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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
J Hum Hypertens. Author manuscript; available in PMC 2010 August 3.
Published in final edited form as:
PMCID: PMC2914456
NIHMSID: NIHMS215681

Carotid artery stiffness, high-density lipoprotein cholesterol and inflammation in men with pre-hypertension

Abstract

Low circulating levels of high density lipoprotein cholesterol (HDL-C) are associated with increased risk for cardiovascular events. HDL-C has a variety of poorly understood atheroprotective effects, including altering lipid metabolism and reducing inflammation. Increased arterial stiffness is an important predictor of subsequent cardiovascular risk. Therefore, in the current study, we sought to determine whether HDL-C levels are associated with carotid arterial stiffness. In addition we examined potential correlates of this association such as inflammatory factors, cardio-respiratory fitness and body fat percentage.

Methods

Carotid artery β stiffness was measured by ultrasound in 47 (23 yrs old) healthy pre-hypertensive men. Low HDL-C was defined as <1.0 mmol/L. Body fat was measured by air displacement plethysmograpy. Cardio-respiratory fitness was measured using a maximal exercise test with metabolic gas analysis and inflammatory markers consisted of C-reactive protein (CRP), white blood cell (WBC) count, and absolute neutrophil count.

Results

Men with low HDL-C had significantly higher carotid artery stiffness, CRP, WBC count, neutrophil count, body fat, fasting glucose and lower cardio-respiratory fitness (p<0.05). Co-varying for cardio-respiratory fitness, % body fat, and glucose had no effect on group differences in carotid artery stiffness. Co-varying for inflammatory markers resulted in groups having similar carotid artery stiffness.

Conclusion

Pre-hypertensive men with low HDL-C have higher carotid artery stiffness when compared with those with higher HDL-C. The detrimental effects of low HDL-C on large artery stiffness in pre-hypertensive men may be mediated by inflammation and not by cardio-respiratory fitness or body fat levels.

Keywords: arterial stiffness, C-reactive protein, maximal oxygen consumption, body fat

INTRODUCTION

Low levels of high density lipoprotein cholesterol (HDL-C) are associated with higher CVD risk 1-4. In vitro examinations note that HDL-C has a favorable effect on the vasculature and in vivo examinations have confirmed an association between HDL-C and vascular function 5-7. Vascular stiffness is now acknowledged as an independent risk factor for future cardiovascular morbidity and mortality 8,9. Pre-hypertensive individuals demonstrate marked vascular stiffening 10, a known antecedent to the development of essential and isolated systolic hypertension 11,12. Although several correlates of vascular structure and function in pre-hypertensives have been examined 13, the influence of blood lipids, markers of inflammation, cardio-respiratory fitness and body fat percentage on arterial stiffness in this cohort remains poorly understood. Hence the primary purpose of this study was to compare carotid artery stiffness in young, otherwise healthy, pre-hypertensive men with low versus higher HDL-C. A secondary purpose was to examine the influences of inflammation, cardio-respiratory fitness, and % body fat on this association.

METHODS

Subjects

Forty-seven young healthy men volunteered for this study. All subjects were free of cardiovascular, metabolic, renal, or respiratory disease and none smoked. Subjects were considered pre-hypertensive if systolic BP/ diastolic BP was 120 to 139/80 to 89 mmHg. Subjects were not diabetic (fasting blood glucose < 7 mmol/L) or hypercholesterolemic (total cholesterol > 6.2 mmol/L) and all were not taking medications of any kind. Family history of hypertension was recorded by questionnaire. All subjects were recruited from a university student population and none were engaged in a formal exercise training regimen. Subjects were separated into two groups using a HDL cut-point of 1.0 mmol/L. This cut-point was chosen based on the National Cholesterol Education Program Adult Treatment Panel III definition of “low” HDL cholesterol 14. All subjects gave written consent and this study was approved by the Institutional Review Board.

