High-molecular-weight polyethylene glycol protects cardiac myocytes from hypoxia- and reoxygenation-induced cell death and preserves ventricular function

Liposomal quercetin: A promising strategy to combat hepatic insulin resistance and inflammation in type 2 diabetes mellitus

In type 2 diabetes mellitus, hepatic insulin resistance is intricately associated with oxidative stress and inflammation. Nonetheless, the lack of therapeutic interventions directly targeting hepatic dysfunction represents a notable gap in current treatment options. Flavonoids have been explored due to their potential antidiabetic effects. However, these compounds are associated with low bioavailability and high metabolization. In the present study, four flavonoids, kaempferol, quercetin, kaempferol-7-O-glucoside and quercetin-7-O-glucoside, were studied in a cellular model of hepatic insulin resistance using HepG2 cells. Quercetin was selected as the most promising flavonoid and incorporated into liposomes to enhance its therapeutic effect. Quercetin liposomes had a mean size of 0.12 µm, with an incorporation efficiency of 93 %. Quercetin liposomes exhibited increased efficacy in modulating insulin resistance. This was achieved through the modulation of Akt expression and the attenuation of inflammation, particularly via the NF-κB pathway, as well as the regulation of PGE2 and COX-2 expression. Furthermore, quercetin liposomes displayed a significant advantage over free quercetin in attenuating the production of reactive pro-oxidant species. These findings open new avenues for developing innovative therapeutic strategies to manage diabetes, emphasizing the potential of quercetin liposomes as a promising approach for targeting both hepatic insulin resistance and associated inflammation.

Intravenous Polyethylene Glycol Alleviates Intestinal Ischemia-Reperfusion Injury in a Rodent Model

Intestinal ischemia-reperfusion injury (IRI) is a common clinical entity, and its outcome is unpredictable due to the triad of inflammation, increased permeability and bacterial translocation. Polyethylene glycol (PEG) is a polyether compound that is extensively used in pharmacology as an excipient in various products. More recently, this class of products have shown to have potent anti-inflammatory, anti-apoptotic, immunosuppressive and cell-membrane-stabilizing properties. However, its effects on the outcome after intestinal IRI have not yet been investigated. We hypothesized that PEG administration would reduce the effects of intestinal IRI in rodents. In a previously described rat model of severe IRI (45 min of ischemia followed by 60 min of reperfusion), we evaluated the effect of IV PEG administration at different doses (50 and 100 mg/kg) before and after the onset of ischemia. In comparison to control animals, PEG administration stabilized the endothelial glycocalyx, leading to reduced reperfusion edema, bacterial translocation and inflammatory reaction as well as improved 7-day survival. These effects were seen both in a pretreatment and in a treatment setting. The fact that this product is readily available and safe should encourage further clinical investigations in settings of intestinal IRI, organ preservation and transplantation.

Concentration Threshold for Membrane Protection by PEO-PPO Block Copolymers with Variable Molecular Architectures

Poloxamer 188, a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer, protects cell membranes in several injury models. However, the nature of the copolymer/membrane interaction and the mechanism of membrane protection remain unknown. Systematic variations of the block copolymer architecture - including PPO-PEO-PPO triblocks and PPO-PEO diblocks - were used to probe the mechanism and evaluate the potential for alternative architectures to yield superior protection. To test the polymers, murine myoblasts were subjected to an osmotic stress, and membrane integrity was quantified by measuring lactate dehydrogenase (LDH) leakage. These experiments exposed a concentration threshold effect where all tested polymers reach 50% leakage of LDH compared to a non-treated buffer only control over a narrow concentration range of 0.8-4 μM. Differences in polymer protection at lower concentrations indicate that protection increases with the PPO-PEO-PPO molecular architecture and increasing hydrophobicity.

Lipid Membrane Binding and Cell Protection Efficacy of Poly(1,2-butylene oxide)-b-poly(ethylene oxide) Copolymers

Poloxamers consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) segments can protect cell membranes against various forms of stress. We investigated the role of the hydrophobic block chemistry on polymer/membrane binding and cell membrane protection by comparing a series of poly(butylene oxide)-b-PEO (PBO-b-PEO) copolymers to poloxamer analogues, using a combination of pulsed-field-gradient (PFG) NMR experiments and a lactate dehydrogenase (LDH) cell assay. We found that the more hydrophobic PBO-b-PEO copolymers bound more significantly to model liposomes composed of 1-palmitol-2-oleoyl-glycero-3-phosphocholine (POPC) compared to poly(propylene oxide) (PPO)/PEO copolymers. However, both classes of polymers performed similarly when compared by an LDH assay. These results present an important comparison between polymers with similar structures but with different binding affinities. They also provide mechanistic insight as enhanced polymer/lipid membrane binding did not directly translate to increased cell protection in the LDH assay, and therefore, additional factors need to be considered when trying to achieve greater membrane protection efficacy.

