Probucol preserves endothelial function by reduction of the endogenous nitric oxide synthase inhibitor level

Probucol promotes osteoblasts differentiation and prevents osteoporosis development through reducing oxidative stress

Probucol (PBC) is a potent cholesterol-lowering drug and has been studied extensively for its powerful antioxidative stress. The purpose of this study is to investigate the role of PBC in ovariectomized rat model and to explore the mechanism of osteogenic differentiation of MC3TE-E1 Cells. RT-qPCR and Immunofluorescence were used to measure the expression level of SOD2, SIRT1, intracellular oxidative stress levels and osteogenic markers proteins. Moreover, CCK-8 assay was conducted to detect cell viability. Alizarin red staining and alkaline phosphatase staining were applied to examine osteogenic function and calcium deposits. The ovariectomized rat model was set up successfully and HE staining were employed to examine femoral trabeculae tissue. Our results showed that PBC suppressed MC3TE-E1 resist oxidative stress to promote osteogenic differentiation. Additionally, it was confirmed that PBC promoted osteogenic differentiation of MC3TE-E1 through inhibiting oxidative stress. Further study indicated that PBC exerted its beneficial function by suppressing oxidative stress-mediated alter bone metabolism to alleviate osteoporosis in vivo. Our research suggested that the PBC-modulated oxidative stress inhibition is responsible for activation of the process of osteogenic differentiation, providing a novel insight into the treatment of osteoporosis.

Enhanced Antioxidant Effects of the Anti-Inflammatory Compound Probucol when Released from Mesoporous Silica Particles

Brain endothelial cells mediate the function and integrity of the blood brain barrier (BBB) by restricting its permeability and exposure to potential toxins. However, these cells are highly susceptible to cellular damage caused by oxidative stress and inflammation. Consequent disruption to the integrity of the BBB can lead to the pathogenesis of neurodegenerative diseases. Drug compounds with antioxidant and/or anti-inflammatory properties therefore have the potential to preserve the structure and function of the BBB. In this work, we demonstrate the enhanced antioxidative effects of the compound probucol when loaded within mesoporous silica particles (MSP) in vitro and in vivo zebrafish models. The dissolution kinetics were significantly enhanced when released from MSPs. An increased reduction in lipopolysaccharide (LPS)-induced reactive oxygen species (ROS), cyclooxygenase (COX) enzyme activity and prostaglandin E₂ production was measured in human brain endothelial cells treated with probucol-loaded MSPs. Furthermore, the LPS-induced permeability across an endothelial cell monolayer by paracellular and transcytotic mechanisms was also reduced at lower concentrations compared to the antioxidant ascorbic acid. Zebrafish pre-treated with probucol-loaded MSPs reduced hydrogen peroxide-induced ROS to control levels after 24-h incubation, at significantly lower concentrations than ascorbic acid. We provide compelling evidence that the encapsulation of antioxidant and anti-inflammatory compounds within MSPs can enhance their release, enhance their antioxidant effects properties, and open new avenues for the accelerated suppression of neuroinflammation.

Effect of probucol on autophagy and apoptosis in the penile tissue of streptozotocin-induced diabetic rats

Autophagy and apoptosis have been regarded as important processes in the development of diabetic erectile dysfunction (DMED). Probucol is considered to have anti-apoptotic effects, but its relationship with autophagy has not been reported. The aim of this study was to investigate the effects and mechanisms of probucol on erectile function. Thirty Sprague–Dawley (SD) male rats (12 weeks old) were fasted for 12 h. Twenty SD rats were injected with a single intraperitoneal injection of 60 mg kg⁻¹ streptozotocin (STZ). Ten rats were given vehicle only and used as a sham group. After 72 h, 20 STZ-treated rats with random blood glucose concentrations consistently greater than 16.7 mmol l⁻¹ were used as successfully established diabetic rats. The diabetic rats were divided randomly into two groups and treated with a daily gavage of probucol at a dose of 0 or 500 mg kg⁻¹ for 12 weeks. After treatment, the intracavernous pressure (ICP) was used to measure erectile function upon electrical stimulation of the cavernous nerve. After euthanasia, penile tissue was examined using immunohistochemistry and Western blot to assess the protein levels of B-cell lymphoma-2 (Bcl-2), BCL2-associated X (Bax), microtubule-associated protein light chain 3-II (LC3-II), mammalian target of rapamycin (mTOR), and sequestosome 1 (P62). Caspase-3 activity was measured to determine apoptosis using a caspase-3 assay kit. After 12 weeks of treatment, the erectile function of the probucol group was significantly better than that of the DM group (P < 0.05). Bax and LC3-II protein expression and caspase-3 activity were significantly lower in the probucol group than those in the DM group (all P < 0.05), while Bcl-2, mTOR, and P62 protein expression levels were significantly higher than those in the DM group (all P < 0.05). We demonstrated that probucol inhibited apoptosis and autophagy in STZ-induced diabetic rats.

Asymmetric dimethylarginine aggravates blood-retinal barrier breakdown of diabetic retinopathy via inhibition of intercellular communication in retinal pericytes

Blood-retinal barrier breakdown is the main pathological characteristics of diabetic retinopathy (DR). Asymmetric dimethylarginine (ADMA) was reported to be elevated in DR patients. In this study, we observed the dynamic profile of ADMA, retinal morphology and permeability of BRB at 2, 4 or 8 week of diabetic rats induced by a single intraperitoneal injection of streptozocin (60 mg/kg) and in cultured rat retinal pericytes pretreated with D-glucose (30 mM) for 1, 3, 5 and 7 days or ADMA (3, 10, 30 μM) for 24, 48 and 72 h, trying to explore the effects of ADMA on blood-retinal barrier in DR. Gap junction intercellular communication (GJIC) and the expression of blood-retinal barrier-specific component connexin 43 (Cx43) were examined in diabetic rats or cultured retinal pericytes to elucidate whether ADMA impacted blood-retinal barrier function via damaging Cx43-GJIC. The results showed that with increasing duration of diabetes, the ultrastructure of blood-retinal barrier of diabetic rats appeared cell junction damage, apoptosis of retinal pericytes and breakdown of barrier successively. The increases in retinal permeability, ADMA levels and Cx43 expression, and abnormal GJIC were observed in diabetic rats and retinal pericytes exposed to D-glucose (30 mM). A glucose-like effect was seen using ADMA or another L-arginine analogue N^G-monomethyl-L-arginine or dimethylarginine dimethylaminohydrolases (DDAHs) siRNA, implicating that ADMA aggravated the breakdown of blood-retinal barrier via damaging Cx43-GJIC.

Piper sarmentosum Promotes Endothelial Nitric Oxide Production by Reducing Asymmetric Dimethylarginine in Tumor Necrosis Factor-α-Induced Human Umbilical Vein Endothelial Cells

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase (eNOS). ADMA is degraded by dimethylarginine dimethylaminohydrolase (DDAH). Elevated levels of ADMA lead to reduction in nitric oxide (NO) production, which is linked to endothelial dysfunction and atherosclerosis. Piper sarmentosum is an herb that has shown stimulation on endothelial NO production by increasing both expression and activity of eNOS. Thus, this study determined whether the positive effect of P. sarmentosum on NO production is related to its modulation on the DDAH-ADMA pathway in cultured human umbilical vein endothelial cells (HUVEC) exposed to tumor necrosis factor-α (TNF-α). HUVEC were divided into four groups: control, treatment with 250 µg/ml of aqueous extract of P. sarmentosum leaves (AEPS), treatment with 30 ng/ml of TNF-α, and concomitant treatment with AEPS and TNF-α for 24 h. After treatments, HUVEC were collected to measure DDAH1 messenger RNA (mRNA) expression using quantitative real-time polymerase chain reaction. DDAH1 protein level was measured using enzyme-linked immunosorbent assay (ELISA), and DDAH enzyme activity was measured using colorimetric assay. ADMA concentration was measured using ELISA, and NO level was measured using Griess assay. Compared to control, TNF-α-treated HUVEC showed reduction in DDAH1 mRNA expression (P < 0.05), DDAH1 protein level (P < 0.01), and DDAH activity (P < 0.05). Treatment with AEPS successfully increased DDAH1 mRNA expression (P < 0.05), DDAH1 protein level (P < 0.01), and DDAH activity (P < 0.05) in TNF-α-treated HUVEC. Treatment with TNF-α caused an increase in ADMA level (P < 0.01) and a decrease in endothelial NO production (P < 0.001). Whereas treatment with AEPS was able to reduce ADMA level (P < 0.01) and restore NO (P < 0.001) in TNF-α-treated HUVEC. The results suggested that AEPS promotes endothelial NO production by stimulating DDAH activity and thus reducing ADMA level in TNF-α-treated HUVEC.

