[Show abstract][Hide abstract] ABSTRACT: Heme oxygenase-1 (HO-1) encoded by the HMOX1 gene is a 32 kDa stress protein that catabolizes heme to biliverdin, free iron and carbon monoxide. Glial HO-1 is over-expressed in the CNS of subjects with Alzheimer's disease (AD), Parkinson's disease (PD) and multiple sclerosis (MS). The HMOX1 gene is exquisitely sensitive to oxidative stress and is induced in brain and other tissues in various models of disease and trauma. Induction of the glial HMOX1 gene may lead to pathological brain iron deposition, intracellular oxidative damage and bioenergetic failure in AD and other human CNS disorders such as PD and MS. Therefore, targeted suppression of glial HO-1 hyperactivity may prove to be a rational and effective therapeutic intervention in AD and related neurodegenerative disorders. In the present study, we report the effects of QC-47, QC-56 and OB-28, novel azole-based competitive and reversible inhibitors of HO-1, on oxidative damage to whole cell and mitochondrial compartments in rat astrocytes transfected with the HMOX1 gene. We also report the effect of OB-28 on the behavior and neuropathology of APPswe/PS1∆E9 mice. OB-28 was found to reduce oxidative damage to whole cell and mitochondrial compartments in rat astrocytes transfected with the HMOX1 gene. Moreover, OB-28 was found to significantly counter behavioural deficits and neuropathological alterations in APPswe/PS1∆E9 mice. Attenuation of AD-associated behavioural deficits and neuropathological changes suggests that HO-1 may be a promising target for neuro-protective intervention in AD and other neurodegenerative diseases.This article is protected by copyright. All rights reserved.
Journal of Neurochemistry 08/2014; · 3.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: E. coli display O antigens on the outer membrane that play an important role in bacterial interactions with the environment. The O antigens of enterohemorrhagic E. coli O104 and O5 contain a Galβ1-3GalNAc- disaccharide at the reducing end of the repeating unit. Several other O antigens contain this disaccharide which is identical to the mammalian O-glycan core 1 or the cancer-associated Thomsen-Friedenreich (TF) antigen. We identified the wbwC genes responsible for the synthesis of the disaccharide in E. coli serotypes O104 and O5. To functionally characterize WbwC, an acceptor substrate analog, GalNAcα-diphosphate-phenylundecyl, was synthesized. WbwC reaction products were isolated by high pressure liquid chromatography and analyzed by mass spectrometry, nuclear magnetic resonance, galactosidase and O-glycanase digestion and anti-TF antibody. The results clearly showed that the Galβ1-3GalNAcα- linkage was synthesized, confirming WbwCECO104 and WbwCECO5 as UDP-Gal: GalNAcα-diphosphate-lipid β1,3-Gal-transferases. Sequence analysis revealed a conserved DxDD motif, and mutagenesis showed the importance of these Asp residues in catalysis. The purified enzymes require divalent cations (Mn(2+)) for activity and are specific for UDP-Gal and GalNAc-diphosphate-lipid substrates. WbwC was inhibited by bis-imidazolium salts having aliphatic chains of 18 to 22 carbons. This work will help to elucidate mechanisms of polysaccharide synthesis in pathogenic bacteria and provide technology for vaccine synthesis.
[Show abstract][Hide abstract] ABSTRACT: Previously, we reported that menadione activated rat, native heme oxygenase-2 (HO-2) and human recombinant heme oxygenase-2 selectively; it did not activate spleen, microsomal heme oxygenase-1. The purpose of this study was to explore some structure-activity relationships of this activation and the idea that redox properties may be an important aspect of menadione efficacy.
Heme oxygenase activity was determined in vitro using rat spleen and brain microsomes as the sources of heme oxygenase-1 and -2, respectively, as well as recombinant, human heme oxygenase-2.
