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T J Gray

Publications and source records attributed to T J Gray.

At least 19 recordsLinked to original sources
PubMed1999

A reporter gene assay to assess the molecular mechanisms of xenobiotic-dependent induction of the human CYP3A4 gene in vitro.

1. A plasmid containing 1 kb of the CYP3A4 regulatory (promoter) region coupled to a reporter gene for secretary placental alkaline phosphatase (SPAP) was transfected into HepG2 cells. Transfected cells were dosed with several known inducers of CYP3A4 and the levels of SPAP were measured. The effect of co-transfecting a plasmid encoding the human glucocorticoid receptor on reporter gene activity was also examined. 2. Dexamethasone induced CYP3A4-dependent reporter gene expression in a concentration-dependent manner and induction was approximately doubled in the presence of the glucocorticoid receptor. Dexamethasone-dependent induction was blocked by RU-486 (a glucocorticoid receptor antagonist), in the presence of the co-transfected glucocorticoid receptor. 3. Induction of CYP3A4-dependent reporter gene expression and enhancement of the induction by the glucocorticoid receptor was also observed with pregnenolone-16alpha-carbonitrile (PCN), rifampicin, phenytoin, carbamazepine, phenylbutazone and phenobarbitone, all known in vivo inducers of CYP3A4 in man. 4. Metyrapone and sulfinpyrazone induced CYP3A4-dependent reporter gene expression, but induction was not enhanced by the glucocorticoid receptor. 5. Clotrimazole, erythromycin and triacetyloleandomycin (TAO) did not induce CYP3A4-dependent reporter gene expression, consistent with the observation that these inducers act through post-transcriptional mechanisms. 6. These results highlight differences in the molecular mechanisms of induction of CYP3A4 by the xenobiotics studied and indicate that the glucocorticoid receptor is involved in the induction of the CYP3A4 gene by some, but not all, CYP3A4 inducers. 7. We propose that the approach described here provides a useful in vitro approach for the identification of transcriptional regulators of the CYP3A4 gene.

Alkaline Phosphatase↗
PubMed1999

Inhibitory mechanisms by which suramin may attenuate neointimal formation after balloon angioplasty.

Restenotic neointimal lesions, a major limitation to coronary angioplasty, develop in response to diverse signals and depend on three properties of activated arterial smooth muscle cells (SMCs): proliferation, migration, and abnormal production of extracellular matrix. Most of the pharmacologic approaches targeting specific pathogenic factors facilitating development of restenosis have failed in clinical trials. Our results indicate that the polysulfonated naphthylurea suramin, a "non-specific drug" that interferes with multiple cellular proteins, inhibits neointimal formation in rabbit iliac arteries after balloon-catheter injury administered throughout the critical period of several weeks after the procedure. In vitro studies aimed at dissecting the mechanism(s) underlying the suramin-dependent effect demonstrated that, in addition to an inhibitory effect on SMC proliferation, suramin inhibited fibronectin and elastin deposition and the migration of SMCs through elastin membranes and into scratch gaps of monolayer cultures. We also demonstrated that suramin causes cell-surface accumulation of the elastin binding protein, a receptor that not only anchors SMCs to the extracellular matrix, but also inhibits SMC response to interleukin-1beta (IL-1beta). We conclude that suramin acts as a multitarget inhibitor of SMC activation and has a therapeutic potential as an agent that may attenuate arterial restenosis after angioplasty.

Angioplasty, Balloon↗
PubMed1998

Molecular basis of non-responsiveness to peroxisome proliferators: the guinea-pig PPARalpha is functional and mediates peroxisome proliferator-induced hypolipidaemia.

The guinea pig does not undergo peroxisome proliferation in response to peroxisome proliferators, in contrast with other rodents. To understand the molecular basis of this phenotype, the peroxisome proliferator activated receptor alpha (PPARalpha) from guinea-pig liver was cloned; it encodes a protein of 467 amino acid residues that is similar to rodent and human PPARalpha. The guinea-pig PPARalpha showed a high substitution rate: maximum likelihood analysis was consistent with rodent monophyly, but could not exclude rodent polyphyly (P approximately 0.06). The guinea-pig PPARalpha cDNA was expressed in 293 cells and mediated the induction of the luciferase reporter gene by the peroxisome proliferator, Wy-14,643, dependent on the presence of a peroxisome proliferator response element. Moreover the PPARalpha RNA and protein were expressed in guinea-pig liver, although at lower levels than in a species which is responsive to peroxisome proliferators, the mouse. To determine whether the guinea-pig PPARalpha mediated any physiological effects, guinea pigs were exposed to two selective PPARalpha agonists, Wy-14, 643 and methylclofenapate; both compounds induced hypolipidaemia. Thus the guinea pig is a useful model for human responses to peroxisome proliferators.

