Pharmacogenetic study of cholesteryl ester transfer protein gene and simvastatin treatment in hypercholesterolaemic subjects

Major Genetic Drivers of Statin Treatment Response in African Populations and Pharmacogenetics of Dyslipidemia Through a One Health Lens

A One Health lens is increasingly significant to address the intertwined challenges in planetary health concerned with the health of humans, nonhuman animals, plants, and ecosystems. A One Health approach can benefit the public health systems in Africa that are overburdened by noncommunicable, infectious, and environmental diseases. Notably, the COVID-19 pandemic revealed the previously overlooked two-fold importance of pharmacogenetics (PGx), for individually tailored treatment of noncommunicable diseases and environmental pathogens. For example, dyslipidemia, a common cardiometabolic risk factor, has been identified as an independent COVID-19 severity risk factor. Observational data suggest that patients with COVID-19 infection receiving lipid-lowering therapy may have better outcomes. However, among African patients, the response to these drugs varies from patient to patient, pointing to the possible contribution of genetic variation in important pharmacogenes. The PGx of lipid-lowering therapies may underlie differences in treatment responses observed among dyslipidemia patients as well as patients comorbid with COVID-19 and dyslipidemia. Genetic variations in APOE, ABCB1, CETP, CYP2C9, CYP3A4, CYP3A5, HMGCR, LDLR, NPC1L1, and SLCO1B1 genes affect the pharmacogenomics of statins, and they have individually been linked to differential responses to dyslipidemia and COVID-19 treatment. African populations are underrepresented in PGx research. This leads to poor accounting of additional diverse genetic variants that could be important in understanding interindividual and between-population variations in therapeutic responses to dyslipidemia and COVID-19. This expert review examines and synthesizes the salient and priority PGx variations, as seen through a One Health lens in Africa, to improve and inform personalized medicine in both dyslipidemia and COVID-19.

Gene-environment interactions due to quantile-specific heritability of triglyceride and VLDL concentrations

"Quantile-dependent expressivity" is a dependence of genetic effects on whether the phenotype (e.g., triglycerides) is high or low relative to its distribution in the population. Quantile-specific offspring-parent regression slopes (β_OP) were estimated by quantile regression for 6227 offspring-parent pairs. Quantile-specific heritability (h²), estimated by 2β_OP/(1 + r_spouse), decreased 0.0047 ± 0.0007 (P = 2.9 × 10^-14) for each one-percent decrement in fasting triglyceride concentrations, i.e., h² ± SE were: 0.428 ± 0.059, 0.230 ± 0.030, 0.111 ± 0.015, 0.050 ± 0.016, and 0.033 ± 0.010 at the 90th, 75th, 50th, 25th, and 10th percentiles of the triglyceride distribution, respectively. Consistent with quantile-dependent expressivity, 11 drug studies report smaller genotype differences at lower (post-treatment) than higher (pre-treatment) triglyceride concentrations. This meant genotype-specific triglyceride changes could not move in parallel when triglycerides were decreased pharmacologically, so that subtracting pre-treatment from post-treatment triglyceride levels necessarily created a greater triglyceride decrease for the genotype with a higher pre-treatment value (purported precision-medicine genetic markers). In addition, sixty-five purported gene-environment interactions were found to be potentially attributable to triglyceride's quantile-dependent expressivity, including gene-adiposity (APOA5, APOB, APOE, GCKR, IRS-1, LPL, MTHFR, PCSK9, PNPLA3, PPARγ2), gene-exercise (APOA1, APOA2, LPL), gene-diet (APOA5, APOE, INSIG2, LPL, MYB, NXPH1, PER2, TNFA), gene-alcohol (ALDH2, APOA5, APOC3, CETP, LPL), gene-smoking (APOC3, CYBA, LPL, USF1), gene-pregnancy (LPL), and gene-insulin resistance interactions (APOE, LPL).

Meta-analysis of genome-wide association studies of HDL cholesterol response to statins

BACKGROUND

In addition to lowering low density lipoprotein cholesterol (LDL-C), statin therapy also raises high density lipoprotein cholesterol (HDL-C) levels. Inter-individual variation in HDL-C response to statins may be partially explained by genetic variation.

