Biotransformation potential of phytosterols under anoxic and anaerobic conditions.

The biotransformation potential of three phytosterols (campesterol, stigmasterol and ß-sitosterol) under denitrifying, sulfate-reducing and fermentative/methanogenic conditions was assessed. Using a group contribution method, the standard Gibbs free energy of phytosterols was calculated and used to perform theoretical energetic calculations. The oxidation of phytosterols under aerobic, nitrate-reducing, sulfate-reducing and methanogenic conditions was determined to be energetically feasible. However, using semi-continuously fed cultures maintained at 20-22 °C over 16 weekly feeding cycles (112 days; retention time, 21 days), phytosterol removal was observed under nitrate-reducing and sulfate-reducing conditions, but not under fermentative/methanogenic conditions. Under sulfate-reducing conditions, stigmast-4-en-3-one was identified as an intermediate of phytosterol biotransformation, a reaction more likely carried out by dehydrogenases/isomerases, previously reported to act on cholesterol under both oxic and anoxic (denitrifying) conditions. Further study of the biotransformation of phytosterols under anoxic/anaerobic conditions is necessary to delineate the factors and conditions leading to enhanced phytosterol biodegradation and the development of effective biological treatment systems for the removal of phytosterols from pulp and paper wastewaters and other phytosterol-bearing waste streams.

Toxicity of lactide in dogs after 2 and 13 weeks of daily oral dosing.

Two-week and 13-week studies were conducted to determine the toxicity of lactide when the compound is administered orally in gelatin capsules to beagle dogs. In the 2-week study, daily doses of 0, 10, 100, 400, 1000 and 2500 mg/kg body weight/day were administered to dogs of both sexes for 14 consecutive days. All dogs survived to the end of the study. Clinical signs consistent with irritation of the alimentary tract occurred in dogs in the 1000 and 2500 mg/kg dose groups. Reductions in body weight gain and in absolute and relative thymus weights were observed in the same two dose groups, and reductions in absolute and relative spleen weights were seen in the 2500 mg/kg dose group. These changes were considered to be secondary to the stress resulting from irritation of the gastrointestinal tract. Gross and microscopic lesions were indicative of irritation, and included dark foci and haemorrhage of the stomach lining, and erosion and ulceration of the stomach and the oesophagus. Also noted in all high-dose dogs was renal tubular regeneration, which may represent repair of previous necrosis of the tubular epithelium. In the 13-week study, no deaths occurred when dogs were given daily oral doses of 0, 4, 20 or 100 mg/kg body weight/day. No clinical signs of toxicity were observed, and the compound had no effect on body weights, food consumption, or any of the clinical chemistry, haematology or urinalysis parameters assessed. Gross and microscopic findings considered to be potentially related to lactide administration were minimal, and included a stomach focus in one dog of each sex in the 100 mg/kg group. The stomach focus in the 100 mg/kg female dog was manifested microscopically as a stomach ulcer. Based on these results, the primary toxic effect of lactide was considered to be irritation of the gastrointestinal tract, and the no-observed-adverse-effect level (NOAEL) after subchronic oral dosing in dogs was considered to be 100 mg/kg/day.

Subchronic toxicity of human immunodeficiency virus and tuberculosis combination therapies in B6C3F1 mice.

Combination therapy with anti-HIV drugs and opportunistic infection drugs is a common practice in treatment of AIDS patients. Although toxic effects of most individual therapies are known, the toxic potential of most combination therapies has not been established. To understand the toxic consequences of combination therapies, the commonly used anti-HIV drug 3'-azido-3'-deoxythymidine (AZT) and tuberculosis infection therapies pyrazinamide, isoniazid, and rifampicin were evaluated by 13-week gavage studies in B6C3F1 mice, either alone or AZT in combination with one of the antituberculosis drugs. The doses include AZT 100, 200, and 400; pyrazinamide 1000 and 1500; isoniazid 50, 100, and 150; and rifampicin 100, 200, and 400 mg/kg/day. AZT alone caused hematopoietic toxicity with dose-related bone marrow suppression, macrocytic anemia, and thrombocytosis. Pyrazinamide or isoniazid alone at the doses tested did not cause significant toxicity. Rifampicin alone caused hematopoietic toxicity and possibly mild hepatic toxicity. Pyrazinamide below 10 times the therapeutic dose when given with AZT did not increase the hematological toxicity of AZT. Isoniazid markedly increased the hematological toxicity of AZT and contributed to mortality at 3 to 4 times the therapeutic dose combinations. Administration of rifampicin with AZT at the calculated therapeutic doses resulted in toxicity of far greater magnitude than that caused by AZT or rifampicin alone. Combination treatment with AZT and rifampicin caused severe anemia with mortality at 2 to 4 times the therapeutic dose combinations. However, AZT did not enhance the hepatotoxicity of rifampicin. Increased hematopoietic toxicity of AZT when given in combination with the above antituberculosis drugs may be due to changes in the metabolism of AZT. Results of these studies indicate that toxicological effects of combination therapies could be considerably more severe than and different from the toxicity of individual therapies.