Amino Acid Sequence↗
PubMed1998

The peroxisome proliferators are hepatocyte mitogens in chemically-defined media: glucocorticoid-induced PPAR alpha is linked to peroxisome proliferator mitogenesis.

Peroxisome proliferator-induced mitogenesis is believed to play a role in hepatocarcinogenesis, but it has not been possible to demonstrate high level induction of DNA synthesis by peroxisome proliferators in cultured hepatocytes. We now show that four structurally dissimilar peroxisome proliferators (methylclofenapate, Wy-14 643, tetradecyl-3-thia acetic acid and clofibrate) cause high level induction of DNA synthesis in primary cultures of rat hepatocytes, routinely 7-9 fold above control, with up to 29% of cells undergoing S-phase. Peroxisome proliferators induce DNA synthesis rapidly, with maximal response 24 h after dosing [compared with 48 h for epidermal growth factor (EGF)]; indeed, peroxisome proliferators were mitogenic in a chemically defined medium, i.e. with no added exogenous growth factors. EGF-treated hepatocytes that had undergone DNA synthesis comprised 23% binucleated cells, whereas hepatocytes induced into S-phase by peroxisome proliferators contained only 3% binucleated cells, demonstrating a distinct response of hepatocytes to peroxisome proliferators and EGF. The presence of a glucocorticoid was essential for peroxisome proliferator-induced DNA synthesis, but not for EGF-induced DNA synthesis, demonstrating that the requirement for glucocorticoids is selective for peroxisome proliferators. Hydrocortisone was shown to induce the expression of peroxisome proliferator activated receptor-alpha (PPAR alpha), and we propose that it is the glucocorticoid-induced expression of PPAR alpha that is essential for peroxisome proliferator mitogenesis. This in vitro system provides a powerful tool for investigating the mechanism and role of peroxisome proliferator-induced mitogenesis in liver growth and carcinogenesis.

Animals↗
PubMed1998

Creatine metabolism in the seminiferous epithelium of rats. I. Creatine synthesis by isolated and cultured cells.

The testis synthesizes creatine from both arginine and glycine precursors, but when rat testicular tissue is separated into seminiferous tubules and interstitial cells, creatine synthesis occurs only in the tubular fraction. The purpose of the work presented here was to define the locus of creatine synthesis within the seminiferous tubules, by using cell separation and culture techniques to examine synthesis in the Sertoli cells and germ cells. The total creatine content, in the cellular compartment and incubation medium, of Sertoli-germ cell co-cultures and of Sertoli cell-enriched cultures, largely free of germ cells, increased by similar amounts over a 24 h incubation period. Sertoli cell-enriched cultures incorporated radioactivity from L-[guanidino-14C]arginine and [1-14C]glycine into both creatine and its biosynthetic precursor, guanidinoacetic acid. Isolated germ cells did not incorporate radioactivity from L-[guanidino-14C]arginine into either creatine or guanidinoacetic acid when incubated at a similar density and protein concentration under similar conditions. It is concluded that the synthesis of creatine observed in isolated rat seminiferous tubules occurs within the Sertoli cells and not the germ cells.

Animals↗
PubMed1998

Creatine metabolism in the seminiferous epithelium of rats. II. Effect of modulators of cellular biochemical function on creatine secretion by cultured Sertoli cells.

