Search

4-Vinylcyclohexene (VCH), an occupational chemical, causes destruction of small preantral follicles (F1) in mice. Previous studies suggested that VCH is bioactivated via cytochromes P450 (CYP450) to the ovotoxic, diepoxide metabolite, VCD. Whereas hepatic CYP450 isoforms 2E1, 2A, and 2B can metabolize VCH, the role of ovarian metabolism is unknown. This study investigated expression of these isoforms in isolated ovarian fractions (F1, 25-100 microm; F2, 100-250 microm; F3, >250 microm; interstitial cells, Int) from B6C3F1 mice dosed daily (15 days; ip) with vehicle, VCH (7.4 mmol/kg/day) or VCD (0.57 mmol/kg/day). Ovaries were removed and either isolated into specific ovarian compartments for mRNA analysis, fixed for immunohistochemistry, or prepared for enzymatic assays. mRNA and protein for all isoforms were expressed/distributed in all ovarian fractions from vehicle-treated mice. In the targeted F1 follicles, VCH or VCD dosing increased (p < 0.05) mRNA encoding CYP2E1 (645 +/- 14% VCH; 582 +/- 16% VCD), CYP2A (689 +/- 8% VCH; 730 +/- 22% VCD), and CYP2B (246 +/- 7% VCH) above control. VCH dosing altered (p < 0.05) mRNA encoding CYP2E1 in nontargeted F3 follicles (168 +/- 7%) and CYP2A in Int (207 +/- 19%) above control. Immunohistochemical analysis revealed the greatest staining intensity for all CYP isoforms in the Int. VCH dosing altered (p < 0.05) staining intensity in Int for CYP2E1 (19 +/- 2.4% below control) and CYP2A (39 +/- 5% above control). Staining intensity for CYP2B was increased (p < 0.05) above control in granulosa cells of small preantral (187 +/- 42%) and antral (63 +/- 8%) follicles. Catalytic assays in ovarian homogenates revealed that CYP2E1 and CYP2B were functional. Only CYP2E1 activity was increased (149 +/- 12% above control; p < 0.05) by VCH dosing. The results demonstrate that mRNA and protein for CYP isoforms known to bioactivate VCH are expressed in the mouse ovary and are modulated by in vivo exposure to VCH and VCD. Interestingly, there is high expression of these isoforms in the Int. Thus, the ovary may contribute to ovotoxicity by promoting bioactivation of VCH to the toxic metabolite, VCD.

Microsomal epoxide hydrolase (mEH) is involved in the detoxification of xenobiotics that are or can form epoxide metabolites, including the ovotoxicant, 4-vinylcyclohexene (VCH). This industrial chemical is bioactivated by hepatic CYP450 to the diepoxide metabolite, VCD, which destroys mouse small preantral follicles (F1). Since ovarian mEH may play a role in VCD detoxification, these studies investigated the expression and activity of mEH in isolated ovarian fractions. Mice were given 1 or 15 daily doses (ip) of VCH (7.4 mmol/kg/day) or VCD (0.57 mmol/kg/day); 4 h following the final dose, ovaries were removed, distinct populations of intact follicles (F1, 25-100 microm; F2, 100-250 microm; F3, > 250 microm) and interstitial cells (Int) were isolated, and total RNA and protein were extracted. Real-time polymerase chain reaction and the substrate cis-stilbene oxide (CSO; 12.5 microM) were used to evaluate expression and specific activity of mEH, respectively. Confocal microscopy evaluated ovarian distribution of mEH protein. Expression of mRNA encoding mEH was increased in F1 (410 +/- 5% VCH; 292 +/- 5% VCD) and F2 (1379 +/- 4% VCH; 381 +/- 11% VCD) follicles following repeated dosing with VCH or VCD. Catalytic activity of mEH increased in F1 follicles following repeated dosing with VCH/VCD (381 +/- 11% VCH; 384 +/- 27% VCD). Visualized by confocal microscopy, mEH protein was distributed throughout the ovary with the greatest staining intensity in the interstitial cells and staining in the theca cells that was increased by dosing (56 +/- 0.8% VCH; 29 +/- 0.9% VCD). We conclude that mEH is expressed and is functional in mouse ovarian follicles. Additionally,in vivo dosing with VCH and VCD affects these parameters.

A number of reports document that Fischer 344 (F344) rats are more susceptible to chemically induced liver injury than Sprague-Dawley (SD) rats. Cadmium (CdCl2), a hepatotoxicant that does not require bioactivation, was used to better define the biological events that are responsible for the differences in liver injury between F344 and SD rats. CdCl2 (3 mg/kg) produced hepatotoxicity in both rat strains, but the hepatic injury was 18-fold greater in F344 rats as assessed by plasma alanine aminotransferase (ALT) activity. This difference in toxicity was not observed when isolated hepatocytes were incubated with CdCl2 in vitro, indicating that other cell types contribute to Cd-induced hepatotoxicity in vivo. Indeed, the sieve plates of hepatic endothelial cells (EC) in F344 rats were damaged to a greater degree than EC in SD rats. Additionally, Kupffer cell (KC) inhibition reduced hepatotoxicity in both strains, suggesting that this cell type is involved in the progression of CdCl2-induced hepatotoxicity. Moreover, enhanced synthesis of heat shock protein 72 occurred earlier in the SD rat. Maximal levels of hepatic metallothionein (MT), a protein associated with cadmium tolerance, were greater in SD rats. These protective factors may limit CdCl2-induced hepatocellular injury in SD compared with F344 rats by reducing KC activation and the subsequent inflammatory response that allows for the progression of hepatic injury.

