Effect of Ezetimibe on Stabilization and Regression of Intracoronary Plaque　― The ZIPANGU Study ―

Abstract

Background: Diminishing yellow color is associated with plaque stabilization. We assessed the hypothesis that a combination of ezetimibe and statin provides more effective plaque stabilization and regression than statin alone as assessed by plaque color.

Methods and Results: Stable coronary artery disease patients (n=131) who underwent elective percutaneous coronary intervention and had yellow plaques were randomized to combination therapy (atorvastatin 10–20 mg and ezetimibe 10 mg/day; Group C) or statin monotherapy (atorvastatin 10–20 mg; Group M). Changes in plaque color and plaque volume during 9 months were assessed by angioscopy and intravascular ultrasound. Low-density lipoprotein cholesterol (LDL-C) decreased from 103±28 to 63±18 mg/dL in Group C (P<0.001) and from 100±28 to 75±17 mg/dL in Group M (P<0.001). Yellow color grade decreased significantly in both Group M (2.1±1.1 vs. 1.7±1.0, P=0.005) and Group C (2.2±1.2 vs. 1.8±1.2, P=0.002), but did not differ between the groups. %plaque volume did not change in Group M (48.5±10.2% vs. 48.2±10.4%, P=0.4), but decreased significantly in Group C (50.0±9.8% vs. 49.3±9.8%, P=0.03).

Conclusions: Compared with statin monotherapy, combination therapy with ezetimibe further reduced LDL-C levels. Significant plaque volume reduction was achieved by the combination therapy, but not statin monotherapy; however, plaque stabilization was similarly achieved by both therapies. Furthermore, reduction in plaque volume was dependent on reduction in LDL-C, regardless of whether it was achieved by statin alone or statin plus ezetimibe.

Low-density lipoprotein cholesterol (LDL-C)-lowering therapy has been shown to be effective for primary and secondary prevention of cerebrovascular and cardiovascular diseases. Ezetimibe, an inhibitor of the Niemann-Pick C1-like 1 cholesterol transporter, is a relatively new drug for LDL-C-lowering therapy.¹ Combination therapy with a statin and ezetimibe produced better clinical outcomes than statin monotherapy in the IMPROVE-IT (Improved Reduction of Outcomes; Vytorin Efficacy International Trial) study.² However, the plaque stabilization and regression effects of these 2 therapies have not been adequately evaluated. We previously investigated the plaque stabilization effect and plaque regression effect of statin therapies by angioscopy and intravascular ultrasound (IVUS), respectively, in the TWINS³ and TOGETHAR⁴ studies.

In the present ZIPANGU (ezetimibe clinical investigation for regression of intracoronary plaque evaluated by angioscopy and ultrasound) study, we compared the effect of combination therapy (statin+ezetimibe) and monotherapy (statin alone) through examination of the plaque stabilization effect by angioscopy and the plaque regression effect by IVUS.

Methods

Study Design

This study was a multicenter, prospective, randomized, open-label, blinded-endpoint (PROBE) trial.⁵ Patients were enrolled at 14 centers: Amagasaki Chuou Hospital, Ehime Prefectural Imabari Hospital, Ehime University Graduate School of Medicine, Higashi-Osaka City General Hospital, Hyogo Prefectural Himeji Circulatory Organ Illness Center, Keiai Hospital, Nihon University Itabashi Hospital, Osaka Police Hospital, Saijo Central Hospital, Saiseikai Matsuyama Hospital, The Hiroshima Municipal Hiroshima Citizen Hospital, Tsukuba University Hospital, Ukima Central Hospital, and Uwajima City Hospital. Patients were allocated by a centralized enrollment method to either monotherapy with atorvastatin alone or combination therapy with atorvastatin and ezetimibe at a ratio of 1:1 in accordance with the following allocation factors: (1) LDL-C level at study enrollment; (2) diabetic status defined as hemoglobin A1c ≥6.1% (Japan Diabetes Society) or ≥6.5% (National Glycohemoglobin Standardization Program); and (3) previous treatment with a statin.

