Transfer and expression of recombinant nitric oxide synthase genes in the cardiovascular system

Nitric oxide synthase gene therapy: progress and prospects

NOS gene therapy has been the focus of extensive research as dysfunction of this enzyme has been implicated in several cardiovascular diseases. Research has concentrated on comparing the effect of gene delivery of NOS isoforms (eNOS, iNOS and nNOS) in healthy and diseased animal models on intimal hyperplasia, restenosis, vascular tone and ischemia-reperfusion injury. Most results demonstrate therapeutic benefits following vascular gene delivery of all NOS in pre-clinical models of cardiovascular disease. eNOS has been shown to have particular promise as it promotes re-endothelialisation and inhibits intimal hyperplasia in injured blood vessels. The ultimate goal is to translate the benefit of NOS gene therapy in animal models into clinical practise. To develop NOS gene therapy for clinical use further work needs to be undertaken to improve delivery systems and vectors to minimise detrimental side-effects and enhance positive treatment outcomes. This review focuses on current research on NOS gene therapy in cardiovascular disease and identifies the next steps that would be necessary to lead to clinical trials.

A cell-based nitric oxide reporter assay useful for the identification and characterization of modulators of the nitric oxide/guanosine 3',5'-cyclic monophosphate pathway

Nitric oxide (NO) plays an important role in protection against the onset and progression of various cardiovascular disorders. Therefore, the NO/guanosine 3',5'-cyclic monophosphate (cGMP) pathway has gained considerable attention and has become a target for new drug development. We have established a rapid, homogeneous, cell-based, and highly sensitive reporter assay for NO generated by endothelial nitric oxide synthase (eNOS). In a coculture system, NO production is indirectly monitored in living cells via soluble guanylyl cyclase (sGC) activation and calcium influx mediated by the olfactory cyclic nucleotide-gated (CNG) cation channel CNGA2, acting as the intracellular cGMP sensor. Using this NO reporter assay, we performed a fully automated high-throughput screening campaign for stimulators of NO synthesis. The coculture system reflects most aspects of the natural NO/cGMP pathway, namely, Ca(2+)-dependent and Ca(2+)-independent regulation of eNOS activity by G protein-coupled receptor agonists, oxidative stress, phosphorylation, and cofactor availability as well as NO-mediated stimulation of cGMP synthesis by sGC activation. The NO reporter assay allows the real-time detection of NO synthesis within living cells and makes it possible to identify and characterize activators and inhibitors of enzymes involved in the NO/cGMP signaling pathway.

Genetic modification of cerebral arterial wall: implications for prevention and treatment of cerebral vasospasm

Genetic modification of cerebral vessels represents a promising and novel approach for prevention and/or treatment of various cerebral vascular disorders, including cerebral vasospasm. In this review, we focus on the current understanding of the use of gene transfer to the cerebral arteries for prevention and/or treatment of cerebral vasospasm following subarachnoid hemorrhage (SAH). We also discuss the recent developments in vascular therapeutics, involving the autologous use of progenitor cells for repair of damaged vessels, as well as a cell-based gene delivery approach for the prevention and treatment of cerebral vasospasm.

Effect of gene delivery of NOS isoforms on intimal hyperplasia and endothelial regeneration after balloon injury

