Increased frequencies of aberrant sperm as indicators of mutagenic damage in mice

We have tested the effects of TEM in 3 strains of mice using the sperm morphology assay. In addition, we have made an attempt to evaluate this test system with respect to experimental design, statistical problems and possible interlaboratory differences. Treatment with TEM results in significant increases in the percent of abnormally shaped sperm. These increases are readily detectable in sperm treated as spermatocytes and spermatogonial stages. Our data indicate possible problems associated with inter-laboratory variation in slide analysis. We have found that despite the introduction of such sources of variation, our data were consistent with respect to the effects of TEM. Another area of concern in the sperm morphology test is the presence of "outlier" animals. In our study, such animals comprised 4% of the total number of animals considered. Statistical analysis of the slides from these animals have shown that this problem can be dealt with and that when recognized as such, "outliers" do not effect the outcome of the sperm morphology assay.

The relationship between use of the maximum tolerated dose and study sensitivity for detecting rodent carcinogenicity

The relationship between maximum tolerated dose (MTD) and study sensitivity for detecting rodent carcinogenicity was evaluated for 216 chemicals found to be carcinogens in laboratory animal studies conducted by the National Cancer Institute (NCI) and the National Toxicology Program (NTP). Approximately two-thirds of these rodent carcinogens would have been detected even without the top dose (estimated MTD), but in many of these studies, some site-specific carcinogenic effects would have been missed. Among the remaining one-third of the rodent carcinogens that required the top dose for statistical significance, approximately 80% had numerically elevated rates of the same site-specific tumors at lower doses as well. Only 13 of the NCI/NTP rodent carcinogens had increased tumor rates limited to the top dose for all sites of carcinogenicity. Alternatively, of the 838 site-specific carcinogenic effects observed in the NCI/NTP studies, 447 (53%) would have been detected even without the top dose. Of the remaining effects, 75% (294/391) showed numerically elevated site-specific tumor rates at lower doses. Our evaluation indicates that most carcinogenic effects observed at the top dose in rodent studies are also present (with reduced incidence that might or might not be statistically significant) at the lower doses typically employed (1/2MTD, 1/4MTD).

Chronic toxicity/oncogenicity evaluation of 60 Hz (power frequency) magnetic fields in B6C3F1 mice

A 2-yr whole-body exposure study was conducted to evaluate the chronic toxicity and possible oncogenicity of 60 Hz (power frequency) magnetic fields in mice. Groups of 100 male and 100 female B6C3F1 mice were exposed to pure, linearly polarized, transient-free 60 Hz magnetic fields at flux densities of 0 Gauss (G) (sham control), 20 milligauss (mG), 2 G, and 10 G; an additional group of 100 male and 100 female B6C3F1 mice received intermittent (1 hr on/1 hr off) exposure to 10 G fields. A small but statistically significant increase in mortality was observed in male mice exposed continuously to 10 G fields; mortality patterns in all other groups of mice exposed to magnetic fields were comparable to those found in sex-matched sham controls. Body weight gains and the total incidence and number of malignant and benign tumors were similar in all groups. Magnetic field exposure did not increase the incidence of neoplasia in any organ, including those sites (leukemia, breast cancer, and brain cancer) that have been identified in epidemiology studies as possible targets of magnetic field action. A statistically significant decrease in the incidence of malignant lymphoma was observed in female mice exposed continuously to 10 G fields, and statistically significant decreases in the incidence of lung tumors were seen in both sexes exposed continuously to 2 G fields. These data do not support the hypothesis that chronic exposure to pure, linearly polarized 60 Hz magnetic fields is a significant risk factor for neoplastic development in mice.

Chronic effects of agar, guar gum, gum arabic, locust-bean gum, or tara gum in F344 rats and B6C3F1 mice

Diets containing 25,000 (2.5%) or 50,000 ppm (5.0%) agar, guar gum, gum arabic, locust-bean gum or tara gum were fed to groups of 50 male and 50 female F344 rats and B6C3F1 mice for 103 wk. Separate groups of 50 rats and 50 mice of each sex served as controls for each study. There were no significant differences in survival between any of the dosed groups of rats or mice and their respective control groups. Depressions in body-weight gain greater than 10% for dosed groups relative to their respective control groups were observed for male (low dose only) and female mice fed diets containing agar, female mice fed diets containing guar gum (high dose only), male mice fed diets containing locust-bean gum (high dose only) and male and female mice fed diets containing tara gum (high dose only). Depressions in body-weight gain greater than 5% were observed for female rats fed diets containing agar, guar gum or gum arabic. There were no histopathological effects associated with the administration of the test materials. Under the conditions of these bioassays, none of the five polysaccharides was carcinogenic for F344 rats or B6C3F1 mice of either sex.

