The susceptibility of Helicobacter pylori to 12 antimicrobial agents, omeprazole and bismuth salts

Decrypting a Cryptic Allosteric Pocket in H. pylori Glutamate Racemase

One of our greatest challenges in drug design is targeting cryptic allosteric pockets in enzyme targets. Drug leads that do bind to these cryptic pockets are often discovered during HTS campaigns, and the mechanisms of action are rarely understood. Nevertheless, it is often the case that the allosteric pocket provides the best option for drug development against a given target. In the current studies we present a successful way forward in rationally exploiting the cryptic allosteric pocket of H. pylori glutamate racemase, an essential enzyme in this pathogen's life cycle. A wide range of computational and experimental methods are employed in a workflow leading to the discovery of a series of natural product allosteric inhibitors which occupy the allosteric pocket of this essential racemase. The confluence of these studies reveals a fascinating source of the allosteric inhibition, which centers on the abolition of essential monomer-monomer coupled motion networks.

Resistance rates of metronidazole and other antibacterials in Helicobacter pylori from previously untreated patients in Norway

The aim of the study was to describe the antimicrobial resistance rate of Helicobacter pylori isolated from previously untreated patients in Norway, including the application of two different methods for the determination of metronidazole susceptibility. Altogether 102 isolates obtained in 2008 and 2009 from previously untreated patients suspected of H. pylori related disease, were examined applying a standardized European study protocol. The activity of amoxicillin, tetracycline, clarithromycin, metronidazole, rifabutin and levofloxacin was recorded after an incubation period of 72-96 h in a microaerobic atmosphere. Strains resistant to metronidazole were re-examined for metronidazole resistance applying anaerobic conditions for the first 24 h. None of the isolates were resistant to amoxicillin or tetracycline, whereas 5, 9% were resistant to clarithromycin and 22, 5% resistant to metronidazole tested conventionally. Applying local standards the metronidazole resistance rate fell to 7, 8%, highlighting the importance of the methodology applied for metronidazole susceptibility testing.

Crystal structure and enzymatic characterization of thymidylate synthase X from Helicobacter pylori strain SS1

Thymidylate synthase X (ThyX) catalyzes the methylation of dUMP to form dTMP in bacterial life cycle and is regarded as a promising target for antibiotics discovery. Helicobacter pylori is a human pathogen associated with a number of human diseases. Here, we cloned and purified the ThyX enzyme from H. pylori SS1 strain (HpThyX). The recombinant HpThyX was discovered to exhibit the maximum activity at pH 8.5, and K(m) values of the two substrates dUMP and CH(2) H(4) folate were determined to be 15.3 ± 1.25 μM and 0.35 ± 0.18 mM, respectively. The analyzed crystal structure of HpThyX with the cofactor FAD and the substrate dUMP (at 2.31 Å) revealed that the enzyme was a tetramer bound to four dUMP and four FAD molecules. Different from the catalytic feature of the classical thymidylate synthase (ThyA), N5 atom of the FAD functioned as a nucleophile in the catalytic reaction instead of Ser84 and Ser85 residues. Our current work is expected to help better understand the structural and enzymatic features of HpThyX thus further providing valuable information for anti-H. pylori inhibitor discovery.

Metronidazole-flavonoid derivatives as anti-Helicobacter pylori agents with potent inhibitory activity against HPE-induced interleukin-8 production by AGS cells

Three series of metronidazole-flavonoid derivatives were generated and evaluated for antimicrobial activity against H. pylori. Among these compounds, high anti-H. pylori activities were observed in isoflavones derivatives 4-7, 19, and 20 but exhibited no inhibitory activity against other sorts of bacteria and fungi, for example, Streptococcus pneumoniae, Bacillus subtilis, Escherichia coli, Pseudomonas fluorescence, and Aspergillus niger. Genistein derivative 6 with the potent activity (MIC=0.39 microg mL(-1)) was >50-fold more than metronidazole, and comparable to the positive control amoxicillin. Additionally, compound 6 can significantly attenuate the increase in interleukin-8 (IL-8) levels in the AGS cells stimulated by H. pylori water extract (HPE) at concentrations of 15, 30, and 60 micromol L(-1), which did not show any effects on the cell viability.

