Prevention of postasphyxia electroretinal dysfunction with a pyridoxal hydrazone

Complexes of Gold(III) with Hydrazones Derived from Pyridoxal: Stability, Structure, and Nature of UV-Vis Spectra

Pyridoxal and pyridoxal 5'-phosphate are aldehyde forms of B6 vitamin that can easily be transformed into each other in the living organism. The presence of a phosphate group, however, provides the related compounds (e.g., hydrazones) with better solubility in water. In addition, the phosphate group may sometimes act as a binding center for metal ions. In particular, a phosphate group can be a strong ligand for a gold(III) ion, which is of interest for researchers for the anti-tumor and antimicrobial potential of gold(III). This paper aims to answer whether the phosphate group is involved in the complex formation between gold(III) and hydrazones derived from pyridoxal 5'-phosphate. The answer is negative, since the comparison of the stability constants determined for the gold(III) complexes with pyridoxal- and pyridoxal 5'-phosphate-derived hydrazones showed a negligible difference. In addition, quantum chemical calculations confirmed that the preferential coordination of two series of phosphorylated and non-phosphorylated hydrazones to gold(III) ion is similar. The preferential protonation modes for the gold(III) complexes were also determined using experimental and calculated data.

A Potential Alternative against Neurodegenerative Diseases: Phytodrugs

Neurodegenerative diseases (ND) primarily affect the neurons in the human brain secondary to oxidative stress and neuroinflammation. ND are more common and have a disproportionate impact on countries with longer life expectancies and represent the fourth highest source of overall disease burden in the high-income countries. A large majority of the medicinal plant compounds, such as polyphenols, alkaloids, and terpenes, have therapeutic properties. Polyphenols are the most common active compounds in herbs and vegetables consumed by man. The biological bioactivity of polyphenols against neurodegeneration is mainly due to its antioxidant, anti-inflammatory, and antiamyloidogenic effects. Multiple scientific studies support the use of herbal medicine in the treatment of ND; however, relevant aspects are still pending to explore such as metabolic analysis, pharmacokinetics, and brain bioavailability.

Oxidative stress, redox signaling, and metal chelation in anthracycline cardiotoxicity and pharmacological cardioprotection

SIGNIFICANCE

Anthracyclines (doxorubicin, daunorubicin, or epirubicin) rank among the most effective anticancer drugs, but their clinical usefulness is hampered by the risk of cardiotoxicity. The most feared are the chronic forms of cardiotoxicity, characterized by irreversible cardiac damage and congestive heart failure. Although the pathogenesis of anthracycline cardiotoxicity seems to be complex, the pivotal role has been traditionally attributed to the iron-mediated formation of reactive oxygen species (ROS). In clinics, the bisdioxopiperazine agent dexrazoxane (ICRF-187) reduces the risk of anthracycline cardiotoxicity without a significant effect on response to chemotherapy. The prevailing concept describes dexrazoxane as a prodrug undergoing bioactivation to an iron-chelating agent ADR-925, which may inhibit anthracycline-induced ROS formation and oxidative damage to cardiomyocytes.

RECENT ADVANCES

A considerable body of evidence points to mitochondria as the key targets for anthracycline cardiotoxicity, and therefore it could be also crucial for effective cardioprotection. Numerous antioxidants and several iron chelators have been tested in vitro and in vivo with variable outcomes. None of these compounds have matched or even surpassed the effectiveness of dexrazoxane in chronic anthracycline cardiotoxicity settings, despite being stronger chelators and/or antioxidants.

CRITICAL ISSUES

The interpretation of many findings is complicated by the heterogeneity of experimental models and frequent employment of acute high-dose treatments with limited translatability to clinical practice.

FUTURE DIRECTIONS

Dexrazoxane may be the key to the enigma of anthracycline cardiotoxicity, and therefore it warrants further investigation, including the search for alternative/complementary modes of cardioprotective action beyond simple iron chelation.

