A Randomized Clinical Trial to Determine the Efficacy of Regimens Containing Clarithromycin, Metronidazole, and Amoxicillin Among Histologic Subgroups for Helicobacter pylori Eradication in a Developing Country

Background: Most treatments deemed effective for Helicobacter pylori eradication in developed countries are less effective in developing countries. Regimens containing clarithromycin, metronidazole, and amoxicillin seem efficacious despite antibiotic resistance, and may be a viable option in developing countries. Materials and Methods: We evaluated the efficacy of a 14‐day regimen with 500 mg clarithromycin b.i.d., 500 mg metronidazole t.i.d., and 500 mg amoxicillin t.i.d. (with and without a proton pump inhibitor), and a 10‐day regimen containing 500 mg clarithromycin b.i.d., 1 g amoxicillin b.i.d., and 20 mg omeprazole b.i.d. in Pasto, Colombia, using a randomized, single‐blind design stratified by presence of atrophic gastritis. Results: H. pylori was eradicated in 86.8% and 85.3% of the participants randomized to a clarithromycin‐metronidazole‐amoxicillin and clarithromycin‐amoxicillin‐omeprazole regimens, respectively (p = .79). Per‐protocol analyses indicated greater efficacy for the clarithromycin‐metronidazole‐amoxicillin regimen (97%) versus the clarithromycin‐amoxicillin‐omeprazole regimen (86%) (p = .04), particularly for participants with atrophic gastritis (clarithromycin‐metronidazole‐amoxicillin = 100%, clarithromycin‐amoxicillin‐omeprazole = 81%; p = .02). Adverse events were mild, but adverse event‐related non‐compliance was reported more often for regimens containing clarithromycin, metronidazole, and amoxicillin. Conclusions: Our results suggest that an eradication rate of > 85% can be achieved with 14‐day clarithromycin, metronidazole, and amoxicillin and 10‐day clarithromycin, amoxicillin, and omeprazole regimens in Pasto, Colombia. The regimens containing clarithromycin, metronidazole, and amoxicillin appear to be superior to the clarithromycin, amoxicillin, and omeprazole regimen for compliant participants and those with atrophic gastritis. Our findings provide treatment options for a population in a developing country with a high prevalence of H. pylori infections and antibiotic resistance.     

Visualization of PLP-bound intermediates in hemeless variants of human cystathionine beta-synthase: evidence that lysine 119 is a general base

Cystathionine beta-synthase catalyzes the condensation of serine and homocysteine to give cystathionine in a pyridoxal phosphate (PLP)-dependent reaction. The human enzyme contains a single heme per monomer that is bound in an N-terminal 69 amino acid extension that is missing from the otherwise highly homologous yeast enzyme. The heme dominates the UV-visible spectrum and obscures kinetic characterization of the PLP-bound reaction intermediates. In this study, we have engineered a hemeless mutant of human cystathionine beta-synthase by deletion of the N-terminal 69 amino acids. The resulting variant displays approximately 40% of the activity seen with the wild type enzyme, binds stoichiometric amounts of PLP, and permits spectral characterization of PLP-based intermediates. The enzyme as isolated exhibits an absorption maximum at 412nm corresponding to a protonated internal aldimine. Addition of serine shifts the lambdamax to 420nm (assigned as the external aldimine) with a broad shoulder between 450 and 500nm (assigned as the aminoacrylate intermediate). Addition of the product, cystathionine, also leads to formation of an external aldimine (420nm). Homocysteine elicits a red shift (and a decrease in absorption) in the spectrum from 412 to 424nm and an increase in absorption at 330nm, presumably due to formation of a dead-end complex. Mutation of K119, the residue that forms the Schiff base, to alanine results in a approximately 10(3)-fold decrease in activity, which increases approximately 2-fold in the presence of an exogenous base, ethylamine. Spectral shifts (412 --> 420nm) consistent with the formation of external aldimines are observed in the presence of serine or cystathionine, but an aminoacrylate intermediate is not formed at detectable levels. These results are consistent with an additional role for K119 as a general base in the reaction catalyzed by human cystathionine beta-synthase.     