PEG35 as a Preconditioning Agent against Hypoxia/Reoxygenation Injury

Pharmacological conditioning is a protective strategy against ischemia/reperfusion injury, which occurs during liver resection and transplantation. Polyethylene glycols have shown multiple benefits in cell and organ preservation, including antioxidant capacity, edema prevention and membrane stabilization. Recently, polyethylene glycol 35 kDa (PEG35) preconditioning resulted in decreased hepatic injury and protected the mitochondria in a rat model of cold ischemia. Thus, the study aimed to decipher the mechanisms underlying PEG35 preconditioning-induced protection against ischemia/reperfusion injury. A hypoxia/reoxygenation model using HepG2 cells was established to evaluate the effects of PEG35 preconditioning. Several parameters were assessed, including cell viability, mitochondrial membrane potential, ROS production, ATP levels, protein content and gene expression to investigate autophagy, mitochondrial biogenesis and dynamics. PEG35 preconditioning preserved the mitochondrial function by decreasing the excessive production of ROS and subsequent ATP depletion, as well as by recovering the membrane potential. Furthermore, PEG35 increased levels of autophagy-related proteins and the expression of genes involved in mitochondrial biogenesis and fusion. In conclusion, PEG35 preconditioning effectively ameliorates hepatic hypoxia/reoxygenation injury through the enhancement of autophagy and mitochondrial quality control. Therefore, PEG35 could be useful as a potential pharmacological tool for attenuating hepatic ischemia/reperfusion injury in clinical practice.

Poloxamer 188 Protects Isolated Adult Mouse Cardiomyocytes from Reoxygenation Injury

Reperfusion injury is a complex pathological event involving processes that can lead to further disruption of the cell membrane and function following an ischemic event. Return of blood flow allows for the needed reperfusion; however, for a period of time before remaining viable cells stabilize, reperfusion results in additional cellular injury. In cardiomyocytes, loss of membrane integrity allows abnormal influx of extracellular calcium, leading to hyper-contracture and cell death. Methods to improve the membrane integrity of cardiomyocytes overwhelmed by pathological disruptions, such as reperfusion injury, are needed to prevent cell death, because of the myocardium's limited ability to regenerate. Research has shown administration of the copolymer P(oloxamer) 188 before ischemia/reperfusion can protect cardiomyocytes through membrane stabilization. This study sought to determine whether the administration of P188 at the beginning of the clinically more relevant time of reperfusion after ischemia will attenuate any additional damage to cardiomyocytes by stabilizing membrane integrity to allow the cells to maintain function. Using an in-vitro cardiomyocyte model subjected to hypoxia/reoxygenation to simulate ischemia/reperfusion injury, we show that reoxygenation significantly potentiates the injury caused by hypoxia itself. P188, with its unique combination of hydrophobic and hydrophilic chemical properties, and only delivered at the beginning of reoxygenation, dose-dependently protected cardiomyocytes from injury due to reoxygenation by repairing cell membranes, decreasing calcium influx, and maintaining cellular morphology. Our study also shows the hydrophobic portion of P188 is necessary for the stabilization of cell membrane integrity in providing protection to cardiomyocytes against reoxygenation injury.

Polyethylene glycol 35 ameliorates pancreatic inflammatory response in cerulein-induced acute pancreatitis in rats

BACKGROUND

Acute pancreatitis (AP) is a sudden inflammatory process of the pancreas that may also involve surrounding tissues and/or remote organs. Inflammation and parenchymal cell death are common pathological features of this condition and determinants of disease severity. Polyethylene glycols (PEGs) are non-immunogenic, non-toxic water-soluble polymers widely used in biological, chemical, clinical and pharmaceutical settings.

AIM

To evaluate the protective effect of a 35-kDa molecular weight PEG (PEG35) on the pancreatic damage associated to cerulein-induced acute pancreatitis in vivo and in vitro.

METHODS

Wistar rats were assigned at random to a control group, a cerulein–induced AP group and a PEG35 treatment group. AP was induced by five hourly intraperitoneal injections of cerulein (50 μg/kg/bw), while the control animals received saline solution. PEG35 was administered intraperitoneally 10 minutes before each cerulein injection in a dose of 10 mg/kg. After AP induction, samples of pancreatic tissue and blood were collected for analysis. AR42J pancreatic acinar cells were treated with increasing concentrations of PEG35 prior to exposure with tumor necrosis factor α (TNFα), staurosporine or cerulein. The severity of AP was determined on the basis of plasma levels of lipase, lactate dehydrogenase activity, pancreatic edema and histological changes. To evaluate the extent of the inflammatory response, the gene expression of inflammation-associated markers was determined in the pancreas and in AR42J-treated cells. Inflammation-induced cell death was also measured in models of in vivo and in vitro pancreatic damage.

