Role of asymmetric dimethylarginine in homocysteine-induced apoptosis of vascular smooth muscle cells

Akut Pankreas İltihabı Süresince Metillenmiş Arginin Rezidüleri ve İlişkili Amino Asitlerdeki Değişimler

Aim: The extent of the spread of inflammation determines the severity of acute pancreatitis (AP). Methylated arginine residues (MAR), a type of inflammatory mediator, reduce nitric oxide levels and cause vasoconstriction-induced endothelial damage. This study aimed to investigate MAR and related amino acids during acute pancreatic inflammation. Material and Method: This prospective, quasi-experimental study was conducted with patients diagnosed with AP and an age-matched control group. The patient samples were taken during the diagnosis and recovery time, whereas during the study for the control group. Mainly, Asymmetric dimethylarginine (ADMA), Arginine (ARG), Citrulline (CIT), and related chemicals were studied via a mass spectrometer. Results: A total of 30 patients with AP (mean age=53.3±17.8) and 30 controls (mean age=53.4±18.0) were included in the study. All patients were identified as non-severe (n=8) and severe (n=22). A decrease was detected in the patients' ADMA levels compared to the control group (p=0.01). MAR did not differ concerning disease severity (p > 0.05). However, MAR levels decreased higher in patients with diabetes or chronic kidney disease (CKD). Between the two samplings, the ARG level and ARG to ADMA ratio increased, while the MAR and CIT to ARG ratio decreased. Conclusion: Our results showed that MAR levels decreased with AP recovery. The start of a decrease in the high-level blood MAR may indicate the healing of pancreatic inflammation. AP inflammation may be more destructive in patients with diabetes or CKD.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

Arginine Derivatives in Cerebrovascular Diseases: Mechanisms and Clinical Implications

The amino acid L-arginine serves as substrate for the nitric oxide synthase which is crucial in vascular function and disease. Derivatives of arginine, such as asymmetric (ADMA) and symmetric dimethylarginine (SDMA), are regarded as markers of endothelial dysfunction and have been implicated in vascular disorders. While there is a variety of studies consolidating ADMA as biomarker of cerebrovascular risk, morbidity and mortality, SDMA is currently emerging as an interesting metabolite with distinct characteristics in ischemic stroke. In contrast to dimethylarginines, homoarginine is inversely associated with adverse events and mortality in cerebrovascular diseases and might constitute a modifiable protective risk factor. This review aims to provide an overview of the current evidence for the pathophysiological role of arginine derivatives in cerebrovascular ischemic diseases. We discuss the complex mechanisms of arginine metabolism in health and disease and its potential clinical implications in diverse aspects of ischemic stroke.

Homocysteine induces human mesangial cell apoptosis via the involvement of autophagy and endoplasmic reticulum stress

Homocysteine (Hcy) level characterizes a progressive increase in chronic kidney disease (CKD). In fact, Hcy accumulation is considered to be a crucial biochemical culprit in CKD progression, but the mechanism underlying this remains poorly understood. This study investigated the role of Hcy in glomerular mesangial cell (MC) apoptosis and the potential involvement of autophagy and endoplasmic reticulum (ER) stress in this process, shedding light on Hcy toxicity in kidney disease. Human mesangial cells (HMCs) were incubated with different concentrations of Hcy for different times. Flow cytometry was used to determine the proportion of apoptotic cells and western blotting was used to analyze protein levels after the administration of Hcy, endoplasmic reticulum inhibitor 4-phenylbutyric acid (4-PBA), and Atg5 siRNA. The results demonstrated that the cell viability gradually decreased and the proportion of HMCs undergoing apoptosis increased with increasing Hcy concentration and prolonged incubation time. Meanwhile, levels of the apoptosis-related proteins Bax and cleaved caspase-3 were significantly increased, while ER stress-related proteins such as ATF4, CHOP, GRP78, and phospho-eIF2α significantly increased. Levels of cleaved LC3, and beclin1 and Atg5 proteins also increased, accompanied by p62 degradation, indicating autophagy activation. 4-PBA effectively inhibited ER stress and reversed Hcy-induced apoptosis and autophagy. Moreover, Atg5 siRNA alleviated Hcy-induced apoptosis. Taken together, these results suggest that Hcy induces HMC apoptosis in a dose- and time-dependent manner via the activation of Atg5-dependent autophagy triggered by ER stress. This study suggests a novel strategy against Hcy toxicity in kidney injury and should help in clarifying the pathogenesis of CKD.

