The C-reactive protein (CRP) is a marker of systemic inflammation that has been associated with an increased risk of incident myocardial infarction and stroke.1–5 Clinical interest in CRP has grown with the observation that the plasma concentration of this protein may be used as a marker of ischemic risk in several population settings.1,4,6 Inflammation has also been hypothesized to play a role in the development of hypertension.7 Cross-sectional evidence demonstrated increased high-sensitivity C-reactive protein (hs-CRP) levels in patients who have hypertension.7–9 Other cross-sectional and prospective studies in normotensive individuals or in heterogeneous cohorts including patients both with and without essential hypertension found a univariate positive association between blood pressure (BP) and plasma CRP concentration.10,11 In the Insulin Resistance Atherosclerosis Study, Festa et al12 reported greater plasma CRP concentrations in treated and untreated hypertensive patients than in normotensive individuals, and this finding has been confirmed recently in healthy American women.13
Higher levels of CRP may increase BP by reducing nitric oxide (NO) production in endothelial cells,14,15 resulting in vasoconstriction and increased production of endothelin-1.16,17 CRP may also function as a proatherosclerotic factor by upregulating angiotensin type 1 receptor expression.18
Inflammation has been shown to correlate with endothelial dysfunction19 and relate to the rennin–angiotensin system.20 As a result, it has been hypothesized that hypertension may be in part an inflammatory disorder. However, clinical data linking inflammation with incident hypertension are scarce.21
Hypertension has been suggested to exert proinflammatory actions through the increased expression of several mediators, including leukocyte adhesion molecules,22,23 chemokines,22 specific growth factors,23,24 heat shock proteins,25 endothelin-1,26 and angiotensin II.27,28 The direct relationship between treatment-induced BP reduction and decrease in some circulating inflammatory markers further confirms hypertension as a potentially proinflammatory condition.28,29 To this purpose, Bae et al demonstrated that hs-CRP plasma levels were decreased after 6 months of treatment with lacidipine in patients with coronary artery disease (CAD).30
It is possible that some antihypertensive drugs may protect against vascular damage and its association with subclinical inflammation in hypertension, possibly exhibiting drug-specific benefits beyond arterial pressure lowering. The ability of some antihypertensive drugs to modulate inflammatory markers levels as hs-CRP may serve as a potential pharmacological mechanism for this possible protective action.
Doxazosin is a well-known long-acting α1-adrenoceptor antagonist; its mechanism of action is complementary to that of each of the other 4 main groups of antihypertensive drugs and, in each case, enhanced efficacy has been observed when α1-blockade has been added to monotherapy with other drug classes.31 These drugs also improve fibrinolysis and reduce left ventricular afterload.31 Moreover, α1-blockers exert positive effects on lipids and exert neutral or positive effects on glucose homeostasis, thus reducing the estimated cardiovascular disease risk of the hypertensive patient.32
We hypothesized that hypertension is in part an inflammatory disorder and that higher plasma levels of inflammatory markers (ie, hs-CRP) are present in hypertensive patients. Furthermore, we verified whether doxazosin therapy could reduce hs-CRP plasma levels in hypertensive patients after 4 months, given that no data are available in the literature about doxazosin therapy on hs-CRP plasma levels. We also determined plasma levels of nitrite/nitrate (stable metabolites of NO) to assess the biosynthesis of NO.
This multicenter trial was conducted in the Department of Internal Medicine and Therapeutics at University of Pavia, and in the “G. Descovich” Atherosclerosis Study Center, “D. Campanacci” Clinical Medicine and Applied Biotechnology Department at the University of Bologna. The study population consisted of 44 normotensive control subjects and 44 patients with never-treated mild-to-moderate hypertension (sitting diastolic blood pressure [DBP] >90 and <105 mm Hg) before and after doxazosin treatment for 4 months. At entry, 23 subjects (52.3%) were male and 21 subjects (47.7%) were female in the control group, and 22 subjects (50.0%) were male and 22 subjects (50.0%) were female in the untreated and treated hypertensive group.
Hypertension was said to be present if the systolic blood pressure (SBP) and DBP were ≥140 and ≥90 mm Hg, respectively, according to the World Health Organization (WHO) criteria.33
Patients received doxazosin, 2 mg once daily as initial dose; all patients were titred up to 4 mg/day, 2 times per day, after 2 weeks, if DBP was still >90 mm Hg. The mean doxazosin dose was 3±1 mg/day.