Menadione analogs with bulky aliphatic groups at position-3, namely vitamins K1 and K2, were not able to activate HO-2. In contrast, several compounds with similar bulky but less lipophilic moieties at position-2 (and -3) were able to activate HO-2 many fold; these compounds included polar, rigid, furan-containing naphthoquinones, furan-benzoxazine naphthoquinones, 2-(aminophenylphenyl)-3-piperidin-1-yl naphthoquinones. To explore the idea that redox properties might be involved in menadione efficacy, we tested analogs such as 1,4-dimethoxy-2-methylnaphthalene, pentafluoromenadione, monohalogenated naphthoquinones, alpha-tetralone and 1,4-naphthoquinone. All of these compounds were inactive except for 1,4-naphthoquinone. Menadione activated full-length recombinant human heme oxygenase-2 (FL-hHO-2) as effectively as rat brain enzyme, but it did not activate rat spleen heme oxygenase.
These observations are consistent with the idea that naphthoquinones such as menadione bind to a receptor in HO-2 and activate the enzyme through a mechanism that may involve redox properties.
[Show abstract][Hide abstract] ABSTRACT: A series of compounds structurally related to astemizole were designed and synthesized with the goal of determining their anti-Plasmodium activity. Several modifications of the astemizole structure, namely the removal of the 4-fluorobenzyl and/or 4-methoxyphenethyl moieties, substitution of the benzene ring of the benzimidazole scaffold, replacement of the fluorine atom in the 4-fluorobenzyl group, and variation of the 4-aminopiperidine moiety, were explored. In vitro evaluation of the anti-Plasmodium activity of these compounds using the ItG strain showed that astemizole and some of its structurally similar derivatives have IC50 values in the nanomolar range and exhibit toxicity towards the parasite over Chinese ovarian hamster (CHO) cells with a selectivity as high as 200. The presence of a secondary cyclic amine at position 2 and substitution with chlorine at positions 4 and 5 in the benzimidazole moiety are two modifications that resulted in potent and selective antimalarials based on astemizole.
[Show abstract][Hide abstract] ABSTRACT: Several analogs based on the lead structure of 1-(4-chlorobenzyl)-2-(pyrrolidin-1-ylmethyl)-1H-benzimidazole (clemizole) were synthesized and evaluated as novel inhibitors of heme oxygenase (HO). Many of the compounds were found to be potent and highly selective for the HO-2 isozyme (constitutive), and had substantially less inhibitory activity on the HO-1 isozyme (inducible). The compounds represent the first report of highly potent and selective inhibitors of HO-2 activity, and complement our suite of selective HO-1 inhibitors. The study has revealed many candidates based on the inhibition of heme oxygenases for potentially useful pharmacological and therapeutic applications.
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Modifications of proteins by O-glycosylation determine many of the properties and functions of proteins. We wish to understand the mechanisms of O-glycosylation and develop inhibitors that could affect glycoprotein functions and alter cellular behavior. METHODS: We expressed recombinant soluble human Gal- and GlcNAc-transferases that synthesize the O-glycan cores 1 to 4 and are critical for the overall structures of O-glycans. We determined the properties and substrate specificities of these enzymes using synthetic acceptor substrate analogs. Compounds that were inactive as substrates were tested as inhibitors. RESULTS: Enzymes significantly differed in their recognition of the sugar moieties and aglycone groups of substrates. Core 1 synthase was active with glycopeptide substrates but GlcNAc-transferases preferred substrates with hydrophobic aglycone groups. Chemical modifications of the acceptors shed light on enzyme - substrate interactions. Core 1 synthase was weakly inhibited by its substrate analog benzyl 2-butanamido-2-deoxy-α-D-galactoside while two of the three GlcNAc-transferases were selectively and potently inhibited by bis-imidazolium salts which are not substrate analogs. CONCLUSIONS: This work delineates the distinct specificities and properties of the enzymes that synthesize the common O-glycan core structures 1 to 4. New inhibitors were found that could selectively inhibit the synthesis of core 1, 2 and 3 but not core 4. General significance These studies help our understanding of the mechanisms of action of enzymes critical for O-glycosylation. The results may be useful for the re-engineering of O-glycosylation to determine the roles of O-glycans and the enzymes critical for O-glycosylation, and for biotechnology with potential therapeutic applications.
