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Dietary two-generation reproduction study of thiabendazole in Sprague-Dawley rats.

The potential reproductive toxicity of the fungicide and anthelmintic thiabendazole (TBZ) was assessed in Sprague-Dawley rats for two generations. Doses of 10, 30 or 90 mg/kg/day were administered by way of the diet beginning at 8 wk of age for the F0 generation and postnatal wk 4 for the F1 generation and continuing until the animals were killed. Concentrations of TBZ in the diet were adjusted weekly, except during the gestation and lactation intervals when concentrations were held constant. There were no TBZ-related deaths or adverse physical signs during the study. TBZ-related effects consisted of decreases in average body weight gains and food consumption in the middle and high dose groups. In both the F0 and F1 generations during the premating and post-cohabitation periods, the effects in the middle-dose group were observed only in males and were generally slight in magnitude (food consumption 3-5% below control, weight gain 7-18% below control), whereas the effects in the high dose group occurred in both sexes and were slight to moderate in magnitude (food consumption 9-13% below control, weight gain 13-46% below control). During gestation of the F0 females there were slight decreases in average weight gain and food consumption (8% and 4-16% below control, respectively); a similar effect on food consumption, but not weight gain, occurred in the F1 generation. There were no effects on F0 or F1 reproductive performance (including indices of mating, fecundity, fertility, length of gestation, litter size, birth weight, and post-implantation survival), nor were any histomorphological changes observed in the reproductive tissues of animals in the high dose group. There was no evidence of developmental toxicity in the TBZ-exposed F1 or F2 generations, except for slight decreases in average pup weights between postnatal days 4 and 21 in the high dose group (5-10% below control). The NOAEL (no-observed-adverse-effect level) for all developmental, growth, survival and reproductive performance parameters assessed in this study was 10 mg/kg/day.

Animals↗

Subchronic toxicity of thiabendazole (TBZ) in ICR mice.

The subchronic toxic effects of thiabendazole (TBZ) administered in the diet at levels of 0 (control), 0.8 and 1.6% for 13 wk to male and female ICR mice were investigated. Mean body weights of male mice fed 0.8 or 1.6% TBZ showed a significant decrease compared with controls, except for wk 3 and 8 for mice fed 0.8% TBZ. Red blood cell parameters in male mice of treated groups were significantly lower than controls. Biochemistry showed increased concentrations of GOT and GPT in male and female mice of the 1.6% TBZ groups. Relative spleen or liver weights were significantly increased in male and female mice of treated groups. Relative kidney weights of treated mice tended to be increased in comparison with controls. Histological findings showed a marked haemosiderosis and extramedullary haematopoiesis in the spleen of treated mice. In the liver, sinusoidal dilatation and enlargement of liver cells were found in treated mice. In the kidney, atrophy of tubules with peritubular fibrosis, cell infiltration and some tubular necrosis were found in treated mice. Slight hyperplasia was found in the urinary bladder of treated mice. The findings in the present study indicate that TBZ caused a slight anaemia and liver or kidney injury at both levels tested, under these conditions.

Administration, Oral↗

Thiabendazole (TBZ) nephrotoxicity and recovery in ICR adult mice.

The nephrotoxicity and recovery following administration of thiabendazole (TBZ) were investigated in ICR adult mice. A single oral administration of TBZ (500-2000 mg/kg body wt.) caused a dose-dependent proximal tubular necrosis in the kidney and increase in serum urea nitrogen 24 h after dosing. These changes were marked in mice of high dose groups (1000 or 2000 mg TBZ/kg body wt.). The time course of changes on kidney of mice treated with 1000 or 2000 mg TBZ/kg body weight were examined at 1, 2, 3, 5, 7 or 10 days after dosing. Light microscopy showed necrosis of proximal convoluted tubules from 1 day after dosing. Tubular necrosis was extensive 2 or 3 days after dosing. Partial regeneration from tubular necrosis was seen 3 days after dosing, and substantial regeneration had occurred from 5 days after dosing. Thus, TBZ-induced renal injury was most severe at 2 or 3 days after dosing and was followed by regeneration. Electron microscopy showed swelling of mitochondria in the proximal tubular epithelium at 1 day after dosing. The pathological changes were correlated with the changes in urinalysis, serum urea nitrogen concentration and kidney weight.

