Tissue damage negatively regulates LPS-induced macrophage necroptosis.

Infection is a common clinical complication following tissue damage resulting from surgery and severe trauma. Studies have suggested that cell pre-activation by antecedent trauma/tissue damage profoundly impacts the response of innate immune cells to a secondary infectious stimulus. Cell necroptosis, a form of regulated inflammatory cell death, is one of the mechanisms that control cell release of inflammatory mediators from important innate immune executive cells such as macrophages (Mφ), which critically regulate the progress of inflammation. In this study, we investigated the mechanism and role of trauma/tissue damage in the regulation of LPS-induced Mφ necroptosis using a mouse model simulating long-bone fracture. We demonstrate that LPS acting through Toll-like receptor (TLR) 4 promotes Mφ necroptosis. However, necroptosis is ameliorated by high-mobility group box 1 (HMGB1) release from damaged tissue. We show that HMGB1 acting through cell surface receptor for advanced glycation end products (RAGE) upregulates caveolin-1 expression, which in turn induces caveolae-mediated TLR4 internalization and desensitization to decrease Mφ necroptosis. We further show that RAGE-MyD88 activation of Cdc42 and subsequent activation of transcription factor Sp1 serves as a mechanism underlying caveolin-1 transcriptional upregulation. These results reveal a previous unidentified protective role of damage-associated molecular pattern (DAMP) molecules in restricting inflammation in response to exogenous pathogen-associated molecular pattern molecules.

Macrophage endocytosis of high-mobility group box 1 triggers pyroptosis.

Macrophages can be activated and regulated by high-mobility group box 1 (HMGB1), a highly conserved nuclear protein. Inflammatory functions of HMGB1 are mediated by binding to cell surface receptors, including the receptor for advanced glycation end products (RAGE), Toll-like receptor (TLR)2, TLR4, and TLR9. Pyroptosis is a caspase-1-dependent programmed cell death, which features rapid plasma membrane rupture, DNA fragmentation, and release of proinflammatory intracellular contents. Pyroptosis can be triggered by various stimuli, however, the mechanism underlying pyroptosis remains unclear. In this study, we identify a novel pathway of HMGB1-induced macrophage pyroptosis. We demonstrate that HMGB1, acting through RAGE and dynamin-dependent signaling, initiates HMGB1endocytosis, which in turn induces cell pyroptosis. The endocytosis of HMGB1 triggers a cascade of molecular events, including cathepsin B release from ruptured lysosomes followed by pyroptosome formation and caspase-1 activation. We further confirm that HMGB1-induced macrophage pyroptosis also occurs in vivo during endotoxemia, suggesting a pathophysiological significance for this form of pyroptosis in the development of inflammation. These findings shed light on the regulatory role of ligand-receptor internalization in directing cell fate, which may have an important role in the progress of inflammation following infection and injury.

The HMGB1/RAGE inflammatory pathway promotes pancreatic tumor growth by regulating mitochondrial bioenergetics.

Tumor cells require increased adenosine triphosphate (ATP) to support anabolism and proliferation. The precise mechanisms regulating this process in tumor cells are unknown. Here, we show that the receptor for advanced glycation endproducts (RAGE) and one of its primary ligands, high-mobility group box 1 (HMGB1), are required for optimal mitochondrial function within tumors. We found that RAGE is present in the mitochondria of cultured tumor cells as well as primary tumors. RAGE and HMGB1 coordinately enhanced tumor cell mitochondrial complex I activity, ATP production, tumor cell proliferation and migration. Lack of RAGE or inhibition of HMGB1 release diminished ATP production and slowed tumor growth in vitro and in vivo. These findings link, for the first time, the HMGB1-RAGE pathway with changes in bioenergetics. Moreover, our observations provide a novel mechanism within the tumor microenvironment by which necrosis and inflammation promote tumor progression.

Role of interleukin-6 in hemopoietic and non-hemopoietic synergy mediating TLR4-triggered late murine ileus and endotoxic shock.