Endothelial cell loss is a critical event in the pathological repair of the injured blood vessel. Impaired endothelial function results in reduced production of key vascular mediators such as nitric oxide (NO) within the vessel wall leading to enhanced smooth muscle cell proliferation and migration and ultimately intimal hyperplasia. The aim of the present study was to directly compare the effects of adenoviral-mediated gene delivery of two nitric oxide synthase (NOS) isoforms, eNOS and iNOS on endothelial regeneration and intimal hyperplasia following endothelial injury in the rabbit carotid artery. The right carotid arteries of male New Zealand white rabbits were denuded by passing a 3French Fogarty balloon catheter along the artery three times. In all, 1 x 10(9) PFU of adenoviral(Ad)eNOS, AdiNOS or Adbeta-galactosidase (Adbeta-Gal) was then delivered intraluminally and allowed to dwell for 20 min. Transgene expression was sought after 3 days by immunohistochemistry and at 7 days by quantitative reverse transcriptase PCR. The effect on intimal hyperplasia was sought using histological staining after 14 days. Evans blue staining was used to determine the effect on endothelial regeneration. eNOS and iNOS expression was detected in transduced arteries. Neointima/media ratios were significantly reduced in eNOS (0.07+/-0.044) and iNOS (0.087+/-0.086) transduced arteries compared with Adbeta-Gal (0.332+/-0.14) transduced arteries (n=7). In addition, AdeNOS treatment (4.21+/-3.12% de-endothelialized area) enhanced endothelial regeneration compared to Adbeta-Gal treatment (10.05+/-4.98), while treatment with AdiNOS (25.17+/-11.92) inhibited endothelial regeneration in the injured rabbit carotid artery (n=7-8). These results highlight the potential of NOS gene therapy, in particular, eNOS gene therapy as a potential therapeutic strategy for the prevention of restenosis after vascular injury.

Adenoviral-mediated gene transfer of nitric oxide synthase isoforms and vascular cell proliferation

OBJECTIVE

Many vascular diseases are associated with reduced nitric oxide (NO) bioavailability. Nitric oxide synthase (NOS) gene therapy to the vasculature is a possible treatment for vascular disease as a means of increasing NO bioavailability, and this may be achieved using any of the NOS isoforms. The aim of our study was to compare the effects of adenoviral-mediated overexpression of the most commonly used NOS isoforms eNOS and iNOS on vascular cell proliferation.

METHODS

Human coronary artery smooth muscle cells (HCSMCs) and human umbilical vein endothelial cells (HUVECs) were transduced with adenoviral vectors encoding eNOS or iNOS at a multiplicity of infection of 100. Control cells were exposed to AdNull (empty vector) or diluent alone. Transgene expression was sought by Western blotting. The Greiss assay was used to measure nitrite levels. Cell proliferation was assessed by cell counting on days 0, 3 and 6. Apoptosis was sought using FACS analysis. Angiogenesis was measured using a commercially available in vitro kit.

RESULTS

Expression of both isoforms was detected in transduced cells by Western blot at all three time points. NOS transduction resulted in increased nitrite levels with higher levels seen in iNOS- compared to eNOS-transduced cells. Cell proliferation was diminished in AdeNOS- and AdiNOS-transduced cells compared with non-transduced cells on days 3 and 6 in both HCSMCs and HUVECs. Apoptosis was not detected in either cell line with either of the isoforms at any timepoint studied. Both eNOS and iNOS gene transfer caused a reduction in angiogenesis.

CONCLUSIONS

NOS gene transfer to both endothelial and vascular smooth muscle cells is antiproliferative and antiangiogenic. The biological effect is identical with both isoforms and there is no evidence to support a differential effect on endothelial and vascular smooth muscle cell biology.

Translational paradigms in cerebrovascular gene transfer

Gene transfer involves the use of an engineered biologic vehicle known as a vector to introduce a gene encoding a protein of interest into a particular tissue. In diseases with known defects at a genetic level, gene transfer offers a potential means of restoring a normal molecular environment via vector-mediated entry (transduction) and expression of genes encoding potentially therapeutic proteins selectively in diseased tissues. The technology of gene transfer therefore underlies the concept of gene therapy and falls under the umbrella of the current genomics revolution. Particularly since 1995, numerous attempts have been made to introduce genes into intracranial blood vessels to demonstrate and characterize viable transduction. More recently, in attempting to translate cerebrovascular gene transfer technology closer to the clinical arena, successful transductions of normal human cerebral arteries ex vivo and diseased animal cerebral arteries in vivo have been reported using vasomodulatory vectors. Considering the emerging importance of gene-based strategies for the treatment of the spectrum of human disease, the goals of the present report are to overview the fundamentals of gene transfer and review experimental studies germane to the clinical translation of a technology that can facilitate genetic modification of cerebral blood vessels.

