Fundamental Toxicological Sciences

2022 - Vol. 9

2022 - Vol. 9

Original Article
Genotoxicity and subchronic toxicity of a kaempferol aglycone-rich product produced from horseradish leaves Vol.9, No.3, p.71-83
Hiroki Kimoto , Sakura Fujiwara , Noriyuki Koyama , Tohru Uesugi
Released: May 19, 2022
Abstract Full Text PDF[933K]

Kaempferol is a kind of natural flavonoid in many edible plants and reportedly has various physiological effects. In the present study, we conducted the genotoxicity (in vitro and in vivo) and 13-week subchronic toxicity studies of a new product, a kaempferol aglycone-rich food produced from enzyme-treated horseradish leaves, to evaluate its safety. In the bacterial reverse mutation test, the kaempferol aglycone-rich product showed positive results in some Salmonella typhimurium strains in the presence or absence of metabolic activation as well as other flavonoids. However, it did not increase micronucleated polychromatic erythrocytes taken from male Sprague−Dawley (SD) rats administered orally by gavage up to 4000 mg/kg for 2 consecutive days. In the 13-week subchronic toxicity study in SD rats, the kaempferol aglycone-rich product was orally administered by gavage once daily to SD rats for 13 weeks (91 days) at a dose of 500, 1000, or 2000 mg/kg/day. No toxic changes were observed at up to 2000 mg/kg/day. In conclusion, these findings indicated that the kaempferol aglycone-rich product was not genotoxic in vivo. The no-observed-adverse-effect level for both male and female rats was 2000 mg/kg/day, the highest dose tested, in the 13-week subchronic toxicity study in rats, suggesting it is safe for use as a food.

Original Article
Potential human health risks of mercury-contaminated cassavas – Preliminary studies Vol.9, No.2, p.61-69
Sylvester Addai-Arhin , Randy Novirsa , Hui Ho Jeong , Quang Dinh Phan , Nana Hirota , Yasuhiro Ishibashi , Hideki Shiratsuchi , Koji Arizono
Released: April 27, 2022
Abstract Full Text PDF[1M]

The inevitable use of mercury (Hg) and the regular release of its waste into the ecosystem through artisanal and small-scale gold mining (ASGM) activities particularly, in developing countries such as Ghana require constant monitoring and evaluation of Hg contamination and its potential toxicities particularly, in samples such as food. This study evaluated the potential human health risks associated with total mercury (THg) and methylmercury (MeHg) levels of mercury-contaminated cassavas from farms in selected ASGM communities around Obuasi, Ghana. The THg and MeHg levels were evaluated using the direct Hg analyser, MA-3000 while the human health risk assessment was done using the USEPA risk assessment model. The estimated average daily intake for ingestion (eAvDI(ing)) (mg/kgbw/day) and the hazard quotient (HQ) for THg levels of the samples were above the USEPA reference values of 3 x 10−4 and 1, respectively. This means that residents ingest more Hg through consumption of cassava, hence long-term repeated exposures to the cassavas may be associated with detrimental human health effects in future. MeHg levels may not cause any human health effects due to eAvDI(ing) and HQ below 1 x 10−4 and 1, respectively. However, constant releases of mercury waste and subsequent bioaccumulation along the food chain can cause MeHg levels to increase with time above the USEPA acceptable daily intake. Such levels may be detrimental to human health. Therefore, there is the need for regular and strict monitoring of ASGM activities within the studied communities and other communities involved in ASGM to protect human health and preserve ecosystem integrity.

Letter
Relationship between micronucleus formation and oxidative stress in human vascular endothelial cells under low dose rate irradiation Vol.9, No.2, p.47-59
Qingmei Meng , Ikue Hayashi , Kumiko Anno , Junya Kobayashi
Released: April 05, 2022
Abstract Full Text PDF[2M]

Acute irradiation stimulates oxidative stress and DNA damage responses. However, it is unknown whether chronic irradiation (IR) at a low dose rate causes similar responses, and epidemiological studies of radiation-exposed people with low doses have reported effects on cardiovascular diseases. Therefore, we investigated the cellular effects under low dose rate of IR in human vascular endothelial cells as a model for cardiovascular diseases. We demonstrated that a low dose rate of IR induces phosphorylation of p38MAPK and STAT1, which is related to cGAS, and increases p21, a cellular senescence-regulatory factor. A low dose rate of IR also causes a remarkable formation of micronuclei in human vascular endothelial cells. DIA proteome analysis in human vascular endothelial cells indicated an increase in oxidative stress- and inflammation-related protein levels, and a decrease in protein levels related to the repression of micronuclei formation following exposure to low dose rate of IR. These results suggest that a low dose rate of IR might induce oxidative stress and micronuclei formation, which could activate the cGAS pathway and subsequently lead to cellular senescence.

