Isolated cells in the study of the molecular mechanisms of reperfusion injury

Liproxstatin-1 Alleviates Lung Transplantation-induced Cold Ischemia-Reperfusion Injury by Inhibiting Ferroptosis

BACKGROUND

Primary graft dysfunction, which is directly related to cold ischemia-reperfusion (CI/R) injury, is a major obstacle in lung transplantation (LTx). Ferroptosis, a novel mode of cell death elicited by iron-dependent lipid peroxidation, has been implicated in ischemic events. This study aimed to investigate the role of ferroptosis in LTx-CI/R injury and the effectiveness of liproxstatin-1 (Lip-1), a ferroptosis inhibitor, in alleviating LTx-CI/R injury.

METHODS

LTx-CI/R-induced signal pathway alterations, tissue injury, cell death, inflammatory responses, and ferroptotic features were examined in human lung biopsies, the human bronchial epithelial (BEAS-2B) cells, and the mouse LTx-CI/R model (24-h CI/4-h R). The therapeutic efficacy of Lip-1 was explored and validated both in vitro and in vivo.

RESULTS

In human lung tissues, LTx-CI/R activated ferroptosis-related signaling pathway, increased the tissue iron content and lipid peroxidation accumulation, and altered key protein (GPX4, COX2, Nrf2, and SLC7A11) expression and mitochondrial morphology. In BEAS-2B cells, the hallmarks of ferroptosis were significantly evidenced at the setting of both CI and CI/R compared with the control, and the effect of adding Lip-1 only during CI was much better than that of only during reperfusion by Cell Counting Kit-8. Furthermore, Lip-1 administration during CI markedly relieved LTx-CI/R injury in mice, as indicated by significant improvement in lung pathological changes, pulmonary function, inflammation, and ferroptosis.

CONCLUSIONS

This study revealed the existence of ferroptosis in the pathophysiology of LTx-CI/R injury. Using Lip-1 to inhibit ferroptosis during CI could ameliorate LTx-CI/R injury, suggesting that Lip-1 administration might be proposed as a new strategy for organ preservation.

Physiological Impact of Hypothermia: The Good, the Bad and the Ugly

Hypothermia is defined as a core body temperature of < 35°C, and as body temperature is reduced the impact on physiological processes can be beneficial or detrimental. The beneficial effect of hypothermia enables circulation of cooled experimental animals to be interrupted for 1-2 h without creating harmful effects, while tolerance of circulation arrest in normothermia is between 4 and 5 min. This striking difference has attracted so many investigators, experimental as well as clinical, to this field, and this discovery was fundamental for introducing therapeutic hypothermia in modern clinical medicine in the 1950's. Together with the introduction of cardiopulmonary bypass, therapeutic hypothermia has been the cornerstone in the development of modern cardiac surgery. Therapeutic hypothermia also has an undisputed role as a protective agent in organ transplantation and as a therapeutic adjuvant for cerebral protection in neonatal encephalopathy. However, the introduction of therapeutic hypothermia for organ protection during neurosurgical procedures or as a scavenger after brain and spinal trauma has been less successful. In general, the best neuroprotection seems to be obtained by avoiding hyperthermia in injured patients. Accidental hypothermia occurs when endogenous temperature control mechanisms are incapable of maintaining core body temperature within physiologic limits and core temperature becomes dependent on ambient temperature. During hypothermia spontaneous circulation is considerably reduced and with deep and/or prolonged cooling, circulatory failure may occur, which may limit safe survival of the cooled patient. Challenges that limit safe rewarming of accidental hypothermia patients include cardiac arrhythmias, uncontrolled bleeding, and "rewarming shock".

