Circadian rhythms in liver physiology and liver diseases

A Study on the Amelioration of Circadian Rhythm Disorders in Fat Mice Using High-Protein Diets

This innovative study investigates the effects of high-protein diets (milk protein) on the circadian rhythm of hepatic lipid metabolism. We aimed to understand how high-protein interventions regulate biological clock genes, maintain lipid metabolism balance, and affect the circadian rhythm of antioxidant levels in vivo. We divided 120 SPF-class C57BL/6J mice into the control, high-fat/low-protein (HF-LP), and high-fat/high-protein (HF-HP) groups. Mice were sacrificed during active (2 a.m. and 8 a.m.) and rest periods (2 p.m. and 8 p.m.). In the HF-LP group, hepatic lipid anabolic enzymes were consistently expressed at high levels, while key lipolytic enzymes slowly increased after feeding with no significant diurnal differences. This led to an abnormal elevation in blood lipid levels, a slow increase in and low levels of superoxide dismutase, and a rapid increase in malondialdehyde levels, deviating from the diurnal trend observed in the control group. However, high-protein interventions in the HF-HP group restored lipid synthase activity and the expression of key catabolic enzymes, exhibiting a precise circadian rhythm. It also improved the lipid-metabolism rhythm, which was disrupted by the high-fat diet. Overall, high-protein interventions restored the expression of key enzymes involved in lipid metabolism, improving the lipid-metabolism rhythm, which was disrupted by the high-fat diet.

Cardiovascular Effects of Weight Loss in Obese Patients with Diabetes: Is Bariatric Surgery the Additional Arrow in the Quiver?

Obesity is an increasingly widespread disease worldwide because of lifestyle changes. It is associated with an increased risk of cardiovascular disease, primarily type 2 diabetes mellitus, with an increase in major cardiovascular adverse events. Bariatric surgery has been shown to be able to reduce the incidence of obesity-related cardiovascular disease and thus overall mortality. This result has been shown to be the result of hormonal and metabolic effects induced by post-surgical anatomical changes, with important effects on multiple hormonal and molecular axes that make this treatment more effective than conservative therapy in determining a marked improvement in the patient's cardiovascular risk profile. This review, therefore, aimed to examine the surgical techniques currently available and how these might be responsible not only for weight loss but also for metabolic improvement and cardiovascular benefits in patients undergoing such procedures.

Physiological Rhythms and Biological Variation of Biomolecules: The Road to Personalized Laboratory Medicine

The concentration of biomolecules in living systems shows numerous systematic and random variations. Systematic variations can be classified based on the frequency of variations as ultradian (<24 h), circadian (approximately 24 h), and infradian (>24 h), which are partly predictable. Random biological variations are known as between-subject biological variations that are the variations among the set points of an analyte from different individuals and within-subject biological variation, which is the variation of the analyte around individuals’ set points. The random biological variation cannot be predicted but can be estimated using appropriate measurement and statistical procedures. Physiological rhythms and random biological variation of the analytes could be considered the essential elements of predictive, preventive, and particularly personalized laboratory medicine. This systematic review aims to summarize research that have been done about the types of physiological rhythms, biological variations, and their effects on laboratory tests. We have searched the PubMed and Web of Science databases for biological variation and physiological rhythm articles in English without time restrictions with the terms “Biological variation, Within-subject biological variation, Between-subject biological variation, Physiological rhythms, Ultradian rhythms, Circadian rhythm, Infradian rhythms”. It was concluded that, for effective management of predicting, preventing, and personalizing medicine, which is based on the safe and valid interpretation of patients’ laboratory test results, both physiological rhythms and biological variation of the measurands should be considered simultaneously.

Aminodihydrophthalazinedione Sodium Transdermal Therapeutic System Specific Activity on an ExperimentalModel of Extensive Liver Resection

Previously, the authors showed that the application of the aminodihydrophthalazinedione sodium (ADPS) immunomodulator transdermal therapeutic system (TTS) to laboratory animals provides bioavailability analogous to the intramuscular administration of this drug at the same dose. At the same time, its maximum blood concentration is significantly reduced, and the retention time of the drug in the body is increased more than 10-fold, which can contribute to prolonging the drug effect. The aim of the work was to identify a possible positive effect of the transdermal administration of the ADPS immunomodulator on reparative liver regeneration on an experimental model of extensive liver resection (ELR). It has been shown that at a period of 48 h after ELR, the percutaneous administration of the immunomodulator has a pronounced stimulating effect on the mitotic activity of rat liver cells; by 72 h after ELR, an accelerated rate of recovery of hepatic homeostasis in the body was observed in laboratory animals in groups with the application of the ADPS TTS versus the control group.

