Why do statins reduce cardiovascular disease more than other lipid modulating therapies?

Insights into Causal Cardiovascular Risk Factors from Mendelian Randomization

PURPOSE OF THE REVIEW

This review summarizes major insights into causal risk factors for cardiovascular disease (CVD) by using Mendelian randomization (MR) to obtain unconfounded estimates, contextualized within its strengths and weaknesses.

RECENT FINDINGS

MR studies have confirmed the role of major CVD risk factors, including alcohol, smoking, adiposity, blood pressure, type 2 diabetes, lipids, and possibly inflammation, but added that the relation with alcohol is likely linear, confirmed the role of diastolic blood pressure, identified apolipoprotein B as the major target lipid, and foreshadowed results of some trials concerning anti-inflammatories. Identifying a healthy diet and the role of early life influences, such as birth weight, has proved more difficult. Use of MR has winnowed empirically driven hypotheses about CVD into a set of genetically validated targets of intervention. Greater inclusion of global diversity in genetic studies and the use of an overarching framework would enable even more informative MR studies.

Investigating sex-specific associations of lipid traits with type 2 diabetes, glycemic traits and sex hormones using Mendelian randomization

BACKGROUND

Low-density lipoprotein (LDL)-cholesterol is positively associated with cardiovascular disease (CVD) and inversely associated with type 2 diabetes, which could detract from lipid modification. Here, we examined whether lipid traits potentially relevant to CVD aetiology, i.e. apolipoprotein B (apoB), triglycerides (TG) and lipoprotein(a) [Lp(a)] exhibited the same associations. We investigated sex-specifically, including the role of sex hormones, because sex disparities exist in lipid profile and type 2 diabetes. We also replicated where possible.

METHODS

We used Mendelian randomization (MR) to examine sex-specific associations of apoB, TG and Lp(a) with type 2 diabetes, HbA1c, fasting insulin, fasting glucose, testosterone and estradiol in the largest relevant sex-specific genome-wide association studies (GWAS) in people of European ancestry and replicated where possible. We also assessed sex-specific associations of liability to type 2 diabetes with apoB, TG and Lp(a).

RESULTS

Genetically predicted apoB and Lp(a) had little association with type 2 diabetes or glycemic traits in women or men. Genetically predicted higher TG was associated with higher type 2 diabetes risk [odds ratio (OR) 1.44 per standard deviation (SD), 95% confidence interval (CI) 1.26 to 1.65], HbA1c and fasting insulin specifically in women. Higher TG was associated with lower testosterone in women and higher testosterone in men, but with lower estradiol in men and women. Genetic liability to type 2 diabetes was associated with higher TG in women, and possibly with lower apoB in men.

CONCLUSIONS

Lipid traits potentially relevant to CVD aetiology do not exhibit contrasting associations with CVD and type 2 diabetes. However, higher TG is associated with higher type 2 diabetes risk and glycemic traits, which in turn further increases TG specifically in women, possibly driven by sex hormones.

Investigating pleiotropic effects of statins on ischemic heart disease in the UK Biobank using Mendelian randomisation

We examined whether specifically statins, of the major lipid modifiers (statins, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors and ezetimibe) have pleiotropic effects on ischemic heart disease (IHD) via testosterone in men or women. As a validation, we similarly assessed whether a drug that unexpectedly likely increases IHD also operates via testosterone. Using previously published genetic instruments we conducted a sex-specific univariable and multivariable Mendelian randomization study in the UK Biobank, including 179918 men with 25410 IHD cases and 212080 women with 12511 IHD cases. Of these three lipid modifiers, only genetically mimicking the effects of statins in men affected testosterone, which partly mediated effects on IHD. Correspondingly, genetically mimicking effects of anakinra on testosterone and IHD presented a reverse pattern to that for statins. These insights may facilitate the development of new interventions for cardiovascular diseases as well as highlighting the importance of sex-specific explanations, investigations, prevention and treatment.

The effect of liver enzymes on body composition: A Mendelian randomization study

Background

Higher alanine transaminase (ALT), indicating poor liver function, is positively associated with diabetes but inversely associated with body mass index (BMI) in Mendelian randomization (MR) studies, suggesting liver function affects muscle mass. To clarify, we assessed the associations of liver enzymes with muscle and fat mass observationally with two-sample MR as a validation.

