Biliverdin reductase isozymes in metabolism

BVR-A Deficiency Leads to Autophagy Impairment through the Dysregulation of AMPK/mTOR Axis in the Brain-Implications for Neurodegeneration

Biliverdin reductase-A (BVR-A) impairment is associated with increased accumulation of oxidatively-damaged proteins along with the impairment of autophagy in the brain during neurodegenerative disorders. Reduced autophagy inhibits the clearance of misfolded proteins, which then form neurotoxic aggregates promoting neuronal death. The aim of our study was to clarify the role for BVR-A in the regulation of the mTOR/autophagy axis by evaluating age-associated changes (2, 6 and 11 months) in cerebral cortex samples collected from BVR-A knock-out (BVR-A^−/−) and wild-type (WT) mice. Our results show that BVR-A deficiency leads to the accumulation of oxidatively-damaged proteins along with mTOR hyper-activation in the cortex. This process starts in juvenile mice and persists with aging. mTOR hyper-activation is associated with the impairment of autophagy as highlighted by reduced levels of Beclin-1, LC3β, LC3II/I ratio, Atg5–Atg12 complex and Atg7 in the cortex of BVR-A^−/− mice. Furthermore, we have identified the dysregulation of AMP-activated protein kinase (AMPK) as a critical event driving mTOR hyper-activation in the absence of BVR-A. Overall, our results suggest that BVR-A is a new player in the regulation of autophagy, which may be targeted to arrive at novel therapeutics for diseases involving impaired autophagy.

Bilirubin remodels murine white adipose tissue by reshaping mitochondrial activity and the coregulator profile of peroxisome proliferator-activated receptor α

Activation of lipid-burning pathways in the fat-storing white adipose tissue (WAT) is a promising strategy to improve metabolic health and reduce obesity, insulin resistance, and type II diabetes. For unknown reasons, bilirubin levels are negatively associated with obesity and diabetes. Here, using mice and an array of approaches, including MRI to assess body composition, biochemical assays to measure bilirubin and fatty acids, MitoTracker-based mitochondrial analysis, immunofluorescence, and high-throughput coregulator analysis, we show that bilirubin functions as a molecular switch for the nuclear receptor transcription factor peroxisome proliferator-activated receptor α (PPARα). Bilirubin exerted its effects by recruiting and dissociating specific coregulators in WAT, driving the expression of PPARα target genes such as uncoupling protein 1 (Ucp1) and adrenoreceptor β 3 (Adrb3). We also found that bilirubin is a selective ligand for PPARα and does not affect the activities of the related proteins PPARγ and PPARδ. We further found that diet-induced obese mice with mild hyperbilirubinemia have reduced WAT size and an increased number of mitochondria, associated with a restructuring of PPARα-binding coregulators. We conclude that bilirubin strongly affects organismal body weight by reshaping the PPARα coregulator profile, remodeling WAT to improve metabolic function, and reducing fat accumulation.

Tat-Biliverdin Reductase A Exerts a Protective Role in Oxidative Stress-Induced Hippocampal Neuronal Cell Damage by Regulating the Apoptosis and MAPK Signaling

Reactive oxygen species (ROS) is major risk factor in neuronal diseases including ischemia. Although biliverdin reductase A (BLVRA) plays a pivotal role in cell survival via its antioxidant function, its role in hippocampal neuronal (HT-22) cells and animal ischemic injury is not clearly understood yet. In this study, the effects of transducible fusion protein Tat-BLVRA on H₂O₂-induced HT-22 cell death and in an animal ischemia model were investigated. Transduced Tat-BLVRA markedly inhibited cell death, DNA fragmentation, and generation of ROS. Transduced Tat-BLVRA inhibited the apoptosis and mitogen activated protein kinase (MAPK) signaling pathway and it passed through the blood-brain barrier (BBB) and significantly prevented hippocampal cell death in an ischemic model. These results suggest that Tat-BLVRA provides a possibility as a therapeutic molecule for ischemia.

The Effect of Silibinin on Protein Expression Profile in White Adipose Tissue of Obese Mice

Objective

To investigate the effect of silibinin on the protein expression profile of white adipose tissue (WAT) in obese mice by using Tandem Mass Tag (TMT) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Methods

According to experimental requirements, 36 C57BL/6JC mice were randomly divided into normal diet group (WC group), high fat diet group (WF group), and high fat diet + silibinin group (WS group). WS group was intragastrically administered with 54 mg/kg body weight of silibinin, and the WC group and the WF group were intragastrically administered with equal volume of normal saline. Serum samples were collected to detect fasting blood glucose and blood lipids. IPGTT was used to measure the blood glucose value at each time point and calculate the area under the glucose curve. TMT combined with LC-MS/MS were used to study the expression of WAT, and its cellular processes, biological processes, corresponding molecular functions, and related network molecular mechanisms were analyzed by bioinformatics. Finally, RT-PCR and LC-MS/MS were used to detect the mRNA and protein expressions of FABP5, Plin4, GPD1, and AGPAT2, respectively.

Results

Although silibinin did not reduce the mice's weight, it did improve glucose metabolism. In addition, silibinin decreased the concentration of TC, TG, and LDL-C and increased the concentration of HDL-C in the serum of mice. In the WF/WS group, 182 differentially expressed proteins were up-regulated and 159 were down-regulated. While in the WS/WF group, 362 differentially expressed proteins were up-regulated and 176 were down-regulated. Further analysis found that these differential proteins are mainly distributed in the peroxisome proliferation-activated receptor (PPAR), lipolysis of fat cells, metabolism of glycerides, oxidative phosphorylation, and other signaling pathways, and participate in cell processes and lipid metabolism through catalysis and integration functions. Specifically, silibinin reduced the expression of several key factors such as FABP5, Plin4, GPD1, and AGPTA2.

Conclusion

High fat diet (HFD) can increase the expression of lipid synthesis and transport-related proteins and reduce mitochondrial related proteins, thereby increasing lipid synthesis, reducing energy consumption, and improving lipid metabolism in vivo. Silibinin can reduce lipid synthesis, increase energy consumption, and improve lipid metabolism in mice in vivo.

