The protective role of Per2 against carbon tetrachloride-induced hepatotoxicity

Biological rhythms of the liver

The biological rhythm is a fundamental aspect of an organism, regulating many physiological processes. This study focuses on the analysis of the molecular basis of circadian rhythms and its impact on the functioning of the liver. The regulation of biological rhythms is carried out by the clock system, which consists of the central clock and peripheral clocks. The central clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus and is regulated by signals received from the retinal pathway. The SCN regulates the circadian rhythm of the entire body through its indirect influence on the peripheral clocks. In turn, the peripheral clocks can maintain their own rhythm, independent of the SCN, by creating special feedback loops between transcriptional and translational factors. The main protein families involved in these processes are CLOCK, BMAL, PER and CRY. Disorders in the expression of these factors have a significant impact on the functioning of the liver. In such cases lipid metabolism, cholesterol metabolism, bile acid metabolism, alcohol metabolism, and xenobiotic detoxification can be significantly affected. Clock dysfunctions contribute to the pathogenesis of various disorders, including fatty liver disease, liver cirrhosis and different types of cancer. Therefore understanding circadian rhythm can have significant implications for the therapy of many liver diseases, as well as the development of new preventive and treatment strategies.

Neuroprotection via Carbon Monoxide Depends on the Circadian Regulation of CD36-Mediated Microglial Erythrophagocytosis in Hemorrhagic Stroke

The molecular basis for circadian dependency in stroke due to subarachnoid hemorrhagic stroke (SAH) remains unclear. We reasoned that microglial erythrophagocytosis, crucial for SAH response, follows a circadian pattern involving carbon monoxide (CO) and CD36 surface expression. The microglial BV-2 cell line and primary microglia (PMG) under a clocked medium change were exposed to blood ± CO (250 ppm, 1 h) in vitro. Circadian dependency and the involvement of CD36 were analyzed in PMG isolated from control mice and CD36-/- mice and by RNA interference targeting Per-2. In vivo investigations, including phagocytosis, vasospasm, microglia activation and spatial memory, were conducted in an SAH model using control and CD36-/- mice at different zeitgeber times (ZT). In vitro, the surface expression of CD36 and its dependency on CO and phagocytosis occurred with changed circadian gene expression. CD36-/- PMG exhibited altered circadian gene expression, phagocytosis and impaired responsiveness to CO. In vivo, control mice with SAH demonstrated circadian dependency in microglia activation, erythrophagocytosis and CO-mediated protection at ZT2, in contrast to CD36-/- mice. Our study indicates that circadian rhythmicity modulates microglial activation and subsequent CD36-dependent phagocytosis. CO altered circadian-dependent neuroprotection and CD36 induction, determining the functional outcome in a hemorrhagic stroke model. This study emphasizes how circadian rhythmicity influences neuronal damage after neurovascular events.

PER2 regulates odontoblastic differentiation of dental papilla cells in vitro via intracellular ATP content and reactive oxygen species levels

Background

Dental papilla cells (DPCs) are one of the key stem cells for tooth development, eventually forming dentin and pulp. Previous studies have reported that PER2 is expressed in a 24-hour oscillatory pattern in DPCs in vitro. In vivo, PER2 is highly expressed in odontoblasts (which are differentiated from DPCs). However, whether PER2 modulates the odontogenic differentiation of DPCs is uncertain. This research was to identify the function of PER2 in the odontogenic differentiation of DPCs and preliminarily explore its mechanisms.

Methods

We monitored the expression of PER2 in DPCs differentiated in vivo. We used PER2 overexpression and knockdown studies to assess the role of PER2 in DPC differentiation and performed intracellular ATP content and reactive oxygen species (ROS) assays to further investigate the mechanism.

Results

PER2 expression was considerably elevated throughout the odontoblastic differentiation of DPCs in vivo. Overexpressing Per2 boosted levels of odontogenic differentiation markers, such as dentin sialophosphoprotein (Dspp), dentin matrix protein 1 (Dmp1), and alkaline phosphatase (Alp), and enhanced mineralized nodule formation in DPCs. Conversely, the downregulation of Per2 inhibited the differentiation of DPCs. Additionally, downregulating Per2 further affected intracellular ATP content and ROS levels during DPC differentiation.

Conclusion

Overall, we demonstrated that PER2 positively regulates the odontogenic differentiation of DPCs, and the mechanism may be related to mitochondrial function as shown by intracellular ATP content and ROS levels.

