Liver microsomal biotransformation of nitro-aryl drugs: mechanism for potential oxidative stress induction

Structural and Mechanistic Investigation of the Unusual Metabolism of Nifurtimox

The oral antiparasitic drug nifurtimox has been used to treat Chagas disease for more than 50 years. Historical studies determined that very little nifurtimox is excreted unchanged, but contemporaneous preclinical studies of radiolabeled nifurtimox found almost all of the radiolabel was rapidly excreted, suggesting that metabolism is extensive. Attempts to study nifurtimox metabolism have had limited success, yet this knowledge is fundamental to characterizing the pharmacokinetics and pharmacodynamics of the drug. We conducted in vitro studies using hepatic and renal sources with 14C-labeled nifurtimox as substrate and obtained samples of urine, plasma, and feces from rats administered 2.5 mg/kg [14C]-nifurtimox, and samples of human urine and plasma from phase 1 clinical studies in which participants received a single dose of 120 mg nifurtimox. Analysis of metabolites was done by high-performance liquid chromatography (HPLC)-high-resolution mass spectrometry (HRMS) and HRMS/MS with offline liquid scintillation counting of radiolabeled samples. Surprisingly, only traces of a few metabolites were identified from in vitro incubations with hepatocytes and subcellular fractions, but more than 30 metabolites were identified in rat urine, mostly with atypical mass changes. We developed an HRMS scouting method for the analysis of human samples based on the sulfur atom in nifurtimox and the natural abundance of 34S, as well as a characteristic tandem mass spectrometry (MS/MS) fragmentation of nifurtimox and metabolites. Fragmentation patterns on HRMS/MS were used to propose structures for 18 metabolites (22 including stereoisomers), and based on these structures, the six most abundant products were synthesized and the structures of the synthetic forms were confirmed by HRMS and two-dimensional nuclear magnetic resonance (2D NMR). Overall, we determined that the metabolism of nifurtimox is almost certainly not mediated by typical hepatic and renal drug-metabolizing enzymes, and instead is rapidly metabolized mainly by reduction or nucleophilic attack, with some evidence of oxidation. Knowledge of the most abundant metabolites of nifurtimox affords the possibility of future studies to investigate levels of exposure and possible drug-drug interactions.

Pharmaceutical and Safety Profile Evaluation of Novel Selenocompounds with Noteworthy Anticancer Activity

Prior studies have reported the potent and selective cytotoxic, pro-apoptotic, and chemopreventive activities of a cyclic selenoanhydride and of a series of selenoesters. Some of these selenium derivatives demonstrated multidrug resistance (MDR)-reversing activity in different resistant cancer cell lines. Thus, the aim of this study was to evaluate the pharmaceutical and safety profiles of these selected selenocompounds using alternative methods in silico and in vitro. One of the main tasks of this work was to determine both the physicochemical properties and metabolic stability of these selenoesters. The obtained results proved that these tested selenocompounds could become potential candidates for novel and safe anticancer drugs with good ADMET parameters. The most favorable selenocompounds turned out to be the phthalic selenoanhydride (EDA-A6), two ketone-containing selenoesters with a 4-chlorophenyl moiety (EDA-71 and EDA-73), and a symmetrical selenodiester with a pyridine ring and two selenium atoms (EDA-119).

Review of pharmacological options for the treatment of Chagas disease

Chagas disease (CD) is a worldwide problem, with over 8 million people infected in both rural and urban areas. CD was first described over a century ago, but only two drugs are currently available for CD treatment: benznidazole (BZN) and nifurtimox (NF). Treating CD-infected patients, especially children and women of reproductive age, is vital in order to prevent long-term sequelae, such as heart and gastrointestinal dysfunction, but this aim is still far from being accomplished. Currently, the strongest data to support benefit-risk considerations come from trials in children. Treatment response biomarkers need further development as serology is being questioned as the best method to assess treatment response. This article is a narrative review on the pharmacology of drugs for CD, particularly BZN and NF. Data on drug biopharmaceutical characteristics, safety and efficacy of both drugs are summarized from a clinical perspective. Current data on alternative compounds under evaluation for CD treatment, and new possible treatment response biomarkers are also discussed. Early diagnosis and treatment of CD, especially in paediatric patients, is vital for an effective and safe use of the available drugs (i.e. BZN and NF). New biomarkers for CD are urgently needed for the diagnosis and evaluation of treatment efficacy, and to guide efforts from academia and pharmaceutical companies to accelerate the process of new drug development.

