Exogenous biliverdin ameliorates ischemia-reperfusion injury in small-for-size rat liver grafts

Biliverdin alleviates cerebral ischemia-reperfusion injury by regulating the P4hb/MAPK/mTOR pathway to inhibit autophagy

BACKGROUND

Biliverdin (BV) exhibits anti-inflammatory and antioxidative effects. Autophagy activation is crucial in the pathogenesis of cerebral ischemia-reperfusion injury (CIRI). This study aimed to investigate whether BV could ameliorate CIRI by regulating autophagy.

METHODS

A middle cerebral artery occlusion-reperfusion (MCAO/R) model in Sprague-Dawley (SD) rats and an oxygen-glucose deprivation/reoxygenation (OGD/R) model in PC12 cells were employed to explore the neuroprotective effects of BV and its underlying mechanisms. In these rats, once BV was administered post-MCAO/R, its treatment efficacy and underlying mechanisms were evaluated through behavioral, morphological, and molecular analyses. Alternatively, for PC12 cells, following successful OGD/R modeling, BV, autophagy activator rapamycin, prolyl 4-hydroxylase beta (P4hb) knockdown or overexpression, and the specific inhibitors of three classic autophagy pathways were applied. Cell viability (using CCK8 assay), Calcein/PI staining, autophagosome staining (using MDC assay), reverse transcription quantitative polymerase chain reaction, and western blot were subsequently carried out to investigate the mechanisms by which BV ameliorates CIRI.

RESULTS

BV alleviated CIRI by inhibiting autophagy. Further investigation suggested that BV downregulated P4hb expression. In vitro experiments showed that P4hb knockdown reduced autophagy in post-CIRI cells, while its overexpression reversed the effects of BV. Rescue experiments indicated that MAPK pathway inhibitors counteracted the effects of P4hb overexpression on autophagy post-CIRI.

CONCLUSION

BV improves CIRI by regulating the P4hb/MAPK/mTOR signaling pathway to inhibit autophagy, offering a novel therapeutic strategy for ischemic stroke.

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.

The brain heme oxygenase/biliverdin reductase system as a target in drug research and development

INTRODUCTION

The heme oxygenase/biliverdin reductase (HO/BVR) system is involved in heme metabolism. The inducible isoform of HO (HO-1) and BVR both exert cytoprotective effects by enhancing cell stress response. In this context, some xenobiotics, which target HO-1, including herbal products, behave as neuroprotectants in several experimental models of neurodegeneration. Despite this, no drug having either HO-1 or BVR as a main target is currently available.

AREAS COVERED

After a description of the brain HO/BVR system, the paper analyzes the main classes of drugs acting on the nervous system, with HO as second-level target, and their neuroprotective potential. Finally, the difficulties that exist for the development of drugs acting on HO/BVR and the possible ways to overcome these hurdles are examined.

EXPERT OPINION

Although the limited clinical evidence has restricted the translational research on the HO/BVR system, mainly because of the dual nature of its by-products, there has been growing interest in the therapeutic potential of these enzymes. Scientists should boost the translational research on the HO/BVR system which could be supported by the significant evidence provided by preclinical studies.

Regulation of inflammation by the antioxidant haem oxygenase 1

Haem oxygenase 1 (HO-1), an inducible enzyme responsible for the breakdown of haem, is primarily considered an antioxidant, and has long been overlooked by immunologists. However, research over the past two decades in particular has demonstrated that HO-1 also exhibits numerous anti-inflammatory properties. These emerging immunomodulatory functions have made HO-1 an appealing target for treatment of diseases characterized by high levels of chronic inflammation. In this Review, we present an introduction to HO-1 for immunologists, including an overview of its roles in iron metabolism and antioxidant defence, and the factors which regulate its expression. We discuss the impact of HO-1 induction in specific immune cell populations and provide new insights into the immunomodulation that accompanies haem catabolism, including its relationship to immunometabolism. Furthermore, we highlight the therapeutic potential of HO-1 induction to treat chronic inflammatory and autoimmune diseases, and the issues faced when trying to translate such therapies to the clinic. Finally, we examine a number of alternative, safer strategies that are under investigation to harness the therapeutic potential of HO-1, including the use of phytochemicals, novel HO-1 inducers and carbon monoxide-based therapies.

