New metabolites of thiabendazole and the metabolism of thiabendazole by mouse embryo in vivo and in vitro

Thiabendazole [2-(4'-thiazolyl)benzimidazole; TBZ], a teratogen in ICR mice, is known to be mainly metabolized to 5-hydroxy-TBZ (5-OH-TBZ) and its conjugates in domestic and laboratory animals. Besides the known metabolites of TBZ, 4-hydroxy-TBZ and 2-acetylbenzimidazole (ABI) were identified as new metabolites of TBZ in the urine of F344 rats and ICR mice. 5-OH-TBZ and ABI, as well as TBZ, were found in the embryos of ICR mice given TBZ orally on day 10 of gestation. In the whole-embryo culture system, 5-OH-TBZ and ABI in the medium, and TBZ, 5-OH-TBZ and ABI in the embryo were detected after 24 hr of culture in 25 or 50 micrograms TBZ ml. However, the amount of metabolites in the embryo in vitro was very small compared with that detected in vivo, whereas the amount of TBZ was comparable. Furthermore, the mouse embryo homogenate, at organogenesis, metabolized TBZ to 5-OH-TBZ or ABI. The specific activity required by this homogenate to form 5-OH-TBZ or ABI was less than 1/1000 of that of the liver microsomal fraction. The results suggested that mouse embryos at organogenesis could metabolize TBZ, although most of the metabolites in the embryo in vivo came from the dam.

In vitro studies with nine known or suspected spindle poisons: results in tests for chromosome malsegregation in Aspergillus nidulans

Within the framework of a coordinated collaborative study for evaluating assays for aneuploidy, nine known or suspected spindle poisons were tested in mitotic segregation assays with Aspergillus nidulans. Experiments with A. nidulans diploid strain P1 revealed a statistically significant increase of whole chromosome segregants (non-disjunctional diploids and haploids) after treatments with chloral hydrate (CH), thiabendazole (TB), thimerosal (TM) econazole (EZ) and hydroquinone (HQ). The latter two chemicals also increased the frequency of mitotic cross-overs. Colchicine (COL), diazepam (DZ), cadmium chloride (CD) and pyrimethamine (PY) were ineffective. Further experiments with CH, TB, TM and EZ in the haploid strain 35 demonstrated that CH, TB and TM induced hyperploid types, thus indicating a primary effect on chromosome segregation in A. nidulans. However, since EZ did not induce putative hyperploids in strain 35 and trisomics in diploid 31, it is suggested that EZ affects chromosome segregation by an indirect mechanism, possibly related to induced structural chromosome damage, as previously shown for HQ.

Effects of 10 known or suspected spindle poisons in the in vitro porcine brain tubulin assembly assay

We tested the 10 known or suspected spindle poisons (colchicine, econazole nitrate, chloral hydrate, hydroquinone, diazepam, thiabendazole, cadmium chloride, thimerosal, pyrimethamine and vinblastine) of the coordinated EEC programme for induction of aneuploidy with the in vitro porcine brain tubulin assembly assay. The influence of the compounds on different parameters [lag-phase, polymerization velocity, endabsorption (steady-state level), reversibility, influence on disassembly at 4 degrees C] was evaluated. Colchicine [IC30 (30% inhibition concentration): 0.002 mM), vinblastine (IC30: 0.002 mM), thimerosal (IC30: 0.03 mM), thiabendazole (IC30: 0.5 mM) and chloral hydrate (IC30: 60 mM) led to an inhibition of tubulin assembly in vitro. No influence on the steady-state level was obtained with econazole nitrate (up to 0.1 mM), diazepam (up to 2.5 mM), cadmium chloride (up to 1 mM), pyrimethamine (up to 1 mM) and hydroquinone (up to 25 mM), the highest dose tested being limited either by precipitation or by reaching the maximal solubility of the compound in the solvent used. Diazepam enhanced the lag-phase and slightly reduced the polymerization velocity dose-dependently; however, all the treated test mixtures reached the same end absorption levels as the control. The influence on the disassembly process was studied at 4 degrees C. Microtubules treated with colchicine, econazole nitrate, diazepam, thiabendazole, cadmium chloride, thimerosal and pyrimethamine reached the same end absorption level after disassembly as the untreated control. Chloral hydrate reduced the disassembly rate but the end absorption of the control was not reached, the 30% reduction concentration being 0.25 mM. Hydroquinone at very high doses (greater than 10 mM) stimulated the disassembly process.(ABSTRACT TRUNCATED AT 250 WORDS)

[The hygienic validation of the MPEL for the fungicide tekto in reservoir water]

Fungicide tecto (thiabendazol) is a low-toxic compound, produces a weak skin-resorptive and local irritating effect. Cumulation coefficient is 3.96. Threshold and subthreshold doses for tecto were determined as a result of 12-months chronic experiment on white rats--3.7 and 0.37 mg/kg, respectively. The allowable 24-hours dose for human exposure to the chemical is 0.6 mg. The threshold tecto concentration according to the effect on the general sanitary regimen of water reservoirs appeared to be 1 mg/l. According to the limiting toxicological index 0.05 mg/l was recommended as tecto MAC for the water of reservoirs.