Using the NTP database to assess the value of rodent carcinogenicity studies for determining human cancer risk

The large database of carcinogenicity results generated by the National Toxicology Program (NTP) provides a unique opportunity to critically evaluate important scientific issues such as (1) the frequency of positive outcomes, (2) the interspecies correlation in carcinogenic response between rats and mice, (3) the correlation between body weight and tumor incidence, (4) estimates of the false-positive and false-negative rates, and (5) the frequency of decreasing tumor incidences. Such database evaluations enable us to better understand the value and limitations of rodent carcinogenicity studies for determining human cancer risk. However, as the NTP database becomes increasingly accessible to the general scientific community, there is also increased opportunity for misuse of the database. This article reexamines and updates previous database evaluations, presents four scientific principles that should be employed by anyone attempting to use this database, and illustrates how failure to apply these principles can lead to misleading results.

Benzyl acetate carcinogenicity, metabolism, and disposition in Fischer 344 rats and B6C3F1 mice

Carcinogenesis studies of benzyl acetate (a fragrance and flavoring agent) were conducted in F344 rats and B6C3F1 mice. The chemical was given in corn oil by gavage once daily, 5 days/week for 103 weeks, to groups of 50 animals of each sex and species. For rats the doses were 0, 250, and 500 mg/kg body weight and for mice the doses were 0, 500, and 1000 mg/kg. Mean body weights of control and dosed rats and mice were not affected adversely by benzyl acetate. The survival of control and low dose female mice was lower than that of the high dose group. A genital tract infection may have contributed to the reduced survival. No other significant difference in survival was observed for dosed rats or mice. Benzyl acetate was absorbed from the gastrointestinal tract of rats and mice, with approximately 90% of the administered dose recovered as various metabolites in the urine within 24 h. The primary metabolite was hippuric acid, with minor amounts of a mercapturic acid, and one or more unidentified metabolites. This capacity for absorption, metabolism, and disposition was unaffected by the amount or number of doses administered. Under the conditions of these studies, benzyl acetate administration was associated with an increased incidence of acinar cell adenoma of the exocrine pancreas in male F344/N rats. No evidence of carcinogenicity was found for female F344/N rats. For male and female B6C3F1 mice there was evidence of carcinogenicity, in that benzyl acetate caused an increased incidence of hepatocellular neoplasms (particularly adenomas) and squamous cell neoplasms of the forestomach.

Effects in rats and guinea pigs of short-term exposures to sulfuric acid mist, ozone, and their combination

Ozone and the oxides of sulfur are common environmental pollutants. The acute pulmonary lesions caused by ozone and sulfuric acid mist in rats and guinea pigs have been characterized. Rats are not affected by sulfuric acid mist in concentrations up to 100 mg/m3 except for reduced body weight at the higher doses. A true alveolitis develops in guinea pigs exposed to more than 20 mg/m3 sulfuric acid mist. The ozone lesion is primarily confined to the terminal bronchioles and proximal alveoli. In combination studies with up to 2 ppm ozone and up to 10 mg/m3 sulfuric acid mist, the pulmonary lesion and lung/body weight data were essentially the same as in exposure to ozone alone, and the number of statistically significant synergistic effects in rats and guinea pigs was about what one would expect to observe by chance alone.

Unique renal tubule changes induced in rats and mice by the peroxisome proliferators 2,4-dichlorophenoxyacetic acid (2,4-D) and WY-14643

