Glucuronidation hydrolysis

Six phase I metabolites were identified by analysing the spectral data alongside an expert chemist s review of the public literature. Meteor (version 7) predicted five of the six metabolites, along with products arising from sulfonation, glucuronidation, hydrolysis and other pathways. Meteor did not predict M3 (Figure 11.11), which is thought to arise from the sequential application of two phase I biotransformations on the parent V-dealkylation and benzylic hydroxylation. Biotransformation likelihood can be attenuated by consideration of whether the process is the first step in a sequence or a subsequent step. On this occasion, the likelihood of the second phase I process... 

Kamata T, Nishikawa M, Katagi M, Tsuchihashi H (2003) Optimized glucuronide hydrolysis for the detection of psiiocin in human urine samples. J Oiromatogr B796(2) 421 27. doi 10.1016/j.jchromb.2003.08.030... 

Biotransformation reactions can be classified as phase 1 and phase 11. In phase 1 reactions, dmgs are converted to product by processes of functionalization, including oxidation, reduction, dealkylation, and hydrolysis. Phase 11 or synthetic reactions involve coupling the dmg or its polar metaboHte to endogenous substrates and include methylation, acetylation, and glucuronidation (Table 1). 

Only the small amounts of T and T that are free in the circulation can be metabolized. The main route is deiodination of T to T and i-T, and from these to other inactive thyronines (21). Most of the Hberated iodide is reabsorbed in the kidney. Another route is the formation of glucuronide and sulfate conjugates at the 4 -OH in the Hver. These are then secreted in the bile and excreted in the feces as free phenols after hydrolysis in the lower gut. 

Several extraction techniques have also been described that use enzymatic or chemical reactions to improve extraction efficiency. A technique that has been used to increase the overall recovery of the marker residue is enzymatic hydrolysis to convert specific phase II metabolites (glucuronides or sulfates) back into the parent residue. Cooper etal used a glucuronidase to increase 10-fold the concentration of chloramphenicol residues in incurred tissue. As an example of a chemical reaction, Moghaddam et al. used Raney nickel to reduce thioether bonds between benomyl and polar cellular components, and as a result achieved a substantially improved recovery over conventional solvent extraction. In choosing to use either of these approaches, thorough characterization of the metabolism in the tissue sample must be available. 

A typical CYP reaction length is 1-2 h, but CYP activity can survive longer at 37 °C. Figure 9.3 shows that product turnover of the CYP reactions occurred over a 6 h incubation (Li, unpublished results). UGT activity can last longer than 24 h [23], With accumulation of product, secondary reactions, such as further oxidation of product or hydrolysis of glucuronide, may become noticeable. Therefore, monitoring the reaction with HPLC-U V-MS is critical for identifying the best time to terminate the reaction. 

Zenser, T.V., Lakshmi, V.M. and Davis, B.B. (1999) Human and Escherichia coli /3-glucuronidase hydrolysis of glucuronide conjugates of benzidine and 4-aminobiphenyl, and their hydroxy metabolites. Drug Metabolism and Disposition The Biological Fate of Chemicals, 27, 1064—1067. 

Metabolism Glucuronidation N-demethylation Ester hydrolysis to morphine Glucuronidation demethylation (CYP2D6) Ester hydrolysis N-demethylation N-Dealkylation, then hydroxylation N-Demethylation Plasma and tissue esterases... 

Although the metabolism of several phthalate esters has been studied in vitro, essentially all of the in vivo studies have involved DEHP. A summary of these experiments which involved exposure offish to aqueous - C-DEHP is presented in Table IV (11,12). Tissue C was isolated and separated into parent and the various metabolites by preparative thin layer chromatography on silica gel. Metabolites were hydrolyzed where appropriate and identified by gas chromatography-mass spectroscopy. In whole catfish, whole fathead minnow and trout muscle, the major metabolite was the monoester while in trout bile the major metabolite was the monoester glucuronide. The fact that in all cases the major metabolite was monoester or monoester glucuronide despite the differences in species, exposure level and duration, etc. represented by these data, suggests that hydrolysis of DEHP to monoester is important in the biotransformation of DEHP by fish. 

For this reason, a further experiment was performed on the hydrolysis of PCP-glucuronide contained in bile on incubation with intestinal mucus of goldfish. 

Phenol red glucuronide was determined after either HC1 or 3-glucuronidase hydrolysis. The presence of the glucuronide was confirmed by thin layer chromatography in three systems (J3). 

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