Nephrotoxicity of thiabendazole in mice depleted of glutathione by treatment with DL-buthionine sulphoximine

Thiabendazole [2-(4'-thiazolyl)benzimidazole; TBZ] is widely used as an anthelmintic and a fungicide. TBZ (50-400 mg/kg body weight administered by oral intubation) produced nephrotoxicity in male ICR mice pretreated with an inhibitor of glutathione synthesis, DL-buthionine sulphoximine (BSO; 4 mmol/kg body weight, ip). The toxicity was characterized by increases in kidney: body weight ratio and serum urea nitrogen concentration and by tubular necrosis. The nephrotoxic effects were both dose and time dependent. TBZ in combination with BSO also produced decreases in p-aminohippurate accumulation and acetylation by renal cortical slices. TBZ (up to 1200 mg/kg/body weight) alone resulted in no nephrotoxicity. Administration (ip) of glutathione monomethyl ester, which is readily hydrolysed to glutathione after being transported into cells, completely protected against the toxicity caused by TBZ in combination with BSO; this result suggests that glutathione depletion is a major factor underlying the toxicological interaction between TBZ and BSO. Treatment with three inhibitors of renal microsomal cytochrome P-450-dependent monooxygenases, piperonyl butoxide, methoxsalen and carbon disulphide, all equally prevented the nephrotoxicity of TBZ given in combination with BSO. These results suggest that metabolism of TBZ is a necessary step in TBZ-induced nephrotoxicity in glutathione-depleted mice.

Effects of thiabendazole on the kidneys of ICR mice

The effects of thiabendazole (TBZ) on the kidneys of male and female Crj:CD-1 (ICR) mice were investigated. The mice were given 0, 250 or 500 mg TBZ/kg body weight/day by gavage (using olive oil as a vehicle) for 1, 3, 5 or 7 days. The 24-hr urine volumes of treated mice were increased, significantly so in male mice given the high dose of TBZ. Protein was present in the urine of both control and treated mice throughout the experiment but electrophoresis of the protein showed the presence of a relatively high-molecular-weight protein in the urine of the treated mice. Levels of serum urea nitrogen were decreased in treated mice, but serum creatinine levels did not differ from those of controls. Relative kidney weights tended to be dose-dependently increased in comparison with the controls. Pathological examination showed that after one dose (at either level) the kidneys of males and females were swollen and white maculae were present. Microscopic examination revealed dilation of the proximal, distal and collecting tubules with flattening and degeneration of the tubular epithelium. Tubular dilation was severe in high-dose male mice. These histological changes paralleled the alterations in the 24-hr urine volume. These data suggested that the increased urine volume may be caused primarily by the prevention of reabsorption of water in the distal and collecting tubules. Electron microscopy revealed the flattening of foot processes of podocytes and oedematous changes in the mesangium of glomeruli in TBZ-treated mice. We conclude that TBZ given by gavage in olive oil affects the kidneys of ICR mice.

Glutathione and cysteine enhance and diethylmaleate reduces thiabendazole teratogenicity in mice

The effects of cysteine (CYS), glutathione (GSH) and diethylmaleate (DM) on the teratogenicity of thiabendazole (TBZ) were investigated. On day 9 of gestation mice were given ip a dose of 0, 50 or 100 mg CYS/kg body weight, or 0, 400 or 800 mg GSH/kg, or 0, 0.05, 0.10, 0.15 or 0.60 DM/kg. One hr later they were dosed orally with 0, 250, 500 or 1000 mg TBZ/kg. All foetuses were removed from the uterus on day 18 of gestation, and were examined for external and skeletal anomalies. The number of malformed foetuses was increased in mice pretreated with CYS or GSH and was decreased in those pretreated with DM, in comparison with numbers in the corresponding group treated with TBZ alone GSH pretreatment enlarged the area under the curve (AUC) of TBZ and 5-hydroxyTBZ, a representative metabolite, in foetal tissue. DM pretreatment reduced the AUC of TBZ and 5-hydroxyTBZ.

A comparison of the genetic activity of pyrvinium pamoate with that of several other anthelmintic drugs in Saccharomyces cerevisiae

Several anthelmintic drugs that are used routinely in oxyuriasis therapy were analyzed for genotoxicity in a diploid mitotic recombination and gene conversion assay (strain D5 of Saccharomyces cerevisiae), and in a haploid yeast reversion assay (strain XV185-14C). Piperazine citrate, piperazine adipate, mebendazole and thiabendazole did not appear to be genotoxic in either yeast strain. Pyrvinium pamoate induced the reversion of the missense, nonsense and frameshift alleles in strain XV185-14C, whereas pyrantel pamoate induced only the reversion of the frameshift allele. Pyrvinium pamoate was recombinogenic in strain D5, and there is an indication that pyrantel pamoate, at the lowest dose that was tested, might induce gene conversion or aneuploidy.

