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

Patient-specific, multiscale modelling of neointimal hyperplasia in lower-limb vein grafts using readily available clinical data

The prediction of neointimal hyperplasia (NIH) growth, leading to vein graft failure in lower-limb peripheral arterial disease (PAD), is hindered by the multifactorial and multiscale mechanobiological mechanisms underlying the vascular remodelling process. Multiscale in silico models, linking patients' hemodynamics to NIH pathobiological mechanisms, can serve as a clinical support tool to monitor disease progression. Here, we propose a new computational pipeline for simulating NIH growth, carefully balancing model complexity/inclusion of mechanisms and readily available clinical data, and we use it to predict NIH growth for an entire vein graft. To this end, three different fittings to published in vitro data of time-averaged wall shear stress (TAWSS) vs nitric oxide (NO) production were tested for predicting long-term graft response (10-month follow-up) on a single patient. Additionally, the sensitivity of the model's predictions to different inflow boundary conditions (BCs) was assessed. The main findings indicate that: (i) a TAWSS-NO hyperbolic relationship best predicts long-term graft response; (ii) the model is insensitive to the inflow BCs if the waveform shape and the systolic acceleration time are comparable with the one acquired at the same time as the computed-tomography scan. This proof-of-concept study demonstrates the potential of using multiscale, computational techniques to predict NIH growth in lower-limb vein grafts, considering the routine clinical scenario of non-standardised data collection and sparse, incomplete datasets.

Comparison of the Apoptotic Effects of Topically Applied Papaverine, Diltiazem, and Nitroprusside to Internal Thoracic Artery

Objective

To detect and to compare the apoptotic effects of intraoperatively topically applied diltiazem, papaverine, and nitroprusside.

Methods

Internal thoracic artery segments of ten patients were obtained during coronary bypass grafting surgery. Each internal thoracic artery segment was divided into four pieces and immersed into four different solutions containing separately saline (Group S), diltiazem (Group D), papaverine (Group P), and nitroprusside (Group N). Each segment was examined with both hematoxylin-eosin and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) method in order to determine and quantify apoptosis.

Results

Apoptotic cells were counted in 50 microscopic areas of each segment. No significant difference was observed among the four groups according to hematoxylin-eosin staining. However, the TUNEL method revealed a significant increase in mean apoptotic cells in the diltiazem group when compared with the other three groups (Group S=4.25±1.4; Group D=13.31±2.8; Group N=9.48±2.09; Group P=10.75±2.37). The differences between groups were significant (P=0.0001). No difference was observed between the samples of the diabetic and non-diabetic patients in any of the study groups.

Conclusion

The benefit of topically applied vasodilator drugs must outweigh the potential adverse effects. In terms of apoptosis, diltiazem was found to have the most deleterious effects on internal thoracic artery graft segments. Of the analyzed medical agents, nitroprusside was found to have the least apoptotic activity, followed by papaverine. Diabetes did not have significant effect on the occurrence of apoptosis in left internal thoracic artery grafts.

Benzo[a]pyrene activates interleukin-6 induction and suppresses nitric oxide-induced apoptosis in rat vascular smooth muscle cells

Benzo[a]pyrene, a ubiquitous environmental pollutant, has been suggested to be capable of initiating and/or accelerating atherosclerosis. Accumulation of vascular smooth muscle cells (VSMCs) in vessel intima is a hallmark of atherosclerosis. Nitric oxide (NO) can suppress VSMCs proliferation and induce VSMCs apoptosis. NO plays a compensatory role in the vascular lesions to reduce proliferation and/or accelerate apoptosis of VSMCs. The aim of this study was to investigate whether benzo[a]pyrene can affect VSMCs growth and apoptosis induced by NO. Benzo[a]pyrene (1–30 μmol/L) did not affect the cell number and cell cycle distribution in VSMCs under serum deprivation condition. Sodium nitroprusside (SNP), a NO donor, decreased cell viability and induced apoptosis in VSMCs. Benzo[a]pyrene significantly suppressed SNP-induced cell viability reduction and apoptosis. VSMCs cultured in conditioned medium from cells treated with benzo[a]pyrene could also prevent SNP-induced apoptosis. Benzo[a]pyrene was capable of inducing the activation of nuclear factor (NF)-κB and phosphorylation of p38 mitogen-activated protein kinase (MAPK) in VSMCs. Both NF-κB inhibitor and p38 MAPK inhibitor significantly reversed the anti-apoptotic effect of benzo[a]pyrene on SNP-treated VSMCs. Incubation of VSMCs with benzo[a]pyrene significantly and dose-dependently increased interleukin (IL)-6 production. A neutralizing antibody to IL-6 effectively reversed the anti-apoptotic effect of benzo[a]pyrene on SNP-treated VSMCs. Taken together, these results demonstrate for the first time that benzo[a]pyrene activates IL-6 induction and protects VSMCs from NO-induced apoptosis. These findings propose a new mechanism for the atherogenic effect of benzo[a]pyrene.

Patient-Specific, Multi-Scale Modeling of Neointimal Hyperplasia in Vein Grafts

Neointimal hyperplasia is amongst the major causes of failure of bypass grafts. The disease progression varies from patient to patient due to a range of different factors. In this paper, a mathematical model will be used to understand neointimal hyperplasia in individual patients, combining information from biological experiments and patient-specific data to analyze some aspects of the disease, particularly with regard to mechanical stimuli due to shear stresses on the vessel wall. By combining a biochemical model of cell growth and a patient-specific computational fluid dynamics analysis of blood flow in the lumen, remodeling of the blood vessel is studied by means of a novel computational framework. The framework was used to analyze two vein graft bypasses from one patient: a femoro-popliteal and a femoro-distal bypass. The remodeling of the vessel wall and analysis of the flow for each case was then compared to clinical data and discussed as a potential tool for a better understanding of the disease. Simulation results from this first computational approach showed an overall agreement on the locations of hyperplasia in these patients and demonstrated the potential of using new integrative modeling tools to understand disease progression.

Nitric oxide regulates cell behavior on an interactive cell-derived extracellular matrix scaffold

During tissue injury and wound healing process, there are dynamic reciprocal interactions among cells, extracellular matrix (ECM), and mediating molecules which are crucial for functional tissue repair. Nitric oxide (NO) is one of the key mediating molecules that can positively regulate various biological activities involved in wound healing. Various ECM components serve as binding sites for cells and mediating molecules, and the interactions further stimulate cellular activities. Human mesenchymal stem cells (hMSCs) can migrate to the wound site and contribute to tissue regeneration through differentiation and paracrine signaling. The objective of this work was to investigate the regulatory effect of NO on hMSCs in an interactive ECM-rich microenvironment. In order to mimic the in vivo stromal environment in wound site, a cell-derived ECM scaffold that was able to release NO within the range of in vivo wound fluid NO level was fabricated. Results showed that the micro-molar level of NO released from the ECM scaffold had an inhibitory effect on cellular activities of hMSCs. The NO impaired cell growth, altered cell morphology, disrupted the F-actin organization, also decreased the expression of focal adhesion related molecules integrin α5 and paxillin. These results may contribute to the elucidation of how NO acts on hMSCs in wound healing process.

Gelatin-siloxane nanoparticles to deliver nitric oxide for vascular cell regulation: synthesis, cytocompatibility, and cellular responses

Nitric oxide (NO) is an important mediator in cardiovascular system to regulate vascular tone and maintain tissue homeostasis. Its role in vascular cell regulation makes it promising to address the post-surgery restenosis problem. However, the application of NO is constrained by its high reactivity. Here, we developed a novel NO-releasing gelatin-siloxane nanoparticle (GS-NO NP) to deliver NO effectively for vascular cell regulation. Results showed that gelatin-siloxane nanoparticles (GS NPs) could be synthesized via sol-gel chemistry with a diameter of ∼200 nm. It could be modified into GS-NO NPs via S-nitrosothiol (RSNO) modification. The synthesized GS-NO NPs could release a total of ∼0.12 µmol/mg NO sustainably for 7 days following a first-order exponential profile. They showed not only excellent cytocompatibility, but also rapid intracellularization within 2 h. GS-NO NPs showed inhibition of human aortic smooth muscle cell (AoSMC) proliferation and promotion of human umbilical vein endothelial cell (HUVEC) proliferation in a dose-dependent manner, which is an important approach to prevent restenosis. With GS-NO NP dose at 100 µg/mL, the proliferation of AoSMCs could be slowed down whereas the growth of HUVECs was significantly promoted. We concluded that GS-NO NPs could have potential to be used as a promising nano-system to deliver NO for vascular cell regulation.

