Biliverdin reductase and bilirubin in hepatic disease

Alterations in the Plasma Metabolome Associated With Maternal Smoking During the First Trimester and Foetal Growth

Tobacco smoking during pregnancy has been associated with an increased risk of adverse outcomes like low birth weight. This study determined changes in the circulating metabolome linked to maternal smoking in the first trimester and correlated these changes to the growth of the foetus. The circulating metabolome was examined from first trimester plasma samples by non-targeted (global) liquid chromatography mass spectrometry-based metabolite profiling of 227 pregnant women (99 smokers and 117 non-smokers) from the Kuopio Birth Cohort Study. Tobacco smoking was self-reported through a questionnaire and verified with cotinine measurements from plasma samples. In summary, 64 significant differences were observed between the groups after correction for multiple testing e.g. in metabolites indicating endocrine disruption (e.g. dehydroepiandrosterone sulphate [DHEA-S], VIP = 2.70, d = 0.68, p < 0.0001), metabolites associated with oxidative stress (e.g. bilirubin, VIP = 2.00, d = 0.50, p < 0.0001) and lipid metabolism (e.g. LysoPC 16:1, VIP = 2.07, d = 0.51, p < 0.0001). Some of these metabolites, e.g. DHEA-S and bilirubin, correlated with low birth weight, and some, e.g. LysoPC 16:1, correlated with small head circumference at birth. In conclusion, maternal smoking during the first trimester of pregnancy was associated with an altered metabolite profile linked to endocrine disruption and increased oxidative stress.

Bilirubin metabolism in relation to cancer

Bilirubin, a metabolite of hemoglobin, was long thought to be a harmful waste product, but recent studies have found it to have antioxidant and anti-tumor effects. With the extensive research on the mechanism of malignant tumor development, the antioxidant effect of bilirubin is increasingly becoming a hotspot in anti-cancer research. At present, there are two main views on the relationship between bilirubin and cancer, namely, its pro-cancer and anti-cancer effects, and in recent years, studies on the relationship between bilirubin and cancer have not been systematically summarized, which is not conducive to the further investigation of the role of bilirubin on cancer. To understand the multifaceted role of bilirubin in tumorigenesis as well as to develop more effective and affordable antitumor therapies, this review provides an overview of the effects of bilirubin on tumors in terms of oxidative, inflammatory, and cellular signaling pathways, as well as the resulting therapeutic ideas and approaches.

Insulin receptor responsiveness governs TGFβ-induced hepatic stellate cell activation: Insulin resistance instigates liver fibrosis

The insulin receptor (INSR) has been shown to be hyperactive in hepatic stellate cells (HSCs) in humans and rodents with liver fibrosis. To explore HSC cellular mechanisms that INSR regulates during pro-fibrotic stimulation, we used CRISPR-Cas9 technology. We knocked out a portion of the INSR gene in human LX2 HSC cells (INSRe5-8 KO) that regulates insulin responsiveness but not the insulin-like growth factor (IGF) or transforming growth factor-β (TGFβ) signaling. The INSRe5-8 KO HSCs had significantly higher cell growth, BrdU incorporation, and lower TP53 expression that suppresses growth, and they also exhibited increased migration compared to the Scramble control. We treated the scramble control and INSRe5-8 KO HSCs with insulin or TGFβ and profiled hundreds of kinase activities using the PamGene PamStation kinome technology. Our analysis showed that serine/threonine kinase (STK) activities were reduced, and most of the protein-tyrosine kinase (PTK) activities were increased in the INSRe5-8 KO compared to the Scramble control HSCs. To study gene transcripts altered in activated Scramble control and INSRe5-8 KO HSCs, we treated them with TGFβ for 24 h. We isolated RNA for sequencing and found that the INSRe5-8 KO cells, compared to control HSCs, had altered transcriptional responsiveness to TGFβ stimulation, collagen-activated signaling, smooth muscle cell differentiation pathways, SMAD protein signaling, collagen metabolic process, integrin-mediated cell adhesion, and notch signaling. This study demonstrates that reduced INSR responsiveness enhances HSC growth and selectively mediates TGFβ-induced HSC activation. These findings provide new insights into the development of more effective treatments for liver fibrosis.

Bilirubin bioconversion to urobilin in the gut-liver-kidney axis: A biomarker for insulin resistance in the Cardiovascular-Kidney-Metabolic (CKM) Syndrome

The rising rates of obesity worldwide have increased the incidence of cardiovascular disease (CVD), making it the number one cause of death. Higher plasma bilirubin levels have been shown to prevent metabolic dysfunction and CVD. However, reducing levels leads to deleterious outcomes, possibly due to reduced bilirubin half-life that escalates the production of its catabolized product, urobilinogen, produced by gut bacteria and naturally oxidized to urobilin. Recent findings suggest that the involvement of the microbiome catabolism of bilirubin to urobilin and its absorption via the hepatic portal vein contributes to CVD, suggesting a liver-gut axis involvement. We discuss the studies that demonstrate that urobilin is frequently raised in the urine of persons with CVD and its probable role in acquiring the disease. Urobilin is excreted from the kidneys into the urine and may serve as a biomarker for Cardiovascular-Kidney-Metabolic (CKM) Syndrome. We deliberate on the newly discovered bilirubin reductase (BilR) bacterial enzyme that produces urobilin. We discuss the bacterial species expressing BilR, how they impact CVD, and whether suppressing urobilin production and increasing bilirubin may provide new therapeutic strategies for CKM. Possible therapeutic mechanisms for achieving this goal are discussed.

Heme oxygenase, biliverdin reductase, and bilirubin pathways regulate oxidative stress and insulin resistance: a focus on diabetes and therapeutics

Metabolic and insulin-resistant diseases, such as type 2 diabetes mellitus (T2DM), have become major health issues worldwide. The prevalence of insulin resistance in the general population ranges from 15.5% to 44.6%. Shockingly, the global T2DM population is anticipated to double by 2050 compared with 2021. Prior studies indicate that oxidative stress and inflammation are instrumental in causing insulin resistance and instigating metabolic diseases. Numerous methods and drugs have been designed to combat insulin resistance, including metformin, thiazolidinediones (TZDs), sodium-glucose cotransporter 2 inhibitors (SGLT2i), glucagon-like peptide 1 receptor agonists (GLP1RA), and dipeptidyl peptidase 4 inhibitors (DPP4i). Bilirubin is an antioxidant with fat-burning actions by binding to the PPARα nuclear receptor transcription factor, improving insulin sensitivity, reducing inflammation, and reversing metabolic dysfunction. Potential treatment with antioxidants like bilirubin and increasing the enzyme that produces it, heme oxygenase (HMOX), has also gained attention. This review discusses the relationships between bilirubin, HMOX, and insulin sensitivity, how T2DM medications affect HMOX levels and activity, and potentially using bilirubin nanoparticles to treat insulin resistance. We explore the sex differences between these treatments in the HMOX system and how bilirubin levels are affected. We discuss the emerging concept that bilirubin bioconversion to urobilin may have a role in metabolic diseases. This comprehensive review summarizes our understanding of bilirubin functioning as a hormone, discusses the HMOX isoforms and their beneficial mechanisms, analyzes the sex differences that might cause a dichotomy in responses, and examines the potential use of HMOX and bilirubin nanoparticle therapies in treating metabolic diseases.

Cytoskeleton Remodeling-Related Proteins Represent a Specific Salivary Signature in PSC Patients

Primary sclerosing cholangitis (PSC) and Primary biliary cholangitis (PBC) are chronic inflammatory biliary diseases characterized by progressive damage of the bile ducts, resulting in hepatobiliary fibrosis and cirrhosis. Currently, specific biomarkers that allow to distinguish between PSC and PBC do not exist. In this study, we examined the salivary proteome by carrying out a comprehensive and non-invasive screening aimed at highlighting possible quali-quantitative protein deregulations that could be the starting point for the identification of effective biomarkers in future. Saliva samples collected from 6 PBC patients were analyzed using a liquid chromatography-tandem mass spectrometry technique, and the results were compared with those previously obtained in the PSC group. We identified 40 proteins as significantly deregulated in PSC patients compared to the PBC group. The Gene Ontology and pathway analyses highlighted that several proteins (e.g., small integral membrane protein 22, cofilin-1, macrophage-capping protein, plastin-2, and biliverdin reductase A) were linked to innate immune responses and actin cytoskeleton remodeling, which is a critical event in liver fibrosis and cancer progression. These findings provide new foundations for a deeper understanding of the pathophysiology of PSC and demonstrate that saliva is a suitable biological sample for obtaining proteomic fingerprints useful in the search for biomarkers capable of discriminating between the two cholestatic diseases.

