L-arginine availability is not limiting for nitric oxide generation from recombinant endothelial nitric oxide synthase

In vivo expression and function of recombinant GTPCH I in the rabbit carotid artery

Tetrahydrobiopterin (BH4) is an essential co-factor for endothelial nitric oxide synthase enzymatic activity. GTP cyclohydrolase I (GTPCH I) is the rate-limiting enzyme in BH4 synthesis. This study set out to test the hypothesis that in vivo gene transfer of GTPCH I to endothelial cells could increase bioavailability of BH4, enhance biosynthesis of nitric oxide and thereby enhance endothelium-dependent relaxations mediated by nitric oxide. In vivo gene transfer was carried out by adenovirus (Ad)-mediated delivery into rabbit carotid arteries. Each artery was transduced by 20-min intraluminal incubation of 10(9) plaque-forming units of Ad-encoding GTPCH I (AdGTPCH) or beta-galactosidase as a control. The rabbits were euthanized 72 h later, and vasomotor function of isolated arteries was assessed by isometric force recording. GTPCH I enzymatic activity, BH4, and oxidized biopterin levels were detected with the use of HPLC, and cGMP was measured with the use of radioimmunoassay. Expression of recombinant proteins was detected predominantly in endothelial cells. Both GTPCH I activity and BH4 levels were increased in arteries transduced with AdGTPCH. However, contraction to phenylephrine (10(-5) to 10(-9) M), endothelium-dependent relaxation to acetylcholine (10(-5) to 10(-9) M) and cGMP levels were not significantly affected by increased expression of GTPCH I. Our results suggest that expression of GTPCH I in vascular endothelium in vivo increases intracellular concentration of BH4. However, under physiological conditions, it appears that this increase does not affect nitric oxide production in endothelial cells of the carotid artery.

Gastrointestinal smooth muscle cell as target for gene transfer of eNOS gene

AIM

To generate an adenoviral vector carrying endothelial nitric-oxide synthase (eNOS) gene in order to mediate the expression of eNOS gene in gastrointestinal smooth muscle cells (SMC) and assess the enzyme activity of eNOS.

METHODS

A recombinant adenovirus (Ad-eNOS) containing the bovine eNOS cDNA fragment was generated by homologous recombination in bacteria. The SMC of distal part of esophagus and gastric fundus of cat were isolated and cultured in vitro and infected with Ad-eNOS. The expression of eNOS gene was detected by Western blot and RT-PCR. The enzyme activity of NOS and the output of NO in SMC were measured by NOS and NO assay kit, furthermore, the different effects of given factors on the enzyme activity and the yield of NO were studied.

RESULTS

The Ad-eNOS can infect the cultured SMC efficiently (MOI = 50, infection rate = 74%). Western blot and RT-PCR confirmed the expression of eNOS in those infected cells. After the cells had been infected with Ad-eNOS, the basal activity of NOS significantly increased from 47±13 nkat/L to 93±13/L (P<0.05), and the level of NO in cell culture supernatants increased by 3 fold (45±13 vs 16±7 μmol/L). In the presence of L-arginine (NOS enzyme substrate), calcium, EGTA (calcium chelating agent), and L-NAME (NOS inhibitor), NOS activity was 94±8, 173±25, 29±6, 58±11 nkat/L and NO level was 48±14, 106±18, 6±2, 17±11 μmol/L, respectively.

CONCLUSION

The constructed recombinant adenovirus, Ad-eNOS, can efficiently mediate the expression of eNOS gene in cultured SMC of digestive tract. The activity of eNOS can be regulated by the concentration of calcium. L-arginine is Not the rate-limiting step for nitric oxide generation from endothelial nitric oxide synthase.

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.