Nitric oxide donor SNAP induces apoptosis in smooth muscle cells through cGMP-independent mechanism

Nitric oxide synthase expression in macrophages of Histoplasma capsulatum-infected mice is associated with splenocyte apoptosis and unresponsiveness

Splenic macrophages from Histoplasma capsulatum-infected mice express inducible nitric oxide synthase (iNOS), and the iNOS expression correlates with severity of the infection. We examined whether production of NO is responsible for apoptosis and the anti-lymphoproliferative response of splenocytes from mice infected with H. capsulatum. In situ terminal deoxynucleotidyl transferase nick end labeling revealed apoptotic nuclei in cryosections of spleen from infected but not normal mice. Splenocytes of infected mice were unresponsive to stimulation by either concanavalin A or heat-killed H. capsulatum yeast cells. Splenocyte responsiveness was restored by addition to the medium of NG-monomethyl-L-arginine, a known inhibitor of NO production. The proliferative response of splenocytes from infected mice was also restored by depletion of macrophages or by replacement with macrophages from normal mice. In addition, expression of iNOS returned to its basal level when the animals had recovered from infection. These results suggest that suppressor cell activity of macrophages is associated with production of NO, which also appears to be an effector molecule for apoptosis of cultured splenocytes from infected mice.

Role of nitric oxide in the control of apoptosis in the microvasculature

Cell death occurs by either apoptosis or necrosis. Apoptosis is a cellular event in which a sequence of biochemical and morphological changes conclude in the death of the cell. Apoptosis is an important mechanism to control the number of cells and maintain tissue architecture. Nitric oxide (NO) is a multifunctional molecule that is synthesized by a family of enzymes, namely nitric oxide synthases (NOS). NO is implicated in several physiological functions within the microvascular environment, i.e. regulation of vascular tone, antiplatelet and antileukocyte properties and modulation of cell growth. Several investigations have demonstrated effects of NO on gene transcription. In this regard, NO has been also implicated in the apoptotic processes. The goal of the present review is to summarize the current knowledge about the relationship between NO and different genes involved in the apoptotic phenomena with focus in the cells of the microvascular environment, i.e. monocytes/macrophages, endothelium and vascular smooth muscle cells. Different studies have revealed that stimulation and inhibition of different genes are required to stimulate apoptosis. NO modulates the expression of bcl-2 family members, p53, interleukin-1 beta-converting enzyme family proteases and the cytokine receptor Fas. Therefore, NO generated from NO donors or synthesized by NOS induces cell death via apoptosis in a variety of different cell types. On the other hand, in the endothelial cells NO seems to have a relevant role in the maintenance of the confluent endothelial monolayer inhibiting apoptotic-related mechanisms. Furthermore, the redox states of the cells play an important role in the effects of NO as promotor of apoptosis. There have been exciting advances in the understanding of the molecular relationship between apoptosis and NO. Therefore, NO could be an important mediator to consider in the context of future therapeutic applications particularly considering apoptosis as a mechanism to maintain vascular architecture.

Local adenovirus-mediated transfer of human endothelial nitric oxide synthase reduces luminal narrowing after coronary angioplasty in pigs

BACKGROUND

Nitric oxide, synthesized from L-arginine by nitric oxide synthase (NOS), is a vasodilator and inhibits vascular smooth muscle cell (SMC) proliferation and migration. The effects of local NOS gene transfer on restenosis after experimental balloon angioplasty were investigated.

METHODS AND RESULTS

Left anterior descending coronary artery angioplasty was performed in 25 pigs. Animals received an intramural injection of adenovirus (1.5 x 10(9) pfu) carrying either the NOS cDNA (AdCMVceNOS) or no cDNA (AdRR5) via the Infiltrator. Local gene transfer efficiency and bioactivity of recombinant protein were assessed after 4 days. Indices of restenosis were evaluated by computerized planimetry on coronary artery sections prepared 28 days after angioplasty. Adenoviral vectors permitted efficient gene delivery to medial SMCs and adventitial cells of coronary arteries. Vascular cGMP levels were depressed after angioplasty from 1.30+/-0.42 to 0.33+/-0.20 pmol/mg protein (P<0.05) but were restored after constitutive endothelial (ce) NOS gene transfer to 1.82+/-0.98 pmol/mg (P<0.05 versus injured group and P=NS versus control). The ratio of the neointimal area to the internal elastic lamina fracture length, maximal neointimal thickness, and percent stenosis were all reduced in AdCMVceNOS- versus AdRR5-transduced pigs (0.59+/-0.14 versus 0.80+/-0.19 mm, P=0.02; 0.75+/-0.21 versus 1.04+/-0.25 mm, P=0.019; and 53+/-15% versus 75+/-11%, P=0.006, respectively). Lumen area was significantly larger (0.70+/-0.35 mm2 in AdCMVceNOS versus 0.32+/-0.18 mm2 in AdRR5, P=0.007).

