Increased circulating concentrations of asymmetric dimethylarginine (ADMA) in white coat hypertension

Association of Beta-2-Microglobulin With Coronary Heart Disease and All-Cause Mortality in the United States General Population

Few prospective studies explored the association of beta-2-microglobulin (B2M) with coronary heart disease (CHD) mortality. The primary objective of this study was to examine the association of serum B2M with CHD and all-cause mortality. This is a prospective cohort study of a nationally representative sample of 4,885 adults, aged 40–85 years, who participated in the National Health and Nutrition Examination Survey (NHANES III) from 1988 to 1994. The relationships between B2M and CHD and all-cause mortality were estimated using Cox proportional hazards regression models. During a median follow-up of 15.5 years, 845 CHD and 3,388 all-cause deaths occurred among 4,885 participants [2,568 women (55.7%); mean (S.D.) age, 66.4 (12.5) years], respectively. In the unadjusted model, B2M concentration was strongly linearly associated with CHD and all-cause mortality (p-trend < 0.001). After adjusting multivariable factors, a positive linear association between B2M and all-cause mortality was still observed (H.R. for Q4 vs. Q1 5.90; 95% CI: 5.31–6.57; p-trend < 0.001). In the multivariable adjustment model, B2M was significantly associated with an increased risk of CHD mortality (H.R. for Q4 vs. Q1 2.72; 95% CI: 2.07–3.57; p-trend < 0.001). In the stratified analyses, the associations of B2M with CHD and all-cause mortality varied by risk factors, such as age, smoking status, and history of hypertension. The findings suggest a significant relationship between the higher serum B2M concentration and increased risk for CHD and all-cause mortality. Further large-scale follow-up studies are also needed to validate this association.

Factors Predisposing to Hypertension in Subjects Formerly Born Preterm: Renal Impairment, Arterial Stiffness, Endothelial Dysfunction or Something Else?

Subjects formerly born preterm subsequently develop arterial - particularly isolated systolic- hypertension more frequently than their peers born at term.

Numerous factors may influence this predisposition, including an incomplete nephrogenesis, implying the presence of kidneys with a reduced number of nephrons and consequent reduction in haematic filtration, increased sodium absorption and activation of renin-angiotensin-aldosterone system, increased arterial rigidity produced by an elastin deficiency previously observed in anatomic specimens of human immature aorta, and reduced endothelial nitric oxide excretion, due to high blood levels of ADMA, a strong direct inhibitor of nitric oxide that exerts a vasoconstrictor effect.

Other possible factors (i.e. excretion of neuroendocrine compounds) may also be implicated. The aim of this paper was to review all possible mechanisms involved in the observed increase in blood pressure in individuals who had been born preterm and/or with intrauterine growth restriction. The outlook for new and promising laboratory techniques capable of identifying alterations in the metabolic pathways regulating blood pressure levels, such as metabolomics, is also provided.

Intraplatelet L-Arginine-Nitric Oxide Metabolic Pathway: From Discovery to Clinical Implications in Prevention and Treatment of Cardiovascular Disorders

Despite the development of new drugs and other therapeutic strategies, cardiovascular disease (CVD) remains still the major cause of morbidity and mortality in the world population. A lot of research, performed mostly in the last three decades, revealed an important correlation between "classical" demographic and biochemical risk factors for CVD, (i.e., hypercholesterolemia, hyperhomocysteinemia, smoking, renal failure, aging, diabetes, and hypertension) with endothelial dysfunction associated directly with the nitric oxide deficiency. The discovery of nitric oxide and its recognition as an endothelial-derived relaxing factor was a breakthrough in understanding the pathophysiology and development of cardiovascular system disorders. The nitric oxide synthesis pathway and its regulation and association with cardiovascular risk factors were a common subject for research during the last decades. As nitric oxide synthase, especially its endothelial isoform, which plays a crucial role in the regulation of NO bioavailability, inhibiting its function results in the increase in the cardiovascular risk pattern. Among agents altering the production of nitric oxide, asymmetric dimethylarginine-the competitive inhibitor of NOS-appears to be the most important. In this review paper, we summarize the role of L-arginine-nitric oxide pathway in cardiovascular disorders with the focus on intraplatelet metabolism.