Biliverdinuria Caused by Exonic BLVRA Deletions in Two Dogs with Green Urine

Background/Objectives: In heme degradation, biliverdin reductase catalyzes the conversion of biliverdin to bilirubin. Defects in the biliverdin reductase A gene (BLVRA) causing biliverdinuria are extraordinarily rare in humans, and this inborn error of metabolism has not been reported in other mammals. The objective of this study was to diagnose biliverdinuria and identify the causal BLVRA variants in two adult mixed-breed dogs with life-long green urine. One of the dogs also had an unexplained regenerative anemia and mild hepatopathy. Methods: Clinicopathological evaluations, urinary mass spectroscopy, and molecular genetic studies were performed. Urine metabolic screening identified increased biliverdin concentrations in both cases relative to control dogs. Results: Whole genome and Sanger sequencing revealed that each case was homozygous for large deletions in BLVRA: UU_Cfam_GSD_1.0/canFam4 chr18:6,532,022-6,551,313 (19,292 bp) in Case 1 and chr18:6,543,863-6,545,908 (2046 bp) in Case 2. These variants were predicted to result in major BLVRA truncations (ENSCAFT00805017018.1 p.[Lys117-Lys296del] and p.[Ala154fs], respectively) and loss of enzyme function. In a genomic variant database, 671 dogs from 63 breeds had coverage over these regions, ruling out homozygosity for the BLVRA deletions. A gene defect for the regenerative anemia in Case 1 was not discovered. Conclusions: While expected to be rare, genotyping for the BLVRA deletions can be used to identify other affected and carrier dogs. This study illustrates the use of targeted metabolic and genomic screening as key diagnostic tools to diagnose a rare metabolic disorder. These are the first confirmed cases of biliverdinuria caused by BLVRA defects in non-human mammals.

Bilirubin, a hepatoprotective agent that activates SIRT1, PGC-1α, and PPAR-α, while inhibiting NF-κB in rats with metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disorder characterized by fatty liver disease alongside overweight or obesity and/or type 2 diabetes mellitus (T2DM). Timely intervention is crucial for a potential cure. This study aimed to investigate the effects of bilirubin, an endogenous antioxidant, on lipid metabolism and inflammation in MAFLD. Specifically, it examined bilirubin's impact on SIRT1, PPAR-α, and NF-κB in the livers of rats with MAFLD induced by a high-fat diet (HFD) and streptozotocin (STZ) administration. Forty eight-week adult male Sprague Dawley rats were divided into five groups (n = 8): Control, HFD-STZ, HFD-S-BR6, HFD-S-BR14, and C-BR14. In the last three groups, bilirubin administration was performed intraperitoneally for 6 and 14 weeks (10 mg/kg/day). We selected the key genes associated with MAFLD and subsequently performed GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses to explore the enriched biological processes and signaling pathways. Hence, the gene expression of SIRT1, PGC-1α, PPAR-α, and inflammatory genes (NF-κB, TNF-α, IL-6, and IL-1β) was measured using Real-time quantitative PCR. Stereological and histopathological alterations of liver structure as well as lipid profile, biochemical indices, and liver indices, were also assessed among different groups. The enrichment analysis identified that several signaling pathways and biological processes might be related to MAFLD. Bilirubin-treated rats contained higher PPAR-α, PGC-1α, and SIRT1 expression levels by approximately 5.7-, 2.1-, and 2.2-fold, respectively, compared to the HFD-receiving rats (p < 0.0001, p < 0.05, and p < 0.05). Whereas, the genes involved in the inflammatory cascades, including NF-κB, TNF-α, and IL-6, were downregulated by 0.6-fold (p < 0.05) following 14-week treatment of bilirubin, while only significantly decreased expression of NF-κB and IL-6 (approximately 0.6-fold, p < 0.05) were observed after 6-week treatment of bilirubin. Remarkably, bilirubin administration favorably reversed the effects of HFD on the liver's volume and cell numbers and ameliorated the related structural changes. It also improved lipid profile, biochemical parameters, and liver indices of HFD-STZ rats. This study indicated that bilirubin acts as a protective/ameliorative compound against MAFLD, particularly through regulating the key genes involved in lipid metabolism and inflammation in HFD-STZ rats.

Advanced deep-tissue imaging and manipulation enabled by biliverdin reductase knockout

We developed near-infrared (NIR) photoacoustic and fluorescence probes, as well as optogenetic tools from bacteriophytochromes, and enhanced their performance using biliverdin reductase-A knock-out model (Blvra-/-). Blvra-/- elevates endogenous heme-derived biliverdin chromophore for bacteriophytochrome-derived NIR constructs. Consequently, light-controlled transcription with IsPadC-based optogenetic tool improved up to 25-fold compared to wild-type cells, with 100-fold activation in Blvra-/- neurons. In vivo , light-induced insulin production in Blvra-/- reduced blood glucose in diabetes by ∼60%, indicating high potential for optogenetic therapy. Using 3D photoacoustic, ultrasound, and two-photon fluorescence imaging, we overcame depth limitations of recording NIR probes. We achieved simultaneous photoacoustic imaging of DrBphP in neurons and super-resolution ultrasound localization microscopy of blood vessels ∼7 mm deep in the brain, with intact scalp and skull. Two-photon microscopy provided cell-level resolution of miRFP720-expressing neurons ∼2.2 mm deep. Blvra-/- significantly enhances efficacy of biliverdin-dependent NIR systems, making it promising platform for interrogation and manipulation of biological processes.

Glucocorticoid resistance remodels liver lipids and prompts lipogenesis, eicosanoid, and inflammatory pathways

We have previously demonstrated that the glucocorticoid receptor β (GRβ) isoform induces hepatic steatosis in mice fed a normal chow diet. The GRβ isoform inhibits the glucocorticoid-binding isoform GRα, reducing responsiveness and inducing glucocorticoid resistance. We hypothesized that GRβ regulates lipids that cause metabolic dysfunction. To determine the effect of GRβ on hepatic lipid classes and molecular species, we overexpressed GRβ (GRβ-Ad) and vector (Vec-Ad) using adenovirus delivery, as we previously described. We fed the mice a normal chow diet for 5 days and harvested the livers. We utilized liquid chromatography-mass spectrometry (LC-MS) analyses of the livers to determine the lipid species driven by GRβ. The most significant changes in the lipidome were monoacylglycerides and cholesterol esters. There was also increased gene expression in the GRβ-Ad mice for lipogenesis, eicosanoid synthesis, and inflammatory pathways. These indicate that GRβ-induced glucocorticoid resistance may drive hepatic fat accumulation, providing new therapeutic advantages.

Nutrition in Gilbert's Syndrome-A Systematic Review of Clinical Trials According to the PRISMA Statement

Gilbert syndrome is the most common hyperbilirubinemia, associated with a mutation in the UGT1A1 bilirubin gene, which produces an enzyme that conjugates bilirubin with glucuronic acid. Episodes of jaundice occurring in GS negatively affect patients' quality of life. This systematic review aimed to analyze clinical studies regarding nutrition in people with GS. The study followed the PRISMA guidelines and utilized the Ebsco, Embase, Cochrane, PubMed, Scopus, and Web of Science databases to search clinical trials focused on diet/nutrition in GS (1963-2023 years). The methodological quality of selected studies was assessed using the Jadad scale. As a result, 19 studies met the inclusion criteria. The research mainly focused on the impact of caloric restriction, consumption of various diet variants, and vegetables and fruits on hyperbilirubinemia and metabolic health. A nutritional intervention consisting of not applying excessive calorie restrictions and consuming fats and biologically active compounds in vegetables and fruits (Cruciferae, Apiaceous, Rutaceae) may prevent the occurrence of jaundice episodes. It is justified to conduct further research on detecting such compounds in food, which, by influencing the expression of the UGT liver enzyme gene, could contribute to regulating bilirubin concentration in the blood of people with GS.

Development of a nomogram for predicting in-hospital mortality in patients with liver cirrhosis and sepsis

In this study, we aimed to investigate the risk factors associated with in-hospital mortality in patients with cirrhosis and sepsis, establish and validate the nomogram. This retrospective study included patients diagnosed with liver cirrhosis and sepsis in the Medical Information Mart for Intensive Care IV (MIMIC-IV). Models were compared by the area under the curve (AUC), integrated discriminant improvement (IDI), net reclassification index (NRI) and decision curve analysis (DCA). A total of 1,696 patients with cirrhosis and sepsis were included in the final cohort. Our final model included the following 9 variables: age, heartrate, total bilirubin (TBIL), glucose, sodium, anion gap (AG), fungal infections, mechanical ventilation, and vasopressin. The nomogram were constructed based on these variables. The AUC values of the nomograms were 0.805 (95% CI 0.776-0.833), which provided significantly higher discrimination compared to that of SOFA score [0.684 (95% CI 0.647-0.720)], MELD-Na [0.672 (95% CI 0.636-0.709)] and ABIC [0.674(95% CI 0.638-0.710)]. We established the first nomogram for predicting in-hospital mortality in patients with liver cirrhosis and sepsis based on these factors. This nomogram can performs well and facilitates clinicians to identify people at high risk of in-hospital mortality.