Biliverdin Reductase A (BVRA) Knockout in Adipocytes Induces Hypertrophy and Reduces Mitochondria in White Fat of Obese Mice

Biliverdin reductase (BVR) is an enzymatic and signaling protein that has multifaceted roles in physiological systems. Despite the wealth of knowledge about BVR, no data exist regarding its actions in adipocytes. Here, we generated an adipose-specific deletion of biliverdin reductase-A (BVRA) (Blvra^FatKO) in mice to determine the function of BVRA in adipocytes and how it may impact adipose tissue expansion. The Blvra^FatKO and littermate control (Blvra^Flox) mice were placed on a high-fat diet (HFD) for 12 weeks. Body weights were measured weekly and body composition, fasting blood glucose and insulin levels were quantitated at the end of the 12 weeks. The data showed that the percent body fat and body weights did not differ between the groups; however, Blvra^FatKO mice had significantly higher visceral fat as compared to the Blvra^Flox. The loss of adipocyte BVRA decreased the mitochondrial number in white adipose tissue (WAT), and increased inflammation and adipocyte size, but this was not observed in brown adipose tissue (BAT). There were genes significantly reduced in WAT that induce the browning effect such as Ppara and Adrb3, indicating that BVRA improves mitochondria function and beige-type white adipocytes. The Blvra^FatKO mice also had significantly higher fasting blood glucose levels and no changes in plasma insulin levels, which is indicative of decreased insulin signaling in WAT, as evidenced by reduced levels of phosphorylated AKT (pAKT) and Glut4 mRNA. These results demonstrate the essential role of BVRA in WAT in insulin signaling and adipocyte hypertrophy.

Heme-Derived Metabolic Signals Dictate Immune Responses

Heme is one of the most abundant molecules in the body acting as the functional core of hemoglobin/myoglobin involved in the O2/CO2 carrying in the blood and tissues, redox enzymes and cytochromes in mitochondria. However, free heme is toxic and therefore its removal is a significant priority for the host. Heme is a well-established danger-associated molecular pattern (DAMP), which binds to toll-like receptor 4 (TLR4) to induce immune responses. Heme-derived metabolites including the bile pigments, biliverdin (BV) and bilirubin (BR), were first identified as toxic drivers of neonatal jaundice in 1800 but have only recently been appreciated as endogenous drivers of multiple signaling pathways involved in protection from oxidative stress and regulators of immune responses. The tissue concentration of heme, BV and BR is tightly controlled. Heme oxygenase-1 (HO-1, encoded by HMOX1) produces BV by heme degradation, while biliverdin reductase-A (BLVR-A) generates BR by the subsequent conversion of BV. BLVR-A is a fascinating protein that possesses a classical protein kinase domain, which is activated in response to BV binding to its enzymatic site and initiates the downstream mitogen-activated protein kinases (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways. This links BLVR-A activity to cell growth and survival pathways. BLVR-A also contains a bZip DNA binding domain and a nuclear export sequence (NES) and acts as a transcription factor to regulate the expression of immune modulatory genes. Here we will discuss the role of heme-related immune response and the potential for targeting the heme system for therapies directed toward hepatitis and cancer.

Relationship between Serum Indirect Bilirubin Level and Insulin Sensitivity: Results from Two Independent Cohorts of Obese Patients with Impaired Glucose Regulation and Type 2 Diabetes Mellitus in China

BACKGROUND

Serum bilirubin is an endogenous antioxidant that has protective effects against obesity-related metabolic diseases.

OBJECTIVES

This study aimed to evaluate the characteristics of total bilirubin (TBIL), direct bilirubin (DBIL), and indirect bilirubin (IBIL) and their relationships with insulin sensitivity in obese patients with impaired glucose regulation and type 2 diabetes mellitus (IGR/T2DM) in China. Patients and Methods. Cohort 1 comprised obese patients (n = 71) was divided into the IGR/T2DM group (n = 38, obesity with IGR/T2DM) and control group (n = 33, obesity without IGR/T2DM). Insulin sensitivity was evaluated using the hyperinsulinemic-euglycemic clamp technique (HEC) with glucose disposal rate (GDR, M value). Cohort 2 comprised obese patients with IGR/T2DM who underwent metabolic surgery (n = 109) as complementary to cohort 1. Insulin sensitivity was evaluated with the Matsuda Index and homeostatic model assessment of insulin sensitivity (HOMA-IS).

RESULTS

In cohort 1, TBIL, DBIL, and IBIL were higher within the physiological range in the IGR/T2DM group compared with the control group; IBIL was positively correlated with M value (r = 0.342, p=0.044) in the IGR/T2DM group, and multivariate logistic regression showed that IBIL might be independent protective factors against insulin resistance (odds ratio (OR) = 0.602; 95% confidence interval (CI): 0.413-0.878; p=0.008). In cohort 2, at 1 month after metabolic surgery, serum bilirubin levels (TBIL, DBIL, and IBIL) increased, and the percentage change in IBIL was positively correlated with the change of the Matsuda Index (r = 0.195, p=0.045).

CONCLUSIONS

The relationships between different types of bilirubin and insulin sensitivity varied. Serum indirect bilirubin might be a protective factor that enhances insulin sensitivity.

Role of Heme Oxygenase as a Modulator of Heme-Mediated Pathways

The heme oxygenase (HO) system is essential for heme and iron homeostasis and necessary for adaptation to cell stress. HO degrades heme to biliverdin (BV), carbon monoxide (CO) and ferrous iron. Although mostly beneficial, the HO reaction can also produce deleterious effects, predominantly attributed to excessive product formation. Underrated so far is, however, that HO may exert effects additionally via modulation of the cellular heme levels. Heme, besides being an often-quoted generator of oxidative stress, plays also an important role as a signaling molecule. Heme controls the anti-oxidative defense, circadian rhythms, activity of ion channels, glucose utilization, erythropoiesis, and macrophage function. This broad spectrum of effects depends on its interaction with proteins ranging from transcription factors to enzymes. In degrading heme, HO has the potential to exert effects also via modulation of heme-mediated pathways. In this review, we will discuss the multitude of pathways regulated by heme to enlarge the view on HO and its role in cell physiology. We will further highlight the contribution of HO to pathophysiology, which results from a dysregulated balance between heme and the degradation products formed by HO.

Bilirubin Safeguards Cardiorenal and Metabolic Diseases: a Protective Role in Health

PURPOSE OF REVIEW

To discuss recent advances indicating that bilirubin safeguards against cardiorenal and metabolic diseases.