ADMA, homocysteine and redox status improvement affected by 7-nitroindazole in spontaneously hypertensive rats

Inhibition of nitric oxide (NO) production can influence blood pressure regulation and increase hypertension. Asymmetric dimethylarginine, ADMA, an analogue of L-arginine, can inhibit NO synthesis, impair endothelial function, and is a risk marker of cardiovascular diseases. Homocysteine (Hcy) level affects oxidative stress production of reactive oxygen species (ROS) in hypertension and also influences changes in signaling and cell damage. The present study was focused on experimental effects of exogenous NOS inhibitors and their effect on ADMA, an endogenous NOS inhibitor, homocysteine and ROS production measured as reactive oxidative metabolites (ROM). We compared effects of the two potential exogenous NO-inhibitors: N^G-nitro L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI). Levels of ADMA, Hcy, ROM and total thiols (TTL) were not changed in the L-NAME group. With 7-NI administration, we observed unchanged NOS activity in the left ventricle and a pronounced decrease of ADMA and Hcy levels, accompanied by ROM over-production in plasma. TTL/ROM ratio was more favorable than in the L-NAME group. We observed that 7-NI, an exogenous NOinhibitor, can decrease and improve the levels of ADMA, Hcy, and ROM, and increase TTL/ROM ratio in the plasma of spontaneously hypertensive rats.

Regulation of c-Jun N-Terminal Protein Kinase (JNK) Pathway in Apoptosis of Endothelial Outgrowth Cells Induced by Asymmetric Dimethylarginine

BACKGROUND Endothelial outgrowth cells (EOCs) are terminal endothelial progenitor cells (EPCs). Asymmetric dimethylarginine (ADMA) has been identified as a novel risk factor for cardiovascular diseases. Our aim in the present study was to investigate the effect of regulation of asymmetric dimethylarginine (ADMA) on EOCs apoptosis and to explore the underlining mechanisms of c-Jun N-terminal protein kinase (JNK) pathway in the process. MATERIAL AND METHODS EOCs were harvested from umbilical cord blood and obtained by using density gradient centrifugation and adhesive culture methods. Endothelial characteristics were identified by immunohistochemistry and fluorescence staining. EOCs were treated with different concentrations of ADMA and detected by flow cytometry. After JNK specific inhibitor (SP600125) was added, EOCs apoptosis protein expressions were measured by Western blot analysis. Proliferation, migration, and vascularization were detected by CCK-8 assay, wound healing assay, and tube-like formation assay, respectively. RESULTS EOCs were successfully extracted from umbilical cord blood and different concentrations of ADMA aggravated EOCs apoptosis. ADMA distinctly activates the phosphorylation activity of JNK. Supplementation of JNK-specific inhibitor (SP600125) decreased expression of Bax and cleaved caspase 3/9, and alleviated ADMA-induced apoptosis. SP600125 also promoted angiogenesis viability. CONCLUSIONS The JNK pathway participates in the apoptosis-promoting process of EOCs, and targeted inhibition of the JNK pathway can alleviate ADMA-induced injury, which I s the potential underlying mechanism of vascular endothelium injury in ischemic stroke.