Peroxisome proliferators are non-mutagenic carcinogens in the liver of rodents, acting both as initiators and promoters. The National Toxicology Program (NTP) conducted a study of several peroxisome proliferators (PPs), including Wyeth (WY)-14643 as a prototypical PP and 2,4-dichlorophenoxyacetic acid (2,4-D) as a weak PP, in Sprague-Dawley rats. B6C3F1 mice, and Syrian hamsters. In the kidney, an unusual change was observed in the outer stripe of the outer medulla, especially in rats treated with 2,4-D or WY-14643. This change was characterized by foci of tubules that were partially or completely lined by basophilic epithelial cells with decreased cytoplasm and high nuclear density. Changes typical of chronic nephropathy such as interstitial fibrosis or basement membrane thickening were not associated with these foci. Results of immunohistochemical staining for catalase and cytochrome P-450 4A in the kidney indicated increased staining intensity in renal tubular epithelial cells primarily in the region where the affected tubules were observed: however, the altered cells were negative for both immunohistochemical markers. Ultrastructurally, affected cells had long brush borders typical of the P3 tubule segment. The most distinguishing ultrastructural change was a decreased amount of electronlucent cytoplasm that contained few differentiated organelles and, in particular, a prominent reduced volume and number of mitochondria; changes in peroxisomes were not apparent. In addition to the lesion in rats, mice treated with the highest dose of 2,4-D, but not WY-14643, manifested similar renal tubular changes as seen by light microscopy. Neither chemical induced renal tubular lesions in hamsters. Hepatocellular changes characteristic of PPs were present in all 3 species treated with WY-14643, but not 2,4-D. These results indicate that the rat is the species most sensitive to the nephrotoxic effects of PPs and there is a site specificity to this toxicity related to areas of PP-related enzyme induction. Although 2,4-D is considered a weak PP for the liver, it was the most effective at inducing renal lesions, indicating that the toxic potency of various PPs will depend on the target organ.

Carcinogenic activity of the flame retardant, 2,2-bis(bromomethyl)-1,3-propanediol in rodents, and comparison with the carcinogenicity of other NTP brominated chemicals

Several brominated chemicals have been shown to be multisite-multispecies carcinogens in laboratory animals, and in this paper we report that the flame retardant, 2,2-bis(bromomethyl)-1,3-propanediol (BMP) is also a multisite carcinogen in both sexes of Fischer 344 rats and B6C3F1 mice. BMP was administered continuously in the diet for up to 2 yr to rats at doses of 0, 2,500, 5,000, or 10,000 ppm and to mice at doses of 0, 312, 625, or 1,250 ppm. Interim groups of rats were examined at 15 mo. An additional recovery group of male rats received the chemical for 3 mo at 20,000 ppm in the feed, and then the control diet for the remainder of the study. Chemical exposure caused neoplasms of the skin, subcutaneous tissue, mammary gland, Zymbal's gland, oral cavity, esophagus, forestomach, small intestine, large intestine, mesothelium, kidney, urinary bladder, lung, thyroid gland, seminal vesicle, hematopoietic system, and pancreas in the male rat; mammary gland, oral cavity, esophagus, and thyroid gland in the female rat; lung, kidney, and Harderian gland in male mice; and subcutaneous tissue, lung, and Harderian gland in the female mouse. The recovery group of male rats presented with the same spectrum of treatment-related neoplasms as in the core study. In this recovery group, BMP (at 20,000 ppm) caused irreversible effects at numerous sites after 90 days of exposure that was not detectable by histologic examination, but without further exposure resulted in carcinogenic responses at 2 yr. BMP is mutagenic in the salmonella test, but it was not determined if the BMP-induced effects that eventually lead to development of neoplasms at multiple sites are the same in both species and in all organ systems affected.

Carcinogenesis studies of 4,4'-methylenedianiline dihydrochloride given in drinking water to F344/N rats and B6C3F1 mice