BP measurements were obtained from each patient (right arm) after 10 min in the supine position, by using a standard mercury (Erkameter 3000, ERKA, Bad Tolz, Germany) column sphygmomanometer and BP was measured in the morning (8:30–9:30 AM) in a quiet room by the same investigator. The I and V phases of the Korotkoff sounds were used with a cuff of appropriate size; 3 measurements were obtained on each occasion, at 5-min intervals, and averaged. Suitable subjects, identified from a review of case notes and/or computerized clinic registers, were contacted personally or by telephone. All patients had essential hypertension documented by appropriate laboratory tests, and none had ever taken any antihypertensive treatment.
We excluded patients with overt coronary artery disease or other organic heart diseases as evidenced by clinical, electrocardiographic, and echocardiographic criteria. We did also not enroll patients with pulmonary fibrosis, hepatic fibrosis, rheumatoid arthritis, cancer, recent surgery, childbirth or steroid use, after a thorough consideration of medical history and examinations.
The study protocol was approved at each site by institutional review boards and was conducted in accordance with the Declaration of Helsinki. All patients provided written informed consent.
Before starting the study, all of the patients underwent an initial screening assessment that included a medical history, physical examination, vital signs, a 12-lead electrocardiogram, and measurement of hs-CRP as inflammation parameter. hs-CRP was determined after a 12-h overnight fast, determined 2 h after lunch. Venous blood samples were taken for all patients between 8:00 and 9:00 AM and were drawn from an antecubital vein with a 19-gauge needle without venous stasis.
We used plasma obtained by addition of Na2-EDTA, 1 mg/mL, and centrifuged at 3000g for 15 min at 4°C. Immediately after centrifugation, the plasma samples were frozen and stored at −80°C for no more than 3 months. hs-CRP was performed in a central laboratory. hs-CRP was measured with the use of latex-enhanced immunonephelometric assays on a BN II analyzer (Dade Behring, Newark, DE). The intra- and interassay coefficients of variation (CsV) were 5.7% and 1.3%, respectively.34
Nitrite and nitrate plasma levels are used clinically as markers for the activity of NO synthase and NO biosynthesis. The assay is based on the determination of nitrite using the Griess reaction. Nitrate was measured as nitrite after enzymatic conversion by nitrate reductase as described by Green et al.35
Data were expressed as mean and standard deviation (SD). Because some variables are not normally distributed (Shapiro-Wilk's test), comparisons for dependent data were performed using the Student t test for paired data; or the nonparametric Wilcoxon matched-pairs test, as appropriate comparisons, for independent data were performed using Student t test for unpaired data or the non parametric Mann-Whitney U test, as appropriate. A P value<0.05 was considered statistically significant. All tests were two-sided. No adjustment for multiple comparisons was made because this study was intended as exploratory rather than confirmatory. Analyses were performed with Statistica for Windows software (StatSoft, Inc. 2004, Tulsa, OK).
A total of 88 patients were enrolled in the trial. The characteristics of the patient population at study entry are shown in Table 1.
SBP and DBP improvement (P<0.0001) were obtained in the hypertensive group with respect to controls, whereas a significant decrease was observed for SBP and DBP (P<0.0001) in the hypertensive group treated for 4 months with respect to untreated hypertensives (Table 1).
A significant increase was observed for hs-CRP in the untreated hypertensive group with respect to controls (P<0.007), whereas hs-CRP was decreased (P<0.05) in treated hypertensive patients after 4 months with respect to those untreated (Table 1).
Nitrite/Nitrate Plasma Levels
Significant decrease was obtained for nitrites/nitrates in the untreated hypertensive group respect to controls (P<0.0001), whereas nitrites/nitrates was increased (P<0.05) in treated hypertensive patients after 4 months with respect to those untreated (Table 1).
Correlation analyses did not indicate various patterns of associations in hs-CRP plasma levels or in nitrites/nitrates with SBP and DBP parameters in the control and hypertensive groups before and after treatment.
In the present study, we detected hs-CRP plasma levels and nitrite/nitrate plasma levels in normotensive subjects and in patients with hypertension before and after 4 months of doxazosin treatment. In particular, hs-CRP plasma levels were shown to be significantly increased in untreated hypertensive patients compared with controls, and nitrite/nitrate plasma levels were decreased in untreated hypertensive patients compared with controls.
