Long-term toxicity studies of chlorpropham and propham in mice and hamsters

Chlorpropham-induced splenotoxicity and its recovery in rats

To determine the reversibility of hematological and pathological changes in spleen induced by sub-chronic administration of chlorpropham (CIPC), male F344 rats were given CIPC in the diet at 0, 600, 3000 or 15,000 ppm for 13 weeks (administration period) and then were given standard (0 ppm) diet for 10 weeks (recovery period). At 0, 1, 2, 4 or 10 weeks in the recovery period, 5 rats in each groups were examined for hematology and pathology. At the end of CIPC administration, dose-dependent and significant methemoglobinemia, anemia, splenomegaly and pathological lesions indicating hemolytic anemia were observed in all the treated groups. The hematological changes, congestion of red pulp, lymphoid atrophy, increased extramedullary hematopoiesis in spleen and hematopoietic cell hyperplasia in bone marrow were diminished during the 10 weeks recovery period. However, increased hemosiderin deposition and capsular fibrosis in spleen of the treated groups remained at the end of recovery period. The results indicated that hematological changes induced by sub-chronic administration of CIPC were reversible but hemosiderin deposition and fibrosis in spleen were not reversible in the recovery period examined, suggesting the significance of splenic lesion in CIPC-toxicity.

Chlorpropham induces mitochondrial dysfunction in rat hepatocytes

The metabolism and action of chlorpropham (isopropyl N-(3-chlorophenyl)carbamate; CIPC, a post-harvest agent) and its metabolites were studied in freshly isolated rat hepatocytes and isolated rat hepatic mitochondria, respectively. The exposure of hepatocytes to CIPC caused a concentration (0.25-1.0 mM)- and time (0-3h)-dependent cell death accompanied by loss of cellular ATP and adenine nucleotides. CIPC at a weakly toxic level (0.5 mM) was metabolized to isopropyl N-(3-chloro-4-hydroxyphenyl)carbamate (4OH-CIPC) and subsequently to its glucuronide and sulfate conjugates (major metabolites) or alternatively to a minor metabolite 3-chloroaniline (3CA). The addition of SKF-525A (50 microM), an inhibitor of microsomal monooxygenase, enhanced the CIPC (0.5 mM)-induced cytotoxicity accompanied by loss of ATP and 4OH-CIPC and inhibited the decrease in the concentration of the parent compound. CIPC led to a strong decrease in cellular ATP content compared to its metabolites, 4OH-CIPC and 3CA. On the other hand, the exposure of isolated hepatic mitochondria to CIPC reduced State 3 respiration with a FAD-linked substrate (succinate plus rotenone) and/or with a NAD+ -linked substrate (pyruvate plus malate), whereas State 3 respiration with ascorbate plus tetramethyl-p-phenylendiamine (cytochrome oxidase-linked respiration) was not affected markedly by CIPC. Further, the addition of CIPC caused an increase in the rate of State 4 oxygen consumption, indicating an uncoupling effect, and a decrease in the rate of State 3 oxygen consumption in a concentration-dependent manner, respectively. In contrast, the addition of neither 4OH-CIPC nor 3CA markedly affected the rate of states 3 and/or 4 oxygen consumption. These results indicate that CIPC-induced cytotoxicity is mediated by the parent compound rather than by its metabolites such as 4OH-CIPC and 3CA, and that the toxicity is associated with a rapid depletion of ATP via impairment of mitochondrial function related to oxidative phosphorylation.

Biotransformation of chlorpropham (CIPC) in isolated rat hepatocytes and xenoestrogenic activity of CIPC and its metabolites by in vitro assays