Study Design

Subjects were tested on two separate occasions. The first visit consisted of a fasting blood draw followed by measures of body composition. During the second visit, subjects were required to rest in the supine position for a minimum of ten minutes, after which time vascular measures were conducted. All subjects were at least 3-hours post prandial and did not exercise or consume caffeine or alcohol for 24-hours prior to testing.

A subset of subjects reported back to the lab for a third visit for repeatability assessment. Vascular measures were carried in out in 34 men at the same time of day to reduce influence of diurnal variation.

Brachial Artery Blood Pressure Assessment

Brachial blood pressure (BP) was measured in the supine position using an automated oscillometric cuff following established guidelines 15.

Carotid Artery Stiffness

Carotid artery diameter was measured by ultrasonography (SSD-5500, Aloka, Tokyo, Japan). The cephalic portion of carotid artery was imaged in a longitudinal section, 1-2 cm proximal to the bifurcation, using a high frequency (7.5 MHz) linear array probe. Carotid artery pressure waveforms were attained using applanation tonometry (Millar Instruments, Houston, TX) and calibrated against brachial mean arterial and diastolic pressure. This technique has been shown to record a pressure wave with harmonic content that does not differ from that of an intra-arterially recorded wave 16. Heart rate (HR) was derived from ECG with a single lead CM5 configuration. β-stiffness index (β) was calculated as a means of adjusting arterial compliance for changes in distending pressure as follows:

β=logP1P0(D1D0D0)

where D1 and D0 are the maximum (systolic) and minimum (diastolic) diameters, and P1 and P0 are the highest (systolic) and lowest (diastolic) carotid pressures. The pressure-strain elastic modulus (epsilon, Ep) of the vessel, as a measure of local arterial elasticity, was calculated as follows:

ε=[(P1P0)(D1D0)]×D0.

Additionally, a one-point pulse wave velocity was calculated from the stiffness parameter, previously described in detail, as PWV = (β P/2ρ)1/2 where ρ is blood density (assumed constant). We have previously demonstrated high measurement repeatability in our laboratory. The ICC for measures of carotid stiffness in a subset of subjects from this investigation, collected on two separate days, was 0.86-0.94 (β-stiffness ICC = 0.94, ε ICC = 0.90, PWV ICC = 0.86).

Cardio-respiratory Fitness

Peak oxygen consumption (VO2 peak) was assessed using a graded cycle ergometry protocol until volitional fatigue. Expired gases were analyzed using a Quark b2 breath-by-breath metabolic system (Cosmed, Rome Italy).

Body Composition

Body composition (% body fat) was determined using whole body air displacement plethysmography (Bod Pod, Life Measurement Inc., Concord CA). Height and weight was measured using a stadiometer (to the nearest 0.5 cm) and a beam balance platform scale, respectively. Body mass index (BMI) was calculated as weight (kg) divided by height (m) squared.

Fasting Blood Chemistries

All blood draws were carried out first thing in the morning with subjects in a fasted state. Fasting glucose was assessed via an oxygen rate method using a Beckman Coulter oxygen electrode (Beckman Coulter, Villapointe, France). Total cholesterol, HDL-C and triglycerides were measured using enzymatic techniques. LDL-C was calculated using the Friedewald formula. White blood cell (WBC) count and absolute neutrophil count were measured using a quantitative automated hematology analyzer (Sysmex XE-2100, Sysmex Corp, Kobe, Japan). Circulating levels of high sensitivity C-reactive protein (hsCRP) was measured by ELISA using a commercially available kit (Diagnostic Automation Inc., Calabasas, CA). Samples with absorbance values exceeding the standard curve were re-run on a separate plate following appropriate dilution. The intra-class correlation between two C-reactive protein measurements during the same study visit for all subjects was 0.99. The intra-class correlation in a subset of subjects collected on 2 separate days was 0.90. The intra-assay and inter-assay CV is 2.3-7.5% and 2.5-4.1% respectively.

