Activation of non-ischemic, hypoxia-inducible signalling pathways up-regulate cytoprotective genes in the murine liver

Hypoxia-inducible factor-1alpha protects the liver against ischemia-reperfusion injury by regulating the A2B adenosine receptor

Hepatic ischemia-reperfusion injury (IRI) is an inevitable complication associated with liver surgical procedures, and its pathological process remains elusive. Therefore, the present study investigated the role and mechanism of hypoxia-inducible factor-1alpha (HIF-1α) in hepatic IRI. Here, we constructed rat models with hepatic IRI and BRL-3A cell models with hypoxia/reoxygenation (H/R) insult. The extent of liver injury was assayed by measuring serum ALT/AST levels and performing H&E staining; the levels of SOD, MDA, MPO, IL-6 and TNF-α were determined using commercial kits; apoptosis was detected using the TUNEL assay and flow cytometry; and the expression of HIF-1α/A2BAR signaling-related molecules and apoptosis-associated indicators was detected using Western blotting or qRT-PCR. The expression level of HIF-1α was significantly upregulated in the liver of rats subjected to IRI, as well as in BRL-3A cells treated with H/R. HIF-1α overexpression exerted a protective effect on hepatic IRI or H/R insult by reducing serum aminotransferase levels and hepatic necrosis, inhibiting inflammation and apoptosis of hepatocytes, and alleviating oxidative stress. In contrast, inhibition of HIF-1α expression exacerbated hepatic injury induced by IR or H/R. Mechanistically, the expression level of A2BAR was markedly increased during hepatic IRI or H/R insult. Moreover, A2BAR expression increased with HIF-1α upregulation and decreased with HIF-1α downregulation. Importantly, inhibition of A2BAR signaling abolished HIF-1α overexpression-mediated hepatoprotection. Taken together, HIF-1α exerts protective effects on hepatic IRI by attenuating liver necrosis, the inflammatory response, oxidative stress and apoptosis, and its mechanism may be related to the upregulation of A2BAR signaling.

Intermittent Hypoxic Conditioning Alleviates Post-Traumatic Stress Disorder-Induced Damage and Dysfunction of Rat Visceral Organs and Brain

Posttraumatic stress disorder (PTSD) causes mental and somatic diseases. Intermittent hypoxic conditioning (IHC) has cardio-, vaso-, and neuroprotective effects and alleviates experimental PTSD. IHC’s ability to alleviate harmful PTSD effects on rat heart, liver, and brain was examined. PTSD was induced by 10-day exposure to cat urine scent (PTSD rats). Some rats were then adapted to 14-day IHC (PTSD+IHC rats), while PTSD and untreated control rats were cage rested. PTSD rats had a higher anxiety index (AI, X-maze test), than control or PTSD+IHC rats. This higher AI was associated with reduced glycogen content and histological signs of metabolic and hypoxic damage and of impaired contractility. The livers of PTSD rats had reduced glycogen content. Liver and blood alanine and aspartate aminotransferase activities of PTSD rats were significantly increased. PTSD rats had increased norepinephrine concentration and decreased monoamine oxidase A activity in cerebral cortex. The PTSD-induced elevation of carbonylated proteins and lipid peroxidation products in these organs reflects oxidative stress, a known cause of organ pathology. IHC alleviated PTSD-induced metabolic and structural injury and reduced oxidative stress. Therefore, IHC is a promising preventive treatment for PTSD-related morphological and functional damage to organs, due, in part, to IHC’s reduction of oxidative stress.

Portal hyperperfusion after major liver resection and associated sinusoidal damage is a therapeutic target to protect the remnant liver