We included patients aged 20–80 years with elective percutaneous coronary intervention (PCI) who had at least 1 yellow plaque of grade ≥2 in the non-PCI target coronary artery segments and hypercholesterolemia (LDL-C >100 mg/dL) with or without statin treatment. We excluded patients with a past history of hypersensitivity to the study drugs, triglycerides ≥400 mg/dL, AST or ALT >3-fold the upper limit of the normal range, serum creatinine ≥2.0 mg/dL, hemoglobin A1c ≥8% (Japan Diabetes Society) or ≥8.4% (National Glycohemoglobin Standardization Program), insulin use, acute coronary syndrome (ACS) in the past 3 months, secondary hypercholesterolemia, malignant tumor, familial hypercholesterolemia, pregnancy, or cyclosporine use. The diagnosis of ACS was made if at least 2 of the following 3 criteria were met: (1) evidence of coronary ischemia on ECG; (2) increase ≥2-fold in serum creatinine kinase or creatinine kinase-MB levels and/or troponin-T positivity; and (3) presence of symptoms suggestive of ACS.

The dosage of ezetimibe was 10 mg/day and that of atorvastatin was initially 10 mg/day. Treatment was started within 72 h of PCI. The target LDL-C level was <100 mg/dL for the monotherapy group and <70 mg/dL for the combination therapy group. If the LDL-C levels within 3 months were ≥100 mg/dL in the monotherapy group or ≥70 mg/dL in the combination group, the dosage of atorvastatin was increased to the maximum of 20 mg, which is the maximum allowed dosage in Japan, regardless of the assigned group. During the follow-up period, medication compliance for the investigational drugs was checked regularly. Patients were counseled on lifestyle improvements in accordance with the Guidelines for Prevention of Atherosclerotic Cardiovascular Diseases 2012 issued by the Japan Atherosclerosis Society.⁶ Diet and medical therapies for other complications or atherosclerosis prevention other than lipid management were administered comprehensively for all enrolled patients based on the individual strategies of their attending physicians.

The examinations by nonobstructive coronary angioscopy and IVUS were serially performed at baseline and 9 months’ follow-up to evaluate the changes in plaque color and plaque volume in as many coronary vessels as possible, although plaques in the PCI target segments (within 5 mm of PCI sites) were excluded from analysis.

The institutional review board at each participating center approved the study, and the first patient was enrolled in November 2011. The details of the study design, including the sample size determination, were previously reported.⁵ The study was registered in the UMIN Clinical Trial Registry (UMIN000006971). Written informed consent was given by all enrolled patients.

Evaluation by Nonobstructive Coronary Angioscopy

A fiber catheter and nonobstructive fiber imaging system (FT-201; InterTec Co. Ltd., Osaka, Japan) were used. Angioscopic observation was performed while blood was cleared away from view by injection of 3% dextran-40 as previously reported.⁷

At the central core laboratory, 2 independent experienced investigators who were unaware of the patient group allocations and imaging dates (baseline or follow-up) performed the analyses. The 2 angioscopic images (blinded for baseline or follow-up) were reviewed together on a display to match the plaques. The color of all plaques detected was classified into 5 grades:⁴ grade 0, white; grade 1, slightly yellow; grade 2, yellow; grade 3, intensely yellow; grade 4, glisteningly yellow. The angioscopic evaluation of yellow color was performed by comparison with standard colors as in previous studies.⁷ The respective inter- and intra-observer reproducibility for the interpretation of angioscopic images was reported⁸ as 85% and 95% for plaque color, and 90% and 100% for thrombus.

Evaluation by IVUS

IVUS was performed with a 40-MHz catheter (Atlantis SR Pro2) using an iLab IVUS System (Boston Scientific Inc., Natick, MA, USA). This system was used to measure plaque volume, vessel lumen, and vessels of at least 5.0 mm in length.

