Brachial Pressure–Independent Reduction in Carotid Stiffness After Long-Term Angiotensin-Converting Enzyme Inhibition in Diabetic Hypertensives
Hypertension and diabetes are associated with an increased arterial stiffness. A direct blood pressure–independent effect of angiotensin-converting enzyme inhibitors on arterial stiffness has never been unequivocally demonstrated. In this mechanistic study, we used an experimental design in which patients responding to 1 month treatment with 4 mg perindopril were randomized double-blind to either 4 mg perindopril or 8 mg perindopril for 6 months. We determined carotid distensibility with echotracking and applanation tonometry at baseline and after the 7-month treatment period in 57 essential hypertensive patients with type 2 diabetes (age 63±7 years). We monitored ambulatory blood pressure at baseline and after treatment. After 7 months treatment, 24-hour ambulatory blood pressure significantly decreased, with no significant difference between 4 mg and 8 mg perindopril. Carotid distensibility increased more after 8 mg perindopril compared with 4 mg perindopril (8 mg: from 13.1±5.9 to 16.0±6.7 kPa−1×10−3; 4 mg: from 13.2±5.2 to 12.7±5.9 kPa−1×10−3; ANOVA, dose-period interaction, P<0.05). Carotid internal diameter and elastic modulus were significantly lower after 8 mg perindopril compared with 4 mg perindopril, independent of blood pressure reduction. These results indicate a dose-dependent and blood pressure–independent reduction in carotid stiffness under chronic treatment with an angiotensin-converting enzyme inhibitor. They suggest that arterial distensibility was increased through an inward remodeling, leading to a reduction in wall stress, thus reducing elastic modulus. They also suggest that long-term administration of high doses (8 mg) of perindopril is required to improve carotid structure and function in hypertensive patients with type 2 diabetes.
Large artery stiffening is a feature of hypertension and type 2 diabetes.1–4 Arterial stiffness has demonstrated its predictive value for cardiovascular (CV) events in patients with hypertension and type 2 diabetes.5–7 Many studies have reported a reduction in arterial stiffness after antihypertensive treatment.8,9 Although some studies have claimed that this effect can be obtained without blood pressure (BP) reduction,10,11 there is still no unequivocal demonstration that antihypertensive drugs can reduce large artery stiffness in humans independent of lowering BP.
It has been suggested that as well as helping to unload the stiff components of the arterial wall, long-term drug administration for hypertension can reduce arterial stiffness through a change in wall components. This includes reducing collagen density and rearranging the wall materials.12 Angiotensin-converting enzyme (ACE) inhibitors are excellent candidates for this, as they inhibit tissue and circulating angiotensin II formation and bradykinin degradation, thus reducing arterial wall fibrosis, collagen synthesis, proliferation of smooth muscle cells, accumulation and activation of inflammatory cells, and endothelial dysfunction.13 All of these factors may be involved in arterial stiffening.12 Also, diabetic hypertensive patients should benefit the most from the effects of angiotensin II suppression on arterial stiffness because of the synergistic interactions between angiotensin II and the insulin-activated signaling pathways in vascular smooth muscle cells.14,15
The aim of this mechanistic study was to demonstrate a BP-independent effect on carotid stiffness of long-term ACE inhibition. We selected hypertensive patients with type 2 diabetes and only included patients who had previously responded to an ACE inhibitor. We compared 2 different treatment doses, assuming that the higher dose would be more effective in reducing arterial stiffness, but would not further reduce BP. We carried out 24-hour ambulatory BP monitoring to determine better the chronic changes in the BP load exerted on the arterial wall. Finally, we used the high precision of echotracking systems16 to measure carotid parameters and performed a multivariate analysis of both the high and low doses and the changes in BP.
Study Design and Patients
The study was conducted in 4 centers (Paris, Fleury, Rouen, and Maastricht) and named DAPHNET (Diabetes Artery Perindopril Hypertension Normalization Excess sTiffness). Type 2 diabetes was defined according to the 1985 World Health Organization criteria (fasting glucose ≥7.8 mmol/L or postchallenge glucose ≥11.1 mmol/L), with glycosylated hemoglobin A <9%. Patients with an essential uncomplicated hypertension, either never treated or treated but requiring a change of treatment, were considered eligible if their office diastolic BP (DBP) was >90 mm Hg and <110 mm Hg or if their DBP was <90 mm Hg and their systolic BP (SBP) >140 mm Hg. Their renal function had to be preserved (creatinin clearance ≥60 mL/min).
