Protective effects of early CD4(+) T cell reduction in hepatic ischemia/reperfusion injury

1-Phosphate receptor agonists: A promising therapeutic avenue for ischemia-reperfusion injury management

Ischemia-reperfusion injury (IRI) - a complex pathological condition occurring when blood supply is abruptly restored to ischemic tissues, leading to further tissue damage - poses a significant clinical challenge. Sphingosine-1-phosphate receptors (S1PRs), a specialized set of G-protein-coupled receptors comprising five subtypes (S1PR1 to S1PR5), are prominently present in various cell membranes, including those of lymphocytes, cardiac myocytes, and endothelial cells. Increasing evidence highlights the potential of targeting S1PRs for IRI therapeutic intervention. Notably, preconditioning and postconditioning strategies involving S1PR agonists like FTY720 have demonstrated efficacy in mitigating IRI. As the synthesis of a diverse array of S1PR agonists continues, with FTY720 being a prime example, the body of experimental evidence advocating for their role in IRI treatment is expanding. Despite this progress, comprehensive reviews delineating the therapeutic landscape of S1PR agonists in IRI remain limited. This review aspires to meticulously elucidate the protective roles and mechanisms of S1PR agonists in preventing and managing IRI affecting various organs, including the heart, kidney, liver, lungs, intestines, and brain, to foster novel pharmacological approaches in clinical settings.

CoQ10 alleviates hepatic ischemia reperfusion injury via inhibiting NLRP3 activity and promoting Tregs infiltration

Hepatic ischemia-reperfusion injury (IRI) has been concerned as a main complication of liver surgery and transplantation. Previous studies show that reactive oxygen species (ROS) associated inflammation response and contribute to the liver damage during IRI. Coenzyme Q10 (CoQ10) has shown many beneficial effects on abrogating ROS production and ameliorating liver injury. This study found lower CoQ10 level in the process of liver IRI in a mouse model of hepatic IRI. Meanwhile, our results showed that CoQ10 administration significantly attenuate hepatic IRI proved by HE staining, serum ALT/AST. The NOD-like receptor protein 3 (NLRP3) inflammasome is activated by ROS which triggers the activation of inflammatory caspases. In this study, NLRP3 was significantly suppressed by CoQ10 while Foxp3 exhibited increased expression in liver. Furthermore, Kupffer cells (KCs) pretreated with CoQ10 under the condition of hypoxia and reoxygenation contributed to improved CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) ratio in co-culture system. Furthermore, NLRP3 inflammasome activator treatment in vivo resulted in higher expression of caspase-1 and NLRP3 and reduction of Tregs in liver, which reversed the protection of CoQ10 in the liver injury. Taken together, our study discovered that CoQ10 can suppress NLRP3 activity in KCs and improves Foxp3⁺ Tregs differentiation depending on M2 macrophage polarization of KCs to ameliorate hepatic IRI.

Preclinical Evaluation of Fingolimod in Rodent Models of Stroke With Age or Atherosclerosis as Comorbidities

Preclinical data indicate that fingolimod improves outcome post-ischaemia. This study used a rigorous study design in normal male C57BL/6JOlaHsd mice and in mice with common stroke comorbidities to further evaluate the translational potential of fingolimod. Stroke was induced via middle cerebral artery electrocoagulation in 8–9-week old mice (young mice), 18 month old mice (aged mice), and in high-fat diet-fed 22-week old ApoE−/− mice (hyperlipidaemic mice). Recovery was evaluated using motor behavioural tests 3 and 7 days after stroke. Tissue damage was evaluated at 7 days. A lower dose of fingolimod, 0.5 mg/kg, but not 1 mg/kg, increased lesion size but decreased ipsilateral brain atrophy in younger mice, without an effect on behavioural outcomes. Fingolimod-treated aged mice showed a significant improvement over saline-treated mice in the foot fault test at 7 days. Fingolimod-treated hyperlipidaemic mice showed a decreased infarct size but no difference in behavioural performance. Increasing fingolimod treatment time to 10 days showed no benefit in young mice. Pooled data showed that fingolimod improved performance in the foot fault test. Flow cytometry studies showed that fingolimod had marked effects on T cell frequencies in various tissues. The results show that the effects of fingolimod in stroke are less robust than the existing literature might indicate and may depend on the inflammatory status of the animals.

