Role of Sulfur Dioxide in Acute Lung Injury Following Limb Ischemia/Reperfusion in Rats

Sulfur dioxide (SO₂) is naturally synthesized by glutamate‐oxaloacetate transaminase (GOT) from l ‐cysteine in mammalian cells. We aim to investigate the role of SO₂ in inflammation in acute lung injury (ALI) following limb ischemia/reperfusion (I/R). Male Wistar rats were subjected to limb I/R and were injected with saline, GOT inhibitor hydroxamate (HDX, 0.47 mmol/kg), or the SO₂ donor Na₂SO₃/NaHSO₃ (0.54 mmol/kg/0.18 mmol/kg). Compared with the sham operation, the plasma SO₂ levels were significantly decreased by limb I/R treatment. In addition, SO₂ concentration and GOT activity in the lung tissue were also reduced in ALI. The occurrence of ALI following limb I/R can be prevented by Na₂SO₃/NaHSO₃ treatment, whereas it can be significantly aggravated by HDX. The plasma IL‐1β, IL‐6, and IL‐10 levels were consistent with myeloperoxidase activity and inflammation in lung tissue. In conclusion, our data suggest that downregulation of endogenous SO₂ production might be involved in pathogenesis of ALI following limb I/R in rats. © 2013 Wiley Periodicals, Inc. J BiochemMol Toxicol 27:389‐397, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21492     

Induction and Role of Indoleamine 2,3 Dioxygenase in Mouse Models of Influenza A Virus Infection

Influenza infection stimulates protective host immune responses but paradoxically enhances lung indoleamine 2,3 dioxygenase (IDO) activity, an enzyme that suppresses helper/effector T cells and activates Foxp3-lineage regulatory CD4 T cells (Tregs). Influenza A/PR/8/34 (PR8) infection stimulated rapid elevation of IDO activity in lungs and lung-draining mediastinal lymph nodes (msLNs). Mice lacking intact IDO1 genes (IDO1-KO mice) exhibited significantly lower morbidity after sub-lethal PR8 infection, and genetic or pharmacologic IDO ablation led to much faster recovery after virus clearance. More robust influenza-specific effector CD8 T cell responses manifested in lungs of PR8-infected IDO1-KO mice, though virus clearance rates were unaffected by IDO ablation. Similar outcomes manifested in mice infected with a less virulent influenza A strain (X31). IDO induction in X31-infected lungs was dependent on IFN type II (IFNγ) signaling and was restricted to non-hematopoietic cells, while redundant IFN type 1 or type II signaling induced IDO exclusively in hematopoietic cells from msLNs. Memory T cells generated in X31-primed IDO1-KO mice protected mice from subsequent challenge with lethal doses of PR8 (100×LD₅₀). However recall T cell responses were less robust in lung interstitial tissues, and classic dominance of TCR Vβ8.3 chain usage amongst memory CD8⁺ T cells specific for influenza nucleoprotein (NP₃₆₆) did not manifest in IDO1-KO mice. Thus, influenza induced IDO activity in lungs enhanced morbidity, slowed recovery, restrained effector T cell responses in lungs and shaped memory T cell repertoire generation, but did not attenuate virus clearance during primary influenza A infection.     

Local Delivery of Polarized Macrophages Improves Reperfusion Recovery in a Mouse Hind Limb Ischemia Model

Aims

Enhancement of collateral development in coronary or peripheral artery disease is a therapeutic target, but it has proven difficult to achieve. Macrophages are key players in collateral remodeling, yet the effect of different macrophage subsets on arteriogenesis has not been investigated.

Methods and Results

Murine macrophages were cultured from bone marrow and polarized into M1 (IFNγ), M2a (IL-4) or M2c (IL-10) subsets. C57BL/6 mice underwent femoral artery ligation followed by intramuscular injection of macrophage subsets. Using eGFP expressing macrophages, cells could be detected at least 6 days after ligation and were located in the perivascular space of collateral vessels. After 14 days, perfusion ratio was increased in animals treated with M1 as well as M2a and M2c macrophages compared to control. Depletion of circulating monocytes by clodronate liposome injections did not hamper reperfusion recovery, however, treatment with exogenous polarized macrophages improved perfusion ratio after 14 days again. We used IL10R^fl/fl/LysMCre⁺ mice to study the effect of inhibition of endogenous polarization towards specifically M2c macrophages on arteriogenesis. Deletion of the IL10-receptor (IL10R) in the myeloid lineage did not affect reperfusion recovery, yet the pro-arteriogenic effect of exogenously injected M2c macrophages was still present.