Methods

In the population-representative “Children of 1997” birth cohort (n = 3,455), we used multivariable linear regression to assess the adjusted associations of ALT and alkaline phosphatase (ALP) at ~17.5 years with muscle mass and body fat percentage observationally. Genetic variants predicting ALT, ALP and gamma glutamyltransferase (GGT) were applied to fat-free and fat mass in the UK Biobank (n = ~331,000) to obtain unconfounded MR estimates.

Results

Observationally, ALT was positively associated with muscle mass (0.11 kg per IU/L, 95% confidence interval (CI) 0.10 to 0.12) and fat percentage (0.15% per IU/L, 95% CI 0.13 to 0.17). ALP was inversely associated with muscle mass (-0.03 kg per IU/L, 95% CI -0.04 to -0.02) and fat percentage (-0.02% per IU/L, 95% CI -0.03 to -0.01). Using MR, ALT was inversely associated with fat-free mass (-0.41 kg per 100% in concentration, 95% CI -0.64 to -0.19) and fat mass (-0.58 kg per 100% in concentration, 95% CI -0.85 to -0.30). ALP and GGT were unclearly associated with fat-free mass or fat mass.

Conclusion

ALT reducing fat-free mass provides a possible pathway for the positive association of ALT with diabetes and suggests a potential target of intervention.

The impact of GDF-15, a biomarker for metformin, on the risk of coronary artery disease, breast and colorectal cancer, and type 2 diabetes and metabolic traits: a Mendelian randomisation study

AIMS/HYPOTHESIS

Growth differentiation factor 15 (GDF-15), a suggested biomarker for metformin use, may explain the potential cardioprotective and anti-cancer properties of metformin. We conducted a Mendelian randomisation study to examine the role of GDF-15 in risk of coronary artery disease (CAD) and breast and colorectal cancer. Secondary analyses included examination of the association of GDF-15 with type 2 diabetes, glycaemic traits, BP, lipids and BMI.

METHODS

We obtained SNPs strongly (p value <5 × 10^-8) predicting GDF-15 from a genome-wide association study (GWAS) (n = 5440) and applied them to genetic studies of CAD (CARDIoGRAMplusC4D 1000 Genomes-based GWAS [n = 184,305]), type 2 diabetes (DIAGRAM [DIAbetes Genetics Replication And Meta-analysis; n = 898,130]), glycaemic traits (MAGIC [the Meta-Analyses of Glucose and Insulin-related traits Consortium; HbA_1c: n = 123,665; fasting glucose: n = 46,186]), BP, breast cancer and colorectal cancer (UK Biobank [n ≤ 401,447]), lipids (GLGC [Global Lipids Genetic Consortium; n ≤ 92,820]) and adiposity (GIANT [Genetic Investigation of ANthropometric Traits Consortium; n = 681,275]). Causal estimates were obtained using inverse variance weighting, taking into account correlations between SNPs. Sensitivity analyses included focusing on the lead SNP (rs888663) and validation for CAD in the UK Biobank and for breast cancer in the Breast Cancer Association Consortium.

RESULTS

Using 5 SNPs, increased GDF-15 was associated with lower CAD (OR 0.93 per SD increase, 95% CI 0.87, 0.99) and breast cancer (OR 0.89 per SD increase, 95% CI 0.82, 0.96), with similar results from lead SNP analysis. However, the associations with CAD (OR 0.99 per SD increase, 95% CI 0.93, 1.04) and breast cancer (OR 0.97 per SD increase, 95% CI 0.94, 1.01) in the validation studies were not as apparent. GDF-15 was not associated with type 2 diabetes, glycaemic traits, CAD risk factors or colorectal cancer.

CONCLUSIONS/INTERPRETATION

There is no convincing evidence that GDF-15 reduces risk of CAD or breast or colorectal cancer. Whether the observed inverse association of metformin use with cancer risk is via other unexplored mechanistic pathways warrants further investigation.

Efficacy and safety of rosuvastatin vs. atorvastatin in lowering LDL cholesterol : A meta-analysis of trials with East Asian populations

BACKGROUND

The VOYAGER meta-analysis reported on the low-density lipoprotein cholesterol (LDL-C)-lowering effect of commonly used statins in Caucasian subjects. As there is limited literature available on the efficacy of statins in Asian populations, the current meta-analysis compared the effects of rosuvastatin and atorvastatin on LDL-C levels in an East Asian population.