FOXS1 is increased in liver fibrosis and regulates TGFβ responsiveness and proliferation pathways in human hepatic stellate cells

Liver fibrosis commences with liver injury stimulating transforming growth factor beta (TGFβ) activation of hepatic stellate cells (HSCs), causing scarring and irreversible damage. TGFβ induces expression of the transcription factor Forkhead box S1 (FOXS1) in hepatocytes and may have a role in the pathogenesis of hepatocellular carcinoma (HCC). To date, no studies have determined how it affects HSCs. We analyzed human livers with cirrhosis, HCC, and a murine fibrosis model and found that FOXS1 expression is significantly higher in fibrotic livers but not in HCC. Next, we treated human LX2 HSC cells with TGFβ to activate fibrotic pathways, and FOXS1 mRNA was significantly increased. To study TGFβ-FOXS1 signaling, we developed human LX2 FOXS1 CRISPR KO and scrambled control HSCs. To determine differentially expressed gene transcripts controlled by TGFβ-FOXS1, we performed RNA-seq in the FOXS1 KO and control cells and over 400 gene responses were attenuated in the FOXS1 KO HSCs with TGFβ-activation. To validate the RNA-seq findings, we used our state-of-the-art PamGene PamStation kinase activity technology that measures hundreds of signaling pathways nonselectively in real time. Using our RNA-seq data, kinase activity data, and descriptive measurements, we found that FOXS1 controls pathways mediating TGFβ responsiveness, protein translation, and proliferation. Our study is the first to identify that FOXS1 may serve as a biomarker for liver fibrosis and HSC activation, which may help with early detection of hepatic fibrosis or treatment options for end-stage liver disease.

Antioxidative Hyaluronic Acid-Bilirubin Nanomedicine Targeting Activated Hepatic Stellate Cells for Anti-Hepatic-Fibrosis Therapy

Liver fibrosis is a life-threatening and irreversible disease. The fibrosis process is largely driven by hepatic stellate cells (HSCs), which undergo transdifferentiation from an inactivated state to an activated one during persistent liver damage. This activated state is responsible for collagen deposition in liver tissue and is accompanied by increased CD44 expression on the surfaces of HSCs and amplified intracellular oxidative stress, which contributes to the fibrosis process. To address this problem, we have developed a strategy that combines CD44-targeting of activated HSCs with an antioxidative approach. We developed hyaluronic acid-bilirubin nanoparticles (HABNs), composed of endogenous bilirubin, an antioxidant and anti-inflammatory bile acid, and hyaluronic acid, an endogenous CD44-targeting glycosaminoglycan biopolymer. Our findings demonstrate that intravenously administered HABNs effectively targeted the liver, particularly activated HSCs, in fibrotic mice with choline-deficient l-amino acid-defined high-fat diet (CD-HFD)-induced nonalcoholic steatohepatitis (NASH). HABNs were able to inhibit HSC activation and proliferation and collagen production. Furthermore, in a murine CD-HFD-induced NASH fibrosis model, intravenously administered HABNs showed potent fibrotic modulation activity. Our study suggests that HABNs have the potential to serve as a targeted anti-hepatic-fibrosis therapy by modulating activated HSCs via CD44-targeting and antioxidant strategies. This strategy could also be applied to various ROS-related diseases in which CD44-overexpressing cells play a pivotal role.

Glycocholic acid supplementation improved growth performance and alleviated tissue damage in the liver and intestine in Pelteobagrus fulvidraco fed a high-pectin diet

In a study on the anti-nutritional effect of dietary fiber, it was noticed that a high-pectin diet (PEC diet) caused growth retardation, hepatic cholestasis, steatosis, fibrosis, and enteritis accompanied by decreased glycocholic acid (GCA) in Pelteobagrus fulvidraco. This study was conducted to investigate the potential alleviating effects of supplementation with GCA. A PEC diet and a diet supplemented with 0.6 g kg-1 GCA based on the PEC diet (named the GCA diet) were formulated and randomly fed to juvenile Pelteobagrus fulvidraco. Compared to fish that were fed the PEC diet for 7 days, the GCA content in liver increased significantly in fish fed the GCA diet, the incidence of abnormal liver color, gallbladder somatic index (GBSI), total bile acid concentration in serum and liver, and the expression of arnesoid X receptor gene (fxr) upregulated and genes involved in bile acid (BA) synthesis and uptake in liver decreased significantly. After 56 days, the SGR, the expression of fxr and genes involved in BA synthesis and transportation in the liver, the serum content of total bilirubin, total protein, and globulin were significantly higher, while the hepatosomatic index, GBSI, liver lipid and collagen content, and the incidence of distal intestine tissue damage were lower in fish fed the GCA diet than in those fed the PEC diet. These results suggested that GCA improved growth performance and alleviated hepatic cholestasis and tissue damage to the liver and intestine induced by a high-pectin diet, which might occur through activating FXR.

Glucocorticoids, their uses, sexual dimorphisms, and diseases: new concepts, mechanisms, and discoveries

The normal stress response in humans is governed by the hypothalamic-pituitary-adrenal (HPA) axis through heightened mechanisms during stress, raising blood levels of the glucocorticoid hormone cortisol. Glucocorticoids are quintessential compounds that balance the proper functioning of numerous systems in the mammalian body. They are also generated synthetically and are the preeminent therapy for inflammatory diseases. They act by binding to the nuclear receptor transcription factor glucocorticoid receptor (GR), which has two main isoforms (GRα and GRβ). Our classical understanding of glucocorticoid signaling is from the GRα isoform, which binds the hormone, whereas GRβ has no known ligands. With glucocorticoids being involved in many physiological and cellular processes, even small disruptions in their release via the HPA axis, or changes in GR isoform expression, can have dire ramifications on health. Long-term chronic glucocorticoid therapy can lead to a glucocorticoid-resistant state, and we deliberate how this impacts disease treatment. Chronic glucocorticoid treatment can lead to noticeable side effects such as weight gain, adiposity, diabetes, and others that we discuss in detail. There are sexually dimorphic responses to glucocorticoids, and women tend to have a more hyperresponsive HPA axis than men. This review summarizes our understanding of glucocorticoids and critically analyzes the GR isoforms and their beneficial and deleterious mechanisms and the sexual differences that cause a dichotomy in responses. We also discuss the future of glucocorticoid therapy and propose a new concept of dual GR isoform agonist and postulate why activating both isoforms may prevent glucocorticoid resistance.

Genetic variations underlying Gilbert syndrome and HBV infection outcomes: a cross-sectional study

Background: Constant cellular damage causes a poor prognosis of hepatitis B virus (HBV) infection. Accumulating evidence indicates the cytoprotective properties of bilirubin. Here, we investigated the association of UDP glucuronosyltransferase family 1 member A1 (UGT1A1), the genetic cause of Gilbert syndrome (GS), a common condition of mild unconjugated bilirubinemia, with HBV infection outcomes. Methods: Patients (n = 2,792) with unconjugated hyperbilirubinemia were screened for HBV infection and host UGT1A1 variations in Ruijin Hospital from January 2015 to May 2023, and those with confirmed HBV exposure were included. The promoter/exons/adjacent intronic regions of UGT1A1 were sequenced. HBV infection outcomes were compared between hosts with wild-type and variant-type UGT1A1. The effect magnitudes of UGT1A1 variations were evaluated using three classification approaches. Results: In total, 175 patients with confirmed HBV exposure were recruited for final analysis. Age, gender, level of HBV serological markers, and antiviral treatment were comparable between UGT1A1 wild-type and disease-causing variation groups. Five known disease-causing mutations (UGT1A1*28, UGT1A1*6, UGT1A1*27, UGT1A1*63, and UGT1A1*7) were detected. The incidence of cirrhosis or hepatocellular carcinoma (LC/HCC) was significantly lower in UGT1A1 variant hosts than in UGT1A1 wild-type hosts (13.14% vs. 78.95%, p < 0.0001). The rarer the UGT1A1 variation a patient possessed, the higher the age at which LC/HCC was diagnosed (R = 0.34, p < 0.05). In contrast, patients without cirrhosis achieving HBsAg clearance were identified only in the UGT1A1 variant group (12.32% vs. 0%). Conclusion: The findings of this study provide insights into the association between preexisting genetically mild bilirubin elevation and viral infection outcome. We showed that the accumulation of UGT1A1 variants or the rarity of the variation is associated with a better prognosis, and the effect magnitude correlates with UGT1A1 deficiency. This study demonstrates the therapeutic potential of host UGT1A1 variations underlying GS against HBV infection outcomes.

Association of liver function with health-related physical fitness: a cross-sectional study

BACKGROUND

In this study, by analyzing the correlation between various components of health-related physical fitness (HPF) and liver function indicators, the indicators of physical fitness that were highly correlated with liver function and could be monitored at home were screened to prevent more serious liver disease in the future, and to provide experimental basis for prescribing personalized exercise.

METHODS

A total of 330 faculties (female = 198) of a university were recruited. The indicators of HPF and liver function were measured. Spearman correlation analysis, multivariate linear regression, and cross-lagged panel model was used to data statistics.

RESULTS

In males, body fat (BF) was positively correlated with alanine aminotransferase (ALT); vital capacity and the vital capacity index were positively correlated with albumin; and vertical jump was positively correlated with globulin and negatively correlated with the albumin-globulin ratio (P < 0.05). However, there was no significant correlation among all indicators controlled confounding factors. In females, BF was negatively correlated with direct bilirubin; VO2max was positively correlated with indirect bilirubin; and vertical jump was positively correlated with the albumin-globulin ratio and significantly negatively correlated with globulin (P < 0.05). Controlled confounding factors, body fat percentage was positively correlated with globulin (β = 0.174) and negatively correlated with direct bilirubin (β = -0.431), and VO2max was positively correlated with indirect bilirubin (β = 0.238, P < 0.05). Cross-lagged panel analysis showed that BF percentage can negatively predict direct bilirubin levels with great significance (β = -0.055, P < 0.05).

