Biliverdin protects against liver ischemia reperfusion injury in swine

Non-invasive assessment of liver fibrosis by serum metabolites in non-human primates and human patients

Liver fibrosis, a rising cause of chronic liver diseases, could eventually develop into cirrhosis and liver failure. Current diagnosis of liver fibrosis relies on pathological examination of hepatic tissues acquired from percutaneous biopsy, which may produce invasive injuries. Here, for non-invasive assessment of liver fibrosis, we applied comparative multi-omics in non-human primates (rhesus macaques) and subsequent serum biopsy in human patients. Global transcriptomics showed significant gene enrichment of metabolism process, in parallel with oxidative stress and immune responses in fibrotic primates. Targeted metabolomics were concordant with transcriptomic patterns, identifying elevated lipids and porphyrin metabolites during hepatic fibrosis. Importantly, liquid biopsy results validated that specific metabolites in the serum (e.g., biliverdin) were highly diagnostic to distinguish human patients from healthy controls. Findings describe the interconnected transcriptional and metabolic network in primate liver fibrosis and provide potential indices for non-invasive detection of liver fibrosis in humans.

Yin/Yang associated differential responses to Psoralea corylifolia Linn. In rat models: an integrated metabolomics and transcriptomics study

ETHNOPHARMACOLOGICAL RELEVANCE

Psoralea corylifolia Linn. (BGZ) is a commonly used traditional Chinese medicine (TCM) for the treatment of kidney-yang deficiency syndrome (Yangsyn) with good curative effect and security. However, BGZ was also reported to induce liver injury in recent years. According to TCM theory, taking BGZ may induce a series of adverse reactions in patients with kidney-yin deficiency syndrome (Yinsyn), which suggests that BGZ-induced liver damage may be related to its unreasonable clinical use.

AIM OF THE STUDY

Liver injury caused by TCM is a rare but potentially serious adverse drug reaction, and the identification of predisposed individuals for drug-induced liver injury (DILI) remains challenging. The study aimed to investigate the differential responses to BGZ in Yangsyn and Yinsyn rat models and identify the corresponding characteristic biomarkers.

MATERIALS AND METHODS

The corresponding animal models of Yangsyn and Yinsyn were induced by hydrocortisone and thyroxine + reserpine respectively. Body weight, organ index, serum biochemistry, and Hematoxylin and Eosin (HE) staining were used to evaluate the liver toxicity effect of BGZ on rats with Yangsyn and Yinsyn. Transcriptomics and metabonomics were used to screen the representative biomarkers (including metabolites and differentially expressed genes (DEGs)) changed by BGZ in Yangsyn and Yinsyn rats, respectively.

RESULTS

The level changes of liver organ index, alanine aminotransferase (ALT), and aspartate aminotransferase (AST), suggested that BGZ has liver-protective and liver-damaging effects on Yangsyn and Yinsyn rats, respectively, and the results also were confirmed by the pathological changes of liver tissue. The results showed that 102 DEGs and 27 metabolites were significantly regulated related to BGZ's protective effect on Yangsyn, which is mainly associated with the glycerophospholipid metabolism, arachidonic acid metabolism, pantothenate, and coenzyme A (CoA) biosynthesis pathways. While 28 DEGs and 31 metabolites, related to the pathway of pantothenate and CoA biosynthesis, were significantly regulated for the BGZ-induced liver injury in Yinsyn. Furthermore, 4 DEGs (aldehyde dehydrogenase 1 family member B1 (Aldh1b1), solute carrier family 25 member 25 (Slc25a25), Pim-3 proto-oncogene, serine/threonine kinase (Pim3), out at first homolog (Oaf)) and 4 metabolites (phosphatidate, phosphatidylcholine, N-Acetylleucine, biliverdin) in the Yangsyn group and 1 DEG [galectin 5 (Lgals5)] and 1 metabolite (5-amino-1-(5-phospho-D-ribosyl)imidazole-4-carboxylate) in Yinsyn group were significantly correlated to the ALT and AST levels of BGZ treated and untreated groups (receiver operating characteristic (ROC) ≥ 0.9).

CONCLUSIONS

Yinsyn and Yangsyn are the predisposed syndromes for BGZ to exert liver damage and liver protection respectively, which are mainly related to the regulation of amino acid metabolism, lipid metabolism, energy metabolism, and metabolism of cofactors and vitamins. The results further suggest that attention should be paid to the selection of predisposed populations when using drugs related to the regulation of energy metabolism, and the Yinsyn/Yangsyn animal models based on the theory of TCM syndromes may be a feasible method for identifying the susceptible population to receive TCM.

Current Helicobacter pylori Infection Is Associated with Early Liver Injury: A Cross-Sectional Study in the General Population

Early prevention of liver injury by controlling risk factors deserves concern because of the heavy liver disease burden. Helicobacter pylori (HP) infection affects half of the world's population and the relationship between it and early liver damage is unclear. This study focuses on assessing the correlation between them in the general population to provide clues to prevent liver disease. A total of 12,931 individuals underwent liver function and imaging tests as well as 13C/14C-urea breath tests. Results showed that the detection rate of HP was 35.9%, and the HP-positive group had a higher rate of liver injury (47.0% versus 44.5%, P = 0.007). Specifically, Fibrosis-4 (FIB-4) and alpha-fetoprotein levels in the HP-positive group were higher whereas the serum albumin level was lower. HP infection would raise the percentage of elevated aspartate aminotransferase (AST; 2.5% versus 1.7%, P = 0.006), elevated FIB-4 (20.2% versus 17.9%, P = 0.002), and abnormal liver imaging (31.0% versus 29.3%, P = 0.048). Most of these results remained stable after covariate adjustment but, for liver injury and liver imaging, the conclusions only held in young people (ORliver injury, odds ratio of liver injury, 1.127, P = 0.040; ORAST, 1.33, P = 0.034; ORFIB-4, 1.145, P = 0.032; ORimaging, 1.149, P = 0.043). Overall, HP infection might be associated with early liver injury, particularly in youth, suggesting that people with early liver injury should pay more attention to HP infection to prevent the occurrence of severe liver diseases.