Impact of dietary supplementation with chokeberry (Aronia melanocarpa, Michx.) on tetrachloride-induced liver injury in Wistar rats: Hematological and biochemical implication

In the current study, we assessed the hematological/biochemical alterations, histopathological changes in the liver, and blood cell disorders in Wistar rats exposed to a toxic concentration of carbon tetrachloride (CCl4 ) and the potential protective effect of a 30-day oral extract of chokeberry (Aronia melanocarpa, AM). The concentration of AM (3.38 mg/kg) obtained by quantitative purification from AM fruit showed the highest antioxidant activity (AOA) in vitro and was used for oral ingestion. In addition to high AOA, high values of total phenols (85.334 mg/g), total phenolic acid (606.95 mg/g), total flavonids (22.10 mg/g), and total anthocyanins (11.01 mg/g) were recorded in chokeberry extract. CCl4 treatment caused serious liver injury, hepatocyte and blood cell impairment. AM extract given to rats before CCl4 application had a moderate hepatoprotective effect in comparison to after CCl4 application. White blood count and leukocytes were significantly altered by CCl4, however, the protective role of AM in leukocyte disorders was not established. A high number of microcytes, stomatocytes, anisocytes, and hemolyzed erythrocytes during CCl4 exposure was reduced by AM extract. Flower erythrocytes in the AM + CCl4 group were recorded. Supplementation with chokeberry extract without CCl4 caused hyperproteinemia and hyperalbuminemia. Although the results indicate a weak protective role for AM, it is nevertheless important for improved erythropoiesis and regulation of the development of anemia. The hepatoprotective role of AM was moderate, and the immune response was not proven. Daily consumption of chokeberry extract can improve health. However, the results of our study showed that the ingestion of AM extract at this dose with the highest AOA would have more effective effects if the supplementation were significantly increased.

Diclofenac Disrupts the Circadian Clock and through Complex Cross-Talks Aggravates Immune-Mediated Liver Injury-A Repeated Dose Study in Minipigs for 28 Days

Diclofenac effectively reduces pain and inflammation; however, its use is associated with hepato- and nephrotoxicity. To delineate mechanisms of injury, we investigated a clinically relevant (3 mg/kg) and high-dose (15 mg/kg) in minipigs for 4 weeks. Initially, serum biochemistries and blood-smears indicated an inflammatory response but returned to normal after 4 weeks of treatment. Notwithstanding, histopathology revealed drug-induced hepatitis, marked glycogen depletion, necrosis and steatosis. Strikingly, the genomic study revealed diclofenac to desynchronize the liver clock with manifest inductions of its components CLOCK, NPAS2 and BMAL1. The > 4-fold induced CRY1 expression underscored an activated core-loop, and the dose dependent > 60% reduction in PER2mRNA repressed the negative feedback loop; however, it exacerbated hepatotoxicity. Bioinformatics enabled the construction of gene-regulatory networks, and we linked the disruption of the liver-clock to impaired glycogenesis, lipid metabolism and the control of immune responses, as shown by the 3-, 6- and 8-fold induced expression of pro-inflammatory CXCL2, lysozyme and ß-defensin. Additionally, diclofenac treatment caused adrenocortical hypertrophy and thymic atrophy, and we evidenced induced glucocorticoid receptor (GR) activity by immunohistochemistry. Given that REV-ERB connects the circadian clock with hepatic GR, its > 80% repression alleviated immune responses as manifested by repressed expressions of CXCL9(90%), CCL8(60%) and RSAD2(70%). Together, we propose a circuitry, whereby diclofenac desynchronizes the liver clock in the control of the hepatic metabolism and immune response.

Attenuation by Time-Restricted Feeding of High-Fat and High-Fructose Diet-Induced NASH in Mice Is Related to Per2 and Ferroptosis

Nonalcoholic steatohepatitis (NASH) is a chronic and progressive disease whose treatment strategies are limited. Although time-restricted feeding (TRF) is beneficial for metabolic diseases without influencing caloric intake, the underlying mechanisms of TRF action in NASH and its efficacy have not yet been demonstrated. We herein showed that TRF effectively alleviated NASH, producing a reduction in liver enzymes and improvements in liver pathology. Regarding the mechanisms by which TRF mitigates NASH, we ascertained that TRF inhibited ferroptosis and the expression of the circadian gene Per2. By adopting a hepatocyte-specific Per2-knockout (Per2^△hep) mice model, we clarified the critical role of Per2 in exacerbating NASH. According to the results of our RNA-Seq analysis, the knockout of Per2 ameliorated NASH by inhibiting the onset of ferroptosis; this was manifested by diminished lipid peroxidation levels, decreased mRNA and protein levels for ferroptosis-related genes, and alleviated morphologic changes in mitochondria. Furthermore, using a ferroptosis inhibitor, we showed that ferroptosis significantly aggravated NASH and noted that this was likely achieved by regulation of the expression of peroxisome proliferator activated receptor (PPAR)α. Finally, we discerned that TRF and hepatocyte-specific knockout of Per2 promoted the expression of PPARα. Our results revealed a potential for TRF to effectively alleviate high-fat and high-fructose diet-induced NASH via the inhibition of Per2 and depicted the participation of Per2 in the progression of NASH by promoting ferroptosis, which was ultimately related to the expression of PPARα.

Period1 mediates rhythmic metabolism of toxins by interacting with CYP2E1

The biological clock is an endogenous biological timing system, which controls metabolic functions in almost all organs. Nutrient metabolism, substrate processing, and detoxification are circadian controlled in livers. However, how the clock genes respond to toxins and influence toxicity keeps unclear. We identified the clock gene Per1 was specifically elevated in mice exposed to toxins such as carbon tetrachloride (CCl₄). Mice lacking Per1 slowed down the metabolic rate of toxins including CCl₄, capsaicin, and acetaminophen, exhibiting relatively more residues in the plasma. Liver injury and fibrosis induced by acute and chronic CCl₄ exposure were markedly alleviated in Per1-deficient mice. These processes involved the binding of PER1 protein and hepatocyte nuclear factor-1alpha (HNF-1α), which enhances the recruitment of HNF-1α to cytochrome P450 2E1 (Cyp2e1) promoter and increases Cyp2e1 expression, thereby promoting metabolism for toxins in the livers. These results indicate that PER1 mediates the metabolism of toxins and appropriate suppression of Per1 response is a potential therapeutic target for toxin-induced hepatotoxicity.