CONCLUSIONS

HPF may play a crucial role in liver function screening, particularly for female faculty members. For males, BF, vertical jump, vital capacity and vital capacity index could be associated with liver function but are susceptible to complex factors such as age, smoking, diabetes, and hypertension. In females, BF percentage is an important predictor of abnormal liver function in addition to VO2max and vertical jump, which are not affected by complex factors.

Heat stress affects dairy cow health status through blood oxygen availability

BACKGROUND

Rises in global warming and extreme weather occurrence make the risk of heat stress (HS) induced by high ambient temperatures more likely in high-yielding dairy cows, resulting in low milk quality and yield. In animals, oxygen is involved in many physiological and metabolic processes, but the effects of HS on oxygen metabolism remain unclear. Thus, the current study aimed to investigate how oxygen metabolism plays a role in health status of dairy cows by measuring the milk yield, milk composition, and blood biochemical variables of cows under different levels of HS: none (No-HS), mild (Mild-HS), and moderate HS (Mod-HS).

RESULTS

The HS significantly increased rectal temperature (Ptreat < 0.01) and respiration rate (Ptreat < 0.01). Under Mod-HS, greater Na+ (P < 0.05) and lower total CO2, and pH (P < 0.05) were observed relative to those under No-HS and Mild-HS. Oxygen concentrations in both coccygeal artery and mammary vein (Ptreat < 0.01) were lower under Mod-HS than under No-HS. Coccygeal vein concentrations of heat shock protein 90 (HSP90) (P < 0.05) increased during Mod-HS compared with those in cows under No-HS. Malondialdehyde increased during Mod-HS, and glutathione peroxidase (P < 0.01) increased during Mild-HS. Coccygeal vein concentrations of vascular endothelial growth factor (P < 0.01), heme oxygenase-1 (P < 0.01), and hypoxia-inducible factor 1α (P < 0.01) were greater in cows under Mod-HS than those under No-HS. Red blood cell count (P < 0.01) and hemoglobin concentration (P < 0.01) were lower in the coccygeal vein of dairy cows under Mild- and Mod-HS than those of cows under No-HS.

CONCLUSIONS

Exposure to HS negatively impacts the health status and lactation performance of dairy cows by limiting oxygen metabolism and transportation. However, the specific mechanism by which HS affects mammary function in cows remains unclear and requires further exploration.

Hepatic insulin receptor: new views on the mechanisms of liver disease

Over 65 % of people with obesity display the metabolic-associated fatty liver disease (MAFLD), which can manifest as steatohepatitis, fibrosis, cirrhosis, or liver cancer. The development and progression of MAFLD involve hepatic insulin resistance and reduced insulin clearance. This review discusses the relationships between altered insulin signaling, hepatic insulin resistance, and reduced insulin clearance in the development of MAFLD and how this provides the impetus for exploring the use of insulin sensitizers to curb this disease. The review also explores the role of the insulin receptor in hepatocytes and hepatic stellate cells and how it signals in metabolic and end-stage liver diseases. Finally, we discuss new research findings that indicate that advanced hepatic diseases may be an insulin-sensitive state in the liver and deliberate whether insulin sensitizers should be used to manage late-stage liver diseases.

Inflammation, Dopaminergic Brain and Bilirubin

Dopamine is a well-known neurotransmitter due to its involvement in Parkinson's disease (PD). Dopamine is not only involved in PD but also controls multiple mental and physical activities, such as the pleasure of food, friends and loved ones, music, art, mood, cognition, motivation, fear, affective disorders, addiction, attention deficit disorder, depression, and schizophrenia. Dopaminergic neurons (DOPAn) are susceptible to stressors, and inflammation is a recognized risk for neuronal malfunctioning and cell death in major neurodegenerative diseases. Less is known for non-neurodegenerative conditions. Among the endogenous defenses, bilirubin, a heme metabolite, has been shown to possess important anti-inflammatory activity and, most importantly, to prevent DOPAn demise in an ex vivo model of PD by acting on the tumor necrosis factor-alpha (TNFα). This review summarizes the evidence linking DOPAn, inflammation (when possible, specifically TNFα), and bilirubin as an anti-inflammatory in order to understand what is known, the gaps that need filling, and the hypotheses of anti-inflammatory strategies to preserve dopamine homeostasis with bilirubin included.

Loss of hepatic PPARα in mice causes hypertension and cardiovascular disease

The leading cause of death in patients with nonalcoholic fatty liver disease (NAFLD) is cardiovascular disease (CVD). However, the mechanisms are unknown. Mice deficient in hepatocyte proliferator-activated receptor-α (PPARα) (PparaHepKO) exhibit hepatic steatosis on a regular chow diet, making them prone to manifesting NAFLD. We hypothesized that the PparaHepKO mice might be predisposed to poorer cardiovascular phenotypes due to increased liver fat content. Therefore, we used PparaHepKO and littermate control mice fed a regular chow diet to avoid complications with a high-fat diet, such as insulin resistance and increased adiposity. After 30 wk on a standard diet, male PparaHepKO mice exhibited elevated hepatic fat content compared with littermates as measured by Echo MRI (11.95 ± 1.4 vs. 3.74 ± 1.4%, P < 0.05), hepatic triglycerides (1.4 ± 0.10 vs. 0.3 ± 0.01 mM, P < 0.05), and Oil Red O staining, despite body weight, fasting blood glucose, and insulin levels being the same as controls. The PparaHepKO mice also displayed elevated mean arterial blood pressure (121 ± 4 vs. 108 ± 2 mmHg, P < 0.05), impaired diastolic function, cardiac remodeling, and enhanced vascular stiffness. To determine mechanisms controlling the increase in stiffness in the aorta, we used state-of-the-art PamGene technology to measure kinase activity in this tissue. Our data suggest that the loss of hepatic PPARα induces alterations in the aortas that reduce the kinase activity of tropomyosin receptor kinases and p70S6K kinase, which might contribute to the pathogenesis of NAFLD-induced CVD. These data indicate that hepatic PPARα protects the cardiovascular system through some as-of-yet undefined mechanism.

The physiology of bilirubin: health and disease equilibrium

Bilirubin has several physiological functions, both beneficial and harmful. In addition to reactive oxygen species-scavenging activities, bilirubin has potent immunosuppressive effects associated with long-term pathophysiological sequelae. It has been recently recognized as a hormone with endocrine actions and interconnected effects on various cellular signaling pathways. Current studies show that bilirubin also decreases adiposity and prevents metabolic and cardiovascular diseases. All in all, the physiological importance of bilirubin is only now coming to light, and strategies for increasing plasma bilirubin levels to combat chronic diseases are starting to be considered. This review discusses the beneficial effects of increasing plasma bilirubin, incorporates emerging areas of bilirubin biology, and provides key concepts to advance the field.

Bilirubin level is decreased in patients with allergic rhinitis

BACKGROUND

There are limitations in detecting methods for early diagnosis and screening of allergic rhinitis. Considering the anti-inflammatory and anti-oxidative effects of bilirubin, this study aims to explore the relationship between bilirubin and allergic rhinitis and to identify bilirubin-related candidate urinary protein biomarkers associated with allergic rhinitis.

METHODS

63 allergic rhinitis patients (AR group) and 86 healthy controls (NC group) were enrolled. Venous blood was obtained to measure serum total IgE levels and bilirubin parameters. Patients in the AR group were then classified into the AR1 group (IgE > 125 IU/mL) and the AR2 group (IgE ≤ 125 IU/mL). After randomly selecting ten urine samples from the AR1 group, ten samples were chosen from the AR2 and the NC groups, respectively, according to age and gender matching. We employed a Tandem Mass Tag-Based liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) proteomics approach and targeted parallel-reaction monitoring(PRM) to identify and validate urinary biomarkers for allergic rhinitis.

RESULTS

Compared with the NC group, the bilirubin levels of the AR group, AR1 group, and AR2 group were significantly lower. Although the bilirubin level of the AR1 group was lower than that of the AR2 group, the difference was not significant. Further urinary proteomics analysis found that the expression levels of proteins related to bilirubin metabolism and transportation in the AR1 and AR2 groups, including ABCC1, GSTA1, GSTO1, GSTM3, GSTM5, and BLVRB, were significantly higher than those in the NC group. By PRM-based quantification, GSTA1 and GSTO1 showed significant differences in different degrees of Allergic Rhinitis groups and healthy controls. The AUC of the combined diagnosis of GSTA1 and GSTO1 was 0.79 (95% CI 0.583-0.997, P = 0.007), and the sensitivity and specificity were 100% and 60.0%, respectively.

CONCLUSIONS

Bilirubin levels are associated with allergic rhinitis. Our study revealed that urine proteomics has a specific value for exploring the pathophysiological mechanism of bilirubin changes in AR patients and screening possible biomarkers.