Letter
Molecular network analysis of RNA viral infection pathway in diffuse- and intestinal-type gastric cancer Vol.9, No.2, p.37-46
Shihori Tanabe , Sabina Quader , Ryuichi Ono , Horacio Cabral , Kazuhiko Aoyagi , Akihiko Hirose , Hiroshi Yokozaki , Hiroki Sasaki
Released: April 05, 2022
Abstract Full Text PDF[4M]

There are several subtypes of gastric cancer, such as diffuse-type gastric cancer (GC) and intestinal-type GC. Diffuse-type GC is known to be more malignant than intestinal-type GC, showing high metastasis, recurrence and anti-cancer drug resistance. The malignant phenotype of diffuse-type GC includes cancer stem cell (CSC)-like features and epithelial-mesenchymal transition (EMT). By analyzing the molecular network in these tumors, it is possible to reveal the mechanisms of anti-cancer drug resistance, therapeutic targets and drug safety. Upon the analyses of the molecular network in diffuse- and intestinal-type GC, a regulatory network for RNA virus infection was obtained. This study aims to reveal the relationship between cancer and RNA virus infection in detail. RNA virus infection-related molecules and cancer-related molecules were analyzed using network analysis tools, such as Ingenuity Pathway Analysis (IPA), and molecular networks related to RNA virus infection mechanisms. Regulator effect analysis revealed the involvement of RNA virus infection network in diffuse-type GC. c-Jun N-terminal kinase (JNK) and BCL2 like 11 (BCL2L11) in the Coronavirus Pathogenesis Pathway were activated. In conclusion, this research suggested the relationship between the mechanisms of RNA virus infection and diffuse-type GC. This study may be useful for virus infection control and cancer drug discovery by clarifying the relationship between the mechanism of RNA virus infection and cancer.

Letter
Absence of in vivo mutagenicity of 4,4'-oxybis(benzenesulfonohydrazide) in liver and glandular stomach of MutaTM Mouse Vol.9, No.2, p.31-36
Takako Iso , Masakatsu Natsume , Yasumasa Murata , Yoshiyuki Shigeta , Nozomu Hirose , Takaaki Umano , Katsuyoshi Horibata , Kenichi Masumura , Kei-ichi Sugiyama , Mariko Matsumoto , Akihiko Hirose
Released: April 05, 2022
Abstract Full Text PDF[860K]

4,4'-Oxybis(benzenesulfonohydrazide) (OBSH) is a blowing agent widely used in the manufacture of porous plastics and rubber. OBSH was notified as an additive in the Japanese positive list system for food utensils, containers and packaging. The in vitro mutagenicity of OBSH was shown extensively in bacterial reverse mutation assays, a DNA repair test, and a chromosomal aberration test. Few studies exist on in vivo genotoxic evaluation on OBSH apart from an in vivo micronuclei test. To clarify in vivo mutagenicity, we conducted a transgenic rodent gene mutation (TGR) assay (OECD TG 488). We dosed male MutaTM Mouse with OBSH by oral gavage at 0 (negative control), 25, 50, and 100 mg/kg/day for 28 consecutive days, and evaluated mutant frequencies (MFs) of lacZ in the liver and glandular stomach (5 mice/group). We observed two deaths and a reduction in body weight at 100 mg/kg/day. Although we exposed MutaTM Mouse to OBSH orally for 28 days up to the maximum tolerated dose, we did not detect in vivo mutagenicity in the liver and glandular stomach. In contrast, in the positive control we detected significantly increased MFs. The results of this study suggest that OBSH is not mutagenic in vivo.

Erratum
Erratum: Utility of murine dendritic cell line DC2.4 for in vitro assay of skin-sensitization potential Vol.9, No.1, p.25-30
Erina Shiraishi , Akiko Ido , Youhei Hiromori , Kento Tanaka , Tomoki Kimura , Hisamitsu Nagase , Tsuyoshi Nakanishi
Released: March 16, 2022
Abstract Full Text PDF[1M]

PDF

Erratum
Erratum: Safety assessment of a soluble dietary fiber, isomaltodextrin, enzymatically produced from starch Vol.9, No.1, p.23-23
Tsuyoshi SadakiyoSadakiyo , Shin-ichiro Inoue , Yuki Ishida , Hikaru Watanabe , Hitoshi Mitsuzumi , Shimpei Ushio
Released: February 28, 2022
Abstract Full Text PDF[509K]

[Fundam. Toxicol. Sci., 4, 57-75 (2017) ]
Page 67, line 6-7 from bottom


Error:
These subjects continued to consume increasing doses of IMD.


Correction:
These subjects stopped to consume increasing doses of IMD.