A direct mechanical method for accurate and efficient adenoviral vector delivery to tissues

We describe a mechanical method for delivery of adenoviral vector to the adventitial surface of arteries and to other tissues. Our goal was to characterize, principally in intact carotid artery, the morphological, biochemical, and functional effects of mechanical delivery of a recombinant beta-galactosidase-expressing adenoviral vector following its direct application using a small paintbrush. Our ex vivo and in vivo data demonstrate efficient, accurate, and rapid transduction of arteries without compromise of their morphological, biochemical, and functional integrity. We also demonstrate the general applicability of this technique in vivo via transduction of skeletal muscle, fibrotendinous tissue, peritoneum, serosal surface of bowel, and wounded skin. We conclude that direct mechanical delivery of an adenoviral vector to tissues using a suitable paintbrush represents an intuitive, accurate, and effective means of augmenting gene transfer efficiency, and may be a useful adjunct to other delivery methods.

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases. This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.

Functional interplay between angiotensin II and nitric oxide: cyclic GMP as a key mediator

Angiotensin II (Ang II) and nitric oxide (NO) signaling pathways mutually regulate each other by multiple mechanisms. Ang II regulates the expression of NO synthase and NO production, whereas NO downregulates the Ang II type I (AT1) receptor. In addition, downstream effectors of Ang II and NO signaling pathways also interact with each other. A feedback mechanism between Ang II and NO is critical for normal vascular structure and function. Imbalance of Ang II and NO has been implicated in the pathophysiology of many vascular diseases. In this review, we focus on the diverse ways in which Ang II and NO interact and the importance of the balance between the signaling pathways activated by these mediators.

Nitric oxide synthase gene therapy for cardiovascular disease

Gene therapy refers to the transfer of specific genes to the host tissue to intervene in a disease process, with resultant alleviation of the symptoms of a particular disease. Cardiovascular gene transfer is not only a powerful technique for studying the function of specific genes in cardiovascular biology and pathobiology, but also a novel and promising strategy for treating cardiovascular diseases. Since the mid-1990s, nitric oxide synthase (NOS), the enzyme that catalyzes the formation of nitric oxide (NO) from L-arginine, has received considerable attention as a potential candidate for cardiovascular gene therapy, because NO exerts critical and diverse functions in the cardiovascular system, and abnormalities in NO biology are apparent in a number of cardiovascular disease processes including cerebral vasospasm, atherosclerosis, postangioplasty restenosis, transplant vasculopathy, hypertension, diabetes mellitus, impotence and delayed wound healing. There are three NOS isoforms, i.e., endothelial (eNOS), neuronal (nNOS) and inducible (iNOS). All three NOS isoforms have been used in cardiovascular gene transfer studies with encouraging results. This review will discuss the rationale of NOS gene therapy in different cardiovascular disease settings and summarize the results of experimental NOS gene therapy from various animal models of cardiovascular disease to date.

Can we model nitric oxide biotransport? A survey of mathematical models for a simple diatomic molecule with surprisingly complex biological activities

Nitric oxide (NO) is a remarkable free radical gas whose presence in biological systems and whose astonishing breadth of physiological and pathophysiological activities have only recently been recognized. Mathematical models for NO biotransport, just beginning to emerge in the literature, are examined in this review. Some puzzling and paradoxical properties of NO may be understood by modeling proposed mechanisms with known parameters. For example, it is not obvious how NO can survive strong scavenging by hemoglobin and still be a potent vasodilator. Recent models do not completely explain how tissue NO can reach effective levels in the vascular wall, and they point toward mechanisms that need further investigation. Models help to make sense of extremely low partial pressures of NO exhaled from the lung and may provide diagnostic information. The role of NO as a gaseous neurotransmitter is also being understood through modeling. Studies on the effects of NO on O2 transport and metabolism, also reviewed, suggest that previous mathematical models of transport of O2 to tissue need to be revised, taking the biological activity of NO into account.