Administration, Oral↗

The effects of single and multiple doses of thiabendazole on growing and arrested stages of the rabbit stomach worm Obeliscoides cuniculi.

Preliminary observations, using 5 rabbits carrying long-standing infections, indicated that single doses of thiabendazole were effective against adult O. cuniculi and that repeated doses may have had some effect on arrested larvae. A multiple dosing regime, consisting of 1 dose at 110 mg kg-1 body weight followed by 8 doses at 70 mg kg-1 body weight at 4-h intervals, was successful in removing 99.12% of developing worms and 86.04% of arrested larvae.

Animals↗

A comparison between the efficacy of thiabendazole and febantel on experimental trichinellosis in rats.

Febantel at a dose level of 5 mg kg-1 had a lethal efficacy of 54.1% against the adult worm and 69.5% against the migrating larvae of Trichinella spiralis in rats. When administered at 15 mg kg-1, it demonstrated lethal effects of 94.4, 92.5 and 74.7% against adult, young and encysted larvae, respectively. Infected rats treated with 300 mg kg-1 died. Thiabendazole had efficiencies of 96.4 and 83.3% against intestinal and migrating early muscle phases, respectively, and was 42% effective against the encysting phase.

Animals↗

The elimination of equine strongyles and hematological and pathological consequences following larvicidal doses of thiabendazole.

Twelve horses were divided into three groups and given various doses of a mixed species strongyle inoculum, representing light, moderate, and heavy infections. Three weeks after the larval inoculations, three animals from each group were given larvicidal doses of thiabendazole (TBZ) (440 mg kg-1 on two consecutive days); one animal from each group served as a non-medicated control. Treatment was repeated three weeks later. One treated animal from each group was designated for long-term study; others were necropsied to study adult and larval parasite loads. Six of the twelve animals with strongylosis developed moderate eosinophilia. TBZ given at 440 mg kg-1 on two consecutive days caused depression, lethargy, and anorexia which lasted for five days. Eosinopenia, lymphopenia, and neutrophilia occurred in treated animals, and lasted for three days. During the course of TBZ treatment, one horse died from what appeared to be a mis-dosing or an anaphylactic reaction. At necropsy, active thrombi of the anterior mesenteric artery were seen in parasitized animals, but not in those treated with TBZ. Five out of seven medicated horses were completely free of adult and larval strongyle parasites. One had a few Strongylus edentatus larvae and another had small strongyles. No Strongylus vulgaris larvae or adults were recovered from any horse treated with TBZ.

Animals↗

Anthelmintic evaluation of a thiabendazole-resistant strain of Ostertagia circumcincta recovered from sheep in England.

A total of 35 worm-free lambs were infected with a strain of Ostertagia circumcincta isolated earlier from sheep in Cheshire, England, and found to be resistant to thiabendazole (TBZ). When patency was established the sheep were divided into groups of six, and dosed orally with either TBZ (44 mg kg-1, 88 mg kg-1), fenbendazole (FBZ; 5 mg kg-1) or levamisole (7.5 mg kg-1) or not treated. Three of the remaining five animals were dosed with FBZ at 10 mg kg-1. Egg hatch tests, post-dosing faecal egg counts and post-mortem worm counts confirmed resistance to TBZ, and a degree of side-resistance to FBZ was also revealed. Only levamisole gave the clearance expected of modern anthelmintics.

Animals↗

Comparison of ivermectin and thiabendazole for treatment of naturally occurring nematode infections of goats in Kenya.

The anthelmintic activity of thiabendazole (TBZ) at 88 mg kg-1 and ivermectin at 0.2 mg kg-1 was examined in goats with naturally-acquired nematode infections. In one experiment, a herd of 450 does was treated with TBZ or ivermectin at 4-week intervals for 9 months and efficacy was measured by reduction in faecal egg counts after each treatment. In a second experiment, 100 kids were treated with ivermectin and effectiveness measured at 2 and 4 weeks after treatment by comparison of their egg counts with those of nontreated controls. In a third experiment, efficacy of treatment with TBZ and ivermectin was determined by recovery of parasites at necropsy in a controlled test with 15 kids. The results indicated that TBZ generally did not reduce egg counts and only removed 19% of Haemonchus contortus in the controlled test. The efficacy of ivermectin approached 100% for reduction in egg counts and elimination of H. contortus. Species of Ostertagia, Trichostrongylus, Nematodirus and Oesophagostomum also were present in some subjects, but not in sufficient numbers to evaluate effectiveness of treatment.