Dichotomous effects of isomeric secondary amines containing an aromatic nitrile and nitro group on human aortic smooth muscle cells via inhibition of cystathionine-γ-lyase

Excessive proliferation of vascular smooth muscle cells (SMC) is an important contributor to the progression of atherosclerosis. Inhibition of proliferation can be achieved by endogenously produced and exogenously supplied nitrogen monoxide, commonly known as nitric oxide (NO). We report herein the dichotomous effects of two isomeric families of secondary amines, precursors to the N-nitrosated NO-donors, on HASMC proliferation. The syntheses of these two families were carried out using two equivalents of homologous, aliphatic monoamines and 2,6-difluoro-3-nitrobenzonitrile (2,6-DFNBN, O family) or 2,4-difluoro-5-nitrobenzonitrile (2,4-DFNBN, P family). The secondary amines belonging to the P family inhibited HASMC proliferation at all concentrations, whereas the O family induced HASMC proliferation at low concentrations, and exhibited inhibitory properties at high concentrations. A probable explanation of these behaviors is proposed herein. l-homocysteine (HCY) is known to induce HASMC proliferation at low concentrations (<1 mM) and inhibit HASMC proliferation at higher concentrations (>2.5 mM). Our findings suggest that these two families of amines inhibit cystathionine-γ-lyase (CSE) to varying extents, which directly results in altered levels of intracellular HCY and consequent changes in HASMC proliferation.

Relationship between post-cardiac arrest myocardial oxidative stress and myocardial dysfunction in the rat

Background

Reperfusion after resuscitation from cardiac arrest (CA) is an event that increases reactive oxygen species production leading to oxidative stress. More specifically, myocardial oxidative stress may play a role in the severity of post-CA myocardial dysfunction. This study investigated the relationship between myocardial oxidative stress and post-CA myocardial injury and dysfunction in a rat model of CA and cardiopulmonary resuscitation (CPR). Ventricular fibrillation was induced in 26 rats and was untreated for 6 min. CPR, including mechanical chest compression, ventilation, and epinephrine, was then initiated and continued for additional 6 min prior to defibrillations. Resuscitated animals were sacrificed at two h (n = 9), 4 h (n = 6) and 72 h (n = 8) following resuscitation, and plasma collected for assessment of: high sensitivity cardiac troponin T (hs-cTnT), as marker of myocardial injury; isoprostanes (IsoP), as marker of lipid peroxidation; and 8-hydroxyguanosine (8-OHG), as marker of DNA oxidative damage. Hearts were also harvested for measurement of tissue IsoP and 8-OHG. Myocardial function was assessed by echocardiography at the corresponding time points. Additional 8 rats were not subjected to CA and served as baseline controls.

Results

Compared to baseline, left ventricular ejection fraction (LVEF) was reduced at 2 and 4 h following resuscitation (p < 0.01), while it was similar at 72 h. Inversely, plasma hs-cTnT increased, compared to baseline, at 2 and 4 h post-CA (p < 0.01), and then recovered at 72 h. Similarly, plasma and myocardial tissue IsoP and 8-OHG levels increased at 2 and 4 h post-resuscitation (p < 0.01 vs. baseline), while returned to baseline 72 h later. Myocardial IsoP were directly related to hs-cTnT levels (r = 0.760, p < 0.01) and inversely related to LVEF (r = -0.770, p < 0.01). Myocardial 8-OHG were also directly related to hs-cTnT levels (r = 0.409, p < 0.05) and inversely related to LVEF (r = -0.548, p < 0.01).

Conclusions

The present study provides evidence that lipid peroxidation and DNA oxidative damage in myocardial tissue are closely related to myocardial injury and LV dysfunction during the initial hours following CA.