Acidic Microenvironment Regulates the Severity of Hepatic Ischemia/Reperfusion Injury by Modulating the Generation and Function of Tregs via the PI3K-mTOR Pathway

Hepatic ischemia/reperfusion injury (HIRI) is a major cause of liver dysfunction and even liver failure after liver transplantation and hepatectomy. One of the critical mechanisms that lead to HIRI is an acidic microenvironment, which develops due to the accumulation of high acid-like substances such as lactic acid and ketone bodies. Previous studies have shown that the adoptive transfer of induced regulatory T cells (iTregs) attenuates HIRI; however, little is known about the function of Tregs in the acidic microenvironment of a HIRI model. In the present study, we examined the effect of acidic microenvironment on Tregs in vitro and in vivo. Here, we report that microenvironment acidification and dysfunction of the liver is induced during HIRI in humans and mice and that an acidic microenvironment can inhibit the generation and function of CD4⁺CD25⁺Foxp3⁺ iTregs via the PI3K/Akt/mTOR signaling pathway. By contrast, the reversal of the acidic microenvironment restored Foxp3 expression and iTreg function. In addition, the results of cell culture in vitro indicated that the proton pump inhibitor omeprazole improves decreased iTreg differentiation caused by the acidic microenvironment, suggesting the potential clinical use of proton pump inhibitors as immunoregulatory therapy in the treatment of HIRI. Furthermore, our findings demonstrate that buffering the acidic microenvironment to attenuate HIRI in mice has an inseparable relationship with Tregs. Thus, an acidic microenvironment is a key regulator in HIRI, involved in modulating the generation and function of Tregs.

Resolvin D1 activates the sphingosine-1-phosphate signaling pathway in murine livers with ischemia/reperfusion injury

Resolvins (Rvs) are endogenous lipid mediators that promote resolution of inflammation and return to homeostasis. We previously reported that RvD1 both facilitates M2 macrophage polarization of Kupffer cells (KCs) and efferocytosis and modulates thioredoxin 2-mediated mitochondrial quality control in liver ischemia/reperfusion (IR) injury. However, the specific cellular or molecular targets of RvD1 remain poorly understood. Sphingosine-1-phosphate (S1P), the natural sphingolipid ligand for a family of G protein-coupled receptors (S1P₁-S1P₅), regulates lymphocyte circulation and various immune responses. Here we investigated the role of RvD1 in IR-induced hepatocellular damage with a focus on S1P signaling. Male C57BL/6 mice were subjected to partial hepatic ischemia for 60 min, followed by reperfusion. Mice were pretreated with RvD1 (15 μg/kg, i.p.) 1 h prior to ischemia and immediately before reperfusion. To deplete KCs, liposome clodronate was administered (100 μL/mice, i.v.) 24 h prior to ischemia. Mice were pretreated with VPC23019 (100 μg/kg, i.p.), an antagonist for S1P₁/S1P₃ 10 min prior to initial RvD1 treatment. Exogenous RvD1 attenuated IR-induced hepatocellular damage as evidenced by serum HMGB1 release. RvD1 attenuated the decrease in hepatic S1P concentration induced by IR. KC depletion by liposome clodronate did not alter the effect of RvD1 on sphingosine kinases (SKs) and S1P receptors, suggesting independency of KCs. Moreover, in purified hepatocytes of mice exposed to IR, mRNA expression of SK1, SK2, S1P₁, and S1P₃ decreased significantly, and this was attenuated by RvD1. Finally, VPC23019 pretreatment abolished the hepatoprotective effects of RvD1 in serum HMGB1 release. Our findings suggest that RvD1 protects the liver against IR injury by activating S1P signaling.

FTY720 Effects on Inflammation and Liver Damage in a Rat Model of Renal Ischemia-Reperfusion Injury

Objective

Ischemia-reperfusion injury (IRI) produces systemic inflammation with the potential for causing organ failure in tissues peripheral to the initial site of injury. We speculate that treatment strategies that dampen inflammation may be therapeutically beneficial to either the initial site of injury or peripheral organs. To test this, we evaluated the impact of FTY720-induced sequestration of circulating mature lymphocytes on renal IRI and secondary organ injury.