RECENT FINDINGS

Several investigations from human patient populations and experimental animal models have shown that bilirubin improves cardiorenal and metabolic dysfunction. The latest studies found an entirely new function of bilirubin suggesting that it acts as a hormone signaling molecule capable of activating nuclear receptors for burning fat, which may explain several of its protective actions. This review highlights the current findings (within the last 3 years) regarding cardiorenal and metabolic protective effects of bilirubin and the latest mechanism(s) that may be mediating these effects.

CRISPR Cas9-mediated deletion of biliverdin reductase A (BVRA) in mouse liver cells induces oxidative stress and lipid accumulation

Obesity is the predominant cause of non-alcoholic fatty liver disease (NAFLD), which is associated with insulin resistance and diabetes. NAFLD includes a spectrum of pathologies that starts with simple steatosis, which can progress to non-alcoholic steatohepatitis (NASH) with the commission of other factors such as the enhancement of reactive oxygen species (ROS). Biliverdin reductase A (BVRA) reduces biliverdin to the antioxidant bilirubin, which may serve to prevent NAFLD, and possibly the progression to NASH. To further understand the role of BVRA in hepatic function, we used CRISPR-Cas9 technology to target the Blvra gene in the murine hepa1c1c7 hepatocyte cell line (BVRA KO). BVRA activity and protein levels were significantly lower in BVRA KO vs. wild-type (WT) hepatocytes. Lipid accumulation under basal and serum-starved conditions was significantly (p < 0.05) higher in BVRA KO vs. WT cells. The loss of BVRA resulted in the reduction of mitochondria number, decreased expression of markers of mitochondrial biogenesis, uncoupling, oxidation, and fusion, which paralleled reduced mitochondrial oxygen consumption. BVRA KO cells exhibited increased levels of ROS generation and decreased levels of superoxide dismutase mRNA expression. In conclusion, our data demonstrate a critical role for BVRA in protecting against lipid accumulation and oxidative stress in hepatocytes, which may serve as a future therapeutic target for NAFLD and its progression to NASH.

Loss of hepatic PPARα promotes inflammation and serum hyperlipidemia in diet-induced obesity

Agonists for PPARα are used clinically to reduce triglycerides and improve high-density lipoprotein (HDL) cholesterol levels in patients with hyperlipidemia. Whether the mechanism of PPARα activation to lower serum lipids occurs in the liver or other tissues is unknown. To determine the function of hepatic PPARα on lipid profiles in diet-induced obese mice, we placed hepatocyte-specific peroxisome proliferator-activated receptor-α (PPARα) knockout (Ppara^HepKO) and wild-type (Ppara^fl/fl) mice on high-fat diet (HFD) or normal fat diet (NFD) for 12 wk. There was no significant difference in weight gain, percent body fat mass, or percent body lean mass between the groups of mice in response to HFD or NFD. Interestingly, the Ppara^HepKO mice on HFD had worsened hepatic inflammation and a significant shift in the proinflammatory M1 macrophage population. These changes were associated with higher hepatic fat mass and decreased hepatic lean mass in the Pparα^HepKO on HFD but not in NFD as measured by Oil Red O and noninvasive EchoMRI analysis (31.1 ± 2.8 vs. 20.2 ± 1.5, 66.6 ± 2.5 vs. 76.4 ± 1.5%, P < 0.05). We did find that this was related to significantly reduced peroxisomal gene function and lower plasma β-hydroxybutyrate in the Ppara^HepKO on HFD, indicative of reduced metabolism of fats in the liver. Together, these provoked higher plasma triglyceride and apolipoprotein B100 levels in the Ppara^HepKO mice compared with Ppara^fl/fl on HFD. These data indicate that hepatic PPARα functions to control inflammation and liver triglyceride accumulation that prevent hyperlipidemia.

HO-1 overexpression and underexpression: Clinical implications

In this review we examine the effects of both over- and under-production of heme oxygenase-1 (HO-1) and HO activity on a broad spectrum of biological systems and on vascular disease. In a few instances e.g., neonatal jaundice, overproduction of HO-1 and increased HO activity results in elevated levels of bilirubin requiring clinical intervention with inhibitors of HO activity. In contrast HO-1 levels and HO activity are low in obesity and the HO system responds to mitigate the deleterious effects of oxidative stress through increased levels of bilirubin (anti-inflammatory) and CO (anti-apoptotic) and decreased levels of heme (pro-oxidant). Site specific HO-1 overexpression diminishes adipocyte terminal differentiation and lipid accumulation of obesity mediated release of inflammatory molecules. A series of diverse strategies have been implemented that focus on increasing HO-1 and HO activity that are central to reversing the clinical complications associated with diseases including, obesity, metabolic syndrome and vascular disease.

Bilirubin and Endothelial Function

Bilirubin is a fundamental metabolic end product of heme degradation. Despite acting as a cytotoxic metabolite at high concentrations, bilirubin at physiological concentrations has antioxidant effects, such as scavenging reactive oxygen species, leading to a decrease in oxidative stress. Endothelial dysfunction is an early feature of and plays an important role in the development and progression of atherosclerosis, leading to cardiovascular complications. One mechanism of endothelial dysfunction is an increase in oxidative stress, by which the bioavailability of nitric oxide is decreased. Therefore, bilirubin is expected to improve endothelial function, to inhibit the progression of atherosclerosis, and to reduce cardiovascular complications by inactivating oxidative stress through its antioxidant effects. In this review, we will focus on the clinical associations of the antioxidant bilirubin with endothelial function and cardiovascular complications.

RNA sequencing in human HepG2 hepatocytes reveals PPAR-α mediates transcriptome responsiveness of bilirubin

Bilirubin is a potent antioxidant that reduces inflammation and the accumulation of fat. There have been reports of gene responses to bilirubin, which was mostly attributed to its antioxidant function. Using RNA sequencing, we found that biliverdin, which is rapidly reduced to bilirubin, induced transcriptome responses in human HepG2 hepatocytes in a peroxisome proliferator-activated receptor (PPAR)-α-dependent fashion (398 genes with >2-fold change; false discovery rate P < 0.05). For comparison, a much narrower set of genes demonstrated differential expression when PPAR-α was suppressed via lentiviral shRNA knockdown (23 genes). Gene set enrichment analysis revealed the bilirubin-PPAR-α transcriptome mediates pathways for oxidation-reduction processes, mitochondrial function, response to nutrients, fatty acid oxidation, and lipid homeostasis. Together, these findings suggest that transcriptome responses from the generation of bilirubin are mostly PPAR-α dependent, and its antioxidant function regulates a smaller set of genes.