Vascular endothelial dysfunction: does tetrahydrobiopterin play a role?

Tetrahydrobiopterin is one of the most potent naturally occurring reducing agents and an essential cofactor required for enzymatic activity of nitric oxide synthase (NOS). The exact role of tetrahydrobiopterin in the control of NOS catalytic activity is not completely understood. Existing evidence suggests that it can act as allosteric and redox cofactors. Suboptimal concentration of tetrahydrobiopterin reduces formation of nitric oxide and favors "uncoupling" of NOS leading to NOS-mediated reduction of oxygen and formation of superoxide anions and hydrogen peroxide. Recent findings suggest that accelerated catabolism of tetrahydrobiopterin in arteries exposed to oxidative stress may contribute to pathogenesis of endothelial dysfunction present in arteries exposed to hypertension, hypercholesterolemia, diabetes, smoking, and ischemia-reperfusion. Beneficial effects of acute and chronic tetrahydrobiopterin supplementation on endothelial function have been reported in experimental animals and humans. Furthermore, it appears that beneficial effects of some antioxidants (e.g., vitamin C) on vascular function could be mediated via increased intracellular concentration of tetrahydrobiopterin. In this review, the potential role of tetrahydrobiopterin in the pathogenesis of vascular endothelial dysfunction and mechanisms underlying beneficial vascular effects of tetrahydrobiopterin will be discussed.

Gene transfer of manganese superoxide dismutase reverses vascular dysfunction in the absence but not in the presence of atherosclerotic plaque

Impaired endothelium-dependent vasorelaxation (EDVR) is observed in hypercholesterolemia both in the presence and absence of morphological abnormalities and may be due to superoxide anions. Our aim was to assess the effect of gene transfer of manganese superoxide dismutase (MnSOD) to blood vessels from hypercholesterolemic animals with and without atherosclerotic plaque and to compare the effects of endothelial nitric oxide synthase (eNOS) and MnSOD over-expression on vascular dysfunction in the setting of atherosclerosis. Rabbits received a high-cholesterol diet for 10 weeks, resulting in abnormal EDVR in the absence of plaque in the carotids and the presence of plaque in the aorta. In Group 1, adenoviral vectors encoding MnSOD (AdMnSOD) or beta-galactosidase (Ad(beta)gal) were delivered to the carotid arteries in vivo. Four days later, transgene expression and vascular reactivity were assessed. In Group 2, segments of the aorta were transduced ex vivo with AdMnSOD, AdeNOS or both. Transgene expression and vascular reactivity were assessed 24 hr later. In Group 1, MnSOD expression was detected in AdMnSOD-ransduced vessels and impaired EDVR was reversed in the absence of atherosclerotic plaque. In Group 2 (with atherosclerotic plaque present), MnSOD and eNOS expression were detected by western analysis, and eNOS, but not MnSOD over-expression, improved EDVR whereas simultaneous over-expression of eNOS and MnSOD was no better than eNOS alone. Adenovirus-mediated gene transfer of MnSOD to nonatherosclerotic carotid arteries, but not atherosclerotic aorta, normalizes EDVR. eNOS gene transfer improves EDVR, even in the presence of plaque.

Gene transfer for cerebrovascular disease

Gene transfer is a powerful, evolving technique that uses a biologic vehicle (eg, an engineered adenovirus) to introduce a specific gene of interest (ie, a recombinant gene) into a target tissue. This approach, which has considerable therapeutic potential, underlies the concept of gene therapy. Several studies have characterized the morphologic, biochemical, and functional effects of recombinant gene expression in animal and human cerebral arteries, and support the possibility of gene therapy for cerebrovascular disease. However, for successful integration into future clinical practice, key issues concerning vector safety, delivery methods, and transduction specificity need to be addressed. Alongside completion of the Human Genome Project, transfer of novel genes into the central nervous system is likely to impact greatly on our ability to favorably modify diseased human tissue. Knowledge of the fundamental concepts of cerebrovascular gene transfer is therefore useful to understanding both its molecular basis and potential clinical utility.