1: The metabolism and action of chlorpropham (isopropyl N-(3-chlorophenyl)carbamate; CIPC, a post-harvest agent) were studied in freshly isolated rat hepatocytes, and the oestrogen-like activity of CIPC and its metabolites was assessed by in vitro assays. The exposure of hepatocyte suspensions to CIPC caused concentration- (0.25-1.0 mM) and time- (0-3 h) dependent cell death, which was assessed by Trypan blue exclusion, accompanied by losses of cellular adenosine triphosphate and adenine nucleotide pools, and formation of cell bleb. 2: CIPC at a weakly toxic level (0.25 or 0.5 mM) was metabolized to isopropyl N-(3-chloro-4-hydroxyphenyl)carbamate (4OH-CIPC) and subsequently to its glucuronide and sulfate conjugates (major metabolites) or alternatively to the minor metabolites 3-chloroaniline (3CA) and 3-chloroacetanilide. CIPC (0.25 mM) added to hepatocyte suspensions was distributed equally between hepatocytes and the extracellular medium during the incubation. The glucuronide rather than the sulfate conjugate of 4OH-CIPC predominantly increased in the medium with time, while the amount of unconjugated free 4OH-CIPC in the extracellular medium increased by approximately threefold compared with the amount in the cell fraction after 0.5 h and then decreased rapidly accompanied by increases in the conjugates. This indicates that unconjugated free 4OH-CIPC produced in hepatocytes was temporarily excreted in the extracellular medium and subsequently converted to the conjugates via re-influx into hepatocytes. 3: Diethylstilbestrol (DES), bisphenol A (BPA) and 4-hydroxybenzoic acid butyl ester (butylparaben), which are known xenoestrogenic compounds, competitively displaced 17beta-oestradiol bound to the oestrogen receptor-alpha (ERalpha) in a concentration-dependent manner; IC50 values of DES, BPA, butylparaben and its derivative 3-chloro-4-hydroxybenzoic acid butyl ester (3-chloro-butylparaben) were approximately 10(-8), 10(-5), 5 x 10(-5) and 5 x 10(-4) M, respectively. In contrast, neither CIPC nor 4OH-CIPC impaired the binding of 17beta-oestradiol to ERalpha at concentrations ranging from 10(-9) to 10(-4) M, whereas at concentrations of >5 x 10(-4) M, the binding affinity of 4OH-CIPC was greater than that of CIPC. In a proliferation assay of MCF-7 cells, CIPC, 4OH-CIPC and 3CA did not increase cell numbers at concentrations ranging from 10(-9) to 10(-5) M, but these compounds at a concentration of 10(-4) M induced a considerable decrease in cell numbers relative to the control. The results suggest that even if CIPC is metabolized to 4OH-CIPC by hepatocytes, the chlorine adjacent to the 4-hydroxy group added to the intermediate as well as 3-chloro-butylparaben obstructs the appearance of oestrogen-like effects via an interaction between the intermediate and the ER.

Chronic toxicity and oncogenicity of N-methylpyrrolidone (NMP) in rats and mice by dietary administration

A two-year feeding study in rats and an 18-month feeding study in mice were conducted to evaluate the potential chronic toxicity and oncogenicity of NMP in Crl:CD (SD)BR rats and B6C3F1/CrlBR mice. Groups of 62 male and female rats were administered diets containing 0, 1600, 5000, or 15,000 ppm of NMP for approximately 2 years. Groups of 50 male and female mice were administered diets containing 0, 600, 1200, or 7200 ppm NMP for approximately 18 months. In vivo parameters were evaluated weekly during the first 3 months of the study, and every other week or monthly during the remainder of the study. For rats, an ophthalmoscopic examination was conducted prior to study start and near the end of the study. Periodically, blood samples were collected from rats and mice for determination of leukocyte differential counts, and from mice for red blood cell morphology. After approximately 2 years of dietary administration in rats and 18 months in mice, all surviving animals were sacrificed. Selected tissues were processed for morphological evaluation. Over the course of the two-year study in rats, test substance-related decrements in body weight and weight gain occurred in 15,000 ppm males and females, which correlated with decreased food consumption and food efficiency. A toxicologically significant, test substance-related increase in the incidence of severe chronic progressive nephropathy occurred in 15,000 ppm males. Several morphological changes noted grossly and/or microscopically were secondary to the increased severity of chronic progressive nephropathy. NMP was not oncogenic in male or female rats at dietary concentrations of 15,000 ppm and below. A test substance-related decrease in the percentage of 15,000 ppm males surviving to the end of the two-year study compared to the control group resulted from the higher incidence of severe chronic progressive nephropathy. However, a sufficient population of 15,000 ppm rats were at risk for potential oncogenicity, so the lower survival did not impair the ability to detect an oncogenic response in this study. There were no adverse, test substance-related effects on the incidences of clinical observations, ophthalmic observations, or differential leukocyte counts in males or females, or on survival of females at any dietary concentration. Male and female mice administered dietary concentrations of 7200 ppm had significantly increased liver weight, significantly increased incidence of hepatocellular adenoma, and significantly increased foci of cellular alteration in the liver. At 7200 ppm, male mice also had an increased incidence of hepatocellular carcinoma while the increased incidence of hepatocellular carcinoma in female mice fell within the historical control range. In addition, the incidence of hepatocellular hypertrophy was increased in 7200 ppm males. Liver weight and hepatocellular hypertrophy were also increased in 1200 ppm males. There were no adverse, test substance-related effects on the incidences of clinical observations, food consumption, body weight, differential leukocyte counts, red blood cell morphology, or survival in either males or females at any dietary concentration. Under the conditions of the study, the no-observed-effect level for NMP was 5000 ppm for male and female rats, 600 ppm for male mice, and 1200 ppm for female mice.