Heme b inhibits class III adenylyl cyclases

Acidic lipid extracts from mouse liver, kidney, heart, brain, and lung inhibited human pseudoheterodimeric adenylyl cyclases (hACs) expressed in HEK293 cells. Using an acidic lipid extract from bovine lung, a combined MS- and bioassay-guided fractionation identified heme b as inhibitor of membrane-bound ACs. IC₅₀ concentrations were 8-12 μM for the hAC isoforms. Hemopexin and bacterial hemophore attenuated heme b inhibition of hAC5. Structurally related compounds, such as hematin, protoporphyrin IX, and biliverdin, were significantly less effective. Monomeric bacterial class III ACs (mycobacterial ACs Rv1625c; Rv3645; Rv1264; cyanobacterial AC CyaG) were inhibited by heme b with similar efficiency. Surprisingly, structurally related chlorophyll a similarly inhibited hAC5. Heme b inhibited isoproterenol-stimulated cAMP accumulation in HEK293 cells. Using cortical membranes from mouse brain hemin efficiently and reversibly inhibited basal and Gsα-stimulated AC activity. The physiological relevance of heme b inhibition of the cAMP generating system in certain pathologies is discussed.

Enterococcus faecalis promotes the progression of colorectal cancer via its metabolite: biliverdin

BACKGROUND

Enterococcus faecalis (Efa) has been shown to be a "driver bacteria" in the occurrence and development of colorectal cancer (CRC). This study aims to explore the effect of specific metabolites of Efa on CRC.

METHODS

The pro-tumor effects of Efa were assessed in colonic epithelial cells. The tumor-stimulating molecule produced by Efa was identified using liquid chromatography mass spectrometry (LC-MS). The proliferative effect of metabolites on CRC cells in vitro was assayed as well. The concentration of vascular endothelial growth factor A (VEGFA) and interleukin-8 (IL-8) was determined using enzyme-linked immunosorbent assay (ELISA). Tubular formation assay of human umbilical vein endothelial cells (HUVEC) and cell migration assay were applied to study angiogenesis. Additionally, western blot analysis was used to investigate key regulatory proteins involved in the angiogenesis pathway. Tumor growth was assessed using mouse models with two CRC cells and human colon cancer organoid.

RESULTS

Co-incubation with the conditioned medium of Efa increased the proliferation of cultured CRC cells. Biliverdin (BV) was determined as the key metabolite produced by Efa using LC-MS screening. BV promoted colony formation and cell proliferation and inhibited cell cycle arrest of cultured CRC cells. BV significantly increased the expression level of IL-8 and VEGFA by regulating the PI3K/AKT/mTOR signaling pathway, leading to the acceleration of angiogenesis in CRC. The up-regulation of proliferation and angiogenesis by BV were also confirmed in mice.

CONCLUSION

In conclusion, BV, as the tumor-stimulating metabolite of Efa, generates proliferative and angiogenic effects on CRC, which is mainly mediated by the activation of PI3K/AKT/mTOR.

Heavy metals exposure is associated with early liver dysfunction among rural residents aged 40-75 years in southwest China

Heavy metals exposure has been associated with liver dysfunction in recent reports, while the hepatoxicity of lead (Pb) and cadmium (Cd) has been well established. However, the combined effects of multi-metal in real-world scenario on liver dysfunction are still unclear. This cross-sectional study examined associations between 10 biomarkers of early liver injury and multiple heavy metals levels. The levels of heavy metals/metalloid (magnesium [Mg], calcium [Ca], iron [Fe], zinc [Zn], arsenic [As], Cd, copper [Cu], and Pb) were measured in blood and urinary sample collected from 725 participants in a Cd-polluted area and an unpolluted area in southwest China. The early liver dysfunction biomarkers included the liver enzymes (ALT, ALP, AST, and GGT), proteins (TP, ALB, and GLO), and bilirubin (TBIL, DBIL, and IBIL). Confounder-adjusted beta coefficients were determined using multiple linear regression model analysis for the group-classified and gender-classified samples. Our results showed that blood Fe, Cd, and Cu levels were found to be positively related to elevated ALT levels and blood Cu was positively associated with AST levels in the Cd-polluted area, while the highest blood Zn quartile in the polluted area and blood Mg quartile in the unpolluted area were associated with lower ALT levels. Our finding implies that industrial pollution results in heavy metals of Cd and Pb exposure and effects of Fe, Cd, Cu, and Pb in the Cd-polluted area may be the main contributors to increase the risk of liver dysfunction while Zn in the Cd-polluted area and Mg in the unpolluted area may be the protective factors.

