Atsuyuki Nishida

Assessment of 8-Methosypsoralen, Lomefloxacin, Sparfloxacin, and Pirfenidone phototoxicity in Long-Evans Rats

Phototoxicity has a strong impact on drug development. Although several animal models have been developed to quantitatively assess human risks, none have been validated for standardized use. In this study, we validated an in vivo phototoxicity model using Long-Evans (LE) rats treated with 4 well-known phototoxic drugs, namely 8-methoxypsoralen, lomefloxacin, sparfloxacin, and pirfenidone. Daily macroscopic observations of skin and eyes, ophthalmological examinations 4 days after dosing, and blood sampling for toxicokinetics (TKs) were performed after exposure of treated animals to ultraviolet, and dose-dependent eye and/or skin reactions were noted for all compounds. Margins of safety were calculated when possible and correlated well with known relative phototoxicity of the 4 compounds. We conclude that the present in vivo phototoxicity assay using LE rats with TK analysis can be used to quantitatively predict the risk of pharmaceutical phototoxicity in humans.

In vitro developmental toxicity of concanavalin A in rat embryos : Analysis of neural crest cell migration using monoclonal antibody HNK-1

The developmental toxicity of concanavalin A (Con A) was evaluated in vitro using a rat whole embryo culture system, and the distributions of the neural crest cells were immunohistochemically investigated in embryos with monoclonal antibody HNK-1. In addition, binding sites of Con A in the embryos were observed according to the avidin-biotin peroxidase complex method with biotin-labeled anti-Con A. The rat embryos on embryonic day 8 were exposed to a final concentration of 12.5, 25, 50, or 100 micrograms/ml of Con A for a 72 hr culture period. Exposure to Con A concentration-dependently resulted in lower viability, decreases in yolk sac diameter, crown-rump length, and number of somites, and increases in the incidence of morphological abnormalities characterized by neural tube defects in the embryos. In the Con A-treated embryos, the distributions of the neural crest cells were restricted in the dorsal and cranial regions, and the migration into the interventricular chamber was delayed in the cardiac region. The Con A-treated embryos were confirmed to have Con A binding on the wall of the outflow tract in the cardiac region and in the mesenchyme of the cranial region, which are thought to be migration pathways of neural crest cells. These findings suggested that Con A inhibited the early migration of neural crest cells by binding directly to some substrates distributed along the pathways in the embryos, so that the neural crest cells could not punctually reach the locations where they would proliferate and differentiate into the destined cell types.

Relationship between Teratogenic Effects and Tissue Binding Pattern of Concanavalin A in Rat Embryos

ABSTRACT This study was conducted to examine the effects of concanavalin A (Con A) on rat neurulation. Con A was injected intravenously to pregnant rats at a single dose of 5, 10, or 20 mg/kg between gestational days (GD) 7.5 and 10.0, and the embryos were macroscopically examined on GD 11.5. Con A induced a high mortality rate, the treatment with 10 and 20 mg/kg on GD 9.5 was completely lethal. Con A caused a high incidence of neural tube defects (NTD), the incidence in the 10 mg/kg on GD 8.0 and 8.5 groups and in the 20 mg/kg on GD 8.0, 8.5 and 9.0 groups being significantly higher than that in the control group. Histological evaluation revealed that Con A inhibited neural tube expansion and altered neural crest cell shape. In the Con A‐treated embryos, the stratified structure of the neuroepithelium was irregular and its extracellular space was expanded. In rat embryos from intact dams, the distribution of receptors for Con A was demonstrated histochemically on the cell surfaces around neurulation sites between GD 8.5 and 10.5, but not on GD 7.5. These findings indicate that Con A bound around the neurulation sites in rat embryos may disturb the cell‐cell communication required to form the neural tube, resulting in NTD.