Functional interdependence and colocalization of endothelial nitric oxide synthase and heat shock protein 90 in cerebral arteries

Heat shock protein 90 (HSP90), an essential component of several signal transduction systems, participates in the activation of endothelial nitric oxide synthase (eNOS) in cells. The objective of the current study was to determine if HSP90 and eNOS were functionally interdependent and colocalized in the cerebral circulation. The authors used isometric force recording, cyclic 3'5'-guanosine monophosphate (cGMP) radioimmunoassay (RIA), and immunogold electron microscopy (EM) to study canine basilar artery. They found that geldanamycin (0.1 to 10 microg/mL), a selective HSP90 inhibitor, caused concentration-dependent contractions in arterial rings (n = 6 dogs). Contractions to geldanamycin were unaffected by a cyclooxygenase inhibitor, indomethacin (10 micromol/L; P < 0.05, n = 6). Functional evidence for interaction between HSP90 and nitric oxide (NO)-mediated signaling included observations that the contractile effect of geldanamycin was the following: (1) endothelium-dependent, (2) abolished by Ng-nitro-L-arginine methylester (L-NAME; 0.3 mmol/L), and (3) non-additive with the contractile effect of this NOS inhibitor (P < 0.01, n = 6 for each). Furthermore, RIA showed significant reduction in cGMP levels in arteries treated with geldanamycin (3 microg/mL; P < 0.02, n = 8), whereas immunogold EM demonstrated areas of colocalization of HSP90 and eNOS selectively in the cytoplasm of endothelial cells. The current findings suggest that in cerebral arteries, endothelial HSP90 plays an important role in modulation of basal NO-mediated signaling. This interaction may be particularly important in stress-induced up-regulation of HSP90 with subsequent alteration of vasomotor function.

Adenovirus-mediated gene transfer to human cerebral arteries

Gene therapy is being investigated as a putative treatment option for cardiovascular diseases, including cerebral vasospasm. Because there is presently no information regarding gene transfer to human cerebral arteries, the principal objective of this study was to characterize adenovirus-mediated expression and function of recombinant endothelial nitric oxide synthase (eNOS) gene in human pial arteries. Pial arteries (outer diameter 500 to 1,000 microm) were isolated from 30 patients undergoing temporal lobectomy for intractable seizures and were studied using histologic staining, histochemistry, electron microscopy, and isometric force recording. Gene transfer experiments were performed ex vivo using adenoviral vectors encoding genes for bovine eNOS (AdCMVeNOS) and Escherichia coli beta-galactosidase (AdCMVLacZ). In transduced arteries, studied 24 hours after exposure to vectors, expression of recombinant beta-galactosidase and eNOS was detected by histochemistry, localizing mainly to the adventitia (n = 4). Immunoelectron microscopy localized recombinant eNOS in adventitial fibroblasts. During contractions to U46619, bradykinin-induced relaxations were significantly augmented in AdCMVeNOS-transduced rings compared with control and AdCMVLacZ-transduced rings (P < 0.01; n = 6). The NOS inhibitor L-nitroarginine methylester (L-NAME) caused significantly greater contraction in AdCMVeNOS-transduced rings (P < 0.001; n = 4) and inhibited bradykinin-induced relaxations in control and transduced rings (P < 0.001; n = 6). The current findings suggest that in AdCMVeNOS-transduced human pial arteries, expression of recombinant eNOS occurs mainly in adventitial fibroblasts where it augments relaxations to NO-dependent agonists such as bradykinin. Findings from the current study might be beneficial in future clinical applications of gene therapy for the treatment or prevention of cerebral vasospasm.

