesized lipid A-subunit analogue GLA-27 combined with muramyl dipeptide via spacers of different carbon chain length

A lipid A-subunit analogue GLA-27, a 4-O-phosphono-D-glucosamine derivative carrying 3-O-tetradecanoyl and N-3-tetradecanoyloxytetradecanoyl groups, exhibited significant biological activities but no detectable pyrogenicity or local Shwarzman activity. In order to synthesize compounds combining GLA-27 with muramyl dipeptide (MDP), the OH group at the C6 position of GLA-27 was first succinylated. A compound which combined a succinylated GLA-27 (GLA-101) with 1-deoxy N-acetyl-muramyl-L-alanyl-D-isoglutamine methyl ester (1-deoxy MDP) via spacers of different carbon chain lengths of 5, 11 and 15, termed GLA-105, GLA-106 and GLA-107, respectively, and their biological activities were investigated. Intraperitoneal administration of combined preparations with spacers, GLA-105 and GLA-107, induced much higher phagocytic activity in peritoneal macrophages than GLA-27, GLA-101 and 1-deoxy MDP. The activity of GLA-106 did not increase by the combination. In induction of natural killer (NK) activity in peritoneal cells, GLA-105 and GLA-107 were significantly more active than 1-deoxy MDP but only comparable with GLA-27. GLA-101 showed stronger NK activity than GLA-27. The activity of GLA-106 was stronger than 1-deoxy MDP but weaker than GLA-27, GLA-105 and GLA-107. Mitogenic, interferon-inducing and tumor necrosis factor-inducing activities decreased by combining GLA-101 with 1-deoxy MDP. GLA-101, GLA-105 and GLA-107 strongly inhibited the formation of lesions on the tail of mice infected with Vaccinia virus. The activity was almost equivalent to that of GLA-27.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin testing

Parenterals, sterile preparations intended to be injected in man or animal, should be free from pyrogenic substances which are able to raise the thermostatic setting in the hypothalamus. This article gives an up-to-date review of the principal detection and quantification methods for these agents, with special attention on the chromogenic Limulus Amebocyte Lysate assay.

Structural requirements for inducing in vitro B lymphocyte activation by chemically synthesized derivatives related to the nonreducing D-glucosamine subunit of lipid A

Mitogenic and polyclonal B cell activation (PBA) activities of 16 synthetic compounds related to the nonreducing D-glucosamine (GlcN-II) subunit of lipid A were investigated. Among compounds possessing the GlcN backbone, a 4-O-phosphorylated GlcN derivative carrying N-linked 3-tetradecanoyloxytetradecanoyl [C14-O-(C14)] and 3-O-linked tetradecanoyl (C14) groups, GLA-27, expressed the highest degree of both activities. Omission of the 3-O-linked C14 group from GLA-27 and transfer of the C14 group to the C-6 position induced critical changes in expression of activities. Both 4-O-phosphorylated compounds carrying an N-linked C14 or 3-hydroxytetradecanoyl (C14OH) group instead of the C14-O-(C14) group in GLA-27 showed no detectable activity. Substituting a 3-O-linked C14 group in GLA-27 for the C14-O-(C14) group also markedly decreased mitogenic and PBA activities. Change of phosphorylation site from the C-4 to the C-6 position and bisphosphorylation at the C-4 and C-6 positions induced somewhat weak depression. Much weaker activities were observed in a compound carrying N-linked 3-dodecanoyloxydodecanoyl [C12-O-(C12)] and 3-O-dodecanoyl (C12) as fatty acid substituents. No detectable activity was seen in a compound carrying N-linked 3-hexadecanoyloxyhexadecanoyl [C16-O-(C16)] and 3-O-hexadecanoyl (C16), indicating that the most suitable carbon chain length for expressing the activities is C14. Regarding structural change of the GlcN backbone, a 1-deoxy derivative of GLA-27 exhibited stronger activity than did GLA-27 itself. Mitogenic and PBA activity of GLA-27 were stronger than those of lipid X, which corresponds to the reducing D-GlcN (GlcN-I) subunit of Escherichia coli lipid A and is a 1-O-phosphorylated GlcN derivative carrying N- and 3-O-linked C14OH groups. These results indicate that N-linked acyloxyacyl and 3-O-linked acyl groups and phosphorylation are critical for expressing both mitogenic and PBA activities.

Comparison of murine B cell clonal expansions by synthetic lipid A and muramyl dipeptide analogs

Direct stimulations of murine B lymphocytes with synthetic lipid A analogs and synthetic muramyl dipeptide (MDP) derivatives were studied using a limiting dilution assay system. Synthetic lipid A analogs, GLA-27 and GLA-40, when conjugated with bovine serum albumin (BSA) had the ability to induce B cell clonal expansion of a single B cell from the spleen or bone-marrow. Their activities were almost the same as those of naturally obtained lipid A, but were lower than that of bacterial lipopolysaccharide (LPS). Addition of dextran sulfate (DXS) enhanced the effect of lipid A analogs. In contrast, synthetic MDP and its derivatives, although they had many biological and immunological activities in experimental animals, could not stimulate a single B cell to induce clonal expansion regardless of the presence or absence of DXS. These results suggested that lipid A analogs can directly cause the proliferation of B cells, but MDPs can not.

