Plukenetia volubilis leaves as source of anti-Helicobacter pylori agents

Introduction

Helicobacter pylori infection is a major issue worldwide, with widespread prevalence, combined with its link to gastritis, peptic ulcers, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma. Meanwhile, effectiveness of current treatment protocols is limited by increasing antibiotic resistance and patient compliance issues due to long regimens and side effects. Plukenetia volubilis, or sacha inchi, is a valuable source of bioactive molecules. However, studies on its antimicrobial activity, especially against H. pylori, are lacking.

Methods

In this study, the anti-H. pylori activity of P. volubilis leaves water extract was explored using in vitro and in silico approaches. High-Performance Liquid Chromatography coupled to Electrospray Ionisation and Quadrupole Time-of-Flight Mass Spectrometry (HPLC-ESI- QTOF-MS-MS) analysis of the water extract from the leaves was used to characterise the chemical composition of the plant and allowed identification of some flavonoids, such as astragalin, and some phenolic compounds. Then, high-speed counter current chromatography (HSCCC) was used to fractionate the ethyl acetate partition obtained from the water extract from the leaves.

Results and Discussion

The presence of flavonoids derived from kaempferol was confirmed and astragalin was isolated for the first time in P. volubilis. The P. volubilis water infusion, ethyl acetate extract and the isolated astragalin exhibited anti-bacterial activity against H. pylori J99 and two clinical isolates (e.g., minimum inhibitory concentrations of 0.53, 0.51 and 0.49 μg/mL, respectively, for clarithromycin-resistant clinical isolate SSR366). Then, using molecular docking for potential protein targets for H. pylori, it was verified that astragalin could interact with these proteins by in silico analysis.

Conclusion

These findings highlight that P. volubilis and astragalin produce a bacteriostatic activity against H. pylori and may have potential to be used in treatment against H. pylori, after further research.

Peptide-Bismuth Bicycles: In Situ Access to Stable Constrained Peptides with Superior Bioactivity

Constrained peptides are promising next-generation therapeutics. We report here a fundamentally new strategy for the facile generation of bicyclic peptides using linear precursor peptides with three cysteine residues and a non-toxic trivalent bismuth(III) salt. Peptide-bismuth bicycles form instantaneously at physiological pH, are stable in aqueous solution for many weeks, and much more resistant to proteolysis than their linear precursors. The strategy allows the in situ generation of bicyclic ligands for biochemical screening assays. We demonstrate this for two screening campaigns targeting the proteases from Zika and West Nile viruses, revealing a new lead compound that displayed inhibition constants of 23 and 150 nM, respectively. Bicyclic peptides are up to 130 times more active and 19 times more proteolytically stable than their linear analogs without bismuth.

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

Metal Binding Ability of Small Peptides Containing Cysteine Residues

The Cd(II)-, Pb(II)-, Ni(II)- and Zn(II)-complexes of small terminally protected peptides containing CXXX, XXXC, XCCX, CXn C (n=1-3) sequences have been studied with potentiometric, UV/Vis and CD spectroscopic techniques. The cysteine thiolate group is the primary binding site for all studied metal ions, but the presence of a histidyl or aspartyl side chain in the molecule contributes to the stability of the complexes. For two-cysteine containing peptides the (S- ,S- ) coordinated species are formed in the physiological pH range and the stability increases in the Ni(II) Collapse

Key Words

• cysteine containing peptides
• metal complexes
• selectivity
• spectroscopic measurements
• stability constant

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MESH Headings

• Amino Acid Sequence
• Chelating Agents/chemistry
• Coordination Complexes/chemistry
• Cysteine/chemistry
• Ligands
• Metals, Heavy/chemistry
• Molecular Structure
• Oligopeptides/chemistry

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Grants

• European Regional Development Fund

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Affiliation(s)

Márton Lukács Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary
Dóra Csilla Pálinkás Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary
Györgyi Szunyog Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary
Katalin Várnagy Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary

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Flavodoxins as Novel Therapeutic Targets against Helicobacter pylori and Other Gastric Pathogens

