Fundamental Toxicological Sciences

2019 - Vol. 6

2019 - Vol. 6

Letter
Genotoxicity evaluation of oil prepared from the internal organs of the Japanese giant scallop (Patinopecten yessoensis) Vol.6, No.4, p.137-143
Koki Sugimoto , Ryota Hosomi , Kenji Fukunaga , Takaki Shimono , Seiji Kanda , Toshimasa Nishiyama , Munehiro Yoshida , Takeya Yoshioka , Koretaro Takahashi
Released: June 13, 2019
Abstract Full Text PDF[797K]

Discarded scallop internal organs, especially the hepatopancreas, are rich in n-3 polyunsaturated fatty acids such as eicosapentaenoic acid and docosahexaenoic acid. However, they have not been utilized because of their contamination with toxic substances, such as cadmium (Cd), and the occurrence of diarrheic shellfish toxins (DST). We have successfully prepared a high-quality scallop oil (SCO) from the internal organs of the Japanese giant scallop (Patinopecten yessoensis), including the hepatopancreas without Cd and DST. These pollutants were removed by liquid-liquid partitioning followed by adsorption to active carbon of fine particle size with high pore surface volume. In this study, we prepared SCO from scallop internal organs obtained from two different processing areas (Mutsu and Uchiura bays, Japan), and referred to them as SCO-M and SCO-U, respectively. Genotoxicity of SCO-M and SCO-U was evaluated by the in vitro bacterial reverse mutation test (Ames test) and in vivo micronucleus test in accordance with the Organisation for Economic Co-operation and Development guidelines. SCO-M and SCO-U showed negative results in the Ames test in the presence or absence of metabolic activation with S9 mix. In addition, no genotoxic effects of SCO-M and SCO-U were observed at all tested doses in the micronucleus test. Based on the results of the present study, it can be concluded that SCO-M and SCO-U are safe products in terms of genotoxicity under these experimental conditions.

Original Article
Validation of the statistical parameters and model selection criteria of the benchmark dose methods for the evaluation of various endpoints in repeated-dose toxicity studies Vol.6, No.4, p.125-136
Mariko Matsumoto , Mutsuko Hirata-Koizumi , Tomoko Kawamura , Sawako Sakuratani , Atsushi Ono , Akihiko Hirose
Released: May 17, 2019
Abstract Full Text PDF[7M]

The benchmark dose (BMD) approach is one of the important techniques in dose-response assessment for the risk assessment of chemicals and adapted by various international organizations. We investigated the appropriateness of the statistical parameters and model selection criteria for BMD lower bound (BMDL) estimation by BMD software (BMDS) (developed by the US Environmental Protection Agency) and PROAST (developed by the National Institute for Public Health and the Environment of the Netherlands). Publicly available repeated-dose toxicity study data (226 dichotomous datasets and 151 continuous datasets) were used for the investigation. Our findings were applied to establish BMD technical guidance for BMDS for the evaluation of various endpoints in repeated-dose toxicity studies. Under the Japan Chemical Substance Control Law (CSCL), the DRA-BMDS guidance (i.e., Division of Risk Assessment-BMDS guidance) is used for the evaluation of a “Priority Assessment Chemical Substance.” Namely, selecting of an extra risk of 10% (dichotomous data) or a level change of 1SD (continuous data) as a default benchmark response. Running all the models without or with parameter constraints. Selecting the model that calculated the lowest BMDL but excluding the one that estimated a BMD/BMDL ratio ≥ 10 or lowest dose/BMDL ratio ≥ 10. We believe that the DRA-BMDS guidance can assist risk assessors in the selection of the BMD model.

Toxicomics Report
Gene expression profiles of immortalized S1, S2, and S3 cells derived from each segment of mouse kidney proximal tubules Vol.6, No.4, p.117-123
Hitomi Fujishiro , Seiichiro Himeno
Released: May 14, 2019
Abstract Full Text PDF[746K]

Kidney proximal tubules are composed of S1, S2, and S3 segments having different properties of excretion and substance reabsorption. Since renal toxicants such as cadmium and cisplatin cause segment-specific toxicity, it is important to examine the segment-specific transport and detoxification systems of renal toxicants. Here, we investigated the gene expression profiles of immortalized S1, S2, and S3 cells derived from each segment of mouse kidney proximal tubules. Microarray analyses showed distinct expression of various genes in each cell line. We compared the expression levels of selected genes related to the transport and detoxification of renal toxicants. Some genes showed segment-specific expression patterns similar to those observed in in vivo studies. The gene expression profiles of each cell line shown in this study will provide a foundation for the future utilization of immortalized S1, S2, and S3 cells for toxicity screenings as well as for the elucidation of renal toxicity mechanisms.