Probucol improves erectile function via Activation of Nrf2 and coordinates the HO-1 / DDAH / PPAR-γ/ eNOS pathways in streptozotocin-induced diabetic rats

BACKGROUND

Diabetic erectile dysfunction (DMED) is mainly attributed to oxidative stress, and Nrf2 plays an important role in cellular antioxidation and regulates NO production in the vascular endothelium. Probucol maintains endothelial function through its antioxidant activity. This study investigated the efficacy and mechanism of probucol in improving erectile function in streptozotocin-induced diabetic rats.

METHODS

In our study, thirty 12-week-old Sprague-Dawley male rats were fasted for 12 h. All rats received a 1-time injection of intraperitoneal streptozotocin(60 mg/kg) or vehicle. After 72 h, STZ-treated rats (with random blood glucose concentrations consistently greater than 16.7 mmol/L) were considered diabetic. The diabetic rats were randomly assigned into 2 groups and treated with daily gavage feedings of probucol at doses of 0 and 500 mg/kg for 12 weeks. A positive control group underwent intraperitoneal injection of normal saline followed by daily gavage of saline solution. Erectile function was assessed by electrical stimulation of the cavernous nerves with real-time intracavernous pressure measurement. After euthanasia, penile tissue was investigated using immunohistochemistry, Western blot, and ELISA to assess the proteins of Nrf2/HO-1/DDAH/PPAR-γ/eNOS pathways.

RESULTS

After treatment, the rats in the probucol group presented significantly improved erectile function (P < 0.05) than that of the diabetic group without probucol treatment (DM). Also, protein expression of Nrf2, DDAH, PPAR-γ, HO-1 and eNOS was significantly higher than that of the DM group (P < 0.05). CGMP concentrations and SOD concentrations of probucol-treated rats were higher than those of DM group (P < 0.05). The MDA levels and ADMA levels were significantly lower than those of DM group rats (P < 0.05).

CONCLUSION

Probucol can improve erectile function via activation of Nrf2, which coordinates the HO-1/DDAH/PPAR-γ/eNOS pathways in streptozotocin-induced diabetic rats.

Murine models of vascular endothelial injury: Techniques and pathophysiology

Vascular endothelial injury (VEI) triggers pathological processes in various cardiovascular diseases, such as coronary heart disease and hypertension. To further elucidate the in vivo pathological mechanisms of VEI, many animal models have been established. For the easiness of genetic manipulation and feeding, murine models become most commonly applied for investigating VEI. Subsequently, countless valuable information concerning pathogenesis has been obtained and therapeutic strategies for VEI have been developed. This review will highlight some typical murine VEI models from the perspectives of pharmacological intervention, surgery and genetic manipulation. The techniques, pathophysiology, advantages, disadvantages and the experimental purpose of each model will also be discussed.

Asymmetric dimethylarginine contributes to retinal neovascularization of diabetic retinopathy through EphrinB2 pathway

Diabetic retinopathy (DR) is a leading cause of vision loss with retinal neovascularization. This study aims to investigate whether Asymmetric dimethylarginine (ADMA) impacts the pathogenesis of DR via focusing on promoting retinal neovascularization and its underlying molecular mechanisms. Diabetic rats were induced by a single intraperitoneal injection of streptozotocin (STZ) for 20 weeks. ADMA levels in aqueous and the influence of hypoxia on ADMA and angiogenesis in RF/6A cells were examined. The effects and underlying molecular mechanisms of ADMA on neovascularization of RF/6A cells were further evaluated by administration of ADMA, DDAH siRNA or ephrinB2 siRNA. Results showed that ADMA levels were elevated in both aqueous from diabetic rats and culture medium in RF/6A cells pretreated with hypoxia. Administration of ADMA directly promoted proliferation, migration, adhesion and tube formation of RF/6A cells, which was further confirmed by DDAH1 siRNA or DDAH2 siRNA. In addition, ephrinB2 expression was increased under diabetic conditions, and the angiogenic effects of ADMA were blocked by ephrinB2 siRNA. In conclusion, ADMA contributes to the neovascularization of retina in diabetic mellitus, which is regulated by ephrinB2.

Time-course changes of nLDL-induced erectile dysfunction

Hyperlipidemia is an important risk factor for atherosclerosis and is frequently seen in patients with erectile dysfunction (ED). This study was designed to evaluate whether the acute effect of native low-density lipoprotein (nLDL) on intracavernosal pressure (ICP) is reversible and related to plasma asymmetrical dimethylarginine (ADMA), endogenous inhibition of endothelial nitric oxide synthase (eNOS) levels and eNOS expression in cavernous tissues. Hyperlipidemia was induced by a single dose of intravenous 4 mg kg^-1 nLDL. Experiments were performed 72 h (72H), 2 weeks (2W) and 8 weeks (8W) after nLDL injection. Endothelium-dependent relaxations, the ratio of ICP to mean arterial pressure (MAP; ICP/MAP), plasma ADMA levels and eNOS mRNA and protein levels were evaluated. The ICP/MAP ratio decreased in both the 2W and 8W groups. Endothelium-dependent relaxation responses to acetylcholine in the rat thoracic aorta were damaged in the 8W group. Plasma ADMA levels increased in the 8W group. mRNA expression of eNOS decreased in a time-dependent manner, whereas the protein expression increased. These results suggest that acute nLDL injection-induced impairments in erectile functions during an 8-week period are irreversible and might be related to an increase in ADMA levels and changes in the regulation of the eNOS/NO pathway.

Toxic Dimethylarginines: Asymmetric Dimethylarginine (ADMA) and Symmetric Dimethylarginine (SDMA)

Asymmetric and symmetric dimethylarginine (ADMA and SDMA, respectively) are toxic, non-proteinogenic amino acids formed by post-translational modification and are uremic toxins that inhibit nitric oxide (NO) production and play multifunctional roles in many human diseases. Both ADMA and SDMA have emerged as strong predictors of cardiovascular events and death in a range of illnesses. Major progress has been made in research on ADMA-lowering therapies in animal studies; however, further studies are required to fill the translational gap between animal models and clinical trials in order to treat human diseases related to elevated ADMA/SDMA levels. Here, we review the reported impacts of ADMA and SDMA on human health and disease, focusing on the synthesis and metabolism of ADMA and SDMA; the pathophysiological roles of these dimethylarginines; clinical conditions and animal models associated with elevated ADMA and SDMA levels; and potential therapies against ADMA and SDMA. There is currently no specific pharmacological therapy for lowering the levels and counteracting the deleterious effects of ADMA and SDMA. A better understanding of the mechanisms underlying the impact of ADMA and SDMA on a wide range of human diseases is essential to the development of specific therapies against diseases related to ADMA and SDMA.

Preservation of vascular DDAH activity contributes to the protection of captopril against endothelial dysfunction in hyperlipidemic rabbits

Endothelial dysfunction plays a pivotal role in the pathogenesis of atherosclerosis. Endogenous inhibitor of nitric oxide synthase (NOS) asymmetric dimethylarginine (ADMA) has been recognized as an independent risk factor of endothelial dysfunction and the biomarker of atherosclerosis. This study was to investigate whether endogenous ADMA and its metabolic enzyme dimethylarginine dimethylaminohydrolase (DDAH) were involved in mechanisms of captopril protection against endothelial dysfunction in high fat diet feeding rabbits. Half of model rabbits were treated with captopril (10mg/kg/d, i.g.) for 12w. Vascular morphology and serum lipid profiles were detected. Serum ADMA concentration were assayed by high performance liquid chromatography. Recombinant DDAH2 gene adenoviruses were ex vivo transferred to thoracic aortas of high fat diet feeding rabbits. Endothelium-dependent relaxation of aortas response to acetylcholine and DDAH activity were measured. Atherosclerosis was confirmed in high fat diet feeding rabbits by increased serum lipid profiles and morphologic changes of vascular wall. Serum ADMA levels were significantly increased in hyperlipidemic rabbits accompanied with impairment of endothelium-dependent relaxation and inhibition of DDAH activity in thoracic aortas. Captopril treatment not only decreased vascular intima thickening and serum ADMA concentration but also preserved vascular DDAH activity and endothelium-dependent relaxation in hyperlipidemic rabbits without influence on serum lipid profiles. Similar beneficial effects on endothelial function and DDAH activity could be achieved by DDAH2 gene transfection. These results indicated that captopril could protect against injuries of vascular morphology and endothelial function in hyperlipidemic rabbits, the mechanisms may be related to the preservation of DDAH activity and decrease of ADMA accumulation in vascular endothelium.