Treatment with sodium (S)-2-hydroxyglutarate prevents liver injury in an ischemia-reperfusion model in female Wistar rats

Background

Ischemia-reperfusion (IR) injury is one of the leading causes of early graft dysfunction in liver transplantation. Techniques such as ischemic preconditioning protect the graft through the activation of the hypoxia-inducible factors (HIF), which are downregulated by the EGLN family of prolyl-4-hydroxylases, a potential biological target for the development of strategies based on pharmacological preconditioning. For that reason, this study aims to evaluate the effect of the EGLN inhibitor sodium (S)-2-hydroxyglutarate [(S)-2HG] on liver IR injury in Wistar rats.

Methods

Twenty-eight female Wistar rats were divided into the following groups: sham (SH, n = 7), non-toxicity (HGTox, n = 7, 25 mg/kg of (S)-2HG, twice per day for two days), IR (n = 7, total liver ischemia: 20 minutes, reperfusion: 60 minutes), and (S)-2HG+IR (HGIR, n = 7, 25 mg/kg of (S)-2HG, twice per day for two days, total liver ischemia as the IR group). Serum ALT, AST, LDH, ALP, glucose, and total bilirubin were assessed. The concentrations of IL-1β, IL-6, TNF, malondialdehyde, superoxide dismutase, and glutathione peroxidase were measured in liver tissue, as well as the expression of Hmox1, Vegfa, and Pdk1, determined by RT-qPCR. Sections of liver tissue were evaluated histologically, assessing the severity of necrosis, sinusoidal congestion, and cytoplasmatic vacuolization.

Results

The administration of (S)-2HG did not cause any alteration in the assessed biochemical markers compared to SH. Preconditioning with (S)-2HG significantly ameliorated IR injury in the HGIR group, decreasing the serum activities of ALT, AST, and LDH, and the tissue concentrations of IL-1β and IL-6 compared to the IR group. IR injury decreased serum glucose compared to SH. There were no differences in the other biomarkers assessed. The treatment with (S)-2HG tended to decrease the severity of hepatocyte necrosis and sinusoidal congestion compared to the IR group. The administration of (S)-2HG did not affect the expression of Hmox1 but decreased the expression of both Vegfa and Pdk1 compared to the SH group, suggesting that the HIF-1 pathway is not involved in its mechanism of hepatoprotection. In conclusion, (S)-2HG showed a hepatoprotective effect, decreasing the levels of liver injury and inflammation biomarkers, without evidence of the involvement of the HIF-1 pathway. No hepatotoxic effect was observed at the tested dose.

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 Protects Against Cerebral Ischemia/Reperfusion Injury by Regulating the miR-27a-3p/Rgs1 Axis

BACKGROUND

We have previously demonstrated that biliverdin has neuroprotective effects that ameliorate cerebral ischemia/reperfusion (I/R) injury in rats. However, the underlying mechanism is unknown. This study aimed at elucidating on the modulatory role of miR-27a-3p on Rgs1 as a mechanism by which biliverdin affects cerebral I/R injury.

METHODS

Middle cerebral artery occlusion/reperfusion (MCAO/R) was used to establish I/R rat models while oxygen glucose deprivation/reoxygenation (OGD/R) was used to induce hippocampal neurons to establish I/R models in vitro. Infarct volume was assessed by TTC staining. Apoptotic analyses of ischemic cortical neurons and cells were performed by TUNEL staining and flow cytometry, respectively. Cell viability was assessed by the CCK-8 assay while the target of miR-27a-3p was determined by double luciferase reporter assay. Relative expression levels of miR-27a-3p and Rgs1 (in vivo and in vitro) as well as markers of inflammation and apoptosis (in vitro) were detected by RT-qPCR. Then, Elisa and western blot were used to assess protein expression levels of inflammatory and apoptotic markers in vitro.

RESULTS

Biliverdin suppressed inflammation and apoptosis in hippocampal neurons upon OGD/R, and reduced cerebral infarction volume as well as apoptosis in the MCAO/R rat model. Furthermore, biliverdin upregulated miR-27a-3p and downregulated hippocampal neuron Rgs1 after OGD/R as well as in rat brain tissues after cerebral I/R. Bioinformatic analysis revealed an miR-27a-3p docking site in the 3'-UTR region of Rgs1. Luciferase reporter assays showed that Rgs1 is an miR-27a-3p target. Moreover, miR-27a-3p upregulation inhibited OGD/R-triggered inflammation and suppressed neuronal apoptosis. Rgs1 knockdown suppressed OGD/R-triggered inflammation and decreased neuronal apoptosis while miR-27a-3p downregulation reversed the protective effect of Rgs1 knockdown. Moreover, miR-27a-3p overexpression and Rgs1 silencing suppressed NF-κB (p65) expression.

CONCLUSION

Biliverdin protects against cerebral I/R injury by regulating the miR-27a-3p/Rgs1 axis, thereby inhibiting inflammation and apoptosis.

Pharmacokinetics of bilirubin-10-sulfonate and biliverdin in the rat

BACKGROUND AND PURPOSE

Biliverdin (BV) administration induces antioxidant and anti-inflammatory effects, with previous reports also identifying anti-anaphylactic potential. Interestingly however, intra-duodenal administration of BV in rats leads to the formation of bilirubin-10-sulfonate (BRS), which might be responsible for BV's purported effects.

EXPERIMENTAL APPROACH

This study aimed to assess the intravenous, intraperitoneal and intraduodenal pharmacokinetics of BRS and BV in order to assess their therapeutic potential in future studies. Bile and venous blood were intermittently collected before and after administration, which was subsequently analysed using liquid chromatography-mass spectrometry for quantification of bile pigment concentrations.