Methods

A microvascular clamp was surgically placed around the left renal pedicle of anesthetized male Sprague-Dawley rats with either vehicle or FTY720 treatment (0.3 mg/kg) intravenously injected after 15 min of ischemia. Blood flow was restored after 60 min. Cohorts of anesthetized rats were euthanized at 6, 24, or 72 hrs with tissue samples collected for analysis.

Results

FTY720 treatment resulted in profound T lymphocyte reduction in peripheral blood. Histopathologic examination, clinical chemistries, and gene transcript expression measurements revealed that FTY720 treatment reduced hepatocellular degeneration, reduced serum markers of liver injury (ALT/AST), and reduced the expression of gene targets associated with IRI.

Conclusion

These findings support an anti-inflammatory effect of FTY720 in the liver where the expression of genes associated with apoptosis, chemotaxis, and the AP-1 transcription factor was reduced. Findings presented here provide the basis for future studies evaluating FTY720 as a potential therapeutic agent to treat complications resulting from renal IRI.

Sinusoidal protection by sphingosine-1-phosphate receptor 1 agonist in liver ischemia-reperfusion injury

BACKGROUND

Functional and structural damages in sinusoidal endothelial cells (SECs) have a crucial role during hepatic ischemia-reperfusion injury (IRI). In regulating endothelial function, sphingosine-1-phosphate receptor 1 (S1PR1), which is a G protein-coupled receptor, has an important role. The present study aimed to clarify whether SEW2871, a selective S1PR1 agonist, can attenuate hepatic damage caused by hepatic IRI, focusing on SEC functions.

METHODS

In vivo, using a 60-min partial-warm IRI model, mice were treated with SEW2871 or without it (with vehicle). In vitro, isolated SECs pretreated with SEW2871 or without it (with vehicle) were incubated with hydrogen peroxide.

RESULTS

Compared with the IRI + vehicle group, SEW2871 administration significantly improved serum transaminase levels and liver damage, attenuated infiltration of Ly-6G and mouse macrophage antigen-1-positive cells, suppressed the expression of vascular cell adhesion molecule-1 and proinflammatory cytokines in the liver, and enhanced the expressions of endothelial nitric oxide synthase (eNOS) and vascular endothelial (VE) cadherin in the liver (eNOS/β-actin [median]: 0.24 versus 0.53, P = 0.008; VE-cadherin/β-actin [median]: 0.21 versus 0.94, P = 0.008). In vitro, compared with the vehicle group, pretreatment of SECs with SEW2871 significantly increased the expressions of eNOS and VE-cadherin (eNOS/β-actin [median]: 0.22 versus 0.29, P = 0.008; VE-cadherin/β-actin [median]: 0.38 versus 0.67, P = 0.008). As results of investigation of prosurvival signals, SEW2871 significantly increased Akt phosphorylation in SECs and decreased lactate dehydrogenase levels in supernatants of SECs.

CONCLUSIONS

These results indicate that S1PR1 agonist induces attenuation of hepatic IRI, which might be provided by preventing SEC damage. S1PR1 may be a therapeutic target for the prevention of early sinusoidal injury after hepatic IRI.

In situ targeting of dendritic cells sets tolerogenic environment and ameliorates CD4+ T-cell response in the postischemic liver

CD4⁺ T cells recruited to the liver play a key role in the pathogenesis of ischemia/reperfusion (I/R) injury. The mechanism of their activation during alloantigen-independent I/R is not completely understood. We hypothesized that liver-resident dendritic cells (DCs) interact with CD4⁺ T cells in the postischemic liver and that modulation of DCs or T-cell-DC interactions attenuates liver inflammation. In mice, warm hepatic I/R (90/120-240 min) was induced. Tolerogenic DCs were generated in situ by pretreatment of animals with the vitamin D analog paricalcitol. A mAb-CD44 was used for blockade of CD4⁺ T-cell-DC interactions. As shown by 2-photon in vivo microscopy as well as confocal microscopy, CD4⁺ T cells were closely colocalized with DCs in the postischemic liver. Pretreatment with paricalcitol attenuated I/R-induced maturation of DCs (flow cytometry), CD4⁺ T-cell recruitment into the liver (intravital microscopy), and hepatocellular/microvascular damage (intravital microscopy, alanine aminotransferase/aspartate aminotransferase, histology). However, interruption of T-cell-DC interaction increased proinflammatory DC maturation and even enhanced tissue damage. Simultaneous treatment with an anti-CD44mAb completely abolished the beneficial effect of paricalcitol on T-cell migration and tissue injury. Our study demonstrates for the first time that hepatic DCs interact with CD4⁺ T cells in the postischemic liver in vivo; modulation of DCs and/or generation of tolerogenic DCs attenuates intrahepatic CD4⁺ T-cell recruitment and reduces I/R injury; and interruption of CD44-dependent CD4⁺ T-cell-DC interactions enhances tissue injury by preventing the modulatory effect of hepatic DCs on T cells, especially type 1 T helper effector cells. Thus, hepatic DCs are strongly involved in the promotion of CD4⁺ T-cell-dependent postischemic liver inflammation.-Funken, D., Ishikawa-Ankerhold, H., Uhl, B., Lerchenberger, M., Rentsch, M., Mayr, D., Massberg, S., Werner, J., Khandoga, A. In situ targeting of dendritic cells sets tolerogenic environment and ameliorates CD4⁺ T-cell response in the postischemic liver.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Mechanism of Action and Clinical Potential of Fingolimod for the Treatment of Stroke

