Inhibition of oxidized low-density lipoprotein-induced apoptosis in endothelial cells by nitric oxide. Peroxyl radical scavenging as an antiapoptotic mechanism

Liquid plasma as a treatment for cutaneous wound healing through regulation of redox metabolism

The skin functions as the outermost protective barrier to the internal organs and major vessels; thus, delayed regeneration from acute injury could induce serious clinical complications. For rapid recovery of skin wounds, promoting re-epithelialization of the epidermis at the initial stage of injury is essential, wherein epithelial keratinocytes act as leading cells via migration. This study applied plasma technology, which has been known to enable wound healing in the medical field. Through in vitro and in vivo experiments, the study elucidated the effect and molecular mechanism of the liquid plasma (LP) manufactured by our microwave plasma system, which was found to improve the applicability of existing gas-type plasma on skin cell migration for re-epithelialization. LP treatment promoted the cytoskeletal transformation of keratinocytes and migration owing to changes in the expression of integrin-dependent focal adhesion molecules and matrix metalloproteinases (MMPs). This study also identified the role of increased levels of intracellular reactive oxygen species (ROS) as a driving force for cell migration activation, which was regulated by changes in NADPH oxidases and mitochondrial membrane potential. In an in vivo experiment using a murine dorsal full-thickness acute skin wound model, LP treatment helped improve the re-epithelialization rate, reaffirming the activation of the underlying intracellular ROS-dependent integrin-dependent signaling molecules. These findings indicate that LP could be a valuable wound management material that can improve the regeneration potential of the skin via the activation of migration-related molecular signaling within the epithelial cell itself with plasma-driven oxidative eustress.

Involvement of Nitric Oxide in Protecting against Radical Species and Autoregulation of M1-Polarized Macrophages through Metabolic Remodeling

When the expression of NOS2 in M1-polarized macrophages is induced, huge amounts of nitric oxide (•NO) are produced from arginine and molecular oxygen as the substrates. While anti-microbial action is the primary function of M1 macrophages, excessive activation may result in inflammation being aggravated. The reaction of •NO with superoxide produces peroxynitrite, which is highly toxic to cells. Alternatively, however, this reaction eliminates radial electrons and may occasionally alleviate subsequent radical-mediated damage. Reactions of •NO with lipid radicals terminates the radical chain reaction in lipid peroxidation, which leads to the suppression of ferroptosis. •NO is involved in the metabolic remodeling of M1 macrophages. Enzymes in the tricarboxylic acid (TCA) cycle, notably aconitase 2, as well as respiratory chain enzymes, are preferential targets of •NO derivatives. Ornithine, an alternate compound produced from arginine instead of citrulline and •NO, is recruited to synthesize polyamines. Itaconate, which is produced from the remodeled TCA cycle, and polyamines function as defense systems against overresponses of M1 macrophages in a feedback manner. Herein, we overview the protective aspects of •NO against radical species and the autoregulatory systems that are enabled by metabolic remodeling in M9-polarized macrophages.

ZAKβ Alleviates Oxidized Low-density Lipoprotein (ox-LDL)-Induced Apoptosis and B-type Natriuretic Peptide (BNP) Upregulation in Cardiomyoblast

Oxidized low-density lipoprotein (ox-LDL) is a type of modified cholesterol that promotes apoptosis and inflammation and advances the progression of heart failure. Leucine-zipper and sterile-α motif kinase (ZAK) is a kinase of the MAP3K family which is highly expressed in the heart and encodes two variants, ZAKα and ZAKβ. Our previous study serendipitously found opposite effects of ZAKα and ZAKβ in which ZAKβ antagonizes ZAKα-induced apoptosis and hypertrophy of the heart. This study aims to test the hypothesis of whether ZAKα and ZAKβ are involved in the damaging effects of ox-LDL in the cardiomyoblast. Cardiomyoblast cells H9c2 were treated with different concentrations of ox-LDL. Cell viability and apoptosis were measured by MTT and TUNEL assay, respectively. Western blot was used to detect apoptosis, hypertrophy, and pro-survival signaling proteins. Plasmid transfection, pharmacological inhibition with D2825, and siRNA transfection were utilized to upregulate or downregulate ZAKβ, respectively. Ox-LDL concentration-dependently reduces the viability and expression of several pro-survival proteins, such as phospho-PI3K, phospho-Akt, and Bcl-xL. Furthermore, ox-LDL increases cleaved caspase-3, cleaved caspase-9 as indicators of apoptosis and increases B-type natriuretic peptide (BNP) as an indicator of hypertrophy. Overexpression of ZAKβ by plasmid transfection attenuates apoptosis and prevents upregulation of BNP. Importantly, these effects were abolished by inhibiting ZAKβ either by D2825 or siZAKβ application. Our results suggest that ZAKβ upregulation in response to ox-LDL treatment confers protective effects on cardiomyoblast.

Superoxide Radicals in the Execution of Cell Death

Superoxide is a primary oxygen radical that is produced when an oxygen molecule receives one electron. Superoxide dismutase (SOD) plays a primary role in the cellular defense against an oxidative insult by ROS. However, the resulting hydrogen peroxide is still reactive and, in the presence of free ferrous iron, may produce hydroxyl radicals and exacerbate diseases. Polyunsaturated fatty acids are the preferred target of hydroxyl radicals. Ferroptosis, a type of necrotic cell death induced by lipid peroxides in the presence of free iron, has attracted considerable interest because of its role in the pathogenesis of many diseases. Radical electrons, namely those released from mitochondrial electron transfer complexes, and those produced by enzymatic reactions, such as lipoxygenases, appear to cause lipid peroxidation. While GPX4 is the most potent anti-ferroptotic enzyme that is known to reduce lipid peroxides to alcohols, other antioxidative enzymes are also indirectly involved in protection against ferroptosis. Moreover, several low molecular weight compounds that include α-tocopherol, ascorbate, and nitric oxide also efficiently neutralize radical electrons, thereby suppressing ferroptosis. The removal of radical electrons in the early stages is of primary importance in protecting against ferroptosis and other diseases that are related to oxidative stress.

Fatty acid nitration in human low-density lipoprotein

Lipid nitration occurs during physiological and pathophysiological conditions, generating a variety of biomolecules capable to modulate inflammatory cell responses. Low-density lipoprotein (LDL) oxidation has been extensively related to atherosclerotic lesion development while oxidative modifications confer the particle pro-atherogenic features. Herein, we reviewed the oxidation versus nitration of human LDL protein and lipid fractions. We propose that unsaturated fatty acids present in LDL can be nitrated under mild nitration conditions, suggesting an anti-atherogenic role for LDL carrying nitro-fatty acids (NFA).

Lovastatin exerts protective effects on endothelial cells via upregulation of PTK2B

Statins are HMG-CoA reductase inhibitors that are used to decrease the blood levels of low-density lipoprotein (LDL). In addition, they have been shown to exert pleiotropic protective effects in the absence of LDL-lowering activity. The present study investigated the effects of lovastatin on global gene expression in human umbilical vein endothelial cells (HUVECs), in order to further explore its ability to protect against oxidized (ox)-LDL-induced cytotoxicity. HUVECs were treated with lovastatin for 2–24 h, and gene expression patterns were analyzed using cDNA microarrays. The results suggested that numerous genes were regulated by lovastatin, including certain genes associated with cell survival, such as PTK2B, BCL2 and MAP3K3. In particular, PTK2B, which has been shown to exert anti-apoptotic effects against ox-LDL-induced cell injury, was upregulated by lovastatin. Knockdown of PTK2B was able to attenuate ox-LDL-induced cell injury, and this was associated with decreased levels of phosphorylated-AKT and eNOS, and inhibition of mitochondrial-dependent apoptosis. In conclusion, the results of the present study suggested that lovastatin protects against ox-LDL-induced cell injury, potentially via the upregulation of PTK2B, which regulates the anti-apoptosis signaling pathway.