Reduced biliverdin reductase-A levels are associated with early alterations of insulin signaling in obesity

Biliverdin reductase-A (BVR-A) is a serine/threonine/tyrosine kinase involved in the regulation of insulin signaling. In vitro studies have demonstrated that BVR-A is a substrate of the insulin receptor and regulates IRS1 by avoiding its aberrant activation, and in animal model of obesity the loss of hepatic BVR-A has been associated with glucose/insulin alterations and fatty liver disease. However, no studies exist in humans. Here, we evaluated BVR-A expression levels and activation in peripheral blood mononuclear cells (PBMC) from obese subjects and matched lean controls and we investigated the related molecular alterations of the insulin along with clinical correlates. We showed that BVR-A levels are significantly reduced in obese subjects and associated with a hyper-activation of the IR/IRS1/Akt/GSK-3β/AS160/GLUT4 pathway. Low BVR-A levels also associate with the presence of obesity, metabolic syndrome, NASH and visceral adipose tissue inflammation. These data suggest that the reduction of BVR-A may be responsible for early alterations of the insulin signaling pathway in obesity and in this context may represent a novel molecular target to be investigated for the comprehension of the process of insulin resistance development in obesity.

Beyond a Measure of Liver Function-Bilirubin Acts as a Potential Cardiovascular Protector in Chronic Kidney Disease Patients

Bilirubin is a well-known neurotoxin in newborn infants; however, current evidence has shown that a higher serum bilirubin concentration in physiological ranges is associated with a lower risk for the development and progression of both chronic kidney disease (CKD) and cardiovascular disease (CVD) in adults. The protective mechanisms of bilirubin in CVD, CKD, and associated mortality may be ascribed to its antioxidant and anti-inflammatory properties. Bilirubin further improves insulin sensitivity, reduces low-density lipoprotein cholesterol levels and inhibits platelet activation in at-risk individuals. These effects are expected to maintain normal vascular homeostasis and thus reduce the incidence of CKD and the risks of cardiovascular complications and death. In this review, we highlight the recent advances in the biological actions of bilirubin in the pathogenesis of CVD and CKD progression, and further propose that targeting bilirubin metabolism could be a potential approach to ameliorate morbidity and mortality in CKD patients.

Is it worth expending energy to convert biliverdin into bilirubin?

Bilirubin (BR) is generated by the reduction of biliverdin (BV), a metabolite that results from the catalytic degradation of heme by the isoforms of heme oxygenase (HO). BV is nontoxic and water-soluble but BR is potentially toxic and lipophilic. Therefore, a further metabolic step is required for BR before excretion is possible. The reductive conversion of BV to BR costs energy and is evolutionarily conserved in human physiology. There must be a compelling reason for this apparently nonsensical evolutionary conservation. In addition to the differences between BR and BV-such as water solubility, antioxidant activity, and participation as a receptor ligand-in the present study, we focused on the chemistry of the two metabolites with regard to an electrophilic functional group called a Michael reaction acceptor (MRA). Our data reveal that the BR reacts with thiol compounds forming adducts, whereas no reaction occurs with BV. Furthermore, the binding of biotin-tagged BR to Kelch-like ECH-associated protein 1 (KEAP1)-a biological electrophile sensor-was prevented by pretreatment with BR or a thiol compound, but was not by pretreatment with BV. In cells, BR could bind to KEAP1 to release and activate nuclear factor-erythroid 2 (NF-E2) p45-related factor 2, a cytoprotective transcription factor, leading to the induction of HO-1. These findings may provide a physiological rationale for the energy-consuming conversion of BV to BR.

Bilirubin, a new therapeutic for kidney transplant?

In patients with end-stage renal disease, kidney transplantation has been associated with numerous benefits, including increased daily activity, and better survival rates. However, over 20% of kidney transplants result in rejection within five years. Rejection is primarily due to a hypersensitive immune system and ischemia/reperfusion injury. Bilirubin has been shown to be a potent antioxidant that is capable of potentially reversing or preventing damage from reactive oxygen species generated from ischemia and reperfusion. Additionally, bilirubin has several immunomodulatory effects that can dampen the immune system to promote organ acceptance. Increased bilirubin has also been shown to have a positive impact on renal hemodynamics, which is critical post-transplantation. Lastly, bilirubin levels have been correlated with biomarkers of successful transplantation. In this review, we discuss a multitude of potentially beneficial effects that bilirubin has on kidney acceptance of transplantation based on numerous clinical trials and animal models. Exogenous bilirubin delivery or increasing endogenous levels pre- or post-transplantation may have therapeutic benefits.

Biliverdin reductase and bilirubin in hepatic disease

The buildup of fat in the liver (hepatic steatosis) is the first step in a series of incidents that may drive hepatic disease. Obesity is the leading cause of nonalcoholic fatty liver disease (NAFLD), in which hepatic steatosis progresses to liver disease. Chronic alcohol exposure also induces fat accumulation in the liver and shares numerous similarities to obesity-induced NAFLD. Regardless of whether hepatic steatosis is due to obesity or long-term alcohol use, it still may lead to hepatic fibrosis, cirrhosis, or possibly hepatocellular carcinoma. The antioxidant bilirubin and the enzyme that generates it, biliverdin reductase A (BVRA), are components of the heme catabolic pathway that have been shown to reduce hepatic steatosis. This review discusses the roles for bilirubin and BVRA in the prevention of steatosis, their functions in the later stages of liver disease, and their potential therapeutic application.

