Assessment of unscheduled and replicative DNA synthesis in hepatocytes treated in vivo and in vitro with unleaded gasoline or 2,2,4-trimethylpentane

Hazardous air pollutants and primary liver cancer in Texas

The incidence of hepatocellular carcinoma (HCC), the most common primary liver cancer, is increasing in the US and tripled during the past two decades. The reasons for such phenomenon remain poorly understood. Texas is among continental states with the highest incidence of liver cancer with an annual increment of 5.7%. Established risk factors for HCC include Hepatitis B and C (HBV, HCV) viral infection, alcohol, tobacco and suspected risk factors include obesity and diabetes. While distribution of these risk factors in the state of Texas is similar to the national data and homogeneous, the incidence of HCC in this state is exceptionally higher than the national average and appears to be dishomogeneous in various areas of the state suggesting that other non-recognized risk factors might play a role. No population-based studies are currently available investigating the effect of exposure to Hazardous Air Pollutants (HAPs) as a contributing risk factor for liver cancer. Incidence rate of liver cancer in Texas by counties for the time period between 2002 and 2012 was obtained from the Texas Cancer Registry (TCR). Through Principal Component Analysis (PCA) a subgroup of pollutants, explaining almost all the dataset variability, were identified and used to cluster Texas counties. The analysis generated 4 clusters showing liver cancer rate either higher or lower than national average in association with either high or low levels of HAPs emission in the environment. The study shows that the selected relevant HAPs, 10 among 253 analyzed, produce a significant correlation (P = 0.01–0.05) and some of these have been previously identified as carcinogens. An association between the increased production and consequent exposure to these HAPs and a higher presence of liver cancer in certain counties is suggested. This study provides a new insight on this complex multifactorial disease suggesting that environmental substances might play a role in the etiology of this cancer.

Safety assessment of isoparaffins as used in cosmetics

The safety of isoparaffins as used in cosmetic products is reviewed in this safety assessment. These ingredients function mostly as solvents and also function as emollients in the 0001% to 90% concentration range. The Cosmetic Ingredient Review (CIR) Expert Panel has reviewed relevant animal and clinical data and concluded that these ingredients are safe in the present practices of use and concentration described in this safety assessment.

Lack of effect of furfural on unscheduled DNA synthesis in the in vivo rat and mouse hepatocyte DNA repair assays and in precision-cut human liver slices

The ability of furfural to induce unscheduled DNA synthesis (UDS) in hepatocytes of male and female B6C3F(1) mice and male F344 rats after in vivo administration and in vitro in precision-cut human liver slices has been studied. Preliminary toxicity studies established the maximum tolerated dose (MTD) of furfural to be 320 and 50 mg/kg in the mouse and rat, respectively. Furfural was dosed by gavage at levels of 0 (control), 50, 175 and 320 mg/kg to male and female mice and 0, 5, 16.7 and 50 mg/kg to male rats. Hepatocytes were isolated by liver perfusion either 2-4 h or 12-16 h after treatment, cultured in medium containing [3H]thymidine for 4 h and assessed for UDS by grain counting of autoradiographs. Furfural treatment did not produce any statistically significant increase or any dose-related effects on UDS in mouse and rat hepatocytes either 2-4 h or 12-16 h after dosing. In contrast, UDS was markedly induced in mice and rats 2-4 h after treatment with 20 mg/kg dimethylnitrosamine and 12-16 h after treatment of mice and rats with 200 mg/kg o-aminoazotoluene and 50 mg/kg 2-acetylaminofluorene (2-AAF), respectively. Precision-cut human liver slices from four donors were cultured for 24 h in medium containing [3H]thymidine and 0-10 mM furfural. Small increases in the net grain count (i.e. nuclear grain count less mean cytoplasmic grain count) observed with 2-10 mM furfural were not due to any increase in the nuclear grain count. Rather, it was the result of concentration-dependent decreases in the mean cytoplasmic grain counts and to a lesser extent in nuclear grain counts, due to furfural-induced cytotoxicity. In contrast, marked increases in UDS (both net grain and nuclear grain counts) were observed in human liver slices treated with 0.02 and 0.05 mM 2-AAF, 0.002 and 0.02 mM aflatoxin B(1) and 0.005 and 0.05 mM 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. This study demonstrates that furfural does not induce UDS in the hepatocytes of male and female B6C3F(1) mice and male F344 rats after oral treatment at doses up to the MTDs. Moreover, human liver slice studies suggest that furfural is also not a genotoxic agent in human liver.