RESULTS

Administration of PEG35 significantly improved pancreatic damage through reduction on lipase levels and tissue edema in cerulein-induced AP rats. The increased associated inflammatory response caused by cerulein administration was attenuated by a decrease in the gene expression of inflammation-related cytokines and inducible nitric oxide synthase enzyme in the pancreas. In contrast, pancreatic tissue mRNA expression of interleukin 10 was markedly increased. PEG35 treatment also protected against inflammation-induced cell death by attenuating lactate dehydrogenase activity and modulating the pancreatic levels of apoptosis regulator protein BCL-2 in cerulein hyperstimulated rats. Furthermore, the activation of pro-inflammatory markers and inflammation-induced cell death in pancreatic acinar cells treated with TNFα, cerulein or staurosporine was significantly reduced by PEG35 treatment, in a dose-dependent manner.

CONCLUSION

PEG35 ameliorates pancreatic damage in cerulein-induced AP and AR42J-treated cells through the attenuation of the inflammatory response and associated cell death. PEG35 may be a valuable option in the management of AP.

Prolonged Cold Ischemia Time in Mouse Heart Transplantation Using Supercooling Preservation

BACKGROUND

Supercooling preservation techniques store a donor organ below 0°C without freezing. This has great advantages in inhibiting metabolism and preserving the organ in comparison to conventional preservation at 4°C. We developed a novel supercooling technique using a liquid cooling apparatus and novel preservation and perfusion solutions. The purpose of this study was to evaluate the preservation effect of our supercooling preservation technique in a mouse heart transplantation model.

METHODS

Syngeneic heterotopic heart transplantation was performed in 3 groups of mice: (1) the nonpreservation group, in which the cardiac grafts were transplanted immediately after retrieval; (2) the conventional University of Wisconsin (UW) group, in which the cardiac grafts were stored in UW solution at 4°C for different periods of time; and (3) the supercooling group, in which the cardiac grafts were stored in a novel supercooling preservation solution at -8°C for different periods of time. The maximal preservation time was investigated. Twenty-four-hour sample data were collected and analyzed to compare supercooling preservation to conventional UW preservation.

RESULTS

Our technique yielded a stable -8°C supercooling state. Cardiac graft revival was successfully achieved after supercooling preservation for 144 hours, and long-term survival was observed after supercooling preservation for 96 hours. Posttransplant outcomes, including myocardial ischemia-reperfusion injury, oxidative stress-related damage, and myocardial cell apoptosis, were improved in comparison to conventional 4°C UW preservation.

CONCLUSIONS

Supercooling heart preservation at -8°C greatly prolonged the preservation time and improved the posttransplant outcomes in comparison to conventional 4°C UW preservation. Supercooling preservation is a promising technique for organ preservation.

Spatial Distribution of PEO-PPO-PEO Block Copolymer and PEO Homopolymer in Lipid Bilayers

Maintaining the integrity of cell membranes is indispensable for cellular viability. Poloxamer 188 (P188), a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer with a number-average molecular weight of 8700 g/mol and containing 80% by mass PEO, protects cell membranes from various external injuries and has the potential to be used as a therapeutic agent in diverse applications. The membrane protection mechanism associated with P188 is intimately connected with how this block copolymer interacts with the lipid bilayer, the main component of a cell membrane. Here, we report the distribution of P188 in a model lipid bilayer comprising 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) using neutron reflectivity (NR) and atomic force microscopy (AFM). We also investigated the association of a PEO homopolymer (PEO8.4K; M_n = 8400 g/mol) that does not protect living cell membranes. These experiments were conducted following incubation of a 4.5 mmol/L polymer solution in a buffer that mimics physiological conditions with supported POPC bilayer membranes followed by washing with the aqueous medium. In contrast to previous reports, which dealt with P188 and PEO in salt-free solutions, both P188 and PEO8.4K penetrate into the inner portion of the lipid bilayer as revealed by NR, with approximately 30% by volume occupancy across the membrane without loss of bilayer structural integrity. These results indicate that PEO is the chemical moiety that principally drives P188 binding to bilayer membranes. No defects or phase-separated domains were observed in either P188- or PEO8.4K-incubated lipid bilayers when examined by AFM, indicating that polymer chains mingle homogeneously with lipid molecules in the bilayer. Remarkably, the breakthrough force required for penetration of the AFM tip through the bilayer membrane is unaffected by the presence of the large amount of P188 and PEO8.4K.