Loss of biliverdin reductase-A promotes lipid accumulation and lipotoxicity in mouse proximal tubule cells

Obesity and increased lipid availability have been implicated in the development and progression of chronic kidney disease. One of the major sites of renal lipid accumulation is in the proximal tubule cells of the kidney, suggesting that these cells may be susceptible to lipotoxicity. We previously demonstrated that loss of hepatic biliverdin reductase A (BVRA) causes fat accumulation in livers of mice on a high-fat diet. To determine the role of BVRA in mouse proximal tubule cells, we generated a CRISPR targeting BVRA for a knockout in mouse proximal tubule cells (BVRA KO). The BVRA KO cells had significantly less metabolic potential and mitochondrial respiration, which was exacerbated by treatment with palmitic acid, a saturated fatty acid. The BVRA KO cells also showed increased intracellular triglycerides which were associated with higher fatty acid uptake gene cluster of differentiation 36 as well as increased de novo lipogenesis as measured by higher neutral lipids. Additionally, neutrophil gelatinase-associated lipocalin 1 expression, annexin-V FITC staining, and lactate dehydrogenase assays all demonstrated that BVRA KO cells are more sensitive to palmitic acid-induced lipotoxicity than wild-type cells. Phosphorylation of BAD which plays a role in cell survival pathways, was significantly reduced in palmitic acid-treated BVRA KO cells. These data demonstrate the protective role of BVRA in proximal tubule cells against saturated fatty acid-induced lipotoxicity and suggest that activating BVRA could provide a benefit in protecting from obesity-induced kidney injury.

Bilirubin in the Liver-Gut Signaling Axis

Bilirubin is a component of the heme catabolic pathway that is essential for liver function and has been shown to reduce hepatic fat accumulation. High plasma bilirubin levels are reflective of liver disease due to an injurious effect on hepatocytes. In healthy liver, bilirubin is conjugated and excreted to the intestine and converted by microbes to urobilinoids, which are reduced to the predominant pigment in feces, stercobilin, or reabsorbed. The function of urobilinoids in the gut or their physiological relevance of reabsorption is not well understood. In this review, we discuss the relationship of hepatic bilirubin signaling to the intestinal microbiota and its regulation of the liver-gut axis, as well as its capacity to mediate these processes.

Redox Functions of Heme Oxygenase-1 and Biliverdin Reductase in Diabetes

In patients with diabetes, the hyperglycemia-driven excess generation of reactive oxygen species (ROS) induces oxidative stress (OS) in a variety of tissues. OS is closely associated with chronic inflammation and has a key role in the pathogenesis of vascular complications. The enzymes that generate ROS and gasotransmitters are redox regulated and are implicated in cellular signaling. As a result of cellular metabolism, cells produce significant amounts of carbon monoxide (CO), mainly from heme degradation catalyzed by heme oxygenases (HOs). These reactions also generate biliverdin, bilirubin (BR), and iron. The conversion of biliverdin to BR is catalyzed by biliverdin reductase-A (BVR-A). In this review, we focus on the importance of the HO-1/CO system and BVR in the pathophysiology and therapy of inflammation associated with diabetes.

A Novel Fluorescence-Based Assay for the Measurement of Biliverdin Reductase Activity

Biliverdin reductase (BVR) is the enzyme responsible for the last step in the production of bilirubin from the breakdown of heme. Bilirubin is one of the most potent antioxidant molecules in the body. Monitoring BVR activity is essential in studying the antioxidant capacity of cells and tissues. Traditional methods of determining BVR activity have relied on the measurement of bilirubin converted from biliverdin using absorbance spectroscopy. The approach has limited sensitivity and requires large quantities of cells or tissues. We have developed a novel fluorescence-based method utilizing the eel protein, UnaG, for the detection of bilirubin produced by BVR. The UnaG protein only fluoresces by the induction of bilirubin. We have also used this approach to measure intracellular bilirubin content of cultured cells. We validated this assay using cell lysates from mouse liver and immortalized murine hepatic cell line (Hepa1c1c7) and kidney cell line (MCT) in which BVR isoform A (BVRA) was either knocked out via CRISPR or stably overexpressed by lentivirus. Also, we tested the method using previously reported putative BVRA inhibitors, Closantel and Ebselen. These studies show a new method for measuring bilirubin intracellularly and in lysates.

A Proteomics Based Approach Reveals Differential Regulation of Visceral Adipose Tissue Proteins between Metabolically Healthy and Unhealthy Obese Patients

Obesity and the metabolic disorders that constitute metabolic syndrome are a primary cause of morbidity and mortality in the world. Nonetheless, the changes in the proteins and the underlying molecular pathways involved in the relevant pathogenesis are poorly understood. In this study a proteomic analysis of the visceral adipose tissue isolated from metabolically healthy and unhealthy obese patients was used to identify presence of altered pathway(s) leading to metabolic dysfunction. Samples were obtained from 18 obese patients undergoing bariatric surgery and were subdivided into two groups based on the presence or absence of comorbidities as defined by the International Diabetes Federation. Two dimensional difference in-gel electrophoresis coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was carried out. A total of 28 proteins were identified with a statistically significant difference in abundance and a 1.5-fold change (ANOVA, p ≤ 0.05) between the groups. 11 proteins showed increased abundance while 17 proteins were decreased in the metabolically unhealthy obese compared to the healthy obese. The differentially expressed proteins belonged broadly to three functional categories: (i) protein and lipid metabolism (ii) cytoskeleton and (iii) regulation of other metabolic processes. Network analysis by Ingenuity pathway analysis identified the NFκB, IRK/MAPK and PKC as the nodes with the highest connections within the connectivity map. The top network pathway identified in our protein data set related to cellular movement, hematological system development and function, and immune cell trafficking. The VAT proteome between the two groups differed substantially between the groups which could potentially be the reason for metabolic dysfunction.

Gene Expression Profiling of Acute Lymphoblastic Leukemia in Children with Very Early Relapse

BACKGROUND AND AIMS

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer worldwide. Mexican patients have high mortality rates, low frequency of good prognosis biomarkers (i.e., ETV6-RUNX1) and a high proportion is classified at the time of diagnosis with a high risk to relapse according to clinical features. In addition, very early relapses are more frequently observed than in other populations. The aim of the study was to identify new potential biomarkers associated with very early relapse in Mexican ALL children through transcriptome analysis.

METHODS

Microarray gene expression profiling on bone marrow samples of 54 pediatric ALL patients, collected at time of diagnosis and/or at relapse, was performed. Eleven patients presented relapse within the first 18 months after diagnosis. Affymetrix Human Transcriptome Array 2.0 (HTA 2.0) was used to perform gene expression analysis. Annotation and functional enrichment analyses were carried out using Gene Ontology, KEGG pathway analysis and Ingenuity Pathway Analysis tools.

