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

On the tear proteome of the house mouse (Mus musculus musculus) in relation to chemical signalling

Mammalian tears are produced by lacrimal glands to protect eyes and may function in chemical communication and immunity. Recent studies on the house mouse chemical signalling revealed that major urinary proteins (MUPs) are not individually unique in Mus musculus musculus. This fact stimulated us to look for other sexually dimorphic proteins that may—in combination with MUPs—contribute to a pool of chemical signals in tears. MUPs and other lipocalins including odorant binding proteins (OBPs) have the capacity to selectively transport volatile organic compounds (VOCs) in their eight-stranded beta barrel, thus we have generated the tear proteome of the house mouse to detect a wider pool of proteins that may be involved in chemical signalling. We have detected significant male-biased (7.8%) and female-biased (7%) proteins in tears. Those proteins that showed the most elevated sexual dimorphisms were highly expressed and belong to MUP, OBP, ESP (i.e., exocrine gland-secreted peptides), and SCGB/ABP (i.e., secretoglobin) families. Thus, tears may have the potential to elicit sex-specific signals in combination by different proteins. Some tear lipocalins are not sexually dimorphic—with MUP20/darcin and OBP6 being good examples—and because all proteins may flow with tears through nasolacrimal ducts to nasal and oral cavities we suggest that their roles are wider than originally thought. Also, we have also detected several sexually dimorphic bactericidal proteins, thus further supporting an idea that males and females may have adopted alternative strategies in controlling microbiota thus yielding different VOC profiles.

Novel roles for AhR and ARNT in the regulation of alcohol dehydrogenases in human hepatic cells

The mechanisms by which pollutants participate in the development of diverse pathologies are not completely understood. The pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) activates the AhR (aryl hydrocarbon receptor) signaling pathway. We previously showed that TCDD (25 nM, 30 h) decreased the expression of several alcohol metabolism enzymes (cytochrome P450 2E1, alcohol dehydrogenases ADH1, 4 and 6) in differentiated human hepatic cells (HepaRG). Here, we show that, as rapidly as 8 h after treatment (25 nM TCDD) ADH expression decreased 40 % (p < 0.05). ADH1 and 4 protein levels decreased 40 and 27 %, respectively (p < 0.05), after 72 h (25 nM TCDD). The protein half-lives were not modified by TCDD which suggests transcriptional regulation of expression. The AhR antagonist CH-223191 or AhR siRNA reduced the inhibitory effect of 25 nM TCDD on ADH1A, 4 and 6 expression 50-100 % (p < 0.05). The genomic pathway (via the AhR/ARNT complex) and not the non-genomic pathway involving c-SRC mediated these effects. Other AhR ligands (3-methylcholanthrene and PCB 126) decreased ADH1B, 4 and 6 mRNAs by more than 78 and 55 %, respectively (p < 0.01). TCDD also regulated the expression of ADH4 in the HepG2 human hepatic cell line, in primary human hepatocytes and in C57BL/6J mouse liver. In conclusion, activation of the AhR/ARNT signaling pathway by AhR ligands represents a novel mechanism for regulating the expression of ADHs. These effects may be implicated in the toxicity of AhR ligands as well as in the alteration of ethanol or retinol metabolism and may be associated further with higher risk of liver diseases or/and alcohol abuse disorders.

Are MUPs a Toxic Waste Disposal System?

Male house mice produce large quantities of major urinary proteins (MUPs), which function to bind and transport volatile pheromones, though they may also function as scavengers that bind and excrete toxic compounds (‘toxic waste hypothesis’). In this study, we demonstrate the presence of an industrial chemical, 2,4-di-tert-butylphenol (DTBP), in the urine of wild-derived house mice (Mus musculus musculus). Addition of guanidine hydrochloride to male and female urine resulted in an increased release of DTBP. This increase was only observed in the high molecular weight fractions (HMWF; > 3 kDa) separated from male or female urine, suggesting that the increased release of DTBP was likely due to the denaturation of MUPs and the subsequent release of MUP-bound DTBP. Furthermore, when DTBP was added to a HMWF isolated from male urine, an increase in 2-sec-butyl-4,5-dihydrothiazole (SBT), the major ligand of MUPs and a male-specific pheromone, was observed, indicating that DTBP was bound to MUPs and displaced SBT. These results suggest that DTBP is a MUP ligand. Moreover, we found evidence for competitive ligand binding between DTBP and SBT, suggesting that males potentially face a tradeoff between eliminating toxic wastes versus transporting pheromones. Our findings support the hypothesis that MUPs bind and eliminate toxic wastes, which may provide the most important fitness benefits of excreting large quantities of these proteins.