Photo-Polymerization Damage Protection by Hydrogen Sulfide Donors for 3D-Cell Culture Systems Optimization

Photo-polymerized hydrogels are ideally suited for stem-cell based tissue regeneration and three dimensional (3D) bioprinting because they can be highly biocompatible, injectable, easy to use, and their mechanical and physical properties can be controlled. However, photo-polymerization involves the use of potentially toxic photo-initiators, exposure to ultraviolet light radiation, formation of free radicals that trigger the cross-linking reaction, and other events whose effects on cells are not yet fully understood. The purpose of this study was to examine the effects of hydrogen sulfide (H₂S) in mitigating cellular toxicity of photo-polymerization caused to resident cells during the process of hydrogel formation. H₂S, which is the latest discovered member of the gasotransmitter family of gaseous signalling molecules, has a number of established beneficial properties, including cell protection from oxidative damage both directly (by acting as a scavenger molecule) and indirectly (by inducing the expression of anti-oxidant proteins in the cell). Cells were exposed to slow release H₂S treatment using pre-conditioning with glutathione-conjugated-garlic extract in order to mitigate toxicity during the photo-polymerization process of hydrogel formation. The protective effects of the H₂S treatment were evaluated in both an enzymatic model and a 3D cell culture system using cell viability as a quantitative indicator. The protective effect of H₂S treatment of cells is a promising approach to enhance cell survival in tissue engineering applications requiring photo-polymerized hydrogel scaffolds.

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.

Rosmarinic acid elicits neuroprotection in ischemic stroke via Nrf2 and heme oxygenase 1 signaling

Rosmarinic acid (RA) can elicit a neuroprotective effect against ischemic stroke, but the precise molecular mechanism remains poorly understood. In this study, an experimental ischemic stroke model was established in CD-1 mice (Beijing Vital River Laboratory Animal Technology, Beijing, China) by occluding the right middle cerebral artery for 1 hour and allowing reperfusion for 24 hours. After intraperitoneally injecting model mice with 10, 20, or 40 mg/kg RA, functional neurological deficits were evaluated using modified Longa scores. Subsequently, cerebral infarct volume was measured using TTC staining and ischemic brain tissue was examined for cell apoptosis with TUNEL staining. Superoxide dismutase activity and malondialdehyde levels were measured by spectrophometry. Expression of heme oxygenase-1 (HO-1), nuclear factor erythroid 2-related factor 2 (Nrf2), Bcl-2, Bax, Akt, and phospho-Ser473 Akt proteins in ischemic brain tissue was detected by western blot, while mRNA levels of Nrf2, HO-1, Bcl-2, and Bax were analyzed using real time quantitative PCR. In addition, HO-1 enzyme activity was measured spectrophotometrically. RA (20 and 40 mg/kg) greatly improved neurological function, reduced infarct volume, decreased cell apoptosis, upregulated Bcl-2 protein and mRNA expression, downregulated Bax protein and mRNA expression, increased HO-1 and Nrf2 protein and mRNA expression, increased superoxide dismutase activity, and decreased malondialdehyde levels in ischemic brain tissue of model mice. However, intraperitoneal injection of a HO-1 inhibitor (10 mg/kg zinc protoporphyrin IX) reversed the neuroprotective effects of RA on HO-1 enzyme activity and Bcl-2 and Bax protein expression. The PI3K/Akt signaling pathway inhibitor LY294002 (10 mM) inhibited Akt phosphorylation, as well as Nrf2 and HO-1 expression. Our findings suggest that RA has anti-oxidative and anti-apoptotic properties that protect against ischemic stroke by a mechanism involving upregulation of Nrf2 and HO-1 expression via the PI3K/Akt signaling pathway.

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.