METHODS AND RESULTS

We performed a meta-analysis of genome-wide association studies (GWAS) to identify variants with an effect on statin-induced high density lipoprotein cholesterol (HDL-C) changes. The 123 most promising signals with p<1×10-4 from the 16 769 statin-treated participants in the first analysis stage were followed up in an independent group of 10 951 statin-treated individuals, providing a total sample size of 27 720 individuals. The only associations of genome-wide significance (p<5×10-8) were between minor alleles at the CETP locus and greater HDL-C response to statin treatment.

CONCLUSIONS

Based on results from this study that included a relatively large sample size, we suggest that CETP may be the only detectable locus with common genetic variants that influence HDL-C response to statins substantially in individuals of European descent. Although CETP is known to be associated with HDL-C, we provide evidence that this pharmacogenetic effect is independent of its association with baseline HDL-C levels.

Seventeen years of statin pharmacogenetics: a systematic review

AIM

We evaluated the evidence of pharmacogenetic associations with statins in a systematic review.

METHODS

Two separate outcomes were considered of interest: modification of low-density lipoprotein cholesterol (LDL-C) response and modification of risk for cardiovascular events.

RESULTS

In candidate gene studies, 141 loci were claimed to be associated with LDL-C response. Only 5% of these associations were positively replicated. In addition, six genome-wide association studies of LDL-C response identified common SNPs in APOE, LPA, SLCO1B1, SORT1 and ABCG2 at genome-wide significance. None of the investigated SNPs consistently affected the risk reduction for cardiovascular events.

CONCLUSION

Only five genetic loci were consistently associated with LDL-C response. However, as effect sizes are modest, there is no evidence for the value of genetic testing in clinical practice.

Impact of CYP3A5 Gene Polymorphism on Efficacy of Simvastatin

Background: One of the promises of human genetics is individualized therapy. Therefore, we evaluated the impact of CYP3A5 gene polymorphism on the effectiveness of simvastatin (a HMG-CoA reductase inhibitor). Methods: Patients (n = 191) with hypercholesterolemia were treated with simvastatin for at least 6 months and were genotyped for the CYP3A5 polymorphism. Results: The frequency of CYP3A5 polymorphism was 0.5% for WT (wild-type), 15.6% for HT (heterozygous, expressors) and 83.9% for HM (homozygous, non-expressors). Differences in lipid profile before and after dose-response of simvastatin treatment were described as % difference {[(variable after-variable before)/variable before]*100}. There was a trend towards the decrease of low density lipoprotein cholesterol (LDL-C) in HT individuals who had a -35.2% reduction with a dose of 20 mg simvastatin and HM individuals who had a slightly higher decrease (-37.5%) despite the lower dose of simvastatin (10 mg, p = 0.07). Furthermore, HT genotype individuals had significantly higher than expected (6-8%) LDL-C % difference between 20 and 40 mg of simvastatin (-35.2 vs -49.2%, p = 0.037). In individuals with HM genotype a significant LDL-C % difference was found between 10 and 40 mg of simvastatin (-37.5 vs -48.4%, p = 0.023). Conclusion: The individuals with HM polymorphism display a trend towards higher LDL-C reductions compared with HT polymorphism. Within the same genotype, differences between doses were also observed. These findings need to be confirmed in larger studies.

Pharmacogenomics of high-density lipoprotein-cholesterol-raising therapies

High levels of HDL cholesterol (HDL-C) have traditionally been linked to lower incidence of cardiovascular disease, prompting the search for effective and safe HDL-C raising pharmaceutical agents. Although drugs such as niacin and fibrates represent established therapeutic approaches, HDL-C response to such therapies is variable and heritable, suggesting a role for pharmacogenomic determinants. Multiple genetic polymorphisms, located primarily in genes encoding lipoproteins, cholesteryl ester transfer protein, transporters and CYP450 proteins have been shown to associate with HDL-C drug response in vitro and in epidemiologic studies. However, few of the pharmacogenomic findings have been independently validated, precluding the development of clinical tools that can be used to predict HDL-C response and leaving the goal of personalized medicine to future efforts.