Stimulation of de novo glutathione synthesis by nitrofurantoin for enhanced resilience of hepatocytes

Toxicity is not only a function of damage mechanisms, but is also determined by cellular resilience factors. Glutathione has been reported as essential element to counteract negative influences. The present work hence pursued the question how intracellular glutathione can be elevated transiently to render cells more resistant toward harmful conditions. The antibiotic nitrofurantoin (NFT) was identified to stimulate de novo synthesis of glutathione in the human hepatoma cell line, HepG2, and in primary human hepatocytes. In intact cells, activation of NFT yielded a radical anion, which subsequently initiated nuclear-factor-erythroid 2-related-factor-2 (Nrf2)-dependent induction of glutamate cysteine ligase (GCL). Application of siRNA-based intervention approaches confirmed the involvement of the Nrf2-GCL axis in the observed elevation of intracellular glutathione levels. Quantitative activation of Nrf2 by NFT, and the subsequent rise in glutathione, were similar as observed with the potent experimental Nrf2 activator diethyl maleate. The elevation of glutathione levels, observed even 48 h after withdrawal of NFT, rendered cells resistant to different stressors such as the mitochondrial inhibitor rotenone, the redox cycler paraquat, the proteasome inhibitors MG-132 or bortezomib, or high concentrations of NFT. Repurpose of the antibiotic NFT as activator of Nrf2 could thus be a promising strategy for a transient and targeted activation of the endogenous antioxidant machinery. Graphical abstract.

Dipyridamole potentiated the trypanocidal effect of nifurtimox and improved the cardiac function in NMRI mice with acute chagasic myocarditis

BACKGROUND

As chronic Chagas disease does not have a definitive treatment, the development of alternative therapeutic protocols is a priority. Dipyridamole (DPY) is an alternative to counteract the pathophysiological phenomena involved in Chagas cardiomyopathy.

OBJECTIVE

To evaluate the therapeutic efficacy of DPY associated with nifurtimox (Nfx) in epimastigote axenic cultures and in mice with acute Chagas disease.

METHODS

NMRI adult male mice were divided into nine groups: three healthy and six Trypanosoma cruzi-infected groups. Mice received vehicle, Nfx or DPY, alone or combined. The doses assayed were Nfx 10 and 40 mg/kg and DPY 30 mg/kg. The treatment efficacy was evaluated by clinical, electrocardiographic, parasitological, biochemical and histopathological methods.

FINDINGS

In vitro, DPY and Nfx had a trypanocidal effect with IC50 values of 372 ± 52 and 21.53 ± 2.13 µM, respectively; DPY potentiated the Nfx effect. In vivo, Nfx (40 mg/kg) with or without DPY had a therapeutic effect, which was reflected in the 84-92% survival rate and elimination of parasitaemia and heart tissue amastigotes. Nfx (10 mg/kg) had a subtherapeutic effect with no survival and persistence of amastigotes, inflammation and fibrosis in heart tissue; adding DPY increased the survival rate to 85%, and all tested parameters were significantly improved.

MAIN CONCLUSION

DPY has a trypanocidal effect in vitro and enhances the Nfx therapeutic effect in an in vivo murine model.

1,4-Dihydropyridine Derivatives: Dihydronicotinamide Analogues-Model Compounds Targeting Oxidative Stress

Many 1,4-dihydropyridines (DHPs) possess redox properties. In this review DHPs are surveyed as protectors against oxidative stress (OS) and related disorders, considering the DHPs as specific group of potential antioxidants with bioprotective capacities. They have several peculiarities related to antioxidant activity (AOA). Several commercially available calcium antagonist, 1,4-DHP drugs, their metabolites, and calcium agonists were shown to express AOA. Synthesis, hydrogen donor properties, AOA, and methods and approaches used to reveal biological activities of various groups of 1,4-DHPs are presented. Examples of DHPs antioxidant activities and protective effects of DHPs against OS induced damage in low density lipoproteins (LDL), mitochondria, microsomes, isolated cells, and cell cultures are highlighted. Comparison of the AOA of different DHPs and other antioxidants is also given. According to the data presented, the DHPs might be considered as bellwether among synthetic compounds targeting OS and potential pharmacological model compounds targeting oxidative stress important for medicinal chemistry.