Extended liver resection results in loss of a large fraction of the hepatic vascular bed, thereby causing abrupt alterations in perfusion of the remnant liver. Mechanisms of hemodynamic adaptation and associated changes in oxygen metabolism after liver resection and the effect of mechanical portal blood flow reduction were assessed. A pig model (n = 16) of extended partial hepatectomy was established that included continuous observation for 24 h under general anesthesia. Pigs were randomly separated into two groups, one with a portal flow reduction of 70% compared with preoperative values, and the other as a control (n = 8, each). In controls, portal flow [mean (SD)] increased from 74 (8) mL·min^-1·100 g^-1 preoperatively to 240 (48) mL·min^-1·100 g^-1 at 6 h after resection (P < 0.001). Hepatic arterial buffer response was abolished after resection. Oxygen uptake per unit liver mass increased from 4.0 (1.1) mL·min^-1·100 g^-1 preoperatively to 7.7 (1.7) mL·min^-1·100 g^-1 8 h after resection (P = 0.004). Despite this increase in relative oxygen uptake, total hepatic oxygen consumption (V̇o₂) was not maintained, and markers of hypoxia and anaerobic metabolism were significantly increased in hepatocytes after resection. Reduced postoperative portal flow was associated with significantly decreased levels of aspartate aminotransferase and bilirubin and increased hepatic clearance of indocyanine green. In conclusion, major liver resection was associated with persistent portal hyperperfusion, loss of the hepatic arterial buffer response, decreased total hepatic V̇o₂ and with increased anaerobic metabolism. Portal flow modulation by partial portal vein occlusion attenuated liver injury after extended liver resection.NEW & NOTEWORTHY Because of continuous monitoring, the experiments allow precise observation of the influence of liver resection on systemic and local abdominal hemodynamic alterations and oxygen metabolism. Major liver resection is associated with significant and persistent portal hyperperfusion and loss of hepatic arterial buffer response. The correlation of portal hyperperfusion and parameters of liver injury and dysfunction offers a novel therapeutic option to attenuate liver injury after extended liver resection.

High-content analysis boosts identification of the initial cause of triptolide-induced hepatotoxicity

Triptolide (TP) has been widely used in China for more than 40 years as an immunosuppressive agent. Recently, serious concerns have been raised over TP-induced liver injury, though the real hepatotoxic mechanism is still unclear, particularly in terms of the initial cause. To our knowledge, this study is the first to screen systematically the mechanism of TP-induced toxicity through a global cytotoxicity profile high-content analysis using three independent cytotoxic assay panels with multiple endpoints of cytotoxicity, including cell loss, mitochondrial membrane potential, nuclear membrane permeability, manganese superoxide dismutase, phosphorylated gamma-H2AX, light chain 3B, lysosome, reactive oxygen species and glutathione. We assessed nine parameters and four stress response pathway models by labeling nuclear factor erythroid 2-related factor 2, activating transcription factor 6, hypoxia inducible factor 1α and nuclear factor κB and found that all testing parameters except glutathione and manganese superoxide dismutase showed concentration- and time-dependent changes, as well as increased cell loss after TP treatment. Considering that RNA polymerase II is the molecular target of TP, we quantified transcription from inducible genes, bromodeoxyuridine incorporation, and expression from transiently transfected green fluorescence protein plasmids in HepG2 cells. The results show that inhibition of global transcription by TP took place at earlier times and at lower concentrations than those observed for cell death. Therefore, global transcriptional suppression and the cell dysfunction it drives play a central role in TP-induced hepatotoxicity. This provides valuable information for the safe use of TP in the clinic.

Liver Zonation in Health and Disease: Hypoxia and Hypoxia-Inducible Transcription Factors as Concert Masters

The liver and its zonation contribute to whole body homeostasis. Acute and chronic, not always liver, diseases impair proper metabolic zonation. Various underlying pathways, such as β-catenin, hedgehog signaling, and the Hippo pathway, along with the physiologically occurring oxygen gradient, appear to be contributors. Interestingly, hypoxia and hypoxia-inducible transcription factors can orchestrate those pathways. In the current review, we connect novel findings of liver zonation in health and disease and provide a view about the dynamic interplay between these different pathways and cell-types to drive liver zonation and systemic homeostasis.

The hemodynamic and molecular mechanism study on the choke vessels in the multi-territory perforator flap transforming into true anastomosis

BACKGROUND

The aim of this study was to explore the hemodynamic and morphological changes of the choke vessels, and to investigate the role of HIF-1α in the flap adaptation to hypoxic and choke vessel transformation after multi-territory perforator flap transplantation.

METHODS

Animal model of single pedicle multi-territory perforator flap was established in the back of SD rats and the blood supply characteristics were studied by gelatin-oxide perfusion technique. HE staining and stereomicroscope were used to observe vascular changes. Afterward, the influence of hypoxia on cell proliferation and apoptosis were detected by MTT assay and flow cytometry, respectively. Besides, the expression of HIF-1α, iNOS and VEGF expression of HUVECs under hypoxia were detected by qRT-PCR and Western blot.