At the central core laboratory, 2 independent experienced investigators who were unaware of the patient group allocations and imaging dates (baseline or follow-up) performed the quantitative IVUS analysis. The 2 IVUS images (blinded for baseline or follow-up) were reviewed together on a display to match the plaques. Every 6th image (0.1 mm apart) was manually traced using commercially available IVUS measurement software (echoPlaque 4; INDEC Systems Inc., Santa Clara, CA, USA). The software automatically interpolated the tracing of the 5 cross-sections between the 2 manually traced images. The lumen area, external elastic membrane (EEM) area, and plaque area (EEM area minus lumen area) were measured. The lumen, EEM, and plaque volume were calculated by integration of these data. The change in plaque volume was evaluated by the net change in % plaque volume defined as (plaque volume)/(EEM volume)×100 over the follow-up period.

Laboratory Data

Lipid profile including the biomarkers of cholesterol synthesis (lathosterol) and absorption (sitosterol and campesterol) and conventional clinical laboratory examinations were performed at enrollment, and 1, 3, and 9±2 months after enrollment. The level of LDL-C was calculated by the Friedewald formula.⁹

Statistical Analysis

Continuous data are presented as mean±SD. Comparisons of baseline patient characteristics between the groups were carried out with Welch’s t-test for continuous variables that would follow a normal distribution, the Mann-Whitney U-test for continuous variables that would not follow a normal distribution, and Pearson’s chi-square test or Fisher’s exact test for categorical variables. For serum LDL-C and high-density lipoprotein cholesterol (HDL-C), the change from baseline to follow-up was assessed by a paired t-test, and intergroup comparisons were performed with Welch’s t-test. Regarding high-sensitivity C-reactive protein (hs-CRP), sitosterol, campesterol, and lathosterol, the changes from baseline to follow-up were assessed by the Wilcoxon signed-rank test, and intergroup comparisons were performed with the Mann-Whitney U-test. For yellow color grade, the change from baseline to follow-up was assessed by the Wilcoxon signed-rank test, and intergroup comparisons were carried out with the Mann-Whitney U-test. The correlation between a change in yellow color grade from baseline to follow-up and the yellow color grade at baseline was assessed by linear regression analysis and Spearman rank correlation coefficient. Intergroup differences in the slope of the regression line were assessed by a type III test using a general linear model. The change in % plaque volume from baseline to follow-up was assessed by a paired t-test. The correlations between the changes in % plaque volume or yellow color grade and follow-up LDL-C, change in LDL-C, %change in LDL-C, or %changes in campesterol, sitosterol, or lathosterol were analyzed by linear regression analysis. The correlations between the changes in % plaque volume and yellow color grade were analyzed by linear regression analysis for all patients and for the monotherapy or combination therapy group. A two-sided significance level of P<0.05 was used for the statistical analyses. All statistical analyses were performed using IBM SPSS Statistics 22.0 (IBM Corporation, Armonk, NY, USA).

Results

Study Patients

Of 131 enrolled patients, 66 were allocated to the monotherapy group and 65 to the combination therapy group (Figure 1). After excluding 12 and 11 patients for violation of inclusion/exclusion criteria or lack of follow-up examination, 54 patients in the monotherapy group and 54 patients in the combination therapy group were included in the analysis.

Figure 1.

Flow chart of ZIPANGU study. Stable coronary artery disease patients (n=131) who underwent elective percutaneous coronary intervention and had yellow plaques were randomized to combination therapy (atorvastatin 10–20 mg and ezetimibe 10 mg/day) or statin monotherapy (atorvastatin 10–20 mg). Changes in plaque color and plaque volume during 9-month study period were assessed by angioscopy and intravascular ultrasound.

