Polyamine-Conjugated Nitroxides Are Efficacious Inhibitors of Oxidative Reactions Catalyzed by Endothelial-Localized Myeloperoxidase

Epigallocatechin-3-gallate as an effective inhibitor of vascular endothelial dysfunction induced by endothelial-localized myeloperoxidase

In inflammatory vasculature, the leukocyte-released myeloperoxidase (MPO) is internalized by endothelial cells and this enzyme promotes endothelial dysfunction by catalytically producing strong oxidant, hypochlorous acid (HOCl). Herein, we developed epigallocatechin-3-gallate (EGCG, the main polyphenolic flavonoid found in green tea) as a novel endothelial-targeted MPO inhibitor. It was shown that culture of MPO and EGCG with vascular endothelial cells could result in their transport into the sub-endothelial space. EGCG significantly suppressed the consumption of enzyme's substrate H2O2 and generation of HOCl catalyzed by endothelial-transcytosed MPO. The binding of EGCG to the hydrophobic domain near the distal active heme cavity of enzyme was proposed by molecular docking and was suggested for the inhibitive effect of flavonoid on MPO activity. In vivo, EGCG attenuated lipopolysaccharide (LPS)-induced endothelial dysfunction in mouse aortas, while it inhibited the infiltration of active MPO into vascular walls. Furthermore, MPO-deficient mice were resistant to the protective effects of EGCG on LPS-induced vascular dysfunction, as compared to wild-type mice. These studies showed that EGCG effectively inhibited local oxidative reactions and endothelial dysfunction catalyzed by vascular-bound MPO. EGCG represents a versatile class of natural antioxidant drugs applicable to target endothelial-transcytosed MPO in inflammatory vasculature.

Targeting vascular adhesion protein-1 and myeloperoxidase with a dual inhibitor SNT-8370 in preclinical models of inflammatory disease

Inflammatory diseases are a major source of morbidity and mortality world-wide, the pathogenesis of which are characterised by the interplay of key pro-inflammatory and oxidative enzymes. Here, we report the development of a small molecule dual inhibitor targeting vascular adhesion protein-1 (VAP-1) and myeloperoxidase (MPO), two clinically relevant pro-inflammatory/oxidative enzymes that play complementary pathogenic roles in various inflammatory diseases. This agent, SNT-8370 [(E)-3-(3-((2-(aminomethyl)-3-fluoroallyl)oxy)benzyl)-2-thioxo-1,2,3,7-tetrahydro-6H-purin-6-one)], irreversibly inhibits VAP-1 and MPO activity with equivalent and enhanced nanomolar potency, respectively, when compared to benchmark clinical VAP-1 and MPO inhibitors. SNT-8370 is selective, exhibiting >100-1000-fold more potency for VAP-1 and MPO versus other mammalian (per)oxidases and shows no significant off-target activity in established preclinical screening panels. In vivo, SNT-8370 is metabolically stable, exhibits a favourable pharmacokinetic/pharmacodynamic profile without CNS penetration, and effectively inhibits VAP-1 and MPO activities. Moreover, compared to monotherapy, SNT-8370 more effectively inhibits leukocyte infiltration in mouse peritonitis, carrageenan air pouch, and lipopolysaccharide-induced lung injury models of acute inflammation. SNT-8370 is also protective in preclinical models of myocardial ischemia-reperfusion injury and unilateral-ureteral-obstruction-induced nephropathy. Collectively, our results support SNT-8370 as a first-in-class, mechanism-based dual inhibitor of VAP-1 and MPO, and as a promising therapeutic for the clinical treatment of inflammatory disorders.

Multi-Oxidant Environment as a Suicidal Inhibitor of Myeloperoxidase

Tissue inflammation drives the infiltration of innate immune cells that generate reactive species to kill bacteria and recruit adaptive immune cells. Neutrophil activation fosters the release of myeloperoxidase (MPO) enzyme, a heme-containing protein generating hypochlorous acid (HOCl) from hydrogen peroxide (H2O2) and chloride ions. MPO-dependent oxidant formation initiates bioactive oxidation and chlorination products and induces oxidative post-translational modifications (oxPTMs) on proteins and lipid oxidation. Besides HOCl and H2O2, further reactive species such as singlet oxygen and nitric oxide are generated in inflammation, leading to modified proteins, potentially resulting in their altered bioactivity. So far, knowledge about multiple free radical-induced modifications of MPO and its effects on HOCl generation is lacking. To mimic this multi-oxidant microenvironment, human MPO was exposed to several reactive species produced simultaneously via argon plasma operated at body temperature. Several molecular gas admixes were used to modify the reactive species type profiles generated. MPO was investigated by studying its oxPTMs, changes in protein structure, and enzymatic activity. MPO activity was significantly reduced after treatment with all five tested plasma gas conditions. Dynamic light scattering and CD-spectroscopy revealed altered MPO protein morphology indicative of oligomerization. Using mass spectrometry, various oxPTMs, such as +1O, +2O, and +3O, were determined on methionine and cysteine (Cys), and -1H-1N+1O was detected in asparagine (Asp). The modification types identified differed between argon-oxygen and argon-nitrogen plasmas. However, all plasma gas conditions led to the deamidation of Asp and oxidation of Cys residues, suggesting an inactivation of MPO due to oxPTM-mediated conformational changes.

Polyamine-Drug Conjugates: Do They Boost Drug Activity?

Over the past two decades, the strategy of conjugating polyamine tails with bioactive molecules such as anticancer and antimicrobial agents, as well as antioxidant and neuroprotective scaffolds, has been widely exploited to enhance their pharmacological profile. Polyamine transport is elevated in many pathological conditions, suggesting that the polyamine portion could improve cellular and subcellular uptake of the conjugate via the polyamine transporter system. In this review, we have presented a glimpse on the polyamine conjugate scenario, classified by therapeutic area, of the last decade with the aim of highlighting achievements and fostering future developments.

Halogenation Activity of Mammalian Heme Peroxidases

Mammalian heme peroxidases are fascinating due to their unique peculiarity of oxidizing (pseudo)halides under physiologically relevant conditions. These proteins are able either to incorporate oxidized halides into substrates adjacent to the active site or to generate different oxidized (pseudo)halogenated species, which can take part in multiple (pseudo)halogenation and oxidation reactions with cell and tissue constituents. The present article reviews basic biochemical and redox mechanisms of (pseudo)halogenation activity as well as the physiological role of heme peroxidases. Thyroid peroxidase and peroxidasin are key enzymes for thyroid hormone synthesis and the formation of functional cross-links in collagen IV during basement membrane formation. Special attention is directed to the properties, enzymatic mechanisms, and resulting (pseudo)halogenated products of the immunologically relevant proteins such as myeloperoxidase, eosinophil peroxidase, and lactoperoxidase. The potential role of the (pseudo)halogenated products (hypochlorous acid, hypobromous acid, hypothiocyanite, and cyanate) of these three heme peroxidases is further discussed.