Involvement of DDAH/ADMA pathway in the pathogenesis of rheumatoid arthritis in rats

Endothelial dysfunction is the early stage of atherosclerosis, which is typically associated with rheumatoid arthritis (RA), a chronic inflammatory autoimmune disorder. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is not only an independent predictor for endothelial dysfunction but also a proinflammatory mediator. It has been shown that the level of ADMA was elevated in patients with RA. In the present study, we investigated the potential effect of ADMA on inflammation process in collagen-induced arthritis (CIA) animal model and primary cultured fibroblast-like synoviocytes (FLS) exposed to tumor necrosis factor-α (TNF-α). In CIA rats, the plasma levels of inflammatory cytokines TNF-α, interleukin-1β (IL-1β) and IL-6 were markedly increased, while the plasma levels of ADMA did not increase. The expression of dimethylarginine dimethylohydrolase2 (DDAH2), the key enzyme for ADMA degradation, was markedly reduced in inflamed joint synovium of CIA rats. Moreover, the expression of anti-inflammatory factor cortistatin (CST) was markedly decreased in joint synovium of CIA rats. Treatment of cultured FLS with TNF-α significantly increased the levels of ADMA, and decreased the expression of DDAH2 mRNA and protein accompany with an increase in the levels of IL-1β and IL-6 and a reduction in the expression of CST mRNA and protein, and the effects of TNF-α were abolished by DDAH2 overexpression. Treatment of FLS with ADMA also significantly increased the levels of IL-1β and IL-6, and reduced the expression of CST. These findings suggest that DDAH/ADMA participates in the pathogenesis of RA, and that the effect of DDAH/ADMA may be mediated by CST.

Asymmetric dimethyarginine as marker and mediator in ischemic stroke

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, is known as mediator of endothelial cell dysfunction and atherosclerosis. Circulating ADMA levels are correlated with cardiovascular risk factors such as hypercholesterolemia, arterial hypertension, diabetes mellitus, hyperhomocysteinemia, age and smoking. Accordingly, clinical studies found evidence that increased ADMA levels are associated with a higher risk of cerebrovascular events. After the acute event of ischemic stroke, levels of ADMA and its analog symmetric dimethylarginine (SDMA) are elevated through augmentation of protein methylation and oxidative stress. Furthermore, cleavage of ADMA through dimethylarginine dimethylaminohydrolases (DDAHs) is reduced. This increase of dimethylarginines might be predictive for adverse clinical outcome. However, the definite role of ADMA after acute ischemic stroke still needs to be clarified. On the one hand, ADMA might contribute to brain injury by reduction of cerebral blood flow. On the other hand, ADMA might be involved in NOS-induced oxidative stress and excitotoxic neuronal death. In the present review, we highlight the current knowledge from clinical and experimental studies on ADMA and its role for stroke risk and ischemic brain injury in the hyperacute stage after stroke. Finally, further studies are warranted to unravel the relevance of the close association of dimethylarginines with stroke.

Involvement of endoplasmic reticulum stress in homocysteine-induced apoptosis of osteoblastic cells

Hyperhomocysteinemia has been shown to increase the incidence of osteoporosis and osteoporotic fractures. Endoplasmic reticulum (ER) stress was recently shown to be associated with apoptosis in several types of cells. In this study, we determined the effect of homocysteine (Hcy) on the apoptosis of osteoblastic cells and investigated whether ER stress participates in Hcy-induced osteoblast apoptosis. Human osteoblastic cells were incubated with Hcy. Hcy dose-dependently decreased cell viability and increased apoptosis in osteoblastic cells. Osteoblastic cells are more susceptible to Hcy-mediated cell death than other cell types. Expression of cleaved caspase-3 was significantly increased by Hcy, and pretreatment with caspase-3 inhibitor rescued the cell viability by Hcy. Hcy treatment led to an increase in release of mitochondrial cytochrome c. It also triggered ER stress by increased expression of glucose-regulated protein 78, inositol-requiring transmembrane kinase and endonuclease 1α (IRE-1α), spliced X-box binding protein, activating transcription factor 4, and C/EBP homologous protein. Silencing IRE-1α expression by small interfering RNA effectively suppressed Hcy-induced apoptosis of osteoblastic cells. Our results suggest that hyperhomocysteinemia induces apoptotic cell death in osteoblasts via ER stress.

