A comprehensive evaluation of catalase-like activity of different classes of redox-active therapeutics

Abstract

The growing insight into the biological role of hydrogen peroxide (H2O2) under physiological and pathological condition and the role it presumably plays in the action of natural and synthetic redox-active drug imparts a need to accurately define the type and magnitude of reactions which may occur with this intriguing and key species of redoxome. Historically, and frequently incorrectly, the impact of catalase-like activity has been assigned to play a major role in the action of many redox-active drugs most so SOD mimics and peroxynitrite scavengers, and in particular MnTBAP3− and Mn salen derivatives. The advantage of one redox-active compound over another has often been assigned to the differences in catalase-like activity. Our studies provide substantial evidence that Mn(III) N-alkylpyridylporphyrins couple with H2O2 in actions other than catalase-related. Herein we have assessed the catalase-like activities of different classes of compounds: Mn porphyrins (MnPs), Fe porphyrins (FePs), Mn(III) salen (EUK-8) and Mn(II) cyclic polyamines (SOD-active M40403 and SOD-inactive M40404). Nitroxide (Tempol), nitrone (NXY-059), ebselen and MnCl2, which have not been reported as catalase-mimics, were used as negative controls, while catalase enzyme was a positive control. The dismutation of H2O2 to O2 and H2O was followed via measuring oxygen evolved with Clark oxygen electrode at 25°C. The catalase enzyme was found to have kcat(H2O2) = 1.5 × 106 M−1 s−1. The yield of dismutation, i.e. the amount of O2 evolved, was assessed also. The magnitude of the yield reflects an interplay between the kcat(H2O2) and the stability of compounds towards H2O2-driven oxidative degradation, and is thus an accurate measure of the efficacy of an catalyst. The kcat(H2O2) values for 12 cationic Mn(III) N-substituted (alkyl and alkoxyalkyl) pyridylporphyrin-based SOD mimics and Mn(III) N,N’-dialkylimidazolium porphyrin, MnTDE-2-ImP5+ ranged from 23 to 88 M−1 s−1. The analogous Fe(III) N-alkylpyridylporphyrins showed ~10-fold higher activity than the corresponding MnPs, but the values of kcat(H2O2) are still ~4 orders of magnitude lower than that of the enzyme. While the kcat(H2O2) values for Fe ethyl and n-octyl analogs were 830 and 360 M1 s−1, respectively, the FePs are more prone to H2O2-driven oxidative degradation therefore allowing for similar yields in H2O2 dismutation as analogous MnPs. The kcat(H2O2) values are dependent upon the electron deficiency of the metal site as it controls the peroxide binding in the 1st step of dismutation process. SOD-like activities depend upon electron-deficiency of the metal site also, as it controls the 1st step of O2.− dismutation. In turn, the kcat(O2.−) parallels the kcat(H2O2). Therefore, the electron-rich anionic non-SOD mimic MnTBAP3− has essentially very low catalase-like activity, kcat(H2O2) = 5.8 M−1 s−1. The catalase-like activity of Mn(III) and Fe(III) porphyrins are at most, 0.0004% and 0.05% of the enzyme activity, respectively. The kcat(H2O2) of 8.2 and 6.5 M−1 s−1 were determined for elect...

Anticancer therapeutic potential of Mn porphyrin/ascorbate system

“…It was subsequently shown that ability of MnPs to catalyze O 2 .− dismutation parallels their ability to reduce ONOO − [8, 9, 68]. It became soon obvious that bioavailability is another major factor that affects MnP therapeutic potential and can compensate for somewhat inferior redox properties [42, 54, 58]. Bioavailability is affected by the charge, size, shape, polarity and lipophilicity of MnPs.…”

Redox-Active Mn Porphyrin-based Potent SOD Mimic, MnTnBuOE-2-PyP5+, Enhances Carbenoxolone-Mediated TRAIL-Induced Apoptosis in Glioblastoma Multiforme

“…MnPs readily cycle with endogenous reductants, ascorbate and thiols - simple thiols and thiols of signaling proteins such as NF-κB. Such cycling is critically involved in the mechanism(s) of MnPs actions [15, 29, 30]. Aqueous chemistry and in vivo reactions of MnPs are summarized in recent review in Redox Biology [15], while therapeutic effects of analogous compounds are summarized in several manuscripts of the Forum Issue on “SOD therapeutics” of Antioxid Redox Signal , 2014 [ Antioxidant & Redox Signaling 2014 Forum Issues on “SOD therapeutics” (vol.20/15)].…”

“…Its oxidation, catalyzed by endogenous metalloproteins resulting in cytotoxic H 2 O 2 production, was proposed as its mode of action. However, we have shown that cationic Mn(III) ortho N -substituted pyridylporphyrins, one of which will be used herein, are superior to endogenous metalloproteins as they are optimized as catalysts for ascorbate oxidation [30, 40]. Thus, such MnPs are prospective for clinical development as enhancers of ascorbate/H 2 O 2 driven cancer cell killing.…”

MnTnBuOE-2-PyP protects normal colorectal fibroblasts from radiation damage and simultaneously enhances radio/chemotherapeutic killing of colorectal cancer cells

“…In contrast, normal cells readily use redundant enzymes to maintain H 2 O 2 at physiological nM levels. [30, 31]. Given the different levels of H 2 O 2 in normal vs cancer cells, the yield of reaction with Mn porphyrins and H 2 O 2 is different in those tissues and, thus, leads to different outcomes in the two cell types [31, 32].…”