Comparative Metabolism Studies of Hexabromocyclododecane (HBCD) Diastereomers in Male Rats Following a Single Oral Dose

Male Sprague-Dawley rats were dosed orally with 3 mg/kg of one of three hexabromocyclododecane (HBCD) diastereomers. Each diastereomer was well absorbed (73-83%), and distributed preferentially to lipophilic tissues. Feces were the major route of excretion; cumulatively accounting for 42% of dose for α-HBCD, 59% for ß-HBCD, and 53% for γ-HBCD. Urine was also an important route of HBCD excretion, accounting for 13% of dose for α-HBCD, 30% for ß-HBCD, and 21% for γ-HBCD. Total metabolism of HBCD diastereomers followed the rank order ß > γ > α, and was >65% of that administered. The metabolites formed were distinct in male rats: α-HBCD did not debrominate or stereoisomerize, but formed two hydroxylated metabolites; ß- and γ-HBCD were both extensively metabolized via pathways of stereoisomerization, oxidation, dehydrogenation, reductive debromination, and ring opening. ß-HBCD was biotransformed to two mercapturic acid pathway metabolites. The metabolites of ß- and γ-HBCD were largely distinct, and could possibly be used as markers of exposure. These isomer-specific data suggest that α-HBCD would be the most dominant HBCD diastereomer in biological tissues because it was metabolized to the lowest degree and also accumulated from the stereoisomerization of the β- and γ- diastereomers.

Proposed mechanistic description of dose-dependent BDE-47 urinary elimination in mice using a physiologically based pharmacokinetic model

Polybrominated diphenyl ethers (PBDEs) have been used in a wide variety of consumer applications as additive flame retardants. In North America, scientists have noted continuing increases in the levels of PBDE congeners measured in human serum. Some recent studies have found that PBDEs are associated with adverse health effects in humans, in experimental animals, and wildlife. This laboratory previously demonstrated that urinary elimination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is saturable at high doses in mice; however, this dose-dependent urinary elimination has not been observed in adult rats or immature mice. Thus, the primary objective of this study was to examine the mechanism of urinary elimination of BDE-47 in adult mice using a physiologically based pharmacokinetic (PBPK) model. To support this objective, additional laboratory data were collected to evaluate the predictions of the PBPK model using novel information from adult multi-drug resistance 1a/b knockout mice. Using the PBPK model, the roles of mouse major urinary protein (a blood protein carrier) and P-glycoprotein (an apical membrane transporter in proximal tubule cells in the kidneys, brain, intestines, and liver) were investigated in BDE-47 elimination. The resulting model and new data supported the major role of m-MUP in excretion of BDE-47 in the urine of adult mice, and a lesser role of P-gp as a transporter of BDE-47 in mice. This work expands the knowledge of BDE-47 kinetics between species and provides information for determining the relevancy of these data for human risk assessment purposes.

Novel and distinct metabolites identified following a single oral dose of α- or γ-hexabromocyclododecane in mice