Conclusions

Local injection of polarized macrophages promotes reperfusion recovery after femoral artery ligation and is not influenced by depletion of circulatory monocytes. Preventing endogenous M2c polarization did not affect reperfusion recovery suggesting that M2c’s are not required for collateralization, but are sufficient to induce collateral formation upon exogenous administration. This is the first study using local injection of macrophage subsets showing the pro-arteriogenic effect of polarized macrophages.     

The Role of N-Acetyltransferase 8 in Mesenchymal Stem Cell-Based Therapy for Liver Ischemia/Reperfusion Injury in Rats

Objective

To evaluate the impact of mesenchymal stem cells (MSCs) against hepatic I/R injury and explore the role of N-acetyltransferase 8 (NAT8) in the process.

Methods

We investigated the potential of injected MSCs systemically via the tail vein in healing injuried liver of the SD rat model of 70% hepatic I/R injury by measuring the biochemical and pathologic alterations. Subsequently, we evaluated the expression levels of NAT8 by western blotting in vivo. Concurrently, hydrogen peroxide (H₂O₂)-induced apoptosis in the human normal liver cell line L02 was performed in vitro to evaluate the protective effects of MSC conditioned medium (MSC-CM) on L02 cells. In addition, we downregulated and upregulated NAT8 expression in L02 cells and induced apoptosis by using H₂O₂ to study the protective role of NAT8.

Results

MSCs implantation led to a significant reduced liver enzyme levels, an advanced protection in the histopathological findings of the acutely injured liver and a significantly lower percentage of TUNEL-positive cells, which were increased after I/R injury. In vitro assays, MSC-CM inhibited hepatocyte apoptosis induced by H₂O_2. Moreover, overexpression or downregulation of NAT8 prevented or aggravated hepatocyte apoptosis induced by H₂O₂, respectively.

Conclusions

MSC transplantation provides support to the I/R-injured liver by inhibiting hepatocellular apoptosis and stimulating NAT8 regeneration.     

Highly Efficient Stable Expression of Indoleamine 2,3 Dioxygenase Gene in Primary Fibroblasts

Indoleamine 2,3 dioxygenase (IDO) is a potent immunomodulatory enzyme that has recently attracted significant attention for its potential application as an inducer of immunotolerance in transplantation. We have previously demonstrated that a collagen matrix populated with IDO-expressing fibroblasts can be applied successfully in suppressing islet allogeneic immune response. Meanwhile, a critical aspect of such immunological intervention relies largely on effective long-term expression of the IDO gene. Moreover, gene manipulation of primary cells is known to be challenging due to unsatisfactory expression of the exogenous gene. In this study, a lentiviral gene delivery system has been employed to transduce primary fibroblasts. We used polybrene to efficiently deliver the IDO gene into primary fibroblasts and showed a significant increase (about tenfold) in the rate of gene transfection. In addition, by the use of fluorescence-activated cell sorting, a 95% pure population of IDO-expressing fibroblasts was successfully obtained. The efficiency of the IDO expression and the activity of the enzyme have been confirmed by Western blotting, fluorescence-activated cell sorting analysis, and Kynurenine assay, respectively. The findings of this study revealed simple and effective strategies through which an efficient and stable expression of IDO can be achieved for primary cells which, in turn, significantly improves its potential as a tool for achieving immunotolerance in different types of transplantation.     

Immuno-Regulatory Function of Indoleamine 2,3 Dioxygenase through Modulation of Innate Immune Responses