Effects of slow, sustained, and rate-tunable nitric oxide donors on human aortic smooth muscle cells proliferation

Smooth muscle cell (SMC) proliferation has been accepted as a common event in the pathophysiology of vascular diseases, including atherogenesis and intimal hyperplasia. Delivery of the nitric oxide synthase (NOS) substrate l-arginine, pharmacological nitric oxide (NO) donors, NO gas or overexpression of NOS proteins can inhibit SMC proliferation and reduce the injury responses within the blood vessel wall. Although commercial development of NO donors that attempt to provide exogenous delivery of NO has accelerated over the last few years, none of the currently available products can provide controlled, sustained, time-tunable release of NO. Nitrosamine-based NO donors, prepared in our laboratory, present a unique and innovative alternative for possible treatments for long-term NO deficiency-related diseases, including atherosclerosis, asthma, erectile dysfunction, cancer, and neurodegenerative diseases. A family of secondary amines prepared via nucleophilic aromatic displacement reactions could be readily N-nitrosated to produce NO donors. NO release takes place in three distinct phases. During the initial phase, the release rate is extremely fast. In the second phase, the release is slower and the rate remains essentially the same during the final stage. These compounds inhibited up to 35% human aortic smooth muscle cell proliferation in a concentration-dependent manner.

The effect of L-arginine or L-citrulline supplementation on biochemical parameters and the vascular aortic wall in high-fat and high-cholesterol-fed rats

The aim of the present study is to investigate the potential role of L-arginine or L-citrulline in rats fed high-fat and high-cholesterol (HFC) diet. HFC feeding increased significantly serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities, urea and all lipid profiles and decreased significantly serum high-density lipoprotein-cholesterol (HDL-c) and non significantly serum nitric oxide levels. L-arginine or L-citrulline administration reversed the increase in serum AST and ALT activities, urea and all lipid profiles. These effects were associated with a concomitant increase in HDL-c and nitric oxide levels. In general, rats fed HFC diet and orally treated with L-arginine or L-citrulline had higher relative percentage of 18:0, 20:0 and 22:6 and lower 16:0 fatty acids than rats fed HFC diet. Light and transmission electron microscopic findings of the thoracic aorta confirmed the biochemical results and demonstrated structural changes in the endothelial cells of the intimal layer, medial smooth muscle cells as well as in the adventitial layer in HFC fed-animals. However, these findings indicate little structural alterations in animals supplemented with L-arginine or L-citrulline along with HFC feeding. In the present study, L-arginine or L-citrulline was effective hypocholesterolemic and hypolipidemic agents in rats.

Effects of isosorbide mononitrate on the restoration of injured artery in mice in vivo

The pharmacological basis of isosorbide mononitrate (ISMN), a widely used drug for cardiovascular diseases, is that it is metabolized to nitric oxide (NO). However, NO is a double-edged sword that results in either beneficial or detrimental effect. Vascular injury is the common consequence of many cardiovascular diseases, but it is not determined whether ISMN influences the restoration of injured artery in vivo. Carotid artery injury was induced by electric stimulation in mice. Vasoconstriction and endothelium-dependent and -independent relaxation were recorded by a multichannel acquisition and analysis system. ISMN (10 mg/kg, p.o.) treatment for 1 week and 1 month had no effect on reendothelialization, histology and function of carotid artery injured by electric stimulation. L-arginine (500 mg/kg, p.o.) and Nomega-nitro-L-arginine methyl ester (L-NAME) (50 mg/kg, p.o.) treatment for 1 week did not affect the reendothelialization process, but L-NAME treatment induced neointimal hyperplasia and inhibited endothelium-dependent relaxation in electrically injured artery. These results suggest that supplement of exogenous or endogenous NO has no effect on the restoration of injured artery, but inhibition of endogenous NO induces neointimal hyperplasia in injured artery. ISMN treatment does not affect the restoration of injured artery.

Isopropylamine NONOate (IPA/NO) moderates neointimal hyperplasia following vascular injury

OBJECTIVE

Isopropylamine NONOate (IPA/NO) is a nitroxyl (HNO) donor at physiologic pH. HNO is a positive inotrope and vasodilator, but little is known about its effect on neointimal hyperplasia. The aims of this study are to determine the effect of IPA/NO on endothelial and vascular smooth muscle cells (VSMC) in vitro and to determine if IPA/NO inhibits neointimal hyperplasia in vivo.

METHODS

VSMC were harvested from the abdominal aortas of male Sprague Dawley rats, and human umbilical vein endothelial cells were purchased from ATCC. In vitro, cellular proliferation was assessed by (3)H-thymidine incorporation, cell migration was assessed using the scrape assay, and cell death was assessed using Guava personal cell analysis (PCA). Cell cycle analysis was performed using propidium iodide staining and flow cytometry analysis. Protein expression was assessed using Western blot analysis. Phosphorylated proteins were assessed using immunoprecipitation and Western blot analysis. In vivo, the carotid artery injury model was performed on male Sprague Dawley rats treated with (n = 12) or without (n = 6) periadventitial IPA/NO (10 mg). Arteries harvested at 2 weeks were assessed for morphometrics using ImageJ. Inflammation was assessed using immunohistochemistry. Endothelialization was assessed by Evans blue staining of carotid arteries harvested 7 days after balloon injury from rats treated with (n = 6) or without (n = 3) periadventitial IPA/NO (10 mg).

RESULTS

In vitro, 1000 micromol/L IPA/NO inhibited both VSMC (38.7 +/- 4.5% inhibition vs control, P = .003) and endothelial cell proliferation (54.0 +/- 2.9% inhibition vs control, P < or = 0.001) without inducing cell death or inhibiting migration. In VSMC, this inhibition was associated with an S-phase cell cycle arrest and increased expression of cyclin A, cyclin D1, and the cyclin-dependent kinase inhibitor p21. No change was noted in the phosphorylation status of cdk2, cdk4, or cdk6 by IPA/NO. In rodents subjected to the carotid artery balloon injury model, IPA/NO caused significant reductions in neointimal area (298 +/- 20 vs 422 +/- 30, P < or = .001) and medial area (311 +/- 14 vs 449 +/- 16, P < or = .001) compared with injury alone, and reduced macrophage infiltration to 1.7 +/- 0.8 from 16.1 +/- 3.5 cells per high power field (P < or = .001). IPA/NO also prevented re-endothelialization compared with injury alone (55.9 +/- 0.5% nonendothelialized vs 21 +/- 4.4%, respectively, P = .001). Lastly, a 50% mortality rate was observed in the IPA/NO-treated groups.

CONCLUSIONS

In summary, while IPA/NO modestly inhibited neointimal hyperplasia by inhibiting VSMC proliferation and macrophage infiltration, it also inhibited endothelial cell proliferation and induced significant mortality in our animal model. Since HNO is being investigated as a treatment for congestive heart failure, our results raise some concerns about the use of IPA/NO in the vasculature and suggest that further studies be conducted on the safety of HNO donors in the cardiovascular system.

Regulation of TGF-beta1 gene transcription in human prostate cancer cells by nitric oxide

BACKGROUND

Overexpression of transforming growth factor (TGF)-beta1 is associated with advanced prostate cancer. Our previous studies showed an inverse correlation between the expressions of TGF-beta1 and inducible nitric oxide synthase (iNOS) in prostatic tumors in mice. The purpose of this study was to investigate regulation of TGF-beta1 expression in human prostate cancer cells by nitric oxide (NO).