Melatonin Attenuates Dysregulation of the Circadian Clock Pathway in Mice With CCl4-Induced Fibrosis and Human Hepatic Stellate Cells

Dysregulation of the circadian clock machinery is a critical mechanism in the pathogenesis of fibrosis. This study aimed to investigate whether the antifibrotic effect of melatonin is associated with attenuation of circadian clock pathway disturbances in mice treated with carbon tetrachloride (CCl₄) and in human hepatic stellate cells line LX2. Mice received CCl₄ 5 μL/g body weight i.p. twice a week for 4 or 6 weeks. Melatonin was given at 5 or 10 mg/kg/day i.p., beginning 2 weeks after the start of CCl₄ administration. Treatment with CCl₄ resulted in fibrosis evidenced by the staining of α-smooth muscle actin (α-SMA) positive cells and a significant decrease of peroxisome proliferator-activated receptor (PPARα) expression. CCl₄ led to a lower expression of brain and muscle Arnt-like protein 1 (BMAL1), circadian locomotor output cycles kaput (CLOCK), period 1–3 (PER1, 2, and 3), cryptochrome 1 and 2 (CRY1 and 2) and the retinoic acid receptor-related orphan receptor (RORα). The expression of the nuclear receptor REV-ERBα showed a significant increase. Melatonin significantly prevented all these changes. We also found that melatonin (100 or 500 μM) potentiated the inhibitory effect of REV-ERB ligand SR9009 on α-SMA and collagen1 expression and increased the expression of PPARα in LX2 cells. Analysis of circadian clock machinery revealed that melatonin or SR9009 exposure upregulated BMAL1, CLOCK, PER2, CRY1, and RORα expression, with a higher effect of combined treatment. Findings from this study give new insight into molecular pathways accounting for the protective effect of melatonin in liver fibrosis.

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.

Circadian time-dependent antioxidant and inflammatory responses to acute cadmium exposure in the brain of zebrafish

Up to date, little information is available on effects of circadian rhythm on metal-induced toxicity in fish. In this study, zebrafish were acutely exposed to 0.97mgL^-1 cadmium for 12h either at ZT0 (the light intensity began to reached maximum) or at ZT12 (light intensity began to reached minimum) to evaluate the temporal sensitivity of oxidative stress and inflammatory responses in the brain of zebrafish. Profiles of responses of some genes at mRNA, protein and activity levels were different between ZT0 and ZT12 in the normal water. Exposure to Cd induced contrary antioxidant responses and similar inflammatory responses between ZT0 and ZT12. However, the number of inflammatory genes which were up-regulated was significantly greater at ZT12 than at ZT0. And, the up-regulated inflammatory genes were more responsive at ZT12 than at ZT0. At ZT12, antioxidant genes were down-regulated at mRNA, protein and activity levels. Contrarily, antioxidant genes were not affected at mRNA levels but activated at the protein and/or activity levels at ZT0. Reactive oxygen species (ROS) sharply increased and remained relatively stable when fish were exposed to Cd at ZT12 and ZT0, respectively. Positive correlations between ROS levels and mRNA levels of nuclear transcription factor κB (NF-κB) and between mRNA levels of NF-κB and its target genes were observed, suggesting that ROS may play an essential role in regulating the magnitude of inflammatory responses. Taken together, oxidative stress and immunotoxicity in the brain were more serious when fish were exposed to Cd in the evening than in the morning, highlighting the importance of circadian rhythm in Cd-induced neurotoxicity in fish.

Bromobenzene-induced lethal toxicity in mouse is prevented by pretreatment with zinc sulfate

In the current study, we evaluated the protective effect of zinc (Zn) against bromobenzene (BB) -induced lethal toxicity. We used Zn because this element is known to be an inducer of metallothionein (MT), which is in turn known to serve as an endogenous scavenger of free radicals. We administered Zn (as ZnSO4) at 50 mg/kg subcutaneously once-daily for 3 successive days prior to a single intraperitoneal administration of 1.2 g/kg BB in male ddY mice. Our results showed that pretreatment with Zn completely abolished the BB-induced mortality of mice until 48 h. We also found that pretreatment of mice with Zn significantly decreased the functional marker levels and reduced the histological damage both in liver and kidney as assessed at 18 h post-BB. We also showed that pretreatment with Zn enhanced antioxidative activity, resulting in decreased lipid peroxidation in both liver and kidney. Moreover, BB-induced calcium levels were downregulated by pretreatment with Zn. In addition, Zn-induced MT was decreased in Zn + BB-treated animals, implying that MT was consumed by BB-induced radicals. These findings suggest that prophylaxis with Zn protects mice from BB-induced lethal toxicity by decreasing oxidative stress in liver and kidney, presumably by induction of MT, which scavenges radicals induced by BB exposure.