Fingolimod (FTY720) is an orally bio-available immunomodulatory drug currently approved by the FDA for the treatment of multiple sclerosis. Currently, there is a significant interest in the potential benefits of FTY720 on stroke outcomes. FTY720 and the sphingolipid signaling pathway it modulates has a ubiquitous presence in the central nervous system and both rodent models and pilot clinical trials seem to indicate that the drug may improve overall functional recovery in different stroke subtypes. Although the precise mechanisms behind these beneficial effects are yet unclear, there is evidence that FTY720 has a role in regulating cerebrovascular responses, blood-brain barrier permeability, and cell survival in the event of cerebrovascular insult. In this article, we critically review the data obtained from the latest laboratory findings and clinical trials involving both ischemic and hemorrhagic stroke, and attempt to form a cohesive picture of FTY720's mechanisms of action in stroke.

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.

Role of the sphingosine metabolism pathway on neurons against experimental cerebral ischemia in rats

Although there is evidence that sphingosine-1-phosphate receptor-1 (S1P1) activation occurs following experimental brain injury, there is little information about its metabolic pathway in cerebral ischemia. The purpose of this study was to evaluate the role of the sphingosine metabolic pathway including S1P1, sphingosine kinases 1 (SphK1), and 2 (SphK2) in transient middle cerebral artery occlusion (MCAO). Fifty-eight male Sprague-Dawley rats were used to asses temporal profiles of S1P1, SphK1 and 2 on neurons in infarct and periinfarct cortices at pre-infarct state, 6, and 24 hours after MCAO. The animals were then treated with vehicle and 0.25 mg/kg FTY720, which is an agonist of S1P receptors, and evaluated regarding neurological function, infarct volume, and S1P1 expression on neurons at 24 hours after MCAO. The expressions of S1P1, SphK1, and SphK2 were significantly decreased after MCAO. Labeling of all markers were reduced in the infarct cortex but remained present in the periinfarct cortex, and some were found to be on neurons. Significant improvements of neurological function and brain injury were observed in the FTY720 group compared with the vehicle and untreated groups, although S1P1 expression on neurons was reduced in the FTY720 group compared with the vehicle group. We demonstrated that S1P1, SphK1, and SphK2 were downregulated in the infarct cortex, whereas they were preserved in the periinfarct cortex where FTY720 reduced neuronal injury possibly via S1P1 activation. Our findings suggest that activation of the sphingosine metabolic pathway may be neuroprotective in cerebral ischemia.

Rodent models of hepatic ischemia-reperfusion injury: time and percentage-related pathophysiological mechanisms