Potassium 2-(1-hydroxypentyl)-benzoate attenuated hydrogen peroxide-induced apoptosis in neuroblastoma SK-N-SH cells

Potassium 2-(1-hydroxypentyl)-benzoate (dl-PHPB) has been shown to have potent neuroprotective effects, such as reducing the infarct volume and improving neurobehavioral deficits in the transient focal cerebral ischemic rat model. The present study is to evaluate the neuroprotective effect of dl-PHPB on hydrogen peroxide (H(2)O(2))-induced apoptosis and the possible mechanism in the human neuroblastoma SK-N-SH cells. Our results showed that dl-PHPB significantly attenuated H(2)O(2)-induced cell death, and reduced neuronal apoptosis. Dl-PHPB partially reversed the decrease of B-cell CLL/lymphoma 2 (Bcl-2) protein level induced by H(2)O(2). Furthermore, dl-PHPB inhibited the elevation of pro-apoptotic Bcl-2-associated X protein (Bax) and caspase3, and alleviated the down-regulation of protein kinase C alpha (PKCα). The PKC inhibitor, Calphostin C significantly attenuated the protective effects of dl-PHPB. The findings suggest that dl-PHPB may protect neurons against H(2)O(2)-induced apoptosis by modulating apoptosis-related proteins, and PKC signaling pathway may be involved in the neuroprotection of dl-PHPB.

Asymmetric dimethylarginine: A novel biomarker of gastric mucosal injury?

Nitric oxide (NO), a multifunctional endogenous gas molecule, is metabolized from L-arginine by enzymatic reaction in the presence of nitric oxide synthase. NO, an important gas signaling molecule, is a gastric mucosa protective factor that contributes significantly to maintain normal gastric mucosa integrity. NO increases gastric mucosa blood flow, regulates the secretion of mucus and bicarbonate, and inhibits the secretion of gastric juice. Asymmetric dimethylarginine (ADMA) has been identified as the major endogenous inhibitor of nitric oxide synthase. The function of ADMA is to decrease NO production via inhibiting nitric oxide synthase activity. Besides inhibiting NO synthesis, ADMA also directly induces oxidative stress and cell apoptosis, and participates in inflammation reaction. Its systemic accumulation was observed in conjunction with several cardiovascular and metabolic diseases. ADMA also mediates gastric ulcer injury induced by ethanol, stress, helicobacter pylori and indomethacin. The mechanism of ADMA directly producing adverse effect in gastric mucosa is incompletely understood. It is widely accepted that NO bioavailability decrease is the majority reason. Promotion of apoptosis and aggravation of inflammation may be other important mechanisms of ADMA-induced gastric injury. ADMA might be a novel clinical and experimental biomarker related to gastric mucosa disorder. Although therapeutic tool targeting to ADMA is available in multiple cardiovascular diseases, it is unknown in gastrointestinal disease. The strategy to inhibit ADMA is beneficial to gastric ulcer induced by ethanol in rats. Thus, ADMA might be a candidate of therapeutic target in gastric mucosa damage.

Reduced proteinuria using ramipril in diabetic CKD stage 1 decreases circulating cell death receptor activators concurrently with ADMA. A novel pathophysiological pathway?

BACKGROUND

Renin-angiotensin system (RAS) blockade improves proteinuria and the endothelial functions in diabetic nephropathy. Plasma asymmetric dimethylarginine (ADMA), abundant in the cell than in the plasma, is also improved by RAS blockage. We hypothesized that RAS blockade may reduce ADMA by reducing injurious cell death.

METHODS

In a hypothesis-generating study, we assessed circulating levels of apoptotic signalling peptides in incident chronic kidney disease (CKD) stage 1 patients (aged >18 years with diabetes mellitus type 2 as the only cause of nephropathy) not previously prescribed statins or RAS blockade. Ninety-three (29 M, 47 ± 5 years) patients with CKD 1 diabetic nephropathy and 38 healthy subjects (20 M, 47 ± 5 years) were enrolled. Ramipril was given (5 mg daily for 12 weeks), and circulating ADMA, soluble Fas (sFas), myostatin and endothelial function [flow-mediated vasodilation (FMD); ultrasound)] were measured.