The metabolism of α- and γ-hexabromocyclododecane (HBCD) was investigated in adult C57BL/6 female mice. α- or γ-[(14)C]HBCD (3 mg/kg bw) was orally administered with subsequent urine and feces collection for 4 consecutive days; a separate group of mice was dosed and sacrificed 3 h postexposure to investigate tissue metabolite levels. Extractable and nonextractable HBCD metabolites were quantitated in liver, blood, fat, brain, bile, urine, and feces and characterized by LC/MS (ESI-). Metabolites identified were distinct between the two stereoisomers. In mice exposed to α-HBCD, four hydroxylated metabolites were detected in fecal extracts, and one of these metabolite isomers was consistently characterized in liver, brain, and adipose tissue extracts. In contrast, fecal extracts from mice exposed to γ-HBCD contained multiple isomers of monohydroxy-pentabromocyclododecene, dihydroxy-pentabromocyclododecene, and dihydroxy-pentabromocyclododecadiene, while in liver and adipose tissues extracts only a single monohydroxy-pentabromocyclododecane metabolite was observed. Both stereoisomers were transformed to metabolites which formed covalent bonds to proteins and/or lipids in the gut as suggested by high fecal nonextractables. The presence of tissue- and excreta-specific metabolic products after in vivo exposure to the two main HBCD stereoisomers supports previous toxicokinetic studies indicating that these two stereoisomers are biologically distinct. The distinct metabolic products identified in this study have the potential to aid in the identification of stereoisomer-specific HBCD exposures in future biomonitoring studies.

Alteration of mouse urinary odor by ingestion of the xenobiotic monoterpene citronellal

Body odors provide a rich source of sensory information for other animals. There is considerable evidence to suggest that short-term fluctuations in body odor can be caused by diet; however, few, if any, previous studies have demonstrated that specific compounds can directly mask or alter mouse urinary odor when ingested and thus alter another animal's behavior. To investigate whether the ingestion of citronellal, a monoterpene aldehyde that produces an intense aroma detected by both humans and mice, can alter mouse urinary odor, mice (C57BL6J) were trained in a Y maze to discriminate between the urinary odors of male donor mice that had ingested either citronellal in aqueous solution or a control solution. Trained mice could discriminate between urinary odors from the citronellal ingestion and control groups. A series of generalization tests revealed that citronellal ingestion directly altered mouse urinary odor. Moreover, trained mice that had successfully discriminated between urinary odors from donor mice of different ages failed to detect age-related changes in urine from male mice that had ingested 50 ppm of citronellal. This study is the first to show that ingestion of a xenobiotic can alter mouse urinary odor and confuse the behavioral responses of trained mice to age-related scents.

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.

Tissue disposition, excretion and metabolism of 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100) in male Sprague–Dawley rats

The absorption, disposition, metabolism and excretion study of orally administered 2,2',4,4',6-pentabromodiphenyl ether (BDE-100) was studied in conventional and bile-duct cannulated male rats. In conventional rats, >70% of the radiolabelled oral dose was retained at 72 h, and lipophilic tissues were the preferred sites for disposition, i.e. adipose tissue, gastrointestinal tract, skin, liver and lungs. Urinary excretion of BDE-100 was very low (0.1% of the dose). Biliary excretion of BDE-100 was slightly greater than that observed in urine, i.e. 1.7% at 72 h, and glucuronidation of phenolic metabolites was suggested. Thiol metabolites were not observed in the bile as had been reported in other PBDE metabolism studies. Almost 20% of the dose in conventional male rats and over 26% in bile-duct cannulated rats was excreted in the faeces, mainly as the unmetabolized parent, although large amounts of non-extractable radiolabel were also observed. Extractable metabolites in faeces were characterized by mass spectrometry. Monohydroxylated pentabromodiphenyl ether metabolites were detected; mono- and di-hydroxylated metabolites with accompanying oxidative debromination were also observed as faecal metabolites. Tissue residues of [(14)C]BDE-100 in liver, gastrointestinal tract and adipose tissue contained only parent material. The majority of the 0-72-h biliary radioactivity was associated with an unidentified 79-kDa protein or to albumin.

Structural basis of pheromone binding to mouse major urinary protein (MUP-I)

The mouse major urinary proteins are pheromone-binding proteins that function as carriers of volatile effectors of mouse physiology and behavior. Crystal structures of recombinant mouse major urinary protein-I (MUP-I) complexed with the synthetic pheromones, 2-sec-butyl-4,5-dihydrothiazole and 6-hydroxy-6-methyl-3-heptanone, have been determined at high resolution. The purification of MUP-I from mouse liver and a high-resolution structure of the natural isolate are also reported. These results show the binding of 6-hydroxy-6-methyl-3-heptanone to MUP-I, unambiguously define ligand orientations for two pheromones within the MUP-I binding site, and suggest how different chemical classes of pheromones can be accommodated within the MUP-I beta-barrel.

