Role of claudin-5 in the attenuation of murine acute lung injury by simvastatin.

The statins are now recognized to have pleiotropic properties, including augmentation of endothelial barrier function. To explore the mechanisms involved, we investigated the effect of simvastatin on endothelial cell (EC) tight junctions. Western blotting of human pulmonary artery ECs treated with simvastatin (5 µM) confirmed a significant time-dependent increase (16-48 h) in claudin-5 protein expression compared with controls, without detectable alterations in zonula occludens-1 or occludin. These effects were associated with membrane translocation of VE-cadherin, whereas translocation of vascular endothelial cadherin (VE-cadherin; silencing RNA) inhibited simvastatin-induced claudin-5 up-regulation. Moreover, simvastatin treatment of ECs induced increased phosphorylation of both FoxO1 and ß-catenin, transcriptional regulators of claudin-5 expression mediated by VE-cadherin. Subsequently, we found no effect of claudin-5 silencing on EC barrier protection by simvastatin in response to thrombin stimulation, as measured by either transendothelial electrical resistance or by EC monolayer flux of FITC-dextran (2,000 kD). However, silencing of claudin-5 did significantly attenuate simvastatin-mediated EC barrier protection in response to thrombin, as measured by monolayer flux of sodium fluorescein (376 Da). Finally, employing a murine model of LPS-induced acute lung injury, there was no effect of claudin-5 silencing in vivo (intratracheal injection) on bronchoalveolar lavage fluid protein or cell counts, but LPS-induced lung tissue extravasation of the small molecular weight markers, sodium fluorescein and Hochst stain (562 Da), were significantly increased in claudin-5-silenced animals compared with simvastatin-treated control animals. These findings implicate a distinct mechanism underlying size-selective endothelial barrier-protective properties of statins, and may ultimately lead to new novel therapeutic targets for patients with acute lung injury.

Nicotinamide phosphoribosyltransferase inhibitor is a novel therapeutic candidate in murine models of inflammatory lung injury.

We previously identified the intracellular nicotinamide phosphoribosyltransferase (iNAMPT, aka pre-B-cell colony enhancing factor) as a candidate gene promoting acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI) with circulating nicotinamide phosphoribosyltransferase potently inducing NF-κB signaling in lung endothelium. iNAMPT also synthesizes intracellular nicotinamide adenine dinucleotide (iNAD) in response to extracellular oxidative stress, contributing to the inhibition of apoptosis via ill-defined mechanisms. We now further define the role of iNAMPT activity in the pathogenesis of ARDS/VILI using the selective iNAMPT inhibitor FK-866. C57/B6 mice were exposed to VILI (40 ml/kg, 4 h) or LPS (1.5 mg/kg, 18 h) after osmotic pump delivery of FK-866 (100 mg/kg/d, intraperitoneally). Assessment of total bronchoalveolar lavage (BAL) protein, polymorphonuclear neutrophil (PMN) levels, cytokine levels (TNF-α, IL-6, IL-1α), lung iNAD levels, and injury scores revealed that FK-866-mediated iNAMPT inhibition successfully reduced lung tissue iNAD levels, BAL injury indices, inflammatory cell infiltration, and lung injury scores in LPS- and VILI-exposed mice. FK-866 further increased lung PMN apoptosis, as reflected by caspase-3 activation in BAL PMNs. These findings support iNAMPT inhibition via FK-866 as a novel therapeutic agent for ARDS via enhanced apoptosis in inflammatory PMNs.

Proline-rich region of non-muscle myosin light chain kinase modulates kinase activity and endothelial cytoskeletal dynamics.

