Dose-dependent metabolic excretion of bromobenzene and its possible relationship to hepatotoxicity in rats

Male Sprague-Dawley rats received an intraperitoneal injection of 0.25-, 0.5-, 1.0-, 2.5-, and 5.0-mmol/kg dose of bromobenzene in corn oil. The metabolic fate of bromobenzene was studied by measuring its various urinary metabolites 24 h following bromobenzene administration. The hepatotoxicity of bromobenzene was estimated by determination of the serum glutamic-oxaloacetic and glutamic-pyruvic transaminase activities (SGOT and SGPT) 24 h after dosing. Treatment of rats with bromobenzene at up to 0.5 mmol/kg did not influence the transaminase activities, but significant increases in such activities began to manifest at a dose of 1 mmol/kg. However, no further increase in hepatotoxic response was induced on exposure to higher doses (2.5 and 5.0 mmol/kg) of bromobenzene. The urinary excretion of toxic doses of bromobenzene was nonlinear, based on the quantitative composition of various urinary metabolites. Furthermore, the fraction of the dose converted to thioethers, p-bromophenol, m-bromophenol, and total phenolic metabolites decreased with increasing toxic dose, suggesting their formation to be capacity-limited. The ratios of thioethers to total phenolic metabolites, of thioethers to p-bromophenol, and of thioethers to o-bromophenol decreased with increasing dose of bromobenzene. The correlation of the dose-dependent fate of metabolic excretion of bromobenzene with the results of the dose-hepatotoxic response curves supports the conclusion that there exists an apparent threshold dose (approximately 1-2.5 mmol/kg) for the toxic effects of bromobenzene that coincides with saturation of the metabolic pathways involving both glutathione/glutathione S-transferase(s) and formation of certain phenolic derivatives for its detoxification. All these results further suggest a role of a saturable, metabolic activation process involving 3,4-epoxide rather than 2,3-epoxide of bromobenzene in the development of its hepatotoxicity.

Effects of drug and chemical pretreatments on biliary excretion of phenylcyclohexene in the rat

The biliary excretion of 14C-phenylcyclohexene and its metabolites were studied in rats pretreated with an inducer or inhibitor of mixed-function oxidases or with an agent known to deplete liver glutathione. Pretreatment of rats with 3-methylcholanthrene or phenobarbital enhanced the biliary excretion of 14C-phenylcyclohexene and/or its metabolites. Conversely, pretreatment of rats with SKF-525A or piperonyl butoxide decreased the biliary excretion of 14C-phenylcyclohexene and/or its metabolites. In contrast, pretreatment of rats with diethylmaleate did not alter significantly the rate of biliary excretion of radioactivity.

Temporal distinction between repair and mutagenesis of benzopyrene adducts after SOS induction in Escherichia coli

Plasmid DNA covalently modified with benzopyrene diol epoxide was introduced into Escherichia coli strains which differed in their capacity for repair and mutagenesis at various times after SOS induction. The uvrA+-dependent repair activity rose and fell before umuC+SOS-dependent mutagenesis was fully expressed.

The dispositional kinetics of phencyclidine and its N-ethylamine analogue in rats

The uptake kinetics of [3H]-labelled phencyclidine (PCP) and N-ethyl-l-phenycyclohexylamine (PCE) in rats, measured in terms of decreases in the blood concentrations of the drugs after i.v. administration of a single 1.09 mumol dose, were not significantly different. Within a week of administration, the rats excreted about 93% of the [3H]-PCP and about 65% of [3H]-PCE via their urine and faeces; their urine contained nore [3H], mainly as metabolites of [3H]-PCP and of [3H]-PCE, than their faeces. Similarly, more [3H] remained in the tissues of rats treated with [3H]-PCE than in the tissues of [3H4-PCP-treated rats. The fact that PCE is metabolized and excreted more slowly than PCP may account for the higher psychotropic effects of PCE.

Disposition and metabolism of diphenyl ether in rats

After i.p. administration of [14C]diphenyl ether (5 mg/kg) to rats, radioactivity was detected rapidly in all organs and tissues. After intragastric administration of [14C]diphenyl ether (10 mg/kg) to rats, unchanged diphenyl ether in the blood was at max. concn. within 15 h and decreased linearly with time, with a biological half-life of about 1.5 h. More than 90% of the intragastrically administered dose was excreted in urine and faeces within three days; greater than 80% dose was in the urine. From g.l.c. and mass-spectral data, it was shown that rats metabolized diphenyl ether to its 2-hydroxy, 4-hydroxy, 4,4'-dihydroxy, 4-methoxy-monohydroxy and 4-methoxy-dihydroxy derivatives.