The Sertoli cells have been identified as the primary locus for creatine synthesis within the seminiferous epithelium. The purpose of the studies reported here was to examine the effect of modulators of Sertoli cell function on creatine secretion by primary cultures of these cells. Sertoli cell-enriched cultures, maintained in a defined medium, secreted creatine into the incubation medium in a manner that was linear with time over at least 6 h, but which had reached a plateau within 24 h. Secretion was stimulated by physiological and toxicological modulators of Sertoli cell function. Incubation of Sertoli cell-enriched cultures in the presence of FSH (> or = 40 mU ml-1), dibutyryl cyclic AMP (> or = 0.1 mmol l-1), mono-(2-ethylhexyl) phthalate (> or = 1 mumol l-1) or cadmium (> or = 3 mumol l-1) increased the secretion of creatine into the incubation medium by at least 85% over 24 h. Creatine secretion by Sertoli cell-enriched cultures, incubated over 4 h in a balanced salt solution, was independent of exogenous L-glutamine. However, the stimulation of secretion induced by 1 mmol dibutyryl cyclic AMP l-1 was dependent on the presence of 4 mmol L-glutamine l-1 in the incubation medium, which suggests that an increase in creatine secretion occurs as a consequence of stimulated glutamine oxidation.

1-Methyl-3-isobutylxanthine↗
PubMed1997

A novel murine P-450 gene, Cyp4a14, is part of a cluster of Cyp4a and Cyp4b, but not of CYP4F, genes in mouse and humans.

Genomic clones for Cyp4a12 and a novel member of the murine Cyp4a gene family were isolated. The novel gene, designated Cyp4a14, has a GC rich sequence immediately 5' of the transcription start site, and is similar to the rat CYP4A2 and CYP4A3 genes. The Cyp4a14 gene spans approximately 13 kb, and contains 12 exons; sequence similarity to the rat CYP4A2 gene sequence falls off 300 bp upstream from the start site. In view of the known sex-specific expression of the rat CYP4A2 gene, the expression and inducibility of Cyp4a14 was examined. The gene was highly inducible in the liver when mice were treated with the peroxisome proliferator, methylclofenapate; induction levels were low in control animals and no sex differences in expression were observed. By contrast, the Cyp4a12 RNA was highly expressed in liver and kidney of control male mice but was expressed at very low levels in liver and kidney of female mice. Testosterone treatment increased the level of this RNA in female liver slightly, and to a greater extent in the kidney of female mice. In agreement with studies on the cognate RNA, expression of Cyp4a12 protein was male-specific in the liver of control mice and extremely high inducibility of Cyp4a10 protein, with no sex differences, was also demonstrated. In view of the overlapping patterns of inducibility of the three Cyp4a genes, we investigated whether the three genes were co-localized in the genome. Two overlapping yeast artificial chromosome (YAC) clones were isolated, and the three Cyp4a genes were shown to be present on a single YAC of 220 kb. The Cyp4a genes are adjacent to the Cyp4b1 gene, with Cyp4a12 most distant from Cyp4b1. The clustering of these two gene subfamilies in the mouse was replicated in the human, where the CYPA411 and CYP4B1 genes were present in a single YAC clone of 440 kb. However, the human CYP4F2 gene was mapped to chromosome 19. Phylogenetic analysis of the CYP4 gene families demonstrated that CYP4A and CYP4B are more closely related than CYP4F.

Amino Acid Sequence↗
PubMed1997

Diaminonaphthalenes and related aminocompounds: mutagenicity, CYP1A induction and interaction with the Ah receptor.

Using 1- and 2-aminonaphthalene as model substrates, we investigated the effect of insertion of a second amino group on mutagenicity, binding to the cytosolic Ah receptor and CYP1A inducibility, and the effects were compared to those elicited by 3,3'-diaminobenzidine and 1-naphthylethylenediamine. 1,5- and 1,8-diaminonaphthalene were effective inducers of CYP1A activity, more potent than 1-aminonaphthalene. 2,3-Diaminonaphthalene was also an inducer of CYP1A, but the effect was similar to that elicited by 2-aminonaphthalene. In contrast, 3,3'-diaminobenzidine and 1-naphthylethylenediamine did not induce CYP1A activity. All aminonaphthalenes displaced [3H]TCDD from the Ah receptor, whereas 3,3'-diaminobenzidine and 1-naphthylethylenediamine failed to do so. The latter two compounds did not elicit a mutagenic response in the Ames test. Introduction of a second amino group at the 3-position of 2-aminonaphthalene did not modulate its mutagenicity. In the case of the non-mutagenic 1-aminonaphthalene, introduction of a second amino group at position 5 had no effect but when it was incorporated at position 8, mutagenic potential was conferred to the molecule. Computer modelling of the putative active site of CYP1A2 revealed that 1,5-diaminonaphthalene is orientated so that the distance of the second amino group from the iron-oxene is 4.037 A while in the case of 1,8-diaminonaphthalene the distance is shorter, 2.744 A, favouring its activation through N-hydroxylation. Of the compounds studied, 1,8-diaminonaphthalene and, to a lesser extent, 2,3-diaminonaphthalene autoinduced their activation. It is concluded that insertion of a second amino group at the 5- or 8-position of 1-aminonaphthalene may enhance biological activity but in the case of 2-aminonaphthalene insertion of a second amino group at position 3 had no major effect.