Letter
Impairment of fertilization efficiency in mice following nano-sized titanium exposure Vol.6, No.3, p.113-116
Nobuhiko Miura , Katsumi Ohtani , Tatsuya Hasegawa , Gi-Wook Hwang , Hiroki Yoshioka
Released: May 14, 2019
Abstract Full Text PDF[914K]

Titanium dioxide nanoparticles (TiNP) are widely used commercially and exist in a broad range of applications and consumer products such as exterior wall paints, antibacterial agents, white pigments, and sunscreens. We previously reported that the testis is a fragile organ against titanium toxicity as compared to the liver; TiNP has been shown to decrease both the sperm motility and the sperm numbers, that is, TiNP quantitatively and qualitatively change the sperm functions. There are, however, few reports regarding to the influence of TiNP on fertility ability. In this paper, we evaluated the influence of TiNP on fertilization rate using in vitro fertility (IVF) assay. Male C57BL/6J mice were administered orally with TiNPs (10 mg/kg or 100 mg/kg). Mice were sacrificed 24 hr after the administration. As a result, TiNP (10 mg/kg group) significantly decreased the fertilization rate. In the higher dose group (100 mg/kg), the degree was weaker than in the lower dose group. Our results indicate that TiNP reduces not only the sperm motility but also the fertility, and it will be useful information in considering the influence of TiNP on next generation.

Letter
Magnoliae Cortex extract protects PC12 cells from cytotoxicity induced by hydrogen peroxide or 6-hydroxydopamine through enzyme induction Vol.6, No.3, p.107-112
Takahito Nishiyama , Yasuhiro Masuda , Tadashi Izawa , Tomokazu Ohnuma , Kenichiro Ogura , Akira Hiratsuka
Released: April 24, 2019
Abstract Full Text PDF[1M]

Alzheimer’s and Parkinson’s disease are neurodegenerative disorders of unknown cause for which there is no cure or way of preventing or slowing its progression. Various genetic and environmental factors are thought to be involved in the onset of neurodegenerative diseases. Oxidative stress, such as the generation of reactive oxygen species and lipid peroxidation, is a major factor in initiating the disease process. However, oxidative stress in cells is known to be suppressed by drug-metabolizing enzymes, such as NAD(P)H:quinone oxidoreductase 1 (NQO1), and antioxidant enzymes, such as catalase. Here, we used PC12 cells, which are a recognized model for neuronal cell death and neurite extension, to investigate whether Magnoliae Cortex derived from the Magnoliaceae plant family can induce these enzyme activities. Our results reveal that Magnoliae Cortex extract induces the activity of both NQO1 and catalase. In addition, the cytotoxic effect of hydrogen peroxide and 6-hydroxydopamine was significantly suppressed by pretreatment of the cells with Magnoliae Cortex extract. Based on our findings, we conclude that induction of these enzyme activities by Magnoliae Cortex extract leads to an enhancement of its cytoprotective effect.

Original Article
Genotoxicity and subchronic toxicity studies of Taiwanofungus camphoratus extract Vol.6, No.3, p.81-106
Jian-Yu Lin , Mei-Chun Chen , Emerson Chiu
Released: April 05, 2019
Abstract Full Text PDF[2M]

Taiwanofungus camphoratus is an edible and medicinal mushroom originating in Taiwan. Several researches have revealed T. camphoratus possessed various biological activities, including anti-cancer, immunomodulation, liver protection and anti-inflammation. Recently, it has been widely used in food supplements and drug development for its health benefits and medicinal properties. Therefore, the safety issue is the primary concern for consumers. The aim of this study was to evaluate the toxicological effects of T. camphoratus extract that was composed of extracts from cut-log cultivated fruiting body and solid-state culture of T. camphoratus. The genotoxicity tests, rodent and non-rodent repeated dose toxicity studies were performed. The results of the genetic toxicology tests including in vitro bacterial reverse mutation assay, in vitro chromosomal aberration test, and in vivo mouse bone marrow micronucleus assay were all negative that indicated neither mutagenicity nor clastogenicity was caused by T. camphoratus extract. Moreover, 13-week and 26-week repeated dose oral toxicity studies in rats showed that no significant adverse effects of T. camphoratus extract were found up to dosages of 3400 mg/kg and 1700 mg/kg for male and female rats, respectively. The results of 28-day repeated dose oral toxicity study in beagle dogs showed no-observed-adverse-effect-level (NOAEL) of T. camphoratus extract up to dosage of 1500 mg/kg for male and female dogs. Accordingly, these results provided the safety information of T. camphoratus extract that supported for using in food supplements or medicinal usage.

