5-Aminoisoquinolinone, a novel inhibitor of poly(adenosine disphosphate-ribose) polymerase, reduces microvascular liver injury but not mortality rate after hepatic ischemia-reperfusion*

Quantitative Determination of 5-Aminoisoquinoline, a PARP-1 Inhibitor by UPLC-MS/MS: In Silico ADME Profile and In Vitro Metabolic Stability Study

5-Aminoisoquinoline (5-AIQ) is a water-soluble, potent and selective Poly (ADP-ribose) polymerase 1 (PARP-1) inhibitor, widely used as a biochemical and pharmacological tool to study the inhibitory effect of PARPs enzyme. In this study, a simple, selective and reliable ultra-performance liquid chromatography-tandem mass spectrometry assay has been developed for the quantitative analysis of 5-AIQ in plasma using pantoprazole as an internal standard (IS). Both 5-AIQ and IS were separated on an Acquity CSH18 (2.1 × 100 mm; 1.7 µm) column after chromatographic elution of mobile phase comprising of 10 mM ammonium acetate and acetonitrile (35:65; v/v) at a flow rate of 0.3 mL/min. Electrospray ionization in positive mode was used for sample ionization and precursor to product ion transitions of 145.0 > 91.0; 145.0 > 117.4 for 5-AIQ and 384.0 > 138.1 for IS were used for detection and quantification in multiple reaction monitoring mode. The assay was linear in the concentration range of 1.0 to 666 ng/mL with correlation coefficient of ≥0.995. The precision and bias were within the acceptable limits of ≤12.68% and −8.6 to 5.9%, respectively, with mean recovery of 79.1% from plasma and negligible matrix effects (92.4%). In silico ADME prediction, 5-AIQ showed to be very soluble in water and high gastrointestinal absorption along with blood–brain barrier (BBB) permeability. The validated assay was successfully applied in a metabolic stability study, and 5-AIQ was moderately metabolized by human liver microsomes with an in vitro half-life of 14.5 min and intrinsic clearance of 47.6 µL/min/mg. The validated method can be utilized for future pharmacokinetic and bio-distribution studies.

Role of Peroxynitrite-Induced Activation of Poly(ADP-Ribose) Polymerase (PARP) in Circulatory Shock and Related Pathological Conditions

Peroxynitrite is a powerful oxidant, formed from the reaction of nitric oxide and superoxide. It is known to interact and modify different biological molecules such as DNA, lipids and proteins leading to alterations in their structure and functions. These events elicit various cellular responses, including cell signaling, causing oxidative damage and committing cells to apoptosis or necrosis. This review discusses nitrosative stress-induced modification in the DNA molecule that results in the formation of 8-nitroguanine and 8-oxoguanine, and its role in disease conditions. Different approaches of cell death, such as necrosis and apoptosis, are modulated by cellular high-energy species, such as ATP and NAD⁺. High concentrations of peroxynitrite are known to cause necrosis, whereas low concentrations lead to apoptosis. Any damage to DNA activates cellular DNA repair machinery, like poly(ADP-ribose) polymerase (PARP). PARP-1, an isoform of PARP, is a DNA nick-sensing enzyme that becomes activated upon sensing DNA breakage and triggers the cleavage of NAD⁺ into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins. Peroxynitrite-induced hyperactivation of PARP causes depletion of NAD⁺ and ATP culminating cell dysfunction, necrosis or apoptosis. This mechanistic pathway is implicated in the pathogenesis of a variety of diseases, including circulatory shock (which is characterized by cellular hypoxia triggered by systemic altered perfusion and tissue oxygen utilization leading end-organ dysfunction), sepsis and inflammation, injuries of the lung and the intestine. The cytotoxic effects of peroxynitrite centering on the participation of PARP-1 and ADP-ribose in previously stated diseases have also been discussed in this review.

Hypothermic machine perfusion ameliorates inflammation during ischemia‑reperfusion injury via sirtuin‑1‑mediated deacetylation of nuclear factor‑κB p65 in rat livers donated after circulatory death

