Plasma asymmetric dimethylarginine and L-arginine levels in patients with cardiac syndrome X

Coronary microvascular dysfunction, arrythmias, and sudden cardiac death: A literature review

The coronary vascular system has a unique structure and function that is adaptive to myocardial demand. It is composed of a continuous network of vessels receding in size from epicardial arteries to the microvascular circulation. Failure to meet myocardial demand results in ischemia, angina, and adverse myocardial outcomes. It is evident that 50 % of patients with angina have a non-obstructive coronary disease and 66 % of these patients have coronary microvascular dysfunction (CMD). The impact of CMD on the atria and ventricles is exhibited through its association with atrial fibrillation and distortion of ventricular repolarization. Ultimately, this influence increases the risk of mortality, morbidity, and sudden cardiac arrest. CMD serves as an independent risk for atrial fibrillation, increases ventricular electrical inhomogeneity, and contributes to the progression of cardiac disease. The underlying pathogenesis may be attributed to oxidative stress evident through reactive oxygen species, impaired vasoactive function, and structural disorders such as fibrotic changes. Myocardial ischemia, brought about by a demand-supply mismatch in CMD, may create a milieu for ventricular arrythmia and sudden cardiac arrest through distortion of ventricular repolarization parameters such as QT dispersion and corrected QT dispersion.

Circulating Biomarkers in Coronary Microvascular Dysfunction

Coronary microvascular dysfunction is an underdiagnosed pathologic process that is associated with adverse clinical outcomes. Biomarkers, molecules measurable in the blood, could inform the clinician by aiding in the diagnosis and management of coronary microvascular dysfunction. We present an updated review of circulating biomarkers in coronary microvascular dysfunction representing key pathologic processes, including inflammation, endothelial dysfunction, oxidative stress, coagulation, and other mechanisms.

Biomarkers of Coronary Microvascular Dysfunction in Patients With Microvascular Angina: A Narrative Review

The current gold standard for diagnosis of coronary microvascular dysfunction (CMD) in the absence of myocardial diseases, whose clinical manifestation is microvascular angina (MVA), is reactivity testing using adenosine or acetylcholine during coronary angiography. This invasive test can be difficult to perform, expensive, and harmful. The identification of easily obtainable blood biomarkers which reflect the pathophysiology of CMD, characterized by high reliability, precision, accuracy, and accessibility may reduce risks and costs related to invasive procedures and even facilitate the screening and diagnosis of CMD. In this review, we summarized the results of several studies that have investigated the possible relationships between blood biomarkers involved with CMD and MVA. More specifically, we have divided the analyzed biomarkers into 3 different groups, according to the main mechanisms underlying CMD: biomarkers of "endothelial dysfunction," "vascular inflammation," and "oxidative stress." Finally, in the last section of the review, we consider mixed mechanisms and biomarkers which are not included in the 3 major categories mentioned above, but could be involved in the pathogenesis of CMD.

The prognostic value of asymmetric dimethylarginine in patients with cardiac syndrome X

Background

The pathophysiology of cardiac syndrome X is multifactorial and endothelial dysfunction has been implicated as important contributing factor. Asymmetric dimethylarginine (ADMA), characterized as a circulating endogenous inhibitor of nitric oxide synthase, may have been implicated as an important contributing factor for the development of endothelial dysfunction. In this study, we aim to assess the predictive power of ADMA for long-term prognosis in patients with cardiac syndrome X.

Methods and results

We enrolled 239 consecutive patients with cardiac syndrome X diagnosed by coronary angiography. The mean age was 58.7±10.1 years. The patients were grouped into tertiles according to the plasma ADMA levels: <0.38 μmol/l (tertile I), 0.38–0.44 μmol/l (tertile II), and >0.44 μmol/l (tertile III). All patients were followed up for a mean period of 6.5±1.5 years (median: 6.3 years, inter-quartile range: 5.7–8.0 years). During the follow-up period, major adverse events (MAE) were observed in 15 patients (6.3%), including 13 deaths. The plasma ADMA levels in patients who developed MAE were significantly higher than those who did not (0.48±0.06 μmol/l vs. 0.42±0.08 μmol/l, p = 0.005). In multivariate Cox regression analysis adjusted for age, eGFR and LVEF, ADMA tertile I and II were identify to be associated with a significantly lower risk of MAE compared to ADMA tertile III (p = 0.017). By considering the plasma ADMA level as a continuous variable, the plasma ADMA level remained a significant independent predictor for outcomes of MAE, and the relative risk of MACE increased by 50% when plasma ADMA level increased by 1 SD of value (p = 0.018).