Biochimica et Biophysica Acta 04/2013; · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Galactosyltransferases (GalTs) extend the glycan chains of mammalian glycoproteins by adding Gal to terminal GlcNAc residues, and thus build the scaffolds for biologically important glycan structures. We have shown that positively charged bivalent imidazolium salts in which the two imidazolium groups are linked by an aliphatic chain of 20 or 22 carbons form potent inhibitors of purified human β3-GalT5, using GlcNAcβ-benzyl as acceptor substrate. The inhibitors are not substrate analogs and also inhibited a selected number of other glycosyltransferases. These bis-imidazolium compounds represent a new class of glycosyltransferase inhibitors with potential as anti-cancer and anti-inflammatory drugs.
[Show abstract][Hide abstract] ABSTRACT: AbstractA series of compounds structurally related to astemizole were designed and synthesized with the goal of determining their anti‐Plasmodium activity. Several modifications of the astemizole structure, namely the removal of the 4‐fluorobenzyl and/or 4‐methoxyphenethyl moieties, substitution of the benzene ring of the benzimidazole scaffold, replacement of the fluorine atom in the 4‐fluorobenzyl group, and variation of the 4‐aminopiperidine moiety, were explored. In vitro evaluation of the anti‐Plasmodium activity of these compounds using the ItG strain showed that astemizole and some of its structurally similar derivatives have IC50 values in the nanomolar range and exhibit toxicity towards the parasite over Chinese ovarian hamster (CHO) cells with a selectivity as high as 200. The presence of a secondary cyclic amine at position 2 and substitution with chlorine at positions 4 and 5 in the benzimidazole moiety are two modifications that resulted in potent and selective antimalarials based on astemizole.
[Show abstract][Hide abstract] ABSTRACT: The interaction between DNA and members of series of bivalent imidazole compounds, monovalent and bivalent imidazolium compounds, and monovalent and bivalent tetrazolium compounds, which had been synthesized and evaluated for their anti-Plasmodium activity, has been examined using the displacement of SYBR Green I as a measure of competitive binding. The degree of interaction with DNA appears to be dependent on both hydrophobic and charge-pairing interactions.
[Show abstract][Hide abstract] ABSTRACT: The development of heme oxygenase (HO) inhibitors, especially those that are isozyme-selective, promises powerful pharmacological tools to elucidate the regulatory characteristics of the HO system. It is already known that HO has cytoprotective properties and may play a role in several disease states, making it an enticing therapeutic target. Traditionally, the metalloporphyrins have been used as competitive HO inhibitors owing to their structural similarity with the substrate, heme. However, given heme's important role in several other proteins (e.g. cytochromes P450, nitric oxide synthase), non-selectivity is an unfortunate side-effect. Reports that azalanstat and other non-porphyrin molecules inhibited HO led to a multi-faceted effort to develop novel compounds as potent, selective inhibitors of HO. This resulted in the creation of non-competitive inhibitors with selectivity for HO, including a subset with isozyme selectivity for HO-1. Using X-ray crystallography, the structures of several complexes of HO-1 with novel inhibitors have been elucidated, which provided insightful information regarding the salient features required for inhibitor binding. This included the structural basis for non-competitive inhibition, flexibility and adaptability of the inhibitor binding pocket, and multiple, potential interaction subsites, all of which can be exploited in future drug-design strategies.