Carcinogenicity of 2',3'-dideoxycytidine in mice.

2',3'-dideoxycytidine (ddC) is a synthetic pyrimidine nucleoside analogue approved for treatment of HIV-positive patients. Previous studies indicated that ddC has the potential to cause thymic lymphoma in C57BL/6 x C3H F1 (hereafter called B6C3F1) mice. In this study, we evaluated the carcinogenic potential of ddC in two different mouse models. B6C3F1 hybrid mice carry ecotropic endogenous proviral sequences that may be activated to cause lymphoma, whereas NIH Swiss mice lack proviral sequences that can be expressed. The mice were treated with ddC by gavage at 500 and 1000 mg/kg/day for up to 6 months (human dose, 2.25 mg/day) and evaluated for toxicity, plasma levels of ddC, and pathological changes. Lymphocyte cell markers from the thymic lymphomas were assessed by immunophenotyping. Expression of p53 protein was evaluated using immunohistochemical staining. Treatment-related thymic lymphomas were present in both mouse models with a higher incidence in NIH Swiss than in B6C3F1 mice. The lymphomas were more prevalent in females than in males of both mouse models. Most mice with thymic lymphoma died during the course of the study. In addition to the thymus, lymphoma was often present in lymph nodes, spleen, and other organs. Lymphomas arose more frequently in mice that lack endogenous ecotropic retroviral sequences and thus were not due to activation of endogenous provirus. During the third month of the study, a few NIH Swiss mice that died had granulosa cell tumors of the ovary. Treatment-related but reversible thymic atrophy was observed in both mouse models. There was a very high correlation between the internal dose of ddC and the incidence of thymic lymphoma in both mouse models. Most of the lymphocytes from control thymuses and ddC-induced lymphomas were positive for Thy-1.2 (pan-T), heat stable antigen, and CD4 and CD8 markers, with no marked differences in the lymphocyte markers of the tumors between sexes or dose groups. p53 protein was detected in only 20% (23/115) of the ddC-induced lymphomas with mostly minimal expression in scattered cells. Because ddC induced lymphomas in two different mouse models, the potential carcinogenic risk should be considered in long-term treatment of HIV-positive patients, especially children and adolescent patients treated with ddC.

Subchronic toxicity studies of t-butyl alcohol in rats and mice.

The purpose of this study was to evaluate the toxicity of t-butyl alcohol, an important commodity chemical, an additive to unleaded gasoline, and a contaminant of drinking water. Ninety-day toxicity studies were conducted in B6C3F1 mice and Fischer 344 (F344) rats of both sexes using dosed water. Dose levels of t-butyl alcohol were 0, 0.25, 0.5, 1, 2, and 4% (w/v). Lethality was observed at the 4% level of both sexes and species. Weight-gain depression was present in all dose levels of male rats; 4% female rats; 1, 2, and 4% male mice; and 2 and 4% female mice. Water consumption was increased at lower dose levels in male rats and decreased in the higher dose levels of both sexes of rats and female mice. Clinical signs in rats were ataxia in both sexes and hypoactivity in males. Clinical signs in mice were ataxia, abnormal posture, and hypoactivity. In rats, urine volumes were reduced, in association with crystalluria. Gross lesions at necropsy were urinary tract calculi, renal pelvic and ureteral dilatation, and thickening of the urinary bladder mucosa. Microscopic lesions were hyperplasia of transitional epithelia and inflammation of the urinary bladder. In male rats treated with t-butyl alcohol, microscopic renal changes were suggestive of alpha-2 mu-globulin nephropathy. No-effect levels for the urinary tract lesions were 1% in male rats and mice (803.7 mg/kg/day for the male rats and 1565.8 mg/kg/day for the male mice) and 2% in female rats and mice (1451.5 mg/kg/day for the female rats and 4362.9 mg/kg/day for the female mice). The results indicate that in rodents the urinary tract is the target organ for t-butyl alcohol toxicity, and males are more sensitive to t-butyl alcohol toxicity than females.