Conclusions

In patients with cardiac syndrome X, elevated plasma ADMA levels appeared to be an independent predictor of long-term adverse clinical outcomes.

Novel biomarkers of coronary microvascular disease

Coronary microvascular disease in the absence of myocardial diseases has traditionally been diagnosed through coronary reactivity testing in the cardiac catheterization laboratory. Compared with invasive procedures, blood-based biomarkers may have reduced cost, less risk of physical harm and greater accessibility, making them ideal for an outpatient management strategy. There are a variety of biomarkers available with potential utility in the management of microvascular disease; however, none have yet been extensively validated or established in this clinical patient population.

Nitric oxide-mediated coronary flow regulation in patients with coronary artery disease: recent advances

Nitric oxide (NO) formed via endothelial NO synthase (eNOS) plays crucial roles in the regulation of coronary blood flow through vasodilatation and decreased vascular resistance, and in inhibition of platelet aggregation and adhesion, leading to the prevention of coronary circulatory failure, thrombosis, and atherosclerosis. Endothelial function is impaired by several pathogenic factors including smoking, chronic alcohol intake, hypercholesterolemia, obesity, hyperglycemia, and hypertension. The mechanisms underlying endothelial dysfunction include reduced NO synthase (NOS) expression and activity, decreased NO bioavailability, and increased production of oxygen radicals and endogenous NOS inhibitors. Atrial fibrillation appears to be a risk factor for endothelial dysfunction. Endothelial dysfunction is an important predictor of coronary artery disease (CAD) in humans. Penile erectile dysfunction, associated with impaired bioavailability of NO produced by eNOS and neuronal NOS, is also considered to be highly predictive of ischemic heart disease. There is evidence suggesting an important role of nitrergic innervation in coronary blood flow regulation. Prophylactic and therapeutic measures to eliminate pathogenic factors inducing endothelial and nitrergic nerve dysfunction would be quite important in preventing the genesis and development of CAD.

Arginine bioavailability ratios are associated with cardiovascular mortality in patients referred to coronary angiography

OBJECTIVES

Arginine is the only source for nitric oxide (NO) synthesis. The bioavailability of NO plays a pivotal role in endothelial function and consequently in cardiovascular disease. The aim of the current study is to investigate the association of arginine bioavailability ratios with markers of endothelial function and cardiovascular mortality in patients referred to coronary angiography.

METHODS

We investigated 2236 patients recruited within the LUdwigshafen RIsk and Cardiovascular Health (LURIC) study that were followed up for a median of 7.7 years. Arginine, ornithine and citrulline were chromatographically determined after precolumn-derivatisation followed by postcolumn continuous reaction with ninhydrin. Global arginine bioavailability (GABR) was calculated by arginine divided by the sum of ornithine plus citrulline.

RESULTS

We observed a significant rise in cardiovascular mortality with decreasing GABR and arginine to ornithine ratio quartiles. The adjusted Cox proportional HRs for GABR were 1.27 (0.88-1.83), 1.27 (0.89-1.80) and 1.75 (1.24-2.45) for the 3rd, the 2nd and the 1st quartile respectively in comparison to the 4th quartile. The HRs for the quartiles of the arginine to ornithine ratio were 1.83 (1.25-2.67), 2.17 (1.50-3.20) and 2.02 (1.39-2.92) respectively. Patients with type 2 diabetes mellitus had a significantly lower GABR than persons without diabetes (0.88 ± 0.23 vs. 0.94 ± 0.24, p<0.001). GABR was found to be inversely correlated with endothelial markers as VCAM-1 (r=-0.301, p<0.001) or ICAM-1 (r=-0.136, p<0.001).

CONCLUSIONS

GABR and the arginine to ornithine ratio are associated with markers of endothelial dysfunction and increased risk of cardiovascular mortality. Further studies are warranted to elucidate the pathobiology and clinical relevance of the arginine bioavailability ratios in cardio-metabolic diseases.