Hypothermic machine perfusion (HMP) effectively reduces ischemia-reperfusion injury (IRI) in livers donated after circulatory death (DCD) when compared with cold storage (CS). However, the underlying mechanisms remain unclear. The current study aimed to investigate the cellular mechanisms by which HMP ameliorates the inflammatory response during IRI. Adult male Sprague-Dawley rat livers were exposed to 30 min of warm ischemia following cardiac arrest and preserved by CS or HMP for 3 h (n=3 per group). The severity of IRI was assessed in vitro on normothermic reperfusion for 2 h, and intrahepatic resistance (IHR) and bile production were subsequently recorded. The perfusate was analyzed for transaminase leakage and oxygen consumption. Livers were subsequently subjected to histological examination, and measurement of adenosine triphosphate (ATP) levels, malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, nicotinamide adenine dinucleotide (NAD)⁺ levels and the ratio of NAD⁺/NADH. In addition, the protein expression of sirtuin-1 (SIRT-1), acetylated-nuclear factor-κB (NF-κB) p65 and NF-κB p65 was detected by western blotting, and the mRNA expression of the inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α was determined by reverse transcription-quantitative polymerase chain reaction. Compared with CS, HMP resulted in significantly lower IHR, transaminase leakage and MDA levels, and higher oxygen consumption, ATP levels and SOD activity. In addition, improved preservation of hepatic histology was observed in HMP compared with CS. The mRNA expression of NF-κB p65, IL-6 and TNF-α was significantly decreased in the HMP group compared with CS samples. Under HMP preservation, SIRT-1 activity and protein expression were increased, while the protein expression of acetylated-NF-κB p65 was decreased, compared with CS. These results indicate that HMP may reduce the inflammatory response during IRI via SIRT-1-mediated deacetylation of NF-κB p65. These findings may provide a theoretical basis for the clinical application of HMP as an effective strategy to preserve DCD livers.

PARP-1 promotes tumor recurrence after warm ischemic liver graft transplantation via neutrophil recruitment and polarization

Poly (ADP-ribose) polymerase 1 (PARP-1) is a crucial contributor to exacerbate ischemia and reperfusion (IR) injury and cancer process. However, there is little research into whether PARP-1 affects the hepatocellular carcinoma (HCC) recurrence after liver transplantation. In this study, we investigated the influence of PARP-1 on hepatic neutrophil mobilizing and phenotype shifting which may lead to HCC recurrence after liver transplantation. We found that rats received the grafts with warm ischemic injury had higher risk of HCC recurrence, which was markedly prevented by pharmacological inhibition of PARP-1 after liver transplantation. In mouse models, the up-regulation of PARP-1 was closely related to the greater tumor burden and increased hepatic susceptibility to recurrence after IR injury. The reason was that high hepatic PARP-1 led to increased liver CXCL1 levels, which in turn promoted recruitment of neutrophils. Both blocking CXCL1/CXCR2 signaling pathway and depleting neutrophils decreased tumor burden. Moreover, these infiltrating neutrophils were programmed to a proangiogenic phenotype under the influence of PARP-1 in vivo after hepatic IR injury. In conclusion, IR-induced PARP-1 up-regulation increased the hepatic recruitment of neutrophils through regulation of CXCL1/CXCR2 signaling and polarized hepatic neutrophils to proangiogenic phenotype, which further promoted HCC recurrence after transplantation.

Fatty acid binding protein-4 (FABP4) is a hypoxia inducible gene that sensitizes mice to liver ischemia/reperfusion injury

BACKGROUND & AIMS

Fatty acid binding protein 4 (FABP4) has been known as a mediator of inflammatory response in the macrophages and adipose tissue, but its hepatic function is poorly understood. The goal of this study is to investigate the role of FABP4 in liver ischemia/reperfusion (I/R), a clinical condition that involves both hypoxia and inflammation.

METHODS

To examine the I/R regulation of FABP4, mice were subjected to I/R surgery before being measured for FABP4 gene expression. Both loss-of-function (by using a pharmacological FABP4 inhibitor) and gain-of-function (by adenoviral overexpression of FABP4) were used to determine the functional relevance of FABP4 expression and its regulation during I/R. To determine the hypoxia responsive regulation of FABP4, primary mouse hepatocytes were exposed to hypoxia. The FABP4 gene promoter was cloned and its regulation by hypoxia inducible factor 1α (HIF-1α) was characterized by luciferase reporter gene, electrophoretic mobility shift, and chromatin immunoprecipitation assays.

RESULTS

We found that the hepatic expression of FABP4 was markedly induced by I/R. At the functional level, pharmacological inhibition of FABP4 alleviated the I/R injury, whereas adenoviral overexpression of FABP4 sensitized mice to I/R injury. We also showed that exposure of primary hepatocytes to hypoxia or transgenic overexpression of HIF-1α in the mouse liver was sufficient to induce the expression of FABP4. Our promoter analysis established FABP4 as a novel transcriptional target of HIF-1α.

