LMNA rs4641 and the muscle lamin A and C isoforms in twins--metabolic implications and transcriptional regulation

CONTEXT

Lamins are essential for nuclear shape and function. Polymorphisms in LMNA may associate with fat and muscle development and aging.

OBJECTIVE

Our aim was to determine the influence of LMNA rs4641 on lean body mass (LBM) and fat mass (FM), in vivo metabolism, and expression of LMNA transcripts in human skeletal muscle.

DESIGN

We genotyped LMNA rs4641 in 196 Danish twins who were extensively phenotypically characterized. We measured mRNA levels of LMNA transcripts, lamin A and C, in basal and insulin-stimulated skeletal muscle biopsies.

RESULTS

The rs4641 T-allele was associated with increased weight and body mass index (P=0.02), including increased FM (P=0.03) and LBM (P=0.004). Impact of rs4641 on FM was seen primarily among elderly twins. The T-allele was associated with elevated fasting plasma insulin levels (P=0.01) and homeostasis model of insulin resistance (P=0.02) in young twins. T-allele carriers did not exhibit consistent changes of first phase insulin secretion, nor did they exhibit significant peripheral or hepatic insulin resistance, and rs4641 did not influence muscle lamin A or C mRNA levels. The lamin A-to-C mRNA ratio was increased with acute insulin stimulation (P<0.0005), and the lamin A and C mRNA levels were diminished in young compared to elderly twins (P<0.001).

CONCLUSIONS

The LMNA rs4641 T-allele is associated with increased LBM and FM with more fat relative to muscle in elderly twins, which may impact risk of type 2 diabetes. Increased mRNA levels of lamins with age may counteract muscle wasting, and influence of insulin on lamin A-to-C ratio suggests a role in cytoskeletal muscle protein regulation.

Development of an in vitro assay for the investigation of metabolism-induced drug hepatotoxicity

In a number of adverse drug reactions leading to hepatotoxicity drug metabolism is thought to be involved by generation of reactive metabolites from nontoxic drugs. In this study, an in vitro assay was developed for measurement of the impact of metabolic activation of compound on the cytotoxicity toward a human hepatic cell line. HepG2 cells were treated for 6 h with compound in the presence or absence of rat liver S9-mix, and the viability was measured using the MTT test. The cytotoxicity of cyclophosphamide was substantially increased by S9-mix in the presence of NADPH. Three NADPH sources were tested: NADPH (1 mmol/L) or NADPH regenerating system with either NADP(+)/glucose 6-phosphate (G6P) or NADP(+)/isocitrate. All three NADPH sources increased the cytotoxicity of cyclophosphamide to a similar extent. Eight test compounds known to cause hepatotoxicity were tested. For these, only the cytotoxicity of diclofenac was increased by S9 enzymes when an NADPH regenerating system was used. The increased toxicity was NADPH dependent. Reactive drug metabolites of diclofenac, formed by NADPH-dependent metabolism, were identified by LC-MS. Furthermore, an increase in toxicity, not related to enzymatic activity but to G6P, was observed for diclofenac and minocycline. Tacrine and amodiaquine displayed decreased toxicity with S9-mix, and carbamazepine, phenytoin, bromfenac and troglitazone were nontoxic at all tested concentrations, with or without S9-mix. The results show that this method, with measurement of the cytotoxicity of a compound in the presence of an extracellular metabolizing system, may be useful in the study of cytotoxicity of drug metabolites.

The association between the val/ala-55 polymorphism of the uncoupling protein 2 gene and exercise efficiency

BACKGROUND

Energy expenditure may partly be determined by genetic variations in uncoupling proteins. We have previously found an increased physical activity but a similar 24-h energy expenditure (EE) in subjects with the val/val-55 UCP2 genotype compared to those with the ala/ala genotype which indicates that the val-55 allele is statistically associated with a higher metabolic efficiency.

DESIGN

EE during bicycling was determined by indirect calorimetry at three different loads (30, 40 and 60% of VO2max in eight subjects with the val/val-55 genotype (35+/-6 y weight=76.8+/-13.6 kg, VO2max=2.79+/-0.71 l/min) and eight subjects with the ala/ala-55 genotype (37+/-3 y, weight=78.3+/-16.5 kg, VO2max=2.66+/-0.41 l/min).

RESULTS

Incremental exercise efficiency across the three different work levels was higher in the val/val (25.3%, c.i. 24.2-26.4%) than in the ala/ala (23.6%, c.i. 22.5-24.7%) genotype P<0.05. Gross exercise efficiency at 40% VO2max was higher in the val/val (15.3+/-0.6%) than in the ala/ala (13.5+/-0.4%) group.