KEY RESULTS

Interestingly, i.p. BRS administration led to a greater circulating concentration and had a reduced excretion rate, which resulted in a substantially elevated AUC₁₈₀ when compared to BV administration. Furthermore, BRS was excreted intact in the bile, in contrast to BV which was excreted after chemical reduction and conjugation. Intraperitoneal and intraduodenal administration substantially increased blood BRS concentrations (p<0.05), however, the bioavailability of BV was higher than BRS following i.p. administration (i.p. BV 28.4%, BRS 15.5%) but lower following i.d. administration (i.d. BV 0.04%, BRS 0.07%), over 180 minutes. When BRS was administered i.v., BRS had a significantly (p<0.05) longer distribution (191.9 vs 54.1 minutes) half-life compared to BV, and significantly reduced (p<0.05) volume of distribution (0.026 vs 0.145 L kg^-1). As a consequence, intraperitoneal and intraduodenal administration resulted in significantly greater blood concentrations of BRS (p<0.05) over 180 minutes. Therefore, BRS may be more likely to induce antioxidant or molecular effects, when compared to BV, due to greater concentrations and a longer half-life.

CONCLUSIONS AND IMPLICATIONS

Cumulatively, these data demonstrate that BRS has a superior pharmacokinetic profile when compared to BV, which is a result of its resistance to hepatic metabolism and excretion. These data therefore provide a basis to explore the capacity of BRS to protect from inflammatory pathology.

Biliverdin and bilirubin sulfonate inhibit monosodium urate induced sterile inflammation in the rat

BACKGROUND

Biliverdin, a by-product of haem catabolism, possesses potent endogenous antioxidant and anti-inflammatory properties. Bilirubin-C10-sulfonate (BRS), an active metabolite formed after enteral administration of BV in the rat, also possess antioxidant properties. Therefore, we investigated the anti-inflammatory and antioxidant activity of BV and BRS in an in vivo model of monosodium urate induced sterile inflammation.

METHODS

Subcutaneous air pouches were created on the dorsal flanks of Wistar rats (10-12 weeks of age). Prior to stimulation of the 6-day old pouch with monosodium urate (25 mg), groups were pre-treated with intraperitoneal BRS (27 mg/kg) and BV (27 mg/kg). Total and differential leukocyte counts were determined in pouch fluid aspirate at 1, 6, 12, 24 and 48 h after monosodium urate stimulation. Biliverdin (BV), BRS and unconjugated bilirubin (UCB) concentrations in the serum and pouch fluid were quantified using liquid chromatography-mass spectrometry. Pouch fluid cytokine concentrations (IL-1β, IL-1α, TNF-α, IL-17A, IL-12, GM-CSF, IL-33, IFN-γ, IL-18, IL-10, MCP-1, CXCL-1 and IL-6) were assessed after 6 h. In addition, 24 h protein carbonyl and chloramine concentrations were assessed in pouch fluid using ELISA and spectrophotometry, respectively.

RESULTS

BRS and BV significantly (p < 0.05) inhibited leukocyte (total, neutrophil and macrophage) infiltration into the pouch fluid from 6 to 48 h. For example, after 6 h neutrophil counts decreased following BRS (0.32 ± 0.11 × 10⁶ cells mL^-1) and BV (0.17 ± 0.03 × 10⁶ cells mL^-1) compared to MSU only (3.51 ± 1.07 × 10⁶ cells mL^-1). Both BV and BRS significantly (p < 0.05) reduced pouch GM-CSF (BV: 5.8 ± 1.2 pg mL^-1, BRS: 6.9 ± 1.5 pg mL^-1 vs MSU only: 13.0 ± 1.9 pg mL^-1) and MCP-1 concentrations at 6 h (BV: 1804 ± 269 pg mL^-1, BRS: 7927 ± 2668 pg mL^-1 vs MSU only: 17,290 ± 4503 pg ml^-1), whilst BV additionally inhibited IL-6 (4354 ± 977 pg mL^-1 vs MSU only: 25,070 ± 5178 pg mL^-1) and IL-18 (17.6 ± 2.0 pg mL^-1 vs MSU only: 81.5 ± 19.9 pg mL^-1) concentrations at 6 h (p < 0.05). Despite these differences, no change in pouch chloramine or protein carbonyl concentrations occurred at 24 h (p > 0.05). Serum BV concentrations rapidly diminished over 6 h, however, BRS was readily detected in the serum over 48 h, and in pouch fluid over 12 h.

CONCLUSIONS

This study is the first to elucidate anti-inflammatory activity of BRS and the efficacy of BV administration in a model of gouty inflammation. Reduced leukocyte infiltration and cytokine production in response to sterile inflammation further support the importance of these molecules in physiology and their therapeutic potential in sterile inflammation.

