The difference between Asian and Western in the effect of LDL-C lowering therapy on coronary atherosclerotic plaque: a meta-analysis report

Background The different effects of LDL-C levels and statins therapy on coronary atherosclerotic plaque between Western and Asian remain to be settled. Methods PubMed, EMBASE, and Cochrane databases were searched from Jan. 2000 to Sep. 2014 for randomized controlled or blinded end-points trials assessing the effects of LDL-C lowering therapy on regression of coronary atherosclerotic plaque (CAP) in patients with coronary heart disease by intravascular ultrasound. The significance of plaques regression was assessed by computing standardized mean difference (SMD) of the volume of CAP between the baseline and follow-up. Results Twenty trials (ten in the West and ten in Asia) were identified. For Westerns, Mean lowering LDL-C by 49.4% and/or to level 61.9 mg/dL in the group of patients with baseline mean LDL-C 123.2 mg/dL could significantly reduce the volume of CAP at follow up (SMD −0.156 mm3, 95% CI −0.248 ~ −0.064, p = 0.001). LDL-C lowering by rosuvastatin (mean 40 mg daily) could significantly decrease the volumes of CAP at follow up. For Asians, Mean lowering LDL-C by 36.1% and/or to level 84.0 mg/dL with baseline mean LDL-C 134.2 mg/dL could significantly reduce the volume of CAP at follow up (SMD −0.211 mm3, 95% CI −0.331 ~ −0.092, p = 0.001). LDL-C lowering by rosuvastatin (mean 14.1 mg daily) and atorvastatin (mean 18.9 mg daily) could significantly decrease the volumes of CAP at follow up. Conclusions There was a different effect of LDL-C lowering on CAP between Westerns and Asians. For regressing CAP, Asians need lower dosage of statins or lower intensity LDL-C lowering therapy than Westerns.


Background
Atherosclerotic plaque is the hallmark and cornerstone of atherosclerotic disease. Disruption of coronary atherosclerotic plaque (CAP) may lead to sudden cardiac death, acute myocardial infarction, or unstable angina [1]. Intravascular ultrasound (IVUS) is considered to be gold standard for measurement of atherosclerotic plaque [2].
The meta-analysis of twenty trials evaluated the effects of LDL-C lowering on CAP indicated that intensive LDL-C lowering with statins could slow atherosclerotic plaque progression and lead to plaque regression [3].
But the meta-analysis did not investigate the effects of LDL-C lowering on CAP in different race.
In this meta-analysis, we investigated the difference between Western and Asian in the effect of LDL-C lowering therapy on the progression of the CAP from the current trials on LDL-C lowering therapy retarding the progression of the CAP and identified the different targets of LDL-C that result in the regression of the CAP for Western and Asian.

Methods
Materials and methods of this meta-analysis were detailed in the paper by Gao et al. [3].

Search strategy and selection criteria
An electronic literature search was performed to identify all relevant studies published in PubMed, EMBASE, and Cochrane databases in the English language from Jan. 1,2000 to Sep. 13, 2014, using the terms "atherosclerosis" and "cholesterol blood level". Trials were included using the criteria as: 1) randomized controlled or prospective, blinded end-points trials, and its primary end point was CAP change detected by IVUS; 2) report of LDL-C levels at baseline and follow-up; 3) data on the volume of CAP at baseline and follow-up, and volume of CAP was calculated as vessel volume minus lumen volume; Exclusion criteria were: 1) only CAP area or volume index or percent atheroma volume were detected; 2) the levels of LDL-C at baseline or follow-up were not provided; and 3) target plaques were unstable.

Data extraction and quality assessment
Two investigators independently reviewed all potentially eligible studies and collected data on patient and study characteristics, and any disagreement was resolved by consensus. The primary end point of this study was the volume change of CAP detected by IVUS. Quality assessments of trials were evaluated with Jadad quality scale.