Evolving roles of circadian rhythms in liver homeostasis and pathology

Circadian clock in mammals is determined by a core oscillator in the suprachiasmatic nucleus (SCN) of the hypothalamus and synchronized peripheral clocks in other tissues. The coherent timing systems could sustain robust output of circadian rhythms in response to the entrainment controlled environmentally. Disparate approaches have discovered that clock genes and clock-controlled genes (CCGs) exist in nearly all mammalian cell types and are essential for establishing the mechanisms and complexity of internal time-keeping systems. Accumulating evidence demonstrates that the control of homeostasis and pathology in the liver involves intricate loops of transcriptional and post-translational regulation of clock genes expression. This review will focus on the recent advances with great importance concerning clock rhythms linking liver homeostasis and diseases. We particularly highlight what is currently known of the evolving insights into the mechanisms underlying circadian clock . Eventually , findings during recent years in the field might prompt new circadian-related chronotherapeutic strategies for the diagnosis and treatment of liver diseases by coupling these processes.

The Tibetan medicine Zuotai influences clock gene expression in the liver of mice

Background. The circadian clock is involved in drug metabolism, efficacy and toxicity. Drugs could in turn affect the biological clock as a mechanism of their actions. Zuotai is an essential component of many popular Tibetan medicines for sedation, tranquil and “detoxification,” and is mainly composed of metacinnabar (β-HgS). The pharmacological and/or toxicological basis of its action is unknown. This study aimed to examine the effect of Zuotai on biological clock gene expression in the liver of mice. Materials and methods. Mice were orally given Zuotai (10 mg/kg, 1.5-fold of clinical dose) daily for 7 days, and livers were collected every 4 h during the 24 h period. Total RNA was extracted and subjected to real-time RT-PCR analysis of circadian clock gene expression. Results. Zuotai decreased the oscillation amplitude of the clock core gene Clock, neuronal PAS domain protein 2 (Npas2), Brain and muscle Arnt-like protein-1 (Bmal1) at 10:00. For the clock feedback negative control genes, Zuotai had no effect on the oscillation of the clock gene Cryptochrome (Cry1) and Period genes (Per1–3). For the clock-driven target genes, Zuotai increased the oscillation amplitude of the PAR-bZip family member D-box-binding protein (Dbp), decreased nuclear factor interleukin 3 (Nfil3) at 10:00, but had no effect on thyrotroph embryonic factor (Tef); Zuotai increased the expression of nuclear receptor Rev-Erbα (Nr1d1) at 18:00, but had little influence on the nuclear receptor Rev-Erbβ (Nr1d2) and RORα. Conclusion. The Tibetan medicine Zuotai could influence the expression of clock genes, which could contribute to pharmacological and/or toxicological effects of Zuotai.

Hepatoprotective activity of Musa paradisiaca on experimental animal models

OBJECTIVE

To investigate the hepatoprotective activity of stem of Musa paradisiaca (M. paradisiaca) in CCl4 and paracetamol induced hepatotoxicity models in rats.

METHODS

Hepatoprotective activity of alcoholic and aqueous extracts of stem of M. paradisiaca was demonstrated by using two experimentally induced hepatotoxicity models.

RESULTS

Administration of hepatotoxins (CCl4 and paracetamol) showed significant biochemical and histological deteriorations in the liver of experimental animals. Pretreatment with alcoholic extract (500 mg/kg), more significantly and to a lesser extent the alcoholic extract (250 mg/kg) and aqueous extract (500 mg/kg), reduced the elevated levels of the serum enzymes like serum glutamic-oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatase (ALP) and bilirubin levels and alcoholic and aqueous extracts reversed the hepatic damage towards the normal, which further evidenced the hepatoprotective activity of stem of M. paradisiaca.

CONCLUSIONS

The alcoholic extract at doses of 250 and 500 mg/kg, p.o. and aqueous extract at a dose of 500 mg/kg, p.o. of stem of M. paradisiaca have significant effect on the liver of CCl4 and paracetamol induced hepatotoxicity animal models.

Hepatoprotective activity of Hepax-a polyherbal formulation

OBJECTIVE

To evaluate the hepatoprotective potential of Hepax, a polyherbal formulation, against three experimentally induced hepatotoxicity models in rats.

METHODS

Hepatoprotective activity of Hepax was studied against three experimentally induced hepatotoxicity models, namely, carbon tetrachloride (CCl4), paracetamol and thiocetamide induced hepatotoxicity in rats.

RESULTS

Administration of hepatotoxins (CCl4, paracetamol and thiocetamide) showed significant morphological, biochemical and histological deteriorations in the liver of experimental animals. Pretreatment with Hepax had significant protection against hepatic damage by maintaining the morphological parameters (liver weight and liver weight to organ weight ratio) within normal range and normalizing the elevated levels of biochemical parameters (SGPT, SGOT, ALP and total bilirubin), which were evidently showed in histopathological study.

CONCLUSIONS

The Hepax has highly significant hepatoprotective effect at 100 and 200 mg/kg, p.o. on the liver of all the three experimental animal models.

