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

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 nanotechnology: An innovative approach in biomedicine

Bilirubin, a product of heme catabolism, is toxic at elevated concentrations (>250-300 μM in blood serum), whereas at therapeutic concentrations (∼20-200 μM) exerts potent antioxidant, anti-inflammatory, immunomodulatory, cytoprotective and neuroprotective effects. Despite the therapeutic potential, its use in clinical practice is hampered by poor aqueous solubility, instability, and rapid metabolism. Nanotechnology overcomes these limitations and additionally imparts to bilirubin the advantages characteristic of nanopreparations: targeted action on the desired organ/tissue, increased therapeutic efficacy by delaying drug elimination from the body, improved transportation over biological barriers, the ability to combine therapeutic and diagnostic properties in a single agent. The review analyses the chemical synthesis, therapeutic mechanisms, and preclinical applications of nanosystems comprising bilirubin. In particular, nanostructures obtained by the covalent binding of bilirubin to macromolecules, bilirubin encapsulation in nanocarriers, bilirubin conjugation with metal nanoparticles and nanofunctionalization of inorganic compounds are considered; the data on the therapeutic trials of nanobilirubin are summarized. While studies on animal models and in vitro systems demonstrate improved biodistribution, reduced toxicity, and enhanced efficacy, no clinical trials to date have validated nanobilirubin formulations. Key barriers may include unresolved challenges in scalable synthesis, long-term biocompatibility, reproducible dosing of nanoformulations. Hence, further development of nanotherapeutic bilirubin agents for clinical practice is urgent.

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.

Urobilin Derived from Bilirubin Bioconversion Binds Albumin and May Interfere with Bilirubin Interacting with Albumin: Implications for Disease Pathology

Background/Objectives: Bilirubin is a hydrophobic molecule that binds the carrier protein albumin for transport through systemic circulation. Bilirubin is cleared from the body through the liver and excreted into the intestines, where the microbiota modifies the chemical structure, forming urobilin, which can be reabsorbed into circulation by the hepatic portal vein. Urobilin has no known function. It is also unknown whether urobilin binds albumin for transport in circulation. We hypothesized that because of the likeness of their chemical structures, urobilin would also bind albumin like bilirubin does. Methods: First, we used in silico docking to predict if urobilin would bind to albumin and compared it to the bilirubin binding sites. To test this binding in vitro, we applied bilirubin's fluorescent property, which occurs when it is bound to a protein, including albumin, and exposed to light. We also used this method to determine if urobilin could exhibit autofluorescence when protein bound. Results: We found that bilirubin was predicted to bind albumin at amino acids E208, K212, D237, and K240 through hydrogen bonds. However, urobilin was predicted to bind albumin using different hydrogen bonds at amino acids H67, K240, and E252. We found that urobilin has a fluorescent property that can be quantified when bound to albumin. We performed a concentration response for urobilin-albumin fluorescent binding and observed a direct relationship between the urobilin level and the fluorescence intensity. Conclusions: The in silico docking analysis and autofluorescence results demonstrate that urobilin binds to albumin and might compete with bilirubin. This is the first study to identify a urobilin-binding protein and the important aspects of its physiological function and transport in circulation.

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.

Bilirubin Levels in Infancy and Their Associations with Body Weight, Levels of Iron-Related Parameters and Steroid Hormone Levels

It is assumed that bilirubin is hormonally regulated and influences weight development by preventing weight gain. However, studies in healthy infants are limited. The present study established reference values for bilirubin and investigated whether bilirubin levels are significantly associated with body weight, levels of ferritin and transferrin as well as steroid hormone levels in a study population of three- and six-month-old healthy infants. Data from a total of 411 study visits from the LIFE Child study (Leipzig, Germany) were analyzed. Associations were examined using linear regression analyses. Besides laboratory parameters, anthropometric data were gathered. We found statistically significant associations between body weight and bilirubin levels. In girls, we observed additional associations between bilirubin levels and both ferritin and transferrin concentrations at three months of age. At six months, steroid hormone levels were significantly associated with concentrations of total and indirect bilirubin, with effects differing by sex. Our study thus confirms associations already reported from animal studies and studies in adult populations. Furthermore, we showed that these associations already exist in the first year of life, are influenced by sex and age and, further, depend on the bilirubin type. Our results provide reference values for bilirubin and assist, therefore, in interpreting bilirubin levels in infancy.

Intermittent glucocorticoid treatment improves muscle metabolism via the PGC1α/Lipin1 axis in an aging-related sarcopenia model

Sarcopenia burdens the older population through loss of muscle energy and mass, yet treatments to functionally rescue both parameters are lacking. The glucocorticoid prednisone remodels muscle metabolism on the basis of frequency of intake, but its mechanisms in sarcopenia are unknown. We found that once-weekly intermittent prednisone administration rescued muscle quality in aged 24-month-old mice to a level comparable to that seen in young 4-month-old mice. We discovered an age- and sex-independent glucocorticoid receptor transactivation program in muscle encompassing peroxisome proliferator-activated receptor γ coactivator 1 α (PGC1α) and its cofactor Lipin1. Treatment coordinately improved mitochondrial abundance through isoform 1 and muscle mass through isoform 4 of the myocyte-specific PGC1α, which was required for the treatment-driven increase in carbon shuttling from glucose oxidation to amino acid biogenesis. We also probed myocyte-specific Lipin1 as a nonredundant factor coaxing PGC1α upregulation to the stimulation of both oxidative and anabolic effects. Our study unveils an aging-resistant druggable program in myocytes for the coordinated rescue of energy and mass in sarcopenia.