BACKGROUND: Early murine endotoxin-induced ileus at 6 h is exclusively mediated by non-hemopoietic TLR4/MyD88 signaling despite molecular activation of hemopoietic cells which included a significant IL-6 mRNA induction. Our objective was to define the role of hemopoietic cells in LPS/TLR4-triggered ileus and inflammation over time, and identify mechanisms of ileus. METHODS: CSF-1(-/-) , TLR4 non-chimera and TLR4 chimera mice were single-shot intraperitoneal injected with ultrapure lipopolysaccharide (UP-LPS) and studied up to 4 days. Subgroups of TLR4(WT) mice were additionally intravenously injected with exogenous recombinant IL-6 (rmIL-6) or murine soluble IL-6 receptor blocking antibody (anti-sIL-6R mAB). KEY RESULTS: Hemopoietic TLR4 signaling independently mediated UP-LPS-induced ileus at 24 h, but chemotactic muscularis neutrophil extravasation was not causatively involved and mice lacking CSF-1-dependent macrophages died prematurely. Synergy of hemopoietic and non-hemopoietic cells determined ileus severity and mortality which correlated with synergistic cell lineage specific transcription of inflammatory mediators like IL-6 within the intestinal muscularis. Circulating IL-6 levels were LPS dose dependent, but exogenous rmIL-6 did not spark off a self-perpetuating inflammatory response triggering ileus. Sustained therapeutic inhibition of functional IL-6 signaling efficiently ameliorated late ileus while preemptive antibody-mediated IL-6R blockade was marginally effective in mitigating ileus. However, IL-6R blockade did not prevent endotoxin-associated mortality nor did it alter circulating IL-6 levels. CONCLUSIONS & INFERENCES: A time-delayed bone marrow-driven mechanism of murine endotoxin-induced ileus exists, and hemopoietic cells synergize with non-hemopoietic cells thereby prolonging ileus and fueling intestinal inflammation. Importantly, IL-6 signaling via IL-6R/gp130 drives late ileus, yet it did not regulate mortality in endotoxic shock.

TLR4/MyD88-induced CD11b+Gr-1 int F4/80+ non-migratory myeloid cells suppress Th2 effector function in the lung.

In humans, environmental exposure to a high dose of lipopolysaccharide (LPS) protects from allergic asthma, the immunological underpinnings of which are not well understood. In mice, exposure to a high LPS dose blunted house dust mite-induced airway eosinophilia and T-helper 2 (Th2) cytokine production. Although adoptively transferred Th2 cells induced allergic airway inflammation in control mice, they were unable to do so in LPS-exposed mice. LPS promoted the development of a CD11b(+)Gr1(int)F4/80(+) lung-resident cell resembling myeloid-derived suppressor cells in a Toll-like receptor 4 and myeloid differentiation factor 88 (MyD88)-dependent manner that suppressed lung dendritic cell (DC)-mediated reactivation of primed Th2 cells. LPS effects switched from suppressive to stimulatory in MyD88(-/-) mice. Suppression of Th2 effector function was reversed by anti-interleukin-10 (IL-10) or inhibition of arginase 1. Lineage(neg) bone marrow progenitor cells could be induced by LPS to develop into CD11b(+)Gr1(int)F4/80(+)cells both in vivo and in vitro that when adoptively transferred suppressed allergen-induced airway inflammation in recipient mice. These data suggest that CD11b(+)Gr1(int)F4/80(+) cells contribute to the protective effects of LPS in allergic asthma by tempering Th2 effector function in the tissue.

Hydrogen inhalation ameliorates oxidative stress in transplantation induced intestinal graft injury.

Ischemia/reperfusion (I/R) injury during small intestinal transplantation (SITx) frequently causes complications including dysmotility, inflammation and organ failure. Recent evidence indicates hydrogen inhalation eliminates toxic hydroxyl radicals. Syngeneic, orthotopic SITx was performed in Lewis rats with 3 h of cold ischemic time. Both donor and recipient received perioperative air or 2% hydrogen inhalation. SITx caused a delay in gastrointestinal transit and decreased jejunal circular muscle contractile activity 24 h after surgery. Hydrogen treatment resulted in significantly improved gastrointestinal transit, as well as jejunal smooth muscle contractility in response to bethanechol. The transplant induced upregulation in the inflammatory mediators CCL2, IL-1 beta, IL-6 and TNF-alpha were mitigated by hydrogen. Hydrogen significantly diminished lipid peroxidation compared to elevated tissue malondialdehyde levels in air-treated grafts demonstrating an antioxidant effect. Histopathological mucosal erosion and increased gut permeability indicated a breakdown in posttransplant mucosal barrier function which was significantly attenuated by hydrogen treatment. In recipient lung, hydrogen treatment also resulted in a significant abatement in inflammatory mRNA induction and reduced neutrophil recruitment. Hydrogen inhalation significantly ameliorates intestinal transplant injury and prevents remote organ inflammation via its antioxidant effects. Administration of perioperative hydrogen gas may be a potent and clinically applicable therapeutic strategy for intestinal I/R injury.

