Endogenous androgen exposures and ischemic heart disease, a separate sample Mendelian randomization study

Appraising the Causal Role of Risk Factors in Coronary Artery Disease and Stroke: A Systematic Review of Mendelian Randomization Studies

BACKGROUND Mendelian randomization (MR) offers a powerful approach to study potential causal associations between exposures and health outcomes by using genetic variants associated with an exposure as instrumental variables. In this systematic review, we aimed to summarize previous MR studies and to evaluate the evidence for causality for a broad range of exposures in relation to coronary artery disease and stroke. METHODS AND RESULTS MR studies investigating the association of any genetically predicted exposure with coronary artery disease or stroke were identified. Studies were classified into 4 categories built on the significance of the main MR analysis results and its concordance with sensitivity analyses, namely, robust, probable, suggestive, and insufficient. Studies reporting associations that did not perform any sensitivity analysis were classified as nonevaluable. We identified 2725 associations eligible for evaluation, examining 535 distinct exposures. Of them, 141 were classified as robust, 353 as probable, 110 as suggestive, and 926 had insufficient evidence. The most robust associations were observed for anthropometric traits, lipids, and lipoproteins and type 2 diabetes with coronary artery; disease and clinical measurements with coronary artery disease and stroke; and thrombotic factors with stroke. CONCLUSIONS Despite the large number of studies that have been conducted, only a limited number of associations were supported by robust evidence. Approximately half of the studies reporting associations presented an MR sensitivity analysis along with the main analysis that further supported the causality of associations. Future research should focus on more thorough assessments of sensitivity MR analyses and further assessments of mediation effects or nonlinearity of associations.

L-carnitine, a friend or foe for cardiovascular disease? A Mendelian randomization study

BACKGROUND

L-carnitine is emerging as an item of interest for cardiovascular disease (CVD) prevention and treatment, but controversy exists. To examine the effectiveness and safety of L-carnitine, we assessed how genetically different levels of L-carnitine are associated with CVD risk and its risk factors. Given higher CVD incidence and L-carnitine in men, we also examined sex-specific associations.

METHODS

We used Mendelian randomization to obtain unconfounded estimates. Specifically, we used genetic variants to predict L-carnitine, and obtained their associations with coronary artery disease (CAD), ischemic stroke, heart failure, and atrial fibrillation, as well as CVD risk factors (type 2 diabetes, glucose, HbA1c, insulin, lipid profile, blood pressure and body mass index) in large consortia and established cohorts, as well as sex-specific association in the UK Biobank. We obtained the Wald estimates (genetic association with CVD and its risk factors divided by the genetic association with L-carnitine) and combined them using inverse variance weighting. In sensitivity analysis, we used different analysis methods robust to pleiotropy and replicated using an L-carnitine isoform, acetyl-carnitine.

RESULTS

Genetically predicted L-carnitine was nominally associated with higher risk of CAD overall (OR 1.07 per standard deviation (SD) increase in L-carnitine, 95% CI 1.02 to 1.11) and in men (OR 1.09, 95% CI 1.02 to 1.16) but had a null association in women (OR 1.00, 95% CI 0.92 to 1.09). These associations were also robust to different methods and evident for acetyl-carnitine.

CONCLUSIONS

Our findings do not support a beneficial association of L-carnitine with CVD and its risk factors but suggest potential harm. L-carnitine may also exert a sex-specific role in CAD. Consideration of the possible sex disparity and exploration of the underlying pathways would be worthwhile.

Menopause and cardiometabolic diseases: What we (don't) know and why it matters

This narrative review discusses the current understanding, knowledge gaps and challenges in expanding our knowledge of the association between menopause and the reproductive aging process and cardiometabolic disease (CMD) in women, with a focus on type 2 diabetes and cardiovascular disease. The physiological changes that occur at different stages of the reproductive life span, as well as type of menopause and timing, are factors widely associated with CMD risk; however, the underlying mechanisms remain either unclear or insufficiently studied. Decreased ovarian estrogen production and relative androgen excess around menopause onset are the most studied factors linking menopause and cardiometabolic health; nevertheless, the evidence is not persuasive and other hypotheses might explain the changes in CMD risk during menopausal transition. In this context, hormone therapy has been widely adopted in the treatment and prevention of CMD, although uncertainty regarding its cardiometabolic effects has raised the need to optimize therapeutic modalities. Mechanisms such as the "iron overload theory" and new "omics" platforms could provide new insights into potential pathways underlying the association between menopause and cardiometabolic health, such as the DNA damage response. Although it has been widely reported that environmental and lifestyle factors affect both menopause and cardiometabolic health, there is little evidence on the role of these exposures in menopause-associated CMD risk.

