Microbial metabolism of oxochlorates: a bioenergetic perspective.

The microbial metabolism of oxochlorates is part of the biogeochemical cycle of chlorine. Organisms capable of growth using perchlorate or chlorate as respiratory electron acceptors are also interesting for applications in biotreatment of oxochlorate-containing effluents or bioremediation of contaminated areas. In this review, we discuss the reactions of oxochlorate respiration, the corresponding enzymes, and the relation to respiratory electron transport that can contribute to a proton gradient across the cell membrane. Enzymes specific for oxochlorate respiration are oxochlorate reductases and chlorite dismutase. The former belong to DMSO reductase family of molybdenum-containing enzymes. The heme protein chlorite dismutase, which decomposes chlorite into chloride and molecular oxygen, is only distantly related to other proteins with known functions. Pathways for electron transport may be different in perchlorate and chlorate reducers, but appear in both cases to be similar to pathways found in other respiratory systems. This article is part of a Special Issue entitled: Evolutionary aspects bioenergetic systems.

Safety, Tolerability, and Pharmacokinetics of the Mineralocorticoid Receptor Modulator AZD9977 in Healthy Men: A Phase I Multiple Ascending Dose Study.

Excessive activation of the mineralocorticoid receptor (MR) underlies the pathophysiology of heart failure and chronic kidney disease. Hyperkalemia risk limits the therapeutic use of conventional MR antagonists. AZD9977 is a nonsteroidal, selective MR modulator that may protect nonepithelial tissues without disturbing electrolyte balance. This phase I study investigated the safety, tolerability, pharmacokinetics, and pharmacodynamics of multiple oral doses of AZD9977 in healthy volunteers. Twenty-seven male participants aged 23-45 years were randomized 3:1 to receive oral AZD9977 or placebo for 8 days (with twice-daily dosing on days 2-7), in dose cohorts of 50, 150, and 300 mg (AZD9977, n = 6 per cohort; placebo, n = 3 per cohort). Adverse events occurred in 4 of 18 participants receiving AZD9977 (22.2%) and 6 of 9 receiving placebo (66.7%), all of mild or moderate severity; none were serious or led to withdrawal. AZD9977 was rapidly absorbed, with median time of maximum concentration of 0.50-0.84 hours across dose groups. Area under the curve and maximum concentration were approximately dose proportional but elimination and accumulation terminal half-life increased with dose. Steady-state was reached after 3-4 days, with dose-dependent accumulation of 1.2-1.7-fold. Renal clearance was 5.9-6.5 L/hour and 24-37% of AZD9977 was excreted in the urine. Serum aldosterone levels increased dose dependently from days -1 to 7 in participants receiving AZD9977, but serum potassium levels and urinary electrolyte excretion were unchanged. AZD9977 was generally well-tolerated with no safety concerns. Exploratory outcomes suggested reduced hyperkalemia risk compared with MR antagonists. These findings support further clinical development of AZD9977.

Periplasmic c cytochromes and chlorate reduction in Ideonella dechloratans.

The aim of this study was to clarify the pathway of electron transfer between the inner membrane components and the periplasmic chlorate reductase. Several soluble c-type cytochromes were found in the periplasm. The optical difference spectrum of dithionite-reduced periplasmic extract shows that at least one of these components is capable of acting as an electron donor to the enzyme chlorate reductase. The cytochromes were partially separated, and the fractions were analyzed by UV/visible spectroscopy to determine the ability of donating electrons to chlorate reductase. Our results show that one of the c cytochromes (6 kDa) is able to donate electrons, both to chlorate reductase and to the membrane-bound cytochrome c oxidase, whereas the roles of the remaining c cytochromes still remain to be elucidated. Peptide extracts of the c cytochromes were obtained by tryptic in-gel digestion for matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis. Peptide sequences obtained indicate that the 6-kDa cytochrome c protein is similar to c cytochromes from the chlorate-reducing bacterium Dechloromonas aromatica.

Effect of increasing esomeprazole and pantoprazole doses on acid control in patients with symptoms of gastro-oesophageal reflux disease: a randomized, dose-response study.

BACKGROUND AND OBJECTIVE: In patients with gastro-oesophageal reflux disease (GORD), dose escalation or drug switching may be considered in those with symptoms that persist despite standard-dose proton pump inhibitor (PPI) therapy. This study set out to assess whether increasing the dosage of oral esomeprazole and pantoprazole improves acid control in GORD patients, and to compare the pharmacodynamic efficacy of esomeprazole and pantoprazole administered at different dosages. METHODS: This was an open-label, randomized, six-way crossover study that included Helicobacter pylori-negative GORD patients (aged 20-60 years) with <30% of time with intragastric pH>4. Patients were treated with oral once-daily esomeprazole 20 mg, 40 mg and 80 mg, and pantoprazole 20 mg, 40 mg and 80 mg, for 5 days. The main outcome measures were time with intragastric pH>4 over 24 hours, median pH over 24 hours and area under the hydrogen ion versus time curve on day 5 for each treatment period. RESULTS: Dose escalation with both PPIs improved acid control. The proportion of time with intragastric pH>4 (day 5) was 46.7% with esomeprazole 20 mg/day, 58.6% with esomeprazole 40 mg/day, and 65.8% with esomeprazole 80 mg/day; the corresponding percentages with pantoprazole were 28.6%, 36.9% and 44.9%, respectively. On a milligram-per-milligram basis, esomeprazole provided greater acid control than pantoprazole (p<0.001). CONCLUSION: Dose escalation with oral esomeprazole and pantoprazole improves acid control in patients with GORD, although esomeprazole provides significantly greater acid control on a milligram-per-milligram basis.