White-coat hypertension is a risk factor for cardiovascular diseases and total mortality

BACKGROUND

Whether white-coat hypertension (WCH) is an innocent phenomenon is controversial.

METHOD

In this study, we evaluated the association of WCH and the risk of cardiovascular diseases (CVDs) and mortality, stratified by baseline antihypertensive treatment status. Databases (PubMed, EMBASE, CINAHL Plus, Scopus, and Google Scholar) were searched for prospective studies with data on CVD and total mortality associated with WCH. The primary outcomes were the risk of CVD and total mortality associated with WCH stratified by antihypertensive treatment status. The relative risks of events compared with normotension were calculated.

RESULTS

A total of 23 cohorts (20 445 individuals), 11 cohorts (8656 individuals), and 12 cohorts (21 336 individuals) were included for analysis of cardiovascular risk associated with WCH in patients without baseline antihypertensive treatment (untreated), or under antihypertensive treatment (treated) or mixed population (including both untreated and treated patients), respectively. In untreated cohorts, WCH was associated with a 38 and 20% increased risk of CVD and total mortality compared with normotension, respectively. In the mixed population, WCH was associated with a 19 and 50% increased risk of CVD and total mortality. However, in the treated patients, neither the risk of CVD, nor total mortality was increased in WCH. Meta-regression analyses indicated that neither differences of clinic blood pressure, nor out-of-office blood pressure variables were correlated with risk of CVD in WCH.

CONCLUSION

We concluded that WCH is associated with long-term risk of CVD and total mortality in patients without antihypertensive treatment. Close follow-up should be performed in WCH patients.

Circulating miR-21 and eNOS in subclinical atherosclerosis in patients with hypertension

OBJECTIVES

The aim of this study is to evaluate the relationship of miR-21, nitric oxide (NOx) and endothelial nitric oxide synthase (eNOS) with subclinical atherosclerosis in carotid arteries by measuring carotid intima media thickness (CIMT) in patients with hypertension and healthy controls.

DESIGN AND METHODS

A total of 28 hypertensive and 28 healthy controls were enrolled. MiR-21 expression was analyzed by quantitative reverse transcription-PCR and NOx, and eNOS levels were measured by ELISA assay. CIMT was evaluated by ultrasonography and CIMT ≥ 0.8 mm was accepted as increased CIMT (iCIMT).

RESULTS

C-reactive protein (CRP) level, plasma miR-21 expression level and CIMT were found to be significantly higher in the hypertension group when compared to the control group (p = 0.009, p = 0.002 and p < 0.001, respectively). NOx and eNOS levels were significantly lower in the hypertension group compared to the control group (p < 0.001, both). MiR-21 level was positively correlated with the clinical systolic blood pressure, clinical diastolic blood pressure, CRP and CIMT. MiR-21 was also negatively correlated with NOx and eNOS. Eighteen patients with hypertension had iCIMT. MiR-21 and CRP levels were significantly higher (p < 0.001 and p = 0.001), whereas NOx and eNOS levels were significantly lower in patients with iCIMT (p < 0.001, both).

CONCLUSION

The decreased levels of NOx and eNOS found in this study indicate the co-existence of endothelial dysfunction and hypertension once more. In the absence of microalbuminuria, the increased miR-21 expression in patients with iCIMT made us conclude that this miRNA might be involved in the early stages of atherosclerotic process in hypertensive patients.