Polyethylene Glycol 35 (PEG35) Protects against Inflammation in Experimental Acute Necrotizing Pancreatitis and Associated Lung Injury

Acute pancreatitis is an inflammatory disorder of the pancreas. Its presentation ranges from self-limiting disease to acute necrotizing pancreatitis (ANP) with multiorgan failure and a high mortality. Polyethylene glycols (PEGs) are non-immunogenic, non-toxic, and water-soluble chemicals composed of repeating units of ethylene glycol. The present article explores the effect of PEG35 administration on reducing the severity of ANP and associated lung injury. ANP was induced by injection of 5% sodium taurocholate into the biliopancreatic duct. PEG35 was administered intravenously either prophylactically or therapeutically. Three hours after ANP induction, pancreas and lung tissue samples and blood were collected and ANP severity was assessed. To evaluate the inflammatory response, gene expression of pro-inflammatory cytokines and chemokine and the changes in the presence of myeloperoxidase and adhesion molecule levels were determined in both the pancreas and the lung. To evaluate cell death, lactate dehydrogenase (LDH) activity and apoptotic cleaved caspase-3 localization were determined in plasma and in both the pancreatic and lung tissue respectively. ANP-associated local and systemic inflammatory processes were reduced when PEG35 was administered prophylactically. PEG35 pre-treatment also protected against acute pancreatitis-associated cell death. Notably, the therapeutic administration of PEG35 significantly decreased associated lung injury, even when the pancreatic lesion was equivalent to that in the untreated ANP-induced group. Our results support a protective role of PEG35 against the ANP-associated inflammatory process and identify PEG35 as a promising tool for the treatment of the potentially lethal complications of the disease.

Silk Sericin Semi-interpenetrating Network Hydrogels Based on PEG-Diacrylate for Wound Healing Treatment

Silk sericin (SS) from the Bombyx mori silk cocoons has received much attention from biomedical scientists due to its outstanding properties, such as antioxidant, antibacterial, UV-resistant, and ability to release moisturizing factors. Unmodified SS does not self-assemble strongly enough to be used as a hydrogel wound dressing. Therefore, there is a need for suitable stabilization techniques to interlink the SS peptide chains or strengthen their structural cohesion. Here, we reported a method to form a silk semi-interpenetrating network (semi-IPN) structure through reacting with the short-chain poly(ethylene glycol) diacrylate (PEGDA) in the presence of a redox pair. Various hydrogels were prepared in aqueous media at the final SS/PEGDA weight percentages of 8/92, 15/85, and 20/80. Results indicated that all semi-IPN samples underwent a sol-gel transition within 70 min. The equilibrium water content (EWC) for all samples was found to be in the range of 70-80%, depending on the PEGDA content. Both the gelation time and the sol fraction decreased with the increased PEGDA content. This was due to the tightened network structure formed within the hydrogel matrices. Among all hydrogel samples, the 15/85 (SS/PEGDA) hydrogel displayed the maximum compressive strength (0.66 MPa) and strain (7.15%), higher than those of pure PEGDA. This implied a well-balanced molecular interaction within the SS/PEGDA/water systems. Based on the direct and indirect MTS assay, the 15/85 hydrogel showed excellent in vitro biocompatibility towards human dermal fibroblasts, representing a promising material for biomedical wound dressing in the future. A formation of a semi-IPN structure has thus proved to be one of the best strategies to extend a practical limit of using SS hydrogels for wound healing treatment or other biomedical hydrogel matrices in the future.

Ischemia/Reperfusion Injury Revisited: An Overview of the Latest Pharmacological Strategies

Ischemia/reperfusion injury (IRI) permeates a variety of diseases and is a ubiquitous concern in every transplantation proceeding, from whole organs to modest grafts. Given its significance, efforts to evade the damaging effects of both ischemia and reperfusion are abundant in the literature and they consist of several strategies, such as applying pre-ischemic conditioning protocols, improving protection from preservation solutions, thus providing extended cold ischemia time and so on. In this review, we describe many of the latest pharmacological approaches that have been proven effective against IRI, while also revisiting well-established concepts and presenting recent pathophysiological findings in this ever-expanding field. A plethora of promising protocols has emerged in the last few years. They have been showing exciting results regarding protection against IRI by employing drugs that engage several strategies, such as modulating cell-surviving pathways, evading oxidative damage, physically protecting cell membrane integrity, and enhancing cell energetics.