The role of cortisol in ischemic heart disease, ischemic stroke, type 2 diabetes, and cardiovascular disease risk factors: a bi-directional Mendelian randomization study

BACKGROUND

Cortisol, a steroid hormone frequently used as a biomarker of stress, is associated with cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM). To clarify whether cortisol causes these outcomes, we assessed the role of cortisol in ischemic heart disease (IHD), ischemic stroke, T2DM, and CVD risk factors using a bi-directional Mendelian randomization (MR) study.

METHODS

Single nucleotide polymorphisms (SNPs) strongly (P < 5 × 10-6) and independently (r2 < 0.001) predicting cortisol were obtained from the CORtisol NETwork (CORNET) consortium (n = 12,597) and two metabolomics genome-wide association studies (GWAS) (n = 7824 and n = 2049). They were applied to GWAS of the primary outcomes (IHD, ischemic stroke and T2DM) and secondary outcomes (adiposity, glycemic traits, blood pressure and lipids) to obtain estimates using inverse variance weighting, with weighted median, MR-Egger, and MR-PRESSO as sensitivity analyses. Conversely, SNPs predicting IHD, ischemic stroke, and T2DM were applied to the cortisol GWAS.

RESULTS

Genetically predicted cortisol (based on 6 SNPs from CORNET; F-statistic = 28.3) was not associated with IHD (odds ratio (OR) 0.98 per 1 unit increase in log-transformed cortisol, 95% confidence interval (CI) 0.93-1.03), ischemic stroke (0.99, 95% CI 0.91-1.08), T2DM (1.00, 95% CI 0.96-1.04), or CVD risk factors. Genetically predicted IHD, ischemic stroke, and T2DM were not associated with cortisol.

CONCLUSIONS

Contrary to observational studies, genetically predicted cortisol was unrelated to IHD, ischemic stroke, T2DM, or CVD risk factors, or vice versa. Our MR results find no evidence that cortisol plays a role in cardiovascular risk, casting doubts on the cortisol-related pathway, although replication is warranted.

Anti-Müllerian Hormone Levels and Cardiometabolic Disturbances by Weight Status Among Men in the 1999 to 2004 National Health and Nutrition Examination Survey

Context

Serum anti-Müllerian hormone level (AMH) and body mass index may be jointly associated with cardiometabolic risk.

Objectives

Examine the contribution of AMH to cardiometabolic disturbances by weight status among US adult men.

Design

Cross-sectional analysis using data from the 1999 to 2004 waves of the National Health and Nutrition Examination Survey.

Setting

Multistage probability sampling of the noninstitutionalized US population.

Participants

US men aged ≥18 years. Final analytic sample sizes ranged from 517 to 1063 participants.

Main Outcome and Exposure Measures

Cardiometabolic disturbances (metabolic syndrome and its components, insulin resistance, diabetes, and chronic inflammation) and AMH were obtained from trained staff and nurses in a mobile examination center or during in-home visits.

Results

AMH was directly associated with insulin resistance among obese men [OR 1.08 (95% CI 1.00, 1.15); P = 0.046; N = 146], whereas AMH was inversely associated with waist circumference (WC) among obese men [OR 0.95 (95% CI 0.91, 0.99); P = 0.049; N = 146]. An inverse relationship was also observed between categorical AMH and diabetes status [medium vs low AMH; OR 0.19 (95% CI 0.043, 0.84); P = 0.030; N = 145] among obese men, with a strong inverse relationship also detected among overweight men [high vs low AMH; OR 0.011 (95% CI 0.0004, 0.27); P = 0.007; N = 193]. An inverse relationship between continuous AMH and diabetes [OR 0.75 (95% CI: 0.59, 0.93); P = 0.011; N = 193] was also detected among overweight men.

Conclusions

AMH was associated with specific cardiometabolic risk factors, including WC, diabetes status, and insulin resistance, in overweight and obese US men.