Cyclic AMP and cyclic GMP suppress TNFalpha-induced hepatocyte apoptosis by inhibiting FADD up-regulation via a protein kinase A-dependent pathway.

Cyclic AMP (cAMP) and cyclic GMP (cGMP) suppress apoptosis in many cell types, including hepatocytes. We have previously shown that membrane-permeable cAMP and cGMP analogs attenuate tumor necrosis factor alpha plus actinomycin D (TNFalpha/ActD)-induced apoptosis in hepatocytes at a step upstream of caspase activation and cytochrome c release. Recently we have also shown that FADD levels increase 10 folds in response to TNFalpha/ActD. Therefore we hypothesized that cAMP and cGMP would inhibit FADD upregulation. We show here that cyclic nucleotide analogs dibutyryl cAMP (db-cAMP) and 8-bromo-cGMP (Br-cGMP) inhibit cell death and the cleavages of multiple caspases including caspase-10, -9, -8, -3, and -2, as well as suppress FADD protein up-regulation in TNFalpha/ActD-induced apoptosis. The inhibitory effects of cAMP were seen at lower concentrations than cGMP. Both cAMP and cGMP prevented FADD overexpression and cell death in hepatocytes transfected with the FADD gene. A protein kinase A (PKA) inhibitor, KT 5720, reversed the inhibition of FADD protein levels induced by cAMP or cGMP. In conclusion, our findings indicate that cAMP and cGMP prevent TNFalpha/ActD-induced apoptosis in hepatocytes and that this occurs in association with a near complete inhibition of the upregulation of FADD via a PKA-dependent mechanism.

Cancer gene therapy using a novel secretable trimeric TRAIL.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF family, is a type II transmembrane cytokine molecule. Soluble TRAIL has been shown to induce apoptosis in a wide variety of cancer cells in vitro and to suppress tumor growth specifically without damaging normal cells and tissues in vivo. In our previous report, we have demonstrated that an artificial gene encoding the polypeptide composed of the three functional elements (a secretion signal, a trimerization domain and an apoptosis-inducing moiety of TRAIL gene sequence) expresses and secretes highly apoptotic trimeric TRAIL into the culture supernatant. Here, as an approach to TRAIL-based cancer gene therapy, we developed an adenoviral vector delivering the gene that encodes our secretable trimeric TRAIL (stTRAIL). This adenovirus (Ad-stTRAIL) potently induced apoptosis in vitro in cancer cell lines such as HeLa, MDA-MB-231, A549, HCT116 and U-87MG. In an animal xenograft tumor model bearing a human glioma cell line U-87MG, intratumoral delivery of Ad-stTRAIL dramatically suppressed tumor growth without showing detectable adverse side effects. Histological analysis revealed that Ad-stTRAIL suppresses tumor growth by inducing apoptotic cell death. Contrary to the known rapid clearance of systemically delivered TRAIL protein from the blood circulation, stTRAIL expressed by Ad-stTRAIL in tumor tissues persisted for more than 4 days. In a comparison of tumor suppressor activity between Ad-stTRAIL and Ad-flTRAIL (delivering the full-length TRAIL gene) after mixing infected cells with uninfected cells and implanting these mixed cells in nude mice, Ad-stTRAIL showed higher tumor suppressor activity than that of Ad-flTRAIL. Our data reveal that a gene therapy using Ad-stTRAIL has a promising potential to treat human cancers including gliomas.

Bistability in apoptosis: roles of bax, bcl-2, and mitochondrial permeability transition pores.

