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Osteoprotegerin (OPG) has been implicated in the process of vascular stiffness. The aim of this study was to evaluate the relationship between fasting serum OPG concentration and carotid-femoral pulse wave velocity (c-f PWV) in hypertensive patients. Fasting blood samples were obtained from 184 participants with or without hypertension. c-f PWV were performed by SphygmoCor system. Serum OPG levels were measured using a commercially available enzyme-linked immunosorbent assay. Hypertensive patients who had diabetes had higher c-f PWV levels than those without diabetes (P=.031). The univariable linear regression analysis showed that age (P<.001), systolic blood pressure (P=.003), pulse pressure (r=0.287; P=.003), log-BUN (P=.011), Cre (P<.001), and log-OPG concentration (P<.001) were positively correlated with c-f PWV levels, while the glomerular filtration rate (P=.005) and HDL-C level (P=.024) was negatively correlated with c-f PWV levels among the hypertensive patients. Multivariable forward stepwise linear regression analysis of the significant variables also showed that log-OPG (β=0.312, regression coefficient: 1.736; 95% confidence interval, 0.809–2.663; P<.001) was still an independent predictor of c-f PWV levels in hypertensive patients. Serum OPG levels positively associated with c-f PWV levels in hypertensive patients.
Arterial stiffness has been recognized as an independent risk factor for cardiovascular morbidity and mortality. Carotid-femoral pulse wave velocity (c-f PWV) is a direct measurement of aortic stiffness and has been recommended as the gold standard measurement for arterial stiffness. An increase of 1 m/s in c-f PWV is associated with an increase of 14% of total cardiovascular events, 15% cardiovascular mortality, and 15% all-cause mortality in a systematic review and meta-analysis study. In large numbers of healthy patients or hypertensive patients, c-f PWV has been demonstrated to be a predictor of future cardiovascular events.
Arterial stiffness is defined by a reduction in arterial distensibility.[3, 4] Recent science suggests that arterial stiffness is associated with endothelial dysfunction, the expression of modified vascular wall matrix proteins, altered vascular smooth muscle cell number, structure and functions, inflammation, and potential genetic determinants. Vascular calcification in blood vessels is an active, cell-regulated process, which may lead to increased arterial stiffness. Osteoprotegerin (OPG) is one of the vascular calcification inhibitors and may reflect endothelial dysfunction. In recent studies, OPG has been associated with increased PWV, progression of arterial calcification, and increased mortality in both end-stage renal failure patients and the general population.[8, 9] c-f PWV is a strong and independent predictor of overall risk and cardiovascular risk in hypertension. Aortic stiffness is also an independent predictor of primary coronary events in patients with essential hypertension. The aim of the current study was to determine the relationship between the fasting serum OPG level and c-f PWV among hypertensive patients.
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The clinical and laboratory characteristics of participants with or without hypertension are presented in Table 1. Hypertensive patients had higher body weight (P<.001), BMI (P<.001), waist circumference (P=.009), TGs (P=.027), fasting glucose (P=.039), CRP (P=.011), SBP (P<.001), and DBP (P<.001) than normotensive participants. The c-f PWV levels, serum OPG levels, sex, and diabetes did not differ statistically in participants with or without hypertension.