Fatty acid metabolism in liver and muscle is strongly modulated by photoperiod in Fischer 344 rats

Circadian and seasonal variations produce variations in physiological processes throughout the day and the year, respectively. In this sense, both the light and the moment of feeding are strong modulators of the central and peripheral clocks. However, little is known about its influence on certain metabolic parameters and on the composition of liver and muscle fatty acids (FA). In the present study, 24 Fischer 344 rats were exposed for 11 weeks to different photoperiods, L6, L12 and L18, with 6, 12 and 18 h of light/day, respectively. They were fed a standard diet. Serum metabolic parameters, gene expression of liver enzymes and gastrocnemius muscle involved in the synthesis, elongation, desaturation and β-oxidation of FA were analyzed. We have found that exposure to different hours of light has a clear effect on FA composition and gene expression in the liver. Mainly, the biosynthesis of unsaturated FA was altered in the L18 animals with respect to those exposed to L12, while the L6 did not show significant changes. At the muscle level, differences were observed in the concentration of mono and polyunsaturated FA. A multivariate analysis confirmed the differences between L12 and L18 in a significant way. We conclude that exposure to long days produces changes in the composition of liver and muscle FA, as well as changes in the gene expression of oxidative enzymes compared to exposure to L12, which could be a consequence of different seasonal eating patterns.

Effects of time-restricted feeding (16/8) combined with a low-sugar diet on the management of non-alcoholic fatty liver disease: A randomized controlled trial

OBJECTIVES

Emerging studies have employed time-restricted feeding (TRF) and a low-sugar diet alone in the management of non-alcoholic fatty liver disease (NAFLD), but their combination has not been tested. The aim of this study was to investigate the effects of TRF combined with a low-sugar diet on NAFLD parameters, cardiometabolic and inflammatory biomarkers, and body composition in patients with NAFLD.

METHODS

A 12-wk randomized controlled trial was performed to compare the effects of TRF (16 h fasting/8 h feeding daily [16/8]) plus a low-sugar diet versus a control diet based on traditional meal distribution in patients with NAFLD. Changes in body composition, anthropometric indices, and liver and cardiometabolic markers were investigated.

RESULTS

TRF 16/8 with a low-sugar diet reduced body fat (26.7 ± 5.4 to 24.2 ± 4.9 kg), body weight (83.8 ± 12.7 to 80.5 ± 12.1 kg), waist circumference (104.59 ± 10.47 to 101.91 ± 7.42 cm), and body mass index (29.1 ± 2.6 to 28 ± 2.7 kg/m²), as well as circulating levels of fasting blood glucose and liver (alanine aminotransferase, 34 ± 13.9 to 21.2 ± 5.4 U/L; aspartate aminotransferase, 26.3 ± 6.2 to 20.50 ± 4 U/L; γ-glutamyl transpeptidase, 33 ± 15 to 23.2 ± 11.1 U/L; fibrosis score, 6.3 ± 1 to 5.2 ± 1.2 kPa; and controlled attenuation parameter, 322.9 ± 34.9 to 270.9 ± 36.2 dB/m), lipids (triacylglycerols, 201.5 ± 35.3 to 133.3 ± 48.7 mg/dL; total cholesterol, 190 ± 36.6 to 157.8 ± 33.6 mg/dL; and low-density lipoprotein cholesterol, 104.6 ± 27.3 to 84 ± 26.3 mg/dL), and inflammatory markers (high-sensitivity C-reactive protein, 3.1 ± 1.1 to 2 ± 0.9 mg/L; and cytokeratin-18, 1.35 ± 0.03 to 1.16 ± 0.03 ng/mL). These results were statistically significant (P < 0.05) compared with the control group.

CONCLUSIONS

TRF plus a low-sugar diet can reduce adiposity and improve liver, lipid, and inflammatory markers in patients with NAFLD.

Regulation of Circadian Genes Nr1d1 and Nr1d2 in Sex-Different Manners during Liver Aging

Background: Circadian rhythm is associated with the aging process and sex differences; however, how age and sex can change circadian regulation systems remains unclear. Thus, we aimed to evaluate age- and sex-related changes in gene expression and identify sex-specific target molecules that can regulate aging. Methods: Rat livers were categorized into four groups, namely, young male, old male, young female, and old female, and the expression of several genes involved in the regulation of the circadian rhythm was confirmed by in silico and in vitro studies. Results: Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses showed that the expression of genes related to circadian rhythms changed more in males than in females during liver aging. In addition, differentially expressed gene analysis and quantitative real-time polymerase chain reaction/western blotting analysis revealed that Nr1d1 and Nr1d2 expression was upregulated in males during liver aging. Furthermore, the expression of other circadian genes, such as Arntl, Clock, Cry1/2, Per1/2, and Rora/c, decreased in males during liver aging; however, these genes showed various gene expression patterns in females during liver aging. Conclusions: Age-related elevation of Nr1d1/2 downregulates the expression of other circadian genes in males, but not females, during liver aging. Consequently, age-related upregulation of Nr1d1/2 may play a more crucial role in the change in circadian rhythms in males than in females during liver aging.