beta-Naphthoflavone- and self-induced metabolism of 3,3',4,4'-tetrachlorobiphenyl in hepatic microsomes of the male, pregnant female and foetal rat

1. The in vitro metabolism of 3,3',4,4'-tetrachloro-[14C]-biphenyl ([14C]-TCB) by hepatic microsomes from the Wistar rat was investigated with liver microsomes from the male, pregnant female and foetus. 2. Three hydroxylated metabolites (4-OH-3,3',4,5'-tetrachlorobiphenyl, 5-OH-3,3',4,4'-tetrachlorobiphenyl, and 6-OH-3,3',4,4'-tetrachlorobiphenyl) were identified by hplc and gc-ms after incubations of liver microsomes from the beta-naphthoflavone-pretreated male rat and TCB-treated pregnant rat. No metabolites of [14C]-TCB were found after incubation with foetal liver microsomes from dams pretreated with [14C]-TCB. The results indicate that the in vivo accumulation of 4-OH-tetraCB in the foetal compartment is probably due to transplacental transport rather than the formation of this metabolite in the foetus. 3. Pretreatment of the male rat with beta-naphthoflavone substantially induced the formation of hydroxylated metabolites, but pretreatment with phenobarbital and dexamethasone was without effect. Based on in vitro incubations of liver microsomes from the beta-naphthoflavone pretreated male rat, an apparent Km and Vmax of 4.5 microM and 240 pmol/mg protein/min respectively was determined for the metabolism of [14C]-TCB. The formation of phenolic metabolites of [14C]-TCB was most likely dependent on P4501A induction.

Biochemical basis for mouse resistance to hyaline droplet nephropathy: Lack of relevance of the α2u-globulin protein superfamily in this male rat-specific syndrome

It is well-established that binding of a chemical to alpha 2u-globulin is the rate-limiting step in the development of male rat-specific hyaline droplet nephropathy. Mice synthesize mouse urinary protein (MUP), a protein which is very similar to alpha 2u-globulin, but this protein does not render the mouse sensitive to a similar renal toxicity. Therefore, the purpose of the present study was to determine the biochemical basis for mouse resistance to hyaline droplet nephropathy. Male Fischer 344 rats and B6C3F1 mice excreted 12.24 +/- 0.60 and 14.88 +/- 0.99 mg of alpha 2u-globulin and MUP daily, indicating that quantitative differences in protein excretion were not involved in the species specificity of the nephropathy. With d-limonene as a model hyaline droplet inducing agent, both rat and mouse liver microsomes oxidized the terpene to its 1,2-epoxide (the metabolite that binds reversibly to alpha 2u-globulin in vivo), demonstrating that metabolic differences do not determine the mouse resistance to this lesion. In spite of the formation of the epoxide intermediate, no binding of [14C]d-limonene equivalents to mouse kidney proteins was observed. In contrast, about 40% of the d-limonene equivalents in male rat kidney was reversibly bound to renal proteins. The renal reabsorption of alpha 2u-globulin and MUP was markedly different, as rats reabsorbed about 60% of the total filtered load of alpha 2u-globulin, but MUP was not reabsorbed by the mouse kidney. Given the absence of MUP in mouse kidney, in vitro equilibrium saturation binding studies were also conducted to determine whether MUP could bind the epoxide metabolite. alpha 2u-Globulin bound [14C]d-limonene-1,2-oxide with an apparent Kd of 4 x 10(-7) M. However, under identical experimental conditions, MUP failed to bind the epoxide. These data indicate that two major biochemical differences between alpha 2u-globulin and MUP contribute to mouse resistance to hyaline droplet nephropathy. Under both in vivo and in vitro conditions, MUP does not bind d-limonene-1,2-oxide, the rate-limiting step in the development of the nephropathy. However, even if MUP did bind the epoxide, the fact that it is not reabsorbed into the mouse kidney precludes its involvement in a syndrome involving renal protein overload. Finally, the absence of an interaction between d-limonene, a model hyaline droplet inducer, and the protein most similar to alpha 2u-globulin suggests that no other protein in the alpha 2u-globulin superfamily is likely to cause hyaline droplet nephropathy in other species.

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.