Structure and function of sedoheptulose-7-phosphate isomerase, a critical enzyme for lipopolysaccharide biosynthesis and a target for antibiotic adjuvants

The barrier imposed by lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria presents a significant challenge in treatment of these organisms with otherwise effective hydrophobic antibiotics. The absence of L-glycero-D-manno-heptose in the LPS molecule is associated with a dramatically increased bacterial susceptibility to hydrophobic antibiotics and thus enzymes in the ADP-heptose biosynthesis pathway are of significant interest. GmhA catalyzes the isomerization of D-sedoheptulose 7-phosphate into D-glycero-D-manno-heptose 7-phosphate, the first committed step in the formation of ADP-heptose. Here we report structures of GmhA from Escherichia coli and Pseudomonas aeruginosa in apo, substrate, and product-bound forms, which together suggest that GmhA adopts two distinct conformations during isomerization through reorganization of quaternary structure. Biochemical characterization of GmhA mutants, combined with in vivo analysis of LPS biosynthesis and novobiocin susceptibility, identifies key catalytic residues. We postulate GmhA acts through an enediol-intermediate isomerase mechanism.

A population-based association study of SNPs of GSTP1, MnSOD, GPX2 and Barrett's esophagus and esophageal adenocarcinoma

Oxidative stress appears to be important in the pathogenesis of Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC). Single-nucleotide polymorphisms (SNPs) of antioxidant enzyme genes may play a part in determining individual susceptibility to these diseases. The Factors Influencing the Barrett's Adenocarcinoma Relationship (FINBAR) study is a population-based, case-control study of BE and EAC in Ireland. DNA from EAC (n = 207), BE (> or =3 cm BE at endoscopy with specialized intestinal metaplasia on biopsy, n = 189) and normal population controls (n = 223) were analyzed. Several SNPs spanning the genes for glutathione S-transferase P1 (GSTP1), manganese superoxide dismutase (MnSOD) and glutathione peroxidase 2 (GPX2) were genotyped using multiplex polymerase chain reaction and SNaPshottrade mark. The chi(2) test was used to compare genotype and allele frequencies between case and control subjects. Linkage disequilibrium between SNPs was quantified using Lewontin's D' value and haplotype frequency estimates obtained using Haploview. Eleven SNPs were genotyped (six for GSTP1, three for MnSOD and two for GPX2); all were in Hardy-Weinberg equilibrium. None was significantly associated with EAC or BE even before Bonferroni correction. Odds ratios for EAC for individual SNPs ranged from 0.68 [95% confidence interval (CI) 0.43-1.08] to 1.25 (95% CI 0.73-2.16), and for BE from 0.84 (95% CI 0.52-1.30) to 1.30 (95% CI 0.85-1.97). SNPs in all three genes were in strong linkage disequilibrium (D' > 0.887) but haplotype analysis did not show any significant association with EAC or BE. SNPs involving the GSTP1, MnSOD and GPX2 genes were not associated with BE or EAC. Further studies aimed at identifying susceptibility genes should focus on different antioxidant genes or different pathways.

Nonsteroidal anti-inflammatory drugs and the esophageal inflammation-metaplasia-adenocarcinoma sequence

Observational studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of esophageal adenocarcinoma, but it is not known at what stage they may act in the esophageal inflammation-metaplasia-adenocarcinoma sequence. In an all-Ireland case-control study, we investigated the relationship between the use of NSAIDs and risk of reflux esophagitis, Barrett's esophagus, and esophageal adenocarcinoma. Patients with esophageal adenocarcinoma, long-segment Barrett's esophagus and population controls were recruited from throughout Ireland. Esophagitis patients were recruited from Northern Ireland only. Data were collected on known and potential risk factors for esophageal adenocarcinoma and on the use of NSAIDs, including aspirin, at least 1 year before interview. Associations between use of NSAIDs and the stages of the esophageal inflammation-metaplasia-adenocarcinoma sequence were estimated by multiple logistic regression. In total, 230 reflux esophagitis, 224 Barrett's esophagus, and 227 esophageal adenocarcinoma and 260 population controls were recruited. Use of aspirin and NSAIDs was associated with a reduced risk of Barrett's esophagus [odds ratio [OR; 95% confidence interval (95% CI)], 0.53 (0.31-0.90) and 0.40 (0.19-0.81), respectively] and esophageal adenocarcinoma [OR (95% CI), 0.57 (0.36-0.93) and 0.58 (0.31-1.08), respectively]. Barrett's esophagus and esophageal adenocarcinoma patients were less likely than controls to have used NSAIDs. Selection or recall bias may explain these results and the results of previous observational studies indicating a protective effect of NSAIDs against esophageal adenocarcinoma. If NSAIDs have a true protective effect on the esophageal inflammation-metaplasia-adenocarcinoma sequence, they may act early in the sequence.

Common variants at the MHC locus and at chromosome 16q24.1 predispose to Barrett's esophagus

Barrett's esophagus is an increasingly common disease that is strongly associated with reflux of stomach acid and usually a hiatus hernia, and it strongly predisposes to esophageal adenocarcinoma (EAC), a tumor with a very poor prognosis. We report the first genome-wide association study on Barrett's esophagus, comprising 1,852 UK cases and 5,172 UK controls in the discovery stage and 5,986 cases and 12,825 controls in the replication stage. Variants at two loci were associated with disease risk: chromosome 6p21, rs9257809 (P(combined) = 4.09 × 10(-9); odds ratio (OR) = 1.21, 95% confidence interval (CI) =1.13-1.28), within the major histocompatibility complex locus, and chromosome 16q24, rs9936833 (P(combined) = 2.74 × 10(-10); OR = 1.14, 95% CI = 1.10-1.19), for which the closest protein-coding gene is FOXF1, which is implicated in esophageal development and structure. We found evidence that many common variants of small effect contribute to genetic susceptibility to Barrett's esophagus and that SNP alleles predisposing to obesity also increase risk for Barrett's esophagus.

Consensus statements for management of Barrett's dysplasia and early-stage esophageal adenocarcinoma, based on a Delphi process

Esophageal adenocarcinoma (EA) is increasingly common among patients with Barrett's esophagus (BE). We aimed to provide consensus recommendations based on the medical literature that clinicians could use to manage patients with BE and low-grade dysplasia, high-grade dysplasia (HGD), or early-stage EA.