Flavodoxins are small soluble electron transfer proteins widely present in bacteria and absent in vertebrates. Flavodoxins participate in different metabolic pathways and, in some bacteria, they have been shown to be essential proteins representing promising therapeutic targets to fight bacterial infections. Using purified flavodoxin and chemical libraries, leads can be identified that block flavodoxin function and act as bactericidal molecules, as it has been demonstrated for Helicobacter pylori (Hp), the most prevalent human gastric pathogen. Increasing antimicrobial resistance by this bacterium has led current therapies to lose effectiveness, so alternative treatments are urgently required. Here, we summarize, with a focus on flavodoxin, opportunities for pharmacological intervention offered by the potential protein targets described for this bacterium and provide information on other gastrointestinal pathogens and also on bacteria from the gut microbiota that contain flavodoxin. The process of discovery and development of novel antimicrobials specific for Hp flavodoxin that is being carried out in our group is explained, as it can be extrapolated to the discovery of inhibitors specific for other gastric pathogens. The high specificity for Hp of the antimicrobials developed may be of help to reduce damage to the gut microbiota and to slow down the development of resistant Hp mutants.

Triplet of cysteines - Coordinational riddle?

Polythiol binding of metal ions plays crucial role in the proper functioning of cysteine-rich proteins that are responsible for metal homeostasis and defending processes against metal toxicity (including heavy metals detoxification). The coordination properties of cysteine residues involved in specific sequencional patterns in proteins (like those present in e.g. metallothioneins) are interesting not only from a chemical point of view but may also lead to a better understanding of the purpose and allocation of metal ions in various biomolecules. In this study, the interaction of Zn²⁺, Cd²⁺ and Ni²⁺ ions with four peptides containing cysteine triplet motif were studied by potentiometric and spectroscopic methods. The main goal of this research was to answer the question how effectively three thiols, each being next to other, are able to bind single metal ion. Two of peptides contain additional, fourth cysteine residue, separated from triplet by two and three other amino acid residues. As results show, all three cysteine residues in the CCC motif are able to participate in the coordination of the metal ion (Cd²⁺, Zn²⁺). Except cysteine thiol groups, amide nitrogen atoms are also involved in the coordination of Ni²⁺.

A comparative study on the nickel binding ability of peptides containing separate cysteinyl residues

Nickel(ii) complexes of peptides CSSACS-NH2, ACSSACS-NH2, SSCSSACS-NH2 and GACAAH-NH2 have been studied by potentiometric and various spectroscopic (UV-vis, CD, NMR, and ESI-MS) techniques. All peptides have high nickel(ii) binding ability in the form of square planar complexes and the stability order of the peptides is: CSSACS-NH2 > ACSSACS-NH2 > SSCSSACS-NH2 ∼ GACAAH-NH2. The different metal binding affinities of these peptides are related to the differences in the speciation and in the binding modes of the major species. An almost exclusive formation of bis(ligand) complexes via an (NH2,S-) 5-membered chelate from the amino terminus is characteristic of CSSACS-NH2. The (NH2,N-,S-) tridentate chelate is the major coordination mode of ACSSACS-NH2 but the distant cysteine can also contribute to metal binding. The higher nickel(ii) binding ability of AC[combining low line]SSAC[combining low line]S-NH2 relative to the peptides containing an N-terminal XY-Cys motif may have important biological consequences. For example, the occurrence of the (NH2,N-,S-,S-) donor set is a common feature of both the ACSSACS-NH2 ligand and the nickel(ii) binding loop of the NiSOD enzyme (HC[combining low line]DLPC[combining low line]G…..,). In the case of SSCSSACS-NH2 and GACAAH-NH2 the amino terminus of one peptide can completely saturate the coordination sphere of the nickel(ii) ion via the formation of the (NH2,N-,N-,S-) binding mode. This rules out the formation of bis(ligand) complexes and any contribution of the distant cysteine or histidine to nickel(ii) binding in the 1 : 1 complexes. On the other hand the distant cysteine of SSCSSACS-NH2 and histidine of GACAAH-NH2 can behave as independent metal binding sites for the formation of dinuclear complexes in the presence of excess metal ions.

Unusual binding modes in the copper(ii) and palladium(ii) complexes of peptides containing both histidyl and cysteinyl residues

The change of the histidine in the peptide chain provides unusual binding behavior of albumin related peptides.