Glomerular filtration rate (GFR) was estimated from serum creatinine measurements. The following formula, developed from the Modification of Diet in Renal Disease Study was used to estimate GFR: GFR [ml·min−1 x (1.73 m2)] = 186 x (sCR)−1.154 * (age)−0.203 x (1.210 if African American).

Statistics

Group differences were then assessed using analysis of variance. Analysis of covariance was performed to examine group differences after adjusting for potential confounders (body fat, VO2peak, fasting blood glucose, LDL-C, triglycerides, CRP, WBC). Since neutrophils are a subtype of WBC, we did not co-vary for absolute neutrophil count due to issues of co-linearity. Chi-square tests were used to compare categorical variables (family history of hypertension). Associations between variables of interest were assessed with univariate and partial correlations. Values are mean ± SD. Statistical significance was set at p<0.05. Statistical analyses were performed using SPSS 12.0 (SPSS, Chicago, IL).

Results

There was a significant negative association between HDL-C and carotid beta-stiffness, PWV, and elastic modulus (Table 2). According to partial correlations, co-varying for body fat, cardi-orespiratory fitness, LDL-C, triglycerides and glucose had no effect on the association between HDL-C and carotid beta-stiffness (−0.539, p<0.05), PWV (−0.537, p<0.05), or elastic modulus (−0.507, p<0.05). However, co-varying for CRP and WBC abolished the association between HDL-C and carotid beta-stiffness (−0.207, p>0.05), PWV (−0.217, p>0.05), and elastic modulus (−0.209, p>0.05).

Table 2
Inter-relation between parameters of carotid artery stiffness, blood lipids, inflammation, fitness and boy fat

Subjects with HDL-C < 1.0 mmol/L and those with HDL-C ≥; 1.0 mmol/L did not differ in age, height, systolic BP, diastolic BP, total cholesterol, LDL cholesterol, triglycerides and family history of hypertension (Table 1). The group with “low” HDL-C had significantly lower HDL-C (observed power = 1.0, ηp2 = 0.46, F-statistic = 37.5) and cardio-respiratory fitness (observed power = 0.52, ηp2 = 0.09, F-statistic = 4.2). The group with “low” HDL-C also had significantly greater body weight (observed power = 0.56, ηp2 = 0.09, F-statistic = 4.7), body mass index (observed power = 0.85, ηp2 = 0.17, F-statistic = 9.3), body fat (observed power = 0.85, ηp2 = 0.17, F-statistic = 9.3), fasting blood glucose (observed power = 0.63, ηp2 = 0.11, F-statistic = 5.5), white blood cell count (observed power = 0.77, ηp2 = 0.14, F-statistic = 7.6), absolute neutrophil count (observed power = 0.87, ηp2 = 0.19, F-statistic = 9.9) and C-reactive protein (observed power = 0.96, ηp2 = 0.25, F-statistic = 14.4).

Table 1
Subject characteristics

Subjects with “low” HDL-C had significantly higher carotid artery β-stiffness (observed power = 0.86, ηp2 = 0.18, F-statistic = 9.8; Figure 1a). When ANCOVA was performed with cardio-respiratory fitness, body fat, LDL-C, triglycerides and fasting glucose entered as co-variates, adjusted means remained significantly different (4.7 vs 3.7, p<0.05). When ANCOVA was performed with CRP and WBC count entered as co-variates, adjusted means were no longer different (4.3 vs 4.0, p>0.05).