CONCLUSIONS

Percutaneous adenovirus-mediated NOS gene transfer resulted in efficient local overexpression of functional NOS after angioplasty in coronary arteries. Restored NO production in injured coronary arteries significantly reduced luminal narrowing, most likely through a combined effect on neointima formation and on vessel remodeling after angioplasty.

Nitric oxide inhibits stress-induced endothelial cell apoptosis

OBJECTIVES

To determine a mechanism by which nitric oxide alters induction of stress-induced endothelial cell apoptosis in vitro. Apoptosis is a form of cellular suicide that has been implicated in the pathogenesis of multiple organ dysfunction syndrome.

DESIGN

Prospective, controlled trial.

SETTING

Research laboratory of a large, academic medical center.

SUBJECTS

Cultured primary porcine aortic endothelial cells.

INTERVENTIONS

Cells were treated with a range of doses of agents that either spontaneously generate nitric oxide (S-nitroso-N-acetyl-D,L-penicillamine [SNAP] or (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1,2-diolate [DETA-NO]) or block nitric oxide production (Nomega-methyl-L-arginine [L-NMA]). The ability of these agents to alter the rate of cell death by apoptosis (induced by the sequence stimuli lipopolysaccharide [LPS] followed by sodium arsenite) was measured. Mechanistic studies included examining the ability of: a) nitric oxide "donors" to alter nuclear factor kappa B (NF-kappaB) DNA binding activity and the level of IkappaBalpha accumulation; and b) a stable cyclic guanosine monophosphate (cGMP) analog (8-bromo-cGMP) to mimic the effect of nitric oxide donors.

MEASUREMENTS AND MAIN RESULTS

The sequence LPS/sodium arsenite increased the rate of endothelial cell apoptosis (47.4%, p< .05 vs. control), as measured by fluorescent-activated cell scanning using annexin V/propidium iodide staining. DETA-NO generated nitric oxide (as indicated by an increase in the concentration of the stable end-products of nitric oxide metabolism) and decreased the rate of endothelial cell apoptosis (20.6% at a dose of 2 mM, p=.0001 vs. control). DETA-NO also decreased NF-kappaB DNA binding activity and the apparent accumulation of its endogenous inhibitor, IkappaBalpha. The 8-bromo-cGMP did not mimic the effects of nitric oxide donors (DETA-NO) on apoptosis.

CONCLUSIONS

These data suggest that exogenous nitric oxide can block stress-induced endothelial cell apoptosis in vitro. The mechanistic studies are consistent with our hypothesis that inhibitors of NF-kappaB DNA binding activity are associated with protection against apoptosis-inducing stimuli. The results do not support a role for cGMP in mediating the protective effect of DETA-NO in our model.

Nitric oxide and its role in apoptosis

Nitric oxide (NO.), a potentially toxic molecule, has been implicated in a wide range of diverse (patho)physiological processes. It is appreciated that the production of NO. from L-arginine is important for nonspecific host defense, helping to kill tumors and intracellular pathogens. Cytotoxicity as a result of a massive NO.-formation is now established to initiate apoptosis. Apoptotic cell death in RAW 264.7 macrophages and several other systems as a result of inducible NO-synthase activation comprises upregulation of the tumor suppressor p53, activation of caspases, chromatin condensation, and DNA fragmentation. The involvement of NO was established by blocking adverse effects by NO-synthase inhibition. Overexpression of the antiapoptotic protein Bcl-2 rescued cells from apoptosis by blocking signal propagation downstream of p53 and upstream of caspase activation. As the wide variety of NO.-effects is achieved through its interactions with targets via redox and additive chemistry, the biological milieu, as a result of internal and external stimuli, may modulate toxicity. Therefore, transducing pathways of NO. are not only adopted to cytotoxicity but also refer to cell protection. NO.-signaling during protection from apoptosis is in part understood by the requirement of gene transcription and protein synthesis. NO.-formation causes upregulation of protective proteins such as heat shock proteins, cyclooxygenase-2, or heme oxygenase-1 which in a cell specific way may attenuate apoptotic cell death. Alternatively, protection may result as a consequence of a diffusion controlled NO./O2- (superoxide) interaction. The NO./O2--interaction redirects the apoptotic initiating activity of either NO. or O2- towards protection as long as reduced glutathione compensates the resultant oxidative stress. Protective principles may further arise from cyclic GMP formation or thiol modification. NO shares with other toxic molecules such as tumor necrosis factor-alpha the unique ability to initiate and to block apoptosis, depending on multiple variables that are being elucidated. The crosstalk between cell destructive and protective signaling pathways, their activation or inhibition under the modulatory influence of NO. will determine the role of NO in apoptotic cell death.