Importance of the C-terminal histidine residues of Helicobacter pylori GroES for Toll-like receptor 4 binding and interleukin-8 cytokine production

Helicobacter pylori infection is associated with the development of gastric and duodenal ulcers as well as gastric cancer. GroES of H. pylori (HpGroES) was previously identified as a gastric cancer-associated virulence factor. Our group showed that HpGroES induces interleukin-8 (IL-8) cytokine release via a Toll-like receptor 4 (TLR4)-dependent mechanism and domain B of the protein is crucial for interactions with TLR4. In the present study, we investigated the importance of the histidine residues in domain B. To this end, a series of point mutants were expressed in Escherichia coli, and the corresponding proteins purified. Interestingly, H96, H104 and H115 were not essential, whereas H100, H102, H108, H113 and H118 were crucial for IL-8 production and TLR4 interactions in KATO-III cells. These residues were involved in nickel binding. Four of five residues, H102, H108, H113 and H118 induced certain conformation changes in extended domain B structure, which is essential for interactions with TLR4 and consequent IL-8 production. We conclude that interactions of nickel ions with histidine residues in domain B help to maintain the conformation of the C-terminal region to conserve the integrity of the HpGroES structure and modulate IL-8 release.

AGHLDDLPGALSAL: A hemoglobin fragment potentially competing with albumin to bind transition metal ions

Protein degradation leads to the formation of endogenous peptides, the biological activity of which is most often unknown. The peptide AGHLDDLPGALSAL, recently isolated from mouse brain homogenates, has been recognized as a fragment of the α-chain of hemoglobin. AGHLDDLPGALSAL has the ability of inhibiting the peripheral hyperalgesic inflammatory responses through the indirect activation of the μ-opioid receptors. A peculiarity of AGHLDDLPGALSAL is the presence, at its N-terminus of a strong binding site for divalent transition metal ions, similar to that characterizing the human albumin and called "ATCUN motif". The consequential metal binding ability of AGHLDDLPGALSAL can be connected to its biological activity. For this reason, we decided to investigate the coordination properties of AGHLDDLPGALSAL towards Cu(II), Ni(II) and Zn(II) ions, reported here for the first time. The results confirm that AGHLDDLPGALSAL is a strong ligand for those metals: it can even compete with albumin under suitable conditions. In vitro assays on the inhibition of Cu(II) toxicity towards different cell lines confirmed that the binding ability of AGHLDDLPGALSAL can imply relevant biological consequences.

The C-terminal disulfide bonds of Helicobacter pylori GroES are critical for IL-8 secretion via the TLR4-dependent pathway in gastric epithelial cells

Helicobacter pylori GroES (HpGroES), a potent immunogen, is a secreted virulence factor that stimulates production of proinflammatory cytokines and may contribute to gastric carcinogenesis. HpGroES is larger than other bacterial orthologs because of an additional C-terminal region, known as domain B. We found that the HpGroES-induced IL-8 release by human gastric epithelial cells was dependent on activation of the MAPK and NF-κB pathways. HpGroES lacking domain B was unable to induce IL-8 release. Additionally, a TLR4 inhibitor significantly inhibited IL-8 secretion and reduced HpGroES-induced activation of MAPKs. Furthermore, HpGroES-induced IL-8 release by primary gastric epithelial cells from TLR4(-/-) mice was significantly lower than from wild-type mice. We also found that HpGroES bound to TLR4 in cell lysates and colocalized with TLR4 on the cell membrane only when domain B was present. We then constructed two deletion mutants lacking C-terminal regions and mutants with point mutations of two of the four cysteine residues, C111 and C112, in domain B and found that the deletion mutants and a double mutant lacking the C94-C111 and C95-C112 disulfide bonds were unable to interact with TLR4 or induce IL-8 release. We conclude that HpGroES, in which a unique conformational structure, domain B, is generated by these two disulfide bonds, induces IL-8 secretion via a TLR4-dependent mechanism.

Specificity of the Zn2+, Cd2+and Ni2+ion binding sites in the loop domain of the HypA protein

The role of the residues in the hypa loop on the stability of its complexes with Zn²⁺, Cd²⁺and Ni²⁺ions.

Current and potential applications of bismuth-based drugs

: Bismuth compounds have been used extensively as medicines and in particular for the treatment of gastrointestinal ailments. In addition to bismuth's well known gastroprotective effects and efficacy in treating H. pylori infection it also has broad anti-microbial, anti-leishmanial and anti-cancer properties. Aspects of the biological chemistry of bismuth are discussed and biomolecular targets associated with bismuth treatment are highlighted. This review strives to provide the reader with an up to date account of bismuth-based drugs currently used to treat patients and discuss potential medicinal applications of bismuth drugs with reference to recent developments in the literature. Ultimately this review aims to encourage original contributions to this exciting and important field.