CONCLUSION

As the val/ala-55 polymorphism is located in a domain of the protein without any known function, the different exercise efficiency between the two genotypes most likely reflects a linkage disequilibrium with a functionally significant polymorphism in UCP2 or in the neighbouring UCP3 gene. The study suggests that variations in the UCP genes may affect not only basal metabolic rate but also influence energy costs of exercise.

Evaluation of blood-brain barrier passage of a muscarine M1 agonist and a series of analogous tetrahydropyridines measured by in vivo microdialysis

PURPOSE

To investigate the blood-brain barrier (BBB) passage of the M1 muscarine agonist Lu 25-109 (5-(2-Ethyl-2H-tetrazol-5-yl)-1,2,3,6-tetrahydro-methylpyridine) and potential metabolites using in vivo microdialysis.

METHODS

Anesthetized rats were administered an intravenous infusion of one of seven analogs with a Log D7.4 ranging from 0.35 to -2.4. Microdialysis probes were implanted in the brain and the jugular vein. The integrity of the BBB was evaluated using 2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid (APPA), a compound not expected to penetrate the BBB. The data was corrected for in vitro recovery.

RESULTS

Lu 25-109, Lu 24-165 (demethylated Lu 25-109) and Lu 25-077 (N-demethylated Lu 25-109) entered the brain in a 1:1 ratio with the blood. Although Lu 29-081 (hydroxylated Lu 25-109) presented a similar Log D7.4 to Lu 25-109 and Lu 24-164, it entered the brain with a lower brain:blood ratio of 0.5. Lu 32-181 (Lu 25-109 N-oxide), Lu 35-026 (deethylated and oxidized Lu 25-109) and Lu 31-126 (deethylated Lu 25-109) were not detected in the brain samples, indicating no penetration. Infusion of Lu 25-109 resulted in a time perspective of the formation and distribution of the two metabolites Lu 25-077 and Lu 32-181. Although the hydroxylated compound (Lu 29-081) had a Log D74 of -0.6, within the range 0.35 to -0.83 of the compounds penetrating the BBB, it showed a brain: blood ratio of 0.5. Lu 35-026 showed an unusual infusion profile with a tmax of 100-150 min and a subsequent decrease in blood concentration.

CONCLUSIONS

Compounds with Log D7.4 above -0.83 penetrated the BBB, whereas compounds below -1.5 did not. Knowledge of Log D7.4 values is not sufficient to evaluate BBB passage because the value does not predict the influence of active transport processes.

Metabolites of [(14)C]-5-(2-ethyl-2H-tetrazol-5-yl)-1-methyl-1,2,3, 6-tetrahydropyridine in mice, rats, dogs, and humans

The M1 muscarine agonist, 5-(2-ethyl-2H-tetrazol-5-yl)-1-methyl-1,2, 3,6-tetrahydropyridine (Lu 25-109), is extensively metabolized in mice, rats, dogs, and humans. The metabolite profile after an oral dose of [(14)C]Lu 25-109 was determined in plasma and in urine. Lu 25-109 was metabolized by N-demethylation (Lu 25-077), N-oxidation (Lu 32-181), and N-deethylation (Lu 31-126). In addition, combined N-demethylation and N-deethylation (Lu 31-190), and formation of a pyridine derivative took place (Lu 31-102). Lu 25-109 was also oxidized to pyridinium (Lu 29-297), 3-hydroxy-pyridinium (Lu 35-080), N-deethyl-2-pyridone (Lu 35-026), and a glucuronide of a 4, 6-dihydroxy-pyridinium ("m/z 398") compounds. A glucuronide of a dihydroxylated dihydro-pyridine compound ("m/z 400") was isolated from human urine, but not fully identified. In vitro studies were undertaken to elucidate the order of formation of the metabolites. In human plasma, the concentrations of Lu 25-109 and the pharmacologically active N-demethyl metabolite (Lu 25-077) were small compared with the N-oxide (Lu 32-181) and the N-deethyl-2-pyridone (Lu 35-026) at the first sample time (0.75 h). The N-deethyl metabolite (Lu 31-126) was the major component in human plasma between 3 and 10 h postdose. The major human metabolites in urine (Lu 32-181, Lu 35-026, and Lu 31-126) and the minor metabolites (Lu 25-077, Lu 35-080, Lu 31-190, and Lu 29-297) were all present in urine from rats, dogs, and mice, whereas m/z 398 was present in only mice and humans, and Lu 31-102 in only rats. The minor human metabolite m/z 400 was not detected in mice, rats, or dogs.