Inhibitors of the Hydrolytic Enzyme Dimethylarginine Dimethylaminohydrolase (DDAH): Discovery, Synthesis and Development

Dimethylarginine dimethylaminohydrolase (DDAH) is a highly conserved hydrolytic enzyme found in numerous species, including bacteria, rodents, and humans. In humans, the DDAH-1 isoform is known to metabolize endogenous asymmetric dimethylarginine (ADMA) and monomethyl arginine (l-NMMA), with ADMA proposed to be a putative marker of cardiovascular disease. Current literature reports identify the DDAH family of enzymes as a potential therapeutic target in the regulation of nitric oxide (NO) production, mediated via its biochemical interaction with the nitric oxide synthase (NOS) family of enzymes. Increased DDAH expression and NO production have been linked to multiple pathological conditions, specifically, cancer, neurodegenerative disorders, and septic shock. As such, the discovery, chemical synthesis, and development of DDAH inhibitors as potential drug candidates represent a growing field of interest. This review article summarizes the current knowledge on DDAH inhibition and the derived pharmacokinetic parameters of the main DDAH inhibitors reported in the literature. Furthermore, current methods of development and chemical synthetic pathways are discussed.

Phosphorylation of Nonmuscle Myosin Light Chain Promotes Endothelial Injury in Hyperlipidemic Rats Through a Mechanism Involving Downregulation of Dimethylarginine Dimethylaminohydrolase 2

Suppression of dimethylarginine dimethylaminohydrolase (DDAH) activation is related to endothelial dysfunction in hyperlipidemia, and nonmuscle myosin regulatory light chain (nmMLC₂₀) has been show to exert transcriptional function in regulation of gene expression. This study aims to explore whether the suppression of DDAH activation promotes endothelial injury under the condition of hyperlipidemia and whether nmMLC₂₀ can regulate DDAH expression in a phosphorylation-dependent manner. The rats were fed with high-fat diet for 8 weeks to establish a hyperlipidemic model, which showed an increase in plasma lipids and endothelial injury, accompanied by an elevation in myosin light chain kinase (MLCK) activity, phosphorylated nmMLC₂₀ (p-nmMLC₂₀) level, and asymmetric dimethylarginine (ADMA) content as well as a reduction in DDAH2 expression, DDAH activity, and nitric oxide (NO) content. Next, human umbilical vein endothelial cells (HUVECs) were incubated with oxidized low-density lipoprotein (ox-LDL; 100 μg/mL) for 24 hours to establish a cellular injury model in vitro. Consistent with the finding in vivo, ox-LDL induced HUVECs injury (apoptosis and necrosis) concomitant with an increase in MLCK activity, p-nmMLC₂₀ level (in total or nuclear proteins), and ADMA content as well as a reduction in DDAH2 expression, DDAH activity, and NO content; these phenomena were attenuated by MLCK inhibitor. Either in hyperlipidemic rats or in ox-LDL-treated HUVECs, there was not significant change in DDAH1 expression. Based on these observations, we conclude that the suppression of DDAH2 expression might account for, at least partially, the vascular endothelial dysfunction in hyperlipidemia, and nmMLC₂₀ plays a role in suppression of DDAH2 expression in a phosphorylation-dependent manner.

Pharmacological modulation of dietary lipid-induced cerebral capillary dysfunction: Considerations for reducing risk for Alzheimer's disease

An increasing body of evidence suggests that cerebrovascular dysfunction and microvessel disease precede the evolution of hallmark pathological features that characterise Alzheimer's disease (AD), consistent with a causal association for onset or progression. Recent studies, principally in genetically unmanipulated animal models, suggest that chronic ingestion of diets enriched in saturated fats and cholesterol may compromise blood-brain barrier (BBB) integrity resulting in inappropriate blood-to-brain extravasation of plasma proteins, including lipid macromolecules that may be enriched in amyloid-β (Aβ). Brain parenchymal retention of blood proteins and lipoprotein bound Aβ is associated with heightened neurovascular inflammation, altered redox homeostasis and nitric oxide (NO) metabolism. Therefore, it is a reasonable proposition that lipid-lowering agents may positively modulate BBB integrity and by extension attenuate risk or progression of AD. In addition to their robust lipid lowering properties, reported beneficial effects of lipid-lowering agents were attributed to their pleiotropic properties via modulation of inflammation, oxidative stress, NO and Aβ metabolism. The review is a contemporary consideration of a complex body of literature intended to synthesise focussed consideration of mechanisms central to regulation of BBB function and integrity. Emphasis is given to dietary fat driven significant epidemiological evidence consistent with heightened risk amongst populations consuming greater amounts of saturated fats and cholesterol. In addition, potential neurovascular benefits associated with the use of hypolipidemic statins, probucol and fenofibrate are also presented in the context of lipid-lowering and pleiotropic properties.

Did we abandon probucol too soon?

PURPOSE OF REVIEW

Probucol is a potent antioxidative drug that has been used for prevention and treatment of atherosclerotic cardiovascular diseases and xanthoma. Probucol has been used as a lipid-lowering drug for a long time especially in Japan, although Western countries quitted its use because of the reduction in serum HDL-cholesterol (HDL-C). This review highlights both basic and clinical studies that provide new insights into the pleiotropic effects of probucol.

RECENT FINDINGS

Recently, the mechanisms for the pharmacologic actions of probucol have been elucidated at the molecular level with a special focus on HDL metabolism and its functions. Probucol enhances plasma cholesteryl ester transfer protein activity and hepatic scavenger receptor class B type I, causing a decrease in HDL-C. It also accelerates the antioxidative function of HDL via increase in paraoxonase 1 activity. Recent retrospective analyses of probucol-treated patients with heterozygous familial hypercholesterolemia and those after coronary revascularization demonstrated a strong beneficial effect of probucol on secondary prevention of cardiovascular events and mortality.

SUMMARY

Probucol has pleiotropic and beneficial therapeutic effects on cardiovascular system. Although statins are effective for lowering LDL-cholesterol (LDL-C) and reducing coronary heart disease risk, probucol should be considered as an option in case statins are not effective.

Haemodynamic responses to tobacco smoke inhalation in male adolescents in Lusaka, Zambia

Background

Tobacco smoke causes changes in the levels of catecholamines in the blood. This leads to an increase in blood pressure and heart rate. This is due to nicotine which has also been noted to cause a decrease in vasodilatory activities leading to an increase in both the blood pressure and heart rate.

Aim

To determine the acute effects of tobacco smoke on haemodynamics in black male adolescents in Lusaka, Zambia.

Study design

This was an observational study done at the University of Zambia School of Medicine Cardiovascular Research Laboratory in the month of December, 2014.

Methodology

Twenty-two (22) black, male-adolescent (age range 19-25 years), active-smokers, consented to participate in the study. The Diasys Ambulatory Blood Pressure Monitoring system (Novacor, France) was used to obtain the Systolic and Diastolic blood pressures (SBP and DBP) and the heart rate. These were obtained 15 minutes before smoking at 5 minute intervals and averaged to obtain the baseline, during the 15 minutes of smoking and on immediate cessation of smoking and thereafter every 15 minutes up to an hour after smoking.

Results

There was a significant rise in SBP (mmHg) during smoking (127.9 ± 13.80 mmHg) from baseline values (113.5 ± 13.15 mmHg) (P = .00). It took 30 minutes for the SBP to return to baseline after cessation of smoking. DBP (mmHg) also increased from baseline (79.5 ± 8.79 mmHg) to 85.6 ± 10.92 mmHg during smoking (P = .01). It returned to baseline values immediately after cessation of smoking. The heart rate (bpm) was also noted to significantly increase during smoking (95.2 ± 16.72 bpm) from the values noted before smoking (74.3 ± 13.75 bpm) (P = .05). The mean value for heart rate returned to baseline value by the 15^th minute of recovery.

Conclusion

The present study demonstrates that smoking may be the cause for the acute increases in SBP, DBP and heart rate in smokers. The smoking caused significant increases in all the haemodynamic indices considered in this study within 15 minutes. Both SBP and DBP increase are indices for stroke and coronary heart disease respectively. The effect of increased SBP was noted to last for 30 minutes while DBP returned to baseline immediately after smoking. A significant increase in heart rate was also noted in the study.

Inhibition of suicidal erythrocyte death by probucol

Probucol, an antioxidant and anti-inflammatory agent counteracting atherosclerosis and restenosis, is partially effective by influencing suicidal cell death or apoptosis. In analogy to apoptosis of nucleated cells, suicidal death of erythrocytes or eryptosis is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptosis is stimulated by increase in cytosolic Ca(2+) activity, for example, after energy depletion or oxidative stress. The present study explored whether probucol influences eryptosis. Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter (FSC), and cytosolic Ca(2+) concentration from fluo-3 fluorescence in flow cytometry. As a result, energy depletion (48-hour glucose removal) increased annexin-V-binding, decreased FSC, and increased fluo-3 fluorescence. Probucol (≤30 μM) did not significantly modify annexin-V-binding, FSC, or fluo-3 fluorescence in the presence of glucose but (at ≥5 μM) blunted the effect of glucose depletion on annexin-V-binding. Probucol (≥20 μM) only slightly blunted the effects of glucose depletion on FSC and fluo-3 fluorescence. Ca(2+) ionophore ionomycin (1 μM) and oxidative stress (30-minute exposure to 0.3 mM of tert-butylhydroperoxide) increased annexin-V-binding, effects again blunted by 30 μM of probucol. In conclusion, probucol blunts cell membrane scrambling after energy depletion and oxidative stress, effects primarily because of interference with the scrambling effects of increased cytosolic Ca(2+) concentration.