Bilirubin Nanoparticle Treatment in Obese Mice Inhibits Hepatic Ceramide Production and Remodels Liver Fat Content

Studies have indicated that increasing plasma bilirubin levels might be useful for preventing and treating hepatic lipid accumulation that occurs with metabolic diseases such as obesity and diabetes. We have previously demonstrated that mice with hyperbilirubinemia had significantly less lipid accumulation in a diet-induced non-alcoholic fatty liver disease (NAFLD) model. However, bilirubin's effects on individual lipid species are currently unknown. Therefore, we used liquid chromatography-mass spectroscopy (LC-MS) to determine the hepatic lipid composition of obese mice with NAFLD treated with bilirubin nanoparticles or vehicle control. We placed the mice on a high-fat diet (HFD) for 24 weeks and then treated them with bilirubin nanoparticles or vehicle control for 4 weeks while maintaining the HFD. Bilirubin nanoparticles suppressed hepatic fat content overall. After analyzing the lipidomics data, we determined that bilirubin inhibited the accumulation of ceramides in the liver. The bilirubin nanoparticles significantly lowered the hepatic expression of two essential enzymes that regulate ceramide production, Sgpl1 and Degs1. Our results demonstrate that the bilirubin nanoparticles improve hepatic fat content by reducing ceramide production, remodeling the liver fat content, and improving overall metabolic health.

Suppressing Hepatic UGT1A1 Increases Plasma Bilirubin, Lowers Plasma Urobilin, Reorganizes Kinase Signaling Pathways and Lipid Species and Improves Fatty Liver Disease

Several population studies have observed lower serum bilirubin levels in patients with non-alcoholic fatty liver disease (NAFLD). Yet, treatments to target this metabolic phenotype have not been explored. Therefore, we designed an N-Acetylgalactosamine (GalNAc) labeled RNAi to target the enzyme that clears bilirubin from the blood, the UGT1A1 glucuronyl enzyme (GNUR). In this study, male C57BL/6J mice were fed a high-fat diet (HFD, 60%) for 30 weeks to induce NAFLD and were treated subcutaneously with GNUR or sham (CTRL) once weekly for six weeks while continuing the HFD. The results show that GNUR treatments significantly raised plasma bilirubin levels and reduced plasma levels of the bilirubin catabolized product, urobilin. We show that GNUR decreased liver fat content and ceramide production via lipidomics and lowered fasting blood glucose and insulin levels. We performed extensive kinase activity analyses using our PamGene PamStation kinome technology and found a reorganization of the kinase pathways and a significant decrease in inflammatory mediators with GNUR versus CTRL treatments. These results demonstrate that GNUR increases plasma bilirubin and reduces plasma urobilin, reducing NAFLD and inflammation and improving overall liver health. These data indicate that UGT1A1 antagonism might serve as a treatment for NAFLD and may improve obesity-associated comorbidities.

Gilbert’s syndrome as a model for studying the effects of bilirubin

Numerous scientific studies conducted over the past years expand our understanding of the physiological and pathophysiological effects of bilirubin. In this review of the literature, the authors, using the example of Gilbert’s syndrome, as a classic condition occurring with hyperbilirubinemia, discuss the results of clinical and experimental studies demonstrating the protective mechanisms and the protective role of elevated bilirubin concentration in relation to diseases accompanied by metabolic inflammation, oncological diseases, and a number of others. The authors focus on the hormonal function of bilirubin and its potential therapeutic effect discussed in recent scientific works. The purpose of this review of the literature is to expand the understanding of bilirubin from the clinician’s usual in the context of the end product of heme and antioxidant metabolism to a signaling molecule involved in the pathophysiology of many diseases.

Bilirubin Levels Are Negatively Correlated with Adiposity in Obese Men and Women, and Its Catabolized Product, Urobilin, Is Positively Associated with Insulin Resistance

Bilirubin levels in obese humans and rodents have been shown to be lower than in their lean counterparts. Some studies have proposed that the glucuronyl UGT1A1 enzyme that clears bilirubin from the blood increases in the liver with obesity. UGT1A1 clearance of bilirubin allows more conjugated bilirubin to enter the intestine, where it is catabolized into urobilin, which can be then absorbed via the hepatic portal vein. We hypothesized that when bilirubin levels are decreased, the urobilin increases in the plasma of obese humans, as compared to lean humans. To test this, we measured plasma levels of bilirubin and urobilin, body mass index (BMI), adiposity, blood glucose and insulin, and HOMA IR in a small cohort of obese and lean men and women. We found that bilirubin levels negatively correlated with BMI and adiposity in obese men and women, as compared to their lean counterparts. Contrarily, urobilin levels were positively associated with adiposity and BMI. Only obese women were found to be insulin resistant based on significantly higher HOMA IR, as compared to lean women. The urobilin levels were positively associated with HOMA IR in both groups, but women had a stronger linear correlation. These studies indicate that plasma urobilin levels are associated with obesity and its comorbidities, such as insulin resistance.

Cutting edge concepts: Does bilirubin enhance exercise performance?

Exercise performance is dependent on many factors, such as muscular strength and endurance, cardiovascular capacity, liver health, and metabolic flexibility. Recent studies show that plasma levels of bilirubin, which has classically been viewed as a liver dysfunction biomarker, are elevated by exercise training and that elite athletes may have significantly higher levels. Other studies have shown higher plasma bilirubin levels in athletes and active individuals compared to general, sedentary populations. The reason for these adaptions is unclear, but it could be related to bilirubin's antioxidant properties in response to a large number of reactive oxygen species (ROS) that originates from mitochondria during exercise. However, the mechanisms of these are unknown. Current research has re-defined bilirubin as a metabolic hormone that interacts with nuclear receptors to drive gene transcription, which reduces body weight. Bilirubin has been shown to reduce adiposity and improve the cardiovascular system, which might be related to the adaption of bilirubin increasing during exercise. No studies have directly tested if elevating bilirubin levels can influence athletic performance. However, based on the mechanisms proposed in the present review, this seems plausible and an area to consider for future studies. Here, we discuss the importance of bilirubin and exercise and how the combination might improve metabolic health outcomes and possibly athletic performance.

Metabolome combined with gut microbiome revealed the lipid-lowering mechanism of Xuezhiping capsule on hyperlipidemic hamster induced by high fat diet

Introduction: Hyperlipidemia is a common metabolic disorder with presence of excess fat or lipids in the blood, may induce liver injury, oxidative stress and inflammatory. Xuezhiping capsule (XZP) is a famous Chinese patent medicine clinically used for anti-hyperlipidemia. However, the regulation mechanism of XZP on hyperlipidemia has not been elucidated so far. Methods: This study aimed to explore the effects of XZP on hypolipidemic, antioxidant and anti-inflammatory effects, and the potential mechanism by a combination of untargeted metabolomics and 16S rRNA sequencing. Results: The results indicated that XZP reduced the level of total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), increased the level of high density liptein cholesterol (HDL-C), alleviated excessive accumulation of lipid droplets in liver. Biochemical indexes of liver function including gamma glutamyl transferase (GGT) and glutamic oxaloacetic transaminase (GOT) in liver were remarkably decreased. Meanwhile, XZP increased the level of oxidative stress biochemical indexes including superoxide dismutase (SOD) and glutathione (GSH). In addition, XZP increased the level of peroxisome proliferators-activated receptors α (PPARα), acetyl CoA carboxylase 1 (ACOX1) and cholesterol 7-alpha hydroxylase (CYP7A1) in liver, and improved lipid metabolism in serum, liver and fecal lipid metabolism. XZP increased diversity index and the ratio of Firmicutes and Bacteroidetes, regulated seventeen genera, and illustrated strong correlations with liver lipid metabolism and phenotypic indicators. Discussion: These findings suggest that XZP reduced blood lipid and liver lipid, protected liver function, anti inflammation and anti-oxidation, ameliorate lipid metabolic disorders by modulating alpha linolenic acid and linoleic acid metabolism, bile acid metabolism, arachidonic acid metabolism, and regulated gut microbiota composition of high-fat diet (HFD) hamsters.

Zinc fingers and homeoboxes 2 is required for diethylnitrosamine-induced liver tumor formation in C57BL/6 mice

Liver cancer, comprised primarily of hepatocellular carcinoma (HCC), is the third leading cause of cancer deaths worldwide and increasing in Western countries. We previously identified the transcription factor zinc fingers and homeoboxes 2 (Zhx2) as a regulator of hepatic gene expression, and many Zhx2 target genes are dysregulated in HCC. Here, we investigate HCC in Zhx2-deficient mice using the diethylnitrosamine (DEN)-induced liver tumor model. Our study using whole-body Zhx2 knockout (Zhx2KO ) mice revealed the complete absence of liver tumors 9 and 10 months after DEN exposure. Analysis soon after DEN treatment showed no differences in expression of the DEN bioactivating enzyme cytochrome P450 2E1 (CYP2E1) and DNA polymerase delta 2, or in the numbers of phosphorylated histone variant H2AX foci between Zhx2KO and wild-type (Zhx2wt ) mice. The absence of Zhx2, therefore, did not alter DEN bioactivation or DNA damage. Zhx2KO livers showed fewer positive foci for Ki67 staining and reduced interleukin-6 and AKT serine/threonine kinase 2 expression compared with Zhx2wt livers, suggesting that Zhx2 loss reduces liver cell proliferation and may account for reduced tumor formation. Tumors were reduced but not absent in DEN-treated liver-specific Zhx2 knockout mice, suggesting that Zhx2 acts in both hepatocytes and nonparenchymal cells to inhibit tumor formation. Analysis of data from the Cancer Genome Atlas and Clinical Proteomic Tumor Consortium indicated that ZHX2 messenger RNA and protein levels were significantly higher in patients with HCC and associated with clinical pathological parameters. Conclusion: In contrast to previous studies in human hepatoma cell lines and other HCC mouse models showing that Zhx2 acts as a tumor suppressor, our data indicate that Zhx2 acts as an oncogene in the DEN-induced HCC model and is consistent with the higher ZHX2 expression in patients with HCC.

