Effects of tris(4-chlorophenyl)methanol on the rat following short-term oral exposure

Tris(4-chlorophenyl)methane and tris(4-chlorophenyl)methanol disrupt pancreatic organogenesis and gene expression in zebrafish embryos

OBJECTIVES

Tris(4-chlorophenyl) methane (TCPM) and tris(4-chlorophenyl)methanol (TCPMOH) are anthropogenic environmental contaminants believed to be manufacturing byproducts of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) due to environmental co-occurrence. TCPM and TCPMOH are persistent, bioaccumulate in the environment, and are detected in human breast milk and adipose tissues. DDT exposures have been previously shown to disrupt insulin signaling and glucoregulation, increasing risk for diabetes. We have previously shown that embryonic exposures organochlorines such as polychlorinated biphenyls disrupted pancreatic development and early embryonic glucoregulatory networks. Here, we determined the impacts of the similar compounds TCPM and TCPMOH on zebrafish pancreatic growth and gene expression following developmental exposures.

METHODS

Zebrafish embryos were exposed to 50 nM TCPM or TCPMOH beginning at 24 hr postfertilization (hpf) and exposures were refreshed daily. At 96 hpf, pancreatic growth and islet area were directly visualized in Tg(ptf1a::GFP) and Tg(insulin::GFP) embryos, respectively, using microscopy. Gene expression was assessed at 100 hpf with RNA sequencing.

RESULTS

Islet and total pancreas area were reduced by 20.8% and 13% in embryos exposed to 50 nM TCPMOH compared to controls. TCPM did not induce significant morphological changes to the developing pancreas, indicating TCPMOH, but not TCPM, impairs pancreatic development despite similarity in molecular responses. Transcriptomic responses to TCPM and TCPMOH were correlated (R²  = .903), and pathway analysis found downregulation of processes including retinol metabolism, circadian rhythm, and steroid biosynthesis.

CONCLUSION

Overall, our data suggest that TCPM and TCPMOH may be hazardous to embryonic growth and development.

Dose-dependent toxicological effects in rats following a 90-day dietary exposure to PCB-156 include retinoid disruption

The toxicity of PCB-156 (2,3,3',4,4',5-hexachlorobiphenyl) was investigated in rats following subchronic dietary exposure. Groups of 10 male and female Sprague-Dawley rats were administered PCB-156 in the diet at 0, 0.01, 0.1, 1 or 10 ppm for 90 days. Dose-dependent increases were detected for the liver, lung and kidney weights, as well as for the liver EROD, PROD and UDPGT enzyme activities and liver uroporphyrin concentration. Dose-dependent decreases were observed in final body weight, body weight gain, and thymus weight. Apolar retinoid concentrations were decreased in the liver and lungs and increased in the kidneys. Histopathological examination of the liver, thyroid, and thymus showed mild to moderate dose-related changes. A LOAEL of 0.01 ppm was established, based on reduced apolar liver retinoid concentration. Benchmark dose-modelling corroborated the sensitivity of liver retinoid endpoints. The lower confidence limits (BMDL) for a 5% decrease in apolar liver retinoid concentrations were 0.0009 and 0.0007 ppm, respectively, in males and females, corresponding to a daily dose of 0.06 μg PCB-156 per kg body weight. Organizing dose-response data for the individual hepatic endpoints along the PCB-156 dosing scale revealed a sequence of events compatible with a causal link between depletion of apolar retinoids and the other liver biochemistry and pathology findings. Taken together, data suggest that the retinoid endpoints should be further evaluated for a causal relationship to PCB-induced liver toxicity and that retinoid system endpoints are identified and characterized to support health risk assessment in the emerging research fields of endocrine disruption and mixture toxicology.