Metabolism and excretion of citalopram in man: identification of O-acyl- and N-glucuronides

The antidepressant citalopram (CT), a selective serotonin uptake inhibitor, was given in its labelled form, [14C]-CT, as a single oral dose in 50 ml aqueous solution (0.1 mmol/30 microCi/1.1 MBq) to four healthy male volunteers. Concentrations of radioactivity in whole blood and plasma were similar. The respective pharmacokinetic parameters were: Cmax = 214+/-41 and 246+/-69 nmol eq./litre, Tmax = 3 and 2 h, AUC = 18289+/-2959 and 14537+/-2883 nmol eq. h/litre, and t1/2 = 90.2+/-22.5 and 79.5 +/- 14.9 h respectively. A mean of 85.2 +/- 10.4% of the radioactive dose was recovered after 17 days of collection of excreta. The majority of radioactivity was excreted in urine (74.7+/-8.9%) and the remaining part in faeces (10.5+/-2.3%). The HPLC profile of urinary components showed that besides the known metabolites of citalopram, three glucuronides were present. The relative amounts of CT and its metabolites in urine collected for 7 days were: CT (26 %), N-demethyl-CT (DCT, 19%), N,N-didemethyl-CT (DDCT,9%), the N-oxide (7%), the quaternary ammonium glucuronide of CT (CT-GLN, 14%), the N-glucuronide of DDCT (DDCT-GLN, 6%), and the glucuronide of the acid metabolite (CT-acid-GLN, 12%) formed by N,N-dimethyl deamination of CT. CT-GLN was isolated using preparative chromatography and identified by LC-MS-MS and NMR. DDCT-GLN and CT-acid-GLN were identified by LC-MS. This study shows that protracted renal excretion represents the major route of elimination, with a small fraction voided with faeces. A considerable portion of the urinary excreted dose consists of N-glucuronides of CT and DDCT together with the O-acyl glucuronide of CT-acid.

In vitro metabolism of the M1-muscarinic agonist 5-(2-ethyl-2H-tetrazol-5-yl)-1-methyl-1,2,3,6-tetrahydropyridine by human hepatic cytochromes P-450 determined at pH 7.4 and 8.5

Biotransformation of the M1-muscarinic agonist Lu 25-109 (5-(2-ethyl-2H-tetrazol-5-yl)-1-methyl-1,2,3,6-tetrahydropyridine) , in development for the treatment of Alzheimer's disease, was investigated to obtain information on the identity of human hepatic cytochrome P-450 enzymes involved in its metabolism. The identification of these P-450s was accomplished through studies using 1) simple regression analysis with 14 phenotyped human liver samples, 2) selective chemical inhibitors, and 3) microsomes containing cDNA-expressed enzymes. The production of some metabolites is enhanced in vitro when the pH of the incubation media is shifted from pH 7.4 to 8.5. The metabolite production in human liver microsomes was NADPH-dependent, suggesting that the metabolism of Lu 25-109 in human liver microsomes is primarily P-450-dependent. Lu 25-109 was metabolized by human liver microsomes to Lu 31-126 (de-ethyl Lu 25-109) mainly by CYP2D6; to Lu 29-297 [3-(2-ethyltetrazol-5-yl)-1-methyl-pyridinium] and Lu 25-077 (demethyl Lu 25-109) mainly by CYP1A2, CYP2A6, CYP2C19, and CYP3A4; and to Lu 32-181 (Lu 25-109 N-oxide) by CYP1A2 and possibly by CYP2C19. One metabolite, Lu 32-181 (N-oxide), could be reduced back to Lu 25-109, a reaction not inhibited by the applied cytochrome P-450 inhibitors. This study did not indicate any involvement of FMO3 or MAO in the in vitro metabolism of Lu 25-109 in human liver microsomes.

Neuroreceptor quantification in vivo by the steady state principle and [123I]iomazenil in rats

A steady state method for neuroreceptor quantification in vivo in small laboratory animals is described, using [123I]iomazenil as tracer for the benzodiazepine receptor. The method was used for determination of the receptor equilibrium constant for a non-radioactive ligand, flumazenil, in rats and involved measurement of the nonspecific binding of [123I]iomazenil. Thirty-five animals were intravenously infused for 2 h with [123I]iomazenil and flumazenil in different proportions to obtain occupancies of the benzodiazepine receptor from close to 0 to about 99%. The nonspecific binding of iomazenil in brain tissue was calculated by an iterative procedure from the data for the highly blocked animals, and it was found to be 1.04 ml per ml plasma (n = 6). The mean cortical Kd of flumazenil was 21 +/- 11 nM (n = 19). The method is discussed with special reference to the problems of ascertaining steady state and nonspecific binding.