Iron chelation-afforded cardioprotection against chronic anthracycline cardiotoxicity: A study of salicylaldehyde isonicotinoyl hydrazone (SIH)

Pyridoxal-derived aroylhydrazone iron chelators have been previously shown as effective cardioprotectants against chronic anthracycline cardiotoxicity. In this study we focused on a novel salicylaldehyde analogue (salicylaldehyde isonicotinoyl hydrazone, SIH), which has been recently demonstrated to possess marked and dose-dependent protective effects against oxidative injury of cardiomyocytes. Therefore, in the present study the cardioprotective potential of SIH against daunorubicin (DAU) cardiotoxicity was assessed in vitro (isolated rat ventricular cardiomyocytes; DAU 10 microM, 48 h exposure) as well as in vivo (chronic DAU-induced cardiomyopathy in rabbits; DAU 3mg/kg, i.v. weekly, 10 weeks). In vitro, SIH (3-100 microM) was able to partially, but significantly decrease the LDH leakage from cardiomyocytes. In vivo, SIH co-administration was capable to reduce (SIH dose of 0.5mg/kg, i.v.) or even to completely prevent (1.0mg/kg, i.v.) the DAU-induced mortality. Moreover, the latter dose of the chelator significantly improved the left ventricular function (LV dP/dt(max)=1185+/-80 kPa/s versus 783+/-53 kPa/s in the DAU group; P<0.05) and decreased the severity of the myocardial morphological changes as well as the plasma levels of cardiac troponin T. Unfortunately, further escalation of the SIH dose (to 2.5mg/kg) resulted in a nearly complete reversal of the protective effects as judged by the overall mortality, functional, morphological as well as biochemical examinations. Hence, this study points out that aroylhydrazone iron chelators can induce a significant cardioprotection against anthracycline cardiotoxicity; however, they share the curious dose-response relationship which is unrelated to the chemical structure or the route of the administration of the chelator.

Safety and tolerability of repeated administration of pyridoxal 2-chlorobenzoyl hydrazone in rabbits

Recently, pyridoxal 2-chlorobenzoyl hydrazone (o-108) has been identified as an effective iron chelator [Link et al., Blood 2003; 101: 4172-79]. Since chronic treatment would be necessary in its potential indications, in the present study, the safety and tolerability of this agent after repeated administration was determined. Three doses of o-108 (25, 50, 100 mg/kg, in 10% Cremophor EL) were administered intraperitoneally, once weekly, for 10 weeks to three groups (n=5 each) of Chinchilla male rabbits. The effects on biochemical, haematological and cardiovascular parameters were examined during the experiment; histopathological examination was performed at the end of the experiment. Results were compared with control (saline 2 mL/kg, n=11) and vehicle groups (10% Cremophor EL, 2 mL/kg, n=12). No premature deaths occurred; the well-being of animals was evidenced by their body weight gain, although lower gain was observed with the highest dose (100 mg/kg). Significant elevations of cardiac troponin T plasma concentrations were observed with the highest dose of o-108, but no abnormalities were found in the cardiovascular function and only minor and inconsistent changes in haematological and biochemical parameters were observed. Histopathological examinations of selected organs revealed only weak and reversible changes through all studied groups. Thus, the data from this study suggest that o-108 remains a promising drug from the standpoint of the possibility of its repeated administration and warrants further investigation.

HPLC study on stability of pyridoxal isonicotinoyl hydrazone

Biocompatible iron chelators are currently under extensive investigation as promising drug candidates. Pyridoxal isonicotinoyl hydrazone (PIH) is a lead compound of the aroylhydrazone group of novel iron chelating agents. In this study, the precise and accurate HPLC analytical methods were used for the stability evaluation of water-soluble PIH salt (PIH x 2HCl) in aqueous media of different pH (2.0, 3.9, 7.0, 9.0 and 12.0) as well as in two selected pharmaceutical co-solvents at both laboratory and elevated (40 degrees C) temperatures. The susceptibility of PIH x 2HCl to oxidative decomposition was studied in the solutions of hydrogen peroxide (3 and 30%). Furthermore, the solid substance of PIH x 2HCl was exposed to UV, dry and wet heat. Our experiments revealed that PIH was considerably sensitive to hydrolytic decomposition in aqueous media, resulting in the splitting of the hydrazone bond. The elevated temperature significantly accelerated the hydrolytic reaction. The lowest rate of hydrolysis of PIH was observed in the phosphate buffer of pH 7.0 and in the pharmaceutical co-solvents (30% PEG-300 and 10% Cremophor EL). No special degradation products were detected in the samples exposed to either hydrogen peroxide or co-solvents. The solid substance of PIH x 2HCl was stable when exposed to UV, dry or wet heat for 33 h.

