Inhaled carbon monoxide inhibits intimal hyperplasia and provides added benefit with nitric oxide

Pharmacological prevention of intimal hyperplasia: A state-of-the-art review

Intimal hyperplasia (IH) occurs in a considerable number of cases of blood vessel reconstruction by stenting or balloon angioplasty, venous bypass grafting, and arteriovenous dialysis accesses. It is triggered by endothelial injury during the vascular intervention and leads to vessel restenosis with life-threatening consequences for patients. To date, the drugs used for IH prevention in clinics-paclitaxel and rapalog drugs-have been focusing primarily on the vascular smooth muscle cell (VSMC) proliferation pathway of IH development. Limitations, such as endothelial toxicity and inappropriate drug administration timing, have spurred the search for new and efficient pharmacological approaches to control IH. In this state-of-the-art review, we present the pathways of IH development, focusing on the key events and actors involved in IH. Subsequently, we discuss different drugs and drug combinations interfering with these pathways based on their effect on peripheral circulation IH models in animal studies, or on clinical reports. The reports were obtained through an extensive search of peer-reviewed publications in Pubmed, Embase, and Google Scholar, with search equations composed based on five concepts around IH and their various combinations. To improve vascular intervention outcomes, rethinking of conventional therapeutic approaches to IH prevention is needed. Exploring local application of drugs and drug combinations acting on different pathophysiological pathways of IH development has the potential to provide effective and safe restenosis prevention.

Carbon Monoxide Suppresses Neointima Formation in Transplant Arteriosclerosis by Inhibiting Vascular Progenitor Cell Differentiation

[Figure: see text].

Emerging Delivery Strategies of Carbon Monoxide for Therapeutic Applications: from CO Gas to CO Releasing Nanomaterials

Carbon monoxide (CO) therapy has emerged as a hot topic under exploration in the field of gas therapy as it shows the promise of treating various diseases. Due to the gaseous property and the high affinity for human hemoglobin, the main challenges of administrating medicinal CO are the lack of target selectivity as well as the toxic profile at relatively high concentrations. Although abundant CO releasing molecules (CORMs) with the capacity to deliver CO in biological systems have been developed, several disadvantages related to CORMs, including random diffusion, poor solubility, potential toxicity, and lack of on-demand CO release in deep tissue, still confine their practical use. Recently, the advent of versatile nanomedicine has provided a promising chance for improving the properties of naked CORMs and simultaneously realizing the therapeutic applications of CO. This review presents a brief summarization of the emerging delivery strategies of CO based on nanomaterials for therapeutic application. First, an introduction covering the therapeutic roles of CO and several frequently used CORMs is provided. Then, recent advancements in the synthesis and application of versatile CO releasing nanomaterials are elaborated. Finally, the current challenges and future directions of these important delivery strategies are proposed.

Systemic vasoprotection by inhaled carbon monoxide is mediated through prolonged alterations in monocyte/macrophage function

Carbon monoxide (CO) is anti-inflammatory and protective in models of disease. Its actions in vitro are short-lived but are sustained in vivo. We hypothesize that systemic CO can mediate prolonged phenotype changes in vivo, with a focus on macrophages (Mφs). Mφs isolated from CO treated rats responded to lipopolysaccharide (LPS) with increased IL6, IL10 and iNOS expression but decreased TNF. Conditioned media (CM) collected from peritoneal Mφs isolated from CO treated rats stimulated endothelial cell (EC) proliferation versus CM from Mφs from air treated rats. This effect was mediated by Mφ released VEGF and HMGB1. Inhaled CO reduced LPS induced Mφ M1 inflammatory phenotype for up to 5 days. Mitochondrial oxygen consumption in LPS treated Mφs from CO treated mice was preserved compared to LPS treated Mφs from control mice. Finally, transient reduction of inflammatory cells at the time of inhaled CO treatment eliminated the vasoprotective effect of CO in a rodent carotid injury model. Thus, inhaled CO induces a prolonged mixed phenotype change in Mφs, and potentially other inflammatory cells, that contribute to vasoprotection. These findings demonstrate the ability of inhaled CO to modify Mφs in a sustained manner to mediate its therapeutic actions, supporting the translational potential of inhaled CO.

