Adjuvant activity of synthetic cell-wall peptidoglycan subunits on monoazobenzenearsonate-N-acetyl-L-tyrosine and bacterial alpha-amylase in guinea pigs

Formulation of vaccine adjuvant muramyldipeptides (MDP). 2. The thermal reactivity and pH of maximum stability of MDP compounds in aqueous solution

The degradation of muramyldipeptides (MDPs) in aqueous solution obeys the rate law kobs = kH+aH+ + ko + kHO-aHO- and the Arrhenius equation. For example, the rate constants for degradation of N-acetylmuramyl-L-threonyl-D-isoglutamine, 3, at 25 degrees C are kH+ = 2.3 X 10(-6) M-1 sec-1, ko = 8.2 X 10(-10) sec-1, and kHO- = 0.19 M-1 sec-1. The degradation rates are dependent on the side-chain substituents; it is predicted that sterically hindered MDP compounds will show an extended shelf life in aqueous solution. Product studies in the weakly acid pH region (where the pH of maximum stability occurs) show that MDP compounds degrade largely by hydrolysis of the dipeptide side chain. These data show that MDP 3 exhibits a shelf life (t90) of greater than 2 years in aqueous solutions of pH 4-4.5, the pH of maximum stability.

The fate of nor-muramyl dipeptide (3H-labelled) after local administration in incomplete Freund's adjuvant in the guinea pig

The fate of 3H-nor-muramyl dipeptide has been investigated after administration with bovine serum albumin (BSA) in Freund's incomplete adjuvant in the guinea pig footpad. Emulsions of two different stiffnesses , both of which were capable of inducing delayed-type hypersensitivity to BSA, were compared. Both emulsions produced stable depots of intact nor-MDP at the injection site. At early times retention of nor-MDP was greater with the stiffer emulsion and circulating levels of nor-MDP were greater with the looser emulsion; at 24 h there were no differences between the two. Distribution of nor-MDP to the draining lymph nodes was highly variable and no difference was apparent between the two emulsions. Levels of radioactivity in more distant lymph nodes were minimal, and in other tissues no radioactivity was detected. Thus it has not been possible to clarify the role of nor-MDP in this system in terms of its distribution through the local lymphatics, however, some information has emerged about the stability and integrity of nor-MDP in local adjuvant formulation.

Pharmacokinetics and metabolism of muramyl dipeptide and nor-muramyl dipeptide [3H-labelled] in the mouse

The fates of 3H-muramyl dipeptide (MDP) and 3H-nor-MDP have been investigated after intravenous (i.v.), intraperitoneal, and subcutaneous injection of a range of doses in the mouse. After i.v. injection both compounds were cleared rapidly from the circulation, distributed initially to the tissues, and finally excreted largely intact in the urine. Most of the tissues contained intact material at 2 min after injection, but the much lower levels of radioactivity persisting at 1 h had undergone considerable metabolism (except in intestine, where some intact material persisted for as long as 24 h). Some accumulation of radioactivity was observed in liver and kidney and there were quantitative and qualitative differences between the two compounds. Characterisation of some of the metabolites in these tissues was undertaken, and the deamidated muramyl dipeptide was tentatively identified which is known to have some biological activity. The mechanism of the biological effects, which may be expressed over a relatively long time period, remains to be explained in view of the rapid excretion of most of the dose.

Anti-inflammatory effects of muramyl dipeptide in experimental models of acute inflammation

Synthetic muramyl dipeptide, N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP), has been tested for activity against acute inflammation. In all models employed (Bayol + Arlacel paw oedema in rats, carrageenan pleurisy in rats, and carrageenan of dextran paw oedema in mice), MDP given in admixture with the phlogistic agents significantly lowered the resulting inflammatory reaction by about 30-40%. 0.1-0.2 mg of MDP per animal was applied. The mechanism of anti-inflammatory activity of this substance remains unknown.

Stimulation of nonspecific resistance to infection induced by 6-O-acyl muramyl dipeptide analogs in mice

The experimental system utilized in investigating the correlation between the chemical structures of muramyl peptides and their protective activities in the sepsis type of systemic infections caused by Escherichia coli was applied in evaluating the enhancement of resistance to infection induced by 32 synthetic glycopeptide analogs, including 6-O-acyl derivatives and 1-alpha-O-benzyl derivatives of muramyl dipeptide (N-acetyl muramyl-L-alanyl-D-isoglutamine). In assessing the 6-O-acyl derivatives of muramyl dipeptide, we found that the degree of protective activity was attributable to the kinds of fatty acids introduced. Acylation of the 6-hydroxy group on the muramic acid moiety in muramyl dipeptide with natural mycolic acid or a synthetic fatty acid possessing either an alpha-branched or an alpha-branched, beta-hydroxylated group resulted in a decrease in or a disappearance of the protective activity of muramyl dipeptide. Acylation with a normal fatty acid or an iso fatty acid resulted in a retention or enhancement of muramyl dipeptide activity. The activity of acylated derivatives containing linear fatty acids was stimulated by increasing the chain length up to 18 carbon atoms. The highest degree of protective activity occurred with the derivatives acylated with straight-chain fatty acids, particularly with the derivatives acylated with palmitic acid and arachidic acid. Benzylation of the 1-hydroxy group of muramyl dipeptide resulted in a decrease in or a loss of protective activity.

