Copper-induced renal toxicity controlled by period1 through modulation of Atox1 in mice.

Copper (Cu) is known to induce oxidative stress and apoptosis in the liver, kidney, and brain. We previously demonstrated the molecular mechanism underlying the Cu-induced hepatic diurnal variation. However, the cellular molecule(s) involved in Cu-induced renal chronotoxicity remain unknown. In this study, we aimed to elucidate the molecular mechanisms underlying Cu-induced diurnal toxicity in the kidneys. We evaluated cell viability and clock gene expression levels in mouse renal cortex tubular cells (MuRTE61 cells) after Cu treatment. We also examined the Cu homeostasis- and apoptosis-related gene levels after period 1 (Per1) overexpression in MuRTE61 cells. Cu treatment decreased MuRTE61 cell viability in a dose-dependent manner. It increased the Per1 expression levels after 24 h. Notably, Per1 overexpression alleviated the Cu-induced inhibition of MuRTE61 cell viability. Moreover, Per1 overexpression downregulated the cleaved caspase-3 and reduced Cu levels by upregulating the antioxidant 1 copper chaperone (Atox1) levels. These results suggest that Cu-induced renal toxicity is associated with Per1 expression via the regulation of the copper chaperone, Atox1.

Diurnal variation of cisplatin-induced renal toxicity in ICR mice.

Cisplatin (CDDP) is a platinum-based anticancer drug widely prescribed for its effectiveness in treating various forms of cancer. However, its major side effect is nephrotoxicity. Although several methods have been developed to mitigate CDDP-induced nephrotoxicity, an optimal approach has yet to be established. This study aimed to investigate the "chronotoxicity" of CDDP as a potential strategy to reduce its side effects. Male ICR mice were treated with CDDP (20 mg/kg, intraperitoneal injection, one shot) at zeitgeber time (ZT) 2 or ZT14 (light or dark phase). After 72 h, we collected plasma and kidney and evaluated several markers. We found that body weight change between ZT2 and ZT14 by CDDP was comparable. In contrast, many toxicological factors, such as plasma blood urine nitrogen, plasma creatinine, renal oxidative stress (malondialdehyde), DNA damage (γH2AX), acute kidney injury biomarker (KIM-1), and inflammation (Tnfα), were significantly induced at ZT14 compared to than that of ZT2. Our present data suggested that chronotoxicology might provide beneficial information on the importance of administration timings for toxic evaluations and unacceptable side effects.

Copper-induced diurnal hepatic toxicity is associated with Cry2 and Per1 in mice.

BACKGROUND: This study aimed to investigate diurnal variations in copper-induced hepatic toxicity and the molecular mechanisms underlying this chronotoxicity. METHODS: Male C57BL/6J mice were intraperitoneally injected with copper chloride (CuCl2) at zeitgeber time 2 (ZT2) or 14 (ZT14), twice per week for 5 or 8 weeks. Seventy-two hours after the final CuCl2 injection, the mice were euthanized, and plasma samples were collected. The livers and kidneys were collected and weighed. In vitro experiments were performed to assess cell viability and fluctuations in clock gene expression levels in Hepa1-6 cells after CuCl2 treatment. We examined copper homeostasis- and apoptosis-related genes under clock genes overexpression. RESULTS: Repeated CuCl2 administration for 8 weeks resulted in more severe toxicity at ZT14 compared to ZT2. CuCl2 administration at ZT14 elevated plasma aspartate aminotransferase, hepatic tumor necrosis factor-α, and interleukin-6 for 5 weeks, whereas the toxic effects of CuCl2 administration at ZT2 were weaker. Moreover, CuCl2 treatment inhibited Hepa1-6 cell viability in a dose-dependent manner. We observed increased expression of three clock genes (Ciart, Cry2, and Per1) after CuCl2 treatment. Among them, overexpression of Cry2 and Per1 accelerated CuCl2-induced inhibition of Hepa1-6 cell viability. Moreover, we found that the overexpression of Cry2 and Per1 regulates cleaved caspase-3 by modulating the copper transporter genes ATP7B and CTR1. CONCLUSION: These results suggest that CuCl2-induced diurnal toxicity is associated with Cry2 and Per1 expression through the regulation of copper transporter genes in mice.

Involvement of Bmal1 and Clock in Bromobenzene Metabolite-Induced Diurnal Renal Toxicity.