Mitochondria-targeted esculetin alleviates mitochondrial dysfunction by AMPK-mediated nitric oxide and SIRT3 regulation in endothelial cells: potential implications in atherosclerosis

Mitochondria-targeted compounds are emerging as a new class of drugs that can potentially alter the pathophysiology of those diseases where mitochondrial dysfunction plays a critical role. We have synthesized a novel mitochondria-targeted esculetin (Mito-Esc) with an aim to investigate its effect during oxidative stress-induced endothelial cell death and angiotensin (Ang)-II-induced atherosclerosis in ApoE^−/− mice. Mito-Esc but not natural esculetin treatment significantly inhibited H2O2- and Ang-II-induced cell death in human aortic endothelial cells by enhancing NO production via AMPK-mediated eNOS phosphorylation. While L-NAME (NOS inhibitor) significantly abrogated Mito-Esc-mediated protective effects, Compound c (inhibitor of AMPK) significantly decreased Mito-Esc-mediated increase in NO production. Notably, Mito-Esc promoted mitochondrial biogenesis by enhancing SIRT3 expression through AMPK activation; and restored H2O2-induced inhibition of mitochondrial respiration. siSIRT3 treatment not only completely reversed Mito-Esc-mediated mitochondrial biogenetic marker expressions but also caused endothelial cell death. Furthermore, Mito-Esc administration to ApoE^−/− mice greatly alleviated Ang-II-induced atheromatous plaque formation, monocyte infiltration and serum pro-inflammatory cytokines levels. We conclude that Mito-Esc is preferentially taken up by the mitochondria and preserves endothelial cell survival during oxidative stress by modulating NO generation via AMPK. Also, Mito-Esc-induced SIRT3 plays a pivotal role in mediating mitochondrial biogenesis and perhaps contributes to its anti-atherogenic effects.

Antihypertensive Effect of a Combination of Uracil and Glycerol Derived from Lactobacillus plantarum Strain TWK10-Fermented Soy Milk

We previously demonstrated that angiotensin-converting enzyme (ACE) could be inhibited by soy milk that had been fermented with the Lactobacillus plantarum strain TWK10, suggesting great potential for the development of antihypertensive products. In this work, the bioactive ACE inhibitors in TWK10-fermented soy milk water extracts were isolated, and a combination of uracil and glycerol (CUG) was identified as one of the ACE inhibitors. We then examined the physiological effects of CUG treatment in short-term and long-term studies using spontaneously hypertensive rats (SHRs) as an experimental model. The results revealed that the fermented soy milk extracts and CUG decreased blood pressure by 11.97 ± 3.71 to 19.54 ± 9.54 mmHg, 8 h after oral administration, and exhibited antihypertensive effects in SHRs in a long-term study. In addition, CUG was shown to decrease blood pressure by suppressing either the renin activity or the ACE activity and, thus, decreasing the downstream vasoconstricting peptide angiotensin II and the hormone aldosterone. CUG also promoted nitric oxide production, resulting in vasodilation and further improvement to hypertension. This important finding suggests that TWK10-fermented soy milk and its functional ingredients, uracil and glycerol, exhibit antihypertensive effects via multiple pathways and provide a healthier and more natural antihypertensive functional food.

Statin‐induced inhibition of breast cancer proliferation and invasion involves attenuation of iron transport: intermediacy of nitric oxide and antioxidant defence mechanisms

Accumulating evidence from in vitro, in vivo, clinical and epidemiological studies shows promising results for the use of statins against many cancers including breast carcinoma. However, the molecular mechanisms responsible for the anti‐proliferative and anti‐invasive properties of statins still remain elusive. In this study, we investigated the involvement of nitric oxide, iron homeostasis and antioxidant defence mechanisms in mediating the anti‐proliferative and anti‐invasive properties of hydrophobic statins in MDA‐MB‐231, MDA‐MB‐453 and BT‐549 metastatic triple negative breast cancer cells. Fluvastatin and simvastatin significantly increased cytotoxicity which was reversed with mevalonate. Interestingly, fluvastatin downregulated transferrin receptor (TfR1), with a concomitant depletion of intracellular iron levels in these cells. Statin‐induced effects were mimicked by geranylgeranyl transferase inhibitor (GGTI‐298) but not farnesyl transferase inhibitor (FTI‐277). Further, it was observed that TfR1 downregulation is mediated by increased nitric oxide levels via inducible nitric oxide synthase (iNOS) expression. NOS inhibitors (asymmetric dimethylarginine and 1400W) counteracted and sepiapterin, a precursor of tetrahydrobiopterin, exacerbated statin‐induced depletion of intracellular iron levels. Notably, fluvastatin increased manganese superoxide dismutase (by repressing the transcription factor DNA damage‐binding protein 2), catalase and glutathione which, in turn, diminished H2O2 levels. Fluvastatin‐induced downregulation of TfR1, matrix metalloproteinase‐2, ‐9 and inhibition of invasion were reversed in the presence of aminotriazole, a specific inhibitor of catalase. Finally, we conclude that fluvastatin, by altering iron homeostasis, nitric oxide generation and antioxidant defence mechanisms, induces triple negative breast cancer cell death.

Statin-induced inhibition of breast cancer proliferation and invasion involves attenuation of iron transport: intermediacy of nitric oxide and antioxidant defence mechanisms

Accumulating evidence from in vitro, in vivo, clinical and epidemiological studies shows promising results for the use of statins against many cancers including breast carcinoma. However, the molecular mechanisms responsible for the anti-proliferative and anti-invasive properties of statins still remain elusive. In this study, we investigated the involvement of nitric oxide, iron homeostasis and antioxidant defence mechanisms in mediating the anti-proliferative and anti-invasive properties of hydrophobic statins in MDA-MB-231, MDA-MB-453 and BT-549 metastatic triple negative breast cancer cells. Fluvastatin and simvastatin significantly increased cytotoxicity which was reversed with mevalonate. Interestingly, fluvastatin downregulated transferrin receptor (TfR1), with a concomitant depletion of intracellular iron levels in these cells. Statin-induced effects were mimicked by geranylgeranyl transferase inhibitor (GGTI-298) but not farnesyl transferase inhibitor (FTI-277). Further, it was observed that TfR1 downregulation is mediated by increased nitric oxide levels via inducible nitric oxide synthase (iNOS) expression. NOS inhibitors (asymmetric dimethylarginine and 1400W) counteracted and sepiapterin, a precursor of tetrahydrobiopterin, exacerbated statin-induced depletion of intracellular iron levels. Notably, fluvastatin increased manganese superoxide dismutase (by repressing the transcription factor DNA damage-binding protein 2), catalase and glutathione which, in turn, diminished H2 O2 levels. Fluvastatin-induced downregulation of TfR1, matrix metalloproteinase-2, -9 and inhibition of invasion were reversed in the presence of aminotriazole, a specific inhibitor of catalase. Finally, we conclude that fluvastatin, by altering iron homeostasis, nitric oxide generation and antioxidant defence mechanisms, induces triple negative breast cancer cell death.

The effect of probiotic-fermented soy milk on enhancing the NO-mediated vascular relaxation factors

BACKGROUND

Soy milk is one of the common soy-based foods in Asia. In this study the effects of soy milk fermented with selected probiotics on nitric oxide (NO)-mediated vascular relaxation factors in cell model systems were investigated.

RESULTS

Soy milk fermented with Lactobacillus plantarum TWK10 or Streptococcus thermophilus BCRC 14085 for 48 h showed a greater transformation of glucoside isoflavones to aglycone isoflavones (P < 0.05). An increase in aglycone isoflavones in ethanol extracts from fermented soy milk stimulated NO production and endothelial NO synthase (eNOS) activity in human umbilical vein endothelial cells. It also had a stimulating effect on superoxide anion scavenging and prostaglandin E₂ production. In addition, it enhanced mRNA expression of the E-prostanoid 4 receptor in rat thoracic aorta smooth muscle cells. Moreover, a small amount of O₂⁻ induced by water extracts from fermented soy milk at low concentration (1 mg mL⁻¹) increased the content of calcium ions and activated eNOS, thereby promoting NO production and the coupling state of eNOS.

CONCLUSION

Soy milk fermented with selected probiotics promotes the relaxation factors of vascular endothelial cells and can be applied in the development of functional foods.