For angioscopic analysis, after excluding 1 more patient in each group for lack of yellow plaques of grade ≥2 at baseline by core laboratory evaluation, we analyzed 53 patients in the monotherapy group and 53 patients in the combination therapy group. For IVUS analysis, after excluding 3 and 5 patients in the monotherapy and combination therapy groups, respectively, for lack of adequate IVUS data, we analyzed 51 patients in the monotherapy group and 49 patients in the combination therapy group. The patient characteristics at baseline are presented in Table 1.

Table 1. Baseline Characteristics of Patients in the ZIPANGU Study

	All	Statin monotherapy	Combination therapy	P value
No. of patients	108	54	54
Male sex, n (%)	85 (79)	44 (81)	41 (76)	0.6
Age, years	69±10	68±11	71±8	0.1
Risk factor, n (%)
Diabetes mellitus	37 (34)	17 (31)	20 (37)	0.6
Hypertension	89 (82)	43 (80)	46 (85)	0.6
Chronic kidney disease	35 (32)	15 (28)	20 (37)	0.4
Current smoking	40 (37)	22 (41)	18 (33)	0.5
Body mass index	24±3	24±3	25±4	0.3
Past history, n (%)
Myocardial infarction	23 (21)	16 (30)	7 (13)	0.05
Angina pectoris	52 (48)	22 (41)	30 (56)	0.1
Stroke	13 (12)	6 (11)	7 (13)	1.0
Peripheral artery disease	7 (6)	3 (6)	4 (7)	1.0
Serum lipid profile, mg/dL
TC	165±34	162±33	168±36	0.3
LDL-C	101±27	100±27	101±27	0.8
HDL-C	46±14	45±9	46±18	0.6
Triglycerides	114±55	113±52	115±58	0.7
Other laboratory data
Hemoglobin A1c, %	5.6±0.7	5.5±0.7	5.7±0.7	0.1
Creatinine, mg/dL	0.8±0.2	0.8±0.2	0.9±0.3	0.9
hs-CRP, mg/dL	6,470±12,127	5,426±12,909	7,555±11,280	0.1
Medication, n (%)
Statin	7 (6)	4 (7)	3 (6)	1.0
Aspirin	105 (97)	53 (98)	52 (96)	1.0
Clopidogrel	103 (95)	50 (93)	53 (98)	0.3
Ticlopidine	3 (3)	3 (6)	0 (0)	0.2

HDL-C, high-density lipoprotein cholesterol; hs-CRP, high-sensitivity C-reactive protein; LDL-C, low-density lipoprotein cholesterol; TC, total cholesterol.

Changes in Laboratory Data

Serum LDL-C decreased significantly from 101±27 to 61±17 mg/dL in the combination therapy group and from 101±27 to 75±16 mg/dL in the monotherapy group (Table 2). Serum HDL-C did not change and hs-CRP decreased significantly from baseline to the 9-month follow-up in both groups. The biomarker of cholesterol synthesis, lathosterol, decreased significantly in both groups. The biomarkers of cholesterol absorption, sitosterol and campesterol, decreased significantly in the combination therapy group but increased significantly in the monotherapy group.