Figure 1
Carotid artery a) beta-stiffness index (top); b) pulse wave velocity (middle); and c) elastic modulus (bottom) is higher in pre-hypertensive men with HDL cholesterol < 1.0 mmol/L. *Significant group difference (p<0.05)

Subjects with “low” HDL-C had significantly higher carotid artery pulse wave velocity (observed power = 0.82, ηp2 = 0.16, F-statistic = 8.6; Figure 1b). When ANCOVA was performed with cardio-respiratory fitness, body fat, LDL-C, triglycerides and fasting glucose entered as co-variates, adjusted means remained significantly different (4.6 vs 4.2 m/s, p<0.05). When ANCOVA was performed with CRP and WBC count entered as co-variates, adjusted means were no longer different (4.5 versus 4.3 m/s, p>0.05).

Subjects with “low” HDL-C had significantly higher carotid artery elastic modulus (observed power = 0.72, ηp2 = 0.13, F-statistic = 6.7; Figure 1c). When ANCOVA was performed with cardio-respiratory fitness, body fat, LDL-C, triglycerides and fasting glucose entered as co-variates, adjusted means remained significantly different (61.2 vs 48.9 kPa, p<0.05). When ANCOVA was performed with CRP and WBC count entered as co-variates, adjusted means were no longer different (56.1 vs 52.7 kPa, p>0.05).

Discussion

Current estimates suggest that 70 million Americans aged 20 years or older are pre-hypertensive 13,17. Pre-hypertensive individuals are eleven times more likely to develop hypertension 18. Subsequently, cardiovascular risk is significantly elevated in this population 19,20. In the present study, there was an inverse association between HDL-C and carotid artery stiffness. Pre-hypertensive men with HDL-C < 1.0 mmol/L had higher carotid artery stiffness when compared to their pre-hypertensive peers with HDL-C > 1.0 mmol/L despite equivalent total cholesterol and LDL-C. This relationship was not affected by cardio-respiratory fitness, body fat, BMI, LDL-C, triglycerides and fasting glucose. Interestingly, when taking into account levels of CRP and WBC count, group differences in carotid artery stiffness no longer prevailed. Thus, the detrimental effect of low HDL-C on the vasculature may be related to a heightened state of inflammation.

HDL cholesterol and arterial stiffness

Low HDL-C may be prevalent in 66% of the population 21. It is commonly accepted that low levels of HDL-C are associated with higher CVD risk, independent of LDL-C level. Our findings extend the detrimental effect of low HDL-C to the vasculature of young apparently healthy pre-hypertensive men by acknowledging an association between low HDL-C and large artery stiffness, a known independent CVD risk factor and antecedent to future development of hypertension.

The role of inflammation

Elevated C-reactive protein (CRP) and white blood cell (WBC) count, markers of subclinical low-grade inflammation, have been shown to predict CVD events and contribute to vascular dysfunction 22-28. CRP and WBC count have also each been shown to be independently associated with the risk of developing hypertension 29-33. Pre-hypertensive populations have higher CRP and WBC count compared with normotensive subjects, suggesting that pre-hypertension might be a pro-inflammatory condition 34,35.

Both acute and chronic inflammatory conditions are associated with increased arterial stiffness 26,36-40. CRP has been shown to induce production of other inflammatory cytokines, decrease tetrahydrobiopeterin (a vital cofactor required for nitric oxide production), downregulate and/or uncouple endothelial nitric oxide synthase, decrease prostacyclin release, increase gene expression/activity of the elastolytic enzyme matrix metalloproteinase-9, and upregulate endothelin-1 41-44. This can reduce vasodilation, enhance vasoconstriction, increase collagen formation, and increase elastin breakdown. WBCs play a role in vascular injury through proteolytic enzymes and plugging of microvessels, which may create rheological abnormalities leading to increased vascular resistance 45. Neutrophil rolling, recruitment and extravasion, considered the initial steps in the vascular inflammatory cascade, leads to subsequent neutrophil-mediated endothelial cell damage and lysis. In the present study, pre-hypertensive men with low HDL-C had higher WBC count, higher neutrophil count and higher CRP, all suggestive of a heightened inflammatory state. The summative effect may produce a structurally and functionally stiffer vessel. Co-varying for CRP and WBC count in the present study abolished the group differences in carotid artery stiffness. Our findings suggest that the damaging effect of low HDL-C on large artery properties in pre-hypertensive men may be mediated by its inflammatory effects.