The specificity of interaction of Zn(2+), Ni(2+) and Cu(2+) ions with the histidine-rich domain of the TjZNT1 ZIP family transporter

The Zrt/Irt-like protein (ZIP) family contributes to the metal homeostasis by regulating the transport of divalent metal cations such as Fe(2+), Zn(2+), Mn(2+), Cd(2+) and sometimes even Cu(2+). Most ZIP members have a long variable loop between transmembrane domains (TMDs) III and IV; this region is predicted to be located in the cytoplasm and is postulated to be the metal ion binding site. In this study, we looked at the thermodynamic behavior and coordination chemistry of Zn(2+), Ni(2+) and Cu(2+) complexes with the histidine-rich domain, Ac-(185)RAHAAHHRHSH(195)-NH2 (HRD), from the yeast TjZNT1 protein, located between TMDs III and IV. The sequence is conserved also in higher species like Thlaspi japonicum. The stability of complexes increases in the series Ni(2+) < Zn(2+)≪ Cu(2+). The geometry of complexes is very different for each metal and in the case of Zn(2+) complexes, high specificity in binding is observed. Moreover, the stability of HRD-Cu(2+) complexes was compared with the five His residues containing peptide from Hpn protein (Helicobacter pylori). The results suggest a high ability of HRD in the binding of all three studied metals.

Ni2+chemistry in pathogens – a possible target for eradication

Nickel homeostasis inHelicobacter pyloriand potential histidine-rich binding sites from various bacterial and fungal pathogens are discussed.

A comparative study on the possible zinc binding sites of the human ZnT3 zinc transporter protein

The brain specific zinc transporter protein ZnT3 can be related to the amyloid neuropathology of Alzheimer's disease. In order to analyze the metal binding ability of human ZnT3 protein, here we report a potentiometric and solution structural (UV-Vis, CD, EPR, NMR) study of nickel(II), copper(II) and zinc(II) complexes of three peptides mimicking the possible metal binding sequences of this protein. The peptide L¹ (Ac-RHQAGPPHSHR-NH2) is a minimalist, the cyclic peptide L² (cyclo(Ac-CKLHQAGPPHSHGSRGAEYAPLEEGPEEKC-NH2) is a more complete model of the intracellular His-rich loop, which is widely accepted as a putative metal binding site. The peptide L³ (Ac-PFHHCHRD-NH2) is the model of the conserved cytoplasmic N-terminal -HHCH- sequence. In the physiological pH-range, the ZnL¹, ZnH3L² and ZnL³ complexes are the major species in the corresponding binary systems, with {3N(im)}, {3N(im),2/3O(amide)} and {3N(im),S(-)} coordination environments, respectively. The species ZnL³ has 3-4 orders of magnitude higher stability than the other two complexes, indicating the presence of a high-affinity zinc-binding site at the N-terminal tail of the human ZnT3 transporter. Moreover, L³ shows preferred zinc binding as compared to nickel (log β(ZnL³) - log β(NiL³) = 2.3), probably due to the higher preference of zinc(II) for tetrahedral geometry. These facts suggest that zinc binding to the N-terminal -HHCH- sequence of human ZnT3 may be involved in the biological activity of this zinc transporter protein in zinc sensing, binding or translocation processes.

The zinc-binding fragment of HypA from Helicobacter pylori: a tempting site also for nickel ions

HypA, a nickel accessory protein from H. pylori, binds a zinc ion in it's structural site, a loop with two conserved CXXC motifs (Ac-ELECKDCSHVFKPNALDYGVCEKCHS-NH(2)). There are at least three hypotheses on the binding mode of this ion. In this paper, we try to understand how Zn(2+) binds to this fragment and why Ni(2+), a metal with quite a high affinity towards thiolic sites, doesn't compete with zinc in the binding to this motif. Potentiometric titrations, mass spectrometry, NMR, UV-Vis and CD spectroscopy help us to compare the coordination modes in both metal complexes and discuss their thermodynamic stabilities.

Recent advances in bioinorganic chemistry of bismuth

Bismuth has been used in medicine for over two centuries for the treatment of various diseases, in particular for gastrointestinal disorders, owing to its antimicrobial activity. Recent structural characterization of bismuth drugs provides an insight into assembly and pharmacokinetic pathway of the drugs. Mining potential protein targets inside the pathogen via metallomic/metalloproteomic approach and further characterization on the interactions of bismuth drugs with these targets laid foundation in understanding the mechanism of action of bismuth drugs. Such studies would be beneficial in rational design of new potential drugs.