Data synthesis and analysis
Volume changes of CAP from baseline to follow-up were analyzed using standardized mean differences (SMD).
Volume changes of plaque in every arm were used for pooled analysis. The trials were firstly grouped into group Western and Asian according to the location of the trials. Then, according to the levels and the reducing percentage of LDL-C at follow-up, the arms were grouped to following groups: ≤70, >70 ≤ 100 HP, >70 ≤ 100 MP, >70 ≤ 100 LP, >100 mg/dL; and <0, ≥0 < 30, ≥30 < 40, ≥40 < 50, ≥50% respectively [3], to investigate the effect of different levels of LDL-C at follow up on CAPs. According to statins, the arms were grouped to: rosuvastatin, atorvastatin, pitavastatin, simvastatin, fluvastatin and pravastatin groups, to investigate the effect of different statins on CAPs. The volume of CAP at follow up was compared with that at baseline to evaluate effect of LDL-C levels on regression of CAP.
Heterogeneity across trials (arms) was assessed via a standard χ 2 test with significance being set at p < 0.10 and also assessed by means of I 2 statistic with significance being set at I 2 > 50%. Pooled analyses were calculated using fixed-effect models, whereas random-effect models were applied in case of significant heterogeneity across trials (arms). Sensitivity analyses (exclusion of one study at one time) were performed to determine the stability of the results. Publication bias was assessed using the Egger regression asymmetry test. Statistical analyses were performed using STATA software 12.0 (StataCorp, College Station, Texas).
All continuous variables were expressed as mean ± SD, and continuous variables were compared between the Western and Asian groups using Student's t test (SigmaStat 3.5). A P value <0.05 was considered to be statistically significant.
Risk of bias of included studies, evaluated through Cochrane's methods, showed an overall acceptable quality of selected trials (Figures 2 and 3).
The effect of the levels of LDL-C at follow-up on regression of coronary atherosclerotic plaque in Western and Asian For Western, meta-analysis indicated that LDL-C lowering in group ≤70 mg/dL could lead to regression of CAP, but LDL-C lowering in group >70 ≤ 100 HP, >70 ≤ 100 MP, >70 ≤ 100 LP and >100 mg/dL could not ( Figure 4, Table 3).
Sensitivity analyses suggested that LDL-C lowering in group ≤70 mg/dL could lead to regression of CAP with reduction of the CAP volume ranged from −0.139 mm 3 (SMD, 95% CI: −0.257~−0.021) when the arm of 2006 ASTEROID Ros was omitted to −0.175 mm 3 (SMD, 95% CI: −0.317~−0.034) when the arm of 2011 SATURN Ros was omitted. No publication bias was found, the values of p by Egger's test was 0.789.
For Asian, according to the levels of LDL-C at follow-up, the arms were grouped to three groups: ≤70, >70 ≤ 100 HP and >100 mg/dL. LDL-C lowering in group ≤70 mg/dL and >70 ≤ 100 HP could lead to regression of CAP, but LDL-C lowering in group >100 mg/dL could not ( Figure 5, Table 3).
No publication bias was found, the values of p by Egger's test for group ≤70 and >70 ≤ 100HP mg/dL were 0.970, 0.083 respectively.
The effect of the LDL-C reducing percentage at follow-up on regression of CAP in Western and Asian For Western, meta-analysis showed that LDL-C lowering in group ≥40 < 50, ≥50% could lead to regression of CAP, but LDL-C lowering in group <0, ≥0 < 30% and ≥30 < 40 could not ( Figure 6, Table 3). In group group <0, ≥0 < 30% and ≥30 < 40, metaanalysis were showed in Table 3.
Sensitivity analyses showed that LDL-C lowering in group ≥30 < 40% could still lead to regression of CAP with reduction of the plaque volume ranged from −0.172 mm 3 (95% CI −0.306~−0.038) when the arm of 2009 JAPAN-ACS Ato was omitted to −0.223 mm 3 (SMD, 95% CI −0.357~−0.089) when 2009 COSMOS Ros was omitted. Publication bias analysis suggested that bias was significant with 0.004 of p value by Egger's test.
Mean levels of LDL-C at baseline and follow up, mean reducing percentage of LDL-C in each group were showed in Table 4.