We propose a mathematical model for mitochondria-dependent apoptosis, in which kinetic cooperativity in formation of the apoptosome is a key element ensuring bistability. We examine the role of Bax and Bcl-2 synthesis and degradation rates, as well as the number of mitochondrial permeability transition pores (MPTPs), on the cell response to apoptotic stimuli. Our analysis suggests that cooperative apoptosome formation is a mechanism for inducing bistability, much more robust than that induced by other mechanisms, such as inhibition of caspase-3 by the inhibitor of apoptosis (IAP). Simulations predict a pathological state in which cells will exhibit a monostable cell survival if Bax degradation rate is above a threshold value, or if Bax expression rate is below a threshold value. Otherwise, cell death or survival occur depending on initial caspase-3 levels. We show that high expression rates of Bcl-2 can counteract the effects of Bax. Our simulations also demonstrate a monostable (pathological) apoptotic response if the number of MPTPs exceeds a threshold value. This study supports our contention, based on mathematical modeling, that cooperativity in apoptosome formation is critically important for determining the healthy responses to apoptotic stimuli, and helps define the roles of Bax, Bcl-2, and MPTP vis-à-vis apoptosome formation.

Dexamethasone protects primary cultured hepatocytes from death receptor-mediated apoptosis by upregulation of cFLIP.

Dexamethasone (DEX) pretreatment protected hepatocytes from TNF-alpha plus actinomycin D (ActD)-induced apoptosis by suppressing caspase-8 activation and the mitochondria-dependent apoptosis pathway. DEX treatment upregulated cellular FLICE inhibitory protein (cFLIP) expression, but did not alter the protein levels of Bcl-2, Bcl-xL, Mcl-1, and cIAP as well as Akt activation. The increased cFLIP mRNA level by DEX was inhibited by ActD, indicating that DEX upregulates cFLIP expression at the transcriptional step. DEX also inhibited Jo2-mediated hepatocyte apoptosis by blocking the formation of the death-inducing signaling complex and caspase-8 activation. Specific downregulation of cFLIP expression using siRNA reversed the antiapoptotic effect of DEX by increasing caspase-8 activation. Moreover, DEX administration into mice increased cFLIP expression in the liver and prevented Jo2-induced hepatic injury by inhibiting caspase-8 and -3 activities. Our results indicate that DEX exerts a protective role in death receptor-induced in vitro and in vivo hepatocyte apoptosis by upregulating cFLIP expression.

Hypoxia renders hepatocytes susceptible to cell death by nitric oxide.

Under normoxic conditions, nitric oxide (NO) suppresses hepatocyte apoptosis. In contrast, NO contributes to hepatocellular injury in conditions associated with ischemia and reperfusion. To understand this paradoxical effect further, we compared the effects of various doses of NO, delivered from the chemical NO donor S-nitroso-N-acetylpenicillamine (SNAP), under both normoxic and hypoxic tissue culture conditions. We found that the cell death induced by NO under hypoxic conditions, which increased the production of reactive oxygen species, was accompanied by a necrotic morphology with a concomitant early decrease in ATP levels. The NO-induced death of hypoxic hepatocytes was reversed by co-incubation with the anti-oxidant N-acetylcysteine. We conclude that hypoxia-induced oxidative stress subsequent to ATP depletion can switch NO from an anti-apoptotic to a hepatotoxic agent. These findings may have implications for NO-induced liver damage in settings of tissue hypoxia.

Reduced hepatic transcription factor activation and expression of IL-6 and ICAM-1 after hemorrhage by NO scavenging.

BACKGROUND: Hemorrhagic shock (HS) elicits an inflammatory response characterized by increased cytokine production and recruitment of polymorphonucleated neutrophilic granulocytes (PMN) that we reported to be inducible nitric oxide synthase (iNOS) dependent. In a previous study, we demonstrated that removing excess induced nitric oxide (NO) by administration of the NO scavenger NOX resulted in reduced PMN infiltration, attenuated liver injury, and improved survival. In this study, we examined the role of NOX treatment in down-modulating the inflammatory response in the liver following HS. METHODS: Rats ( n=5) were subjected to severe HS with mean arterial blood pressure (MAP) of 40 mmHg for 100 min followed by resuscitation and killing at 24 h. RESULTS: Shock animals demonstrated increased mRNA levels of interleukin (IL)-6 and intercellular adhesion molecule (ICAM)-1 and increased activation of the transcription factors nuclear factor kappa B (NF-kappa B) and signal transducers and activators of transcription 3 (Stat3). Treatment with NOX (30 mg/kg/h) infused 60 min following the onset of shock over 4 h resulted in significant reduction in cytokine mRNA expression and transcriptional factor activation. These results suggest that excessive NO contributes to hemorrhage-induced tissue inflammation and that reducing the bioavailability of NO using NOX may be beneficial in HS. CONCLUSION: These data indicate that NOX prevents liver injury in this HS model, possibly through down-modulation of proinflammatory signaling and the shock-induced inflammatory response.