Effects of pretreatment with SKF-525A or sodium phenobarbital on thiabendazole-induced teratogenicity in ICR mice

To study the effects of SKF-525A, an inhibitor of cytochrome P-450, and of sodium phenobarbital (PB), a drug-metabolizing enzyme inducer, on the teratogenicity of thiabendazole (TBZ), pregnant mice were given ip either a single dose of 40 mg SKF-525A/kg 1 hr before oral dosing with 250 or 500 mg TBZ/kg or a dose of 75 mg PB/kg/day on three consecutive days before oral administration of a dose of 500 or 1000 mg TBZ/kg. In either case the TBZ dose was given on day 9 of gestation. All foetuses were removed from the uterus on day 18 of gestation, and were examined for external and skeletal anomalies. The spectrum of malformations in the groups of mice pretreated with SKF-525A or PB was similar to that in mice treated only with TBZ. In the group pretreated with SKF-525A, however, the incidence of resorbed foetuses was higher than in the group treated with TBZ alone and there was a tendency towards an increase in the number of foetuses with skeletal fusion and reduction deformity of the limbs, an anomaly characteristically induced by TBZ. On the other hand, in mice pretreated with PB, the incidence of resorbed foetuses tended to be lower, the numbers and body weights of live foetuses were higher and the incidence of external and skeletal malformations was lower than in the groups treated with TBZ only. No reduction deformity of the limbs was observed in the groups pretreated with PB. These results suggest that with TBZ the ultimate teratogen may be the parent compound rather than its metabolites.

Enhancing effect of thiabendazole on urinary bladder carcinogenesis induced by sodium o-phenylphenate in F344 rats

Sodium o-phenylphenate (OPP-Na), a urinary bladder carcinogen in rats, and another fungicide, thiabendazole (TBZ) were fed separately or simultaneously to F344/DuCrj rats of both sexes. The rats were fed one of six diets, either the basal (control) diet or basal diet containing 0.2% TBZ (group T), 1% OPP-Na (1% SO), 2% OPP-Na (2% SO), 1% OPP-Na plus 0.2% TBZ (1% SO-T) or 2% OPP-Na plus 0.2% TBZ (2% SO-T) for 13 or 65 wk. In the 13-wk study, in which groups of ten rats of each sex were used, urinary bladder tumours appeared in 8/10 males in each of three groups--the 2% SO, 1% SO-T and 2% SO-T groups--but not in the remaining animals. Of these tumours, carcinoma accounted for 3/8 tumours in the 2% SO group, 2/8 in the 1% SO-T group and 8/8 in the 2% SO-T group. In the 65-wk study, in which groups of 15 rats were used, the tumour incidence in males was 1/15 in the T group and 15/15, 12/15 and 14/15 in the 2% SO, 1% SO-T and 2% SO-T groups, respectively, while in the females, tumours were found in 2/15, 1/15 and 12/15 animals in the 2% SO, 1% SO-T and 2% SO-T groups, respectively. Of these tumours, carcinoma accounted for 10/15, 11/12 and 10/14 in the males of the 2% SO, 1% SO-T and 2% SO-T groups, respectively, and for 1/2 and 6/12 in the 2% SO and 2% SO-T females, respectively. The tumour incidences in the 1% SO-T males in the two studies and in the 2% SO-T females in the 65-wk study showed a statistically significant increase over those in the 1% SO males or the 2% SO females. Thus, TBZ apparently enhanced the carcinogenic effects of OPP-Na in the rat urinary bladder.

Effects of thiabendazole on the mouse limb-bud organ and cell in culture

In relation to the mouse limb malformations caused by thiabendazole (TBZ), we tested the teratogenicity of TBZ in a mouse limb bud culture system. TBZ interfered with the development of the explants under our experimental conditions. Comparison of the protein and DNA content of the forelimbs of TBZ-treated and control animals showed that TBZ tended to reduce the amounts of DNA more than those of protein. Studies on the biosynthesis of proteoglycan as an index of limb chondrogenesis demonstrated that TBZ impaired its biosynthesis in the limb bud cell system. These results may indicate that TBZ directly causes the abnormalities in mouse limb development. The site and mechanism of teratogenic action of TBZ are also discussed.