Probing of bismuth antiulcer drug targets in H. pylori by laser ablation-inductively coupled plasma mass spectrometry

A method that allows partial denaturation of protein ligands in Bi- and Zn-protein complexes, leaving the metal coordination centre intact, was developed. It was based on the reduction of the S-S bridges with tris(2-carboxyl)phosphine followed by derivatization with iodoacetamide. Consequently conditions that allow the separation of Bi- and Zn-protein complexes using SDS electrophoresis were found. The separation efficiency was much higher than that in non-denaturating blue native electrophoresis. The method allowed the detection of seven Bi-binding protein candidates in H. pylori treated with bismuth subcitrate, some of which-fructose-bisphosphate aldolase (33.6 kDa), urease alpha subunit (26.4 kDa), and the 16.8 kDa proteins: 30S ribosomal protein S6 and neutrophil activating protein (NapA)-were bio-induced during the treatment. The method also allowed the monitoring of the changes in the Zn-proteome during treatment of H. pylori with the Bi-drug, which was found to increase the concentration of the Zn-binding proteins with particularly strong expression of the urease, S-adenosylmethionine synthetase and the above 16.8 kDa proteins.

Coordination of Ni2+ and Cu2+ to metal ion binding domains of E. coli SlyD protein

The C-terminal region of Escherichia coli SlyD is unstructured and extremely rich in potential metal-binding amino acids, especially in histidine residues. SlyD is able to bind two to seven nickel ions per molecule, in a variety of coordination geometries and coordination numbers. This protein contributes to the insertion of nickel into the hydrogenase precursor protein and it has a peptidyl-prolyl cis/trans-isomerase activity which can be regulated through nickel ions. This inspired us to undertake systematic studies on the coordination ability of two histidine-rich peptides from the C-terminus of the SlyD protein with nickel. Also, it is known that histidine-rich regions are part of a Cu(2+) binding domain involved in copper uptake under conditions of metal starvation in vivo in other bacteria. For this reason we decided to examine the complex formation of Ac-AHGHVHGAHDHHHD-NH(2) and Ac-GHGHDHGHEHG-NH(2) fragments with copper ions, which are also reference metal ions in this study. Experiments were performed in a DMSO/water 30:70 solvent. The Ac-AHGHVHGAHDHHHD-NH(2) and Ac-GHGHDHGHEHG-NH(2) fragments were synthesized and their interactions with Ni(2+) and Cu(2+) ions were studied by potentiometric, mass spectrometric, UV-vis, CD, EPR, and NMR spectroscopic techniques in solution. The results show that the Ac-GHGHDHGHEHG-NH(2) fragment forms equimolar complexes with both nickel and copper ions. At physiological pH, the metal ion is bound only through nitrogens from imidazole sidechain of histidine residues. On the contrary, Ac-AHGHVHGAHDHHHD-NH(2) binds 2 metal ions per molecule, at pH range 5 to 7, even if the 1:2 metal:peptide ratios were used. NMR studies indicate the involvement of all His residues in this pH-range in metal binding of the latter peptide. At higher pH, the stoichiometry changes to 1:1 and the His residues are displaced by amide nitrogens.

Metal binding ability of cysteine-rich peptide domain of ZIP13 Zn2+ ions transporter

The coordination modes and thermodynamic stabilities of the complexes of the cysteine-rich N-terminal domain fragment of the ZIP13 zinc transporter (MPGCPCPGCG-NH(2)) with Zn(2+), Cd(2+), Bi(3+), and Ni(2+) have been studied by potentiometric, mass spectrometric, NMR, CD, and UV-vis spectroscopic methods. All of the studied metals had similar binding modes, with the three thiol sulfurs of cysteine residues involved in metal ion coordination. The stability of the complexes formed in solution changes in the series Bi(3+) ≫ Cd(2+) > Zn(2+) > Ni(2+), the strongest being for bismuth and the weakest for nickel. The N-terminal fragment of the human metalothionein-3 (MDPETCPCP-NH(2)) and unique histidine- and cysteine-rich domain of the C-terminus of Helicobacter pyroli HspA protein (Ac-ACCHDHKKH-NH(2)) have been chosen for the comparison studies. It confirmed indirectly which groups were the anchoring ones of ZIP13 domain. Experimental data from all of the used techniques and comparisons allowed us to propose possible coordination modes for all of the studied ZIP13 complexes.