Treatment of Helicobacter pylori Infection: A Review of the World Literature

Background. None of the currently used anti- Helicobacter pylori drug regimens cures the infection 100%, and cure results still vary considerably. The present article reviews the effectiveness of currently used antimicrobial regimens, aimed to cure H. pylori infection.
Methods. Data collection started from the beginning of the anti- H. pylori -therapy era until May 1995. No attempt at formal metanalysis has been made, because many studies have been published only in abstract form. Attempts were made to exclude duplicates of studies by comparison to previously reported ones; the authors of suspected duplicates were contacted. After amalgamation of the number of included patients and the number of successfully treated patients, the mean values of eradication rates and the 95% confidence intervals were calculated.
Results. A total of 237 treatment arms were analyzed. Bismuth triple therapy continues to reach high eradication rates worldwide (78–89%). Side effects leading to diminished patient compliance and the marked decline of eradication efficacy in cases of metronidazole resistance are considered to be the major drawbacks of this therapy. Proton pump inhibitor (PPI) dual therapy is better tolerated with fewer side effects than is bismuth triple therapy. The mean eradication rates vary from 55 to 75%, and the extremes lie between 24 and 93%. PPI triple therapies have been shown to be very effective against H. pylori (eradication rates, 80–89%). Quadruple therapy leads to a mean eradication rate of 96%.
Conclusion. Based on efficacy, PPI triple or bismuth triple therapy are recommended as first-line treatment for H. pylori infection. Quadruple therapy could serve as second-line treatment for eradication of initial failures and in case of metronidazole resistance.     

Potassium channel blocker crafted by α-hairpinin scaffold engineering

The α-Hairpinins are a family of plant defense peptides with a common fold presenting two short α-helices stabilized by two invariant S–S-bridges. We have shown previously that substitution of just two amino acid residues in a wheat α-hairpinin Tk-AMP-X2 leads to Tk-hefu-2 that features specific affinity to voltage-gated potassium channels K_V1.3. Here, we utilize a combined molecular modeling approach based on molecular dynamics simulations and protein surface topography technique to improve the affinity of Tk-hefu-2 to K_V1.3 while preserving its specificity. An important advance of this work compared with our previous studies is transition from the analysis of various physicochemical properties of an isolated toxin molecule to its consideration in complex with its target, a membrane-bound ion channel. As a result, a panel of computationally designed Tk-hefu-2 derivatives was synthesized and tested against K_V1.3. The most active mutant Tk-hefu-10 showed a half-maximal inhibitory concentration of ～150 nM being >10 times more active than Tk-hefu-2 and >200 times more active than the original Tk-hefu. We conclude that α-hairpinins provide an attractive disulfide-stabilized scaffold for the rational design of ion channel inhibitors. Furthermore, the success rate can be considerably increased by the proposed “target-based” iterative strategy of molecular design.     

BmBKTx1, a novel Ca2+-activated K+ channel blocker purified from the Asian scorpion Buthus martensi Karsch

BmBKTx1 is a novel short chain toxin purified from the venom of the Asian scorpion Buthus martensi Karsch. It is composed of 31 residues and is structurally related to SK toxins. However, when tested on the cloned rat SK2 channel, it only partially inhibited rSK2 currents, even at a concentration of 1 microm. To screen for other possible targets, BmBKTx1 was then tested on isolated metathoracic dorsal unpaired median neurons of Locusta migratoria, in which a wide variety of ion channels are expressed. The results suggested that BmBKTx1 could specifically block voltage-gated Ca(2+)-activated K(+) currents (BK-type). This was confirmed by testing the BmBKTx1 effect on the alpha subunits of BK channels of the cockroach (pSlo), fruit fly (dSlo), and human (hSlo), heterologously expressed in HEK293 cells. The IC(50) for channel blocking by BmBKTx1 was 82 nm for pSlo and 194 nm for dSlo. Interestingly, BmBKTx1 hardly affected hSlo currents, even at concentrations as high as 10 microm, suggesting that the toxin might be insect specific. In contrast to most other scorpion BK blockers that also act on the Kv1.3 channel, BmBKTx1 did not affect this channel as well as other Kv channels. These results show that BmBKTx1 is a novel kind of blocker of BK-type Ca(2+)-activated K(+) channels. As the first reported toxin active on the Drosophila Slo channel dSlo, it will also greatly facilitate studying the physiological role of BK channels in this model organism.     

ScrepYard: An online resource for disulfide‐stabilized tandem repeat peptides

Receptor avidity through multivalency is a highly sought‐after property of ligands. While readily available in nature in the form of bivalent antibodies, this property remains challenging to engineer in synthetic molecules. The discovery of several bivalent venom peptides containing two homologous and independently folded domains (in a tandem repeat arrangement) has provided a unique opportunity to better understand the underpinning design of multivalency in multimeric biomolecules, as well as how naturally occurring multivalent ligands can be identified. In previous work, we classified these molecules as a larger class termed secreted cysteine‐rich repeat‐proteins (SCREPs). Here, we present an online resource; ScrepYard, designed to assist researchers in identification of SCREP sequences of interest and to aid in characterizing this emerging class of biomolecules. Analysis of sequences within the ScrepYard reveals that two‐domain tandem repeats constitute the most abundant SCREP domain architecture, while the interdomain “linker” regions connecting the functional domains are found to be abundant in amino acids with short or polar sidechains and contain an unusually high abundance of proline residues. Finally, we demonstrate the utility of ScrepYard as a virtual screening tool for discovery of putatively multivalent peptides, by using it as a resource to identify a previously uncharacterized serine protease inhibitor and confirm its predicted activity using an enzyme assay.     