Microsomal oxidative stress induced by NADPH is inhibited by nitrofurantoin redox biotranformation

Nitrofurantoin is used in the antibacterial therapy of the urinary tract. This therapy is associated with various adverse effects whose mechanisms remain unclear. Diverse studies show that the nitro reductive metabolism of nitrofurantoin leads to ROS generation. This reaction can be catalyzed by several reductases, including the cytochrome P450 (CYP450) reductase. Oxidative stress arising from this nitro reductive metabolism has been proposed as the mechanism underlying the adverse effects associated with nitrofurantoin. There is, however, an apparent paradox between these findings and the ability of nitrofurantoin to inhibit lipid peroxidation provoked by NADPH in rat liver microsomes. This work was aimed to show the potential contribution of different enzymatic systems to the metabolism of this drug in rat liver microsomes. Our results show that microsomal lipid peroxidation promoted by NADPH is inhibited by nitrofurantoin in a concentration-dependent manner. This suggests that the consumption of NADPH in microsomes can be competitively promoted by lipid peroxidation and nitrofurantoin metabolism. The incubation of microsomes with NADPH and nitrofurantoin generated 1-aminohidantoin. In addition, the biotransformation of a classical substrate of CYP450 oxidative system was competitively inhibited by nitrofurantoin. These results suggest that nitrofurantoin is metabolized through CYP450 system. Data are discussed in terms of the in vitro redox metabolism of nitrofurantoin.

Ameliorative effect of lycopene against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced rat liver microsomal toxicity

The objective of the current study was to investigate the potential oxidative damage of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) in hepatic microsomal fractions in vitro and to further elucidate the potential modulatory effect of lycopene. Rat liver microsomes were divided into four groups. Group I served as a control and is incubated with vehicle (toluene). Groups II and IV were incubated with 20 µM lycopene for 1 h before further incubating; groups III and IV with 15 nM of TCDD for further 1 h. Hydrogen peroxide (H2O2) production, lipid peroxidation (LPO), protein carbonyl content and activities of uridine 5′-diphospho-glucuronyltransferase (UDPGT) and P450 were significantly increased. Moreover, the activity of antioxidant enzymes superoxide dismutase, glutathione peroxidase, catalse, glutathione- S-transferase and glutathione reductase as well as the microsomal thiol content were significantly decreased. Incubation with lycopene (group IV) maintained near normal activities of the enzymes, normalized thiol and carbonyl content and significantly reduced LPO and H2O2 production. In conclusion, the findings of the study indicate that TCDD induces a significant oxidative stress in liver microsomes as manifested by increased LPO, H2O2 production, protein carbonyl content and activities of UDPGT and P450 and decreased antioxidant enzymes activities and thiol content. By the reversal of biochemical and oxidative markers toward normalcy, the protective role of lycopene is illuminated in rat liver microsomal toxicity.

Pyrogallol red oxidation induced by superoxide radicals: application to evaluate redox cycling of nitro compounds

The bleaching of the pyrogallol red (PGR) dye mediated by superoxide anion radicals (O(2)(-)) generated from the xanthine/xanthine oxidase system (X/XO) was studied by UV-visible spectrophotometry. The absorption band (at 540 nm) of PGR quickly decreased in the presence of X/XO, implying an efficient reaction of O(2)(-) with PGR. The process was unaffected by catalase (CAT), but completely abolished by superoxide dismutase (SOD). A mechanism of the reaction involving the consumption of one PGR molecule by two O(2)(-) to generate one molecule of H(2)O(2) is proposed. PGR was used as a probe to estimate the rate of O(2)(-) generation in redox cycling reactions of a series of nitro compounds mediated by rat liver microsomes. The consumption of PGR induced by the redox cycling of nitrofurantoin was totally eliminated by the addition of SOD but unaffected by CAT. The initial rate of consumption of PGR mediated by the redox cycling of others nitro derivatives follows the order: furazolidindione > nitrofurantoin > nifurtimox > benznidazole > chloramphenicol. We concluded that PGR can be used as a probe to estimate the release of O(2)(-) from enzymatic systems or from the redox cycling of nitro compounds.