Cardiomyocyte damage control in heart failure and the role of the sarcolemma

The cardiomyocyte plasma membrane, termed the sarcolemma, is fundamental for regulating a myriad of cellular processes. For example, the structural integrity of the cardiomyocyte sarcolemma is essential for mediating cardiac contraction by forming microdomains such as the t-tubular network, caveolae and the intercalated disc. Significantly, remodelling of these sarcolemma microdomains is a key feature in the development and progression of heart failure (HF). However, despite extensive characterisation of the associated molecular and ultrastructural events there is a lack of clarity surrounding the mechanisms driving adverse morphological rearrangements. The sarcolemma also provides protection, and is the cell's first line of defence, against external stresses such as oxygen and nutrient deprivation, inflammation and oxidative stress with a loss of sarcolemma viability shown to be a key step in cell death via necrosis. Significantly, cumulative cell death is also a feature of HF, and is linked to disease progression and loss of cardiac function. Herein, we will review the link between structural and molecular remodelling of the sarcolemma associated with the progression of HF, specifically considering the evidence for: (i) Whether intrinsic, evolutionary conserved, plasma membrane injury-repair mechanisms are in operation in the heart, and (ii) if deficits in key 'wound-healing' proteins (annexins, dysferlin, EHD2 and MG53) may play a yet to be fully appreciated role in triggering sarcolemma microdomain remodelling and/or necrosis. Cardiomyocytes are terminally differentiated with very limited regenerative capability and therefore preserving cell viability and cardiac function is crucially important. This review presents a novel perspective on sarcolemma remodelling by considering whether targeting proteins that regulate sarcolemma injury-repair may hold promise for developing new strategies to attenuate HF progression.

Membrane raft redox signalling contributes to endothelial dysfunction and vascular remodelling of thoracic aorta in angiotensin II-infused rats

NEW FINDINGS

What is the central question of this study? Is the membrane raft redox signalling pathway involved in blood pressure increase, endothelial dysfunction and vascular remodelling in an angiotensin II-induced hypertensive animal model? What is the main finding and its importance? The membrane raft redox signalling pathway was involved in endothelial dysfunction and medial remodelling in angiotensin II-induced hypertension.

ABSTRACT

The membrane raft (MR) redox pathway is characterized by NADPH oxidase activation via the clustering of its subunits through lysosome fusion and the activation of acid sphingomyelinase (ASMase). Our previous study shows that the MR redox signalling pathway is associated with angiontensin II (AngII)-induced production of reactive oxygen species (ROS) and endothelial dysfunction in rat mesenteric arteries. In the present study, we hypothesized that this signalling pathway is involved in blood pressure increase, endothelial dysfunction and vascular remodelling in an AngII-induced hypertensive animal model. Sixteen-week-old male Sprague-Dawley rats were subjected to AngII infusion for 2 weeks with or without treatment with the lysosome fusion inhibitor bafilomycin A1 and ASMase inhibitor amitriptyline. After treatments, aortas were harvested for further study. The results showed that the MR redox signalling pathway was activated as indicated by the increase of MR formation, ASMase activity and ROS production in aorta from AngII-infused rats compared with that from control rats. MR formation and ROS production were significantly inhibited in thoracic aorta from AngII-induced rats treated with bafilomycin A1 and amitriptyline. Both treatments significantly attenuated blood pressure increase, endothelial dysfunction and vascular remodelling including medial hypertrophy, and increased collagen and fibronectin deposition in thoracic aortas from AngII-infused rats. Finally, both treatments significantly prevented the increase of inflammatory factors including monocyte chemotactic protein 1, intercellular adhesion molecule 1 and tumour necrosis factor α in thoracic aorta from AngII-infused rats. In conclusion, the present study demonstrates that the MR redox signalling pathway was involved in endothelial dysfunction and medial remodelling in AngII-induced hypertension.

Inhibition of Postinfarction Ventricular Remodeling by High Molecular Weight Polyethylene Glycol

BACKGROUND

Myocardial infarction (MI) is a major etiology for the development of heart failure. We have previously shown that high molecular weight polyethylene glycol (PEG) can protect cardiac myocytes from hypoxia-reoxygenation injury in vitro. In this study, we investigated the potential protective effects of 15-20 kD PEG postinfarction without reperfusion.

METHODS

One milliliter of PEG 15-20 was delivered intravenously following permanent left anterior descending ligation in adult male rats with phosphate buffer saline (PBS) as control (n = 9 in each group). Echocardiography was performed at baseline and at 8 wk post-MI. Left ventricles (LVs) were harvested to quantify fibrosis, apoptosis, cell survival signaling, regulation of β-adrenergic signaling, and caveolin (Cav) expression.