Ischemia and reperfusion (IR) injury remains one of the major problems in liver surgery and transplantation, which determines the viability of the hepatic tissue after resection and of the grafted organ. This review aims to elucidate the mechanisms involved in IR injury of the liver in rodent experimental studies and the preventative methods and pharmacologic agents that have been applied. Many time- and percentage-related liver IR injury rodent models have been used to examine the pathophysiological mechanisms and the parameters implicated with different morbidity, mortality, and pathology findings. The most preferred experimental rodent model of liver IR is the induction of 70% IR for 45 min, which is associated with almost 100% survival. In this model, plasma levels of several parameters such as alanine transaminase, aspartate aminotransferase, gamma-glutamyltransferase, endothelin-1, malonodialdehyde, tumor necrosis factor α, interleukin 1b, inducible nitric oxide synthase, and caspases are increased. The increase of caspases is associated with the initiation of hepatic cellular apoptosis. The main injuries observed 24 h after reperfusion are nuclear pyknosis, cytoplasmic hypereosinophilia, severe necrosis, and loss of intercellular borders. Both ischemic pre- and post-conditioning preventative methods and pharmacologic agents are successfully applied to alleviate the IR injuries. The selection of the time- and percentage-related liver IR injury rodent model and the potential preventative method should be related to the clinical question being answered.

FTY720 ameliorates acute ischemic stroke in mice by reducing thrombo-inflammation but not by direct neuroprotection

BACKGROUND AND PURPOSE

Lymphocytes are important players in the pathophysiology of acute ischemic stroke. The interaction of lymphocytes with endothelial cells and platelets, termed thrombo-inflammation, fosters microvascular dysfunction and secondary infarct growth. FTY720, a sphingosine-1-phosphate receptor modulator, blocks the egress of lymphocytes from lymphoid organs and has been shown to reduce ischemic neurodegeneration; however, the underlying mechanisms are unclear. We investigated the mode of FTY720 action in models of cerebral ischemia.

METHODS

Transient middle cerebral artery occlusion (tMCAO) was induced in wild-type and lymphocyte-deficient Rag1(-/-) mice treated with FTY720 (1 mg/kg) or vehicle immediately before reperfusion. Stroke outcome was assessed 24 hours later. Immune cells in the blood and brain were counted by flow cytometry. The integrity of the blood-brain barrier was analyzed using Evans Blue dye. Thrombus formation was determined by immunohistochemistry and Western blot, and was correlated with cerebral perfusion.

RESULTS

FTY720 significantly reduced stroke size and improved functional outcome in wild-type mice on day 1 and day 3 after transient middle cerebral artery occlusion. This protective effect was lost in lymphocyte-deficient Rag1(-/-) mice and in cultured neurons subjected to hypoxia. Less lymphocytes were present in the cerebral vasculature of FTY720-treated wild-type mice, which in turn reduced thrombosis and increased cerebral perfusion. In contrast, FTY720 was unable to prevent blood-brain barrier breakdown and transendothelial immune cell trafficking after transient middle cerebral artery occlusion.

CONCLUSIONS

Induction of lymphocytopenia and concomitant reduction of microvascular thrombosis are key modes of FTY720 action in stroke. In contrast, our findings in Rag1(-/-) mice and cultured neurons argue against direct neuroprotective effects of FTY720.

Changes of intestinal tight junctions in rat ileums after partial hepatectomy

BACKGROUND

Increased intestinal permeability and bacterial translocation have been observed after partial hepatectomy (PH).

METHODS

Rats (n = 40) were randomly divided into four groups: control; PH 1d, PH 3d and PH 5d. PH animals underwent two-thirds partial hepatectomy before sacrifice at 1, 3, or 5 days thereafter. The intestinal tight junction (TJ) morphology was observed by transmission electron microscopy. Distribution of TJ protein occludin in lipid raft microdomains was examined using Western blot analysis.

RESULTS

Intestinal TJ structures revealed significant changes at 1 day after PH that had partly recovered by 5 days. During this period, occludin protein decreased significantly in lipid raft microdomains, increasing partially by 5 days.

CONCLUSION

PH induced disruption of TJ structures in rat ilea, which was associated with redistribution of occludin protein in lipid raft microdomains.

The immunomodulatory role of carbon monoxide during transplantation

The number of organ and tissue transplants has increased worldwide in recent decades. However, graft rejection, infections due to the use of immunosuppressive drugs and a shortage of graft donors remain major concerns. Carbon monoxide (CO) had long been regarded solely as a poisonous gas. Ultimately, physiological studies unveiled the endogenous production of CO, particularly by the heme oxygenase (HO)-1 enzyme, recognizing CO as a beneficial gas when used at therapeutic doses. The protective properties of CO led researchers to develop uses for it, resulting in devices and molecules that can deliver CO in vitro and in vivo. The resulting interest in clinical investigations was immediate. Studies regarding the CO/HO-1 modulation of immune responses and their effects on various immune disorders gave rise to transplantation research, where CO was shown to be essential in the protection against organ rejection in animal models. This review provides a perspective of how CO modulates the immune system to improve transplantation and suggests its use as a therapy in the field.