The effect of lowering LDL-C by statins on regression of coronary atherosclerotic plaque in Western and Asian
For Western, atorvastatin, rosuvastatin, pravastatin and simvastatin were used in trials to investigate the effects of LDL-C lowering on CAP. Meta-analysis indicated that LDL-C lowering by rosuvastatin could lead to regression of CAP, but LDL-C lowering by atorvastatin, pravastatin, and simvastatin could not (Figure 8, Table 5).
LDL-C lowering by rosuvastatin (mean 40.0 mg daily for mean 24 months) could significantly decrease the volumes of CAP at follow up, compared with the volumes at baseline (SMD −0.158 mm 3 , 95% CI: −0.253~−0.064, p = 0.001). There was no significant heterogeneity among arms (χ 2 for heterogeneity = 0.18, p =0.672, I 2 = 0%).   Sensitivity analyses suggested that lowering LDL-C by rosuvastatin could lead to regression of CAP with reduction of the plaque volume ranged from −0.142 mm 3 (SMD, 95% CI: −0.263~−0.020) when the arm of 2006 ASTEROID Ros was omitted to −0.183 mm 3 (SMD, 95% CI: −0.332~−0.035) when the arm of 2011 SATURN Ros was omitted. But publication bias was found, the values of p by Egger's test was 0.000 (Table 5).
For Asian, atorvastatin, rosuvastatin, pitavastatin, pravastatin, fluvastatin and simvastatin were used in trials to investigate the effects of LDL-C lowering on CAP. Meta-analysis indicated that LDL-C lowering by rosuvastatin, atorvastatin could lead to regression of CAP, but LDL-C lowering by pitavastatin, pravastatin, fluvastatin and simvastatin could not (Figure 9, Table 5). Sensitivity analyses suggested that lowering LDL-C by rosuvastatin could not significantly lead to regression of CAP when the arm of 2012 ARTMAP Ros or 2009 COSMOS Ros was omitted. Also, Lowering LDL-C by atorvastatin could not significantly lead to regression of CAP when the arm of 2009 JAPAN-ACS Ato was omitted. No publication bias was found, the values of p by Egger's test for rosuvastatin and atorvastatin group were 0.660, 0.456 respectively ( Table 5).
Intensity of lowering LDL-C by different statins was shown in Table 6. Rosuvastatin and atorvastatin could reduce LDL-C by more than 40%.

The difference between Western and Asian in usage of statins
The meta analysis showed that rosuvastatin and atorvastatin can regress CAP (Table 5). LDL-C levels, intensity of lowering LDL-C by rosuvastatin and atorvastatin, its dosage and duration were compared between Western and Asian ( Table 7). Intensity of lowering LDL-C by rosuvastatin and atorvastatin in Western group were similar to that in Asian group, but the dosages of rosuvastatin and atorvastatin in Asian group were significantly lower than those in Western group, and the duration of statins administration in Asian group were significantly shorter than those in Western, as showed in Table 7.

Discussion
This meta-analysis revealed that intensive LDL-C lowering can regress CAP both in Western and Asian. For regressing CAP, the dosage of statins administrated in Westerns was different from that in Asians. Asians need lower dosage of atorvastatin or rosuvastatin than Westerns though there was no difference between Westerns and Asians in pharmacokinetic and pharmacodynamic study [32,33].

The effect difference of LDL-C lowering on CAP between Western and Asian
For Western including American, Canadian, German, French, English, Australian and Dane [10,[5][6][7]16,[23][24][25][26]28], the meta-analysis (Table 3) in subgroup ≤70 mg and ≥40 < 50% of Western indicated that LDL-C level lowering to <69.3 mg or reducing by > 45% for 22.6 months of follow up (Table 4) could lead to regression of CAP, but the meta-analysis (Table 3) in subgroup >70 ≤ 100 HP mg of Western showed that LDL-C level lowering to 73.2 mg or reducing by 43.6% for 21.7 months of follow up (Table 4) was not enough for regressing CAP.
For Asian including Japanese and Korean [20,11-15, 17,22,29,30], the meta-analysis in subgroup ≤70 mg and ≥40 < 50% of Asian indicated that LDL-C level lowering to 57.0 mg or reducing by 47.2% for 6.9 months of follow up could lead to regression of CAP, but sensitivity analyses showed that LDL-C lowering in this two subgroup could not significantly lead to regression of CAP when the arm of 2012 ARTMAP Ros or 2012 ARTMAP Ato was omitted ( Table 3). The meta-analysis in subgroup ≥ 30 < 40% of Asian indicated that LDL-C level lowering to 84.6 mg or reducing by 36.0% for 10.9 months of follow up could also lead to regression of CAP, but publication bias was significant. The meta-analysis in subgroup >70 ≤ 100HP mg of Asian with good sensitivity and no publication bias indicated that LDL-C level lowering to 84.0 mg or reducing   (Table 3).
Taken all the results of meta-analysis together, for Western, it was recommended that LDL-C level might be reduced by >45% or to a target level < 69 mg/dL for regressing CAP; for Asian, LDL-C level might be reduced by >36% or to a target level < 84 mg/dL.