METHODS

The MEDLINE, PubMed, Embase, Cochrane Library, and Web of Science databases were searched for randomized controlled trials comparing lipid-lowering effects of rosuvastatin and atorvastatin in an East Asian population. Data on the study design, participant characteristics, and outcomes were extracted. Odds ratios (OR), weighted mean differences (WMD), or standardized mean differences were calculated using the random-effects model.

RESULTS

The meta-analysis comprised 16 randomized controlled trials with 5930 participants. Compared with atorvastatin, patients treated with rosuvastatin had a significant reduction in LDL-C: WMD = -7.15 mg/dl (95% confidence intervals [CI]: -10.71--3.60) mg/dl, p < 0.0001. Meta-regression analyses revealed no significant association between the superior benefits of rosuvastatin and other variables including age, sex, baseline LDL-C level, and follow-up duration. Additionally, the rosuvastatin group of patients, who were treated with half the dose of atorvastatin, achieved a significantly greater reduction in LDL-C levels (WMD = -3.57; 95% CI: -5.40--1.74 mg/dl, p < 0.001). Both rosuvastatin and atorvastatin were well tolerated, with similar incidences of adverse events.

CONCLUSION

Similar to the VOYAGER meta-analysis, which reported a greater efficacy of rosuvastatin in comparison with atorvastatin and simvastatin in Caucasian patients, we found that the efficacy of rosuvastatin was superior to atorvastatin in East Asian patients with hypercholesterolemia.

Therapeutic target discovery using Boolean network attractors: improvements of kali

In a previous article, an algorithm for identifying therapeutic targets in Boolean networks modelling pathological mechanisms was introduced. In the present article, the improvements made on this algorithm, named kali, are described. These improvements are (i) the possibility to work on asynchronous Boolean networks, (ii) a finer assessment of therapeutic targets and (iii) the possibility to use multivalued logic. kali assumes that the attractors of a dynamical system, such as a Boolean network, are associated with the phenotypes of the modelled biological system. Given a logic-based model of pathological mechanisms, kali searches for therapeutic targets able to reduce the reachability of the attractors associated with pathological phenotypes, thus reducing their likeliness. kali is illustrated on an example network and used on a biological case study. The case study is a published logic-based model of bladder tumorigenesis from which kali returns consistent results. However, like any computational tool, kali can predict but cannot replace human expertise: it is a supporting tool for coping with the complexity of biological systems in the field of drug discovery.

Thyroid function and ischemic heart disease: a Mendelian randomization study

To clarify the role of thyroid function in ischemic heart disease (IHD) we assessed IHD risk and risk factors according to genetically predicted thyroid stimulating hormone (TSH), free thyroxine (FT4) and thyroid peroxidase antibody (TPOAb) positivity. Separate-sample instrumental variable analysis with genetic instruments (Mendelian randomization) was used in an extensively genotyped case (n = 64,374)-control (n = 130,681) study, CARDIoGRAMplusC4D. Associations with lipids, diabetes and adiposity were assessed using the Global Lipids Genetics Consortium Results (n = 196,475), the DIAbetes Genetics Replication And Meta-analysis case (n = 34,380)-control (n = 114,981) study, and the Genetic Investigation of ANthropometric Traits (body mass index in 152,893 men and 171,977 women, waist-hip ratio in 93,480 men and 116,741 women). Genetically predicted thyroid function was not associated with IHD (odds ratio (OR) per standard deviation for TSH 1.05, 95% confidence interval (CI) 0.97 to 1.12; for FT4 1.01, 95% CI 0.91 to 1.12; for TPOAb positivity 1.10, 95% CI 0.83 to 1.46) or after Bonferroni correction with risk factors, except for an inverse association of FT4 with low-density lipoprotein-cholesterol. The associations were generally robust to sensitivity analyses using a weighted median method and MR Egger. This novel study provides little indication that TSH, FT4 or TPOAb positivity affects IHD, despite potential effects on its risk factors.

Vascular Endothelial Growth Factor and Ischemic Heart Disease Risk: A Mendelian Randomization Study

BACKGROUND

Vascular endothelial growth factor (VEGF) has angiogenic and possibly proatherosclerotic properties. Observationally it is positively associated with cardiovascular disease, although these observations could be confounded or due to reverse causation. We assessed ischemic heart disease (IHD) risk by genetically predicted VEGF, ie, using Mendelian randomization.