RESULTS

The PEG group had significant recovery of LV function at 8 wk compared with the PBS group. There was less LV fibrosis in both the infarct and remote territory. Cell survival signaling was upregulated in the PEG group with increased Akt and ERK phosphorylation. PEG inhibited apoptosis as measured by terminal deoxynucleotidyl transferase [TdT]-mediated dUTP nick-end labeling positive nuclei and caspase-3 activity. There was maintenance of Cav-1, Cav-2, and Cav-3 expression following PEG treatment versus a decline in the PBS group. Negative regulators of β-adrenergic signaling, G protein-coupled receptor kinase-2, and β-arrestin 1 and 2 were all upregulated in PBS-treated samples compared to normal control; however, PEG treatment led to decreased expression.

CONCLUSIONS

These data suggest that PEG 15-20 may have significant protective effects post-MI even in the setting of no acute reperfusion. Upregulation of Cav expression appears to be a key mechanism for the beneficial effects of PEG on ventricular remodeling and function.

PEO-PPO Diblock Copolymers Protect Myoblasts from Hypo-Osmotic Stress In Vitro Dependent on Copolymer Size, Composition, and Architecture

Poloxamer 188, a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), protects cellular membranes from various stresses. Though numerous block copolymer variants exist, evaluation of alternative architecture, composition, and size has been minimal. Herein, cultured murine myoblasts are exposed to the stresses of hypotonic shock and isotonic recovery, and membrane integrity was evaluated by quantifying release of lactate dehydrogenase. Comparative evaluation of a systematic set of PEO-PPO diblock and PEO-PPO-PEO triblock copolymers demonstrates that the diblock architecture can be protective in vitro. Short PPO blocks hinder protection with >9 PPO units needed for protection at 150 μM and >16 units needed at 14 μM. Addition of a tert-butyl end group enhances protection at reduced concentration. When the end group and PPO length are fixed, increasing the PEO length improves protection. This systematic evaluation establishes a new in vitro screening tool for evaluating membrane-sealing amphiphiles and provides mechanistic insight to guide future copolymer design for membrane stabilization in vivo.

Polyethylene glycols: An effective strategy for limiting liver ischemia reperfusion injury

Liver ischemia-reperfusion injury (IRI) is an inherent feature of liver surgery and liver transplantation in which damage to a hypoxic organ (ischemia) is exacerbated following the return of oxygen delivery (reperfusion). IRI is a major cause of primary non-function after transplantation and may lead to graft rejection, regardless of immunological considerations. The immediate response involves the disruption of cellular mitochondrial oxidative phosphorylation and the accumulation of metabolic intermediates during the ischemic period, and oxidative stress during blood flow restoration. Moreover, a complex cascade of inflammatory mediators is generated during reperfusion, contributing to the extension of the damage and finally to organ failure. A variety of pharmacological interventions (antioxidants, anti-cytokines, etc.) have been proposed to alleviate graft injury but their usefulness is limited by the local and specific action of the drugs and by their potential undesirable toxic effects. Polyethylene glycols (PEGs), which are non-toxic water-soluble compounds approved by the FDA, have been widely used as a vehicle or a base in food, cosmetics and pharmaceuticals, and also as adjuvants for ameliorating drug pharmacokinetics. Some PEGs are also currently used as additives in organ preservation solutions prior to transplantation in order to limit the damage associated with cold ischemia reperfusion. More recently, the administration of PEGs of different molecular weights by intravenous injection has emerged as a new therapeutic tool to protect liver grafts from IRI. In this review, we summarize the current knowledge concerning the use of PEGs as a useful target for limiting liver IRI.

Polyethylene Glycol Preconditioning: An Effective Strategy to Prevent Liver Ischemia Reperfusion Injury

Hepatic ischemia reperfusion injury (IRI) is an inevitable clinical problem for liver surgery. Polyethylene glycols (PEGs) are water soluble nontoxic polymers that have proven their effectiveness in various in vivo and in vitro models of tissue injury. The present study aims to investigate whether the intravenous administration of a high molecular weight PEG of 35 kDa (PEG 35) could be an effective strategy for rat liver preconditioning against IRI. PEG 35 was intravenously administered at 2 and 10 mg/kg to male Sprague Dawley rats. Then, rats were subjected to one hour of partial ischemia (70%) followed by two hours of reperfusion. The results demonstrated that PEG 35 injected intravenously at 10 mg/kg protected efficiently rat liver against the deleterious effects of IRI. This was evidenced by the significant decrease in transaminases levels and the better preservation of mitochondrial membrane polarization. Also, PEG 35 preserved hepatocyte morphology as reflected by an increased F-actin/G-actin ratio and confocal microscopy findings. In addition, PEG 35 protective mechanisms were correlated with the activation of the prosurvival kinase Akt and the cytoprotective factor AMPK and the inhibition of apoptosis. Thus, PEG may become a suitable agent to attempt pharmacological preconditioning against hepatic IRI.