A new esomeprazole packet (sachet) formulation for suspension: in vitro characteristics and comparative pharmacokinetics versus intact capsules/tablets in healthy volunteers.

BACKGROUND: A packet (sachet) formulation of esomeprazole for suspension has been developed for use in patients who have difficulty swallowing. OBJECTIVES: This article reports the in vitro characteristics of the new esomeprazole formulation, including stability in suspension and suitability for administration orally or via enteral tubes. It also describes the pharmacokinetic profile of the esomeprazole 40-mg packet compared with that of existing solid dosage forms (capsules and tablets) in a clinical bioequivalence study. METHODS: The stability in suspension of the packet formulation was assessed after reconstitution at various strengths (2.5, 10, and 40 mg) and a different pH (3.4-5.0) in strength-appropriate volumes of water held at temperatures ranging from 5 degrees C to 37 degrees C for up to 60 minutes. Suitability for oral administration was examined in terms of reconstitution time and the actual dose delivered after simulated oral administration, as well as in terms of the actual dose delivered by enteral tubes ranging in diameter from 6 to 20 Fr. Chemical stability and suspension characteristics were also analyzed using alternative reconstitution vehicles (applesauce, apple juice, and orange juice). The comparative pharmacokinetics of the packet, capsule, and tablet formulations of esomeprazole were evaluated in a randomized, open-label, 3-way crossover study in healthy volunteers, who received single 40-mg doses of each formulation. Bioequivalence was assumed if the 90% CIs for the ratios of the geometric mean AUC and CmaX were between 0.80 and 1.25. Reversephase liquid chromatography with ultraviolet detection was used to assess the esomeprazole content and/or degradation products of esomeprazole in the tests for in-suspension stability, dose delivery, and acid resistance. Normal-phase liquid chromatography was used to assess the esomeprazole content of the plasma samples in the bioequivalence study. RESULTS: At the pH and temperature ranges investigated, the packet formulation was stable for up to 60 minutes after reconstitution. Chemical degradation was low (<0.1%) for all reconstitution vehicles investigated. Reconstitution time was 2 minutes with water and 9 to 10 minutes with apple or orange juice. Dose delivery was >/=98% after simulated oral administration and was generally >/=96% after administration via enteral tubes. Ninety-six healthy volunteers (56 women, 40 men; mean age, 24.9 years; mean weight, 68.9 kg) participated in the randomized, crossover, comparative pharmacokinetic study of the packet and capsule/tablet formulations. The estimated ratios of the geometric mean AUC and C(max) for the packet:capsule and packet: tablet formulations were 0.98 (90% CI, 0.93-1.03) and 0.99 (90% CI, 0.94-1.04), respectively. CONCLUSIONS: In these analyses, the packet (sachet) formulation of esomeprazole was chemically stable in suspension and when administered orally and via enteral tubes. The formulation had a short reconstitution time, remaining fully dispersed in water for at least 30 minutes, and was dispersed in applesauce, apple juice, or orange juice without compromising its stability or dispersion characteristics. The packet formulation met the regulatory definition for bioequivalence to the tablet and capsule formulations.

Purification and characterization of a soluble cytochrome c capable of delivering electrons to chlorate reductase in Ideonella dechloratans.

The electron donor for periplasmic chlorate reductase of Ideonella dechloratans has been suggested to be a soluble cytochrome c. We describe here the purification of the 9-kDa periplasmic cytochrome c, denoted cytochrome c-Id1, and demonstrate its ability to serve as an electron donor for purified chlorate reductase. The reaction rate was found to be linearly dependent on the cytochrome c concentration in the range of 0.6-4 µM. A route for electron transport involving a soluble cytochrome c is similar to that found for other periplasmic oxidoreductases of the dimethyl sulfoxide reductase family, but different from that suggested for the (per)chlorate reductase of Dechloromonas species.

Characterization of a cytochrome c gene located at the gene cluster for chlorate respiration in Ideonella dechloratans.

Anaerobic chlorate respiration requires electron transport from the bacterial inner membrane to the soluble periplasmic chlorate reductase. We have recently demonstrated that soluble c cytochromes function as electron carriers for chlorate reduction in Ideonella dechloratans (Smedja Bäcklund et al. 2009). In the present work, we describe a gene encoding soluble c-type cytochrome [cyt; GenBank ID: EU768872] located close to the gene cluster for chlorate reduction in I. dechloratans. The predicted amino acid sequence does not match any of the peptide masses or partial sequences obtained earlier from periplasmic c cytochromes. The gene, without the predicted signal sequence, was expressed heterologously in E. coli and the recombinant protein was purified, refolded and reconstituted with heme. The reconstituted protein shows spectral properties characteristic for c cytochromes, with an absorption maximum at 553 nm for the alpha band in the reduced state. Pyridine hemochrome analysis demonstrates the formation of covalently bound heme.