The Short Time Exposure (STE) test method is an in vitro method for assessing the eye irritation potential of chemicals and is used to classify the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) Category 1 and No Category (NC). The method has been adopted by the Organisation for Economic Co-operation and Development (OECD) as test guideline (TG) 491 since 2015. While this method can be used to classify GHS NC, it is not suitable for testing highly volatile substances and solids other than surfactants. Here we evaluated highly volatile substances to expand the applicability domain. According to TG 491, acetone, ethanol, iso-propanol, and methyl acetate as highly volatile substances resulted in false negatives. Saline was selected as a solvent of these false negatives. In this study, mineral oil was used as the solvent, because these false negatives were amphiphilic. Based on this change, four highly volatile substances were correctly evaluated. The predictive performance for classifying GHS NC was then verified using a substance dataset constructed in reference to the Draize eye test Reference Database and STE Summary Review Document. The accuracy and false-negative rate were 86.6% (194/224) and 3.8% (3/80), respectively. Collectively, the applicability domain was expanded by changing the solvent to mineral oil for highly volatile substances, and the predictive performance for the new applicability domain including highly volatile substances was excellent. The STE test method is suitable to classify GHS NC, indicating its applicability as a test method in a bottom-up approach.
Although obesity is increasing worldwide, experimental studies examining the possible association between obesity and susceptibility to chemical toxicity are limited. In the present study, we performed a 13-week toxicity study for acetaminophen (APAP), a well-known drug that exhibits hepatotoxicity as an adverse effect, using an obese rat model to investigate the differences in susceptibility between obese and normal individuals. Male F344 and obese Zucker (lean and fatty) rats were administered 0, 80, 253, 800, 2,530, or 8,000 ppm APAP in the diet for 13 weeks. No significant toxicity related to APAP treatment was observed in terms of clinical signs and hematology in all three strains. Body weight gain in F344 and lean rats was significantly decreased by 8,000 ppm APAP treatment. Significant increases in serum total cholesterol level and relative liver weights were detected in F344 rats in the highest dose group. On histopathological assessment, centrilobular hepatocellular hypertrophy was observed in the 8,000 ppm groups of F344 and lean rats, whereas no histopathological changes were induced by APAP in fatty rats. The no-observed-adverse-effect levels (NOAELs) of APAP were evaluated to be 2,530 ppm in F344 and lean rats (142.1 and 152.8 mg/kg bw/day, respectively) and more than 8,000 ppm in fatty rats (> 539.9 mg/kg bw/day). These results suggested that obese Zucker rats may be less susceptible to APAP-dependent toxicity in the liver than their lean counterparts.
Teriparatide, a drug used in the treatment of osteoporosis, was administered to rats subcutaneously for the duration of 3 months, at a frequency of either once weekly or once daily to demonstrate the varying levels of anabolic action the drug can have on bone depending on the dosing frequency. The levels of biomarkers in the blood were compared and found to vary in osteocalcin (OC), a biomarker of bone formation, and cross-linked N-telopeptide of type 1 collagen (NTx), a biomarker of bone resorption, according to the dosing frequency. In the once-weekly regimen, teriparatide did not affect NTx levels at any of the doses studied, while OC levels increased with dose, peaking at 72 hr, then returning to normal before the next injection (after 1 week). Bone mineral density (BMD) levels increased moderately with no difference between doses. This was thought to result from the steady state achieved following increases in bone formation and bone absorption. In the once-daily dosing regimen, meanwhile, NTx levels increased with dose, and OC levels were markedly higher when compared to those with the once-weekly dosing. BMD levels were higher than those with the once-weekly dosing, but with no difference between doses. This was considered a result of unlimited, excessive increases in bone formation due to daily administration of the drug. These results suggest that teriparatide promotes normal bone metabolism (“stationary mini-modeling”) when administered once weekly, and has an anabolic action with high metabolic turnover (“high-turnover remodeling”) when administered once daily.
The nuclear receptor pregnane X receptor (PXR) plays a major role in the xenobiotic-induced expression of drug-metabolizing enzymes. PXR activation is also associated with several adverse events in the liver. Especially, the receptor enhances hepatocyte proliferation mediated by chemical liver tumor promoters, suggesting that exposure to PXR activators increases the risk of liver cancer. In this study, we have investigated the influences of food additives on PXR to understand their potential adverse effects when they are taken in combination with other chemical compounds. We first screened 25 food additives and related compounds for their PXR-activating ability using reporter assays in HepG2 cells expressing mouse PXR, and found that imazalil dose-dependently activated mouse PXR. Next, to investigate whether imazalil could activate mouse PXR in vivo, mice were treated with imazalil and we found that imazalil treatment increased hepatic mRNA levels of Cyp3a11, a PXR target gene. Finally, to investigate the influence of imazalil exposure on the hepatocyte proliferation induced by nuclear receptor constitutive active/androstane receptor (CAR), mice were treated with imazalil with or without mouse CAR activator TCPOBOP. Although imazalil alone did not induce hepatocyte proliferation, co-treatment with imazalil facilitated the TCPOBOP-dependent proliferation, indicated by the increases in cell proliferation marker levels, Ki-67-positive nuclei and Mcm2 mRNA levels. These results suggest that in mice imazalil activates PXR to enhance hepatocyte proliferation mediated by CAR-activating liver tumor promoters.