Carbon Monoxide Inhibits Islet Apoptosis via Induction of Autophagy

AIM

Carbon monoxide (CO) functions as a therapeutic molecule in various disease models because of its anti-inflammatory and antiapoptotic properties. We investigated the capacity of CO to reduce hypoxia-induced islet cell death and dysfunction in human and mouse models.

RESULTS

Culturing islets in CO-saturated medium protected them from hypoxia-induced apoptosis and preserved β cell function by suppressing expression of proapoptotic (Bim, PARP, Cas-3), proinflammatory (TNF-α), and endoplasmic reticulum (ER) stress (glucose-regulated protein 94, grp94, CHOP) proteins. The prosurvival effects of CO on islets were attenuated when autophagy was blocked by specific inhibitors or when either ATG7 or ATG16L1, two essential factors for autophagy, was downregulated by siRNA. In vivo, CO exposure reduced both inflammation and cell death in grafts immediately after transplantation, and enhanced long-term graft survival of CO-treated human and mouse islet grafts in streptozotocin-induced diabetic non-obese diabetic severe combined immunodeficiency (NOD-SCID) or C57BL/6 recipients.

INNOVATION

These findings underline that pretreatment with CO protects islets from hypoxia and stress-induced cell death via upregulation of ATG16L1-mediated autophagy.

CONCLUSION

Our results suggested that CO exposure may provide an effective means to enhance survival of grafts in clinical islet cell transplantation, and may be beneficial in other diseases in which inflammation and cell death pose impediments to achieving optimal therapeutic effects. Antioxid. Redox Signal. 28, 1309-1322.

Carbon Monoxide and Its Controlled Release: Therapeutic Application, Detection, and Development of Carbon Monoxide Releasing Molecules (CORMs)

Carbon monoxide (CO) is attracting increasing attention because of its role as a gasotransmitter with cytoprotective and homeostatic properties. Carbon monoxide releasing molecules (CORMs) are spatially and temporally controlled CO releasers that exhibit superior and more effective pharmaceutical traits than gaseous CO because of their chemistry and structure. Experimental and preclinical research in animal models has shown the therapeutic potential of inhaled CO and CORMs, and the biological effects of CO and CORMs have also been observed in preclinical trials via the genetic modulation of heme oxygenase-1 (HO-1). In this review, we describe the pharmaceutical use of CO and CORMs, methods of detecting CO release, and developments in CORM design and synthesis. Many valuable clinical CORMs formulated using macromolecules and nanomaterials are also described.

Organic CO Prodrugs: Structure-CO-Release Rate Relationship Studies

Carbon monoxide (CO) is an endogenously produced gasotransmitter in mammals, and may have signaling roles in bacteria as well. It has many recognized therapeutic effects. A significant challenge in this field is the development of pharmaceutically acceptable forms of CO delivery with controllable and tunable release rates. Herein, the structure-release rate studies of the first class of organic CO prodrugs that release CO in aqueous solution at neutral pH is described.

Click and Release: A Chemical Strategy toward Developing Gasotransmitter Prodrugs by Using an Intramolecular Diels-Alder Reaction

Prodrug strategies have been proven to be a very effective way of addressing delivery problems. Much of the chemistry in prodrug development relies on the ability to mask an appropriate functional group, which can be removed under appropriate conditions. However, developing organic prodrugs of gasotransmitters represent unique challenges. This is especially true with carbon monoxide, which does not have an easy "handle" for bioreversible derivatization. By taking advantage of an intramolecular Diels-Alder reaction, we have developed a prodrug strategy for preparations of organic CO prodrugs that are stable during synthesis and storage, and yet readily release CO with tunable release rates under near physiological conditions. The effectiveness of the CO prodrug system in delivering a sufficient quantity of CO for possible therapeutic applications has been studied using a cell culture anti-inflammatory assay and a colitis animal model. These studies fully demonstrate the proof of concept, and lay a strong foundation for further medicinal chemistry work in developing organic CO prodrugs.