Closer look at white-coat hypertension

This review aims to clarify novel concepts regarding the clinical and laboratory aspects of white-coat hypertension (WCHT). Recent studies on the clinical and biological implications of WCHT were compared with existing knowledge. Studies were included if the WCHT patients were defined according to the 2013 European Society of Hypertension guidelines, i.e., an office blood pressure (BP) of ≥ 140/90 mmHg, a home BP of ≤ 135/85 mmHg, and a mean 24-h ambulatory BP of ≤ 130/80 mmHg. WCHT studies published since 2000 were selected, although a few studies performed before 2000 were used for comparative purposes. True WCHT was defined as normal ABPM and home BP readings, and partial WCHT was defined as an abnormality in one of these two readings. The reported prevalence of WCHT was 15%-45%. The incidence of WCHT tended to be higher in females and in non-smokers. Compared with normotensive (NT) patients, WCHT was associated with a higher left ventricular mass index, higher lipid levels, impaired fasting glucose, and decreased arterial compliance. The circadian rhythm in WCHT patients was more variable than in NT patient’s, with a higher pulse pressure and non-dipping characteristics. Compared with sustained hypertension patients, WCHT patients have a better 10-year prognosis; compared with NT patients, WCHT patients have a similar stroke risk, but receive more frequent drug treatment. There are conflicting results regarding WCHT and markers of endothelial damage, oxidative stress and inflammation, and the data imply that WCHT patients may have a worse prognosis. Nitric oxide levels are lower, and oxidative stress parameters are higher in WCHT patients than in NT patients, whereas the antioxidant capacity is lower in WCHT patients than in NT patients. Clinicians should be aware of the risk factors associated with WCHT and patients should be closely monitored especially to identify target organ damage and metabolic syndrome.

White-coat hypertension

1. Numerous studies have examined whether white-coat hypertension (WCHT) is associated with increased cardiovascular risk, but with definitions of WCHT that were not sufficiently robust, results have been inconsistent. The aim of the present review was to standardize the evidence by only including studies that used a definition of WCHT consistent with international guidelines. 2. Published studies were reviewed for data on vascular dysfunction, target organ damage, risk of future sustained hypertension and cardiovascular events. 3. White-coat hypertension has a population prevalence of approximately 15% and is associated with non-smoking and slightly elevated clinic blood pressure. Compared with normotensives, subjects with WCHT are at increased cardiovascular risk due to a higher prevalence of glucose dysregulation, increased left ventricular mass index and increased risk of future diabetes and hypertension. 4. In conclusion, management of a patient with WCHT should focus on cardiovascular risk factors, particularly glucose intolerance, not blood pressure alone.

Endothelial damage in white coat hypertension: role of lectin-like oxidized low-density lipoprotein-1

The aims of this study included an examination of soluble lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (sLOX-1) levels in hypertensive (HT) patients. Another aim examined sLOX-1 associations with oxidized LDL (oxLDL), nitric oxide synthase (eNOS) and nitric oxide (NOx). A final aim was to compare these parameters between HT patients, white-coat hypertensive (WCH) patients and healthy controls. The three groups, HT, WCH and controls, were comprised of 35 patients each. sLOX-1 and oxLDL levels were significantly increased in WCH and HT patients compared with controls. The eNOS activation was significantly lower in HT than in the control group. sLOX-1 and oxLDL levels were significantly negatively correlated with eNOS levels in the WCH and HT groups. Carotid intima-media thickness (CIMT) measurements were significantly higher in the WCH and HT groups compared with controls. There was a significant positive correlation between CIMT and sLOX-1 and oxLDL; however, there was a negative correlation with eNOS in WCH. Regression analysis revealed that sLOX-1 was the variable that had a significant effect on blood pressure (P<0.001, odds ratio (95% confidence interval=23.273 (5.843-92.688)). A possible endothelial impairment may act as a cardiovascular risk factor in WCH. Necessary measures should be considered in terms of atherosclerosis risk with HT, especially in early identification of endothelial damage by looking at sLOX-1 levels. We believe sLOX-1 levels are strong biomarkers for determining early endothelial damage in HT, and especially in WCH patients.