METHODS

Expression of TGF-beta1 in the three well-characterized lines of human prostate cancer cells (PC-3MM2, LNCaP, and DU145) was determined by using the enzyme-linked immunoabsorbance assay (ELISA), real-time reverse-transcriptase PCR (RT-PCR), nuclear run-on, and promoter activity analyses.

RESULTS

Expression of both TGF-beta1 protein and mRNA was inhibited in both dose- and time-dependent manners by NO donors sodium nitroprusside (SNP), S-nitroso-N-acetylpenicilamine (SNAP), S-nitrosoglutathione (GSNO), and (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexeneamide (NOR-1) and by transfection of iNOS. The inhibitory effects of SNP and iNOS on TGF-beta1 expression were reduced in cells treated with NO scavengers N-dithiocarboxysarcosine (DTCS), 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), and hemoglobin, or with the iNOS inhibitor N-methyl-arginine (NMA). SNP downregulated the in vitro transcription of TGF-beta1 mRNA, inhibited TGF-beta1 promoter activity, but had no significant effects on TGF-beta1 mRNA stability.

CONCLUSION

These results show that NO downregulates TGF-beta1 expression in prostate cancer cells at transcription level by suppressing the de novo synthesis of TGF-beta1 mRNA.

Modulation by bradykinin and nitric oxide of angiotensin II-induced apoptosis in a vascular smooth muscle cell phenotype

There is evidence for a clinical benefit of ACE inhibitors or AT1 antagonists in cardiovascular diseases with deleterious smooth muscle cells (SMC) apoptosis. We have previously shown that angiotensin II (Ang II) induces a phenotype-dependent SMC apoptosis. We asked whether bradykinin (BK) and nitric oxide (NO) could modulate Ang II-induced SMC apoptosis. BK alone did not induce significant apoptosis in either spindle (Sp-SMC) or epithelioid (Ep-SMC) SMC phenotypes cultured in serum reduction, but phenotype-dependently, reduced cell proliferation. Pretreatment with BK partly impaired Ang II-induced reduction of Ep-SMC culture viability and partly prevented apoptotic features. Pretreatment with sodium nitroprusside completely prevented all Ang II-induced deleterious effects in Ep-SMC, i. e. reduction of culture viability, Annexin V binding, nuclear condensation and cell fragmentation. These findings indicate that the BK-NO system may phenotype-dependently modulate SMC survival and in particular may oppose, mostly by NO, Ang II-induction of apoptosis in the Ep-SMC phenotype.

The role of nitric oxide in the pathophysiology of intimal hyperplasia

Since its discovery, nitric oxide (NO) has emerged as a biologically important molecule and was even named Molecule of the Year by Science magazine in 1992. Specific to our interests, NO has been implicated in the regulation of vascular pathology. This review begins with a summary of the molecular biology of NO, from its discovery to the mechanisms of endogenous production. Next, we turn our attention to describing the arterial injury response of neointimal hyperplasia, and we review the role of NO in the pathophysiology of neointimal hyperplasia. Finally, we review the literature regarding NO-based therapies. This includes the development of inhalational-based NO therapies, systemically administered L-arginine and NO donors, NO synthase gene therapy, locally applied NO donors, and NO-releasing prosthetic materials. By reviewing the current literature, we emphasize the tremendous clinical potential that NO-based therapies can have on the development of neointimal hyperplasia.

Preconditioning with low concentration NO attenuates subsequent NO-induced apoptosis in vascular smooth muscle cells via HO-1-dependent mitochondrial death pathway

Nitric oxide (NO) signaling pathways are important in both the maintenance of vascular homeostasis and disease progression. Overproduction of NO has been associated with ischemia/reperfusion (I/R) injury. Growing evidences suggest that NO preconditioning has cytoprotective effects against I/R injury. However, the mechanism with which NO mediates these effects remains to be elucidated. The purpose of this study was to examine the mechanism of how NO preconditioning inhibits subsequent NO-induced apoptosis in vascular smooth muscle cells (VSMC), specifically focusing on heme oxygenase-1 (HO-1). According to our data, sodium nitroprusside (SNP) increased HO-1 expression in a concentration dependent manner. Preconditioning with low concentration SNP (0.3mM) inhibited subsequent high concentration SNP (1.5mM)-induced apoptosis, and this effect was reversed by the HO-1 inhibitor SnPP. Low concentration SNP-mediated protection involved p38 kinase inactivation and increased Bcl-2 expression. Furthermore, mitochondrial membrane potential was concomitantly increased with decreased expressions of Bax, Apaf-1, and activity of caspase-3, which was reversed by SnPP treatment. Our results show that low concentration SNP preconditioning suppresses subsequent high concentration SNP-induced apoptosis by inhibiting p38 kinase and mitochondrial death pathway via HO-1-dependent mechanisms in VSMC.

L-arginine and phosphodiesterase (PDE) inhibitors counteract fibrosis in the Peyronie's fibrotic plaque and related fibroblast cultures

Inducible nitric oxide synthase (iNOS) is expressed in both the fibrotic plaque of Peyronie's disease (PD) in the human, and in the PD-like plaque elicited by injection of TGFbeta1 into the penile tunica albuginea (TA) of the rat. Long-term inhibition of iNOS activity, presumably by blocking nitric oxide (NO)- and cGMP-mediated effects triggered by iNOS expression, exacerbates tissue fibrosis through an increase in: (a) collagen synthesis, (b) levels of reactive oxygen species (ROS), and (c) the differentiation of fibroblasts into myofibroblasts. We have now investigated whether: (a) phosphodiesterase (PDE) isoforms, that regulate the interplay of cGMP and cAMP pathways, are expressed in both the human and rat TA; and (b) L-arginine, that stimulates NOS activity and hence NO synthesis, and PDE inhibitors, that increase the levels of cGMP and/or cAMP, can inhibit collagen synthesis and induce fibroblast/myofibroblast apoptosis, thus acting as antifibrotic agents. We have found by immunohistochemistry, RT/PCR, and Western blot that PDE5A-3 and PDE4A, B, and D variants are indeed expressed in human and rat normal TA and PD plaque tissue, as well as in their respective fibroblast cultures. As expected, in the PD fibroblast cultures, pentoxifylline (non-specific cAMP-PDE inhibitor) increased cAMP levels without affecting cGMP levels, whereas sildenafil (PDE5A inhibitor) raised cGMP levels. Both agents and L-arginine reduced the expression of collagen I (but not collagen III) and the myofibroblast marker, alpha-smooth muscle actin, as determined by immunocytochemistry and quantitative image analysis. These effects were mimicked by incubation with 8-Br-cGMP, which in addition increased apoptosis, as measured by TUNEL. When L-arginine (2.25 g/kg/day), pentoxifylline (10 mg/kg/day), or sildenafil (10 mg/kg/day) was given individually in the drinking water for 45 days to rats with a PD-like plaque induced by TGF beta1, each treatment resulted in a 80-95% reduction in both plaque size and in the collagen/fibroblast ratio, as determined by Masson trichrome staining. Both sildenafil and pentoxiphylline stimulated fibroblast apoptosis within the TA. Our results support the hypothesis that the increase in NO and/or cGMP/cAMP levels by long-term administration of nitrergic agents or inhibitors of PDE, may be effective in reversing the fibrosis of PD, and more speculatively, other fibrotic conditions.

Sodium nitroprusside and peroxynitrite effect on hepatic DNases: an in vitro and in vivo study

Background

It has been documented that nitric oxide (NO) donor sodium nitroprusside (SNP) and authentic peroxynitrite are capable of promoting apoptosis in a number of different cell types. Various endonucleases have been proposed as candidates responsible for the internucleosomal cleavage of the genomic DNA observed during apoptosis, but the main effect is attributed to the alkaline-DNases (Mg²⁺- and caspase-dependent) and acid-DNase. The aim of this study was to examine an in vivo and in vitro possibility for alkaline- and acid-DNases to be activated by SNP and peroxynitrite.