Assessment in rats of the reproductive toxicity of gasoline from a gasoline vapor recovery unit

Gasoline (CAS 86290-81-5) is one of the world's largest volume commercial products. Although numerous toxicology studies have been conducted, the potential for reproductive toxicity has not been directly assessed. Accordingly, a two-generation reproductive toxicity study in rats was conducted to provide base data for hazard assessment and risk characterization. The test material, vapor recovery unit gasoline (68514-15-8), is the volatile fraction of formulated gasoline and the material with which humans are most likely to come in contact. The study was of standard design. Exposures were by inhalation at target concentrations of 5000, 10 000, and 20 000 mg/m(3). The highest exposure concentration was approximately 50% of the lower explosive limit and several orders of magnitude above anticipated exposure during refueling. There were no treatment-related clinical or systemic effects in the parental animals, and no microscopic changes other than hyaline droplet nephropathy in the kidneys of the male rats. None of the reproductive parameters were affected, and there were no deleterious effects on offspring survival and growth. The potential for endocrine modulation was also assessed by analysis of sperm count and quality as well as time to onset of developmental landmarks. No toxicologically important differences were found. Therefore, the NOAEL for reproductive toxicity in this study was > or =20 000 mg/m(3). The only systemic effects, in the kidneys of the male rats, were consistent with an alpha-2 u-globulin-mediated process. This is a male rat-specific effect and not relevant to human health risk assessment.

Lack of effect of coumarin on unscheduled DNA synthesis in the in vivo rat hepatocyte DNA repair assay

The ability of coumarin to induce UDS in male Sprague-Dawley CD rat hepatocytes in vivo was assessed using the unscheduled DNA synthesis (UDS) assay. From a preliminary toxicity study the oral maximum tolerated dose (MTD) of coumarin was determined to be 320 mg/kg body weight. For the UDS studies, rats were treated with 0 (corn oil control), 32 (one-tenth the MTD), 107 (one-third the MTD) and 320 (MTD) mg/kg coumarin via oral gavage. Rats were also treated with 20mg/kg body weight dimethylnitrosamine (DMN) or 50mg/kg body weight 2-acetylaminofluorene (2-AAF) as positive controls for the 2-4 hr and 12-16 hr expression of UDS, respectively. Hepatocytes were isolated by liver perfusion either 2-4 hr or 12-16 hr after treatment and cultured in medium containing [methyl-(3)H]thymidine for 4 hr and assessed for UDS by grain counting of autoradiographs. Coumarin treatment at doses of 32-320 mg/kg body weight had no statistically significant or dose-related effect on UDS in rat hepatocytes either 2-4 hr or 12-16 hr after dosing. In contrast, both DMN 2-4 hr after dosing and 2-AAF 12-16 hr after dosing produced significant increases in UDS assessed as the net nuclear grain count. Both genotoxins also increased the percentage of hepatocyte nuclei with greater than 5 net grains. Treatment with coumarin, DMN and 2-AAF had no statistically significant effect on the proportion of rat hepatocytes undergoing replicative DNA synthesis. In summary, this study demonstrates that coumarin does not induce UDS in hepatocytes of male Sprague-Dawley CD rats after oral administration at doses up to the MTD of 320 mg/kg. The responsiveness of the animals used in this study to genotoxic agents was demonstrated by the clear induction of DNA repair after treatment with DMN and 2-AAF.

