Elevated plasma lipoprotein(a) [Lp(a)] levels are an independent and likely causal risk factor for atherosclerotic cardiovascular disease (CVD). However, there are no pharmacological therapies currently approved for targeting elevated Lp(a). Aspirin is one of the most well-established therapies for secondary prevention of CVD and may be of benefit to individuals with elevated plasma Lp(a) in the primary prevention setting specifically.1,2
Plasma Lp(a) levels are largely genetically determined and heritable, meaning Lp(a)-associated genotypes can be used as a proxy to identify high-risk individuals in the absence of measured Lp(a) levels.3 Recently, Lacaze et al2 showed that individuals with elevated plasma Lp(a)-associated genotypes were more likely to benefit from aspirin in primary prevention and that the benefits of aspirin outweighed harms (bleeding risk) in this subgroup of the older population. The findings came from the ASPREE (Aspirin in Reducing Events in the Elderly) randomized trial of daily 100 mg aspirin versus placebo with a median 4.7 years follow-up, where an interaction was observed between the LPA gene variant rs3798220-C and aspirin (P = 0.049) for major adverse cardiovascular events (MACE). The study2 further examined the effect of an Lp(a)-genomic risk score (GRS) comprising 43 variants from within the LPA gene.3,4 This LPA-GRS was found to be associated with increased CVD risk in the placebo group of ASPREE, but the risk was attenuated in the aspirin group. However, no interaction was observed between the LPA-GRS as a continuous variable and aspirin allocation for MACE (P = 0.90).
In the present analysis, we sought to test whether an updated GRS (containing 110 plasma Lp(a)-associated variants, including new variants outside the LPA gene)5 interacted with aspirin in the same analyses of the ASPREE trial. Our hypothesis was that newly associated variants, including those outside the LPA gene, may provide further specificity to identify individuals who benefit from aspirin. We analyzed the same 12,031 unrelated (close relatives with a genetic relationship >0.05 were removed) ASPREE participants of non-Finnish European ancestry aged ≥70 years without prior CVD events at enrollment, using the same methods as described previously2 but testing the new GRS. The new score based on 110 independent (a stringent linkage disequilibrium r2 threshold <0.01 was used) genome-wide significant variants (P < 5 × 10−8) was reported in a recent genome-wide association study of plasma Lp(a) levels.5
Primary analysis involved testing the interaction between the updated GRS as a continuous variable (per SD) and categorical variable (low [Q1], medium [Q2-4], and high [Q5] groups) and aspirin allocation using a Cox proportional hazards model for incidence of MACE and clinically significant bleeding (CSB) events,2 adjusting for age, sex, and the top 3 principal components of genetic ancestry (consistent with previous studies).2,3 In secondary analysis, we tested for interaction between the 110 variants (minor-allele carrying status) and aspirin allocation individually using the same model.
The updated GRS, as a continuous variable, was associated with increased MACE risk in all participants (HR per SD of 1.10; 95% CI: 1.00-1.21; P = 0.043) in the model without interaction. This was consistent with our previous result using the previous 43-variant GRS.2 As a new finding, unlike the older GRS, we observed a significant interaction between the updated GRS as a continuous variable and aspirin allocation for MACE (interaction HR: 1.21 [95% CI: 1.00-1.47]), P = 0.046) (Table 1). The subgroup analyses for aspirin and placebo arms (Table 1) suggested benefit from aspirin therapy for those with higher Lp(a) levels genetically according to the new GRS. The interactions between the new GRS categorical groups and aspirin allocation were with larger effect sizes (interaction HR: 1.32 [95% CI: 0.78-2.21] for medium vs low GRS, and HR: 1.74 [95% CI: 0.95-3.19] for high vs low GRS) but not significant (P > 0.05) (Table 1), possibly due to smaller participant numbers in categorical subgroups, which may reduce power.
Table 1.