Disruption of the pulmonary endothelial barrier and subsequent vascular leak is a hallmark of acute lung injury. Dynamic rearrangements in the endothelial cell (EC) peripheral membrane and underlying cytoskeleton are critical determinants of barrier function. The cytoskeletal effector protein non-muscle myosin light chain kinase (nmMLCK) and the actin-binding regulatory protein cortactin are important regulators of the endothelial barrier. In the present study we functionally characterize a proline-rich region of nmMLCK previously identified as the possible site of interaction between nmMLCK and cortactin. A mutant nmMLCK construct deficient in proline residues at the putative sites of cortactin binding (amino acids 973, 976, 1019, 1022) was generated. Co-immunoprecipitation studies in human lung EC transfected with wild-type or mutant nmMLCK demonstrated similar levels of cortactin interaction at baseline and after stimulation with the barrier-enhancing agonist, sphingosine 1-phosphate (S1P). In contrast, binding studies utilizing recombinant nmMLCK fragments containing the wild-type or proline-deficient sequence demonstrated a two-fold increase in cortactin binding (p<0.01) to the mutant construct. Immunofluorescent microscopy revealed an increased stress fiber density in ECs expressing GFP-labeled mutant nmMLCK at baseline (p=0.02) and after thrombin (p=0.01) or S1P (p=0.02) when compared to wild-type. Mutant nmMLCK demonstrated an increase in kinase activity in response to thrombin (p<0.01). Kymographic analysis demonstrated an increased EC membrane retraction distance and velocity (p<0.01) in response to the barrier disrupting agent thrombin in cells expressing the mutant vs. the wild-type nmMLCK construct. These results provide evidence that critical prolines within nmMLCK (amino acids 973, 976, 1019, 1022) regulate cytoskeletal and membrane events associated with pulmonary endothelial barrier function.

Role of migratory inhibition factor in age-related susceptibility to radiation lung injury via NF-E2-related factor-2 and antioxidant regulation.

Microvascular injury and increased vascular leakage are prominent features of radiation-induced lung injury (RILI), and often follow cancer-associated thoracic irradiation. Our previous studies demonstrated that polymorphisms in the gene (MIF) encoding macrophage migratory inhibition factor (MIF), a multifunctional pleiotropic cytokine, confer susceptibility to acute inflammatory lung injury and increased vascular permeability, particularly in senescent mice. In this study, we exposed wild-type and genetically engineered mif(-/-) mice to 20 Gy single-fraction thoracic radiation to investigate the age-related role of MIF in murine RILI (mice were aged 8 wk, 8 mo, or 16 mo). Relative to 8-week-old mice, decreased MIF was observed in bronchoalveolar lavage fluid and lung tissue of 8- to 16-month-old wild-type mice. In addition, radiated 8- to 16-month-old mif(-/-) mice exhibited significantly decreased bronchoalveolar lavage fluid total antioxidant concentrations with progressive age-related decreases in the nuclear expression of NF-E2-related factor-2 (Nrf2), a transcription factor involved in antioxidant gene up-regulation in response to reactive oxygen species. This was accompanied by decreases in both protein concentrations (NQO1, GCLC, and heme oxygenase-1) and mRNA concentrations (Gpx1, Prdx1, and Txn1) of Nrf2-influenced antioxidant gene targets. In addition, MIF-silenced (short, interfering RNA) human lung endothelial cells failed to express Nrf2 after oxidative (H2O2) challenge, an effect reversed by recombinant MIF administration. However, treatment with an antioxidant (glutathione reduced ester), but not an Nrf2 substrate (N-acetyl cysteine), protected aged mif(-/-) mice from RILI. These findings implicate an important role for MIF in radiation-induced changes in lung-cell antioxidant concentrations via Nrf2, and suggest that MIF may contribute to age-related susceptibility to thoracic radiation.

Hydrogen sulfide attenuates particulate matter-induced human lung endothelial barrier disruption via combined reactive oxygen species scavenging and Akt activation.