Hepatic kinome atlas: An in-depth identification of kinase pathways in liver fibrosis of humans and rodents

BACKGROUND AND AIMS

Resolution of pathways that converge to induce deleterious effects in hepatic diseases, such as in the later stages, have potential antifibrotic effects that may improve outcomes. We aimed to explore whether humans and rodents display similar fibrotic signaling networks.

APPROACH AND RESULTS

We assiduously mapped kinase pathways using 340 substrate targets, upstream bioinformatic analysis of kinase pathways, and over 2000 random sampling iterations using the PamGene PamStation kinome microarray chip technology. Using this technology, we characterized a large number of kinases with altered activity in liver fibrosis of both species. Gene expression and immunostaining analyses validated many of these kinases as bona fide signaling events. Surprisingly, the insulin receptor emerged as a considerable protein tyrosine kinase that is hyperactive in fibrotic liver disease in humans and rodents. Discoidin domain receptor tyrosine kinase, activated by collagen that increases during fibrosis, was another hyperactive protein tyrosine kinase in humans and rodents with fibrosis. The serine/threonine kinases found to be the most active in fibrosis were dystrophy type 1 protein kinase and members of the protein kinase family of kinases. We compared the fibrotic events over four models: humans with cirrhosis and three murine models with differing levels of fibrosis, including two models of fatty liver disease with emerging fibrosis. The data demonstrate a high concordance between human and rodent hepatic kinome signaling that focalizes, as shown by our network analysis of detrimental pathways.

CONCLUSIONS

Our findings establish a comprehensive kinase atlas for liver fibrosis, which identifies analogous signaling events conserved among humans and rodents.

Dose- and time-dependent manners of moxifloxacin induced liver injury by targeted metabolomics study

Moxifloxacin is the most widely prescribed antibiotics due to its excellent oral bioavailability and broad-spectrum antibacterial effect. Despite of its popularity, the rare and severe liver injury induced by moxifloxacin is a big concern that cannot be ignored in clinical practice. However, the early warning and related metabolic disturbances of moxifloxacin induced hepatoxicity were rarely reported. In this study, the dose- and time-dependent manners of moxifloxacin induced liver injury were investigated by a targeted metabolomics method. In dose-dependent experiment, three different dosages of moxifloxacin were administered to the rats, including 36 mg kg⁻¹ d⁻¹, 72 mg kg⁻¹ d⁻¹, and 108 mg kg⁻¹ d⁻¹. In time-dependent experiment, moxifloxacin was orally administered to the rats for 3, 7 or 14 consecutive days. Pathological analysis showed that moxifloxacin caused obvious transient hepatotoxicity, with the most serious liver injury occurred in the 7 days continuous administration group. The transient liver injury can be automatically restored over time. Serum levels of liver function related biochemical indicators, including ALT, AST, TBIL, alkaline phosphatase, superoxide dismutase, and malondialdehyde, were also measured for the evaluation of liver injury. However, these indicators can hardly be used for the early warning of hepatotoxicity caused by moxifloxacin due to their limited sensitivity and significant hysteresis. Targeted metabolomics study demonstrated that serum concentrations of fatty acyl carnitines, fatty acids and dehydroepiandrosterone can change dynamically with the severity of moxifloxacin related liver injury. The elevated serum levels of fatty acyl carnitine, fatty acid and dehydroepiandrosterone were promising in predicting the hepatotoxicity induced by moxifloxacin.

Molecular mechanisms of metabolic associated fatty liver disease (MAFLD): functional analysis of lipid metabolism pathways

The metabolic-associated fatty liver disease (MAFLD) is a condition of fat accumulation in the liver in combination with metabolic dysfunction in the form of overweight or obesity and insulin resistance. It is also associated with an increased cardiovascular disease risk, including hypertension and atherosclerosis. Hepatic lipid metabolism is regulated by a combination of the uptake and export of fatty acids, de novo lipogenesis, and fat utilization by β-oxidation. When the balance between these pathways is altered, hepatic lipid accumulation commences, and long-term activation of inflammatory and fibrotic pathways can progress to worsen the liver disease. This review discusses the details of the molecular mechanisms regulating hepatic lipids and the emerging therapies targeting these pathways as potential future treatments for MAFLD.

Antioxidant Therapy Significantly Attenuates Hepatotoxicity following Low Dose Exposure to Microcystin-LR in a Murine Model of Diet-Induced Non-Alcoholic Fatty Liver Disease

We have previously shown in a murine model of Non-alcoholic Fatty Liver Disease (NAFLD) that chronic, low-dose exposure to the Harmful Algal Bloom cyanotoxin microcystin-LR (MC-LR), resulted in significant hepatotoxicity including micro-vesicular lipid accumulation, impaired toxin metabolism as well as dysregulation of the key signaling pathways involved in inflammation, immune response and oxidative stress. On this background we hypothesized that augmentation of hepatic drug metabolism pathways with targeted antioxidant therapies would improve MC-LR metabolism and reduce hepatic injury in NAFLD mice exposed to MC-LR. We chose N-acetylcysteine (NAC, 40 mM), a known antioxidant that augments the glutathione detoxification pathway and a novel peptide (pNaKtide, 25 mg/kg) which is targeted to interrupting a specific Src-kinase mediated pro-oxidant amplification mechanism. Histological analysis showed significant increase in hepatic inflammation in NAFLD mice exposed to MC-LR which was attenuated on treatment with both NAC and pNaKtide (both p ≤ 0.05). Oxidative stress, as measured by 8-OHDG levels in urine and protein carbonylation in liver sections, was also significantly downregulated upon treatment with both antioxidants after MC-LR exposure. Genetic analysis of key drug transporters including Abcb1a, Phase I enzyme-Cyp3a11 and Phase II metabolic enzymes-Pkm (Pyruvate kinase, muscle), Pklr (Pyruvate kinase, liver, and red blood cell) and Gad1 (Glutamic acid decarboxylase) was significantly altered by MC-LR exposure as compared to the non-exposed control group (all p ≤ 0.05). These changes were significantly attenuated with both pNaKtide and NAC treatment. These results suggest that MC-LR metabolism and detoxification is significantly impaired in the setting of NAFLD, and that these pathways can potentially be reversed with targeted antioxidant treatment.

Associations of body shape index (ABSI) and hip index with liver, metabolic, and inflammatory biomarkers in the UK Biobank cohort

Associations of liver, metabolic, and inflammatory biomarkers in blood with body shape are unclear, because waist circumference (WC) and hip circumference (HC) are dependent on overall body size, resulting in bias. We have used the allometric "a body shape index" (ABSI = WC_(mm)[Formula: see text]Weight_(kg)^-2/3[Formula: see text]Height_(m)^5/6) and hip index (HI_women = HC_(cm)[Formula: see text]Weight_(kg)^-0.482[Formula: see text]Height_(cm)^0.310, HI_men = HC_(cm)[Formula: see text]Weight_(kg)^-2/5[Formula: see text]Height_(cm)^1/5), which are independent of body mass index (BMI) by design, in multivariable linear regression models for 121,879 UK Biobank men and 135,559 women. Glucose, glycated haemoglobin (HbA1c), triglycerides, low-density-lipoprotein cholesterol, apolipoprotein-B, alanine aminotransferase (ALT), gamma-glutamyltransferase, and lymphocytes were associated positively with BMI and ABSI but inversely with HI. High-density-lipoprotein cholesterol and apolipoprotein-A1 were associated inversely with BMI and ABSI but positively with HI. Lipid-related biomarkers and ALT were associated only with HI in obese men. C-reactive protein, neutrophils, monocytes, and alkaline phosphatase were associated positively, while bilirubin was associated inversely, with BMI and ABSI but not with HI. Associations were consistent within the clinical reference ranges but were lost or changed direction for low or high biomarker levels. Our study confirms associations with waist and hip size, independent of BMI, for metabolic biomarkers but only with waist size for inflammatory biomarkers, suggesting different contribution of the mechanistic pathways related to body shape.