RESULTS

BLVRB, ZCCHC7, PAX5, EBF1, TMOD1 and BLNK were differentially expressed (fold-change >2.0 and p value <0.01) between relapsed and non-relapsed patients. Functional analysis of abnormally expressed genes revealed their important role in cellular processes related to the development of hematological diseases, cancer, cell death and survival and in cell-to-cell signaling interaction.

CONCLUSIONS

Our data support previous findings showing the relevance of PAX5, EBF1 and ZCCHC7 as potential biomarkers to identify a subgroup of ALL children in high risk to relapse.

HO-1 Induction in Cancer Progression: A Matter of Cell Adaptation

The upregulation of heme oxygenase-1 (HO-1) is one of the most important mechanisms of cell adaptation to stress. Indeed, the redox sensitive transcription factor Nrf2 is the pivotal regulator of HO-1 induction. Through the antioxidant, antiapoptotic, and antinflammatory properties of its metabolic products, HO-1 plays a key role in healthy cells in maintaining redox homeostasis and in preventing carcinogenesis. Nevertheless, several lines of evidence have highlighted the role of HO-1 in cancer progression and its expression correlates with tumor growth, aggressiveness, metastatic and angiogenetic potential, resistance to therapy, tumor escape, and poor prognosis, even though a tumor- and tissue-specific activity has been observed. In this review, we summarize the current literature regarding the pro-tumorigenic role of HO-1 dependent tumor progression as a promising target in anticancer strategy.

Mice with hyperbilirubinemia due to Gilbert's syndrome polymorphism are resistant to hepatic steatosis by decreased serine 73 phosphorylation of PPARα

Gilbert's syndrome in humans is derived from a polymorphism (TA repeat) in the hepatic UGT1A1 gene that results in decreased conjugation and increased levels of unconjugated bilirubin. Recently, we have shown that bilirubin binds directly to the fat-burning nuclear peroxisome proliferator-activated receptor-α (PPARα). Additionally, we have shown that serine 73 phosphorylation [Ser(P)⁷³] of PPARα decreases activity by reducing its protein levels and transcriptional activity. The aim of this study was to determine whether humanized mice with the Gilbert's polymorphism (HuUGT*28) have increased PPARα activation and reduced hepatic fat accumulation. To determine whether humanized mice with Gilbert's mutation (HuUGT*28) have reduced hepatic lipids, we placed them and C57BL/6J control mice on a high-fat (60%) diet for 36 wk. Body weights, fat and lean mass, and fasting blood glucose and insulin levels were measured every 6 wk throughout the investigation. At the end of the study, hepatic lipid content was measured and PPARα regulated genes as well as immunostaining of Ser(P)⁷³ PPARα from liver sections. The HuUGT*28 mice had increased serum bilirubin, lean body mass, decreased fat mass, and hepatic lipid content as well as lower serum glucose and insulin levels. Also, the HuUGT*28 mice had reduced Ser(P)⁷³ PPARα immunostaining in livers and increased PPARα transcriptional activity compared with controls. A chronic but mild endogenous increase in unconjugated hyperbiliubinemia protects against hepatic steatosis through a reduction in Ser(P)⁷³ PPARα, causing an increase in PPARα transcriptional activity.

Tat-biliverdin reductase A protects INS-1 cells from human islet amyloid polypeptide-induced cytotoxicity by alleviating oxidative stress and ER stress

Human islet amyloid polypeptide (hIAPP), a major constituent of islet amyloid deposits, induces pancreatic β-cell apoptosis and eventually contributes to β-cell deficit in patients with type 2 diabetes mellitus (T2DM). In this study, Tat-mediated transduction of biliverdin reductase A (BLVRA) was investigated in INS-1 cells to examine whether exogenous supplementation of BLVRA prevented hIAPP-induced apoptosis and dysfunction in insulin secretion in β-cells. Tat-BLVRA fusion protein was efficiently delivered into INS-1 cells in a time- and dose-dependent manner. Exposure of cells to hIAPP induced apoptotic cell death, which was dose-dependently inhibited by pre-treatment with Tat-BLVRA for 1 h. Transduced Tat-BLVRA reduced hIAPP-evoked generation of reactive oxygen species, a crucial mediator of β-cell destruction. Immunoblot analysis showed that Tat-BLVRA suppressed hIAPP-induced increase in the levels of proteins involved in endoplasmic reticulum (ER) stress and apoptosis signaling. Transduced Tat-BLVRA also recovered hIAPP-induced dysfunction in basal and glucose-stimulated insulin secretions. These results suggested that transduced Tat-BLVRA enhanced the tolerance of β-cells against IAPP-induced cytotoxicity by alleviating oxidative stress and ER stress. Therefore, Tat-mediated transduction of BLVRA may provide a potential tool to ameliorate β-cell deficit in pancreas with T2DM.

Differentiating tumor heterogeneity in formalin-fixed paraffin-embedded (FFPE) prostate adenocarcinoma tissues using principal component analysis of matrix-assisted laser desorption/ionization imaging mass spectral data

RATIONALE

Many patients with adenocarcinoma of the prostate present with advanced and metastatic cancer at the time of diagnosis. There is an urgent need to detect biomarkers that will improve the diagnosis and prognosis of this disease. Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) is playing a key role in cancer research and it can be useful to unravel the molecular profile of prostate cancer biopsies.

METHODS

MALDI imaging data sets are highly complex and their interpretation requires the use of multivariate statistical methods. In this study, MALDI-IMS technology, sequential principal component analysis (PCA) and two-dimensional (2-D) peak distribution tests were employed to investigate tumor heterogeneity in formalin-fixed paraffin-embedded (FFPE) prostate cancer biopsies.

RESULTS

Multivariate statistics revealed a number of mass ion peaks obtained from different tumor regions that were distinguishable from the adjacent normal regions within a given specimen. These ion peaks have been used to generate ion images and visualize the difference between tumor and normal regions. Mass peaks at m/z 3370, 3441, 3447 and 3707 exhibited stronger ion signals in the tumor regions.

CONCLUSIONS

This study reports statistically significant mass ion peaks unique to tumor regions in adenocarcinoma of the prostate and adds to the clinical utility of MALDI-IMS for analysis of FFPE tissue at a molecular level that supersedes all other standard histopathologic techniques for diagnostic purposes used in the current clinical practice. Copyright © 2016 John Wiley & Sons, Ltd.