Table 2. Changes in Laboratory Data in the ZIPANGU Study

	Monotherapy group (atorvastatin 10–20 mg/day)				Combination therapy group (atorvastatin 10–20 mg/day and ezetimibe 10 mg/day)
	Baseline	1 month	3 months	9 months	Baseline	1 month	3 months	9 months
Serum lipid profile, mg/dL
TC	162±33	150±27	144±21*	140±21**	168±36	126±24**,††	129±23**,†	126±25**,†
LDL-C	101±27	81±19**	77±19**	75±16**	101±27	61±16**,††	63±14**,††	61±17**,††
HDL-C	45±9	46±11	46±10	45±11	47±19	46±12	47±11	44±12
Triglycerides	113±52	127±77	114±67	109±54	114±58	98±50	111±71	95±46*
Other laboratory data
Hemoglobin A1c,%	5.5±0.7	–	–	5.6±0.7	5.7±0.7	–	–	5.9±0.9*,†
Creatinine, mg/dL	0.8±0.2	0.9±0.2	0.9±0.2*	0.9±0.2	0.9±0.3	0.9±0.2	0.9±0.3	0.8±0.2
hs-CRP, ng/dL	5,510±13,018	–	–	988±1,521**	7,653±11,370	–	–	1,699±2,830**
Campesterol, μg/mL	4.0±1.6	–	–	4.6±1.6**	4.4±2.0	–	–	2.1±0.7**,††
Sitosterol, μg/mL	2.1±0.9	–	–	2.4±0.9**	2.2±0.9	–	–	1.3±0.4**,††
Lathosterol, μg/mL	1.3±0.7	–	–	1.1±0.2*	1.5±1.0	–	–	1.2±0.4*,††
Campesterol, μg/100 mg TC	248±90	–	–	330±102**	267±107	–	–	166±46**,††
Sitosterol, μg/100 mg TC	130±54	–	–	171±58**	137±57	–	–	109±29**,††
Lathosterol, μg/100 mg TC	83±37	–	–	77±18	91±47	–	–	95±25*,††

*P<0.05 vs. baseline. **P<0.001 vs. baseline. ^†P<0.05 vs. monotherapy. ^††P<0.001 vs. monotherapy. Significant based on a Bonferroni correction. Abbreviations as in Table 1.

Changes in Yellow Color Grade by Angioscopy

The number of yellow plaques detected was 115 and 131 in total and 2.2±1.3 and 2.6±1.4 per patient in the monotherapy group and combination therapy group, respectively. The yellow color grade decreased significantly from baseline to follow-up in both the monotherapy group (2.1±1.1 vs. 1.7±1.0, P=0.005) and combination therapy group (2.2±1.2 vs. 1.8±1.2, P=0.002) (Figure 2A,B). The change in yellow color grade from baseline to follow-up did not differ significantly between the monotherapy and combination therapy groups (−0.4±1.4 vs. −0.4±1.4, P=0.6).

Figure 2.

Changes in yellow color grade from baseline to follow-up and relationship between yellow color grade at baseline and its change during follow-up. The yellow color grade decreased significantly from baseline to follow-up in both the monotherapy group (A): 2.1±1.1 vs. 1.7±1.0, P=0.005) and combination therapy group (B): 2.2±1.2 vs. 1.8±1.2, P=0.002). The change in yellow color grade from baseline to follow-up did not differ significantly between the monotherapy group and the combination therapy group (−0.4±1.4 vs. −0.4±1.4, P=0.6). The change in yellow color grade was significantly associated with the yellow color grade at baseline in both the monotherapy group (C): Y=−0.949X+1.623, Spearman’s rank correlation coefficient=−0.552, P<0.001) and combination therapy group (D): Y=−0.707X+1.187, Spearman’s rank correlation coefficient=−0.499, P<0.001). There was no significant difference in the slope of the regression lines between the monotherapy and combination therapy groups (P=0.05). The size of each circle indicates the number of yellow plaques.

The change in yellow color grade from baseline to follow-up was significantly associated with the grade at baseline in both the monotherapy group (Y=−0.949X+1.623, Spearman’s rank correlation coefficient=−0.552, P<0.001) and combination therapy group (Y=−0.707X+1.187, Spearman’s rank correlation coefficient=−0.499, P<0.001) (Figure 2C,D). There was no significant difference in the slope of the regression lines between the monotherapy and combination therapy groups (P=0.05).

Changes in %Plaque Volume by IVUS

The number of plaques detected was 152 and 154 in total and 3.0±1.9 and 3.1±1.7 per patient in the monotherapy group and combination therapy group, respectively. The %plaque volume did not change from baseline to follow-up in the monotherapy group (48.5±10.2% vs. 48.2±10.4%, P=0.4), but decreased significantly in the combination therapy group (50.0±9.8% vs. 49.3±9.8%, P=0.03) (Figure 3).