1-Naphthylamine↗
PubMed1996

Developmental toxicity study of mangafodipir trisodium injection (MnDPDP) in New Zealand white rabbits.

Mangafodipir trisodium injection (MnDPDP) is an intravenously administered manganese chelate undergoing clinical evaluation for magnetic resonance imaging contrast enhancement of the hepatobiliary system. The anticipated single clinical dose for adults is 5 micromol/kg body wt. MnDPDP, as well as the inorganic salt, MnCl2, was previously shown to induce a specific syndrome of skeletal abnormalities in rats. The syndrome malformations included angulated or irregularly shaped clavicle, femur, fibula, humerus, ilium, radius, scapula, tibia, and/or ulna. The objective of the present study was to assess the developmental toxicity of MnDPDP in a second mammalian species, the New Zealand White rabbit. MnDPDP was intravenously administered daily to groups of rabbits (22 per group) on Days 6 through 18 of pregnancy at doses of 0 (saline), 5, 20, 40, and 60 micromol/kg MnDPDP. Fetuses were examined on Day 29 of pregnancy for external, visceral, and skeletal abnormalities. Treatment with MnDPDP did not result in overt symptoms of maternal toxicity, and there were no significant effects on maternal body weight gains or feed consumption. The maternal no-observed-adverse-effect level (NOAEL), therefore, was 60 micromol/kg MnDPDP. Treatment with MnDPDP resulted in a significant increase in postimplantation loss at 60 micromol/kg, but there was no significant increase in external, visceral, or skeletal abnormalities at any dose. The developmental NOAEL for MnDPDP, therefore, was 40 micromol/kg. These results indicate that the developmental toxicity profile of MnDPDP differs considerably in the rat and rabbit. In the rat, this compound induces specific skeletal abnormalities, whereas in the rabbit, embryo/fetal toxicity is the most sensitive developmental endpoint with no evidence for the induction of specific skeletal abnormalities.

Abnormalities, Drug-Induced↗
PubMed1996

Interaction with the aromatic hydrocarbon receptor, CYP1A induction, and mutagenicity of a series of diaminotoluenes: implications for their carcinogenicity.

The present study was undertaken to provide a rationale for the marked difference in carcinogenic potential among isomeric diaminotoluenes, in relation to their ability to induce their own bioactivation through CYP1A induction, their genotoxic potential, and their ability to bind to the cytosolic aromatic hydrocarbon (Ah) receptor. Of the four possible diaminotoluenes only the 2,3- and, to a lesser extent, the 2,4-isomer induced CYP1A activity. Similarly, only these two isomers could displace [3H]T-CDD from the hepatic cytosolic Ah receptor. In the presence of Aroclor 1254- induced microsomes, 2,4- and 2,6-diaminotoluene were potent mutagens in the Ames test. Only 2,4-diaminotoluene could autoinduce its activation. Of the four isomers only 2,4-diaminotoluene is an established carcinogen and this is compatible with the present observations that it is the only isomer that stimulates its own activation through CYP1A induction, is metabolically converted to genotoxic intermediates, and binds to the Ah receptor. 2,6-Diaminotoluene is recognized as a mutagenic noncarcinogen and in the present studies it elicited a positive mutagenic response in the Ames test but failed to induce CYP1A activity and its own activation, and could not bind to the Ah receptor even at concentrations as high as 5 x 10(-4) M. The present findings demonstrate that in vitro studies are very useful tools in predicting the carcinogenic potency of isomeric chemicals.

Animals↗
PubMed1996

Comparative hypolipidaemic and peroxisomal effects of ciprofibrate, clofibric acid, and their respective difluorocyclopropyl and 4-fluoro-substituted analogues in rat.