"Thinking" vs. "Talking": Differential Autocrine Inflammatory Networks in Isolated Primary Hepatic Stellate Cells and Hepatocytes under Hypoxic Stress

We hypothesized that isolated primary mouse hepatic stellate cells (HSC) and hepatocytes (HC) would elaborate different inflammatory responses to hypoxia with or without reoxygenation. We further hypothesized that intracellular information processing (“thinking”) differs from extracellular information transfer (“talking”) in each of these two liver cell types. Finally, we hypothesized that the complexity of these autocrine responses might only be defined in the absence of other non-parenchymal cells or trafficking leukocytes. Accordingly, we assayed 19 inflammatory mediators in the cell culture media (CCM) and whole cell lysates (WCLs) of HSC and HC during hypoxia with and without reoxygenation. We applied a unique set of statistical and data-driven modeling techniques including Two-Way ANOVA, hierarchical clustering, Principal Component Analysis (PCA) and Network Analysis to define the inflammatory responses of these isolated cells to stress. HSC, under hypoxic and reoxygenation stresses, both expressed and secreted larger quantities of nearly all inflammatory mediators as compared to HC. These differential responses allowed for segregation of HSC from HC by hierarchical clustering. PCA suggested, and network analysis supported, the hypothesis that above a certain threshold of cellular stress, the inflammatory response becomes focused on a limited number of functions in both HSC and HC, but with distinct characteristics in each cell type. Network analysis of separate extracellular and intracellular inflammatory responses, as well as analysis of the combined data, also suggested the presence of more complex inflammatory “talking” (but not “thinking”) networks in HSC than in HC. This combined network analysis also suggested an interplay between intracellular and extracellular mediators in HSC under more conditions than that observed in HC, though both cell types exhibited a qualitatively similar phenotype under hypoxia/reoxygenation. Our results thus suggest that a stepwise series of computational and statistical analyses may help decipher how cells respond to environmental stresses, both within the cell and in its secretory products, even in the absence of cooperation from other cells in the liver.

Downregulation of connexin 32 attenuates hypoxia/reoxygenation injury in liver cells

Gap junction intercellular communication is involved in ischemia-reperfusion (IR) injury of organs. Connexins are proteins that are critical to the function of gap junctions. To clarify the role of gap junctions in IR injury in liver cells, the function of gap junctions was modulated in an in vitro hypoxia/reoxygenation (H/R) model. BRL-3A rat liver cells, endogenously expressing connexins Cx32 and Cx43, were used to model the process of hepatic IR injury. Suppression of gap junction activity was achieved genetically, using Cx32-specific small interfering RNA (siRNA), or chemically, with pharmacological inhibitors, oleamide, and 18-α-GA. BRL-3A cells subjected to H/R exhibited reduced cell survival and pathologies indicative of IR injury. Cx32-specific siRNA, oleamide, and 18-α-GA, respectively, decreased gap junction permeability, as assessed by the parachute assay. Pretreatment with Cx32-specific siRNA increased cell survival. Pretreatment with oleamide or 18-α-GA did not improve cell survival. Modulating gap junction by Cx32 gene silencing protected BRL-3A liver cells from H/R.

New Insights into the Cellular and Molecular Mechanisms of Cold Storage Injury

Solid organ grafts, but also other biologic materials requiring storage for a few hours to a few days, are usually stored under hypothermic conditions. To decrease graft injury during cold storage, organ preservation solutions were developed many years ago. However, since then, modern biochemical and cell biologic methods have allowed further insights into the molecular and cellular mechanisms of cold storage injury, including further insights into alterations of the cellular ion homeostasis, the occurrence of a mitochondrial permeability transition, and the occurrence of free–radical-mediated hypothermic injury and cold-induced apoptosis. These new aspects of cold storage injury, which are not covered by preservation solutions in current clinical use and offer the potential for improvement of organ and tissue preservation, are presented here.

New method of delivering gene-altered Kupffer cells to rat liver: studies in an ischemia-reperfusion model

BACKGROUND & AIMS

Kupffer cells play a major role in the pathogenesis of several diseases. They release physiologically active substances that often lead to localized tissue injury. Therefore, the aim of this study was to establish a model to protect the liver through supplementation of Kupffer cells that have been transduced by recombinant adenovirus.

METHODS

Optimal conditions for intravenous injection in rats were established using carbon-labeled Kupffer cells. Adenoviral-transduced Kupffer cells encoding the Cu/Zn-SOD gene (Ad.SOD1) or beta-galactosidase reporter gene (Ad.LacZ) were transplanted into recipient rats. Twenty-four hours after transplantation, 70% hepatic ischemia-reperfusion was used to induce hepatic oxidative stress, and liver injury was determined 8 or 24 hours later.