Exposure to particulate air pollution is associated with increased cardiopulmonary morbidity and mortality, although the pathogenic mechanisms are poorly understood. We previously demonstrated that particulate matter (PM) exposure triggers massive oxidative stress in vascular endothelial cells (ECs), resulting in the loss of EC integrity and lung vascular hyperpermeability. We investigated the protective role of hydrogen sulfide (H(2)S), an endogenous gaseous molecule present in the circulation, on PM-induced human lung EC barrier disruption and pulmonary inflammation. Alterations in EC monolayer permeability, as reflected by transendothelial electrical resistance (TER), the generation of reactive oxygen species (ROS), and murine pulmonary inflammatory responses, were studied after exposures to PM and NaSH, an H(2)S donor. Similar to N-acetyl cysteine (5 mM), NaSH (10 µM) significantly scavenged PM-induced EC ROS and inhibited the oxidative activation of p38 mitogen-activated protein kinase. Concurrent with these events, NaSH (10 µM) activated Akt, which helps maintain endothelial integrity. Both of these pathways contribute to the protective effect of H(2)S against PM-induced endothelial barrier dysfunction. Furthermore, NaSH (20 mg/kg) reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in bronchoalveolar lavage fluids in a murine model of PM-induced lung inflammation. These data suggest a potentially protective role for H(2)S in PM-induced inflammatory lung injury and vascular hyperpermeability.

Role of sphingolipids in murine radiation-induced lung injury: protection by sphingosine 1-phosphate analogs.

Clinically significant radiation-induced lung injury (RILI) is a common toxicity in patients administered thoracic radiotherapy. Although the molecular etiology is poorly understood, we previously characterized a murine model of RILI in which alterations in lung barrier integrity surfaced as a potentially important pathobiological event and genome-wide lung gene mRNA levels identified dysregulation of sphingolipid metabolic pathway genes. We hypothesized that sphingolipid signaling components serve as modulators and novel therapeutic targets of RILI. Sphingolipid involvement in murine RILI was confirmed by radiation-induced increases in lung expression of sphingosine kinase (SphK) isoforms 1 and 2 and increases in the ratio of ceramide to sphingosine 1-phosphate (S1P) and dihydro-S1P (DHS1P) levels in plasma, bronchoalveolar lavage fluid, and lung tissue. Mice with a targeted deletion of SphK1 (SphK1(-/-)) or with reduced expression of S1P receptors (S1PR1(+/-), S1PR2(-/-), and S1PR3(-/-)) exhibited marked RILI susceptibility. Finally, studies of 3 potent vascular barrier-protective S1P analogs, FTY720, (S)-FTY720-phosphonate (fTyS), and SEW-2871, identified significant RILI attenuation and radiation-induced gene dysregulation by the phosphonate analog, fTyS (0.1 and 1 mg/kg i.p., 2×/wk) and to a lesser degree by SEW-2871 (1 mg/kg i.p., 2×/wk), compared with those in controls. These results support the targeting of S1P signaling as a novel therapeutic strategy in RILI.

Particulate matter air pollution disrupts endothelial cell barrier via calpain-mediated tight junction protein degradation.

BACKGROUND: Exposure to particulate matter (PM) is a significant risk factor for increased cardiopulmonary morbidity and mortality. The mechanism of PM-mediated pathophysiology remains unknown. However, PM is proinflammatory to the endothelium and increases vascular permeability in vitro and in vivo via ROS generation. OBJECTIVES: We explored the role of tight junction proteins as targets for PM-induced loss of lung endothelial cell (EC) barrier integrity and enhanced cardiopulmonary dysfunction. METHODS: Changes in human lung EC monolayer permeability were assessed by Transendothelial Electrical Resistance (TER) in response to PM challenge (collected from Ft. McHenry Tunnel, Baltimore, MD, particle size >0.1 µm). Biochemical assessment of ROS generation and Ca2+ mobilization were also measured. RESULTS: PM exposure induced tight junction protein Zona occludens-1 (ZO-1) relocation from the cell periphery, which was accompanied by significant reductions in ZO-1 protein levels but not in adherens junction proteins (VE-cadherin and ß-catenin). N-acetyl-cysteine (NAC, 5 mM) reduced PM-induced ROS generation in ECs, which further prevented TER decreases and atteneuated ZO-1 degradation. PM also mediated intracellular calcium mobilization via the transient receptor potential cation channel M2 (TRPM2), in a ROS-dependent manner with subsequent activation of the Ca2+-dependent protease calpain. PM-activated calpain is responsible for ZO-1 degradation and EC barrier disruption. Overexpression of ZO-1 attenuated PM-induced endothelial barrier disruption and vascular hyperpermeability in vivo and in vitro. CONCLUSIONS: These results demonstrate that PM induces marked increases in vascular permeability via ROS-mediated calcium leakage via activated TRPM2, and via ZO-1 degradation by activated calpain. These findings support a novel mechanism for PM-induced lung damage and adverse cardiovascular outcomes.

