Similar findings in the Women’s Health Study
Dr. Lacaze and colleagues point out that similar results have also been seen in another large aspirin primary prevention study – the Women’s Health Study (WHS).
The WHS compared aspirin 100 mg every other day with placebo in initially healthy younger women. Previously reported results showed that women carrying the rs3798220-C variant, associated with highly elevated Lp(a) levels, had a twofold higher risk of cardiovascular events than noncarrier women in the placebo group, but this risk was reduced in the aspirin group. And there was no increased risk of bleeding in women with elevated Lp(a).
“These results, in the absence of any other randomized controlled trial evidence or approved therapy for treating Lp(a)-associated risk, have been used by some physicians as justification for prescribing aspirin in patients with elevated Lp(a),” Dr. Lacaze and colleagues note.
“In the present study of the ASPREE trial population, our results were consistent with the WHS analysis, despite randomizing older individuals (both men and women),” they add.
They say this validation of the WHS result provides evidence that a very high-risk subgroup of individuals with highly elevated Lp(a) – those carrying the rs3798220-C allele – may benefit from low-dose aspirin for the primary prevention of cardiovascular events. Further, the benefits in this subgroup specifically may outweigh any bleeding risk.
But they point out that rs3798220-C carriers comprise only a small portion of all individuals with elevated Lp(a) in the general population, while the polygenic LPA-GRS explains about 60% of the variation in directly measured plasma Lp(a) levels and has the potential advantage of being able to identify a larger group of individuals at increased risk.
The researchers note, however, that it is not clear to what extent the LPA-GRS results add further evidence to suggest that individuals with elevated Lp(a), beyond rs3798220-C carriers, may be more likely to benefit from aspirin.
“If the benefit of aspirin extends beyond very high-risk rs3798220-C carriers alone, to the broader 20%-30% of individuals with elevated Lp(a), the potential utility of aspirin for the primary prevention of cardiovascular events would increase substantially,” they say.
‘Very high clinical relevance’
In an accompanying editorial, Ana Devesa, MD, Borja Ibanez, MD, PhD, and Valentin Fuster, MD, PhD, The National Center for Cardiovascular Research, Madrid, say that: “[Dr.] Lacaze et al. are to be congratulated for a study of very high clinical relevance that represents a first indication for primary prevention for patients at high cardiovascular risk.”
They explain that the pathogenic mechanism of Lp(a) is believed to be a combination of prothrombotic and proatherogenic effects, and the current findings support the hypothesis that the prothrombotic mechanism of Lp(a) is mediated by platelet aggregation.
This would explain the occurrence of thrombotic events in the presence of atherosclerosis in that elevated Lp(a) levels may induce platelet adhesion and aggregation to the activated atherosclerotic plaque, thus enhancing the atherothrombotic process. Moreover, activated platelets release several mediators that result in cell adhesion and attraction of chemokines and proinflammatory cytokines, driving an inflammatory response and mediating atherosclerosis progression, they add.
The editorialists highlight the limitations of the study already acknowledged by the authors: The analysis used genotypes rather than elevated Lp(a) levels and included only those of European ancestry, meaning the results are difficult to extrapolate to other populations.
“The next steps in clinical practice should be defined, and there are still questions to be answered,” they conclude. “Will every patient benefit from antithrombotic therapies? Should all patients who have elevated Lp(a) levels be treated with aspirin?”
The ASPREE Biobank is supported by grants from the Commonwealth Scientific and Industrial Research Organisation, Monash University, Menzies Research Institute, Australian National University, University of Melbourne, National Institutes of Health, National Health and Medical Research Council of Australia, and the Victorian Cancer Agency. Dr. Lacaze is supported by a National Heart Foundation Future Leader Fellowship.
A version of this article first appeared on Medscape.com.