RESULTS

In initial experiments, 10%-20% of the injected carbon-labeled cells were localized in the host liver after 24 hours, representing approximately 1% of the total population of Kupffer cells. Pretreatment of the recipient with a single dose of cyclosporin A maximized Kupffer cell reseeding up to 4%-10% of the total Kupffer cell population, suggesting that efficiency is limited by host immune response. Moreover, reseeded Kupffer cells were retained in host livers for up to 14 days after transplant. In livers of animals injected with Kupffer cells transduced with Ad.LacZ, transgene expression was observed, indicating Kupffer cell functional integrity. Injection of Kupffer cells transduced with Ad.SOD1 significantly blunted the increase in serum transaminases and liver injury because of ischemia-reperfusion compared with controls.

CONCLUSIONS

This novel approach allows delivery of transduced Kupffer cells in rats, which can be used as an investigative tool as well as a therapeutic strategy against inflammatory liver diseases.

Mammalian cell injury induced by hypothermia- the emerging role for reactive oxygen species

Hypothermia is a well-known strategem to protect biological material against injurious or degradative processes and is widely used in experimental and especially in clinical applications. However, hypothermia has also proved to be strongly injurious to a variety of cell types. Hypothermic injury to mammalian cells has long been attributed predominantly to disturbances of cellular ion homeostasis, especially of sodium homeostasis. For many years, reactive oxygen species have hardly been considered in the pathogenesis of hypothermic injury to mammalian cells. In recent years, however, increasing evidence for a role of reactive oxygen species in hypothermic injury to these cells has accumulated. Today there seems to be little doubt that reactive oxygen species decisively contribute to hypothermic injury in diverse mammalian cells. In some cell types, such as liver and kidney cells, they even appear to play the central role in hypothermic injury, outruling by far a contribution of the cellular ion homeostasis. In these cells, the cellular chelatable, redox-active iron pool appears to be decisively involved in the pathogenesis of hypothermic injury and of cold-induced apoptosis that occurs upon rewarming of the cells after a (sublethal) period of cold incubation.

Comparison of the effect of adenoviral delivery of three superoxide dismutase genes against hepatic ischemia-reperfusion injury

The purpose of this study was to investigate the effectiveness of superoxide dismutase (SOD) overexpression in an acute model of hepatic oxidative stress. Oxidative stress was established using a warm ischemia-reperfusion model, where nearly 70% of the liver was made hypoxic by clamping the hepatic artery and a branch of the portal vein for 1 hr followed by restoration of blood flow. Animals were infected i.v. with 1 x 10(9) plaque-forming units (PFU) of adenovirus containing the transgene for cytosolic Cu/Zn-SOD (Ad.SOD1), mitochondrial Mn-SOD (Ad.SOD2), extracellular Cu/Zn-SOD (Ad.SOD3), or the bacterial reporter gene for beta-galactosidase (Ad.lacZ) 3 days prior to experiments. Ad.SOD1 and Ad.SOD2 caused a three-fold increase in SOD expression and activity in liver compared to Ad.lacZ-treated control animals. Intravenous administration of Ad.SOD3 increased SOD activity slightly in serum but not in liver. Increases in serum transaminases and pathology due to ischemia-reperfusion were blunted by Ad.SOD1 and Ad.SOD2; however, extracellular SOD had no significant effect. Moreover, lipid-derived free radical adducts (a(N) = 15.65 G and a(H)(beta) = 2.78 G) were increased by ischemia-reperfusion. This effect was blunted by about 60% in Ad.SOD1- and Ad.SOD2-infected animals, but was unaffected by Ad.SOD3. However, when high doses of Ad.SOD3 (3 x 10(10) PFU) were administered. serum SOD activity was elevated three-fold and was protective against hepatic ischemia-reperfusion injury under these conditions. These data demonstrate that adenoviral delivery of superoxide dismutase can effectively reduce hepatic oxidative stress.

Large-scale isolation of sinusoidal endothelial cells from pig and human liver

OBJECTIVE

Hepatic in vitro studies, like those on hypoxia/reperfusion injury in liver transplants, demand large numbers of cultivated sinusoidal endothelial cells (SECs). In this article, we present and evaluate a new method for the isolation of SECs from porcine and human livers.

METHODS

SECs were isolated employing a four-step collagenase perfusion. The sinusoidal character of the cells was validated by transmission and scanning electron microscopy, exclusion of Weibel-Palade bodies and factor VIII-related antigen, expression of scavenger receptor, and incorporation of latex beads.

