Studies on the metabolism of arylacetic acids. 5. The metabolic fate of 2-naphthylacetic acid in the rat, rabbit and ferret

Examples of Alternative Use in Toxicology for Common Species

The principle of refinement of animal usage in toxicology dictates that the appropriateness of a particular animal species for a particular protocol or experiment be thoroughly explored. Species are selected all too often on the basis of convenience or tradition. Rats are traditionally used for acute lethality testing and carcinogenicity testing. Dogs are traditionally used as a “nonrodent” species for general toxicity assessments. This review seeks to make the case that, for both scientific and economic reasons, other species can be appropriately substituted for rats or dogs for general toxicity assessment studies. These alternative species need not be totally exotic, but can, in fact, be species used in other areas of toxicology. Earthworms and fish are nonvertebrate animals used in environmental assessment studies. Earthworms could be used for lethality assessment in place of rodents, particularly for “QC batch” release or toxicity rating purposes. Fish could be used to further define hepatic carcinogenicity. Guinea pigs are frequently used for dermatologic studies, but rarely for other purposes. While a rodent, the guinea pig possesses many physiologic and metabolic characteristics that may make it more appropriate than rats for the chronic testing of certain classes of chemicals (NSAIDs, peroxisomal proliferators). Ferrets have been well studied in teratologic assessments, but have not gained wide acceptance as a “nonrodent” model. This review discusses in detail the available technology and published data that justifies the expanded and appropriate use of these “alternative” species. Special emphasis is given to xenobiotic metabolism, which is a major determinant in speciesrelated differences in toxicity.

Participation of a medium chain acyl-CoA synthetase in glycine conjugation of the benzoic acid derivatives with the electron-donating groups

Glycine conjugation of a series of benzoic acid derivatives was investigated in bovine liver mitochondria. Benzoic acids with chlorine, methyl, methoxy or ethoxy substituents in the para-or meta-positions of the benzene ring showed a high degree of glycine conjugation. In contrast, the acids with cyano, nitro, amino, or acetylamino groups were conjugated to a small extent with glycine. A medium chain acyl-CoA synthetase that activates carboxylic acids was purified from bovine liver mitochondria. The purified medium chain acyl-CoA synthetase accepted not only medium chain fatty acids but also aromatic and arylacetic acids as substrates. There was a good correlation between the activity of the purified medium chain acyl-CoA synthetase and glycine conjugation of ten benzoic acids with electron-donating substituents. These findings indicate that the purified medium chain acyl-CoA synthetase is a major enzyme for glycine conjugation of benzoic acids with electron-donating groups in bovine live mitochondria.

Studies on the metabolism of arylacetic acids. 6. Comparative metabolic conjugation of 1- and 2-naphthylacetic acids in the guinea pig, mouse, hamster and gerbil

The patterns of metabolic conjugation of the isomeric 1- and 2-naphthylacetic acids have been compared in guinea pig, mouse, hamster and gerbil. Equimolar doses of [carboxy-14C]1- and 2-naphthylacetic acids were given to these species by i.p. injection, their urine collected and urinary metabolites examined by t.l.c. before and after treatment with beta-glucuronidase or mild alkali. 2. Urinary excretion of 14C following administration of 14C-1-naphthylacetic acid was 76-93% of dose in 72 h, the bulk being eliminated in 24 h. Urinary metabolites comprised 1-naphthylacetic-glycine and -glucuronide together with the unchanged acid. 3. Following administration of 14C-2-naphthylacetic acid, some 68-94% of the 14C dose was recovered in the urine in 72 h, with the majority in the 0-24 h urine. All four species excreted 2-naphthylacetyl-glucuronide and -glycine: additionally, 2-naphthylacetyl-taurine was excreted by mouse, gerbil and hamster and the glutamine conjugate was also present in hamster urine.

Studies on the metabolism of arylacetic acids. 7. The influence of varying dose size upon the conjugation pattern of 2-naphthylacetic acid in the guinea pig, mouse and hamster

1. The influence of dose size upon the metabolic conjugation of 2-naphthylacetic acid with various amino acids and glucuronic acid has been studied in the guinea pig, mouse and hamster. 2. Guinea pigs conjugated 2-naphthylacetic acid with glycine and glucuronic acid. 3. Mice conjugated 2-naphthylacetic acid with glycine, taurine and glucuronic acid. Taurine conjugation had the highest capacity, and both this and the glycine mechanism were saturated at doses above 100 mg/kg. 4. Hamsters utilized glutamine, glycine, taurine and glucuronic acid for the conjugation of 2-naphthylacetic acid. No conjugation pathway was saturated by doses up to 200 mg/kg. 5. The thus-far unique ability of 2-naphthylacetic acid to evoke multiple amino acid conjugations, using the taurine and glutamine mechanisms hitherto unknown in these species, appears to be due to its affinity for previously unrecognized enzyme systems, rather than to saturation of 'normal' pathways revealing novel routes at high doses.

Effect of Plasmodium berghei infection on benzoic acid metabolism in mice

The metabolism of benzoic acid was studied in Plasmodium berghei infected mice both in vitro and in vivo. Results of in vitro studies showed a considerable decrease in the ability of the infected liver to detoxify benzoic acid by hippuric acid formation. The in vivo study showed that hippuric acid formation decreases with increasing parasitemia and the emergence of benzoyl-glucuronide. This new pathway stops operating with further increase in parasitemia.