Upper gastrointestinal complications after renal transplantation: a 3-yr sequential study

BACKGROUND

Upper gastrointestinal complications have historically resulted in considerable morbidity and mortality to renal transplant recipients. Over the last decade, antiulcer prophylaxis with proton-pump inhibitors and immunosuppression with tacrolimus-based regimes have been introduced. Little has been written about foregut complications after renal transplantation since the use of these agents. The aim of this study was to compare the frequency of upper gastrointestinal complications after renal transplantation in patients treated with (i) omeprazole vs. ranitidine, and (ii) tacrolimus vs. cyclosporin based immunosuppression.

METHODS

Information on 236 patients undergoing renal transplantation between January 1996 and December 1998 was collected prospectively onto a computerized database.

RESULTS

Overall, 20 patients (8%) developed upper gastrointestinal complications, opportunistic infections accounted for 9/20 (45%). No patient developed gastroduodenal ulceration, required laparotomy, suffered graft loss or died. There was no significant difference in the frequency of complications between patients that received antisecretory therapy with omeprazole (9/118, 8%) and those that received ranitidine (11/118, 9%), nor between those that were on tacrolimus (7/101, 7%) and those on cyclosporin (13/135, 10%) based immunosuppression regimes. Patients that developed foregut complications were significantly older than those not developing complications (mean age 50 vs. 43 yrs, p=0.05). Further, patients that developed opportunistic infections were more frequently diabetic than those in whom opportunistic infections were not seen (4/31, 13% vs. 5/205, 2%), p=0.02.

CONCLUSIONS

We observed a low frequency (8%) of upper gastrointestinal tract complications after renal transplantation. There was no difference in the frequency of complications between patients on tacrolimus and those on cyclosporin based immunosuppression. Furthermore, the complication rates were similar in those that received omeprazole and those that received ranitidine as antiulcer prophylaxis, indicating the equivalence of these two agents in this setting.

Clarithromycin dual therapy regimens for eradication of Helicobacter pylori: a review

BACKGROUND

Peptic ulcer disease can be cured by eradication of Helicobacter pylori during treatment to heal the ulcer. Dual therapy regimens were among the first to be granted approval for use. Reports of dual therapies including clarithromycin as the sole antibiotic are reviewed.

METHODS

Reports were identified from literature up to May 1997. Information reviewed included patient population, medical diagnosis, trial design, eradication regimens, and H. pylori eradication rates. The great diversity between studies limits formal meta-analysis but a measure of relative efficacy has been obtained by comparison of eradication rates derived by clearly defined methods and by pooling data.

RESULTS

Seventy-five reports of trials with 104 dual therapy treatment arms were reviewed. H. pylori eradication rates reported with ranitidine bismuth citrate plus clarithromycin range from 70-96% with a pooled observed rate of 85%. With omeprazole plus clarithromycin, reported eradication rates range from 27-90% with the pooled reported rate being 66%. Few data are available with either lansoprazole or ranitidine hydrochloride plus clarithromycin.

CONCLUSION

High H. pylori eradication rates derived by consistent and clearly defined methods have been seen with ranitidine bismuth citrate plus clarithromycin. Lower and more variable rates are reported with clarithromycin and either a proton pump inhibitor or a histamine H2-receptor antagonist.