Heme Oxygenase-1 in liver transplant ischemia-reperfusion injury: From bench-to-bedside

Hepatic ischemia-reperfusion injury (IRI), a major risk factor for early allograft dysfunction (EAD) and acute or chronic graft rejection, contributes to donor organ shortage for life-saving orthotopic liver transplantation (OLT). The graft injury caused by local ischemia (warm and/or cold) leads to parenchymal cell death and release of danger-associated molecular patterns (DAMPs), followed by reperfusion-triggered production of reactive oxygen species (ROS), activation of inflammatory cells, hepatocellular damage and ultimate organ failure. Heme oxygenase 1 (HO-1), a heat shock protein-32 induced under IR-stress, is an essential component of the cytoprotective mechanism in stressed livers. HO-1 regulates anti-inflammatory responses and may be crucial in the pathogenesis of chronic diseases, such as arteriosclerosis, hypertension, diabetes and steatosis. An emerging area of study is macrophage-derived HO-1 and its pivotal intrahepatic homeostatic function played in IRI-OLT. Indeed, ectopic hepatic HO-1 overexpression activates intracellular SIRT1/autophagy axis to serve as a key cellular self-defense mechanism in both mouse and human OLT recipients. Recent translational studies in rodents and human liver transplant patients provide novel insights into HO-1 mediated cytoprotection against sterile hepatic inflammation. In this review, we summarize the current bench-to-bedside knowledge on HO-1 molecular signaling and discuss their future therapeutic potential to mitigate IRI in OLT.

Therapeutic strategies for ischemia reperfusion injury in emergency medicine

Ischemia reperfusion (IR) injury occurs when blood supply, perfusion, and concomitant reoxygenation is restored to an organ or area following an initial poor blood supply after a critical time period. Ischemia reperfusion injury contributes to mortality and morbidity in many pathological conditions in emergency medicine clinical practice, including trauma, ischemic stroke, myocardial infarction, and post‐cardiac arrest syndrome. The process of IR is multifactorial, and its pathogenesis involves several mechanisms. Reactive oxygen species are considered key molecules in reperfusion injury due to their potent oxidizing and reducing effects that directly damage cellular membranes by lipid peroxidation. In general, IR injury to an individual organ causes various pro‐inflammatory mediators to be released, which could then induce inflammation in remote organs, thereby possibly advancing the dysfunction of multiple organs. In this review, we summarize IR injury in emergency medicine. Potential therapies include pharmacological treatment, ischemic preconditioning, and the use of medical gases or vitamin therapy, which could significantly help experts develop strategies to inhibit IR injury.

Plasma metals and serum bilirubin levels in workers from manganese-exposed workers healthy cohort (MEWHC)

Few studies specifically address the possible associations between multiple-metal exposures and liver damage among the occupational population. This study aimed to explore the cross-sectional relationships of plasma metals with liver function parameters. For 571 on-the-spot workers in the manganese-exposed workers healthy cohort (MEWHC), we determined liver function parameters: total bilirubin (TBILI), direct bilirubin (DBILI), indirect bilirubin (IBILI), alanine transaminase (ALT) and aspartate transaminase (AST). Total concentrations of 22 plasma metals were measured by ICP-MS. The LASSO (least absolute shrinkage and selection operator) penalized regression model was applied for selecting plasma metals independently associated with liver function parameters. Multiple linear regression analyses and restricted cubic spline (RCS) were utilized for identifying the exposure-response relationship of plasma metals with liver function parameters. After adjusting for covariates and selected metals, a 1-SD increase in log-10 transformed levels of iron was associated with increases in the levels of TBILI, DBILI and IBILI by 20.3%, 12.1% and 23.7%, respectively; similar increases in molybdenum for decreases in levels of TBILI, DBILI and IBILI by 6.1%, 2.6% and 8.3%, respectively. The effect of a 1-SD increase in plasma copper corresponded decreases of 3.2%, 3.4% and 5.0% in TBILI, AST and ALT levels, respectively. The spline analyses further clarified the non-linear relationships between plasma iron and bilirubin whilst negative linear relationships for plasma molybdenum and bilirubin. Plasma iron was positively whilst plasma molybdenum was negatively associated with increased serum bilirubin levels. Further studies are needed to validate these associations and uncover the underlying mechanisms.

Systems metabolic engineering of Corynebacterium glutamicum for the bioproduction of biliverdin via protoporphyrin independent pathway

Background

Biliverdin, a prospective recyclable antioxidant and one of the most important precursors for optogenetics, has received growing attention. Biliverdin is currently produced by oxidation of bilirubin from mammalian bile using chemicals. However, unsustainable procedures of extraction, chemical oxidation, and isomer separation have prompted bio-based production using a microbial cell factory.

Results

In vitro thermodynamic analysis was performed to show potential candidates of bottleneck enzymes in the pathway to produce biliverdin. Among the candidates, hemA and hemL were overexpressed in Corynebacterium glutamicum to produce heme, precursor of biliverdin. To increase precursor supply, we suggested a novel hemQ-mediated coproporphyrin dependent pathway rather than noted hemN-mediated protoporphyrin dependent pathway in C. glutamicum. After securing precursors, hmuO was overexpressed to pull the carbon flow to produce biliverdin. Through modular optimization using gene rearrangements of hemA, hemL, hemQ, and hmuO, engineered C. glutamicum BV004 produced 11.38 ± 0.47 mg/L of biliverdin at flask scale. Fed-batch fermentations performed in 5 L bioreactor with minimal medium using glucose as a sole carbon source resulted in the accumulation of 68.74 ± 4.97 mg/L of biliverdin, the highest titer to date to the best of our knowledge.

Conclusions

We developed an eco-friendly microbial cell factory to produce biliverdin using C. glutamicum as a biosystem. Moreover, we suggested that C. glutamicum has the thermodynamically favorable coproporphyrin dependent pathway. This study indicated that C. glutamicum can work as a powerful platform to produce biliverdin as well as heme-related products based on the rational design with in vitro thermodynamic analysis.

