Exogenous biliverdin improves the function of lung grafts from brain dead donors in rats

Biliverdin as a disease-modifying agent: An integrated viewpoint

Biliverdin is one of the three by-products of heme oxygenase (HO) activity, the others being ferrous iron and carbon monoxide. Under physiological conditions, once formed in the cell, BV is reduced to bilirubin (BR) by the biliverdin reductase (BVR). However, if BVR is inhibited by either genetic variants, as occurs in the Inuit ethnicity, or dioxin intoxication, BV accumulates in cells giving rise to a clinical syndrome known as green jaundice. Preclinical studies have demonstrated that BV not only has a direct antioxidant effect by scavenging free radicals, but also targets many signal transduction pathways, such as BVR, soluble guanylyl cyclase, and the aryl hydrocarbon receptor. Through these direct and indirect mechanisms, BV has shown beneficial roles in ischemia/reperfusion-related diseases, inflammatory diseases, graft-versus-host disease, viral infections and cancer. Unfortunately, no clinical data are available to confirm these potential therapeutic effects and the kinetics of exogenous BV in humans is unknown. These limitations have so far excluded the possibility of transforming BV from a mere by-product of heme degradation into a disease-modifying agent. A closer collaboration between basic and clinical researchers would be advantageous to overcome these issues and promote translational research on BV in free radical-induced diseases.

Effects of Exogenous Biliverdin Treatment on Neurobehaviors in Mice

The neuroprotective effects of heme oxygenase (HO) have been well investigated. The potential effects of exogenous supplementation of biliverdin (BVD), one of the main products catalyzed by HO, on neurobehaviors are still largely unknown. The present study aimed to investigate the effects of BVD treatment on depression, anxiety, and memory in adult mice. Mice were injected with BVD through tail vein daily for a total 5 d, and depression- and anxiety-like behaviors were conducted by using open field test (OFT), novelty suppressed feeding (NSF), forced swimming test (FST) and tail suspension test (TST) since the third day of BVD administration. Novel object recognition (NOR) paradigm was used for memory formation test. After the final test, serum and hippocampal levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) of mice were analyzed by enzyme-linked immunosorbent assay (ELISA). The results showed that BVD treatment at low dose (2 mg/kg) induced depression-like behaviors, and high dose (8 mg/kg) BVD injection increased anxiety-like behaviors and impaired memory formation in mice. ELISA data showed that BVD treatment significantly increased hippocampal IL-6 and TNF-α level while only decreasing serum IL-6 level of mice. The present data suggest that exogenous BVD treatment induced depression- and anxiety-like phenotypes, which may be related to inflammatory factors, providing BVD may be a potential target for the prevention of mental disorders.

Pharmacological actions and therapeutic potentials of bilirubin in islet transplantation for the treatment of diabetes

Islet transplantation is the experimental strategy to treat type 1 diabetes by transplanting isolated islets from a donor pancreas into the recipient. While significant progress has been made in the islet transplantation field, islet loss before and after transplantation is still the major obstacle that currently precludes its widespread application. Islet must survive from possible cellular damages during the isolation procedure, storage time, islet injection process and post-transplantation immune rejection, only then the survived islets could produce insulin, actively regulating the blood glucose level. Therefore, islet protection needs to be addressed, especially regarding oxidative stress and immune response induced islet cell damages in diabetic patients. Many clinical data have shown that mildly elevated bilirubin levels in the body negatively correlate to the occurrence of an array of diseases that are related to increased oxidative stress, especially diabetes, and its complications. Recent studies confirmed that bilirubin helps receivers to suppress immune reaction and enable prolonged tolerance to islet transplantation. In this paper, we will review the pharmacological mechanism of bilirubin to modulate oxidative cellular damage and chronic inflammatory reaction in both diabetes and islet transplantation process. Also, we will present the clinical evidence of a strong correlation in bilirubin and diabetes. More importantly, we will summarize undergoing therapeutic applications of bilirubin in islet transplantation and discuss formulation approaches designed to overcome bilirubin delivery issues for future use.