The nephrotoxic potential of styrene in Sprague-Dawley rats

Pre-fasted (16 h) Sprague-Dawley male rats were treated i.p. with 0, 0.2, 0.4, 0.8 and 1.2 g/kg of styrene in corn oil. Renal functions were assessed at 0-24, 24-48 and 48-72 h after the exposure. Urinary creatinine was decreased at 0.8 g/kg of styrene during 0-24 h after the treatment compared to control, whereas such a decrease was noticed in 1.2 g/kg styrene-treated rats when compared to control groups during 0-24 and 0-48 h after the dose. Urine pH and urinary contents of sodium, potassium and chloride were all decreased in a dose-dependent manner at 0.8 and 1.2 g/kg of styrene compared to both control animals during 0-24 h, whereas urinary proteins were not affected significantly. In another experiment, groups of pre-fasted (16 h) rats were treated i.p. with 0, 0.8 and 1.2 g/kg of styrene in corn oil and were then fasted for another 24 h to induce more stress prior to collection of blood and urine. Urinary pH and excretions of sodium and potassium were all decreased in styrene-treated rats 24 h after the dose. Urinary proteins were elevated and relative kidney weights were increased in 1.2 g/kg styrene-treated rats only compared to both control and 0.8 g/kg styrene-treated groups. A significant increase in serum creatinine and an increase close to significant in blood urea nitrogen were observed at 1.2 g/kg dose. These results suggest an impairment of renal functional parameters due to acute styrene exposure and further demonstrate a possible dose-dependent nephrotoxic potential of styrene in rats.

Biological properties of acmycin, a new polyene antibiotic

Acmycin, a new polyene antibiotic, was fungistatic at low and fungicidal at high concentrations. It produced malformations in conidia of Helminthosporium oryzae and Curvularia lunata and caused leakage of yeast cells. Acmycin was fairly nontoxic to germinating seeds. The intravenous LD50 was 300-400 and intraperitoneal maximum tolerated dose 100-500 mg/kg body mass of mice.

Metabolic disposition and irreversible binding of 1-phenylcyclohexene in rats

The metabolic disposition of 1-[14C]phenylcyclohexene ([14C]PC) was examined in rats after ip or iv drug administration. Radioactivity, which was accumulated by various organs, peaked within 30 min after ip administration of [14C]PC (0.21 mg/kg). A significant amount of this radioactivity was not extractable by repeated methanol extractions, indicating irreversible binding of [14C]PC metabolite(s) to tissue proteins. Following iv administration of [14C]PC (0.42 mg/kg), [14C]PC concentrations in blood declined biphasically with time; the blood elimination half-life of [14C]PC is 77 min. About 83% of the dose given was excreted in urine and feces within 54 hr of administration. About 35% of the dose was excreted in the bile in 1 hr. At least four [14C]PC metabolites were detected in the urine or bile. The bulk of the urinary radioactivity was composed of metabolites since less than 6% of [14C]PC given was excreted unchanged in the urine.

Irreversible binding of 14C-diphenyl ether-derived radioactivity to liver microsomes in vitro and tissue proteins in vivo

Following ip administration of 14C-diphenyl ether (5 mg/kg) to rats, a significant amount of radioactivity was found to bind irreversibly with tissue proteins of liver, lung and kidney, indicating the in vivo formation of reactive diphenyl ether metabolite(s). Irreversibly bound 14C-diphenyl ether-derived radioactivity to these organs peaked 2-4 h after the chemical was administered. Incubation of 14C-diphenyl ether in rat liver microsomes demonstrated that the hepatic mixed-function oxidase system mediated the formation of the chemically reactive metabolite(s) of 14C-diphenyl ether. The apparent Vmax and Km were, respectively, 23.3 pmol/mg microsomal protein/min and 1.33 x 10(-4)M.

Frequency of gamma-Ray Induced Specific Locus and Recessive Lethal Mutations in Mature Germ Cells of the Zebrafish, BRACHYDANIO RERIO

Specific locus and recessive lethal mutations are induced by gamma-rays with approximately first order kinetics in the zebrafish (Brachydanio rerio) with frequencies of 4 x 10(-5) r(-1 ) and 4 x 10(-3) r(-1), respectively. The surprisingly low ratio (100:1) of recessive lethals to specific locus mutations may be due to the induction of large deficiencies by gamma-rays.

A new streptomycete and a new polyene antibiotic, acmycin

A new antifungal antibiotic named acmycin was isolated from a soil streptomycete. Detailed comparative taxonomic studies showed that the organism differed from three related species of streptomycetes. The organism was referred to as Streptomyces sp. AC2. The isolated antibiotic appears to be of polyene nature.

Retinitis pigmentosa associated with hearing loss, thyroid disease, vitiligo, and alopecia areata: retinitis pigmentosa and vitiligo

A 54-year-old woman with retinitis pigmentosa and hearing loss developed white skin patches that were subsequently diagnosed as vitiligo. A review of the literature reveals that, although the association of vitiligo with various tapedoretinal degenerations has been reported on several occasions, the association with typical retinitis pigmentosa is quite rare. This combination of disorders associated with pigment loss is of interest as immunologic disturbances have been implicated on both.