Survival and Fertility of Boar Spermatozoa After Freeze-Thawing in Extender Supplemented With Butylated Hydroxytoluene

This study evaluated the protective effect of butylated hydroxytoluene (BHT), a lipid-soluble antioxidant, against cryopreservation injuries to boar spermatozoa. In experiment 1, the lowest BHT concentrations able to reduce lipid peroxidation in boar spermatozoa were determined. Nine BHT concentrations (ranging from 0.025 to 3.2 mM) were evaluated, and the lowest (P <.05) production of malondialdehyde (MDA), as an indicator of lipid peroxidation, was obtained when BHT ranged from 0.2 to 1.6 mM. In experiment 2, sperm survivability was evaluated when BHT was added to a postthaw freezing extender by measuring the degree of sperm lipid peroxidation (using MDA production) and by measuring parameter such as motility, plasma membrane and acrosome integrity, and cell apoptosis. The ability of thawed spermatozoa to fertilize in vitro-matured oocytes and of embryos to develop to the blastocyst stage in vitro was also assessed. Pooled sperm-rich fractions collected from 3 mature Pietrain boars were frozen in 0.5-mL straws after dilution with lactose-egg yolk-glycerol-Orvus ES Paste extender supplemented with 0, 0.2, 0.4, 0.8, and 1.6 mM BHT. Postthaw sperm survival, evaluated 30 and 150 minutes after thawing, was higher in BHT-treated spermatozoa, being significant (P <.05) when the freezing extender was supplemented with 0.2, 0.4, and 0.8 mM BHT. The addition of BHT to the freezing extender resulted in a significant (P <.05) decrease in the MDA concentration in thawed spermatozoa, irrespective of the level of BHT used. BHT had no effect on oocyte cleavage rates, but the development to blastocyst was improved for embryos derived from spermatozoa frozen in extender supplemented with 0.4 mM BHT (16% vs 29% of blastocysts per total oocytes; P <.05). In conclusion, under the conditions tested in the present study, the addition of BHT to the freezing extender improved the overall efficiency of thawed boar spermatozoa.

Early intervention of tyrosine nitration prevents vaso-obliteration and neovascularization in ischemic retinopathy

Diabetic retinopathy and retinopathy of prematurity are blinding disorders that follow a pathological pattern of ischemic retinopathy and affect premature infants and working-age adults. Yet, the treatment options are limited to laser photocoagulation. The goal of this study is to elucidate the molecular mechanism and examine the therapeutic effects of inhibiting tyrosine nitration on protecting early retinal vascular cell death and late neovascularization in the ischemic retinopathy model. Ischemic retinopathy was developed by exposing neonatal mice to 75% oxygen [postnatal day (p) 7-p12] followed by normoxia (21% oxygen) (p12-p17). Peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTPPS) (1 mg/kg), the nitration inhibitor epicatechin (10 mg/kg) or the thiol donor N-acetylcysteine (NAC, 150 mg/kg) were administered (p7-p12) or (p7-p17). Vascular endothelial cells were incubated at hyperoxia (40% oxygen) or normoxia (21% oxygen) for 48 h. Vascular density was determined in retinal flat mounts labeled with isolectin B4. Expression of vascular endothelial growth factor, caspase-3, and poly(ADP ribose) polymerase (PARP), activation of Akt and p38 mitogen-activated protein kinase (MAPK), and tyrosine nitration of the phosphatidylinositol (PI) 3-kinase p85 subunit were analyzed by Western blot. Hyperoxia-induced peroxynitrite caused endothelial cell apoptosis as indicated by expression of cleaved caspase-3 and PARP leading to vaso-obliteration. These effects were associated with significant tyrosine nitration of the p85 subunit of PI 3-kinase, decreased Akt activation, and enhanced p38 MAPK activation. Blocking tyrosine nitration of PI 3-kinase with epicatechin or NAC restored Akt phosphorylation, and inhibited vaso-obliteration at p12 and neovascularization at p17 comparable with FeTPPS. Early inhibition of tyrosine nitration with use of epicatechin or NAC can represent safe and effective vascular-protective agents in ischemic retinopathy.

Review

Production of superoxide anion O2*- by the membrane-bound enzyme NADPH oxidase of phagocytes is a long-known phenomenon; it is generally assumed that O2*-helps phagocytes kill bacterial intruders. The details and the chemistry of the killing process have, however, remained a mystery. Isoforms of NADPH oxidase exist in membranes of nearly every cell, suggesting that reactive oxygen species (ROS) participate in intra- and intercellular signaling processes. What the nature of the signal is exactly, how it is transmitted, and what structural characteristics a receptor of a "radical message" must have, have not been addressed convincingly. This review discusses how the action of messengers is in agreement with radical-specific behavior. In search for the smallest common denominator of cellular free radical activity we hypothesize that O2*- and its conjugate acid, HO2*, may have evolved under primordial conditions as regulators of membrane mechanics and that isoprostanes, widely used markers of "oxidative stress", may be an adventitious correlate of this biologic activity of O2*-/HO2*. An overall picture is presented that suggests that O2*-/HO2* radicals, by modifying cell membranes, help other agents gain access to the hydrophobic region of phospholipid bilayers and hence contribute to lipid-dependent signaling cascades. With this, O2*-/HO2* are proposed as indispensable adjuvants for the generation of cellular signals, for membrane transport, channel gating and hence, in a global sense, for cell viability and growth. We also suggest that many of the allegedly O2*- dependent bacterial pathologies and carcinogenic derailments are due to membrane-modifying activity rather than other chemical reactions of O2*-/HO2*. A consequence of this picture is the potential evolution of the "radical theory of ageing" to a "lipid theory of aging".

L-Xylulose reductase is involved in 9,10-phenanthrenequinone-induced apoptosis in human T lymphoma cells

9,10-Phenanthrenequinone (9,10-PQ), a major component in diesel exhaust particles, is suggested to generate reactive oxygen species (ROS) through its redox cycling, leading to cell toxicity. l-Xylulose reductase (XR), a NADPH-dependent enzyme in the uronate pathway, strongly reduces alpha-dicarbonyl compounds and was thought to act as a detoxification enzyme against reactive carbonyl compounds. Here, we have investigated the role of intracellular ROS generation in apoptotic signaling in human acute T-lymphoblastic leukemia MOLT-4 cells treated with 9,10-PQ and the role of XR in the generation of ROS. Treatment with 9,10-PQ elicited not only apoptotic signaling, including mitochondrial membrane dysfunction and activation of caspases and poly(ADP-ribose) polymerase, but also intracellular ROS generation and consequent glutathione depletion. The apoptotic effects of 9,10-PQ were drastically mitigated by pretreatment with intracellular ROS scavengers, such as N-acetyl-l-cysteine, glutathione monoethyl ester, and polyethylene glycol-conjugated catalase, indicating that intracellular ROS generation is responsible for the 9,10-PQ-evoked apoptosis. Surprisingly, the ROS generation and cytotoxicity by 9,10-PQ were augmented in an XR-transformed cell line. XR indeed reduced 9,10-PQ and produced superoxide anion through redox cycling. In addition, the expression levels of XR and its mRNA in the T lymphoma cells were markedly enhanced after the exposure to 9,10-PQ, and the induction was completely abolished by the ROS scavengers. Moreover, the 9,10-PQ-induced apoptosis was partially inhibited by the pretreatment with XR-specific inhibitors. These results suggest that initially produced ROS induce XR, which accelerates the generation of ROS.

Magnesium tanshinoate B protects endothelial cells against oxidized lipoprotein-induced apoptosisThis article is one of a selection of papers published in this special issue (part 2 of 2) on the Safety and Efficacy of Natural Health Products

The activation of c-Jun N-terminal kinase (JNK) signaling pathway plays an important role in the induction of cell apoptosis. We previously reported that magnesium tanshinoate B (MTB), a compound purified from a Chinese herb danshen ( Salvia miltiorrhiza ), could inhibit ischemia/reperfusion-induced myocyte apoptosis in the heart. The objective of the present study was to investigate whether MTB can prevent oxidized lipoprotein-induced apoptosis in endothelial cells. Human umbilical vein endothelial cells (HUVECs) were incubated with copper-oxidized very low density lipoprotein (Cu-OxVLDL) or copper-oxidized low density lipoprotein (Cu-OxLDL). Treatment of cells with Cu-OxVLDL or Cu-OxLDL resulted in a 3-fold increase in the JNK activity. The amount of cytochrome c released and the activity of caspase-3 in cells treated with Cu-OxVLDL or Cu-OxLDL were significantly elevated, indicating the occurrence of apoptosis. The presence of MTB was able to abolish the JNK activation, cytochrome c release, and caspase-3 activation induced by Cu-OxVLDL or Cu-OxLDL, resulting in a marked reduction in apoptosis in endothelial cells. The data from this study indicate that oxidized lipoproteins induce apoptosis in endothelial cells. We postulate that the inhibition of the JNK signaling pathway by MTB is a key mechanism that protects these cells from oxidized lipoprotein-induced apoptosis.