Hibernation reduces cellular damage caused by warm hepatic ischemia-reperfusion in ground squirrels

During the hibernation season, livers from 13-lined ground squirrels (Ictidomys tridecemlineatus) are resistant to damage induced by ex vivo, cold ischemia-warm reperfusion (IR) compared with livers from summer squirrels or rats. Here, we tested the hypothesis that hibernation also reduces damage to ground squirrel livers in an in vivo, warm IR model, which more closely resembles complications associated with traumatic injury or surgical interventions. We also examined whether protection is mediated by two metabolites, inosine and biliverdin, that are elevated in ground squirrel liver during interbout arousals. Active squirrels in spring and hibernators during natural arousals to euthermia (body temperature 37 °C) were subject to liver IR or sham treatments. A subset of hibernating squirrels was pre-treated with compounds that inhibit inosine synthesis/signaling or biliverdin production. This model of liver IR successfully induced hepatocellular damage as indicated by increased plasma liver enzymes (ALT, AST) and hepatocyte apoptosis index compared to sham in both seasons, with greater elevations in spring squirrels. In addition, liver congestion increased after IR to a similar degree in spring and hibernating groups. Microvesicular steatosis was not affected by IR within the same season but was greater in sham squirrels in both seasons. Plasma IL-6 increased ~twofold in hibernators pre-treated with a biliverdin synthesis inhibitor (SnPP) prior to IR, but was not altered by IR in untreated squirrels. The results show that hibernation provides protection to ground squirrel livers subject to warm IR. Further research is needed to clarify mechanisms responsible for endogenous protection of liver tissue under ischemic stress.

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.

Improving Research Practice in Rat Orthotopic and Partial Orthotopic Liver Transplantation: A Review, Recommendation, and Publication Guide

Background: Due to a worldwide shortage of donor organs for liver transplantation, alternative approaches, such as split and living donor liver transplantations, were introduced to increase the donor pool and reduce mortality on liver transplant waiting lists. Numerous details concerning the mechanisms and pathophysiology of liver regeneration, small-for-size syndrome, rejection, and tolerance in partial liver transplantation facilitated the development of various animal models. The high number of preclinical animal studies contributed enormously to our understanding of many clinical aspects of living donor and partial liver transplantations. Summary: Microsurgical rat models of partial orthotopic liver transplantation are well established and widely used. Nevertheless, several issues regarding this procedure are controversial, not clarified, or not yet properly standardized (graft rearterialization, size reduction techniques, etc.). The major aim of this literature review is to give the reader a current overview of rat orthotopic liver transplantation models with a special focus on partial liver transplantation. The aspects of model evolution, microsurgical training, and different technical problems are analyzed and discussed in detail. Our further aim in this paper is to elaborate a detailed publication guide in order to improve the quality of reporting in the field of rat liver transplantation according to the ARRIVE guidelines and the 3R principle. Key Messages: Partial orthotopic liver transplantation in rats is an indispensable, reliable, and cost-efficient model for transplantation research. A certain consensus on different technical issues and a significant improvement in scientific reporting are essential to improve transparency and comparability in this field as well as to foster refinement.

Bilirubin participates in protecting of heme oxygenase-1 induction by quercetin against ethanol hepatotoxicity in cultured rat hepatocytes

To attenuate alcohol liver disease (ALD) is extremely urgent since ALD has been emerged as a major liver disease. The aim of the present study is to investigate the hepatoprotective effect against ethanol-induced injury of bilirubin, a product of heme metabolism degradation via HO and biliverdin reductase catalysis. Ethanol-incubated primary rat hepatocytes (100 mmol/L) were treated by quercetin, bilirubin, inflammatory factors, and/or HO-1 inducer/inhibitor for 24 h, and the cellular damage was assayed. Quercetin lowered ethanol-induced glutathione depletion and superoxide dismutase inactivation, inhibited the overproduction of malondialdehyde and reactive oxygen species, and decreased the leakage of cellular aspartate aminotransferase and lactate dehydrogenase, accompanying the normalization of bilirubin level. The effect of quercetin was mimicked by exogenous bilirubin in a dose-dependent manner to some extent (within 25 μmol/L) and pharmacological HO-1 inducer hemin, but abolished by HO-1 inhibitor zinc protoporphyrin-IX. Inflammatory challenge of TNF-α plus IL-6 further aggravated ethanol-induced oxidative damage, which was also attenuated by bilirubin in part. These findings shed a light on the anti-oxidative and anti-inflammatory role of bilirubin released from quercetin/HO-1 and biliverdin reductase pathway against ethanol hepatotoxicity and highlight a prospective strategy of nutritional intervention for ALD by naturally occurring quercetin to induce HO-1 with the release of bioactive end-products.