My Continuing Evolution as a Surgeon-Scientist: A Decade after the Jacobson Promising Investigator Award

THE SECOND JOAN L AND JULIUS H JACOBSON PROMISING INVESTIGATOR AWARDEE, EDITH TZENG MD, FACS: In 2005, the Surgical Research Committee of the American College of Surgeons was tasked with selecting the recipient of a newly established award, "The Joan L and Julius H Jacobson Promising Investigator Award." According to the Jacobsons, the award funded by Dr Jacobson should be given at least once every 2 years to a surgeon investigator at "the tipping point," who can demonstrate that his or her research shows the promise of leading to a significant contribution to the practice of surgery and patient safety. Every year, the Surgical Research Committee receives many excellent nominations and has the difficult task of selecting one awardee. The first awardee was Michael Longaker MD, FACS, who 10 years later reflected on the award and the impact it had on his career.¹ This year, Edith Tzeng, MD, FACS, the second Jacobson awardee, reflects on her 10-year journey after receiving the award. Dr Tzeng is now a national and international figure in the field of vascular surgery and has studied the effect of nitric oxide and carbon monoxide on intimal hyperplasia. Kamal MF Itani, MD, FACS and Leigh Neumayer, MD, FACS, on behalf of the Surgical Research Committee of the American College of Surgeons.

Toward Carbon Monoxide-Based Therapeutics: Critical Drug Delivery and Developability Issues

Carbon monoxide (CO) is an intrinsic signaling molecule with importance on par with that of nitric oxide. During the past decade, pharmacologic studies have amply demonstrated the therapeutic potential of carbon monoxide. However, such studies were mostly based on CO inhalation and metal-based CO-releasing molecules. The field is now at the stage that a major effort is needed to develop pharmaceutically acceptable forms of CO for delivery via various routes such as oral, injection, infusion, or topical applications. This review examines the state of the art, discusses the existing hurdles to overcome, and proposes developmental strategies necessary to address remaining drug delivery issues.

Delayed inhaled carbon monoxide mediates the regression of established neointimal lesions

OBJECTIVE

Intimal hyperplasia (IH) contributes to the failure of vascular interventions. While many investigational therapies inhibit the development of IH in animal models, few of these potential therapies can reverse established lesions. Inhaled carbon monoxide (CO) dramatically inhibits IH in both rats and pigs when given perioperatively. It also prevented the development of pulmonary arterial hypertension in rodents. Interestingly, CO could reverse pulmonary artery structural changes and right heart hemodynamic changes when administered after the establishment of pulmonary hypertension. Thus, we hypothesize that inhaled CO may mediate the regression of established neointimal lesions.

METHODS

Rats underwent carotid artery balloon angioplasty injury. Carotid arteries were collected at 2 and 4 weeks after injury for morphometric analysis of the neointima. Another group was treated with inhaled CO (250 parts per million) for 1 hour daily from week 2 until week 4. Additional rats were sacrificed 3 days after initiating CO treatment, and the carotid arteries were examined for apoptosis by terminal deoxynucleotidyl transferase dUTP nick end-labeling, proliferation by Ki67 staining, and autophagy by microtubule-associated protein light chain 3 I/II staining.

RESULTS

At 2 weeks following injury, sizable neointimal lesions had developed (intimal/media = 0.92 ± 0.22). By 4 weeks, lesion size remained stable (0.80 ± 0.09). Delayed inhaled CO treatment greatly reduced neointimal lesion size vs the 2- and 4-week control mice (0.38 ± 0.05; P < .05). Arteries from the CO-treated rats exhibited significantly reduced apoptosis compared with control vessels (3.18% ± 1.94% vs 16.26% ± 5.91%; P = .036). Proliferation was also dramatically reduced in the CO-treated animals (2.98 ± 1.55 vs 10.37 ± 2.80; P = .036). No difference in autophagy between control and CO-treated rats was detected.

CONCLUSIONS

Delayed administration of inhaled CO reduced established neointimal lesion size. This effect was mediated by the antiproliferative effect of CO on medial and intimal smooth muscle cells without increases in arterial wall apoptosis or autophagy. Future studies will examine additional time points to determine if there is temporal variation in the rates of apoptosis and autophagy.

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.

Carbon monoxide: an unusual drug

The highly toxic gas carbon monoxide (CO) displays many physiological roles in several organs and tissues. Although many diseases, including cancer, hematological diseases, hypertension, heart failure, inflammation, sepsis, neurodegeneration, and sleep disorders, have been linked to abnormal endogenous CO metabolism and functions, CO administration has therapeutic potential in inflammation, sepsis, lung injury, cardiovascular diseases, transplantation, and cancer. Here, insights into the CO-based therapy, characterized by the induction or gene transfer of heme oxygenase-1 and either gas or CO-releasing molecule administration, are reviewed.

