Genetic invalidation of Lp-PLA2 as a therapeutic target: Large-scale study of five functional Lp-PLA2-lowering alleles

Abstract

Aims Darapladib, a potent inhibitor of lipoprotein-associated phospholipase A₂ (Lp-PLA₂), has not reduced risk of cardiovascular disease outcomes in recent randomized trials. We aimed to test whether Lp-PLA₂ enzyme activity is causally relevant to coronary heart disease. Methods In 72,657 patients with coronary heart disease and 110,218 controls in 23 epidemiological studies, we genotyped five functional variants: four rare loss-of-function mutations (c.109+2T > C (rs142974898), Arg82His (rs144983904), Val279Phe (rs76863441), Gln287Ter (rs140020965)) and one common modest-impact variant (Val379Ala (rs1051931)) in PLA2G7, the gene encoding Lp-PLA₂. We supplemented de-novo genotyping with information on a further 45,823 coronary heart disease patients and 88,680 controls in publicly available databases and other previous studies. We conducted a systematic review of randomized trials to compare effects of darapladib treatment on soluble Lp-PLA₂ activity, conventional cardiovascular risk factors, and coronary heart disease risk with corresponding effects of Lp-PLA₂-lowering alleles. Results Lp-PLA₂ activity was decreased by 64% ( p = 2.4 × 10^-25) with carriage of any of the four loss-of-function variants, by 45% ( p < 10^-300) for every allele inherited at Val279Phe, and by 2.7% ( p = 1.9 × 10^-12) for every allele inherited at Val379Ala. Darapladib 160 mg once-daily reduced Lp-PLA₂ activity by 65% ( p < 10^-300). Causal risk ratios for coronary heart disease per 65% lower Lp-PLA₂ activity were: 0.95 (0.88-1.03) with Val279Phe; 0.92 (0.74-1.16) with carriage of any loss-of-function variant; 1.01 (0.68-1.51) with Val379Ala; and 0.95 (0.89-1.02) with darapladib treatment. Conclusions In a large-scale human genetic study, none of a series of Lp-PLA₂-lowering alleles was related to coronary heart disease risk, suggesting that Lp-PLA₂ is unlikely to be a causal risk factor.

Keywords: Human genetics; coronary heart disease; darapladib; lipoprotein-associated phospholipase A2; target validation.

Figure 1.

Summary of study design. (a) Flow chart of study design. (b) Exonic structure of the PLA2G7 gene and location of variants used in this study. ExAc: Exome Aggregation consortium; NHLBI ESP: National Heart Lung and Blood Institute Exome Sequencing Project; Lp-PLA₂: lipoprotein-associated phospholipase A₂; RCT: randomized controlled trial; UniProt/Swissprot: manually annotated and reviewed section of the Universal Protein resource database.

Figure 2.

Mean per allele differences in Lp-PLA₂ activity and cardiovascular risk factor levels by Lp-PLA₂-lowering alleles or with darapladib 160 mg daily. To enable comparison of the magnitude of associations across several different markers, analyses were undertaken with standardized units of measurement for each marker. Associations are presented as per allele change in the biomarker expressed as standard deviations. Numbers of participants are provided in Table 1. Details of contributing studies are provided in Supplementary Material Tables 2 and 3 online. *Carriage of any of the four loss-of-function variants c.109+2T>C, Arg82His, Val279Phe, Gln287Ter. BMI: body-mass index; CI: confidence interval; DBP: diastolic blood pressure; eGFR: estimated glomerular filtration rate; HDL-c: high-density lipoprotein cholesterol; LDL: low-density lipoprotein cholesterol; LoF: loss-of-function; Lp-PLA₂: lipoprotein associated phospholipase A₂; SBP: systolic blood pressure

Figure 3.

Association of Lp-PLA₂-lowering alleles with Lp-PLA₂ activity and CHD risk. Spectrum of functional alleles in PLA2G7 and effects on Lp-PLA2 activity (red estimates) and coronary heart disease risk (black estimates); *Carriage of any of the four loss-of-function variants c.109+2T>C, Arg82His, Val279Phe, Gln287Ter. ^†One study did not provide tabular data to enable calculation of CHD odds ratios in heterozygotes or homozygotes. Hence, numbers are less than those presented for the per allele analysis in Table 2. CHD: coronary heart disease; CI: confidence interval; LoF: loss-of-function; Lp-PLA₂: lipoprotein associated phospholipase A₂.