Carcinogenesis studies of 4,4'-methylenedianiline dihydrochloride (98.6% pure) were conducted by administering this chemical in the drinking water of F344/N rats and B6C3F1 mice. Groups of 50 rats and 50 mice of each sex received drinking water containing 150 or 300 ppm 4,4'-methylenedianiline dihydrochloride (dosage expressed as the free base) for 103 wk. Groups of 50 rats and 50 mice of each sex, given drinking water adjusted with 0.1 N HCl to the pH (3.7) of the 300-ppm formulation, served as controls. Survival was comparable among groups except for male mice receiving the 300-ppm dose of 4,4'-methylenedianiline dihydrochloride; survival in that group was lower than that in controls. Mean body weight was reduced in 300-ppm-dose female rats and 300-ppm-dose male and female mice compared to controls. Water consumption was reduced in a dose-related manner in both sexes of rats. No compound-related clinical effects were observed. Under the conditions of these studies, there was clear evidence of carcinogenicity for F344/N rats and for B6C3F1 mice in that 4,4'-methylenedianiline dihydrochloride caused increased incidences of (1) follicular-cell carcinomas of the thyroid gland (controls, 0/49; low dose, 0/47; high dose, 7/48, 15%; p less than or equal to 0.012) and neoplastic nodules of the liver (controls, 1/50, 2%; low dose, 12/50, 24%; high dose, 25/50, 50%; p less than or equal to 0.001) in male rats, (2) follicular-cell adenomas (controls, 0/47; low dose, 2/47, 4%; high dose, 17/48, 35%; p less than or equal to 0.001) and C-cell adenomas (controls, 0/47; low dose, 3/47, 6%; high dose, 6/48, 13% p less than or equal to 0.029) of the thyroid gland in female rats, (3) follicular-cell adenomas of the thyroid gland (controls, 0/47; low dose, 3/49, 6%; high dose, 16/49, 33%; p less than or equal to 0.001), carcinomas of the liver (controls, 10/49, 20%; low dose, 33/50, 66%; high dose, 29/50, 58%; p less than or equal to 0.001), and pheochromocytomas of the adrenal gland in male mice (controls, 2/48, 4%; low dose, 12/49, 24%; high dose, 14/49, 29%; p less than or equal to 0.001), and (4) follicular-cell adenomas of the thyroid gland (controls, 0/50; low dose, 1/47, 2%; high dose, 13/50, 26%; p less than or equal to 0.001), carcinomas (controls, 1/50, 2%; low dose, 6/50, 12%; high dose, 11/50, 22%; p less than or equal to 0.002) and adenomas (controls, 3/50, 6%; low dose, 9/50, 18%; high dose, 12/50, 24%.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth, body weight, survival, and tumor trends in (C57BL/6 X C3H/HeN) F1 (B6C3F1) mice during a nine-year period

Time trends for growth, body weight, survival and tumor prevalences in 121 diet control groups with a total of 4,636 male B6C3F1 mice and 123 diet control groups with a total of 4,758 female mice of NCI-NTP 2-yr chemical carcinogenicity studies started during a 9-yr period (1973 to 1981) in 11 laboratories were evaluated. Male and female mice did not show substantial changes in growth patterns. Both sexes had highly significant time trends with decreasing body weights in the more recent studies. This apparent trend was due to high body weights during the first 3 yr and highly significant interlaboratory variability. Time trends for survival of both sexes were not significant. Prevalences of liver tumors, lung tumors, and lymphoma in males and lung tumors in females did not show significant time trends. There were significant positive time trends for prevalences of liver tumors and lymphoma in female mice, but the trends were not significant when adjusted for interlaboratory variability. The positive time trend for anterior pituitary tumors of females was highly significant and may be due in part to an increase in the amount of pituitary tissue examined in the more recent studies. Histological reevaluation of liver and anterior pituitary tissue in 208-249 female mice at each of 4 different times periods did not substantially change the prevalences or the time trends. The major factor influencing time trends in mice appeared to be interlaboratory variability.

Comparative chronic toxicities and carcinogenic potentials of 2-ethylhexyl-containing compounds in rats and mice

Four compounds containing a 2-ethylhexyl moiety [di(2-ethylhexyl)phthalate (DEHP), di(2-ethylhexyl)adipate (DEHA), tris(2-ethylhexyl)phosphate (TEHP), and 2-ethylhexyl sulfate (EHS)] were tested for carcinogenic and other chronic and subchronic toxic effects in 90-day and 2-year studies in male and female Fischer 344 rats and B6C3F1 mice. The low generalized toxic potencies of the test chemicals allowed relatively high doses of all of these compounds to be administered. Despite differences in chemical structure, all four chemicals were related to increased occurrences of hepatocellular neoplasms, principally carcinomas, in female mice. DEHA and DEHP also induced hepatocellular neoplasms in male mice, while DEHP caused hepatocellular neoplasms in both male and female rats. No other neoplasms were considered to be unequivocally related to compound administration in these studies. There was a positive correlation between the magnitude of the hepatocarcinogenic response in female mice and the probability of a hepatocarcinogenic response in male mice and in male and female rats, suggesting quantitative differences in the carcinogenic potentials of these agents. These results suggest that compounds containing a 2-ethylhexyl moiety (and 2-ethylhexanol, by implication) may possess some carcinogenic potential, especially for the rodent liver. No other organ-specific toxic effects common to two or more test chemicals were observed in these studies.