Effects of exogenous carbon monoxide on p38 MAPKs expression in rats with intestinal ischemia reperfusion injury

AIM: To investigate the possible mechanism underlying the preventive effect of exogenous carbon monoxide (CO) on multiple organ injury induced by intestinal ischemia-reperfusion (IIR) in rats.

METHODS: Sixty-four male Wistar rats were randomly and equally allocated into eight groups. IIR was induced in rats by clamping the superior mesenteric artery (SMA) for 60 min and reperfusing for 120 min. Group A and sham operation did not undergo SMA clamping. Group B underwent SMA clamping for 60 min and reperfusing for 120 min. Groups C1/C2, D1/D2, and E1/E2 inhaled 100 and 250 µL/L CO 10, 60 min before SMA clamping and 60 min after reperfusion, respectively. The expression of p38 mitogen-activated protein kinases (MAPKs) in different tissues was detected by Western blot.

RESULTS: Compared to Group A, the expression of p38 MAPKs in the intestine, lung and liver increased in Group B, but the differences were not significant (0.468 ± 0.213 vs 0.474 ± 0.151; 0.439 ± 0.111 vs 0.482 ± 0.103; 0.622 ± 0.112 vs 0.654 ± 0.016, all P > 0.05). Compared to Group B, a marked increase in p38 MAPKs expression in the intestine, lung and liver was detected in Groups C1/C2, D1/D2, and E1/E2 (1.540 ± 0.346, 1.626 ± 0.277, 1.36 5± 0.233, 1.483 ± 0.265, 1.353 ± 0.234, 1.372 ± 0.2731 vs 0.474 ± 0.151; 1.654 ± 0.211, 1.701 ± 0.101, 1.398 ± 0.245, 1.444 ± 0.272, 1.288 ± 0.218, 1.366 ± 0.244 vs 0.482 ± 0.103; 1.695 ± 0.234, 1.723 ± 0.213, 1.423 ± 0.221, 1.586 ± 0.254, 1.322 ± 0.261, 1.411 ± 0.296 vs 0.654 ± 0.016, all P < 0.05).

CONCLUSION: Exogenous CO provides protection against IIR-induced multiple organ injury possibly by modulating the expression of p38 MAPKs in rats.

Ex vivo carbon monoxide delivery inhibits intimal hyperplasia in arterialized vein grafts

AIMS

Veins are still the best conduits available for arterial bypass surgery. When these arterialized vein grafts fail, it is often due to the development of intimal hyperplasia (IH). We investigated the feasibility and efficacy of the ex vivo pre-treatment of vein grafts with soluble carbon monoxide (CO) in the inhibition of IH.

METHODS AND RESULTS

The inferior vena cava was excised from donor rats and placed as an interposition graft into the abdominal aorta of syngeneic rats. Prior to implantation, vein grafts were stored in cold Lactated Ringer (LR) solution with or without CO saturation (bubbling of 100% CO) for 2 h. Three and 6 weeks following grafting, vein grafts treated with cold LR for 2 h developed IH, whereas grafts implanted immediately after harvest demonstrated significantly less IH. Treatment in CO-saturated LR significantly inhibited IH and reduced vascular endothelial cell (VEC) apoptosis. Electron microscopy revealed improved VEC integrity with less platelet/white blood cell aggregation in CO-treated grafts. The effects of CO in preventing IH were associated with activation of hypoxia inducible factor-1α (HIF-1α) and an increase in vascular endothelial growth factor (VEGF) expression at 3-6 h after grafting. Treatment with a HIF-1α inhibitor completely abrogated the induction of VEGF by CO and reversed the protective effects of CO on prevention of IH.

CONCLUSION

Ex vivo treatment of vein grafts in CO-saturated LR preserved VEC integrity perioperatively and significantly reduced neointima formation. These effects appear to be mediated through the activation of the HIF1α/VEGF pathway.