Artificial Peptide Ligand of Potassium Channel KV1.1 with High Selectivity

Journal of Evolutionary Biochemistry and Physiology - In mammals, about 40 isoforms of voltage-gated potassium channels (KVs) have been found. To study such a variety of KVs, substances are needed...     

Two recombinant α-like scorpion toxins from Mesobuthus eupeus with differential affinity toward insect and mammalian Na channels

α-Scorpion toxins are modulators of voltage-gated Na⁺ channels (Na_vs), which bind to the receptor site 3 to inhibit the fast inactivation of the channels. MeuNaTxα-12 and MeuNaTxα-13 are two new α-scorpion toxin-like peptides identified by cDNA cloning from the scorpion Mesobuthus eupeus with unknown functions. Here, we report their recombinant production, oxidative refolding, structural and functional features. By in vitro renaturation from bacterial inclusion bodies and further purification through reverse phase high-performance liquid chromatography, we obtained high purity recombinant products with a native-like conformation identified by circular dichroism analysis. Two-electrode voltage clamp recordings on five cloned mammalian Na_v subtypes (rNa_v1.1, rNa_v1.2, rNa_v1.4, rNa_v1.5, and mNa_v1.6) and the insect counterpart DmNa_v1, all expressed in Xenopus laevis oocytes, showed that these two peptides inhibited rapid inactivation of the sensitive Na⁺ channels with significant preference for DmNa_v1. The half maximal effective concentrations (EC₅₀) of MeuNaTxα-12 and MeuNaTxα-13 for this channel are 19.95 ± 2.99 nM and 65.50 ± 7.28 nM, respectively, showing 45 and 38 folds higher affinities than for rNa_v1.1, the most sensitive mammalian channel among the five isoforms. Our functional data confirms that these two peptides belong to the α-like scorpion toxin group. A combined analysis of the site 3 sequences and the pharmacological data illuminates the importance of the loop L_D4:S5–S6 of the channel in interacting with the toxins whereas affinity variations between MeuNaTxα-12 and MeuNaTxα-13 highlight a key functional role of a cationic side chain at position 28 of MeuNaTxα-12. Successful expression together with structural and functional characterization of these two new α-like scorpion toxins lays basis for further studies of their structure–function relationship.     

A Centipede Toxin Family Defines an Ancient Class of CSαβ Defensins

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Electrophysiological characterization of Tityus obscurus β toxin 1 (To1) on Na+-channel isoforms

To1, previously named Tc49b, is a peptide neurotoxin isolated from venom of the scorpion Tityus obscurus that is responsible for lethal human poisoning cases in the Brazilian Amazonian region. Previously, To1 was shown to be lethal to mice and to change Na⁺ permeation in cerebellum granular neurons from rat brain. In addition, To1 did not affect Shaker B K⁺ channels. Based on sequence similarities, To1 was described as a β-toxin. In the present work, To1 was purified from T. obscurus venom and submitted to an electrophysiological characterization in human and invertebrate Na_V channels. The analysis of the electrophysiological experiments reveal that To1 enhances the open probability at more negative potentials of human Na_V 1.3 and 1.6, of the insect channel BgNa_V1 and of arachnid VdNa_V1 channel. In addition, To1 reduces the peak of Na⁺ currents in some of the Na_Vs tested. These results support the classification of the To1 as a β-toxin. A structure and functional comparison to other β-toxins that share sequence similarity to To1 is also presented.     

Functional heteromerization of HCN1 and HCN2 pacemaker channels

An important step toward understanding the molecular basis of the functional diversity of pacemaker currents in spontaneously active cells has been the identification of a gene family encoding hyperpolarization-activated cyclic nucleotide-sensitive cation nonselective (HCN) channels. Three of the four gene products that have been expressed so far give rise to pacemaker channels with distinct activation kinetics and are differentially distributed among the brain, with considerable overlap between some isoforms. This raises the possibility that HCN channels may coassemble to form heteromeric channels in some areas, similar to other K(+) channels. In this study, we have provided evidence for functional heteromerization of HCN1 and HCN2 channels using a concatenated cDNA construct encoding two connected subunits. We have observed that heteromeric channels activate several-fold faster than HCN2 and only a little slower than HCN1. Furthermore, the voltage dependence of activation is more similar to HCN2, whereas the cAMP sensitivity is intermediate between HCN1 and HCN2. This phenotype shows marked similarity to the current arising from coexpressed HCN1 and HCN2 subunits in oocytes and the native pacemaker current in CA1 pyramidal neurons. We suggest that heteromerization may increase the functional diversity beyond the levels expected from the number of HCN channel genes and their differential distribution.