RESULTS

After the study, ADMA, sFas, myostatin, insulin resistance, high-sensitive C-reactive protein (hsCRP), estimated glomerular filtration rate (eGFR), blood pressure and proteinuria levels were decreased, and FMD and serum albumin levels increased (P < 0.05 for all). ADMA and sFas levels were independently related to FMD levels both before (rho = -0.33; P < 0.005 and rho = -0.26; P < 0.02, respectively) and after (rho = -0.39; P < 0.001 and rho = -0.28; P < 0.002, respectively) ramipril treatment. Changes in sFas and ADMA were related to the change in FMD (-0.32; P > 0.004 and -0.31; P < 0.004, respectively).

CONCLUSION

A reduction of proteinuria in CKD 1 diabetic kidney disease is accompanied by lower circulating sFas, myostatin and ADMA, suggesting that increased cell death may contribute to ADMA formation and endothelial dysfunction in diabetic CKD.

Asymmetric dimethylarginine damages connexin43-mediated endothelial gap junction intercellular communication

Asymmetric dimethylarginine (ADMA), a major endogenous inhibitor of nitric oxide synthase, is recently defined as a novel atherogenic factor. Communication via gap junction (GJIC) is involved in the regulation of a variety of endothelial activities, such as cell differentiation and senescence. The aim of this study is to explore the effects of ADMA on connexin43 (Cx43) mediated endothelial GJIC. Lysophosphatidylcholine (LPC) caused the downregulation of Cx43 expression and GJIC dysfunction in cultured human umbilical vein endothelial cells (HUVECs), which were significantly ameliorated by decreasing ADMA accumulation. Furthermore, we found that ADMA (10 µmol·L–1, 24 h) markedly downregulated Cx43 expression and damaged GJIC function in HUVECs. ADMA also increased production of intracellular reactive oxygen species (ROS) and induced phosphorylation of p38 MAPK. Furthermore, the inhibitory effect of ADMA on Cx43-mediated GJIC could be attenuated by NADPH oxidase inhibitor diphenyleneiodonium and apocynin as well as p38 MAPK inhibitor SB203580, respectively. In conclusion, our present results suggest that ADMA inhibits endothelial GJIC function via downregulating Cx43 expression, which suggesting a novel mechanism linking between elevated ADMA level and progression of atherosclerosis.

All-trans retinoic acid inhibits cobalt chloride-induced apoptosis in PC12 cells: role of the dimethylarginine dimethylaminohydrolase/asymmetric dimethylarginine pathway

Previous studies have shown that the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and its specific hydrolase dimethylarginine dimethylaminohydrolase (DDAH) are involved in the regulation of apoptosis in different cell types. In the present study, we investigated the role of the DDAH/ADMA pathway in cobalt chloride (CoCl(2))-induced apoptosis and the antiapoptotic effect of all-trans retinoic acid (atRA) in undifferentiated pheochromocytoma (PC12) cells. Treatment of CoCl(2) (125 microM) for 48 hr significantly induced the apoptosis of PC12 cells, concomitantly with increased intracellular reactive oxygen species (ROS) production and caspase-3 activity. CoCl(2) treatment also decreased the activity of DDAH and the expression of DDAH2 (mRNA and protein), resulting in an increased level of ADMA. All these alterations induced by CoCl(2) were attenuated by atRA (0.1, 1, or 10 microM). Interestingly, the antiapoptotic effects of atRA were inhibited by DDAH2 small RNA interference. In contrast, DDAH2 overexpression inhibited the proapoptotic effects of CoCl(2). We also found that treatment of exogenous ADMA (3, 10, or 30 microM) induced the apoptosis of PC12 cells in a concentration- and time-dependent manner, which was inhibited by the antioxidant or the caspase-3 inhibitor. These findings suggest that the modulation of the DDAH/ADMA/ROS pathway plays an important role in CoCl(2)-induced apoptosis and the antiapoptotic effects of atRA in undifferentiated PC12 cells.