Role of asymmetrical dimethylarginine in the progression of renal disease

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid found in tissues and cells that circulates in plasma and is excreted in urine. It inhibits nitric oxide synthases (NOs) and produces considerable cardiovascular biological effects. Several studies have suggested that plasma concentrations of ADMA provide a marker of risk for endothelial dysfunction and cardiovascular disease. In animal and in population studies ADMA has been associated with progression of CKD. Several mechanisms may be involved in this association, such as compromise of the integrity of the glomerular filtration barrier and development of renal fibrosis. This review summarizes the existing literature on the biology and physiology of ADMA focusing on its role in the progression of renal disease.

Oxidative stress in patients with essential hypertension: a comparison of dippers and non-dippers

BACKGROUND

Oxidative stress seems to play an important role in the pathophysiology of essential hypertension. We aimed to examine serum MDA, NO, 8-OHdG, ADMA, NT, CoQ10 and TAC as biomarkers of oxidative stress in dipper and non-dipper hypertensive patients.

METHODS

Eighteen dipper hypertensives, 20 non-dipper hypertensives and 22 healthy control subjects were included in the study. Clinical assessment and ambulatory blood pressure monitoring were performed in patients. Serum MDA, TAC and NO levels were measured by using spectrophotometric methods. CoQ10 levels were measured by HPLC method. 8-OHdG, ADMA and NT were quantitated by ELISA methods.

RESULTS

MDA levels were significantly higher in dipper and non-dipper groups compared to controls (p<0.05 and p<0.01, respectively). TAC levels were found at low level in patients dipper and non-dipper patients compared to control group (p<0.01). Higher ADMA and NT levels but lower CoQ10 levels were found in non-dipper group compared to healthy controls (p<0.01, p<0.05, and p<0.05, respectively). ADMA levels were found higher in non-dipper group than those of dipper group (p<0.01).

DISCUSSION

Increased ADMA, NT levels and decreased CoQ10 levels in non-dipper hypertensive patients might indicate more severe oxidative stres compared with dipper hypertensive patients, which plays an important role in the development of cardiovascular diseases. Increased MDA and reduced TAC levels might be considered as prospective prognostic markers of the development of cardiovascular diseases in dipper and non-dipper hypertensive patients.

Diagnosis and management of patients with white-coat and masked hypertension

White-coat hypertension is characterized by an elevation in clinic blood pressure but normal home or ambulatory blood-pressure values, whereas patients with masked hypertension have normal clinic blood pressure and elevated ambulatory or home blood-pressure load. Both white-coat and masked hypertension are frequent clinical entities that need appropriate recognition and a close diagnostic follow-up. White-coat and masked hypertension seem to be associated with organ damage and increased cardiovascular risk, although not invariably. In addition, patients with masked or white-coat hypertension have an increased risk of abnormalities affecting their glucose and lipid profiles. Therefore, the diagnosis of these conditions should be accurate and include the assessment of cardiovascular as well as of metabolic risk. Once diagnosed, first-line therapeutic interventions should be nonpharmacological and aim at lifestyle changes, but drug treatment can be indicated, particularly when the patient's cardiovascular risk profile is elevated or when target-organ damage is detected.

Vascular endothelial-specific dimethylarginine dimethylaminohydrolase-1-deficient mice reveal that vascular endothelium plays an important role in removing asymmetric dimethylarginine

BACKGROUND

Asymmetrical methylarginines inhibit NO synthase activity and thereby decrease NO production. Dimethylarginine dimethylaminohydrolase 1 (DDAH1) degrades asymmetrical methylarginines. We previously demonstrated that in the heart DDAH1 is predominantly expressed in vascular endothelial cells. Because an earlier study showed that mice with global DDAH1 deficiency experienced embryonic lethality, we speculated that a mouse strain with selective vascular endothelial DDAH1 deficiency (endo-DDAH1(-/-)) would largely abolish tissue DDAH1 expression in many tissues but possibly avoid embryonic lethality.