Oxidized low density lipoprotein receptor-1 mediates oxidized low density lipoprotein-induced apoptosis in human umbilical vein endothelial cells: Role of reactive oxygen species

Studies have shown that oxidized low density lipoprotein (ox-LDL) elicits both necrotic and apoptotic cell death and several mechanisms have been proposed. Ox-LDL induces reactive oxygen species (ROS), a second messenger that might be involved in apoptosis, formation in different types of cells including endothelial cells (ECs) and smooth muscle cells (SMCs). As lectin-like ox-LDL receptor-1 (LOX-1) was the main receptor for ox-LDL, this study was designed to determine whether the apoptosis induced by ox-LDL was mediated by LOX-1 in cultured human umbilical vein endothelial cells (HUVECs) and whether there is an association between LOX-1 mediated apoptosis and the production of ROS. After exposure to ox-LDL (50,100, and 150 microg/ml for 18 h), HUVECs exhibit typical apoptotic characteristics as determined by transmission electron microscopy and flow cytometry analysis in a dose-dependent pattern. Ox-LDL increases intracellular ROS formation including superoxide anion (O2-) and hydrogen peroxide (H2O2) in a dose-dependent and time-dependent manner. Pretreatment with anti-LOX-1 mAb, Vitamin C, apocynin or catalase significantly reduced ROS production and prevented ox-LDL-induced apoptosis, while indomethacin or allopurinol had no effect. These results suggest that LOX-1 mediates ox-LDL-induced apoptosis in endothelial cells and that ROS production and NADPH oxidase might play an important role in ox-LDL-induced apoptosis.

Proteome analysis suggests that mitochondrial dysfunction in stressed endothelial cells is reversed by a soy extract and isolated isoflavones

Apoptosis is a driving force in atherosclerosis development. A soy extract or a combination of the soy isoflavones genistein and daidzein inhibited apoptosis induced by oxidized LDL in endothelial cells. Proteome analysis revealed that the LDL-induced alterations of numerous proteins were reversed by the extract and the genistein/daidzein mixture but only three protein entities, all functionally linked to mitochondrial dysfunction, were regulated in common by both treatments.

Hydrogen peroxide induces nitric oxide and proteosome activity in endothelial cells: a bell-shaped signaling response

We investigated nitric oxide (*NO)-mediated proteosomal activation in bovine aortic endothelial cells (BAEC) treated with varying fluxes of hydrogen peroxide (H(2)O(2)) generated from glucose/glucose oxidase (Glu/GO). Results revealed a bell-shaped *NO signaling response in BAEC treated with Glu/GO (2-20 mU/ml). GO treatment (2 mU/ml) enhanced endothelial nitric oxide synthase (eNOS) phosphorylation and *NO release in BAEC. With increasing GO concentrations, phospho eNOS and *NO levels decreased. Bell-shaped responses in proteasomal function and *NO induction were observed in BAEC treated with varying levels of GO (2-10 mU/ml). Proteosomal activation induced in GO-treated BAEC was inhibited by N(omega)-nitro-L-arginine-methyl ester pretreatment, suggesting that *NO mediates proteasomal activation. Intracellular *NO induced by H(2)O(2) was detected by isolating the 4,5-diaminoflourescein (DAF-2)/*NO/O(2)-derived "green fluorescent product" using the high-performance liquid chromatography-fluorescence technique, a more rigorous and quantitative methodology for detecting the DAF-2/*NO/O(2) reaction product. Finally, the relationships between H(2)O(2) flux, proteasomal activation/inactivation, endothelial cell survival, and apoptosis are discussed.

Effects of venous needle turbulence during ex vivo hemodialysis on endothelial morphology and nitric oxide formation

Arteriovenous grafts used for hemodialysis frequently develop intimal hyperplasia (IH), which ultimately leads to graft failure. Although the turbulent jet from the dialysis needle may contribute to vessel wall injury, its role in the pathogenesis of IH is relatively unexplored. In the current study, using bovine aortic endothelial cells (BAEC) cultured on the inner surface of a compliant tube, we evaluated the effects of simulated hemodialysis conditions on morphology and nitric oxide (NO) production. The flows via the graft and needle were 500 ml/min (Reynolds number=819) and 100ml/min (Reynolds number=954), respectively. In the presence of the needle jet for 6h, 19.3% (+/-1.53%) of BAEC were sheared off, whereas no loss of BAEC was observed in the presence of graft flow alone (P<0.05). In the presence of graft flow alone, assessment of cell orientation by the Saltykov method revealed that BAEC were oriented along the flow direction. This alignment, however, was lost in the presence of needle flow. Finally, NO production was also significantly decreased in the presence of the needle flow compared to the presence of graft flow alone (16+/-3.1 vs 34.7+/-1.9 nmol/10(6)cells/h, P<0.05). NO is a key player in vascular homeostasis mechanisms modulating vasomotor tone, inhibiting inflammation and smooth muscle cell proliferation. Thus, the loss of NO signaling and the loss of endothelial integrity caused by needle jet turbulence may contribute to the cascade of events leading to IH formation during hemodialysis.

Upregulation of immunoproteasomes by nitric oxide: potential antioxidative mechanism in endothelial cells

Nitric oxide (*NO) was shown to stimulate the proteasomal function and the ubiquitin-proteasome pathway and to ameliorate endothelial apoptotic signaling induced by oxidants. Understanding the regulatory mechanisms by which *NO stimulates proteasomes and affords cytoprotection in endothelial cells has therapeutic implications, as many vascular diseases are characterized by a deficiency in *NO. Here we report that *NO/cGMP/cAMP-induced immunoproteasome subunit expression is responsible for the increased proteasomal activities. Cells pretreated with protein kinase G and protein kinase A inhibitors markedly attenuated *NO-dependent proteasome activation. Results show that the *NO/cGMP/cAMP signaling mechanism enhanced the phosphorylation of the transcription factor cAMP-response element-binding protein, elevated the cAMP-response element-promoter activity and induced the expression of immunoproteasomal subunits (LMP2 and LMP7). *NO-dependent proteasomal activity was abrogated in cells transfected with antisense LMP2 and LMP7 oligonucleotides. Lower levels of LMP2 and LMP7 were detected in aorta of iNOS(-/-) mice compared to wild-type controls, suggesting that endogenous production of *NO is important in the basal regulation of immunoproteasome. The *NO/cGMP/cAMP signaling pathway mitigates transferrin-iron-mediated oxidative stress and apoptosis through induction of immunoproteasomes. These results provide new insights on the regulatory mechanisms by which the *NO-mediated immunoproteasome signaling pathway affords cytoprotection in endothelial cells.

Asymmetric dimethylarginine induces apoptosis via p38 MAPK/caspase-3-dependent signaling pathway in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is emerging as a key contributor for endothelial dysfunction and its effects on endothelium are not yet completely defined. The aim of this study was to investigate ADMA-induced apoptosis and its mechanisms in human umbilical vein endothelial cells (HUVECs). Apoptosis was evaluated by in situ terminal uridine nick end labeling (TUNEL) assay and DNA fragmentation analysis. Caspase-3 activity was measured using a colorimetric protease assay kit. Activations of mitogen-activated protein kinases (MAPKs) were characterized by Western blot and immunofluorescence. Intracellular oxidant production was measured using H(2)DCF-DA, an oxidant-sensitive fluorescent indicator. ADMA (3-30 microM) induced apoptosis of HUVECs in a dose- and time-dependent manner. Caspase-3 was activated during apoptosis and its specific inhibitor DEVD-CHO significantly attenuated ADMA-induced apoptosis. Phosphorylation of p38 MAPK was induced by ADMA, and p38 MAPK specific inhibitor SB203580 concentration-dependently prevented ADMA-induced caspase-3 activation and cell apoptosis. ADMA increased intracellular oxidant production, which was significantly suppressed by intracellular antioxidant PDTC, l-arginine or antisense endothelial NOS mRNA. They also markedly prevented ADMA-induced phosphorylation of p38 MAPK and cell apoptosis. In conclusion, our present results demonstrate that ADMA induces apoptosis of endothelial cell via elevation of intracellular oxidant production, which involves p38 MAPK/caspase-3-dependent signaling pathway.

Nitric oxide, proteasomal function, and iron homeostasis--implications in aging and neurodegenerative diseases

In this chapter, oxidant-induced transferrin receptor-mediated iron-signaling and apoptosis are described in endothelial and neuronal cells exposed to oxidants. The role of nitric oxide in the regulation of iron homeostasis and oxidant-induced apoptosis is described. The interrelationship between oxidative stress, iron-signaling, and nitric oxide-dependent proteasomal function provides a rational mechanism that connects both oxidative and nitrative modifications.