Lack of effect of coumarin on unscheduled DNA synthesis in precision-cut human liver slices

In this study the effect of coumarin on unscheduled DNA synthesis (UDS) in precision-cut human liver slices has been examined. Liver slices from tissue samples from four donors were cultured for 24 hr in medium containing [3H]thymidine and 0-5.0 mM coumarin using a dynamic organ culture system and processed for autoradiographic evaluation of UDS. As positive controls liver slices were also cultured with three known genotoxic agents, namely 0.02 and 0.05 mM 2-acetylaminofluorene (2-AAF), 0.002 and 0.02 mM aflatoxin B1 (AFB1) and 0.005 and 0.05 mM 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP). UDS was quantified as the net grain count in centrilobular hepatocytes and as the percentage of centrilobular hepatocyte nuclei with more than five net grains. Compared with control liver slice cultures, treatment with 0.05-5.0 mM coumarin had no effect on UDS. In contrast, treatment with 0.02 and 0.05 mM 2-AAF, 0.002 and 0.02 mM AFB1 and 0.005 and 0.05 mM PhIP produced significant increases in the net grain counts of centrilobular hepatocytes. The greatest induction of UDS was observed in liver slices treated with 0.05 mM PhIP. Treatment with 2-AAF, AFB1 and PhIP also produced significant increases in the number of centrilobular hepatocyte nuclei with more than five net grains. At the concentrations examined neither coumarin. 2-AAF, AFB1 nor PhIP had any significant effect on replicative DNA synthesis in 24 hr cultured human liver slices. These results demonstrate that coumarin does not induce UDS in cultured human liver slices. However, all three positive control compounds produced marked significant increases in UDS, thus confirming the functional viability of the human liver slice preparations used in this study. The results of this study suggest that coumarin is not a genotoxic agent in human liver.

Identification of hepatic mitogenic and cytochrome P-450-inducing fractions of unleaded gasoline in B6C3F1 mice

Unleaded gasoline (UG), a complex mixture of over 300 hydrocarbons, induced liver tumors selectively in female mice and exhibited liver tumor promoting activity. UG also induced cell proliferation and cytochrome P-450-related enzyme activities in mouse liver, properties commonly associated with liver tumor promoters. To determine if the mitogenic and/or cytochrome P-450-inducing properties of UG reside in individual fractions of UG, UG was separated into four fractions on the basis of boiling point (BP): fraction 1, BP < 66 degrees C; fraction 2, 66 degrees C < BP < 100 degrees C; fraction 3, 100 degrees C < BP < 132 degrees C; fraction 4, BP > 132 degrees C. Fractions 1 and 2 were combined to form "light UG" (BP < 100 degrees C), and fractions 3 and 4 were combined to form "heavy UG" (BP > 100 degrees C). Female B6C3F1 mice were implanted with osmotic pumps containing 5-bromo-2'-deoxyuridine (BrdU) on d 1, treated by intragastric intubation with corn oil or 3000 mg/kg/d of light, heavy, or whole UG on d 2-4, and euthanized on d 5. Pentoxyresorufin O-dealkylase (PROD) and ethoxyresorufin O-deethylase (EROD) activities were assayed in hepatic microsomes, and hepatocyte BrdU labeling index (LI) was determined in liver sections. Whole UG and heavy UG caused comparable increases in hepatic PROD and EROD activities and the hepatocyte LI. Light UG caused relatively small increases in hepatic PROD and EROD activities and did not increase the hepatocyte LI. When fractions 3 and 4 were tested separately in the above treatment protocol, both fractions strongly induced hepatic PROD and weakly induced hepatic EROD activities. However, only fraction 3 increased the hepatocyte LI. To isolate mitogenic components in fraction 3, equimolar doses of individual chemicals in fraction 3 were tested in the above treatment protocol. Toluene did not increase the hepatocyte LI, whereas 2,2,3-trimethylpentane (TMP), 2,2,4-TMP, and 2,3,4-TMP all dramatically increased the hepatocyte LI. Thus, while the hepatic cytochrome P-450-inducing activity of UG was concentrated in components of UG with BPs > 100 degrees C, this activity apparently resides in UG components with a wide range of BPs. The mitogenic activity of UG, in contrast, was highly concentrated in components of UG with BPs ranging from approximately 100 to 132 degrees C, and quite possibly in specific TMPs.