Electronic supplementary material

The online version of this article (10.1186/s13036-019-0156-5) contains supplementary material, which is available to authorized users.

Unprecedented Microbial Conversion of Biliverdin into Bilirubin-10-sulfonate

Biliverdin (BV) possesses antioxidant and anti-inflammatory properties, with previous reports identifying protection against oxidant and inflammatory injury in animal models. Recent reports indicate that intra-duodenal administration of BV results in the formation of an uncharacterised metabolite, which is potently absorbed into the blood and excreted into the bile. This compound may be responsible for protection against inflammatory responses. This study aimed to identify novel, enterally-derived BV metabolites and determine the source of their metabolic transformation. Rat duodena and bacterial cultures of Citrobacter youngae were treated with BV and subsequently analysed via high performance liquid chromatography/high resolution tandem mass spectrometry to identify and characterise metabolites of BV. A highly abundant metabolite was detected in duodenal wash and bacterial culture supernatants with a 663.215 m/z (3 ppm mass accuracy) and a composition of C₃₃N₄O₉H₃₆S, which conformed to the predicted structure of bilirubin-10-sulfonate (BRS) and possessed a λ_max of 440 nm. Bilirubin-10-sulfonate was then synthesized for comparative LCMS/MS analysis and matched with that of the biologically formed BV metabolite. This report confirms the formation of a previously undocumented metabolite of BV in mammals, indicating that a new metabolic pathway likely exists for BV metabolism requiring enteric bacteria, Citrobacter youngae. These data may have important implications with regard to understanding and harnessing the therapeutic efficacy of oral BV administration.

Biliverdin administration regulates the microRNA-mRNA expressional network associated with neuroprotection in cerebral ischemia reperfusion injury in rats

Inflammatory response has an important role in the outcome of cerebral ischemia reperfusion injury (CIR). Biliverdin (BV) administration can relieve CIR in rats, but the mechanism remains unknown. The aim of the present study was to explore the expressional network of microRNA (miRNA)-mRNA in CIR rats following BV administration. A rat middle cerebral artery occlusion model with BV treatment was established. After neurobehavior was evaluated by neurological severity scores (NSS), miRNA and mRNA expressional profiles were analyzed by microarray technology from the cerebral cortex subjected to ischemia and BV administration. Then, bioinformatics prediction was used to screen the correlation between miRNA and mRNA, and 20 candidate miRNAs and 33 candidate mRNAs were verified by reverse transcription-quantitative polymerase chain reaction. Furthermore, the regulation relationship between ETS proto-oncogene 1 (Ets1) and miRNA204-5p was examined by luciferase assay. A total of 86 miRNAs were differentially expressed in the BV group compared with the other groups. A total of 10 miRNAs and 26 candidate genes were identified as a core 'microRNA-mRNA' regulatory network that was linked with the functional improvement of BV administration in CIR rats. Lastly, the luciferase assay results confirmed that miRNA204-5p directly targeted Ets1. The present findings suggest that BV administration may regulate multiple miRNAs and mRNAs to improve neurobehavior in CIR rats, by influencing cell proliferation, apoptosis, maintaining ATP homeostasis, and angiogenesis.

Mesenchymal Stem Cells Ameliorate Hepatic Ischemia/Reperfusion Injury via Inhibition of Neutrophil Recruitment

Ischemia/reperfusion injury (IRI) remains a major problem in organ transplantation, which represents the main cause of graft dysfunction posttransplantation. Hepatic IRI is characterized by an excessive inflammatory response within the liver. Mesenchymal stem cells (MSCs) have been shown to be immunomodulatory cells and have the therapeutic action on IRI in several organs. However, the mechanism of regulatory effect of MSCs on IRI remains unclear. In the present study, we examined the impact of MSCs on hepatic inflammatory response such as neutrophil influx and liver damage in a rat model of 70% hepatic IRI. Treatment with MSCs protected rat against hepatic IRI, with significantly decreased serum levels of liver enzymes, attenuated hepatic neutrophil infiltration, reduced expression of apoptosis-associated proteins, and ameliorated liver pathological injury. MSCs also significantly enhanced the intracellular activation of p38 MAPK phosphorylation, which led to decreased expression of CXCR2 on the surface of neutrophils. In addition, MSCs significantly diminished neutrophil chemoattractant CXCL2 production by inhibiting NF-κB p65 phosphorylation in macrophages. These results demonstrate that MSCs significantly ameliorate hepatic IRI predominantly through its inhibitory effect on hepatic neutrophil migration and infiltration.

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.

Biliverdin Protects the Isolated Rat Lungs from Ischemia-reperfusion Injury via Antioxidative, Anti-inflammatory and Anti-apoptotic Effects

Background:

Biliverdin (BV) has a protective role against ischemia-reperfusion injury (IRI). However, the protective role and potential mechanisms of BV on lung IRI (LIRI) remain to be elucidated. Thus, we aimed to investigate the protective role and potential mechanisms of BV on LIRI.

Methods:

Lungs were isolated from Sprague-Dawley rats to establish an ex vivo LIRI model. After an initial 15 min stabilization period, the isolated lungs were subjected to ischemia for 60 min, followed by 90 min of reperfusion with or without BV treatment.