The role of cardio-respiratory fitness and body fatness

This is the first study to specifically examine the influence of cardio-respiratory fitness and body fat levels on the relation between HDL-C on large artery properties in men with pre-hypertension. It has been suggested that the detrimental effect of low HDL-C on the vasculature and inflammatory status may be secondary to levels of cardio-respiratory fitness and/or body fatness 5. Both low fitness and high body fat are associated with low HDL-C, heightened inflammation and concomitant vascular dysfunction 46-49. In the present study, pre-hypertensive men with low HDL-C had slightly lower cardio-respiratory fitness and higher body fat than pre-hypertensive men with high HDL-C. However, these factors do not appear responsible for the higher carotid artery stiffness in men with low HDL-C as adjusting for these factors had no effect on group differences in carotid artery stiffness. Thus, the negative effects of HDL cholesterol on carotid artery stiffness may not be due to the direct influence of cardio-respiratory fitness or body fat.

We noted a clustering of risk factors in men with low HDL-C that may also categorize them as having pre-metabolic syndrome. Men with low HDL-C had higher BMI/body fat, higher glucose, higher LDL-C and higher triglycerides. However, adjusting for these risk factors had no effect on group differences in carotid artery stiffness. Although these variables were not directly associated with measures of carotid artery stiffness, they were associated with inflammatory markers. Thus it remains plausible that pre-metabolic syndrome risk factors indirectly modulate vascular stiffness via inflammation (i.e. release of inflammatory cytokines from adipose tissue stores). It has been shown that inflammation reduces HDL-C via several mechanisms including increased activity of endothelial lipase, increased activity of soluble phospholipase A2, and replacement of apoA-1 in HDL-C with serum amyloid A 50. Indeed, when in a state of systemic inflammation, HDL-C may even become pro-oxidant 51. Thus, an alternative interpretation of the present findings may be that the high inflammatory state in men with pre-hypertension and high body fat instigated low HDL-C levels.

Limitations

The sample size used in the present investigation is small. Findings may be due to other factors associated with low HDL-C that were not measured in this study (i.e. insulin resistance). Given the cross-sectional nature of our study, we cannot determine causality and statistically adjusting for group differences in various risk factors does not prove a definitive physiologic link. These findings are restricted to young, male cohort and may not extrapolated to older individuals or women.

Table 3
Summary of main findings

Acknowledgements

This study was supported by predoctoral student research grants from the American Heart Association and the American College of Sports Medicine.