After a single-blind placebo washout period lasting 4 weeks, patients with a DBP >90 mm Hg and <110 mm Hg or with a DBP <90 mm Hg and a SBP >140 mm Hg were included and treated single-blind with 4 mg perindopril for 1 month. Patients were considered as responsive to 4 mg perindopril if they had a decrease in SBP >10 mm Hg, no increase in serum potassium (ie, remaining <5.2 mmol/L), and no major change in serum creatinin (ie, an increase lower than 50 μmol/L). Patients responsive to perindopril were randomized double-blind, using a computer, to either 4 mg perindopril or 8 mg perindopril every morning for 6 months. The objective was to obtain the same reduction in BP in both groups. If the reduction in SBP remained <10 mm Hg, either at the 2-months visit or at every subsequent visit, we added 1.5 mg indapamide slow release once daily.
We carried out 24-hour ambulatory BP monitoring (Spacelab 90127) and arterial measurements after the placebo washout period (baseline) and after the 7-month treatment period (1 month of 4 mg perindopril then either 4 mg perindopril or 8 mg perindopril for 6 months). We collected demographic data with details of CV risk factors with the arterial measurements. Height and weight were measured, and the body mass index was computed. Hypercholesterolemia was indicated by a previous diagnosis or by the use of an oral cholesterol-lowering agent. We defined smoking status as current use. We obtained routine laboratory tests at inclusion.
From the Celimene study,17 we calculated that 28 patients per group would be required to show a 13% difference in carotid distensibility, at an α risk <0.05 and 80% power. The protocol was approved by the ethical committees of each participating center. Written informed consent to participate in the study was obtained from each subject.
Arterial Noninvasive Measurements
The investigation was carried out in a controlled environment at 22±1°C after being recumbent for 15 minutes. The carotid internal diameter and wall thickness were measured on the right common carotid artery and 2 cm beneath the carotid bifurcation, using a 7.5 MHz pulsed ultrasound echotracking system (Wall Track System, Esaote Pie Medical). We analyzed the radio-frequency signal originating from an M line perpendicular to the longitudinal and transversal axes of the artery, selected on the 2-dimensional B-mode image (Sigma 44 KONTRON). This system has been validated16 and described in detail and has been used in various clinical studies.17–19 We determined common carotid artery pressure waveforms noninvasively with applanation tonometry using a pencil-type probe incorporating a high-fidelity strain gauge transducer (SPT-301, Millar Instruments), as previously described and validated.17–19
Common carotid artery intima-media thickness (IMT) and internal diastolic diameter were measured on the distal wall of the right common carotid artery, 1 cm beneath the bifurcation. The short-term within-observer within-patient repeatability between 2 determinations, taken at 15-minute intervals by a senior technician and physician, has been previously published.17,18 The absolute difference between measurement 1 and measurement 2 did not exceed 6% of the mean value for each parameter.16,17 For the first 37 patients included in this study, we also determined the medium-term within-observer within-patient repeatability between 2 determinations taken at a 1-month interval (before and at the end of the single-blind placebo washout period).
Arterial wall cross-sectional area (WCSA) was calculated in diastole as WCSA=πRe2−πRi2 where Re and Ri are the values of diastolic external and internal radii, respectively, as previously described and validated.17–19 Wall to lumen ratio was calculated in diastole as 2 hd/Dd, where hd and Dd are the values of wall thickness and internal diameter during end-diastole.
Circumferential wall stress (σθ, kPa) was calculated according to Lamé’s equation as σθ=(MBP.Dm)/2 hm, where MBP is mean blood pressure, and Dm and hm are the mean values of internal diameter and wall thickness during the cardiac cycle.19
Arterial Elastic Properties
Additional parameters were measured. They are linked together and with circumferential stress, but give separate useful information. Indeed, the elastic properties of the artery as a hollow structure were assessed through arterial distensibility, determined from the systolic-diastolic variations in arterial cross-sectional area (ΔA) and local pulse pressure (ΔP), as previously described,17–19 assuming the lumen to be circular. Cross-sectional distensibility coefficient was calculated as DC=ΔA/A ΔP, where A is the diastolic lumen area, ΔA is the stroke change in lumen area, and ΔP is local pulse pressure (PP). Cross-sectional compliance coefficient was calculated as CC=ΔA/ΔP. Local carotid artery PP, directly measured with applanation tonometry, was used in these calculations. The elastic properties of the arterial wall material were estimated by the incremental Young’s elastic modulus (Einc), calculated, as previously described18 as Einc=[3(1+A/WCSA)]/DC, where A is the diastolic lumen area, WCSA is the mean wall cross-sectional area, and DC is the cross-sectional distensibility.
