title: Antioxidant properties of calcium antagonists related to membrane biophysical interactions.
abstract: The antioxidant activities of representative calcium antagonists, including amlodipine, verapamil, and diltiazem, were measured in hepatic microsomal membranes by the Fe-catalyzed, hydroxyl radical-producing system (dihydroxyfumarate + Fe3+) and assessed by malondialdehyde (MDA) formation. Despite the absence of L-type calcium channels in this membrane preparation, the calcium antagonists showed dose-dependent antioxidant activity. The biophysical mechanism for calcium-antagonist antioxidant activity was evaluated using radioligand binding assays, high-resolution differential scanning calorimetry, and small-angle x-ray diffraction approaches. These analyses demonstrated that calcium-antagonist antioxidant potency correlated directly with the compounds' relative affinity for the membrane lipid bilayer and ability to modulate membrane thermodynamic properties (amlodipine >> verapamil > diltiazem). The charged 1,4-dihydropyridine calcium antagonist, amlodipine, had the highest affinity for the membrane lipid bilayer (Kp>10(4)) and produced the largest changes in membrane thermodynamic properties, including a reduction in thermal phase transition temperature (-11%), enthalpy (-14%), and cooperative unit size (-59%), relative to control phosphatidylcholine liposomes. Electron density profiles generated from x-ray diffraction data demonstrated that amlodipine effected a broad and dose-dependent increase in molecular volume associated with the membrane hydrocarbon core. These data indicate that lipophilic calcium antagonists inhibit lipid peroxidation in cellular membranes as a result of modulating physicochemical properties of the membrane lipid bilayer, independently of calcium channel inhibition. Amlodipine had the most potent antioxidant activity as a result of distinct biophysical interactions with the membrane lipid bilayer. The nonreceptor-mediated antioxidant activity of calcium antagonists may contribute to cytoprotective mechanisms of action in cardiovascular diseases.
authors.affiliation: Department of Biochemistry and Medicine, MCP-Hahnemann University School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: R P
authors.initials: RP
authors.lastname: Mason
authors.forename: I T
authors.initials: IT
authors.lastname: Mak
authors.forename: M W
authors.initials: MW
authors.lastname: Trumbore
authors.forename: P E
authors.initials: PE
authors.lastname: Mason
mesh_terms: D017311:Amlodipine / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D002152:Calorimetry, Differential Scanning; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D014700:Verapamil / Q000494:pharmacology; D014961:X-Ray Diffraction
chemical_list: D000975:Antioxidants; D002121:Calcium Channel Blockers; D017311:Amlodipine; D014700:Verapamil; D004110:Diltiazem