We have previously reported that renal carcinogens examined in rats increase tubular cell proliferation and topoisomerase (Topo) IIα⁺ cells. The present study was aimed at identifying early prediction markers of carcinogens after 28-day treatment in rats. Following gene expression screening by microarrays in renal tubules with renal carcinogens, immunohistochemical analysis and TUNEL-assay were performed with carcinogens targeting different organs. All renal carcinogens tested (ferric nitrilotriacetic acid, ochratoxin A (OTA), monuron, tris(2-chloroethyl) phosphate, and potassium bromate) increased tubular cells immunoreactive for minichromosome maintenance 3 (Mcm3) or ubiquitin D (Ubd) or those showing apoptosis, compared with untreated controls or non-carcinogenic renal toxicants. Carcinogens targeting the liver (thioacetamide (TAA), fenbendazole, piperonyl butoxide (PBO) and methyleugenol), thyroid (sulfadimethoxine), urinary bladder (phenylethyl isothiocyanate), forestomach (butylated hydroxyanisole), glandular stomach (catechol), and colon (chenodeoxycholic acid and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) were examined for induction of Mcm3, Ubd, Topo IIα, Ki-67 and apoptosis using non-carcinogenic toxicants as negative controls. All carcinogens increased Mcm3⁺, Ubd⁺, Topo IIα⁺, Ki-67⁺ or TUNEL⁺ cells, except for hepatocarcinogen PBO and both colon carcinogens, which did not increase cell proliferation. Ubd⁺ cells co-expressing Topo IIα was increased without changing phospho-Histone H3-co-expressing cell population as examined with OTA and TAA. Results revealed cooperative responses of Topo IIα, Ubd and apoptosis by carcinogens inducing high proliferation activity, irrespective of target organs, examined here after a 28-day administration. Aberrant expression of Ubd at G₂ phase and increased apoptosis reflecting aberrant cell cycle regulation may be the common feature of these carcinogens.

View full abstract

We previously demonstrated that 28-day administration of carcinogens that evoked cell proliferation as determined by immunoreactivity for Ki-67 or minichromosome maintenance 3 (Mcm3), in many target organs, increased the numbers of topoisomerase (Topo) IIα⁺, ubiquitin D (Ubd)⁺, and TUNEL⁺ apoptotic cells. We also found increased co-expression of Topo IIα and Ubd, suggestive of increased spindle checkpoint disruption at the M phase. To investigate the roles of these markers in the early stages of carcinogenesis, we examined distribution changes in several carcinogenic target organs using rat initiation-promotion models. Promoting agents targeting the liver (piperonyl butoxide, methapyrilene hydrochloride), thyroid (sulfadimethoxine), urinary bladder (phenylethyl isothiocyanate), and forestomach and glandular stomach (catechol) were administered to rats after initiation treatment for each target organ. Numbers of Ki-67⁺, Mcm3⁺, Topo IIα⁺ and TUNEL⁺ cells increased within preneoplastic lesions as determined by glutathione S-transferase placental form in the liver or phospho-p44/42 mitogen-activated protein kinase in the thyroid, and hyperplastic lesions having no known preneoplastic markers in the urinary bladder, forestomach and glandular stomach. On the other hand, Ubd⁺ cells did not increase within these preneoplastic lesions, but increased within hyperplastic lesions. These results suggest that both cell proliferation and apoptosis may be involved in the formation of preneoplastic lesions in the liver and thyroid examined here; however, spindle checkpoint disruption may not be involved in this process. Changes in hyperplastic lesions of the urinary bladder, forestomach and glandular stomach are similar to the 28-day carcinogen-treated cases, suggestive of the hyperplastic cellular character before the preneoplastic state.