Original Article
Age-dependent aggravation of oral malodor and periodontal disease in dogs Vol.6, No.3, p.75-79
Naoki Iwashita , Kazutoshi Sugita , Sayaka Murata , Keiko Ichimura , Mitsuyuki Shirai , Masaharu Hisasue , Miyoko Saito , Takuma Aoki , Yukihiko Takagi , Fumitoshi Asai
Released: April 04, 2019
Abstract Full Text PDF[743K]

Halitosis or oral malodor is correlated with the concentration of volatile sulfur compounds (VSCs) produced in the oral cavity by metabolic activity of periodontal pathogenic germs. Our previous study demonstrated that VSCs in canine breath air can be measured using a portable VSC monitor. The aim of this study was to assess the association between oral malodor and periodontal disease in dogs. Forty-three laboratory Beagle dogs (1-16 years of age, 24 males, 19 females) were included in this study. Oral halitosis was evaluated by the organoleptic test score (OS) and by measuring the oral levels of VSCs: hydrogen sulfide (H2S; HS), methyl mercaptan (CH3SH; MM), and dimethyl sulfide (CH3SCH3; DMS) using OralChroma™. The calculus index (CI) and the gingival index (GI) were measured as periodontal parameters. Oral levels of halitosis parameters (OS, HS, MM, CI, and GI) in Group 2 dogs (7-16 years of age) were significantly higher than those in Group 1 dogs (1-6 years of age). In addition, significant positive relationships were found between oral malodor and periodontal disease, both of which are age-dependent in dogs. The present study suggested that aging is an important factor for oral malodor and periodontal disease in dogs.

Original Article
Twenty-eight-day oral toxicity study of L-hydroxyproline in rats with 14-day post-treatment observation period Vol.6, No.3, p.65-74
Saori Akiduki , Yoko Kawada , Fumiko Watanabe , Toshikazu Kamiya , Koji Morishita
Released: April 04, 2019
Abstract Full Text PDF[1M]

Repeated-dose oral toxicity of L-hydroxyproline (Hyp) was assessed in male and female SD rats by gavage for 28 days at dose level of 40, 200, 1,000 or 4,000 mg/kg/day. The reversibility of treatment-related changes was also examined by providing 14-day recovery period in the control group and 4,000 mg/kg group. In the results, reduced body weight gain with decreased food consumption was noted in males at 4,000 mg/kg/day. The histopathological evaluation revealed increased incidences of focal dilatation of the renal tubules with narrowing of the tubular cell liner and focal interstitial fibroplasia in the kidney of males at 1,000 and 4,000 mg/kg and females at 4,000 mg/kg. The lack of kidney specific serum chemical or urinalysis findings supported that the renal changes were very mild. Based on the above results, it was concluded that the no observed adverse effect level (NOAEL) of Hyp was 200 mg/kg/day.

Original Article
Effects of benzotriazole ultraviolet stabilizers on rat PXR, CAR and PPARα transcriptional activities Vol.6, No.2, p.57-63
Yoko Watanabe , Shoko Hattori , Chieri Fujino , Ken Tachibana , Hiroyuki Kojima , Kouichi Yoshinari , Shigeyuki Kitamura
Released: March 19, 2019
Abstract Full Text PDF[1M]