Use of precision-cut liver slices for studies of unscheduled DNA synthesis

Precision-cut liver slices were prepared from untreated and Aroclor 1254 (ARO)-treated male Sprague-Dawley rats with a Krumdieck tissue slicer. Liver slices were cultured for 24 hr in medium containing [3H]thymidine and 0-0.1 mM 2-acetylaminofluorene (2-AAF) using a dynamic organ culture system and processed for autoradiographic evaluation of unscheduled DNA synthesis (UDS). Compared with control (i.e. 0 mM 2-AAF) liver slice cultures, 2-AAF produced a concentration-dependent increase in UDS, the effect being more marked in liver slices from ARO-treated than from untreated rats. With liver slices from untreated rats, 2-AAF produced the greatest increase in UDS in centrilobular hepatocytes. 2-AAF-induced UDS in liver slices from ARO-treated rats was most marked in centrilobular hepatocytes but the effect also extended to other areas of the liver lobule. These results demonstrate that precision-cut liver slices may be a valuable alternative in vitro system to hepatocyte cultures for screening chemicals for potential genotoxicity. Unlike hepatocyte cultures, liver slices permit the study of zonal differences in UDS. Moreover, this technique could be applied to other tissues and the study of species differences in response.

Recommendations for the performance of UDS tests in vitro and in vivo

The Working Group (WG) dealt with the harmonization of routine methodologies of tests for unscheduled DNA synthesis (UDS) both in vitro and in vivo. In contrast to the existing guidelines from OECD, EPA and EC on in vitro UDS tests (there is no Japanese UDS guideline), the Working Group recommends that in general in vitro UDS tests should be performed with primary hepatocytes. For routine applications any other cell types would need special justification. Hepatocytes from male rats are preferable, unless there are contra-indications on the basis of e.g. toxicokinetic data. According to the OECD, EPA and EC guidelines, UDS may be analysed by means of autoradiography (AR) or liquid scintillation counting (LSC). The WG recommends use of AR. LSC is less suitable due to the problem of differentiation between UDS activity and replicative DNA synthesis, and the disadvantage that cells cannot be analysed individually. Since a specific cell type was recommended by the WG, methodological aspects could be described in more detail than in the present guidelines. For in vitro tests, it was agreed that the initial viability of freshly isolated hepatocytes should be at least 70%. With regard to the need for confirmatory experiments in the event of a clear-cut negative result, the majority view was that confirmation by a second (normally not identical) experiment is still needed; this is in line with the present OECD and EC guidelines. Evaluation of results from UDS tests should be based primarily on net nuclear grain (NNG) values, although it is recognised that nuclear and cytoplasmic grains result from different biological processes. Since grain counts are influenced by a number of methodological parameters, no global threshold NNG value can be recommended for discrimination of positive and negative UDS results. For in vitro assays, the criteria for positive findings go beyond those of the present guidelines and two alternative approaches are given which are based on (1) dose-dependent increases in NNG values and (2) reproducibility, dose-effect relationship and cytotoxicity. At present there is no official guideline on the performance of in vivo UDS tests. Some fundamental recommendations given for in vitro methodology also apply to the in vivo assay. For routine testing with the in vivo UDS test, again the general use of hepatocytes from male rats is recommended. However, concerning the requirement to use one or two sexes, consistency with other in vivo genotoxicity assays (e.g. the micronucleus assay) would be preferable. As for the in vitro methodology, AR is preferred rather than LSC.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatocyte cell proliferation in mice after inhalation exposure to unleaded gasoline vapor

Chronic inhalation exposure to unleaded gasoline (UG) induced an increase in liver tumors in female but not male mice. Unleaded gasoline exhibits little, if any, genotoxic activity in vitro or in vivo in the female mouse liver, suggesting that other biological effects such as the induction of cell turnover or altered growth control may play a role in this carcinogenic process. To better understand the role of UG-induced hepatocyte proliferation with respect to the dose- and sex-specific tumor response, male and female B6C3F1 mice were housed in 1-m3 single-pass flow-through inhalation chambers and administered UG under exposure conditions that produced tumors in the chronic studies. Mice were exposed to targeted concentrations of 67, 292, or 2056 ppm PS-6 blend of UG vapor 6 h/d, 5 d/wk, for up to 13 wk. Liver weights were elevated significantly in male and female mice exposed to 2056 ppm UG at wk, 1, 3, 6, and 13. No elevation in liver-specific serum enzymes was noted in treated animals, nor were there any significant histopathological changes in the liver, indicating a lack of overt hepatotoxicity. Hepatocyte proliferation, expressed as nuclear labeling index (Ll), was measured immunohistochemically after 5-bromo-2'-deoxyuridine administration via an osmotic minipump implanted three days before the animals were killed. A 6-to 10-fold increase in Ll compared to controls was observed in male and female mice exposed to 2056 ppm UG at wk 1, with a return to control levels at wk 3, 6, and 13. Mice exposed to 67 or 292 ppm UG did not show any increase in Ll. The mode by which an agent induces cell proliferation is an important consideration in mechanistic studies and the risk assessment process. These data indicate an early transient mitogenic stimulation of cell proliferation, rather than regeneration secondary to cytotoxicity, in the livers of UG-treated mice. The observed proliferative response after UG exposure in the male mouse in the absence of a tumorigenic response suggests that effects in addition to the early transient hepatocyte proliferation response are critical in understanding the sex-specific hepatocarcinogenic response of this complex mixture.