Cholesteryl Ester Transfer Protein and ATP-Binding Cassette Transporter A1 Genotype Alter the Atorvastatin and Simvastatin Efficacy

We compared the efficacy of atorvastatin with simvastatin according to cholesteryl ester transfer protein (CETP) and adenosine triphosphate-binding cassette transporter A1 ( ABCA1) genes. Patients treated with atorvastatin (n = 254) or simvastatin (n = 332) were genotyped for CETP (TaqIB and I405V) and ABCA1 (R219K) genetic variants. For genotype B1B2, atorvastatin compared with simvastatin treatment resulted in a greater decrease in total cholesterol (35.4% vs 31.6%, P = .035) and a lower increase in high-density lipoprotein cholesterol (2% vs 8%, P = .05). For genotype B2B2, atorvastatin compared with simvastatin treatment resulted in a lower decrease in low-density lipoprotein cholesterol (31.85 vs 42%, P = .029). For genotypes RR and KK, atorvastatin compared with simvastatin treatment resulted in a greater decrease of triglycerides (27% vs 17% and 35% vs 15%, respectively; P = .02 for all comparisons). The TaqIB and R219K (opposite to I405V) gene polymorphisms seem to modify the response to lipid-lowering therapy with simvastatin or atorvastatin treatment.

Ideal lipid profile and genes for an extended life span

PURPOSE OF REVIEW

The world population is aging and a rapid increase is being seen in the very elderly (aged >80 years). Cholesterol levels in general rise with age and high cholesterol has been associated with extreme longevity. The relationship between lipids and cardiovascular events in the extreme elderly is unclear.

RECENT FINDINGS

A number of genetic factors associated with lipid metabolism have also been described as having potential antiaging roles, including the genes encoding lipoprotein-associated factors - apolipoprotein E and cholesterol ester transfer protein; adipose tissue metabolism - adiponectin, leptin, glycaemia; and blood pressure - angiotensinogen. Clinical trials of lipid-lowering therapies have recruited subgroups of moderately elderly patients, but only the Prospective Study of Pravastatin in the Elderly at Risk (PROSPER) trial specifically recruited an elderly population. There is no direct equivalent of the Hypertension in the Very Elderly trial (HYVET) study of antihypertensive patients in the extreme elderly. No heterogeneity has been seen with the effects of statin therapy in the elderly compared with younger age groups on classical cardiovascular endpoints of coronary heart disease and stroke.

SUMMARY

The optimal cholesterol target, long-term tolerability and the specific effects of statins on other vascular-associated diseases of aging, for example arterial aneurysms, microvascular renal and cerebral disease (dementias), remain to be determined.

Cholesteryl ester transfer protein gene and effectiveness of lipid lowering of atorvastatin

Cholesteryl ester transfer protein (CETP) plays a key role in lipid metabolism. Thus, variations in the CETP gene may be clinically relevant. Newly started atorvastatin users (n=212) were genotyped for CETP genetic variants (TaqIB and I405V). Homozygotes for B1 allele of TaqIB polymorphism had lower plasma high density lipoprotein cholesterol (HDL-C) compared with B1B2 or B2B2 genotypes (p=0.03, for each). Homozygotes for I allele of I405V polymorphism had lower plasma HDL-C compared with IV or VV genotypes (p=0.001, for each). In the whole population, the B1 carriers increased HDL-C levels by 4% after atorvastatin treatment, compared with B2 carriers, where a 4% decrease occurred (p=0.03). Also homozygotes for B1 allele decreased triglyceride levels to a lesser, though not significant, degree compared to B1B2 or B2B2 genotypes. CETP TaqIB or I405V polymorphisms seem to modify the lipid lowering response to atorvastatin treatment. This knowledge may help design more effective hypolipidaemic treatment.

Common variants of HMGCR, CETP, APOAI, ABCB1, CYP3A4, and CYP7A1 genes as predictors of lipid-lowering response to atorvastatin therapy