1. We investigated the biological activity of the difluoro analogue (WIN 36117) of ciprofibrate, a potent peroxisome proliferator, and re-examined the relative activity of clofibric acid and its 4-fluoro analogue (fluorofibric acid) in the rat. 2. Twenty-four hours after a single dose, ciprofibrate and WIN 36117 produced dosage-related reductions in plasma cholesterol (16-42 and 9-34% respectively) and triglycerides (14-32 and 9-22% respectively). However, a single dose of clofibric acid or fluorofibric acid produced hypocholesterolaemia only (32-58 and 9-29% reductions respectively). 3. After treatment for 7 days reductions in cholesterol were similar at all dosages of ciprofibrate (45% reduction, mean across groups) whereas the effects of WIN 36117, clofibric acid and fluorofibric acid were still dosage related (reductions of 21-44, 37-43 and 2-28% respectively). Hypotriglyceridaemia was produced by all compounds (ciprofibrate 36-50%, WIN 36117 14-36%, clofibric acid 18-48%, fluorofibric acid 6-28%). 4. After treatment for 14 days all compounds produced dosage-related decreases in plasma fibrinogen (ciprofibrate 18-33%, WIN 36117 7-11%, clofibric acid 13-26%, fluorofibric acid 7-15%). 5. Peroxisomal beta-oxidation activity was increased by WIN 36117 (4.8-fold) and fluorofibric acid (4.2-fold) although these increases were less than those produced by ciprofibrate (13.6-fold) and clofibric acid (7.0-fold). WIN 36117 and fluorofibric acid also produced smaller increases in peroxisome numbers, liver weight, and carnitine acetyl transferase activity and smaller decreases in glutathione S-transferase and glutathione peroxidase activities. 6. Maximal increases in peroxisomal beta-oxidation activity produced in cultured rat hepatocytes by WIN 36117 and fluorofibric acid were 58 and 72% of those produced by ciprofibrate and clofibric acid respectively. 7. These results indicate the difluoro and 4-fluoro analogues of ciprofibrate and clofibric acid are hypolipidaemic agents and peroxisome proliferators but with reduced potencies relative to the parent molecules.

Animals↗
PubMed1995

Chromosomal localisation, inducibility, tissue-specific expression and strain differences in three murine peroxisome-proliferator-activated-receptor genes.

Three murine peroxisome-proliferator-activated-receptor (PPAR) genes were localised to chromosome 15 (PPAR alpha), chromosome 17 (PPAR beta) and chromosome 6 (PPAR gamma). The expression of the three PPAR RNAs was determined using a specific RNase protection assay. In liver RNA, PPAR alpha was expressed at the highest level, with 20-fold lower levels of PPAR beta, and very low levels of PPAR gamma. The three PPAR RNAs showed no sex-specific differences in expression, and the levels of these transcripts were unaffected by treatment of mice with testosterone or the potent peroxisome proliferator, methylclofenapate. In agreement with this data, the level of PPAR alpha protein in liver was unchanged after treatment of mice with methylclofenapate. Investigation of the tissue-specific distribution revealed that the PPAR alpha RNA was expressed at highest levels in liver, to moderate levels in kidney and brown adipose tissue, and at low levels elsewhere. PPAR beta was expressed at moderate levels in liver, and lower levels in other tissues, including brown adipose tissue. In contrast, PPAR gamma RNA was expressed at low levels in liver or epididymal white adipose tissue and at very low levels elsewhere, but was expressed at high levels in brown adipose tissue. The tissue distribution of these receptors suggests an important role in lipid metabolism and toxicity for individual members of the PPAR family. The expression of PPAR alpha and PPAR beta RNAs was examined in 13 strains of mice, and the levels of expression varied within a fourfold range. Polymorphism in the size of PPAR alpha RNA from Swiss-Webster mice was detected, and shown to be due to a 2-bp mutation in the 3' non-coding region of PPAR alpha in Swiss Webster mice.

Adipose Tissue, Brown↗
PubMed1995

Developmental toxicity of mangafodipir trisodium and manganese chloride in Sprague-Dawley rats.