Glucuronidation and UGT isozymes in bladder: new targets for the treatment of uroepithelial carcinomas?

Bladder cancer has been linked to numerous toxins which can be concentrated in the bladder after being absorbed into the blood and filtered by the kidneys. Excessive carcinogenic load to the bladder urothelium may result in the development of cancer. However, enzymes within the bladder can metabolize carcinogens into substrates that are safer. Importantly, these proteins, namely the UGT's (uridine 5'-diphospho-glucuronosyltransferases), have been shown to possibly prevent bladder cancer. Also, studies have shown that the UGT1 expression is decreased in uroepithelial carcinomas, which may allow for the accumulation of carcinogens in the bladder. In this review, we discuss the UGT system and its' protective role against bladder cancer, UGT genetic mutations that modulate risk from chemicals and environmental toxins, as well as targeting of the UGT enzymes by nuclear receptors.

Brain iron overload following intracranial haemorrhage

Intracranial haemorrhages, including intracerebral haemorrhage (ICH), intraventricular haemorrhage (IVH) and subarachnoid haemorrhage (SAH), are leading causes of morbidity and mortality worldwide. In addition, haemorrhage contributes to tissue damage in traumatic brain injury (TBI). To date, efforts to treat the long-term consequences of cerebral haemorrhage have been unsatisfactory. Incident rates and mortality have not showed significant improvement in recent years. In terms of secondary damage following haemorrhage, it is becoming increasingly apparent that blood components are of integral importance, with haemoglobin-derived iron playing a major role. However, the damage caused by iron is complex and varied, and therefore, increased investigation into the mechanisms by which iron causes brain injury is required. As ICH, IVH, SAH and TBI are related, this review will discuss the role of iron in each, so that similarities in injury pathologies can be more easily identified. It summarises important components of normal brain iron homeostasis and analyses the existing evidence on iron-related brain injury mechanisms. It further discusses treatment options of particular promise.

Biliverdin Reductase A Attenuates Hepatic Steatosis by Inhibition of Glycogen Synthase Kinase (GSK) 3β Phosphorylation of Serine 73 of Peroxisome Proliferator-activated Receptor (PPAR) α

Non-alcoholic fatty liver disease is the most rapidly growing form of liver disease and if left untreated can result in non-alcoholic steatohepatitis, ultimately resulting in liver cirrhosis and failure. Biliverdin reductase A (BVRA) is a multifunctioning protein primarily responsible for the reduction of biliverdin to bilirubin. Also, BVRA functions as a kinase and transcription factor, regulating several cellular functions. We report here that liver BVRA protects against hepatic steatosis by inhibiting glycogen synthase kinase 3β (GSK3β) by enhancing serine 9 phosphorylation, which inhibits its activity. We show that GSK3β phosphorylates serine 73 (Ser(P)⁷³) of the peroxisome proliferator-activated receptor α (PPARα), which in turn increased ubiquitination and protein turnover, as well as decreased activity. Interestingly, liver-specific BVRA KO mice had increased GSK3β activity and Ser(P)⁷³ of PPARα, which resulted in decreased PPARα protein and activity. Furthermore, the liver-specific BVRA KO mice exhibited increased plasma glucose and insulin levels and decreased glycogen storage, which may be due to the manifestation of hepatic steatosis observed in the mice. These findings reveal a novel BVRA-GSKβ-PPARα axis that regulates hepatic lipid metabolism and may provide unique targets for the treatment of non-alcoholic fatty liver disease.

Does bilirubin prevent hepatic steatosis through activation of the PPARα nuclear receptor?

Several large population studies have demonstrated a negative correlation between serum bilirubin levels and the development of obesity, hepatic steatosis, and cardiovascular disease. Despite the strong correlative data demonstrating the protective role of bilirubin, the mechanism by which bilirubin can protect against these pathologies remains unknown. Bilirubin has long been known as a powerful antioxidant and also has anti-inflammatory actions, each of which may contribute to the protection afforded by increased levels. We have recently described a novel function of bilirubin as a ligand for the peroxisome proliferator-activated receptor-alpha (PPARα), which we show specifically binds to the nuclear receptor. Bilirubin may function as a selective PPAR modulator (SPPARM) to control lipid accumulation and blood glucose. However, it is not known to what degree bilirubin activation of PPARα is responsible for the protection afforded to reduce hepatic steatosis. We hypothesize that bilirubin, acting as a novel SPPARM, increases hepatic fatty acid metabolism through a PPARα-dependent mechanism which reduces hepatic lipid accumulation and protects against hepatic steatosis and non-alcoholic fatty liver disease (NAFLD).

Interaction of human biliverdin reductase with Akt/protein kinase B and phosphatidylinositol-dependent kinase 1 regulates glycogen synthase kinase 3 activity: a novel mechanism of Akt activation

Biliverdin reductase A (BVR) and Akt isozymes have overlapping pleiotropic functions in the insulin/PI3K/MAPK pathway. Human BVR (hBVR) also reduces the hemeoxygenase activity product biliverdin to bilirubin and is directly activated by insulin receptor kinase (IRK). Akt isoenzymes (Akt1-3) are downstream of IRK and are activated by phosphatidylinositol-dependent kinase 1 (PDK1) phosphorylating T(308) before S(473) autophosphorylation. Akt (RxRxxSF) and PDK1 (RFxFPxFS) binding motifs are present in hBVR. Phosphorylation of glycogen synthase kinase 3 (GSK3) isoforms α/β by Akts inhibits their activity; nonphosphorylated GSK3β inhibits activation of various genes. We examined the role of hBVR in PDK1/Akt1/GSK3 signaling and Akt1 in hBVR phosphorylation. hBVR activates phosphorylation of Akt1 at S(473) independent of hBVR's kinase competency. hBVR and Akt1 coimmunoprecipitated, and in-cell Förster resonance energy transfer (FRET) and glutathione S-transferase pulldown analyses identified Akt1 pleckstrin homology domain as the interactive domain. hBVR activates phosphorylation of Akt1 at S(473) independent of hBVR's kinase competency. Site-directed mutagenesis, mass spectrometry, and kinetic analyses identified S(230) in hBVR (225)RNRYLSF sequence as the Akt1 target. Underlined amino acids are the essential residues of the signaling motifs. In cells, hBVR-activated Akt1 increased both GSK3α/β and forkhead box of the O class transcription class 3 (FoxO3) phosphorylation and inhibited total GSK3 activity; depletion of hBVR released inhibition and stimulated glucose uptake. Immunoprecipitation analysis showed that PDK1 and hBVR interact through hBVR's PDK1 binding (161)RFGFPAFS motif and formation of the PDK1/hBVR/Akt1 complex. sihBVR blocked complex formation. Findings identify hBVR as a previously unknown coactivator of Akt1 and as a key mediator of Akt1/GSK3 pathway, as well as define a key role for hBVR in Akt1 activation by PDK1.-Miralem, T., Lerner-Marmarosh, N., Gibbs, P. E. M., Jenkins, J. L., Heimiller, C., Maines, M. D. Interaction of human biliverdin reductase with Akt/protein kinase B and phosphatidylinositol-dependent kinase 1 regulates glycogen synthase kinase 3 activity: a novel mechanism of Akt activation.