Figure 3.

Changes in %plaque volume from baseline to follow-up. The %plaque volume did not change from baseline to follow-up in the monotherapy group (48.5±10.2% vs. 48.2±10.4%, P=0.4), but decreased significantly in the combination therapy group (50.0±9.8% vs. 49.3±9.8%, P=0.03).

Correlations Between Changes in %Plaque Volume or Yellow Color Grade and Cholesterol-Related Markers

There were no significant correlations between the changes in %plaque volume or of yellow color grade and LDL-C, campesterol, sitosterol, or lathosterol (Figure 4).

Figure 4.

Correlations between changes in %plaque volume or yellow color grade and cholesterol-related markers. The correlations between the change in %plaque volume and follow-up (A), change in LDL-C (B), and %change in LDL-C (C), and %change in campesterol (G), sitosterol (H), or lathosterol shown as a ratio to total cholesterol (I) are presented. The correlations between the change in yellow color grade and follow-up (D), changes in LDL-C (E), and %change in LDL-C (F), and %change of campesterol (J), sitosterol (K), or lathosterol shown as a ratio to total cholesterol (L) are presented. LDL-C, low-density lipoprotein cholesterol.

Correlations Between Changes in %Plaque Volume and Changes in Yellow Color Grade

There was no significant correlation between the changes in %plaque volume and the changes in yellow color grade when analyzed with all patients or with combination therapy group patients (Figure 5). However, among the statin monotherapy group patients, the reduction in the yellow color grade was weakly but significantly associated with the reduction in %plaque volume.

Figure 5.

Correlations between change in %plaque volume and change in yellow color grade. There was no significant correlation between the change in %plaque volume and the change in yellow color grade when analyzed with all patients (A) or with combination therapy group patients (C). However, in the statin monotherapy group, the reduction in yellow color grade was weakly but significantly associated with the reduction in % plaque volume (B).

Discussion

This is the first report to compare plaque stabilization and plaque regression effects simultaneously between statin monotherapy and combination therapy with statin and ezetimibe. The plaque stabilization effect was evaluated by reduction in yellow color grade using angioscopy and the plaque regression effect was examined by the reduction in %plaque volume using IVUS, in accordance with our previous studies.^3,10 In the present study, the achieved LDL-C level was 61±17 mg/dL in the combination therapy group and 75±16 mg/dL in the monotherapy group, and the treatment period was 9 months. Under these conditions, both monotherapy and the combination therapy significantly and similarly stabilized the plaques. However, only with the combination therapy, and not the monotherapy, was there significant regression in plaque size. Plaque stabilization may occur after a relatively short treatment period with relatively mild LDL-C reduction, but plaque regression may require a longer treatment period with stronger LDL-C reduction.

Plaque Stabilizing Effect of LDL-C Reduction

In previous studies, plaque stabilization indicated by a reduction in yellow color grade was achieved by various treatments. In the TWINS study, a significant reduction in mean yellow color grade from 1.5 to 1.1 was achieved by 28-week statin treatment with a reduction of LDL-C from 144 to 86 mg/dL; however, no further reduction in yellow color grade was detected thereafter until 80 weeks.³ In the TOGETHAR study, a significant reduction in mean yellow color grade from 2.9 to 2.6 was achieved by 52-week statin treatment with a reduction in LDL-C from 145 to 94 mg/dL.⁴ In the present ZIPANGU study, a significant reduction in mean yellow color grade from 2.1 to 1.7 was achieved by 36-week statin monotherapy with a reduction in LDL-C from 101 to 75 mg/dL, and a significant reduction in mean yellow color grade from 2.2 to 1.8 was achieved by 36-week combination therapy with a reduction in LDL-C from 101 to 61 mg/dL. Judging from these data, similar reductions in yellow color grade appeared to be achieved by statin treatment, with or without ezetimibe, independent of the degree of LDL-C reduction or duration of treatment.