Pharmacokinetics of the neuroprotective glutamate antagonist NBQX (6-nitro-7-sulfamoyl-benzo(f)quinoxaline-2,3-dione) in mice, rats, and dogs. Interactions with probenecid

NBQX [6-nitro-7-sulfamoyl-benzo(f)quinoxaline-2,3-dione] has proven effective in protecting against cerebral ischemic insult in rodents. The preclinical development included pharmacokinetic and toxicological investigations in mice, rats, and dogs. For these purposes, NBQX was given as an intravenous bolus dose (in mice, rats, and dogs) or as a constant infusion for up to 4 weeks in rats and dogs. In NMRI mice t1/2, CL, and V2 were 1-4 hr, 0.6-1 liter/kg/hr, and 1-4 liters/kg following 3, 10, or 30 mg/kg. In Wistar and Sprague-Dawley rats, the mean +/- SD values of t1/2, CL, and Vz were 0.8 +/- 0.35 hr, 3.2 +/- 1.0 liters/kg/hr, and 4.0 +/- 1.1 liters/kg, respectively. About 33 +/- 5.2% of the dose was excreted unchanged in urine. The CLR was 0.90 +/- 0.20 liter/kg/hr. The pH of the urine samples ranged from pH 6.2 to 8.8, with a mean of 7.9 +/- 0.72. The plasma concentrations were proportional to the dose rate in the dose range 0.3-10 mg/kg/hr, independent of sex, and did not change during 4 weeks of infusion. CL and CLR were decreased to half their value when NBQX was administered in combination with probenecid. In beagle dogs, t1/2 and Vz were 1-3 hr and 1-3 liters/kg, respectively. The CL was determined to be 1.5 +/- 0.4 liters/kg/hr (N = 18) following 2 days of infusion (0.2-1 mg/kg/hr), but after 1 month CL had decreased significantly (p < 0.0001) to 1.0 +/- 0.1 liter/kg/hr.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of paroxetine on cerebrospinal fluid concentrations of neurotransmitter metabolites in depressed patients

This paper describes the effect of the selective serotonin reuptake inhibiting drug (SSRI), paroxetine, on cerebrospinal fluid concentrations of neurotransmitter metabolites in depressed patients. 5-Hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured at baseline and after 3 weeks of treatment with 30 mg paroxetine daily. In line with similar studies on other SSRIs, influence on both the serotonin and noradrenaline metabolite was found. The mechanism behind the action of paroxetine on both 5-HIAA and MHPG is assumed to be an expression of the linkage between the serotonergic and noradrenergic systems in the brain. A frequently reported correlation between 5-HIAA and HVA was also found. The analysis of paroxetine in CSF proves the transportation of the drug into the central nervous system.

Benzodiazepine receptor equilibrium constants for flumazenil and midazolam determined in humans with the single photon emission computer tomography tracer [123I]iomazenil

This study is based on the steady state method for the calculation of Kd values recently described by Lassen (J. Cereb. Blood Flow Metab. 12 (1992), 709), in which a constant infusion of the examined nonradioactive ligand is used with a bolus injection of tracer. Eight volunteers were examined twice, once without receptor blockade and once with a constant degree of partial blockade of the benzodiazepine receptors by infusion of nonradioactive flumazenil (Lanexat) or midazolam (Dormicum). Single photon emission computer tomography and blood sampling were performed intermittently for 6 h after bolus injection of [123I]iomazenil. The tracer in plasma was determined by high-pressure liquid chromatography and also by a simple octanol extraction procedure. The free concentration of flumazenil and midazolam in plasma water averaged 52% and 3.5% of that in whole plasma. The Kd values for the entire cortical rim for flumazenil were 7.4, 10.0, 10.3 and 17.7 nmol/l plasma water and, for midazolam, 73, 76, 58 and 30 nmol/l plasma water. The variation exceeds random methodological error and is probably due to interindividual differences in receptor affinity. The Kd level of midazolam is considerably higher than expected from the results of in vitro studies.