Hematologic toxicity of AZT and ddC administered as single agents and in combination to rats and mice.

Toxicity studies of 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC) were conducted in F344/N rats and B6C3F1 mice. The drugs were administered as single agents and in combination. In all studies, animals were treated by oral gavage twice a day, 7 days a week. In studies of the individual compounds, each was administered for 13 weeks at the following concentrations: AZT in rats, 0, 125, 250, 500, 1000 mg/kg and in mice, 0, 25, 50, 100, 400, 1000 mg/kg; ddC in rats and mice, 0, 250, 1000, 2000 mg/kg. Additional male rats and female mice that were treated with 0, 250, 1000, or 2000 mg/kg ddC and male and female mice treated with 0, 50, 400, 1000 mg/kg AZT were maintained for 30 days after treatment was stopped (at 94 days) to evaluate the reversibility of toxic effects. Hematologic variables were measured on Days 5, 23, and 94 (last day of dosing), and on Day 123 (after a 30-day period without treatment). AZT and ddC produced dose-related, poorly regenerative, macrocytic anemias as evidenced by decreases in erythrocyte counts, hematocrits, and hemoglobin concentrations and increases in mean corpuscular hemoglobin and mean corpuscular volume. Bone marrow samples in rats treated with AZT were hyperplastic whereas those in mice treated with AZT and rats and mice treated with ddC were hypoplastic. The hematologic toxicity of AZT was more severe than that of ddC. Generally, toxic effects of either chemical were greater in mice than in rats and more pronounced in female than in male animals. After 30 days without dosing, hematologic effects either resolved or dramatically improved. In studies in which ddC and AZT were administered in combination for 4 weeks at concentrations of 0/0, 0/500, 500/0, 10/500, 100/500, 500/500, and 500/1000 mg/kg ddC/AZT, there was macrocytic anemia in animals in the lower doses and marked microcytic anemia in surviving male mice in higher dose groups. Most female mice died in the 500/500 and 500/1000 mg/kg ddC/AZT dose groups. At lower concentrations (100/500, 500/1000 mg/kg ddC/AZT), effects of the two drugs were similar to those in the single drug studies. At higher concentrations (500/500 and 500/1000 mg/kg ddC/AZT), the combination treatment produced enhanced hematopoietic toxicity. These studies demonstrated the early and progressive time course of toxicity of AZT and ddC, species differences in sensitivities and responses, and reversibility of effects after termination of treatment. Based on these findings, a chronic toxicity study is being conducted with AZT in mice.

Furan-induced hepatic cholangiocarcinomas in Fischer 344 rats.

In a 2-yr carcinogenicity bioassay, 0, 2, 4, or 8 mg furan/kg body weight (BW) was administered to male and female Fischer (F344) rats and resulted in an 86-100% incidence of cholangiocarcinomas with occasional metastasis. In a separate but concurrent study, male F344 rats dosed with 30 mg furan/kg BW for 90 days developed marked cholangiofibrosis and cholangiohepatitis and, when subsequently maintained without further treatment for an additional 6, 12, or 18 months, the cholangiofibrosis progressed to yield a 100% incidence of cholangiocarcinomas. Transplantation of 21 primary cholangiocarcinomas into syngeneic recipients resulted in growth from 4 donors. The 4 transplanted lines were successfully transferred through 8 serial passages and resulted in metastases in the recipients. The progressive growth of these proliferative hepatocholangial lesions over time, their transplantability, and the development of metastases in some of the cases provide biological evidence of the malignant potential of the furan-induced liver changes.

Pharmacological and toxicological properties of arotinoids SMR-2 and SMR-6 in mice.

