Cholesterol-d1 is the deuterated form of Cholesterol. Cholesterol is the principal sterol found in mammals, comprising 20-25% of the plasma membrane's structural components. While the membrane allows high permeability to water, it remains relatively impermeable to ions and protons. Cholesterol is crucial for defining membrane fluidity and permeability characteristics, as well as for the function of transport and signaling proteins. Additionally, Cholesterol acts as an endogenous agonist of the estrogen-related receptor α (ERRα).