In vivo-in vitro replicative DNA synthesis (RDS) test using perfused rat livers as an early prediction assay for nongenotoxic hepatocarcinogens: I. Establishment of a standard protocol

To establish a standard protocol for an in vivo-in vitro hepatocyte replicative DNA synthesis (RDS) test using male F344 rats for screening nongenotoxic (the Ames-negative) hepatocarcinogens, experimental conditions were examined. After treatment with three model hepatocarcinogens, isolated hepatocytes showed highest RDS incidences when plated at a density of 5 x 10(4) cells/ml. Spontaneous RDS incidences in hepatocytes from rats aged 9 weeks or older showed a constant value. The use of hepatocytes from 9-week-old rats at the 5 x 10(4) cells/ml plating density was therefore determined as the standard. Based on the distribution of mean spontaneous RDS incidences over 105 additional experiments (0.4 +/- 0.18%, with SEM), an RDS incidence of over 1% was adopted as the criterion for a positive response in our rat liver RDS test.

Induction by cyproterone acetate of DNA synthesis and mitosis in primary cultures of adult rat hepatocytes in serum free medium

The aim of this study was to elucidate whether serum-free conditions could be found in primary hepatocyte cultures under which the growth inducing properties of xenobiotics and hormones could be tested. Cyproterone acetate (CPA), a steroid with anti-androgenic and progestogenic activity, was chosen as a model compound because of its known strong mitogenic properties in rat liver in vivo. EGF served as a positive control. Induction of DNA synthesis was studied by [3H]-thymidine labeling and autoradiography. Mitoses were counted in hematoxylin stained specimens. The main steps which led to an efficient stimulation of DNA synthesis by CPA were (i) reduction of hormone concentrations to levels approaching (approx. 10x) physiological concentrations better than the previously used pharmacological ones (up to 2500x); (ii) supplementation with glucocorticoid (most effective at 10-100 nM dexamethasone); (iii) selection of the interval for cumulative labeling with thymidine at 44-68 h; (iv) lowering of cell density at seeding to 50,000 cells/cm2 (subconfluency); (v) treatment with concentrations of 10-100 microM CPA. With these conditions CPA labelling was 13-20% (increase 4- to 9-fold). Mitotic incidence was 0.56% (CPA) versus 0.08% in controls. From a dose response study (0.1-100 microM) a no-effect-level for induction of DNA synthesis was found in the range of 0.1-1 microM. None of the high concentrations of CPA did cause cytotoxicity as estimated by morphological observations or release of lactate dehydrogenase into the medium. This work demonstrates that CPA under appropriate, defined culture conditions induces DNA synthesis and mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Testing of hydralazine in in vivo-in vitro hepatocyte assays for UDS and stimulation of replicative DNA synthesis

The vasodilator hydralazine was tested for induction of DNA-repair synthesis and stimulation of replicative DNA synthesis in rat hepatocytes after administration in vivo, either once or repetitively. No increase in unscheduled or replicative DNA synthesis was observed. By contrast, positive controls clearly induced DNA-repair synthesis, either after a single treatment (4-aminobiphenyl, dimethylnitrosamine and methyl methanesulphonate) or after repetitive treatment (benzo[a]pyrene), or stimulated replicative DNA synthesis (carbon tetrachloride and dimethylnitrosamine). Thus, hydralazine displayed no genotoxic and no tumour-promoting activity in these in vivo-in vitro test systems.