Biliverdin inhibits Toll-like receptor-4 (TLR4) expression through nitric oxide-dependent nuclear translocation of biliverdin reductase

The cellular response to an inflammatory stressor requires a proinflammatory cellular activation followed by a controlled resolution of the response to restore homeostasis. We hypothesized that biliverdin reductase (BVR) by binding biliverdin (BV) quells the cellular response to endotoxin-induced inflammation through phosphorylation of endothelial nitric oxide synthase (eNOS). The generated NO, in turn, nitrosylates BVR, leading to nuclear translocation where BVR binds to the Toll-like receptor-4 (TLR4) promoter at the Ap-1 sites to block transcription. We show in macrophages that BV-induced eNOS phosphorylation (Ser-1177) and NO production are mediated in part by Ca(2+)/calmodulin-dependent kinase kinase. Furthermore, we show that BVR is S-nitrosylated on one of three cysteines and that this posttranslational modification is required for BVR-mediated signaling. BV-induced nuclear translocation of BVR and inhibition of TLR4 expression is lost in macrophages derived from Enos(-/-) mice. In vivo in mice, BV provides protection from acute liver damage and is dependent on the availability of NO. Collectively, we elucidate a mechanism for BVR in regulating the inflammatory response to endotoxin that requires eNOS-derived NO and TLR4 signaling in macrophages.

Preconditioning with cobalt protoporphyrin protects human gastric mucosal cells from deoxycholate-induced apoptosis

In this study, a known inducer of heme oxygenase-1 (HO-1) expression, cobalt protoporphyrin, and the introduction of a recombinant plasmid expressing HO-1 were examined for their ability to protect gastric epithelial cells from deoxycholate-induced injury. Physiologic levels of the secondary bile salt induce apoptosis in a human gastric adenocarcinoma mucosal cell line. Cobalt protoporphyrin induced expression of HO-1 protein with maximal levels attaining a plateau at 48 hours. Pretreatment with cobalt protoporphyrin before challenge with 200 μM deoxycholate inhibited cell death, DNA fragmentation, the appearance of cytosolic nucleosomes, and cleavage of caspase-3, caspase-9, and poly-(ADP-ribose) polymerase 1. Similarly, expression of HO-1 by introduction of a recombinant plasmid also showed a resistance to deoxycholate-induced apoptosis. These results implicate a possible role for HO-1 in modulating apoptosis in gastric epithelial cells.

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.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

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

BACKGROUND

Biliverdin, a product of heme oxygenase-1 (HO-1), ameliorates the posttransplant functions of heart, kidney, and liver. In this study, we investigated the effects of biliverdin on lung grafts from brain dead (BD) rat donors.

METHODS

Male Wistar rats were randomly divided into 3 groups. The sham group (n = 7), did not undergo BD. Both donor and recipient rats in the BD biliverdin group (n = 8) were injected with biliverdin (35 mg/kg in 1 mL) intraperitoneally after confirmed BD and transplantation. In the BD group (n = 8), both donor and recipient rats received the same volume of saline (35 mg/kg in 1 mL) as the BD biliverdin group. All donor rats were observed for 1.5 hours before undergoing lung transplantation. Two hours after transplantation, we obtained blood and lung graft samples.

RESULTS

Biliverdin reversed the aggravation of Pa(O(2)) in recipients, reduced the grafts wet/dry ratio, decreased the severity of lung injury measured by histologic examination, reduced serum tumor necrosis factor-alpha and interleukin-8 levels and inhibited myeloperoxidase activity (MPO) in the grafts. Furthermore, it significantly decreased malonaldehyde levels and increased superoxide dismutase levels. Biliverdin reduced cell apoptosis, activated protein expression of biliverdin reductase, and inhibited expression of HO-1 and nuclear factor (NF)-kappaB in lung grafts.

CONCLUSION

Biliverdin exerts protective effects on lung grafts from BD donors through anti-inflammatory, antioxidant, and anti-apoptotic mechanisms.