Direct and indirect antioxidant properties of α-lipoic acid and therapeutic potential

Diabetes has emerged as a major threat to worldwide health. The exact mechanisms underlying the disease are unknown; however, there is growing evidence that the excess generation of reactive oxygen species (ROS) associated with hyperglycemia, causes oxidative stress in a variety of tissues. In this context, various natural compounds with pleiotropic actions like α-lipoic acid (LA) are of interest, especially in metabolic diseases such as diabetes. LA, either as a dietary supplement or a therapeutic agent, modulates redox potential because of its ability to match the redox status between different subcellular compartments as well as extracellularly. Both the oxidized (disulfide) and reduced (di-thiol: dihydro-lipoic acid, DHLA) forms of LA show antioxidant properties. LA exerts antioxidant effects in biological systems through ROS quenching but also via an action on transition metal chelation. Dietary supplementation with LA has been successfully employed in a variety of in vivo models of disease associated with an imbalance of redox status: diabetes and cardiovascular diseases. The complex and intimate association between increased oxidative stress and increased inflammation in related disorders such as diabetes, makes it difficult to establish the temporal sequence of the relationship.

Beneficial effects of the active principle component of Korean cabbage kimchi via increasing nitric oxide production and suppressing inflammation in the aorta of apoE knockout mice

The present study investigated the effects of 3'-(4'-hydroxyl-3',5'-dimethoxyphenyl)propionic acid (HDMPPA), the active principle compound of kimchi, on vascular damage in the experimental atherosclerotic animal. HDMPPA was administrated by an intraperitoneal injection of 10 mg/kg per d for 8 weeks to apoE knockout (KO) mice with an atherogenic diet containing 1 % cholesterol, and its effects were compared with vehicle-treated control mice. HDMPPA increased NO content in the aorta, accompanied by a decrease in reactive oxygen species (ROS) concentration. Furthermore, in the HDMPPA-treated group, aortic endothelial NO synthase (eNOS) expression was up-regulated compared with the control group. These results suggested that HDMPPA could maintain NO bioavailability through an increasing eNOS expression and preventing NO degradation by ROS. Furthermore, HDMPPA treatment in apoE KO mice inhibited eNOS uncoupling through an increase in vascular tetrahydrobiopterin content and a decrease in serum asymmetric dimethylarginine levels. Moreover, HDMPPA ameliorates inflammatory-related protein expression in the aorta of apoE KO mice. Therefore, the present study suggests that HDMPPA, the active compound of kimchi, a Korean functional food, may exert its vascular protective effect through the preservation of NO bioavailability and suppression of the inflammatory response.

Cardiovascular risk in autoimmune disorders: role of asymmetric dimethylarginine

Mounting evidence indicates that cardiovascular events are a main cause of excessive mortality of autoimmune disorders like type I diabetes mellitus and rheumatic diseases. Inflammation and endothelial dysfunction, independent predictors to cardiovascular disease, are hallmarks of autoimmunity. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, can cause or contribute to the inflammatory syndrome and endothelial dysfunction. Recently, elevated ADMA levels have been demonstrated in many autoimmune diseases, suggesting that ADMA might play an important role for the associated manifestations of cardiovascular disease. In the review, we discuss the role of ADMA in the excessive cardiovascular morbidity and mortality associated with autoimmune diseases.

Protective effect of neferine on endothelial cell nitric oxide production induced by lysophosphatidylcholine: the role of the DDAH–ADMA pathway

Neferine, extracted from the seed embryo of Nelumbo nucifera Gaertn., has multiple cardiovascular pharmacological effects. The dimethylarginine dimethylaminohydrolase (DDAH) – asymmetric dimethylarginine (ADMA) system is a novel pathway for modulating nitric oxide (NO) production. The aim of this study was to investigate whether the protective effect of neferine on endothelial NO production was related to the DDAH–ADMA pathway. Human umbilical vein endothelial cells (HUVECs) were first exposed to neferine (0.1, 1.0, or 10.0 μmol/L) for 1 h, and then incubated with lysophosphatidylcholine (LPC; 10 μg/mL) in the presence of neferine for 24 h. The medium was collected for measuring the levels of NO, maleic dialdehyde (MDA), as well as ADMA. The endothelial cells were collected for measuring DDAH activity and the level of reactive oxygen species (ROS). LPC significantly decreased NO concentration and DDAH activity and increased the levels of ADMA, ROS, and MDA. Neferine could partially counteract the changes induced by LPC. These findings suggested that neferine could modulate the DDAH–ADMA pathway via its antioxidant properties, which was involved in its beneficial effect on endothelial NO production.

3,4,5,6-Tetrahydroxyxanthone preserves intercellular communication by reduction of the endogenous nitric oxide synthase inhibitor level

To observe the direct effects of 3,4,5,6-tetrahydroxyxanthone on connexin43 (Cx43) expression in cultured endothelial cells, cells were treated with lysophosphatidylcholine (LPC, 10 mg/l) for 24 h in the presence or absence of different concentrations of 3,4,5,6-tetrahydroxyxanthone (1, 3, or 10 μmol l(- 1)). The reactive oxygen species (ROS) production, cell viability, asymmetric dimethylarginine (ADMA) levels, and Cx43 expression were detected. 3,4,5,6-Tetrahydroxyxanthone significantly inhibited the increase in ROS production and ADMA level, increased cell viability and up-regulated Cx43 mRNA and protein expression induced by LPC. 3,4,5,6-Tetrahydroxyxanthone has protective effect in LPC-induced atherosclerotic lesions, which is at least partly related to the reduction of ADMA level and downregulation of Cx43 expression.

Nitric oxide synthase inhibitors and cerebral vasospasm

L-arginine is a source of nitric oxide (NO) that is cleaved from the terminal guanidino nitrogen atom by nitric oxide synthase (NOS). NO evokes, because of its free radical properties and affinity to heme, ferrous iron and cysteine, a wide spectrum of physiological and pathophysiological effects. For many years, different exogenous NOS inhibitors were used to elucidate the role of NOS and NO in health and disease. Later, endogenous NOS inhibitors, as asymmetric dimethylarginine (ADMA) were discovered. Endogenous inhibitors as ADMA are produced by post-translational methylation of L-arginine which is catalyzed by a family of protein N-methyltransferases (PRMT), using S-adenosylmethionine as a methyl group donor. ADMA is eliminated by dimethylarginine dimethylaminohydrolases (DDAH I or II). ADMA hydrolysis increases NOS activity and NO production. Furthermore, L-citrulline, a by-product of ADMA hydrolysis as well as of NO production by NOS, can in turn inhibit DDAH. Therefore, endogenous inhibition of NOS can be modified via different ways (1) changing the availability of L-arginine and/or of L-citrulline; (2) stimulating or inhibiting DDAH activity; (3) modifying methylation via regulating availability of adenosylmethionine; or (4) modifying PRMT activity. Research elucidating the role of NOS inhibitors in respect of delayed cerebral vasospasm after subarachnoid hemorrhage is summarized.

Alpha-lipoic acid activates dimethylarginine dimethylaminohydrolase in cultured endothelial cells

Asymmetric dimethylarginine (ADMA) is a risk factor of cardiovascular diseases. alpha-Lipoic acid (ALA) was shown to improve vascular dysfunction, and to decrease plasma ADMA level. In this study, we investigated whether ALA activates dimethylarginine dimethylaminohydrolase (DDAH), the metabolizing enzyme of ADMA, in cultured endothelial cells. ALA significantly decreased ADMA level in culture media of endothelial cells. ALA increased the gene expression and activity of DDAH, and signal transducer and activator of transcription (STAT)3 phosphorylation. Transfection of STAT3 increased DDAH II promoter activity, and ALA amplified it. ALA-induced increase in DDAH II promoter activity was attenuated in the promoter that had mutation in putative STAT3-binding site. These results suggest that ALA reduces ADMA level by enhancing DDAH activity and DDAH II gene expression, thus providing a novel mechanism by which ALA regulates endothelial function.

Effect of supplementation with B vitamins and antioxidants on levels of asymmetric dimethylarginine (ADMA) and C-reactive protein (CRP): a double-blind, randomised, factorial design, placebo-controlled trial

PURPOSE

Cardiovascular risk factors such as elevated levels of asymmetric dimethylarginine (ADMA)/C-reactive protein (CRP) and homocysteine are potentially related to essential micronutrients such as certain B vitamins and antioxidant vitamins. The aim of the present study was to investigate whether supplementation with moderate doses of B vitamins and/or antioxidants could alter either ADMA and/or CRP concentrations in middle-aged, apparently healthy men with mildly elevated homocysteine levels.