The ecotoxicological contaminant tris(4-chlorophenyl)methanol (TCPMOH) impacts embryonic development in zebrafish (Danio rerio)

Tris(4-chlorophenyl)methanol (TCPMOH) is a water contaminant with unknown etiology, but is believed to be a byproduct of DDT manufacturing. It is highly persistent in the environment, and bioaccumulates in marine species. TCPMOH has also been measured in human breast milk, which poses a risk for developing infants. However, almost no toxicity data is currently available. In this study, we investigate the hazard posed by developmental TCPMOH exposures using the zebrafish model (Danio rerio). Zebrafish (Danio rerio) embryos were exposed to 0, 0.1, 0.5, 1, or 5 µM TCPMOH beginning at 24 h post fertilization (hpf). Embryonic mortality and incidence of morphological deformities increased in a concentration-dependent manner with TCPMOH exposure. RNA sequencing assessed changes in gene expression associated with acute (4 hour) exposures to 50 nM TCPMOH. Developmental exposure to TCPMOH decreased expression of ahr2, as well as metabolic enzymes cyp1a1, cyp1b1, cyp1c1, cyp1c2, and cyp2y3 (p<0.05). These findings were concordant with decreased Cyp1a1 induction measured by the ethoxyresorufin-O-deethylase (EROD) assay (p<0.05). Pathways associated with xenobiotic metabolism, lipid metabolism, and transcriptional and translational regulation were decreased. Pathways involved in DNA replication and repair, carbohydrate metabolism, and endocrine function were upregulated. Overall, this study demonstrates that TCPMOH is acutely toxic to zebrafish embryos at elevated concentrations.

Disposition of tris(4-chlorophenyl)methanol and tris(4-chlorophenyl)methane in male and female Harlan Sprague Dawley rats and B6C3F1/N mice following oral and intravenous administration

Tris(4-chlorophenyl)methane (TCPME) and tris(4-chlorophenyl)methanol (TCPMOH) have been detected in various biota and human tissues. The current studies were undertaken to investigate the disposition and metabolism of TCPME and TCPMOH in rats and mice. [¹⁴C]TCPME was well absorbed (≥66%) in male rats and mice following a single oral administration of 1, 10, or 100 mg/kg. The excretion of [¹⁴C]TCPME-derived radioactivity in urine (≤2.5%) and feces (≤18%) was low. The administered dose was retained in tissues (≥ 64%) with adipose containing the highest concentrations. The metabolism of TCPME was minimal. The disposition and metabolism of [¹⁴C]TCPME in females was similar to males. The time to reach maximum concentration was ≤7 h, the plasma elimination half-life was ≥31 h, and the bioavailability was ≥82% following a 10 mg/kg oral dose of [¹⁴C]TCPME in male rats and mice. The disposition of [¹⁴C]TCPMOH was similar to that of [¹⁴C]TCPME. Following an intravenous administration of [¹⁴C]TCPME or [¹⁴C]TCPMOH in male rats and mice, the pattern of disposition was similar to that of oral administration. In conclusion, both TCPME and TCPMOH are readily absorbed and highly bioavailable following a single oral administration pointing to importance of assessing the toxicity of these chemicals.

Interaction between tris(4-chlorophenyl)methanol and the human androgen receptor in vitro

The interaction between tris(4-chlorophenyl)methanol (TCPM), an environmental contaminant of uncertain origin, and the human androgen receptor was examined in vitro using a previously characterized human androgen receptor reporter gene assay in which PC-3 LUC(AR+) cells respond to 5alpha-dihydrotestosterone (DHT) with enhanced luciferase activity. In two preliminary studies, TCPM (1 microM) had no effect on androgen receptor activation in the absence of DHT (50 pM), but DHT-mediated activation of the androgen receptor was decreased more than 90% by TCPM at 1 microM. This was not due to an effect of TCPM on cell viability since, with TCPM concentrations of 0.1 and 1.0 microM, cell viability was 111 and 102%, respectively, but at 10 microM TCPM, cell viability was reduced to 60% compared with controls. For kinetic studies of the effects of TCPM on androgen receptor activation, DHT was added at 0, 5, 25, 50, 75, 100, 250 and 500 pM and the TCPM concentrations used were 0, 1, 10, 100, 300 and 1000 nM. This range incorporated the levels of TCPM in human adipose tissue, where concentrations up to 55 nM (20 ng/g lipid) have been measured. TCPM increased the value of the K(m(app)) of the androgen receptor for DHT 4-6-fold with little or no effect on the V(max(app)). Slope and intercept replots revealed that TCPM inhibited the DHT-mediated activation of the androgen receptor in a competitive manner with K(i(app)) values of 0.26, 0.26 and 0.20 microM compared with respective K(m(app)) values of 9.8, 3.1 and 3.9 pM. Thus, TCPM is a competitive antagonist of human androgen receptor activation and the value of the K(i(app)) indicates that TCPM would be approximately 10-50 times more potent as an inhibitor than the previously identified androgen receptor antagonists p,p'-DDE and vinclozilin and also, the K(i(app)) values (200-260 nM) are very close to the concentration of TCPM found in the adipose tissue of some humans (55 nM).

