SELECT Mediation Analysis: Known Risk Factors Explain Only About a Third of Semaglutide's Cardiovascular Benefit

A pre-specified mediation analysis of the SELECT trial has found that improvements in conventional cardiovascular risk factors account for only a minority of semaglutide查看药品详情's cardiovascular benefit in adults with overweight or obesity (搜索)搜索该疾病 and established cardiovascular disease (搜索)搜索该疾病 but without diabetes. The analysis, published in the European Heart Journal, estimated that body weight, blood pressure, cholesterol and blood glucose jointly explained 31.4% of the treatment effect, leaving roughly 68.6% unaccounted for, though the statistical uncertainty was too large to treat that proportion as precise.

The underlying SELECT trial enrolled 17,604 adults aged 45 years or older with a BMI of at least 27 kg/m2 and clinically validated pre-existing cardiovascular disease (搜索)搜索该疾病, excluding those with diabetes. Participants were followed for a mean of 39.8 months. Weekly subcutaneous semaglutide查看药品详情 at a target dose of 2.4 mg reduced major adverse cardiovascular events, defined as cardiovascular death, non-fatal myocardial infarction or non-fatal stroke, from 8.0% with placebo to 6.5%, a 20% relative reduction.

What the mediation model measured

Investigators applied counterfactual mediation modeling to the SELECT cohort, using the Vansteelandt repeated regression method alongside time-dependent Cox proportional hazards models. The analysis evaluated 12 candidate mediators with repeated measurements through at least 24 months and mediation estimated at 36 months. Measures included body weight, waist circumference, high-sensitivity C-reactive protein, glycated hemoglobin, systolic and diastolic blood pressure, lipid fractions including HDL, LDL and triglycerides, estimated glomerular filtration rate, and urinary albumin-to-creatinine ratio.

Assignment to semaglutide查看药品详情 was associated with significant improvements across all 12 candidate measures. In individual counterfactual models, the largest estimated mediation was for change in waist circumference at 64.0%, followed by hsCRP at 42.1%, HbA1c at 29.0% and body weight at 19.5%. Triglycerides produced an estimate of 18.6%, urinary albumin-to-creatinine ratio 14.6%, systolic blood pressure 14.3% and LDL cholesterol 10.9%. The authors noted that substantial statistical uncertainty limited confidence in the size of these individual effects.

Investigators call for a broader view of the drug

The study was led by Professor Helen Colhoun from the University of Edinburgh查看公司主页. "Our analyses could not fully ascribe the effects of semaglutide查看药品详情 on cardiovascular disease (搜索)搜索该疾病 to known risk factors with any certainty," Colhoun said. "Whether we combine all risk factors together or look at some subsets of the risk factors, no more than half of the reduction in heart disease could be explained by the changes in these risk factors. These results suggest that semaglutide should be considered as a cardiovascular disease reduction drug and not just as a weight loss drug."

Colhoun said the mechanism behind the residual benefit remains unknown. "We don't know how else semaglutide查看药品详情 could be preventing heart disease, but many other mechanisms have been proposed. These include anti-inflammatory effects not fully captured by the risk factors measured in the trial, and other direct effects on heart muscle or on the lining of blood vessels. We need more research to fully explore other potential mechanisms of how semaglutide reduces cardiovascular disease (搜索)搜索该疾病."

The paper discusses additional speculative possibilities, including effects on atherosclerotic plaque biology, steatohepatitis, epicardial fat and circulating proteins. The authors state that the analysis could not establish with certainty that changes in body weight, waist circumference or the other measured factors fully accounted for the reduction in MACE, and that unmeasured biological pathways may contribute.

Limitations and caveats

Sensitivity analyses raised the possibility that estimates involving body weight and waist circumference were affected by unintentional weight loss related to comorbid illness or frailty, particularly among placebo participants. The researchers caution that frailty-related weight loss can increase rather than decrease cardiovascular risk. They also note that the trial ran during the COVID-19 pandemic, which affected data collection, and that the findings rest on estimates of risk. Additional limitations cited include assumptions about unmeasured confounding inherent to mediation analyses, missing mediator data and the frequency of measurements.

Editorial: mechanism questions should not delay adoption

In an accompanying editorial, Professor Subodh Verma of the University of Toronto查看公司主页 and colleagues described the GLP-1 receptor (搜索)搜索该靶点 agonist story in cardiovascular medicine as one of serendipity. "The conclusion of this paper is appropriately humble. Known risk factor changes could not, with any confidence, explain all of the GLP-1RA effects on major adverse cardiovascular events," they wrote. "So, in summary, while the magic of semaglutide查看药品详情 and GLP-1RAs on cardiometabolic outcomes is real, our search for the mechanistic underpinnings continues."

The editorial argued that unresolved mechanism should not limit clinical use. "At the end of the day, mechanistic knowledge is only useful if it sharpens how we deploy these remarkable drugs to save lives. The lack of clear mechanistic understanding should not be a barrier to therapeutic adoption to reduce vascular events."

The authors of the mediation analysis conclude that their findings support further research into biological pathways beyond the measured risk factors to clarify how semaglutide查看药品详情 reduces cardiovascular events. The work is described as the first mediation analysis of a GLP-1 receptor (搜索)搜索该靶点 agonist cardiovascular outcome trial in people with established cardiovascular disease (搜索)搜索该疾病 but without diabetes at baseline.