ABSTRACT
Male rat fetuses exposed to certain phthalate esters (PEs) during sexual differentiation display reproductive tract malformations due to reductions in testosterone (T) production and the expression of steroidogenesis- and INSL3-related genes. In the current study, we used a 96-well real-time PCR array containing key target genes representing sexual determination and differentiation, steroidogenesis, gubernaculum development, and androgen signaling pathways to rank the relative potency of several PEs. We executed dose-response studies with diisobutyl (DIBP), dipentyl (DPeP), dihexyl (DHP), diheptyl (DHeP), diisononyl (DINP), or diisodecyl phthalate (DIDP) and serial dilutions of a mixture of nine phthalates. All phthalates, with the exception of DIDP, reduced fetal testicular T production. Several genes involved in cholesterol transport, androgen synthesis, and Insl3 also were downregulated in a dose-responsive manner by DIBP, DPeP, DHP, DHeP, DINP, and the 9-PE mixture. Despite speculation of peroxisome proliferator activated receptor (PPAR) involvement in the effects of PEs on the fetal testis, no PPAR-related genes were affected in the fetal testes by exposure to any of the tested PEs. Furthermore, the potent PPARα agonist, Wy-14,643, did not reduce fetal testicular T production following gestational day 14-18 exposure, suggesting that the antiandrogenic activity of PEs is not PPARα mediated. The overall sensitivity of the fetal endpoints (gene expression or T production) for the six phthalates from most to least was Cyp11b1 > Star = Scarb1 > Cyp17a1 = T production > Cyp11a1 = Hsd3b = Insl3 > Cyp11b2. The overall potency of the individual phthalates was DPeP > DHP > DIBP ≥ DHeP > DINP. Finally, the observed mixture interaction was adequately modeled by the dose-addition model for most of the affected genes. Together, these data advance our understanding of the collective reproductive toxicity of the PE compounds.
Subject(s)
Developmental Biology/methods , Gene Expression Regulation, Developmental/genetics , Genetic Markers , Phthalic Acids/toxicity , Real-Time Polymerase Chain Reaction , Reproduction/drug effects , Testis/drug effects , Toxicity Tests/methods , Animals , Dose-Response Relationship, Drug , Female , Gestational Age , Male , Maternal Exposure , Models, Theoretical , Pregnancy , Rats , Rats, Sprague-Dawley , Reproduction/genetics , Risk Assessment , Testis/embryology , Testis/metabolism , Testosterone/metabolism , Tissue Culture TechniquesABSTRACT
3,4,4'-Trichlorocarbanilide (triclocarban, TCC) is widely used as an antimicrobial agent in a variety of consumer and personal care products. TCC is considered a potential endocrine disruptor, but its potential toxic effects in humans are still largely unknown. Because of its widespread uses, the potential for human exposure to TCC is high. In order to identify adequate exposure biomarkers of TCC, we investigated the metabolic profile of TCC in adult female Sprague Dawley rats after administering TCC once (500 mg/kg body weight) by oral gavage. Urine was collected 0-24 h before dosing, and 0-24 h and 24-48 h after dosing. Serum was collected at necropsy 48 h after dosing. We identified several metabolites of TCC in urine and serum by on-line solid phase extraction-high performance liquid chromatography-mass spectrometry. We unambiguously identified two major oxidative metabolites of TCC, 3'-hydroxy-TCC and 2'-hydroxy-TCC, by comparing their chromatographic behavior and mass spectral fragmentation patterns with those of authentic standards. By contrast, compared to these oxidative metabolites, we detected very low levels of TCC in the urine or serum. Taken together these data suggest that in rats, oxidation of TCC is a major metabolic pathway. We also measured TCC and its oxidative metabolites in 50 urine and 16 serum samples collected from adults in the United States. The results suggest differences in the metabolic profile of TCC in rats and in humans; oxidation appears to be a minor metabolic pathway in humans. Total (free plus conjugated) TCC could serve as a potential biomarker for human exposure to TCC.
