Synthesis, Characterization and Activity of Antamanide and its Analogues as Inhibitors of the Mitochondrial Permeability Transition Pore.

Antamanide, a cyclic decapeptide derived from the mushroom Amanita phalloides, is known for its antitoxic activity against phallotoxins and amatoxins contained in the fungus itself. The mechanism of this action is still unclear. In the present study, we show that this peptide also desensitizes the opening of the mitochondrial permeability transition pore (MPTP), a central effector in the induction of necrotic and apoptotic cell death. We show that Antamanide inhibits Cyclophilin D (CypD), a protein implicated in the regulation of MPTP, and that its activity is not additive to that of Cyclosporin A (CsA), a well known CypD inhibitor. Like CsA, Antamanide requires the presence of phosphate and is not effective on CypD knockout cell. Our studies on Antamanide analogues showed that two amino acid residues (Phe6 and Phe9) are crucial for the preservation of activity toward CypD. Indeed, analogues in which these two Phe residues are replaced by Gly or Tyr did not show any regulation of MPTP. We also demonstrate how the inhibition of toxic effects of phalloidin occurs with a MPTP-independent mechanism. Therefore, our studies identify Antamanide as a CypD ligand and a new MPTP inhibitor. Inhibition of CypD, preventing the opening of MPTP and, therefore, apoptosis may play an important pharmacological function, for example in neurodegenerative diseases. The recent discovery that lack of CypD improves learning and memory in animal models of Alzheimer's disease supports this hypothesis.