Enzymic synthesis of two glucuronides of the hydroxyisoxazole GABA-agonist, THIP, and the in vivo glucuronidation of THIP in rat

1. A method for preparative enzymic synthesis of two glucuronides of THIP (3-hydroxy-4,5,6,7-tetrahydro-isoxazolo[5,4-c]pyridine) is described. 2. Using FAB mass spectrometry, u.v. and 1H- and 13C-n.m.r. spectroscopy, the two glucuronides were identified as N- and O-glucuronides respectively. 3. An h.p.l.c. method for determination of THIP and the two intact glucuronides in urine has been developed. 4. The glucuronidation pattern of THIP in rats has been examined; THIP was excreted as a THIP-O-glucuronide but not as a THIP-N-glucuronide.

Resolution and binding site determination of D,L-thyronine by high-performance liquid chromatography using immobilized albumin as chiral stationary phase. Determination of the optical purity of thyroxine in tablets

Human and bovine serum albumin bound to silica or aminopropyl silica were used as chiral stationary phases (CSPs). D,L-Thyronine, D,L-tryptophan, N-benzoyl-D,L-phenylalanine, D,L-warfarin and D,L-benzoin could be resolved on these CSPs using a mobile phase of 0.05 M phosphate buffer, pH 7.0. The capacity factor of D-thyronine was higher than that of L-thyronine. The resolution of D,L-thyronine was completely lost by the presence of bilirubin in the mobile phase, but only little affected by caprylate. By contrast, the resolution of D,L-tryptophan was not affected by bilirubin, but lost by the presence of caprylate. These results are consistent with binding of D-thyronine to the bilirubin binding site and L-tryptophan to the caprylate binding site in albumin, respectively, and suggests that such "displacement chromatography" can be used for the determination of binding sites. The optical purity of D-thyroxine in tablets was determined indirectly after de-iodination by catalytic hydrogenation.

Determination of trichloroethylene metabolites in rat liver homogenate using headspace gas chromatography

An headspace gas chromatographic (HSGC) method for determination of trichloroethylene metabolites in rat liver homogenates is described. These metabolites are chloral hydrate (CH), trichloroethanol (TCE), trichloroacetic acid (TCA) and the glucuronic acid conjugate of trichloroethanol (TCE-beta-glucuronide). The method is based on selective thermal conversion of CH and TCA into chloroform, which is determined together with trichloroethanol by HSGC using electron-capture detection. TCE-beta-glucuronide was determined as the difference between free TCE and total TCE after enzymatic hydrolysis with beta-glucuronidase. Synthesized TCE-beta-glucuronide was used to compare the efficiency of enzymatic and acid hydrolysis of the conjugate. Enzymatic hydrolysis was found to be advantageous for determination of TCE-beta-glucuronide.

Isolation and identification of the rearrangement products of diflunisal 1-O-acyl glucuronide

A preparative reversed-phase high-performance liquid chromatographic method is described for the simultaneous separation of eight different isomers formed from the 1-O-acyl glucuronide of diflunisal. All isomers were formed when the acyl glucuronide was incubated under mildly alkaline conditions in aqueous solution. Various forms of two-dimensional NMR studies were performed in order to identify each isomer. Seven of the isomers were identified as alpha- and beta-forms of esters in which diflunisal forms an ester with one of the four alcohol groups in the glucupyranuronic acid. One isomer was identified as the ether glucuronide of diflunisal. To establish the exact chemical shift of the different protons, simulation of the one-dimensional NMR spectra and iterative analyses were performed.

Reversed-phase high-performance liquid chromatographic assay for the simultaneous determination of diflunisal and its glucuronides in serum and urine. Rearrangement of the 1-O-acylglucuronide

A reversed-phase ion-pair high-performance liquid chromatographic assay for the simultaneous determination of diflunisal and its ester and ether glucuronide in urine and serum has been developed. The determination of the ester glucuronide in serum has not been previously reported. The genuine glucuronide conjugates isolated from urine were used as standards. The ester glucuronide is found to be unstable, especially in neutral and basic solutions, and special precautions therefore have to be taken during sampling and sample treatment. Nine rearrangement/degradation products of the ester glucuronide were detected.

Headspace gas chromatographic determination of beta-galactosidase activity using electron-capture detection

A headspace gas chromatographic method for the determination of beta-galactosidase (E.C. 3.2.1.23) activity is described. The method, in which 2,2,2-trichloroethyl beta-D-galactopyranoside (beta-TCG) is used as substrate, involves determination of the liberated 2,2,2-trichloroethanol by gas chromatography with electron capture detection. The preparation of beta-TCG and of 2,2,2-trichloroethyl alpha-D-galactopyranoside is described. A Km = 0.80 mM was found for the enzymatic hydrolysis of beta-TCG employing beta-galactosidase from Escherichia coli. The assay has been applied to the quantitative determination of E. coli bacteria.