Results:

Lungs in the I/R group exhibited significant decrease in tidal volume (1.44 ± 0.23 ml/min in I/R group vs. 2.41 ± 0.31 ml/min in sham group; P < 0.001), lung compliance (0.27 ± 0.06 ml/cmH₂O in I/R group vs. 0.44 ± 0.09 ml/cmH₂O in sham group; P < 0.001; 1 cmH₂O=0.098 kPa), and oxygen partial pressure (PaO₂) levels (64.12 ± 12 mmHg in I/R group vs. 114 ± 8.0 mmHg in sham group; P < 0.001; 1 mmHg = 0.133 kPa). In contrast, these parameters in the BV group (2.27 ± 0.37 ml/min of tidal volume, 0.41 ± 0.10 ml/cmH₂O of compliance, and 98.7 ± 9.7 mmHg of PaO₂) were significantly higher compared with the I/R group (P = 0.004, P < 0.001, and P < 0.001, respectively). Compared to the I/R group, the contents of superoxide dismutase were significantly higher (47.07 ± 7.91 U/mg protein vs. 33.84 ± 10.15 U/mg protein; P = 0.005) while the wet/dry weight ratio (P < 0.01), methane dicarboxylic aldehyde (1.92 ± 0.25 nmol/mg protein vs. 2.67 ± 0.46 nmol/mg protein; P < 0.001), and adenosine triphosphate contents (297.05 ± 47.45 nmol/mg protein vs. 208.09 ± 29.11 nmol/mg protein; P = 0.005) were markedly lower in BV-treated lungs. Histological analysis revealed that BV alleviated LIRI. Furthermore, the expression of inflammatory cytokines (interleukin-1β, interleukin-6, and tumor necrosis factor-β) was downregulated and the expression of cyclooxygenase-2, inducible nitric oxide synthase, and Jun N-terminal kinase was significantly reduced in BV group (all P < 0.01 compared to I/R group). Finally, the apoptosis index in the BV group was significantly decreased (P < 0.01 compared to I/R group).

Conclusion:

BV protects lung IRI through its antioxidative, anti-inflammatory, and anti-apoptotic effects.

Exogenous vascular endothelial growth factor delivery prior to endothelial precursor cell transplantation in orthotopic liver transplantation-induced hepatic ischemia/reperfusion injury

Vascular endothelial growth factor (VEGF) promotes angiogenesis in vivo. We hypothesized that exogenous delivery of VEGF prior to bone marrow-derived endothelial precursor cell (EPC) transplantation may improve orthotopic liver transplantation (OLT)-induced hepatic ischemia/reperfusion injury (HIRI). OLT between Sprague Dawley donor rats and inbred LEW Wistar recipient rats was performed in 6 experimental groups to comparatively assess the effects of the VEGF gene: an untreated normal control group, a surgical control group, a liposomal control group, a VEGF group receiving only the liposome-encapsulated VEGF plasmid, an EPC group receiving only EPCs, and an EPC+VEGF group receiving the liposome-encapsulated VEGF plasmid followed by EPCs. VEGF plasmid delivery to liver tissue, endogenous VEGF, and vascular endothelial growth factor receptor (VEGFR) expression, liver transaminase levels, hepatocellular injury levels, apoptosis, apoptotic biomarkers, hepatotrophic mitogens, angiogenesis, and nitric oxide synthase (NOS) activity were assayed after OLT. Exogenous VEGF gene delivery prior to EPC transplantation significantly increased endogenous VEGF and VEGFR expression, significantly reduced liver transaminase levels, significantly reduced hepatocellular injury levels, significantly reduced hepatic apoptosis levels, and significantly reduced several apoptotic biomarkers (ie, B cell lymphoma 2-associated X protein/B cell lymphoma 2 ratio, caspase 3 activity, and heat shock protein 70 expression) in post-OLT-induced HIRI. Moreover, VEGF gene delivery prior to EPC transplantation significantly increased hepatotrophic mitogen expression (ie, epidermal growth factor, heparin-binding epidermal growth factor-like growth factor, hepatocyte growth factor, and transforming growth factor α), angiogenesis, and NOS activity in post-OLT-induced HIRI. In conclusion, exogenous liposomal delivery of the VEGF gene prior to bone marrow-derived EPC transplantation may be an effective strategy in decreasing OLT-induced HIRI. Liver Transplantation 23 804-812 2017 AASLD.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

Heme as a danger molecule in pathogen recognition

Appropriate control of redox mechanisms are critical for and effective innate immune response, which employs multiple cell types, receptors and molecules that recognize danger signals when they reach the host. Recognition of pathogen-associated pattern molecules (PAMPs) is a fundamental host survival mechanism for efficient elimination of invading pathogens and resolution of the infection and inflammation. In addition to PAMPs, eukaryotic cells contain a plethora of intracellular molecules that are normally secured within the confines of the plasma membrane, but if liberated and encountered in the extracellular milieu can provoke rapid cell activation. These are known as Alarmins or Danger-Associated Molecular Patterns (DAMPs) and can be released actively by cells or passively as a result of sterile cellular injury after trauma, ischemia, or toxin-induced cell rupture. Both PAMPs and DAMPs are recognized by a series of cognate receptors that increase the generation of free radicals and activate specific signaling pathways that result in regulation of a variety of stress response, redox sensitive genes. Multiple mediators released, as cells die include, but are not limited to ATP, hydrogen peroxide, heme, formyl peptides, DNA or mitochondria provide the second signal to amplify immune responses. In this review, we will focus on how sterile and infective stimuli activate the stress response gene heme oxygenase-1 (Hmox1, HO-1), a master gene critical to an appropriate host response that is now recognized as one with enormous therapeutic potential. HO-1 gene expression is regulated in large part by redox-sensitive proteins including but not limited to nrf2. Both PAMPs and DAMPs increase the activation of nrf2 and HO-1. Heme is a powerful pro-oxidant and as such should be qualified as a DAMP. With its degradation by HO-1a molecule of carbon monoxide (CO) is generated that in turn serves as a bioactive signaling molecule. PAMPs such as bacterial endotoxin activate HO-1, and the CO that is generated diffuses into the extracellular milieu where it interacts with bacteria, altering their behavior to increase production of ATP, which then functions as a second signal danger molecule. This two-hit cycle scenario results in efficient and effective activation of host leukocytes to attack and clear bacteria in part via enhanced reactive oxygen species generation. We discuss this intimate communication that occurs between host and bacteria and how these molecules serve as critical regulators of the acute inflammatory response, the overall redox status of the cell, and survival of the host.

