Inertness of Superoxide Dismutase Mimics Mn(II) Complexes Based on an Open-Chain Ligand, Bioactivity, and Detection in Intestinal Epithelial Cells

Abstract

Oxidative stress is known to play a major role in the pathogenesis of inflammatory bowel diseases (IBDs), and, in particular, superoxide dismutase (SODs) defenses were shown to be weakened in patients suffering from IBDs. SOD mimics, also called SOD mimetics, as low-molecular-weight complexes reproducing the activity of SOD, constitute promising antioxidant catalytic metallodrugs in the context of IBDs. A Mn(II) complex SOD mimic (Mn1) based on an open-chain diaminoethane ligand exerting antioxidant and anti-inflammatory effects on an intestinal epithelial cellular model was shown to experience metal exchanges between the manganese center and metal ions present in the biological environment (such as Zn(II)) to some degrees. As the resulting complexes (mainly Zn(II)) were shown to be inactive, improving the kinetic inertness of Mn(II) complexes based on open-chain ligands is key to improve their bioactivity in a cellular context. We report here the study of three new Mn(II) complexes resulting from Mn1 functionalization with a cyclohexyl and/or a propyl group meant to limit, respectively, (a) metal exchanges and (b) deprotonation of an amine from the 1,2-diaminoethane central scaffold. The new manganese-based SOD mimics display a higher intrinsic SOD activity and also improved kinetic inertness in metal ion exchange processes (with Zn(II), Cu(II), Ni(II), and Co(II)). They were shown to provide anti-inflammatory and antioxidant effects in cells at lower doses than Mn1 (down to 10 μM). This improvement was due to their higher inertness against metal-assisted dissociation and not to different cellular overall accumulations. Based on its higher inertness, the SOD mimic containing both the propyl and the cyclohexyl moieties was suitable for intracellular detection and quantification by mass spectrometry, quantification, that was achieved by using a 13C-labeled Co-based analog of the SOD mimics as an external heavy standard.

Deciphering the Metal Speciation in Low‐Molecular‐Weight Complexes by IMS‐MS: Application to the Detection of Manganese Superoxide Dismutase Mimics in Cell Lysates

“…To avoid this possible bias and to also determine the amount of intact metal complex in cells, we wanted to directly track it in cell lysates. We showed previously using LC/MS‐MS, [25] that Mn1 penetrates the cells but the fact that the m / z peak of [Mn1] + (408.1465) is very close to that of the m / z peak of [Fe1−H] + (408.1355), with overlapping isotopic patterns prevented any reliable quantitative analysis, as previously performed with a more inert analogue [69] . Recently, to investigate the Mn1 subcellular location, a multimodal Re‐tris carbonyl probe was conjugated to the ligand.…”

“…A comprehensive evaluation of high‐performance liquid chromatography‐mass spectrometry (HPLC‐MS) for a large‐scale study of metal complexes was reported elsewhere [68] . It has been also applied very recently to a more inert Mn‐based complex similar to Mn1 [69] . More labile compounds present additional problems, especially when they interact with the stationary phase and the tubing of the system.…”

“…[68] It has been also applied very recently to a more inert Mn-based complex similar to Mn1. [69] More labile compounds present additional problems, especially when they interact with the stationary phase and the tubing of the system. These interactions can lead to metal exchange and the decomposition of the target metal complexes.…”

A New Manganese Superoxide Dismutase Mimetic Improves Oxaliplatin-Induced Neuropathy and Global Tolerance in Mice

“…Superoxide dismutase mimetics are low-molecular-weight complexes that mimic the activity of superoxide dismutase [ 10 , 11 , 12 ]. Such compounds may present antioxidant and anti-inflammatory activity [ 13 , 14 , 15 , 16 ], and they have also been evaluated for their antitumoral activity [ 17 ]. SOD mimetics are proposed to lead to an increase in cellular H 2 O 2 , which induces antitumoral activity in vitro due to the difference in hydrogen peroxide cellular sensitivity between normal and cancer cells [ 3 , 6 , 18 , 19 , 20 ].…”

“…Mn1 [ 31 ] is a MnSOD mimic bio inspired by the active site of MnSOD, specific of superoxide, [ 32 ] with better intracellular diffusion compared to mangafodipir [ 13 , 15 , 16 ]. It was shown to exert anti-inflammatory activity in a cellular model of inflammatory bowel diseases (HT29-MDM2) associated with an antioxidant effect [ 13 ].…”