REFERENCES

1. Wilson PW, Abbott RD, Castelli WP, The Framingham Heart Study High density lipoprotein cholesterol and mortality. Arteriosclerosis. 1988;8:737–741. [PubMed]
2. Tanne D, Yaari S, Goldbourt U. High-density lipoprotein cholesterol and risk of ischemic stroke mortality. A 21-year follow-up of 8586 men from the Israeli Ischemic Heart Disease Study. Stroke. 1997;28:83–87. [PubMed]
3. Jacobs DR, Jr., Mebane IL, Bangdiwala SI, Criqui MH, Tyroler HA. High density lipoprotein cholesterol as a predictor of cardiovascular disease mortality in men and women: the follow-up study of the Lipid Research Clinics Prevalence Study. Am J Epidemiol. 1990;131:32–47. [PubMed]
4. Castelli WP, Garrison RJ, Wilson PW, Abbott RD, Kalousdian S, Kannel WB, The Framingham Study Incidence of coronary heart disease and lipoprotein cholesterol levels. JAMA. 1986;256:2835–2838. [PubMed]
5. Havlik RJ, Brock D, Lohman K, Haskell W, Snell P, O’Toole M, et al. High-density lipoprotein cholesterol and vascular stiffness at baseline in the activity counseling trial. Am J Cardiol. 2001;87:104–107. A109. [PubMed]
6. Kuvin JT, Patel AR, Sidhu M, Rand WM, Sliney KA, Pandian NG, et al. Relation between high-density lipoprotein cholesterol and peripheral vasomotor function. Am J Cardiol. 2003;92:275–279. [PubMed]
7. Kuvin JT, Ramet ME, Patel AR, Pandian NG, Mendelsohn ME, Karas RH. A novel mechanism for the beneficial vascular effects of high-density lipoprotein cholesterol: enhanced vasorelaxation and increased endothelial nitric oxide synthase expression. Am Heart J. 2002;144:165–172. [PubMed]
8. Willum-Hansen T, Staessen JA, Torp-Pedersen C, Rasmussen S, Thijs L, Ibsen H, et al. Prognostic value of aortic pulse wave velocity as index of arterial stiffness in the general population. Circulation. 2006;113:664–670. [PubMed]
9. Boutouyrie P, Tropeano AI, Asmar R, Gautier I, Benetos A, Lacolley P, et al. Aortic stiffness is an independent predictor of primary coronary events in hypertensive patients: a longitudinal study. Hypertension. 2002;39:10–15. [PubMed]
10. Celik T, Iyisoy A, Kursaklioglu H, Turhan H, Cagdas Yuksel U, Kilic S, et al. Impaired aortic elastic properties in young patients with prehypertension. Blood Press Monit. 2006;11:251–255. [PubMed]
11. Arnett DK, Boland LL, Evans GW, Riley W, Barnes R, Tyroler HA, et al. ARIC Investigators Hypertension and arterial stiffness: the Atherosclerosis Risk in Communities Study. Am J Hypertens. 2000;13:317–323. [PubMed]
12. Liao D, Arnett DK, Tyroler HA, Riley WA, Chambless LE, Szklo M, et al. The ARIC study Arterial stiffness and the development of hypertension. Hypertension. 1999;34:201–206. [PubMed]
13. Zhu H, Yan W, Ge D, Treiber FA, Harshfield GA, Kapuku G, et al. Cardiovascular characteristics in American youth with prehypertension. Am J Hypertens. 2007;20:1051–1057. [PubMed]
14. Executive Summary of The Third Report of The National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, And Treatment of High Blood Cholesterol In Adults (Adult Treatment Panel III) JAMA. 2001;285:2486–2497. [PubMed]
15. Pickering TG, Hall JE, Appel LJ, Falkner BE, Graves JW, Hill MN, et al. Recommendations for blood pressure measurement in humans: an AHA scientific statement from the Council on High Blood Pressure Research Professional and Public Education Subcommittee. J Clin Hypertens (Greenwich) 2005;7:102–109. [PubMed]
16. Kelly R, Hayword C, Ganis J, Daley J, Avolio A, O’Rourke M. Noninvasive registration of the arterial pressure pulse waveform using high-fidelity applanation tonometry. J Vasc Med Biol. 1989;1:142–149.
