Losartan, a widely used blood-pressure medicine, increased brown-fat activity and energy expenditure in mouse experiments reported in a Nature study published Oct. 14. The result grew out of a much larger analysis of human medical images and records, but the study did not test the drug for this purpose in people.
Researchers at Rockefeller University and Memorial Sloan Kettering Cancer Center analyzed PET/CT scans and medical records from 101,243 cancer-center patients. Using a machine-learning system, they quantified brown adipose tissue activity in roughly 8,700 people. Unlike white fat, which stores energy, brown fat burns energy to produce heat.
A human association led to mouse experiments
The retrospective analysis found that cardiovascular and psychiatric diagnoses were less prevalent among patients with detectable brown fat. Higher brown-fat activity was also associated with more favorable blood-sugar, lipid, inflammatory and heart-imaging measures.
Those links are associations, not proof that brown fat prevented disease. The cohort came from a cancer center, and the study relied on scans and records collected for clinical care rather than randomly assigning people to a treatment.
One medication signal stood out: People taking angiotensin receptor blockers, the drug class that includes losartan, were more likely to have detectable brown fat. The researchers then tested losartan in cultured brown fat cells and found that it increased their metabolic activity.
Healthy mice given losartan showed higher energy expenditure, oxygen consumption and carbon dioxide production while maintaining steady body weight, according to an NIH summary. The researchers also reported that the pathway behind this effect differed from the one responsible for losartan's blood-pressure-lowering action.
What the study does and does not show
The findings provide a rationale for studying whether a common drug can be repurposed to stimulate brown fat, but they do not show that losartan activates brown fat in humans. The work also does not establish that taking the drug would cause weight loss or prevent cardiovascular, metabolic or psychiatric illness.
Researchers said the distinct molecular pathways may eventually make it possible to isolate the brown-fat effect without lowering blood pressure. That remains a future research goal. Human trials would be needed to determine whether the preclinical effect can be reproduced safely and whether it produces a meaningful health benefit.