Heme oxygenase-1 prevents non-alcoholic steatohepatitis through suppressing hepatocyte apoptosis in mice

Objective

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, has been reported to have potential antioxidant properties. However, the role of HO-1 on hepatocyte apoptosis remains unclear. We aim to elucidate the effects of HO-1 on oxidative stress related hepatocellular apoptosis in nutritional steatohepatitis in mice.

Methods

C57BL/6J mice were fed with methionine-choline deficient (MCD) diet for four weeks to induce hepatic steatohepatitis. HO-1 chemical inducer (hemin), HO-1 chemical inhibitor zinc protoporphyrin IX (ZnPP-IX) and/or adenovirus carrying HO-1 gene (Ad-HO-1) were administered to mice, respectively. Hepatocyte apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay, the mRNA and protein expression of apoptosis related genes were assayed by quantitative real-time PCR and Western blot.

Results

Hepatocyte signs of oxidative related apoptotic injury were presented in mice fed with MCD diet for 4 weeks. Induction of HO-1 by hemin or Ad-HO-1 significantly attenuated the severity of liver histology, which was associated with decreased hepatic lipid peroxidation content, reduced number of apoptotic cells by TUNEL staining, down-regulated expression of pro-apoptosis related genes including Fas/FasL, Bax, caspase-3 and caspase-9, reduced expression of cytochrome p4502E1 (CYP2E1), inhibited cytochrome c (Cyt-c) release, and up-regulated expression of anti-apoptosis gene Bcl-2. Whereas, inhibition of HO-1 by ZnPP-IX caused oxidative stress related hepatic injury, which concomitant with increased number of TUNEL positive cells and up-regulated expression of pro-apoptosis related genes.

Conclusions

The present study provided evidences for the protective role of HO-1 in preventing nutritional steatohepatitis through suppressing hepatocyte apoptosis in mice.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

Matrix metalloproteinase 2 in reduced-size liver transplantation: beyond the matrix

We studied the contribution of matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) to the beneficial effects of preconditioning (PC) in reduced-size orthotopic liver transplantation (ROLT). We also examined the role of c-Jun N-terminal kinase (JNK) and whether it regulates MMP2 in these conditions. Animals were subjected to ROLT with or without PC and pharmacological modulation, and liver tissue samples were then analyzed. We found that MMP2, but notMMP9, is involved in the beneficial effects of PC in ROLT. MMP2 reduced hepatic injury and enhanced liver regeneration. Moreover, inhibition of MMP2 in PC reduced animal survival after transplantation. JNK inhibition in the PC group decreased hepatic injury and enhanced liver regeneration. Furthermore, JNK upregulated MMP2 in PC. In addition, we showed that Tissue inhibitors of matrix metalloproteinases 2 (TIMP2) was also upregulated in PC and that JNK modulation also altered its levels in ROLT and PC. Our results open up new possibilities for therapeutic treatments to reduce I/R injury and increase liver regeneration after ROLT, which are the main limitations in living-donor transplantation.

Heme oxygenase-1, a critical arbitrator of cell death pathways in lung injury and disease

Increases in cell death by programmed (i.e., apoptosis, autophagy) or nonprogrammed mechanisms (i.e., necrosis) occur during tissue injury and may contribute to the etiology of several pulmonary or vascular disease states. The low-molecular-weight stress protein heme oxygenase-1 (HO-1) confers cytoprotection against cell death in various models of lung and vascular injury by inhibiting apoptosis, inflammation, and cell proliferation. HO-1 serves a vital metabolic function as the rate-limiting step in the heme degradation pathway and in the maintenance of iron homeostasis. The transcriptional induction of HO-1 occurs in response to multiple forms of chemical and physical cellular stress. The cytoprotective functions of HO-1 may be attributed to heme turnover, as well as to beneficial properties of its enzymatic reaction products: biliverdin-IXalpha, iron, and carbon monoxide (CO). Recent studies have demonstrated that HO-1 or CO inhibits stress-induced extrinsic and intrinsic apoptotic pathways in vitro. A variety of signaling molecules have been implicated in the cytoprotection conferred by HO-1/CO, including autophagic proteins, p38 mitogen-activated protein kinase, signal transducer and activator of transcription proteins, nuclear factor-kappaB, phosphatidylinositol 3-kinase/Akt, and others. Enhanced HO-1 expression or the pharmacological application of HO end-products affords protection in preclinical models of tissue injury, including experimental and transplant-associated ischemia/reperfusion injury, promising potential future therapeutic applications.