METHODS

A randomised, double-blind, factorial design, intervention study was carried out on 132 men with mildly elevated homocysteine levels, allocated to four groups (a) B vitamins alone--1 mg folic acid, 7.2 mg pyridoxine, 0.02 mg cyanocobalamin daily, (b) antioxidants alone--150 mg ascorbic acid, 67 mg vitamin E, 9 mg β-carotene daily, (c) B vitamins with antioxidant vitamins, or (d) placebo. A total of 101 men completed the study to 8 weeks.

RESULTS

When the percentage of baseline ADMA and CRP was examined at 8 weeks, no statistically significant differences were observed between the four groups (p = 0.21 and p = 0.90, respectively). Similar non-significant results were observed when analysis was stratified based on baseline CRP levels (<1.0 mg/L, p = 0.10; ≥1.0 mg/L, p = 0.64) and smoking status (all p ≥ 0.05).

CONCLUSIONS

Supplementation with moderate doses of B vitamins and/or antioxidants did not alter either ADMA or CRP concentrations in these middle-aged, apparently healthy men with mildly elevated homocysteine levels.

Protective effects of kaempferol against endothelial damage by an improvement in nitric oxide production and a decrease in asymmetric dimethylarginine level

Previous investigations have shown that asymmetric dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS) and that ADMA is a risk factor for endothelial dysfunction. The objective of this study was to investigate the protective effect of kaempferol, a naturally occurring flavonoid antioxidant agent, against endothelial damage and the mechanisms involved. The experiments were performed in aorta and plasma from C57BL/6J control and apolipoprotein E-deficient (ApoE(-/-)) mice treated or not with kaempferol (50 or 100mg/kg, intragastrically) for 4 weeks, and in human umbilical vein endothelial cells (HUVECs) pretreated or not with kaempferol (1, 3 or 10 microM) for 1h and exposed to lysophosphatidylcholine (LPC) (10 microg/mL) for 24h. Kaempferol treatment improved endothelium-dependent vasorelaxation, increased the maximal relaxation value, and decreased the half-maximum effective concentration concomitantly with an increase in nitric oxide plasma concentration, a decrease in ADMA and malondialdehyde (MDA) plasma concentrations, and increase in the expression of aortic endothelial NOS (eNOS) as well as dimethylarginine dimethylaminohydrolase II (DDAH II) in ApoE(-/-) mice. In addition, LPC caused a reduction in NO production, an increase in ADMA concentration concomitantly with a decreased expression of eNOS and DDAH II in HUVECs, and the effect of LPC was abolished by kaempferol. Treatment with kaempferol also significantly decreased reactive oxygen species production in mice aorta and in HUVECs. The present results suggest that the protective effect of kaempferol against endothelial damage may be associated with an improvement in NO production and a decrease in ADMA level.

Asymmetric dimethylarginine (ADMA) and endothelial dysfunction: implications for atherogenesis

Atherosclerotic coronary heart disease is the leading cause of morbidity and mortality in industrialized countries, and endothelial dysfunction is considered a precursor phenomenon. The nitric oxide produced by the endothelium under the action of endothelial nitric oxide synthase has important antiatherogenic functions. Its reduced bioavailabilty is the beginning of the atherosclerotic process. The addition of two methyl radicals to arginine, through the action of methyltransferase nuclear proteins, produces asymmetric dimethylarginine, which competes with L-arginine and promotes a reduction in nitric oxide formation in the vascular wall. The asymmetric dimethylarginine, which is itself considered a mediator of the vascular effects of the several risk factors for atherosclerosis, can be eliminated by renal excretion or by the enzymatic action of the dimethylarginine dimethylaminohydrolases. Several basic science and clinical research studies suggest that the increase in asymmetric dimethylarginine occurs in the context of chronic renal insufficiency, dyslipidemia, high blood pressure, diabetes mellitus, and hyperhomocysteinemy, as well as with other conditions. Therapeutic measures to combat atherosclerosis may reverse these asymmetric dimethylarginine effects or at least reduce the concentration of this chemical in the blood. Such an effect can be achieved with competitor molecules or by increasing the expression or activity of its degradation enzyme. Studies are in development to establish the true role of asymmetric dimethylarginine as a marker and mediator of atherosclerosis, with possible therapeutic applications. The main aspects of the formation and degradation of asymmetric dimethylarginine and its implication in the atherogenic process will be addressed in this article.

Randomized placebo-controlled trial assessing a treatment strategy consisting of pravastatin, vitamin E, and homocysteine lowering on plasma asymmetric dimethylarginine concentration in mild to moderate CKD

BACKGROUND

Chronic kidney disease (CKD) is associated with an increased incidence of cardiovascular disease (CVD). The Anti-oxidant Therapy In Chronic Renal Insufficiency (ATIC) Study showed that a multistep treatment strategy improved carotid intima-media thickness, endothelial function, and microalbuminuria in patients with stages 2 to 4 CKD. Increased plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, have been linked to greater CVD risk in patients with CKD. The aim of this study is to assess effects of the multistep intervention on plasma ADMA concentrations in the ATIC Study.

STUDY DESIGN

Secondary analysis of a randomized double-blind placebo-controlled trial.

SETTING & PARTICIPANTS

93 patients with creatinine clearance of 15 to 70 mL/min/1.73 m(2) (according to the Cockcroft-Gault equation) from 7 outpatient clinics in Amsterdam, The Netherlands.

INTERVENTION

The treatment group received sequential treatment consisting of pravastatin, 40 mg/d. After 6 months, vitamin E, 300 mg/d, was added, and after another 6 months, homocysteine-lowering therapy (folic acid, 5 mg/d; pyridoxine, 100 mg/d; and vitamin B(12), 1 mg/d, all in 1 tablet) were added and continued for another year. The control group received matching placebos.

OUTCOME & MEASURES

Plasma ADMA levels.

RESULTS

36 participants (77%) in the treatment group and 38 (83%) in the placebo group completed the study. Mean ADMA and symmetric dimethylarginine concentrations in the total study population were 0.53 +/- 0.07 (SD) and 1.14 +/- 0.46 mumol/L, respectively. After 24 months, there was no overall effect of the treatment strategy on ADMA concentrations (beta = -0.006; P = 0.27). Analysis of separate treatment effects suggested that vitamin E significantly decreased ADMA levels by 4% in the treatment group compared with the placebo group (multiple adjusted P = 0.02).

LIMITATIONS

The study was a secondary analysis, power calculation was based on the primary end point of carotid intima-media thickness, mean plasma ADMA levels were relatively low.

CONCLUSION

Overall, a multistep treatment strategy consisting of pravastatin, vitamin E, and B vitamins had no effect on plasma ADMA levels in a stage 2 to 4 CKD population. This suggests that the beneficial effects of the intervention were not mediated by changes in ADMA levels. Possible ADMA-lowering effects of vitamin E deserve further attention.

New and emerging risk factors for CVD

Morphological and immunocytochemical studies have elucidated the complex processes involved in atherogenesis. The notion of plaque instability has emerged from this work and underscored the importance of inflammation in determining clinical complications associated with atherosclerosis, such as acute coronary syndrome. Cells of the immune system have been detected within atherosclerotic lesions and auto-antibodies directed against modified LDL and heat-shock proteins have been identified in the blood of individuals with atherosclerosis. The use of risk 'engines', e.g. the Framingham coronary risk score, has facilitated the identification of individuals at high risk, but the constituent classical risk factors used in these algorithms do not adequately differentiate individuals at moderate risk. As age is a major component of the equations used in these algorithms they are not particularly useful in young adults, and their applicability to non-Caucasian populations has been questioned. Biomarkers of early disease and plaque instability have therefore both been sought. Although some of these markers have been shown individually to be associated with a significant hazard ratio, no substantial improvement in discrimination has been demonstrated when they are incorporated into a risk 'engine'. The latter has generally been assessed by receiver operator characteristic curve analysis, although this approach has been criticised. Other modalities, including imaging and functional assessments of vascular function, are now being developed for clinical use.