RESULTS

The results revealed that all the choke vessels immediately began to expand after operation. The day after operation, some of the choke vessels continued to grow and expand, turning into the true anastomosis, while the others gradually dwindled and finally disappeared. Compared with the control group, the day after transplantation, the expression levels of both HIF-1α and iNOS were significantly increased. The only different was that HIF-1α was then maintained a high level, iNOS was significantly decreased aftertimes. What's more, the expression of VEGF was increased to the maximum at 3 days after operation and then decreased. In HUVECs, hypoxia increased the expression of HIF-1α, iNOS and VEGF protein. Besides, it also promoted the proliferation and inhibited the apoptosis. In addition, we also found that hypoxia-induced VEGF and iNOS upregulation is mediated by HIF-1α overexpression and HIF-1α knockout can reverse the effects induced by hypoxia.

CONCLUSIONS

We found that HIF-1α may participate in the early vascular dilatation of transregional skin flap by inducing iNOS expression and promoting the reconstruction of choke vessels through increase VEGF expression.

Donor Treatment With a Hypoxia-Inducible Factor-1 Agonist Prevents Donation After Cardiac Death Liver Graft Injury in a Rat Isolated Perfusion Model

The protective role of hypoxia-inducible factor-1 (HIF-1) against liver ischemia-reperfusion injury has been well proved. However its role in liver donation and preservation from donation after cardiac death (DCD) is still unknown. The objective of this study was to test the hypothesis that pharmaceutical stabilization of HIF-1 in DCD donors would result in a better graft liver condition. Male SD rats (6 animals per group) were randomly given the synthetic prolyl hydroxylase domain inhibitor FG-4592 (Selleck, 6 mg/kg of body weight) or its vehicle (dimethylsulfoxide). Six hours later, cardiac arrest was induced by bilateral pneumothorax. Rat livers were retrieved 30 min after cardiac arrest, and subsequently cold stored in University of Wisconsin solution for 24 h. They were reperfused for 60 min with Krebs-Henseleit bicarbonate buffer in an isolated perfused liver model, after which the perfusate and liver tissues were investigated. Pretreatment with FG-4592 in DCD donors significantly improved graft function with increased bile production and synthesis of adenosine triphosphate, decreased perfusate liver enzyme release, histology injury scores and oxidative stress-induced cell injury and apoptosis after reperfusion with the isolated perfused liver model. The beneficial effects of FG-4592 is attributed in part to the accumulation of HIF-1 and ultimately increased PDK1 production. Pretreatment with FG-4592 in DCD donors resulted in activation of the HIF-1 pathway and subsequently protected liver grafts from warm ischemia and cold-stored injury. These data suggest that the pharmacological HIF-1 induction may provide a clinically applicable therapeutic intervention to prevent injury to DCD allografts.

Hypoxia-activated cytotoxic agent tirapazamine enhances hepatic artery ligation-induced killing of liver tumor in HBx transgenic mice

Transarterial chemoembolization (TACE) is the main treatment for intermediate stage hepatocellular carcinoma (HCC) with Barcelona Clinic Liver Cancer classification because of its exclusive arterial blood supply. Although TACE achieves substantial necrosis of the tumor, complete tumor necrosis is uncommon, and the residual tumor generally rapidly recurs. We combined tirapazamine (TPZ), a hypoxia-activated cytotoxic agent, with hepatic artery ligation (HAL), which recapitulates transarterial embolization in mouse models, to enhance the efficacy of TACE. The effectiveness of this combination treatment was examined in HCC that spontaneously developed in hepatitis B virus X protein (HBx) transgenic mice. We proved that the tumor blood flow in this model was exclusively supplied by the hepatic artery, in contrast to conventional orthotopic HCC xenografts that receive both arterial and venous blood supplies. At levels below the threshold oxygen levels created by HAL, TPZ was activated and killed the hypoxic cells, but spared the normoxic cells. This combination treatment clearly limited the toxicity of TPZ to HCC, which caused the rapid and near-complete necrosis of HCC. In conclusion, the combination of TPZ and HAL showed a synergistic tumor killing activity that was specific for HCC in HBx transgenic mice. This preclinical study forms the basis for the ongoing clinical program for the TPZ-TACE regimen in HCC treatment.