Circadian rhythms are endogenous oscillators that regulate 24 h behavioral and physiological processes. Our previous investigation demonstrated that bromobenzene metabolite (4-bromocatechol: 4-BrCA) exhibited chronotoxicity (i.e., the nephrotoxicity induced by 4-BrCA was observed during the dark phase, while not observed at light phase in mice). However, the molecular mechanism is still unknown. The aim of the present study is to investigate the cellular molecule(s) involved in the 4-BrCA-induced nephrotoxicity using mouse renal cortex tubular cell lines (MuRTE61 cells). We found that 4-BrCA showed dose dependent (0.01-1 mM) cell proliferation defect in MuRTE61 cells. By treating with 0.03 mM 4-BrCA, we demonstrated that major clock genes (Bmal1, Clock, Cry1, Cry2, Per1, and Per2) were significantly downregulated. Interestingly, the expression levels of two genes, Bmal1 and Clock, continued to decrease after 3 h of treatment with 4-BrCA, while Cry1, Per1, and Per2 were unchanged until 24 h of treatment. Moreover, BMAL1 and CLOCK levels are higher at light phase. We speculated that BMAL1 and CLOCK might function defensively against 4-BrCA-induced nephrotoxicity since the expression levels of Bmal1 and Clock were rapidly decreased. Finally, overexpression of Bmal1 and Clock restored 4-BrCA-induced cell proliferation defect in MuRTE61 cells. Taken together, our results suggest that Bmal1 and Clock have protective roles against 4-BrCA-induced nephrotoxicity.

Involvement of Npas2 and Per2 modifications in zinc-induced acute diurnal toxicity in mice.

Zinc (Zn) is one of the most essential trace elements in the body and an integral part of many enzyme systems. Zn deficiency is characterized by growth retardation, loss of appetite, and impaired immune function. In contrast, Zn overdoses can be associated with liver, kidney, and stomach damage. We focused on the "chronotoxicity," or the relationship between injection time and severity of chemical toxicity. The aim of this study was to investigate the chronotoxicity of Zn and the in vivo factors involved. Seven-week-old male ICR mice were administered Zn at six different time points per day (zeitgeber time [ZT]: ZT2, ZT6, ZT10, ZT14, ZT18, and ZT22). Mortality was monitored for 7-days after administration. The mice were tolerant to Zn administered at ZT2 and ZT6, and were highly sensitive at ZT14 and ZT18. Furthermore, when mice were administered a non-lethal dose of Zn, the levels of hepatic injury indicators (AST and ALT) were much higher at ZT14 than at ZT2. To explore the mechanism of Zn-induced diurnal hepatotoxicity, we performed an in vitro experiment, focusing on the clock genes. We found that Zn downregulated the expression levels of several clock genes, neuronal PAS domain protein 2 (Npas2) and Peroid2 (Per2), in Hepa1-6 cells. Interestingly, overexpression of both Npas2 and Per2 restored Zn-induced toxicity in Hepa1-6 cells. Since NPAS2 and PER2 are known to modulate the hepatic injury induced by carbon tetrachrolide or acetaminophen, our results suggest that Zn-induced diurnal toxicity may be associated with modulation of Npas2 and Per2 gene expression.

Mitochondrial LETM1 drives ionic and molecular clock rhythms in circadian pacemaker neurons.

The mechanisms that generate robust ionic oscillation in circadian pacemaker neurons are under investigation. Here, we demonstrate critical functions of the mitochondrial cation antiporter leucine zipper-EF-hand-containing transmembrane protein 1 (LETM1), which exchanges K+/H+ in Drosophila and Ca2+/H+ in mammals, in circadian pacemaker neurons. Letm1 knockdown in Drosophila pacemaker neurons reduced circadian cytosolic H+ rhythms and prolonged nuclear PERIOD/TIMELESS expression rhythms and locomotor activity rhythms. In rat pacemaker neurons in the hypothalamic suprachiasmatic nucleus (SCN), circadian rhythms in cytosolic Ca2+ and Bmal1 transcription were dampened by Letm1 knockdown. Mitochondrial Ca2+ uptake peaks late during the day were also observed in rat SCN neurons following photolytic elevation of cytosolic Ca2+. Since cation transport by LETM1 is coupled to mitochondrial energy synthesis, we propose that LETM1 integrates metabolic, ionic, and molecular clock rhythms in the central clock system in both invertebrates and vertebrates.

Metastasis of Breast Cancer Promoted by Circadian Rhythm Disruption due to Light/Dark Shift and its Prevention by Dietary Quercetin in Mice.

