Cholesterol-13C5 is a form of cholesterol labeled with carbon-13 isotopes. Cholesterol is the predominant sterol in mammals, constituting 20-25% of the plasma membrane structure. While the plasma membrane is highly permeable to water, it is relatively impermeable to ions and protons. Cholesterol is crucial in determining membrane fluidity and permeability features, as well as the function of transport and signaling proteins. Additionally, cholesterol acts as an endogenous agonist of estrogen-related receptor α (ERRα).