Tolerance induction ameliorates allograft vasculopathy in rat aortic transplants. Influence of Fas-mediated apoptosis

Based on successful induction of donor-specific unresponsiveness by alloantigenic stimulation in several animal models of acute rejection, we hypothesized that similar immune manipulations would also inhibit the evolution of chronic rejection and transplant vasculopathy. To induce immune tolerance, DA rats received a PVG heart allograft and were immunosuppressed with cyclosporine for 30 d. At day 100 the animals were challenged with a PVG aortic allograft after either 1 or 18 h of cold ischemia. 8 wk after the aortic transplantation, the grafts were investigated for morphological changes, infiltrating cells, apoptosis, and Fas-Fas ligand expression. Control allografts showed advanced transplant arteriosclerosis, whereas tolerance-induced aortic allografts displayed reduced neointimal formation, less medial atrophy, fewer apoptotic cells, and fewer Fas- and FasL-expressing cells. Prolonged ischemic storage time did not profoundly alter the morphological changes of the allografts. Fas expression was found in T cells, macrophages, vascular smooth muscle cells, and endothelial cells, whereas FasL was expressed mainly by T cells and macrophages. FasL mRNA expression was evident throughout the entire allograft wall. In conclusion, induction of allospecific tolerance can effectively prevent transplant arteriosclerosis. Cold ischemia damage does not abrogate the beneficial effect of tolerance, but creates a separate identity of mainly endothelial lesions. Furthermore, Fas-mediated apoptosis appears to be involved in the pathological lesions seen in chronic rejection.

Cigarette smoke extract is a modulator of mitogenic action in vascular smooth muscle cells

Cigarette smoking is associated with an increased incidence of atherosclerotic disease. In this study, we examined the mechanism underlying the growth-modulating effects of cigarette smoke extract (CSE) in confluent vascular smooth muscle cells (VSMCs). The treatment of VSMC by CSE decreased the activities of superoxide dismutase (SOD), catalase and glutathione peroxidase of VSMC in a time-dependent manner. In mitogenesis assays using the confluent cells, CSE was not a direct mitogen for VSMC, but potentiated the stimulatory effect of hydrogen peroxides. The reduction of activities of catalase and glutathione peroxidase was partially prevented by SH-containing compounds. In summary, CSE enhanced the mitogenic effect response of hydrogen peroxides, largely depending on the dysregulation of the activities of SOD, catalase and glutathione peroxidase by CSE.

Overexpression of human endothelial nitric oxide synthase in rat vascular smooth muscle cells and in balloon-injured carotid artery

Endothelial cells in normal blood vessels might prevent the unscheduled proliferation of smooth muscle cells (SMCs) by the expression of cell migration and growth inhibitors. NO, a potent vasodilator, generated by endothelium-specific constitutive NO synthase (ecNOS) might be such an inhibitor. To test this hypothesis, we overexpressed human ecNOS in syngeneic rat arterial SMCs using retrovirus-mediated gene transfer. Compared with SMCs transduced with vector alone (LXSN SMCs), DNA synthesis and cell proliferation were inhibited in the ecNOS-expressing SMCs (LCNSN SMCs). Basal and stimulated (by the calcium ionophore A23187) secretion of NO and intracellular cGMP were increased in LCNSN SMCs. Nomega-Nitro-L-arginine (L-NA), an inhibitor of NO synthesis, enhanced the proliferation of LCNSN SMCs but had no effect on LXSN SMCs. LCNSN SMCs seeded onto the luminal surface of balloon-injured rat carotid arteries inhibited neointimal formation by 37% and induced marked dilatation (3-fold increase in vessel diameter) at 2 weeks compared with LXSN SMC-seeded arteries. Orally administered L-NA blocked these changes. Phosphorylation of vasodilator-stimulated phosphoprotein, which is regulated in part by NO, was elevated in LCNSN SMCs and in LCNSN SMC-seeded arteries. This study demonstrates that NO generation by ecNOS inhibits SMC proliferation in vitro and modulates vascular tone locally in vivo.