The chronic hepatic or renal toxicity of di(2-ethylhexyl) phthalate, acetaminophen, sodium barbital, and phenobarbital in male B6C3F1 mice: autoradiographic, immunohistochemical, and biochemical evidence for levels of DNA synthesis not associated with carcinogenesis or tumor promotion

Male B6C3F1 mice, 6 weeks of age, were fed diets or water containing di(2-ethylhexyl) phthalate (DEHP) at 12,000 or 6000 ppm, acetaminophen (ACT) at 10,000 or 5000 ppm, sodium barbital (BBS) at 1000 ppm, or phenobarbital (PB) at 500 ppm for 40 weeks. Groups of six mice were terminated at 2, 8, 24, and 40 weeks for evaluation of liver and kidney weights, histopathology, and thymidine kinase (TK) activity in liver and kidney and levels of DNA synthesis, measured by tritiated thymidine [( 3H]T) autoradiography or bromodeoxyuridine (BrdU) immunohistochemistry. Liver weights, as percentage of body weight, were significantly elevated at most time intervals for mice exposed to all chemicals at each dose. The hepatocyte labeling indices (LI) with [3H]T autoradiography or BrdU immunocytochemistry were significantly elevated in mice fed DEHP at 12,000 ppm at 24 and 40 weeks or BBS and ACT at 2 weeks. LI were not elevated in mice fed PB. Hepatic TK activity was significantly elevated in mice fed DEHP, BBS, or ACT at Weeks 2 and 8. Histopathologic hepatic lesions were associated with these elevations, while hepatic lesions were not associated with changes in TK activity in PB-treated mice. In contrast, only DEHP and BBS induced toxic renal lesions. Persistent or transient elevation of the renal LI and TK activity accompanied renal toxicity. Thus, the hepatic toxin DEHP induced chronic renal hyperplasia without evidence of renal carcinogenicity or tumor promotion in previous studies at the doses used. ACT, a hepatotoxin, produced transient chronic hepatic hyperplasia without evidence of carcinogenicity in B6C3F1 mice in earlier studies at the same doses used. Thus, persistent or transient hepatic or renal hyperplasia was associated with carcinogenic or tumor promoting activity of these chemicals in some cases but not in others.

Leupeptin-mediated alteration of renal phagolysosomes: similarity to hyaline droplet nephropathy of male rats exposed to unleaded gasoline

alpha 2u-Globulin, a protein of hepatic origin found in the urine of male rats, is accumulated in the kidney cortex during exposure to unleaded gasoline and has been implicated in the development of fuel hydrocarbon-induced nephropathy and renal neoplasia. The principal morphological feature of gasoline-induced nephropathy is accumulation of hyaline droplets (enlarged secondary lysosomes or phagolysosomes) in epithelial cells of the proximal convoluted tubule S1 and S2 segments. Inhibition of cathepsin B (a major lysosomal peptidase) by treatment of male rats with leupeptin causes rapid accumulation of phagolysosomes and alpha 2u-globulin in the kidney very similar to gasoline exposure. Further, the renal cortical subcellular distribution of alpha 2u-globulin, determined with an electron microscopic immunochemical method, is almost totally confined to phagolysosomes following administration of either gasoline or leupeptin. These results, taken together, indicate that the mechanism of nephrotoxicity of gasoline involves inhibition of renal phagolysosomal proteolysis.

Rapid postexposure decay of alpha 2u-globulin and hyaline droplets in the kidneys of gasoline-treated male rats