Asymmetrical dimethylarginine triggers lipolysis and inflammatory response via induction of endoplasmic reticulum stress in cultured adipocytes

Protein energy wasting, a state of decreased stores of body protein and fat, is a risk factor for mortality in advanced chronic kidney disease (CKD). Little is known about the mechanism underlying loss of fat in CKD. Accumulation of asymmetric dimethylarginine (ADMA) is prevalent in advanced CKD. Here we assessed the effect of ADMA on cellular perturbation in cultured 3T3-L1 adipocytes. Exposure of adipocytes to ADMA induced lipolysis and decreased perilipin A, with no alteration of lipases expression or activity. ADMA treatment also upregulated the expression of inflammatory adipocytokines via activation of nuclear factor-kappaB (NF-kappaB). Blocking the inflammatory responses with NF-kappaB inhibitor partly inhibited the ADMA-induced lipolysis. Furthermore, ADMA treatment triggered endoplasmic reticulum (ER) stress, revealed by phosphorylation of PKR-like eukaryotic initiation factor 2alpha kinase, eukaryotic translational initiation factor 2alpha, c-Jun NH2-terminal kinase, and overexpression of glucose-regulated protein 78. Treatment with ER stress inhibitor completely abolished the ADMA-induced lipolysis and inflammatory responses. Moreover, conditioned medium from the ADMA-treated adipocytes increased protein degradation in cultured C2C12 myotubes, suggesting that the ADMA-induced adipocyte perturbation may promote skeletal muscle proteolysis. These data suggest that elevated ADMA promoted the adipocyte perturbation through induction of ER stress, which might have implication for protein energy wasting in CKD.

The aggravatory effect of nicotine on Helicobacter pylori-induced gastric mucosa injury: role of asymmetric dimethylarginine

BACKGROUND AND GOAL

Nitric oxide (NO) is a well-known gastric mucosa protection factor. Recently, it has been reported that methylated arginine compound such as asymmetric dimethylarginine (ADMA), which inhibits nitric oxide synthesis, may be related to the development of gastric mucosa injury in patients with Helicobacter pylori infection. In the present study, we tested the relationship between endogenous ADMA and gastric mucosa injury in H. pylor- infected patients and cultured gastric epithelial cells.

METHODS

One hundred and fifty subjects with gastric diseases were entered in this study. The levels of ADMA in gastric juice and plasma were measured in both H. pylori+ and H. pylori- patients. We analyzed independent risk factors that contribute to ADMA levels by multiple linear regression analyses. Mucosal epithelium cells were treated with nicotine (10 microM) for 24 hours in the presence or absence of H. pylori. The concentrations of ADMA in the culture medium and the rate of cell apoptosis were determined.

RESULTS

The ADMA level in gastric juice was significantly increased in H. pylori+ patients (P<0.05), whereas there were no differences in the content of ADMA in the plasma between H. pylori+ patients and H. pylori- patients. Smoking and H. pylori infection were 2 independent risk factors contributing to ADMA levels, and in the population of H. pylori+ patients, the level of ADMA in smokers was higher compared with nonsmokers. Incubation of nicotine (10 microM) with epithelial cells for 24 hours further increased the elevated level of ADMA and the rate of cell apoptosis owing to H. pylori infection.

CONCLUSIONS

H. pylori infection caused an increase of ADMA levels in gastric juice, which was aggravated by smoking. Endogenous ADMA may be an important factor contributing to gastric mucosa injury.