17. Wang Y, Wang QJ. The prevalence of prehypertension and hypertension among US adults according to the new joint national committee guidelines: new challenges of the old problem. Arch Intern Med. 2004;164:2126–2134. [PubMed]
18. Chobanian AV, Bakris GL, Black HR, Cushman WC, Green LA, Izzo JL, Jr., et al. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report. JAMA. 2003;289:2560–2572. [PubMed]
19. Greenlund KJ, Croft JB, Mensah GA. Prevalence of heart disease and stroke risk factors in persons with prehypertension in the United States, 1999-2000. Arch Intern Med. 2004;164:2113–2118. [PubMed]
20. Qureshi AI, Suri MF, Kirmani JF, Divani AA, Mohammad Y. Is prehypertension a risk factor for cardiovascular diseases? Stroke. 2005;36:1859–1863. [PubMed]
21. Alsheikh-Ali AA, Lin JL, Abourjaily P, Ahearn D, Kuvin JT, Karas RH. Prevalence of low high-density lipoprotein cholesterol in patients with documented coronary heart disease or risk equivalent and controlled low-density lipoprotein cholesterol. Am J Cardiol. 2007;100:1499–1501. [PubMed]
22. Brown DW, Ford ES, Giles WH, Croft JB, Balluz LS, Mokdad AH. Associations between white blood cell count and risk for cerebrovascular disease mortality: NHANES II Mortality Study, 1976-1992. Ann Epidemiol. 2004;14:425–430. [PubMed]
23. Brown DW, Giles WH, Croft JB. White blood cell count: an independent predictor of coronary heart disease mortality among a national cohort. J Clin Epidemiol. 2001;54:316–322. [PubMed]
24. Ensrud K, Grimm RH., Jr. The white blood cell count and risk for coronary heart disease. Am Heart J. 1992;124:207–213. [PubMed]
25. Lee CD, Folsom AR, Nieto FJ, Chambless LE, Shahar E, Wolfe DA. White blood cell count and incidence of coronary heart disease and ischemic stroke and mortality from cardiovascular disease in African-American and White men and women: atherosclerosis risk in communities study. Am J Epidemiol. 2001;154:758–764. [PubMed]
26. Lee YJ, Lee JW, Kim JK, Lee JH, Kim JH, Kwon KY, et al. Elevated white blood cell count is associated with arterial stiffness. Nutr Metab Cardiovasc Dis. 2008 [PubMed]
27. Smit JJ, Ottervanger JP, Slingerland RJ, Kolkman JJ, Suryapranata H, Hoorntje JC, et al. Comparison of usefulness of C-reactive protein versus white blood cell count to predict outcome after primary percutaneous coronary intervention for ST elevation myocardial infarction. Am J Cardiol. 2008;101:446–451. [PubMed]
28. Ridker PM, Rifai N, Rose L, Buring JE, Cook NR. Comparison of C-reactive protein and low-density lipoprotein cholesterol levels in the prediction of first cardiovascular events. N Engl J Med. 2002;347:1557–1565. [PubMed]
29. Nakanishi N, Sato M, Shirai K, Suzuki K, Tatara K. White blood cell count as a risk factor for hypertension; a study of Japanese male office workers. J Hypertens. 2002;20:851–857. [PubMed]
30. Friedman GD, Selby JV, Quesenberry CP., Jr. The leukocyte count: a predictor of hypertension. J Clin Epidemiol. 1990;43:907–911. [PubMed]
31. Gillum RF, Mussolino ME. White blood cell count and hypertension incidence. The NHANES I Epidemiologic Follow-up Study. J Clin Epidemiol. 1994;47:911–919. [PubMed]
32. Sesso HD, Buring JE, Rifai N, Blake GJ, Gaziano JM, Ridker PM. C-reactive protein and the risk of developing hypertension. JAMA. 2003;290:2945–2951. [PubMed]
33. Schillaci G, Pirro M, Pucci G, Ronti T, Vaudo G, Mannarino MR, et al. Prognostic value of elevated white blood cell count in hypertension. Am J Hypertens. 2007;20:364–369. [PubMed]
34. Chrysohoou C, Pitsavos C, Panagiotakos DB, Skoumas J, Stefanadis C. Association between prehypertension status and inflammatory markers related to atherosclerotic disease: The ATTICA Study. Am J Hypertens. 2004;17:568–573. [PubMed]
