Fundamental Toxicological Sciences Vol. 4(2017) No. 3

It is known that phototoxicity is related to chemical structure. We have previously reported a prediction method of chemical structure-based in silico phototoxicity for in vitro 3T3 NRU-PT assay. To improve the concordance of the method, here we added new descriptors related to another mechanism of phototoxicity. We focused on potential energy, which certainly contributes to chemical reactivity regardless of photo-irradiation. As a result, stretch-bend, a form of potential energy, was found as a new descriptor of phototoxicity. Our analysis strongly indicates that chemical reactivity is an important factor for phototoxic outcome.

To analyze the permeability of rat skin to silver nanoparticles, the dorsal skin of Sprague-Dawley rats was exposed to 5 nm Ag nanoparticles or silver nitrate (Ag⁺ ions) percutaneously for 24 hr after disruption of the epidermal barrier by tape stripping (TS) or acetone wiping (AC). Systemic toxicity was examined hematologically and histopathologically, and by assessing blood biochemistry. Although parakeratosis, decrease in keratohyaline granule, and thickening in the epidermis occurred following exposure to both 5 nm Ag nanoparticles and Ag⁺ ions after TS or AC, no Ag-specific changes were observed. Inductively coupled plasma mass spectrometry (ICP-MS) showed silver in the skin of rats exposed to both 5 nm Ag nanoparticles and Ag⁺ ions after TS or AC. Silver was only detected in the liver of rats exposed to Ag⁺ ions after TS, but not exposed to 5 nm Ag nanoparticles after TS or AC. No abnormal histopathological changes in the liver were observed in all rats. In the blood, silver was below detectable levels in all rats and had no adverse effects on hematology or blood biochemistry. These results indicate that silver ions released from 5 nm Ag nanoparticles can percutaneously infiltrate the body only when the skin barrier is disrupted, but does not induce any acute toxicity.

Animal tests, such as the local lymph node assay (LLNA), are the gold standard for assaying skin-sensitizing potential. However, because of concerns about animal welfare, extensive research has been conducted on the use of various cell lines, such as human leukemia cells, for in vitro assays of skin-sensitizing potential, but such assays have not replaced animal tests as stand-alone assays. Because Langerhans cells—a type of dendritic cell—are the main antigen-presenting cells in the epidermis and because they play a central role in the induction of allergic skin disorders, these cells may be useful for skin-sensitizing-potential assays. Here, we investigated the utility of the murine dendritic cell line DC2.4 for in vitro assay of the skin-sensitization potential of 2,4-dinitrochlorobenzene (DNCB), 2-mercaptobenzothiazole (MBT), and α-hexyl cinnamaldehyde (HCA), which are categorized as extremely, moderately, and weakly sensitizing, respectively, on the basis of LLNA results. DC2.4 cell viability decreased dose-dependently with increasing concentration upon treatment with each of the compounds for 24 hr; the DNCB, MBT, and HCA concentrations that resulted in 75% cell viability were 6.07, 120.14, and 118.70 μg/mL, respectively. At nontoxic concentrations (concentrations less than the 75% cell viability concentrations), these compounds dose-dependently upregulated the expression of both CD86 and CD54 on the surface of DC2.4 cells. Their potency decreased in the order DNCB > MBT > HCA, which agrees with the order indicated by the LLNA. These results suggest that DC2.4 cells may be a viable replacement for human leukemia cells in in vitro assays of skin-sensitization potential.

Drug candidates sometimes cause a prolongation of the electrocardiogram QT-interval (QT) and torsades de pointes in humans, despite the fact that they do not cause them in non-rodent animals. Recent studies suggest that the cardiomyocytes derived from human induced-pluripotent stem cells (hiPS-CMs) are of sufficient quality to assess the cardiotoxicity of drugs in the preclinical setting. Thus, the usefulness of hiPS-CMs in correctly predicting the cardiotoxicity of drug candidates in the clinical setting, was examined using conventional drugs in the calcium transient analysis system FDSS/µCELL and the multielectrode array system MED64. The selection of the test drugs was based on previously reported studies. E-4031 and cisapride prolong the QT in humans, dogs and monkeys. Both drugs prolonged the calcium fluorescence peak width (PWD) in the FDSS/µCELL system and the field potential duration (FPD) in the MED64 system, both of which are thought to be surrogates of the QT. Diphenhydramine, famotidine and E-8010 prolong the QT in humans but not in dogs or monkeys. These drugs prolonged the PWD and FPD. On the other hand, verapamil and nifedipine prolong the QT in dogs or monkeys but not in humans. Both drugs shortened the PWD and FPD. These results suggest that the hiPS-CMs assay could correctly predict the QT effects in humans. The hiPS-CMs would be useful for predicting the effects of drug candidates on the QT of humans in preclinical in vitro studies.