Mutual antagonism between circadian protein period 2 and hepatitis C virus replication in hepatocytes

BACKGROUND

Hepatitis C virus (HCV) infects approximately 3% of the world population and is the leading cause of liver disease, impacting hepatocyte metabolism, depending on virus genotype. Hepatic metabolic functions show rhythmic fluctuations with 24-h periodicity (circadian), driven by molecular clockworks ticking through translational-transcriptional feedback loops, operated by a set of genes, called clock genes, encoding circadian proteins. Disruption of biologic clocks is implicated in a variety of disorders including fatty liver disease, obesity and diabetes. The relation between HCV replication and the circadian clock is unknown.

METHODS

We investigated the relationship between HCV core infection and viral replication and the expression of clock genes (Rev-Erbα, Rorα, ARNTL, ARNTL2, CLOCK, PER1, PER2, PER3, CRY1 and CRY2) in two cellular models, the Huh-7 cells transiently expressing the HCV core protein genotypes 1b or 3a, and the OR6 cells stably harboring the full-length hepatitis C genotype 1b replicon, and in human liver biopsies, using qRT-PCR, immunoblotting, luciferase assays and immunohistochemistry.

RESULTS

In Huh-7 cells expressing the HCV core protein genotype 1b, but not 3a, and in OR6 cells, transcript and protein levels of PER2 and CRY2 were downregulated. Overexpression of PER2 led to a consistent decrease in HCV RNA replicating levels and restoration of altered expression pattern of a subset of interferon stimulated genes (ISGs) in OR6 cells. Furthermore, in liver biopsies from HCV genotype 1b infected patients, PER2 was markedly localized to the nucleus, consistent with an auto-inhibitory transcriptional feedback loop.

CONCLUSIONS

HCV can modulate hepatic clock gene machinery, and the circadian protein PER2 counteracts viral replication. Further understanding of circadian regulation of HCV replication and rhythmic patterns of host-hosted relationship may improve the effectiveness of HCV antiviral therapy. This would extend to hepatic viral infections the current spectrum of chronotherapies, implemented to treat metabolic, immune related and neoplastic disease.

Carbon tetrachloride-induced hepatic injury through formation of oxidized diacylglycerol and activation of the PKC/NF-κB pathway

Protein kinase C (PKC) participates in signal transduction, and its overactivation is involved in various types of cell injury. PKC depends on diacylglycerol (DAG) for its activation in vivo We have previously reported that DAG peroxides (DAG-O(O)H) activate PKC in vitro more strongly than unoxidized DAG, suggesting that DAG-O(O)H, if generated in vivo under oxidative stress, would act as an aberrant signal transducer. The present study examined whether DAG-O(O)H are formed in carbon tetrachloride (CCl(4))-induced acute rat liver injury in association with activation of the PKC/nuclear factor (NF)-κB pathway. A single subcutaneous injection of CCl(4) resulted in a marked increase in hepatic DAG-O(O)H content. At the molecular level, immunohistochemistry and subcellular fractionation combined with immunoblotting localized PKCα, βI, βII and δ isoforms to cell membranes, while immunoblotting showed phosphorylation of the p65 subunit of NF-κB, and immunoprecipitation using isoform-specific anti-PKC antibodies revealed specific association of PKCα and p65. In addition, expression of tumor necrosis factor α (TNFα) and neutrophil invasion increased in the CCl(4)-treated rats. Furthermore, we demonstrated that Vitamin E, one of the most important natural antioxidants that suppresses peroxidation of membrane lipids, significantly inhibited the CCl(4)-induced increase in hepatic DAG-O(O)H content and TNFα expression as well as phosphorylation of PKCα and p65. These data demonstrate for the first time that DAG-O(O)H are generated in the process of CCl(4)-induced liver injury, resulting in activation of the PKC/NF-κB pathway and TNFα-mediated aggravation of liver injury.

Diurnal variation of hepatic antioxidant gene expression in mice

Background

This study was aimed to examine circadian variations of hepatic antioxidant components, including the Nrf2- pathway, the glutathione (GSH) system, antioxidant enzymes and metallothionein in mouse liver.

Methods and Results

Adult mice were housed in light- and temperature-controlled facilities for 2 weeks, and livers were collected every 4 h during the 24 h period. Total RNA was isolated, purified, and subjected to real-time RT-PCR analysis. Hepatic mRNA levels of Nrf2, Keap1, Nqo1 and Gclc were higher in the light-phase than the dark-phase, and were female-predominant. Hepatic GSH presented marked circadian fluctuations, along with glutathione S-transferases (GST-α1, GST-µ, GST-π) and glutathione peroxidase (GPx1). The expressions of GPx1, GST-µ and GST-π mRNA were also higher in females. Antioxidant enzymes Cu/Zn superoxide dismutase (Sod1), catalase (CAT), cyclooxygenase-2 (Cox-2) and heme oxygenase-1 (Ho-1) showed circadian rhythms, with higher expressions of Cox-2 and CAT in females. Metallothionein, a small non-enzymatic antioxidant protein, showed dramatic circadian variation in males, but higher expression in females. The circadian variations of the clock gene Brain and Muscle Arnt-like Protein-1(Bmal1), albumin site D-binding protein (Dbp), nuclear receptor Rev-Erbα (Nr1d1), period protein (Per1 and Per2) and cryptochrome 1(Cry1) were in agreement with the literature. Furthermore, acetaminophen hepatotoxicity is more severe when administered in the afternoon when hepatic GSH was lowest.