View full abstract

Rebound is known to occur most typically when topical glucocorticoids are abruptly discontinued; however, its frequency and severity are poorly characterized. We previously created a novel murine model of topical glucocorticoid-induced pruritus; however, the mechanism underlying pruritus in this model has not been elucidated. Using this murine model, we aimed to determine the cause of augmentation of pruritus with a focus on the production of prostaglandin (PG) D₂. BALB/c mice with chronic allergic contact dermatitis induced by 5 weeks of repeated application of 2,4,6-trinitro-1-chlorobenzene (TNCB) were treated topically with dexamethasone for 5 weeks immediately after the elicitation of dermatitis and after ear-swelling and scratching behavior were measured. RBL-2H3 mast cells were used to investigate the effect of dexamethasone on degranulation or PGD₂ production in IgE/antigen-stimulated mast cells. The scratching behavior induced by TNCB was augmented by topical application of dexamethasone, but dexamethasone did not have any effect on scratching bouts in mice that had not been treated with TNCB. Topical dexamethasone reduced the PGD₂ level, which increase in TNCB-treated mice, to the baseline level. Moreover, dexamethasone significantly decreased the PGD₂ production in IgE/antigen-stimulated RBL-2H3 mast cells; however, the same concentration of dexamethasone did not have any effect on the degranulation of stimulated mast cells. Topical glucocorticoids may exacerbate pruritus in a mouse model of allergic contact dermatitis via inhibition of PGD₂ production in antigen-mediated activated mast cells in the skin.

View full abstract

Flutriafol is a triazole fungicide that induces spontaneous and depolarization-stimulated release of dopamine from rat striatum, although the neurochemical mechanism by which this fungicide induces this effect is unknown. The purpose of the present work was to assess the implication of ionotropic glutamatergic receptors and nitric oxide (NO) production in the flutriafol-induced dopamine release from rat striatum. To this, we have used non-competitive antagonists of NMDA (dizocilpine, MK-801), and (AMPA)/kainate (6-cyano-7-nitroquinoxaline-2,3-dione, CNQX) receptors, or nitric oxide synthase (NOS) inhibitors (Nomega-nitro-L-arginine -L-NARG - and 7-nitro-indazol - 7-NI), to study the striatal dopamine release induced by flutriafol. Intrastriatal infusion of 6 mM flutriafol increased the dopamine levels to 984 ± 141%, with respect to basal levels. Infusion of flutriafol (6 mM) in MK-801 (500 μM) or CNQX (500 μM) pretreated animals, increased striatal dopamine levels to 489 ± 74% and 477 ± 78%, with respect to basal levels, respectively, these increases being 50.3% and 51.5% smaller than those induced by flutriafol in non-pretreated animals. Infusion of flutriafol (6 mM) in L-NARG (1 mM) or 7-NI (100 μM) pretreated animals, increased the extracellular dopamine levels to 400 ± 88.5 and 479 ± 69.4%, with respect to basal levels, respectively, these increases being 59.3 and 51% smaller than those induced by flutriafol in non-pretreated animals. In summary, flutriafol appears to act, at least in part, through an overstimulation of NMDA receptors with possible NO production to induce dopamine release, and the administration of NMDA and AMPA/kainate receptor antagonists and NOS inhibitors protects against flutriafol-induced dopamine release from rat striatum.

View full abstract

Diclofenac (DCF), a nonsteroidal anti-inflammatory drug, is well known to induce idiosyncratic hepatotoxicity. Although there remains much to be elucidated about its onset mechanism, it is widely accepted as a hypothesis that idiosyncratic hepatotoxicity arises from a specific immune response to a hapten formed by covalent binding of drugs or their reactive metabolites to hepatic tissues. In this study, we investigated the effects of covalent binding of DCF reactive metabolites to hepatic tissues using a rat model of liver injury induced by co-treatment with lipopolysaccharide (LPS) at a non-hepatotoxic dose. In studies done in vitro using hepatic microsomes prepared from rats treated with LPS alone, 4’- and 5-hydroxylation activities on DCF metabolism and adducts of reactive metabolites to dansyl glutathione (dGSH) were markedly decreased associated with a decrease in total P450 content. However, in studies done in vivo, the LPS/DCF co-treatment significantly increased adducts of 5-hydroxydiclofenac (5-OH-DCF) to rat hepatic tissues and delayed the elimination of 5-OH-DCF from plasma. Furthermore, we investigated the effects of co-treatment on hepatic GSH level in rats. A decrease of hepatic GSH was observed with the LPS/DCF co-treatment but not with LPS or DCF alone. The results suggest that covalent binding of reactive metabolites via 5-OH-DCF to hepatic tissues may play an important role in the onset of DCF-induced idiosyncratic hepatotoxicity, especially under decreased GSH conditions.