Time to learn: The role of the molecular circadian clock in learning and memory

The circadian system plays an important role in aligning biological processes with the external time of day. A range of physiological functions are governed by the circadian cycle, including memory processes, yet little is understood about how the clock interfaces with memory at a molecular level. The molecular circadian clock consists of four key genes/gene families, Period, Clock, Cryptochrome, and Bmal1, that rhythmically cycle in an ongoing transcription-translation negative feedback loop that maintains an approximately 24-hour cycle within cells of the brain and body. In addition to their roles in generating the circadian rhythm within the brain's master pacemaker (the suprachiasmatic nucleus), recent research has suggested that these clock genes may function locally within memory-relevant brain regions to modulate memory across the day/night cycle. This review will discuss how these clock genes function both within the brain's central clock and within memory-relevant brain regions to exert circadian control over memory processes. For each core clock gene, we describe the current research that demonstrates a potential role in memory and outline how these clock genes might interface with cascades known to support long-term memory formation. Together, the research suggests that clock genes function locally within satellite clocks across the brain to exert circadian control over long-term memory formation and possibly other biological processes. Understanding how clock genes might interface with local molecular cascades in the hippocampus and other brain regions is a critical step toward developing treatments for the myriad disorders marked by dysfunction of both the circadian system and cognitive processes.

Effect of Bariatric Surgery on Metabolic Diseases and Underlying Mechanisms

Obesity is a highly prevalent public health concern, attributed to multifactorial causes and limited in treatment options. Several comorbidities are closely associated with obesity such as the development of type 2 diabetes mellitus (T2DM), cardiovascular and cerebrovascular diseases, and nonalcoholic fatty liver disease (NAFLD). Bariatric surgery, which can be delivered in multiple forms, has been remarked as an effective treatment to decrease the prevalence of obesity and its associated comorbidities. The different types of bariatric surgery create a variety of new pathways for food to metabolize in the body and truncate the stomach's caliber. As a result, only a small quantity of food is tolerated, and the body mass index noticeably decreases. This review describes the improvements of obesity and its comorbidities following bariatric surgery and their mechanism of improvement. Additionally, endocrine function improvements after bariatric surgery, which contributes to the patients' health improvement, are described, including the role of glucagon-like peptide-1 (GLP-1), fibroblast growth factors 19 and 21 (FGF-19, FGF-21), and pancreatic peptide YY (PYY). Lastly, some of the complications of bariatric surgery, including osteoporosis, iron deficiency/anemia, and diarrhea, as well as their potential mechanisms, are described.

Role of circadian rhythm and autonomic nervous system in liver function: a hypothetical basis for improving the management of hepatic encephalopathy

Hepatic encephalopathy (HE) is a common, incapacitating complication of cirrhosis that affects many patients with cirrhosis. Although several therapies have proven effective in the treatment and prevention of this condition, several patients continue to suffer from covert disease or episodes of relapse. The circadian rhythm has been demonstrated to be pivotal for many body functions, including those of the liver. Here, we explore the impact of circadian rhythm-dependent signaling on the liver and discuss the evidence of its impact on liver pathology and metabolism. We describe the various pathways through which circadian influences are mediated. Finally, we introduce a novel method for improving patient response to drugs aimed at treating HE by utilizing the circadian rhythm. A digital system that introduces a customization-based technique for improving the response to therapies is presented as a hypothetical approach for improving the effectiveness of current medications used for the treatment of recurrent and persistent hepatic encephalopathy.

Effects of circadian rhythm on Narcotrend index and target-controlled infusion concentration of propofol anesthesia

Background

The effects of circadian rhythms on drug metabolism and efficacy are being increasingly recognized. However, the extent to which they affect general anesthesia remains unclear. This study aims to investigate the effects of circadian rhythms on anesthetic depth and the concentrations of propofol target-controlled infusion (TCI).

Methods

Sixty patients undergoing laparoscopic surgeries were sequentially assigned to four groups. Group ND (n = 15): Propofol TCI with Narcotrend monitor during the day (8:00–18:00), Group NN (n = 15): Propofol TCI with Narcotrend monitor during the night (22:00–5:00), Group CLTD (n = 15): Propofol closed-loop TCI guided by bispectral index (BIS) during the day (8:00–18:00), Group CLTN (n = 15): Propofol closed-loop TCI guided by BIS during the night (22:00–5:00). The Narcotrend index, mean arterial pressure (MAP) and heart rate (HR) were compared between group ND and NN at 7 time points, from 5 min before induction to the end of operation. The propofol TCI concentrations, MAP and HR were compared between group CLTD and CLTN at 7 time points, from 5 min after induction to the end of operation.

Results

The Narcotrend index, MAP, and HR in group NN were lower than those in group ND from the beginning of mechanical ventilation to the end of operation (p < 0.05). The propofol TCI concentrations in group CLTN were lower than those in group CLTD from the beginning of operation to the end of operation (p < 0.05).

Conclusion

Circadian rhythms have a significant effect on the depth of anesthesia and drug infusion concentrations during propofol TCI. When using general anesthesia during night surgery, the propofol infusion concentration should be appropriately reduced compared to surgery during the day.