The utilization of exogenous taurine for the conjugation of xenobiotic acids in the ferret

Although the occurrence of the taurine conjugation mechanism for various xenobiotic acids is well established, nothing is known of the source of the taurine used for this conjugation. [14C]Taurine was administered alone and in combination with 2-naphthylacetic acid or clofibric acid (both of which are known to form taurine conjugates) to to ferrets, and the 0--24 h urine collected. Of the dose of [14C]taurine, 26% was recovered in the urine in 24 h and the only 14C-containing material present was unchanged taurine. When either 2-naphthylacetic acid or clofibric acid was co-administered with [14C]taurine, 21 and 17%, respectively, of the 14C dose was recovered in the 0--24 h urine. In both cases, two 14C compounds were present--unchanged taurine (minor) and the taurine conjugate of the acid in question (major). Comparison of these results with those previously obtained with 14C-labelled 2-naphthylacetic and clofibric acids, shows that the taurine used for their conjugation is derived from a pool freely accessible to exogenous taurine. The results are discussed in terms of the availability for metabolic utilization of taurine in the animal body, and of the use of co-administration of [14C]taurine with a xenobiotic acid for the identification of taurine conjugates.

The formation of beta-glucuronidase resistant glucuronides by the intramolecular rearrangement of glucuronic acid conjugates at mild alkaline pH

It is well known to carbohydrate chemists that substituted sugars may undergo facile rearrangement involving the migration of the aglycone from --OH to adjacent --OH. Despite the importance of glycoside conjugates, notably involving glucuronic acid, in the metabolism of xenobiotics, drug metabolism workers have neglected this phenomenon. The potential rearrangement of glucuronides from the biosynthetic C-1 isomers to other positional and stereo-isomers is important, since only 1-O-substituted beta-D-glucosiduronates are substrates for beta-glucuronidase, which is commonly used to identify such conjugates. The intramolecular rearrangement of clofibryl glucuronide has been studied over the pH range 5.2-8.6, by enzymic hydrolysis with beta-glucuronidase, and by HPLC. The amount of clofibric acid released from the conjugate by beta-glucuronidase falls with increasing pH of preincubation above pH 7.4, and this is accompanied by the appearance of three new peaks, each containing both clofibric and glucuronic acids, in the HPLC traces of the incubation mixtures. Similar experiments with three other glucuronides, those of p-nitrophenol, phenolphthalein and 7-hydroxycoumarin, did not show any conversion to beta-glucuronidase resistant forms. The phenomenon of intramolecular rearrangement of ester glucuronides must be considered whenever beta-glucuronidase is used in the analysis of conjugates of carboxylic acids.

The enhanced biliary secretion of a taurine conjugate in the rat after intraduodenal administration of high doses of fenclozic acid

1. The metabolic fate of [14C]fenclozic acid (ICI 54450) in rat was determined after intraduodenal administration at different doses. 2. Increasing the dose from 2 to 100 mg/kg resulted in a five-fold increase in drug-related material secreted in bile. 3. At a dose of 2 mg/kg the taurine conjugate was a relatively minor metabolite, whereas at 100 mg/kg this conjugate was the major metabolite in bile and urine. 4. Enhanced biliary secretion of the taurine conjugate in rats receiving multiple doses of fenclozic acid results in exposure of the intestinal cells to much greater concn. of drug-related metabolites.

Metabolic conjugation of some carboxylic acids in the horse

1. 14C-Labelled benzoic acid, salicylic acid and 2-naphthylacetic acid were administered orally to horses, and urinary metabolites investigated by chromatographic and mass spectral techniques. 2. [14C]Benzoic acid (5 mg/kg) was eliminated rapidly in the urine, and quantitatively recovered in 24 h. The major urinary metabolite was hippuric acid (95% of dose) with much smaller amounts of benzoic acid, benzoyl glucuronide and 3-hydroxy-3-phenylpropionic acid. Administration of [ring-D5]benzoic acid together with [14C]benzoic acid to a pony permitted the mass spectral determination of metabolites of the exogenous benzoic acid metabolites in the presence of the same endogenous compounds. 3. [14C]Salicylic acid (35 mg/kg) was eliminated rapidly in the urine, 98% of the 14C dose being excreted in 24 h. The major excretion product was unchanged salicylate (94% of dose). Gentisic acid, salicyluric acid and the ester and ether glucuronides of salicylic acid were very minor metabolites. 4. 2-Naphthyl[14C]acetic acid (2 mg/kg) was excreted very slowly in the urine, with 53 and 77% of the 14C dose being recovered in six days. 2-Naphthylacetylglycine was the major metabolite (26 and 38% dose) and in addition, the glucuronic acid and taurine conjugates were excreted together with unchanged 2-naphthylacetic acid. 5. The study has shown that the horse can utilize glycine, taurine and glucuronic acid for conjugation of xenobiotic carboxylic acids, and that the relative extents of these pathways are governed by the structure of the carboxylic acid.