Eeyarestatin 1 interferes with both retrograde and anterograde intracellular trafficking pathways

BACKGROUND

The small molecule Eeyarestatin I (ESI) inhibits the endoplasmic reticulum (ER)-cytosol dislocation and subsequent degradation of ERAD (ER associated protein degradation) substrates. Toxins such as ricin and Shiga/Shiga-like toxins (SLTx) are endocytosed and trafficked to the ER. Their catalytic subunits are thought to utilise ERAD-like mechanisms to dislocate from the ER into the cytosol, where a proportion uncouples from the ERAD process, recovers a catalytic conformation and destroys their cellular targets. We therefore investigated ESI as a potential inhibitor of toxin dislocation.

METHODOLOGY AND PRINCIPAL FINDINGS

Using cytotoxicity measurements, we found no role for ES(I) as an inhibitor of toxin dislocation from the ER, but instead found that for SLTx, ESI treatment of cells was protective by reducing the rate of toxin delivery to the ER. Microscopy of the trafficking of labelled SLTx and its B chain (lacking the toxic A chain) showed a delay in its accumulation at a peri-nuclear location, confirmed to be the Golgi by examination of SLTx B chain metabolically labelled in the trans-Golgi cisternae. The drug also reduced the rate of endosomal trafficking of diphtheria toxin, which enters the cytosol from acidified endosomes, and delayed the Golgi-specific glycan modifications and eventual plasma membrane appearance of tsO45 VSV-G protein, a classical marker for anterograde trafficking.

CONCLUSIONS AND SIGNIFICANCE

ESI acts on one or more components that function during vesicular transport, whilst at least one retrograde trafficking pathway, that of ricin, remains unperturbed.

Microsomal oxidative damage promoted by acetaminophen metabolism

Adverse reactions of acetaminophen have been associated to oxidative stress, which may be elicited by reactive oxygen species (ROS) and/or production of the metabolite NAPQI. Both phenomena would arise through the activity of liver cytochrome P450 (CYP450) system, but their contribution to this oxidative stress is yet to be clarified. A NADPH oxidase activity has been proposed in rat liver microsomes. This activity may be due to the presence of NAD(P)H oxidase (NOX) isoforms in liver endoplasmic reticulum. Both NOX and the CYP450 system activities can catalyze ROS generation using NADPH as a cofactor. Therefore, acetaminophen biotransformation, which requires NADPH, may promote ROS generation through either activity or both. To discriminate between these possibilities, rat liver microsomes were incubated with acetaminophen and NADPH in the presence or absence of specific inhibitors. Incubation with NADPH and acetaminophen elicited lipid peroxidation and decreased thiol content and glutathione-S-transferase (GST) activity. The NOX inhibitors apocynin and plumbagin prevented all these phenomena but the decrease in thiol content. In contrast, this decrease was completely prevented by the specific CYP450 system inhibitor SKF-525A. These data suggest that ROS generation following incubation of microsomes with acetaminophen and NADPH appears to be mainly caused by a NOX activity. In light of these data, toxicity of acetaminophen is discussed.

