Towards new cholera prophylactics and treatment: Crystal structures of bacterial enterotoxins in complex with GM1 mimics.

Cholera is a life-threatening disease in many countries, and new drugs are clearly needed. C-glycosidic antagonists may serve such a purpose. Here we report atomic-resolution crystal structures of three such compounds in complexes with the cholera toxin. The structures give unprecedented atomic details of the molecular interactions and show how the inhibitors efficiently block the GM1 binding site. These molecules are well suited for development into low-cost prophylactic drugs, due to their relatively easy synthesis and their resistance to glycolytic enzymes. One of the compounds links two toxin B-pentamers in the crystal structure, which may yield improved inhibition through the formation of toxin aggregates. These structures can spark the improved design of GM1 mimics, either alone or as multivalent inhibitors connecting multiple GM1-binding sites. Future developments may further include compounds that link the primary and secondary binding sites. Serving as decoys, receptor mimics may lessen symptoms while avoiding the use of antibiotics.

Momordica charantia extracts inhibit uptake of monosaccharide and amino acid across rat everted gut sacs in-vitro.

The inhibitory effects of Momordica charantia extracts were studied on the uptake of glucose and tyrosine across rat everted gut sacs in vitro. The aqueous extract of the plant was found to inhibit primarily the uptake of glucose in a dose-dependent manner. Uptake of tyrosine was affected at high substrate concentrations only. The extract was also found to decrease the absorptive capacity of fluid across the small intestine and sodium ions. It is hypothesized that the effects of Momordica could involve a washout of glucose from the blood stream.

A practical method to study functional impairment of proteins by glycation and effects of inhibitors using current coagulation/fibrinolysis reagent kits.

Objectives We undertook the present work to device a simple method to study the effects of inhibitors on functional impairment of proteins by the action of glycating agents. Design and methods For that purpose, we first tested the feasibility and optimized the conditions to employ glycation of human plasma coupled with AT III and plasminogen activity measurement, using coagulation test kits available in most clinical laboratories. Results Using D-BUT-CHT-lys-pNA as a plasmin-specific substrate, we show that incubation of plasma with fructose, glyceraldehyde or MG but not glucose decreases plasminogen activity reaching more than 40% in 16 h. A parallel dose-dependent decrease in heparin activation of AT III by up to a 50% was demonstrated using SAR-PRO-ARG-pNA as a specific thrombin substrate. We studied the effects of aminoguanidine, carnosine, quercetin aglycone, alpha tocopherol and ascorbic acid. Conclusion The methods afforded good discrimination between the known different reactivities of glycating sugars as well as the action of known antiglycation agents. They provide a practical system for monitoring the action of putative antiglycation agents.

Enhancement of bacterial adhesion by shear forces: characterization of the haemagglutination induced by Aeromonas salmonicida strain 438.

Application of a viscometric assay to the haemagglutination induced by Aeromonas salmonicida strain 438 showed that shear forces can enhance the strength of bacterial adhesion. The D-mannose/L-fucose-sensitive reaction proceeded in two phases, an initial phase in which the degree of aggregation remained constant during shearing and a second stage, induced by shear, in which agglutination was enhanced as shear was maintained. The results strongly paralleled those found in studies of concanavalin A-induced haemagglutination, providing good evidence that adhesion in this species took place via lectin-like molecules. Methyl-alpha-D-mannoside, which strongly inhibits haemagglutination in this system, would not fully reverse the shear-dependent reaction. EGTA inhibited and reversed both phases, however. The effects of bacterial concentration, temperature, time of growth, pH, and a spectrum of monosaccharide inhibitors were also studied. The results demonstrated that the shear-dependent reaction has a number of features which distinguish it from the initial stage of haemagglutination, implying differences in the underlying biochemical mechanisms involved.