Effect of 13 week magnetic field exposures on DMBA-initiated mammary gland carcinomas in female Sprague-Dawley rats

Several studies suggest that exposure to 50 Hz magnetic fields may promote chemically induced breast cancer in rats. Groups of 100 female Sprague-Dawley rats were initiated with four weekly 5 mg gavage doses of 7,12-dimethylbenz[a]anthracene (DMBA) starting at 50 days of age. After the first weekly DMBA administration, exposure to ambient fields (sham exposed), 50 Hz magnetic fields at either 1 or 5 G field intensity or 60 Hz fields at 1 G for 18.5 h/day, 7 days/week was initiated. Exposure continued for 13 weeks. A vehicle control group without DMBA was included. In a second study, using lower doses of DMBA, groups of 100 female Sprague-Dawley rats were initiated with four weekly doses of 2 mg of DMBA starting at 50 days of age followed, after the first weekly DMBA administration, by exposure to ambient fields (sham exposed) or 50 Hz magnetic fields at either 1 or 5 G field intensity for 18.5 h/day, 7 days/week for 13 weeks. Rats were weighed and palpated weekly for the presence of tumors. There was no effect of magnetic field exposure on body weight gains or on the time of appearance of mammary tumors in either study. At the end of 13 weeks, the animals were killed and the mammary tumors counted and measured. Mammary gland masses found grossly were examined histologically. In the first 13 week study, the mammary gland carcinoma incidences were 92, 86, 96 and 96% for the DMBA controls, 1 G, 50 Hz, 5 G, 50 Hz and 1 G, 60 Hz groups, respectively. The total numbers of carcinomas were 691, 528 (P < 0. 05, decrease), 561 and 692 for the DMBA controls, 1 G, 50 Hz, 5 G, 50 Hz and 1 G, 60 Hz groups, respectively. In study 2, the mammary gland carcinoma incidences were 43, 48 and 38% for the DMBA controls, 1 G, 50 Hz and 5 G, 50 Hz groups, respectively. The total numbers of carcinomas were 102, 90 and 79 for the DMBA controls, 1 G, 50 Hz and 5 G, 50 Hz groups, respectively. There was no effect of magnetic field exposure on tumor size either by in-life palpation or by measurement at necropsy in either study. There was no evidence that 50 or 60 Hz magnetic fields promoted breast cancer in these studies in female rats. These studies do not support the hypothesis that magnetic field exposure promotes breast cancer in this DMBA rat model.

Occurrence and relevance of chemically induced benign neoplasms in long-term carcinogenicity studies

Recent carcinogenicity studies conducted and evaluated by the National Toxicology Program/National Institute of Environmental Health Sciences were examined to determine the frequency of chemically increased incidences of neoplasia. Many of the chemicals originally selected for study were chosen because of an a priori suggestion that they might be carcinogens. Of the 143 chemical studies evaluated, usually involving male and female rats and mice, 42 (29%) did not induce any neoplasms, 20 (14%) gave marginal or equivocal neoplastic responses, and 81 (57%) showed positive neoplastic responses in one or more of the 524 species-gender experiments. Of these 81 positive studies, 60 (74%) were considered positive based on malignant neoplasia, 16 (20%) were positive due primarily to benign neoplasia, but had supporting evidence of malignant neoplasia in the same organ/tissue, and 5 (6%) were positive based only on benign neoplasia. These five chemicals are a) allyl isothiocyanate (transitional cell papillomas of the urinary bladder in male rats), b) 2-amino-4-nitrophenol (tubular cell adenomas of the kidney in male rats), c) asbestos intermediate range chrysotile (adenomatous polyps of the large intestine in male rats), d) decabromodiphenyl oxide (neoplastic nodules of the liver in male and female rats), and e) nitrofurazone (fibroadenomas of the mammary gland in female rats and benign mixed tumors and granulosa cell tumors of the ovary in female mice). For all but one of these lesions (mammary gland), the occurrence in historic controls is low. Thus, only 5 of the 143 chemicals studied (3.5%) induced benign neoplasia alone, and those observed benign neoplasms are known to progress to malignancy. Accordingly, we consider chemically induced benign neoplasia to be an important indicator of a chemical's carcinogenic potential in rodents, and believe it should continue to be made an integral part of the overall weight-of-the-evidence evaluation process for identifying potential human health hazards.