Putative role of carbon monoxide signaling pathway in penile erectile function

INTRODUCTION

Erectile response depends on nitric oxide (NO) generated by NO synthase (NOS) enzyme of the nerves and vascular endothelium in the cavernous tissue. NO activates soluble guanylate cyclase (sGC), leading to the production of cyclic guanosine monophosphate (cGMP). cGMP activates cGMP-dependent protein kinase that activates Ca(2+)/ATPase pump that activates Ca(2+)/K efflux pump extruding Ca(2+) across the plasma membrane with consequent smooth muscle cell relaxation. A role similar to that of NOS/NO signaling has been postulated for carbon monoxide (CO) produced in mammals from heme catabolism by heme oxygenase (HO) enzyme.

AIM

To assess CO signaling pathway for erectile function by reviewing published studies.

METHODS

A systematic review of published studies on this affair based on Pubmed and Medical Subject Heading databases, with search for all concerned articles.

MAIN OUTCOME MEASURES

Documentation of positive as well as negative criteria of CO/HO signaling focused on penile tissue.

RESULTS

The concept that HO-derived CO could play a role in mediating erectile function acting in synergism with, or as a potentiator for, NOS/NO signaling pathway is gaining momentum. CO/HO signaling pathway has been shown to partially mediate the actions of oral phosphodiesterase type 5 inhibitors. In addition, it was shown that the use of CO releasing molecules potentiated cavernous cGMP levels. However, increased CO production or release was reported to be associated, in some studies, with vasoconstriction.

CONCLUSION

This review sheds a light on the significance of cavernous tissue CO signaling pathway that may pave the way for creation of therapeutic modalities based on this pathway.

Carbon Monoxide: Vascular Therapeutic for the Future

In the past decade, carbon monoxide has lost its reputation as a toxic gas and has gained a following of scientists who now appreciate its potential therapeutic utility as an anti-inflammatory and cytoprotective agent. Its vasoprotective properties have also gained a tremendous amount of attention, especially its ability to inhibit intimal hyperplasia. This review will provide a historical perspective of carbon monoxide biology and summarize its function in disease modulation with a special focus on its potential role as a vascular therapeutic.

Effects of antiatherosclerosis in carotid artery by RNAi-mediated silencing of MCP-1 expression

BACKGROUND

Our objective was to identify the effects of MCP-1 siRNA in vivo transfection in an atherosclerosis model on local expression of MCP-1 and pathogenesis of atherosclerosis.

METHODS

Carotid atherosclerosis was induced in 28 New Zealand white rabbits. Rabbits were divided into three groups randomly: RNAi group, model group, and blank plasmid group. siRNA-expressing vector was transfected to blood vessels by liposomes. The carotid arteries were processed for morphological evaluation. Local expression of MCP-1 was detected by immunohistochemistry, RT-PCR, and Western blot.

RESULTS

On hematoxylin and eosin-stained sections, partial endothelial cells detached while intimae were less thickened in the RNAi group compared to the model and blank plasmid groups; the I:M ratio was significantly reduced to 1.46 in the RNAi group compared to the model and blank plasmid groups (5.55 and 5.27, respectively). The results of immunohistochemistry showed that MCP-1 expression was less colorized and less positive in the RNAi group. RT-PCR and Western blot showed reduced expression in the RNAi group than in the model and blank plasmid groups. There were highly positive correlations between semiquantitative RT-PCR and the I:M ratio (r = 0.968).

CONCLUSION

Expression of MCP-1 was successfully inhibited by transfecting MCP-1 siRNA expression plasmid to the carotid artery, and the progression of atherosclerosis was restricted by RNAi-mediated silencing of MCP-1 expression.