Regression of tumors in guinea pigs after treatment with synthetic muramyl dipeptides and trehalose dimycolate

A high incidence of tumor regression was observed in guinea pigs bearing transplantable, line-10 hepatocellular carcinomas when synthetic muramyl dipeptides combined with trehalose dimycolate in oil-in-water emulsions were injected directly into the tumors. These compounds are promising candidates to replace viable bacillus Calmette-Guérin in cancer immunotherapy in humans and animals.

Immunostimulant activities of a lipophilic muramyl dipeptide derivative and of desmuramyl peptidolipid analogs

The immunostimulant properties of a new muramyl dipeptide (MDP) derivative bearing a lipophilic moiety on the C-terminal end of the peptide chain are described. It is shown, in particular, that 1,O-(acetylmuramyl-L-alanyl-D-isoglutamine-L-alanyl)-glycerol-3-mycolate had increased immunostimulant activity in comparison with MDP. It induced hypersensitivity even when administered with an antigen in saline, and it gave higher protection against bacterial infections than did MDP. A quite unexpected finding was obtained with the corresponding desmuramyl compound 1,O-(L-alanyl-D-isoglutamine-L-alanyl)-glycerol-3-mycolate, which had no activity in producing humoral antibodies but was just as active as the muramic acid-containing compound in stimulating nonspecific resistance to bacterial infections. It was not pyrogenic. Modifications of the peptide moiety or the lipid moiety of this peptidolipid led to decrease, or even loss, of activity. These results show the importance of the N-acetylmuramyl moiety in MDP for humoral antibody production. The peptidolipid 1,O-(L-alanyl-D-isoglutamine-L-alanyl)-glycerol-3-mycolate is the first member of a new category of nonspecific immunostimulants.

Fate of the synthetic immunoadjuvant, muramyl dipeptide (14C-labelled) in the mouse

Synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine (muramyl dipeptide or MDP) represents the smallest unit that can substitute for whole Mycobacteria in Freund's complete adjuvant. In this paper the fate of 14C-labelled (on the muramyl moiety) MDP is reported. Following intravenous or subcutaneous injection into mice, more than 50% of 14C-MDP was recovered in the urine after 30 min and more than 90% after 2 h. The labelled compound was found unchanged in the urine, as shown by detailed analyses. However, MDP was sequestered for a longer time at the site of injection when administered as a water-in-oil emulsion. Considering the relatively rapid elimination observed, it is suggested that the biological effects of MDP and related compounds, when administered in an aqueous medium, may be due to their activity at minute concentrations and/or an immediate action at the cellular level.

Adjuvant activity of mycobacterial fractions: adjuvant activity of synthetic N-acetylmuramyl-dipeptide and the related compounds

Immunological activity of synthetic cell wall peptidoglycan subunits was examined in guinea pigs and mice. It was concluded that the minimal adjuvant-active subunit of cell wall peptidoglycan for the induction of delayed-type hypersensitivity to monoazobenzenearsonate-N-acetyl-L-tyrosine and for circulating-antibody formation to bacterial alpha-amylase and the thymus-independent antigen DNP-Ficoll was N-acetylmuramyldipeptide, MurNAc-L-Ala-D-isoGln. N-acetylmuramyldipeptide and 6-O-stearoyl-N-acetylmuramyldipeptide showed no adjuvant activity in the generation of cell-mediated cytotoxic effector cells in the spleens of C57Bl/6J mice after in vivo immunization with the allogeneic antigen mastocytoma P815-X2 cells, but N-acetylmuramyldipeptide showed adjuvant activity after in vitro sensitization of C57Bl/6J mouse spleen cells to the alloantigen mitomycin C-treated DBA/2 mouse spleen cells. It was also shown that 6-O-stearoylation of N-acetylmuramylpeptide could not potentiate the adjuvant activity of N-acetylmuramyldipeptide. Mitogenic and antitumor activities were not observed in either N-acetylmuramyldipeptide or 6-O-stearoyl-N-acetylmuramyldipeptide in mouse systems.