Trial registration

The present study was registered on the ClinicalTrials.gov website (NCT02440269) and approved by the Medical Ethics Committee of Southwest Hospital of Third Military Medical University (ethics lot number: 2016 Research No. 93). All patients provided informed written consent to participate in the study.

Photoperiod-induced alterations in biomarkers of oxidative stress and biochemical pathways in rats of different ages: Focus on individual physiological reactivity

Effects of photoperiodicity caused by both the age and individual physiological reactivity estimated by resistance to hypobaric hypoxia on the levels of lipid peroxidation, protein oxidation (aldehydic and ketonic derivatives), total antioxidant capacity, activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase), and biochemical parameters of aerobic and anaerobic pathways in hepatic tissue depending on the blood melatonin level were studied. The study was carried out on 96 6- and 21-month-old male rats divided into hypoxia resistance groups (LR, low resistance, HR, high resistance). The analyses were conducted at four photoperiods: winter (January), spring (March), summer (July), and autumn (October). Our results indicate a significant effect of melatonin, i.e. over 80%, revealed by the complete statistical model of the studied biomarkers of oxidative stress and oxygen-dependent parameters of metabolism. The effects of melatonin vary with age and between photoperiods, which in turn was determined by individual physiological reactivity. In terms of the photoperiods, the melatonin content in the group of the adult animals with low resistance to hypoxia decreased from winter to summer. In a group of old animals in comparison with adults, the melatonin content in all the studied photoperiods was much lower as well, regardless of their hypoxia resistance. In the group of old animals with low resistance to hypoxia, the melatonin content decreased throughout the photoperiods as follows: winter, autumn, summer, and spring. As can be concluded, spring is a critical period for old animals, particularly those with low hypoxia resistance. The important role of melatonin in these processes was also confirmed by our correlation analysis between oxidative stress biomarkers, energy-related metabolites, and antioxidant enzymes in the hepatic tissue of rats of different ages, with different resistance to hypoxia, and in different photoperiods. The melatonin concentration in the blood of highly resistant rats was higher than in those with low resistance to hypoxia. Melatonin determines the individual constitutional level of resistance to hypoxia and is responsible for individual enzymatic antioxidative responses, depending on the four photoperiods. Our studies have shown that melatonin levels are related to the redox characteristics of antioxidant defenses against lipid peroxidation and oxidative modification of proteins in old rats with low resistance to hypoxia, compared to a group of highly resistant adults. Finally, the melatonin-related mechanisms of antioxidative protection depend on metabolic processes in hepatic tissue and exhibit photoperiodical variability in adult and old rats.

Neutrophil infiltration regulates clock-gene expression to organize daily hepatic metabolism

Liver metabolism follows diurnal fluctuations through the modulation of molecular clock genes. Disruption of this molecular clock can result in metabolic disease but its potential regulation by immune cells remains unexplored. Here, we demonstrated that in steady state, neutrophils infiltrated the mouse liver following a circadian pattern and regulated hepatocyte clock-genes by neutrophil elastase (NE) secretion. NE signals through c-Jun NH2-terminal kinase (JNK) inhibiting fibroblast growth factor 21 (FGF21) and activating Bmal1 expression in the hepatocyte. Interestingly, mice with neutropenia, defective neutrophil infiltration or lacking elastase were protected against steatosis correlating with lower JNK activation, reduced Bmal1 and increased FGF21 expression, together with decreased lipogenesis in the liver. Lastly, using a cohort of human samples we found a direct correlation between JNK activation, NE levels and Bmal1 expression in the liver. This study demonstrates that neutrophils contribute to the maintenance of daily hepatic homeostasis through the regulation of the NE/JNK/Bmal1 axis.

Every day, the body's biological processes work to an internal clock known as the circadian rhythm. This rhythm is controlled by ‘clock genes’ that are switched on or off by daily physical and environmental cues, such as changes in light levels. These daily rhythms are very finely tuned, and disturbances can lead to serious health problems, such as diabetes or high blood pressure.

The ability of the body to cycle through the circadian rhythm each day is heavily influenced by the clock of one key organ: the liver. This organ plays a critical role in converting food and drink into energy. There is evidence that neutrophils – white blood cells that protect the body by being the first response to inflammation – can influence how the liver performs its role in obese people, by for example, releasing a protein called elastase. Additionally, the levels of neutrophils circulating in the blood change following a daily pattern. Crespo, González-Terán et al. wondered whether neutrophils enter the liver at specific times of the day to control liver’s daily rhythm.

