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Biotransformation of muroctasin in mice
1Research Institute, Daiichi Seiyaku Co., Ltd., Tokyo, Japan.
Abstract:
The main metabolite of N2-[(N-acetylmuramoyl)-L-alanyl-D-isoglutaminyl]-N6-stearoyl-L-lysine MDP-Lys(L18), muroctasin), excreted to the urine and accounting for 15% of the dose, was identified to be R-D-lactic acid by the reverse isotope dilution method in which the metabolite was derivatized to p-bromophenacyl ester, recrystallized and separated into enantiomers by HPLC. The configuration of the lactate moiety in MDP-Lys(L18) was retained during the metabolism. Five metabolites were detected in the liver 5 hours after the administration and 4 of them were identified by TLC as des(GlcNAc)-MDP-Lys(L18), lactic acid, MDP-Lys(L18) and N-acetylmuramic acid in comparison with respective authentic compounds. N-Acetylmuramic acid was confirmed further by the reverse isotope dilution method in which it was converted to peracetylated methyl ester and separated by gas chromatography. It was the main metabolite and accounted for 40% of the radioactivity detected in the liver. MDP-Lys which was supposed to be the pharmacologically active metabolite was not detected. The metabolic pathway in which MDP-Lys(L18) was mainly metabolized to N-acetylmuramic acid, lactic acid and carbon dioxide, successively, was proposed. Some portion of the drug was converted to lactic acid via des(GlcNAc)-MDP-Lys(L18). A novel cleavage reaction of the ether linkage between the 3 position of sugar and lactic acid moiety in N-acetylmuramic acid was observed.
Insights
The main metabolite excreted in urine from muroctasin (MDP-Lys(L18)) is R-D-lactic acid, retaining its configuration. In the liver, N-acetylmuramic acid was the primary metabolite, suggesting a metabolic pathway involving successive breakdown products.
Area of Science:
- Pharmacology and Metabolism
- Biochemistry
Background:
- Muroctasin (MDP-Lys(L18)) is an immunomodulatory compound.
- Understanding its metabolic fate is crucial for its therapeutic application.
Purpose of the Study:
- To identify and characterize the metabolites of muroctasin (MDP-Lys(L18)) in vivo.
- To elucidate the metabolic pathway and identify potential active metabolites.
Main Methods:
- Reverse isotope dilution method using p-bromophenacyl ester derivatization and HPLC for R-D-lactic acid identification.
- Thin-layer chromatography (TLC) for metabolite separation and identification in liver tissue.
- Gas chromatography of peracetylated methyl ester for N-acetylmuramic acid confirmation.
Main Results:
- R-D-lactic acid was identified as the main urinary metabolite (15% of dose), with retained lactate configuration.
- N-acetylmuramic acid (40% of liver radioactivity) and lactic acid were major liver metabolites.
- Des(GlcNAc)-MDP-Lys(L18) was also detected; the expected active metabolite MDP-Lys was not found.
Conclusions:
- Muroctasin undergoes metabolism primarily to N-acetylmuramic acid and lactic acid, with a proposed pathway involving successive degradation.
- A novel ether linkage cleavage in N-acetylmuramic acid during metabolism was observed.
- The pharmacologically active metabolite MDP-Lys was not detected, suggesting it may not be formed or is rapidly metabolized.