Molecular pathways in protecting the liver from ischaemia/reperfusion injury: a 2015 update

Ischaemia/reperfusion injury is an important cause of liver damage during surgical procedures such as hepatic resection and liver transplantation, and represents the main cause of graft dysfunction post-transplantation. Molecular processes occurring during hepatic ischaemia/reperfusion are diverse, and continuously include new and complex mechanisms. The present review aims to summarize the newest concepts and hypotheses regarding the pathophysiology of liver ischaemia/reperfusion, making clear distinction between situations of cold and warm ischaemia. Moreover, the most updated therapeutic strategies including pharmacological, genetic and surgical interventions, as well as some of the scientific controversies in the field are described.

Intraperitoneally administered biliverdin protects against UVB-induced skin photo-damage in hairless mice

Oxidative stress is shown to be responsible for ultraviolet B (UVB) irradiation-induced skin cancer and premature aging. Biliverdin (BVD), a product of heme oxygenase-1, has strong anti-oxidant and anti-inflammatory properties. In the present study, we investigated the effects of BVD on UVB-induced skin photo-damage in hairless mice. Mice were divided into three groups: control group, UVB group (only UVB irradiation) and BVD+UVB group (mice were intraperitoneally injected with BVD before each UVB irradiation). Intraperitoneal BVD injection resulted in a significant photoprotective effect by reducing morphological and histopathological changes to the skin. BVD also exhibited a significant antioxidant effect by increasing the superoxide dismutase (SOD) level and decreasing the thiobarbituric acid reactive substances (TBARS) level compared with the control group. In addition, BVD activated biliverdin reductase (BVR) expression and inhibited the UVB-induced increase of p38 mitogen-activated protein kinase phosphorylation (p-p38MAPK), MMP (matrix metalloproteinase)-1 and MMP-3 expression (p<0.05). It also significantly decreased the interleukin (IL)-6 level compared with the UVB group (p<0.05). In conclusion, these data suggest that the intraperitoneally administered BVD can prevent UVB irradiation-induced skin photo-damage in hairless mice and that this is likely mediated by its antioxidant and anti-inflammatory mechanisms and cell signal regulatory action.

Endogenous Tetrapyrroles Influence Leukocyte Responses to Lipopolysaccharide in Human Blood: Pre-Clinical Evidence Demonstrating the Anti-Inflammatory Potential of Biliverdin

Sepsis is associated with abnormal host immune function in response to pathogen exposure, including endotoxin (lipopolysaccharide; LPS). Cytokines play crucial roles in the induction and resolution of inflammation in sepsis. Therefore, the primary aim of this study was to investigate the effects of endogenous tetrapyrroles, including biliverdin (BV) and unconjugated bilirubin (UCB) on LPS-induced cytokines in human blood. Biliverdin and UCB are by products of haem catabolism and have strong cytoprotective, antioxidant and anti-inflammatory effects. In the present study, whole human blood supplemented with BV and without was incubated in the presence or absence of LPS for 4 and 8 hours. Thereafter, whole blood was analysed for gene and protein expression of cytokines, including IL-1β, IL-6, TNF, IFN-γ, IL-1Ra and IL-8. Biliverdin (50 μM) significantly decreased the LPS-mediated gene expression of IL-1β, IL-6, IFN-γ, IL-1Ra and IL-8 (P<0.05). Furthermore, BV significantly decreased LPS-induced secretion of IL-1β and IL-8 (P<0.05). Serum samples from human subjects and, wild type and hyperbilirubinaemic Gunn rats were also used to assess the relationship between circulating bilirubin and cytokine expression/production. Significant positive correlations between baseline UCB concentrations in human blood and LPS-mediated gene expression of IL-1β (R=0.929), IFN-γ (R=0.809), IL-1Ra (R=0.786) and IL-8 (R=0.857) were observed in blood samples (all P<0.05). These data were supported by increased baseline IL-1β concentrations in hyperbilirubinaemic Gunn rats (P<0.05). Blood samples were also investigated for complement receptor-5 (C5aR) expression. Stimulation of blood with LPS decreased gene expression of C5aR (P<0.05). Treatment of blood with BV alone and in the presence of LPS tended to decrease C5aR expression (P=0.08). These data indicate that supplemented BV inhibits the ex vivo response of human blood to LPS. Surprisingly, however, baseline UCB was associated with heighted inflammatory response to LPS. This is the first study to explore the effects of BV in a preclinical human model of inflammation and suggests that BV could represent an anti-inflammatory target for the prevention of LPS mediated inflammation in vivo.