Cannabinoid Inhibition of Divalent Metal Transporter-1 Activity

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DESCRIPTION (provided by applicant): ?9-tetrahydrocannabinol (?9-THC) is the major psychoactive component of the marijuana plant Cannabis sativa, and it produces a number of behavioral and pharmacological effects mediated through interactions with the central nervous system cannabinoid receptor CB1 and the peripheral receptor CB2. Endogenous cannabinoids also activate these G-protein coupled receptors to negatively regulate adenylate cyclase activity and positively regulate inward rectifying K+ channels. Receptor-independent effects of cannabinoids have also been reported to negatively regulate a number of ion channels, including T-type Ca2+ channels, TASK-1 channels, and Na+ channels. In a recent screen of small molecule libraries containing known bioactive molecules, it was discovered that ?9-THC also potently blocks iron uptake by Divalent Metal Transporter-1 (DMT1). DMT1 is responsible for dietary iron absorption across the intestine as well as the delivery of iron to peripheral tissues after receptor-mediated uptake of the serum iron-binding protein transferrin. This completely unexpected and novel finding raises immediate and profound questions about the relationships between iron metabolism and cannabinoid action. To develop new insights to explain how cannabinoids perturb iron transport by DMT1 and to determine what physiological consequences ensue from this activity, the proposed project will: 1) Examine changes in the iron status of weanling rats resulting from chronic ?9-THC administration; 2) Explore G protein-coupled regulation of DMT1 activity through CB receptor interactions; and 3) Study binding of cannabinoids to DMT1 and changes in the phosphorylation state of the transporter that may be elicited through such interactions. PUBLIC HEALTH RELEVANCE: This project will determine how cannabinoids interfere with iron uptake by Divalent Metal Transporter-1. There is significant interest in identifying targets of cannabinoid action since drugs that modify endogenous cannabinoid activity are being developed to control obesity (Rimonabant), to prevent osteoporosis (HU-308) and to treat multiple sclerosis (Sativex), and are in current use for AIDS and cancer patients (Marinol).