Journal of The Royal Society Interface 10/2012; · 4.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The enterohemorrhagic O157 strain of Escherichia coli, which is one of the most well-known bacterial pathogens, has an O-antigen repeating unit structure with the sequence [-2-d-Rha4NAcα1-3-l-Fucα1-4-d-Glcβ1-3-d-GalNAcα1-]. The O-antigen gene cluster of E. coli O157 contains the genes responsible for the assembly of this repeating unit and includes wbdN. In spite of cloning many O-antigen genes, biochemical characterization has been done on very few enzymes involved in O-antigen synthesis. In this work, we expressed the wbdN gene in E. coli BL21, and the His-tagged protein was purified. WbdN activity was characterized using the donor substrate UDP-[(14)C]Glc and the synthetic acceptor substrate GalNAcα-O-PO(3)-PO(3)-(CH(2))(11)-O-Ph. The enzyme product was isolated by high pressure liquid chromatography, and mass spectrometry showed that one Glc residue was transferred to the acceptor by WbdN. Nuclear magnetic resonance analysis of the product structure indicated that Glc was β1-3 linked to GalNAc. WbdN contains a conserved DxD motif and requires divalent metal ions for full activity. WbdN activity has an optimal pH between 7 and 8 and is highly specific for UDP-Glc as the donor substrate. GalNAcα derivatives lacking the diphosphate group were inactive as substrates, and the enzyme did not transfer Glc to GlcNAcα-O-PO(3)-PO(3)-(CH(2))(11)-O-Ph. Our results illustrate that WbdN is a specific UDP-Glc:GalNAcα-diphosphate-lipid β1,3-Glc-transferase. The enzyme is a target for the development of inhibitors to block O157-antigen synthesis.
[Show abstract][Hide abstract] ABSTRACT: Several α-(1H-imidazol-1-yl)-ω-phenylalkanes were synthesized and evaluated as novel inhibitors of heme oxygenase (HO). These compounds were found to be potent and selective for the stress-induced isozyme HO-1, showing mostly weak activity toward the constitutive isozyme HO-2. The introduction of an oxygen atom in the alkyl linker produced analogues with decreased potency toward HO-1, whereas the presence of a sulfur atom in the linker gave rise to analogues with greater potency toward HO-1 than the carbon-containing analogues. The most potent compounds studied contained a five-atom linker between the imidazolyl and phenyl moieties, whereas the most HO-1-selective compounds contained a four-atom linker between these groups. The compounds with a five-atom linker containing a heteroatom (O or S) were found to be the most potent inhibitors of HO-2; 1-(N-benzylamino)-3-(1H-imidazol-1-yl)propane dihydrochloride, with a nitrogen atom in the linker, was found to be inactive.
[Show abstract][Hide abstract] ABSTRACT: The development of heme oxygenase (HO) inhibitors is critical in dissecting and understanding the HO system and for potential therapeutic applications. We have established a program to design and optimize HO inhibitors using structure-activity relationships in conjunction with X-ray crystallographic analyses. One of our previous complex crystal structures revealed a putative secondary hydrophobic binding pocket which could be exploited for a new design strategy by introducing a functional group that would fit into this potential site. To test this hypothesis and gain further insights into the structural basis of inhibitor binding, we have synthesized and characterized 1-(1H-imidazol-1-yl)-4,4-diphenyl-2-butanone (QC-308). Using a carbon monoxide (CO) formation assay on rat spleen microsomes, the compound was found to be ∼15 times more potent (IC(50) = 0.27±0.07 µM) than its monophenyl analogue, which is already a potent compound in its own right (QC-65; IC(50) = 4.0±1.8 µM). The crystal structure of hHO-1 with QC-308 revealed that the second phenyl group in the western region of the compound is indeed accommodated by a definitive secondary proximal hydrophobic pocket. Thus, the two phenyl moieties are each stabilized by distinct hydrophobic pockets. This "double-clamp" binding offers additional inhibitor stabilization and provides a new route for improvement of human heme oxygenase inhibitors.
