2,2',3',4,4'5,5'-Hepatachlorobiphenyl (PCB 180)--on its toxicokinetics, biotransformation and porphyrinogenic action in female rats

PCBs enhance collagen I expression from human peritoneal fibroblasts

OBJECTIVE

To test the effect of four polychlorinated biphenyl congeners (PCB-77, PCB-105, PCB 153, and PCB 180) on expression of three adhesion markers (transforming growth factor [TGF] beta1, vascular endothelial growth factor [VEGF], and type I collagen) in normal human peritoneal and adhesion fibroblasts.

DESIGN

Cell culture study.

SETTINGS

University research laboratory.

PATIENT(S)

Primary cultures of normal peritoneal and adhesion fibroblasts were established from three patients.

INTERVENTION(S)

Fibroblasts were treated with PCB-77, PCB-105, PCB-153, or PCB-180 at 20 ppm for 24 hours. Total RNA was extracted from each treatment and subjected to real-time reverse transcriptase polymerase chain reaction (RT-PCR). MAIN OUTCOME AND MEASURE(S): The mRNA levels of type I collagen, VEGF, and TGF-beta1.

RESULT(S)

Normal human peritoneal fibroblasts expressed type I collagen, VEGF, and TGF-beta1. Exposure of normal human fibroblasts to PCB-77, PCB-105, PCB-153, or PCB-180 did not affect mRNA levels of beta-actin, the housekeeping gene used to normalized RNA levels for the real-time RT-PCR, nor did it affect cell viability as assessed by trypan blue exclusion. The PCB treatments, compared with control, resulted in no significant change for TGF-beta1 or VEGF mRNA levels in normal peritoneal and adhesion fibroblasts. In marked contrast, type I collagen mRNA levels were markedly increased in response to the brief 24 hours' exposure to each PCB treatment in both cell types.

CONCLUSION(S)

The finding that PCB-77, PCB-105, PCB-153, and PCB-180 increased the expression of type I collagen in human normal peritoneal and adhesion fibroblasts is the first demonstration of involvement of organochlorines in the pathogenesis of tissue fibrosis. This may implicate organochlorine exposure as an etiologic factor in a wide variety of previously unlinked human ailments characterized by fibrosis.

Polychlorinated biphenyl-77 induces adipocyte differentiation and proinflammatory adipokines and promotes obesity and atherosclerosis

BACKGROUND

Obesity, an inflammatory condition linked to cardiovascular disease, is associated with expansion of adipose tissue. Highly prevalent coplanar polychlorinated biphenyls (PCBs) such as 3,3',4,4'-tetrachlorobiphenyl (PCB-77) accumulate in adipose tissue because of their lipophilicity and increase with obesity. However, the effects of PCBs on adipocytes, obesity, and obesity-associated cardiovascular disease are unknown.

OBJECTIVES

In this study we examined in vitro and in vivo effects of PCB-77 on adipocyte differentiation, proinflammatory adipokines, adipocyte morphology, body weight, serum lipids, and atherosclerosis.

METHODS

PCB-77 or 2,2',4,4,5,5'-hexachlorobiphenyl (PCB-153) was incubated with 3T3-L1 adipocytes either during differentiation or in mature adipocytes. Concentration-dependent effects of PCB-77 were contrasted with those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). For in vivo studies, we treated C57BL/6 wild-type (WT) or aryl hydrocarbon receptor (AhR)(-/-) mice with vehicle or PCB-77 (49 mg/kg, by intraperitoneal injection) and examined body weight gain. In separate studies, we injected ApoE(-/-) mice with vehicle or PCB-77 over a 6-week period and examined body weight, adipocyte size, serum lipids, and atherosclerosis.

RESULTS

Low concentrations of PCB-77 or TCDD increased adipocyte differentiation, glycerol-3-phosphate dehydrogenase activity, and expression of peroxisome proliferator-activated receptor gamma, whereas higher concentrations inhibited adipocyte differentiation. Effects of PCB-77 were abolished by the AhR antagonist alpha-naphthoflavone. PCB-77 promoted the expression and release of various proinflammatory cytokines from 3T3-L1 adipocytes. Administration of PCB-77 increased body weight gain in WT but not AhR(-/-) mice. ApoE(-/-) mice injected with PCB-77 exhibited greater body weight, adipocyte hypertrophy, serum dyslipidemia, and augmented atherosclerosis.

CONCLUSIONS

Our findings suggest that PCB-77 may contribute to the development of obesity and obesity-associated atherosclerosis.