Previous observations showed increased hs-CRP levels in patients who have hypertension.7–9 The presence of increased plasma hs-CRP concentration in hypertensive subjects confirms a number of studies in which plasma concentrations of other humoral markers of systemic inflammation, including soluble leukocyte adhesion molecules,22,23 chemotactic and proinflammatory cytokines,22 specific growth factors,22,24 and heat shock proteins,25 were found to be increased in patients with essential hypertension.
Our results provide evidence for a critical role of inflammation in the development of hypertension. In fact hs-CRP has been reported to decrease production of NO by endothelial cells14,15 and upregulate angiotensin type-1 receptor expression18 affecting the renin–angiotensin system and contributing to the pathogenesis of hypertension. In our study, nitrite/nitrate plasma levels was decreased in hypertensive patients as widely demonstrated,36,37 and doxazosin therapy partially restores nitrite/nitrate plasma levels. Another result of our study was that doxazosin therapy significantly reduced hs-CRP plasma levels. These results suggest that doxazosin may have an anti-inflammatory action in the setting of hypertension. To our knowledge, there are no data regarding doxazosin action on subclinical inflammatory parameters and nitrite/nitrate plasma levels.
A recent study demonstrated that hs-CRP plasma levels were decreased after 6 months of treatment with lacidipine in patients with CAD.30 However, valsartan appears to reduce serum tumor necrosis factor-α and interleukin-6, but not hs-CRP in hypertensive subjects.38 Thus, it may be interesting to see the effect of other antihypertensive drugs on the hs-CRP plasma levels in hypertensive patients.
Hypertension is one of the major cardiovascular risk factors in hearth disease. There are several pathophysiologic mechanisms that link both diseases. Hypertension induces endothelial dysfunction, exacerbates the atherosclerotic process, and contributes toward making the atherosclerotic plaque more unstable.39 The decrease of hs-CRP levels and the increase of nitrite/nitrate plasma levels suggest that an anti-inflammatory action of doxazosin may also participate in the stabilization of atherosclerotic plaque. Moreover, inflammation is strongly interrelated with oxidative stress: increased reactive oxygen species induces increased expression of inflammatory genes and production of inflammatory mediators.40 Oxidative stress per se could contribute to the pathogenesis of hypertension,40 whereas the chronic presence of high blood pressure can elicit arterial oxidative stress by multiple mechanisms.41,42 Therefore, it is possible that the anti-inflammatory effect of doxazosin is nonspecific and related to the reduction of the chronic high BP-induced oxidative stress and consequent inflammation, but also that doxazosin could exert an anti-inflammatory effect by means of its supposed antioxidative action.43,44
Although doxazosin increased nitrite/nitrate plasma levels in our study, the reason for the observed changes in hs-CRP plasma levels after treatment with doxazosin is not yet clear. It could be speculated that there is a different pharmacologically specific action or an effect on a different step in the long-term process of vascular remodeling in hypertension, and it is possible that a different hemodynamic doxazosin action may add in part to the differential effect of these drugs in plasma levels of hs-CRP after antihypertensive treatment.
This study is limited by the relatively small patient numbers, but this sample size is broad compared to the patient number studies in previous works.30 Moreover, we have no data on the effect of doxazosin on cyclooxygenase-1 and -2, nor on proinflammatory cytokines such as tumor necrosis factor-α or interleukin-6. Because available literature about this argument is lacking and because of the encouraging results observed in this study, we anticipate carrying out more specific research on that subject. However, if an antihypertensive drug such as doxazosin can reduce BP and hs-CRP, we have to consider this option in our daily work because it could contribute to stabilizing atherosclerotic plaque.
In conclusion, we found that levels of hs-CRP were increased at baseline in patients with hypertension and doxazosin therapy reduced both BP and hs-CRP, whereas nitrite/nitrate plasma levels were decreased at baseline in patients with hypertension and doxazosin therapy increased these levels.
Further trials are necessary to clarify the relationship between hs-CRP and cardiovascular risk factors as possible clinical markers in hypertension, and whether other antihypertensive drugs provide a possible beneficial protective effect beyond BP reduction.
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