2-Mercaptobenzimidazole (MBI) and its methyl derivatives 4-methyl-MBI (4-MeMBI), 5-methyl-MBI (5-MeMBI), and 4(or 5)-methyl-MBI (4(5)-MeMBI) are widely applied industrial agents with substantial thyrotoxicity and hepatotoxicity detected in rats in vivo. Here, we examined the in vitro cytotoxicity of MBI and its derivates in cultured SIRC rabbit corneal cells. SIRC cells were cultured in the presence of the test chemicals for 72 hr, and cell viability was determined by estimating the number of cells using a crystal violet staining assay. The median lethal concentration (LC₅₀) was calculated for each of the chemicals. The methyl derivatives showed higher cytotoxicity than MBI, which is in contrast to previous in vivo findings demonstrating higher thyrotoxicity and hepatotoxicity of MBI compared to its derivates. According to the LC₅₀ values, the ranking of the tested agents in terms of cytotoxicity was 5-MeMBI (761.5 µM) ≥ 4-MeMBI (796.3 µM) ≥ 4(5)-MeMBI (822.9 µM) > MBI (1002.9 µM). The present results suggest that the lower thyrotoxicity and hepatotoxicity of methyl derivatives of MBI is related to their faster detoxification in vivo, because SIRC cells are considered to have lower drug-metabolizing activity than hepatic cells.

There are both advantages and disadvantages in the application of electromagnetic fields (EMF) for health: the former is deep brain stimulation for neurodegenerative disease in medicine and the latter is the possible association with a tumor. In this study, we examined the effect of EMF (50 Hz; 100 μT) on rat neural stem cells in vitro. During handling with culture cells, there are two phases of the state of neural stem cells isolated from rat brains; one phase is a cellular suspension in the medium (no anchorage), and another phase is anchorage to the bottom of the culture dishes. The effect of EMF on neural stem cells in vitro was dependent on these cellular phases. Upon anchorages, the cultured neural stem cells migrated along the radial axis, and exposure of these migratory neural stem cells to EMF (50 Hz; 100 μT) facilitates the migration and incorporation of BrdU 1.3~1.4 folds. However, these effects of EMF were not seen once the cellular suspension (no anchorage) was exposed. Even when the neural stem cells fully migrated, there were no effects of EMF on the retinoic acid-induced differentiation. Thus, there is a cell phase sensitive to EMF in the cultured neural stem cells.

3-Methylpentane, isooctane, and isononane are acyclic branched saturated hydrocarbons with carbon numbers C6, C8, and C9, respectively. To assess human risk, we conducted a combined repeated-dose and reproductive/developmental oral toxicity studies in rats. [Organization for Economic Co-operation and Development (OECD) Test Guideline 422]. Each hydrocarbon was administered by gavage to rats at three doses (plus a control group). All three chemicals targeted the liver and kidney. An increase in liver weight without hepatic injury was observed as the adaptive response to the chemical treatments. Males treated by each chemical showed α2u-globulin nephropathy, which is a rat-specific finding that bears no human relevance. Reproduction/developmental toxicity parameters showed no treatment-related effects in parents or offspring at any dose for the three chemicals, except for the retardation of offspring bodyweight development which may be a secondary effect of a maternal systemic condition or direct effect on offspring in isononane. No observed adverse effect levels (NOAELs) of repeated toxicity in either sex were determined to be 300 mg/kg/day for 3-methylpentane, 100 mg/kg/day for isooctane, and 250 mg/kg/day for isononane. NOAELs of reproductive/developmental toxicity in parents and offspring were determined to be 1000 mg/kg/day for 3-methylpentane, and 300 mg/kg/day for isooctane. For isononane, NOAELs were determined to be 1000 mg/kg/day for reproduction, and 250 mg/kg/day for offspring development. These results provide new toxicological information and support the category assessment of published reports that evaluate the acyclic branched saturated hydrocarbons as low-toxicity substances.