There is interindividual variation in lipid-lowering response to statins. The objective of this study was to investigate whether common variation in genes involved in lipid and statin metabolism modify the effect of statins on serum total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), and high-density lipoprotein-cholesterol concentration in coronary artery disease (CAD) patients. We studied the association between 18 single-nucleotide polymorphisms (SNPs) in six genes (HMGCR, CETP, APOAI, ABCB1, CYP3A4, CYP7A1) in response to atorvastatin therapy (20 mg/day) in 265 newly diagnosed CAD patients using multivariable adjusted general linear regression. Variant alleles of ABCB1 (-41A/G), HMGCR SNP29 G/T, rs5908A/G, rs12916C/T, and CYP7A1-204A/C polymorphisms were significantly associated with attenuated LDL-C reduction and variant alleles of CETP TaqI, -629C/A, and APOAI PstI polymorphisms were associated with higher increase in high-density lipoprotein-cholesterol. A three-loci interaction model consisting of CYP7A1rs892871AA/APOAIPstIP1P1/HMGCR rs12916CT was a better predictor for LDL-C lowering, when compared with single polymorphisms analysis on statin response. Variant genotypes of APOAI -2500C/T, CETP 405I/V, and ABCB1 3435C/T showed higher risk of myocardial infarction events (p < 0.05) in a 1-year follow-up of CAD patients. These results suggest that SNPs in lipid and statin pathway genes are associated with reduced LDL-C lowering by statins and identify individuals who may be resistant to maximal LDL-C lowering by statins.

Lack of association between the cholesteryl ester transfer protein gene--TaqIB polymorphism and coronary restenosis following percutaneous transluminal coronary angioplasty and stenting: a pilot study

BACKGROUND

The most widely studied variation at the cholesteryl ester transfer protein (CETP) gene locus is a silent base change called the Thermobius aquaticus IB (TaqIB) polymorphism. TaqIB has been shown to affect levels/activity of CETP, plasma levels of high-density lipoprotein cholesterol (HDL-C), and to contribute to the risk of developing atherosclerosis and coronary heart disease (CHD). Ongoing studies are investigating possible associations between CETP gene polymorphisms and the development of coronary restenosis following percutaneous transluminal coronary angioplasty (PTCA) and stenting.

METHODS AND RESULTS

The primary objective of the present study was to investigate the frequency of TaqIB-polymorphism, and a possible association with post-PTCA coronary restenosis, in 204 Greek patients who had undergone PTCA and stenting. As a secondary objective, the analysis was extended to explore possible interacting or additive effects by various CHD risk factors, and a deletion in the alpha(2B)-adrenergic receptor gene. The frequency of TaqIB was 54%, similar to the frequency of the polymorphism in a group of 35 healthy controls.

CONCLUSIONS

The results from this study do not indicate that the TaqIB variation at the CETP gene locus is a significant predictor for assessing the risk of developing coronary restenosis following PTCA and stenting. This result was not affected when considering any one of the additionally studied factors.

Common variation in the CETP gene and the implications for cardiovascular disease and its treatment: an updated analysis

Human plasma contains cholesteryl ester transfer protein (CETP) which, besides other functions, enables the transfer of cholesteryl esters in plasma from high-density lipoproteins (HDL) towards triglyceride-rich lipoproteins, thereby contributing to lower HDL cholesterol. Variations in the CETP gene, including the intronic TaqIB polymorphism (rs708272), are common in the population. Although HDL cholesterol is approximately 10% higher in TaqIB B2B2 than in B1B1 carriers, the association of this polymorphism with cardiovascular disease has not been unequivocally established. We present an updated pooled analysis concerning the association of cardiovascular disease with the TaqIB polymorphism, including only studies that predominantly comprise Caucasian subjects. The distribution of this CETP genotype was observed to be different in population-based studies (n = 10,526) compared with studies in populations selected by high cardiovascular risk (n = 10,947), with B2B2 carriers being less frequent among cases from high-risk populations compared with cases from population-based studies (p = 0.0009 for the difference in genotype distribution). In population-based studies, the odds ratio (OR) for cardiovascular disease was found to be 1.45 (95% CI: 1.07–1.95) in B2B2 compared with B1B1 carriers, contrasting the lower OR of 0.84 (95% CI: 0.74–0.96) in B2B2 versus B1B1 carriers from high-risk populations. Thus, it is possible that in the general population, the B2 allele is associated with higher cardiovascular risk, despite higher HDL cholesterol. Our analysis agrees with the contention that selection towards a lower frequency of B2B2 homozygotes may have occurred in selected populations, which would result in a apparently protective effect of the B2 allele when determined in high-risk populations. We also evaluated whether the TaqIB polymorphism would predict efficacy of lipid-lowering treatment with respect to plasma lipids and cardiovascular outcome, but the results of published studies were contradictory. Likewise, no definite conclusion can be made at present concerning the effect of this CETP polymorphism on the lipid response to diet intervention.