Mangafodipir trisodium (MnDPDP) is a manganese chelate being developed as a contrast agent for magnetic resonance imaging of the hepatobiliary system. The intended clinical dose is 5 mumol/kg. The potential for MnDPDP to induce embryotoxicity and/or teratogenicity in Sprague-Dawley rats was investigated. Twenty five inseminated rats/group were intravenously administered 0, 2, 5, or 20 mumol/kg MnDPDP from days 6-17 of gestation. Maternal toxicity was not observed at any dose of MnDPDP. There were no treatment-related effects on the numbers of fetuses, fetal viability, numbers of resorptions, implantations and corpora lutea, or the percent of pre- and post-implantation losses. However, at 20 mumol/kg, fetal body weights were significantly decreased (3.3 g vs. 3.9 g for control) and increased skeletal malformations were observed (141/270 vs. 0/285 in control). The malformations were of a specific type, which included angulated or irregularly shaped clavicle, femur, fibula, humerus, ilium, radius, scapula, tibia, and/or ulna. To better define the developmental stage that is most susceptible to the effects of MnDPDP, a segmented developmental study was conducted. Twelve inseminated rats were administered 0, 20, 40, or 80 mumol/kg MnDPDP on days 6-8, 9-11, 12-14, or 15-17 of gestation. Skeletal malformations, identical to those seen in the previous study, were increased in a dose-dependent manner with the highest incidence occurring in fetuses from females dosed from days 15-17 of gestation. A third study, in which 15 rats/group were dosed intravenously with 0, 5, 20, or 40 mumol/kg MnCl2 on days 6-17 of gestation, produced identical skeletal malformations to those seen with MnDPDP, indicating that manganese is the active moiety responsible for these specific malformations.

Abnormalities, Drug-Induced↗
PubMed1995

A study of the nephrotoxicity of three cephalosporins in rabbits using 1H NMR spectroscopy.

Male New Zealand White rabbits received a single intravenous injection of 125 mg/kg cephaloridine, 500 mg/kg cefoperazone or 1000 mg/kg cephalothin. Histological examination of kidneys at 48 h post-dose confirmed the presence of bilateral necrosis of the proximal convoluted tubules in the cephaloridine-treated animals. 1H-NMR urinalysis of cephaloridine-treated rabbits detected drug-related resonances, decreased hippurate and increased glucose at 0-24 h post-dose accompanied by elevated levels of lactate, glycine, citrate, glutamine/glutamate and alanine at 24-48 h post-dose. No histopathological changes were observed following administration of cefoperazone or cephalothin. 1H-NMR spectra of urine collected from these animals showed drug-related resonances and decreased hippurate levels at 0-24 h post-dose, and increased glucose levels at 24-48 h post-dose. Analysis of urine by conventional clinical-chemistry failed to reveal any statistically significant differences between the treatment groups. Under the conditions of this study, the nephrotoxic effects of cephaloridine and the minimal effects of cefoperazone and cephalothin could be clearly distinguished by 1H-NMR urinalysis but not by conventional urinalysis.

Alanine↗
PubMed1995

Effect of manganese dipyridoxal diphosphate on liver magnetic resonance imaging and serum bilirubin in rats with removable biliary obstruction.

RATIONALE AND OBJECTIVES: It is known that manganese dipyridoxal diphosphate (Mn-DPDP) causes persisting liver enhancement in cholestatic rats, that free Mn++ plus bilirubin induces intrahepatic cholestasis, and that free Mn++ is released in vivo after Mn-DPDP injection. Hence, there is a concern about potential secondary intrahepatic cholestasis in patients who have biliary obstruction. In this study, we further investigated this issue. METHODS: Removable total biliary obstruction (RTBO) was induced in 12 rats. Six of them (group A) received Mn-DPDP (25 mumol/kg). The others (group B) served as control animals. The data from serial magnetic resonance imaging and serum bilirubin tests were compared. RESULTS: Without Mn-DPDP, a minimal increase of the liver intensity was observed in both groups because of cholestasis. In group A, the intensity of the liver was strongly enhanced with Mn-DPDP but normalized within 48 hr after removal of the obstruction. In both groups, total bilirubin levels increased up to 131.67 mumol/l 2 days after RTBO but rapidly decreased within 4 hr and almost normalized within 24 hr after removal of the obstruction, suggesting a lack of Mn-DPDP influence on the bilirubin level. CONCLUSION: We found that Mn-DPDP did not cause secondary intrahepatic cholestasis. Retained Mn++ is likely eliminated after restoration of bile flow. These results indicate that Mn-DPDP can be used in patients who have obstructive jaundice as long as it is followed by successful bile drainage.

Animals↗
PubMed1995

1H NMR spectroscopic studies on the reactions of haloalkylamines with bicarbonate ions: formation of N-carbamates and 2-oxazolidones in cell culture media and blood plasma.

