Protective stabilization of mitochondrial permeability transition and mitochondrial oxidation during mitochondrial Ca2+ stress by melatonin's cascade metabolites C3‐OHM and AFMK in RBA1 astrocytes

• Published in: Journal of pineal research 2019-01, Vol.66 (1), p.e12538-n/a
• Main Authors: Jou, Mei‐Jie, Peng, Tsung‐I, Reiter, Russel J.
• Format: Article
• Language: English
• Subjects: AFMK; C3‐OHM; mCa2; melatonin; mitochondrial permeability transition; mitochondria‐targeted antioxidant; mROS
• ISSN: 0742-3098; 1600-079X
• DOI: 10.1111/jpi.12538

Cyclic 3‐hydroxymelatonin (C3‐OHM) and N1‐acetyl‐N2‐formyl‐5‐methoxykynuramine (AFMK) are two major cascade metabolites of melatonin. We previously showed melatonin provides multiple levels of mitochondria‐targeted protection beyond as a mitochondrial antioxidant during ionomycin‐induced mitochondrial Ca2+ (mCa2+) stress in RBA1 astrocytes. Using noninvasive laser scanning fluorescence coupled time‐lapse digital imaging microscopy, this study investigated whether C3‐OHM and AFMK also provide mitochondrial levels of protection during ionomycin‐induced mCa2+ stress in RBA1 astrocytes. Interestingly, precise temporal and spatial dynamic live mitochondrial images revealed that C3‐OHM and AFMK prevented specifically mCa2+‐mediated mitochondrial reactive oxygen species (mROS) formation and hence mROS‐mediated depolarization of mitochondrial membrane potential (△Ψm) and permanent lethal opening of the MPT (p‐MPT). The antioxidative effects of AFMK, however, were less potent than that of C3‐OHM. Whether C3‐OHM and AFMK targeted directly the MPT was investigated under a condition of “oxidation free‐Ca2+ stress” using a classic antioxidant vitamin E to remove mCa2+‐mediated mROS stress and the potential antioxidative effects of C3‐OHM and AFMK. Intriguingly, two compounds still effectively postponed “oxidation free‐Ca2+ stress”‐mediated depolarization of △Ψm and p‐MPT. Measurements using a MPT pore‐specific indicator Calcein further identified that C3‐OHM and AFMK, rather than inhibiting, stabilized the MPT in its transient protective opening mode (t‐MPT), a critical mechanism to reduce overloaded mROS and mCa2+. These multiple layers of mitochondrial protection provided by C3‐OHM and AFMK thus crucially allow melatonin to extend its metabolic cascades of mitochondrial protection during mROS‐ and mCa2+‐mediated MPT‐associated apoptotic stresses and may provide therapeutic benefits against astrocyte‐mediated neurodegeneration in the CNS.