Successful long-term treatment of type-1 diabetes mainly relies on replacement of β-cells via islet transplantation. Donor shortage is one of the main obstacles preventing transplantation from becoming the treatment of choice. Although animal organs could be an alternative source for transplantation, common immunosuppressive treatments demonstrate low efficacy in preventing xenorejection. Immunoprotective effects of indoleamine 2,3-dioxygenase (IDO) on T-cell mediated allorejection has been extensively studied. Our studies revealed that IDO expression by fibroblasts, induced apoptosis in T-cells while not affecting non-immune cell survival/function. Since macrophages play a pivotal role in xenograft rejection, herein we investigated the effect of IDO-induced tryptophan deficiency/kynurenine accumulation on macrophage function/survival. Moreover, we evaluated the local immunosuppressive effect of IDO on islet-xenograft protection. Our results indicated that IDO expression by bystander fibroblasts significantly reduced the viability of primary macrophages via apoptosis induction. Treatment of peritoneal macrophages by IDO-expressing fibroblast conditioned medium significantly reduced their proinflammatory activity through inhibition of iNOS expression. To determine whether IDO-induced tryptophan starvation or kynurenine accumulation is responsible for macrophage apoptosis and inhibition of their proinflammatory activity, Raw264.7 cell viability and proinflammatory responses were evaluated in tryptophan deficient medium or in the presence of kynurenine. Tryptophan deficiency, but not kynurenine accumulation, reduced Raw264.7 cell viability and suppressed their proinflammatory activity. Next a three-dimensional islet-xenograft was engineered by embedding rat islets within either control or IDO–expressing fibroblast-populated collagen matrix. Islets morphology and immune cell infiltration were then studied in the xenografts transplanted into the C57BL/6 mouse renal sub-capsular space. Local IDO significantly decreased the number of infiltrating macrophages (11±1.47 vs. 70.5±7.57 cells/HPF), T-cells (8.75±1.03 vs. 75.75±5.72 cells/HPF) and iNOS expression in IDO-expressing xenografts versus controls. Islet morphology remained intact in IDO-expressing grafts and islets were strongly stained for insulin/glucagon compared to control. These findings support the immunosuppressive role of IDO on macrophage-mediated xeno-rejection.     

BK通道对大鼠肾脏缺血再灌注损伤的作用及机制

目的:探讨缺血再灌注损伤早期肾脏皮质内大电导钙依赖性钾通道(BK)通道的表达及意义。方法:建立成年SD大鼠肾脏急性缺血再灌注损伤模型,快速收集24小时缺血大鼠与对照大鼠血和损伤侧肾脏皮质标本,使用ELISA方法检测血肌酐和尿素氮含量,实时荧光定量RT-PCR和蛋白免疫印迹方法检测肾脏组织中BK通道α亚基的m RNA表达水平和蛋白表达水平。结果:(1)急性缺血再灌注大鼠损伤侧肾脏皮质BK通道α亚基m RNA水平较对照大鼠同侧肾脏皮质的表达明显降低(P0.01)。(2)急性缺血再灌注大鼠损伤侧肾脏皮质BK通道α亚基蛋白水平较对照大鼠同侧肾脏皮质的表达也明显降低(P0.05)。(3)NS1619预处理缺血再灌注大鼠血尿素氮和血肌酐含量显著降低(P0.05)。结论:BK通道表达和功能的改变是参与大鼠肾脏缺血再灌注损伤的重要机制。     

Sex Differences in Ischemia/Reperfusion Injury: The Role of Mitochondrial Permeability Transition

Neurochemical Research - Brain and heart ischemia are among the leading causes of death and disability in both men and women, but there are significant sex differences in the incidence and severity...     

The Role of Indoleamine 2,3-Dioxygenase in Diethylnitrosamine-Induced Liver Carcinogenesis

Indoleamine 2,3-dioxygenase (IDO), a tryptophan-catabolizing intracellular enzyme of the L-kynurenine pathway, causes preneoplastic cells and tumor cells to escape the immune system by inducing immune tolerance; this mechanism might be associated with the development and progression of human malignancies. In the present study, we investigated the role of IDO in diethylnitrosamine (DEN)-induced hepatocarcinogenesis by using IDO-knockout (KO) mice. To induce hepatocellular carcinoma (HCC), hepatic adenoma, and preneoplastic hepatocellular lesions termed foci of cellular alteration (FCA), male IDO-wild-type (WT) and IDO-KO mice with a C57BL/6J background received a single intraperitoneal injection of DEN at 2 weeks of age. The mice were sacrificed to evaluate the development of FCA and hepatocellular neoplasms. HCC overexpressed IDO and L-kynurenine compared to surrounding normal tissue in the DEN-treated IDO-WT mice. The number and cell proliferative activity of FCAs, and the incidence and multiplicity of HCC were significantly greater in the IDO-WT than in the IDO-KO mice. The expression levels of the IDO protein, of L-kynurenine, and of IFN-γ, COX-2, TNF-α, and Foxp3 mRNA were also significantly increased in the DEN-induced hepatic tumors that developed in the IDO-WT mice. The mRNA expression levels of CD8, perforin and granzyme B were markedly increased in hepatic tumors developed in IDO-KO mice. Moreover, Foxp3-positive inflammatory cells had infiltrated into the livers of DEN-treated IDO-WT mice, whereas fewer cells had infiltrated into the livers of IDO-KO mice. Induction of IDO and elevation of L-kynurenine might play a critical role in both the early and late phase of liver carcinogenesis. Our findings suggest that inhibition of IDO might offer a promising strategy for the prevention of liver cancer.     