Hypoxia-inducible factors as molecular targets for liver diseases

Liver disease is a growing global health problem, as deaths from end-stage liver cirrhosis and cancer are rising across the world. At present, pharmacologic approaches to effectively treat or prevent liver disease are extremely limited. Hypoxia-inducible factor (HIF) is a transcription factor that regulates diverse signaling pathways enabling adaptive cellular responses to perturbations of the tissue microenvironment. HIF activation through hypoxia-dependent and hypoxia-independent signals have been reported in liver disease of diverse etiologies, from ischemia-reperfusion-induced acute liver injury to chronic liver diseases caused by viral infection, excessive alcohol consumption, or metabolic disorders. This review summarizes the evidence for HIF stabilization in liver disease, discusses the mechanistic involvement of HIFs in disease development, and explores the potential of pharmacological HIF modifiers in the treatment of liver disease.

The role of hypoxia-inducible factors in organ donation and transplantation: the current perspective and future opportunities

Hypoxia-inducible factors are the universal cellular oxygen-sensitive transcription factors that activate a number of hypoxia responsive genes, some of which are responsible for protective cellular functions. During organ donation, allografts are exposed to significant periods of hypoxia and ischemia. Exploiting this pathway during donor management and organ preservation could prevent and reduce allograft injury and improve the outcomes of organ transplantation. We review the evidence on this pathway in organ preservation, drawing on experimental studies on donor management and ischemia reperfusion injury focusing on kidney, liver, cardiac and lung transplantation. We review the major technical and experimental challenges in exploring this pathway and suggest potential future avenues for research.

Females transplanted with ovaries subjected to hypoxic preconditioning show impair of ovarian function

Background

Cryopreservation of the ovarian tissue has shown promising results. However, there remain controversial issues such as the short half-life of grafts. In this aspect, there are some evidences that preconditioning the ovarian tissue before transplantation is beneficial.

Objective

To determine the effect of hypoxic preconditioning in vitro on ovarian tissue prior to transplantation.

Methods

Eighteen female adult Wistar rats, were sorted into three experimental groups. Ovaries were maintained in DMEM low glucose serum free at 37°C with 5% CO2, at atmospheric oxigen concentration (normoxia) or 1% O₂ (hypoxia) for 16 hours. Oxigen concentration was determined by injection of nitrogen in the incubator. Animals submitted to ovarian transplantation immediately after oophorectomy were the Control Group (C). After this, the ovaries were implanted in the retroperitoneum with nonabsorbable suture and animals evaluated for thirty days after transplantation. Beginning on postoperative (PO) day 11, a daily collection of vaginal smear was carried out. Analyses comprised morphological, morphometric (counting ovarian follicles and corpora lutea) and immunohistochemistry for cleaved caspase-3 (apoptosis).

Results

In normoxia and control groups all animals recovered their estrous cycles, while in the hypoxia group, two animals did not ovulate but, among those which did, resumption took longer than in the other groups (p < 0.05). The number of ovarian follicles and corpora lutea decreased significantly in the hypoxia group when compared to the other two groups (p < 0.001) and apoptosis was increased in the few ovarian follicles which remained viable (p < 0.001).

Conclusion

The hypoxic preconditioning in vitro was not beneficial to the graft and worsened their viability, compromising its functionality or delaying the return of this.

Promise of neurorestoration and mitochondrial biogenesis in Parkinson's disease with multi target drugs: an alternative to stem cell therapy

There is an unmet need in progressive neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. The present therapeutics for these diseases at best is symptomatic and is not able to delay disease or possess disease modifying activity. Thus an approach to drug design should be made to slow or halt progressive course of a neurological disorder by interfering with a disease-specific pathogenetic process. This would entail the ability of the drug to protect neurons by blocking the common pathway for neuronal injury and cell death and the ability to promote regeneration of neurons and restoration of neuronal function. We have now developed a number of multi target drugs which possess neuroprotective, and neurorestorative activity as well as being able to active PGC-1α (peroxisome proliferator-activated receptor γ coactivator-1α), SIRT1 (NAD-dependent deacetylase protein) and NTF (mitochondrial transcription factor) that are intimately associated with mitochondrial biogenesis.

Role of cAMP-responsive element-binding protein (CREB)-regulated transcription coactivator 3 (CRTC3) in the initiation of mitochondrial biogenesis and stress response in liver cells

Peroxisome proliferator-activated receptor α, coactivator 1α (PGC-1α) is the master regulator of mitochondrial biogenesis. PGC-1α expression is under the control of the transcription factor, cAMP-responsive element-binding protein (CREB). In searching for candidate transcription factors that mediate mitochondrial stress-initiated mitochondria-to-nucleus signaling in the regulation of mitochondrial biogenesis, we assessed the effect of silencing CREB-regulated transcription co-activators (CRTC). CRTC isoforms are co-activators of CREB-regulated transcription by a CREB phosphorylation-independent pathway. Using cultured HepG2 cells and primary mouse hepatocytes, we determined that mitochondrial stress imposed by the complex I inhibitor rotenone elicited mitochondrial biogenesis, which was dependent on an induction of PGC-1α, which was inhibited by silencing PGC-1α. PGC-1α induction in response to rotenone was inhibited by silencing the expression of CRTC3, which blocked downstream mitochondria biogenesis. In contrast, silencing CRTC2 did not affect the induction of this pathway in response to rotenone. Thus, CRTC3 plays a selective role in mitochondrial biogenesis in response to rotenone.