No induced apoptosis accompanying the change of oncoprotein expression and the activation of CPP32 protease

Previously we have shown that nitric oxide (NO) donors induced apoptosis in vascular smooth muscle cells (VSMCs). However, the mechanisms by which NO induced apoptosis in VSMCs are entirely unknown. In the present study, we intended to identify the mechanism by which NO donors induce apoptosis in VSMCs. First, we evaluated the expression of c-Myc, P53, and Bcl-2 proteins in VSMCs treated by NO donors. c-Myc and P53 protein expression increased after VSMCs were incubated with NO donors for 6 hr and reached a maximum level at 24 hr, while Bcl-2 protein decreased after 12 hr incubation. Next we investigated to see whether the CPP32 protease activation was involved in NO donors-induced apoptosis. In VSMCs treated by NO donors, the increase of CPP32 protease activity was observed and specific inhibition of CPP32 activity significantly prevented apoptosis induced by NO donors in a dose-dependent manner. These results suggest that NO donors induced apoptosis through proto-oncoprotein expression and CPP32-like protease activation.

Expression and localization of inducible nitric oxide synthase in the rat ovary: a possible involvement of nitric oxide in the follicular development

In the present study, using Northern blot analysis, we demonstrated that the level of iNOS mRNA in the ovary of immature rats decreased after 6 h of pregnant mare serum gonadotropin administration and recovered gradually up to the untreated level 48 h after the administration. Both in situ hybridization and immunohistochemistry revealed that iNOS mRNA and protein was predominantly localized in granulosa cells in most of immature follicles, but not in mature follicles with an antrum, which was a consistent finding regardless of gonadotropin treatment. Furthermore, we found that cultured granulosa cells had the ability to express iNOS mRNA in the presence of cytokines such as tumor necrosis factor-alpha, interleukin-1 beta and interferon-gamma, which are inherently detectable in the ovary. These results raise the possibility that locally produced NO synthesized by iNOS may be involved in the developmental status of ovarian follicles in concert with gonadotropin.

Nitric oxide donor NOR 3 inhibits ketogenesis from oleate in isolated rat hepatocytes by a cyclic GMP-independent mechanism

Studies were conducted to clarify the effects of nitric oxide donors NOR 3 ((+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide, FK409), SIN-1 (3-morpholinosydnonimine) and SNAP (S-nitroso-N-acetylpenicillamine) on the accumulation of cGMP and cAMP and Ca2+ mobilization as well as ketogenesis from oleate in isolated rat hepatocytes. NOR 3 caused inhibition of ketogenesis from oleate along with stimulation of cGMP accumulation in rat hepatocytes, whereas SIN-1 and SNAP exerted no effect on ketogenesis despite their marked stimulation of cGMP accumulation. Although the nitric oxide trapping agent, carboxy-PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide), antagonized the stimulation by NOR 3 of cGMP accumulation, it failed to modulate the anti-ketogenic action of NOR 3. Furthermore, neither 8-bromoguanosine-3',5'-cyclic monophosphate nor N2,2'-O-dibutyrylguanosine-3',5'-cyclic monophosphate mimicked the anti-ketogenic action of NOR 3. It is concluded in the present study that NOR 3-induced inhibition of ketogenesis in rat hepatocytes is not mediated by cGMP. The present study revealed that the remaining structure of NOR 3 from which nitric oxide had been spontaneously released had no anti-ketogenic action. We first and clearly demonstrated that nitrite production was dramatically enhanced when NOR 3 was incubated in the presence of rat hepatocytes. The mechanism whereby NOR 3 inhibits ketogenesis in rat hepatocytes will be discussed.