Two-year inhalation carcinogenesis studies of methyl methacrylate in rats and mice: inflammation and degeneration of nasal epithelium

Methyl methacrylate (MMA), a liquid monomer, is used as a chemical intermediate in the manufacture of plexiglass and other acrylic products and as "bone cement" in orthopedic and dental surgery. Toxicology and carcinogenesis inhalation studies of MMA were conducted because of: (1) widespread human exposure; (2) evidence of mutagenicity; and (3) inadequacy of previously conducted long-term oral, dermal, and inhalation studies. Groups of 50 male F344/N rats were exposed to MMA by inhalation at 0, 500, or 1000 ppm, female F344/N rats at 0, 250, or 500 ppm, and male and female B6C3F1 mice at 0, 500, or 1000 ppm, 6 h a day, 5 days a week for 102 weeks. Survival rates of male and female rats and mice exposed to MMA were similar to those of their respective controls. Body weights were reduced in the low and high dose male (3-6% and 5-10%, respectively) and female (5-7% and 8-10%) rats exposed to MMA for more than 80 weeks and in male (7-19% and 6-17%) and female (0-13% and 0-17%) mice for more than 20 weeks. Inhalation exposure of MMA for 102 weeks did not induce any increased incidences of neoplasms in male or female rats or mice. Non-neoplastic lesions in the nasal cavity of MMA-exposed rats and mice were significantly increased and these included inflammation and degeneration of the olfactory epithelium of MMA-exposed male and female rats and inflammation, hyperplasia, cytoplasmic inclusions in the respiratory epithelium, and degeneration of the olfactory epithelium in male and female mice.

Effects of a polybrominated biphenyl mixture in the rat and mouse. II. Lifetime study

This study was undertaken to characterize the long-term toxic and carcinogenic potential of a polybrominated biphenyl (PBB) mixture in rats and mice of both sexes. Fischer 344 rats and B6C3F1 mice were given 125 po doses of PBB over a 6-month period at 0 (control), 0.1, 0.3, 1.0, 3.0, and 10.0 mg/kg body weight/day (5 days/week) and observed for an additional 23 months for rats and 24 months for mice (lifetime observation). The treatments (0.3 mg/kg or higher dosages) shortened the survival time in male rats whereas no such effect was observed in treated females. There was also evidence of shortened survival time in mice treated with 10.0 mg/kg PBB. As observed by uv light, hepatic porphyrin markedly increased at the 6-month observation, then tended to decrease, primarily in mice, following cessation of exposure. Significantly higher incidences of atypical hepatocellular foci, neoplastic nodules, hepatocellular carcinomas, and cholangiocarcinomas were observed in exposed rats. The incidence of hepatocellular carcinoma was also increased in both male (95%) and female (88%) mice (highest dose level) compared with control male (48%) and female (0%) mice. The incidence of hepatic neoplasms appeared to be dose dependent in both species. Liver tumors were observed primarily in those groups of animals to which PBB was given in doses sufficient to induce readily observable hepatic toxicity. Under the conditions of this experiment, polybrominated biphenyl mixture (Firemaster FF-1) was carcinogenic for Fischer 344 rats and B6C3F1 mice of both sexes. Lesions included neoplastic nodules, hepatocellular carcinomas, and cholangiocarcinomas in rats and hepatocellular carcinomas in mice. Other manifestations of toxicity included porphyrogenic effects and hepatotoxicity. A significantly higher incidence of chronic progressive nephropathy was observed in male rats of the 1.0, 3.0, and 10.0 mg/kg dosage groups when compared with control males. Gastric ulcers and hyperplastic gastropathy of the glandular portion of the stomach were observed more frequently in male rats, primarily in the high dosage groups.

Antiretroviral therapy effects on genetic and morphologic end points in lymphocytes and sperm of men with human immunodeficiency virus infection

Many human immunodeficiency virus (HIV)-infected persons receive prolonged treatment with DNA-reactive antiretroviral drugs. A prospective study was conducted of 26 HIV-infected men who provided samples before treatment and at multiple times after beginning treatment, to investigate effects of antiretrovirals on lymphocyte and sperm chromosomes and semen quality. Several antiretroviral regimens, all including a nucleoside component, were used. Lymphocyte metaphase analysis and sperm fluorescence in situ hybridization were used for cytogenetic studies. Semen analyses included conventional parameters (volume, concentration, viability, motility, and morphology). No significant effects on cytogenetic parameters, semen volume, or sperm concentration were detected. However, there were significant improvements in sperm motility for men with study entry CD4 cell counts >200 cells/mm(3), sperm morphology for men with entry CD4 cell counts < or =200 cells/mm(3), and the percentage of viable sperm in both groups. These findings suggest that nucleoside-containing antiretrovirals administered via recommended protocols do not induce chromosomal changes in lymphocytes or sperm but may produce improvements in semen quality.

