Bile Acid Sequestrants Based on Natural and Synthetic Gels

Bile acid sequestrants (BASs) are non-systemic therapeutic agents used for the management of hypercholesterolemia. They are generally safe and not associated with serious systemic adverse effects. Usually, BASs are cationic polymeric gels that have the ability to bind bile salts in the small intestine and eliminate them by excretion of the non-absorbable polymer-bile salt complex. This review gives a general presentation of bile acids and the characteristics and mechanisms of action of BASs. The chemical structures and methods of synthesis are shown for commercial BASs of first- (cholestyramine, colextran, and colestipol) and second-generation (colesevelam and colestilan) and potential BASs. The latter are based on either synthetic polymers such as poly((meth)acrylates/acrylamides), poly(alkylamines), poly(allylamines) and vinyl benzyl amino polymers or biopolymers, such as cellulose, dextran, pullulan, methylan, and poly(cyclodextrins). A separate section is dedicated to molecular imprinting polymers (MIPs) because of their great selectivity and affinity for the template molecules used in the imprinting technique. Focus is given to the understanding of the relationships between the chemical structure of these cross-linked polymers and their potential to bind bile salts. The synthetic pathways used in obtaining BASs and their in vitro and in vivo hypolipidemic activities are also introduced.