Plasma disappearance and biliary excretion of bromosulfophthalein in styrene-treated and styrene oxide-treated rats

Treatment with a single ip dose of styrene (908 mg/kg) 5 h before iv injection of bromosulfophthalein (BSP) (50 mg/kg) in rats resulted in (1) a decrease (approximately 30%) in biliary flow during 10-25 min but an increase in such flow during 60-90 min after the BSP dose, (2) a delay in cumulative excretion (approximately 50%) of BSP in bile during 5-60 min (but the latter became close to the control value after 75 min, and (3) no change in plasma disappearance of BSP. The first two effects seemed to depend on the dose of styrene. After pretreatment (2 h) with styrene oxide (375 mg/kg ip), a greater diminution of bile flow (approximately 50%) and of cumulative excretion of BSP was observed during the entire 5-90 min of bile collection after BSP administration, but the plasma disappearance of BSP remained unaffected. These results suggest that intrahepatic metabolism (and not hepatic uptake) of BSP and/or its transport from liver to bile are impaired after styrene- or styrene oxide-induced liver injury.

Effects of microsomal induction and inhibition on styrene-induced acute hepatotoxicity in rats

Administration of a single high dose of styrene (878 mg/kg ip in corn oil) to young male rats produced significant elevations in the activities of serum transaminases: 230, 209, and 71% increases in the activity of serum glutamic-oxaloacetic transaminase (SGOT) and 163, 437, and 227% in that of serum glutamic-pyruvic transaminase (SGPT) at 2, 6, and 24 h, respectively, after the dose. These results demonstrated that styrene could produce acute hepatic injury in young rats. Urinary nonprotein sulfhydryl contents and mandelic, phenylglyoxylic, and hippuric acids were all increased. Pretreatment of rats with phenobarbital and 3-methylcholanthrene did not further enhance the activities of SGOT and SGPT after styrene, but produced changes in other biochemical parameters, for example, an increase in liver weight, decrease in serum albumin and globulin concentrations, increase in serum alkaline phosphatase activity at 2 and 6 h, and increase in urinary urobilinogen concentrations. In addition, such pretreatments further increased the nonprotein sulfhydryl contents at 2 and 6 h after styrene injection. Pretreatment of rats with the microsomal enzyme inhibitor SKF 525-A failed to prevent the hepatotoxicity induced by styrene and did not modify the overall urinary excretion profiles of styrene metabolites. This study suggests that the mechanism of the activation/deactivation process leading to the metabolism and hepatotoxicity of styrene is complex and that alternative pathways not dependent on cytochrome P-450 might also be involved.

Metabolism and acute hepatotoxicity of styrene oxide in rats

The metabolism and acute hepatotoxicity of styrene oxide were studied after ip administration of a high dose of 375 mg/kg to adult male rats. Liver glutathione was significantly depleted at 2 h, but became normal at 6 h. The activity of serum glutamic-oxaloacetic transaminase was increased during the entire period (24 h) of study, while the activities of alkaline phosphatase and serum glutamic-pyruvic transaminase were elevated at 2 and 24 h, respectively, after administration of the dose. Decreased body weights and increased liver weights were observed at 24 h. Both prothrombin time and urinary urobilinogen concentration were temporarily increased. While urinary mandelic and phenylglyoxylic acids were increased during the entire time period, urinary (but no fecal) nonprotein sulfhydryl contents were increased at 2 and 6 h. The results of biochemical tests of liver function suggest a mild liver pattern in rats treated acutely with styrene oxide.

Influence of free fatty acid anion on the binding of warfarin to cytoplasmic proteins from rat liver

In vitro binding studies have shown that warfarin binds strongly to both ligandins (Y) and Z protein obtained from rat liver cytosol with dissociation constants of 11.7 and 10.1 microM respectively. Increasing concentrations of oleate ion significantly increased the dissociation constant of warfarin with either protein, whereas laurate ion showed the same behavior only with Z protein. On the other hand, the binding of warfarin to liver cytoplasmic proteins in vivo was decreased in 72-h-pre-fasted rats, although such fasting failed to produce any increase in the in vivo levels of the cytoplasmic free fatty acids (FFA). However, based on the results of the in vitro binding study, it is suggested that changes in the composition of hepatic cytoplasmic free fatty acids as a result of fasting could reduce the in vivo binding of warfarin to Y and Z proteins and hence could lead to an increase of unbound warfarin in liver cytosol.

Bioavailability of phenytoin in dogs: effect of crystal form and particle size

Significant differences in bioavailability were observed in dogs when phenytoin crystals of different particle size were administered. No significant differences in bioavailability were observed when different crystal forms were compared.