Animal models of human disease have been widely used in drug discovery, but they are rarely utilized in toxicological research and screening (except for transgenic models in carcinogenicity testing). Although genetic and/or acquired pathophysiological alterations associated with a particular disease may greatly exacerbate toxic responses to drugs in certain patient subsets, these pre-existing pathological conditions are usually not considered in preclinical safety assessment. Examples of disease-related determinants of susceptibility include disruption of the cytokine network in pro-inflammatory conditions, mitochondrial alterations and oxidative stress in certain neurodegenerative diseases, altered antioxidant defense in certain viral infections, and altered gene expression and mitochondrial dysfunction in type 2 diabetes. Hence, if cellular stress caused by drugs or metabolites and the disease-related effects are superimposed, then an individual can become sensitized to potential drug toxicity. Animal models of modest inflammation indeed can potentiate the toxicity of certain drugs. Similarly, rodent models of type 2 diabetes predispose the animals to hepatotoxic effects of thiazolidinediones antidiabetics. In conclusion, it is suggested that tailor-made and simplified models be adopted and increasingly used, in spite of clear limitations, as optimal substrates for satellite toxicity studies to facilitate candidate selection, help predict rare and unexpected toxicity, and identify new biomarkers.

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We investigated the mechanism of hemolytic anemia detected in a repeated-dose toxicity study using cynomolgus monkeys that were treated with a humanized antibody drug. This drug was an IgG₁ monoclonal antibody (MoAb) that binds to the human HM1.24 antigen named anti-HM1.24 MoAb. The presence of the HM1.24 antigen on the erythrocyte membranes and the erythrocyte agglutination following the addition of anti-HM1.24 MoAb was examined. In addition, an indirect Coombs' test, a hemolysis assay and the measurement of anti-single stranded-DNA antibodies were performed using test animal serum or plasma.
The specific binding of FITC- and ¹²⁵I-labeled anti-HM1.24 MoAb to the erythrocyte membrane was not observed. HM1.24 antigen was not identified on the erythrocyte membranes. However, a high concentration (more than 713 μg/mL) of anti-HM1.24 MoAb hemagglutinated the erythrocyte suspensions. The cause of this agglutination was unclear, but it is assumed that the non-specific binding and/or adhesion caused the direct agglutination. In the examination using test serum from the anemic monkeys, a positive reaction in the indirect Coombs' test was noted. Moreover, in these Coombs' test-positive animals, the production of anti-single stranded-DNA antibodies was sequentially increased. In the female monkey sacrificed in extremis due to severe anemia, an in vitro hemolytic reaction was detected attributable to complement activation.
From these results, the hemolytic anemia detected in the repeated-dose toxicity study was diagnosed as a drug-induced autoimmune hemolytic anemia (AIHA) and the primary cause was assumed to be production of IgG class anti-erythrocyte autoantibodies.

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Cypridina luciferin analogs have been widely used as a specific chemiluminescence probe for the detection of superoxide anion (O₂^•−) and singlet oxygen (¹O₂). However, light emission during the reaction of Cypridina luciferin analogs and other active oxygen species (AOS) has not been reported in detail. Therefore, we re-evaluated 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazine-3-one (MCLA), one of the Cypridina luciferin analogs, as a chemiluminescence probe to detect various AOS. MCLA-dependent chemiluminescence was observed when MCLA was incubated with the following systems; 1) hypoxanthine plus xanthine oxidase (O₂^•−), 2) thermolysis of endoperoxide (¹O₂), 3) hydrogen peroxide plus ferrous ion (hydroxyl radical), 4) ferrous ion, 5) thermolysis of azo compound (alkyl peroxyl radical) and 6) hydrogen peroxide. Superoxide dismutase inhibited MCLA-dependent chemiluminescence observed during ferrous ion-induced decomposition of hydrogen peroxide. Alkyl peroxyl radical reacted with MCLA, but light was not emitted when the concentration of MCLA was high. These results suggest that radicals, except O₂^•−, appeared not to be direct inducers of MCLA-dependent light emission. In summary, MCLA-dependent chemiluminescence was induced by various AOS in addition to O₂^•− and ¹O₂, but active species must be O₂ ^•− and ¹O₂ in many cases. These points should be appreciated when Cypridina luciferin analogs, such as MCLA, are used for the detection of AOS.

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Pregnant rats were administered flutamide (0 and 10 mg/kg, p.o.) from gestation Day 14 to post-parturition Day 3 and effects on responsiveness to androgens (testosterone propionate, TP; dihydrotestosterone, DHT) in male offspring were examined with a Hershberger assay.
Male pups of each group were assigned to 6 subgroups as follows: Group 1, castration and euthanized at postnatal Day 46 (PND 46); Group 2, castration + vehicle; Group 3, castration + TP; Group 4, castration + DHT; Group 5, vehicle; Group 6, DHT. After castrations were conducted at PND 36, animals were treated with TP (2 mg/kg in corn oil, s.c.) or DHT (1.25 mg/kg in corn oil, s.c.) once a day for 10 days, beginning at PND 46. At PND 56, the following organs/tissues were removed and weighed: ventral prostate, dorso-lateral prostate, seminal vesicles with coagulating glands, levator ani muscle plus bulbocavernosus muscle, Cowper's gland, and glands penis. Analysis of serum testosterone, LH and FSH in Groups 2, 3, 4, 5 and 6, and RT-PCR using prostate tissue from Groups 2, 3 and 4 were carried out.
Perinatal exposure to flutamide caused decreased weights of androgen-dependent organs. Responses to androgens were recognized in organs of all castrated groups, with increased organ weights, especially in animals administered TP where values were essentially equal to or greater than those of intact animals in both the control and the 10 mg/kg group. On the other hand, the degree of weight increase of the ventral prostate and seminal vesicles with TP or DHT treatment in castrated animals was smaller in the flutamide administration group than in the controls. In hormone assays, castrated + vehicle animals showed higher serum LH than the other groups. Serum FSH was high in the castrated groups (Group2>Group 4>Group3), while in the noncastrated group a constant level was noted, with or without flutamide. No effect of flutamide administration was observed regarding sex hormone. RT-PCR using ventral prostate tissue revealed no significant differences in expression of AR, C3, VEGF, TGF-beta1, beta2, KGF and CK8 mRNA after androgen treatment between the control and flutamide treatment groups. C3 mRNA was increased in androgen-treated animals, whereas AR, TGF-beta and KGF mRNAs were decreased.
Perinatal exposure to anti-androgen causes irreversible abnormalities in male pups. Concerning the responsiveness to TP and DHT, the degrees of weight changes in ventral prostate and seminal vesicles in castrated animals were decreased. However, the other organ weights, the sex hormone levels and androgen-reactive gene expression in the ventral prostate were not influenced by perinatal flutamide treatment in the present study.

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The current study was designed to examine the modulating effects of bisphenol A (BPA) on prostate cancer risk in male offspring exposed transplacentally and lactationally. BPA was administered to F344 female rats by gavage at 0, 0.05, 7.5, 30, 120 mg/kg/day during pregnancy and lactation periods. When F₁ males reached 5 weeks old, they were given 10 subcutaneous injections of 3,2'-dimethyl-4-aminobiphenyl (DMAB) or corn oil vehicle and rats were then sacrificed under ether anesthesia at week 60. There were no observable effects on the accessory sex organ weights of male offspring. Transplacental and lactational exposure to BPA did not affect the incidences of preneoplastic and neoplastic lesions in the accessory sex organs (prostate and seminal vesicle) of F₁ rats and did not induce any proliferating lesions without DMAB. Our data suggest that maternal exposure to BPA during the period of pregnancy and lactation does not affect the risk of prostate carcinogenesis in male offspring.

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In order to clarify the in vivo genotoxicity of dicyclanil with the potential of hepatocarcinogenicity, the stomach, colon, liver, kidney, urinary bladder, lung, brain and bone marrow of male ddY mice given a single oral administration of 100 and 200 mg/kg body weight of dicyclanil were evaluated in an alkaline single-cell gel electrophoresis (comet) assay. In addition, to investigate its possible initiation activity, partially hepatectomized male F344 rats given a single oral administration of 75 mg/kg body weight of dicyclanil were examined by a short-term liver initiation assay. Three and 24 hr after administration, cell migration, as a marker of DNA damage in comet assay, was not observed in any of the tissues of dicyclanil-treated mice. There were no significant differences in the number and area of glutathione S-transferase placental form (GST-P) positive foci, as a marker of hepatocellular preneoplastic lesions in rats, between treated and control groups. These results indicate that dicyclanil has neither in vivo genotoxicity nor initiation activity, and suggest that the hepatocarcinogenicity in mice induced by dicyclanil is attributable to a non-genotoxic mechanism.

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Methyl methanesulfonate (MMS), a methylating agent, is known to be a genotoxicant in testis. The purpose of this study was to investigate roles of oxidative stress-responsive proteins, heme oxygenase-1 (HO-1) and metallothionein-1/2 (MT-1/2), in genotoxicity of MMS. Cadmium, a potent genotoxicity inducer, induced HO-1 and MT-1/2 in rat livers and kidneys. Then we comparatively investigated MMS-induced HO-1 and MT-1/2 in rat livers, kidneys and testes. We found that a single administration of MMS (40 mg/kg) resulted in the induction of MT-1/2 mRNA in the liver, but not HO-1 mRNA, reaching maximum level at 6 hr and returning to the control levels by 24 hr. Interestingly, MMS induced both HO-1 and MT-1/2 mRNAs in the kidney. In contrast, MMS induced HO-1 mRNA, but not MT-1/2 mRNA in the testis. Since HO-1 and MT-1/2 have been recognized to respond to various oxidative stimuli, we further examined the inducing effect of MMS on these two proteins. MMS at dosages of 20 to 40 mg/kg for 2 consecutive weeks induced HO-1 mRNA (123 to 187% of the control) and protein (274 to 404% of the control) in rat testes. However, MT-1/2 mRNA was not induced by MMS administration, although a high level of expression was observed in comparison with the liver and kidney. These findings suggest that MMS induces HO-1 and/or MT-1/2 mRNA and its protein tissue-dependently, and the heme catabolites by HO-1 in the testis may contribute in some manner to its genotoxicity.

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