Influence of tris(4-chlorophenyl)methanol (TCPM) on gap junction-mediated intercellular communication of cultured bovine granulosa cells

Tris(4-chlorophenyl)methanol (TCPM) is a by-product in the manufacture of technical grade DDT, which is known to alter properties and functions of the female reproductive system. We investigated whether in vitro TCPM has an influence on the function of gap junction-mediated intercellular communication (GJIC) and gap junction protein expression of connexin 43 (Cx43) in cultured bovine granulosa cells. GJIC was assessed by fluorescent dye microinjection (dye-coupling). After a 1-h exposure to TCPM at a concentration of 32 microM, a significant (P<0.05) reduction in dye coupling occurred. The same result was obtained with o,p'-DDT. At a concentration of 32 microM both pesticides were cytotoxic as indicated by significant (P<0.05) increased propidium iodide staining of the cell nuclei. Little or no effect on the stainable pattern of connexons occurred after 1 h incubation time, while after 3 h treatment from 16 to 64 microM TCPM, a significant inhibition in the immunostaining resulted and the concentrations of 32 and 64 microM TCPM were cytotoxic for the granulosa cells. The freeze-fracture electron microscopy resulted in small differences in the morphology of gap junction plaques of cell cultures treated for 3 h with 8 or 16 microM TCPM in comparison to untreated cells. After treatment with 32 microM TCPM, gap junction plaques were very rarely detected and the lateral intramembraneous particles (IMP) distribution of many plasma membranes was strongly altered. Estimation of the cellular parameters may lead to an enhanced understanding of the mechanism of chemically induced toxicity by TCPM, that causes a general toxic effect on granulosa cells. We can conclude that TCPM is a toxic risk in the same manner as DDT.

Tris (4-chlorophenyl) methane and tris (4-chlorophenyl) methanol in marine mammals from the Estuary and Gulf of St. Lawrence

Levels of tris (4-chlorophenyl) methanol (TCPM) and its presumed precursor tris (4-chlorophenyl) methane (TCPMe) are reported in marine mammals from the Estuary and Gulf of St. Lawrence, Canada. These compounds were measured in blubber samples of seals and whales using ion trap mass spectrometry (MS/MS) detection. Detectable concentrations of both TCPM and TCPMe were observed in all of the samples analysed. Concentrations of these compounds varied with species ranging from 1.7 to 153 and from 1.3 to 50.6 ng/g lipid wt. for TCPM and TCPMe, respectively. TCPM was from 1.3 to 10 times more concentrated than TCPMe. The highest levels of both TCPM and TCPMe were observed in adult male beluga whales (Delphinapterus leucas) from the St. Lawrence Estuary, while adult female beluga whales from the same area showed levels similar to those in the seals examined. Among the four seal species investigated, TCPM and TCPMe levels were the highest in grey (Halichoerus grypus) and hooded (Cystophora cristata) seals, and lowest in harp seals (Phoca groenlandica). Intermediate levels were found in harbour seals (Phoca vitulina); however, their concentrations might be underestimated considering the younger mean age of these animals. Ratios of both 4,4'-DDE/sigma DDT and TCPM/sigma TCP were very similar between animals from the same species. Strong correlations between sigma TCP and sigma DDT were also observed for each species of mammals, most likely indicating that both sigma TCP and sigma DDT are bioaccumulated in marine mammals. The relationships between sigma DDT and sigma TCP also demonstrate that sigma TCP are less bioaccumulated than sigma DDT by the marine mammal species examined.