The regulation of mitogenesis and apoptosis in response to the persistent stimulation of alpha1-adrenoceptors: a possible role of 15-lipoxygenase

1. Activation of alpha1-adrenoceptor stimulation regulates eicosanoid metabolism and growth in vascular smooth muscle cells (VSMCs). The purpose of this study was to investigate the functional implications of lipoxygenase pathway in alpha1-adrenoceptor-stimulated VSMCs growth through mutually exclusive biological functions, that is cell proliferation and cell death. 2. Phenylephrine (10 microM), a specific alpha1-adrenoceptor agonist, enhanced [3H]-thymidine incorporation by 300% above basal. Nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, caused 36 and 50% decrease in phenylephrine (10 microM)-stimulated [3H]-thymidine incorporation at concentrations of 1 microM and 10 microM respectively. 3. Inversely, treatment of phenylephrine (10 microM)-stimulated VSMCs with NDGA induced DNA fragmentation in a dose-dependent fashion. The level of induction of DNA fragmentation by NDGA was 225, 319 and 406% above the phenylephrine (10 microM)-level at concentrations of 0.1 microM, 1 microM and 10 microM, respectively. This induction of DNA fragmentation was partially prevented by exogenous 15-hydroxyeicosatetraenoic acid (15-HETE). The inhibition of apoptosis was 53 and 63% at concentrations of 5 microM and 10 microM of 15HETE, respectively, as compared with phenylephrine (10 microM) in the presence of NDGA (10 microM). 4. Furthermore, we performed the time-course analysis of Bcl-2 protein expression in phenylephrine (10 microM)-stimulated VSMCs. The expression of Bcl-2 protein disappeared after a 2 h incubation in the presence of NDGA (10 microM), but remained stable after a 2 h incubation period in the absence of NDGA (10 microM). 5, These results suggest that the lipoxygenase pathway is involved in cell proliferation by preventing apoptosis through the level of Bcl-2 protein expression.

Nitric oxide donor-induced apoptosis in smooth muscle cells is modulated by protein kinase C and protein kinase A

We have demonstrated previously that exogenously applied nitric oxide (NO) redox species induced apoptosis in smooth muscle cells. The present studies were undertaken to characterize further the potential role of protein kinase C and protein kinase A in the regulation of S-nitroso-N-acetylpenicillamine-induced apoptosis in smooth muscle cells. S-nitroso-N-acetylpenicillamine-induced apoptosis was prevented by the protein kinase C inhibitors, calphostin C and H-7, and was potentiated by protein kinase C activator, phorbol 12-myristate 13-acetate (PMA). Furthermore, S-nitroso-N-acetylpenicillamine prolonged membrane translocation of protein kinase C-epsilon. The membrane permeable analogue, dibutyryl-cAMP (Db-cAMP), potentiated S-nitroso-N-acetylpenicillamine-induced apoptosis, whereas the selective protein kinase A competitive inhibitor, Rp-cAMP, prevented S-nitroso-N-acetylpenicillamine-induced apoptosis. These results indicate that both protein kinase C and protein kinase A are involved in S-nitroso-N-acetylpenicillamine-induced apoptosis in smooth muscle cells.

Role of the lipoxygenase pathway in phenylephrine-induced vascular smooth muscle cell proliferation and migration

We studied the effects of phenylephrine-stimulated proliferation and migration of vascular smooth muscle cells and the role of 12-lipoxygenase-mediated pathways under normal as well as high glucose conditions. Phenylephrine-induced increases in cellular proliferation and migration were attenuated by the specific 12-lipoxygenase inhibitor baicalein. In contrast, neither of the cyclo-oxygenase inhibitors, indomethacin or ibuprofen, had any effect. Direct addition of the 12-lipoxygenase product, 12-S-hydroxyeicosatetraenoic acid (12-HETE), increased the proliferation and migration of vascular smooth muscle cells treated with both phenylephrine and nordihydroguaiaretic acid. Furthermore, we observed that phenylephrine induced greater increases in the proliferation and migration of vascular smooth muscle cells and also that the 12-lipoxygenase inhibitor prevented the enhancement of proliferation and migration of vascular smooth muscle cells induced by phenylephrine in the presence of high glucose (25 mmol/l). These results suggest that 12-lipoxygenase activation plays a key role in phenylephrine-induced responses of vascular smooth muscle cells under normal and hyperglycemic conditions. 12-lipoxygenase may be a good pharmacological target for treatment of vascular disease of hypertension and diabetes mellitus.