Gene therapy for atherosclerotic cardiovascular disease: a time for optimism and caution

Cardiovascular disease is the leading cause of death in the Western world, and gene therapy approaches to several cardiovascular disorders have been proposed. One of the major stumbling blocks to be overcome before widespread clinical use of this technology is how to deliver DNA efficiently and safely to cells in vivo. While delivery of DNA alone is inefficient, use of viral vectors may overcome this problem. Adenoviral vectors are most commonly used in cardiovascular gene delivery, but toxicity related to these vectors remains a concern. In addition, duration of gene expression with use of these vectors is limited, which may be advantageous in settings in which transient expression is satisfactory to obtain a therapeutic effect. Gene therapy has been suggested as an approach to multiple conditions, including restenosis after angioplasty, therapeutic neovascularization, and bypass graft restenosis. Phase 1 clinical trials were recently reported. While proof of principle has been established in preclinical animal models, convincing efficacy data in humans do not yet exist. Improvements in vector technology and methods of catheter-mediated vascular gene delivery are needed before widespread clinical application of this therapy.

In vivo gene transfer of endothelial nitric oxide synthase to carotid arteries from hypercholesterolemic rabbits enhances endothelium-dependent relaxations

BACKGROUND AND PURPOSE

Hypercholesterolemia is associated with abnormal endothelium-dependent vasorelaxation due to decreased nitric oxide bioavailability. Our aim was to examine the effect of adenovirus-mediated gene transfer of endothelial nitric oxide synthase (eNOS) to the hypercholesterolemic rabbit carotid artery in vivo. In addition, we examined whether adenovirus-mediated gene transfer was associated with vascular dysfunction.

METHODS

Rabbits were fed a 1% cholesterol diet for 4 weeks followed by a 0.5% cholesterol diet for 6 weeks. Vascular reactivity was assessed in nontransduced carotid arteries from chow- and cholesterol-fed animals. In addition, carotid arteries were surgically isolated, and 2 separate doses of adenoviral vectors encoding eNOS or beta-galactosidase (AdbetaGal) on the contralateral side were delivered to the lumen (1x10(10) and 5x10(10) pfu/mL).

RESULTS

Abnormal acetylcholine-mediated endothelium-dependent vasorelaxation was detected in the carotid artery from cholesterol-fed animals, whereas responses to calcium ionophore A23187 and diethylamine NONOate were normal. Vascular reactivity was similar in nontransduced and AdbetaGal-transduced hypercholesterolemic vessels. In vessels transduced with eNOS, transgene expression was demonstrated by immunostaining in both the endothelium and the adventitia and by Western blot analysis. High-dose but not low-dose eNOS gene transfer enhanced endothelium-dependent relaxation in vessels from cholesterol-fed rabbits.

CONCLUSIONS

Adenovirus-mediated gene transfer of eNOS to carotid arteries of cholesterol-fed animals improves endothelium-dependent relaxation when an optimal viral titer is administered.

Tumor necrosis factor alpha enhances the cytotoxicity induced by nitric oxide in cultured cerebral endothelial cells