Relationship between L-arginine/asymmetric dimethylarginine, homocysteine, folic acid, vitamin B levels, and coronary artery ectasia

BACKGROUND

Coronary artery ectasia (CAE) is characterized by an abnormal dilatation of the coronary arteries. The ratio of L-arginine/asymmetric dimethylarginine (ADMA) and homocysteine are important factors for endothelial function. In this study, we investigate the ratio of L-arginine/ADMA, homocysteine, and folic acid/vitamin B levels in patients with CAE.

METHODS

Forty patients diagnosed with CAE using coronary angiography were included in the study (24 male; mean age, 56 ± 11 years). The control group consisted of 30 patients who had normal coronary arteries as determined by coronary angiography (11 male; mean age, 54 ± 8 years). The ratio of L-arginine/ADMA and plasma homocysteine was measured using high-performance liquid chromatography.

RESULTS

The L-arginine/ADMA ratio and L-arginine levels were significantly lower in the CAE group compared with the control group (110 ± 27 vs. 149 ± 77, P=0.02 and 157 ± 32 μmol/l vs. 187 ± 59 μmol/l, P=0.02, respectively). Plasma ADMA levels were similar in the two groups. Patients with CAE had higher plasma homocysteine levels (P=0.01). Plasma folic acid, vitamin B6, and vitamin B12 levels were similar between the two groups.

CONCLUSION

This study shows that patients with CAE have a lower L-arginine/ADMA ratio and higher plasma homocysteine levels. These results show a potential relationship between endothelial dysfunction and CAE.

Definitions and incidence of cardiac syndrome X: review and analysis of clinical data

There is no consensus regarding the definition of cardiac syndrome X (CSX). We systematically reviewed recent literature using a standardized search strategy. We included 57 articles. A total of 47 studies mentioned a male/female distribution. A meta-analysis yielded a pooled proportion of females of 0.56 (n = 1,934 patients, with 95% confidence interval: 0.54-0.59). As much as 9 inclusion criteria and 43 exclusion criteria were found in the 57 articles. Applying these criteria to a population with normal coronary angiograms and treated in 1 year at a general hospital, the attributable CSX incidence varied between 3 and 11%. The many inclusion and exclusion criteria result in a wide range of definitions of CSX and these have large effects on the incidence. This shows the need for a generally accepted definition of CSX.

Association between plasma asymmetrical dimethylarginine activity and saphenous vein graft disease in patients with coronary bypass

BACKGROUND

Coronary vein graft disease is an important contributor to the morbidity after coronary artery bypass graft surgery. Graft occlusion is a serious complication, which limits the use of the saphenous vein as a coronary bypass conduit. Asymmetrical dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and it reduces the bioavailability of nitric oxide and begets endothelial dysfunction. The goal of this study was to examine the association between plasma ADMA activity and saphenous vein graft disease.

METHODS

One hundred and three patients were enrolled in this study. Group 1 consisted of 42 patients (13 female, 29 male) who had diseased saphenous vein grafts and group 2 consisted of 61 patients (10 female, 51 male) with nondiseased saphenous vein grafts. ADMA activity was measured by the enzyme-linked immunosorbent assay kit.

RESULTS

Mean ADMA activity in group 1 was significantly higher than in group 2 (2.0+/-0.6 vs. 1.1+/-0.5 micromol/l, P<0.001, respectively). Mean platelet volume was also significantly higher in group 1 than in group 2 (8.7+/-1.5 vs. 8.2+/-0.6 fl, P=0.03, respectively). In a multivariate linear regression analysis, ADMA activity (beta=2.902, P<0.001) and mean platelet volume (beta=0.595, P=0.03) were found to be independent predictors of saphenous vein graft disease.

CONCLUSION

Our results showed that ADMA activity was higher in patients with saphenous vein graft disease. Increased ADMA activity might lead to the acceleration of saphenous vein graft disease. ADMA may be a precious marker for detecting late saphenous vein graft patency.