Protective effects of TREK-1 against oxidative injury induced by SNP and H2O2

AIM

TREK-1 (TWIK-related K+ channel-1) is a 2-pore-domain K+ channel subtype. The present study investigated the role of TREK-1 in cell death induced by oxidative stress.

METHODS

The cell viability of wild-type Chinese hamster ovary (CHO) and TREK-1-transfected CHO cells (TREK-1/CHO cells) was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in the presence of sodium nitroprusside (SNP) or hydrogen peroxide (H2O2). Apoptosis of wild-type CHO and TREK-1/CHO cells was detected using Hoechst33342 staining.

RESULTS

Both SNP and H2O2 caused dose- and time-dependent growth inhibition of wild-type CHO and TREK-1/ CHO cells. Following a 12 h exposure to SNP, the 50% inhibition (IC(50)) values for wild-type CHO and TREK-1/CHO cells were calculated as 0.69 mmol/L and 1.14 mmol/L, respectively. The IC(50) values were 0.07 mmol/L and 0.09 mmol/L in H2O2-treated wild-type CHO and TREK-1/CHO cells, respectively, following 12 h exposure to H2O2. Moreover, SNP/H2O2 induced less apoptosis in TREK-1/ CHO cells than that in wild-type CHO cells (P<0.05).

CONCLUSION

The results demonstrated that TREK-1 played a protective role against oxidative injury.

Asymmetric dimethylarginine induces TNF-alpha production via ROS/NF-kappaB dependent pathway in human monocytic cells and the inhibitory effect of reinioside C

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, has been implicated in vascular inflammation through induction of reactive oxygen species (ROS) and proinflammatory genes in endothelial cells. However, relatively few attentions have been paid to the effect of ADMA on monocytes, one of the important cells throughout all stages of atherosclerosis. In the present study, we found that reinioside C, the main component extracted from Polygala fallax Hemsl., dose-dependently inhibited tumor necrosis factor-alpha (TNF-alpha) production induced by ADMA in monocytes, Furthermore, reinioside C attenuated ADMA-induced generation of reactive oxygen species and activation of nuclear factor-kappaB (NF-kappaB) activity in monocytes in a dose-dependent manner, this effect was inhibited by l-arginine (NOS substrate) and PDTC (inhibitor of NF-kappaB). These data suggest that reinioside C could attenuate the increase of TNF-alpha induced by exogenous ADMA through inhibition ROS/NF-kappaB pathway in monocytes.

Natriuretic peptides in vascular physiology and pathology

Four major natriuretic peptides have been isolated: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and Dendroaspis-type natriuretic peptide (DNP). Natriuretic peptides play an important role in the regulation of cardiovascular homeostasis maintaining blood pressure and extracellular fluid volume. The classical endocrine effects of natriuretic peptides to modulate fluid and electrolyte balance and vascular smooth muscle tone are complemented by autocrine and paracrine actions that include regulation of coronary blood flow and, therefore, myocardial perfusion; modulation of proliferative responses during myocardial and vascular remodeling; and cytoprotective anti-ischemic effects. The actions of natriuretic peptides are mediated by the specific binding of these peptides to three cell surface receptors: type A natriuretic peptide receptor (NPR-A), type B natriuretic peptide receptor (NPR-B), and type C natriuretic peptide receptor (NPR-C). NPR-A and NPR-B are guanylyl cyclase receptors that increase intracellular cGMP concentration and activate cGMP-dependent protein kinases. NPR-C has been presented as a clearance receptor and its activation also results in inhibition of adenylyl cyclase activity. The wide range of effects of natriuretic peptides might be the base for the development of new therapeutic strategies of great benefit in patients with cardiovascular problems including coronary artery disease or heart failure. This review summarizes current literature concerning natriuretic peptides, their receptors and their effects on fluid/electrolyte balance, and vascular and cardiac physiology and pathology, including primary hypertension and myocardial infarction. In addition, we will attempt to provide an update on important issues regarding natriuretic peptides in congestive heart failure.