View full abstract

Small minipigs (Microminipig, registered as a novel variety of pig in Japan) were developed for use in non-clinical pharmacological/toxicological studies for new drug development. To assess the pharmacokinetics of selective substrates of human cytochrome P450s in Microminipigs, caffeine (human P450 1A2), warfarin (P450 2C9), omeprazole (P450 2C19), metoprolol (P450 2D6), and midazolam (P450 3A) were administered in combination, intravenously (0.20 mg kg⁻¹) or orally (1.0 mg kg⁻¹). Plasma samples obtained, up to 24 hr after dosing, from four male and four female Microminipigs were analyzed by liquid chromatography tandem mass spectrometry to estimate typical pharmacokinetic parameters for each analyte. Bioavailabilities were approximately 80% for caffeine and warfarin, but less than 10% for omeprazole, metoprolol, and midazolam. No significant differences were noted, for the five probes, in area under the plasma concentration-time curve and peak plasma concentration values obtained from male and female Microminipigs. Clearance of caffeine, warfarin, omeprazole or midazolam in vivo, mediated mainly by cytochrome P450s 1A, 2C or 3A in Microminipigs, was similar to data reported for human. However, metoprolol metabolism, mediated by P450 2D enzymes in Microminipigs, was faster than reported for in vivo human kinetic parameters and in vitro in a human liver microsomal system. The results of this study suggest that the Microminipig is a suitable animal model for use in biological experiments for comparisons of pharmacokinetics of drugs in humans. The five-probes in combination used in this study demonstrate the disposition of typical P450 drugs in Microminipigs in vivo, with the aim of use in non-clinical pharmacological/toxicological studies.

View full abstract

Hepatic encephalopathy (HE) is a syndrome observed in patients with liver dysfunction such as hepatitis and cirrhosis, and is characterized by cognitive impairment, personality changes, and a depressed level of consciousness. The detailed mechanism underlying the pathogenesis of HE remains unclear. In the present study, our aim was to establish an animal model for HE with cirrhosis. Therefore, we carried out behavioral and biochemical analysis of cirrhotic rats after treatment with thioacetamide (TAA) for 20 weeks. The rats subjected to chronic TAA treatment (TAA rats) showed reduction of cognitive scores in the novel object recognition test (NOR), and a decrease in immobility and an increase in swimming in the forced swim test (FST). In biochemical analyses, the TAA rats exhibited elevated blood levels of ammonia, and increased metabolic activities of serotonergic and noradrenergic neurons in the brain, while the levels of Glu and GABA were not affected. Post-oral treatment of lactulose, a clinically utilized drug for HE, effectively reduced the elevated blood ammonia levels, and restored the reduced cognitive scores and the decreased immobility, without any effects on neurotransmitter contents in the brain, compared with the control. These results indicated lactulose-restorable memory disturbance and irritated mood in the TAA rats. In other words, rats treated chronically with TAA are a potential model for cirrhosis-HE, and the combination of NOR and FST in TAA rats may be useful as a simple assay system for the screening and development of anti-HE agents.

View full abstract

The present study was performed to elucidate toxicity profile of citrinin (CTN) after repeated oral doses for 90 days, especially on the kidneys and female reproductive organs using female BALB/c mice. We first performed a 70-day repeated oral dose toxicity study of CTN by setting the doses at 1.25 and 7.5 ppm in the drinking water (Experiment 1). As a result, CTN did not produce any toxicity in the kidneys, liver, and female genital organs/tracts, except for a slight increase of relative ovary weight. We, next, performed 90-day repeated oral dose toxicity study of CTN by increasing the dose levels at 15 and 30 ppm in the drinking water. The results suggested that CTN did not produce any toxicity in the kidneys, liver, and female genital organs/tracts, except for increase of both absolute and relative ovary weights accompanying increase of large follicles at ≥ 15 ppm. On the basis of these findings, the lowest-observable-adverse-effect level of CTN was 15 ppm (2.25 mg/kg body weight/day) in the drinking water for female BALB/c mice after 90-day oral treatment.