The biochemistry, measurement and current clinical significance of asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide synthase and an important cause of endothelial dysfunction. Its increased plasma concentration is associated with a variety of traditional cardiovascular risk factors, and may mediate their effects on the vascular endothelium. ADMA is also an independent predictor of cardiovascular events and mortality, and predicts outcomes in critically ill patients in the intensive care unit. This work has provided insights into the role of ADMA as an endogenous regulator of nitric oxide synthesis. At present there is no specific therapy to modify ADMA concentration, but increasing interest and work on protein arginine methyltransferases and dimethylarginine dimethylaminohydrolase, which synthesize and metabolize ADMA, respectively, might provide novel therapeutic targets.

Diminished global arginine bioavailability and increased arginine catabolism as metabolic profile of increased cardiovascular risk

OBJECTIVES

We hypothesized that an integrated assessment of arginine with its catabolic products might better predict cardiovascular risks than arginine levels alone.

BACKGROUND

Arginine is the sole nitrogen source for nitric oxide (NO) synthesis. The major catabolic products of arginine are ornithine and citrulline.

METHODS

Plasma levels of free arginine, ornithine, citrulline, and the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) were measured with liquid chromatography coupled with tandem mass spectrometry. We examined the relationship of global arginine bioavailability ratio (GABR) (defined as arginine/[ornithine + citrulline]) versus arginine and its catabolic metabolites to prevalence of significantly obstructive coronary artery disease (CAD) and incidence of major adverse cardiovascular events (MACE) (death, myocardial infarction, stroke) over a 3-year follow-up in 1,010 subjects undergoing elective cardiac catheterization.

RESULTS

Patients with significantly obstructive CAD had significantly lower GABR (median [interquartile range]: 1.06 [0.75 to 1.31] vs. 1.27 [0.96 to 1.73], p < 0.001) and arginine levels [mean: 68 +/- 20 micromol/l vs. 74 +/- 24 micromol/l, p < 0.001) than those without significantly obstructive CAD. After adjusting for Framingham risk score, C-reactive protein, and renal function, lower GABR (but not arginine levels) and higher citrulline levels remained significantly associated with both the prevalence of significantly obstructive CAD (adjusted odds ratio: 3.93, p < 0.001, and 5.98, p < 0.001, respectively) and 3-year risk for the incidence of MACE (adjusted hazard ratio: 1.98, p = 0.025, and 2.40, p = 0.01, respectively) and remained significant after adjusting for ADMA.

CONCLUSIONS

GABR might serve as a more comprehensive concept of reduced NO synthetic capacity compared with systemic arginine levels. Diminished GABR and high citrulline levels are associated with both development of significantly obstructive atherosclerotic CAD and heightened long-term risk for MACE.

Serum ADMA concentration-- an independent factor determining FMD impairment in cardiac syndrome X

Mechanisms of decreased endogenous vascular reactivity in individuals with cardiac syndrome X (CSX) are not fully understood.

AIM

To evaluate the following serum markers: total nitric oxide (NO), asymmetric dimethylarginine (ADMA), platelet-derived growth factor (PDGF), and to establish their relation to ultrasound indexes of endothelial function and structural remodeling in CSX patients.

METHOD

The study group consisted of 43 CSX patients (mean age: 56.3 +/- 9 years), while the control group included 21 healthy subjects (mean age: 54.86 +/- 6.9 years). The high-resolution ultrasound was performed to measure: flow-mediated vasodilatation (FMD), nitroglycerine-mediated vasodilatation (NMD) and intima-media thickness (IMT) of carotid arteries.

RESULTS

In CSX patients, significantly lower FMD (9.06 +/- 3.2%) and significantly higher IMT (0.667 +/- 0.14 mm) values were observed compared to healthy individuals (17.42 +/- 8.4%, 0.571 +/- 0.2 mm; P < 0.05). Mean total NO serum concentration was significantly higher in the CSX group (48.2 +/- 18.2 micromol/L) as compared to controls (32.1 +/- 1.4 micromol/L; P < 0.0001). There were no differences in serum ADMA and PDGF levels. In CSX patients, FMD values correlated with NO (r = 0.323; P = 0.039) and ADMA (r = -0.387; P = 0.012) serum levels; however, there were no significant correlations between NO and ADMA concentrations.

CONCLUSION

Serum ADMA concentration is the only independent factor determining FMD impairment.