Different effects of statins on Westerns and Asians
Whether statins has different effect on Westerns and Asians remains to be settled.
The study by Lee E et al. [34] and MEGA Study [35] suggested statins have different effects on Westerns and Asians. In 2005, Lee E et al. [34] prospectively examined the pharmacokinetics of rosuvastatin in White and Asian individuals living in Singapore, and reported that plasma exposure to rosuvastatin and its metabolites was significantly higher in Chinese, Malay, and Asian-Indian subjects compared with Western subjects living in the same environment. But the mechanisms underlying ethnic differences in rosuvastatin disposition remain to be unearthed [36]. MEGA Study [35] indicated that a small dose of pravastatin that was half the dose administered to western patients, reduced LDL-C by 19-22% (which is lower than that reductions of 23-35% in western patients), but could substantially reduce the risk of coronary heart disease in Japanese.
But two meta-analysis did not demonstrate the difference of rosuvastatin and atorvastatin on Westerns and Asians. The meta-analysis including the 36 trials of pharmacodynamics of rosuvastatin in Western and Asian hypercholesterolemia patients did not confirm that there was significant difference in the exposureresponse relationship for LDL-C reduction between Westerners and Asians [33].The meta-analysis including 22 pharmacokinetic studies also demonstrated no differences in the systemic exposure to atorvastatin between Asian and Caucasian subjects [32].
Our meta-analysis revealed that there were difference of rosuvastatin and atorvastatin in lowering LDL-C and regressing CAP between Westerns and Asians. The meta-analysis of rosuvastatin including 2 trials with 869 Western patients indicated that 40 mg of rosuvastatin daily for 24 months with reducing LDL-C by 49.9% could regress CAP. But the meta-analysis of     Asian patients demonstrated that 18.9 mg of atorvastatin daily for 7.8 months with reducing LDL-C by 40.7% could significantly regress CAP though the result of sensitivity analyses is not as good as that expected (Table 5).
Comparison between Western and Asian in using rosuvastatin and atorvastatin indicated that the dosages of rosuvastatin and atorvastatin in Asian group were significantly lower than those in Western (Table 7).

Study limitation
As with the meta-analysis [3], this study has some limitations. There might be publication bias, difference of the method detected and follow up duration. But those differences in measurements and plaque selection did not affect the change of the target plaque with LDL-C levels. So, it has little effect on homogeneous of studies, and on the relationship between CAP change and LDL-C level. But the trials of single statin on LDL-C and CAP of specific population (for example, 2 trials about atorvastatin on Western with 727 participants or 6 on Asian with 366 in Table 5) were limited, the effect of statin on specific population remains to be investigated. The duration of follow up between Western and Asian was different (Table 4, 6 and 7), and treatment duration might have some effect on CAP regression. But the trials from Asian and Western were respectively meta-analysed in this study. Therefore, the difference in follow-up duration between Asian and Western did not influence the results of the metaanalysis. The CAP regression in short period of statins therapy in Asian suggested that the CAPs in Asian were easily regressed by statins.
This meta-analysis did not investigate the effect of reduction of LDL-C on adverse cardiovascular events because all participants of the included trial must be alive at follow up. But in the Extended-ESTABLISH study, the incidence of adverse cardiovascular events in statin group with CAP regression were reduced to half that seen in the control group [37]. In the Extended JAPAN-ACS study [38], there was no significantly different association of incidence of adverse cardiovascular events with the CAP regression extent, but that greater external elastic membrane volume regression (<−6.56%) had a significantly lower incidence of cumulative events than the lesser suggested the importance of CAP regression in reducing adverse cardiovascular events. A meta-analysis [39] included 7864 CAD patients showed that rates of plaque volume regression were significantly associated with the incidence of MI or revascularization.
Conclusions LDL-C lowering therapy has a different effect on atherosclerotic plaque between Westerns and Asians. This systemic review demonstrated that there is a different effect of LDL-C lowering on CAP between Westerns and Asians. For regressing CAP, Asians need lower dosage of statins or lower intensity LDL-C lowering therapy (by >36%) than Westerns (by 45%). Submit your manuscript at www.biomedcentral.com/submit