Study of daunorubicin cardiotoxicity prevention with pyridoxal isonicotinoyl hydrazone in rabbits

Risk of cardiotoxicity is the most serious drawback of the clinical usefulness of anthracycline antineoplastic antibiotics, which however, remain among the most powerful and widely employed anticancer drugs. In this study we have used daunorubicin-induced cardiomyopathy in rabbits as a model to investigate possible cardioprotective effects of pyridoxal isonicotinoyl hydrazone (PIH)-a principal representative of a novel group of aroylhydrazone iron chelators. Three groups of animals were used: a control group (n=11; i.v. saline), daunorubicin-treated animals (n=11; 3mg/kg, i.v.), and animals pretreated with PIH (n=9, 25 mg/kg, i.p.) 60 min before daunorubicin administration. All substances were administered once weekly for 10 weeks. Repeated administration of daunorubicin caused premature death in four animals and induced conspicuous histopathological changes in the myocardium, progressive and significant impairment of systolic heart function (a decrease in left ventricular dP/dt(max), ejection fraction, an increase in the pre-ejection period/left ventricular ejection time index), and a gradual increase in cardiac troponin T plasma concentrations. On the contrary, all the PIH-treated animals have survived all daunorubicin applications. Furthermore, in this group, the daunorubicin-induced cardiac changes were in most functional, biochemical as well as morphological parameters less pronounced than in the group receiving daunorubicin alone. Hence, PIH and other aroylhydrazones merit further investigation as potentially protective agents against anthracycline-induced cardiotoxicity.

Pyridoxal isonicotinoyl hydrazone inhibits iron-induced ascorbate oxidation and ascorbyl radical formation

Previous work from our laboratory demonstrated that pyridoxal isonicotinoyl hydrazone (PIH) has in vitro antioxidant activity against iron plus ascorbate-induced 2-deoxyribose degradation due to its ability to chelate iron; the resulting Fe(III)-PIH(2) complex is supposedly unable to catalyze oxyradical formation. A putative step in the antioxidant action of PIH is the inhibition of Fe(III)-mediated ascorbate oxidation, which yields the Fenton reagent Fe(II) [Biochim. Biophys. Acta 1523 (2000) 154]. In this work, we demonstrate that PIH inhibits Fe(III)-EDTA-mediated ascorbate oxidation (measured at 265 nm) and the formation of ascorbyl radical (in electron paramagnetic resonance (EPR) studies). The efficiency of PIH against ascorbate oxidation, ascorbyl radical formation and 2-deoxyribose degradation was dose dependent and directly proportional to the period of preincubation of PIH with Fe(III)-EDTA. The efficiency of PIH in inhibiting ascorbate oxidation and ascorbyl radical formation was also inversely proportional to the Fe(III)-EDTA concentration in the media. When EDTA was replaced by the weaker iron ligand nitrilotriacetic acid (NTA), PIH was much more effective in preventing ascorbate oxidation, ascorbyl radical formation and 2-deoxyribose degradation. Moreover, the replacement of EDTA with citrate, a physiological chelator with a low affinity for iron, also resulted in PIH having a higher efficiency in inhibiting iron-mediated ascorbate oxidation and 2-deoxyribose degradation. These results demonstrate that PIH removes iron from EDTA (or from either NTA or citrate), forming an iron-PIH complex that cannot induce ascorbate oxidation effectively, thus inhibiting iron-mediated oxyradical formation. These results are of pharmacological relevance because PIH has been considered for experimental chelating therapy in iron-overload diseases.

Pyridoxal isonicotinoyl hydrazone (PIH) prevents copper-mediated in vitro free radical formation

Pyridoxal isonicotinoyl hydrazone (PIH) is an iron chelator with antioxidant activity, low toxicity and is useful in the experimental treatment of iron-overload diseases. Previous studies on x-ray diffraction have revealed that PIH also forms a complex with Cu(II). Since the main drug of choice for the treatment of Wilson's disease, d-penicillamine, causes a series of side effects, there is an urgent need for the development of alternative copper chelating agents for clinical use. These chelators must also have antioxidant activity because oxidative stress is associated with brain and liver copper-overload. In this work we tested the ability of PIH to prevent in vitro free radical formation mediated by Cu(II), ascorbate and dissolved O2. Degradation of 2-deoxyribose mediated by 10 microM Cu(II) and 3 mM ascorbate was fully inhibited by 10 microM PIH (I50 = 6 microM) or 20 microM d-penicillamine (I50 = 10 microM). The antioxidant efficiency of PIH remained unchanged with increasing concentrations (from 1 to 15 mM) of the hydroxyl radical detector molecule, 2-deoxyribose, indicating that PIH does not act as a hydroxyl scavenger. On the other hand, the efficiency of PIH (against copper-mediated 2-deoxyribose degradation and ascorbate oxidation) was inversely proportional to the Cu(II) concentration, suggesting a competition between PIH and ascorbate for complexation with Cu(lI). An almost full inhibitory effect by PIH was observed when the ratio PIH:copper was 1:1. A similar result was obtained with the measurement of copper plus ascorbate-mediated O2 uptake. Moreover, spectral studies of the copper and PIH interaction showed a peak at 455 nm and also indicated the formation of a stable Cu(II) complex with PIH with a 1:1 ratio. These data demonstrated that PIH prevents hydroxyl radical formation and oxidative damage to 2-deoxyribose by forming a complex with Cu(II) that is not reactive with ascorbate (first step of the reactions leading to hydroxyl radical formation from Cu(II), ascorbate and O2) and does not participate in Haber-Weiss reactions.