The purpose of this study was to investigate the discriminative stimulus properties of morphine and codeine using different administration routes to that used at drug discrimination training. Rats were trained to discriminate morphine at 3 mg/kg from saline by the intraperitoneal route in a standard two-lever drug discrimination paradigm. Generalization of morphine by the subcutaneous and the oral routes, and codeine by the intraperitoneal and the oral routes to the discriminative stimulus properties of the morphine training dose were investigated. Morphine at 3 mg/kg by the subcutaneous route generalized to the morphine training dose and 10 of 12 rats showed 80% or more morphine-lever responses. In the administration of morphine by the oral route, morphine at 30 mg/kg generalized to the morphine training dose and all rats showed 80% or more morphine-lever responses within the range of 3 to 30 mg/kg. In the administration of codeine by the intraperitoneal route, codeine at 20 mg/kg generalized to the morphine training dose and 14 of the 15 animals showed 80% or more morphine-lever responses within the range of 3 to 20 mg/kg. In the administration of codeine by the oral route, codeine at 60 mg/kg generalized to the morphine training dose and 14 of the 15 animals showed 80% or more morphine-lever responses within the range of 10 to 60 mg/kg. Thus, the discriminative stimulus properties of morphine and codeine were comparable when using different administration routes to those at discrimination training.
Total mercury (THg) and methylmercury (MeHg) bioaccumulation was explored in the Bimastus parvus species of earthworm (B. parvus) native to the leachate-contaminated forest soils around a Hg-polluted traditional landfill in Japan. General soil properties and concentrations of THg and MeHg in forest soils and in B. parvus were determined. The results indicated that the average THg concentrations in B. parvus and in forest soils in the leachate-contaminated sites were 10.21 and 14.90 times higher than those in the reference sites, respectively, whereas similar average MeHg concentrations were observed in forest soils (< 0.01 mg kg-1) and in B. parvus (0.100-0.114 mg kg-1) across all sampled sites. The average bioaccumulation factors of THg in B. parvus (BAFTHg) in forest soil were similar between the leachate-contaminated sites and the reference sites. Cluster and regression analyses demonstrated that the B. parvus Hg (THg and MeHg) and soil THg were positively correlated with each other and with soil organic matter (SOM) and clays, but were negatively correlated with sand and hardly correlated with silts and pH in leachate-contaminated forest soils. From these results, it was proposed that Hg exposure to food chains is possible through B. parvus, because B. parvus showed a high ability to accumulate THg and MeHg in both leachate-contaminated and reference forest soils. Together, these findings indicated that the role of B. parvus in MeHg production is not clear, and it is possible that the MeHg in B. parvus was firstly formed within forest soils and then accumulated in their tissues.
It has been demonstrated that successive ingestion of matured hop extract (MHE), produced by extraction from heat-treated hops, results in body fat reduction in animals and humans; however, preclinical safety studies have not been reported. In this study, we conducted in vitro and in vivo safety studies for MHE. Genotoxicity was evaluated using the Ames test, in vitro chromosomal aberration test, and in vivo micronucleus test. To assess acute safety, a single, oral administration of MHE to rats was monitored. Subchronic safety was assessed by repeated feeding with MHE for 90 days. The in vitro chromosomal aberration test was positive at 3,330 μg/mL and 5,000 μg/mL without metabolic activation. However, MHE did not induce any reverse mutation with or without metabolic activation in the Ames test, and no abnormalities were observed at a dose of 2,000 mg/kg body weight in the rat micronucleus test. In the acute and subchronic safety studies, no deaths or toxicological signs were recorded during the observation period. In addition, no changes in body weights, feed/water consumption, clinical signs, ophthalmoscopy, urinalysis, hematology, blood biochemistry, organ weights, or histopathology were observed after repeated administration of MHE. Therefore, the no-observed-adverse-effect-level (NOAEL) of MHE was considered to be over 3,484 and 4,022 mg/kg body weight/day in males and females, respectively. These results indicate that there is no safety concern for MHE in the present preclinical safety study.