View full abstract

Multiwalled carbon nanotubes (MWCNTs) with unique chemical and electromechanical properties are ideal candidates for the development of drug delivery platforms. The scarce knowledge for the effects of exposure to MWCNTs during pregnancy on postnatal outcomes motivated us to investigate whether intraperitoneal injections (i.p.) of MWCNTs during mating and early pregnancy affect on reproductive and neurobehavioral endpoints and psychobiological status of pups. Thirty virgin female mice were divided to three groups (n = 10 for each); two treated groups injected i.p. with 1 and 10 mg of MWCNTs suspended in 1 ml of phosphate buffered saline solution (PBS) in both mating day and gestation day 3, respectively. The control group was injected i.p. with an equal volume of PBS as a vehicle. MWCNT-treated dams did not exhibit considerable changes in their reproductive performance in gestation and lactation periods. MWCNT-treated pups exhibited similar ontogenetic expressions of neurobehavioral and physical endpoints as compared with control group. Most notably, exposure to MWCNTs was increased depressive and anxious behaviors of treated pups in parallel to adverse effect on their internal organ weights. The absolute thymus weight was declined in MWCNT-treated groups while absolute weights of liver and spleen decreased in group treated by 1 mg of MWCNT as compared to control group. Relative organ weights in MWCNT-treated groups were almost similar to control group.

View full abstract

MicroRNAs (miRNAs) are 19~24 nt non-coding RNA molecules that regulate expression of target genes at the post-transcriptional level. Evidence indicates that miRNAs play an essential role in physiological and pathological conditions including pulmonary development, inflammation, fibrosis and cancer. The aim of the present study is to investigate the altered miRNAs expression profile in rats with experimental silicosis. We duplicated silicosis rat model, and identify the miRNA expression pattern of silicosis rat with miRNA microarray. Compared with normal lung tissue, fourteen miRNAs were found significantly up-regulated while the other twenty-five down-regulated in silicosis samples. The differential expression of two selected miRNAs was confirmed by stem-loop real-time reverse transcription–polymerase chain reaction. Our results indicate that the 39 altered miRNAs may be involved in lung fibrosis of rats that were exposed to silica dust. Furthermore, the microarray results provide a solid basis for further validation, such as identification of other miRNAs that may be related to inflammation and fibrosis. The findings are paving way for silicosis early prevention, prognosis and possible therapy.

View full abstract

Oseltamivir, a prodrug of the neuraminidase inhibitor [3R, 4R, 5S]-4-Acetamide-5-amino-3-(1-ethylpropyl)-1-cyclohexene-1-carboxylate phosphate (Ro 64-0802), is widely used for treatment of influenza infections in Japan, but may be associated with mental instability and suicidal tendencies as a rare side effect, especially in infants and young patients. We examined developmental changes in the brain distribution of oseltamivir and Ro 64-0802, and in the expression of P-glycoprotein (P-gp) at the blood-brain barrier (BBB) in rats by 8 weeks. Brain concentration and Kp_,app,brain (brain-to-plasma concentration ratio) of oseltamivir were highest in 2-week-old rats (1.45 µg/g brain and 0.14, respectively), and were negatively correlated with both age and P-gp expression at the BBB. In contrast, brain concentration and Kp_,app,brain of Ro 64-0802 after oral gavage of oseltamivir were lowest in 2-week-old rats (0.02 µg/g brain and 0.02), and increased with age. Mass imaging analysis revealed that both compounds were distributed homogenously in brain cross-sections, including the hippocampus. From these results, it was estimated that oseltamivir concentration throughout the brain cross-sections was 70-fold and 0.9-fold higher than that of Ro 64-0802 in 2-week-old and 8-week-old rats, respectively. Such developmental changes of prodrug/drug concentration ratio, if they also occur in humans, may provide a rational basis for the putative central nervous system (CNS) side effects in young patients.

View full abstract