1H NMR spectroscopic methods have been applied to compare the in vitro reactivity of the renal papillary nephrotoxin 2-bromoethanamine (BEA) with those of selected halide-substituted nephrotoxic analogues, 2-chloroethanamine (CEA), 2-fluoroethanamine (FEA), and 1-phenyl-2-iodoethanamine (PIEA). The primary 1H NMR-detectable transformation during a 24 h incubation of confluent Madin Darby canine kidney (MDCK) cells with BEA, CEA, and FEA (at concentrations up to the IC50 determined by neutral red uptake) was the appearance in cell culture media of 2-oxazolidone (OX). Additional novel signals assigned as FEA carbamate (N-carbamoyl-2-fluoroethanamine) were observed in media collected following incubation of cells with FEA. We propose that N-carbamate intermediates are formed from the spontaneous reaction of these haloalkylamines with HCO(3-)-buffered growth media and that OX is formed from the carbamate via elimination of the hydrogen halide. Further 1H NMR experiments, conducted for up to 8 h at 25 degrees C on 5 mM solutions of BEA, CEA, and FEA in 2H2O containing a 20-fold excess of HCO3- at pH 7.6, demonstrated a time-dependent decrease in the concentration of the free haloalkylamines accompanied by the production of N-carbamate intermediates and OX. Under these pseudo-first-order reaction conditions, the formation of OX from BEA was complete within approximately 6 h. In similar reaction conditions OX formation from CEA (24 h after initiation) had reached 54% of its final equilibrium concentration. Equivalent experiments demonstrated that PIEA was almost completely converted to 4-phenyl-2-oxazolidinone (PHOX) within 2 h. These observations reveal the strong disposition of this series of haloalkylamines toward reaction with HCO3- and indicate that the compounds in this family may exist only transiently as free amines in vivo, where there will virtually always be excess HCO3-. The physiological relevance of the in vitro findings is further indicated by the NMR-detectable conversion of BEA to OX and also an alkylating aziridine (AZ) moiety in rat plasma containing BEA. The ability to form carbamoylated species and OX (or PHOX) may mediate the toxicity of this series of haloalkylamines and hence is potentially of considerable significance.

Animals↗
PubMed1994

The relative hypolipidaemic activity and hepatic effects of ciprofibrate enantiomers in the rat.

The aim of this study was to establish whether the individual enantiomers of racemic ciprofibrate, a potent hypolipidaemic agent and peroxisome proliferator, differ significantly in either pharmacological potency or toxic potential. After a single oral dose to male Fischer F344 rats at dosages below 10 mg/kg, S(-) ciprofibrate produced slightly, but statistically significantly, greater reductions in plasma concentrations of cholesterol than R(+) ciprofibrate. Similarly, at low concentrations in F344 rat hepatocyte cultures, S(-) ciprofibrate produced slightly, but statistically significantly, greater inductions of peroxisomal beta-oxidation activity than R(+) ciprofibrate. However, after seven daily doses, the differences in pharmacological effects of the two enantiomers were no longer apparent. Furthermore, in contrast to its effects in vitro, R(+) ciprofibrate produced slightly, but statistically significantly, greater inductions of peroxisomal beta-oxidation activity in vivo than S(-) ciprofibrate. These observations may be possibly explained on the basis that following multiple dosing, plasma concentrations of R(+) ciprofibrate 24 hr post-dose were greater than those of its optical antipode. Thus the slightly greater potency of the S(-) enantiomer after a single dose may have been overcome by the greater plasma concentrations of the less potent enantiomer. Both enantiomers produced similar reductions in plasma concentrations of thyroxine. The data indicate that at low dosages S(-) ciprofibrate is a slightly more potent hypolipidaemic agent after a single dose in rats and a slightly more potent peroxisome proliferator at low concentrations in vitro. However, following multiple dosing, both enantiomers produced changes in plasma concentrations of lipids, hepatic enzyme activities and plasma concentrations of thyroxine which were of comparable magnitude to those produced by the racemate. Since these early changes have been linked mechanistically to the chronic toxicity of the racemate in the rat, it could be predicted that the individual enantiomers of ciprofibrate under conditions employed in chronic safety studies, would produce the same spectrum of rodent toxicity as the racemate.

Animals↗