Crespo, González-Terán et al. revealed that neutrophils visit the liver in a pattern that peaks when it gets light and dips when it gets dark by counting the number of neutrophils in the livers of mice at different times of the day. During these visits, neutrophils secreted elastase, which activated a protein called JNK in the cells of the mice’s liver. This subsequently blocked the activity of another protein, FGF21, which led to the activation of the genes that allow cells to make fat molecules for storage. JNK activation also switched on the clock gene, Bmal1, ultimately causing fat to build up in the mice’s liver. Crespo, González-Terán et al. also found that, in samples from human livers, the levels of elastase, the activity of JNK, and whether the Bmal1 gene was switched on were tightly linked. This suggests that neutrophils may be controlling the liver’s rhythm in humans the same way they do in mice.

Overall, this research shows that neutrophils can control and reset the liver's daily rhythm using a precisely co-ordinated series of molecular changes. These insights into the liver's molecular clock suggest that elastase, JNK and BmaI1 may represent new therapeutic targets for drugs or smart medicines to treat metabolic diseases such as diabetes or high blood pressure.

Adipogenesis: A Necessary but Harmful Strategy

Obesity is considered to significantly increase the risk of the development of a vast range of metabolic diseases. However, adipogenesis is a complex physiological process, necessary to sequester lipids effectively to avoid lipotoxicity in other tissues, like the liver, heart, muscle, essential for maintaining metabolic homeostasis and has a crucial role as a component of the innate immune system, far beyond than only being an inert mass of energy storage. In pathophysiological conditions, adipogenesis promotes a pro-inflammatory state, angiogenesis and the release of adipokines, which become dangerous to health. It results in a hypoxic state, causing oxidative stress and the synthesis and release of harmful free fatty acids. In this review, we try to explain the mechanisms occurring at the breaking point, at which adipogenesis leads to an uncontrolled lipotoxicity. This review highlights the types of adipose tissue and their functions, their way of storing lipids until a critical point, which is associated with hypoxia, inflammation, insulin resistance as well as lipodystrophy and adipogenesis modulation by Krüppel-like factors and miRNAs.

Circadian Clock Genes in the Metabolism of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a common disease, which is characterized by the accumulation of triglycerides in the hepatocytes without excess alcohol intake. Circadian rhythms can participate in lipid, glucose, and cholesterol metabolism and are closely related to metabolism seen in this disease. Circadian clock genes can modulate liver lipid metabolism. Desynchrony of circadian rhythms and the influences imparted by external environmental stimuli can increase morbidity. By contrast, synchronizing circadian rhythms can help to alleviate the metabolic disturbance seen in NAFLD. In this review, we have discussed the current research connections that exist between the circadian clock and the metabolism of NAFLD, and we have specifically focused on the key circadian clock genes, Bmal1, Clock, Rev-Erbs, Rors, Pers, Crys, Nocturnin, and DECs.

2,3,7,8-Tetrachlorodibenzo-p-dioxin abolishes circadian regulation of hepatic metabolic activity in mice

Aryl hydrocarbon receptor (AhR) activation is reported to alter the hepatic expression of circadian clock regulators, however the impact on clock-controlled metabolism has not been thoroughly investigated. This study examines the effects of AhR activation on hepatic transcriptome and metabolome rhythmicity in male C57BL/6 mice orally gavaged with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) every 4 days for 28 days. TCDD diminished the rhythmicity of several core clock regulators (e.g. Arntl, Clock, Nr1d1, Per1, Cry1, Nfil3) in a dose-dependent manner, involving either a ≥ 3.3-fold suppression in amplitude or complete loss of oscillation. Accordingly, protein levels (ARNTL, REV-ERBα, NFIL3) and genomic binding (ARNTL) of select regulators were reduced and arrhythmic following treatment. As a result, the oscillating expression of 99.6% of 5,636 clock-controlled hepatic genes was abolished including genes associated with the metabolism of lipids, glucose/glycogen, and heme. For example, TCDD flattened expression of the rate-limiting enzymes in both gluconeogenesis (Pck1) and glycogenesis (Gys2), consistent with the depletion and loss of rhythmicity in hepatic glycogen levels. Examination of polar hepatic extracts by untargeted mass spectrometry revealed that virtually all oscillating metabolites lost rhythmicity following treatment. Collectively, these results suggest TCDD disrupted circadian regulation of hepatic metabolism, altering metabolic efficiency and energy storage.

Hydrogen Sulfide as a Novel Regulatory Factor in Liver Health and Disease

Hydrogen sulfide (H₂S), a colorless gas smelling of rotten egg, has long been recognized as a toxic gas and environment pollutant. However, increasing evidence suggests that H₂S acts as a novel gasotransmitter and plays important roles in a variety of physiological and pathological processes in mammals. H₂S is involved in many hepatic functions, including the regulation of oxidative stress, glucose and lipid metabolism, vasculature, mitochondrial function, differentiation, and circadian rhythm. In addition, H₂S contributes to the pathogenesis and treatment of a number of liver diseases, such as hepatic fibrosis, liver cirrhosis, liver cancer, hepatic ischemia/reperfusion injury, nonalcoholic fatty liver disease/nonalcoholic steatohepatitis, hepatotoxicity, and acute liver failure. In this review, the biosynthesis and metabolism of H₂S in the liver are summarized and the role and mechanism of H₂S in liver health and disease are further discussed.