Nitric oxide synthases and cardiac muscle. Autocrine and paracrine influences

The different cell types comprising cardiac muscle express one or more of the three isoforms (neuronal NOS, or nNOS; inducible NOS, or iNOS; and endothelial NOS, or eNOS) of nitric oxide synthase (NOS). nNOS is expressed in orthosympathetic nerve terminals and regulates the release of catecholamines in the heart. eNOS constitutively expressed in endothelial cells inhibits contractile tone and the proliferation of underlying vascular smooth muscle cells, inhibits platelet aggregation and monocyte adhesion, promotes diastolic relaxation, and decreases O2 consumption in cardiac muscle through paracrinally produced NO. eNOS is also constitutively expressed in cardiac myocytes from rodent and human species, where it autocrinally opposes the inotropic action of catecholamines after muscarinic cholinergic and beta-adrenergic receptor stimulation. iNOS gene transcription and protein expression are induced in all cell types after exposure to a variety of inflammatory cytokines. Aside from participating in the immune defense against intracellular microorganisms and viruses, the large amounts of NO produced autocrinally or paracrinally mediate the vasoplegia and myocardial depression characteristic of systemic immune stimulation and promote cell death through apoptosis. In cardiac myocytes, NO may regulate L-type calcium current and contraction through activation of cGMP-dependent protein kinase and cGMP-modulated phosphodiesterases. Other mechanisms independent of cGMP elevations may operate through interaction of NO with heme proteins, non-heme iron, or free thiol residues on target signaling proteins, enzymes, or ion channels. Given the multiplicity of NOS isoforms expressed in cardiac muscle and of the potential molecular targets for the NO produced, tight molecular regulation of NOS expression and activity at the transcriptional and posttranscriptional level appear to be needed to coordinate the many roles of NO in heart function in health and disease.

Increased blood flow induces regression of intimal hyperplasia

We have previously shown that high shear stress inhibits growth of developing neointima in a primate model of polytetrafluoroethylene (PTFE) graft healing. We used this model to test the hypothesis that increased shear stress can cause atrophy of an established neointima. High porosity PTFE grafts were inserted into the aorto-iliac circulation bilaterally in baboons. These grafts develop neointimal hyperplasia comprising smooth muscle cells and a luminal surface of confluent endothelium. Neointima was allowed to develop for 2 months. At that time 8 animals were sacrificed. In eight other animals blood flow in one of two grafts was increased by construction of a femoral arterio-venous fistula. These animals were sacrificed 2 months later (4 months after graft placement). At four months, intimal cross sectional area was smaller on the high shear stress side compared to the contralateral, normal shear stress side (2.53 +/- 0.75 versus 6.83 +/- 0.65 mm2, P < .05). Neointima from grafts exposed to 2 months normal shear stress followed by 2 months of high shear stress had regressed when compared to normal-shear stress grafts studied at 2 months (2.53 +/- 0.75 versus 4.56 +/- 0.68 mm2, P < .05). Morphometric analysis using transmission electron microscopy revealed that the decrease in intimal cross sectional area was attributable to a loss of both smooth muscle cells and matrix. Endothelial nitric oxide synthase was induced in high-flow graft intima. These observations support the conclusion that elevated shear stress can cause vessel wall atrophy. This process might be mediated by nitric oxide.

Targeting nitric oxide (NO) delivery in vivo. Design of a liver-selective NO donor prodrug that blocks tumor necrosis factor-alpha-induced apoptosis and toxicity in the liver

We have designed a drug that protects the liver from apoptotic cell death by organ-selective pharmacological generation of the bioregulatory agent, nitric oxide (NO). The discovery strategy involved three steps: identifying a diazeniumdiolate ion (R2N[N(O)NO]-, where R2N = pyrrolidinyl) that spontaneously decomposes to NO with a very short half-life (3 s) at physiological pH; converting this ion to a series of potential prodrug derivatives by covalent attachment of protecting groups that we postulated might be rapidly removed by enzymes prevalent in the liver; and screening the prodrug candidates in vitro and in vivo to select a lead and to confirm the desired activity. Of five cell types examined, only cultured hepatocytes metabolized O2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO) to NO, triggering cyclic guanosine 3',5'-monophosphate (cGMP) synthesis and protecting the hepatocytes from apoptotic cell death induced by treatment with tumor necrosis factor-alpha (TNF alpha) plus actinomycin D. In vivo, V-PYRRO/NO increased liver cGMP levels while minimally affecting systemic hemodynamics, protecting rats dosed with TNF alpha plus galactosamine from apoptosis and hepatotoxicity. The results illustrate the potential utility of diazeniumdiolates for targeting NO delivery in vivo and suggest a possible therapeutic strategy for hepatic disorders such as fulminant liver failure.