Table 1. Clinical and Analytical Characteristics of 184 Participants With or Without Hypertension
|Items||No Hypertension (n=78)||Hypertension (n=106)||P Value|
|Body weight, kg||63.67±9.39||70.28±12.36||<.001|
|Waist circumference, cm||89.51±9.47||93.27±9.70||.009|
|Body mass index, kg/m2||24.73±2.76||26.82±3.50||<.001|
|Total cholesterol, mg/dL||170.46±40.04||171.97±38.20||.795|
|Fasting glucose, mg/dL||120.64±42.19||137.79±59.04||.039|
|Blood urea nitrogen, mg/dL||15.62±4.21||17.28±6.26||.097|
|Glomerular filtration rate, mL/min||73.15±14.94||69.67±21.18||.216|
|Total calcium, mg/dL||9.07±0.35||9.15±0.36||.141|
|Ca×P product, mg2/dL2||32.67±5.37||31.97±4.91||.361|
|Systolic blood pressure, mm Hg||119.69±11.12||136.94±17.47||<.001|
|Diastolic blood pressure, mm Hg||68.69±8.41||74.92±10.72||<.001|
|Pulse pressure, mm Hg||51.00±12.25||62.03±16.35||<.001|
|C-reactive protein, mg/dL||0.20±0.09||0.34±0.40||.011|
|c-f PWV, m/s||9.24±3.51||9.56±2.69||.485|
The clinical and laboratory characteristics of the hypertensive patients are presented in Table 2. The medical histories of the hypertensive patients included dyslipidemia (n=85 [80.2%]), coronary artery disease (n=70 [66.0%]), and congestive heart failure (n=15 [14.1%]). The medications prescribed to the hypertensive patients included angiotensin receptor blockers (ARBs; n=58 [54.7%]), angiotensin-converting enzyme (ACE) inhibitors (n=36 [34.0%]), calcium channel blocker (CCBs; n=53 [50.0%]), β-blockers (n=63 [59.4%]), statins (n=59 [55.7%]), fibrate (n=24 [22.6%]), aspirin (n=61 [57.5%]), and clopidogrel (n=26 [24.5%]). Normotensive participants (P=.040) or hypertensive patients (P=.031) who had diabetes had higher c-f PWV levels than those without diabetes (Figure 1). The c-f PWV levels did not differ statistically based on sex, coexisting dyslipidemia or coronary artery disease or congestive heart failure, and ARB, ACE inhibitor, CCB, β-blocker, statin, fibrate, aspirin, or clopidogrel use.
Table 2. Clinical Characteristics and Carotid-Femoral Pulse Wave Velocity Levels of 106 Hypertensive Patients
|Characteristic||Number (%)||c-f PWV, m/s||P Value|
Figure 1. Clustered dots plot with means±standard deviations of carotid-femoral pulse wave velocity (c-f PWV) levels with or without diabetes mellitus (DM) among participants without (a) or with (b) hypertension.
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The univariable linear analysis of c-f PWV levels in normotensive participants or hypertensive patients is presented in Table 3. Age (r=0.349; P=.02) was positively correlated with c-f PWV levels in normotensive participants. Age (r=0.370; P<.01), SBP (r=0.282; P=.003), pulse pressure (r=0.287; P=.003), log-BUN (r=0.234; P=.011), Cre (r=0.360; P<.001), and the log-OPG concentration (r=0.392; P<.001) were positively correlated with c-f PWV levels, while the GFR (r=−0.273; P=.005) and HDL-C level (r=−0.219; P=.024) was negatively correlated with c-f PWV levels among the hypertensive patients. Two-dimensional scattered plots of c-f PWV levels among the 106 hypertensive patients are shown in Figure 2 and Figure 3.
Table 3. Correlation of Carotid-Femoral Pulse Wave Velocity and Clinical Variables by Univariable Linear Regression Analysis Among Participants With or Without Hypertension
|Variable||No Hypertension (n=78)||Hypertension (n=106)|
|r Value||P Value||r Value||P Value|
|Body weight, kg||−0.087||.447||−0.047||.629|
|Waist circumference, cm||−0.188||.099||0.070||.474|
|Body mass index, kg/m2||0.038||.744||−0.023||.818|
|Systolic blood pressure, mm Hg||0.101||.380||0.282||.003b|
|Diastolic blood pressure, mm Hg||−0.026||.820||0.022||.824|
|Pulse pressure, mm Hg||0.110||.340||0.287||.003b|
|Total cholesterol, mg/dL||0.058||.612||−0.091||.356|
|Glomerular filtration rate, mL/min||−0.131||.255||−0.273||.005b|
|Total calcium, mg/dL||−0.066||.567||−0.060||.544|
|Ca×P product, mg2/dL2||0.163||.153||−0.062||.528|
Figure 2. Two-dimensional scattered plots of carotid-femoral pulse wave velocity (c-f PWV) levels with (a) age, (b) systolic blood pressure (SBP), (c) pulse pressure, and (d) high-density lipoprotein cholesterol (HDL-C) among 106 hypertensive patients. Dashed lines represent 95% confidence intervals.
