Methylsulphone metabolites of m-dichlorobenzene as ligands for alpha 2u-globulin in rat kidney and urine

The effect of dose on 2,3,7,8-TCDD tissue distribution, metabolism and elimination in CYP1A2 (-/-) knockout and C57BL/6N parental strains of mice

Numerous metabolism studies have demonstrated that the toxic contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is poorly metabolized. A hallmark feature of TCDD exposure is induction of hepatic CYP1A2 and subsequent sequestration leading to high liver-to-fat concentration ratios. This study was initiated to determine whether TCDD was inherently poorly metabolized or unavailable for metabolism because of sequestration to CYP1A2. [(3)H]TCDD was administered as a single, oral dose (0.1 and 10 microg/kg) to 12 male C57BL/6N mice or 12 CYP1A2 (-/-) mice. At 96 h, less than 5% of the dose was eliminated in the urine of all groups, and TCDD detected in urine was bound to mouse major urinary protein (mMUP). Feces were the major elimination pathway (24-31% of dose), and fecal extracts and non-extractables were quantitated by HPLC for metabolites. No great differences in urinary or fecal elimination (% dose) were observed between the high and low dose treatments. TCDD concentrations were the highest in adipose tissue for CYP1A2 knockout mice but in liver for C57BL/6N mice supporting the role of hepatic CYP1A2 in the sequestration of TCDD. Overall metabolism between parental and knockout strains showed no statistical differences at either the high or low doses. The data suggested that metabolism of TCDD is inherently slow, due principally to CYP1A1, and that hepatic CYP1A2 is not an active participant in the metabolism of TCDD in male mice. Rather, CYP1A2 governs the pharmacokinetics of TCDD by making it unavailable for hepatic CYP1A1 through sequestration and attenuating extrahepatic tissue disposition.

Binding of brominated diphenyl ethers to male rat carrier proteins

1. Two [(14)C]-labelled brominated diphenyl ethers, 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) and decabromodiphenyl ether (BDE-209), were separately administered to the male Sprague-Dawley rat as a single oral dose (2.2 mg kg(-1) body weight and 3.0 mg kg(-1), respectively). 2. Very low [(14)C] urine excretion was observed for both congeners (<1% of the dose), and cumulative biliary excretion was approximately 4% for BDE-99 and 9% for BDE-209. 3. More than 6% of the pooled urine from the BDE-99-treated rat was protein-bound to an 18-kDa protein characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western immunoblot analysis as alpha(2u)-globulin. Eighteen per cent of the radioactivity from the pooled urine from the BDE-209 treated rat was bound to albumin; no binding to alpha(2u)-globulin was detected. 4. In bile, 27-39% of the radioactivity from the BDE-99-dosed rat was bound to an unidentified 79-kDa protein, whereas essentially all (>87%) of the biliary radioactivity from BDE-209 was bound to the 79-kDa protein. Both parent BDE-99 and-209 and their metabolites were detected by thin layer chromatography in the extracted fraction of this bile protein. 5. By differential centrifugation, the subcellular localization of the (14)C derived from each congener in selected tissues was quantified. The cytosolic [(14)C] from livers of the BDE-209-treated rat was bound to a 14-kDa protein, which was characterized as a fatty acid-binding protein.

Comparative metabolism of the renal carcinogen 1,4-dichlorobenzene in rat: identification and quantitation of novel metabolites

1. The metabolism of 1,4-dichlorobenzene has been studied in the male and female Fisher 344 rat over 72 h after oral administration of 14C-1,4-dichlorobenzene (900 mg = 96.8 microCi/kg). No covalent binding of radioactivity could be detected in samples of liver, kidney, lung and spleen. The major route of excretion was with urine accounting for 41.3% of the dose for male and 37.8% of the dose for female rat within 72 h after dosing. 2. Urinary metabolites of 1,4-dichlorobenzene were identified and quantified. The major metabolites identified in the urine of both the male and female rat, were the sulphate and glucuronide of 2,5-dichlorophenol. Minor amounts of 2,5-dichlorohydroquinone were excreted as an unidentified conjugate. 3. 2-(N-acetyl-cysteine-S-yl)-1,4-dichlorobenzene and 2-(N-acetyl-cysteine-S-yl)-2,3-dihydro-3-hydroxy-1,3-hydroxy-1,4-dich lorobenzen e were minor metabolites excreted in the urine of both sexes. 4. A novel biotransformation pathway for 1,4-dichlorobenzene may be postulated, leading to the urinary excretion of a mercapturic acid of chlorophenol. 5. No marked differences in the distribution and excretion of metabolites of 1,4-dichlorobenzene were observed between the male and female Fisher 344 rat.