METHODS AND RESULTS

By using the LoxP/Cre approach, we generated the endo-DDAH1(-/-) mice. The endo-DDAH1(-/-) mice had no apparent defect in growth or development compared with wild-type littermates. DDAH1 expression was greatly reduced in kidney, lung, brain, and liver, indicating that in these organs DDAH1 is distributed mainly in vascular endothelial cells. The endo-DDAH1(-/-) mice showed a significant increase of asymmetric dimethylarginine concentration in plasma (1.41 micromol/L in the endo-DDAH1(-/-) versus 0.69 micromol/L in the control mice), kidney, lung, and liver, which was associated with significantly increased systolic blood pressure (132 mm Hg versus 113 mm Hg in wild-type). The endo-DDAH1(-/-) mice also exhibited significantly attenuated acetylcholine-induced NO production and vessel relaxation in isolated aortic rings.

CONCLUSIONS

Our study demonstrates that DDAH1 is highly expressed in vascular endothelium and that endothelial DDAH1 plays an important role in regulating blood pressure. In the context that asymmetric methylarginines are broadly produced by many type of cells, the strong DDAH1 expression in vascular endothelium demonstrates for the first time that vascular endothelium can be an important site to actively dispose of toxic biochemical molecules produced by other types of cells.

Asymmetric dimethylarginine plasma concentrations and L-arginine/asymmetric dimethylarginine ratio in patients with slow coronary flow

OBJECTIVE

Elevated levels of nitric oxide synthase inhibitor, asymmetric dimethylarginine (ADMA) is considered to be a marker of endothelial dysfunction and increased risk of cardiovascular disease. Recent reports have implicated endothelial dysfunction as an underlying pathophysiological mechanism of slow coronary flow (SCF) phenomenon. Accordingly, we investigated plasma L-arginine, ADMA concentrations and L-arginine/ADMA ratio in patients with SCF in comparison with participants having normal coronary flow.

METHODS

We measured plasma levels of L-arginine and ADMA by high-performance liquid chromatography in 31 participants with SCF and 31 age and sex matched control participants with normal coronary flow. Coronary flow was quantified using the thrombolysis in myocardial infarction (TIMI) frame count method.

RESULTS

The patients with SCF were detected to have significantly higher concentrations of plasma ADMA (P=0.006) and lower L-arginine/ADMA ratio compared with participants with normal coronary flow (P=0.002). In addition, both ADMA and L-arginine/ADMA ratio were significantly correlated with mean TIMI frame count and TIMI frame count for each coronary artery in patients with SCF and multivariate regression analysis identified plasma ADMA as an independent predictor for SCF. In the receiver operator characteristics curve analysis, patients with SCF were detected by plasma ADMA level with a sensitivity, specificity of 64.5%, 74.2%, at a cut-off of >2.4 micromol/l and L-arginine/ADMA ratio with a sensitivity, specificity of 77.4%, 67.7% at a cut-off of <36.6.

CONCLUSION

Our findings provide evidence to support the hypothesis that endothelial dysfunction may be an important factor in the pathogenesis of SCF.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.

Asymmetrical dimethylarginine independently predicts total and cardiovascular mortality in individuals with angiographic coronary artery disease (the Ludwigshafen Risk and Cardiovascular Health study)

BACKGROUND

Asymmetrical dimethylarginine (ADMA) is increased in conditions associated with increased risk of atherosclerosis. We investigated the use of ADMA to predict total and cardiovascular mortality in patients scheduled for coronary angiography.

METHODS

In 2543 persons with and 695 without coronary artery disease (CAD) identified by angiography we measured ADMA and recorded total and cardiovascular mortality during a median follow-up of 5.45 years.