A cortactin CTTN coding SNP contributes to lung vascular permeability and inflammatory disease severity in African descent subjects.

The cortactin gene (CTTN), encoding an actin-binding protein critically involved in cytoskeletal dynamics and endothelial cell (EC) barrier integrity, contains single nucleotide polymorphisms (SNPs) associated with severe asthma in Black patients. As loss of lung EC integrity is a major driver of mortality in the Acute Respiratory Distress Syndrome (ARDS), sepsis, and the acute chest syndrome (ACS), we speculated CTTN SNPs that alter EC barrier function will associate with clinical outcomes from these types of conditions in Black patients. In case-control studies, evaluation of a nonsynonymous CTTN coding SNP Ser484Asn (rs56162978, G/A) in a severe sepsis cohort (725 Black subjects) revealed significant association with increased risk of sepsis mortality. In a separate cohort of sickle cell disease (SCD) subjects with and without ACS (177 SCD Black subjects), significantly increased risk of ACS and increased ACS severity (need for mechanical ventilation) was observed in carriers of the A allele. Human lung EC expressing the cortactin S484N transgene exhibited: (i) delayed EC barrier recovery following thrombin-induced permeability; (ii) reduced levels of critical Tyr486 cortactin phosphorylation; (iii) inhibited binding to the cytoskeletal regulator, nmMLCK; and (iv) attenuated EC barrier-promoting lamellipodia dynamics and biophysical responses. ARDS-challenged Cttn+/- heterozygous mice exhibited increased lung vascular permeability (compared to wild-type mice) which was significantly attenuated by IV delivery of liposomes encargoed with CTTN WT transgene but not by CTTN S484N transgene. In summary, these studies suggest that the CTTN S484N coding SNP contributes to severity of inflammatory injury in Black patients, potentially via delayed vascular barrier restoration.

Type 2 deiodinase and host responses of sepsis and acute lung injury.

The role of thyroid hormone metabolism in clinical outcomes of the critically ill remains unclear. Using preclinical models of acute lung injury (ALI), we assessed the gene and protein expression of type 2 deiodinase (DIO2), a key driver for synthesis of biologically active triiodothyronine, and addressed potential association of DIO2 genetic variants with ALI in a multiethnic cohort. DIO2 gene and protein expression levels in murine lung were validated by microarrays and immunoblotting. Lung injury was assessed by levels of bronchoalveolar lavage protein and leukocytes. Single-nucleotide polymorphisms were genotyped and ALI susceptibility association assessed. Significant increases in both DIO2 gene and D2 protein expression were observed in lung tissues from murine ALI models (LPS- and ventilator-induced lung injury), with expression directly increasing with the extent of lung injury. Mice with reduced levels of DIO2 expression (by silencing RNA) demonstrated reduced thyroxine levels in plasma and increased lung injury (increased bronchoalveolar lavage protein and leukocytes), suggesting a protective role for DIO2 in ALI. The G (Ala) allele of the Thr92Ala coding single-nucleotide polymorphism (rs225014) was protective in severe sepsis and severe sepsis-associated ALI after adjustments for age, sex, and genetic ancestry in a logistic regression model in European Americans. Our studies indicate that DIO2 is a novel ALI candidate gene, the nonsynonymous Thr92Ala coding variant of which confers ALI protection. Increased DIO2 expression may dampen the ALI inflammatory response, thereby strengthening the premise that thyroid hormone metabolism is intimately linked to the integrated response to inflammatory injury in critically ill patients.