Rac1 inhibition protects against hypoxia/reoxygenation-induced lipid peroxidation in human vascular endothelial cells

Both in vivo models of ischemia/reperfusion and in vitro models of hypoxia (H)/reoxygenation (R) have demonstrated the crucial role of the Rac1-regulated NADPH oxidase in the production of injurious reactive oxygen species (ROS) by vascular endothelial cells (ECs). Since membrane lipid peroxidation has been established as one of the mechanisms leading to cell death, we examined lipid peroxidation in H/R-exposed cultured human umbilical vein ECs (HUVECs) and the role of Rac1 in this process. H (24 h at 1% O2)/R (5 min) caused an increase in intracellular ROS production compared to a normoxic control, as measured by dichlorofluorescin fluorescence. Nutrient deprivation (ND; 24 h), a component of H, was sufficient to induce a similar increase in ROS under normoxia. Either H(24 h)/R (2 h) or ND (24 h) induced increases in lipid peroxidation of similar magnitude as measured by flow cytometry of diphenyl-1-pyrenylphosphine-loaded HUVECs and Western blotting analysis of 4-hydroxy-2-nonenal-modified proteins in cell lysates. In cells infected with a control adenovirus, H (24 h)/R (2 h) and ND (24 h) resulted in increases in NADPH-dependent superoxide production by 5- and 9-fold, respectively, as measured by lucigenin chemiluminescence. Infection of HUVECs with an adenovirus that encodes the dominant-negative allele of Rac1 (Rac1N17) abolished these increases. Rac1N17 expression also suppressed the H/R- and ND-induced increases in lipid peroxidation. In conclusion, ROS generated via the Rac1-dependent pathway are major contributors to the H/R-induced lipid peroxidation in HUVECs, and ND is able to induce Rac1-dependent ROS production and lipid peroxidation of at least the same magnitude as H/R.

Coordinated induction of iNOS-VEGF-KDR-eNOS after resveratrol consumption: a potential mechanism for resveratrol preconditioning of the heart

Existing evidence indicates that resveratrol, a red wine and grape-derived polyphenolic antioxidant, can pharmacologically precondition the heart in a nitric oxide (NO)-dependent manner. To further explore the role of NO in resveratrol-mediated cardioprotection, the induction for the expression of the potential molecular targets of NO including VEGF and KDR as well as iNOS and eNOS were examined by Western blot analysis and immunohistochemistry. Two groups of rats were studied, one group of animals was fed resveratrol for 7 days while the other group was given water only. After 1, 3, 5 and 7 days, the rats were sacrificed and the expression of the proteins was examined by Western blot analysis. Western blot detected an overexpression of iNOS and VEGF within 24 h of resveratrol treatment while the induction of KDR was not increased until after 3 days and eNOS expression after 5 days of resveratrol treatment. These expressions were further increased after 7 days of resveratrol treatment, when the rats were sacrificed for the isolated working heart preparation. Resveratrol provided cardioprotection as evidenced by superior post-ischemic ventricular recovery, reduced myocardial infarct size and decreased number of apoptotic cardiomyocytes. Immunohistochemistry was performed in the hearts at baseline, and at the end of 30-min ischemia/2-h reperfusion. The hearts obtained from resveratrol-treated rats revealed enhanced expression for iNOS, eNOS and VEGF and KDR compared to control hearts at the end of reperfusion. The results of this study demonstrate that resveratrol leads to a coordinated upregulation of iNOS-VEGF-KDR-eNOS, which is likely to play a role in resveratrol-mediated cardioprotection.

Oxidized LDL induces mitochondrially associated reactive oxygen/nitrogen species formation in endothelial cells

Exposure of cells to complex mixtures of oxidized lipids such as those found in oxidized low-density lipoprotein (oxLDL) induce reactive oxygen and nitrogen species (ROS/RNS) formation. The source of the ROS/RNS within cells is unknown; it is thought they may be involved in redox cell signaling. Although this possibility was initially overlooked, it is becoming clear that mitochondria, which are a source of superoxide and hydrogen peroxide, may play a critical role in the response of cells on exposure to oxidized lipids. In this study, we tested the possibility that mitochondria are a potential source of oxLDL-dependent formation of ROS/RNS in endothelial cells. Using confocal microscopy, we demonstrated that a significant proportion of oxLDL-dependent dichlorodihydrofluorescein (DCF) fluorescence is colocalized to mitochondria. In support of this concept, rho0 endothelial cells showed a substantial decrease in ROS/RNS formation stimulated by oxLDL. In contrast, mostly nonmitochondrial DCF fluorescence was detected in cells exposed to an extracellular source of hydrogen peroxide. The exposure of cells to a nitric oxide synthase inhibitor and urate resulted in a decrease in oxLDL-induced DCF fluorescence that was restored by addition of nitric oxide donors to the medium. Taken together, these results suggest that oxLDL-dependent DCF fluorescence is mitochondrially associated and may be due to the formation of peroxynitrite.

Effects of STZ-induced diabetes and its treatment with vanadyl sulphate on cyclosporine A-induced nephrotoxicity in rats

The aim of this study was to analyze the effect of streptozotocin (STZ)-induced diabetic state and the insulin-like acting, vanadyl sulphate (VS) on cyclosporine A (CyA) related nephrotoxicity in rats. Male Wistar rats were divided into six groups, of 12 animals each: The control, diabetic rats and diabetic rats whose drinking VS in the drinking water in a concentration of 1 mg/ml. Another three similarly treated groups were injected intra-peritoneally (ip) with CyA in a dose of 25 mg/kg/day for ten doses, 10 days after diabetic induction by using a single dose of STZ of 65 mg/kg. Rats were sacrificed 48 h after the last CyA dose and serum as well as kidneys were isolated and analyzed. Treatment with CyA to control normoglycemic rats resulted in significant increases in kidney weight, serum creatinine, urea nitrogen, cholesterol and triglycerides (TG) levels. Also, the kidney tissue of CyA-treated control animals showed significant increases in total nitrate/nitrite (NO(x)) concentration and malondialdehyde (MDA) production level as well as depletion of glutathione (GSH) content and glutathione peroxidase (GSH-P(x)) activity level. Histopathologic evaluation of CyA-treated control rats revealed tubular atrophy, hyaline casts and focal tubular necrosis. However, treatment of diabetic rats with CyA showed significant reduction in serum creatinine and elevation in TG level as well as reductions in the kidney NO(x) concentration and MDA production level and increase in GSH concentration compared to CyA-treated control rats. Moreover, histopathology of the kidney of CyA-treated diabetics showed typical changes of the diabetic controls revealing glomerular hypertrophy and tubular dilation. On the other hand, treatment with CyA to those diabetic animals administered VS in the drinking water resulted in exacerbation of renal dysfunction, manifested by significant increases in serum indices of nephrotoxicity, cholesterol, TG and bilirubin levels. Also, VS administration to CyA-treated diabetics showed significant increase in kidney NO(x) concentration compared to those CyA-treated diabetics drinking plain tap water, and to a level significantly lower than those CyA-treated controls. Histopathologically, kidney of CyA/VS-treated diabetic showed marked CyA related changes. In conclusion, STZ-induced diabetes might provide partial protection against CyA-induced renal dysfunction. Also, treatment of hyperglycemia with VS might exacerbate CyA related nephrotoxicity.

Benidipine, a dihydropyridine-calcium channel blocker, prevents lysophosphatidylcholine-induced injury and reactive oxygen species production in human aortic endothelial cells

Lysophosphatidylcholine (lysoPC) is a component of oxidized low-density lipoproteins (oxLDLs), which play an important role in the pathogenesis of atherosclerosis. In this study, we examined whether benidipine hydrochloride (benidipine), a dihydropyridine-calcium channel blocker with antioxidant activity, prevents lysoPC (C 16:0)-induced injury of human aortic endothelial cells (HAEC). Treatment of HAECs with lysoPC changed cell morphology, decreased cell viability and induced DNA fragmentation, leading to apoptosis. Additionally, lysoPC species containing palmitoyl (C 16:0) or stearoyl (C 18:0), which are the major components of oxLDLs, stimulated reactive oxygen species (ROS) production and induced caspase-3/7-like activity in HAECs, but lysoPC species with short acyl chains did not affect either ROS production or caspase-3/7-like activity. Pretreatment with benidipine (0.3-3 micromol/L) for 24 h protected against lysoPC-induced cytotoxicity in the endothelial cells and the drug inhibited both lysoPC-stimulated ROS production and caspase-3/7-like activation with a similar potency. Since caspase-3/7 is involved in executing the apoptotic process, the reduction of the activity of this enzyme by benedipine may explain the anti-apoptotic effect of the drug. However, benidipine did not suppress lysoPC-induced phosphorylation of mitogen-activated protein kinases and Ca2+ influx in HAECs. These results suggest that the anti-oxidant properties of benidipine may be responsible for its ability to inhibit ROS production, resulting in reduced activation of caspase-3/7. In conclusion, benidipine suppresses lysoPC-induced endothelial dysfunction through inhibition of ROS production, which is due at least in part to its antioxidant effect, and not through the inhibition of L-type voltage-dependent calcium channels.