Antioxidant enzymes suppress nitric oxide production through the inhibition of NF-kappa B activation: role of H(2)O(2) and nitric oxide in inducible nitric oxide synthase expression in macrophages.

Reactive molecules O(-)(2), H(2)O(2), and nitrogen monoxide (NO) are produced from macrophages following exposure to lipopolysaccharide (LPS) and involved in cellular signaling for gene expression. Experiments were carried out to determine whether these molecules regulate inducible nitric oxide synthase (iNOS) gene expression in RAW264.7 macrophages exposed to LPS. NO production was inhibited by the antioxidative enzymes catalase, horseradish peroxidase, and myeloperoxidase but not by superoxide dismutase (SOD). In contrast, the NO-producing activity of LPS-stimulated RAW264.7 cells was enhanced by the NO scavengers hemoglobin (Hb) and myoglobin. The antioxidant enzymes decreased levels of iNOS mRNA and protein in LPS-stimulated RAW264.7 cells, whereas the NOS inhibitor N(G)-monomethyl-L-arginine as well as Hb increased the level of iNOS protein but not mRNA, indicating that NO inhibits iNOS protein expression. NF-kappa B was activated in LPS-stimulated RAW264.7 cells and the activation was significantly inhibited by antioxidant enzymes, but not by Hb. Similar results were obtained using LPS-stimulated rodent peritoneal macrophages. Extracellular O(-)(2) generation by LPS-stimulated macrophages was suppressed by SOD, but not by antioxidative enzymes, while accumulation of intracellular reactive oxygen species was inhibited by antioxidative enzymes, but not by SOD. Exogenous H(2)O(2) induced NF-kappa B activation in macrophages, which was inhibited by catalase and pyrroline dithiocarbamate (PDTC). H(2)O(2) enhanced iNOS expression and NO production in peritoneal macrophages when added with interferon-gamma, and the effect of H(2)O(2) was inhibited by catalase and PDTC. These findings suggest that H(2)O(2) production from LPS-stimulated macrophages participates in the upregulation of iNOS expression via NF-kappa B activation and that NO is a negative feedback inhibitor of iNOS protein expression.

Nitric oxide suppresses the expression of Bcl-2 binding protein BNIP3 in hepatocytes.

Nitric oxide (NO) is not only an important signaling molecule, but it also regulates the expression of a number of genes in the liver. We have previously shown that apoptosis in hepatocytes exposed to tumor necrosis factor-alpha and actinomycin D is prevented by NO derived from the inducible nitric-oxide synthase (iNOS), by mechanisms that are both dependent on and independent of modulation of cyclic guanosine monophosphate (cGMP) subsequent to activation of soluble guanylyl cyclase (sGC). We hypothesize that one mechanism by which NO exerts these effects is by regulating the expression of genes involved in apoptosis. We used differential display-polymerase chain reaction to isolate NO-regulated genes in hepatocytes from iNOS knockout mice (to eliminate endogenous inducible NO production). Using this analysis, we identified a NO-suppressed gene fragment homologous with the pro-apoptotic Bcl-2 binding protein BNIP3. Northern analysis confirmed the NO-dependent suppression of BNIP3 in cultured cells. Similarly, the NO donor S-nitroso-N-acetyl-dl-penicillamine (1-1000 microm) down-regulated the expression of BNIP3 in both iNOS knockout and wild-type hepatocytes. This effect of NO was reversed by the sGC inhibitor 1H-(1,2,4)-oxadiazole[4,3-a]quinoxalon-1-one (ODQ),suggesting the involvement of the sGC/cGMP pathway in the modulation of BNIP3 by NO. We propose that suppression of BNIP3 expression is one sGC/cGMP-dependent mechanism by which NO might affect the process of hepatocyte apoptosis.