Transdermal sensitization by Glupearl 19S, which is a hydrolyzed wheat protein with a molecular weight of tens of thousands and present in a facial soap, has been reported. Intact skin is considered to function as a barrier; thus, a substance with molecular weight as high as that of Glupearl 19S cannot penetrate to the skin and cause sensitization. We studied whether moderate- or high-molecular-weight materials could penetrate into the skin by using intact and injured Yucatan micropig skin in vitro. Fluorescein isothiocyanate (FITC)-labeled dextran (MW 4000, FD4) and ovalbumin (FITC-OVA) were applied as 1% aqueous solutions with or without 1% sodium dodecyl sulfate (SDS) as a surfactant. FD4 penetrated in the stratum corneum of intact and delipidized skin, especially when combined with SDS. It also penetrated into the dermis of stripped skin (the stratum corneum was removed by tape stripping). FD4 was observed in some scratches of the skin and diffused into the epidermis. FITC-OVA was partially observed in the stratum corneum of intact and delipidized skin. In the case of stripped skin, FITC-OVA did not penetrate in the viable epidermis or dermis because it could not pass through tight junctions even if they were open. FITC-OVA was observed in every scratch 2 min after the application and did not diffuse into the surrounding area as FD4 did. It is considered that FITC-OVA penetrates skin defects and remains at the site, which increases the possibility of sensitization by Langerhans cells.

The effects of N^G-Nitro-_L-arginine-methyl ester (_L-NAME), an inhibitor of nitric oxide (NO) synthase, on decidual cell proliferation were examined to investigate possible NO depletion-mediated mechanisms of reproductive toxicity. Mid-to-late pregnant rats were injected intraperitoneally with _L-NAME (100 mg/kg body weight) and 5-bromo-2′-deoxyuridine (BrdU, 100 mg/kg body weight) at 12 hr and 1 hr before sacrifice, respectively, on day 13.5, 17.5, or 21.5, and the BrdU-positive proliferating decidual cells were detected. In control rats, proliferating decidual cells were observed sporadically on days 13.5 and 17.5; however, fewer such cells were observed at day 21.5. _L-NAME reduced the number of proliferating decidual cells by approximately half at days 13.5 and 17.5 but not at day 21.5. These results suggested that in mid-to-late pregnant rats, decidual cell proliferation was maintained by a mechanism involving NO signaling, and NO depletion reduced it only to a limited extent. The absent effect at day 21.5 may be due to the low incidence of proliferating decidual cells or the changing role of NO near the term of pregnancy.

Obesity and type 2 diabetes mellitus have become worldwide epidemics. Evidence indicates that glucose-dependent insulinotropic polypeptide (GIP) secreted by the intestines may partially underlie these conditions, considering that GIP levels are associated with lipid deposition and fat mass expansion. However, recent studies have found that GIP is also present in other tissues, such as the liver. Notably, one study discovered through microarray analyses of livers from obese diabetic rats that the transcriptional modulation of GIP also occurred in the liver. Otsuka Long-Evans Tokushima Fatty (OLETF) rats were chosen for this experiment because previous studies have shown that thiamine (vitamin B1) could successfully decrease the tendency of the animal toward obesity and mitigate the complications of diabetes. Here, the rats were randomly assigned to either the control (non-supplemented) or thiamine-supplemented (2 g thiamine/L in drinking water) groups. For this investigation, unlike that for young rats, OLETF rats were chosen for the experimental period at 93 weeks of age. Ageing is also a risk factor for diabetes and its complications. In this study, hepatic GIP expression was analysed using western blotting, suggesting that GIP was present in the livers of both obese diabetic OLETF rats and obese diabetic rats that received ongoing thiamine supplementation. Results showed that hepatic GIP expression had occurred and that liver-derived GIP may exist. Moreover, results showed that ongoing thiamine supplementation modified the hepatic GIP expression and prevented additional weight gain and complications arising from obesity and diabetes.