氨磷汀对氧糖剥夺引起的PC12细胞缺血再灌注损伤的保护作用研究

目的：研究氨磷汀对体外培养的神经元样细胞的缺血再灌注损伤的保护作用,为其最终用于临床脑缺血的治疗打下基础。方法：体外培养的PC12细胞氧糖剥夺4h后复氧复糖,给予不同浓度的氨磷汀处理,20h后镜下观察细胞形态学变化,用MTT和LDH检测细胞活力和损伤情况,免疫荧光染色观察凋亡细胞,流式细胞仪计数凋亡细胞的比例。结果：高浓度氨磷汀对正常PC12细胞活力有抑制作用（P〈0.05）,而低浓度则无。氨磷汀可以提高缺血再灌注损伤PC12细胞活力（P〈0.05）,减少LDH释放（P〈0.05）,保护细胞正常形态,抑制细胞凋亡（P〈0.05）。结论：氨磷汀对氧糖剥夺引起的神经元样细胞的缺血再灌注损伤具有保护作用。     

氨磷汀对氧糖剥夺引起的PC12 细胞缺血再灌注损伤的保护作用研究

目的:研究氨磷汀对体外培养的神经元样细胞的缺血再灌注损伤的保护作用,为其最终用于临床脑缺血的治疗打下基础。方法:体外培养的PC12细胞氧糖剥夺4h后复氧复糖,给予不同浓度的氨磷汀处理,20h后镜下观察细胞形态学变化,用MTT和LDH检测细胞活力和损伤情况,免疫荧光染色观察凋亡细胞,流式细胞仪计数凋亡细胞的比例。结果:高浓度氨磷汀对正常PC12细胞活力有抑制作用(P<0.05),而低浓度则无。氨磷汀可以提高缺血再灌注损伤PC12细胞活力(P<0.05),减少LDH释放(P<0.05),保护细胞正常形态,抑制细胞凋亡(P<0.05)。结论:氨磷汀对氧糖剥夺引起的神经元样细胞的缺血再灌注损伤具有保护作用。     

The Attenuation of Lung Ischemia Reperfusion Injury by Oxymatrine

To investigate the protective effects of oxymatrine (OMT) on lung ischemia reperfusion injury (LIRI) in rabbits, models of LIRI in rabbit were used. Thirty-two rabbits were randomly divided into four groups: control group (n = 8), ischemia reperfusion group (I/R group, n = 8), OMTl group (n = 8), OMT2 group (n = 8). Lung tissue samples were collected at 40, 80, 120 min time-points after lung ischemia reperfusion. TNF-α, 1I-8, IL-10, apoptosis index (AI), and index of quantitative assessment of histologic lung injury (IQA) were measured in each group. TNF-α and IL-8 in I/R group were significantly higher than those of the control group and OMT2 group (P < 0.01), but in OMT2 group they were significantly lower than those of OMTl group (P < 0.05). IL-10 in OMT2 group and OMTl group was significantly higher than that of I/R group (P < 0.01). But in OMTl group it was significantly lower than that of OMT2 group (P < 0.05). AI in I/R group was significantly higher than that of OMT2 group and the control group at 80 min after lung ischemia reperfusion (P < 0.01). IQA in OMTl group and OMT2 group was significantly lower than that of the I/R group (P < 0.01). Oxymatrine can protect against LIRI in rabbits by upregulating levels of IL-10 and downregulating levels of TNF-α and IL-8, inhibiting the alveolar cells apoptosis and inflammatory response, and attenuating the acute LIRI.     

Amniotic Fluid Derived Stem Cells with a Renal Progenitor Phenotype Inhibit Interstitial Fibrosis in Renal Ischemia and Reperfusion Injury in Rats

Objectives

Mesenchymal stem cells derived from human amniotic fluid (hAFSCs) are a promising source for cellular therapy, especially for renal disorders, as a subpopulation is derived from the fetal urinary tract. The purpose of this study was to evaluate if hAFSCs with a renal progenitor phenotype demonstrate a nephroprotective effect in acute ischemia reperfusion (I/R) model and prevent late stage fibrosis.