Nifurtimox induces apoptosis of neuroblastoma cells in vitro and in vivo

Neuroblastoma is the most common extracranial solid tumor in children and, when disseminated, carries a poor prognosis. Even with aggressive combinations of chemotherapy, surgery, autologous bone marrow transplant, and radiation, long-term survival remains at 30% and new therapies are needed. Recently, a patient with neuroblastoma who acquired Chagas disease was treated with nifurtimox with subsequent reduction in tumor size. The effect of nifurtimox on the neuroblastoma cell lines CHLA-90, LA1-55n, LA-N2, SMS-KCNR, and SY5Y was examined. Nifurtimox decreased cell viability in a concentration-dependent manner. Cell morphology, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assay, and caspase-3 activation indicate that cell death was primarily due to apoptosis. Nifurtimox also suppressed basal and TrkB-mediated Akt phosphorylation, and the cytotoxicity of nifurtimox was attenuated by a tyrosine hydroxylase inhibitor (alpha-methyl-tyrosine). Nifurtimox killed catecholaminergic, but not cholinergic, autonomic neurons in culture. In vivo xenograft models showed inhibition of tumor growth with a histologic decrease in proliferation and increase in apoptosis. These results suggest that nifurtimox induces cell death in neuroblastoma. Therefore, further studies are warranted to develop nifurtimox as a promising new treatment for neuroblastoma.

Nitroreductive metabolic activation of some carcinogenic nitro heterocyclic food contaminants in rat mammary tissue cellular fractions

Several nitrofurans and nitroimidazoles have been widely used in veterinary medicine. Some of these compounds are breast carcinogens in rodents and their mechanism of action is hypothesized to be related to reactive metabolites generated by nitroreduction and/or via oxygen-dependent redox cycling. The present work describes the nitroreductive metabolism of nitrofurazone, nitrofurantoin, furazolidone, and metronidazole by the cytosolic and microsomal fractions of mammary tissue from female Sprague-Dawley rats. The data obtained were compared with those obtained with nifurtimox and benznidazole, two well-known rodent carcinogen/mutagens nitroheterocycles. The nitroreductase activity of pure milk xanthine-oxidoreductase (XOR) was evaluated for screening purposes. All the nitrofurans were nitroreduced either by the pure XOR or the cytosolic fraction in the presence of hypoxanthine, and these activities were inhibited by allopurinol. Furthermore, they were nitroreduced by the microsomal fraction in the presence of NADPH, except for the nitrofurazone, suggesting the participation of cytochrome P450 reductase. Nitrofurans metabolism was significantly more intense than that of NFX. No equivalent nitroreductase activity was observed in either subcellular fraction using nitroimidazolic compounds as substrates. These results suggest that the nitroreductive metabolism of nitrofurans and the subsequent redox cycling might be involved in the associated mammary tissue carcinogenic effects.

Computational models to assign biopharmaceutics drug disposition classification from molecular structure

PURPOSE

We applied in silico methods to automatically classify drugs according to the Biopharmaceutics Drug Disposition Classification System (BDDCS).

MATERIALS AND METHODS

Models were developed using machine learning methods including recursive partitioning (RP), random forest (RF) and support vector machine (SVM) algorithms with ChemDraw, clogP, polar surface area, VolSurf and MolConnZ descriptors. The dataset consisted of 165 training and 56 test set molecules.

RESULTS

RF model 3, RP model 1, and SVM model 1 can correctly predict 73.1, 63.6 and 78.6% test compounds in classes 1, 2 and 3, respectively. Both RP and SVM models can be used for class 4 prediction. The inclusion of consensus analysis resulted in improved test set predictions for class 2 and 4 drugs.

CONCLUSIONS

The models can be used to predict BDDCS class for new compounds from molecular structure using readily available molecular descriptors and software, representing an area where in silico approaches could aid the pharmaceutical industry in speeding drugs to the patient and reducing costs. This could have significant applications in drug discovery to identify molecules that may have future developability issues.