Novel Function for Bilirubin as a Metabolic Signaling Molecule: Implications for Kidney Diseases

Bilirubin is the end product of the catabolism of heme via the heme oxygenase pathway. Heme oxygenase generates carbon monoxide (CO) and biliverdin from the breakdown of heme, and biliverdin is rapidly reduced to bilirubin by the enzyme biliverdin reductase (BVR). Bilirubin has long been thought of as a toxic product that is only relevant to health when blood levels are severely elevated, such as in clinical jaundice. The physiologic functions of bilirubin correlate with the growing body of evidence demonstrating the protective effects of serum bilirubin against cardiovascular and metabolic diseases. Although the correlative evidence suggests a protective effect of serum bilirubin against many diseases, the mechanism by which bilirubin offers protection against cardiovascular and metabolic diseases remains unanswered. We recently discovered a novel function for bilirubin as a signaling molecule capable of activating the peroxisome proliferator-activated receptor α (PPARα) transcription factor. This review summarizes the new finding of bilirubin as a signaling molecule and proposes several mechanisms by which this novel action of bilirubin may protect against cardiovascular and kidney diseases.

Heme Oxygenase-1: An Anti-Inflammatory Effector in Cardiovascular, Lung, and Related Metabolic Disorders

The heme oxygenase (HO) enzyme system catabolizes heme to carbon monoxide (CO), ferrous iron, and biliverdin-IXα (BV), which is reduced to bilirubin-IXα (BR) by biliverdin reductase (BVR). HO activity is represented by two distinct isozymes, the inducible form, HO-1, and a constitutive form, HO-2, encoded by distinct genes (HMOX1, HMOX2, respectively). HO-1 responds to transcriptional activation in response to a wide variety of chemical and physical stimuli, including its natural substrate heme, oxidants, and phytochemical antioxidants. The expression of HO-1 is regulated by NF-E2-related factor-2 and counter-regulated by Bach-1, in a heme-sensitive manner. Additionally, HMOX1 promoter polymorphisms have been associated with human disease. The induction of HO-1 can confer protection in inflammatory conditions through removal of heme, a pro-oxidant and potential catalyst of lipid peroxidation, whereas iron released from HO activity may trigger ferritin synthesis or ferroptosis. The production of heme-derived reaction products (i.e., BV, BR) may contribute to HO-dependent cytoprotection via antioxidant and immunomodulatory effects. Additionally, BVR and BR have newly recognized roles in lipid regulation. CO may alter mitochondrial function leading to modulation of downstream signaling pathways that culminate in anti-apoptotic, anti-inflammatory, anti-proliferative and immunomodulatory effects. This review will present evidence for beneficial effects of HO-1 and its reaction products in human diseases, including cardiovascular disease (CVD), metabolic conditions, including diabetes and obesity, as well as acute and chronic diseases of the liver, kidney, or lung. Strategies targeting the HO-1 pathway, including genetic or chemical modulation of HO-1 expression, or application of BR, CO gas, or CO donor compounds show therapeutic potential in inflammatory conditions, including organ ischemia/reperfusion injury. Evidence from human studies indicate that HO-1 expression may represent a biomarker of oxidative stress in various clinical conditions, while increases in serum BR levels have been correlated inversely to risk of CVD and metabolic disease. Ongoing human clinical trials investigate the potential of CO as a therapeutic in human disease.

Reactive Oxygen Species (ROS) and Antioxidants as Immunomodulators in Exercise: Implications for Heme Oxygenase and Bilirubin

Exercise is commonly prescribed as a lifestyle treatment for chronic metabolic diseases as it functions as an insulin sensitizer, cardio-protectant, and essential lifestyle tool for effective weight maintenance. Exercise boosts the production of reactive oxygen species (ROS) and subsequent transient oxidative damage, which also upregulates counterbalancing endogenous antioxidants to protect from ROS-induced damage and inflammation. Exercise elevates heme oxygenase-1 (HO-1) and biliverdin reductase A (BVRA) expression as built-in protective mechanisms, which produce the most potent antioxidant, bilirubin. Together, these mitigate inflammation and adiposity. Moderately raising plasma bilirubin protects in two ways: (1) via its antioxidant capacity to reduce ROS and inflammation, and (2) its newly defined function as a hormone that activates the nuclear receptor transcription factor PPARα. It is now understood that increasing plasma bilirubin can also drive metabolic adaptions, which improve deleterious outcomes of weight gain and obesity, such as inflammation, type II diabetes, and cardiovascular diseases. The main objective of this review is to describe the function of bilirubin as an antioxidant and metabolic hormone and how the HO-1-BVRA-bilirubin-PPARα axis influences inflammation, metabolic function and interacts with exercise to improve outcomes of weight management.

Relationship of circulating total bilirubin, UDP-glucuronosyltransferases 1A1 and the development of non-alcoholic fatty liver disease: a cross-sectional study

Background

This study aimed to investigate the correlation of circulating total bilirubin (TB) and UGT1A1 with NAFLD in Chinese Han population.

Methods

172 adults were enrolled from the Qingdao Municipal Hospital from May 2019 to October 2020. All individuals were examined with MRI-PDFF and divided into no steatosis, mild steatosis, moderate steatosis, and severe steatosis groups according to the MRI-PDFF values. The biochemical indexes and UGT1A1 were measured.

Results

There was no significant difference of circulating TB and UGT1A1 levels between NAFLD group and controls. In the moderate steatosis and severe steatosis groups, the circulating TB levels were higher than that in control group (all P < 0.05). In addition, circulating TB levels were weak positively associated with liver fat fraction in NAFLD patients (ρ = 0.205, P = 0.001). There was no significant correlation between circulating UGT1A1 levels with liver fat fraction in patients with NAFLD (ρ = 0.080, P = 0.179), but positively correlation was found in patients with severe steatosis (ρ = 0.305, P = 0.026).

Conclusions

The circulating TB levels were significant high in patients with moderate and severe steatosis. Circulating TB levels were weakly associated with liver fat fraction in patients with NAFLD, and the circulating UGT1A1 levels were positively correlated with liver fat fraction in NAFLD patients with severe steatosis.

Trial registration: ChiCTR, ChiCTR1900022744. Registered 24 April 2019 – Retrospectively registered, http://www.chictr.org.cn/edit.aspx?pid=38304&htm=4.

Adipose-Specific PPARα Knockout Mice Have Increased Lipogenesis by PASK-SREBP1 Signaling and a Polarity Shift to Inflammatory Macrophages in White Adipose Tissue

The nuclear receptor PPARα is associated with reducing adiposity, especially in the liver, where it transactivates genes for β-oxidation. Contrarily, the function of PPARα in extrahepatic tissues is less known. Therefore, we established the first adipose-specific PPARα knockout (PparaFatKO) mice to determine the signaling position of PPARα in adipose tissue expansion that occurs during the development of obesity. To assess the function of PPARα in adiposity, female and male mice were placed on a high-fat diet (HFD) or normal chow for 30 weeks. Only the male PparaFatKO animals had significantly more adiposity in the inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT) with HFD, compared to control littermates. No changes in adiposity were observed in female mice compared to control littermates. In the males, the loss of PPARα signaling in adipocytes caused significantly higher cholesterol esters, activation of the transcription factor sterol regulatory element-binding protein-1 (SREBP-1), and a shift in macrophage polarity from M2 to M1 macrophages. We found that the loss of adipocyte PPARα caused significantly higher expression of the Per-Arnt-Sim kinase (PASK), a kinase that activates SREBP-1. The hyperactivity of the PASK-SREBP-1 axis significantly increased the lipogenesis proteins fatty acid synthase (FAS) and stearoyl-Coenzyme A desaturase 1 (SCD1) and raised the expression of genes for cholesterol metabolism (Scarb1, Abcg1, and Abca1). The loss of adipocyte PPARα increased Nos2 in the males, an M1 macrophage marker indicating that the population of macrophages had changed to proinflammatory. Our results demonstrate the first adipose-specific actions for PPARα in protecting against lipogenesis, inflammation, and cholesterol ester accumulation that leads to adipocyte tissue expansion in obesity.

Bilirubin: The yellow hormone?

Bilirubin is a tetrapyrrolic compound originating from heme catabolism. Although originally considered only a potentially dangerous waste product, it has become increasingly evident that this molecule represents an important modulator of various biological functions in the human body. Bilirubin appears to have versatile functions, from cell signaling (behaving almost like a "real" hormonal substance), modulation of metabolism, to immune regulation, affecting biological activities with apparent clinical and even therapeutic consequences. These activities may be the reason for the lower incidence of diseases of civilisation (cardiovascular diseases, arterial hypertension, diabetes, obesity, metabolic syndrome, certain cancers, autoimmune, and neurodegenerative diseases) observed in individuals with a chronic mild unconjugated hyperbilirubinemia, a typical sign of Gilbert's syndrome. While higher serum concentrations of unconjugated bilirubin may serve as an important protective factor against these diseases, low levels of bilirubin are associated with the opposite effect.