Epidemiological studies have indicated that a disturbed circadian rhythm resulting from night-shift work is a potential risk factor for breast cancer. However, the mechanism of increased risk of breast cancer by night-shift work remains unclear, and there have been few in vivo studies conducted to definitively associate the two factors. In this study, BJMC3879Luc2 mouse breast cancer cells were transplanted into BALB/c mice. Mice were maintained under lighting conditions that modeled the two-shift system and were investigated for the effect of light/dark cycle disruption on tumor growth and lymph node metastasis. Circadian dysfunction, which was confirmed by measuring circadian locomotor activities using a nano tag device in our light/dark shift model, did not affect tumor growth. However, a significant increase in the number of lymph nodes with distant metastasis was observed. Neutrophil-to-lymphocyte ratio, which is an adverse prognostic factor of breast cancer and also indicator of inflammation, also increased. It has been demonstrated that a chronic inflammatory response is associated with cancer malignancy and poor prognosis in various cancers. These results suggest that night-shift work may also affect distant metastasis and prognosis. In addition, we investigated whether dietary quercetin has anti-metastatic activity against light/dark shift-induced metastasis. A diet containing 0.3 % quercetin significantly inhibited distant lymph node metastasis, particularly metastasis to the iliac and kidney lymph nodes. Our results contribute to our understandings of the effects of the external light environment on breast cancer metastasis and provide a glimpse into potential protective effects of dietary quercetin on light/dark disturbance-induced metastasis.

Different Renal Chronotoxicity of Bromobenzene and Its Intermediate Metabolites in Mice.

Bromobenzene (BB) is known to pose a serious threat to human health. We previously demonstrated that BB showed chronotoxicity, that is, daily fluctuations in the severity of hepatotoxicity induced in mice. Although BB showed mild nephrotoxicity, a daily fluctuation was not observed in this toxicity. This might be attributed to the fact that BB-induced chronotoxicity is observed only in the liver and not in the kidneys and that the damage caused by BB is prominent in the liver, masking the daily fluctuation in nephrotoxicity. To confirm these two possibilities, we examined the daily fluctuations in nephrotoxicity due to BB intermediate metabolites that target the kidneys: 3-bromophenol, bromohydroquinone, and 4-bromocatechol. Mice were injected with 3-bromophenol, bromohydroquinone, or 4-bromocatechol intraperitoneally at six different time points in a day (zeitgeber time (ZT): ZT2, ZT6, ZT10, ZT14, ZT18, or ZT22). Mortality was monitored for 7 d post-injection. Mice were more sensitive to the acute toxicity of these metabolites around at ZT14 (dark-phase) exposure than around at ZT2 (light-phase) exposure. Furthermore, mice administered with a non-lethal dose of 4-bromocatechol showed significant increases in the levels of plasma blood urea nitrogen and renal malondialdehyde at ZT14 exposure. Moreover, glutathione peroxidase-4, a ferroptosis indicator, was attenuated at ZT14 exposure. These results indicate the toxicity of BB metabolites was higher during the dark-phase exposure, and demonstrate the reason why the diurnal variation of nephrotoxicity by BB was not observed in our previous report is that renal damage was masked due to severe hepatic damage.

Increased putrescine levels due to ODC1 overexpression prevents mitochondrial dysfunction-related apoptosis induced by methylmercury.

AIMS: We had previously reported that addition of putrescine to the culture medium was reported to reduce methylmercury toxicity in C17.2 neural stem cells. Here, we have examined the inhibition of methylmercury-induced cytotoxicity by putrescine using ODC1-overexpressing C17.2 cells. MATERIALS AND METHODS: We established stable ODC1-overexpressing C17.2 cells and evaluated methylmercury-induced apoptosis by examining the TUNEL assay and cleaved caspase-3 levels. Mitochondria-mediated apoptosis was also evaluated by reduction of mitochondrial membrane potential and recruitment of Bax and Bak to the mitochondria. KEY FINDINGS: ODC is encoded by ODC1 gene, and putrescine levels in ODC1-overexpressing cells were significantly higher than in control cells. Overexpression of ODC1 and addition of putrescine to the culture medium suppressed DNA fragmentation and caspase-3 activation, which are observed when apoptosis is induced by methylmercury. Moreover, mitochondrial dysfunction and reactive oxygen species (ROS) generation, caused by methylmercury, were also inhibited by the overexpression of ODC1 and putrescine; pretreatment with ODC inhibitor, however, promoted both ROS generation and apoptosis by methylmercury. Finally, we found that Bax and Bak, the apoptosis-promoting factors, to be increased in mitochondria, following methylmercury treatment, and the same was inhibited by overexpression of ODC1. These results suggest that overexpression of ODC1 may prevent mitochondria-mediated apoptosis by methylmercury via increase of putrescine levels. SIGNIFICANCE: Our findings provide important clues to clarify mechanisms involved in the defense against methylmercury toxicity and suggest novel biological functions of putrescine.