Timcodar (VX-853) Is a Non-FKBP12 Binding Macrolide Derivative That Inhibits PPARγ and Suppresses Adipogenesis

Nutrient overload and genetic factors have led to a worldwide epidemic of obesity that is the underlying cause of diabetes, atherosclerosis, and cardiovascular disease. In this study, we used macrolide drugs such as FK506, rapamycin, and macrolide derived, timcodar (VX-853), to determine their effects on lipid accumulation during adipogenesis. Rapamycin and FK506 bind to FK506-binding proteins (FKBPs), such as FKBP12, which causes suppression of the immune system and inhibition of mTOR. Rapamycin has been previously reported to inhibit the adipogenic process and lipid accumulation. However, rapamycin treatment in rodents caused immune suppression and glucose resistance, even though the mice lost weight. Here we show that timcodar (1 μM), a non-FKBP12-binding drug, significantly (p < 0.001) inhibited lipid accumulation during adipogenesis. A comparison of the same concentration of timcodar (1 μM) and rapamycin (1 μM) showed that both are inhibitors of lipid accumulation during adipogenesis. Importantly, timcodar potently (p < 0.01) suppressed transcriptional regulators of adipogenesis, PPARγ and C/EBPα, resulting in the inhibition of genes involved in lipid accumulation. These studies set the stage for timcodar as a possible antiobesity therapy, which is rapidly emerging as a pandemic.

Bilirubin Binding to PPARα Inhibits Lipid Accumulation

Numerous clinical and population studies have demonstrated that increased serum bilirubin levels protect against cardiovascular and metabolic diseases such as obesity and diabetes. Bilirubin is a potent antioxidant, and the beneficial actions of moderate increases in plasma bilirubin have been thought to be due to the antioxidant effects of this bile pigment. In the present study, we found that bilirubin has a new function as a ligand for PPARα. We show that bilirubin can bind directly to PPARα and increase transcriptional activity. When we compared biliverdin, the precursor to bilirubin, on PPARα transcriptional activation to known PPARα ligands, WY 14,643 and fenofibrate, it showed that fenofibrate and biliverdin have similar activation properties. Treatment of 3T3-L1 adipocytes with biliverdin suppressed lipid accumulation and upregulated PPARα target genes. We treated wild-type and PPARα KO mice on a high fat diet with fenofibrate or bilirubin for seven days and found that both signal through PPARα dependent mechanisms. Furthermore, the effect of bilirubin on lowering glucose and reducing body fat percentage was blunted in PPARα KO mice. These data demonstrate a new function for bilirubin as an agonist of PPARα, which mediates the protection from adiposity afforded by moderate increases in bilirubin.

Translational Significance of Heme Oxygenase in Obesity and Metabolic Syndrome

The global epidemic of obesity continues unabated with sequelae of diabetes and metabolic syndrome. This review reflects the dramatic increase in research on the role of increased expression of heme oxygenase (HO)-1/HO-2, biliverdin reductase, and HO activity on vascular disease. The HO system engages with other systems to mitigate the deleterious effects of oxidative stress in obesity and cardiovascular disease (CVD). Recent reports indicate that HO-1/HO-2 protein expression and HO activity have several important roles in hemostasis and reactive oxygen species (ROS)-dependent perturbations associated with metabolic syndrome. HO-1 protects tissue during inflammatory stress in obesity through the degradation of pro-oxidant heme and the production of carbon monoxide (CO) and bilirubin, both of which have anti-inflammatory and anti-apoptotic properties. By contrast, repression of HO-1 is associated with increases of cellular heme and inflammatory conditions including hypertension, stroke, and atherosclerosis. HO-1 is a major focus in the development of potential therapeutic strategies to reverse the clinical complications of obesity and metabolic syndrome.

Evidences of Biological Functions of Biliverdin Reductase A in the Bovine Epididymis

Epididymal sperm binding protein 1 (ELSPBP1) is secreted by the epididymal epithelium via epididymosomes and is specifically transferred to dead spermatozoa during epididymal transit. We identified biliverdin reductase A (BLVRA) as a partner of ELSPBP1 by immunoprecipitation followed by tandem mass spectrometry. Pull down assays showed that these two proteins interact in the presence of zinc ions. The BLVRA enzyme is known to convert biliverdin to bilirubin, both of which possess antioxidant activity. Assessment by real-time RT-PCR showed that BLVRA is highly expressed in the caput and the corpus epididymis, but is expressed at lower levels in the testis and the cauda epididymis. It is primarily found in the soluble fraction of the caput epididymal fluid, is barely detectable in the cauda fluid, and is detectable to a lesser extent in the epididymosome fraction of both caput and cauda fluids. Immunocytometry on epididymal sperm showed that BLVRA is found on all sperm recovered from the caput region, whereas it is undetectable on cauda sperm. Biliverdin and bilirubin are found in higher concentrations in the caput epididymal fluid, as measured by mass spectrometry. Lipid peroxidation was limited by 1 μM of biliverdin, but not bilirubin when caput spermatozoa were challenged with 500 μM H2O2. Since immature spermatozoa are a source of reactive oxygen species, BLVRA may be involved in the protection of maturing spermatozoa. It is also plausible that BLVRA is implicated in haemic protein catabolism in the epididymal luminal environment.