The involvement of reactive oxygen species and arachidonic acid in alpha 1-adrenoceptor-induced smooth muscle cell proliferation and migration

1. In a previous study, we demonstrated phenylephrine-stimulated arachidonic acid (AA) release in rabbit cultured aortic smooth muscle cells. Therefore, we have investigated the functional implications of AA which are involved in the cellular response to phenylephrine, particularly proliferation and migration of rabbit cultured aortic smooth muscle cells. 2. First, to determine whether AA directly modifies proliferation and mobility of vascular smooth muscle cells (VSMCs), we exposed the cells to AA. AA induced proliferation and migration of the cells in a dose-dependent fashion. Concomitantly added catalase inhibited the proliferation and chemotaxis induced by AA of VSMCs. Conversely, aminotriazole enhanced the proliferation and migration induced by AA. 3. Secondly, we investigated whether the proliferation and migration of VSMCs by phenylephrine were related to AA and hydrogen peroxide (H2O2). The proliferation and chemotaxis of VSMCs by phenylephrine were inhibited by a phospholipase A2 (PLA2) inhibitor, or catalase. 4. Lastly, we investigated the effects of AA and phenylephrine on the content of H2O2 in VSMCs. AA and phenylephrine treatment led to an increase of H2O2 in a dose-dependent manner. 5. These results suggest that the addition of phenylephrine to the cells caused the enhancement of proliferation and migration, probably by mediating AA release and reactive oxygen species (ROS) production.

Transforming growth factor beta is a modulator of platelet-derived growth factor action in vascular smooth muscle cells: a possible role for catalase activity and glutathione peroxidase activity

Transforming growth factor-beta (TGF-beta) has been implicated in mediating the growth of vascular smooth muscle cells (VSMCs) after vascular injury. In this study, we examined the mechanism underlying the growth-modulating effects of TGF-beta in confluent VSMCs. Stimulation of rat VSMC by TGF-beta decreased both their catalase activity and glutathione peroxidase activity in a dose-dependent manner. In mitogenesis assays using the confluent cells, TGF-beta was not a direct mitogen for VSMC, but potentiated the stimulatory effect of platelet-derived growth factor (PDGF)-BB. This enhancement of mitogenesis was blunted by the addition of the scavenging enzyme catalase or the chemical antioxidant N-acetyl-L-cysteine. In summary, TGF-beta enhances the mitogenic effect response of PDGF-BB, largely depending on the dysregulation of catalase activity and glutathione peroxidase activity by TGF-beta.

Effects of sodium nitroprusside in the rat cortical collecting duct are independent of the NO pathway

Recently we described K+ channels in the basolateral membrane of principal cells of rat cortical collecting duct (CCD) which are regulated by a cGMP-dependent protein kinase (Pflugers Arch 429:338-344, 1995). We examined the effects of the NO-liberator sodium nitroprusside (SNP) on single channel activity and membrane voltage (Vm) in principal cells of rat CCD, and on transepithelial voltage, lumen-to-bath Na+ fluxes, and osmotic water permeability in isolated perfused rat CCD tubules. While in patch clamp experiments SNP (10 microM) hyperpolarized principal cells from -54 +/- 10 mV to -71 +/- 5 mV (N = 5) and increased the activity of the described K+ channels from 0.05 +/- 0.03 to 0.45 +/- 0.14 (N = 5) in cell-attached and from 0.04 +/- 0.02 to 0.25 +/- 0.05 (N = 4) in excised patch clamp experiments, it had no effect on basal or AVP-dependent transepithelial voltage, Na+ fluxes, or the osmotic water permeability. In addition, neither 50 microM SIN-1, another liberator of NO, nor 1 mM L-NAME, an inhibitor of the NO-synthase, changed Vm significantly. Furthermore, in cGMP-assays SNP failed to increase intracellular cGMP in CCD segments. Thus, we conclude that in the rat CCD transport is not regulated via the NO-pathway and that SNP acts as an cGMP independent activator of K+ channels in the basolateral membrane of these cells.