Gene transfer of dimethylarginine dimethylaminohydrolase-2 improves the impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells induced by lysophosphatidylcholine

Dimethylarginine dimethylaminohydrolase (DDAH) is a key enzyme responsible for the metabolism of nitric oxide (NO) synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA), and DDAH2 is the predominant isoform in vascular endothelium. Lysophosphatidylcholine (LPC) and ADMA are implicated in endothelial dysfunction of atherosclerosis. This study was to examine changes in DDAH/ADMA/NOS/NO pathway in endothelial cells after exposure to LPC and investigate whether DDAH2 gene transfer could reverse LPC-induced changes. Human endothelial cell line ECV304 cells were transfected with recombinant pcDNA3.1-hDDAH2 plasmid and incubated with 3 micromol/L LPC for 48 h. Cells were harvested for assays of DDAH transcription, DDAH and NOS activities. The culture medium was collected for measurements of ADMA and nitrite/nitrate concentrations. LPC treatment suppressed DDAH2 transcription and DDAH activity in parallel with increased ADMA concentration, inhibited NOS activity and decreased NO metabolites content. DDAH2 gene transfer not only prevented the suppression of DDAH activity and the elevation of endogenous ADMA, but also attenuated the inhibition of NOS activity and the reduction of NO level induced by LPC in endothelial cells. These results suggest that LPC induces impairments of DDAH/ADMA/NOS/NO pathway, and DDAH2 gene transfer could improve the LPC-elicited impairments in endothelial cells.

The new oral immunomodulating drug DiNAC induces brachial artery vasodilatation at rest and during hyperemia in hypercholesterolemic subjects, likely by a nitric oxide-dependent mechanism

OBJECTIVES

To investigate if the immunomodulator drug DINAC (1) affects arterial dimensions in asymptomatic patients with hypercholesterolemia, (2) has effects on leucocyte markers of inflammation and (3) has in vitro effects on nitric oxide synthase (NOS) in human umbilical vein endothelial cells (HUVEC).

METHODS AND RESULTS

One hundred and fifty-three patients with asymptomatic hypercholesterolemia were randomized to either 100 or 500 mg of DINAC or placebo in a double-blind, parallel-group fashion for 24 weeks. Treatment at the highest dose induced a significant increase in resting brachial artery diameter measured by ultrasound and also induced a significant increase in vessel diameter during hyperemia. However, flow-mediated vasodilation (FMD) and the vasodilatory response to nitroglycerin, lipid levels or leukocyte count were unaltered. Expression of several cell surface markers of inflammation, like CD11b and CD25, were reduced by treatment. In vitro, DINAC counteracted TNF-alpha induced reductions in NO levels and in NOS protein and mRNA levels.

CONCLUSION

The immunomodulator drug DINAC increased brachial artery diameter at rest and during hyperemia in asymptomatic subjects with hypercholesterolemia without affecting blood lipid levels. Based on parallel in vitro studies this effect is likely due to an enhancement of NOS activity.

Nitric oxide deficiency in chronic kidney disease

The overall production of nitric oxide (NO) is decreased in chronic kidney disease (CKD) which contributes to cardiovascular events and further progression of kidney damage. There are many likely causes of NO deficiency in CKD and the areas surveyed in this review are: 1. Limitations on substrate (l-Arginine) availability, probably due to impaired renal l-Arginine biosynthesis, decreased transport of l-Arginine into endothelial cells and possible competition between NOS and competing metabolic pathways, such as arginase. 2. Increased circulating levels of endogenous NO synthase (NOS) inhibitors, in particular asymmetric dimethylarginine (ADMA). Increased methylation of proteins and their subsequent breakdown to release free ADMA may contribute but the major culprit is probably reduced ADMA catabolism by the enzymes dimethylarginine dimethylaminohydrolases. 3. Reduced renal cortex abundance of the neuronal NOS (nNOS)α protein correlates with injury while increasing nNOSβ abundance may provide a compensatory, protective response. Interventions that can restore NO production by targeting these various pathways are likely to reduce the cardiovascular complications of CKD as well as slowing the rate of progression.

Dysfunction of nitric oxide synthases as a cause and therapeutic target in delayed cerebral vasospasm after SAH

Nitric oxide (NO), also known as endothelium-derived relaxing factor, is produced by endothelial nitric oxide synthase (eNOS) in the intima and by neuronal nitric oxide synthase (nNOS) in the adventitia of cerebral vessels. It dilates the arteries in response to shear stress, metabolic demands, pterygopalatine ganglion stimulation, and chemoregulation. Subarachnoid haemorrhage (SAH) interrupts this regulation of cerebral blood flow. Hemoglobin, gradually released from erythrocytes in the subarachnoid space destroys nNOS-containing neurons in the conductive arteries. This deprives the arteries of NO, leading to the initiation of delayed vasospasm. But such vessel narrowing increases shear stress, which stimulates eNOS. This mechanism normally would lead to increased production of NO and dilation of arteries. However, a transient eNOS dysfunction evoked by an increase of the endogenous competitive nitric oxide synthase (NOS) inhibitor, asymmetric dimethyl-arginine (ADMA), prevents this vasodilation. eNOS dysfunction has been recently shown to be evoked by increased levels of ADMA in CSF in response to the presence of bilirubin-oxidized fragments (BOXes). A direct cause of the increased ADMA CSF level is most likely decreased ADMA elimination due to the disappearance of ADMA-hydrolyzing enzyme (DDAH II) immunoreactivity in the arteries in spasm. This eNOS dysfunction sustains vasospasm. CSF ADMA levels are closely associated with the degree and time-course of vasospasm; when CSF ADMA levels decrease, vasospasm resolves. Thus, the exogenous delivery of NO, inhibiting the L-arginine-methylating enzyme (IPRMT3) or stimulating DDAH II, may provide new therapeutic modalities to prevent and treat vasospasm. This paper will present results of preclinical studies supporting the NO-based hypothesis of delayed cerebral vasospasm development and its prevention by increased NO availability.

''Iatrogenic Gilbert syndrome''--a strategy for reducing vascular and cancer risk by increasing plasma unconjugated bilirubin

The catabolism of heme, generating biliverdin, carbon monoxide, and free iron, is mediated by heme oxygenase (HO). One form of this of this enzyme, heme oxygenase-1, is inducible by numerous agents which promote oxidative stress, and is now known to provide important antioxidant protection, as demonstrated in many rodent models of free radical-mediated pathogenesis, and suggested by epidemiology observing favorable health outcomes in individuals carrying high-expression alleles of the HO-1 gene. The antioxidant impact of HO-1 appears to be mediated by bilirubin, generated rapidly from biliverdin by ubiquitously expressed biliverdin reductase. Bilirubin efficiently scavenges a wide range of physiological oxidants by electron donation. In the process, it is often reconverted to biliverdin, but biliverdin reductase quickly regenerates bilirubin, thereby greatly boosting its antioxidant potential. There is also suggestive evidence that bilirubin inhibits the activity or activation of NADPH oxidase. Increased serum bilirubin is associated with reduced risk for atherogenic disease in epidemiological studies, and more limited data show an inverse correlation between serum bilirubin and cancer risk. Gilbert syndrome, a genetic variant characterized by moderate hyperbilirubinemia attributable to reduced hepatic expression of the UDP-glucuronosyltransferase which conjugates bilirubin, has been associated with a greatly reduced risk for ischemic heart disease and hypertension in a recent study. Feasible strategies for boosting serum bilirubin levels may include administration of HO-1 inducers, supplementation with bilirubin or biliverdin, and administration of drugs which decrease the efficiency of hepatic bilirubin conjugation. The well-tolerated uricosuric drug probenecid achieves non-competitive inhibition of hepatic glucuronidation reactions by inhibiting the transport of UDP-glucuronic acid into endoplasmic reticulum; probenecid therapy is included in the differential diagnosis of hyperbilirubinemia, and presumably could be used to induce an ''iatrogenic Gilbert syndrome''. Other drugs, such as rifampin, can raise serum bilirubin through competitive inhibition of hepatocyte bilirubin uptake--although unfortunately rifampin is not as safe as probenecid. Measures which can safely achieve moderate serum elevations of bilirubin may prove to have value in the prevention and/or treatment of a wide range of disorders in which oxidants play a prominent pathogenic role, including many vascular diseases, cancer, and inflammatory syndromes. Phycobilins, algal biliverdin metabolites that are good substrates for biliverdin reductase, may prove to have clinical antioxidant potential comparable to that of bilirubin.

Probucol mediates vascular remodeling after percutaneous transluminal angioplasty via down-regulation of the ERK1/2 signaling pathway

Although probucol is known to prevent restenosis by regulating vascular remodeling after percutaneous transluminal coronary angioplasty, the mechanisms remain unclear. The present study was designed to investigate whether probucol mediates vascular remodeling via the extracellular signal-regulated kinase 1/2 (ERK1/2) signalling pathway. A rabbit restenosis model was used, in which the New Zealand white rabbits received angioplasty with a 3.5 F angioplasty balloon catheter and the proliferation and migration of smooth muscle cells (SMCs) was induced by oxidized low-density lipoprotein (ox-LDL). We evaluated several vascular remodeling parameters and found that probucol prevented lumen restenosis and mediated expansive remodeling with a remodeling index greater than 1 and that the proliferation and migration of SMCs was inhibited. Based on Western blot analyses, probucol decreased the expression of phospho-mitogen-activated protein kinase kinases 1 (p-MEK1) and phospho-ERK1/2 and enhanced the expression of mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) and caveolin-1. Cells treated with the MEK1 inhibitor PD98059 demonstrated a remarkable suppression of the effects of probucol. Furthermore, immunofluorescence analysis showed that probucol inhibited the activation of ERK1/2 by preventing its translocation to the nucleus. It was also found that c-myc expression in aortic tissue after angioplasty and the activator protein 1 (AP1) activity in SMCs induced by ox-LDL were decreased with probucol treatment. In conclusion, probucol mediated vascular remodeling to prevent restenosis after angioplasty by down-regulating the ERK1/2 signaling pathway.