Methods

A total of 45 male 12-wk-old Wistar rats were divided into three equal groups;: rats subjected to I/R injury and treated with Chang Medium, rats subjected to I/R injury and treated with hAFSCs and sham-operated animals. In the first part of this study, hAFSCs that highly expressed CD24, CD117, SIX2 and PAX2 were isolated and characterized. In the second part, renal I/R injury was induced in male rats and cellular treatment was performed 6 hours later via arterial injection. Functional and histological analyses were performed 24 hours, 48 hours and 2 months after treatment using serum creatinine, urine protein to creatinine ratio, inflammatory and regeneration markers and histomorphometric analysis of the kidney. Statistical analysis was performed by analysis of variance followed by the Tukey’s test for multiple comparisons or by nonparametric Kruskal-Wallis followed by Dunn. Statistical significance level was defined as p <0.05.

Results

hAFSCs treatment resulted in significantly reduced serum creatinine level at 24 hours, less tubular necrosis, less hyaline cast formation, higher proliferation index, less inflammatory cell infiltration and less myofibroblasts at 48h. The treated group had less fibrosis and proteinuria at 2 months after injury.

Conclusion

hAFSCs contain a renal progenitor cell subpopulation that has a nephroprotective effect when delivered intra-arterially in rats with renal I/R injury, and reduces interstitial fibrosis on long term follow-up.     

Eritoran对大鼠肾脏缺血再灌注损伤的保护作用

目的:观察eritoran对大鼠肾脏缺血再灌注损伤模型的.方法:建立SD大鼠缺血再灌注模型,给予eritoran治疗而对照组给予生理盐水治疗,观察各组的肾功能情况、肾组织光镜病理,并采用核糖核酸酶保护测定检测肾组织炎症因子/趋化因子的表达.结果:与模型组相比,eritoran预处理可显著改善大鼠的肾功能,减轻缺血再灌注引起的肾小管损伤,减轻肾组织病变,减少肾组织单核细胞浸润并下调多种炎症因子的表达(TNF-α,IL-6,IL-1β和MCP-1).结论:本研究证实通过eritoran抑制Toll样受体4,可减轻大鼠肾脏缺血再灌注损伤中的炎症反应,减轻肾脏缺血再灌注损伤,eritoran可望成为肾脏I/R损伤的新治疗手段.     

MicroRNAs对缺血再灌注损伤的调控作用

MicroRNA（miRNA）是一类小的（～20个核苷酸）、非编码的单链RNA分子,能够负调控基因表达,涉及多种信号途径和病理生理过程。缺血再灌注损伤(ischemia reperfusion injury,IRI)指组织器官缺血后重新获得血液的再灌注过程,灌注后组织、器官功能不能恢复,造成功能障碍和结构损伤的现象。IRI是影响多个组织与器官复杂的、系统的生理病理过程,并能够产生很多不可逆的损伤,导致级联的多器官功能障碍。现已发现多种miRNA在组织器官IRI中发生明显的变化,表明miRNA能够直接或者间接影响组织器官IRI。本文综述了miRNA的靶基因以及在心、脑、肝和肾IRI中的调控作用。miRNA 不仅参与了器官IR 损伤的病理生理过程,而且作为IR损伤的特定标志物在临床诊断和干预治疗中具有广阔的前景。     

七氟烷对糖尿病心肌缺血/再灌注损伤的影响

糖尿病是一种常见病、多发病,严重威胁着人类的健康。现已明确,糖尿病是冠心病发病的一个重要因素。心肌缺血/再灌注(ischemia/reperfusion,I/R)损伤是临床常见的病理过程,同时是冠心病发病及心肌血运重建治疗过程中的核心环节,如何减轻I/R损伤一直是国际研究热点之一。糖尿病与I/R损伤对心肌都有损害作用,相关研究证明糖尿病能够进一步恶化I/R损伤对心肌的损伤作用。研究表明,缺血预处理(ischemia preconditioning,IPC)可以延缓或减轻心肌I/R损伤,同时,麻醉药预处理(anesthetic induced preconditioning,APC)也具有IPC样的心肌保护作用。其中,七氟烷作为现阶段临床较常用的吸入麻醉药,同样对心肌I/R损伤具有保护作用。本文就七氟烷对糖尿病心肌I/R损伤的影响及其机制做一综述。     