Letter
A novel high-purity carbon-nanotube yarn electrode used to obtain biopotential measurements in small animals: flexible, wearable, less invasive, and gel-free operation Vol.9, No.1, p.17-21
Yuhji Taquahashi , Shuji Tsuruoka , Koichi Morita , Masaki Tsuji , Kousuke Suga , Ken-ich Aisaki , Satoshi Kitajima
Released: January 18, 2022
Abstract Full Text PDF[1M]

Carbon-nanotube yarn (CNT-Y) made from high-purity, highly crystalized, double-walled carbon nanotubes is an advanced material with excellent electrical conductivity and flexibility; hence, it could potentially be used as a novel electrode for biopotential measurements. To our knowledge, the present study is the first in which CNT-Y electrodes were used to conduct electrocardiography (ECG) and electroencephalography (EEG) on experimental animals. All procedures and biopotential measurements were performed under isoflurane anesthesia. The CNT-Y electrodes were attached to the animals by creating a single interrupting suture on the skin. The lead II electrode configuration was used for ECG recording, i.e., the positive, negative, and body-earth electrodes were placed on the left apex of the auricular surface, the interscapular region, and the cervical region, respectively. The bipolar lead was used for EEG recording, with the exploring and reference electrodes on the bregma and base of the right auricular surface, respectively. Using CNT-Y electrodes, we obtained a clear ECG waveform from rats and a guinea pig; the QRS amplitude was ~1.4 mV. In rats, we obtained an EEG waveform with an amplitude of ~150 µV; the peak frequency was 0.8 Hz and the range was ~3 Hz according to power spectral density analysis. In the guinea pig, we obtained an EEG waveform with an amplitude of ~500 µV; the first peak was 0.1 Hz, the second peak was 1 Hz, and the range was ~3 Hz. These results show that CNT-Y could be used in toxicology studies to easily and inexpensively obtain high-resolution biological signals.

Letter
Dietary rapeseed (canola) oil suppresses testosterone production and increases plasma aldosterone level in stroke-prone spontaneously hypertensive rats (SHRSP) Vol.9, No.1, p.7-16
Mai Nishikawa , Naoki Ohara , Yukiko Naito , Chihiro Amma , Yoshiaki Saito , Kenjiro Tatematsu , Jinhua Baoyindugurong , Daisuke Miyazawa , Yoko Hashimoto , Harumi Okuyama
Released: January 15, 2022
Abstract Full Text PDF[2M]

The present study was conducted to survey the influence of canola oil (CAN) ingestion on the steroid hormone production in stroke-prone spontaneously hypertensive rats (SHRSP). Male SHRSP were fed a diet containing 10 wt/wt% soybean oil (SOY, the control) or CAN as the sole dietary fat for 8 weeks. Plasma concentration of luteinizing hormone (LH) was similar in the 2 dietary groups. However, the plasma testosterone level in the CAN group, 1.36 ± 0.271 ng/mL, was lower than in the SOY group, 2.79 ± 0.514 ng/mL (p < 0.05, unpaired t-test; n = 10), and plasma concentration of aldosterone in the CAN group, 345 ± 79.6 pg/mL, was higher than in the SOY group, 159 ± 33.7 pg/mL (p < 0.05, unpaired t-test; n = 10). In the testis, the expressions of mRNA for StAR, CYP11A1, CYP17, 3βHSD and 17βHSD and the amounts of the corresponding proteins were significantly decreased. However, in the adrenal gland, the expressions of mRNA for StAR, CYP11A1, 3βHSD and CYP11B1 in the CAN group were not different from those in the SOY group, but the expression of mRNA and the amount of the corresponding protein for CYP11B2 were increased significantly in the CAN group. These findings are indicative of a peripheral, testicular toxicity of CAN. The decreased testosterone and the concomitantly increased aldosterone may play a role in the aggravation by CAN of the genetic diseases (i.e., metabolic syndrome-like complications) in male SHRSP.

Letter
Glyceraldehyde 3-phosphate dehydrogenase converts methylmercury to its sulfur adduct with lowered toxicity through sulfane sulfur atoms on Cys247 Vol.9, No.1, p.1-5
Yumi Abiko , Eiko Yoshida , Yoshito Kumagai
Released: January 15, 2022
Abstract Full Text PDF[2M]

Methylmercury (MeHg) reacts with nucleophilic sulfur species to form sulfur adducts, such as the low-toxic metabolite bismethylmercury sulfide [(MeHg)2S]. We found that protein-bound persulfides interact with MeHg to form (MeHg)2S and identified glutathione S-transferase pi 1 as a S-sulfhydrated protein involved in (MeHg)2S formation. Although glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a house-keeping protein abundantly expressed in various tissues, has been reported to undergo S-sulfhydration in the presence of sulfur donors or cystathionine γ-lyase, the biological significance of this post-translational modification is poorly understood. In this study, we investigated the possible interaction between GAPDH and MeHg to form (MeHg)2S. High-performance liquid chromatography/atomic absorption spectrophotometry revealed that (MeHg)2S was formed during the reaction of MeHg with a model of cysteine persulfide and GAPDH following incubation of the protein with NaHS. After reacting with NaHS, GAPDH C152S and C156S mutants transformed MeHg into (MeHg)2S, whereas formation of the sulfur adduct was not observed for the C247S mutant, suggesting that Cys247 is critical for conversion of MeHg to (MeHg)2S. These results suggest that the sulfane sulfur on Cys247 of GAPDH plays a protective role in reducing MeHg toxicity.