High eradication rate of Helicobacter pylori using a four-drug regimen in patients previously treated unsuccessfully

The objective of this study was to assess the efficacy of a new regimen in eradicating Helicobacter pylori (Hp) in patients with duodenal ulcer (DU) who were previously treated unsuccessfully with standard triple therapy (tripotassium dicitratobismuthate [TDB] 120 mg QID, metronidazole 500 mg TID, and tetracycline 500 mg QID) or proton-pump inhibitor (PPI) dual therapy (omeprazole 20 mg BID and amoxicillin 500 mg QID). The study included 133 consecutive patients aged 17 to 83 years with endoscopically diagnosed DU (diameter > or = 5 mm) in whom standard triple therapy or PPI dual therapy had failed to eradicate Hp. A rapid urease (CLO) test was performed on four biopsy specimens at study entry and at least 1 month after the end of treatment to confirm Hp colonization and eradication, respectively. Patients were considered to be Hp positive if any CLO test was positive within 2 hours, and Hp was considered to be eradicated if all CLO tests were still negative after 24 hours. In 31 randomly selected patients, Hp eradication was confirmed histologically as well. Patients were given omeprazole 60 mg/d (20 mg in the morning and 40 mg in the evening) plus amoxicillin 500 mg QID for 10 days and subsequently were given metronidazole 500 mg TID for 10 days plus TDB 120 mg QID for 6 weeks. One hundred and twenty-four patients were followed up; five (4%) withdrew because of side effects (protracted diarrhea, stomatitis, skin rashes). Per-protocol analysis showed Hp eradication in 113 of 119 patients (95%) and ulcer healing in 118 of 119 (99%). Intent-to-treat analysis showed an Hp eradication rate of 85% (113 of 133 patients) and an ulcer healing rate of 89% (118 of 133 patients). In per-therapy analysis, the Hp eradication rate was 91% (113 of 124 patients), and the ulcer healing rate was 95% (118 of 124 patients). Side effects were observed in 39 of 119 patients (33%) and were generally mild. The four-drug regimen used in this study, when given to patients previously treated unsuccessfully with standard triple therapy or PPI dual therapy, was highly effective in eradicating Hp and healing DUs and had no major side effects.

Gastric diffusion of antibiotics used against Helicobacter pylori

Only a few pharmacological studies have been carried out on men and guinea pigs to determine the gastric diffusion of antibiotics, which are active against Helicobacter pylori. The results of these studies have been analysed in considering the physicochemical nature, the mode of administration, the way of gastric diffusion (topic and/or systemic) and the pharmacological interactions. The correlation of these pharmacokinetic results with those obtained in clinical trials is difficult because of the heterogeneity of the pharmacological and pharmacodynamic data. The absence of a convenient and suitable animal or in vitro study model renders further standardized pharmacokinetic studies in infected man and at steady state necessary.

Susceptibility of Helicobacter pylori to bactericidal properties of medium-chain monoglycerides and free fatty acids

Previous studies have shown that various short- and medium-chain free fatty acids (FFAs) and their corresponding monoacylglycerol esters (MGs) have antibacterial activity in vitro against primarily gram-positive bacteria. More recent studies have also shown that the growth of Helicobacter spp. is inhibited by linoleic acid and arachidonic acid. The purpose of the present study was to evaluate the susceptibility of Helicobacter pylori to the in vitro bactericidal properties of medium-chain MGs and FFAs. Incubation of H. pylori with saturated MGs, ranging in carbon chain length from C10:0 to C14:0, at 1 mM caused a 4-log-unit or greater reduction in the number of viable bacteria after exposure for 1 h. Lower levels of bactericidal activity were observed with C9:0, C15:0, and C16:0 MGs. In contrast, lauric acid (C12:0) was the only medium-chain saturated FFA with bactericidal activity against H. pylori. The MGs and FFAs were bactericidal after incubation for as little as 15 min at neutral or acidic pHs. Higher levels of MGs and FFAs were required for bactericidal activity in the presence of higher amounts of protein in liquid diets. We also found that the frequency of spontaneous development of resistance by H. pylori was higher for metronidazole and tetracycline (10(-5) to 10(-6)) than for C10:0 MG, C12:0 MG, and C12:0 FFA (< 10(-8)). Collectively, our data demonstrate that H. pylori is rapidly inactivated by medium-chain MGs and lauric acid and exhibits a relatively low frequency of spontaneous development of resistance to the bactericidal activity of MGs. Further studies are needed to establish whether MGs may be useful either alone or with other known therapeutic agents in the management of H. pylori infections in humans.