Results

The effect on liver tissue alkaline and acid DNase activity together with the markers of tissue and plasma oxidative and nitrosative stress (lipid peroxidation, SH group content, carbonyl groups and nitrotyrosine formation) was investigated in plasma and liver tissue. The activity of liver alkaline DNase increased and that of acid DNase decreased after in vivo treatment with either SNP or peroxynitrite. A difference observed between the in vivo and in vitro effect of oxide donor (i.e., SNP) or peroxynitrite upon alkaline DNase activity existed, and it may be due to the existence of the "inducible" endonuclease. After a spectrophotometric scan analysis of purified DNA, it was documented that both SNP and peroxynitrite induce various DNA modifications (nitroguanine formation being the most important one) whereas DNA fragmentation was not significantly increased.

Conclusion

Alkaline DNase activation seems to be associated with the programmed destruction of the genome, leading to the fragmentation of damaged DNA sites. Thus, the elimination of damaged cells appears to be a likely factor in prevention against mutation and carcinogenesis.

Nitric oxide-induced apoptosis is mediated by Bax/Bcl-2 gene expression, transition of cytochrome c, and activation of caspase-3 in rat vascular smooth muscle cells

BACKGROUND

In contrast to the anti-apoptotic action of nitric oxide (NO) on endothelial cells, NO exerts a pro-apoptotic effect on vascular smooth muscle cells (VSMCs). This study was designed to elucidate the mechanism underlying NO-induced apoptosis in rat VSMCs.

METHODS AND RESULTS

(1) Using the terminal deoxynucleotidyl transferase-mediated digoxigenin-11-dUTP nick end labeling (TUNEL) assay and fluorescence activated cell sorter (FACS) analyses, apoptosis of rat VSMCs were confirmed after exposure to sodium nitroprusside (SNP) (0.5 to 4 mmol/l), an exogenous NO donor. The effects of SNP were blocked by hemoglobin. (2) A universal caspase inhibitor, z-VAD-fmk, dose-dependently inhibited NO-induced apoptosis. VSMCs degraded Ac-DEVD-pNA rather than Ac-WHED-pNA after exposure to SNP, which suggested that the activation of caspase 3 rather than caspase 1 was involved in the process. Immunoblot analysis confirmed the activation of caspase-3. (3) Exposure to SNP induced the release of cytochrome c from the mitochondria to the cytosol, which was detected by immunoblot analysis of mitochondrial and cytosol fractions. (4) SNP exposure increased the ratio of Bax/Bcl-2 protein expression twofold by immunoblot analysis.

CONCLUSIONS

The mechanism of NO-induced apoptosis in rat VSMCs involves an increase in the ratio of Bax/Bcl-2 gene expression, which leads to the release of cytochrome c from the mitochondria to the cytosol, finally activating caspase-3 and resultant apoptosis.

Effect of chronic hypoxia on inducible nitric oxide synthase expression in rat myocardial tissue

The purpose of our study was to evaluate the effect of chronic exposure to low cellular oxygen tension (90% N2 and 10% O2 for 14 days) in inducing apoptosis and activation of transcription and translation of inducible nitric oxide (NO) synthase (iNOS) in rat hearts tissue. Rats were divided into four groups: normoxic, hypoxic, rats maintained in normoxic condition for 7 days and subjected to hypoxic conditions for another 7 days, and rats maintained in hypoxic condition for 7 days and subjected to normoxic conditions for another 7 days. At the 7th and 14th days, five rats from each group were sacrificed. Immunohistochemical and Western blot analysis were performed on myocardial tissue to reveal the presence of iNOS. Expression of iNOS was determined by RT-PCR. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and by detection of internucleosomal DNA fragmentation by electrophoresis. Electrophoretic analysis of DNA showed oligonucleosomal fragmentation in the hypoxic groups, but no ladder was observed in the other groups. This data was confirmed through end labeling with streptavidin-biotin (biotin d-UTP). iNOS expression was evaluated through immunohistochemical techniques (Ab anti-iNOS) and Western blotting, and the results were quantified with a computerized imaging analysis. The expression of iNOS protein was greater in the hypoxic groups; in the normoxic groups, only a nonspecific background was detected. This data was supported with results obtained through RT-PCR, which showed the specific transcription of mRNA for iNOS in the same experimental conditions. In addition, the iNOS activity was also evaluated and was found to be more active in the hypoxic groups (0.1 +/- 0.01 vs 0.02 +/- 0.003). The present study shows that exposure to low oxygen tension is capable of inducing programmed cell death and activating iNOS.

Branched chain fatty acids induce nitric oxide-dependent apoptosis in vascular smooth muscle cells

Clinical observations in patients with peroxisomal disorders and studies employing corresponding mouse models have shown that supraphysiological concentrations of dietary branched chain fatty acids (BCFAs) are associated with a high level of toxicity, which is poorly understood at present. Here we show that phytanic and pristanic acid, two BCFAs that are metabolized in peroxisomes, promote apoptosis in cultured vascular smooth muscle cells of human, rat, and porcine origin. Under the conditions used, the apoptosis-promoting effect of BCFAs was neither shared by saturated or unsaturated straight chain fatty acids nor by artificial peroxisome proliferators, which, like phytanic and pristanic acid, have been shown to activate the peroxisome proliferator-activated receptor alpha (PPARalpha). We could demonstrate, however, that BCFA induced tumor necrosis factor alpha (TNFalpha) activation and secretion, which is an obligatory step required for induction of apoptosis by BCFAs. Furthermore, incubation of VSMCs with BCFA increased inducible nitric-oxide synthase (iNOS) mRNA and protein concentrations markedly within 2 h of treatment. Correspondingly, apoptosis was significantly reduced when the cells were co-treated with the competitive NOS inhibitors monomethyl-L-arginine monoacetate and aminoguanidine. Moreover, co-incubation with TGFbeta1, previously shown to destabilize iNOS mRNA, also abolished apoptosis. These results establish a new signaling cascade in which natural BCFA induced NO-dependent apoptosis, which is apparently triggered by autocrine secretion of TNFalpha in cultured VSMCs.

Different contribution of apoptosis to the antiproliferative effects of L-arginine, enalapril and losartan on neointimal growth inhibition after balloon arterial injury

It remains to be clarified how angiotensin-converting enzyme inhibitor-induced function (ie, increased NO related action or the inhibition of angiotensin II AT1 receptor dependent action) affects apoptosis of smooth muscle cells in the neointima following arterial injury. Saline (control), enalapril, L-arginine, combined enalapril and L-arginine, or losartan was administered for 14 days to Sprague-Dawley rats after balloon carotid injury and the ratio of intima to media areas (I/M), inducible NO synthase (iNOS) concentrations and %TUNEL were measured. I/M decreased similarly in the enalapril, L-arginine and losartan groups, and the combination of enalapril and L-arginine resulted in the largest I/M decrease. TUNEL positivity was increased compared with controls in the following order: losartan, L-arginine, enalapril and combination of enalapril and L-arginine. The intensity of immunostaining for iNOS was increased approximately 1.9-fold compared with the control in the combined enarapril and L-arginine group as well as in the enalapril group. These data suggest that the apoptosis in the neointima is different for L-arginine, losartan and enalapril under similar conditions and was higher under treatment with enalapril, not only via the action of NO or blocking of the AT1, but also by upregulation of iNOS.

Regulation of endothelial cell apoptosis in atherothrombosis

Increasing evidence suggests that endothelial cell apoptosis might contribute to atherogenesis, plaque erosion and acute coronary syndromes. The present review article summarizes the current findings and discusses the potential role of endothelial cell apoptosis for coronary artery disease progression. Moreover, the signalling events that critically regulate endothelial cell apoptosis are discussed. The article focuses on the regulation of endothelial cell apoptosis by the redox balance, which is mainly determined by reactive oxygen species and nitric oxide. Moreover, the role of S-nitrosylation of protein targets for protection of endothelial cell apoptosis will be discussed.

