We have reported that four transcription factors (PAX4, PAX6, TCF3, and HMGA1) were markedly activated in the cerebellum of mice treated with methylmercury. In this study, to clarify the relationship between these transcription factors and methylmercury toxicity, siRNA targeting each of the four transcription factors were introduced individually into C17.2 mouse neural stem cells, and the sensitivity of the cells to methylmercury was investigated. Among the four transcription factors, knockdown of the gene for TCF3 increased the methylmercury sensitivity of C17.2 cells. Therefore, we suggest that TCF3 may have a protective effect against methylmercury toxicity.

β, β-dimethylacrylalkannin is a major active chemical component extracted from Lithospermum erythrorhizon, a traditional Chinese medicine that exhibits strong antimicrobial, anti-cancer and anti-inflammatory activities. However, its potential toxicity has not been rigorously studied. To confirm its safety, the oral toxicity of β, β-dimethylacrylalkannin was evaluated in vivo. An acute oral toxicity study in mice demonstrated that β, β-dimethylacrylalkannin was practically nontoxic based on its high median lethal dose (LD₅₀ > 10 g/kg). No deaths or abnormal responses were observed in the acute toxicity test using Wistar rats, suggesting that the maximum tolerated dose of β, β-dimethylacrylalkannin was greater than 10 g/kg. Chronic toxicity studies also revealed an absence of mortality and clinical symptoms, and no treatment-related adverse effects were detected by hematology, blood biochemistry and urinalysis examinations in all rats treated with 10-160 mg/kg/day β, β-dimethylacrylalkannin during a 6-month period. Increases in the relative organ weight of the lungs of females and the liver of males were observed at 160 mg/kg. Histopathological analyses revealed brown pigmentation in renal tubular epithelial cells at the middle and high doses (40-160 mg/kg/day). The no-observed-adverse-effect level (NOAEL) of β, β-dimethylacrylalkannin is 10 mg/kg/day. These results suggest that β, β-dimethylacrylalkannin is potentially safe for further development as a therapeutic agent in humans.

A series of safety studies were conducted using isomaltodextrin (IMD), a new dietary fiber that is produced from starch using enzymes. IMD consists of only alpha linkaged glucose molecules, has an average molecular weight of approximately 5,000, is freely soluble in water, and contains greater than 80% fiber (AOAC 2001.03). No genotoxicity was observed when IMD was assayed in standardized bacterial reverse mutation, micronucleus, and chromosome aberration tests. The LD₅₀ of IMD was found to be more than 2,000 mg/kg in an acute toxicity study in rats, and the no observed adverse effect level (NOAEL) was determined to be 1,000 mg/kg/day in a 90-day subacute gavage toxicity study in rats. No animals died, and no abnormal findings due to consumption of IMD were observed in either of these studies. Both NOAEL values were the highest doses tested. The NOAEL for loose stools was examined in humans in two separate studies. Based on these results, the NOAEL for IMD-related loose stools was considered to be 0.8 g/kg-BW. In a 4-week high-dose ingestion study in humans and a 12-week low-dose ingestion study in humans, laboratory values were found to be within the normal range of variation. The results of the current safety assessment studies suggest that isomaltodextrin is safe for human consumption.

We aimed to identify novel biomarkers using toxicoproteomics to profile the urinary proteome of renal papillary necrosis (RPN) in experimental model rats. RPN was induced in rats by a single intraperitoneal injection of 2-bromoethylamine hydrobromide (BEA). Urinary proteins from four groups (control group; BEA-treated but no RPN; BEA-treated with RPN but no increase in blood urea nitrogen [BUN]; and BEA-treated with RPN and increase in BUN) were pooled. Relative quantitation of pooled urinary proteins was then performed by two-dimensional liquid chromatography-tandem mass spectrometry with the isobaric labeling technique. We found 77 proteins were changed in RPN model rat urine.

A repeated-dose ocular instillation toxicity study is a type of general toxicity study having unique design characteristics of species selection and administration methods, because the test article, an eye drop formulation, is instilled in the eyes. The present survey was conducted to reveal the current status of the design of repeated-dose ocular instillation toxicity studies. Information on study design was collected from the common technical documents of 21 eye-drop drugs approved in the last decade in Japan. The species most frequently employed was rabbits, followed by monkeys, then dogs. The most frequently used breed of rabbit was New Zealand white, followed by Dutch-belted. Both sexes were used in almost all the studies. In most cases, the maximum concentration of test articles was set as 3- to 10-fold higher than the clinical doses, and dosing frequency per day was set as 1.5 to 2 times the clinical usages. In many cases, a single eye of each animal was instilled with one or two drops or a fixed volume (e.g., 0.050 mL/eye in rabbits, 0.030 mL/eye in monkeys, and 0.030 to 0.100 mL/eye in dogs) of the test article. As optional ophthalmological examinations, measurements of intraocular pressure and corneal thickness were integrated frequently. In conclusion, this survey revealed design characteristics of repeated-dose ocular instillation toxicity studies, which were different in some respects from systemic dose toxicity studies. The results can be used as a baseline when considering the study design of such studies.

The effects of ∆⁹-tetrahydricannabinol (∆⁹-THC), cannabidiol (CBD), cannabidiolic acid (CBDA), and 2-methyl-2’-fluoro-anandamide (MF-AEA, a stable analog of anandamide) on the enzymatic activity of purified human calpain-1 (CAPN1) were investigated in the present study. Although leupeptin, a calpain inhibitor, reduced calpain-1 activity in a dose-dependent manner (1, 5, and 25 µM), among the four cannabinoids tested, ∆⁹-THC and CBD exerted stimulatory effects on calpain-1 enzymatic activity in the same concentration range as leupeptin. CBDA and MF-AEA did not modulate calpain-1 activity, indicating that the phenol structure in ∆⁹-THC/CBD is a key point, and the carboxylic acid moiety appears to be negatively involved. This is the first study to show that the phytocannabinoids, ∆⁹-THC and CBD have the ability to activate the enzymatic activity of human calpain-1.