Obesity linking to hepatocellular carcinoma: A global view

Hepatocellular carcinoma (HCC) is the commonest primary liver cancer and the second leading cause of cancer death worldwide. Obesity is rapidly becoming pandemic and associated with increased carcinogenesis. In this review, we describe the obesity-related factors that influence the development of HCC. We provide evidence of strong links between neural regulation, endocrine and HCC in obesity. We discuss recent advances in our understanding of how adipose tissue alters hepatic metabolism and immune response in HCC development through inter-organ communication. Taken together, our review aims to provides a concise and up-to date summary about the connection between obesity and HCC, with emphasis on the opportunities for effective strategies in preventing the development of HCC in obese individuals.

Impact of Time-Restricted Feeding and Dawn-to-Sunset Fasting on Circadian Rhythm, Obesity, Metabolic Syndrome, and Nonalcoholic Fatty Liver Disease

Obesity now affects millions of people and places them at risk of developing metabolic syndrome, nonalcoholic fatty liver disease (NAFLD), and even hepatocellular carcinoma. This rapidly emerging epidemic has led to a search for cost-effective methods to prevent the metabolic syndrome and NAFLD as well as the progression of NAFLD to cirrhosis and hepatocellular carcinoma. In murine models, time-restricted feeding resets the hepatic circadian clock and enhances transcription of key metabolic regulators of glucose and lipid homeostasis. Studies of the effect of dawn-to-sunset Ramadan fasting, which is akin to time-restricted feeding model, have also identified significant improvement in body mass index, serum lipid profiles, and oxidative stress parameters. Based on the findings of studies conducted on human subjects, dawn-to-sunset fasting has the potential to be a cost-effective intervention for obesity, metabolic syndrome, and NAFLD.

Profiling of the circadian metabolome in thioacetamide-induced liver cirrhosis in mice

Liver cirrhosis can disturb circadian rhythms, decreasing patient quality of life. Changes in metabolic products in cirrhosis are poorly understood. We evaluated changes in liver metabolism products using a thioacetamide‐induced mouse model of liver cirrhosis exhibiting circadian rhythm disturbance. Principal component analysis indicated that the circular progression found in the control group was disrupted in the thioacetamide group, and Jonckheere‐Terpstra‐Kendall analysis showed an imbalanced pattern of oscillating metabolic products. In addition to changes in serotonin and other vitamin A–related metabolites, differences in metabolic products associated with energetics, redox homeostasis, bile acid production, inflammation, and other processes were identified. Carbohydrate metabolism showed a reduction in metabolic products associated with the tricarboxylic acid cycle, suggesting up‐regulation of glycolysis and reduced mitochondrial activity. Lipid metabolism showed an increase in ω‐oxidation products, suggesting decreased β‐oxidation. Conclusion: These data will be useful for chronotherapy and modulation of circadian rhythms in patients with liver damage. (Hepatology Communications 2017;1:704–718)

Autonomic Nervous System and the Liver

The liver is innervated by both the sympathetic and the parasympathetic nerve systems. These nerves are derived from the splanchnic and vagal nerves that surround the portal vein, hepatic artery, and bile duct. The afferent fiber delivers information regarding osmolality, glucose level, and lipid level in the portal vein to the central nervous system (CNS). In contrast, the efferent fiber is crucial in the regulation of metabolism, blood flow, and bile secretion. Furthermore, liver innervation has been associated with hepatic fibrosis, regeneration, and circadian rhythm. Knowledge of these mechanisms can be applied for potential liver disease treatment.

PPARs and Mitochondrial Metabolism: From NAFLD to HCC

Metabolic related diseases, such as type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease (NAFLD), are widespread threats which bring about a significant burden of deaths worldwide, mainly due to cardiovascular events and cancer. The pathogenesis of these diseases is extremely complex, multifactorial, and only partially understood. As the main metabolic organ, the liver is central to maintain whole body energetic homeostasis. At the cellular level, mitochondria are the metabolic hub connecting and integrating all the main biochemical, hormonal, and inflammatory signaling pathways to fulfill the energetic and biosynthetic demand of the cell. In the liver, mitochondria metabolism needs to cope with the energetic regulation of the whole body. The nuclear receptors PPARs orchestrate lipid and glucose metabolism and are involved in a variety of diseases, from metabolic disorders to cancer. In this review, focus is placed on the roles of PPARs in the regulation of liver mitochondrial metabolism in physiology and pathology, from NAFLD to HCC.