A 4-amino analogue of tetrahydrobiopterin attenuates endotoxin-induced hemodynamic alterations and organ injury in rats

Most recently we have shown that 4-aminotetrahydrobiopterin (4-ABH4), an analogue of tetrahydrobiopterin (cofactor of NO synthase), even administered 2 h after endotoxin challenge, improves survival rate in rats. The following experiment was performed to examine the effects of 4-ABH4 with respect to endotoxin-induced hemodynamic alterations and organ failure. At 2 h after endotoxic challenge (10 mg kg(-1) body weight) animals received 4-ABH4 at a dose of 1, 10, or 100 mg kg(-1) body weight. The controls were treated similarly but received saline at the same volume. Eight hours after endotoxin challenge cardiac index and stroke volume were significantly increased in animals treated with 10 mg 4-ABH4 compared to controls (0.23 +/- 0.06 vs. 0.16 +/- 0.04 mL min(-1) kg(-1) and 0.29 +/- 0.05 vs. 0.22 +/- 0.03 mL beat(-1)) while mean arterial pressure and peripheral vascular resistance index did not significantly differ among the groups. Plasma alanine aminotransferase (ALT) and creatinine levels were significantly increased in endotoxin controls compared with laboratory controls (ALT: 1643 +/- 1436 vs. 74 +/- 17 U L(-1); Creatinine: 91 +/- 29 vs. 42 +/- 3 micromol L(-1)) which was attenuated in animals treated with 10 mg kg(-1) 4-ABH4 (ALT: 417 +/- 318 U L(-1); Creatinine: 78 +/- 26 micromol L(-1)). Moreover, endotoxin-induced lung edema and intestinal necrosis were significantly reduced by 4-ABH4. Our study provides information that tetrahydrobiopterin analogue, 4-ABH4, improves LPS induced hemodynamic conditions and organ injury. This may, at least in part, account for the previously observed protection of rats by 4-ABH4 against endotoxin-induced mortality in the same endotoxic shock model.

Cilostazol enhances IL-1beta-induced NO production and apoptosis in rat vascular smooth muscle via PKA-dependent pathway

Interleukin-1beta (IL-1beta) stimulates nitric oxide (NO) production and induces apoptosis in several tissues. Cilostazol is a Type 3 phosphodiesterase inhibitor. We investigated whether cilostazol affects IL-1beta-induced NO production and apoptosis in rat vascular smooth muscle cells. Cilostazol (100 nM-10 microM) potentiated NO production triggered by IL-1beta. The mRNA and protein expression of inducible NO synthase was also upregulated by cilostazol. KT5720, an inhibitor of protein kinase A, and N(G)-monomethyl-L-arginine, an inhibitor of NO synthase, abrogated cilostazol-enhanced IL-1beta-stimulated NO production and apoptosis. These results shows that cilostazol potentiates IL-1beta-induced NO production via PKA-pathway and thereafter augments apoptosis via NO-dependent pathway.

Arachidonic acid release by cPLA2 may be causally related to NO-induced apoptosis in vascular smooth muscle cells

Apoptosis has been shown to occur in vascular smooth muscle cells during the development of atherosclerosis. In order to investigate the possible role of arachidonic acid during apoptosis in vascular smooth muscle, we induced apoptosis in cultured rat aortal smooth muscle cells (SMCs) by treatment with either UV (ultraviolet) radiation, tumor necrosis factor-alpha (TNF-alpha) or NO donor drugs (sodium nitroprusside, or S-nitroso-N-acetyl-D-penicillamine, SNAP). Apoptosis was detected by either DNA fragmentation analysis or by TUNEL analysis. UV radiation, TNF-alpha and NO were observed to stimulate apoptosis in the cells as well as to stimulate arachidonate release from the cells. NO also increased levels of cPLA2 in the cells, which is an enzyme that is frequently activated in cells that release arachidonate. These agents stimulated arachidonate release somewhat earlier than they stimulated apoptosis in the cells. The inhibition of cPLA2 by arachidonyl trifluoromethyl ketone (AACOCF3) also led to the inhibition of arachidonate release from the cells as well as the inhibition of nitroprusside stimulated apoptosis. Arachidonic acid itself could induce apoptosis in the cultured cells. These observations provide evidence that arachidonate may be involved in apoptosis in vascular smooth muscle.

Humic acid induces the generation of nitric oxide in human umbilical vein endothelial cells: stimulation of nitric oxide synthase during cell injury

Humic acid (HA) has been implicated as an etiological factor in the peripheral vasculopathy of blackfoot disease (BFD). In this study, we examined the effects of HA upon the generation of nitric oxide (NO) during the process of lethal cell injury in cultured human umbilical vein endothelial cells (HUVECs). NO production was measured by the formation of nitrite (NO(2)(-)), the stable end-metabolite of NO. Cell death was assessed by measuring the release of intracellular lactate dehydrogenase (LDH). Treatment HUVECs with HA at a concentration of 50, 100, and 200 microg/ml concentration-dependently increased nitrite levels, reaching a peak at 12 h subsequent to HA treatment, with a maximal response of approximately 400 pmole nitrite (from 1 x 10(4) cells). HA-induced nitrite formation was blocked completely by N(G)-nitro-L-arginine methyl ester (L-NAME) and also by N(G)-methyl-L-arginine (L-NMA), both being specific inhibitors of NO synthase. The LDH released from endothelial cells was evoked at from 24 h after the addition of HA (50, 100, 200 microg/ml) in a concentration- and time-dependent manner. The HA-induced LDH release was also reduced by the presence of both L-NAME and L-NMA. The addition of Ca(2+) chelator (BAPTA) inhibited both nitrite formation and LDH release by HA. Moreover, the antioxidants (superoxide dismutase, vitamin C, vitamin E) and protein kinase inhibitor (H7) effectively suppressed HA-induced nitrite formation. These results suggest that HA treatment of endothelial cells stimulates NO production, which can elicit cell injury via the stimulation of Ca(2+)-dependent NO synthase activity by increasing cytosolic Ca(2+) levels. Because the destruction of endothelial cells has been implicated in triggering the onset of BFD, the induction of excessive levels of NO and consequent endothelial-cell injury may be important to the etiology of HA-induced vascular disorders associated with BFD for humans.

Potentiation of nitric oxide-induced apoptosis in p53-/- vascular smooth muscle cells

The functional role of p53 in nitric oxide (NO)-mediated vascular smooth muscle cell (VSMC) apoptosis remains unknown. In this study, VSMC from p53-/- and p53+/+ murine aortas were exposed to exogenous or endogenous sources of NO. Unexpectedly, p53-/- VSMC were much more sensitive to the proapoptotic effects of NO than were p53+/+ VSMC. Furthermore, this paradox appeared to be specific to NO, because other proapoptotic agents did not demonstrate this differential effect on p53-/- cells. NO-induced apoptosis in p53-/- VSMC occurred independently of cGMP generation. However, mitogen-activated protein kinase (MAPK) pathways appeared to play a significant role. Treatment of the p53-/- VSMC with S-nitroso-N-acetylpenicillamine resulted in a marked activation of p38 MAPK and, to a lesser extent, of c-Jun NH(2)-terminal kinase, mitogen-activated protein kinase kinase (MEK) 1/2, and p42/44 (extracellular signal-regulated kinase, ERK). Furthermore, basal activity of the MEK-p42/44 (ERK) pathway was increased in the p53+/+ VSMC. Inhibition of p38 MAPK with SB-203580 or of MEK1/2 with PD-98059 blocked NO-induced apoptosis. Therefore, p53 may protect VSMC against NO-mediated apoptosis, in part, through differential regulation of MAPK pathways.

Nitric oxide as a regulator in preimplantation embryo development and apoptosis

OBJECTIVE

To investigate the mechanisms of nitric oxide (NO) in the development and apoptosis of preimplantation mouse embryos.

DESIGN

Prospective, controlled study.

SETTING

Medical college laboratory.

SUBJECT(S)

Two-cell embryos from outbred ICR mice.

INTERVENTION(S)

Hyperstimulation protocol, two-cell embryos were collected, then treated with or without an NO synthase inhibitor (L-NAME) or an NO donor (SNP) and combined with a cGMP analogue (8-Br-cGMP) or a selective inhibitor of NO-sensitive soluble guanylyl cyclase (ODQ).