RESULTS

In 23 pigs, an average of 9 x 10(4) SECs were harvested from each liver. Cells were cultivated under standard conditions, as well as in multilayer cocultures of isolated SECs and hepatocytes in a "sandwich" configuration. Standard cultures showed an average of 90% SECs in primary cultures and 100% SECs after the first passage. The possibility of isolation of SECs from human livers was demonstrated in eight cases.

CONCLUSION

With the four-step collagenase perfusion it is possible to easily isolate large numbers of viable and pure SECs from one organ. A further advantage is the possibility of isolating hepatocytes from the same organ.

Morphologic, biochemical and molecular mitochondrial changes during reperfusion phase following brief renal ischemia

Ischemia/reperfusion of organs and cells induces apoptosis through a complicated series of changes in mitochondria, mainly the generation of oxygen free radicals, permeability transitions, calcium translocations, and release of apoptogenic factors such as cytochrome c and Bcl-2 family members. The liberation of these factors occurs very early after reoxygenation and it has been assumed that it takes place without any structural alteration of the mitochondrial membranes. The aim of this study was to detect ultrastructural changes of mitochondria in the initial stages of reperfusion at the time when Bcl-2 and succinic dehydrogenase, located in the outer and inner membranes, respectively, were released. Ischemia/reperfusion was produced in adult rats by clamping one renal artery for 60 min and reoxygenating for 60, 120, 180, and 240 min. A model of chemical hypoxia with intra-arterial 50 mM sodium azide served as comparison, allowing free blood flow for 30, 60, 120 and 180 min. Light and electron microscopy, immunostaining for Bcl-2, and enzyme histochemistry for succinic dehydrogenase were performed. Our results showed mitochondrial swelling, rupture of inner and outer membranes, and leakage of mitochondrial matrix into the cytoplasm in ischemia after 120 min of reperfusion. Bcl-2 immunoreactivity and focal lowering of SDH reactivity were also noted and became more pronounced at the same time that the mitochondrial ultrastructure demonstrated more evident changes including rupture of the inner and outer membranes. Our studies seem to indicate that in early ischemia-reperfusion and in chemical hypoxia-induced apoptosis, the earliest ultrastructural changes take place in mitochondria and that swelling and rupture of mitochondrial membranes occur in parallel with the loss of Bcl-2 and SDH activity.

Hypothermia injury/cold-induced apoptosis--evidence of an increase in chelatable iron causing oxidative injury in spite of low O2-/H2O2 formation

When incubated at 4 degrees C, cultured rat hepatocytes or liver endothelial cells exhibit pronounced injury and, during earlier rewarming, marked apoptosis. Both processes are mediated by reactive oxygen species, and marked protective effects of iron chelators as well as the protection provided by various other antioxidants suggest that hydroxyl radicals, formed by classical Fenton chemistry, are involved. However, when we measured the Fenton chemistry educt hydrogen peroxide and its precursor, the superoxide anion radical, formation of both had markedly decreased and steady-state levels of hydrogen peroxide did not alter during cold incubation of either liver endothelial cells or hepatocytes. Similarly, there was no evidence of an increase in O2-/H2O2 release contributing to cold-induced apoptosis occurring on rewarming. In contrast to the release/level of O2- and H2O2, cellular homeostasis of the transition metal iron is likely to play a key role during cold incubation of cultured hepatocytes: the hepatocellular pool of chelatable iron, measured on a single-cell level using laser scanning microscopy and the fluorescent indicator phen green, increased from 3.1 +/- 2.3 microM (before cold incubation) to 7.7 +/- 2.4 microM within 90 min after initiation of cold incubation. This increase in the cellular chelatable iron pool was reversible on rewarming after short periods of cold incubation. The cold-induced increase in the hepatocellular chelatable iron pool was confirmed using the calcein method. These data suggest that free radical-mediated hypothermia injury/cold-induced apoptosis is primarily evoked by alterations in the cellular iron homeostasis/a rapid increase in the cellular chelatable iron pool and not by increased formation of O2-/H2O2.