Conclusions

Circadian variations and gender differences in transcript levels of antioxidant genes exist in mouse liver, which could affect body responses to oxidative stress at different times of the day.

Sodium butyrate potentiates carbon tetrachloride-induced acute liver injury in mice

Histone deacetylase 2 (HDAC2), a prominent member of the class I HDAC family, plays crucial roles in inflammation and other pathological processes. Recent studies have found that the activity and expression of HDAC2 were altered under oxidative stress conditions. The aim of the current study was to elucidate the expression and the possible pathophysiological significance of HDAC2 in CCl(4)-induced oxidative hepatitis. Our resultant data indicated that the expression of HDAC2 in liver increased after CCl(4) exposure, which was attenuated by antioxidants N-acetyl-L-cysteine or α-lipoic acid. Administration of sodium butyrate (NaB), a representative HDAC inhibitor resulted in further elevation of serum aminotransferase levels, enhanced oxidative stress, reduced antioxidant enzyme activities, increased production of proinflammatory cytokines and aggravated hepatocellular necrosis as well as leukocyte infiltration in liver. The results suggested that oxidative stress in CCl(4)-exposed mice induce the expression of HDAC2, while inhibition of HDAC result in exacerbated liver injury. Therefore, HDAC might be involved in the pathogenesis of CCl(4)-induced liver injury and provide protective benefit.

Deletion of clock gene Per2 exacerbates cholestatic liver injury and fibrosis in mice

The Period 2 (Per2) gene is an important component of the circadian system and is thought to modulate many physiological and pathological processes in mammals. In the previous study, we have disclosed the protective role of Per2 against carbon tetrachloride induced liver injury and fibrosis. Here we further assess the effect of Per2 deficiency on cholestatic hepatic injury and fibrosis. Cholestasis was induced by bile duct ligation (BDL) for 10 days in wild-type (WT) and Per2(-/-) mice. Masson trichrome staining and analysis of α-SMA immunohistochemistry were performed to show the collagen accumulation and the HSC activation, respectively. The mRNA levels of fibrosis-related genes were monitored by quantitative real-time PCR. Following BDL, livers from Per2(-/-) mice exhibited markedly increased extent of bile infarct and extracellular matrix (ECM) deposition compared with WT mice. Furthermore, the expressions of fibrosis-related genes like TNF-α, TGF-β1, Col1α1 and TIMP-1 were dramatically elevated in Per2(-/-) cholestatic liver. Our observations indicated that clock gene Per2 plays a protective role in mediating liver injury and fibrosis during cholestasis.

Protective effects of salecan against carbon tetrachloride-induced acute liver injury in mice

Carbon tetrachloride (CCl₄) is a well-established model for screening hepato-protective drugs. The aim of the present study was to evaluate the potential protective effects of a novel soluble β-glucan salecan on acute liver injury induced by CCl₄ in mice and to further explore the underlying mechanisms. Mice were given salecan (40 mg kg⁻¹) or phosphate-buffered saline for 3 days prior to treatment with a single intraperitoneal dose of CCl₄ (1 ml kg⁻¹ body weight). Animals were sacrificed at 0, 12, 24, 48, 72 and 96 h post-injection of CCl₄. Serum liver enzyme levels, histology, lipid peroxidation, glutathione (GSH) content, expression of antioxidant enzymes and hepatocyte proliferation were subsequently evaluated. The serum levels of hepatic enzyme markers were markedly reduced in the salecan pretreatment group compared with the control group. Histopathological examination of the livers revealed that hepatocellular degeneration and necrosis were significantly attenuated at an early stage during CCl₄ intoxication and liver recovery was markedly accelerated at a later stage in salecan pre-administered mice. Furthermore, salecan administration remarkably alleviated lipid peroxidation and restored GSH depletion. Meanwhile, the expression of antioxidant genes was significantly elevated in the salecan-treated group. Interestingly, the administration of salecan remarkably enhanced hepatocyte proliferation in the recovery phase after CCl₄ injection. Taken together, these results demonstrated that salecan exhibits a protective action on acute hepatic injury induced by CCl₄ through attenuating oxidative stress and accelerating hepatocyte regeneration.

Drug-induced toxicity on mitochondria and lipid metabolism: mechanistic diversity and deleterious consequences for the liver