A novel ligand-independent apoptotic pathway induced by scavenger receptor class B, type I and suppressed by endothelial nitric-oxide synthase and high density lipoprotein

Scavenger receptor class B, type I (SR-BI)/ApoE double null mice develop severe atherosclerosis within 4 weeks, whereas ApoE null mice take several months to develop the disease, indicating that SR-BI plays a pivotal role in atherosclerosis. Importantly, SR-BI/ApoE double null mice have lower plasma cholesterol levels than ApoE null mice, suggesting involvement of a non-lipids mechanism. In the present study, we revealed a novel ligand-independent apoptotic pathway induced by SR-BI, and regulated by endothelial nitric-oxide synthase (eNOS) and high density lipoprotein (HDL). SR-BI significantly induces apoptosis in three independent cell systems. In contrast to known ligand-dependent apoptotic pathways, SR-BI-induced apoptosis is ligand-independent. We further showed that SR-BI-induced apoptosis is suppressed by eNOS and HDL. By using a single site mutation, we demonstrated that SR-BI induces apoptosis through a highly conserved CXXS redox motif. We finally demonstrated that SR-BI-induced apoptosis is via the caspase-8 pathway. We hypothesize that in healthy cells, the SR-BI apoptotic pathway is turned off by eNOS and HDL which prevents inappropriate apoptotic damage to the vascular wall. When HDL levels are low, oxidative stress causes the relocation of eNOS away from caveolae, which turns on SR-BI-induced apoptosis and rapidly clears damaged cells to prevent further inflammatory damage to neighboring cells. The current studies offer a new paradigm in which to study the non-cholesterol effects of SR-BI, HDL, and eNOS on the development of atherosclerosis and potentially other cardiovascular diseases.

The intimate relation between nitric oxide and superoxide in apoptosis and cell survival

Intra- and intercellular communication in or between cells allows adaptation to changes in the environment. Formation of reactive oxygen (ROS) and nitrogen (RNS) species in response to external insults gained considerable attention in provoking cell demise along an apoptotic subroute of cell death, thus attributing radical formation to pathologies. In close association, stabilization of the tumor suppressor p53 and activation of caspases convey proapoptotic signaling. Complexity was added with the notion that ROS and RNS signals overlap and/or produce synergistic as well as antagonistic effects. With respect to nitric oxide (NO) signaling, it became clear that the molecule is endowed with pro- or antiapoptotic signaling capabilities, depending to some extend on the concentration and cellular context, i.e., ROS generation. Here, some established concepts are summarized that allow an explanation of p53 accumulation under the impact of NO and an understanding of NO-evoked cell protection at the level of caspase inhibition, cyclic GMP formation, or expression of antiapoptotic proteins. In addition, the overlapping sphere of ROS and RNS signaling is recapitulated to appreciate cell physiology/pathology with the notion that marginal changes in the flux rates of either NO or superoxide may shift vital signals used for communication and cell survival into areas of pathology in close association with apoptosis/necrosis.

Genistein acutely stimulates nitric oxide synthesis in vascular endothelial cells by a cyclic adenosine 5'-monophosphate-dependent mechanism

Genistein may improve vascular function, but the mechanism of this effect is unclear. We tested the hypothesis that genistein directly regulates vascular function through stimulation of endothelial nitric oxide synthesis. Genistein activated endothelial nitric oxide synthase (eNOS) in intact bovine aortic endothelial cells and human umbilical vein endothelial cells over an incubation period of 10 min. The maximal eNOS activity was at 1 microm genistein. Consistent with this activation pattern, 1 microm genistein maximally stimulated the phosphorylation of eNOS at serine 1179 at 10 min of incubation. The rapid activation of eNOS by genistein was not dependent on RNA transcription or new protein synthesis and was not blocked by a specific estrogen receptor antagonist. In addition, inhibition of MAPK or phosphatidylinositol 3-OH kinase/Akt kinase had no affect on eNOS activation by genistein. Furthermore, the genistein effect on eNOS was also independent of tyrosine kinase inhibition. However, inhibition of cAMP-dependent kinase [protein kinase A (PKA)] by H89 completely abolished the genistein-stimulated eNOS activation and phosphorylation, suggesting that genistein acted through a PKA-dependent pathway. These findings demonstrated that genistein had direct nongenomic effects on eNOS activity in vascular endothelial cells, leading to eNOS activation and nitric oxide synthesis. These effects were mediated by PKA and were unrelated to an estrogenic effect. This cellular mechanism may underlie some of the cardiovascular protective effects proposed for soy phytoestrogens.

Oxidation of indole-3-acetic acid by horseradish peroxidase induces apoptosis in G361 human melanoma cells

The combination of indole-3-acetic acid (IAA) and horseradish peroxidase (HRP) has recently been proposed as a novel cancer therapy. However, the mechanism underlying the cytotoxic effect involved is substantially unknown. Here, we show that IAA/HRP treatment induces apoptosis in G361 human melanoma cells, whereas IAA or HRP alone have no effect. It is known that IAA produces free radicals when oxidized by HRP. Because oxidative stress could induce apoptosis, we measured the production of free radicals at varying concentrations of IAA and HRP. Our results show that IAA/HRP produces free radicals in a dose-dependent manner, which are suppressed by ascorbic acid or (-)-epigallocatechin gallate (EGCG). Furthermore, antioxidants prevent IAA/HRP-induced apoptosis, indicating that the IAA/HRP-produced free radicals play an important role in the apoptotic process. In addition, IAA/HRP was observed to activate p38 mitogen-activated protein (MAP) kinase and c-Jun N-terminal kinase (JNK), which are almost completely blocked by antioxidants. We further investigated the IAA/HRP-mediated apoptotic pathways, and found that IAA/HRP activates caspase-8 and caspase-9, leading to caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage. These events were also blocked by antioxidants, such as ascorbic acid or EGCG. Thus, we propose that IAA/HRP-induced free radicals lead to the apoptosis of human melanoma cells via both death receptor-mediated and mitochondrial apoptotic pathways.

Nitric oxide mitigates peroxide-induced iron-signaling, oxidative damage, and apoptosis in endothelial cells: role of proteasomal function?

In this mini-review, oxidant-induced transferrin receptor-mediated iron-signaling and apoptosis are described in endothelial and neuronal cells exposed to a variety of oxidative stresses. The role of nitric oxide and nitration in the regulation of iron homeostasis and oxidant-induced apoptosis is described. The interrelationship between oxidative stress, iron-signaling, and nitric oxide-dependent proteasomal function provides a rational mechanism that connects both oxidative and nitrative modifications.

Argininosuccinate synthase expression is required to maintain nitric oxide production and cell viability in aortic endothelial cells

Although cellular levels of arginine greatly exceed the apparent K(m) for endothelial nitric-oxide synthase, current evidence suggests that the bulk of this arginine may not be available for nitric oxide (NO) production. We propose that arginine regeneration, that is the recycling of citrulline back to arginine, defines the essential source of arginine for NO production. To support this proposal, RNA interference analysis was used to selectively reduce the expression of argininosuccinate synthase (AS), because the only known metabolic role for AS in endothelial cells is in the regeneration of l-arginine from l-citrulline. Western blot analysis demonstrated a significant and dose-dependent reduction of AS protein as a result of AS small interfering RNA treatment with a corresponding diminished capacity to produce basal or stimulated levels of NO, despite saturating levels of arginine in the medium. Unanticipated, however, was the finding that the viability of AS small interfering RNA-treated endothelial cells was significantly decreased when compared with control cells. Trypan blue exclusion analysis suggested that the loss of viability was not because of necrosis. Two indicators, reduced expression of Bcl-2 and an increase in caspase activity, which correlated directly with reduced expression of AS, suggested that the loss of viability was because of apoptosis. The exposure of cells to an NO donor prevented apoptosis associated with reduced AS expression. Overall, these results demonstrate the essential role of AS for endothelial NO production and cell viability.