Hypoxia regulates assembly of cilia in suppressors of Tetrahymena lacking an intraflagellar transport subunit gene

We cloned a Tetrahymena thermophila gene, IFT52, encoding a homolog of the Chlamydomonas intraflagellar transport protein, IFT52. Disruption of IFT52 led to loss of cilia and incomplete cytokinesis, a phenotype indistinguishable from that of mutants lacking kinesin-II, a known ciliary assembly transporter. The cytokinesis failures seem to result from lack of cell movement rather than from direct involvement of ciliary assembly pathway components in cytokinesis. Spontaneous partial suppressors of the IFT52 null mutants occurred, which assembled cilia at high cell density and resorbed cilia at low cell density. The stimulating effect of high cell density on cilia formation is based on the creation of pericellular hypoxia. Thus, at least under certain conditions, ciliary assembly is affected by an extracellular signal and the Ift52p function may be integrated into signaling pathways that regulate ciliogenesis.     

Human cystathionine beta-synthase is a heme sensor protein. Evidence that the redox sensor is heme and not the vicinal cysteines in the CXXC motif seen in the crystal structure of the truncated enzyme

Elevated levels of homocysteine, a sulfur-containing amino acid, are correlated with increased risk for cardiovascular diseases and Alzheimers disease and with neural tube defects. The only route for the catabolic removal of homocysteine in mammals begins with the pyridoxal phosphate- (PLP-) dependent beta-replacement reaction catalyzed by cystathionine beta-synthase. The enzyme has a b-type heme with unusual spectroscopic properties but as yet unknown function. The human enzyme has a modular organization and can be cleaved into an N-terminal catalytic core, which retains both the heme and PLP-binding sites and is highly active, and a C-terminal regulatory domain, where the allosteric activator S-adenosylmethionine is presumed to bind. Studies with the isolated recombinant enzyme and in transformed human liver cells indicate that the enzyme is approximately 2-fold more active under oxidizing conditions. In addition to heme, the enzyme contains a CXXC oxidoreductase motif that could, in principle, be involved in redox sensing. In this study, we have examined the role of heme versus the vicinal thiols in modulating the redox responsiveness of the enzyme. Deletion of the heme domain leads to loss of redox sensitivity. In contrast, substitution of either cysteine with a non-redox-active amino acid does not affect the responsiveness of the enzyme to reductants. We also report the crystal structure of the catalytic core of the enzyme in which the vicinal cysteines are reduced without any discernible differences in the remainder of the protein. The structure of the catalytic core is compared to those of other members of the fold II family of PLP-dependent enzymes and provides insights into active site residues that may be important in interacting with the substrates and intermediates.     

Oxygen uptake through gills and skin in relation to body weight of an air-breathing siluroid fish, Saccobranchus (=Heteropneustes) fossilis

Oxygen uptake through gills and skin has been measured in juvenile and adult Saccobranchus fossilis and its relationship represented by the equation Vo₂= aW^b. When air-breathing is allowed the O₂ uptake via the gills and skin together increases by powers of 1 -084, 0–986 and 1–328 in juvenile, adult and juvenile+adult respectively. When air-breathing is prevented the slope (b) for O₂ uptake via the gills appear to be less in juveniles (0–765) than in adults (0–784) and juveniles+adults together (0–814). Under the same experimental condition, the slope for O₂ uptake via the gills+skin is also less in juveniles (0–478) than in adults (0–799) and juveniles+adults (0–755). Further decrease in the exponent value is found for the oxygen uptake of skin in relation to body weight under surfacing-prevented conditions ( b = 0–542). Different exponent values for juvenile and adult fishes may be due to their different growth pattern and physiology.     

Velocity and wall shear stress patterns in the human right coronary artery.

Blood flow dynamics in the human right coronary artery have not been adequately quantified despite the clinical significance of coronary atherosclerosis. In this study, a technique was developed to construct a rigid flow model from a cast of a human right coronary artery. A laser photochromic method was used to characterize the velocity and wall shear stress patterns. The flow conditions include steady flow at Reynolds numbers of 500 and 1000 as well as unsteady flow with Womersley parameter and peak Reynolds number of 1.82 and 750, respectively. Characterization of the three-dimensional geometry of the artery revealed that the largest spatial variation in curvature occurred within the almost branch-free proximal region, with the greatest curvature existing along the acute margin of the heart. In the proximal segment, high shear stresses were observed on the outer wall and lower, but not negative, stresses along the inner wall. Low shear stress on the inner wall may be related to the preferential localization of atherosclerosis in the proximal segment of the right coronary artery. However, it is possible that the large difference between the outer and inner wall shear stresses may also be involved.