Species- and gender-related differences in amine, alcohol and phenol sulphoconjugations

Patient variation in veterinary medicine--part II--influence of physiological variables

In veterinary medicine, the characterization of a drug's pharmacokinetic properties is generally based upon data that are derived from studies that employ small groups of young healthy animals, often of a single breed. In Part I of the series, we focused on the potential influence of disease processes, stress, pregnancy and lactation on drug pharmacokinetics. In this Part II of the series, we consider other covariates, such as gender, heritable traits, age, body composition, and circadian rhythms. The impact of these factors with respect to predicting the relationship between dose and drug exposure characteristics within an animal population is illustrated through the use of Monte Carlo simulations. Ultimately, an appreciation of these potential influences will improve the prediction of situations when dose adjustments may be appropriate.

NMR-based metabonomic approaches for evaluating physiological influences on biofluid composition

Strategies such as genomics, proteomics and metabonomics are being applied with increasing frequency in the pharmaceutical industry. For each of these approaches, toxicological response can be measured by terms of deviation from control or baseline status. However, in order to accurately define drug-induced response, it is necessary to characterize the normal degree of physiological variation in the absence of stimuli. Here, 1H NMR spectroscopic-based analyses of the metabolic composition of urine in experimental animals under various normal physiological conditions are reviewed. In particular, the effects of inter-animal and diurnal variation, gender, age, diet, species, strain, hormonal status and stress on the biochemical composition of urine are explored. Pattern recognition methods facilitate the comparison of urine NMR spectra over a given time-course, enabling the establishment of changes in profile and highlighting the dynamic metabolic status of an organism. Thus metabonomic approaches based on information-rich spectroscopic data sets can be used to evaluate normal physiological variation and for investigation of drug safety issues.

Sexual dimorphism in urinary metabolite profiles of Han Wistar rats revealed by nuclear-magnetic-resonance-based metabonomics

Gender-dependent metabolic variation in Han Wistar rats (n=25 male and n=25 female) was investigated using (1)H nuclear magnetic resonance (NMR) spectroscopy of urine coupled with chemometric methods. Statistically discriminatory regions of the spectra for male and female rats were identified and biomarker characterization was achieved by the further application of solid-phase extraction chromatography with NMR detection and high-performance liquid chromatography mass spectrometry. A novel discriminating molecule was identified as the sulfate conjugate of m-hydroxyphenylpropionic acid, which was excreted in higher concentrations by male rats. Other gender-related metabolite differences in the urine profiles included higher levels of trimethylamine-N-oxide, N,N'-dimethylglycine, m-hydroxyphenylpropionic acid, N-acetylglycoprotein, and cholate in samples from female animals. These studies emphasize the utility of multicomponent metabolic profiling for investigating physiological and genetic variation in experimental animals that may be of relevance to their use as models of toxicity and disease.

Interindividual Variability in 5-Fluorouracil Metabolism and Procainamide N-Acetylation in Human Liver Cytosol

We investigated the enzymatic kinetics and interindividual variability of the metabolism of 5-fluorouracil and procainamide by human liver cytosol and/or microsomes. The Km values for the 5-fluorouracil dihydropyrimidine dehydrogenase (DPD) and procainamide N-acetyltransferase activities in pooled liver cytosol, and procainamide hydrolysis in pooled liver microsomes were 3.9, 1670, and 969 microM, respectively, and the intrinsic clearance (Vmax/Km) values for these reactions were 128, 0.192, and 0.0059 microl/min/mg protein, respectively. The cytosolic activities of 5-fluorouracil metabolism and procainamide N-acetylation ranged from 145 to 790 (469+/-156, mean+/-S.D., n=22) and <1 to 152 (52+/-48, n=12) pmol/min/mg protein, respectively, and the DPD activity of 5-fluorouracil was neither gender-related nor age-dependent. Procainamide N-acetylation activities among 12 human cytosol samples were highly correlated with sulfamethazine N-acetylation activities, suggesting that procainamide N-acetylation is catalyzed by N-acetyltransferase-2. These results suggest that the N-acetylation reaction is more important than the hydrolysis in the metabolic pathway of procainamide, and that there are large interindividual differences in the enzyme activities towards the respective metabolic pathways of 5-fluorouracil and procainamide in human liver.

N-sulphoconjugation of amines by human cytosolic hydroxysteroid sulphotransferase

1. N- and O-sulphoconjugation of various substrates were studied with human liver cytosol and purified cytosolic sulphotransferase in the presence of 3-phosphoadenosine 5-phosphosulphate. 2. Human liver cytosol catalysed N-sulphoconjugation of alicyclic and aryl-amines, and O-sulphoconjugation of hydroxysteroid and phenol. Activities of amine sulphoconjugation in the cytosol correlated well with those of hydroxysteroid but not with phenol. 3. Alicyclic amine sulphotransferase in human liver cytosol was purified to homogeneity by anion exchange, affinity and hydroxyapatite chromatography. Sulphoconjugating activities of alicyclic amine co-purified with those for hydroxysteroid conjugation. Subunit molecular weight of the purified sulphotransferase was 34 kDa. Contents of the purified enzyme correlated with the sulphoconjugating activities of hydroxysteroid and alicyclic amine. From these results, we concluded that the alicyclic amine sulphotransferase purified in this study was identical to hydroxysteroid sulphotransferse in human liver cytosol. 4. The results of this study indicate that hydroxysteroid sulphotransferase in human liver cytosol catalyses N-sulphoconjugation of alicyclic and aryl-amines. Hydroxysteroid sulphotransferase in the cytosol is reported to catalyse O-sulphoconjugations of various compounds including hydroxysteroids, bile acids, cholesterol, and aliphatic and benzylic alcohols. The present and previously reported results indicate that hydroxysteroid sulphotransferase in the cytosol catalyses both N- and O-sulphoconjugations of several substrates.

Purification and characterization of two amine N-sulfotransferases, AST-RB1 (ST3A1) and AST-RB2 (ST2A8), from liver cytosols of male rabbits

Two sulfotransferases (STs), designated as AST-RB1 (ST3A1) and AST-RB2 (ST2A8), with high a amine N-sulfonating activity, were purified from male rabbit liver cytosols. AST-RB1 and AST-RB2 were purified to homogeneity by the anion-exchange, affinity, and hydroxyapatite chromatography. The N-terminus of both enzymes were blocked. The subunit molecular mass of both enzymes was estimated to be 34 kDa on SDS-PAGE. AST-RB1 efficiently catalyzed N-sulfonation of alicyclic, alkyl, and arylamines such as 4-phenyl-1,2,3, 6-tetrahydropyridine, 1-[(5-chloro-2-oxo-3(2H)-benzothiazolyl)acetyl]-piperazine, desipramine, and aniline, whereas its catalytic activities toward 2-naphthol and dehydroepiandrosterone (DHEA) were very low. On the other hand, AST-RB2 efficiently catalyzed sulfonation of desipramine and DHEA, but had no activity toward 2-naphthol. Amino acid sequences of peptide fragments derived from the purified AST-RB1 showed no significant homology with previously reported STs, but those from the purified AST-RB2 shared a high similarity with those of the ST2 family. Both enzymes were expressed specifically in the liver. The present results strongly suggest that the purified AST-RB1 is a novel enzyme in terms of structure and catalytic properties showing high selectivity for amine substrates, and AST-RB2 is a quite unique from among ST2A enzymes of other species in its substrate specificity.