1. The metabolism and excretion of celecoxib, a specific cyclooxygenase 2 (COX-2) inhibitor, was investigated in mouse, rabbit, the EM (extensive) and PM (poor metabolizer) dog, and rhesus and cynomolgus monkey. 2. Some sex and species differences were evident in the disposition of celecoxib. After intravenous (i.v.) administration of [14C]celecoxib, the major route of excretion of radioactivity in all species studied was via the faeces: EM dog (80.0%), PM dog (83.4%), cynomolgus monkey (63.5%), rhesus monkey (83.1%). After oral administration, faeces were the primary route of excretion in rabbit (72.2%) and the male mouse (71.1%), with the remainder of the dose excreted in the urine. After oral administration of [14C]celecoxib to the female mouse, radioactivity was eliminated equally in urine (45.7%) and faeces (46.7%). 3. Biotransformation of celecoxib occurs primarily by oxidation of the aromatic methyl group to form a hydroxymethyl metabolite, which is further oxidized to the carboxylic acid analogue. 4. An additional phase I metabolite (phenyl ring hydroxylation) and a glucuronide conjugate of the carboxylic acid metabolite was produced by rabbit. 5. The major excretion product in urine and faeces of mouse, rabbit, dog and monkey was the carboxylic acid metabolite of celecoxib.

No abstract

The study reported herein examined the metabolism of 14C-labeled hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) resulting from a single oral gavage of 5 ml/kg to male and female Yucatan miniature pigs (43 mg/kg, 56 microCi/kg in 0.5% carboxymethylcellulose in water). Blood, urine, and feces were collected at selected times of 1, 6, 12, and 24 h postdose. At 24 h postdose, liver samples were collected. Blood, plasma, liver, and excreta were analyzed for total RDX-derived radioactivity and metabolites were identified. Urine was the major route of elimination of 14C-RDX-derived radioactivity in both males and females. Relatively low levels of radioactivity were found in gastrointestinal contents and in feces, suggesting nearly complete absorption of 14C-RDX following an oral dose. Analysis of urine by liquid chromatography-mass spectrometry (LC/MS) identified quantifiable levels of two ring-cleavage metabolites, 4-nitro-2,4-diazabutanal and 4-nitro-2,4-diaza-butanamide, as well as parent RDX. The 4-nitro-2,4-diazabutanal, was seen in earlier studies of aerobic metabolism of RDX. The 4-nitro-2,4-diaza-butanamide, an amide, was not previously reported but was tentatively identified in this study. Analysis by a more sensitive method (LC/MS/MS) also showed trace amounts of the RDX metabolites 1-nitroso-3,5-dinitro-1,3,5-triazacyclohexane (MNX) (in both male and female urine) and 1-nitro-3,5-dinitroso-1,3,5-triazacyclohexane (DNX) (in male urine). Analysis of plasma by LC/MS/MS also revealed quantifiable levels of RDX and trace levels of MNX, DNX, and 1,3,5-trinitroso-1,3,5-triazacyclohexane (TNX). None of the liver extracts showed quantifiable levels of RDX or any identifiable metabolites. Most of the radioactivity was in the form of water-soluble high-molecular-weight compounds. RDX when given orally to pigs was rapidly metabolized by loss of two nitro groups followed by ring cleavage.

No abstract

L-Canavanine, 2-amino-4-(guanidinooxy)butyric acid, and L-arginine incorporation into de novo synthesized proteins was compared in six organisms. Utilizing L-[guanidinooxy14C]canavanine and L-[guanidino14C]arginine at substrate saturation, the canavanine to arginine incorporation ratio was determined in de novo synthesized proteins. Caryedes brasiliensis and Sternechus tuberculatus, canavanine utilizing insects; Canavalia ensiformis, a canavanine storing plant; and to a lesser extent Heliothis virescens, a canavanine resistant insect, failed to accumulate significant canavanyl proteins. By contrast, Manduca sexta, a canavanine-sensitive insect, and Glycine max, a canavanine free plant, readily incorporated canavanine into newly synthesized proteins. This study supports the contention that the incorporation of canavanine into proteins in place of arginine contributes significantly to canavanine's antimetabolic properties.

After 1.5 h, 35% of the administered radiolabeled canaline was converted to acetone-soluble products; this amount decreased with time to 5.3% at 12 h. This fraction was primarily responsible for respiratory loss of 14C as 14C02, which reached 52% of the administered canaline after 12 h. The water-soluble, neutral fraction accounted for no more than 10% of the injected canaline. The water-soluble, charged materials contained 35-40% of the 14C at each time period; five compounds were identified within this fraction. They are homoserine, phosphohomoserine, lysine, canavanine, and canaline glyoxylate oxime. Canavanine-administered plants provided a degradation pattern remarkably similar to that of canaline-administered plants, indicating the importance of arginase-mediated hydrolysis of canavanine to canaline in the process of canavanine catabolism.L-Canavanine, the 2-amino-4-(guanidinooxy)butyric acid

An arginase, purified from the leaf of the jack bean, Canavalia ensiformis, can effectively hydrolyze both l- and d-arginine. Arginases, examined from a number of other plant and animal sources, exhibit marked substrate stereospecificity and fail to catabolize d-arginine. In order to provide essential nitrogen, jack bean leaf arginase also catabolizes l-canavanine, an arginine analog that is a predominant nitrogen-storing metabolite of this legume. The ability of arginase to metabolize both stereoisomers of arginine may result from the requirement for this enzyme to exhibit limited substrate specificity in order to hydrolyze both arginine and canavanine.

No abstract