Benzotriazole ultraviolet stabilizers (BUVSs) are widely used as ultraviolet filters in various consumer and industrial products. For this purpose, we examined the effects of 10 BUVSs and benzotriazole itself on transcriptional activation mediated by nuclear receptors: pregnane X receptor (PXR), constitutive androstane receptor (CAR) and peroxisome proliferator-activated receptor alpha (PPARα). UV-090 and UV-9 showed rat PXR-agonistic activity in the concentration range of 1-30 μM in reporter gene assay using simian kidney COS-1 cells. UV-090 showed the highest activity (REC20 value: 3.85 × 10-6 M). UV-090 was also positive in rat CAR activation assay, while UV-P showed inverse agonistic activity towards CAR. In the presence of the CAR agonist artemisinin (10 μM), UV-P also showed dose-dependent CAR-antagonistic activity in the concentration range of 10-30 μM. UV-090 and UV-9 activated rat PPARα. Overall, these results suggest that UV-090, UV-9 and UV-P modulate PXR, CAR and/or PPARα activation.

Original Article
Cytotoxic effects of parathion, paraoxon, and their methylated derivatives on a mouse neuroblastoma cell line NB41A3 Vol.6, No.2, p.45-56
Yunbiao Wang , ByungHoon Kim , Ashley Walker , Shayla Williams , Ashley Meeks , Yong-Jin Lee , Seong S. Seo
Released: March 12, 2019
Abstract Full Text PDF[2M]

Organophosphorus compounds (OPCs) are widely used as pesticides, but often show high toxicity in mammalian cells. To assess the toxic potential of OPCs, we examined the cytotoxicity of paraoxon, methyl-paraoxon, parathion, and methyl-parathion exposures on NB41A3 neuroblastoma mouse cell lines. The LC50s (median lethal concentrations) at 24 hr of exposure were determined from the acute toxicity test including time course experiments. The LC50 values suggest higher toxicity of paraoxon (0.42 mM) compared to parathion (0.66 mM). In addition, the methylated derivatives of both OPCs indicated similar but slightly lower levels of toxicity compared to paraoxon and parathion (0.46 mM for methyl-paraoxon and 0.77 mM for methyl-parathion). However, the results from time course experiments indicated obvious reduction of cell viability for parathion and methyl-parathion as early as 1 hr of exposure, whereas the effects of paraoxon and methyl-paraoxon were not significant before 6 hr of exposure. We also report the most affected biological processes in NB41A3 cells in response to parathion exposure using microarray experiment. Among the statistically overrepresented biological processes are the ones related to neuronal development, apoptosis, cell stress, and cell signaling.

Original Article
Acute hepatotoxicity and drug/chemical interaction toxicity of 10-nm silver nanoparticles in mice Vol.6, No.2, p.37-44
Katsuhiro Isoda , Naoki Kobayashi , Yuichiro Taira , Ikuko Taira , Yoshimi Shimizu , Yoshihiro Akimoto , Hayato Kawakami , Isao Ishida
Released: March 06, 2019
Abstract Full Text PDF[4M]

Nanomaterials with nanoscale microstructures have new properties in which reactions to stimuli such as heat, light, and voltage differ from those of macroscale materials. For that reason, the development of nanotechnology using nanomaterials has been remarkable, and these technologies have been put to practical use in various fields such as medicine and electronics. Nanomaterials have been researched as new materials with superior properties that have not been seen in the past, but concerns remain about the influence of nanomaterials on living bodies. Silver nanoparticles are materials with excellent optical, electrical, and antibacterial properties. However, few reports have described the influence of silver nanoparticles on the living body and interactions between chemicals such as pharmaceuticals. We therefore investigated the effect of silver nanoparticles on the living body and drug interactions. We administered silver nanoparticles with particle diameters of 10, 50, and 200 nm (SnP10, SnP50, and SnP200, respectively) to mice through the tail vein. As a result, acute liver injury was induced only in the SnP10 group. Furthermore, liver injury was induced by co-administering SnP10 with carbon tetrachloride, streptomycin, or cisplatin. SnP10 appears to induce liver injury through acute and drug interactions.

