4,4'-Methylenebis(2-chloroaniline) (MOCA): The Effect of Multiple Oral Administration, Route, and Phenobarbital Induction on Macromolecular Adduct Formation in the Rat

The effect of multiple oral administration of MOCA, a suspecthuman carcinogen, was studied in the adult male rat. As manyas 28 consecutive daily doses of [¹⁴C]MOCA at 28.1µmol/kgbody wt (5 µC1/day) were administered and rats were euthanizedat weekly intervals for 7 weeks. MOCA adduct formation for globinand serum albumin was evaluated by determination of [¹⁴C]MOCAcovalent binding. The covalent binding associated with globinshowed a linear increase over the 28-day exposure period with342 fmol/mg globin 24 hr after the final dose. More extensivecovalent binding was detected for albumin with 443 fmol/mg albuminafter the final dose, but increases were not linear. After cessationof dosing, the albumin adduct levels decreased rapidly (t _1/2=4.6 days) in relation to globin adduct levels (t _1/2 =16.1days). The MOCA-globin adduct t _1/2 is consistent with thatdetermined after a single 281 µmol/kg oral dose of MOCA.Significant differences related to route of administration weredetected for 24-hr globin covalent binding with ip > po >dermal. Distribution of undifferentiated [¹⁴C]MOCA was highestin the liver at 24 hr with tissue levels for liver > kidney> lung > spleen > testes > urinary bladder. Inductionof cytochrome P450 enzymes by administration of phenobarbital(100 mg/kg/day/3 days) resulted in a significant (p < 0.05)increase in MOCA-globin adduct formation detected with 33.5pmol/ mg globin for induced rats versus 13.6 pmol/mg globinfor control rats. Although MOCA-globin and albumin adducts showdiffering stability, quantification of such MOCA adducts maybe useful for long-term industrial biomonitoring of MOCA.     

Pulmonary Toxicity of Cytostatic Drugs: Cell Kinetics

Pulmonary Toxicity of Cytostatic Drugs: Cell Kinetics. WITSCHI,H., GODFREY, G., FROME, E., and LINDENSCHMIDT, R. C. (1987).Fundam. Appl. Toxicol. 8, 253–262. Mice were treated withthree cytostatic drugs: cyclophosphamide, busulfan, or l,3-bis(2-chloroethyl)-l-nitro-sourea(BCNU). The alveolar labeling index was measured following drugadministration with a pulse of ³H-labeled thymidine and autoradiography.In cyclophosphamide-treated animals, peak alveolar cell proliferationwas seen 5 days after injection of the drug. In animals treatedwith busulfan or BCNU, proliferation was even more delayed (occurring2–3 weeks after administration). In contrast, with oleicacid, the highest alveolar cell labeling was found 2 days afterintravenous administration. In animals exposed to a cytostaticdrug, proliferation of type II alveolar cells was never a prominentfeature whereas in animals treated with oleic acid there wasan initial burst of type II cell proliferation. It is concludedthat the patterns of pulmonary repair vary between chemicalsdesigned to interfere with DNA replication as compared to agentswhich produce acute lung damage such as oleic acid.     

4,4'-Methylene-bis(2-chloroaniline) (MOCA): Comparison of Macromolecular Adduct Formation after Oral or Dermal Administration in the Rat

4,4'-Methylene-bis(2-chloroaniline) (MOCA): Comparison of MacromolecularAdduct Formation after Oral or Dermal Administration in theRat. CHEEVER, K. L., RICHARDS, D. E., WEIGEL, W. W., BEGLEY,K. B., DEBORD, D. G., SWEARENGIN, T. F., AND SAVAGE, R. E. JR.(1990). Fundam. Appl. Toxicol. 14, 273–283. The macromolecularbinding of 4,4'-methylene-bis(2-chloroaniline) (MOCA), a suspecthuman carcinogen, was studied in the adult male Sprague-Dawleyrat after both oral and dermal administration. Rats were euthanized1, 3, 7, 10, 14, and 29 days after a single 281 µmol/kgbody wt dose of [¹⁴C]MOCA (oral, 213 µCi/kg; dermal, 904µCi/kg). DNA from various tissues and hemoglobin wereisolated for determination of the time course of MOCA macromolecularbinding. After oral administration adduct formation was rapidwith maximum levels appearing at 24 hr. The 24-hr covalent bindingassociated with the globin was 7.84 pmol/mgglobin (t? = 14.3days). More extensive 24-hr covalent binding was detected forliver DNA with 49.11 pmol/mg DNA (t? = 11.1 days). After dermaladministration of MOCA the major portion of the dose, 86.2%,remained at the application site throughout the study. For theserats the 24-hr covalent binding determined for liver DNA was0.38 pmol/mg DNA (t? = 15.6 days). Although lower levels weredetected after dermal application, similar stability of MOCA-DNAadducts indicates that quantification of such MOCA adducls maybe useful for the long-term industrial biomonitoring of MOCAexposure and for the evaluation of human DNA-MOCA adduct formation,a lesion thought to be associated with the production of cancer.     