MAIN OUTCOME MEASURE(S)

The development of ICR mouse embryo from two cells to blastocyst stages in vitro.

RESULT(S)

The development of blastocyst was inhibited by L-NAME in a concentration-dependent manner (0.1-10 microM) and 0.1 microM SNP reversed this effect (80.5% of control). Annexin-V/propidium iodide and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling techniques demonstrated that excessive NO (> or =10 microM) might induce apoptosis in the mouse embryos. 8-Br-cGMP reversed the inhibitory effect of L-NAME and rescued the embryo growth. ODQ inhibited the embryo development in a dose-responsive fashion (0.1--100 microM) but had no effect in the NO-induced embryo apoptosis. P53 and Bax were found to be up-regulated during the embryo fragmentation.

CONCLUSION(S)

These results indicate that the cGMP pathway might be involved in the NO-regulated embryonic development, but not in NO-induced apoptosis, for which P53/Bax pathway might be involved.

Nitric oxide attenuates H(2)O(2)-induced endothelial barrier dysfunction: mechanisms of protection

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated injury in porcine pulmonary artery endothelial cells (PAECs) and modulates intracellular levels of cGMP and cAMP. We hypothesized that.NO attenuates H(2)O(2)-induced PAEC monolayer barrier dysfunction through cyclic nucleotide-dependent signaling mechanisms. To examine this hypothesis, cultured PAEC monolayers were treated with H(2)O(2), and barrier function was measured as transmonolayer albumin clearance. H(2)O(2) caused significant PAEC barrier dysfunction that was attenuated by intracellular as well as extracellular.NO generation.NO increased PAEC cGMP and cAMP levels, but treatment with inhibitors of soluble guanylate cyclase or protein kinase G did not abrogate.NO-mediated barrier protection. In contrast, H(2)O(2) decreased protein kinase A activity, and inhibiting protein kinase A abrogated the protective effect of.NO. H(2)O(2)-induced barrier dysfunction was not associated with decreased levels of cGMP or cAMP. 3-Isobutyl-1-methylxanthine and the cGMP analog 8-bromo-cGMP had little effect on H(2)O(2)-mediated endothelial barrier dysfunction, whereas 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine was protective. These results indicate that.NO modulates vascular endothelial barrier function through cAMP-dependent signaling mechanisms.

Nitric oxide is a downstream mediator of agrin-induced acetylcholine receptor aggregation

The synaptic basal lamina protein, agrin, is required for the formation of the neuromuscular junction. Agrin signals through a muscle-specific receptor tyrosine kinase (MuSK) initiating a cascade of events that lead to the aggregation of acetylcholine receptors (AChR) at the postsynaptic site. Another important synaptic signalling molecule is nitric oxide (NO), which is produced by the enzyme, nitric oxide synthase (NOS). We investigated the interaction between the agrin signalling cascade and the NO signalling cascade by treating cultured myotubes with agrin, NOS inhibitors, and NO donors. NOS inhibitors prevented agrin induced AChR aggregation and phosphorylation of the AChR beta subunit. Furthermore, NO donors induced AChR aggregation in the absence of agrin, as well as phosphorylation of the AChR beta subunit. These results demonstrate a role for NO as a downstream mediator of agrin induced AChR aggregation and AChR beta subunit phosphorylation at the neuromuscular junction.

Erythropoietin regulates vascular smooth muscle cell apoptosis by a phosphatidylinositol 3 kinase-dependent pathway

BACKGROUND

Recent studies have shown that several cytokines could induce apoptosis in vascular smooth muscle cells (VSMCs) via the induction of nitric oxide (NO). In the present study, we explored whether human recombinant erythropoietin (rHuEPO) has a modulatory effect of apoptosis on interleukin-1beta (IL-1beta) or NO donor sodium nitroprusside (SNP)-induced apoptosis in rat cultured VSMCs.

METHODS

The quantitation of apoptosis among VSMCs was assessed by nuclear morphological analysis with fluorescent DNA-binding dye Hoechst 33258. Apoptotic changes were also confirmed by the detection of DNA fragmentation. The expression of EPO receptor (EpoR), cellular protein tyrosine phosphorylation, including EpoR and Janus kinase (JAK) 2, and the association of p85 subunit of phosphatidylinositol 3 kinase (PI3-kinase) to tyrosine-phosphorylated proteins, including EpoR, were explored by using Western blotting analysis combined in part with immunoprecipitation.

RESULTS

rHuEPO inhibited the apoptosis induced by IL-1beta or SNP in a dose- and time-dependent manner. The anti-apoptotic effects of rHuEPO were diminished in the presence of a tyrosine kinase (TK) inhibitor genistein or anti-EpoR antibody. After stimulation with rHuEPO, EpoR and JAK 2 were tyrosine phosphorylated, and p85 subunits were associated with EpoR. Also, rHuEPO induced phosphorylation of Akt through a PI3-kinase-dependent pathway. The phosphorylation of Akt and the anti-apoptotic effects of rHuEPO were diminished in the presence of a PI3-kinase inhibitor, wortmannin.

CONCLUSION

Our present study demonstrates that rHuEPO inhibites IL-1beta or SNP-induced VSMC apoptosis. The TK-dependent pathway, particularly the PI3-kinase-dependent pathway, seems to be critical to the countervailing effect of rHuEPO on IL-1beta and SNP-induced VSMC apoptosis.

Mechanisms of vascular atrophy and fibrous cap disruption

The process of plaque destabilization and rupture remains an area of intense investigation. While reductions in lumen cross-sectional area induced by early, non-occlusive lesions are compensated by remodeling and expansion of the artery, further plaque enlargement leads to an uncompensated reduction in lumen area and an increase in surface shearing forces. We hypothesize that these local increases in wall shear stress lead to a reduction in smooth muscle cell proliferation and increase in cell death. Using a primate prosthetic graft model, we have observed that alterations in nitric oxide and platelet-derived growth factor metabolism are important regulators of intimal growth and regression. We suggest that these factors may also be influential in the process of fibrous cap atrophy and plaque rupture.

Increased apoptosis susceptibility in mesangial cells from spontaneously hypertensive rats

We have examined the susceptibility to apoptosis in mesangial cells from spontaneously hypertensive rats (SHR) or from normotensive rats (WKY) and the possible involvement of nitric oxide in this process. Mesangial cells monolayers from either SHR or normal rats were incubated for 12 h in medium with or without fetal calf serum (FCS) and with or without thapsigargin (Tg, 10(-6) M). A series of cultures from rats of both groups was treated with N(G)-nitro-l-arginine methyl ester (l-NAME, 10(-4) M). We assessed apoptosis by propidium iodide staining, by TUNEL nitrite production (Griess reaction), by inducible nitric oxide synthase (iNOS) and Bcl-2 and Bax by Western blot. Incubated with a FCS-free medium, cells from SHR showed a significantly higher apoptotic rate (10.7 +/- 2.0) than with 10% FCS (10% FCS, 4.7 +/- 0.3), while WKY cells did not show this increment (10% FCS, 4.7 +/- 0.3; 0% FCS, 5.9 +/- 0. 3). Apoptosis in cells from WKY increased when incubated with thapsigargin in FCS-free medium (0% FCS+ Tg, 17.7 +/- 2.9%) and increased even more in SHR cells (0% FCS+ Tg, 19.7 +/- 2.9%). Treatment with l-NAME decreased thapsigargin-induced apoptosis in both SHR (8.2 +/- 2.4%) and WKY cells (9.3 +/- 2.4%). An increase in nitrite production and iNOS expression was detected in groups in which the apoptosis rate was elevated. A high rate of apoptosis was also associated with a decrease in the Bcl-2/Bax ratio. Our results indicate that in SHR cells, short-term serum deprivation and the increase in intracellular free calcium concentration with thapsigargin are able to enhance the apoptosis rate in primary cultures and that the expression of iNOS, and hence NO production, is involved in this effect.