Animals↗

Resistance to thiabendazole, fenbendazole and levamisole in Haemonchus and Trichostrongylus species in sheep on a Kenyan farm.

Resistance to thiabendazole (TBZ), fenbendazole (FBZ) and levamisole (LVM) in naturally acquired gastrointestinal nematode parasites in sheep was investigated on a farm where anthelmintic resistance was suspected. This was measured by both the in vitro egg hatch assay, and reductions in faecal egg and worm counts in treated animals. In the egg hatch assay, nematode eggs were incubated in various concentrations of either TBZ or LVM. The level of resistance was expressed as the drug concentration inhibiting 50% of the eggs from hatching (LC50). The nematode population had LC50 values of 0.26 microgram ml-1 TBZ and 3.12 micrograms ml-1 LVM. In the faecal egg and worm count reduction test, naturally infected sheep were treated with either TBZ (88 mg kg-1), FBZ (10 mg kg-1) or LVM (15 mg kg-1). Faecal egg and total worm counts from these sheep were then compared with counts from untreated sheep. TBZ, FBZ and LVM failed to reduce the faecal egg counts and total worm counts by more than 90%. Based on the identification of larvae from faecal cultures, the most predominant nematode species in the resistant population were Haemonchus (62%) and Trichostrongylus (28%). TBZ reduced faecal egg counts for both species by less than 90%. FBZ and LVM also reduced Haemonchus spp. eggs by less than 90%. Other nematode species numbers did not satisfy criteria for the determination of efficacy.

Animals↗

Identification of thiabendazole-resistant cyathostome species in Louisiana.

A critical trial was performed with five ponies 6-9 months of age and raised on a horse farm with demonstrated benzimidazole-resistant cyathostomes. Eleven species of cyathostomes were recovered, seven of which had resistance to thiabendazole. Degrees of resistance varied among ponies and from species to species. Resistant species were Cyathostomum coronatum, Cyathostomum catinatum, Cylicostephanus minutus, Cylicostephanus calicatus, Cylicostephanus longibursatus, Cylicostephanus goldi and Cylicocylus nassatus. This is the first study identifying resistant cyathostome species in the Gulf Coast region of the USA and, although no new resistant species were found, results differed somewhat from those of other authors in that none of the cyathostome populations that have been studied contain the same complement of resistant species.

Animals↗

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.

Abnormalities, Drug-Induced↗

Rapid simultaneous determination of o-phenylphenol, diphenyl, thiabendazole, imazalil and its major metabolite in citrus fruits by liquid chromatography-mass spectrometry using atmospheric pressure photoionization.

A simple and rapid simultaneous analytical method of four post-harvest fungicides, o-phenylphenol (OPP), diphenyl (DP), thiabendazole (TBZ), imazalil (IMZ) and its major metabolite R14821 (IMZ-M) in citrus fruits was developed. These compounds were extracted under basic conditions with diethyl ether. The organic layer was washed with water and evaporated at moderate pressure adding methanol. These compounds were determined by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure photoionization (APPI). The recoveries of the five compounds added to citrus fruits at 1 microg/g ranged from 67 to 100%, with relative standard deviations (R.S.D.) ranging from 2 to 8%. The detection limits (S/N = 3) were 0.01 microg/g and 0.05 microg/g (DP).

Atmospheric Pressure↗

Effect of thiabendazole on some rat hepatic xenobiotic metabolising enzymes.

