Glycine conjugation, species

Imidacloprid will be used to illustrate the fate of neonicotinoid insecticides (Figure 8.32). Imidacloprid is reduced (1) and then becomes the triazine derivative (2). It can be hydroxv-lated at the imidazole ring to become themonohydroxylated derivatives (3 and 4). Reduction of parent imidacloprid to the nitroso derivative (5) occurs in some animal species. Imidacloprid is also cleaved to become the nitroiminoimidazololidine (6). Further metabolism involves olefin formation (7), glycine conjugation (8), and others. 

Although glycine conjugates are the most commonly found metabolites, the specific amino acid acceptor depends on both the animal species and the chemical structure of the xenobiotic. Little is known about this conjugation pathway in parasites. A. suum,... 

M. expansa, H. diminuta and F. hepatica failed to form hippurate, the glycine conjugate of benzoic acid (8), although small amounts of this product were detected in M. benedeni (60). Given that several other amino acids besides glycine can often serve as acyl acceptors particularly in invertebrate species (3), additional studies are needed before concluding that amino acid conjugation is not a pathway of parasite xenobiotic metabolism. 

The main bile acids present in man, rat, rabbit, and pig are illustrated in Fig. 4. All occur as taurine or glycine conjugates. Hydroxyl functions are found at one or more of the following positions 3a. 6a. 7a, and I2a. The 6a-hydroxylated structures appear thus far to be exclusive for the pig whose bile acids consist in major of chenodeoxycholic and hyocholic acids. 6j3-Hydroxylated acids are only formed to a minor extent. The 7/5-hydroxylated derivative isolated after the administration of chenodeoxycholic acid to the rat (Hsia et al., 1958) has been shown through experiments with a C-7j8 tritiated structure to arise through the inversion of the 7a-hydroxy isomer via the keto structure (Bergstrom et al., 1960b). 16a-Hydroxylated acids have been isolated from boas and pythons but not from a variety of other species of snakes examined (Hazlewood, 1959). The most recent references to pertinent studies are listed in Table I. 

Wang et al. (1996) found that a 1 ppm solution of 1,4-dichlorobenzene was taken up by carrots Daucus car Ota, 49%), soybeans Glycine max, 50%), and red goosefoot Chenopodium rubrum, 62%), but not by tomatoes (Lycopersicon esculentum). Only the soybean cell cultures provided evidence of the existence of metabolites of this compound, probably conjugates of chlorophenol. The authors further observed that the uptake, metabolism, and toxicity of 1,4-dichlorobenzene differed among the species tested. 

Benzoic acid is metabolized in the liver by conjugation with glycine, and is rapidly excreted in the urine as hippuric acid in most of animal species. It can also be excreted as benzoilglucoronic acid when ingested in a large dose. Benzoic acid can be found in urine as a metabolite of benzaldehyde and numerous other compounds [4, 48]. 

---