Cardiac lipotoxicity and fibrosis underlie impaired contractility in a mouse model of metabolic dysfunction-associated steatotic liver disease

The leading cause of death among patients with metabolic dysfunction-associated steatotic liver disease (MASLD) is cardiovascular disease. A significant percentage of MASLD patients develop heart failure driven by functional and structural alterations in the heart. Previously, we observed cardiac dysfunction in hepatocyte-specific peroxisome proliferator-activated receptor alpha knockout (Ppara HepKO), a mouse model that exhibits hepatic steatosis independent of obesity and insulin resistance. The goal of the present study was to determine mechanisms that underlie hepatic steatosis-induced cardiac dysfunction in Ppara HepKO mice. Experiments were performed in 30-week-old Ppara HepKO and littermate control mice fed regular chow. We observed decreased cardiomyocyte contractility (0.17 ± 0.02 vs. 0.24 ± 0.02 μm, p < 0.05), increased cardiac triglyceride content (0.96 ± 0.13 vs. 0.68 ± 0.06 mM, p < 0.05), collagen type 1 (4.65 ± 0.25 vs. 0.31 ± 0.01 AU, p < 0.001), and collagen type 3 deposition (1.32 ± 0.46 vs. 0.05 ± 0.03 AU, p < 0.05). These changes were associated with increased apoptosis as indicated by terminal deoxynucleotidyl transferase dUTP nick end labeling staining (30.9 ± 4.7 vs. 13.1 ± 0.8%, p < 0.006) and western blots showing increased cleaved caspase-3 (0.27 ± 0.006 vs. 0.08 ± 0.01 AU, p < 0.003) and pro-caspase-3 (5.4 ± 1.5 vs. 0.5 ± 0.3 AU, p < 0.02), B-cell lymphoma protein 2-associated X (0.68 ± 0.07 vs. 0.04 ± 0.04 AU, p < 0.001), and reduced B-cell lymphoma protein 2 (0.29 ± 0.01 vs. 1.47 ± 0.54 AU, p < 0.05). We further observed elevated circulating natriuretic peptides and exercise intolerance in Ppara HepKO mice when compared to controls. Our data demonstrated that lipotoxicity, and fibrosis underlie cardiac dysfunction in MASLD.

From big data to big insights: statistical and bioinformatic approaches for exploring the lipidome

The goal of lipidomic studies is to provide a broad characterization of cellular lipids present and changing in a sample of interest. Recent lipidomic research has significantly contributed to revealing the multifaceted roles that lipids play in fundamental cellular processes, including signaling, energy storage, and structural support. Furthermore, these findings have shed light on how lipids dynamically respond to various perturbations. Continued advancement in analytical techniques has also led to improved abilities to detect and identify novel lipid species, resulting in increasingly large datasets. Statistical analysis of these datasets can be challenging not only because of their vast size, but also because of the highly correlated data structure that exists due to many lipids belonging to the same metabolic or regulatory pathways. Interpretation of these lipidomic datasets is also hindered by a lack of current biological knowledge for the individual lipids. These limitations can therefore make lipidomic data analysis a daunting task. To address these difficulties and shed light on opportunities and also weaknesses in current tools, we have assembled this review. Here, we illustrate common statistical approaches for finding patterns in lipidomic datasets, including univariate hypothesis testing, unsupervised clustering, supervised classification modeling, and deep learning approaches. We then describe various bioinformatic tools often used to biologically contextualize results of interest. Overall, this review provides a framework for guiding lipidomic data analysis to promote a greater assessment of lipidomic results, while understanding potential advantages and weaknesses along the way.

Human soluble prorenin receptor expressed in mouse renal collecting duct shows sex-specific effect on cardiorenal function

Soluble prorenin receptor (sPRR), a component of the renin-angiotensin system (RAS), has been identified as a plasma biomarker for hypertension and cardiovascular diseases in humans. Despite studies showing that sPRR in the kidney is produced by tubular cells in the renal collecting duct (CD), its biological actions modulating cardiorenal function in physiological conditions remain unknown. Therefore, the objective of our study was to investigate whether CD-derived human sPRR (HsPRR) expression influences cardiorenal function and examine sex and circadian differences. Thus, we investigated the status of the intrarenal RAS, water and electrolyte balance, renal filtration capacity, and blood pressure (BP) regulation in CD-HsPRR and control (CTL) mice. CD-HsPRR mice were generated by breeding human sPRR-Myc-tag mice with Hoxb7/Cre mice. Renal sPRR expression increased in CD-HsPRR mice, but circulating sPRR and RAS levels were unchanged compared with CTL mice. Only female littermates expressing CD-HsPRR showed 1) increased 24-h BP, 2) an impaired BP response to an acute dose of losartan and attenuated angiotensin II (ANG II)-induced hypertension, 3) reduced angiotensin-converting enzyme activity and ANG II content in the renal cortex, and 4) decreased glomerular filtration rate, with no changes in natriuresis and kaliuresis despite upregulation of the β-subunit of the epithelial Na+ channel in the renal cortex. These cardiorenal alterations were displayed only during the active phase of the day. Taken together, these data suggest that HsPRR could interact with ANG II type 1 receptors mediating sex-specific, ANG II-independent renal dysfunction and a prohypertensive phenotype in a sex-specific manner.NEW & NOTEWORTHY We successfully generated a humanized mouse model that expresses human sPRR in the collecting duct. Collecting duct-derived human sPRR did not change circulating sPRR and RAS levels but increased daytime BP in female mice while showing an attenuated angiotensin II-dependent pressor response. These findings may aid in elucidating the mechanisms by which women show uncontrolled BP in response to antihypertensive treatments targeting the RAS, improving approaches to reduce uncontrolled BP and chronic kidney disease incidences in women.

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.

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.

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.