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Figure 3. Two-dimensional scattered plots of carotid-femoral pulse wave velocity (cf PWV) levels with (a) creatinine, (b) log-transformed blood urea nitrogen (BUN), (c) glomerular filtration rate (GFR), and (d) log-transformed osteoprotegerin among 106 hypertensive patients. Dashed lines represent 95% confidence interval.
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Multivariable forward stepwise linear regression analysis of the variables that were significantly associated with c-f PWV levels (diabetes, age, SBP, pulse pressure, HDL-C, log-BUN, creatinine, GFR, and log-OPG) among hypertensive patients showed that age (β=0.268, regression coefficient: 0.071; 95% confidence interval [CI], 0.023–0.119; P=.004), HDL-C (β=−0.234, regression coefficient: 0.050; 95% CI, −0.086 to −0.013; P=.008), Cre (β=0.207; regression coefficient: 1.645; 95% CI, 0.254–3.036; P=.021), and log-OPG (β=0.312; regression coefficient: 1.736; 95% CI, 0.809–2.663; P<.001) were the independent predictors of c-f PWV levels in hypertensive patients (Table 4).
Table 4. Correlation Between Carotid-Femoral Pulse Wave Velocity Among Hypertensive Patients
|Variables||Correlation Coefficient (β)||Regression Coefficient (95% Confidence Interval)||P Value|
|Age, y||0.268||0.071 (0.023–0.119)||.004a|
|HDL-C, mg/dL||−0.234||0.050 (−0.086 to −0.013)||.008a|
|Creatinine, mg/dL||0.207||1.645 (0.254–3.036)||.021a|
|Log-osteoprotegerin, pg/L||0.312||1.736 (0.809–2.663)||<.001a|
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The results of our study showed that diabetes, age, SBP, BUN, Cre, and OPG concentration were positively correlated with c-f PWV levels, while GFR and HDL-C levels were negatively correlated with c-f PWV levels among hypertensive patients. After adjusting for significant variables by multivariable forward stepwise linear regression analysis, it was shown that OPG was still an independent predictor of c-f PWV levels in hypertensive patients.
Obesity and weight gain are major risk factors for hypertension. Metabolic syndrome has been shown to be a risk factor for cardiovascular disease and, as the prevalence of obesity increases, the prevalence of hypertension with its associated cardiovascular risk increases as well. CRP is significantly predictive of incident hypertension. Our study also showed that hypertensive patients had higher body weight, BMI, waist circumference, fasting glucose, TGs, and CRP than normotensive participants.
Contraction of the left ventricle generates a pulse wave that is propagated throughout the arterial tree. PWV is calculated as the distance traveled by the pulse wave divided by the time taken to travel the distance. c-f PWV is a direct measurement of aortic stiffness, and has been recommended as the gold standard measurement for arterial stiffness. Aging of the arterial system is accompanied by progressive structural changes, consisting of fragmentation and degeneration of elastin, increases in collagen, thickening of the arterial wall, endothelium damage, and progressive dilation of the arteries. Diabetes is a disease of accelerated arterial ageing, as shown by stiffer arteries and consequently steeper increases in pulse pressure with age in these patients. Our results show that age and diabetes are associated with c-f PWV levels in normotensive and hypertensive patients. Patients with lecithin-cholesterol acyltransferase mutation had low HDL-C levels that increased arterial stiffness. HDL-C was inversely associated with c-f PWV in community-dwelling individuals and healthy adults undergoing a general health examination in China.[23, 24] The possible mechanisms of HDL-C of anti-atheromatous effects on the arterial wall by promoting macrophage cholesterol efflux and reverse cholesterol transport activity and nonatheromatous effects on the arterial wall, such as the stimulation of endothelial nitric oxide production and repair, as well as anti-apoptotic, anti-inflammatory, and anti-oxidant effects that may improve arterial stiffness. Arterial stiffness leads to an increase in SBP because a heart pumping blood into a stiffer arterial bed must generate higher end-systolic pressures for the same net stroke volume. This leads to increased decay of arterial pressure and volume during systole, causing reduced arterial volume at the onset of diastole, which, in turn, causes an enhanced fall in DBP. The increase in SBP, which subsequently increases left ventricular afterload, and the decrease in DBP may reduce coronary perfusion. Therefore, arterial stiffness increases peak- and end-systolic pressures in the ascending aorta, thereby raising myocardial pressure load and oxygen consumption, and decreasing DBP and subendocardial blood flow and increasing pulse pressure. Individuals with metabolic syndrome also have increased arterial stiffness. Patients with decreased GFR exhibited a significant reverse association with c-f PWV in women with normal to mildly impaired renal function. Schillaci and colleagues reported that the decreased GFR was a major determinant of aortic stiffness in hypertensive patients with normal renal function. Reduced GFR were associated with central arterial stiffness by higher augmentation index. Our study showed that SBP, log-BUN, and Cre levels were positively correlated, while the GFR and HDL-C levels were negatively correlated with c-f PWV levels among hypertensive patients. In our study, age, Cre, and HDL-C levels were also independent predictors of c-f PWV levels in hypertensive patients after multivariable analysis.