Toxicomics Report
Effects of lithium on developmental toxicity, teratogenicity and transcriptome in medaka embryos Vol.6, No.2, p.31-36
Nobuaki Tominaga , Seiya Shino , Masaya Uchida , Hiroshi Ishibashi , Midori Iida , Tadashi Okobira , Kayla Arizono , Noriaki Yoshida , Koji Arizono
Released: February 15, 2019
Abstract Full Text PDF[2M]

In this study, we assessed embryonic developmental toxicity and teratogenicity of lithium (Li) on medaka (Oryzias latipes) and predict the molecular mechanisms of their effects using a nanosecond pulsed electric field (nsPEF) technique and bioinformatics analysis. The microscopic observation revealed that the 1 mg/L LiCl treatment causes the most severe deformation effects, such as thrombus, heart hypertrophy, deformation of eyes, and growth retardation to embryos. The RNA-seq analysis identified 2,483 up- and down-regulated genes, such as histogenesis and organ growth related genes, in 2 day post-fertilization embryos after treatment with nsPEF and 1 mg/L LiCl. In addition, bioinformatic analyses showed that LiCl affects several aspects of gene ontology, such as molecular functions and cellular components, and some pathways, such as spliceosome, cell cycle, selenocompound metabolism, TGF-β signaling, and RNA degradation. The upregulation of GSK3B (signal transduction and cell growth), BAX (apoptosis), and MAP3K8 (cell death, arrest of cell cycle, and inflammation) genes were also observed in embryos exposed to LiCl. Our results suggest that the incorporation of Li compounds into medaka eggs using nsPEF shows adverse effects to the development and teratogenicity, and that these toxic effects may be affected by the alterations of certain gene expression in medaka embryos.

Letter
Protective effect of the Kampo formula “Juzen-taiho-to” on isoniazid- and rifampicin-induced hepatotoxicity in mice Vol.6, No.1, p.25-29
Hiroki Yoshioka , Shiori Fukaya , Sarah Tominaga , Akito Nagatsu , Nobuhiko Miura , Tohru Maeda
Released: February 06, 2019
Abstract Full Text PDF[1M]

The aim of this study was to investigate whether the Japanese herbal medicine Juzentaiho-to (JTX) showed attenuating effects on isoniazid- and rifampicin-induced liver injury. Seven-weekold male Institute of Cancer Research mice were orally administered JTX or saline once a day at 9:00 for 3 days. Additionally, the mice received a mixture of 80 mg/kg isoniazid and 160 mg/kg rifampicin (10 mL/kg) via intraperitoneal injection three times (at 19:30) per 24 hr period. Twenty-four hours after the last administration of isoniazid/rifampicin, the mice in each group were sacrificed and blood was removed to obtain the plasma and livers. Mice that had received isoniazid/rifampicin showed high plasma levels of alanine aminotransferase, aspartate aminotransferase, and interleukin-6. In addition, the mice injected with isoniazid/rifampicin displayed increased hepatic lipid peroxidation and receptor-interacting protein-1 and -3 levels. Treatment with JTX prevented an isoniazid/rifampicin-induced increase in levels of alanine aminotransferase and aspartate aminotransferase, lipid peroxidation, and receptor-interacting protein changes. Our results suggest that JTX protects against isoniazid/rifampicin-induced hepatic injury by modulating oxidative stress and inflammatory responses.

Original Article
Supplementation with lower doses of EGCg reduces liver injury markers of type 2 diabetic rats Vol.6, No.1, p.15-23
Kazuki Mochizuki , Yu Tan , Yumiko Uchiyama , Takuji Suzuki , Natsuyo Hariya , Toshinao Goda
Released: January 30, 2019
Abstract Full Text PDF[1M]

(-)-Epigallocatechin-3-gallate (EGCg), a major catechin in green tea, eliminates reactive oxygen species and development of lifestyle-related diseases. However, excessive EGCg intake could induce adverse effects, particularly liver injury. We examined whether optimal dietary doses of EGCg reduces the risk of liver injuries in non-obese type 2 diabetic Goto-Kakizaki (GK) rats by examining gene expression of the proinflammatory cytokines interleukin (IL)-1β, IL-18 and tumor necrosis factor-α (TNF-α) and fibrosis-related matrix metalloproteinases (MMPs) in the liver. GK rats at 9 weeks of age were fed a control high-fat diet or a high-fat diet containing 0.1%, 0.2% or 0.5% EGCg (w/w) for 25 weeks. Expression of mRNA and proteins related to inflammation were determined by qRT-PCR and western blot analysis, respectively. IL-1β and IL-18 mRNA in the liver were reduced by EGCg supplementation at concentrations of 0.1% and 0.1%-0.2%, respectively, but not at concentrations of 0.2% and 0.5% (IL-1β) or 0.5% (IL-18) EGCg. TNF-α mRNA in the liver was reduced by supplementation with EGCg at concentrations of 0.1%-0.5%. Expression of MMP2 in the liver was reduced by EGCg supplementation at a concentration of 0.2%, but not 0.1% or 0.5%. Importantly, IL-18 protein levels in the liver and serum were reduced by 0.1% EGCg, but not by 0.5%. EGCg supplementation at concentrations from 0.1% to 0.5% did not induce increases in the expression of liver injury marker genes, while low doses (0.1%–0.2%) of EGCg in GK rats reduced expression of injury-associated genes in the liver.