Differences in alpha 2u-globulins increased in male rat kidneys following treatment with several alpha 2u-globulin accumulating agents: cystein protease(s) play(s) an important role in production of kidney-type-alpha 2u-globulin

Effects of alpha 2u-globulin accumulating agents on alpha 2u-globulins in rat kidneys were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analysis. Treatment of male animals with decalin (150 mg/kg), 2,2,4-trimethylpentane (50 mg/kg), isophorone (150 mg/kg), d-limonene (150 mg/kg) or 1,4-dichlorobenzene (150 mg/kg) by gavage for 14 consecutive days in each case resulted in a marked intensification of a protein band corresponding to kidney-type-alpha 2u-globulin, with a molecular mass calculated to be approximately 16 kDa. However, intraperitoneal treatment with leupeptin and E-64 (two times 0.07 mmol/kg, for each), well known cystein protease inhibitors, while only slightly increasing this kidney-type-alpha 2u-globulin band, caused the intensification of a approximately 19-kDa molecular mass protein band which was revealed to be a native-type-alpha 2u-globulin by SDS-PAGE and immunoblotting. These results indicated that at least two types of alpha 2u-globulin can be increased in male rat kidney by chemical treatment. Moreover, cystein protease(s) appear(s) to play an important role in the degradation of alpha 2u-globulin and particularly in the conversion of native-type-alpha 2u-globulin to kidney-type-alpha 2u-globulin in rat kidneys.

Male rat specific nephrotoxicity resulting from subchronic administration of hexachlorobenzene

Male rats are more sensitive to the nephrocarcinogenic effect of hexachlorobenzene (HCB) than are female rats. The purpose of this study was to shed light on this phenomenon by investigating mechanisms of subchronic nephrotoxicity of HCB. Groups of rats were administered HCB in corn oil (po) at 100 mg/kg, 5 days per week for 15 days or at 50 mg/kg, 5 days per week for 50 days. Urine was collected on Days 1, 8, and 15 for the 15-day treatment and on Day 50 for the 50-day treatment. Glucosuria, proteinuria, and enzymuria (gamma-glutamyl transpeptidase) were measured to assess renal function. Twenty-four hours after the last HCB treatment, the animals were killed and kidneys were removed for histopathological evaluation. Urine analyses showed no indication of renal dysfunction in treated animals compared to controls during the 15-day treatment. However, histology of male rat kidneys revealed degenerative and regenerative cellular foci accompanied by an increased accumulation of protein droplets in epithelial cells of the proximal tubules. The same histological observations were also made in male rats after a 50-day HCB treatment but this time they were accompanied by renal function alterations. In female rats, no such renal functional or histological alterations were observed. The histopathological observations in male rats correspond well with the protein droplet nephropathy; the latter is characteristic of the accumulation in kidney cells of alpha 2u-globulin probably caused by the reversible binding of a chemical to alpha 2u that renders the protein indigestible to kidney proteases. alpha 2u-Globulin was measured in the cytosol of male rats and was found to be increased 11-fold compared to controls. Also, HCB was found to be bound reversibly to alpha 2u. These results suggest that HCB induces a male rat specific nephropathy that could explain the higher incidence of kidney tumors in male rats compared to female rats.

A methylsulfonyl metabolite of a polychlorinated biphenyl can serve as a ligand for liver fatty acid binding protein in rat intestinal mucosa

When a 100,000 x g supernatant from rat intestinal mucosa was incubated with 4,4'-bis([3H]methylsulfonyl)-2,2',5,5'-tetrachlorobiphenyl, [(CT3SO2)2TCB] a (CT3SO2)2TCB-protein complex was formed. The (CT3SO2)2TCB-protein complex was isolated and purified using gel filtration and ion-exchange chromatography. The protein portion of this complex was characterized to be liver fatty acid binding protein (L-FABP) by SDS-polyacrylamide gel electrophoresis and immunoblot analysis. No cross reactivity was observed in the immunoblot analysis between the purified protein and anti-heart or anti-intestinal fatty acid binding protein. (CT3SO2)2TCB was extractable from L-FABP and therefore not covalently bound to L-FABP.

A methylsulphonyl metabolite of a polychlorinated biphenyl can serve as a ligand for alpha 2mu-globulin in rat and major-urinary-protein in mice

1. Kidneys from rats given an intraperitoneal dose of 4,4'-bis[( 3H]methylsulphonyl)-2,2',5,5'- tetrachlorobiphenyl[(CT3SO2)2TCB)] contained (CT3SO2)2TCB associated with a protein which has been isolated and characterized by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblot and immunodiffusion analysis to be alpha 2 mu-globulin (alpha 2 mu). 2. The same radioactive alpha 2 mu-globulin complex was isolated from urine of rats given an i.p. dose of (CT3SO2)2TCB. This complex represented 12.3% (0.27% dose) and 9.3% (0.06% dose) of the radioactivity excreted in 0-24 h and 24-48 h urine, respectively. 3. The radioactivity was extractable from alpha 2 mu and characterized by t.l.c. (co-chromatography in two solvent systems) to be (CT3SO2)2TCB. 4. A radioactive-protein complex was isolated from urine of mice given an i.p. dose of (CT3SO2)2 TCB. The radioactive-protein complex was characterized to be mouse major urinary protein (MUP) by SDS-PAGE, immunoblot and immunodiffusion analysis. This complex was not detected in mouse kidney. 5. Urinary excretion of radioactive-MUP complex represented 51.7% (2.3% dose) and 28% (1.3% dose) of the radioactivity excreted in 0-24 h and 24-48 h urine, respectively.