PLoS ONE 01/2012; 7(1):e29514. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: While substantial progress has been made in elucidating the roles of heme oxygenases-1 (HO-1) and -2 (HO-2) in mammals, our understanding of the functions of these enzymes in health and disease is still incomplete. A significant amount of our knowledge has been garnered through the use of nonselective inhibitors of HOs, and our laboratory has recently described more selective inhibitors for HO-1. In addition, our appreciation of HO-1 has benefitted from the availability of tools for increasing its activity through enzyme induction. By comparison, there is a paucity of information about HO-2 activation, with only a few reports appearing in the literature. This communication describes our observations of the up to 30-fold increase in the in-vitro activation of HO-2 by menadione. This activation was due to an increase in V(max) and was selective, in that menadione did not increase HO-1 activity.
Canadian Journal of Physiology and Pharmacology 11/2011; · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cell surface mucins configure the cell surface by presenting extended protein backbones that are heavily O-glycosylated. The glycopeptide structures establish physicochemical properties at the cell surface that enable and block the formation of biologically important molecular complexes. Some mucins, such as MUC1, associate with receptor tyrosine kinases and other cell surface receptors, and engage in signal transduction in order to communicate information regarding conditions at the cell surface to the nucleus. In that context, the MUC1 cytoplasmic tail (MUC1CT) receives phosphorylation signals from receptor tyrosine kinases and serine/threonine kinases, which enables its association with different signaling complexes that conduct these signals to the nucleus and perhaps other subcellular organelles. We have detected the MUC1CT at promoters of over 500 genes, in association with several different transcription factors, and have shown that promoter occupancy can vary under different growth factor conditions. However, the full biochemical nature of the nuclear forms of MUC1 and its function at these promoter regions remain undefined. I will present evidence that nuclear forms of the MUC1CT include extracellular and cytoplasmic tail domains. In addition, I will discuss evidence for a hypothesis that the MUC1CT possesses a novel catalytic function that enables remodeling of the transcription factor occupancy of promoters, and thereby engages in regulation of gene expression.
[Show abstract][Hide abstract] ABSTRACT: A series of compounds containing bivalent imidazolium rings and one triazolium analog were synthesized and evaluated for their ability to inhibit the replication of Plasmodium falciparum cultures. The activity and selectivity of the compounds for P. falciparum cultures were found to depend on the presence of electron-deficient rings that were spaced an appropriate distance apart. The activity of the compounds was not critically dependent on the nature of the linker between the electron-deficient rings, an observation that suggests that the rings were responsible for the primary interaction with the molecular target of the compounds in the parasite. The bivalent imidazolium and triazolium compounds disrupted the process whereby merozoites gain entry into erythrocytes, however, they did not appear to prevent merozoites from forming. The compounds were also found to be active in a murine Plasmodium berghei infection, a result consistent with the compounds specifically interacting with a parasite component that is required for replication and is conserved between two Plasmodium species.
[Show abstract][Hide abstract] ABSTRACT: Labile 1,6-dihydroxy-2-hexanone (4) was prepared from the corresponding triol by selective di-O-tritylation, Collins oxidation, and careful detritylation of the resulting keto compound 3 under mild, acidic conditions. As shown by its 1Hmr and 13Cmr spectra, 4 exists as a 3:2 mixture of open-chain and cyclic forms, respectively, at equilibrium in deuterium oxide (25 °C). Upon standing, 4 is slowly converted into a hemiacetalic dimer. Under acidic conditions, dehydrative dimerization takes place to give the corresponding tricyclic dianhydride, one or both of the possible isomers (1:1 mixture) of which being formed according to the presence or absence of water in the medium. The structure (trans) of the thermodynamic isomer 5 was firmly established by an X-ray crystallographic analysis.