Circadian Amplitude Regulation via FBXW7-Targeted REV-ERBα Degradation

Defects in circadian rhythm influence physiology and behavior with implications for the treatment of sleep disorders, metabolic disease, and cancer. Although core regulatory components of clock rhythmicity have been defined, insight into the mechanisms underpinning amplitude is limited. Here, we show that REV-ERBα, a core inhibitory component of clock transcription, is targeted for ubiquitination and subsequent degradation by the F-box protein FBXW7. By relieving REV-ERBα-dependent repression, FBXW7 provides an unrecognized mechanism for enhancing the amplitude of clock gene transcription. Cyclin-dependent kinase 1 (CDK1)-mediated phosphorylation of REV-ERBα is necessary for FBXW7 recognition. Moreover, targeted hepatic disruption of FBXW7 alters circadian expression of core clock genes and perturbs whole-body lipid and glucose levels. This CDK1-FBXW7 pathway controlling REV-ERBα repression defines an unexpected molecular mechanism for re-engaging the positive transcriptional arm of the clock, as well as a potential route to manipulate clock amplitude via small molecule CDK1 inhibition.

Hydrophobic bile acid apoptosis is regulated by sphingosine-1-phosphate receptor 2 in rat hepatocytes and human hepatocellular carcinoma cells

The hepatotoxic bile acid glycochenodeoxycholate (GCDC) modulates hepatocyte cell death through activation of JNK, Akt, and Erk. The nonhepatotoxic bile acid taurocholate activates Akt and Erk through the sphingosine-1-phosphate receptor 2 (S1PR2). The role of the S1PR2 in GCDC-mediated apoptosis and kinase activation is unknown. Studies were done in rat hepatocytes, HUH7 cells, and HUH7 cells stably transfected with rat Ntcp (HUH7-Ntcp). Cells were treated with GCDC and apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for the active cleaved fragment of caspase 3. Kinase activation was determined by immunoblotting with phospho-specific antibodies. JTE-013, an inhibitor of S1PR2, significantly attenuated morphological evidence of GCDC-induced apoptosis and prevented caspase 3 cleavage in rat hepatocytes and HUH7-Ntcp cells. In hepatocytes, JTE-013 mildly suppressed, augmented, and had no effect on GCDC-induced JNK, Akt, and Erk phosphorylation, respectively. Similar results were seen in HUH7-Ntcp cells except for mild suppression of JNK and Erk phosphorylation. Knockdown of S1PR2 in HUH7-Ntcp augmented Akt, inhibited JNK, and had no effect on Erk phosphorylation. GCDC failed to induce apoptosis or kinase activation in HUH7 cells. In conclusion, SIPR2 inhibition attenuates GCDC-induced apoptosis and inhibits and augments GCDC-induced JNK and Akt phosphorylation, respectively. In addition, GCDC must enter hepatocytes to mediate cell death or activate kinases. These results suggest that SIPR2 activation is proapoptotic in GCDC-induced cell death but that this effect is not due to direct ligation of the S1PR2 by the bile acid.

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.

Significant lethality following liver resection in A20 heterozygous knockout mice uncovers a key role for A20 in liver regeneration

Hepatic expression of A20, including in hepatocytes, increases in response to injury, inflammation and resection. This increase likely serves a hepatoprotective purpose. The characteristic unfettered liver inflammation and necrosis in A20 knockout mice established physiologic upregulation of A20 as integral to the anti-inflammatory and anti-apoptotic armamentarium of hepatocytes. However, the implication of physiologic upregulation of A20 in modulating hepatocytes' proliferative responses following liver resection remains controversial. To resolve the impact of A20 on hepatocyte proliferation and the liver's regenerative capacity, we examined whether decreased A20 expression, as in A20 heterozygous knockout mice, affects outcome following two-third partial hepatectomy. A20 heterozygous mice do not demonstrate a striking liver phenotype, indicating that their A20 expression levels are still sufficient to contain inflammation and cell death at baseline. However, usually benign partial hepatectomy provoked a staggering lethality (>40%) in these mice, uncovering an unsuspected phenotype. Heightened lethality in A20 heterozygous mice following partial hepatectomy resulted from impaired hepatocyte proliferation due to heightened levels of cyclin-dependent kinase inhibitor, p21, and deficient upregulation of cyclins D1, E and A, in the context of worsened liver steatosis. A20 heterozygous knockout minimally affected baseline liver transcriptome, mostly circadian rhythm genes. Nevertheless, this caused differential expression of >1000 genes post hepatectomy, hindering lipid metabolism, bile acid biosynthesis, insulin signaling and cell cycle, all critical cellular processes for liver regeneration. These results demonstrate that mere reduction of A20 levels causes worse outcome post hepatectomy than full knockout of bona fide liver pro-regenerative players such as IL-6, clearly ascertaining A20's primordial role in enabling liver regeneration. Clinical implications of these data are of utmost importance as they caution safety of extensive hepatectomy for donation or tumor in carriers of A20/TNFAIP3 single nucleotide polymorphisms alleles that decrease A20 expression or function, and prompt the development of A20-based liver pro-regenerative therapies.