Correction to: Genotoxicity assessment of titanium dioxide nanoparticle accumulation of 90 days in the liver of gpt delta transgenic mice.

[This corrects the article DOI: 10.1186/s41021-020-0146-3.].

Genotoxicity assessment of titanium dioxide nanoparticle accumulation of 90 days in the liver of gpt delta transgenic mice.

BACKGOUND: A variety of in vivo and in vitro studies to assess the genotoxicity of titanium dioxide nanoparticles (TiO2 NPs) have been reported, but the results are inconsistent. Recently, we reported that TiO2 NPs exhibit no genotoxic effects in the liver and erythrocytes during a relatively brief period following intravenous injection into mice. However, there is no information about long-term genotoxicity due to TiO2 NP accumulation in tissues. In this study, we investigated the long-term mutagenic effects of TiO2 NPs and the localization of residual TiO2 NPs in mouse liver after multiple intravenous injections. RESULTS: Male gpt delta C57BL/6 J mice were administered with various doses of TiO2 NPs weekly for 4 consecutive weeks. The long-term mutagenic effects on the liver were analyzed using gpt and Spi- mutation assays 90 days after the final injection. We also quantified the amount of titanium in the liver using inductively coupled plasma mass spectrometry and observed the localization of TiO2 NPs in the liver using transmission electron microscopy. Although TiO2 NPs were found in the liver cells, the gpt and Spi- mutation frequencies in the liver were not significantly increased by the TiO2 NP administration. CONCLUSIONS: These results clearly show that TiO2 NPs have no mutagenic effects on the liver, even though the particles remain in the liver long-term.

Chronotoxicity of Streptomycin-Induced Renal Injury in Mice.

The aim of the present study was to investigate the "chronotoxicity" of streptomycin (SM) in relation to its circadian periodicity. Male ICR mice were injected intraperitoneally with SM (780 mg/kg, one shot) one of six time points throughout the day. Mortality was monitored until 14 d after the injection and clearly differed depending on the timing of the injection (i.e., mice were more sensitive to injection during the dark phase). Moreover, when mice were administered with non-lethal doses of SM (550 mg/kg, every 24 h for 3 d, in the light phase or dark phase), the levels of nephrotoxicity indicators (blood urea nitrogen and renal levels of malondialdehyde and cyclooxygenase-2) were significantly increased by the injection in the dark phase, but not in the light phase. These results suggested that SM showed clear chronotoxicity. Our current data indicated that chronotoxicology may provide valuable information on the importance of injection timings for evaluations of toxicity and undesirable side effects.

Biphasic adverse effect of titanium nanoparticles on testicular function in mice.

The male reproductive system is being recognized as toxic targets of nanoparticles including titanium dioxide nanoparticles (TiNP). Most of these reports are, however, obtained from the results of long-term exposure of TiNP. In this study, we diversely examined the acute effects of TiNP on the male reproductive system. Male C57BL/6J mice were administered a single intravenous injection of TiNP (10, 50 mg/kg), and were sacrificed at 1, 3, and 9 days post-injection. Testicular functions (estimated by sperm motility and sperm number) were measured via computer-assisted sperm analysis (CASA). Results indicated that sperm motility was significantly reduced from 1 day following TiNP injection (in both dose), and this reduction persisted up to 9 days post-TiNP injection (10 mg/kg injection group). Interestingly, we observed no significant decrease in sperm numbers in both the testis and the cauda epididymis in either treatment groups during the course of the experiment. Therefore, we hypothesized that TiNP may target the mature spermatozoa. In addition, sperm suspensions directly incubated with TiNP showed reduced sperm motility, [3H]-thymidine incorporation, and ATP level. Our results indicated that TiNP possesses "biphasic effects"; the obstacles to mature sperms (short term effect) in addition to the impairment in testis (long-term effect).

Diurnal Variation of Sitagliptin-Induced Pharmacological Effects in C57BL/6J Mice.