Liver preneoplastic changes in mice treated with the herbicide fomesafen

1. Effect of the diphenyl ether herbicide fomesafen on liver preneoplastic changes and porphyrin biosynthesis was examined in male C57BL/6J mice (0.23% in the diet for 14 months) and ICR mice (0.3% in the diet for 50 weeks). Fomesafen treatment resulted in preneoplastic changes (liver nodules and foci of altered hepatocytes) in both strains, uroporphyria developed only in ICR mice. 2. Iron pretreatment (600 mg/kg as a single dose) accelerated the development of fomesafen-induced preneoplastic changes in both mouse strains. The number of foci containing altered hepatocytes, as well as the number and size of liver nodules, were increased in iron-pretreated animals. 3. A single injection of iron induced marked uroporphyria in C57BL/6J mice after 14 months (liver porphyrin content 102 nmol/g). This uroporphyria was further potentiated by fomesafen administration (208 nmol/g). 4. In ICR mice, liver histology was apparently normal after a 3 month recovery from fomesafen treatment (0.32% for 9 months). Liver porphyrin content (260 nmol/g) started to decrease immediately after fomesafen withdrawal, but was still significantly elevated after 3 months (5 nmol/g), as compared to controls (1 nmol/g). 5. It is concluded that the toxicological evaluation of fomesafen should focus on liver porphyrin biosynthesis.

Congener-specific distribution of polychlorinated biphenyls in brain regions, blood, liver, and fat of adult rats following repeated exposure to Aroclor 1254

Our previous in vitro studies with both isolated organelles and primary neuronal cell cultures found that intracellular signal transduction can be perturbed by some noncoplanar PCBs at exposure levels of </=10 microM. However, it is not clear whether such concentrations are achievable in brain in vivo. Also, the pattern of congener disposition and quantities of the PCB accumulation in tissues of animals exposed to commercial PCB mixtures is not well studied. In the present study, we have conducted PCB congener-specific analysis in different brain regions, liver, blood, and fat of adult male Long-Evans rats dosed orally with Aroclor 1254 (0 or 30 mg/kg/day; once per day, 5 days/week for 4 weeks) in corn oil. Twenty-four hours after the last dose, rats were euthanized, and the brains were removed and dissected to obtain cerebellum, frontal cortex, and striatum. Liver, blood, and fat samples were also collected at the same time. Congener-specific analysis of PCBs was performed by high-resolution gas chromatography with electron capture detection. While PCB concentrations in control rat brain regions were less than 0.02 ppm, total PCB congeners in treated animals accumulated to much higher levels. Total levels in the frontal cortex, cerebellum, and striatum were 15.1 +/- 0.3, 13.1 +/- 1.7, and 8.2 +/- 2.6 ppm, respectively. The levels of PCBs in the fat, liver, and blood were 0.041, 0.002, and 0.001 ppm in control rats and 552, 38.3, and 1.6 ppm in treated rats, respectively. In addition to the differential total uptake between tissues, there was differential accumulation of PCBs with respect to the number of chlorines. In all the tissues, the more lightly chlorinated (tetra- and penta-) congeners accumulated less than their respective proportions in the parent Aroclor 1254 mixture. On the other hand, heavily chlorinated (hexa- to nona-) congeners accumulated more than the proportion of these congeners found in Aroclor 1254 mixture. This shift toward accumulation of heavily chlorinated congeners seems to be more pronounced in the brain than liver and fat. Predominant congeners (5-32% of total PCBs) detected in different brain regions, blood, liver, and fat are: 2,3,3',4',5,6- (no. 163) + 2,2',3,4,4',5- (no. 138) (coeluted); 2,2',4,4',5,5'- (no. 153) + 2, 2',3,3',4,6'- (no. 132) (coeluted); 2,3,3',4,4',5- (no. 156) + 2,2', 3,3',4,4',6- (no. 171) (coeluted); 2,3',4,4',5- (no. 118); 2,2',4,4', 5-(no. 99); and 2,3,3',4,4'- (no. 105). These congeners together accounted for about two thirds of the total PCB load in brain. All these predominant congeners are ortho-substituted and therefore are noncoplanar in nature. The total PCB concentrations accumulated in brain were as high as 50 microM (based on average molecular weight of 326.4 for Aroclor 1254) and, at these concentrations, intracellular second messengers were significantly affected in neuronal cultures and brain homogenate preparations in vitro. These results indicate that concentrations that altered Ca2+ disposition and second messenger systems in vitro are achievable in brain in vivo following repeated exposure.