Maternal obesity programs offspring non-alcoholic fatty liver disease through disruption of 24-h rhythms in mice

BACKGROUND

Maternal obesity increases offspring propensity to metabolic dysfunctions and to non-alcoholic fatty liver disease (NAFLD), which may lead to cirrhosis or liver cancer. The circadian clock is a transcriptional/epigenetic molecular machinery synchronising physiological processes to coordinate energy utilisation within a 24-h light/dark period. Alterations in rhythmicity have profound effects on metabolic pathways, which we sought to investigate in offspring with programmed NAFLD.

METHODS

Mice were fed a standard or an obesogenic diet (OD), before and throughout pregnancy, and during lactation. Offspring were weaned onto standard or an OD at 3 weeks postpartum and housed in 12:12 light/dark conditions. Biochemical and histological indicators of NAFLD and fibrosis, analysis of canonical clock genes with methylation status and locomotor activity were investigated at 6 months.

RESULTS

We show that maternal obesity interacts with an obesogenic post-weaning diet to promote the development of NAFLD with disruption of canonical metabolic rhythmicity gene expression in the liver. We demonstrate hypermethylation of BMAL-1 (brain and muscle Arnt like-1) and Per2 promoter regions and altered 24-h rhythmicity of hepatic pro-inflammatory and fibrogenic mediators.

CONCLUSIONS

These data implicate disordered circadian rhythms in NAFLD and suggest that disruption of this system during critical developmental periods may be responsible for the onset of chronic liver disease in adulthood.

Bile acid signaling in metabolic disease and drug therapy

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates hepatobiliary secretion of lipids, lipophilic metabolites, and xenobiotics. In the intestine, bile acids are essential for the absorption, transport, and metabolism of dietary fats and lipid-soluble vitamins. Extensive research in the last 2 decades has unveiled new functions of bile acids as signaling molecules and metabolic integrators. The bile acid-activated nuclear receptors farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, vitamin D receptor, and G protein-coupled bile acid receptor play critical roles in the regulation of lipid, glucose, and energy metabolism, inflammation, and drug metabolism and detoxification. Bile acid synthesis exhibits a strong diurnal rhythm, which is entrained by fasting and refeeding as well as nutrient status and plays an important role for maintaining metabolic homeostasis. Recent research revealed an interaction of liver bile acids and gut microbiota in the regulation of liver metabolism. Circadian disturbance and altered gut microbiota contribute to the pathogenesis of liver diseases, inflammatory bowel diseases, nonalcoholic fatty liver disease, diabetes, and obesity. Bile acids and their derivatives are potential therapeutic agents for treating metabolic diseases of the liver.

Visualizing hepatitis C virus infection in humanized mice

Hepatitis C virus (HCV) establishes frequently persistent infections. Chronic carriers can develop severe liver disease. HCV has been intensely studied in a variety of cell culture systems. However, commonly used cell lines and primary hepatocyte cultures do not or only in part recapitulate the intricate host environment HCV faces in the liver. HCV infects readily only humans and chimpanzees, which poses challenges in studying HCV infection in vivo. Consequently, tractable small animal models are needed that are not only suitable for analyzing HCV infection but also for testing novel therapeutics. Here, we will focus our discussion on humanized mice, i.e. mice engrafted with human tissues or expressing human genes, which support HCV infection. We will further highlight novel methods that can be used to unambiguously detect HCV infected cells in situ, thereby facilitating a spatio-temporal dissection of HCV infection in the three dimensional context of the liver.

Murine models of hepatitis C: what can we look forward to?

The study of interactions between hepatitis C virus (HCV) with its mammalian host, along with the development of more effective therapeutics and vaccines has been delayed by the lack of a suitable small animal model. HCV readily infects only humans and chimpanzees, which poses logistic, economic and ethical challenges with analyzing HCV infection in vivo. Progress has been made in understanding the determinants that dictate HCV's narrow host range providing a blueprint for constructing a mouse model with inheritable susceptibility to HCV infection. Indeed, genetically humanized mice were generated that support viral uptake, replication and production of infectious virions--albeit at low levels. These efforts are complemented with attempts to select for viral variants that are inherently more capable of replicating in non-human species. In parallel, engraftment of relevant human tissues into improved xenorecipients is being continuously refined. Incorporating advances in stem-cell-biology and tissue engineering may allow the generation of patient-specific humanized mice. Construction of such mouse "avatars" may allow analyzing functionally patient-specific differences with respect to susceptibility to infection, disease progression and responses to treatment. In this review, we discuss the three, before mentioned approaches to overcome current species barriers and generate a small animal model for HCV infection, i.e. genetic modification of mice to increase their susceptibility to the virus; genetic modification of HCV, to increase its pathogenicity for mice; and the introduction of human liver and immune cells into immunodeficient mice, to create "humanized" mice. Although in the foreseeable future there will not be a single model that perfectly mimics the natural course of HCV in humans there is reason for optimism. The spectrum of murine animal models for hepatitis C provides a broad arsenal for analyzing the disease. These models may play an important role by prioritizing vaccine candidates and possibly refining combination anti-viral drug therapies. This article forms part of a symposium in Anti-viral Research on "Hepatitis C: next steps toward global eradication."