Iida, Yasuhiko

We recently reported that expression of recombinant endothelial nitric oxide (NO) synthase (eNOS) gene in adventitial fibroblasts restores NO formation in canine cerebral arteries without endothelium in response to bradykinin ex vivo and in vivo. The present study was designed to further characterize the stimuli that can activate recombinant eNOS enzyme expressed in the adventitia of cerebral arteries. To stimulate recombinant eNOS, we used serum (0.1–10%), substance P (10−11–3 × 10−9M), and ANG II (10−7–10−5M) because they increase intracellular calcium concentrations in fibroblasts. Endothelium-denuded segments of canine basilar arteries were incubated with an adenoviral vector encoding β-galactosidase gene or eNOS gene for 30 min at 37°C. After 24 h, vasomotor activity and cGMP formation in eNOS or β-galactosidase arteries were examined by isometric force recording and by radioimmunoassay, respectively. In control arteries and β-galactosidase gene-transduced arteries, serum caused concentration-dependent contractions, whereas in recombinant eNOS gene-transduced arteries, serum produced concentration-dependent relaxations. Substance P and ANG II had no effect on vascular tone in control and β-galactosidase arteries but caused concentration-dependent relaxations as well as a significant increase in cGMP levels in eNOS arteries. These relaxations were blocked by the NOS inhibitor NG-nitro-l-arginine methyl ester. Chemical treatment or mechanical inactivation of adventitial function significantly attenuated substance P-induced relaxations and ANG II-induced relaxations. These findings demonstrate that serum, substance P, and ANG II cause adventitia-dependent relaxations in cerebral arteries expressing the recombinant eNOS gene. This mechanism of vasodilatation may have beneficial effects in the prevention and treatment of vascular disorders characterized by the diminished bioavailability of NO, such as cerebral vasospasm.

Resistance arteries are an important target for vascular gene therapy because they play a key role in the regulation of tissue blood flow. The present study was designed to determine the effects of recombinant endothelial (e) nitric oxide synthase (NOS) gene expression on vasomotor reactivity of small brain stem arteries (internal diameter, 253 ± 2.5 μm). Arterial rings were exposed ex vivo to an adenoviral vector (109and 1010plaque-forming units/ml) encoding eNOS gene or β-galactosidase gene. Twenty-four hours after transduction, vascular function was examined by isometric force studies. Transgene expression was evident mainly in adventitia. In arteries with endothelium transduced with eNOS gene but not with control β-galactosidase gene, relaxations to bradykinin and substance P were significantly augmented. Removal of endothelium abolished relaxations to bradykinin and substance P in control and β-galactosidase arteries. However, in endothelium-denuded arteries transduced with recombinant eNOS, bradykinin and substance P caused relaxations that were abolished in the presence of the NOS inhibitor NG-nitro-l-arginine methyl ester. In control arteries, endothelium removal augmented relaxations to the nitric oxide donors sodium nitroprusside and diethylamine NONOate. This augmentation was absent in eNOS gene-transduced arteries without endothelium. Our results suggest that, in small brain stem arteries, expression of recombinant eNOS increases biosynthesis of nitric oxide. Adventitia of small arteries is a good target for expression of recombinant eNOS. Genetically engineered adventitial cells may serve as a substitute source of nitric oxide in cerebral arteries with dysfunctional endothelium.

Our previous ex vivo and in vivo studies reported that expression of the recombinant endothelial nitric oxide (NO) synthase (eNOS) gene in adventitial fibroblasts recovers NO production in arteries without endothelium in response to bradykinin. The present study was designed to characterize subtypes of bradykinin receptors on adventitial fibroblasts coupled to the activation of recombinant eNOS. Endothelium-denuded segments of canine basilar arteries were transduced with β-galactosidase (β-Gal) gene or eNOS gene ex vivo, using a replication-defective adenoviral vector (1010plaque-forming units/ml) for 30 min at 37°C. Twenty-four hours later, isometric force recording or cGMP measurement was carried out. B1bradykinin receptor agonist (des-Arg9-bradykinin, 10−10-10−8mol/l) did not significantly affect vascular tone in control or β-Gal gene-transduced canine basilar arteries without endothelium. In contrast, this agonist caused concentration-dependent relaxations in recombinant eNOS gene-transduced arteries without endothelium. Relaxations to B1receptor agonist in the eNOS arteries were abolished by B1receptor antagonist (des-Arg9-[Leu8]bradykinin, 6 × 10−9mol/l) but not by B2receptor antagonist (Hoe-140, 5 × 10−8mol/l). Bradykinin did not significantly alter vascular tone in control or β-gal arteries without endothelium, whereas this peptide (10−11-10−8mol/l) induced concentration-dependent relaxations, as well as an increase in cGMP formation in endothelium-denuded eNOS-transduced arteries. Stimulatory effects of bradykinin were prevented in the presence of a B2receptor antagonist but not in the presence of a B1receptor antagonist. B1and B2receptor antagonists had no effect on relaxations to substance P, confirming the selectivity of the compounds. Our results suggest that B1and B2bradykinin receptors are coupled to activation of recombinant eNOS expressed in adventitial fibroblasts.

Background and Purpose—The role of hydrogen peroxide in the regulation of cerebral arterial tone is not completely understood. Previous studies have demonstrated that hydrogen peroxide causes vasodilation of small cerebral arteries. The present study was designed to determine the mechanisms responsible for relaxations of large cerebral arteries to hydrogen peroxide.Methods—Rings of canine middle cerebral arteries without endothelium were suspended for isometric force recording in modified Krebs-Ringer bicarbonate solution bubbled with 94% O2/6% CO2(37°C, pH 7.4). Radioimmunoassay technique was used to determine the levels of cAMP and cGMP.Results—During contraction to UTP (3×10−6or 10−5mol/L), hydrogen peroxide (10−6to 10−4mol/L) caused concentration-dependent relaxations. Catalase (1200 U/mL) abolished the relaxations to hydrogen peroxide. Inhibition of cyclooxygenase by indomethacin (10−5mol/L) significantly reduced relaxations to hydrogen peroxide. In arteries contracted by KCl (20 mmol/L), the relaxations to hydrogen peroxide were significantly reduced. In the presence of a nonselective potassium channel inhibitor, BaCl2(10−4mol/L), a delayed rectifier potassium channel inhibitor, 4-aminopyridine (10−3mol/L), or a calcium-activated potassium channel inhibitor, charybdotoxin (3×10−8mol/L), the relaxations to hydrogen peroxide were also significantly reduced. An ATP-sensitive potassium channel inhibitor, glyburide (5×10−6mol/L), did not affect the relaxations to hydrogen peroxide. Hydrogen peroxide produced concentration-dependent increase in levels of cAMP. Indomethacin (10−5mol/L) inhibited the stimulatory effect of hydrogen peroxide on cAMP production. In contrast, hydrogen peroxide did not affect the levels of cGMP.Conclusions—These results suggest that hydrogen peroxide may cause relaxations of large cerebral arteries in part by activation of arachidonic acid metabolism via cyclooxygenase pathway with subsequent increase in cAMP levels and activation of potassium channels.