Studies were conducted to define primary pharmacological and toxicological properties of two arotinoids, SMR-2 and SMR-6, in male B6D2F1 mice. Mice were gavaged daily for up to 22 days with retinoids in corn oil (0.1, 0.2, or 0.4 mg/kg day SMR-2 or SMR-6 or 2.5, 10, or 30 mg/kg all-trans-retinoic acid as a reference control). Toxicological and biochemical endpoints were assayed after 8, 15, and 22 days. At toxic doses, i.e., those inducing weight loss, morphological changes were observed in skin, lymph nodes, spleen, bone marrow, liver, thymus, forestomach, adrenal, bone, and testes. Biochemical alterations included elevated serum alkaline phosphatase, corticosterone, and interleukins-1, -2, and -3. Additional immune alterations included increased responsiveness of spleen cells to both thymus-dependent and thymus-independent mitogens and increases in the total number of B cells in the spleen. At doses not inducing weight loss, target organ effects included the appearance of plasma cells and infiltration of polymorphonuclear cells in lymph nodes; myeloid cell hypercellularity in bone marrow; hematopoiesis in spleen; subacute inflammation in forestomach; and periportal cytoplasmic vacuolization in liver. At the low doses, SMR-2 resulted in decreased responsiveness of spleen cells to mitogens and SMR-6 caused increased responsiveness. SMR-6 also increased interleukin-1 and-2 production at low doses. Biochemical effects included reduced activities of liver aryl hydrocarbon hydroxylase (AHH) and soluble brain protein kinase C. Overall, the results suggest that leukopoiesis and reduced liver AHH and reduced soluble protein kinase C activities are the primary and initial pharmacological and toxicological effects of retinoids.

Modification of retinyl acetate toxicity in rats by coadministration of menhaden oil.

Menhaden oil, which has hypolipidemic and anticarcinogenic activity, reduces the hypertriglyceridemia caused by retinyl acetate. Male Sprague-Dawley rats were dosed daily for 30 days by gavage with either corn oil (CO); menhaden oil (MO); 20, 80, and 250 mg/kg retinyl acetate (ROAc) in CO; or 20, 80, or 250 mg/kg ROAc in MO. Hypertriglyceridemia by ROAc was reduced by coadministration of MO, and serum cholesterol values were reduced to levels similar to those for rats receiving MO alone. Coadministration of MO reduced the ROAc-induced fracture incidence at 80 mg/kg but not at 250 mg/kg. For groups dosed with ROAc and CO or MO, there were no differences in weight-gain depression, elevation of serum alkaline phosphatase, or reduction of food consumption, suggesting that reduced absorption of ROAc was not the basis for the activity of MO. The reduction in retinoid toxicity by MO suggests a need for further study of the toxicity and anticarcinogenicity of retinoid/menhaden oil combinations.

Toxicologic and immunologic evaluations of N-(all-trans-retinoyl)-DL-leucine and N-(all-trans-retinoyl)glycine.

Sprague-Dawley rats were dosed by gavage daily for 28 days with 5, 15, or 50 mg/kg of N-(all-trans-retinoyl)-DL-leucine (RL), N-(all-trans-retinoyl)glycine (RG), or all-trans-retinoic acid (RA). On the basis of mortality incidence, fracture incidence, body weight, and histopathologic effects, RG was slightly to moderately less toxic than RA, and RL was significantly less toxic than RA or RG. Doses that had no effect on weight loss and produced no bone fractures were approximately 5 and 15 mg/kg/day for RA administered to males or females, respectively; greater than 15 mg/kg/day for RG administered to males or females; and greater than 50 mg/kg/day for RL administered to males or females. At these doses, RA and RG produced effects, detectable at the microscopic level, of lymphoid hyperplasia and hematopoietic cell proliferation in the spleen, lymphoid hyperplasia in lymph nodes, necrosis of the cortex of the thymus, hypertrophy of the zona fasciculata of the adrenal, a periportal pattern of cytoplasmic vacuolization in hepatocytes, hematopoietic cell proliferation in the liver, epithelial hyperplasia and subacute inflammation in the forestomach, and osteodystrophy. Serological alterations consisted of reduced serum albumin levels and elevated levels of triglycerides and alkaline phosphatase. For RL, similar microscopic effects, dependent on dose level and sex, were observed in spleen, thymus, adrenal, and liver. In vitro, RL was as active as RA in potentiating pokeweed mitogen-induced lymphocyte proliferation; RG was inactive. This study indicates that, relative to RA and RG, RL has less toxicity but similar immunological effects. Since RL and RG expressed little or no binding affinity for cellular RA-binding protein, the immunological effects of these retinoids may be expressed by mechanisms not linked to this protein.

Chordomas in Fischer 344 rats.