Canadian Journal of Chemistry 02/2011; 63(6):1222-1227. · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aminohydroxycyclopentanemethanols are important precursors for the synthesis of cyclopentane analogs of purine and pyrimidine nucleosides. The regiospecific synthesis of two new aminohydroxycyclopentanemethanols, 17 and 22, is described. In these syntheses the desired configuration in the cyclopentane ring is obtained by opening the cis-acetoxy-1,3-cyclopentanedicarboxylic acid anhydride 3 with either ammonia or methanol. The attack by each nucleophile occurs at the carbonyl carbon farthest away from the acetoxy group to give a carbamoyl or an ester function at this position. Since the ester function is destined to become the hydroxymethyl substituent and the carbamoyl function the amino substituent, the type of nucleophile used to open the anhydride determines whether the 2-deoxy or the 3-deoxy isomer is obtained. Coupling of the aminohydroxycyclopentanemethanols with 3-ethoxypropenoyl isocyanate followed by cyclization of the acyl ureas in 2 N H2SO4 gave two new cyclopentane analogs of uracil nucleosides. Coupling of the aminohydroxycyclopentanemethanols with 3-ethoxypropenoyl isothiocyanate followed by cyclization of the acyl thioureas in 15 N aqueous ammonia gave two new cyclopentane analogs of 2-thiouracil nucleosides.
Canadian Journal of Chemistry 02/2011; 63(10):2787-2797. · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Synthesis of new carbocyclic analogs of 1-(2′,3′-dideoxy-glycero-pentofuranosyl)pyrimidine nucleosides having the uracil (34), 2-thiouracil (33), 2-thiothymine (31), cytosine (44), and 5-methylcytosine (43) bases is described. The nucleoside analogs having the uracil, 2-thiouracil, and 2-thiothymine bases were prepared by coupling cis-3-aminocyclopentanemethanol (8) with 3-ethoxypropenoyl isocyanate (26), 3-ethoxypropenoyl isothiocyanate (25), and 3-methoxy-2-methylpropenoyl isothiocyanate (23), respectively, to give the corresponding acyl urea (30) and acyl thioureas (29 and 27). The acyl urea was cyclized in 2 N H2SO4 and the acyl thioureas in 15 N aqueous ammonia to give the corresponding nucleoside analogs. The nucleoside analogs containing the cytosine (44) and 5-methylcytosine (43) bases were prepared from the uracil and thymine nucleoside analogs, respectively, by way of the 4-chloropyrimidinone intermediates (42 and 41). The synthesis of cis-3-aminocyclopentanemethanol (8) from norbornene by way of cis-1,3-cyclopentanedicarboxylic acid anhydride (3) is also described. In addition, the ease of nucleophilic opening of compound 3 is compared to the opening of camphoric anhydride (9), which contains a cis-vicinal substituent at position 2. The relative ease of opening of compound 3 is discussed with respect to the effect, observed in an earlier study, that a cis-vicinal acetoxy group has on the course of the nucleophilic opening of such anhydrides. The 1H magnetic resonance spectra at 200 MHz of all of the synthetic intermediates and of the nucleoside analogs have been determined and discussed. The nucleoside analogs were screened for cell-growth inhibition using K-562 cells. Nucleoside analogs having the 2-thiouracil (33), 2-thiothymine (31), cytosine (44), and 5-methylcytosine (43) bases showed some growth inhibition with activity 150 to 300 times lower than that shown by 5-fluorouracil in this test system.
Canadian Journal of Chemistry 02/2011; 66(1):61-70. · 0.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A highly convergent synthesis of the pentacyclic indole alkaloid (+)-mostueine (1) is described. The key step involved the coupling of the dianion derived from (1′S)-3-(1′-hydroxyethyl)-4-methylpyridine (4) with the iminium salt 3,4-dihydro-2-methyl-9-(p-toluenesulfonyl)-β-carbolinium iodide (3). Low asymmetric induction (15% de) at the C-1 position of the β-carboline ring system (C-3 of mostueine) was obtained. The nonfermenting baker's yeast-mediated reduction of 3-acetyl-4-methylpyridine provided the hydroxyethylpyridine component in acceptable yield (67%) and high optical purity (99.0% ee). This synthesis of 1 has established that the absolute stereochemistry of mostueine is (3S, 19R).
Canadian Journal of Chemistry 02/2011; 70(12):2922-2928. · 0.96 Impact Factor