Effects of water-soluble antioxidant from spinach, NAO, on doxorubicin-induced heart injury

Doxorubicin (DOX) produces clinically restorative responses in numerous human cancers, but its cardiotoxicity has limited its usefulness. Because reactive oxygen species may affect DOX-induced antitumor activity and cardiotoxicity, we evaluated the prophylactic effect of spinach natural antioxidant (NAO) on DOX-induced cardiotoxicity and oxidative stress in female Balb/c mice using histological, electron microscopical and biochemical parameters. Mice were treated with NAO for 7 days prior to and/or for 6 days after DOX administration. Pretreatment with NAO (cumulative dose: 130 mg/kg) did not hinder the effectiveness of DOX. Light and electron microscopy of DOX-treated heart revealed myocardial degeneration. When administered combined before and after DOX, NAO conferred the most significant cardiac protection. The effects of NAO on the lipid peroxidation product, malondialdehyde, and on H2O2/ hydroperoxides were examined on day 6 following DOX administration; levels of both were elevated in DOX-treated mice, compared to control. Pretreatment with NAO prevented these changes. Pretreatment with NAO before DOX administration decreased catalase and increased superoxide dismutase activities compared to the DOX group. Our results suggest usage of NAO in combination with DOX as a prophylactic strategy to protect heart muscle from DOX-induced cellular damage.

The association between severe nephropathy and pheochromocytoma in the male F344 rat -- the National Toxicology Program experience

The possible correlation between the severity of chronic progressive glomerulonephropathy (CPN) and the incidence of adrenal pheochromocytoma was examined in selected studies of male Fischer 344 (F344) rats at the National Toxicology Program (NTP). The NTP historical control database was first examined in order to determine whether there was association between the severity of CPN and the occurrence of adrenal pheochromocytoma in unexposed animals. Following this analysis, the 125 most recent NTP studies conducted in F344 rats were examined in order to determine how frequently chemicals that cause increased severity of CPN showed an increased incidence of pheochromocytoma. Finally, we examined the association between the incidence of pheochromocytoma and the severity of CPN in those NTP studies with chemically related increased rates of pheochromocytoma. In control male F344 rats surviving beyond 21 mo, the incidence of adrenal pheochromocytoma was consistently higher in animals with more severe CPN. This association was significant (p < 0.05) both for 900 NTP inhalation study controls and 900 NTP feeding study controls. An association was not consistently observed when dosed groups were considered. Although 22% (28/125) of NTP studies reported a chemically related increased severity of CPN, only 3 of these reported a corresponding significant increase in the incidence of pheochromocytoma. Of 6 NTP studies that reported increased incidence of pheochromocytoma, animals with pheochromocytoma from 5 of those studies had some degree of increased severity of CPN. However, the estimated strength of the correlation with the severity of CPN varied from study to study and was often quite different from that indicated by an analysis of the more extensive NTP control databases. The possible correlation between the severity of CPN and the incidence of pheochromocytoma may influence interpretation of carcinogenic effects observed at this site.

The carcinogenicity of di(2-ethylhexyl) phthalate (DEHP) in perspective

The commonly used plasticizer di(2-ethylhexyl) phthalate (DEHP) was recently tested for chronic toxic potential by incorporation into the diet of rats and mice for approximately 2 yr. Upon reviewing the test results, the sponsoring organization concluded that DEHP was carcinogenic to the rats and mice, as indicated by increased occurrences of liver tumors in the DEHP-exposed animals in comparison to controls. Another group has disagreed with this conclusion, however, citing perceived methodological deficiencies and improper interpretations in the study, and has also suggested that rodents may not be adequate models of human response to DEHP. This communication compares the conduct of the DEHP bioassay favorably with state-of-the-art procedures in animal carcinogenicity testing and documents approval of the study interpretations by several independent peer review groups. The carcinogenic potential of DEHP is placed in perspective by evaluating the evidence for DEHP-induced tumors in rodent species in light of dose response relationships, other biochemical and toxicological effects of DEHP, and its comparative metabolism and disposition in rodent and primate species. A composite analysis of the currently available information indicates that DEHP has been shown to be carcinogenic to rodents in a valid chronic test, indicating that it should be considered as a potential carcinogen in humans, as well. Further experimental inquiry will be required, however, to accurately assess the potential health risks posed to humans by exposure to small amounts of this plasticizer.