The change in yellow color grade from baseline to follow-up was significantly associated with the yellow color grade at baseline in the present study, consistent with the finding in the TOGETHAR study.⁴ Furthermore, the association in the present study did not differ significantly between the monotherapy and combination therapy groups, suggesting that the plaque stabilization effect did not differ between the 2 groups even when the influence of the baseline yellow color grade was taken into consideration.

Plaque Regression Effect of LDL-C Reduction

In previous studies, plaque regression indicated by a reduction in plaque volume was achieved by various treatments. In the TWINS study, a significant reduction in mean plaque volume by −8.3% was achieved at 28 weeks and a further reduction by −17.8% was achieved at 80 weeks under the conditions of LDL-C reduction from 144 mg/dL to 86 mg/dL at 28 weeks and 89 mg/dL at 80 weeks.³ In the TOGETHAR study, no significant reduction in %plaque volume was achieved by 52-week statin treatment with a reduction of LDL-C from 145 to 94 mg/dL.⁴ In the present ZIPANGU study, no significant reduction in %plaque volume was achieved by 36-week statin monotherapy with a reduction in LDL-C from 101 to 75 mg/dL, but a significant reduction in %plaque volume from 50.0% to 49.3% was achieved by 36-week combination therapy with a reduction in LDL-C from 101 to 61 mg/dL. Based on these data, the reduction in plaque volume appeared to be achieved according to the degree of LDL-C reduction and the duration of treatment regardless of the drug used (statin and ezetimibe).

The relationship between the degree of plaque volume reduction shown by the change in %plaque volume and the achieved mean LDL-C level in both groups in the present study was consistent with other studies^4,11–16 using statins alone or statin plus PCSK9 inhibitor (Figure 6). These findings suggest that the reduction in LDL-C by statin alone and by combination therapy with ezetimibe had the same effect on plaque regression, depending on the achieved LDL-C level. This finding from the IVUS examinations is consistent with, and a probable explanation for, the clinical findings in the IMPROVE-IT trial,² from which it was concluded that, when added to statin therapy, ezetimibe resulted in incremental lowering of LDL-C levels and improved cardiovascular outcomes.

Figure 6.

Relationship between mean LDL-C level and mean percent atheroma volume change in various IVUS trials. The relationship between the degree of plaque volume reduction shown by the change in %atheroma volume and the achieved mean LDL-C level in both groups in the present study was consistent with results from previous studies of statin monotherapy. These findings suggest that the reduction in LDL-C by statin monotherapy and that by combination therapy with ezetimibe has the same effect on plaque regression depending only on the achieved LDL-C level. LDL-C, low-density lipoprotein cholesterol.

Recently, the PRECISE-IVUS trial reported very similar results to those of the present study, including Japanese ACS and stable coronary artery disease (CAD) patients with a follow-up interval of 10 months.¹⁷ In the PRECISE-IVUS trial, LDL-C was reduced from 108 to 73 mg/dL by statin monotherapy and from 110 to 63 mg/dL by statin plus ezetimibe; and the %plaque volume was significantly (P=0.001) reduced by the combination therapy from 51.3% to 49.3% but did not differ between baseline and follow-up (50.9% vs. 50.4%, P=0.08) with the monotherapy among the subgroup of stable CAD patients. The fact that 2 independent trials revealed very similar results on the plaque regression effect of adding ezetimibe to statin treatment is important for confirming the reliability of the findings.

Although a rough correlation between LDL-C reduction and plaque volume reduction has been demonstrated by multiple studies, including ours, as shown in Figure 6, the PRECISE-IVUS trial failed to show a significant correlation between the achieved LDL-C level and the change in %plaque volume among stable CAD patients. We also had similar results in the present study, as shown in Figure 4. Although this discrepancy might be very important, the reason is unclear and further investigations are needed to clarify it. Although the reduction in cholesterol absorption by ezetimibe might be a possible mechanism that truly is associated with plaque volume reduction, this correlation was not demonstrated in the present study or in the stable CAD patients in the PRECISE-IVUS trial.