Protective Effect of Intravenous High Molecular Weight Polyethylene Glycol on Fatty Liver Preservation

Ischemia reperfusion injury (IRI) leads to significant tissue damage in liver surgery. Polyethylene glycols (PEGs) are water soluble nontoxic polymers that have proved their effectiveness against IRI. The objective of our study was to investigate the potential protective effects of intravenous administration of a high molecular weight PEG of 35 kDa (PEG 35) in steatotic livers subjected to cold ischemia reperfusion. In this study, we used isolated perfused rat liver model to assess the effects of PEG 35 intravenous administration after prolonged cold ischemia (24 h, 4°C) and after reperfusion (2 h, 37°C). Liver injury was measured by transaminases levels and mitochondrial damage was determined by confocal microscopy assessing mitochondrial polarization (after cold storage) and by measuring glutamate dehydrogenase activity (after reperfusion). Also, cell signaling pathways involved in the physiopathology of IRI were assessed by western blot technique. Our results show that intravenous administration of PEG 35 at 10 mg/kg ameliorated liver injury and protected the mitochondria. Moreover, PEG 35 administration induced a significant phosphorylation of prosurvival protein kinase B (Akt) and activation of cytoprotective factors e-NOS and AMPK. In conclusion, intravenous PEG 35 efficiently protects steatotic livers exposed to cold IRI.

Emerging concepts in liver graft preservation

The urgent need to expand the donor pool in order to attend to the growing demand for liver transplantation has obliged physicians to consider the use of suboptimal liver grafts and also to redefine the preservation strategies. This review examines the different methods of liver graft preservation, focusing on the latest advances in both static cold storage and machine perfusion (MP). The new strategies for static cold storage are mainly designed to increase the fatty liver graft preservation via the supplementation of commercial organ preservation solutions with additives. In this paper we stress the importance of carrying out effective graft washout after static cold preservation, and present a detailed discussion of the future perspectives for dynamic graft preservation using MP at different temperatures (hypothermia at 4 °C, normothermia at 37 °C and subnormothermia at 20 °C-25 °C). Finally, we highlight some emerging applications of regenerative medicine in liver graft preservation. In conclusion, this review discusses the "state of the art" and future perspectives in static and dynamic liver graft preservation in order to improve graft viability.

High-molecular-weight polyethylene glycol inhibits myocardial ischemia-reperfusion injury in vivo

OBJECTIVES

Cardiac ischemia-reperfusion (I-R) injury remains a significant problem as there are no therapies available to minimize the cell death that can lead to impaired function and heart failure. We have shown that high-molecular-weight polyethylene glycol (PEG) (15-20 kD) can protect cardiac myocytes in vitro from hypoxia-reoxygenation injury. In this study, we investigated the potential protective effects of PEG in vivo.

METHODS

Adult rats underwent left anterior descending artery occlusion for 60 minutes followed by 48 hours or 4 weeks of reperfusion. One milliliter of 10% PEG solution or phosphate-buffered saline (PBS) control (n = 10 per group) was administered intravenously (IV) immediately before reperfusion.

RESULTS

Fluorescein-labeled PEG was robustly visualized in the myocardium 1 hour after IV delivery. The PEG group had significant recovery of left ventricular ejection fraction at 4 weeks versus a 25% decline in the PBS group (P < .01). There was 50% less LV fibrosis in the PEG group versus PBS with smaller peri-infarct and remote territory fibrosis (P < .01). Cell survival signaling was upregulated in the PEG group with increased Akt (3-fold, P < .01) and ERK (4-fold, P < .05) phosphorylation compared to PBS controls at 48 hours. PEG also inhibited apoptosis as measured by TUNEL-positive nuclei (56% decrease, P < .02) and caspase 3 activity (55% decrease, P < .05).

CONCLUSIONS

High-molecular-weight PEG appears to have a significant protective effect from I-R injury in the heart when administered IV immediately before reperfusion. This may have important clinical translation in the setting of acute coronary revascularization and myocardial protection in cardiac surgery.

High molecular weight polyethylene glycol (PEG 15-20) maintains mucosal microbial barrier function during intestinal graft preservation

BACKGROUND

During organ transplantation, it is inevitable that tissues undergo cold ischemia during harvest and transport before implantation. Polyethylene-based polymers have been proposed and tested as preservation agents, with promising results. We have previously reported that a high molecular weight polyethylene glycol (PEG) (15-20,000 MW; PEG 15-20) protects the intestinal epithelium against a variety of cellular stresses, including radiation injury and microbial invasion, by mechanisms that appear to involve lipid rafts. The aim of this study was to determine the preservation effect of PEG 15-20 on the integrity of intestine grafts harvested for subsequent transplantation.

