Effects of Manganese Porphyrins on Cellular Sulfur Metabolism

Abstract

Manganese porphyrins (MnPs), MnTE-2-PyP5+, MnTnHex-2-PyP5+ and MnTnBuOE-2-PyP5+, are superoxide dismutase (SOD) mimetics and form a redox cycle between O2 and reductants, including ascorbic acid, ultimately producing hydrogen peroxide (H2O2). We previously found that MnPs oxidize hydrogen sulfide (H2S) to polysulfides (PS; H2Sn, n = 2–6) in buffer. Here, we examine the effects of MnPs for 24 h on H2S metabolism and PS production in HEK293, A549, HT29 and bone marrow derived stem cells (BMDSC) using H2S (AzMC, MeRho-AZ) and PS (SSP4) fluorophores. All MnPs decreased intracellular H2S production and increased intracellular PS. H2S metabolism and PS production were unaffected by cellular O2 (5% versus 21% O2), H2O2 or ascorbic acid. We observed with confocal microscopy that mitochondria are a major site of H2S production in HEK293 cells and that MnPs decrease mitochondrial H2S production and increase PS in what appeared to be nucleoli and cytosolic fibrillary elements. This supports a role for MnPs in the metabolism of H2S to PS, the latter serving as both short- and long-term antioxidants, and suggests that some of the biological effects of MnPs may be attributable to sulfur metabolism.

H2O2‐Driven Anticancer Activity of Mn Porphyrins and the Underlying Molecular Pathways

“…•include hydrogen peroxide (H 2 O 2 ), ClO -, nitric oxide ( • NO), glutathione (GSH), ascorbate, hydrogen sulfide (H 2 S) [66,67], oxygen (O 2 ), sulfite (SO 3 2-), tetrahydrobiopterin (BH 4 ), and protein (cysteine) thiols (R-SH) [4,62]. Due to the complex chemistry of MnPs with 4 oxidation states available for in vivo reactions, and complex biological milieu, many more reactions are to be uncovered.…”

“…•-, namely, ONOO -, ClO -, H 2 S, ascorbate, H 2 O 2 , and thiols via the GPx-like reactivity [4,48,49,[65][66][67]. Numerous efficacy studies further demonstrated that the more potent the SOD mimic Mn porphyrin is, the more efficacious therapeutic it tends to be [2-4, 62, 68, 69].…”

“…The highvalent Mn(V) dioxo species can also oxidize its own porphyrin ligand giving rise to the Mn(IV) porphyrin π-cation radical, O = MnðIVÞP •+ , which would result in the degradation of the Mn complex [75]. The involvement of H 2 S/MnP in the S-glutathionylation of proteins was also implicated [66,67]. In the study of Tome's lab, MnP oxidizes primarily cys38 of the p65 subunit of NF-κB and to a lesser degree cys62 of the p50 subunit.…”

SOD mimics: From the tool box of the chemists to cellular studies

“…Recently, an increasing interest has grown about potential 'side reactions' performed more specifically by Mn-porphyrins (MnPs) with reactive oxygen species (ROS) or cellular compounds (ONOO À , H 2 O 2 , H 2 S, CO 3 -, ascorbate, and GSH) [13] and their mechanism of action in cells [7, 18,63]. As early as 2004, an increase in extracellular SOD and MnSOD was reported [64] after incubating cells with MnPs, suggesting that these compounds may act not solely as a direct antioxidant by reducing ROS concentration but also indirectly: they may induce antioxidant cell feedback through a prooxidant effect, enhancing the protective cell arsenal.…”

“…Batinic et al have reported such a pro-oxidant effect of MnPs in 2012 [65,66]. They have extensively shown then that besides their reactions against ROS and reactive nitrogen species (RNS), MnPs display an effect on thiols regulation and cellular sulfur metabolism [7, 18,63,67], which activates the Nrf2 [68] pathway. This is interesting as the Keap1-Nrf2 pathway [69,70] constitutes the major defense system against electrophilic and oxidative stress: Keap1 acts as a redox sensor through the oxidation or modification of its cysteine residues upon oxidative/electrophilic stress, which results in the Nrf2-induced up-regulation of several antioxidant enzymes (see Figure 1).…”