METHODS AND RESULTS

Single nucleotide polymorphisms (SNPs) predicting VEGF level, at genome-wide significance, were applied to the CARDIoGRAMplusC4D 1000 Genomes-based genome-wide association study IHD case (n=60 801)-control (n=123 504) study. We obtained unconfounded estimates using instrumental variable analysis by combining the Wald estimates for each SNP using inverse variance weighting and Mendelian randomization-Egger regression. Based on 9 SNPs independently predicting VEGF (rs1740073 [C6orf223], rs2375981 [KCNV2], rs2639990 [ZADH2], rs4782371 [ZFPM1], rs6921438 [LOC100132354], rs7043199 [VLDLR-AS1], rs10761741 [JMJD1C], rs6993770 [ZFPM2], and rs114694170 [MEF2C]), VEGF was unrelated to IHD (odds ratio 0.99 per log-transformed pg/mL, 95%CI 0.96-1.02) using inverse variance weighting. However, Mendelian randomization-Egger regression suggested an inverse relation of VEGF with IHD (odds ratio 0.95, 95%CI 0.91-0.99), although the association was not evident after excluding the lead SNP (rs6921438) or additionally excluding the pleiotropic SNP (rs6993770).

CONCLUSIONS

Our study does not provide strong evidence for a positive effect of VEGF on IHD but does not rule out the possibility that some specific types of VEGF, for which genetic predictors have not yet been identified, might play a role.

Liver Enzymes and Risk of Ischemic Heart Disease and Type 2 Diabetes Mellitus: A Mendelian Randomization Study

We used Mendelian randomization to estimate the causal effects of the liver enzymes, alanine aminotransferase (ALT), alkaline phosphatase (ALP) and gamma glutamyltransferase (GGT), on diabetes and cardiovascular disease, using genetic variants predicting these liver enzymes at genome wide significance applied to extensively genotyped case-control studies of diabetes (DIAGRAM) and coronary artery disease (CAD)/myocardial infarction (MI) (CARDIoGRAMplusC4D 1000 Genomes). Genetically higher ALT was associated with higher risk of diabetes, odds ratio (OR) 2.99 per 100% change in concentration (95% confidence interval (CI) 1.62 to 5.52) but ALP OR 0.92 (95% CI 0.71 to 1.19) and GGT OR 0.88 (95% CI 0.75 to 1.04) were not. Genetically predicted ALT, ALP and GGT were not clearly associated with CAD/MI (ALT OR 0.74, 95% CI 0.54 to 1.01, ALP OR 0.86, 95% CI 0.64 to 1.16 and GGT OR 1.08, 95% CI 0.97 to 1.19). We confirm observations of ALT increasing the risk of diabetes, but cannot exclude the possibility that higher ALT may protect against CAD/MI. We also cannot exclude the possibility that GGT increases the risk of CAD/MI and reduces the risk of diabetes. Informative explanations for these potentially contradictory associations should be sought.

Birth weight and risk of ischemic heart disease: A Mendelian randomization study

Low birth weight is a risk factor for cardiovascular disease. However, the association could be confounded by many factors. We used Mendelian randomization to clarify the role of birth weight in ischemic heart disease (IHD) and lipids. We used all 7 single nucleotide polymorphisms (SNPs) independently contributing to birth weight at genome wide significance (p < 5 × 10⁻⁸) in separate sample instrumental variable analysis to estimate the effect of birth weight on IHD using the CARDIoGRAMplusC4D 1000 Genomes based GWAS case (n = 60,801)-control (n = 123,504) study and on lipids using GLGC (n = 188,577). Higher genetically predicted birth weight was associated with lower risk of IHD (odds ratio (OR) 0.96 per 100 grams, 95% confidence interval (CI) 0.93 to 0.99), but the association was not robust to sensitivity analyses excluding SNPs related to height or use of weighted median methods. Genetically predicted birth weight was not associated with low density lipoprotein cholesterol or triglycerides, but was associated with lower high density lipoprotein cholesterol (−0.014 standard deviation, 95% CI −0.027 to −0.0005) and the association was more robust to the sensitivity analyses. Our study does not show strong evidence for an effect of birth weight on IHD and lipids.