Reductive metabolism of the dinitrobenzamide mustard anticancer prodrug PR-104 in mice

PURPOSE

PR-104, a bioreductive prodrug in clinical trial, is a phosphate ester which is rapidly metabolized to the corresponding alcohol PR-104A. This dinitrobenzamide mustard is activated by reduction to hydroxylamine (PR-104H) and amine (PR-104M) metabolites selectively in hypoxic cells, and also independently of hypoxia by aldo-keto reductase (AKR) 1C3 in some tumors. Here, we evaluate reductive metabolism of PR-104A in mice and its significance for host toxicity.

METHODS

The pharmacokinetics of PR-104, PR-104A and its reduced metabolites were investigated in plasma and tissues of mice (with and without SiHa or H460 tumor xenografts) and effects of potential oxidoreductase inhibitors were evaluated.

RESULTS

Pharmacokinetic studies identified extensive non-tumor reduction of PR-104A to the 5-amine PR-104H (identity of which was confirmed by chemical synthesis), especially in liver. However, high concentrations of PR-104H in tumors that suggested intra-tumor activation is also significant. The tissue distribution of PR-104M/H was broadly consistent with the target organ toxicities of PR-104 (bone marrow, intestines and liver). Surprisingly, hepatic nitroreduction was not enhanced when the liver was made more hypoxic by hepatic artery ligation or breathing of 10% oxygen. A screen of non-steroidal anti-inflammatory drugs identified naproxen as an effective AKR1C3 inhibitor in human tumor cell cultures and xenografts, suggesting its potential use to ameliorate PR-104 toxicity in patients. However, neither naproxen nor the pan-CYP inhibitor 1-aminobenzotriazole inhibited normal tissue reduction of PR-104A in mice.

CONCLUSIONS

PR-104 is extensively reduced in mouse tissues, apparently via oxygen-independent two-electron reduction, with a tissue distribution that broadly reflects toxicity.

Adenosine-dependent activation of hypoxia-inducible factor-1 induces late preconditioning in liver cells

The cellular mechanisms by which ischemic preconditioning increases liver tolerance to ischemia/reperfusion injury are still poorly understood. This study investigated the role of the hypoxia-inducible factor-1 (HIF-1) in the protection associated with the late phase of liver preconditioning. Late preconditioning was induced in primary cultured rat hepatocytes by a transient (10 minute) hypoxic stress or by 15 minutes incubation with the adenosine A(2A) receptors agonist CGS21680 24 hours before exposure to 90 minutes of hypoxia in a serum-free medium. Late preconditioning induced the nuclear translocation of HIF-1 and the expression of carbonic anhydrase IX (CAIX), a HIF-1-regulated transmembrane enzyme that catalyzes bicarbonate production. Such effects were associated with prevention of hepatocyte killing by hypoxia and the amelioration of intracellular acidosis and Na+ accumulation. The inhibition of PKC-mediated and PI3-kinase-mediated signals with, respectively, chelerythrine and wortmannin abolished HIF-1 activation and blocked both CAIX expression and the protective action of late preconditioning. CAIX expression was also prevented by interfering with the transcriptional activity of HIF-1 using a dominant negative HIF-1beta subunit. The inhibition of CAIX with acetazolamide or the block of bicarbonate influx with disodium-4-acetamido-4'-isothiocyanato-stilben-2,2'-disulfonate also reverted the protective effects of late preconditioning on intracellular acidosis and Na+ accumulation.

CONCLUSION

The stimulation of adenosine A(2A) receptors induced late preconditioning in liver cells through the activation of HIF-1. HIF-1-induced expression of CAIX increases hepatocyte tolerance to ischemia by maintaining intracellular Na+ homeostasis. These observations along with the importance of HIF-1 in regulating cell survival indicates HIF-1 activation as a possible key event in liver protection by late preconditioning.