Chronopharmacology is the study of the varying responses of drugs to changes in biological timing and endogenous periodicities. The dipeptidyl peptidase-4 inhibitor sitagliptin is a globally prescribed anti-hyperglycemic drug. Although dipeptidyl peptidase-4 inhibitors are usually administered once, the specific intake time is generally not mentioned. Therefore, this study aimed at investigating the diurnal effects of sitagliptin-induced anti-hyperglycemia in high-fat diet (HFD)-induced obesity in mice. Five-week-old male C57BL/6J mice were fed normal (control) diet or HFD for 10 weeks. During the last 2 weeks, the mice were administered saline or sitagliptin (10 mg/kg, per os) in the light or dark phase, respectively. At the end of the experiment, the mice were euthanized after an 18 h fasting period, and plasma and tissue samples (liver, kidney, and epididymal white adipose tissues) were collected, or the oral glucose tolerance test was performed. Sitagliptin administration in the light phase significantly decreased plasma glucose levels, insulin levels, hepatic steatosis, and restored the glucose tolerance compared with the HFD group. In contrast, these parameters remained unchanged in the dark phase-treated mice. Our data therefore suggests that sitagliptin portrays definite chronopharmacology, which may provide valuable information on the importance of drug administration timing for maximum pharmacological effects.

Chronopharmacology of dapagliflozin-induced antihyperglycemic effects in C57BL/6J mice.

Chronopharmacology is the study of the varying responses of drugs to changes in biological timing and endogenous periodicities. The selective sodium-glucose cotransporter 2 inhibitor, dapagliflozin, is a globally prescribed antihyperglycemic drug. Although dapagliflozin is usually administered once a day, the specific intake time is generally not mentioned. Therefore, this study aimed at investigating the diurnal effects of dapagliflozin on high-fat diet (HFD)-induced obesity in mice. Five-week-old male C57BL/6J mice were fed a normal (control) diet or HFD for 10 weeks. During the last 2 weeks, the mice were administered olive oil/ethanol emulsion or dapagliflozin (1mg/kg, p.o.) in the light or dark phase. At the end of the experiment, the mice were euthanized after an 18h fasting period, and plasma and tissue samples (epididymal white adipose tissues, liver, and kidney) were collected. Dapagliflozin administration in the light phase significantly decreased plasma glucose levels, insulin levels, adipose adipokines, and decreased the size of adipocytes, compared with the HFD group. In contrast, these parameters remained unchanged in the mice treated during the dark phase. Our data therefore suggests that dapagliflozin portrays definite chronopharmacology, which may provide valuable information on the importance of drug administration timing for maximal pharmacological effects.

Effects of work schedule and period of exposure on changes in urinary chromium and nickel excretion among rotating shift workers in a stainless-steel plant.

We investigated the association between the period of exposure and changes in urinary excretion of chromium and nickel among rotating shift workers in a stainless-steel plant. The study participants were composed of two groups: the workers who were occupationally exposed to metals ("exposed group") and those who were not occupationally exposed to metals ("unexposed group"). The exposed and unexposed groups consisted of 56 and 40 male rotating shift workers, respectively. Urine samples were collected immediately before and immediately after the day shift, evening shift, and night shift. Urinary chromium and nickel were measured using inductively coupled plasma mass spectrometry. To correct for variations in urine dilution, urinary metal concentrations were expressed as a ratio to urinary creatinine concentration. In the exposed group, post-shift urinary excretion of chromium was significantly higher than pre-shift excretion. However, although urinary chromium excretion clearly increased after the day and night shift [63% (p < .0001) and 87% (p < .0001), respectively], urinary chromium excretion after the evening shift was only slightly higher than that measured before the evening shift (8%, p = .028). Similar patterns were found for urinary nickel excretion (p = .0001, 0.20, and 0.18 for the day, evening, and night shifts, respectively). Non-uniform urinary excretion of metals between the day shift, evening shift, and night shift were observed in the exposed group; specifically, urinary metal excretion increased only slightly during the evening shift. In the unexposed group, no significant increase or decrease was found in median urinary chromium or nickel excretion (p= .63-0.87). Work shift-specific permissible exposure level would be necessary.

1O, 20O-diacetyl kamebakaurin protects against acetaminophen-induced hepatotoxicity in mice.