Nitroaryl-1,4-dihydropyridines as antioxidants against rat liver microsomes oxidation induced by iron/ascorbate, nitrofurantoin and naphthalene

1,4-Dihydropyridines (DHPs) used in the treatment of cardiovascular diseases, are calcium channel antagonists and also antioxidant agents. These drugs are metabolized through cytochrome P(450) oxidative system, majority localized in the hepatic endoplasmic reticulum. Several lipophilic drugs generate oxidative stress to be metabolized by this cellular system. Thus, DHP antioxidant properties may prevent the oxidative stress associated with hepatic biotransformation of drugs. In this work, we tested the antioxidant capacity of several synthetic nitro-phenyl-DHPs. These compounds (I-IV) inhibited the microsomal lipid peroxidation, UDPGT oxidative activation and microsomal thiols oxidation; all phenomena induced by Fe(3+)/ascorbate, a generator system of oxygen free radicals. As the same manner, these compounds inhibited the oxygen consumption induced by Cu(2+)/ascorbate in the absence of microsomes. Furthermore, compound III (2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridin-3,5-ethyl-dicarboxylate) and compound V (N-ethyl-2,6-dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridin-3,5-methyl-dicarboxylate) inhibited the microsomal lipid peroxidation induced by Nitrofurantoin and naphthalene in the presence of NADPH. Oxidative stress induced on endoplasmic reticulum may alter the biotransformation of drugs, so, modifying their plasmatic concentrations and therapeutic effects. When drugs which are activated by biotransformation are administered together with antioxidant drugs, such as DHPs, oxidative stress induced in situ may be prevented.

Copper modifies liver microsomal UDP-glucuronyltransferase activity through different and opposite mechanisms

Treatment of hepatic microsomes with Fe(3+)/ascorbate activates UDP-glucuronyltransferase (UGT), a phenomenon totally prevented and reversed by reducing agents. At microM concentrations, iron and copper ions catalyze the formation of ROS through Fenton and/or Haber-Weiss reactions. Unlike iron ions, indiscriminate binding of copper ions to thiol groups of proteins different from the specialized copper-binding proteins may occur. Thus, we hypothesize that incubation of hepatic microsomes with the Cu(2+)/ascorbate system will lead to both UGT oxidative activation and Cu(2+)-binding induced inhibition, simultaneously. We studied the effects of Cu(2+) alone and in the presence of ascorbate on rat liver microsomal UGT activity. Our results show that the effects of both copper alone and in the presence of ascorbate were copper ion concentration- and incubation time-dependent. At very low Cu(2+) (25nM), this ion did not modify UGT activity. In the presence of ascorbate, however, UGT activity was increased. At higher copper concentrations (10 and 50microM), this ion led to UGT activity inhibition. In the presence of ascorbate, 10microM Cu(2+) activated UGT at short incubation periods but inhibited this enzyme at longer incubation times; 50microM Cu(2+) only inhibited UGT activity. Thiol reducing agent 2,4-dithiothreitol prevented and reversed UGT activation while EDTA prevented both, UGT activation and inhibition. Our results are consistent with a model in which Cu(2+)-induced oxidation of UGT leads to the activation of the enzyme, while Cu(2+)-binding leads to its inhibition. We discuss physiological and pathological implications of these findings.

Inhibition of cytosolic glutathione S-transferase activity from rat liver by copper

H(2)O(2) inactivation of particular GST isoforms has been reported, with no information regarding the overall effect of other ROS on cytosolic GST activity. The present work describes the inactivation of total cytosolic GST activity from liver rats by the oxygen radical-generating system Cu(2+)/ascorbate. We have previously shown that this system may change some enzymatic activities of thiol proteins through two mechanisms: ROS-induced oxidation and non-specific Cu(2+) binding to protein thiol groups. In the present study, we show that nanomolar Cu(2+) in the absence of ascorbate did not modify total cytosolic GST activity; the same concentrations of Cu(2+) in the presence of ascorbate, however, inhibited this activity. Micromolar Cu(2+) in either the absence or presence of ascorbate inhibited cytosolic GST activity. Kinetic studies show that GSH but no 1-chloro-2,4-dinitrobenzene prevent the inhibition on cytosolic GST induced by micromolar Cu(2+) either in the absence or presence of ascorbate. On the other hand, NEM and mersalyl acid, both thiol-alkylating agents, inhibited GST activity with differential reactivity in a dose-dependent manner. Taken together, these results suggest that an inhibitory Cu(2+)-binding effect is likely to be negligible on the overall inhibition of cytosolic GST activity observed by the Cu(2+)/ascorbate system. We discuss how modification of GST-thiol groups is related to the inhibition of cytosolic GST activity.