Role of asymmetric dimethylarginine in inflammatory reactions by angiotensin II

Previous investigations have demonstrated that angiotensin (Ang) II induces inflammatory reactions and asymmetric dimethylarginine (ADMA), an endogenous NOS inhibitor, might be a novel inflammatory factor. Endothelial cell activation was induced by incubation with Ang II or ADMA. Incubation with Ang II (10(-6) M) for 24 h elevated the levels of ADMA and decreased the levels of nitrite/nitrate concomitantly with a significant increase in the expression of protein arginine methyltransferase and a decrease in the activity of dimethylarginine dimethylaminohydrolase (DDAH). Exposure to Ang II (10(-6) M for 24 h) also enhanced intracellular ROS elaboration and the levels of tumor necrosis factor (TNF)-alpha and interleukin (IL)-8, upregulated chemokine receptor CXCR2 mRNA expression, increased adhesion of endothelial cells to monocytes and induced a significant increase in the activity of nuclear factor (NF)-kappaB, which was attenuated by pretreatment with the Ang II receptor blocker losartan (1, 3 and 10 muM). Exogenous ADMA (30 microM) also increased ROS generation and the levels of TNF-alpha and IL-8, decreased the levels of nitrite/nitrate, upregulated CXCR2 gene expression, increased endothelial cell binding with monocytes and activated the NF-kappaB pathway, which was inhibited by pretreatment with losartan or L-arginine. These data suggest that ADMA is a potential proinflammatory factor and may be involved in the inflammatory reaction induced by Ang II.

Taurine protects against low-density lipoprotein-induced endothelial dysfunction by the DDAH/ADMA pathway

Asymmetric dimethylarginine (ADMA), a major endogenous nitric oxide (NO) synthase inhibitor, is thought to be a key contributor for endothelial dysfunction. Decrease in activity of dimethylarginine dimethylaminohydrolase (DDAH), a major hydrolase of ADMA, causes accumulation of ADMA in some risk factors of atherosclerosis, including hypercholesterolemia. Taurine is a semi-essential amino acid that has previously been shown to have endothelial protective effects. The present study was to test whether the protective effect of taurine on endothelial function is related to modulation of the DDAH/ADMA pathway. A single injection of native LDL (4 mg/kg, i.v.) markedly reduced endothelium-dependent vasorelaxation and the plasma level of NO, and increased plasma concentrations of ADMA, malondialdehyde (MDA) and tumor necrosis factor-alpha (TNF-alpha). Treatment with taurine in vivo (60 or 180 mg/kg) significantly attenuated the inhibition of endothelium-dependent vasorelaxation and the reduced level of NO, and decreased the elevated levels of ADMA, MDA, and TNF-alpha. Incubation human umbilical vein endothelial cells (HUVECs) with ox-LDL (100 microg/ml) for 24 h markedly increased the medium levels of lactate dehydrogenase (LDH), ADMA, TNF-alpha and MDA, and decreased the level of NO in the medium and the intracellular activity of DDAH. Taurine (1 or 5 microg/ml) significantly attenuated the increases in the levels of LDH, ADMA, TNF-alpha and MDA, and the decrease in the level of NO and the activity of DDAH induced by ox-LDL in HUVECs. The present results suggested that taurine protected against endothelial dysfunction induced by native LDL in vivo or by ox-LDL in endothelial cells, and the protective effect of taurine on the endothelium is related to decrease in ADMA level by increasing of DDAH activity.

Effect of asymmetric dimethylarginine on atherogenesis and erythrocyte deformability in apolipoprotein E deficient mice

Previous investigations have shown that the level of asymmetric dimethylarginine (ADMA) was increased in hypercholesterolemic animal and humans, and the decreased erythrocyte deformability has been suggested to be a factor contributing to atherogenesis. In the present study, we investigated the effect of ADMA, endogenous or exogenous, on atherogenesis and erythrocyte deformability in apolipoprotein E deficient (ApoE-/-) mice. On a regular chow diet, ApoE-/- mice or C57BL/6 J mice at 12 weeks of age were treated with ADMA (5 mg/kg/day) for 4 weeks. Atherosclerotic lesion area, erythrocyte deformability, plasma lipids and asymmetric dimethylarginine (ADMA) level were determined. Plasma concentrations of triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC), ADMA, and atherosclerotic lesion area were significantly increased, and the level of plasma high-density lipoprotein-cholesterol (HDL-C), erythrocyte deformability in ApoE-/- mice were markedly decreased compared with that of C57BL/6J mice (P<0.05 or P<0.01). Exogenous ADMA treatment increased the plasma TG level, produced atherosclerotic lesions, and decreased erythrocyte deformability in C57BL/6J mice (P<0.05 or P<0.01). Treatment with exogenous ADMA further increased the plasma TG level and lesion areas, and decreased erythrocyte deformability in ApoE-/- mice. In vitro, exogenous ADMA caused a decrease of erythrocyte deformability in a concentration-dependent manner, and the effect of ADMA was reversed by L-arginine. The present results suggest that endogenous ADMA is an important contributor to the development of atherosclerosis and that reduction of erythrocyte deformability and impaired endothelial function induced by ADMA may be an important factor facilitating atherosclerotic lesions.

Asymmetric dimethylarginine reduced erythrocyte deformability in streptozotocin-induced diabetic rats

To investigate the effect of asymmetric dimethylarginine on erythrocyte deformability in streptozotocin-induced diabetic rats, a single intraperitoneal injection of streptozotocin (STZ, 65 mg/kg) in male Sprague-Dawley rats was carried out to induce diabetes and normal erythrocytes were incubated with asymmetric dimethylarginine or aortic rings from diabetic rats in the presence of L-arginine or vitamin E. We found that erythrocyte deformability was significantly decreased in diabetic rats. The levels of asymmetric dimethylarginine in plasma and erythrocytes of diabetic rats were elevated significantly from 2-week diabetic duration to 8-week diabetic duration. Nitric oxide in erythrocytes was decreased at 8-week diabetic duration while plasma nitric oxide remained unchanged all along. The content of malondialdehyde in erythrocytes of diabetic rats was increased. After incubation of erythrocytes with asymmetric dimethylarginine (10(-6) M) for 30 min, erythrocyte deformability and nitric oxide level in erythrocytes were decreased markedly. Reactive oxygen species and malondialdehyde production in erythrocytes were promoted by asymmetric dimethylarginine. Both L-arginine and vitamin E reversed the effects of asymmetric dimethylarginine. After incubation of erythrocytes with aortic rings from diabetic rats, erythrocyte deformability was decreased, which was attenuated by L-arginine. These results indicated that reduction of erythrocyte deformability in diabetic rats was associated with promoted oxidant stress as well as impaired nitric oxide synthesis by elevation of asymmetric dimethylarginine.

Relationship between protective effects of rosiglitazone on endothelium and endogenous nitric oxide synthase inhibitor in streptozotocin-induced diabetic rats and cultured endothelial cells

BACKGROUND

Previous investigations have indicated that the level of asymmetric dimethylarginine (ADMA) is increased in diabetic patients and animals, and rosiglitazone has a protective effect on the endothelium. In the present study, we tested the relationship between protective effects of rosiglitazone and ADMA in streptozotocin (STZ)-induced diabetic rats and cultured endothelial cells.

METHODS

Blood samples were collected from carotid artery. Vasodilator responses to acetylcholine (ACh) in the isolated aortic rings were measured, and serum concentrations of glucose, lipid, nitrite/nitrate, ADMA and tumour necrosis factor-alpha (TNF-alpha) were determined. Cultured endothelial cells were treated with ADMA, and the concentrations of intercellular adhesion molecule (ICAM-1), TNF-alpha, and the activity of nuclear factor-kappaB (NF-kappaB) were determined.

RESULTS

Vasodilator responses to ACh were decreased markedly and the serum concentrations of TNF-alpha, nitrite/nitrate and ADMA were increased significantly in diabetic rats. Rosiglitazone (3, 10 or 30 mg/kg) produced a significant reduction of the inhibition of vasodilator responses to ACh, but had no effect on the serum concentrations of glucose, lipid, nitrite/nitrate and ADMA in diabetic rats. ADMA (30 microM) significantly increased the activity of NF-kappaB and elevated the levels of ICAM-1 and TNF-alpha, and pre-treatment with rosiglitazone (10 or 30 microM) markedly inhibited the increased activity of NF-kappaB and reduced the elevated levels of TNF-alpha and ICAM-1 induced by ADMA in cultured endothelial cells.