The novel role of the mu opioid receptor in lung cancer progression: a laboratory investigation.

BACKGROUND: The possibility that µ opioid agonists can influence cancer recurrence is a subject of recent interest. Epidemiologic studies suggested that there were differences in cancer recurrence in breast and prostate cancer contingent on anesthetic regimens. In this study, we identify a possible mechanism for these epidemiologic findings on the basis of µ opioid receptor (MOR) regulation of Lewis lung carcinoma (LLC) tumorigenicity in cell and animal models. METHODS: We used human lung tissue and human non-small cell lung cancer (NSCLC) cell lines and evaluated MOR expression using immunoblot and immunohistochemical analysis. LLC cells were treated with the peripheral opioid antagonist methylnaltrexone (MNTX) or MOR shRNA and evaluated for proliferation, invasion, and soft agar colony formation in vitro and primary tumor growth and lung metastasis in C57BL/6 and MOR knockout mice using VisEn fluorescence mediated tomography imaging and immunohistochemical analysis. RESULTS: We provide several lines of evidence that the MOR may be a potential target for lung cancer, a disease with high mortality and few treatment options. We first observed that there is ∼5- to 10-fold increase in MOR expression in lung samples from patients with NSCLC and in several human NSCLC cell lines. The MOR agonists morphine and [D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin (DAMGO) increased in vitro LLC cell growth. Treatment with MNTX or silencing MOR expression inhibited LLC invasion and anchorage-independent growth by 50%-80%. Injection of MOR silenced LLC lead to a ∼65% reduction in mouse lung metastasis. In addition, MOR knockout mice do not develop significant tumors when injected with LLC in comparison with wild-type controls. Finally, continuous infusion of the peripheral opioid antagonist MNTX attenuates primary LLC tumor growth and reduces lung metastasis. CONCLUSIONS: Taken together, our data suggest a possible direct effect of opiates on lung cancer progression, and provide a plausible explanation for the epidemiologic findings. Our observations further suggest a possible therapeutic role for opioid antagonists.

Single nucleotide polymorphisms in the MYLKP1 pseudogene are associated with increased colon cancer risk in African Americans.

INTRODUCTION: Pseudogenes are paralogues of functional genes historically viewed as defunct due to either the lack of regulatory elements or the presence of frameshift mutations. Recent evidence, however, suggests that pseudogenes may regulate gene expression, although the functional role of pseudogenes remains largely unknown. We previously reported that MYLKP1, the pseudogene of MYLK that encodes myosin light chain kinase (MLCK), is highly expressed in lung and colon cancer cell lines and tissues but not in normal lung or colon. The MYLKP1 promoter is minimally active in normal bronchial epithelial cells but highly active in lung adenocarcinoma cells. In this study, we further validate MYLKP1 as an oncogene via elucidation of the functional role of MYLKP1 genetic variants in colon cancer risk. METHODS: Proliferation and migration assays were performed in MYLKP1-transfected colon and lung cancer cell lines (H441, A549) and commercially-available normal lung and colon cells. Fourteen MYLKP1 SNPs (MAFs >0.01) residing within the 4 kb MYLKP1 promoter region, the core 1.4 kb of MYLKP1 gene, and a 4 kb enhancer region were selected and genotyped in a colorectal cancer cohort. MYLKP1 SNP influences on activity of MYLKP1 promoter (2kb) was assessed by dual luciferase reporter assay. RESULTS: Cancer cell lines, H441 and A549, exhibited increased MYLKP1 expression, increased MYLKP1 luciferase promoter activity, increased proliferation and migration. Genotyping studies identified two MYLKP1 SNPs (rs12490683; rs12497343) that significantly increase risk of colon cancer in African Americans compared to African American controls. Rs12490683 and rs12497343 further increase MYLKP1 promoter activity compared to the wild type MYLKP1 promoter. CONCLUSION: MYLKP1 is a cancer-promoting pseudogene whose genetic variants differentially enhance cancer risk in African American populations.