The Protective Role of the Heme Catabolic Pathway in Hepatic Disorders

Significance: As the central metabolic organ, the liver is exposed to a variety of potentially cytotoxic, proinflammatory, profibrotic, and carcinogenic stimuli. To protect the organism from these deleterious effects, the liver has evolved a number of defense systems, which include antioxidant substrates and enzymes, anti-inflammatory tools, enzymatic biotransformation systems, and metabolic pathways. Recent Advances: One of the pivotal systems that evolved during phylogenesis was the heme catabolic pathway. Comprising the important enzymes heme oxygenase and biliverdin reductase, this complex pathway has a number of key functions including enzymatic activities, but also cell signaling, and DNA transcription. It further generates two important bile pigments, biliverdin and bilirubin, as well as the gaseous molecule carbon monoxide. These heme degradation products have potent antioxidant, immunosuppressive, and cytoprotective effects. Recent data suggest that the pathway participates in the regulation of metabolic and hormonal processes implicated in the pathogenesis of hepatic and other diseases. Critical Issues: This review discusses the impact of the heme catabolic pathway on major liver diseases, with particular focus on the involvement of cellular targeting and signaling in the pathogenesis of these conditions. Future Directions: To utilize the biological consequences of the heme catabolic pathway, several unique therapeutic strategies have been developed. Research indicates that pharmaceutical, nutraceutical, and lifestyle modifications positively affect the pathway, delivering potentially long-term clinical benefits. However, further well-designed studies are needed to confirm the clinical benefits of these approaches. Antioxid. Redox Signal. 35, 734-752.

Biliverdin reductase as a target in drug research and development: Facts and hypotheses

Biliverdin reductase-A (BVR) catalyzes the reduction of heme-derived biliverdin into bilirubin, this latter being a powerful endogenous free radical scavenger. Furthermore, BVR is also endowed with both serine/threonine/tyrosine kinase and scaffold activities, through which it interacts with the insulin receptor kinase, conventional and atypical protein kinase C isoforms, mitogen-activated protein kinases as well as the phosphatidylinositol-3 kinase/Akt system. By regulating this complex array of signal transduction pathways, BVR is involved in the pathogenesis of neurodegenerative, metabolic, cardiovascular and immune-inflammatory diseases as well as in cancer. In addition, both BVR and BVR-B, this latter being an alternate isozyme predominant during fetal development but sometimes detectable through adulthood, have been studied as peripheral biomarkers for an early detection of Alzheimer's disease, atherosclerosis and some types of cancer. However, despite these interesting lines of evidence, to date BVR has not been considered as an appealing drug target. Only limited evidence supports the neuroprotective effects of atorvastatin and ferulic acid through BVR regulation in the aged canine brain and human neuroblastoma cells, whereas interesting results have been reported regarding the use of BVR-based peptides in preclinical models of cardiac diseases and cancer.

UGT1A1 dysfunction increases liver burden and aggravates hepatocyte damage caused by long-term bilirubin metabolism disorder

UGT1A1 is the only enzyme that can metabolize bilirubin, and its encoding gene is frequently mutated. UGT1A1*6 (G71R) is a common mutant in Asia which leads to the decrease of UGT1A1 activity and abnormal bilirubin metabolism. However, it is not clear whether low UGT1A1 activity-induced bilirubin metabolism disorder increases hepatocyte fragility. ugt1a^+/- mice were used to simulate the UGT1A1*6 (G71R) population. Under the same CCl₄ induction condition, ugt1a^+/- mice showed severer liver damage and fibrosis, indicating that ugt1a1 dysfunction increased liver burden and aggravated hepatocyte damage. In the animal experiment with a continuous intraperitoneal injection of bilirubin, the ugt1a^+/- mice livers had more serious unconjugated bilirubin accumulation. The accumulated bilirubin leads to hyperphosphorylation of IκB-α, Ikk-β, and p65 and a significant increase of inflammatory factor. The α-SMA and Collagen I proteins markedly up-regulated in the ugt1a^+/- mice livers. Immunofluorescence and confocal microscopy showed that hepatic stellate cells and Kupffer cells were activated in ugt1a^+/- mice. Comprehensive results show that there was a crosstalk relationship between low UGT1A1 activity-bilirubin-liver damage. Furthermore, cell experiments confirmed that unconjugated bilirubin activated the NF-κB pathway and induced DNA damage in hepatocytes, leading to the significant increase of inflammatory factors. UGT1A1 knockdown in hepatocytes aggravated the toxicity of unconjugated bilirubin. Conversely, overexpression of UGT1A1 had a protective effect on hepatocytes. Finally, Schisandrin B, an active ingredient with hepatoprotective effects, extracted from a traditional Chinese medicinal herb, which could protect the liver from bilirubin metabolism disorders caused by ugt1a1 deficiency by downregulating p65 phosphorylation, inhibiting Kupffer cells, reducing inflammation levels. Our data clarified the mechanism of liver vulnerability caused by cross-talk between low UGT1A1 activity bilirubin, and provided a reference for individualized prevention of liver fragility in Gilbert's syndrome.

Bilirubin as a metabolic hormone: the physiological relevance of low levels

Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.

Protective Effects of Kirenol against Lipopolysaccharide-Induced Acute Lung Injury through the Modulation of the Proinflammatory NFκB Pathway and the AMPK2-/Nrf2-Mediated HO-1/AOE Pathway

Acute lung injury (ALI) is an acute and life-threatening inflammatory disease of the lung parenchyma that is associated with high mortality worldwide. No therapeutic strategies have been developed for the mitigation of the proinflammatory response that characterizes ALI. Kirenol has anti-inflammatory, antiarthritic, and immunoregulatory effects. In the present study, we investigated the protective effects of kirenol against lipopolysaccharides (LPS)-induced ALI in mice. Kirenol reduced the LPS-induced histopathology changes involving edema and thickening of the interstitial or alveolar walls, infiltration of leukocytes, formation of hyaline membrane. Pretreatment with kirenol reduced leukocytes infiltration in bronchoalveolar lavage fluid (BALF), the alveolar-capillary barrier disruption and lipid peroxidation in lung tissues induced by LPS. Kirenol significantly inhibited the secretion of cytokines, IL-1β, IL6, and TNFα, into the BALF of the mice with LPS-induced ALI through NFκB activation. Moreover, kirenol attenuated the downregulation of the antioxidant enzymes, superoxide dismutase, glutathione peroxidase, and catalase that was induced by LPS. HO-1 expression and the phosphorylation of Nrf2 and AMPK2 were also induced by kirenol. The results indicate that kirenol can be developed as a treatment strategy for ALI, and its effects are induced through the inhibition of the NF-κB proinflammatory pathway and promotion of AMPK2/Nrf2-mediated HO-1 and antioxidant enzymes (AOE) activation.

Natural Product Heme Oxygenase Inducers as Treatment for Nonalcoholic Fatty Liver Disease

Heme oxygenase (HO) is a critical component of the defense mechanism to a wide variety of cellular stressors. HO induction affords cellular protection through the breakdown of toxic heme into metabolites, helping preserve cellular integrity. Nonalcoholic fatty liver disease (NAFLD) is a pathological condition by which the liver accumulates fat. The incidence of NAFLD has reached all-time high levels driven primarily by the obesity epidemic. NALFD can progress to nonalcoholic steatohepatitis (NASH), advancing further to liver cirrhosis or cancer. NAFLD is also a contributing factor to cardiovascular and metabolic diseases. There are currently no drugs to specifically treat NAFLD, with most treatments focused on lifestyle modifications. One emerging area for NAFLD treatment is the use of dietary supplements such as curcumin, pomegranate seed oil, milk thistle oil, cold-pressed Nigella Satvia oil, and resveratrol, among others. Recent studies have demonstrated that several of these natural dietary supplements attenuate hepatic lipid accumulation and fibrosis in NAFLD animal models. The beneficial actions of several of these compounds are associated with the induction of heme oxygenase-1 (HO-1). Thus, targeting HO-1 through dietary-supplements may be a useful therapeutic for NAFLD either alone or with lifestyle modifications.

Reduced Biliverdin Reductase-A Expression in Visceral Adipose Tissue is Associated with Adipocyte Dysfunction and NAFLD in Human Obesity

Biliverdin reductase A (BVR-A) is an enzyme involved in the regulation of insulin signalling. Knockout (KO) mice for hepatic BVR-A, on a high-fat diet, develop more severe glucose impairment and hepato-steatosis than the wild type, whereas loss of adipocyte BVR-A is associated with increased visceral adipose tissue (VAT) inflammation and adipocyte size. However, BVR-A expression in human VAT has not been investigated. We evaluated BVR-A mRNA expression levels by real-time PCR in the intra-operative omental biopsy of 38 obese subjects and investigated the association with metabolic impairment, VAT dysfunction, and biopsy-proven non-alcoholic fatty liver disease (NAFLD). Individuals with lower VAT BVR-A mRNA levels had significantly greater VAT IL-8 and Caspase 3 expression than those with higher BVR-A. Lower VAT BVR-A mRNA levels were associated with an increased adipocytes’ size. An association between lower VAT BVR-A expression and higher plasma gamma-glutamyl transpeptidase was also observed. Reduced VAT BVR-A was associated with NAFLD with an odds ratio of 1.38 (95% confidence interval: 1.02–1.9; χ² test) and with AUROC = 0.89 (p = 0.002, 95% CI = 0.76–1.0). In conclusion, reduced BVR-A expression in omental adipose tissue is associated with VAT dysfunction and NAFLD, suggesting a possible involvement of BVR-A in the regulation of VAT homeostasis in presence of obesity.