Sphingosine-1-phosphate: a Janus-faced mediator of fibrotic diseases

Sphingosine-1-phosphate (S1P) is a pleiotropic lipid mediator that acts either on G protein-coupled S1P receptors on the cell surface or via intracellular target sites. In addition to the well established effects of S1P in angiogenesis, carcinogenesis and immunity, evidence is now continuously accumulating which demonstrates that S1P is an important regulator of fibrosis. The contribution of S1P to fibrosis is of a Janus-faced nature as S1P exhibits both pro- and anti-fibrotic effects depending on its site of action. Extracellular S1P promotes fibrotic processes in a S1P receptor-dependent manner, whereas intracellular S1P has an opposite effect and dampens a fibrotic reaction by yet unidentified mechanisms. Fibrosis is a result of chronic irritation by various factors and is defined by an excess production of extracellular matrix leading to tissue scarring and organ dysfunction. In this review, we highlight the general effects of extracellular and intracellular S1P on the multistep cascade of pathological fibrogenesis including tissue injury, inflammation and the action of pro-fibrotic cytokines that stimulate ECM production and deposition. In a second part we summarize the current knowledge about the involvement of S1P signaling in the development of organ fibrosis of the lung, kidney, liver, heart and skin. Altogether, it is becoming clear that targeting the sphingosine kinase-1/S1P signaling pathway offers therapeutic potential in the treatment of various fibrotic processes. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Adenovirus-mediated dual gene expression of human interleukin-10 and hepatic growth factor exerts protective effect against CCl4-induced hepatocyte injury in rats

BACKGROUND

Hepatocyte injury is a common pathological cause of various liver diseases. Due to a lack of an effective preventive treatment, gene therapy has become an interesting approach to prevent and alleviate liver injury.

AIMS

A protective effect of adenovirus-mediated dual gene expression of human interleukin-10 (hIL-10) and human hepatocyte growth factor (hHGF) was investigated against tetrachloromethane (CCl(4))-induced hepatocyte injury in rats.

METHODS

An adenoviral vector carrying the hIL-10 and hHGF genes was constructed, and its protective effect against rat hepatocyte injury was investigated both in vivo and in vitro.

RESULTS

In the in vitro CCl(4)-induced cell injury model, simultaneous transfection of hIL-10 and hHGF genes via an adenoviral vector resulted in production of anti-hepatocyte biological factors by an autocrine mechanism, then significantly improved hepatocyte viability. In the in vivo rat model, synergistic effects of these two gene products protected hepatocytes from damage by reducing the CC1(4)-induced hepatocyte degeneration, hepatic fibrosis, and intrahepatic inflammatory cell infiltration, thereby preserving liver function.

CONCLUSION

Adenovirus-mediated dual gene expression of hIL-10 and hHGF effectively protected against liver damage by likely regulating immune responses to reduce hepatocyte injury and by promoting hepatocyte regeneration. The hIL-10 and hHGF dual gene expression vector has significant potential in the field of liver disease therapeutics and constitutes one of the most promising current strategies for gene therapy.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.

Dehydroepiandrosterone improves hepatic antioxidant reserve and stimulates Akt signaling in young and old rats

This study examined, in the liver of young and old (3- and 24-month-old, respectively) healthy Wistar rats, the in vivo effect of dehydroepiandrosterone (DHEA) (10mg/kg body weight) administered subcutaneously for 5 weeks. Reduced (GSH) and oxidized (GSSG) glutathione levels, glucose-6-phosphate dehydrogenase (G6PDH), glutathione-S-transferase (GST), glutathione peroxidase (GPx) and catalase (CAT) activities, hydrogen peroxide concentration, GST and p-Akt/Akt immunocontent ratio were assessed in hepatic tissue. DHEA treatment significantly increased total glutathione content (17%) and GSH (22%) in 3- and 24-month-old treated groups when compared to control groups. The aging factor increased G6PDH (51%) and GPx (22%) activities as well as the hydrogen peroxide concentration (33%), independently of treatment. DHEA treatment increased p-Akt (54%) and p-Akt/Akt ratio (36%) immunocontents in both treated groups. Increased serum levels of alanine aminotransferase (ALT) in aged rats were reduced by DHEA treatment (34%).

