Hemopressin peptides as modulators of the endocannabinoid system and their potential applications as therapeutic tools.

The endocannabinoid system is activated by the binding of natural arachidonic acid derivatives (endogenous cannabinoids or endocannabinoids) as lipophilic messengers to cannabinoid receptors CB1 and CB2. The endocannabinoid system comprises also many hydrolytic enzymes responsible for the endocannabinoids cleavage, such as FAAH and MAGL. These two enzymes are possible therapeutic targets for the development of new drugs as indirect cannabinoid agonists. Recently a new family of endocannabinoid modulators was discovered; the lead of this family is the nonapeptide hemopressin produced from enzymatic cleavage of the α-chain of hemoglobin and acting as negative allosteric modulator of CB1. Hemopressin shows several physiological effects, e.g. antinociception, hypophagy, and hypotension. It is still matter of debate whether this peptide, isolated from the brain of rats is a real neuromodulator of the endocannabinoid system. Recent evidence indicates that hemopressin could be a by-product formed by chemical degradation of a longer peptide RVD-hemopressin during the extraction from the brain homolysate. Indeed, RVD-hemopressin is more active than hemopressin in certain biological tests and may bind to the same subsite as Rimonabant, which is an inverse agonist for the CB1 receptor and a μ-opioid receptor antagonist. These findings have stimulated several studies to verify this hypothesis and to evaluate possible therapeutic applications of hemopressin, its peptidic derivatives and synthetic analogues, opening new perspectives to the development of novel cannabinoid drugs.