The effect of thiabendazole (TB) on some rat hepatic xenobiotic metabolising enzymes has been investigated. Male Sprague-Dawley rats were fed control diet or diets containing 102-5188 ppm TB for 28 days. As a positive control for induction of hepatic xenobiotic metabolism, rats were also fed diets containing 1457 and 10,155 ppm butylated hydroxytoluene (BHT). Treatment with TB and BHT resulted in dose-dependent increases in relative liver weight. TB was found to be a mixed inducer of cytochrome P450 (CYP) forms in the CYP1A and CYP2B subfamilies. The administration of high doses of TB resulted in the induction of 7-ethoxyresorufin O-deethylase and 7-pentoxyresorufin O-depentylase activities, CYP1A1, CYP1A2, CYP2B1 and CYP2B1/2 mRNA levels and CYP1A2 and CYP2B1/2 apoprotein levels. In contrast, BHT was a CYP2B form inducer, increasing 7-pentoxyresorufin O-depentylase activity, CYP2B1 and CYP2B1/2 mRNA levels and CYP2B1/2 apoprotein levels. Both TB and BHT induced GSH S-transferase activities towards a range of substrates. In addition, TB and BHT markedly induced GSTP1 mRNA levels, but had only a small effect on GSTT1 mRNA levels. In summary, these results demonstrate that TB induces both phase I and II xenobiotic metabolising enzymes in rat liver.

Acyltransferases↗

Synthesis, X-ray crystal structure, antimicrobial activity and photodynamic effects of some thiabendazole complexes.

An interesting series of metal complexes of thiabendazole (tbz) is synthesized and characterized by elemental analyses and spectroscopic studies. The crystal structure of the hydrogen bonded one dimensional Co(II) complex, namely [Co(tbz)(2)(NO(3))(H(2)O)](NO(3)) is solved by single crystal X-ray diffraction. The complex crystallizes in monoclinic space group P2(1)/a with unit cell parameters, a=14.366(2), b=11.459(4), c=15.942(3) A, beta=113.78(3) degrees and z=4. The unit cell packing reveals an extensive hydrogen bonding involving a water molecule, nitrate ligands and the protonated nitrogen atoms of the tbz ligands, resulting in a one dimensional hydrogen bonding pattern. The antimicrobial activity of the complexes against selected bacteria (Escherichia coli and Bacillus subtilis) and yeast (Aspergillus flavues) is estimated. The relationship between the enzymatic production of ROS and antimicrobial activity of the complexes is examined, and a good correlation between two factors is found. Photodynamic quantum yields of singlet oxygen production (RNO bleaching assay) and rate of superoxide generation (SOD inhibitable ferricytochrome c reduction assay and EPR spin trapping experiments using 5,5-dimethyl-1-pyrroline-N-oxide as spin trap) by the metal complexes have been studied.

Animals↗

The role of protein tyrosine kinases in CYP1A1 induction by omeprazole and thiabendazole in rat hepatocytes.

Benzimidazoles compounds like omeprazole (OME) and thiabendazole (TBZ) mediate CYP1A1 induction differently from classical aryl hydrocarbon receptor (AhR) ligands, 3-methylcholanthrene (3-MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). To clarify the involvement of an intracellular signal pathway in CYP1A1 induction by OME and TBZ, the TBZ, OME and 3-MC signal-transducing pathways were compared by using specific protein tyrosine kinase inhibitors in primary culture of rat hepatocytes. The effect of OME and TBZ (75-250 microM) on cytochrome P450 1A1 (CYP1A1) expression was therefore studied in primary cultures of rat hepatocytes after 24 h, 48 h and 72 h of exposure. Both compounds provoked a dose- and time-dependent increase in CYP1A1 (EROD activity, protein and mRNA levels), but OME was less effective at all the concentrations and times tested. The mechanism of benzimidazole-mediated induction of CYP1A1 was investigated by comparison with 3-MC, a prototypical AhR ligand. As expected, OME and TBZ were unable to displace [(3)H]-TCDD from its binding sites to the AhR in competitive binding studies. Moreover, classic tyrosine kinase inhibitor herbimycin A (HA) inhibited the two benzimidazoles-mediated CYP1A1 inductions, but only partially inhibited the 3-MC-mediated one. Another two tyrosine kinase inhibitors, Lavendustin A (LA) and genistein (GEN), had no effect on CYP1A1 induction by benzimidazoles and 3-MC. These results are consistent with the implication of a tyrosine kinase, most probably the Src tyrosine kinase, in the mechanism of CYP1A1 induction in rat hepatocytes.

Animals↗

A novel genotoxic aspect of thiabendazole as a photomutagen in bacteria and cultured human cells.