Vegan proteins may reduce risk of cancer, obesity, and cardiovascular disease by promoting increased glucagon activity

Amino acids modulate the secretion of both insulin and glucagon; the composition of dietary protein therefore has the potential to influence the balance of glucagon and insulin activity. Soy protein, as well as many other vegan proteins, are higher in non-essential amino acids than most animal-derived food proteins, and as a result should preferentially favor glucagon production. Acting on hepatocytes, glucagon promotes (and insulin inhibits) cAMP-dependent mechanisms that down-regulate lipogenic enzymes and cholesterol synthesis, while up-regulating hepatic LDL receptors and production of the IGF-I antagonist IGFBP-1. The insulin-sensitizing properties of many vegan diets--high in fiber, low in saturated fat--should amplify these effects by down-regulating insulin secretion. Additionally, the relatively low essential amino acid content of some vegan diets may decrease hepatic IGF-I synthesis. Thus, diets featuring vegan proteins can be expected to lower elevated serum lipid levels, promote weight loss, and decrease circulating IGF-I activity. The latter effect should impede cancer induction (as is seen in animal studies with soy protein), lessen neutrophil-mediated inflammatory damage, and slow growth and maturation in children. In fact, vegans tend to have low serum lipids, lean physiques, shorter stature, later puberty, and decreased risk for certain prominent 'Western' cancers; a vegan diet has documented clinical efficacy in rheumatoid arthritis. Low-fat vegan diets may be especially protective in regard to cancers linked to insulin resistance--namely, breast and colon cancer--as well as prostate cancer; conversely, the high IGF-I activity associated with heavy ingestion of animal products may be largely responsible for the epidemic of 'Western' cancers in wealthy societies. Increased phytochemical intake is also likely to contribute to the reduction of cancer risk in vegans. Regression of coronary stenoses has been documented during low-fat vegan diets coupled with exercise training; such regimens also tend to markedly improve diabetic control and lower elevated blood pressure. Risk of many other degenerative disorders may be decreased in vegans, although reduced growth factor activity may be responsible for an increased risk of hemorrhagic stroke. By altering the glucagon/insulin balance, it is conceivable that supplemental intakes of key non-essential amino acids could enable omnivores to enjoy some of the health advantages of a vegan diet. An unnecessarily high intake of essential amino acids--either in the absolute sense or relative to total dietary protein--may prove to be as grave a risk factor for 'Western' degenerative diseases as is excessive fat intake.

Nitric oxide triggers programmed cell death (apoptosis) of adult rat ventricular myocytes in culture

Excessive nitric oxide (NO) production within the heart is implicated in the pathogenesis of myocyte death, but the mechanism whereby NO kills cardiac myocytes is not known. To determine whether NO may trigger programmed cell death (apoptosis) of adult rat ventricular myocytes in culture, the NO donor S-nitroso-N-acetylpenicillamine (SNAP) was shown to kill purified cardiac myocytes in a dose-dependent fashion. In situ analysis of ventricular myocytes plated on chamber slides using nick-end labeling of DNA demonstrated that SNAP induces cardiac myocyte apoptosis, which was confirmed by the identification of oligonucleosomal DNA fragmentation on agarose gel electrophoresis. Similarly, treatment of cardiac myocytes with cytokines that induce inducible NO synthase was shown to cause an NO-dependent induction of apoptosis. Addition of reduced hemoglobin to scavenge NO liberated by SNAP extinguished both the increase in percentage of apoptotic cells and the appearance of DNA ladders. Treatment with SNAP (but not with N-acetylpenicillamine or SNAP + hemoglobin) not only induced apoptosis but resulted in a marked increase in p53 expression in cardiac myocytes detected by Western blotting and immunohistochemistry. These data indicate that NO has the capacity to kill cardiac myocytes by triggering apoptosis and suggest the involvement of p53 in this process.

Aminoguanidine induces constrictive vascular remodeling and inhibits smooth muscle cell death after balloon injury

We examined the effects of aminoguanidine, an inhibitor of inducible nitric oxide synthase, in the rat model of balloon injury. Arteries were assessed by histomorphometry, and vascular smooth muscle cell death and proliferation were examined 24 h and 14 days after balloon injury by in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) of fragmented DNA and expression of proliferating cell nuclear antigen, respectively. Aminoguanidine decreased the luminal area 14 days after balloon injury (0.19+/-0.04 mm2 vs. 0.35+/-0.02 mmr2; P < 0.005), and this effect was attributable to reduction of the total vessel area, i.e., constrictive vascular remodeling (0.42+/-0.03 mm2 vs. 0.55+/-0.03 mm2; P < 0.005). At 24 h after injury, the percentage of TUNEL-positive cells in the medial layer was reduced by aminoguanidine (2.0+/-1.0% vs. 17.3+/-5.4%; P < 0.05), and the percentage of proliferating cells was increased (18.4+/-5.5% vs. 4.9+/-2.2%; P < 0.05). Aminoguanidine did not influence the density of VSMC nuclei in the injured artery wall, systemic blood pressure or endothelium-dependent vasorelaxation. We conclude, that in the rat model of balloon injury, aminoguanidine induces luminal loss by constrictive vascular remodeling in association with reduced early VSMC death and increased proliferation.

Nitric oxide mediates either proliferation or cell death in cardiomyocytes. Involvement of polyamines

Nitric oxide (NO) is a molecule involved in several signal transduction pathways leading either to proliferation or to cell death. Induction of ornithine decarboxylase (ODC), the key enzyme of polyamine biosynthesis, represents an early event preceding DNA synthesis. In some cell types increased ODC activity seems to be involved in cytotoxic response. We investigated the role of NO and ODC induction on the events linked to cell proliferation or to cell death in cultured chick embryo cardiomyocytes. Exposure of cardiomyocytes to tumor necrosis factor (TNF) and lipopolysaccharide (LPS) caused NO synthase (NOS) and ODC induction as well as increased incorporation of [3H]-thymidine. This last effect was blocked by a NOS inhibitor and was strongly reduced by difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. Sodium nitroprusside (SNP), an exogenous NO donor, inhibited the increases of NOS and ODC activities and abolished the mitogenic effect of TNF and LPS. Moreover, SNP alone caused cell death in a dose dependent manner. The cytotoxicity of SNP was not affected by DFMO while it was prevented by antioxidants. The results suggest that different pathways would mediate the response of cardiomyocytes to NO: they can lead either to ODC induction and DNA synthesis when NO is formed through NOS induction or to growth inhibition and cell death, when NO is supplied as NO donor. Increased polyamine biosynthesis would mediate the proliferative response of NO, while the cytotoxicity of exogenous NO seems to involve some oxidative reactions and to depend on the balance between NO availability and cellular redox mechanisms.

Nitric oxide and apoptosis

Apoptosis occurs during normal development of an organism but also plays an important role under pathophysiological conditions. Nitric oxide (NO) exhibits a double-edged role in apoptosis induction. Both pro- and antiapoptotic effects of NO have been demonstrated. The proapoptotic effects appear to be linked to pathophysiological conditions, where high concentrations of NO are produced by the inducible nitric oxide synthase, especially in macrophages. In contrast, NO also prevents apoptosis induction by various stimuli. The antiapoptotic effects thereby were mainly mediated by low amounts of NO or stimulation of the constitutive, endothelial nitric oxide synthase. The present review characterizes the apoptotic cell death program and aims to give a detailed insight into the function of NO in affecting apoptotic processes in biological systems, with special regards to the immune and cardiovascular systems.