Immunopharmacological activities of a synthetic counterpart of a biosynthetic lipid A precursor molecule and of its analogs

Synthetic lipid A analogs (compounds 404 through 406) were examined for their immunopharmacological activities. These compounds had two amide-bound and two ester-bound (R)-3-hydroxytetradecanoyl groups at the C-2 and C-2' and the C-3 and C-3' positions, respectively, of beta (1-3)glucosamine disaccharide. In all of the in vitro assays, these synthetic compounds exhibited high activities comparable to those of a reference lipid A prepared from Escherichia coli O8:K27 Re-mutant strain F515. The compounds activated the clotting enzyme cascade of the horseshoe crab, activated the human complement via the classical pathway, caused polyclonal B-cell activation, stimulated the phagocytosis of sheep erythrocytes by murine peritoneal macrophages, and enhanced the migration of human polymorphonuclear leukocytes. They also increased the thymidine uptake of splenocytes of BALB/c nu/nu and C3H/HeN mice but not those of C3H/HeJ (a nonresponder to lipopolysaccharide). A dephosphorylated derivative, compound 403, was barely active in all of the above assays except for the enhancement of polymorphonuclear leukocyte migration. However, compounds 404 through 406 were feeble in pyrogenicity and could not prepare the local Shwartzman reaction, although they were very lethal to galactosamine-loaded mice. Therefore, synthetic lipid A analogs described here were fully immunopharmacologically active in in vitro assays, but all of them were far less active than natural E. coli F515 lipid A regarding the biological activities characteristic of endotoxic lipopolysaccharides and lipid A's. The high lethal toxicity of compound 406 (1,4'-bisphosphate) to the galactosamine-loaded mice may not reflect its real toxicity to normal mice. In all activities examined, compound 406 was quite comparable to a biosynthetic lipid A precursor, a natural counterpart of compound 406. The immunopharmacological activities of these newly synthesized lipid A analogs, especially compound 406, were much stronger than those of compounds that had been synthesized earlier by using the originally proposed model of the lipid A structure. The findings described in this report justify the acylation pattern of a disaccharide backbone of lipid A, revised on the basis of recent analytical studies. The low in vivo endotoxic activities of the present lipid A analogs are most probably due to the fact that the kinds of acyl groups were different from those of the complete lipid A from E. coli, although there were no differences in the acylation positions on the disaccharide backbone.

B cell activation and adjuvant activities of chemically synthesized analogues of the nonreducing sugar moiety of lipid A

Immunological activities of synthetic lipid A analogues (derivatives of 3-O-tetradecanoyl D-glucosamine) were investigated. Compounds possessing a N-tetradecanoyloxytetradecanoyl group with or without a 4-O-phosphoryl group exhibited both mitogenic and polyclonal B cell activating activities. Among these, the phosphorylated compound exhibited strong activity. 4-O-phosphorylated analogues with a N-tetradecanoyl group or 6-O-tetradecanoyl group in addition to N-3-hydroxyacyl groups showed no activity. All the analogues tested showed adjuvant activity, which was determined by augmentation of IgM antibody response against sheep erythrocytes. Relationship between chemical structure and biological activities is also discussed.

Biological activities of analogues of lipid A based chemically on the revised structural model. Comparison of mediator-inducing, immunomodulating and endotoxic activities

Lipid A analogues were chemically synthesized based on the model structure recently revised, and biological activities of the analogues were tested. The analogue, (beta-1,6)-linked glucosamine disaccharide carrying ester-bound 3-hydroxytetradecanoic acids at 3 and 3' position of reducing and nonreducing glucosamine in addition to amide-bound 3-hydroxytetradecanoic acids and glycosidic-linked and ester-linked phosphate groups, showed much stronger activities for mediator inducing and immunomodulating as well as endotoxic activities than those exhibited by the previously synthesized analogues based on the old model. Among the activities tested, induction of interferon and tumor necrosis factor as well as mitogenicity, adjuvanticity and pyrogenicity were, however, not expressed so strongly as natural lipid A used as controls. In contrast, the analogue exhibited comparable activities to those of control lipid A in the test of lethal toxicity to mice and gelating activity of Limulus amebocyte lysate. Other synthetic analogues carrying a phosphate group showed comparable, slightly stronger or weaker activities depending on the test, but nonphosphorylated analogue exhibited no apparent or only very weak activities.