Determination of 4,4'-Methylene-bis(2-chloroaniline)-DNA Adduct Formation in Rat Liver and Human Uroepithelial Cells by the 32P Postlabeling Assay

The probable human carcinogen 4,4'-methylene-bis(2-chloroaniline)(MOCA) was utilized to develop biomarkers of exposure to occupationalcarcinogens. The ³²P postlabeling assay, utilizing the nucleaseP1 enhancement procedure, was used to evaluate MOCA-DNA adductformation in target tissues. Male Sprague-Dawley rats were treatedwith different dosing regimens of MOCA, and DNA was isolatedfrom the liver. Additionally, a human uroepithelial cell (HUC)line was treated with N-hydroxy MOCA for 24 hr, cells were harvested,and DNA was isolated. DNA was analyzed for MOCA-DNA adduct formationby the ³²P postlabeling assay. Five MOCA adducts were detectedin rat liver DNA. Adduct A, which corresponded to N-(deoxyadenosin-8-yl)-4-amino-3-chlorobenzylalcohol, was the major adduct in rat liver DNA appearing inall treatment groups. Levels of adduct A were higher when MOCAwas administered by ip injection versus oral gavage. Phenobarbitalpretreatment increased the amount of adduct A approximately12-fold. The pathway leading to the formation of adduct A inDNA from HUC appeared to be saturated at the concentrationsused: 2.5, 5, and 10 µM. However, an additional adduct(E) was observed at the 10 µM treatment level only. Amajor DNA adduct was detected in the target tissue of rats andtarget human cells for MOCA-induced carcinogenesis, thus makingit useful as a biomarker of exposure. Other DNA adducts werealso observed with the different doses and routes of exposureinvestigated.     

Comparison of the Enhancing Effects of Dehydroepiandrosterone with the Structural Analog 16{alpha}-Fluoro-5-androsten-17-one on Aflatoxin B1 Hepatocarcinogenesis in Rainbow Trout

Dehydroepiandrosterone (DHEA) is an adrenal steroid with chemoprotectiveeffects against a wide variety of conditions including cancer,obesity, diabetes, and cardiovascular disease. However, DHEAis also a carcinogen in laboratory animals, possibly throughits function as a precursor of sex steroids or peroxisome proliferation.The structural analog 16-fluoro-5-androsten-17-one (8354) hasbeen reported to have enhanced chemopreventive activity withoutthe steroid precursor and peroxisome proliferating effects ofDHEA. This study compares DHEA and 8354 in rainbow trout, aspecies that is resistant to peroxisome proliferation but ishighly susceptible to the carcinogenic and tumor enhancing effectsof DHEA. Trout were exposed as fry to aflatoxin B₁ (AFB₁) orgiven a sham exposure, then were fed diets containing 444 ppmDHEA or 8354 for 6 months. Postinitiation treatment with DHEAsignificantly increased liver tumor incidence, multiplicity,and size compared to initiated controls. The analog 8354 slightlyincreased tumor incidence (p=0.06) but had no effect on multiplicityor size. Six percent of trout treated with DHEA alone developedtumors, whereas no tumors occurred in noninitiated trout fedcontrol or 8354-containing diets. Serum levels of androstenedionewere elevated by DHEA (48-fold) or 8354 (6-fold) treatment Serumß-estradiol titers were increased in DHEA-but not8354-treated trout. Vitellogenin was induced significantly byeither DHEA (434-fold) or 8354 (21-fold). Peroxisomal ß-oxidationwas not increased by either compound and catalase activity wasdecreased in DHEA-treated animals. Both steroids were potentinhibitors in vitro of trout liver glucose-6-phosphate dehydrogenasewith IC50s of 24 and 0.5 µM for DHEA and 8354, respectively.