In vitro cytotoxicity of the nitric oxide donor, S-nitroso-N-acetyl-penicillamine, towards cells from human oral tissue

The cytotoxicity of the nitric oxide donor, S-nitroso-N-acetyl-penicillamine (SNAP), towards cultured human cells from oral tissue was evaluated. The toxicity of SNAP to Smulow-Glickman gingival epithelial cells was correlated with the liberation of nitric oxide, as N-acetyl-D,L-penicillamine, the SNAP metabolites, N-acetyl-D,L-penicillamine disulfide and nitrite, and preincubated (denitrosylated) SNAP did not affect viability. Comparing equimolar concentrations of various nitric oxide donors, cytotoxicity appeared to be inversely related to the relative stability (i.e., half-life) of the test compound; the sequence of cytotoxicity for a 4 hr exposure was S-nitrosoglutathione>>spermine NONOate> SNAP>DPTA NONOate>>DETA NONOate. Intracellular reduced glutathione (GSH) was lowered in S-G cells exposed to SNAP. Pretreatment of the cells with the GSH depleter, 1,3-bis-(chloroethyl)-1-nitrosourea (BCNU), enhanced the toxicity of SNAP Similar findings of enhanced sensitivity to SNAP were noted with gingival fibroblasts and periodontal ligament cells pretreated with BCNU. The toxicity of SNAP towards the gingival epithelial cells was decreased by cotreatment with the antioxidants, N-acetyl-L-cysteine, L-ascorbic acid, and (+)-catechin. Cells exposed to SNAP exhibited nuclear aberrations, including multilobed nuclei and multinucleation. SNAP-induced cell death was apparently by apoptosis, as noted by fluorescence microscopy and DNA agarose gel electrophoresis.

Ceramide generation in nitric oxide-induced apoptosis. Activation of magnesium-dependent neutral sphingomyelinase via caspase-3

Sodium nitroprusside (SNP), a NO donor, has been recognized as an inducer of apoptosis in various cell lines. Here, we demonstrated the intracellular formation of ceramide, a lipid signal mediator, in SNP-induced apoptosis in human leukemia HL-60 cells and investigated the mechanisms of ceramide generation. The levels of intracellular ceramide increased to, at most, 160% of the control level in a time- and dose-dependent manner when the cells were treated with 1 mM SNP. SNP also decreased the sphingomyelin level to approximately 70% of the control level and increased magnesium-dependent neutral sphingomyelinase (N-SMase) activity to 160% of the control activity 2 h after treatment. Neither acid SMase nor magnesium-independent N-SMase was affected by SNP. Caspases are thought to be key enzymes in apoptotic cell death. Acetyl-Asp-Glu-Val-Asp-aldehyde, a synthetic tetrapeptide inhibitor of caspases, inhibited magnesiumdependent N-SMase, ceramide generation, and apoptosis. Moreover, recombinant purified caspase-3 increased magnesium-dependent N-SMase in a cell-free system. These results suggest that the findings that SNP increased ceramide generation and magnesium-dependent N-SMase activity via caspase-3 are interesting to future study to determine the relation between caspases and sphingolipid metabolites in NO-mediated signaling.

Nitric oxide induces apoptotic death of cardiomyocytes via a cyclic-GMP-dependent pathway

Recently, we have reported that excess amounts of nitric oxide (NO) produced by inducible NO synthase are involved in the development of myocardial damage in rats with induced myocarditis. However, there remain many problems to be solved concerning its mechanism of action. In this study, we examined whether NO induces apoptotic cell death in cardiomyocytes. Cultured neonatal rat cardiomyocytes were exposed to S-nitroso-N-acetylpenicillamine (SNAP) and (+/-)-E-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamine (NOR 3), as NO donors, or 8-bromo-cyclic GMP (cGMP), an analog of cGMP which functions as a second messenger in cells stimulated by NO. DNA fragmentation was confirmed by electron microscopy, by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) method, and by agarose gel electrophoresis. Exogenously supplied SNAP or NOR 3 induced cardiomyocyte apoptosis in a dose- and time-dependent manner. Cardiomyocytes exposed to SNAP displayed typical features of apoptosis as demonstrated by electron microscopy. Treatment of the cells with 8-bromo-cGMP also induced apoptosis. In cardiomyocytes, SNAP-induced apoptosis was completely blocked by a PKG inhibitor (KT5823) and by a soluble guanylate cyclase inhibitor (ODQ) and was suppressed by hemoglobin and was completely blocked by ZVAD-FMK, a caspase inhibitor. These results show that NO-mediated apoptosis of cardiomyocytes is cGMP dependent and that caspases are involved in this process.

Nitric oxide reduces nontransferrin-bound iron transport in HepG2 cells

Nitric oxide (NO) donors S-nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprusside (SNP) modulate iron regulatory protein (IRP) activity and may, therefore, affect iron uptake through transferrin receptor expression. However, iron also enters the cell as nontransferrin-bound iron (NTBI), and the aim of this study was to evaluate the effects of NO donors on NTBI transport in HepG2 cells, a model of liver physiology. Incubation with SNP and SNAP led to a time- and concentration-dependent reduction in Fe3+ and Fe2+ uptake, thus indicating an effect on the transporter rather than on the reductase. In terms of Fe2+ uptake, no variations in the Michaelis-Menten constant (Km) and a reduction in maximum uptake (Vmax) (50, 33, and 16.6 fmol/microgram protein/min in control, SNP-, and SNAP-treated cells, respectively) were detected, which suggested a decrease in the number of putative NTBI transport protein(s). Gel shift assays showed that IRP activity was reduced by SNP and slightly increased by SNAP. Northern blot analysis of transferrin receptor messenger RNA (mRNA) levels showed variations similar to those observed for IRPs, but both NO donors increased L-ferritin mRNA levels and had no effect on the stimulator of Fe transport (SFT) mRNA. In conclusion, NO donors significantly reduce NTBI transport in HepG2 cells, an effect that seems to be IRP and SFT independent. Moreover, the reduction in NTBI uptake after NO treatment suggests that this form of iron may play a minor role in the increased hepatic iron stores observed in inflammation or that other liver cells are more involved in this pathological condition.

Apoptosis. Basic concepts and implications in coronary artery disease

Apoptosis is an active form of cell death that is intricately regulated and distinct from necrosis. Data suggest that apoptosis may play a role in the pathophysiology of coronary atherosclerotic disease. Anatomic evidence of apoptosis has been observed in coronary atherosclerosis, restenosis, and transplant arteriopathy, accompanied by an increase in biochemical and genetic markers of apoptosis. Vasoactive substances such as nitric oxide and angiotensin II also regulate vascular smooth muscle cell apoptosis; vasodilating factors may induce apoptosis, whereas vasoconstricting factors may inhibit apoptosis. The aim of this article is to review key points regarding the detection of apoptosis, its regulation, and its possible role in the pathogenesis of coronary artery disease.

Adenovirus-mediated gene transfer of cGMP-dependent protein kinase increases the sensitivity of cultured vascular smooth muscle cells to the antiproliferative and pro-apoptotic effects of nitric oxide/cGMP

Studies in vitro have underestimated the importance of cGMP-dependent protein kinase (PKG) in the modulation of vascular smooth muscle cell (SMC) proliferation and apoptosis in vivo. This is attributable, in part, to a rapid decline in PKG levels as vascular SMC are passaged in culture. We used a recombinant adenovirus encoding PKG (Ad.PKG) to augment kinase activity in cultured rat pulmonary artery SMC (RPaSMC). Incubation of Ad. PKG-infected RPaSMC (multiplicity of infection = 200) with 8-Br-cGMP decreased serum-stimulated DNA synthesis by 85% and cell proliferation at day 5 by 74%. The effect of 8-Br-cGMP on DNA synthesis in Ad.PKG-infected RPaSMC was blocked by KT5823 (PKG inhibitor), but not by KT5720 (cAMP-dependent protein kinase inhibitor). A nitric oxide (NO) donor compound, S-nitrosoglutathione, at concentrations as low as 100 nM, inhibited DNA synthesis in Ad. PKG-infected RPaSMC, but not in uninfected cells or in cells infected with a control adenovirus. In addition, 8-Br-cGMP and S-nitrosoglutathione induced apoptosis in serum-deprived RPaSMC infected with Ad.PKG, but not in uninfected cells or in cells infected with a control adenovirus. These results demonstrate that modulation of PKG levels in vascular SMC can alter the sensitivity of these cells to NO and cGMP. Moreover, these observations suggest an important role for PKG in the regulation of vascular SMC proliferation and apoptosis by NO and cGMP.