Unleaded gasoline induces nephropathy, characterized by rapid accumulation of hyaline (protein resorption) droplets in epithelial cells of the renal proximal convoluted tubules, only in male rats. The hepatic synthesis of the male rat-specific protein alpha 2u-globulin, a constituent of renal hyaline droplets, is unaltered by gasoline treatment (Olson et al., 1987). Renal alpha 2u-globulin content increased to 210% of control within 18 h of a single oral dose of gasoline (2.0 ml/kg); maximal levels (320% of control) were attained following gasoline administration for 3 d. Increases in renal alpha 2u-globulin caused by gasoline were accompanied by concurrent proliferation of hyaline droplets. However, within 3 d of terminating gasoline administration renal alpha 2u-globulin content decreased to the same level as that in unexposed rats, although renal hyaline droplet number returned to pretreatment levels somewhat more slowly. The conjoint effect of postexposure recovery and estradiol (an inhibitor of hepatic alpha 2u-globulin synthesis) administration was also determined in male rats. On postexposure d 3, 6, and 9, estradiol treatment (1 mg/kg, sc, 4 d, starting on d 9 of gasoline treatment) decreased renal alpha 2u-globulin content to 75%, 59%, and 48%, respectively, of that in rats allowed to recover from gasoline with no hormone treatment. Hepatic alpha 2u-globulin content in estradiol-treated rats was decreased by 74%, 97%, and 96% at the same intervals. Estradiol treatment during recovery from gasoline also appeared to increase the removal of accumulated hyaline droplets from the renal cortex. Thus, accumulation of alpha 2u-globulin-containing hyaline droplets after subacute exposure of male rats to gasoline is rapidly reversible, dependent on continuous exposure to gasoline and maintenance of the normal rate of hepatic alpha 2u-globulin synthesis. These results emphasize the dynamic state of renal cortical hyaline droplets and suggest strongly that gasoline hydrocarbons cause hyaline droplet accumulation by prolonging the half-time of degradation of alpha 2u-globulin.

Decision criteria for the in vitro rat hepatocyte UDS assay

The induction of unscheduled DNA synthesis (UDS) in rat primary hepatocytes is used as an in vitro screen for genotoxicity. The purpose of this study was to develop criteria for statistical evaluation of autoradiographic grain counts from the UDS assay. Based on our historical solvent control population (N = 17), we first established a predictive two-sided symmetric tolerance interval providing 95% confidence for coverage of 99% of the distribution of the mean net nuclear grain count for a new solvent control observation. The tolerance interval was determined to run from -2.82 to 4.03 net nuclear grains. When the concurrent solvent control (C) proves admissible (-2.82 less than C less than 4.03), the mean net nuclear grain counts from treatment groups are compared to the concurrent solvent control value. If the difference exceeds 3.09 at two successive concentrations, the test compound is considered positive. We have tested eight carcinogens (MNNG, AFB1, 4DAB, 4NQO, DMBA, 2AAF, DEN and 2AA) utilizing these criteria. All eight were positive. Four non-carcinogens (2AB, pyrene, anthracene and alpha NA) were negative. Each of these chemicals was tested twice using our standard protocol, which employs a preliminary range-finding cytotoxicity assay. We conclude that these criteria provide adequate sensitivity and specificity to be applicable for the evaluation of the results of routine UDS assays with compounds of unknown genotoxic potential.

Accumulation of alpha 2u-globulin in the renal proximal tubules of male rats exposed to unleaded gasoline

Saturated branched-chain aliphatic hydrocarbons, found in motor fuels, induce nephrotoxicity in male rats. Treatment of male rats with unleaded gasoline (0.04-2.0 ml/kg body wt, po) for 9 days increased markedly the number and size of hyaline (protein resorption) droplets in epithelial cells of the renal proximal convoluted tubules (PCT) and enhanced cellular exfoliation at high dose levels. No other treatment-related pathological effects were observed in the glomeruli, distal tubules, or medulla. The renal content of alpha 2u-globulin, a major urinary protein of male rats, was increased maximally by about 4.4-fold after gasoline administration (1.0 ml/kg, po, 9 days); no further increase was observed at higher doses. Immunoperoxidase staining of kidney tissue sections for alpha 2u-globulin revealed large accumulations of antigen localized in many of the PCT epithelial cells which contained hyaline droplets. The hepatic content of alpha 2u-globulin and its mRNA were not altered by gasoline administration. These data show, for the first time, that alpha 2u-globulin is accumulated in the kidneys of gasoline-intoxicated male rats and sequestered specifically in some of the hyaline droplets characteristic of gasoline-induced nephropathy. A hydrocarbon-induced defect in the renal lysosomal degradation of low-molecular-weight urinary proteins, rather than increased synthesis of these proteins, appears to cause hyaline droplet accumulation.