Letter
Investigation of DNA damage of glycidol and glycidol fatty acid esters using Fpg-modified comet assay Vol.6, No.1, p.9-14
Ryo Inagaki , Kohei Uchino , Yuko Shimamura , Shuichi Masuda
Released: January 18, 2019
Abstract Full Text PDF[2M]

Glycidol fatty acid esters (GEs) are food process contaminants detected in edible oils. It has been thought that glycidol is released from GEs by lipase in vivo, and shows genotoxicity. While DNA damage from glycidol has been reported, there is very little information on the DNA damaging potency of GEs in vivo. Therefore, we estimated DNA damage of glycidol and glycidyl oleate, which is one type of GEs, using the standard comet assay and a formamidopyrimidine glycosylase(Fpg)-modified comet assay. ICR male mice were orally administrated glycidol and glycidyl oleate (1.0 and 2.0 mmol/kg body weight) at 24 and 3 hr prior to dissection. In the standard comet assay, DNA damage (tail length and % tail DNA) in liver, kidney and blood samples of glycidol-treated groups were increased in a concentration-dependent manner. In Fpg-modified comet assay, glycidol showed DNA damage with higher sensitivity compared with the standard comet assay. DNA damage was not observed in the administration group of glycidyloleate in the standard comet assay. However, in Fpg-modified comet assay, glycidyl oleate showed significant DNA damage in the liver, kidney and blood samples compared with the standard comet assay. In this study, it was revealed that glycidol and glycidyl oleate induce DNA damage, such as oxidative and alkylation damage, recognized by Fpg protein.

Original Article
Thiamine supplementation modulates oxidative stress by inhibiting hepatic adenosine diphosphate (ADP)-ribosylation in obese diabetic rats Vol.6, No.1, p.1-8
Yuka Kohda , Junpei Ueda , Rie Azuma , Yuuka Nakatani , Hiroto Murase , Kanta Matsui , Yuka Takezoe , Eiko Nagata , Risa Matsui , Takao Tanaka , Hitoshi Matsumura
Released: January 16, 2019
Abstract Full Text PDF[2M]

Diabetic hyperglycemia is typically accompanied by various protein modifications, indicating hyperglycemic glucotoxicity. Overactivation of poly [adenosine diphosphate (ADP)-ribose] polymerase 1 (PARP-1) has been implicated in the pathogenesis of oxidative stress-related diseases including diabetes and its complications. Furthermore, obesity and diabetes are known to be associated with a substantial risk of chronic liver disease. We have previously reported that thiamine supplementation prevented obesity and diabetes-related liver disease. As a step forward, in the present study, we focus on hepatic ADP-ribosylation that reflects PARP-1 activation and an increased oxidative stress condition. Otsuka Long-Evans Tokushima Fatty (OLETF) rats were randomly divided into the following groups: thiamine-supplemented and unsupplemented control groups. The thiamine-supplemented group received 2 g of thiamine/L of drinking water for 33 weeks. ADP-ribosylated protein expression was analyzed in the livers of OLETF rats using Western blotting. Moreover, the fasting blood glucose level was measured in these rats. The obese diabetic OLETF rats exhibited high ADP-ribosylated protein expression in the liver. Interestingly, hepatic ADP-ribosylated protein expression and fasting blood glucose levels were lower in the thiamine-supplemented OLETF group than in the control OLETF group. These results suggest that thiamine supplementation attenuates oxidative stress by inhibiting hepatic ADP-ribosylation in OLETF rats. The beneficial effect of high-dose thiamine on oxidative stress-related diseases could be attributed to its inhibitory effect on PARP-1 activation, in addition to its role as a coenzyme. Furthermore, we found that thiamine supplementation prevented fasting hyperglycemia, suggesting that high-dose thiamine modifies the hepatic glucose metabolism and obesity-induced hepatic insulin resistance.