Relationship Between Plaque Stabilizing and Plaque Regression Effects

Statin therapy is known to increase fibrous cap thickness and decrease the yellow color grade of plaque; therefore, the reduction in yellow color grade and in plaque volume may occur independently. One possible explanation of the findings shown in Figure 5 is that statin caused both fibrous cap thickening and plaque volume reduction simultaneously while ezetimibe mainly caused plaque volume reduction, possibly because of the different anti-inflammatory effects of the statin and ezetimibe.

Study Limitations

In the present study, stable CAD patients were treated for a relatively short period; and thus, the plaque stabilization or regression effect might be relatively small, and might be different in other groups of patients with different treatment durations. The patients’ characteristics were generally similar, but not completely matched, between the monotherapy and the combination therapy groups. A past history of myocardial infarction, which appeared more common in the monotherapy group, might have influenced the results, because the effect of cholesterol reduction therapy is known to be stronger in ACS patients than in non-ACS patients. Although we excluded patients who were diagnosed as familial hypercholesterolemia, some familial hypercholesterolemia patients might have been included because of the difficulty in its diagnosis. Worsening of diabetes mellitus was observed in the combination therapy group, judging from the change in hemoglobin A1c, which might have influenced the results. Although the evaluations of plaque stabilization and plaque regression were simultaneously performed in the same patient, the plaques evaluated by angioscopy and those by IVUS were not matched.

Conclusions

Compared with statin monotherapy, combination therapy with the statin and ezetimibe further reduced the LDL-C levels. Significant plaque volume reduction was achieved by the combination therapy, but not by the monotherapy; however, plaque stabilization shown by yellow color reduction was similarly achieved by both therapies. Moreover, the reduction in plaque volume was dependent on the reduction in LDL-C, regardless of whether it was achieved by statin alone or by statin plus ezetimibe.

Acknowledgments

The ZIPANGU study was conducted by the Japan Health Promotion Foundation with funding from Bayer Yakuhin, Ltd. The authors acknowledge the contributions made by Natsuko Yamamoto to IVUS core laboratory management.

Disclosures

Y.U. has received honoraria for lecture from Daiichi Sankyo, Novartis, AstraZeneca, MSD, Goodman, Sanofi, Abbott Vascular, Eisai, Toaeiyo, Mochida, Takeda, Boehringer Ingelheim, Bristol-Myers Squibb, Kowa, Sumitomo Dainippon Pharma, Teijin, Boston Scientific, Astellas, and Amgen Astellas BioPharma; and has received research grant from Abbott Vascular, Pfizer, Sanofi, Bayer, Ono Pharmaceutical, Nihon Kohden, and Novartis. T.H. has received honoraria for lecture from Bayer, Kowa, Pfizer, Amgen Astellas Biopharma, Astellas, Sanofi, Shionogi, AstraZeneca, and Daiich Sankyo; and has belonged to endowed course by Boston Scientific. A.H. has belonged to endowed course by Boston Scientific. A.H. is a consultant for Toaeiyo Pharmaceutical; has received honoraria for lecture from Bayer, Pfizer, Amgen Astellas Biopharma, Astellas, Sanofi, Takeda, AstraZeneca, Bristole-Mayers Squibb, MSD, Ono Pharmaceutical, Sanwa Chemicals, and Daiich Sankyo; and has belonged to endowed course by Boston Scientific. S.K. is a consultant for Nemoto Kyorin-Do. Masaharu Ishihara has received honoraria for lecture from MSD, Bayer, and AstraZeneca; and has received scholarship fund from Abbott Vascular, Boston Scientific, Sanofi, MSD, Astellas, Bayel, Pfizer, Daiichi Sankyo, MID, and Goodman. All other authors have reported that they have no relationships relevant to the content of this paper to disclose.

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