Tissue injury by reactive oxygen species and the protective effects of flavonoids

Reactive oxygen species contribute decisively to a great variety of diseases. Flavonoids are benzo-gamma-pyrone derivatives of plant origin found in various fruits and vegetables but also in tea and in red wine. Some of the flavonoids, such as quercetin and silibinin, can effectively protect cells and tissues against the deleterious effects of reactive oxygen species. Their antioxidant activity results from scavenging of free radicals and other oxidizing intermediates, from the chelation of iron or copper ions and from inhibition of oxidases. For their free radical scavenging properties, scavenging of lipid- and protein-derived radicals is presumably of special importance. A non-radical reactive oxygen species effectively trapped by flavonoids is hypochlorous acid. In general, the antioxidative properties of flavonoids are favoured by a high degree of OH substitution. On the other hand, inhibition of enzymatic functions other than oxidases, e.g., inhibition of lipoxygenase and thus prevention of the formation of leukotrienes, may also participate in the cell and tissue protective properties of flavonoids.

Cold-induced release of reactive oxygen species as a decisive mediator of hypothermia injury to cultured liver cells

The mechanisms of hypothermia-induced cell injury are still unclear. The present study provides experimental evidence for the involvement of reactive oxygen species in hypothermia injury: cultured rat hepatocytes incubated in cold (4 degrees C) Krebs-Henseleit buffer or cell culture medium were injured under normoxic conditions and even more so under hyperoxic conditions, whereas the hepatocytes were protected under hypoxic conditions. During warm (37 degrees C) incubation in cell culture medium, on the other hand, cell injury was minimal under normoxic conditions, only slightly increased under hyperoxic conditions, but substantially increased under hypoxic conditions. The injury occurring during cold normoxic incubation was also largely decreased by the addition of the spin-trap 5,5-dimethyl-1-pyrroline N-oxide, the hydroxyl radical scavenger dimethyl sulfoxide, the flavonoid silibinin, or the transition metal chelator 2,2'-dipyridyl to the medium, or by preincubating the cells with the iron chelator deferoxamine or the lipophilic antioxidant alpha-tocopherol before the hypothermic incubation. In addition, marked lipid peroxidation was observed during cold incubations without inhibitors, but not during warm incubations. Similar results were obtained with cultured rat liver endothelial cells. These results suggest that in hepatocytes and in liver endothelial cells, cold-induced release of reactive oxygen species, most likely of hydroxyl radicals, is the main injurious factor under hypothermic conditions.

Cell detachment during sinusoidal reperfusion after liver preservation: an in vitro model

BACKGROUND

Sinusoidal endothelial cells (SEC) are significantly more vulnerable to cold storage and reperfusion than hepatocytes. Swelling and disruption of the sinusoidal lining induce the microcirculatory disturbances seen after reperfusion. In this article, the investigation of a method to assess the adhesion and morphology of SEC in vitro during reperfusion after preservation is described.

METHODS

Time-lapse video microscopy analysis was performed and cell detachment rates and cell lengths were determined. Preservation intervals between 6 and 24 hr and flow rates ranging from 3 L/min to 9 L/min (resulting in shear stresses between 5.1 and 15.3 dynes/cm2 on the monolayer surface) during reperfusion period were compared. SEC that were stored for 6 hr in University of Wisconsin solution and nonpreserved control cultures were compared.

RESULTS

Varying the preservation intervals from 6 hr to 24 hr during reperfusion at a flow rate of 3 L/min led to increased cell erosion rates (6 hr, 35.5+/-15.2%; 12 hr, 38.0+/-7.6%; 18 hr, 54.3+/-5.7%; 24 hr, 76.7+/-6.7%; nonpreserved cells, 3.4+/-3.4%). Storage periods from 12 hr to 24 hr led to significantly higher cell detachment rates than occurred in nonpreserved cells.

CONCLUSIONS

This method allows the investigation of the adhesion capability and morphology of individual cells in vitro. Indications of the kind of preservation/reperfusion injury that occurs after treatment with several preservation solutions and the resultant repair behavior can be obtained.