Data are expressed as mean±SD, unless otherwise stated. The homogeneity of the randomized groups at baseline was determined using an unpaired Student t test for continuous variables and a χ2 test for categorical variables. For comparison of serial changes in BP and arterial parameters, we used repeated-measures ANOVA to detect differences in the response to treatments, through a significant dose-period interaction.20 The effects of relevant variables (baseline arterial parameters and magnitude of MBP and PP change with treatment) on the study end points were analyzed using a multivariate regression analysis. We included the dose (either 4 mg perindopril or 8 mg perindopril) in this analysis as dummy variable to determine whether there were drug-specific effects. A value of P<0.05 was considered significant. The statistical analysis was performed using NCSS 6.0 software (Hintze JL, Kaysville, Utah).
We included 73 hypertensive patients. After 1 month of treatment with perindopril, 57 were considered as responders and were randomized to either 4 mg perindopril (n=29) or 8 mg perindopril (n=28).
The 29 and 28 patients randomized to treatments with 4 mg perindopril and 8 mg perindopril, respectively, were similar with respect to age, sex ratio, body mass index, and blood biochemistry (including glycosylated hemoglobin and fasting glycemia). The baseline characteristics of the 2 groups are presented in Table 1.
We observed a significant reduction in 24-hour ambulatory SBP, DBP, MBP, and PP after 7 months of treatment with perindopril (Table 2). However, we found no significant difference between the 2 doses for changes (no significant dose-period interaction). Among the 4-mg- and 8-mg-perindopril groups, 4 and 8 patients, respectively (no significant difference, χ2 test), required indapamide to achieve the required blood pressure. No significant change in heart rate was observed. Changes in laboratory values were not statistically significant after 7 months of treatment (data not shown).
Carotid Artery Parameters
Repeatability of Measurements
For the first 37 patients included in the study, we determined the medium-term within-observer within-patient repeatability between 2 determinations taken at a 1-month interval, ie, before and at the end of the single-blind placebo washout period lasting 4 weeks (ie, 2 and 1 month before randomization to 4 or 8 mg) (Figure). The absolute difference between measurement 1 and measurement 2 did not exceed 6% and 11% of the mean value (ie, variation coefficient) for internal diameter and intima-media thickness, respectively. Mean values, determined 1 month apart, were very close and not significantly different for internal diameter (6.23±0.81 versus 6.19±0.86 mm), intima-media thickness (819±181 versus 813±173 μm), distensibility (13.1±4.7 versus 13.4±5.7 kPa−1 10−3), and elastic modulus (716±303 versus 728±330 kPa).
Effects of Treatment
At baseline, the mean carotid artery parameters were not significantly different between the groups (29 and 28 patients randomized to 4 mg perindopril and 8 mg perindopril, respectively). After 7 months of perindopril treatment, carotid intima media thickness had decreased significantly and to the same extent in both groups (Table 3) (entire population: from 779±180 to 733±182 μm; P<0.05). Table 3 shows the mean values of carotid artery parameters at baseline and during follow-up. The carotid internal diameter, elastic modulus, circumferential wall stress, and local pulse pressure were all significantly lower for the 8 mg perindopril patients than the 4 mg perindopril patients, and the carotid distensibility was significantly higher for the 8 mg perindopril patients than the 4 mg perindopril patients (significant dose-period interactions, Table 3 and Figure). Changes in carotid intima-media thickness, wall cross-sectional area, stroke change in diameter, and compliance during the 7-month treatment period did not differ significantly between the groups. We observed similar results when we restricted the analysis to the 25 and 20 patients who had received 4 mg and 8 mg perindopril, respectively, but no indapamide.
Determinants of Arterial Stiffness
We carried out a multivariate regression analysis for the entire population and found that the decrease in carotid artery diameter after 7 months of treatment was significantly related to the perindopril dose (a higher effect for 8 mg than for 4 mg), independent of baseline carotid diameter, baseline MBP, and 24-hour MBP reduction (Table 4). Similarly, we found significant differences between the perindopril doses for the decrease in the Young’s elastic modulus of the carotid artery and the increase in carotid distensibility after 7 months of treatment (a higher effect for 8 mg than 4 mg), independent of baseline carotid Young’s modulus (or distensibility), baseline MBP, and 24-hour MBP reduction (Table 4). The reduction in BP was not statistically significant as an independent determinant of the changes in carotid diameter, Young’s elastic modulus, and distensibility. The dose of perindopril explained 15% of the variance (R2 increment, Table 4) of the increase in carotid distensibility and 25% of the variance of the decrease in Young’s elastic modulus. The dose of perindopril remained significant for the reduction in carotid diameter and elastic modulus and increase in carotid distensibility, when 24-hour MBP was replaced by 24 hour, day-time, or night-time SBP, DBP, MBP, or PP (data not shown). The dose of perindopril also remained significant for the reduction in carotid diameter and elastic modulus and increase in carotid distensibility, when additional adjustments were performed on either (1) baseline glycohemoglobin, (2) change in glycohemoglobin, (3) actual 24-hour MBP (rather than change in 24-hour MBP), (4) glycohemoglobin and actual 24-hour MBP, or (5) reduction in glycohemoglobin and actual 24-hour MBP (data not shown). Results did not differ significantly when we restricted the analysis to the 25 and 20 patients who received 4 mg and 8 mg perindopril, respectively, but no indapamide.