The iron chelator pyridoxal isonicotinoyl hydrazone inhibits mitochondrial lipid peroxidation induced by Fe(II)-citrate

Pyridoxal isonicotinoyl hydrazone (PIH) is able to prevent iron-mediated hydroxyl radical formation by means of iron chelation and inhibition of redox cycling of the metal. In this study, we investigated the effect of PIH on Fe(II)-citrate-mediated lipid peroxidation and damage to isolated rat liver mitochondria. Lipid peroxidation was quantified by the production of thiobarbituric acid-reactive substances (TBARS) and by antimycin A-insensitive oxygen consumption. PIH at 300 microM induced full protection against 50 microM Fe(II)-citrate-induced loss of mitochondrial transmembrane potential (deltapsi) and mitochondrial swelling. In addition, PIH prevented the Fe(II)-citrate-dependent formation of TBARS and antimycin A-insensitive oxygen consumption. The antioxidant effectiveness of 100 microM PIH (on TBARS formation and mitochondrial swelling) was greater in the presence of 20 or 50 microM Fe(II)-citrate than in the presence of 100 microM Fe(II)-citrate, suggesting that the mechanism of PIH antioxidant action is linked with its Fe(II) chelating property. Finally, PIH increased the rate of Fe(II) autoxidation by sequestering iron from the Fe(II)-citrate complex, forming a Fe(III)-PIH, complex that does not participate in Fenton-type reactions and lipid peroxidation. These results are of pharmacological relevance since PIH is a potential candidate for chelation therapy in diseases related to abnormal intracellular iron distribution and/or iron overload.

The iron chelator pyridoxal isonicotinoyl hydrazone (PIH) and its analogues prevent damage to 2-deoxyribose mediated by ferric iron plus ascorbate

Iron chelating agents are essential for treating iron overload in diseases such as beta-thalassemia and are potentially useful for therapy in non-iron overload conditions, including free radical mediated tissue injury. Deferoxamine (DFO), the only drug available for iron chelation therapy, has a number of disadvantages (e.g., lack of intestinal absorption and high cost). The tridentate chelator pyridoxal isonicotinoyl hydrazone (PIH) has high iron chelation efficacy in vitro and in vivo with high selectivity and affinity for iron. It is relatively non-toxic, economical to synthesize and orally effective. We previously demonstrated that submillimolar levels of PIH and some of its analogues inhibit lipid peroxidation, ascorbate oxidation, 2-deoxyribose degradation, plasmid DNA strand breaks and 5,5-dimethylpyrroline-N-oxide (DMPO) hydroxylation mediated by either Fe(II) plus H(2)O(2) or Fe(III)-EDTA plus ascorbate. To further characterize the mechanism of PIH action, we studied the effects of PIH and some of its analogues on the degradation of 2-deoxyribose induced by Fe(III)-EDTA plus ascorbate. Compared with hydroxyl radical scavengers (DMSO, salicylate and mannitol), PIH was about two orders of magnitude more active in protecting 2-deoxyribose from degradation, which was comparable with some of its analogues and DFO. Competition experiments using two different concentrations of 2-deoxyribose (15 vs. 1.5 mM) revealed that hydroxyl radical scavengers (at 20 or 60 mM) were significantly less effective in preventing degradation of 2-deoxyribose at 15 mM than 2-deoxyribose at 1.5 mM. In contrast, 400 microM PIH was equally effective in preventing degradation of both 15 mM and 1.5 mM 2-deoxyribose. At a fixed Fe(III) concentration, increasing the concentration of ligands (either EDTA or NTA) caused a significant reduction in the protective effect of PIH towards 2-deoxyribose degradation. We also observed that PIH and DFO prevent 2-deoxyribose degradation induced by hypoxanthine, xanthine oxidase and Fe(III)-EDTA. The efficacy of PIH or DFO was inversely related to the EDTA concentration. Taken together, these results indicate that PIH (and its analogues) works by a mechanism different than the hydroxyl radical scavengers. It is likely that PIH removes Fe(III) from the chelates (either Fe(III)-EDTA or Fe(III)-NTA) and forms a Fe(III)-PIH(2) complex that does not catalyze oxyradical formation.

Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions

Tannic acid (TA), a plant polyphenol, has been described as having antimutagenic, anticarcinogenic and antioxidant activities. Since it is a potent chelator of iron ions, we decided to examine if the antioxidant activity of TA is related to its ability to chelate iron ions. The degradation of 2-deoxyribose induced by 6 microM Fe(II) plus 100 microM H2O2 was inhibited by TA, with an I50 value of 13 microM. Tannic acid was over three orders of magnitude more efficient in protecting against 2-deoxyribose degradation than classical *OH scavengers. The antioxidant potency of TA was inversely proportional to Fe(II) concentration, demonstrating a competition between H2O2 and AT for reaction with Fe(II). On the other hand, the efficiency of TA was nearly unchanged with increasing concentrations of the *OH detector molecule, 2-deoxyribose. These results indicate that the antioxidant activity of TA is mainly due to iron chelation rather than *OH scavenging. TA also inhibited 2-deoxyribose degradation mediated by Fe(III)-EDTA (iron = 50 microM) plus ascorbate. The protective action of TA was significantly higher with 50 microM EDTA than with 500 microM EDTA, suggesting that TA removes Fe(III) from EDTA and forms a complex with iron that cannot induce *OH formation. We also provided evidence that TA forms a stable complex with Fe(II), since excess ferrozine (14 mM) recovered 95-96% of the Fe(II) from 10 microM TA even after a 30-min exposure to 100-500 microM H2O2. Addition of Fe(III) to samples containing TA caused the formation of Fe(II)n-TA, complexes, as determined by ferrozine assays, indicating that TA is also capable of reducing Fe(III) ions. We propose that when Fe(II) is complexed to TA, it is unable to participate in Fenton reactions and mediate *OH formation. The antimutagenic and anticarcinogenic activity of TA, described elsewhere, may be explained (at least in part) by its capacity to prevent Fenton reactions.

The iron chelator pyridoxal isonicotinoyl hydrazone (PIH) protects plasmid pUC-18 DNA against *OH-mediated strand breaks

Pyridoxal isonicotinoyl hydrazone (PIH) has previously been studied for use in iron chelation therapy in iron-overload diseases. It is an efficient in vitro antioxidant due to its Fe(III) complexing activity (Schulman, H. M., et al. Redox Report 1:373-378; 1995). Pathologies associated with iron-overload include hepatic and other cancers. Since oxidative alterations of DNA can be linked to the development of cancer, we decided to study whether PIH protects DNA against in vitro oxidative stress. We report here that pUC-18 plasmid DNA is damaged by *OH radicals generated from Fe(II) plus H2O2 or from Fe(II) plus hypoxanthine/xanthine oxidase. The DNA damage was quantified by determining the diminution of supercoiled DNA forms after oxidative attack using agar gel electrophoresis. Micromolar amounts of PIH (20-30 microM) were able to half-protect DNA from iron (1-7.5 microM)-mediated *OH formation. The antioxidant capacity of PIH was significantly higher than that of some of its analogs and desferrioxamine. PIH and some of its analogues could also inhibit the oxidative degradation of 2-deoxyribose caused by Fenton reagents. Since we observed that PIH enhances the Fe(II) autoxidation rate, measured by the ferrozine technique, PIH may limit *OH formation and consequently DNA damage by decreasing the amount of Fe(II) available to catalyze Fenton reactions.

Development of iron chelators to treat iron overload disease and their use as experimental tools to probe intracellular iron metabolism

The development of an orally effective iron (Fe) chelator for the treatment of Fe overload diseases such as beta-thalassemia has been a difficult challenge. Even though the drug in current clinical use, desferrioxamine (DFO), is efficient and remarkably free of toxicity, it suffers from not being orally effective and requiring long subcutaneous infusion to mobilize sufficient quantities of Fe. In addition, DFO is very expensive, which precludes it from treating most of the world's thalassemic population. Therefore, the development of an economical and orally effective Fe chelator is of great importance. Despite the screening of a wide range of structurally diverse ligands from both natural and synthetic sources, few compounds have been promising enough to proceed to clinical trials. In the current review, the properties of an ideal chelator are discussed, followed by a description of the most successful ligands that have been identified. Apart from the use of Fe chelators as therapeutic agents, some of these compounds have also been useful as experimental probes to investigate cellular Fe metabolism. We describe here the most important of these studies.