35. King DE, Egan BM, Mainous AG, 3rd, Geesey ME. Elevation of C-reactive protein in people with prehypertension. J Clin Hypertens (Greenwich) 2004;6:562–568. [PubMed]
36. Duprez DA, Somasundaram PE, Sigurdsson G, Hoke L, Florea N, Cohn JN. Relationship between C-reactive protein and arterial stiffness in an asymptomatic population. J Hum Hypertens. 2005;19:515–519. [PubMed]
37. Kampus P, Muda P, Kals J, Ristimae T, Fischer K, Teesalu R, et al. The relationship between inflammation and arterial stiffness in patients with essential hypertension. Int J Cardiol. 2006;112:46–51. [PubMed]
38. Kim JS, Kang TS, Kim JB, Seo HS, Park S, Kim C, et al. Significant association of C-reactive protein with arterial stiffness in treated non-diabetic hypertensive patients. Atherosclerosis. 2007;192:401–406. [PubMed]
39. Kullo IJ, Seward JB, Bailey KR, Bielak LF, Grossardt BR, Sheedy PF, 2nd, et al. C-reactive protein is related to arterial wave reflection and stiffness in asymptomatic subjects from the community. Am J Hypertens. 2005;18:1123–1129. [PubMed]
40. Mahmud A, Feely J. Arterial stiffness is related to systemic inflammation in essential hypertension. Hypertension. 2005;46:1118–1122. [PubMed]
41. Fichtlscherer S, Breuer S, Schachinger V, Dimmeler S, Zeiher AM. C-reactive protein levels determine systemic nitric oxide bioavailability in patients with coronary artery disease. Eur Heart J. 2004;25:1412–1418. [PubMed]
42. Ikeda U, Takahashi M, Shimada K. C-reactive protein directly inhibits nitric oxide production by cytokine-stimulated vascular smooth muscle cells. J Cardiovasc Pharmacol. 2003;42:607–611. [PubMed]
43. Singh U, Devaraj S, Vasquez-Vivar J, Jialal I. C-reactive protein decreases endothelial nitric oxide synthase activity via uncoupling. J Mol Cell Cardiol. 2007;43:780–791. [PMC free article] [PubMed]
44. Verma S, Wang CH, Li SH, Dumont AS, Fedak PW, Badiwala MV, et al. A self-fulfilling prophecy: C-reactive protein attenuates nitric oxide production and inhibits angiogenesis. Circulation. 2002;106:913–919. [PubMed]
45. Ito BR, Schmid-Schonbein G, Engler RL. Effects of leukocyte activation on myocardial vascular resistance. Blood Cells. 1990;16:145–163. discussion 163-146. [PubMed]
46. Aronson D, Sheikh-Ahmad M, Avizohar O, Kerner A, Sella R, Bartha P, et al. C-Reactive protein is inversely related to physical fitness in middle-aged subjects. Atherosclerosis. 2004;176:173–179. [PubMed]
47. Church TS, Barlow CE, Earnest CP, Kampert JB, Priest EL, Blair SN. Associations between cardiorespiratory fitness and C-reactive protein in men. Arterioscler Thromb Vasc Biol. 2002;22:1869–1876. [PubMed]
48. Church TS, Finley CE, Earnest CP, Kampert JB, Gibbons LW, Blair SN. Relative associations of fitness and fatness to fibrinogen, white blood cell count, uric acid and metabolic syndrome. Int J Obes Relat Metab Disord. 2002;26:805–813. [PubMed]
49. Boreham CA, Ferreira I, Twisk JW, Gallagher AM, Savage MJ, Murray LJ. Cardiorespiratory fitness, physical activity, and arterial stiffness: the Northern Ireland Young Hearts Project. Hypertension. 2004;44:721–726. [PubMed]
50. Ansell BJ, Watson KE, Fogelman AM, Navab M, Fonarow GC. High-density lipoprotein function recent advances. J Am Coll Cardiol. 2005;46:1792–1798. [PubMed]
51. deGoma EM, deGoma RL, Rader DJ. Beyond high-density lipoprotein cholesterol levels evaluating high-density lipoprotein function as influenced by novel therapeutic approaches. J Am Coll Cardiol. 2008;51:2199–2211. [PMC free article] [PubMed]