Tissue sections and records of 56 rats with chordoma, identified in the National Toxicology Program's (NTP) data base of approximately 115,000 rats, were examined to determine morphological characteristics, incidence, and aspects of biological behavior. Chordomas occurred in aged rats, originated predominantly in lumbosacral vertebrae, were highly malignant, occurred three times more often in male versus female rats, and commonly produced bilateral posterior paresis, paralysis, and/or distention of the colon and rectum.

Preliminary toxicity profile of arotinoids SMR-2 and SMR-6 in male B6D2F1 mice.

Arotinoids, which are analogs of retinoic acid (RA) and retinol (RO) with the carbon skeleton in a rigid conformation, have more favorable therapeutic indices relative to all-trans-RA and all-trans-RO. The purpose of this investigation was to obtain preliminary in vivo toxicity data on SMR-2(analog of RO) and SMR-6 (analog of RA), arotinoids with promising activity (ED50's of 20 X 10(-11) and 5 X 10(-11) M, respectively; ED50 of RA = 1 X 10(-11) M) for reversal of keratinization in tracheal organ culture. A preliminary toxicity study was conducted in male B6D2F1 mice with gavage of retinoids in corn oil (0.01, 0.05, and 0.1 mg/kg/day of SMR-2 or SMR-6; 1, 5, and 10 mg/kg/day of RA as reference control). Due to lack of toxicity, each dose level for SMR-2 and SMR-6 was increased by 4-fold on Day 29 of dosing. The study was terminated on Day 57. Hypervitaminosis A (weight loss, alopecia, skin scaling, and bone thinning) was induced in the mid- and high-dose SMR groups; weight-gain depression was predominant in the high-dose RA group. The SMR compounds were approximately 100-fold more toxic, based on weight loss, than RA. In the SMR dose groups with hypervitaminosis A, white blood cell counts were elevated 2- to 4-fold; and there were microscopic lesions in skin, testes, epididymis, bone, thymus, bone marrow, peripheral lymph nodes, spleen, stomach, adrenal, and pituitary. The leukocytosis was attributed to leukopoiesis in spleen and bone marrow, which may be due to either a direct effect and/or a secondary response to a subacute inflammatory reaction in skin. Only peripheral lymph node hyperplasia was observed in SMR-2 and RA low-dose groups. Enlarged thymus, lymph node hyperplasia, leukopoiesis in spleen and bone marrow, elevated alkaline phosphatase with bone hypertrophy, and testicular degeneration were observed in the mid-dose RA group. The results indicate that immune stimulation may be a primary early response to retinoids and that skin, leukopoietic tissues, reproductive organs, stomach, and bone are primary targets for retinoid toxicity.

Encephalopathy in rats and nephropathy in rats and mice after subchronic oral exposure to benzaldehyde.

Male and female Fischer 344 rats and B6C3F1 mice were treated daily (5 days/wk) with benzaldehyde by gavage either in 12 doses of 0 (vehicle control), 100 (rats only), 200, 400, 800, 1600 or (for mice only) 3200 mg/kg body weight/day (followed by 2 days' observation without treatment), or for 90 days in doses of 0, 50, 100, 200, 400 or 800 mg/kg/day (rats) or 0, 75, 150, 300, 600 or 1200 mg/kg/day (mice). In the acute studies, benzaldehyde induced deaths and decreased body-weight gain in both sexes of rats given 800 or 1600 mg/kg/day and caused deaths in both sexes of mice given 1600 or 3200 mg/kg/day. In the 90-day studies, deaths occurred in both sexes of rats on 800 mg/kg/day and in male mice on 1200 mg/kg/day. Body-weight gain was depressed in male rats on 800 mg/kg/day, in male mice on 600 mg/kg/day and in female mice on 1200 mg/kg/day. Necrotic and degenerative lesions were seen in the cerebellar and hippocampal regions of the brain in both sexes of rats given 800 mg/kg/day, but not in mice. Renal tubular necrosis occurred in male and female rats on 800 mg/kg/day and in male mice on 1200 mg/kg/day. Mild epithelial hyperplasia or hyperkeratosis of the forestomach was seen in male and female rats on 800 mg/kg/day. In this limited study, the no-observed-toxic-effect doses of benzaldehyde administered by gavage were 400 mg/kg/day in male and female rats, 300 mg/kg/day in male mice and 600-1200 mg/kg/day in female mice.