To our knowledge, this is the first controlled, double-blind study showing a dose-dependent reduction in carotid artery stiffness under chronic antihypertensive treatment, independent of 24-hour BP reduction.
Considering the important local action of angiotensin II on arterial stiffening, we used a long-term treatment with an ACE inhibitor. The ACE inhibitor perindopril has previously been shown to inhibit tissue ACE with a high efficiency in the aortic wall in rats and to reduce endothelial dysfunction and carotid stiffness in hypertensive patients.8–10 Also, we selected hypertensive patients with type 2 diabetes because carotid stiffness is predominantly increased in this population4,7,21 and blocking the synergistic interactions between angiotensin II and the insulin-activated signaling pathways in vascular smooth muscle cells should result in a beneficial reduction of carotid stiffness.14,15,22 Perindopril was administered for 7 months. Thus, it was possible to observe a significant remodeling of the carotid artery wall likely because the ACE activity was lowered under a certain “threshold” for a long period of time.
We also carried out 24-hour ambulatory BP monitoring at baseline and after treatment to determine better the chronic changes in the BP load exerted on the arterial wall. Although a dose-dependent effect of perindopril has been largely documented in hypertensive patients,23 we assumed that, by only including patients who had previously responded to the usual dose in clinical practice (4 mg perindopril), the higher dose (8 mg) would not further reduce BP. Indeed, we found no significant difference in BP between these 2 doses, whereas only the 8 mg group showed an increase in distensibility.
We also took advantage of the high precision of the echotracking technique for measuring carotid parameters.16–19 This was exemplified in the repeatability study that we performed during the single-blind placebo washout period, with small absolute differences between measurement 1 and measurement 2. Finally, we performed a multivariate analysis including both the high and low doses and the BP changes. We ruled out any “regression to the mean” effects by including the baseline values in the multivariate analysis20 and by showing an excellent repeatability of carotid parameters.
However, there were limitations to our study. First, although this study provides a proof of principle, it concerns a particular group of diabetic hypertensives who were responsive to perindopril, making generalization difficult. Second, although there was no significant dose-period interaction for the reduction in 24-hour BP (ie, BP reduction was not significantly more pronounced in the 8 mg group than in the 4 mg group), it is still possible that a BP difference could have been missed by the relatively small number of patients. It should be noted, however, that the ANOVA/interaction analysis, which takes into account not only baseline and post-treatment levels, but also the dose, increases the statistical power of the study. We performed additional multivariate stepwise analyses including both BP levels and dose to strengthen our conclusions. The dose of perindopril remained significant for the reduction in carotid diameter and elastic modulus and increase in carotid distensibility, after adjustment on BP changes. Thus, we can reasonably conclude that carotid changes were influenced by the dose and not by BP reduction, whether there was an undetected difference in BP reduction between doses.
Interpretation of Findings
Although we found no significant difference in the reduction of 24-hour ambulatory BP between 4 mg and 8 mg perindopril, only the 8 mg group showed an increase in distensibility and a decrease in elastic modulus. Moreover, a multivariate analysis including the changes in BP showed no independent influence of BP reduction on the increase in distensibility and the decrease in elastic modulus, whereas there was a significant relationship with the dose (a higher effect for 8 mg compared with 4 mg). We observed similar results for the internal diameter and circumferential wall stress.
These data confirm our working hypothesis that the higher dose would be more effective in reducing arterial stiffness, without further reducing 24 hour BP, in patients responding to the 4 mg dose. We can suggest a mechanistic pathway for these consistent changes, in which long-term ACE inhibition would induce an inward remodeling of the carotid artery, reducing circumferential wall stress, and thus unloading the stiff components of the wall material, which would ultimately increase carotid distensibility.