The regulatory role of nitric oxide in apoptosis.

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.

Catecholamines decrease nitric oxide production by cytokine-stimulated hepatocytes.

BACKGROUND: Catecholamines are significantly elevated in inflammatory responses and play a regulatory role in sepsis. Nitric oxide (NO), also a key inflammatory mediator in sepsis, is produced in large amounts by the inducible nitric oxide synthase (iNOS) in the liver. The purpose of this study was to test the hypothesis that catecholamines play a role in the regulation of NO production by hepatocytes. METHODS: Primary hepatocytes were isolated from healthy male Sprague-Dawley rats and either cultured with normal medium or stimulated with cytomix (interleukin-1 beta, interferon-gamma, and tumor necrosis factor-alpha) in the presence or absence of epinephrine or norepinephrine at varying concentrations. Total RNA was isolated 6 hours after treatment and analyzed by Northern blotting for iNOS mRNA. Protein extracts were obtained at 12 hours and were analyzed by Western immunoblotting for iNOS. Cell culture supernatants were analyzed for NO, determined as the stable end-product NO(2)(-), at 24 hours. RESULTS: Epinephrine and norepinephrine significantly decreased NO(2)(-) levels in stimulated hepatocytes but had no effect on iNOS mRNA or protein levels. The decrease in NO(2)(-) was reproduced by the adenylate cyclase stimulator, forskolin. The catecholamine-induced decrease in NO(2)(-) was completely reversed by the protein kinase A inhibitor Rp-8-Br-cyclic adenosine monophosphate. CONCLUSIONS: Catecholamines decrease hepatocyte production of NO in response to cytokine stimulation. This effect seems to be due to post-translational events and appears to be mediated in part by cyclic adenosine monophosphate.

Adenovirus-mediated gene transfer of human inducible nitric oxide synthase in porcine vein grafts inhibits intimal hyperplasia.

OBJECTIVE: The aim of this study is to determine whether adenoviral inducible nitric oxide synthase (iNOS) gene transfer could inhibit intimal hyperplasia (IH) in porcine internal jugular veins interposed into the carotid artery circulation. METHODS: Porcine internal jugular veins were transduced passively with 1 x 10(11) particles of an adenoviral vector carrying either the human iNOS (AdiNOS) or beta-galactosidase (AdlacZ) cDNA for 30 minutes and then interposed into the carotid artery circulation. Segments of each vein graft were maintained in an ex vivo organ culture to measure nitrite accumulation, a marker of nitric oxide synthesis. The grafts were analyzed immunohistochemically for the presence of neutrophils, macrophages, and leukocytes by staining for myeloperoxidase, ED1, and CD45, respectively, at 3 (n = 4) and 7 (n = 4) days. Morphometric analyses and cellular proliferation (Ki67 staining) were assessed at 3 (n = 4), 7 (n = 4), and 21 days (n = 8). RESULTS: AdlacZ-treated vein grafts demonstrated high levels of beta-galactosidase expression at 3 days with a gradual decline thereafter. Nitrite production from AdiNOS-treated vein grafts was approximately fivefold greater than AdlacZ-treated grafts (P =.00001). AdiNOS or AdlacZ treatment was associated with minimal graft inflammation. Cellular proliferation rates were significantly reduced in AdiNOS-treated grafts as compared with controls at both 3 (41%, P =.000004) and 7 days (32%, P =.0001) after bypass. This early antiproliferative effect was most pronounced at the distal anastomosis (65%, P =.0005). The iNOS gene transfer reduced the intimal/medial area ratio in vein grafts at 7 (36%, P =.009) and 21 days (30%, P =.007) versus controls. This inhibition of IH was again more prominent in the distal segments of the grafts (P =.01). CONCLUSION: Adenovirus-mediated iNOS gene transfer to porcine internal jugular vein grafts effectively reduced cellular proliferation and IH. Although iNOS gene transfer reduced IH throughout the entire vein graft, the most pronounced effect was measured at the distal anastomosis. These results suggest potential for iNOS-based genetic modification of vein grafts to prolong graft patency.