The present study aimed to investigate the protective effects of kamebakaurin (KA) and 1O, 20O-diacetyl kamebakaurin (Ac2KA) on acetaminophen (APAP)-induced hepatotoxicity and compare the hepatoprotective mechanisms of the two chemicals. Seven-week-old male C57BL/6J mice were orally administered KA, Ac2KA, or an ethanol/olive oil emulsion once per day for 7-days. Twenty-four hours after the final administration, the mice were fasted and then intraperitoneally injected with 450 mg/kg APAP or saline. At 16 h after injection, the mice were euthanized and blood samples were collected for plasma analysis. Pretreatment with KA and Ac2KA significantly attenuated APAP-induced hepatic injury. The protective effect of Ac2KA was stronger than that of KA. These two chemicals attenuated oxidative stress, inflammatory cytokine production, c-jun N-terminal kinase activation, and receptor-interacting protein (RIP)-3 activation. Ac2KA also decreased APAP-induced RIP-1 activation and nuclear factor kappa B (NF-κB) p65 translocation. Moreover, Ac2KA repressed mRNA expression of Cyp1a2/2e1 in the liver. Our results showed that KA and Ac2KA exerted protective effects against APAP-induced hepatotoxicity. The responsible mechanisms may be related to the chemicals' antioxidant activity and the inhibition of c-jun N-terminal kinase activation and RIP-3 activation. The effects of Ac2KA included those of KA, as well as RIP-1 inactivation, NF-κB inhibition, and Cyp inhibition.

Activation of ornithine decarboxylase protects against methylmercury toxicity by increasing putrescine.

We previously reported significantly increased level of putrescine, a polyamine, in the brains of mice administered methylmercury. Moreover, addition of putrescine to culture medium reduced methylmercury toxicity in C17.2 mouse neural stem cells. In this study, the role of ornithine decarboxylase (ODC), an enzyme involved in putrescine synthesis, in response to methylmercury toxicity was investigated. Methylmercury increased ODC activity in mouse cerebrum and cerebellum, but this increase was hardly observed in the kidney and liver, where methylmercury accumulated at a high concentration. In the cerebrum and cerebellum, increased putrescine was observed with methylmercury administration. Methylmercury increased ODC activity in C17.2 cells, but this was almost completely abolished in the presence of an ODC inhibitor. Methylmercury also increased the level of ODC protein in mouse brain and C17.2 cells. In addition, C17.2 cells pretreated with ODC inhibitor showed higher methylmercury sensitivity than control cells. These results suggest that the increased ODC activity by methylmercury is involved in the increase in putrescine level, and ODC plays an important role in the reduction of methylmercury toxicity. This is the first study to provide evidence that increased ODC activity may be a protective response against methylmercury-induced neurotoxicity.

Lethal chronotoxicity induced by seven metal compounds in mice.

The aim of the present study is to investigate the "chronotoxicity" of seven metal compounds (Hg, Pb, Ni, Cr, Cu, Zn, or Fe) by assessing how their toxicity varies with circadian periodicity. Male ICR mice were injected with each metal compound intraperitoneally at 6 different time points over the course of a day (zeitgeber time [ZT]: ZT2, ZT6, ZT10, ZT14, ZT18 and ZT22). Mortality was then monitored until 14 days after the injection. Our investigation demonstrated that mice were tolerant against Ni toxicity during dark phase, on the other hand, they were tolerant against Cr toxicity during light phase. The chronotoxicity of Hg and Pb seemed to be biphasic. Further, mice were susceptible to toxicities against Cu and Zn in the time zone during which light and dark were reversed. Interestingly, no significant differences were observed for Fe exposure at any time of the day. Our results propose that the chronotoxicology may provide valuable information regarding the importance of injection timing for not only toxicity evaluation tests but also the reproducibility of animal experiments. Furthermore, our data suggests that chronotoxicology may be an important consideration when evaluating the quality of risk assessments for night shift workers who may be exposed to toxic substances at various times of the day.

Non-toxic Level of Acetaminophen Potentiates Carbon Tetrachloride-Induced Hepatotoxicity in Mice.

A wide range of medications are routinely used to maintain and improve human health. Hence, it is essential that we understand and predict adverse effects caused by the combined use of multiple medications. In the present study, we investigated whether the combination of carbon tetrachloride (CCl4) and acetaminophen (APAP) had a detrimental effect on the liver. Mice injected with APAP (100 mg/kg) showed no significant changes in hepatic injury markers (alanine aminotransferase and aspartate aminotransferase), histopathological findings, pro-inflammatory cytokine levels, or hepatic oxidative stress. In contrast, a single injection of CCl4 (15 mg/kg) led to a significant increase in hepatic injury, in addition to an increase in pro-inflammatory cytokine levels and oxidative stress. Co-administration of APAP and CCl4 resulted in exacerbation of these hepatic injuries. Our results suggest that a non-toxic dose of APAP has the potential to increase CCl4-induced liver damage and oxidative stress.