Benefits and risks of testosterone therapy in older men

Adult-onset hypogonadism is used to define androgen deficiency and its associated symptoms commonly occurring in middle-aged and elderly men, who are unable to mount an adequate compensatory gonadotropin response but may also have an element of testicular failure. It often occurs in relation with chronic metabolic conditions such as diabetes and the metabolic syndrome. There is a growing demand from elderly men for testosterone therapy. The physician should therefore be well-informed so as the patient can make an informed decision. Indeed, testosterone therapy in older men has been a matter of debate, especially with regard to its impact on cardiovascular events and mortality. Not all studies have reported consistent results regarding its effect on diabetes, obesity and the metabolic syndrome. In contrast, it appears to improve sexual, physical function and bone density and it does not appear to increase the risk of prostate cancer; however, it increases hematocrit and hemoglobin levels. Therefore, testosterone therapy might provide significant beneficial effects in older symptomatic hypogonadal men; treatment should be individualized, and comorbidities addressed. Further research is required into its long-term effects.

Genetic predictors of testosterone and their associations with cardiovascular disease and risk factors: A Mendelian randomization investigation

BACKGROUND

Testosterone supplementation has been linked to increased cardiovascular disease risk in some observational studies. The causal role of testosterone can be investigated using a Mendelian randomization approach.

METHODS AND RESULTS

We assessed genetic associations of variants in two gene regions (SHBG and JMJD1C) with several cardiovascular risk factors (lipids, adiponectin, blood pressure, anthropometric traits) plus male pattern baldness, including control outcomes and potential mediators. We assessed genetic associations with coronary artery disease (CAD) risk in the CARDIoGRAMplusC4D consortium (171,191 individuals including 60,801 cases), and associations with CAD and ischaemic stroke risk in the UK Biobank (367,643 individuals including 25,352 CAD cases and 3650 ischaemic stroke cases). Genetic predictors of increased serum testosterone were associated with lipids, blood pressure, and height. There was some evidence of an association with risk of CAD (SHBG gene region: odds ratio (OR) 0.95 per 1 unit increase in log-transformed testosterone [95% confidence interval: 0.81-1.12, p = 0.55]; JMJD1C gene region: OR 1.24 [1.01-1.51, p = 0.04]) and ischaemic stroke both overall (SHBG: OR 1.05 [0.64, 1.73, p = 0.83]; JMJD1C: OR 2.52 [1.33, 4.77, p = 0.005]) and in men. However, associations with some control outcomes were in the opposite direction to that expected.

CONCLUSIONS

Sex hormone-related mechanisms appear to be relevant to cardiovascular risk factors and for stroke (particularly for men). However, the extent that these findings are specifically informative about endogenous testosterone or testosterone supplementation is unclear. These findings underline a fundamental limitation for the use of Mendelian randomization where biological knowledge about the function of genetic variants is uncertain.

Testosterone treatment in older men: clinical implications and unresolved questions from the Testosterone Trials

A decrease in the concentration of circulating testosterone in many older men is a biomarker and possibly a rectifiable contributing factor to ill health. Low circulating testosterone concentration has been associated with cardiovascular disease, reduced cognition, fracture risk, and anaemia. However, randomised placebo-controlled trials are essential to clarify the benefits and possible risks of testosterone treatment in men without hypothalamic, pituitary, or testicular disease. The Testosterone Trials (T-Trials) were a coordinated set of trials that, following a screening-to-enrolment ratio of 65:1, randomly assigned 790 men aged 65 years or older who had a baseline testosterone concentration of less than 9·54 nmol/L and symptoms consistent with hypogonadism, but no recognisable hypothalamic-pituitary-testicular axis pathology, to daily transdermal testosterone or placebo for 12 months. In the main trial, testosterone treatment resulted in a modest benefit for sexual function, whereas the other primary outcomes of vitality and physical function were not met. Data from concomitant substudies raised a possible concern over changes in coronary plaque volume, showed a neutral effect on memory and other cognitive functions, and revealed improvements in volumetric bone mineral density and anaemia. Although insufficient to alter the existing clinical equipoise, the T-Trials provided substantial new data on organ-specific outcomes for testosterone treatment in older men. Further clinical trials are necessary to determine whether testosterone treatment will translate into patient-valued health outcomes and to clarify effects on the cardiovascular system.