Cyanogenic glycosides and cyanohydrins in plant tissues. Qualitative and quantitative determination by enzymatic post-column cleavage and electrochemical detection, after separation by high-performance liquid chromatography

A rapid, simple and reproducible high-performance liquid chromatography procedure is described for the qualitative and quantitative analysis of mixtures of cyanogenic glycosides. The separation is achieved by means of a reversed-phase (C8) column eluted with a phosphate buffer, pH 5.0, containing either 15 or 7.5% (v/v) methanol, 7.5% being necessary for resolution of epimeric pairs of the more hydrophilic glycosides. When this separation is combined with enzymatic post-column cleavage and electrochemical detection of the cyanide formed, a highly specific and very sensitive system is obtained. The method was applied to cyanogenic glycosides in crude plant tissue extracts, and compared with both a thin-layer chromatographic method and to a traditional determination of total cyanide released after hydrolysis. Sensitivity, selectivity and accuracy were found sufficient to enable its routine use for analysis of food and fodder samples, for example. Cyanohydrins could be detected qualitatively.

Electrochemical detection of cyanogenic glycosides after enzymatic post-column cleavage

Crude and partly purified extracts from Helix pomatia and linamarase from cassava were immobilized on columns packed with porous glass or silica and used as post-column reactors in the high-performance liquid chromatography of cyanogenic glycosides. Sodium hydroxide (2 M) was added to the flowstream after the enzyme-reactor resulting in the formation of cyanide, which was then detected at a silver electrode by an amperometric measurement at 0 V with reference to a silver-silver chloride electrode. The selective detection of cyanide allows measurements in a complex matrix. The response is linear and the detection limit is in the low picomole range.

Determination of trimethoprim metabolites including conjugates in urine using high-performance liquid chromatography with combined ultraviolet and electrochemical detection

A high-performance liquid chromatographic method for the determination of trimethoprim metabolites in pig urine was developed. The metabolites-glucuronic acid and sulphuric acid conjugates of phenolic metabolites formed by demethylation of trimethoprim-were quantitated after treatment of urine with beta-glucuronidase (Escherichia coli). The sulphuric acid conjugate was not susceptible to enzymatic hydrolysis and was therefore assayed as the conjugate by use of ion-pair chromatography on the reversed-phase column. In order to find suitable conditions for enzymatic hydrolysis of the glucuronides, the conjugates were obtained by gel chromatography of urine from a [14C] trimethoprim-treated pig.

Assay for beta-glucuronidase utilizing headspace gas chromatography

An assay for beta-glucuronidase is described. The assay uses 1-(beta-D-glucopyranuronosyl)pyridinium hydroxide, inner salt, as substrate and the quantitative determination is performed with headspace gas chromatography, measuring one of the products, pyridine, in the gas phase. The assay has been developed utilizing commercially available beta-glucuronidase (EC 3.2.1.31.) from Escherichia coli, and has been applied to various sources of beta-glucuronidase. Crude homogenates can be assayed directly with a minimum of manipulative steps and the method is suited for automation.

A sulphate metabolite of trimethoprim in goats and pigs

1. Urine from goats and pigs after intravenous administration of [14C]trimethoprim contained an unidentified fraction of 'other water-soluble metabolites'. This fraction accounts for 56% of the administered dose in goat urine and 65% in pig urine. 2. A sulphate metabolite comprising the major part of the latter fraction in both goat and pig urine was isolated by gel filtration and paper chromatography and identified by spectroscopic methods as 2,4-diamino-5-(3,4-dimethoxy-5-sulphooxybenzyl)pyrimidine. 3. No hydrolysis of the sulphate metabolite occurred on treatment with aryl sulphatase from (a) Helix pomatia, (b) limpets and (c) Aerobacter aerogenes, while treatment with aryl sulphatase from abalone entrails led to very slow hydrolysis.

Skeletal-rearrangement fragments in the mass spectra of β-thiopropionic acid derivatives

The mass spectra of S-alkyl-β-thiopropionic acids contain skeletal- rearrangement ions which arise by hydroxyl migration to a carbonium-ion centre followed by elimination of a neutral molecule (e.g. ketene or formaldehyde). In contrast, those of methyl S-alkyl-β-thiopropionates contain peaks which are formed by methoxyl migration to sulphur, followed by loss of ketene.