Optimizing endothelial nitric oxide activity may slow endothelial aging

The capacity of vascular endothelium to generate bioactive nitric oxide (NO) decreases with advancing age, even in healthy subjects with a relatively benign risk factor profile; this phenomenon may reflect decreased expression of NO synthase, as well as increased production of superoxide, and evidently contributes importantly to the increased vascular risk associated with aging. Studies with cultured endothelial cells suggest that the rate of endothelial aging is determined primarily by the rate of cell turnover and the associated progressive shortening of telomeres; endothelial cells transfected with the catalytic subunit of telomerase--which preserves a youthful telomere length--do not show a reduction in NO synthase expression after numerous doublings, in contrast to the marked reduction observed in control cells. Also consistent with this view is the fact that, following balloon denudation of arteries, the regenerated endothelium makes less NO. In the vasculature of adults, the rate of endothelial cell mitosis is evidently a reflection of the rate of endothelial cell apoptosis. Numerous cell culture studies demonstrate that physiological levels of NO protect endothelial cells from apoptosis induced by a wide range of noxious stimuli--including vascular risk factors such as oxidized LDL, angiotensin II, and hyperglycemia. In the human vasculature, endothelial cells with disproportionately short telomeres are found capping atheromatous lesions and in atheroma-prone areas where blood flow is turbulent; these findings evidently reflect increased endothelial cell turnover in regions where NO bioactivity is relatively weak. It can be deduced that lifelong adherence to an "endotheliophilic lifestyle" that optimizes vascular NO production, while minimizing that of superoxide, will literally slow the rate of aging of vascular endothelium, such that, at any given advanced age, the optimal functional capacity of the vascular endothelium will be superior to that of age-matched controls. These considerations underline the desirability of actively promoting vascular health in younger and middle-aged individuals in whom risk for vascular events may still be quite low. The impact of lifelong caloric restriction on endothelial aging requires further study, preferably in primates.

Endothelial stress by gravitational unloading: effects on cell growth and cytoskeletal organization

All organisms on Earth have evolved to survive within the pull of gravity. Orbital space flights have clearly demonstrated that the absence or the reduction of gravity profoundly affects eukaryotic organisms, including man. Because (i). endothelial cells are crucial in the maintenance of the functional integrity of the vascular wall, and (ii). cardiovascular deconditioning has been described in astronauts, we evaluated whether microgravity affected endothelial functions. We show that microgravity reversibly stimulated endothelial cell growth. This effect correlated with an overexpression of heat shock protein 70 (hsp70) and a down-regulation of interleukin 1 alpha (IL-1alpha), a potent inhibitor of endothelial cell growth, also implicated in promoting senescence. In addition, gravitationally unloaded endothelial cells rapidly remodelled their cytoskeleton and, after a few days, markedly down-regulated actin through a transcriptional mechanism. We hypothesize that the reduction in the amounts of actin in response to microgravity represents an adaptative mechanism to avoid the accumulation of redundant actin fibers.

Glyceryl trinitrate, a nitric oxide donor, abrogates ferric nitrilotriacetate-induced oxidative stress and renal damage

Ferric nitrilotriacetate (Fe-NTA), a common water pollutant and a known renal carcinogen, acts through the generation of oxidative stress and hyperproliferative response. In the present study, we show that the nitric oxide (NO) generated by the administration of glyceryl trinitrate (GTN) affords protection against Fe-NTA-induced oxidative stress and proliferative response. Administration of Fe-NTA resulted in a significant (P<0.001) depletion of renal glutathione (GSH) content with concomitant increase in lipid peroxidation and elevated tissue damage marker release in serum. Parallel to these changes, Fe-NTA also caused down-regulation of GSH metabolizing enzymes including glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferase and several fold induction in ornithine decarboxylase (ODC) activity and rate of DNA synthesis. Subsequent exogenous administration of GTN at doses of 3 and 6mg/kg body weight resulted in significant (P<0.001) recovery of GSH metabolizing enzymes and amelioration of tissue GSH content, in a dose-dependent manner. GTN administration also inhibited malondialdehyde (MDA) formation, induction of ODC activity, enhanced rate of DNA synthesis, and pathological deterioration in a dose-dependent fashion. Further, administration of NO inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), exacerbated Fe-NTA-induced oxidative tissue injury, hyperproliferative response, and pathological damage. Overall, the study suggests that NO administration subsequent to Fe-NTA affords protection against ROS-mediated damage induced by Fe-NTA.

Nitric oxide inhibits H2O2-induced transferrin receptor-dependent apoptosis in endothelial cells: Role of ubiquitin-proteasome pathway

We investigated here the mechanism of cytoprotection of nitric oxide (*NO) in bovine aortic endothelial cells treated with H2O2. NONOates were used as *NO donors that released *NO slowly at a well defined rate in the extracellular and intracellular milieus. H2O2-mediated intracellular dichlorofluorescein fluorescence and apoptosis were enhanced by the transferrin receptor (TfR)-mediated iron uptake. *NO inhibited the TfR-mediated iron uptake, dichlorofluorescein fluorescence, and apoptosis in H2O2-treated cells. *NO increased the proteasomal activity and degradation of nitrated TfR via ubiquitination. Nomega-nitro-L-arginine methyl ester, a nonspecific inhibitor of endogenous *NO biosynthesis, decreased the trypsin-like activity of 26S proteasome. *NO, by activating proteolysis, mitigates TfR-dependent iron uptake, dichlorodihydrofluorescein oxidation, and apoptosis in H2O2-treated bovine aortic endothelial cells. The relevance of biological nitration on redox signaling is discussed.

The role of oxidant-mediated pathways in the cytotoxicity of endothelial cells exposed to mesenteric lymph from rats subjected to trauma-hemorrhagic shock

Because gut-derived factors carried in mesenteric lymph are implicated in multiple organ dysfunction syndrome and have been shown to injure endothelial cells, we investigated several cellular pathways by which this process could occur. To accomplish this, mesenteric lymph (5%, v/v) collected at 1 to 3 h postshock from male rats undergoing trauma (5-cm laparotomy) and hemorrhagic shock (90 min of mean arterial pressure [MAP] of 30 mmHg; T/HS) was tested for endothelial cell cytotoxicity on human umbilical vein endothelial cells (HUVECs). Over 30 pharmacologic agents that had been reported to inhibit endothelial cell death were tested for their ability to prevent T/HS lymph-induced HUVEC cell death. These included agents documented to protect against oxidant-mediated, calcium-mediated, and arachidonic acid pathway-mediated endothelial cell injury and death. These pharmacologic inhibitors were preincubated with HUVECs for 1 h or were added to the HUVECs simultaneously with lymph, and were then incubated for 18 h. Controls were lymph alone, inhibitor alone, or medium alone. Mitochondrial tetrazolium (MTT) and LDH release assays were used to determine cell viability. The inhibitors that significantly protected HUVECs from the cytotoxicity of T/HS lymph (P < 0.001) included the antioxidant combination of vitamins C and E and the antioxidant-lipooxygenase inhibitor nordihydroguaretic acid (NDGA). These agents were equally effective when added simultaneously with lymph or preincubated with the HUVECs, suggesting an extracellular or membrane-bound process. In summary, the inhibitors that provided protection from toxic lymph appear to work at the membrane and are involved in limiting membrane peroxidation. Based on this study, it appears that an oxidant pathway is involved in T/HS lymph-induced endothelial cell injury and death.

Hyperoxia induces retinal vascular endothelial cell apoptosis through formation of peroxynitrite

Hyperoxia exposure induces capillary endothelial cell apoptosis in the developing retina, leading to vaso-obliteration followed by proliferative retinopathy. Previous in vivo studies have shown that endothelial nitric oxide synthase (NOS3) and peroxynitrite are important mediators of the vaso-obliteration. Now we have investigated the relationship between hyperoxia, NOS3, peroxynitrite, and endothelial cell apoptosis by in vitro experiments using bovine retinal endothelial cells (BREC). We found that BREC exposed to 40% oxygen (hyperoxia) for 48 h underwent apoptosis associated with activation of caspase-3 and cleavage of the caspase substrate poly(ADP-ribose) polymerase. Hyperoxia-induced apoptosis was associated with increased formation of nitric oxide, peroxynitrite, and superoxide anion and was blocked by treatment with uric acid, nitro-L-arginine methyl ester, or superoxide dismutase. Analyses of the phosphatidylinositol 3-kinase/Akt kinase survival pathway in cells directly treated with peroxynitrite revealed inhibition of VEGF- and basic FGF-induced activation of Akt kinase. These results suggest that hyperoxia-induced formation of peroxynitrite induces BREC apoptosis by crippling key survival pathways and that blocking peroxynitrite formation prevents apoptosis. These data may have important clinical implications for infants at risk of retinopathy of prematurity.