Effects of chlorpropham (CIPC) on the hemopoietic system of rats

Male F344 rats were given 0 or 3% chlorpropham in the diet and at 2, 4, 6, 8 or 13 weeks of administration, five rats in each group were examined for hematology, plasma clinical chemistry and pathology. Marked splenomegaly and hepatomegaly were observed in treated rats at 2-13 weeks of administration. Red blood cell counts, hemoglobin concentration, packed cell volume and platelet counts were significantly decreased and methemoglobin level, mean corpuscular volume and white blood cell counts were significantly increased in treated rats at 2-13 weeks of administration. The covalent binding of m-chloraniline m-CA, (the hydrolytic metabolite of chlorpropham) was observed in hemoglobin or splenic protein of treated rats, but only small amounts of free m-CA were present in blood or spleen. Congestion, hemosiderin deposits, extramedullary hemopoiesis and lymphoid atrophy in spleen and hyperplasia of hemopoietic cells in bone marrow were observed in treated rats at 2-13 weeks and fibrosis in splenic capsule were observed in treated rats at 4-13 weeks. The pathological changes in spleen rather than hematological changes progressed during administration, suggesting splenotoxicity of CIPC in rats.

Subchronic toxicity of chlorpropham (CIPC) in ICR mice

Male and female ICR mice were given 0, 1875, 7500 or 30,000 ppm of chlorpropham (CIPC) in the diet for 13 weeks. Methemoglobin levels of male and female mice in the 7500 and 30,000 ppm groups were significantly elevated. Hemoglobin concentration, packed cell volume, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration and white blood cell count of male and female mice in the 30,000 ppm group were significantly increased. Dose-dependent splenomegaly was observed in male and female mice in the 7500 and 30,000 ppm group. Congestion, increased hemosiderin deposition and increased extramedullary hematopoiesis in the spleen, hematopoietic cell hyperplasia and hemosiderin deposition in bone marrow was observed dose dependently in male and female mice in the 7500 or 30,000 ppm group. Eosinophilic granular cytoplasm of hepatocytes, sinusoidal dilatation, hemosiderin deposition, extramedullary hematopoiesis and necrosis of hepatocytes were observed in the liver of male and female mice in the 30,000 ppm group. Hemosiderin deposition was increased in the kidney of male and female mice in the 30,000 ppm group. Administration of CIPC in diet for 13 weeks caused methemoglobinemia and splenomegaly in ICR mice.

Reproductive and neurobehavioural toxicity study of chlorpropham in mice

Chlorpropham was given in the diet to provide levels of 0 (control), 500, 1,000, and 2,000 mg/kg from 5 weeks of age of the F0 generation to 9 weeks of age of the F1 generation in mice, and selected reproductive and neurobehavioural parameters were measured. There were no adverse effects of chlorpropham on either litter size or litter weight and sex ratio at birth. The average body weight of offspring was significantly reduced in the middle-dose group at postnatal days (PNDs) 0 and 4 in female offspring, and was significantly increased in the middle-dose group at PND 14 in male offspring. In neurobehavioural parameters, surface righting at PND 4 was significantly affected in a dose-related manner, and negative geotaxis at PND 4 was significantly accelerated in a dose-related manner in female offspring. In male offspring, surface righting at PND 7 was significantly depressed in the middle-dose group, and olfactory orientation at PND 14 was significantly affected in the low- and middle-dose groups. The dose levels of chlorpropham in the present study produced few adverse effects in reproductive and neurobehavioural parameters in mice.

Hemotoxicity of chlorpropham (CIPC) in F344 rats

Chlorpropham[Isopropyl-N-(3-chlorophenyl)carbamate; CIPC] is a widely used sprout suppressant. Groups of ten male and ten female F344 rats were given 0, 7500, 15,000 or 30,000 ppm of CIPC in the diet for 13 weeks. Body weight gain of male and female rats in the 30,000 ppm-group was depressed. Spleen and liver weights of male and female rats in the treated groups were dose-dependently increased. Red blood cell count, hemoglobin concentration, hematocrit, mean corpuscular hemoglobin concentration and platelet count were decreased in male and female rats of the treated groups. Methemoglobin level, mean corpuscular volume and mean corpuscular hemoglobin were increased in male and female rats of the treated groups. Those hematological changes were dose-dependent and were marked in the 15,000 and 30,000 ppm-groups. White blood cell count of male and female rats in the 30,000 ppm-group were significantly higher than those of the control group. Congestion, increased hemosiderin deposition, increased extramedullary hemopoiesis, lymphoid atrophy and fibrosis were seen in spleen of male and female rats of all treated groups in a dose-dependent manner. Hemopoietic cell hyperplasia was marked in bone marrow of male and female rats in all treated groups. The results suggested that the erythrocyte is one of the primary targets of CIPC toxicity in rats.