It has been shown that independent sources of nitric oxide (NO) and the inflammatory cytokine tumor necrosis factor alpha (TNFalpha) contribute to the breakdown of the blood-brain barrier (BBB) in the pathogenesis of a number of brain disorders. However, the interaction of NO and TNFalpha has not been elucidated. The present study was designed to determine whether the toxicity induced by NO is altered by TNFalpha in brain capillary endothelial cells (BCECs), and if so, whether it is related to the generation of superoxide. TNFalpha (50-400 U/ml) did not produce toxicity until at a concentration of 800 U/ml. This toxic effect was completely blocked by copper-zinc superoxide dismutase (SOD)/catalase or N(omega)-nitro-L-arginine methyl ester (L-NAME) or oxyhemoglobin (HbO2). Sodium nitroprusside (SNP) reduced with 0.4 mM ascorbate (SNP/Vc) significantly increased Lactate dehydrogenase (LDH) efflux in a concentration-dependent manner. This cytotoxicity of SNP/Vc was also completely inhibited by SOD/catalase or HbO2. When SNP/Vc used in combination with 400 U/ml TNFalpha, a more remarkable LDH efflux was induced than SNP/Vc alone, even as little as 0.01 mM SNP/Vc was toxic, although a dose of 400 U/ml TNFalpha alone had no effect on LDH efflux. In addition, either 0.4 mM SNP/Vc and 800 U/ml TNFalpha alone or 0.4 mM SNP/Vc and 400 U/ml TNFalpha in combination significantly increased malondialdehyde (MDA) content, but nitric oxide synthase (NOS) activity was inhibited only by SNP/Vc and TNF in combination. These results suggest that TNFalpha enhances the toxicity of NO in BCECs and that at least part of this enhancement involves the generation of superoxide.

Nitric oxide and the cerebral vascular function

The presence of a cholinergic vasodilator innervation to cerebral circulation is well established. Despite its high endogenous concentration in cerebral blood vessels, acetylcholine (ACh) is not the transmitter for vasodilation. This finding has led to the discovery that nitric oxide (NO), which is coreleased with ACh and neural peptides such as vasoactive intestinal polypeptide (VIP) from the respective cholinergic-nitrergic (nitric oxidergic) nerves and the VIPergic-nitrergic nerves, is the primary transmitter in relaxing smooth muscle. ACh and VIP act presynaptically to inhibit and facilitate, respectively, the release of NO. Release of NO from cerebral vascular endothelial cells is also well established. A similar system for recycling L-citrulline to L-arginine for synthesizing more NO has been demonstrated in both cerebral perivascular nerves and endothelial cells. Neuronal and endothelial NO appears to play an important role in controlling cerebral vascular tone and circulation in health and disease.

Gene transfer of endothelial nitric oxide synthase to the lung of the mouse in vivo. Effect on agonist-induced and flow-mediated vascular responses

The effects of transfer of the endothelial nitric oxide synthase (eNOS) gene to the lung were studied in mice. After intratracheal administration of AdCMVbetagal, expression of the beta-galactosidase reporter gene was detected in pulmonary airway cells, in alveolar cells, and in small pulmonary arteries. Gene expression with AdCMVbetagal peaked 1 day after administration and decayed over a 7- to 14-day period, whereas gene expression after AdRSVbetagal transfection peaked on day 5 and was sustained over a 21- to 28-day period. One day after administration of AdCMVeNOS, eNOS protein levels were increased, and there was a small reduction in mean pulmonary arterial pressure and pulmonary vascular resistance. The pressure-flow relationship in the pulmonary vascular bed was shifted to the right in animals transfected with eNOS, and pulmonary vasodepressor responses to bradykinin and the type V cGMP-selective phosphodiesterase inhibitor zaprinast were enhanced, whereas systemic responses were not altered. Pulmonary vasopressor responses to endothelin-1 (ET-1), angiotensin II, and ventilatory hypoxia were reduced significantly in animals transfected with the eNOS gene, whereas pressor responses to norepinephrine and U46619 were not changed. Systemic pressor responses to ET-1 and angiotensin II were similar in eNOS-transfected mice and in control mice. Intratracheal administration of AdRSVeNOS attenuated the increase in pulmonary arterial pressure in mice exposed to the fibrogenic anticancer agent bleomycin. These data suggest that transfer of the eNOS gene in vivo can selectively reduce pulmonary vascular resistance and pulmonary pressor responses to ET-1, angiotensin II, and hypoxia; enhance pulmonary depressor responses; and attenuate pulmonary hypertension induced by bleomycin. Moreover, these data suggest that in vivo gene transfer may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders.