N,N’-[(Cyclohexylmethylene)di-4,1-phenylene]bis[2-(1-pyrrolidinyl)acetamide] (1) is a novel antiprion compound, termed a designer molecular chaperone, that we recently developed. The administration of compound 1 prolonged the survival time of prion-infected mice and slowed the development of neurological and psychological symptoms in prion-infected macaques. The aim of this study was to investigate the oral toxicity of compound 1 to rats and cynomolgus monkeys. Compound 1 was administered orally to rats at doses of 31.3, 125, and 500 mg/kg. Although two of ten rats died at a dose of 500 mg/kg, no serious safety problems were identified at doses of 31.3 and 125 mg/kg. Repeated oral administration of compound 1 to rats at a dosage of 31.3 mg/kg/day for a week led to no significant toxic effects in the rats. An acute toxicity test in cynomolgus monkeys revealed that the administration of compound 1 at a dose of 60 mg/kg induced vomiting and fecal abnormalities. The monkeys did not die even at a dose of 250 mg/kg. A dose-dependent increase in the plasma concentrations of compound 1 in the cynomolgus monkeys as measured by LC/MS/MS analysis indicated that compound 1 migrated into the bloodstream. These results suggest that compound 1 might have potential as a therapeutic agent for prion diseases.

Antimony (Sb) is a useful metalloid in many industries and a therapeutic agent for leishmaniasis in developing countries. Thus, it is expected that humans and wild animals face the risk of exposure to Sb. Although Sb is generally recognized as a toxic element, the mechanisms underlying its toxicity have not been fully elucidated yet. The objective of this study was to evaluate species differences in Sb distribution in blood and urine between rat and hamster. Antimony was more preferably accumulated in rat red blood cells (RBCs) than hamster RBCs. On the other hand, it has been reported that arsenic is bound to a specific cysteine residue in rat hemoglobin, which results in the substantial accumulation of arsenic in rat RBCs. These have led us to formulate the hypothesis that Sb, which belongs to the same group in the periodic table as arsenic, is also accumulated in the same manner as arsenic. However, because Sb was less accumulated than arsenic even in rat RBCs, Sb seemed to have less affinity for the cysteine residue than arsenic. Trivalent Sb showed greater accumulation than pentavalent Sb in rat RBCs. Consequently, species differences in Sb distribution between rat and hamster could be attributed to the affinity for the specific cysteine residue in hemoglobin.

A standard animal model for phototoxicity evaluation does not appear in any guideline. Sprague-Dawley (SD) rats have been widely used in general toxicity and toxicokinetic studies and can be used in phototoxicity evaluation to reduce animal usage. To standardize phototoxicity procedures of SD rat, we investigated skin site- and sex-related differences in sensitivity to drug-induced phototoxicity at 3 facilities. Six-week-old male and female SD rats were orally administered 30 or 100 mg/kg lomefloxacin and light irradiation 1 hr after dosing; an ultraviolet (UV) irradiation device (10 J/cm2, UVA) or solar simulator (18 J/cm2, UVA) was used as light sources. Phototoxic reactions on ventral skin, dorsal skin, and auricle were observed macroscopically at 2, 24, 48, and 72 hr after irradiation. Plasma concentrations of lomefloxacin were also measured in non-irradiated, conscious rats. Skin reaction scores for ventral skin were highest and those of dorsal skin were lowest among the skin sites examined at all dose levels and facilities. Although drug concentrations in plasma were almost similar between sexes or higher in males than females, skin reaction scores appeared higher in females than males for ventral or dorsal skin. A difference in skin reaction scores among facilities was also observed; however, the order of skin sites based on sensitivity was approximately the same. We therefore suggest that appropriate conditions be drafted at each facility as differences in sensitivity to phototoxicity are dependent on skin site or sex in SD rats. Furthermore, we encourage multi-site validation studies to standardize experimental conditions in in-vivo phototoxicity studies.

Methylmercury is an environmental pollutant that causes central nervous system injury. We reported that the expression of the inflammatory cytokines TNF-α and IL-1β was specifically induced in the brains of methylmercury-treated mice. In addition, we recently found that cytotoxic microglia (M1-microglia) may be involved in the induction of inflammatory cytokine expression by methylmercury in mouse cerebral slice cultures. In the current study, we investigated the involvement of M1-microglia in the neuronal cell death caused by methylmercury using mouse cerebral slice cultures. The results revealed that methylmercury activated steady state microglia (M0-microglia) to M1-microglia, but this activation was suppressed by pretreatment with minocycline, a microglial activation inhibitor. In addition, under the same conditions, minocycline suppressed neuronal cell death by methylmercury. These results suggest that methylmercury may induce neuronal cell death via activation to M1-microglia.

Cyclopentyl methyl ether (CPME, CAS No. 5614-37-9) is used as an alternative to other ethereal solvents in pharmaceutical chemical process development. Although brief summaries on the repeated dose toxicity or genotoxicity of CPME are available, no detailed toxicity information has been reported. This study performed a detailed hazard characterization of CPME using new reproductive/developmental toxicity data and existing data for a 28-day repeated dose toxicity and genotoxicity study of CPME. Sprague-Dawley (SD) rats were treated with CPME by gavage at doses of 50, 150, or 450 mg/kg/day in the reproductive/developmental toxicity study or at doses of 15, 150, and 700 mg/kg/day in the 28-day study. In the reproductive/developmental toxicity study, lower body weight in males and longer gestational lengths were observed in the F0 animals receiving the 450 mg/kg/day dose. In the F1 animals, lower body weight gain during days 1-7 of life was detected in the 450 mg/kg/day groups in both sexes. In the 28-day study, 6 of 10 males showed poor clinical conditions, resulting in unscheduled deaths in the 700 mg/kg/day group. Based on these findings, the NOAELs for both the reproductive/developmental and 28-day repeated dose toxicity studies were estimated at 150 mg/kg/day. The results of all genotoxicity studies including the bacterial reverse mutation test, in vitro mammalian cell chromosome aberration test, and in vivo mouse micronucleus test were negative. A permitted daily exposure (PDE) of 15 mg/day was suggested based on the present findings to help determine the PDE for the ICH guidelines on impurities in pharmaceuticals.