Numerous investigations have shown that mitochondrial dysfunction is a major mechanism of drug-induced liver injury, which involves the parent drug or a reactive metabolite generated through cytochromes P450. Depending of their nature and their severity, the mitochondrial alterations are able to induce mild to fulminant hepatic cytolysis and steatosis (lipid accumulation), which can have different clinical and pathological features. Microvesicular steatosis, a potentially severe liver lesion usually associated with liver failure and profound hypoglycemia, is due to a major inhibition of mitochondrial fatty acid oxidation (FAO). Macrovacuolar steatosis, a relatively benign liver lesion in the short term, can be induced not only by a moderate reduction of mitochondrial FAO but also by an increased hepatic de novo lipid synthesis and a decreased secretion of VLDL-associated triglycerides. Moreover, recent investigations suggest that some drugs could favor lipid deposition in the liver through primary alterations of white adipose tissue (WAT) homeostasis. If the treatment is not interrupted, steatosis can evolve toward steatohepatitis, which is characterized not only by lipid accumulation but also by necroinflammation and fibrosis. Although the mechanisms involved in this aggravation are not fully characterized, it appears that overproduction of reactive oxygen species by the damaged mitochondria could play a salient role. Numerous factors could favor drug-induced mitochondrial and metabolic toxicity, such as the structure of the parent molecule, genetic predispositions (in particular those involving mitochondrial enzymes), alcohol intoxication, hepatitis virus C infection, and obesity. In obese and diabetic patients, some drugs may induce acute liver injury more frequently while others may worsen the pre-existent steatosis (or steatohepatitis).

Sex and circadian modulatory effects on rat liver as assessed by transcriptome analyses

The present study was designed to fully uncover sex and circadian modulatory effects on rat liver. Hepatic transcriptome analyses were performed at 4 hr intervals of a day-night cycle using young adult male and female rats. Sexually dimorphic genes, which were identified by a cross-sex comparison of time series data, included representative sex-predominant genes such as male- or female-predominant cytochrome P450 subfamilies (Cyp2c11, Cyp2c12, Cyp2c13, and Cyp3a2), sulfotransferases, and glutathione S-transferase Yc2. The identified sexually dimorphic genes were over-represented in the metabolism of retinols, xenobiotics, linoleic acids, or androgen and estrogen, or bile acid biosynthesis. Furthermore, transcription factor targets modeling suggested that transcription factors SP1, hepatocyte nuclear factor 4-alpha (HNF4-alpha), and signal transducer and activator of transcription 5b (STAT5b) serve as core nodes in the regulatory networks. On the other hand, Fourier transform analyses extracted universal circadian-regulated genes in both sexes. The circadian-regulated genes included clock or clock-controlled genes such as aryl hydrocarbon receptor nuclear translocator-like (Arntl), period homolog 2 (Per2), and D site albumin promoter binding protein (Dbp). The extracted cyclic genes were over-represented in major tissue activities, e.g. the urea cycle and the metabolism of amino acids, fatty acids, or glucose, indicating that the major liver functions are under circadian control. The transcription factor targets modeling suggested that transcription factors SP1, HNF4-alpha, and c-Myc proto-oncogene protein (c-MYC) serve as major hubs in the circadian-regulatory gene networks. Interestingly, transcription factors SP1 and HNF4-alpha are likely to orchestrate not only sexually dimorphic, but also circadian-regulated genes even though each criterion was rather mutually exclusive. This suggests the cross-talk between those regulations. Sexual dimorphism is likely to interact with circadian rhythmicity via overlapping gene regulatory networks on rat liver.

The clock gene Per2 is required for normal platelet formation and function

INTRODUCTION

Apoptotic cell death is a highly regulated genetic program, which has been observed in mature megakaryocytes fragmenting into platelets. The clock gene Per2, a key component of core clock oscillator, was involved in affecting both cell cycle control and apoptosis. Thus, loss of Per2 function may be considered potential influence of platelet formation and function.

METHODS

Per2-null mice and C57BL/6 mice were used in the study. Bleeding time, platelet count, megakaryocyte count, megakaryocyte ploidy, megakaryocyte apoptosis, rate of proplatelet formation, clot retraction, platelet aggregation and secretion were performed to evaluate thrombopoiesis and hemostasis. Quantitative RT-PCR was employed to analyze genes expression in liver, bone marrow and enriched megakaryocytes.

RESULTS

The Per2-null mice had nearly 50% platelet counts in peripheral blood. Per2-null platelets were compromised in their ability to aggregate and secretion, consistent with a marked reduction in the number of dense and a-granules. Megakaryocytes from Per2-null mice showed no significant variation in number but increased in ploidy. Ultrastructural examination of Per2-null megakaryocytes revealed many vacuoles in demarcation membranes and reduction in platelet granules. Megakaryocytes from Per2-null bone marrow decreased the rate of proplatelet formation and impaired apoptosis. Per2-null mice showed increased both in Tpo in livers and its receptors C-mpl in bone marrow, and the megakaryocytes from these mice decreased P53 expression, consequently increased Bcl-xl and Bcl-2 level.

CONCLUSIONS

The clock gene Per2 modulating the apoptosis of megakaryocytes was required for platelet formation and function.

Loss of clock gene mPer2 promotes liver fibrosis induced by carbon tetrachloride

AIM

  The clock gene mPer2 controls circadian periods and plays a critical role in clock resetting and responses to drugs of abuse. Mice deficient in mPer2 exhibit a marked susceptibility to acute liver injury. Clinical observations have demonstrated the existence of a relationship between circadian rhythm and liver cirrhosis. Here, we sought direct evidence for clock function to liver fibrosis using mPer2-deficient mice.