Widespread contamination by tris(4-chlorophenyl)methane and tris(4-chlorophenyl)methanol in cetaceans from the North Pacific and Asian coastal waters

For understanding global distribution, transport and behavior of tris(4-chlorophenyl)methane (TCPMe) and tris(4-chlorophenyl)methanol (TCPMOH), the two newly identified microcontaminants, the present study determined their concentrations and other persistent organochlorines (OCs) in the blubber of nine species of adult male cetaceans collected from various locations in the North Pacific Ocean and coastal waters of some Asian countries, during 1985-97. Concentrations of TCPMe and TCPMOH were found to be highest in northern right whale dolphins, which may be attributable to wide distribution of this species, including some heavily polluted areas such as coastal California. Elevated residue levels of TCPMe and TCPMOH were observed in both off-shore and coastal species, suggesting widespread contamination of these compounds in the marine environment. Higher contamination of TCPMe and TCPMOH was found in cetaceans from temperate and cold waters than those from tropical regions. The latitudinal distribution of TCPMe and TCPMOH in cetaceans from the North Pacific and Asian coastal waters was similar to that of DDTs, suggesting less transportable nature of TCPMe and TCPMOH in the marine environment. Data on the occurrence of TCPMe and TCPMOH further indicated high bioaccumulation potential of these compounds, which was comparable to DDTs. Relative concentrations of TCPMe/TCPMOH in cetaceans were apparently higher than those observed in seals, suggestive of lower metabolic capacity for these compounds in cetaceans than in pinnipeds, which is similar to classic contaminants like polychlorinated biphenyls and DDTs.

Reproductive effects of tris(4-chlorophenyl)methanol in the rat

Tris(4-chlorophenyl)methanol (TCPM) is a global contaminant of unknown origin that is structurally related to the endocrine modulating pesticides 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and Dicofol. Therefore, the potential reproductive toxic effects of TCPM were investigated in sexually mature male Sprague Dawley rats (n = 20) treated with 1.0, 10.0 or 100 ppm of TCPM mixed in the diet for 28 days. The calculated TCPM intake was 0.0, 0.1, 1.2 and 12.4 mg/kg/day, respectively. Serum concentrations of follicle stimulating hormone (FSH) in terminal blood samples were significantly (P < 0.02) elevated in the highest dose group compared to the controls. In contrast, dietary exposure to TCPM had no effect on circulating levels of luteinizing hormone (LH), testosterone (T) and the T/LH ratio. Incubation of MCF-7 cells with increasing concentrations of TCPM failed to either induce proliferation or to block the proliferative effect induced by estradiol indicating that TCPM is neither estrogenic or anti-estrogenic. Relative binding affinity studies using androgen receptors from the prostate revealed that TCPM has a binding affinity comparable to 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), the principle metabolite of DDT. In addition, the calculated Ki (0.62 microM) for TCPM is lower than the reported Ki's for the antiandrogenic pesticides p,p'-DDE and vinclozolin. Although TCPM binds with the androgen receptor in vitro, the absence of both an effect on serum T levels and morphological changes in the testis suggests that the mechanism of action for elevated FSH levels seen in vivo may not involve an antiandrogenic effect of TCPM at the dose level used in this study. The no adverse effect level for reproductive effects of TCPM is 10 ppm which is equivalent to a calculated intake of 1.2 mg/kg/day.

Effects of four organohalogen environmental contaminants on cytochrome P450 forms that catalyze 4- and 2-hydroxylation of estradiol in the rat liver

The four environmental pollutants studied (3,3',4,4',5-pentachlorobiphenyl, 2,2',4,4'-tetrabromodiphenyl ether, Tris-(p-chlorophenyl)methanol, and 3,4,5-trichloroguaiacol) were all found to induce a significant increase in 4-hydroxylation of estradiol activity in male rat liver microsomes. However, only 3,3',4,4',5-pentachlorobiphenyl was found to significantly increase 4- and 2-hydroxylation of estradiol in female rat liver microsomes. 4-Hydroxylation has been suggested to be responsible for the development of estrogen-dependent tumors and, therefore, it cannot be excluded that these pollutants can be a risk for the development of estrogen-dependent tumors in humans and wildlife.