Visualization of liver sinusoidal endothelial cell repair behavior after preservation by in vitro time-lapse video microscopy

Sinusoidal endothelial cells are significantly more vulnerable to cold storage and reperfusion than hepatocytes. In this study, a method for assessing the repair behavior of sinusoidal endothelial cells in vitro, after preservation, was investigated. Time-lapse video microscopy analysis was performed and migration rates, division rates, and cell detachment rates were determined. Preservation intervals between 3 and 24 hr and reoxygenation times between 4 and 24 hr were compared. A comparison between sinusoidal endothelial cultures that were stored for 6 hr in University of Wisconsin solution and nonpreserved control cultures was performed. This method allows the investigation of the repair capability of individual cells in vitro. Indications of the kind of preservation/reoxygenation injury that occurs after treatment with several preservation solutions and the resultant repair behavior can be obtained.

Involvement of reactive oxygen species in the preservation injury to cultured liver endothelial cells

We have previously demonstrated an energy-dependent injury to cultured liver endothelial cells during cold incubation in University of Wisconsin (UW) solution. In the present study, we report experimental evidence for the involvement of reactive oxygen species in this injury: LDH release during 48 h of cold incubation in UW solution was decreased from 40-55% under aerobic conditions to less than 20% under hypoxic conditions or by the presence of KCN (1 mM). Similar protection was achieved by the addition of the spin trap 5,5-dimethyl-1-pyrroline N-oxide, the hydroxyl radical scavenger dimethyl sulfoxide, or the flavonoid silibinin to UW solution under aerobic conditions. Preincubating the cells with the iron chelator deferoxamine even decreased the injury to less than 5%. The residual injury (as observed after longer incubation times) under hypoxic conditions or in cells preincubated with deferoxamine was no longer energy dependent. The amount of thiobarbituric acid-reactive substances markedly increased during cold incubation of the cells in UW solution. This increase was not observed in UW solution to which KCN had been added, i.e., under the conditions of energy depletion. These results suggest that an iron-dependent generation of reactive oxygen species with subsequent lipid peroxidation is involved in the pathogenesis of the injury to cultured liver endothelial cells in cold UW solution.

Reduction of hepatic reperfusion injury by indomethacin-mediated vasoconstriction: a rat model with temporary splenocaval shunt

For reduction of radical formation during reperfusion, a lower oxygen supply by limiting the reperfusion flow rate should be beneficial for the organ. Thus, indomethacin was given prior to reperfusion for induction of temporary postischemic vasoconstriction. In an in vivo model (female Wistar rats, 200-250 g, n = 16) with portal decompression by a splenocaval shunt, hepatic ischemia was induced for 30 min by cross-clamping of the hepatoduodenal ligament followed by portal intravenous injection of indomethacin (2 mg/kg body wt) at the end of ischemia. Liver injury was assessed by serum levels of Aspartat-aminotransferase (ASAT) and Alaninaminotransferase (ALAT) that were determined prior to ischemia, on days 2, 4, 6 and 21 postoperatively. The local tissue pO2 was measured preischemically, 1 h after reperfusion and on day 21. Application of indomethacin significantly reduced the local tissue-pO2 by about 50% after 1 h of reperfusion (p < .05). The increase in serum ASAT levels on day 2 was significantly diminished after indomethacin application (p < .05). ALAT values on day 2 showed a significant increase in the control group but did not differ from baseline in the indomethacin group. These data support the hypothesis that temporarily limited reperfusion results in an amelioration of reperfusion injury, although further studies with more selectively vasoactive agents must still be performed since indomethacin also has a major effect on the eicosanoid metabolism.

Effect of vitamin E on reoxygenation injury experienced by isolated rat hepatocytes

The pathogenic role of lipid peroxidation in the reperfusion injury of the liver is still controversial. This study was performed to determine whether the damage caused by oxygen free radicals during reoxygenation in perfused rat hepatocytes is related to lipid peroxidation. Superoxide anion was detected by lucigenin-enhanced chemiluminescence. Lipid peroxidation and cell injury were assessed by the release of malondialdehyde and lactic dehydrogenase. Upon reoxygenation following 2.5 h of anoxia, isolated hepatocytes generated considerable amount of O2-. Following O2- formation, a significant increase in malondialdehyde release was measured. Cell injury was temporally delayed relative to O2- generation, but preceded the occurrence of a significant lipid peroxidation. Treatment with Vitamin E abolished lipid peroxidation but had no effect upon superoxide anion formation and cell injury. These results suggest that in perfused rat hepatocytes non-peroxidative mechanisms are more important than peroxidative mechanisms in the pathogenesis of the early phases of reoxygenation injury.