Repeated daily dosing of rats with the occupational chemical 4- vinylcyclohexene or its diepoxide metabolite (VCD) for 15 days destroys the smallest ovarian follicles. VCD acutely reduced hepatic levels of the antioxidant, glutathione (GSH); therefore, these studies were designed to evaluate whether GSH concentrations mediate VCD-induced ovotoxicity. Immature female Fischer 344 rats were dosed once or daily for 15 days with VCD (0.57 mmol/kg, ip) or the GSH synthesis inhibitor buthionine sulfoximine (BSO, 2 mmol/kg, ip). Animals were euthanized 2, 6, or 26 h following a single dose, and 2 or 26 h following 15 days of daily dosing. Reduced (p < 0.05) hepatic GSH was seen within 2 h of a single dose of either VCD (51 +/- 5% of control) or BSO (42 +/- 9%), but only BSO reduced ovarian GSH (71 +/- 5% at 6 h, p = 0.05) as measured by HPLC. Within 26 h, GSH levels had returned to control levels with either treatment. Hepatic GSH levels were reduced (< 0.05) 2 h after 15 daily doses with BSO (42 +/- 5%) or VCD (70 +/- 4%), but only BSO decreased ovarian GSH (64 +/- 3%). GSH levels in 15-day tissues were similar to controls 26 h after the final dose. Neither BSO nor VCD increased hepatic or ovarian concentrations of the oxidized dimer of GSH (GSSG) or thiobarbituric acid-reactive substances (TBARS), indicators of oxidative stress. These results suggest these treatments did not cause an oxidative stress. Histological counts of ovarian small follicle numbers were reduced (p < 0.05) in 15-day VCD-treated rats, whereas BSO did not affect follicle numbers, even though BSO reduced ovarian GSH content. These results support the conclusion that alterations in ovarian GSH levels are not involved in VCD-induced ovotoxicity.

1,2-Dichlorobenzene (1,2-DCB) is a potent hepatotoxicant in male Fischer 344 (F344) rats and previous studies have suggested that reactive oxygen species may play a role in the development of hepatotoxicity. Since reactive oxygen species can damage lipid membranes, this study was conducted to determine the extent of lipid peroxidation after administration of 1,2-DCB by immunohistochemical analysis of 4-hydroxynonenal (4-HNE) protein adduct formation in liver and conjugated diene formation in liver and serum. The contribution of Kupffer cells to the lipid peroxidation was also investigated. Male F344 rats were administered 1,2-DCB (3.6 mmol/kg ip in corn oil) and killed at selected times between 3 and 48 h. Time course studies revealed the greatest abundance of 4-HNE protein adducts in the centrilobular regions of the liver 24 h after 1,2-DCB administration, with much lower levels at 16 h. Adducts were present in necrotic and vacuolized centrilobular hepatocytes of 1,2-DCB treated rats but not in livers of controls. Further, conjugated dienes were significantly increased in liver and serum 16 and 24 h after 1,2-DCB administration, peaking at 24 h. These data correlated with hepatocellular injury, determined by serum alanine aminotransferase activity and histopathological evaluation, which was markedly elevated within 16 h and peaked at 24 h. When rats were pretreated with gadolinium chloride (GdCl 3 ; 10 mg/kg iv 24 h prior to 1,2-DCB), an inhibitor of Kupffer cells, hepatotoxicity was decreased by 89 and 86%, at 16 and 24 h, respectively. Conjugated diene concentrations were decreased to control values at these times after 1,2-DCB administration. Moreover, no 4-HNE protein adducts were detected in livers of 1,2-DCB-treated rats pretreated with GdCl 3 . Finally, Kupffer cells isolated from 1,2-DCB-treated rats produced significantly more superoxide anion than Kupffer cells isolated from vehicle controls. These data, along with previous findings, suggest that lipid peroxidation associated with 1,2-DCB is mediated in part by Kupffer cell-derived reactive oxygen species.

The Interactions between Retinol and Five Different Hepatotoxicants in the Swiss Webster Mouse. Rosengren, R. J., Sauer, J.-M., Hooser, S. B., and Sipes, I. G. (1995). Fundam. Appl. Toxicol. 25, 281-292. The interactive effects between retinol and various hepatotoxicants (allyl alcohol, acetaminophen, carbon tetrachloride, D-galactosamine, and phalloidin) were studied in the male Swiss Webster mouse. The mice were administered retinol at 75 mg/kg/day (or the vehicle of retinol) by oral gavage for 7 days. Hepatoxicity produced by the chemicals was determined by plasma alanine aminotransferase (ALT) activity and histopathology. After 7 days of retinol pretreatment, the hepatotoxicities of allyl alcohol, acetaminophen, and galactosamine were potentiated. Interestingly, the hepatotoxicity of carbon tetrachloride and phalloidin was protected by identical retinol pretreatment. Microscopic examination of histologic liver sections demonstrated the specific hepatic necrosis associated with each individual chemical and confirmed the ALT values obtained. Once an interaction between retinol and the five hepatotoxicants was established, the duration of retinol pretreatment necessary to elicit an interaction was determined for each hepatotoxicant. Results demonstrated that the duration of retinol pretreatment was specific for each hepatotoxicant. The accumulation of retinoids in the liver during retinol pretreatment was determined using high-performance liquid chromatography analysis. Significant increases in the basal liver levels of retinol and retinyl palmitate were seen within 1 to 3 days of retinol treatment compared to control. Retinol pretreatment resulted in potentiation or protection of specific hepatotoxicant-induced liver damage. Currently, studies are being conducted which probe into the mechanisms of these interactions.