Association of Lipoprotein(a) Genomic Risk Score With MACE Risk in the ASPREE Trial
| Lipoprotein(a) GRS 110 Variants | All Participants (N = 12,031) MACE (n = 410) | Aspirin Arm (n = 5,974) MACE (n = 179) | Placebo Arm (n = 6,057) MACE (n = 231) | |
|---|---|---|---|---|
| Continuous | Interaction (GRS ∗aspirin) | 1.21 (1.00-1.47), P = 0.046 | ||
| GRS (per SD) | 0.98 (0.85-1.14), P = 0.804 | 1.19 (1.06-1.34), P = 0.004 | ||
| Categorical | Interaction (medium vs low GRS ∗aspirin) Interaction (high vs low GRS ∗aspirin) |
1.32 (0.78-2.21), P = 0.296 1.74 (0.95-3.19), P = 0.075 |
||
| Low GRS (Q1) Medium GRS (Q2-Q4) High GRS (Q5) |
Reference 0.88 (0.61-1.27), P = 0.487 0.97 (0.62-1.53), P = 0.903 |
Reference 1.17 (0.81-1.69), P = 0.403 1.69 (1.13-2.54), P = 0.011 |
||
Values are HR (95% CI). Bold indicates a significant association (P < 0.05).
ASPREE = Aspirin in Reducing Events in the Elderly; GRS = genomic risk score; MACE = major adverse cardiovascular events; Q = quintile.
In secondary analysis, out of the 110 variants, 6 individual variants—rs9458011 (PLG gene), rs9457648 (LOC101929142), rs60227172 (intergenic), rs11970263 (ZDHHC14), rs78229704 (intergenic), and rs1247347 (LOC102724087)—all outside the LPA gene, were observed with interaction (testing minor-allele carrier status) with aspirin allocation for MACE (P < 0.05). While these results suggest the possibility that single-nucleotide polymorphisms outside the LPA gene may confer aspirin-specific effects, these associations did not remain significant after multiple testing correction, and therefore, should be interpreted with caution. Furthermore, compared to the original 43 variants within the LPA gene,4 the variants outside the LPA gene may have pleiotropic effects, which could introduce bias in the interaction effect. Further studies are warranted to investigate the potential pleiotropic effects of these variants.
We tested for interaction between the GRS and all above genotypes (new GRS or single variants) with aspirin allocation for bleeding (CSB) events, but found no interactions (all P > 0.05, data not shown), also consistent with our previous study.2
In conclusion, this analysis provides further evidence that aspirin may benefit older individuals with elevated Lp(a) genotypes in primary prevention of CVD events and that using an updated GRS containing Lp(a)-associated variants outside of the LPA gene may provide further specificity to detect an aspirin response. Further studies are warranted to replicate these findings in independent aspirin trials.
Footnotes
The ASPREE Biobank is supported by a Flagship cluster grant (including the Commonwealth Scientific and Industrial Research Organisation, Monash University, Menzies Research Institute, Australian National University, University of Melbourne), grants U01AG029824 and U19AG062682 from the National Institute on Aging and the National Cancer Institute at the National Institutes of Health, by grants 334047 and 1127060 from the National Health and Medical Research Council of Australia, and Monash University and the Victorian Cancer Agency. Dr Lacaze is supported by a National Heart Foundation Future Leader Fellowship (102604). Dr McNeil is supported by a National Health and Medical Research Council Leadership Fellowship (IG1173690). Bayer AG provided low-dose aspirin and placebo tablets for the clinical trial but had no other relationship with the work. Dr Tonkin has received research support from Bayer for materials in ASPREE; and has received honoraria for Advisory Board participation or lectures from Amgen, AstraZeneca, Boehringer Ingelheim, Novartis, and Pfizer. Dr Tsimikas is a co-inventor and receives royalties from patents owned by University of California San Diego (UCSD) and is a co-founder and has an equity interest in Oxitope and Kleanthi Diagnostics, and has a dual appointment at UCSD and Ionis Pharmaceuticals; the terms of this arrangement have been reviewed and approved by the UCSD in accordance with its conflict-of-interest policies. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. The authors thank the ASPREE trial staff and participants, and the general practitioners and staff of the medical clinics who cared for the participants.
The authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the Author Center.
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