TLR2 and TLR4 expression after kidney ischemia and reperfusion injury in mice treated with FTY720

Ischemia and reperfusion injury (IR) is an antigen independent inflammatory process that causes tissue damage. After IR, kidneys up-regulate leukocyte adhesion molecules and toll-like receptors (TLRs). Moreover, injured kidneys can also secrete factors (i.e. heat shock protein) which bind to TLRs and trigger intracellular events culminating with the increase in the gene expression of inflammatory cytokines. FTY720 is an immunomodulatory compound and protects at least in part kidneys submitted to IR. The mechanisms associated with FTY720's beneficial effects on kidneys after IR remain elusive. We investigated whether FTY720 administration in mice submitted to kidney IR is associated with modulation of TLR2 and TLR4 expression. C57BL/6 mice submitted to 30min of renal pedicles clamp were evaluated for serum parameters (creatinine, urea and nitric oxide), kidney histology, spleen and kidney infiltrating cells expression of TLR2 and TLR4, resident kidney cells expression of TLR2 and TLR4 and IL-6 protein expression in kidney. FTY720-treated mice presented decrease in serum creatinine, urea and nitric oxide, diminished expression of TLR2 and TLR4 both in spleen and kidney infiltrating cells, and reduced kidney IL-6 protein expression in comparison with IR non-treated mice. However, acute tubular necrosis was present both in IR non-treated and IR+FTY720-treated groups. Also, FTY720 did not prevent TLR2 and TLR4 expression in kidney resident cells. In conclusion, FTY720 can promote kidney function recovery after IR by reducing the inflammatory process. Further studies are needed in order to establish whether TLR2 and TLR4 down regulation should be therapeutically addressed as protective targets of renal function and structure after IR.

Selectivity and specificity of sphingosine-1-phosphate receptor ligands: caveats and critical thinking in characterizing receptor-mediated effects

Receptors for sphingosine-1-phosphate (S1P) have been identified only recently. Their medicinal chemistry is therefore still in its infancy, and few selective agonists or antagonists are available. Furthermore, the selectivity of S1P receptor agonists or antagonists is not well established. JTE-013 and BML-241 (also known as CAY10444), used extensively as specific S1P₂ and S1P₃ receptors antagonists respectively, are cases in point. When analyzing S1P-induced vasoconstriction in mouse basilar artery, we observed that JTE-013 inhibited not only the effect of S1P, but also the effect of U46619, endothelin-1 or high KCl; JTE-013 strongly inhibited responses to S1P in S1P² receptor knockout mice. Similarly, BML-241 has been shown to inhibit increases in intracellular Ca²⁺ concentration via P₂ receptor or α_1A-adrenoceptor stimulation and α_1A-adrenoceptor-mediated contraction of rat mesenteric artery, while it did not affect S1P₃-mediated decrease of forskolin-induced cyclic AMP accumulation. Another putative S1P_1/3 receptor antagonist, VPC23019, does not inhibit S1P₃-mediated vasoconstriction. With these examples in mind, we discuss caveats about relying on available pharmacological tools to characterize receptor subtypes.

Adoptive transfer of FTY720-treated immature BMDCs significantly prolonged cardiac allograft survival

A sphingosine 1 phosphate receptor modulator, FTY720, has been used to alleviate symptoms in allotransplantation and autoimmune disease models with impressive efficacy, while it only achieved moderate success in clinical trials. Infusion of immature bone marrow-derived dendritic cell (BMDC) progenitors before transplantation could induce donor specific tolerance. In this study, we investigated the possibility of using FTY720-DCs (FTY720-treated immature BMDCs) to prevent severe alloimmune response. Our results indicate that FTY720-DCs could markedly prolong graft survival compared with Ctrl-DCs (nonconditioned immature BMDCs) as manifested by reduced inflammatory infiltration into the graft. IFN-γ production by CD4(+) and CD8(+) T cells were significantly reduced, while FoxP3(+) regulatory T cells among CD4(+) T cells were upregulated. Although FTY720 seldom altered the phenotype or the phagocytosis of BMDCs in vitro, it severely hampered their capability to trigger antigen-specific and allogeneic T-cell response. When splenic T cells were co-cultured with FTY720-DCs, the proportion of regulatory T cells increased, accompanied by elevated IL-10 production. Consistently, infusion of FTY720-DCs could preferentially promote Treg proliferation and upregulate PD-1 expression on conventional T cells in allogeneic mature BMDC priming experiment. These results suggest that infusion of FTY720-DCs before cardiac transplantation could significantly prolong functional graft survival by acting as a balancer of alloimmune response.