Immune challenge-induced oxidative damage may be mitigated by biliverdin

An effective immune response results in the elimination of pathogens, but this immunological benefit may be accompanied by increased levels of oxidative damage. However, organisms have evolved mechanisms to mitigate the extent of such oxidative damage, including the production and mobilization of antioxidants. One potential mechanism of mitigating immune challenge-induced changes in oxidative physiology is increasing biliverdin production. Biliverdin is chemically an antioxidant, but within-tissue correlations between biliverdin concentration and oxidative damage have never been directly examined. To test how biliverdin tissue concentrations are associated with physiological responses to an immune challenge, we exposed northern bobwhite quail (Colinus virginianus) to one of four treatments: injection of a non-pathogenic antigen - either lipopolysaccharide or phytohemagglutinin, control injection of phosphate-buffered saline or a sham procedure with no injection. Twenty-four hours later, we quantified oxidative damage and triglyceride concentration in the plasma, and biliverdin concentration in the plasma, liver and spleen. We found that both types of immune challenge increased oxidative damage relative to both non-injected and vehicle-injected controls, but treatment had no effects on any other metric. However, across all birds, oxidative damage and biliverdin concentration in the plasma were negatively correlated, which is consistent with a localized antioxidant function of biliverdin. Additionally, we uncovered multiple links between biliverdin concentration, change in mass during the immune challenges and triglyceride levels, suggesting that pathways associated with biliverdin production may also be associated with aspects of nutrient mobilization. Future experiments that manipulate biliverdin levels or oxidative damage directly could establish a systemic antioxidant function or elucidate important physiological impacts on body mass maintenance and triglyceride storage, mobilization or transport.

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.

Biliverdin administration ameliorates cerebral ischemia reperfusion injury in rats and is associated with proinflammatory factor downregulation

Biliverdin (BV), one of the heme oxygenase-1 (HO-1) catalytic products, has been demonstrated to have protective effects in liver ischemia reperfusion injury (IRI). The present study aimed to explore the effects of BV on cerebral IRI, and to investigate the potential mechanisms thereof. Adult male SD rats, weighing 200-240 g, were randomly divided into sham (group S), cerebral ischemia reperfusion control (group C) and BV (group BV) groups. Rats in group C underwent transient middle cerebral artery occlusion (tMCAO) and received 2 ml normal saline; rats in group BV received BV (35 mg/kg) intraperitoneally 15 min prior to reperfusion and 4 h after reperfusion, then twice a day thereafter for 5 days. Group S served as the control. Neurological Severity Scores (NSS) were evaluated at days 1-5 following reperfusion. Staining with 2, 3, 5-triphenyltetrazolium chloride was performed to determine the cerebral infarction at 48 h post reperfusion. mRNA expression levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, inducible nitric oxide synthase (iNOS) and HO-1 in the ischemic cerebral cortex were detected via reverse transcription-quantitative polymerase chain reaction at 3, 6, 12 and 24 h after reperfusion. Western blotting was used to detect the protein expression levels at 3 h after reperfusion. Compared with group S, the NSS, cerebral infarct volume, and the mRNA and protein expression levels of TNF-α, IL-6, IL-1β, iNOS and HO-1 of Group C were significantly increased (P<0.05). However, BV administration significantly improved and reduced these expression levels (P<0.01). The present study indicates that BV is able to ameliorate cerebral IRI in rats and that the mechanism may be associated with the downregulation of proinflammatory factors.

Suppression of human alloreactive T cells by linear tetrapyrroles; relevance for transplantation

The main limitation to successful transplantation is the antigraft response developed by the recipient immune system, and the adverse side effects of immunosuppressive agents which are associated with significant toxicity and counter indications such as infection and cancer. Furthermore, immunosuppressants do little to prevent ischemia-reperfusion injury during the transplantation procedure itself hence there is a growing need to develop novel immunosuppressive drugs specifically aimed at prolonging graft survival. Linear tetrapyrroles derived from the breakdown of mammalian heme have been shown in numerous studies to play a protective role in allograft transplantation and ischemia-reperfusion injury; however, commercial sources of these products have not been approved for use in humans. Plants and algae produce equivalent linear tetrapyrroles called bilins that serve as chromophores in light-sensing. One such marine-derived tetrapyrrole, phycocyanobilin (PCB), shows significant structural similarity to mammalian biliverdin (BV) and may prove to be a safer alternative for use in the clinic if it can exert direct effects on human immune cells. Using a mixed lymphocyte reaction, we quantified the allogeneic responses of recipient cells to donor cells and found that PCB, like BV, effectively suppressed proliferation and proinflammatory cytokine production. In addition, we found that BV and PCB can directly downregulate the proinflammatory responses of both innate dendritic cells and adaptive T cells. We therefore propose that PCB may be an effective therapeutic drug in the clinical setting of transplantation and may also have wider applications in regulating inappropriate inflammation.

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.

Evaluating the beneficial and detrimental effects of bile pigments in early and later life

The heme degradation pathway has been conserved throughout phylogeny and allows for the removal of a pro-oxidant and the generation of unique molecules including bile pigments with important cellular functions. The impact of bile pigments on health and disease are reviewed, as is the special circumstance of neonatal hyperbilirubinemia. In addition, the importance of promoter polymorphisms in the UDP-glucuronosyl transferase gene (UGTA1), which is key to the elimination of excess bilirubin and to the prevention of its toxicity, are discussed. Overall, the duality of bile pigments as either cytoprotective or toxic molecules is highlighted.