MATERIALS AND METHODS

We harvested intestinal grafts from mice using a complete surgical technique for intestinal transplantation and assessed them for the effect of PEG on graft tissue integrity. We preserved half of the grafts in histidine-tryptophan-ketoglutarate solution (HTK) alone and half in HTK-PEG 15-20 solution at 4°C for 24 h. We examined gross morphology, wet to dry ratios, histology, terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine, 5'-triphosphate nick end labeling assay for apoptosis, goblet cell numbers, and bacterial localization studies to evaluate the effect of PEG on tissue integrity.

RESULTS

Results demonstrated that PEG 15-20 had a superior preservation effect over HTK alone in all parameters tested. The effect of PEG was notable on attenuation of epithelial apoptosis, preservation of mucus-producing cells, and bacterial adherence to the epithelium.

CONCLUSIONS

Taken together, these studies suggest that use of PEG 15-20 as a potential adjuvant during intestinal transplant may offer significant promise to prolong graft survival during organ harvest.

A novel cardiomyocyte-enriched microRNA, miR-378, targets insulin-like growth factor 1 receptor: implications in postnatal cardiac remodeling and cell survival

Postnatal cardiac remodeling is characterized by a marked decrease in the insulin-like growth factor 1 (IGF1) and IGF1 receptor (IGF1R) expression. The underlying mechanism remains unexplored. This study examined the role of microRNAs in postnatal cardiac remodeling. By expression profiling, we observed a 10-fold increase in miR-378 expression in 1-week-old neonatal mouse hearts compared with 16-day-old fetal hearts. There was also a 4-6-fold induction in expression of miR-378 in older (10 months) compared with younger (1 month) hearts. Interestingly, tissue distribution analysis identified miR-378 to be highly abundant in heart and skeletal muscles. In the heart, specific expression was observed in cardiac myocytes, which was inducible by a variety of stressors. Overexpression of miR-378 enhanced apoptosis of cardiomyocytes by direct targeting of IGF1R and reduced signaling in Akt cascade. The inhibition of miR-378 by its anti-miR protected cardiomyocytes against H(2)O(2) and hypoxia reoxygenation-induced cell death by promoting IGF1R expression and downstream Akt signaling cascade. Additionally, our data show that miR-378 expression is inhibited by IGF1 in cardiomyocytes. In tissues such as fibroblasts and fetal hearts, where IGF1 levels are high, we found either absent or significantly low miR-378 levels, suggesting an inverse relationship between these two factors. Our study identifies miR-378 as a new cardioabundant microRNA that targets IGF1R. We also demonstrate the existence of a negative feedback loop between miR-378, IGF1R, and IGF1 that is associated with postnatal cardiac remodeling and with the regulation of cardiomyocyte survival during stress.

SNARE-mediated rapid lysosome fusion in membrane raft clustering and dysfunction of bovine coronary arterial endothelium

The present study attempted to evaluate whether soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) mediate lysosome fusion in response to death receptor activation and contribute to membrane raft (MR) clustering and consequent endothelial dysfunction in coronary arterial endothelial cells. By immunohistochemical analysis, vesicle-associated membrane proteins 2 (VAMP-2, vesicle-SNAREs) were found to be abundantly expressed in the endothelium of bovine coronary arteries. Direct lysosome fusion monitoring by N-(3-triethylammoniumpropyl)-4-[4-(dibutylamino)styryl]pyridinium dibromide (FM1-43) quenching demonstrated that the inhibition of VAMP-2 with tetanus toxin or specific small interfering ribonucleic acid (siRNA) almost completely blocked lysosome fusion to plasma membrane induced by Fas ligand (FasL), a well-known MR clustering stimulator. The involvement of SNAREs was further confirmed by an increased interaction of VAMP-2 with a target-SNARE protein syntaxin-4 after FasL stimulation in coimmunoprecipitation analysis. Also, the inhibition of VAMP-2 with tetanus toxin or VAMP-2 siRNA abolished FasL-induced MR clustering, its colocalization with a NADPH oxidase unit gp91(phox), and increased superoxide production. Finally, FasL-induced impairment of endothelium-dependent vasodilation was reversed by the treatment of bovine coronary arteries with tetanus toxin or VAMP-2 siRNA. VAMP-2 is critical to lysosome fusion in MR clustering, and this VAMP-2-mediated lysosome-MR signalosomes contribute to redox regulation of coronary endothelial function.