Fingolimod provides long-term protection in rodent models of cerebral ischemia

OBJECTIVE

The sphingosine-1-phosphate (S1P) receptor agonist fingolimod (FTY720), that has shown efficacy in advanced multiple sclerosis clinical trials, decreases reperfusion injury in heart, liver, and kidney. We therefore tested the therapeutic effects of fingolimod in several rodent models of focal cerebral ischemia. To assess the translational significance of these findings, we asked whether fingolimod improved long-term behavioral outcomes, whether delayed treatment was still effective, and whether neuroprotection can be obtained in a second species.

METHODS

We used rodent models of middle cerebral artery occlusion and cell-culture models of neurotoxicity and inflammation to examine the therapeutic potential and mechanisms of neuroprotection by fingolimod.

RESULTS

In a transient mouse model, fingolimod reduced infarct size, neurological deficit, edema, and the number of dying cells in the core and periinfarct area. Neuroprotection was accompanied by decreased inflammation, as fingolimod-treated mice had fewer activated neutrophils, microglia/macrophages, and intercellular adhesion molecule-1 (ICAM-1)-positive blood vessels. Fingolimod-treated mice showed a smaller infarct and performed better in behavioral tests up to 15 days after ischemia. Reduced infarct was observed in a permanent model even when mice were treated 4 hours after ischemic onset. Fingolimod also decreased infarct size in a rat model of focal ischemia. Fingolimod did not protect primary neurons against glutamate excitotoxicity or hydrogen peroxide, but decreased ICAM-1 expression in brain endothelial cells stimulated by tumor necrosis factor alpha.

INTERPRETATION

These findings suggest that anti-inflammatory mechanisms, and possibly vasculoprotection, rather than direct effects on neurons, underlie the beneficial effects of fingolimod after stroke. S1P receptors are a highly promising target in stroke treatment.

Fingolimod (FTY720): discovery and development of an oral drug to treat multiple sclerosis

The discovery of fingolimod (FTY720/Gilenya; Novartis), an orally active immunomodulatory drug, has opened up new approaches to the treatment of multiple sclerosis, the most common inflammatory disorder of the central nervous system. Elucidation of the effects of fingolimod--mediated by the modulation of sphingosine 1-phosphate (S1P) receptors--has indicated that its therapeutic activity could be due to regulation of the migration of selected lymphocyte subsets into the central nervous system and direct effects on neural cells, particularly astrocytes. An improved understanding of the biology of S1P receptors has also been gained. This article describes the discovery and development of fingolimod, which was approved by the US Food and Drug Administration in September 2010 as a first-line treatment for relapsing forms of multiple sclerosis, thereby becoming the first oral disease-modifying therapy to be approved for multiple sclerosis in the United States.

Ischemia/reperfusion injury: The role of immune cells

Ischemia/reperfusion (I/R) injury is an inflammatory condition that is characterized by innate immunity and an adaptive immune response. This review is focused on the acute inflammatory response in I/R injury, and also the adaptive immunological mechanisms in chronic ischemic disease that lead to increased vulnerability during acute events, in relation to the cell types that have been shown to mediate innate immunity to an adaptive immune response in I/R, specifically myocardial infarction. Novel aspects are also highlighted in respect to the mechanisms within the cardiovascular system and cardiovascular risk factors that may be involved in the inflammatory response accompanying myocardial infarction. Experimental myocardial I/R has suggested that immune cells may mediate reperfusion injury. Specifically, monocytes, macrophages, T-cells, mast cells, platelets and endothelial cells are discussed with reference to the complement cascade, toll-like receptors, cytokines, oxidative stress, renin-angiotensin system, and in reference to the microvascular system in the signaling mechanisms of I/R. Finally, the findings of the data summarized in this review are most important for possible translation into clinical cardiology practice and possible avenues for drug development.