Transforming Toxicity into Therapy: Exploring Bilirubin's Benefits and Its Molecular Role in Cardiac Health and Disease.

Bilirubin, historically recognized solely as a waste product of heme catabolism, has recently gained attention for its potential protective role in the cardiovascular system. Experimental and clinical studies suggest that bilirubin exhibits potent antioxidant, anti-inflammatory, anti-apoptotic, and cytoprotective properties that may protect the heart against oxidative stress, ischemia-reperfusion injury, and the progression of cardiovascular diseases, such as heart failure. As an endogenous hormone, bilirubin activates peroxisome proliferator-activated receptor-α (PPARα), a nuclear receptor that controls energy balance and lipid metabolism. Moderately elevated circulating bilirubin levels have been associated with a reduced risk of coronary artery disease, heart failure, and myocardial infarction; however, the mechanisms underlying bilirubin's protective effects remain incompletely understood. Conversely, the gut microbiota's metabolism of bilirubin to urobilin is detrimental, given urobilin's association with cardiometabolic dysfunction. The therapeutic potential of bilirubin in the management of cardiovascular disease is becoming increasingly apparent, supported by preclinical research and emerging technologies that enhance bilirubin delivery via nanoparticles and methods to elevate plasma bilirubin levels. Collectively, these scientific advancements position bilirubin as a promising, biologically plausible endogenous therapeutic for the prevention and treatment of heart disease.