Testosterone and All-Cause Mortality in Older Men: The Role of Metabolic Syndrome

Previous studies have shown controversial results about the role of testosterone in all-cause mortality in elderly men. We hypothesized that metabolic syndrome (MetS) could partly explain this discrepancy. We therefore examined the association of all-cause mortality with total and bioavailable testosterone, taking into account the MetS. We used data from the Three-City Cohort (3C) study with 12-year follow-up. The 3C study included 3650 men aged >65 years in three French cities. Hormone was measured in a random subsample of 444 men, and MetS was determined as stated by the International Diabetes Federation criteria. We used inverse-probability-weighted Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs). Of 444 men included in the analysis, 106 (23.9%) had MetS at baseline, and 166 died over the follow-up. There was a significant interaction between testosterone level and MetS for all-cause mortality (P = 0.002 and P = 0.008 for total and bioavailable testosterone, respectively). Among men with MetS, a decrease in one standard deviation of testosterone was associated with higher mortality risk [HR 1.78 (95% CI 1.13 to 2.78) and HR 1.83 (95% CI 1.17 to 2.86) for total and bioavailable testosterone, respectively]. By contrast, there was no association of testosterone with mortality risk among men without MetS. Our results suggest that MetS modifies the association between testosterone and mortality in older men. If confirmed, these findings could contribute to improve risk stratification and better manage the health of older men.

MendelianRandomization: an R package for performing Mendelian randomization analyses using summarized data

MendelianRandomization is a software package for the R open-source software environment that performs Mendelian randomization analyses using summarized data. The core functionality is to implement the inverse-variance weighted, MR-Egger and weighted median methods for multiple genetic variants. Several options are available to the user, such as the use of robust regression, fixed- or random-effects models and the penalization of weights for genetic variants with heterogeneous causal estimates. Extensions to these methods, such as allowing for variants to be correlated, can be chosen if appropriate. Graphical commands allow summarized data to be displayed in an interactive graph, or the plotting of causal estimates from multiple methods, for comparison. Although the main method of data entry is directly by the user, there is also an option for allowing summarized data to be incorporated from the PhenoScanner database of genotype-phenotype associations. We hope to develop this feature in future versions of the package. The R software environment is available for download from [https://www.r-project.org/]. The MendelianRandomization package can be downloaded from the Comprehensive R Archive Network (CRAN) within R, or directly from [https://cran.r-project.org/web/packages/MendelianRandomization/]. Both R and the MendelianRandomization package are released under GNU General Public Licenses (GPL-2|GPL-3).

Tachykinin neurokinin 3 receptor antagonists: a new treatment for cardiovascular disease?

Great progress has been made in reducing cardiovascular mortality over the past 50 years. Nevertheless, prevalence is rising in some settings and remains higher in men than in women, even with the same level of established risk factors. To gain new insights, researchers are now considering cardiovascular disease in relation to the well known evolutionary biology model of growth and reproduction trading off against longevity, with trials of calorie restriction underway. However, calorie restriction has not been as successful as expected in primates and it is increasingly realised that effects on the reproductive axis might also be important. In this paper, the modulation of the reproductive axis using existing agents that have such properties-tachykinin neurokinin 3 receptor antagonists-is proposed as a way of reducing cardiovascular disease and combating a leading cause of global morbidity and mortality.

Plasma levels of the anti-coagulation protein C and the risk of ischaemic heart disease. A Mendelian randomisation study

Protein C is an environmentally modifiable anticoagulant, which protects against venous thrombosis, whether it also protects against ischaemic heart disease is unclear, based on observational studies and relatively small genetic studies. It was our study aim to clarify the role of protein C in ischaemic heart disease. The risk of coronary artery disease/myocardial infarction (CAD/MI) was assessed according to genetically predicted protein C in very large studies. Associations with lipids and diabetes were similarly assessed to rule out effects via traditional cardiovascular disease risk factors. Separate sample instrumental variable analysis with genetic instruments (Mendelian randomisation) was used to obtain an unconfounded estimate of the association of protein C (based on (rs867186 (PROCR), rs3746429 (EDEM2), rs7580658 (inter/PROC)) with CAD/MI in an extensively genotyped case (n=64374)-control (n=130681) study, CARDIoGRAMplusC4D. Associations with lipids and diabetes were similarly assessed using the Global Lipids Genetics Consortium Results (n=196,475) and the DIAbetes Genetics Replication And Meta-analysis case (n=34,380)-control (n=114,981) study. Genetically predicted protein C was negatively associated with CAD/MI, odds ratio (OR) 0.85 µg/ml, 95 % confidence interval 0.80 to 0.90, but had no such negative association with lipids or diabetes. Results were similar for the SNP rs867186 functionally relevant to protein C, and including additional potentially pleiotropic SNPs (rs1260326 (GCKR), rs17145713 (BAZ1B) and rs4321325 (CYP27C1)). In conclusion, protein C may protect against CAD/MI. Whether environmental or dietary items that raise protein C protect against ischaemic cardiovascular disease by that mechanism should be investigated.