CONCLUSIONS

FABP4 is a hypoxia inducible gene that sensitizes mice to liver I/R injury. FABP4 may represent a novel therapeutic target, and FABP4 inhibitors may be used as therapeutic agents to manage hepatic I/R injury.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Molecular Biology of Apoptosis in Ischemia and Reperfusion

This study reviews the current understanding of the mechanisms that mediate the complex processes involved in apoptosis secondary to ischemia and reperfusion (I/R) and is not intended as a complete literature review of apoptosis. Several biochemical reactions trigger a cascade of events, which activate caspases. These caspases exert their effect through downstream proteolysis until the final effector caspases mediate the nuclear features characteristic of apoptosis, DNA fragmentation and condensation. Within the context of ischemia, the hypoxic environment initiates the expression of several genes involved in inflammation, the immune response, and apoptosis. Many of these same genes are activated during reperfusion injury in response to radical oxygen species generation. It is plausible that inhibition of specific apoptotic pathways via inactivation or downregulation of those genes responsible for the initiation of inflammation, immune response, and apoptosis may provide promising molecular targets for ameliorating reperfusion injury in I/R-related processes. Such inhibitory mechanisms are discussed in this review. Important targets in I/R-related pathologies include the brain during stroke, the heart during myocardial infarction, and the organs during harvesting and/or storage for transplantation. In addition, we present data from our ongoing research of specific signal transduction-related elements and their role in ischemia/reperfusion injury. These data address the potential therapeutic application of anti-inflammatory and anti-ischemic compounds in the prevention of I/R damage.

Poly(ADP-ribose) polymerase activity in different pathologies--the link to inflammation and infarction

DNA repair and aging are two phenomena closely connected to each other. The poly(ADP-ribosyl)ation reaction has been implicated in both of them. Poly(ADP-ribose) was originally discovered as an enzymatic reaction product after DNA damage. Soon it became evident that it is necessary for regulation of different repair pathways. Also, evidence accumulated that poly(ADP-ribose) formation capacity is at least correlated with the life span of mammalian species. As a NAD(+)-consuming process, poly(ADP-ribosyl)ation can lead to cell death by energy depletion. This finding opened the area for investigation of poly(ADP-ribose) polymerase activity and polymer formation in pathologies. This review provides an introduction into the wide and complex field of poly(ADP-ribosyl)ation in different pathologies with regards of cell death regulation, inflammation and resulting tissue damage.

Effect of PJ-34 PARP-Inhibitor on Rat Liver Microcirculation and Antioxidant Status

BACKGROUND

Ischemia-reperfusion (I-R) injury during liver resection leads to the production of toxic free radicals and oxidants that influence the microcirculation. DNA single-strand breaks can be induced by these reactive species. In response to excessive DNA damage, PARP [poly(ADP-ribose) polymerase] becomes overactivated, which can lead to cellular ATP depletion and cell death. The aim of our study was to evaluate whether PARP is expressed in post-ischemic liver, and to examine the effect of the administration of PJ-34 PARP inhibitor on liver function, histopathology, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) reaction, and the oxidative state of the liver after injury.

METHODS

Male Wistar rats (weighing 250 g) underwent 60 min of normothermic, segmental liver ischemia followed by 30 min of reperfusion. The animals (n = 45) were divided into three groups: sham operated; I-R (control) treated with saline; and PJ-34 pre-treated (10 mg/kg i.v.). Hepatic microcirculation was monitored by a laser Doppler flowmeter. The reperfusion was characterized as the integral of the reperfusion area (RA) and the maximal plateau (PM). Histological alterations, TUNEL-reaction, serum, and liver tissue antioxidant levels, as well as serum ALT and AST levels were measured.

RESULTS

Upon reperfusion, the PJ-34 group had significantly (P < 0.05) higher flow rates than control groups (PM(PJ-34): 58%, PM(control): 37%; RA(PJ-34.): 48%, RA(control): 25%). At the end of the 30 min reperfusion, PJ-34 resulted in significantly (P < 0.05) lower serum ALT and AST levels and chemiluminescent intensity (free radicals) of the liver. The liver's free SH-group concentration and H-donor ability of the plasma was elevated in the PARP-inhibitor treated group. Positive staining for TUNEL, after PJ-34 pre-treatment was significantly increased (P < 0.05); in contrast, the control tissues were less positively stained for TUNEL but necrotic tissue was abundant.

CONCLUSION

PARP plays a pathogenetic role in the deterioration of the hepatic microcirculation and promotes hepatocellular necrosis in liver reperfusion injury.

Combination therapy of poly (ADP-ribose) polymerase inhibitor 3-aminobenzamide and gemcitabine shows strong antitumor activity in pancreatic cancer cells

BACKGROUND AND AIM

Poly (ADP-ribose) polymerase (PARP) inhibitors such as 3-aminobenzamide (3-ABA) enhance the in vitro cytotoxicity of DNA mono-functional alkylating agents such as radiation or chemotherapeutic agents. The aim of this study was to test an approach combining the PARP inhibitor 3-ABA with standard gemcitabine therapy in human pancreatic cancer cells.