CONCLUSIONS

Rosiglitazone improves endothelial function in diabetic rats, which is related to the reduction of the inflammatory response induced by ADMA.

Dysfunction of nitric oxide synthases as a cause and therapeutic target in delayed cerebral vasospasm after SAH

Nitric oxide (NO), also known as endothelium-derived relaxing factor, is produced by endothelial nitric oxide synthase (eNOS) in the intima and by neuronal nitric oxide synthase (nNOS) in the adventitia of cerebral vessels. It dilates the arteries in response to shear stress, metabolic demands, pterygopalatine ganglion stimulation and chemoregulation. Subarachnoid hemorrhage (SAH) interrupts this regulation of cerebral blood flow. Hemoglobin, gradually released from erythrocytes in the subarachnoid space, destroys nNOS-containing neurons in the conductive arteries. This deprives the arteries of NO, leading to initiation of delayed vasospasm. But such vessel narrowing increases shear stress, which stimulates eNOS. This mechanism normally would lead to increased production of NO and dilation of arteries. However, a transient eNOS dysfunction evoked by an increase in the endogenous competitive NOS inhibitor, asymmetric dimethylarginine (ADMA), prevents this vasodilation. eNOS dysfunction has been recently shown to be evoked by increased levels of ADMA in cerebrospinal fluid (CSF) in response to the presence of bilirubin-oxidized fragments (BOXes). A direct cause of the increased ADMA CSF level is most likely decreased ADMA elimination owing to disappearance of ADMA-hydrolyzing enzyme [dimethylarginine dimethylaminohydrolase II (DDAH II)] immunoreactivity in the arteries in spasm. This eNOS dysfunction sustains vasospasm. CSF ADMA levels are closely associated with the degree and time course of vasospasm; when CSF ADMA levels decrease, vasospasm resolves. Thus, exogenous delivery of NO, inhibiting the L-arginine-methylating enzyme or stimulating DDAH II, may provide new therapeutic modalities to prevent and treat vasospasm. This paper will present results of pre-clinical studies supporting the NO-based hypothesis of delayed cerebral vasospasm development and its prevention by increased NO availability.

Protective Mechanism of Adenosine to the Rat Arterial Endothelial Dysfunction Induced by Hydrogen Peroxide

This study was designed to examine the in vitro effects of adenosine (Ado) on hydrogen peroxide-induced endothelial dysfunction in rats. Endothelial dysfunction was induced by exposing isolated rat mesenteric arteries to hydrogen peroxide (0.5 mM) for 12 h using an organ culture system. The protective effects of adenosine were tested by exposing isolated mesenteric arteries to adenosine (3 x 10(-7) mol/l, 10(-6) mol/l, 3 x 10(-6) mol/l)+hydrogen peroxide (0.5 mM) for 12 h. This exposure to hydrogen peroxide induced a significant concentration-dependent inhibition of endothelium-dependent relaxation (EDR). Coculture of segments of mesenteric artery with adenosine (3 x 10(-7), 10(-6), and 3 x 10(-6) mol/l) attenuated the hydrogen peroxide-induced impairment of vasorelaxation. This impairment was accompanied by a reduction in nitrite/nitrate, nitric oxide (NO) synthase (NOS), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and an increasing in malondislehyde (MDA) and lactate dehydrogenase (LDH) activities in the aorta. These results indicate that adenosine can be used to attenuate hydrogen peroxide-induced endothelial dysfunction, an effect that may be related to antioxidation, thus enhancing NO production by preventing the decrease in NOS.

Arginine, arginine analogs and nitric oxide production in chronic kidney disease

Nitric oxide (NO) production is reduced in renal disease, partially due to decreased endothelial NO production. Evidence indicates that NO deficiency contributes to cardiovascular events and progression of kidney damage. Two possible causes of NO deficiency are substrate (L-arginine) limitation and increased levels of circulating endogenous inhibitors of NO synthase (particularly asymmetric dimethylarginine [ADMA]). Decreased L-arginine availability in chronic kidney disease (CKD) is due to perturbed renal biosynthesis of this amino acid. In addition, inhibition of transport of L-arginine into endothelial cells and shunting of L-arginine into other metabolic pathways (e.g. those involving arginase) might also decrease availability. Elevated plasma and tissue levels of ADMA in CKD are functions of both reduced renal excretion and reduced catabolism by dimethylarginine dimethylaminohydrolase (DDAH). The latter might be associated with loss-of-function polymorphisms of a DDAH gene, functional inhibition of the enzyme by oxidative stress in CKD and end-stage renal disease, or both. These findings provide the rationale for novel therapies, including supplementation of dietary L-arginine or its precursor L-citrulline, inhibition of non-NO-producing pathways of L-arginine utilization, or both. Because an increase in ADMA has emerged as a major independent risk factor in end-stage renal disease (and probably also in CKD), lowering ADMA concentration is a major therapeutic goal; interventions that enhance the activity of the ADMA-hydrolyzing enzyme DDAH are under investigation.

The Protective Effect of Captopril on Nicotine-Induced Endothelial Dysfunction in Rat

This study was designed to examine the in vivo and in vitro effects of captopril, an angiotensin-converting enzyme inhibitor, on nicotine-induced endothelial dysfunction in rats. Endothelial dysfunction was induced by exposing isolated rat mesenteric arteries to nicotine (0.01, 0.1, or 1 mM) for 24 hr using an organ culture system, or by treating rats with nicotine (2 mg/kg/day, intraperitoneally) for 4 weeks. The protective effects of captopril were tested by exposing isolated mesenteric arteries to captopril (0.01, 0.03, or 0.1 mM) + nicotine (0.1 mM) for 24 hr, or by treating rats with captopril (3 mg/kg/day, intravenously) + nicotine (2 mg/kg/day, intraperitoneally) for 4 weeks. Exposure of the isolated mesenteric arteries to nicotine induced a significant concentration -dependent inhibition of endothelium-dependent relaxation. Co-culture of segments of mesenteric artery with captopril (0.03 or 0.1 mM) attenuated the nicotine-induced impairment of vasorelaxation in a dose-dependent manner. Administration of nicotine to rats for 4 weeks significantly impaired endothelium-dependent relaxation compared with control rats. This impairment was accompanied by a reduction in nitrite/nitrate, nitric oxide (NO) synthase (NOS), and superoxide dismutase (SOD) activities in the serum and aorta. Chronic captopril treatment not only improved the impairment of endothelium-dependent relaxation, but also prevented the reduction of nitrite/nitrate contents and of NOS and SOD activities in the serum and aorta. However, there were no significant differences in serum angiotensin-converting enzyme activity among the three groups. These results indicate that captopril can be used to attenuate nicotine-induced endothelial dysfunction, an effect that may be related not only to antioxidation, but also to enhancing NO production by preventing the decrease in NOS.

Probucol Decreases Asymmetrical Dimethylarginine Level by Alternation of Protein Arginine Methyltransferase I and Dimethylarginine Dimethylaminohydrolase Activity

HYPOTHESIS

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor (NOS), may play an important role in endothelium dysfunction. Probucol, a potent antioxidant drug, may improve endothelium function via reduction of NOS inhibitor level. The present study examined whether the decreased level of ADMA by probucol is related to enhancement of protein arginine methyltransferase I (PRMT I) expression and reduction of dimethylarginine dimethylaminohydrolase (DDAH) activity.

METHODS

Endothelial cells were cultured and used for all these studies. ADMA concentration and DDAH activity were determined by HPLC. Expression of PRMT I and eNOS were characterized by western blot.

RESULTS

Pretreatment with oxidized-low density lipoprotein (ox-LDL) (10, 30 or 100 microg/ml) or lysophosphatidylcholine (LPC) (1.0, 2.5 or 5.0 microg/ml) for 12, 24 or 48 h markedly increased the activity of lactate dehydrogenase (LDH) in cultured endothelial cell. Incubation ofendothelial cells with ox-LDL (100 microg/ml) or LPC (5.0 microg/ml) for 48 h significantly increased the expression of PRMT I, and levels of MDA and ADMA, and decreased the concentration of nitrite/nitrate, the expression of eNOS and the activity of DDAH. Probucol significantly decreased the level of ADMA, concomitantly with reduction of PRMT I expression and elevation of DDAH activity and up-regulation of eNOS expression.

CONCLUSION

In summary, the present results suggest that the protective effect of probucol on endothelium is related to reduction of ADMA concentration by inhibition of PRMT I expression and enhancement of DDAH activity.