The potential role of chemically induced hyperplasia in the carcinogenic activity of the hypolipidemic carcinogens

Di(2-ethylhexyl)phthalate (DEHP) is a widely used plasticizing agent resulting in substantial human exposure and environmental contamination. In a chronic bioassay, high doses of DEHP induced hepatocellular carcinomas in female Fischer-344 rats and male and female B6C3F1 mice. Thus, there is considerable concern as to the species specificity, mechanism of action, and human risk assessment of DEHP. DEHP belongs to a class of agents described as hypolipidemic hepatocarcinogens. These chemicals share the ability to induce hepatic peroxisomal proliferation and range from very weak to very potent hepatocarcinogens. Unlike most identified carcinogens, the hypolipidemic carcinogens lack DNA reactivity in sensitive cell culture systems such as the Ames test. It has been proposed that active oxygen radicals, produced as a result of peroxisomal proliferation, induce DNA damage. While this is an attractive hypothesis, no genotoxic activity has been observed in hepatocytes with peroxisomal proliferation in treated animals. Another biological activity shared by this class of compounds is their ability to stimulate liver growth or hyperplasia. This additive hyperplasia results from direct mitogenic stimulation rather than regenerative growth following liver toxicity. This hyperplasia can be dramatic, with liver to body weight ratios from treated animals reaching two to three times normal. The degree of induced hyperplasia correlates well with the carcinogenic potency of these agents, whereas genotoxicity does not correlate at all. Increased cellular growth may result in spontaneous mutational events or promotional effects. While some feedback mechanism eventually inhibits liver growth, it is possible that key genes related to the regulation of cellular growth and cancer remain stimulated during continued administration of the chemical. Thus, determination of hyperplastic activity represents an attractive first-step approach to the short-term detection and study of the mode of action of nongenotoxic carcinogens.

Correlation of the carcinogenic potential of di(2-ethylhexyl)phthalate (DEHP) with induced hyperplasia rather than with genotoxic activity

It has been reported that in a long-term feeding study 12,000 ppm of di(2-ethylhexyl)phthalate (DEHP) in the diet produced hepatocellular carcinomas in male and female F-344 rats while 6000 ppm DEHP produced the same tumor type in male and female B6C3F1 mice. In terms of the actual numbers of animals with tumors DEHP produced a greater response in mice than rats. DEHP and its principal hydrolysis product, mono(2-ethylhexyl)phtalate (MEHP) produce multiple effects in the animal such as liver peroxisomal proliferation and hyperplasia. Accordingly, genotoxicity as DNA repair or unscheduled DNA synthesis (UDS) and cell replication as the percentage of cells undergoing scheduled DNA synthesis (SDS or S phase) were determined in mouse hepatocytes in vitro and in vivo in response to DEHP and MEHP. UDS and SDS were determined by autoradiographic quantitation of [3H]-thymidine incorporation in primary hepatocyte cultures treated directly or isolated from B6C3F1 male mice treated in vivo. No DNA repair was observed in mouse hepatocyte cultures treated with up to 1.0 mM DEHP or 0.5 mM MEHP. No DNA repair was observed in cultures from mice treated with up to 500 mg/kg DEHP 12, 24 or 48 h previously or from animals treated up to 28 days with 6000 ppm DEHP in the diet. At 24 h following treatment with 500 mg/kg DEHP, 3.1% of the hepatocytes were in S phase compared to control values of 0.2%. Administration of DEHP in the diet at 6000 ppm produced 9.2% of the cells in S phase at day 7 with the value returning to control levels by day 14. On day 28 of the feeding study the liver to body weight ratios had almost doubled in the group treated with DEHP compared to controls. No increase in the liver-specific enzyme alanine aminotransferase was seen in the serum following treatment with 500 mg/kg DEHP, indicating that the hyperplasia was due to mitogenic stimulation rather than regenerative hyperplasia in response to cytotoxicity. Increases in the endpoints relating to hyperplasia in response to DEHP were greater in the mouse than those that have been reported in the rat. Thus, the carcinogenic response of DEHP correlates better with induced hyperplasia rather than with genotoxicity.