Theophylline-induced mesenteric periarteritis in F344/N rats

The toxicity and carcinogenic potential of theophylline (an alkaloid bronchodilator drug) was investigated in male and female F344/N rats in 16-day, 14-week, and 2-year gavage and feeding studies. In 16-day studies, rats were fed diets containing 0, 500, 1000, 2000, 4000, and 8000 ppm of theophylline or given 0, 12.5 (twice daily), 25 (once daily), 50 (once daily), 50 (twice daily), 100 (once daily), 200 (once daily), 200 (twice daily), and 400 (once daily) mg theophylline/kg body weight in corn oil by gavage. In 14-week studies, rats were fed diets containing 0, 1000, 2000, and 4000 ppm theophylline or given 0, 37.5, 75, and 150 mg/kg body weight theophylline in corn oil by gavage. In 2-year gavage studies, rats were given 0, 7.5, 25, and 75 mg/kg body weight in corn oil. In 16-day gavage studies, treatment-related periarteritis occurred in arteries of the pancreas and adjacent to the mesenteric lymph nodes of early death male and female rats given 400 mg/kg once daily. In the 14-week studies, treatment-related periarteritis occurred at similar sites and in male rats exposed to 75 and 150 mg/kg, and in all exposed female rats (gavage studies), in females exposed to 1000 ppm, and in both sexes exposed to 2000 and 4000 ppm (feeding studies). In the 2-year study, chronic periarteritis was significantly increased only in the males receiving 75 mg/kg of theophylline. The adventitia, media and intima of medium- and large-sized mesenteric arteries were involved. Similar to other vasodilator chemicals, the pathogenesis of theophylline-induced vascular lesions may be a consequence of hemodynamic changes induced in the vascular wall.

Effects of antioxidants apocynin and the natural water-soluble antioxidant from spinach on cellular damage induced by lipopolysaccaride in the rat

Oxidative damage plays a key role in septic shock induced by the endotoxin lipopolysaccaride (LPS) by enhancing the formation of reactive oxygen species such as superoxide anion radicals, peroxides, and their secondary product, malondialdehyde, especially in the liver. In this study, histopathologic changes in several organs were compared among groups of male Wistar rats that had been injected with LPS following prophylactic pretreatment with either of 2 antioxidants, a group that had been injected with LPS without pretreatment with antioxidants, an untreated control group, and groups that had been injected with either of the 2 antioxidants only. The antioxidants used were a water-soluble natural antioxidant from spinach (NAO) and the NADPH oxidase inhibitor apocynin. Hematoxylin-and-eosin-stained slides were prepared, and lesions were semiquantitatively scored. Exposure to LPS alone was associated with multifocal hepatocellular necrosis and acute inflammation, thymic and splenic lymphoid necrosis, ocular retinal hemorrhage and acute endophthalmitis, adrenal medullary vacuolation and necrosis and acute inflammation, and decreased adrenal cortical cytoplasmic vacuolation (consistent with depletion of steroidal hormone contents). Results indicated that pretreatment with both antioxidants for 8 days reduced, in some organs, the necrotic and inflammatory changes associated with the LPS challenge. These findings suggest a potential therapeutic application for these antioxidants in clinical sepsis.

An examination of the association between maximum-tolerated dose and carcinogenicity in 326 long-term studies in rats and mice

The association between rodent carcinogenicity and maximum-tolerated dose (MTD) was evaluated in 326 long-term carcinogenicity studies in mice and rats. Others investigating this association have focused primarily on positive studies, but our investigation considered all experimental outcomes. We found that chemicals with low MTDs were somewhat more likely to be rodent carcinogens than chemicals with high MTDs, but this association was limited primarily to gavage studies. Overall, the MTD was not a reliable predictor of whether or not a chemical would be a rodent carcinogen. Our investigation confirms that comparisons of carcinogenic potencies based only on positive studies may result in artifactually elevated estimates of the underlying association between chemical toxicity and rodent carcinogenicity and thus may also inflate the estimated interspecies correlation in carcinogenic response. Nevertheless, the results of our study are consistent with the frequently cited 75% concordance in carcinogenicity outcome between rats and mice. This concordance is quite high, particularly since 80% is approximately the maximum level of observable interspecies concordance achievable for a set of chemicals with relatively low carcinogenic potency, because of the variability in observed tumor responses that can induce false negative or false positive outcomes in either of the two species. Thus, the underlying qualitative interspecies correlation in carcinogenic response between rats and mice may be greater than is commonly recognized.