Recipient death during a live donor liver transplantation: who gets the "orphan" graft?

The limited availability of deceased organ donors, prolongation of waiting time, and increasing number of patients dying awaiting transplantation have contributed to the increased use of adult-to-adult living-donor liver transplant. In the event that the intended recipient dies after the donor graft has been procured but before it has been transplanted, what should be done with the graft? A structured, nine-item oral survey of 26 experts in liver transplantation was conducted in June and July 2003. Respondents were selected primarily because of their extensive experience with liver transplantation, especially adult-to-adult living-donor transplant. All respondents said the surgical team should try to use the available graft for another recipient. Twenty-one respondents believed consent from the donor or the donor's family was required for allocation, whereas 19% believed consent desirable but not required. Nine respondents recommended an allocation organization place the graft, whereas 17 respondents recommended placement within the donor hospital. Two of the respondents had previously encountered this situation, whereas four had experienced an intraoperative recipient death before procurement of a live donor graft. On the basis of the responses, we offer the following recommendations for handling orphan liver grafts: (1) obtain predonation informed consent from all donors that indicates what the donor would want to have done with the "orphan graft" in all cases of living-donor liver transplantation; (2) avoid the premature removal of the donor graft until the recipient hepatectomy and survival are likely; (3) if a live donor graft has been procured and cannot be transplanted into the intended recipient, and if informed consent has been obtained before the donor operation, the organ should be reallocated without delay to minimize cold ischemia time and maximize the utility of the graft.

Methylnaltrexone potentiates the anti-angiogenic effects of mTOR inhibitors.

BACKGROUND: Recent cancer therapies include drugs that target both tumor growth and angiogenesis including mammalian target of rapamycin (mTOR) inhibitors. Since mTOR inhibitor therapy is associated with significant side effects, we examined potential agents that can reduce the therapeutic dose. METHODS: Methylnaltrexone (MNTX), a peripheral mu opioid receptor (MOR) antagonist, in combination with the mTOR inhibitors temsirolimus and/or rapamycin, was evaluated for inhibition of VEGF-induced human pulmonary microvascular endothelial cell (EC) proliferation and migration as well as in vivo angiogenesis (mouse Matrigel plug assay). RESULTS: MNTX inhibited VEGF-induced EC proliferation and migration with an IC50 of approximately 100 nM. Adding 10 nM MNTX to EC shifted the IC50 of temsirolimus inhibition of VEGF-induced proliferation and migration from approximately 10 nM to approximately 1 nM and from approximately 50 to approximately 10 nM respectively. We observed similar effects with rapamycin. On a mechanistic level, we observed that MNTX increased EC plasma membrane-associated tyrosine phosphate activity. Inhibition of tyrosine phosphatase activity (3,4-dephostatin) blocked the synergy between MNTX and temsirolimus and increased VEGF-induced tyrosine phosphorylation of Src with enhanced PI3 kinase and mTOR Complex 2-dependent phosphorylation of Akt and subsequent activation of mTOR Complex 1 (rapamycin and temsirolimus target), while silencing Src, Akt or mTOR complex 2 components blocked VEGF-induced angiogenic events. CONCLUSIONS: Our data indicate that MNTX exerts a synergistic effect with rapamycin and temsirolimus on inhibition of VEGF-induced human EC proliferation and migration and in vivo angiogenesis. Therefore, addition of MNTX could potentially lower the dose of mTOR inhibitors which could improve therapeutic index.