Novel therapies for cyclic GMP control of vascular smooth muscle growth

Cyclic GMP, guanosine 3',5'-cyclic monophosphate, is a critical and multifunctional second-messenger molecule that mediates diverse physiological and pathophysiological functions in cardiac and vascular tissues. Synthesized through nitric oxide, carbon monoxide, and/or natriuretic peptide-mediated guanylate cyclase stimulation and guanosine triphosphate dephosphorylation, cyclic GMP is capable of stimulating a cascade of serine/threonine kinase events, including signaling through cyclic GMP- and/or cyclic AMP-dependent protein kinases, eliciting protein kinase-independent actions such as modulation of ion channels or transporters, or undergoing hydrolytic degradation through actions of cyclic GMP-regulated phosphodiesterases. Substrates, enzymes, cofactors, and associated variables in this multifaceted system have historically been targets of vital pharmacotherapies with perhaps most common the use of vascular smooth muscle-targeting organonitrates in cardiac patients and phosphodiesterase inhibitors in individuals with erectile dysfunction. Accumulating basic science and clinical evidence, however, suggests that cyclic GMP signaling is compromised under conditions of disease or elevated physiological stresses. Moreover, nitric oxide can stimulate an array of cytotoxic effects and nitric oxide-based therapies can be limited by diminished bioactivity and the development of tachyphylaxis or tolerance after prolonged use. Consequently, an emerging area for clinical drug development and therapeutic drug evaluation for conditions of cardiovascular adversity has focused on identification of cyclic GMP signaling pathways that act under oxidized or nitric oxide-unresponsive conditions and/or that operate irrespective of nitric oxide-induced complications. The aim of this therapeutic review is to describe novel, nitric oxide-alternate avenues for cyclic GMP signaling in vascular smooth muscle growth with particular emphasis on pharmacotherapeutics of recently characterized cyclic GMP-specific approaches.

Effects of exogenous carbon monoxide on polymorphonuclear neutrophil, TNF-α and IL-10 expression in rats with intestinal ischemia-reperfusion injury

AIM: To investigate the effects of carbon monoxide (CO) on multiple organ injury induced by intestinal ischemia-reperfusion (IIR) in rats.

METHODS: Sixty-four male Wistar rats were randomly allocated to eight groups with eight in each group. Different groups were handlinged. The numbers of PMN in different tissues were observed at light microscopy, and the plasma TNF-α, IL-10 concentrations were determined using radio-immunifaction method.

RESULTS: Marked differences in PMN of intestine, lung and liver were detected among groups, but not in kidney (66 ± 6 vs 60 ± 4, 55 ± 3, 49 ± 4, 42 ± 4, 37 ± 3, 30 ± 2, 26 ± 2; 52 ± 5 vs 43 ± 5, 42 ± 4, 34 ± 2, 32 ± 2, 25 ± 2, 23 ± 2, 18 ± 2; 35 ± 3 vs 30 ± 3, 26 ± 1, 23 ± 2, 20 ± 1, 19 ± 1, 16 ± 1, all P < 0.05). Significant differences in TNF-α, IL-10 were detected among all group (3.15 ± 0.05 vs 2.37 ± 0.14, 2.07 ± 0.07, 1.89 ± 0.07, 1.69 ± 0.09, 1.53 ± 0.06, 1.31 ± 0.06, 1.15 ± 0.04; 138.9 ± 11.37, 118.75 ± 7.69, 100.55 ± 4.86, 83.12 ± 5.13, 61.41 ± 6.88, 40.56 ± 2.85 vs 23.55 ± 4.94, 23.55 ± 4.9415 vs36 ± 2.37, all P < 0.05).

CONCLUSION: Exogenous CO provides protection against multiple organ injury induced by IIR, partly through inhibiting PMN aggregation in tissues, inhibiting the elevation of TNF-α and promoting the release of IL-10.

Gene therapy via inducible nitric oxide synthase: a tool for the treatment of a diverse range of pathological conditions

Nitric oxide (NO(.)) is a reactive nitrogen radical produced by the NO synthase (NOS) enzymes; it affects a plethora of downstream physiological and pathological processes. The past two decades have seen an explosion in the understanding of the role of NO(.) biology, highlighting various protective and damaging modes of action. Much of the controversy surrounding the role of NO(.) relates to the differing concentrations generated by the three isoforms of NOS. Both calcium-dependent isoforms of the enzyme (endothelial and neuronal NOS) generate low-nanomolar/picomolar concentrations of NO(.). By contrast, the calcium-independent isoform (inducible NOS (iNOS)) generates high concentrations of NO(.), 2-3 orders of magnitude greater. This review summarizes the current literature in relation to iNOS gene therapy for the therapeutic benefit of various pathological conditions, including various states of vascular disease, wound healing, erectile dysfunction, renal dysfunction and oncology. The available data provide convincing evidence that manipulation of endogenous NO(.) using iNOS gene therapy can provide the basis for future clinical trials.