Surgical inflammation: a pathophysiological rainbow

Tetrapyrrole molecules are distributed in virtually all living organisms on Earth. In mammals, tetrapyrrole end products are closely linked to oxygen metabolism. Since increasingly complex trophic functional systems for using oxygen are considered in the post-traumatic inflammatory response, it can be suggested that tetrapyrrole molecules and, particularly their derived pigments, play a key role in modulating inflammation.

In this way, the diverse colorfulness that the inflammatory response triggers during its evolution would reflect the major pathophysiological importance of these pigments in each one of its phases. Therefore, the need of exploiting this color resource could be considered for both the diagnosis and treatment of the inflammation.

Analysis of the hibernation cycle using LC-MS-based metabolomics in ground squirrel liver

A hallmark of hibernation in mammals is metabolic flexibility, which is typified by reversible bouts of metabolic depression (torpor) and the seasonal shift from predominantly carbohydrate to lipid metabolism from summer to winter. To provide new insight into the control and consequences of hibernation, we used LC/MS-based metabolomics to measure differences in small molecules in ground squirrel liver in five activity states: summer, entering torpor, late torpor, arousing from torpor, and interbout arousal. There were significant alterations both seasonally and within torpor-arousal cycles in enzyme cofactor metabolism, amino acid catabolism, and purine and pyrimidine metabolism, with observed metabolites reduced during torpor and increased upon arousal. Multiple lipids also changed, including 1-oleoyllysophosphatidylcholine, cholesterol sulfate, and sphingosine, which tended to be lowest during torpor, and hexadecanedioic acid, which accumulated during a torpor bout. The results reveal the dramatic alterations that occur in several classes of metabolites, highlighting the value of metabolomic analyses in deciphering the hibernation phenotype.

Molecular mediators of liver ischemia and reperfusion injury: a brief review

Ischemia and reperfusion injury is a dynamic process that involves multiple organ systems in various clinical states including transplantation, trauma, and surgery. Research into this field has identified key molecular and signaling players that mediate, modulate, or augment cellular, tissue, and organ injury during this disease process. Further elucidation of the molecular mechanisms should provide the rationale to identify much-needed novel therapeutic options to prevent or ameliorate organ damage due to ischemia and reperfusion in clinics.

Adenoviral cardiotrophin-1 transfer improves survival and early graft function after ischemia and reperfusion in rat small-for-size liver transplantation model

This study was to investigate the effect of donor liver adenoviral cardiotrophin-1 (CT-1) gene transfer on early graft survival and function in rat small-for-size liver transplantation. We constructed a recombinant murine CT-1 adenoviral vector. Donor rats were transduced in vivo with adenoviruses expressing CT-1 (AdCT-1) or control vector (AdEGFP). Livers were harvested 4 days later, reduced to 40% of weight, and transplanted. A syngeneic rat orthotopic liver transplantation model was performed using 40% small-for-size grafts. Graft survival, liver function, hepatic architecture change, the degree of necrosis and apoptosis, and cell survival signaling pathways were assessed. AdCT-1 pretreatment markedly improved liver function and the survival of small-for-size grafts. In the CT-1 treatment group, hepatic architecture was well protected, apoptotic and necrotic cells were reduced; anti-apoptotic protein bcl-2 was up-regulated and pro-apoptotic cleaved caspase-3 was down-regulated, cell survival signaling pathways were activated by phosphorylation of protein kinase B (Akt), extracellular-regulated kinase (ERK) and Signal transducer and activator of transcription-3 (Stat-3) after transplantation. In conclusion, donor liver adenoviral CT-1 transfer ameliorated ischemia/reperfusion injury by decreasing hepatic necrosis and apoptosis in small-for-size liver transplantation, mediated in part by activation of the Akt, ERK, and Stat-3 survival signaling pathways. These results may provide a potential clinical strategy to improve the outcome of small-for-size liver grafts.