Reproductive and neurobehavioral effects of chlorpropham administered to mice in the diet

Chlorpropham was given in the diet to provide levels of 0(control), 0.15, 0.30, and 0.60%, from 5 weeks of age of the F0 generation to 9 weeks of age of the F1 generation in mice, and selected reproductive and neurobehavioral parameters were measured. There were no adverse effects of chlorpropham on either litter size or litter weight and sex ratio at birth. The average body weight of offspring was significantly affected in the low-dose group of each sex and in the high-dose group of females, and was increased in the middle-dose group of males during the lactation period. In neurobehavioral parameters, surface righting at postnatal day (PND) 7 was significantly affected in male offspring in a dose-related manner. Swimming head angle at PND 4 was significantly restrained in male offspring in a dose-related manner, and olfactory orientation at PND 14 was significantly depressed in female offspring in a dose-related manner. The dose levels of chlorpropham in the present study produced some adverse effects in reproductive and neurobehavioral parameters in mice.

Developmental toxicity of chlorpropham in mice

The present studies were designed to evaluate the developmental toxicity of chlorpropham in mice. The first study was conducted to determine administration time, and the second study was designed to evaluate dose-response effects. Chlorpropham was administered to pregnant mice by gavage on Days 8, 8.3, 9, 9.3, 10, and 11 of gestation at a level of 3000 mg/kg bw, and the females were killed on Day 18 of gestation. The administration on Day 8.3 of gestation induced the highest percentage of external malformations with brachyury occurring among more litters than in other groups. Chlorpropham was administered to pregnant mice by gavage at a level of 0 (control), 750, 1500, and 3000 mg/kg bw on Day 8.3 of gestation, and the females were killed on Day 18 of gestation. The total resorption rate was significantly increased in the 3000 mg/kg bw group. The average fetal body weight of each sex was significantly reduced in the 3000 mg/kg treatment group. The total incidence of external malformations was significantly increased in the two highest dose groups in a dose-related manner. Again brachyury was significantly increased in the 3000 mg/kg bw group.

Quantitative risk assessment of carcinogenicity of urethane (ethyl carbamate) on the basis of long-term oral administration to B6C3F1 mice

A carcinogenicity study of urethane was performed for quantitative assessment of its risk in humans. Three hundred 6-week-old male B6C3F1 mice were divided into 6 groups, each consisting of 50 mice, and urethane was given ad libitum in drinking water at levels of 0 (control), 0.6, 3, 6, 60 and 600 ppm for 70 weeks. The tumors with a clear dose-response relationship were lung tumor (alveolar/bronchiolar adenoma or carcinoma) and liver tumor (hemangioma or angiosarcoma). The incidences of these two types of tumor were applied to estimation of the virtually safe dose (VSD) at the level of 10(-6) by using four mathematical models (Logit, Probit, Weibull and Multistage models). The VSD based on the incidences of lung tumor by using the Logit model was estimated to be 1.8 x 10(-4) mg/kg body weight/day. On the other hand the VSD based on those of liver tumor by using the Weibull model was 7.2 x 10(-5) mg/kg body weight/day. Thus, the VSDs based on the incidences of the two different types of tumor using the most compatible mathematical model in each case, as judged from the P-values, were similar.

Quantitative correlation with carcinogenic potency of different short term tests

The following short term parameters evaluating essentially genotoxic effects were considered: liver DNA alkaline fragmentation (DFI), morphological transformation in hamster embryo cells (TPI), and mutagenicity in the Ames' test (MPI). The internal consistency of the carcinogenicity data (OPI) was rather high (r approximately or equal to 0.8). The correlation with OPI of DFI and MPI was statistically significant but rather modest, about 0.4-0.5. The best correlation between OPI and TPI was 0.65. This level of correlation was observed only when some kind of dose-response relationship for transformation could be established. When comparisons were attempted for exactly the same 27 compounds for all three tests, a general decrease in predictability was observed. This could be mainly due to problems of representation of the ideal population of chemicals using small samples. The more general problem of the quantitative approach to the predictability of short term tests was also discussed.