METHODS

  Hepatic fibrosis was induced in wild-type (WT) and mPer2(-/-) mice by repetitive intraperitoneal carbon tetrachloride (CCl(4) ) injection. Masson trichrome staining and analysis of α-smooth muscle actin (α-SMA) immunohistochemistry were performed to show the collagen accumulation and the hepatic stellate cell (HSC) activation, respectively. The mRNA levels of fibrosis-related genes were monitored by quantitative real-time polymerase chain reaction. The protein level of TIMP-1 was determined by immunohistochemistry. Transferase deoxytidyl uridine end labeling, α-SMA double staining and 4',6'-diamidino-2-phenylindole dihydrochloride staining were performed to show HSC apoptosis in vivo and in vitro, respectively.

RESULTS

  CCl(4) caused much more severe liver fibrosis and activated more HSC in mPer2 null mice as compared to WT animals. Meanwhile, mPer2 null mice exhibited less efficiency in fibrosis resolution. Apoptotic HSC were significantly fewer in mPer2 null mice compared with WT mice after CCl(4) ; transfected Per2 cDNA into cultured HSC resulted in more HSC apoptosis with upregulation of TRAIL-R2/DR5 expression.

CONCLUSION

  Loss of clock gene mPer2 predisposes liver fibrosis by increasing HSC activation and inhibiting HSC apoptosis.

Lack of guanylate cyclase C results in increased mortality in mice following liver injury

Background

Guanylate Cyclase C (GC-C) expression in the intestine plays a role in the regulation of fluid and ion transport, as well as epithelial cell apoptosis and proliferation. In the adult rat liver, GC-C expression is increased in response to injury. We hypothesized that GC-C is required for repair/recovery from liver injury.

Methods

We subjected wild type (WT) and GC-C deficient mice to acute liver injury with a single injection of the hepatotoxin carbon tetrachloride. Changes in the level of expression of GC-C and its ligands uroguanylin and guanylin were quantified by real-time PCR. Liver morphology, and hepatocyte necrosis, apoptosis and proliferation, were examined at 1-3 days post-injury in mice on a mixed genetic background. Survival was followed for 14 days after carbon tetrachloride injection in wild type and GC-C deficient mice on both a mixed genetic background and on an inbred C57BL6/J background.

Results

GC-C deficient mice on the mixed genetic background nearly all died (median survival of 5 days) following carbon tetrachloride injection while WT littermates experienced only 35% mortality. Elevated levels of TUNEL-positive hepatocyte death on post-injury day 1, increased apoptosis on day 2, and increased areas of centrilobular necrosis on days 2 and 3, were evident in livers from GC-C null mice compared to WT. Collectively these data suggest increased hepatocyte death in the GC-C null mice in the early time period after injury. This corresponds temporally with increased expression of GC-C and its ligands guanylin and uroguanylin in post-injury WT mouse liver. The hepatocyte proliferative response to injury was the same in both genotypes. In contrast, there was no difference in survival between GC-C null and WT mice on the inbred C57BL/6 J background in response to acute liver injury.

Conclusions

Signalling via GC-C promotes hepatocyte survival in vivo and is required for effective recovery from acute toxic injury to the liver in a strain-specific manner.

Clock gene mPer2 functions in diurnal variation of acetaminophen induced hepatotoxicity in mice

The circadian clock gene Period2 (Per2) plays important roles in many physiologic and pathologic processes in mammals. In the previous study, we have reported the protective role of mPer2 against carbon tetrachloride induced hepatotoxicity. Here, we further explore the contribution of this gene to acetaminophen (APAP) induced liver injury in mice. It is reported that the hepatotoxicity induced by APAP exhibited a circadian rhythm in which the peak sensitive injection time is 20:00 while when the administration time becomes to 08:00, it caused markedly decreased liver damage. Thus, we injected APAP into wide type (WT) and mPer2 null mice at the dose of 300 mg/kg at both 08:00 and 20:00. Interestingly, the liver damage showed no significant difference between WT and mPer2 null mice when administered at 08:00, however, liver injury occurred in mPer2 null mice displayed less severe than WT at 20:00. In addition, Cyp1a2, one of the most important cytochrome P450 isoforms responsible for APAP bioactivation, decreased mRNA level at 20:00 in mPer2 null mice while its expression was not different in both strain mice at 08:00. Coincidently, the hepatic circadian rhythm expression of Per2 revealed that its mRNA level was weak at 08:00 but reached peak expression during 24 h at 20:00 in WT mice. Therefore, it is speculated that clock gene mPer2 may function in diurnal variation of APAP induced hepatotoxicity via modulating Cyp1a2 expression in mice.

Altered circadian rhythm of the clock genes in fibrotic livers induced by carbon tetrachloride

Disruption in circadian rhythms either by mutation in mice or by shiftwork in people, is associated with an increased risk for the development of multiple organ diseases. In turn, organ disease may influence the function of clock genes and peripheral circadian systems. Here we showed that hepatic fibrosis induced by carbon tetrachloride in mice leads to alterations in the circadian rhythms of hepatic clock genes. Especially, we found an impaired daily Cry2 rhythm in the fibrotic livers, with markedly decreased levels during the day time while compared with control livers. Associatively, the expressions of two important clock-regulated genes peroxisome proliferator-activated receptor alpha and cytochrome P450 oxidoreductase lost circadian rhythm with significantly decreased levels during the light-dark (12/12h) cycle in fibrotic livers.