Activation of NAD(P)H oxidase by lipid hydroperoxides: mechanism of oxidant-mediated smooth muscle cytotoxicity

Oxidized lipids, such as 13-hydroperoxyoctadecadienoic acid (13-HPODE), have been implicated in the pathogenesis of atherosclerosis. 13-HPODE, a constituent of oxidized low-density lipoproteins, can induce cytotoxicity of vascular smooth muscle cells (SMC), which may facilitate plaque destabilization and/or rupture. 13-HPODE-induced cytotoxicity has been linked to oxidative stress, although the mechanisms by which this occurs are unknown. In the present study, we show that 13-HPODE and 9-HPODE (10-30 microM) increased superoxide (O2*-) production and induced cytotoxicity in SMC. The 13-HPODE-induced increase in O2*- was blocked by transfecting the cells with antisense oligonucleotides against p22phox, suggesting that the O2*- was produced by NAD(P)H oxidase. Similar concentrations of the corresponding HPODE reduction products, 13-hydroxyoctadecadienoic acid (13-HODE) and 9-HODE, neither increased O2*- production nor induced cytotoxicity, while 4-hydroxy nonenal (4-HNE), an unsaturated aldehyde lipid peroxidation product, induced cytotoxicity without increasing O2*- production. Treatment with superoxide dismutase or Tiron to scavenge O2*-, or transfection with p22phox antisense oligonucleotides to inhibit O2*- production, attenuated 13-HPODE-induced cytotoxicity, but not that induced by 4-HNE. These findings suggest that activation of NAD(P)H oxidase, and production of O2*-, play an important role in lipid hydroperoxide-induced smooth muscle cytotoxicity.

Apoptosis and necrosis after warm ischemia-reperfusion injury of the pig liver and their inhibition by ONO-1714

BACKGROUND

It is still controversial whether a major mode of cell death during hepatic ischemia-reperfusion (I/R) injuries is apoptosis or necrosis. Moreover, the correlation between these cell deaths and the effects of a novel inducible nitric oxide synthase inhibitor (ONO-1714) has not been studied before.

METHODS

Pigs were subjected to 180 min of hepatic warm I/R under extracorporeal circulation. The control group was not administered ONO-1714. In the ONO-1714 group, ONO-1714 was administered 5 min before ischemia at a dose of 0.05 mg/kg through a portal vein catheter. The apoptotic and necrotic changes after reperfusion were examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and hematoxylin-eosin staining. Nitrotyrosine, active caspase-3, and cytochrome c were examined by immunohistochemistry. The plasma NO + NO, aspartate aminotransferase, and lactate dehydrogenase levels were also examined.

RESULTS

In the control group, the frequency of apoptotic cells was only 2.6%; nevertheless, that of necrotic cells was 37% at 24 hr after reperfusion. ONO-1714 significantly attenuated apoptosis and necrosis, the expression of nitrotyrosine, and the increases of the plasma aspartate aminotransferase, lactate dehydrogenase, and NO(2)- + NO(3)- levels in the reperfusion phase.

CONCLUSIONS

A major mode of cell death during hepatic warm I/R injury was necrosis, and apoptosis was not dominant. These necrotic changes were caused by the excess production of peroxynitrite, and ONO-1714 greatly attenuated I/R injuries as the result of inhibition of the peroxynitrite production.

Oxidative stress-induced iron signaling is responsible for peroxide-dependent oxidation of dichlorodihydrofluorescein in endothelial cells: role of transferrin receptor-dependent iron uptake in apoptosis

Dichlorodihydrofluorescein (DCFH) is one of the most frequently used probes for detecting intracellular oxidative stress. In this study, we report that H2O2-dependent intracellular oxidation of DCFH to a green fluorescent product, 2',7'-dichlorofluorescein (DCF), required the uptake of extracellular iron transported through a transferrin receptor (TfR) in endothelial cells. H2O2-induced DCF fluorescence was inhibited by the monoclonal IgA-class anti-TfR antibody (42/6) that blocked TfR endocytosis and the iron uptake. H2O2-mediated inactivation of cytosolic aconitase was responsible for activation of iron regulatory protein-1 and increased expression of TfR, resulting in an increased iron uptake into endothelial cells. H2O2-mediated caspase-3 proteolytic activation was inhibited by anti-TfR antibody. Similar results were obtained in the presence of a lipid hydroperoxide. We conclude that hydroperoxide-induced DCFH oxidation and endothelial cell apoptosis required the uptake of extracellular iron by the TfR-dependent iron transport mechanism and that the peroxide-induced iron signaling, in general, has broader implications in oxidative vascular biology.

Mildly oxidized LDL particle subspecies are distinct in their capacity to induce apoptosis in endothelial cells: role of lipid hydroperoxides

The risk of atherosclerosis is intimately related to the heterogeneity of low-density lipoprotein (LDL) particles. The potential relationship between oxidative modification of distinct LDL subspecies and induction of apoptosis in arterial wall cells is indeterminate. The capacity of light LDL3 versus dense LDL5 to induce cytotoxicity in endothelial cells as a function of the degree of copper-mediated oxidation was compared. Mildly oxidized LDL3 (oxLDL3) exerted potent cytotoxicity, which was intimately related to both the degree of oxidation and the oxLDL3 concentration based on either cholesterol content or particle number. In contrast, dense LDL5 particles exerted a minor effect on cell viability. Cells incubated with oxLDL3 exhibited apoptotic features, with cytoplasmic condensation, cell or nuclear fragmentation, and accumulation of DNA fragments. OxLDL3-induced apoptosis involved cytoplasmic release of cytochrome c, with a concomitant increase in caspase-3-like protease activity. OxLDL3 particles were uniquely distinct from oxLDL5 particles in their elevated content of lipid hydroperoxides. Hydroperoxide removal by NaBH4 markedly reduced oxLDL3-induced cytotoxicity, leading to an increase in cell viability. Lipid hydroperoxide content of oxidatively modified LDL subclasses is therefore a major determinant of the induction of apoptosis in endothelial cells. These data are highly relevant to atherogenic hypercholesterolemia, in which the LDL phenotype is dominated by elevated concentrations of light LDL3.

Attenuation of increased myocardial ischaemia-reperfusion injury conferred by hypercholesterolaemia through pharmacological inhibition of the caspase-1 cascade

1. Hypercholesterolaemia has been shown to be associated with greater myocardial ischaemia-reperfusion injury, in which apoptosis and inflammation-mediated necrosis both play a key role. 2. Caspase-1 is involved in the activation of both apoptosis and inflammation, through the intermediate of interleukin-1beta (IL-1beta). We herein examined whether pharmacological inhibition of the caspase-1 cascade, using Ac-Tyr-Val-Ala-Asp-CH(2)Cl (Ac-YVAD.cmk), after myocardial ischaemia have greater protective effects on myocardial ischaemia-reperfusion injury in diet-induced hypercholesterolaemic rabbits. 3. Male rabbits fed with standard chow or chow supplemented with 0.5% cholesterol and 10% coconut oil for 8 weeks were subjected to 30 min of left circumflex artery occlusion followed by 4 h of reperfusion. An intravenous bolus of Ac-YVAD.cmk (1.6 mg kg(-1)) or vehicle was given 20 min after coronary occlusion. 4. Postischaemic administration of Ac-YVAD.cmk markedly decreased infarct size from 26+/-3% to 12+/-2% in normally fed rabbits (P=0.005) and from 41+/-6% to 14+/-2% in cholesterol-fed rabbits (P<0.001). 5. In the ischaemic non-necrotic area, treatment with Ac-YVAD.cmk markedly reduced the percentage of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL)-positive cardiomyocytes from 15.5+/-0.8% to 2.2+/-0.1% in normally fed rabbits (P<0.001) and from 39.0+/-2.3% to 2.2+/-0.1% in cholesterol-fed rabbits (P<0.001). 6. Ac-YVAD.cmk treatment resulted in a reduction not only of IL-1beta and caspase-1, but also of caspase-3 in the ischaemic myocardium in both normally fed and cholesterol-fed rabbits. 7. No differences in infarct size, the percentage of TUNEL-positive cardiomyocytes, IL-1beta levels or activity of caspase-1 and caspase-3 were observed between Ac-YVAD.cmk-treated normally fed and cholesterol-fed rabbits. 8. This study demonstrates that injection of a selective caspase-1 inhibitor after myocardial ischaemia markedly reduced the detrimental effect conferred by hypercholesterolaemia on myocardial ischaemia-reperfusion injury by attenuating both necrotic as well as apoptotic cell death pathways through inhibition of IL-1beta production and activation of caspase-1 and caspase-3.