Although these changes have been observed in other clinical trials,10,17,24 we believe this is the first time they have been shown to occur in response to long-term ACE inhibition independent of chronic BP reduction. Previous studies10,17,24 either did not use local PP measurements for determining carotid distensibility24 or did not measure ambulatory BP.10,17,24 Indeed, BP reduction can decrease arterial stiffness both acutely, by unloading the stiff components of the arterial wall, and chronically, by lowering wall stress. This can change mechanotransduction, thus remodeling large amounts of artery wall material and ultimately decreasing arterial stiffness. Although in these previous studies mean BP measurements were not significantly different between the 2 treatment groups during arterial investigation, a significant difference in BP patterns in a 24-hour period may go undetected in the absence of ambulatory BP monitoring.25
As expected, cross-sectional compliance was not significantly increased because of the counteracting effect of the decrease in internal diameter. That we observed no significant change with time (period effect, Table 3) in internal diameter, circumferential wall stress, distensibility, and Young’s elastic modulus during treatment, irrespective the dose, is likely because of the opposite effects of 4 mg and 8 mg perindopril on these parameters.
Carotid IMT was significantly reduced by treatment, irrespective of the dose. The lack of difference in carotid IMT between the 8 mg dose and the 4 mg dose may be because of the limited power with relatively few patients and short duration of treatment, which was shorter than the 2 to 4 years normally used in most regression studies.26 Because carotid internal diameter was reduced to a greater extent after 8 mg than after 4 mg (Table 4), it may have masked a significant reduction in IMT. Thus, we calculated WCSA, which gives information on the true arterial mass, independently of geometric changes. In multivariate analysis, the reduction in WCSA was significantly influenced by baseline WCSA (P<0.001), and marginally but not significantly by the dose (P=0.07), and not by carotid local PP.
The present study suggests that high doses of ACE inhibitors, administered for a long period of time, are required in hypertensive patients with type 2 diabetes to obtain a marked inhibition of the renin–angiotensin system27 and to reduce carotid stiffness. Although arterial stiffness has been reported as a surrogate end point in end-stage renal disease patients only,28 long-term reduction in arterial stiffness with antihypertensive treatment in patients with a high CV risk should, theoretically, reduce the number of CV events. Our data are consistent with the results of large clinical trials using higher doses of ACE inhibitors in patients with a high CV risk, including patients with hypertension and type 2 diabetes. For example, in the Events With Perindopril in Stable Coronary Artery Disease (EUROPA) study, patients taking 8 mg perindopril had a 20% less chance of experiencing cardiovascular death, myocardial infarction or cardiac arrest than patients taking placeboes.29 In the type 2 DIABetes, HYpertension, CArdiovascular events and Ramipril (DIABHYCAR) study, low dose (1.25 mg) ramipril had no effect on cardiovascular and renal outcomes of patients with type 2 diabetes and albuminuria,30 whereas the Heart Outcome Prevention Evaluation (HOPE) study31 showed that high dose (10 mg) ramipril significantly reduced the rates of death, myocardial infarction, and stroke. In these trials, it was claimed that only a small part of the benefit could be attributed to the reduction in BP.
These results indicate a dose-dependent and 24-hour BP-independent reduction in carotid stiffness after chronic treatment with an ACE inhibitor. They suggest that arterial distensibility was increased through an inward remodeling, leading to a reduction in wall stress, and thus a reduction in elastic modulus. They also suggest that high doses (8 mg) of perindopril, administered for a long period of time, are required in hypertensive patients with type 2 diabetes to obtain a marked inhibition of the renin–angiotensin system, in addition to BP reduction, to remodel the carotid wall and reduce carotid stiffness. Although arterial stiffness has been reported as a surrogate end point in end-stage renal disease patients only, long-term reduction in arterial stiffness with antihypertensive treatment in patients with a high CV risk should, theoretically, reduce the number of CV events. Our data are consistent with the results of large clinical trials (HOPE and EUROPA) using higher doses of ACE inhibitors in patients with a high CV risk, including patients with hypertension and type 2 diabetes. Further studies remain to be done to determine whether a reduction in arterial stiffness is a desirable therapeutic goal in terms of hard clinical end points such as morbidity and mortality. We also need to demonstrate whether a therapeutic strategy aiming at normalizing arterial stiffness proves to be more effective in preventing CV events than usual care.
Sources of Funding
This study was performed with the help of Laboratoires Servier (funding of the study), INSERM (recurrent funding of the research team), and Association Claude Bernard.
- Received February 9, 2006.
- Revision received March 9, 2006.
- Accepted April 19, 2006.
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