In vivo inhibition of adenosine triphosphate (ATP) synthesis associated with thiabendazole-induced teratogenesis in mice and rats

Ogata et al. (1984) reported that thiabendazole (TBZ) was teratogenic in mice when olive oil was used as a vehicle, but not teratogenic when administered in gum arabic. Results of investigations into the possible association between TBZ-induced teratogenicity and adenosine triphosphate (ATP) are reported here. ATP levels in the limb buds were measured at day 10 of gestation in controls and mice treated with 1300 mg/kg TBZ 24 h previously. The results showed that there was a correlation between the dosage of TBZ and the ATP levels of fore and hind limb buds (r = -0.827 and r = -0.799, respectively). ATP levels in mouse limbs were reduced to 22-31% of control values when TBZ was given in olive oil, but the ATP reduction was only 6-9% when TBZ was given in gum arabic. This suggests that there may be a relationship between the teratogenic and ATP-depressing action of TBZ on the limb buds of mouse embryos. Pregnant rats were also treated with TBZ. TBZ at a dose level of 1000 mg/kg was given orally on day 11 of gestation. After 24 h, ATP levels in fetal rat limbs were still 82% of control values. These results confirm the observations of Ogata et al. on the vehicle effect and the difference in response between mice and rats.

Irreversible in vivo binding of thiabendazole to macromolecules in pregnant mice and its relation to teratogenicity

The binding of [14C]thiabendazole ([14C]TBZ) to macromolecules in the liver, foetus and other tissues was investigated in Jcl:ICR mice on day 13 of gestation. TBZ suspended in olive oil was given orally in a dose of 1 g/kg body weight (5 microCi/mouse) and the mice (in groups of three) were killed 0.5, 1, 3, 6, 24 and 96 hr later. The bound radioactivity in the liver and foetus was at a maximum between 3 and 24 hr after treatment. The rate of decrease of the bound radioactivity was slower than that of total radioactivity. Bound radioactivity was also present in other tissues (including kidney, lung, heart, placenta and spleen). The level of bound radioactivity was measured in the liver and foetuses after oral administration of teratogenic doses of 200-1600 mg/kg. Disproportionate increases in bound radioactivity were observed in both tissues after administration of the highest dose.

Teratogenicity of thiabendazole in ICR mice

Thiabendazole (TBZ) was tested for teratogenicity using Jcl:ICR mice. TBZ suspended in olive oil was given orally to pregnant mice at different stages of organogenesis. All foetuses were removed from the uterus on day 18 of gestation, and were examined for external and skeletal anomalies. In mice given 700, 1300 or 2400 mg TBZ/kg body weight/day on days 7-15 of gestation, dose-dependent external and skeletal anomalies, especially cleft palate and fusion of vertebrae, were observed. In mice given a single dose of TBZ (2400 mg/kg) on any one of days 6-13, an increased number of malformations was observed. Various types of malformation occurred, especially in the mice treated on day 9. Reduction deformity of limbs was found in mice given TBZ on days 9-12, a change that has not previously been observed to occur spontaneously in normal ICR mice in our laboratory. In order to determine a dose-response relationship, groups of mice were given one of 17 doses of TBZ (30-2400 mg/kg) on day 9 of gestation. The number of litters having foetuses with reduction deformity of limbs and of those having foetuses with skeletal fusion increased in proportion to the dose of TBZ. The regression lines of Y (probit response) on X (log dose) for reduction deformity of limbs and for skeletal fusion were Y = 2.47X - 3.65 and Y = 1.54X + 0.48, respectively. The effective doses (ED1) for the two malformations were 362.0 and 26.4 mg/kg, respectively.

Determination of thiabendazole and 5-hydroxythiabendazole in human serum by fluorescence-detected high-performance liquid chromatography

We have developed a rapid, sensitive and precise high-performance liquid chromatographic method using fluorescence detection for the simultaneous determination of thiabendazole and unconjugated 5-hydroxythiabendazole in serum. Sample pretreatment consists only of protein precipitation with acetonitrile containing the internal standard, 2-methylindole. Detection limits were found to be 0.1 microgram/ml serum for thiabendazole and 0.4 microgram/ml serum for 5-hydroxythiabendazole. Between-day analytical precision coefficients of variation for serum-based controls were 7% and 11% for thiabendazole levels of 1 and 5 micrograms/ml, respectively; and 43% and 8% for 5-hydroxythiabendazole levels of 6 and 60 micrograms/ml, respectively. We also devised a microenzymatic method for the conversion of the glucuronide and sulfate esters of 5-hydroxythiabendazole using beta-glucuronidase [EC 3.2.1.31] and sulfatase [EC 3.1.6.1]. Thus, quantitation of the separate metabolites was possible. We also utilized a special adaptation of the chromatographic procedure for the determination of the 5-hydroxythiabendazole metabolites in the sera of uremic patients, which can contain large amounts of interfering fluorescent substances. The method should be particularly useful for monitoring thiabendazole therapy in patients unable to eliminate the potentially toxic metabolites.