Subject(s)
Anti-Infective Agents, Local/metabolism , Carbanilides/metabolism , Environmental Exposure/adverse effects , Water Pollutants, Chemical/metabolism , Animals , Anti-Infective Agents, Local/blood , Anti-Infective Agents, Local/urine , Biomarkers/blood , Biomarkers/urine , Carbanilides/blood , Carbanilides/urine , Chromatography, High Pressure Liquid , Female , Humans , Mass Spectrometry , Oxidation-Reduction , Rats , Rats, Sprague-Dawley , Solid Phase Extraction , Species Specificity , Time Factors , Water Pollutants, Chemical/blood , Water Pollutants, Chemical/urineABSTRACT
Commercial di-isononyl phthalate (DiNP) is a mixture of various branched-chain dialkyl phthalates mainly containing nine-carbon alkyl isomers. At high doses in rodents, DiNP is a carcinogen, and a developmental toxicant. After exposure, the diester isomers are de-esterified to form hydrolytic monoesters, monoisononyl phthalates (MiNP), which subsequently metabolize to form oxidative metabolites. These metabolites can be excreted in urine or feces. The urinary excretion of DiNP metabolites was monitored in adult female Sprague-Dawley rats after oral administration of a single dose (300 mg/kg) of commercial DiNP. The metabolites were extracted from urine, resolved with high performance liquid chromatography, analyzed by mass spectrometry, and tentatively identified based on their chromatographic separation and mass spectrometric fragmentation pattern. Because DiNP is an isomeric mixture, its metabolites were also isomeric mixtures that eluted from the HPLC column with close retention times. Mono(carboxy-isooctyl)phthalate (MCiOP) was identified as the major metabolite of DiNP; in addition, mono(hydroxy-isononyl)phthalate (MHiNP) and mono(oxo-isononyl)phthalate (MOiNP) were present. Furthermore, metabolites of di-isooctyl phthalate (DiOP) and di-isodecyl phthalate (DiDP) were also detected. Excretion toxicokinetics of the DiNP metabolites in urine followed a biphasic pattern with initial rapid decay in concentration. Despite potential differences in the metabolism of DiNP among species, MCiOP, MHiNP and MOiNP were detected in humans with no known exposure to DiNP at levels significantly higher than MiNP suggesting that these oxidative metabolites may be better urinary biomarkers of human exposure to DiNP than is MiNP.
Subject(s)
Phthalic Acids/urine , Administration, Oral , Animals , Biomarkers/chemistry , Biomarkers/urine , Female , Humans , Inactivation, Metabolic , Molecular Structure , Phthalic Acids/chemistry , Rats , Rats, Sprague-Dawley , Reproducibility of Results , Sensitivity and Specificity , Spectrometry, Mass, Electrospray IonizationABSTRACT
Di-n-octyl phthalate (DnOP) is a plasticizer used in polyvinyl chloride plastics, cellulose esters, and polystyrene resins. The metabolism of DnOP results in the hydrolysis of one ester linkage to produce mono-n-octyl phthalate (MnOP), which subsequently metabolizes to form oxidative metabolites. We investigated the toxicokinetics of DnOP in adult female Sprague-Dawley rats by monitoring the excretion of DnOP metabolites in urine after oral administration of DnOP (300 mg/kg). By using authentic standards, the presence of urinary phthalic acid (PA), MnOP, and the major DnOP metabolite, mono-(3-carboxypropyl) phthalate (MCPP) was clearly established. Furthermore, we identified five additional urinary DnOP oxidative metabolites based on their chromatographic behavior and mass spectrometric fragmentation pattern. These DnOP oxidative metabolites, are postulated to be mono-carboxymethyl phthalate (MCMP), mono-(5-carboxy-n-pentyl) phthalate (MCPeP), mono-(7-carboxy-n-heptyl) phthalate (MCHpP), and isomers of mono-hydroxy-n-octyl phthalate (MHOP) (e.g., mono-(7-hydroxy-n-octyl) phthalate) and of mono-oxo-n-octyl phthalate (MOOP) (e.g., mono-(7-oxo-n-octyl) phthalate). The urinary excretion of DnOP metabolites followed a biphasic excretion pattern. The metabolite levels decreased significantly after the first day of DnOP administration although MCPP, MCHpP, MHOP, and MOOP were detectable after 4 days. We also studied the in vitro metabolism of DnOP and MnOP by rat liver microsomes. DnOP produced MnOP, MHOP, and PA in vitro whereas, MnOP produced MHOP and PA in vitro at detectable levels.