METHODS

Cell viability was determined by proliferation assay (XTT). Cell-cycle analysis (FACS), ELISA (M30 Apoptosense), Western blot for caspase 8 and PARP, and electron microscopy were used to identify apoptosis. Tumor growth and survival was assessed in nude mice by subcutaneously injected Capan-1 cells. In addition, Ki67 staining was performed on tumors for cell proliferation and in vivo apoptosis induction was measured by TUNEL assay and ELISA.

RESULTS

Combination therapy of gemcitabine and 3-ABA suppressed tumor cell growth more than gemcitabine alone in XTT, FACS and ELISA analysis.

CONCLUSION

This in vivo study demonstrated a significantly reduced tumor weight and increased survival up to 40 days after cell inoculation with combination therapy compared to animals treated with PBS, gemcitabine or 3-ABA alone. Furthermore, TUNEL assay revealed a significant apoptosis induction and reduced proliferation in the combination group.

Protective effects of PARP inhibition on liver microcirculation and function after haemorrhagic shock and resuscitation in male rats

OBJECTIVE

The aim of this study was to investigate the impact of the water-soluble poly-(ADP)-ribose-polymerase (PARP) inhibitor 5-aminoisoquinolinone (5-AIQ) on liver microcirculation and function after haemorrhagic shock and resuscitation.

DESIGN

Controlled, randomized animal study.

SETTING

University animal care facility and research laboratory.

SUBJECT

Male Sprague-Dawley rats were subjected to haemorrhagic shock for 1 h, followed by resuscitation with shed blood and crystalloid solution for a total of 5 h.

INTERVENTIONS

The PARP inhibitor 5-AIQ (3 mg/kg; n=7) or vehicle (n=7) was administered 5 min prior to resuscitation. Sham-operated animals without induction of shock served as controls (n=7).

MEASUREMENTS AND RESULTS

Using intravital fluorescence microscopy hepatic microcirculation was assessed at baseline, end of shock phase as well as 1 h and 5 h after resuscitation. Systemic arterial blood pressure and bile flow were continuously monitored. 5-AIQ treatment attenuated shock/resuscitation-induced increase of intrahepatic leukocyte-endothelial cell interaction with a marked reduction of both sinusoidal leukostasis and venular leukocyte adherence. Moreover, nutritive perfusion was found improved, guaranteeing sufficient oxygen supply to tissue, as indicated by low NADH autofluorescence, which was not different to that in controls. Most notably, excretory liver function reached baseline level over 5 h of reperfusion in 5-AIQ-treated animals.

CONCLUSIONS

In the present setting of shock/resuscitation in male rats the PARP inhibitor 5-AIQ proved to be very effective in ameliorating compromised liver microcirculation and function. Further research has to confirm that PARP inhibition is a suitable tool in the acute treatment of patients suffering from reduced circulating blood volume and thus microcirculatory organ dysfunction.

Junctional adhesion molecule-A deficiency increases hepatic ischemia-reperfusion injury despite reduction of neutrophil transendothelial migration

The endothelial receptors that control leukocyte transmigration in the postischemic liver are not identified. We investigated the role of junctional adhesion molecule-A (JAM-A), a receptor expressed in endothelial tight junctions, leukocytes, and platelets, for leukocyte transmigration during hepatic ischemia-reperfusion (I/R) in vivo. We show that JAM-A is up-regulated in hepatic venular endothelium during reperfusion. I/R-induced neutrophil transmigration was attenuated in both JAM-A-/- and endothelial JAM-A-/- mice as well as in mice treated with an anti-JAM-A antibody, whereas transmigration of T cells was JAM-A independent. Postischemic leukocyte rolling remained unaffected in JAM-A-/- and endothelial JAM-A-/- mice, whereas intravascular leukocyte adherence was increased. The extent of interactions of JAM-A-/- platelets with the postischemic endothelium was comparable with that of JAM-A+/+ platelets. The I/R-induced increase in the activity of alanine aminotransferase (ALT)/aspartate aminotransferase (AST) and sinusoidal perfusion failure was not reduced in JAM-A-/- mice, while the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL)-positive hepatocytes was significantly higher. Thus, we show for the first time that JAM-A is up-regulated in hepatic venules and serves as an endothelial receptor of neutrophil transmigration, but it does not mediate leukocyte rolling, adhesion, or platelet-endothelial cell interactions. JAM-A deficiency does not reduce I/R-induced microvascular and hepatocellular necrotic injury, but increases hepatocyte apoptosis, despite attenuation of neutrophil infiltration. (Blood. 2005;106:725-733)