Synthesis and Initial in Vitro Evaluations of Novel Antioxidant Aroylhydrazone Iron Chelators with Increased Stability against Plasma Hydrolysis

Abstract

Oxidative stress is known to contribute to a number of cardiovascular pathologies. Free intracellular iron ions participate in the Fenton reaction and therefore substantially contribute to the formation of highly toxic hydroxyl radicals and cellular injury. Earlier work on the intracellular iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) has demonstrated its considerable promise as an agent to protect the heart against oxidative injury both in vitro and in vivo. However, the major limitation of SIH is represented by its labile hydrazone bond that makes it prone to plasma hydrolysis. Hence, in order to improve the hydrazone bond stability, nine compounds were prepared by a substitution of salicylaldehyde by the respective methyl- and ethylketone with various electron donors or acceptors in the phenyl ring. All the synthesized aroylhydrazones displayed significant iron-chelating activities and eight chelators showed significantly higher stability in rabbit plasma than SIH. Furthermore, some of these chelators were observed to possess higher cytoprotective activities against oxidative injury and/or lower toxicity as compared to SIH. The results of the present study therefore indicate the possible applicability of several of these novel agents in the prevention and/or treatment of cardiovascular disorders with a known (or presumed) role of oxidative stress. In particular, the methylketone HAPI and nitro group-containing NHAPI merit further in vivo investigations.

Comparison of various iron chelators and prochelators as protective agents against cardiomyocyte oxidative injury

“…Our third tested chelator was HAPI, the novel methyl ketone derivative of SIH [26]. Our results demonstrated good chelating efficiency of HAPI in buffered solution and in cells.…”

“…Inherent toxicity of HAPI was low after 24 h incubation but greatly increased after 72 h. We speculate that the greater cytotoxicity observed for HAPI and ICL670A compared to SIH at the longer exposure time may be due to differences in the stabilities of these structures. HAPI is significantly more resistant to plasma hydrolysis than SIH [26], and ICL670A is known to have a long plasma half-life [50]. Whereas the chelating efficiency of SIH self-destructs over time, the other agents could potentiate their toxicity by removing or withholding Fe from critical Fe-containing proteins, or otherwise interfering with normal metal metabolism [12].…”

“…BSIH-PD is a BSIH analog that contains a pinanediol boronic ester instead of pinacol. The prochelator BHAPI is derived from HAPI, an SIH analog with improved hydrolytic stability [26], but the direct boronic ester group of BSIH is replaced with a self-immolative spacer that undergoes spontaneous elimination after reacting with H 2 O 2 [27]. In addition, two novel triazole prochelators were derived from the clinically-used Fe chelator ICL670A, both with the self-immolative spacer and boronic acid (TIP) or its pinacol diol ester (TRA-IMM) [27].…”

Prooxidant and antioxidant properties of salicylaldehyde isonicotinoyl hydrazone iron chelators in HepG2 cells

“…SIH prevented toxicity in: i) H9c2 rat cardiomyoblasts exposed to catecholamines [1], hydrogen peroxide [2] or tert-butylhydroperoxide [3]; A549 human lung adenocarcinoma cells exposed to hydrogen peroxide/ferrous iron [4]; iii) ARPE-19 human retinal pigment epithelial cells exposed to hydrogen peroxide [5]; and iv) primary rat cardiomyocytes exposed to ferrous sulfate or hydrogen peroxide [6]. SIH readily diffuses into cells by virtue of its hydrophobicity and low molecular weight, binds ferric iron in the labile iron pool (LIP, the transitory pool of cellular chelatable redox-active iron) with high affinity and prevents its reduction to ferrous iron [5,6].…”

“…For this reason, the mechanism of SIH-induced cytoprotection is suggested to be the prevention of the formation of ferrous iron and ROS [5]. Experimental evidence to support this hypothesis includes the observation that SIH decreased the intracellular formation of ROS in H9c2 cells exposed to catecholamines (which reduce ferric to ferrous iron) [1], tert-butyl hydroperoxide [9] or ferric iron [3]. In addition, SIH decreased lipid oxidation in A549 cells exposed to hydrogen peroxide/ferrous iron [4], and in HepG2 human hepatoma cells exposed to cumene hydroperoxide [10].…”