Agmatine and alpha-methylagmatine: permeabilizing the outer mitochondrial membrane.

Agmatine a molecule belonging to the polyamine family, is a biogenic diamine with about two positive charges at physiological pH, which acts as a neuromodulator and neurotransmitter. It has different biochemical effects among which the induction of ornithine decarboxylase antizyme and the inhibition of proliferation by suppressing intracellular polyamine levels [1]. Agmatine exhibits opposite effects at the level of the mitochondrial permeability transition (MPT) in isolated mitochondria, that is inhibition at high concentrations or induction at low concentrations [2]. This latter process involves the formation of the transition pore at contact sites between the mitochondrial outer and inner membranes, causing a permeability increase of the membranes [3]. Considering that the MPT induction is strongly correlated with the release of the pro-apoptotic factors, reasonably high agmatine concentrations should not be able to induce their release. Instead, we observed that, while this amine is inhibiting the MPT, it causes the release of some pro-apoptotic factors such as cytochrome C (cyt C) and SMAC/DIABLO, but not Apoptosis Inducing Factor (AIF). This differential release induced by agmatine could be correlated with the localization of the proapoptotic factors, hypothesizing that the permeabilization of the only mitochondrial outer membrane (MOMP), but not of the inner membrane, can cause the release of the intermembrane space proteins (cyt C and SMAC/DIABLO) and not of transmembrane proteins of the inner membrane (AIF) [4,5]. Moreover we observed that a more stable agmatine analogue, alpha-methylagmatine (a-Meagmatine), is a powerful inhibitor of the MPT, if compared with the amine. Thus, first of all, we investigated if the transport mechanism of the analogue can be mediated by the same agmatine transporter. Then, by considering the pathophysiological significance of the pro-apoptotic factors release, we performed a comparison between the effects of agmatine and the analogue on the above release