Arterial stiffness is associated with vascular calcification. The mechanisms underlying the postulated role of OPG in arterial stiffness may involve endothelial and ventricular dysfunction, inflammation, and calcification. The vascular role of OPG is multifaceted and depends on the interplay with its ligands, receptor activator of NF-κB ligand, and tumor necrosis factor–related apoptosis-inducing ligand, and a bidirectional modulation involving osteogenic, inflammatory, and apoptotic responses. OPG is expressed in vivo by endothelial cells, vascular smooth muscle cells, and osteoblasts. The production of OPG is enhanced by inflammatory cytokines and may reflect endothelial dysfunction. Additionally, the failing myocardium, plaque rupture, and other inflamed tissues could contribute to elevated circulating OPG concentrations.[7, 30] Studies in vitro and in animal models suggest that OPG inhibits vascular calcification. In addition to inhibiting apoptotic passive calcification, the ability of OPG to inhibit alkaline phosphatase–mediated osteogenic differentiation of vascular cells is also likely to contribute to the protective role of OPG. Clinical studies also suggest that an increase in serum OPG levels is associated with vascular calcification, coronary artery disease, stroke, and future cardiovascular events. Serum OPG was positively associated with c-f PWV in healthy patients, patients with peripheral artery disease, patients with chronic kidney disease, hemodialysis patients, and with the extent of coronary artery disease.[31-34] Serum OPG level was significantly related to severity and 10-year progression of carotid atherosclerosis. Elevated serum concentrations of OPG are found in a range of cardiovascular pathologies, suggesting the potential value of OPG as a biomarker of vascular risk and prognosis. Our study showed that serum log-OPG concentrations were positively correlated with c-f PWV levels among hypertensive patients. Multivariable forward stepwise linear regression analysis of the significant variables also showed that serum log-OPG concentration was also an independent predictor of c-f PWV levels in the current study.
Pharmacologic interventions have been shown to influence c-f PWV in humans. Specifically, a significantly greater reduction from baseline with valsartan/hydrochlorothiazide compared with amlodipine has been shown with aortic PWV. However, one of the interesting findings from the Conduit Artery Function Evaluation (CAFE]), the Preterax in Regression of Arterial Stiffness in a Controlled Double-Blind Study (REASON), and the Effect of the Fixed Dose Combination Amlodipine/Valsartan on Central Aortic Blood Pressure in Uncontrolled Essential Hypertension With Amlodipine 5 mg (EXPLOR) trials is that different antihypertension regimens produced clear differential effects on central aortic systolic and pulse pressures but little difference in PWV between the treatments compared in the studies. In addition, a systematic review paper also could not safely conclude the effect of statins on arterial stiffness, as estimated by PWV measurements. Our results did not show a relationship between statins and fibrate or other medications (ARBs, ACE inhibitors, CCBs, β-blockers, aspirins, or clopidogrel) and c-f PWV levels among patients with hypertension. Further studies are therefore required to elucidate the relationship between medication and c-f PWV levels in hypertensive patients.