Thiabendazole (TBZ) is a post-harvest fungicide commonly used on imported citrus fruits. We recently found that TBZ showed photomutagenicity with UVA-irradiation in the Ames test using plate incorporation method. In the present study, potential of DNA-damaging activity, mutagenicity, and clastogenicity were investigated by short pulse treatment for 10 min with TBZ (50-400 microg/ml) and UVA-irradiation (320-400 nm, 250 microW/cm2) in bacterial and human cells. UVA-irradiated TBZ caused DNA damage in Escherichia coli and human lymphoblastoid WTK1 cells assayed, respectively, by the umu-test and the single cell gel electrophoresis (comet) assay. In a modified Ames test using Salmonella typhimurium and E. coli, strong induction of -1 frameshift mutations as well as base-substitution mutations were detected. TBZ at 50-100 microg/ml with UVA-irradiation significantly induced micronuclei in WTK1 cells in the in vitro cytochalasin-B micronucleus assay. Pulse treatment for 10 min with TBZ alone did not show any genotoxicity. Although TBZ is a spindle poison that induces aneuploidy, we hypothesize that the photogenotoxicity of TBZ in the present study was produced by a different mechanism, probably by DNA adduct formation. We concluded that UVA-activated TBZ is genotoxic in bacterial and human cells in vitro.

Bacteria↗

Evidence for cytochrome P4501A2-mediated protein covalent binding of thiabendazole and for its passive intestinal transport: use of human and rabbit derived cells.

Thiabendazole (TBZ), an anthelmintic and fungicide benzimidazole, was recently demonstrated to be extensively metabolized by cytochrome P450 (CYP) 1A2 in man and rabbit, yielding 5-hydroxythiabendazole (5OH-TBZ), the major metabolite furtherly conjugated, and two minor unidentified metabolites (M1 and M2). In this study, exposure of rabbit and human cells to 14C-TBZ was also shown to be associated with the appearance of radioactivity irreversibly bound to proteins. The nature of CYP isoforms involved in this covalent binding was investigated by using cultured rabbit hepatocytes treated or not with various CYP inducers (CYP1A1/2 by beta-naphthoflavone, CYP2B4 by phenobarbital, CYP3A6 by rifampicine, CYP4A by clofibrate) and human liver and bronchial CYP-expressing cells. The covalent binding to proteins was particularly increased in beta-naphthoflavone-treated rabbit cells (2- to 4-fold over control) and human cells expressing CYP1A2 (22- to 42-fold over control). Thus, CYP1A2 is a major isoenzyme involved in the formation of TBZ-derived residues bound to protein. Furthermore, according to the good correlation between covalent binding and M1 or 5OH-TBZ production, TBZ would be firstly metabolized to 5OH-TBZ and subsequently converted to a chemically reactive metabolic intermediate binding to proteins. This metabolic activation could take place preferentially in liver and lung, the main biotransformation organs, rather than in intestines where TBZ was shown to be not metabolized. Moreover, TBZ was rapidly transported by passive diffusion through the human intestinal cells by comparison with the protein-bound residues which were not able to cross the intestinal barrier. Consequently, the absence of toxicity measured in intestines could be related to the low degree of TBZ metabolism and the lack of absorption of protein adducts. Nevertheless, caution is necessary in the use of TBZ concurrently with other drugs able to regulate CYP1A2, particularly in respect to liver and lung tissues, recognised as sites of covalent-binding.

Animals↗

Application of ion-exchange cartridge clean-up in food analysis. I. Simultaneous determination of thiabendazole and imazalil in citrus fruit and banana using high-performance liquid chromatography with ultraviolet detection.

A simple, rapid and reproducible analytical method for thiabendazole (TBZ) and imazalil (IMA) in citrus fruit and banana has been developed. The method involves the use of an ion-exchange cartridge for sample clean-up followed by ion-pair high-performance liquid chromatography with ultraviolet detection. The recoveries of TBZ and IMA from citrus fruits spiked at levels of 10 microgram/g and 5 microgram/g were in the range of 94-98% and 93-98% with coefficients of variation of 0.5-2.2% and 1.6-2.7%, respectively. The recoveries of TBZ and IMA from banana spiked at levels of 3 microgram/g and 2 microgram/g were 94% and 94% with coefficients of variation 1.1% and 4.9%, respectively. The detection limits for TBZ and IMA were 0.1 microgram/g in citrus fruit and 0.05 microgram in banana.

Anthelmintics↗