Technical modifications of the orthotopic lung transplantation model in rats with brain-dead donors

BACKGROUND

Microsurgical lung transplantation in rats has allowed us to obtain new knowledge about lung transplantation. However, some aspects in human transplantation technique still have not been included in this model, which could interfere with the clinical interpretation and extrapolation of results.

METHODS

Twenty left lung transplantations were performed with a cuff technique and technical modifications, such as brain death induction, the control of ischemia time and retrograde perfusion in the donor and the controlled sequential reperfusion of the implanted lung in the recipient.

RESULTS

Survival rate was 80%. The transplanted lungs showed proper perfusion and ventilation with good permeability of the anastomoses. Signs of ischemia-reperfusion injury were observed in all animals while mild acute rejection was seen in half of them.

CONCLUSIONS

The model shown proves valid and is very similar to the procedure carried out in humans, which would reduce the number of possible variables derived from the surgical technique when extrapolating the study results to clinical use.

Biliverdin Rescues the HO-2 Null Mouse Phenotype of Unresolved Chronic Inflammation Following Corneal Epithelial Injury

PURPOSE. The heme oxygenase system (HO-1 and HO-2) represents an intrinsic cytoprotective and anti-inflammatory pathway based on its ability to modulate leukocyte migration and to inhibit the expression of inflammatory cytokines and proteins by its products biliverdin/bilirubin and carbon monoxide. Corneal injury in HO-2 null mice leads to impaired healing and chronic inflammatory complications, including ulceration and neovascularization. The authors examined whether topically administered biliverdin can counteract the effects of HO deficiency in a corneal epithelial injury model. METHODS. HO-2 null mice were treated with biliverdin 1 hour before epithelial injury and twice a day thereafter. Reepithelialization and neovascularization were assessed by fluorescein staining and vital microscopy, respectively, and were quantified by image analysis. Inflammation was quantified by histology and Gr-1-specific immunofluorescence, and oxidative stress was assessed by DHE fluorescence. RESULTS. Treatment with biliverdin accelerated wound closure, inhibited neovascularization and reduced epithelial defects. It also reduced inflammation, as evidenced by a reduction in the appearance of inflammatory cells and the expression levels of inflammatory and oxidant proteins, including KC and NOXs. CONCLUSIONS. The results clearly show that biliverdin, directly or through its metabolism to bilirubin by biliverdin reductase-the expression of which is increased after injury-rescues the aberrant inflammatory phenotype, further underscoring the importance of the HO system in the cornea for the execution of an ordered inflammatory and reparative response.

Protection against lung graft injury from brain-dead donors with carbon monoxide, biliverdin, or both

BACKGROUND

The process of brain death can induce acute lung injury in donors and aggravate ischemia-reperfusion injury in grafts. Carbon monoxide (CO) and biliverdin (BV) have been shown to attenuate ischemia-reperfusion injury. We therefore examined if the administration of both CO and BV provide enhanced cytoprotection against lung graft injury from brain-dead (BD) rat donors.

METHODS

Brain death was induced in all donors, after which they were observed for 1.5 hours and then underwent lung transplantation. The recipients were ventilated with 40% oxygen (control group), ventilated with 250 ppm CO in 40% oxygen (CO group), treated with BV (35 mg/kg) intraperitoneally (BV group), or treated with CO and BV conjointly (COBV group) before transplantation (n = 8 each group). The recipients were sacrificed 2 hours after lung transplantation by exsanguination. Serum levels of interleukin (IL)-8 and tumor necrosis factor (TNF)-α were measured by enzyme-linked immunosorbent assay.

RESULTS

CO and/or BV treatment attenuated partial pressure of arterial oxygen (Pao(2))/fraction of inspired oxygen (Fio(2)) aggravation in the recipients after reperfusion, reduced the wet weight/dry weight ratio, decreased the lung injury score, inhibited the activity of myeloperoxidase in grafts, and decreased serum levels of IL-8 and TNF-α compared with the control group (p < 0.05). The COBV group had significantly decreased malonaldehyde levels and increased superoxide dismutase levels in lung grafts compared with the CO group (p < 0.05). The static pressure-volume curve of the lungs was ameliorated in the CO group, BV group, and COBV group compared with the control group (p < 0.05).

CONCLUSIONS

CO and BV exert protective effects through anti-inflammatory and anti-oxidant mechanisms, and dual treatment provided enhanced cytoprotection against lung graft injury from BD rat donors.