RESULTS

ADMA was correlated positively to age, female sex, diabetes mellitus, former and current smoking, and C-reactive protein and inversely to HDL cholesterol and triglycerides. ADMA was not associated with body mass index, hypertension, LDL cholesterol, or the presence or absence of angiographic CAD. Glomerular filtration rate and homocysteine were the strongest predictors of ADMA. At the 2nd, 3rd and 4th quartile of ADMA, hazard ratios for all-cause mortality adjusted for age, sex, and cardiovascular risk factors were 1.12 [95% confidence interval (CI) 0.83-1.52], 1.35 (95% CI 1.01-1.81), and 1.87 (95% CI 1.43-2.44), respectively, compared with the 1st quartile. Hazard ratios for cardiovascular death were 1.13 (95% CI 0.78-1.63), 1.42 (95% CI 1.00-2.02), and 1.81 (95% CI 1.31-2.51). ADMA in the highest quartile remained predictive of mortality after accounting for medication at baseline. The predictive value of ADMA was similar to that in the entire cohort in persons with CAD, stable or unstable, but was not statistically significant in persons without angiographic CAD.

CONCLUSIONS

ADMA concentration predicts all-cause and cardiovascular mortality in individuals with CAD independently of established and emerging cardiovascular risk factors.

Oxidative stress in human in sustained and white coat hypertension

Oxidative stress is thought to play a critical role in the pathogenesis of hypertension. Protein oxidation is defined here as the covalent modification of a protein induced either directly by reactive oxygen species or indirectly by reaction with secondary by-products of oxidative stress. The aim of our study was to evaluate the protein oxidation and to examine the function of the antioxidative system in sustained and white coat hypertensives (WCH) and compare with normotensives. This study was designed to investigate the protein oxidation parameters [protein carbonyls (PCOs)] in sustained hypertensives (17 males and 20 females) and WCH (18 males and 19 females). PCO and the endogenous antioxidant components protein thiol (P-SH), CuZn-superoxide dismutase (CuZn-SOD) and glutathione (GSH) were analysed using spectrophotometric and kinetic methods. Sustained hypertensive and WCH groups exhibited higher protein oxidation and lower P-SH, CuZn-SOD and GSH activities than normotensives. With regard to these parameters, there was no significant difference between sustained hypertensive and WCH groups. Blood pressure correlates positively with PCO groups and negatively with others. There exists an imbalance between oxidants and antioxidants in WCH because of the increase of oxidants associated with the decrease of antioxidant capacity. This may cause endothelial dysfunction just like in sustained hypertension. It may be necessary to add antioxidants to conventional antihypertensive therapy to balance the oxidative status in WCH.

L-NAME- and ADMA-induced sympathetic neural activation in conscious rats

Although studies in anesthetized, sino-aortic denervated animals indicate that inhibition of central nitric oxide (NO) causes an excitatory influence on efferent sympathetic nerve activity (SNA) that is normally offset by baroreflex activation, studies in conscious animals have not provided clear-cut evidence for a sympathoexcitatory effect of N(omega)-nitro-l-arginine methyl ester (L-NAME) or the endogenous circulating NO synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA). Thus our goals were to 1) use surgical sino-aortic denervation to test for a sympathoexcititatory effect of intravenous l-NAME in conscious rats, and 2) to determine whether SNA responses to intravenous L-NAME can be extrapolated directly to intravenous ADMA. We recorded mean arterial blood pressure and renal SNA in both intact and sino-aortic-denervated conscious rats during 3 h of continuous intravenous infusion with either L-NAME or ADMA. When we eliminated the confounding influence of the sino-aortic baroreceptors, L-NAME produced a progressive increase in SNA with the peak response exceeding the baseline level of nerve firing by 150%. The same type of frank sympathetic activation was observed with intravenous ADMA. Taken together, these data offer straightforward evidence for l-NAME, as well as ADMA-induced sympathetic activation with direct recordings of SNA in conscious animals. These data confirm and extend the concept that circulating endogenous NOS inhibitors can constitute an excitatory signal to SNA.