The Synergistic Local Immunosuppressive Effects of Neural Stem Cells Expressing Indoleamine 2,3-Dioxygenase (IDO) in an Experimental Autoimmune Encephalomyelitis (EAE) Animal Model

Neurodegenerative diseases provoke robust immunological reactions in the central nervous system (CNS), which further deteriorate the neural tissue damage. We hypothesized that the expression levels of indoleamine 2,3-dioxygenase (IDO), an enzyme that has potent immune suppressive activities, in neural stem cells (NSCs) would have synergistic therapeutic effects against neurodegenerative diseases, since NSCs themselves have low IDO expression. In this study, the synergistic immune suppressive effects of rat fetal NSCs expressing IDO (rfNSCs-IDO) were validated by mixed leukocyte reaction (MLR) in vitro and an experimental autoimmune encephalomyelitis (EAE) animal model in vivo. rfNSCs-IDO showed significantly more suppressive effects on T cell proliferation in the MLR compared to control rfNSCs (rfNSCs-Cont). Importantly, IDO inhibition using 1-methyl-DL-tryptophan (1-MT), an IDO inhibitor, reversed the synergistic effects, confirming IDO-specific effects in rfNSCs-IDO. In the EAE animal model, systemic rfNSCs-IDO injections resulted in significant local immune suppression in the cervical lymph nodes and CNS, evidenced by a reduction in the number of activated T lymphocytes and an increase in regulatory T cell numbers, which induced significantly fewer clinical symptoms and faster recovery. In contrast, rfNSCs-Cont failed to reduce symptoms in the EAE animal models, although they showed local immune suppression, which was significantly less than that in rfNSCs-IDO. Taken together, IDO expression in NSCs synergistically potentiates the immune suppression activities of NSCs and could be applicable for the development of therapeutic modalities against various neurodegenerative diseases.     

Biliverdin Protects against Liver Ischemia Reperfusion Injury in Swine

Ischemia reperfusion injury (IRI) in organ transplantation remains a serious and unsolved problem. Organs that undergo significant damage during IRI, function less well immediately after reperfusion and tend to have more problems at later times when rejection can occur. Biliverdin has emerged as an agent that potently suppress IRI in rodent models. Since the use of biliverdin is being developed as a potential therapeutic modality for humans, we tested the efficacy for its effects on IRI of the liver in swine, an accepted and relevant pre-clinical animal model. Administration of biliverdin resulted in rapid appearance of bilirubin in the serum and significantly suppressed IRI-induced liver dysfunction as measured by multiple parameters including urea and ammonia clearance, neutrophil infiltration and tissue histopathology including hepatocyte cell death. Taken together, our findings, in a large animal model, provide strong support for the continued evaluation of biliverdin as a potential therapeutic in the clinical setting of transplantation of the liver and perhaps other organs.     

Protective Role of p70S6K in Intestinal Ischemia/Reperfusion Injury in Mice

The mTOR signaling pathway plays a crucial role in the regulation of cell growth, proliferation, survival and in directing immune responses. As the intestinal epithelium displays rapid cell growth and differentiation and is an important immune regulatory organ, we hypothesized that mTOR may play an important role in the protection against intestinal ischemia reperfusion (I/R)-induced injury. To better understand the molecular mechanisms by which the mTOR pathway is altered by intestinal I/R, p70S6K, the major effector of the mTOR pathway, was investigated along with the effects of rapamycin, a specific inhibitor of mTOR and an immunosuppressant agent used clinically in transplant patients. In vitro experiments using an intestinal epithelial cell line and hypoxia/reoxygenation demonstrated that overexpression of p70S6K promoted cell growth and migration, and decreased cell apoptosis. Inhibition of p70S6K by rapamycin reversed these protective effects. In a mouse model of gut I/R, an increase of p70S6K activity was found by 5 min and remained elevated after 6 h of reperfusion. Inhibition of p70S6K by rapamycin worsened gut injury, promoted inflammation, and enhanced intestinal permeability. Importantly, rapamycin treated animals had a significantly increased mortality. These novel results demonstrate a key role of p70S6K in protection against I/R injury in the intestine and suggest a potential danger in using mTOR inhibitors in patients at risk for gut hypoperfusion.