Rhamnan sulfate attenuates methylmercury cytotoxicity in rat thymic lymphocytes

Rhamnan sulfate, one of sulfated polysaccharides from seaweeds, is considered to have various characteristics such as antioxidant, anticoagulant, anti-inflammatory, antitumor, contraceptive, and antiviral activities, for the treatment of several diseases. We examined the effect of rhamnan sulfate on thymic lymphocytes treated simultaneously with methylmercury chloride, a toxic organometallic compound, using a flow-cytometric techniques with fluorescent probes, fluo-3-AM (an indicator for intracellular Ca2+) and propidium iodide (an indicator for dead cells). Rhamnan sulfate attenuated the methylmercury-induced increase in cell lethality. This effect of rhamnan sulfate is supposed to be due to the attenuation of methylmercury-induced elevation of intracellular Ca2+ levels. Rhamnan sulfate may be useful for the prevention of organometallic intoxication

非微生物素材表面への大腸菌の初期付着を抑制する穀類抽出液の分析

We examined the initial attachment of E. coli to abiotic surfaces conditioned with cereal extracts. The extracts were water-soluble fractions prepared from flours of barley, quinoa, rice and wheat. Strains used were E. coli ATCC 8739, E. coli NBRC 3301, E. coli NBRC 3302, E. coli NBRC 13168, E. coli NBRC 13891, and E. coli O157:H7 sakai. When surfaces of glass and stainless steel were conditioned at 25°C for 30 min with 0.5% cereal extracts, significantly lower numbers of E. coli cells attached to the conditioned surfaces than unconditioned ones, irrespective of strains used. The highest activity in reduction of the number of E. coli cells attached to the abiotic surfaces was found in the wheat extract. The suppressive activity was stable after treatments of the extract by autoclave and enzymatic digestion with α-amylase and Proteinase K. We purified the active compound by ammonium sulfate fractionation and gel filtration with HiPrep 16/60 Sephacryl S-200 HR after the enzymatic treatments. The purified compound showed an average molecular mass of about 300 kDa by light-scattering measurements. Analyses of its components indicated that the active compound was arabinoxylan; the molar ratios were 1.0 (arabinose) to 2.46 (xylose). Commercially available arabinoxylan (average molecular mass: 370 kDa) also showed the similar activity. To our knowledge, this is the first report on a dietary fiber from cereals which suppresses the initial attachment of E. coli to abiotic surfaces

Binding affinity of poly-γ-glutamate to Shiga toxin

We examined poly-γ-glutamate from natto, a Japanese fermented food, in the ability to adsorb Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2). The polymer was immobilized by direct coupling to EAH-SepharoseTM. The poly-γ-glutamate-Sepharose (about 10 mg of ligand/mL of gel) adsorbed Stx2, but not Stx1: its dissociation constant (Kd) against Stx2 was calculated to be 14.0 μM. To analyze the binding site of poly-γ-glutamate against Stx2, we similarly immobilized glutamate and glutarate. Glutamate- and glutarate-Sepharoses (each 7 μmol of ligand/mL of gel) similarly adsorbed Stx2, but not Stx1; Kd values against Stx2 were calculated to be 14.0 and 30.0, respectively, μM. The common structures of PGA-, glutamate-, and glutarate-Sepharoses were considered to be glutaryl groups. When we added the mixture of Stx2 and poly-γ-glutamate-Sepharose to Caco-2 cells (a human colon epithelial cell line), poly-γ-glutamate-Sepharose was found to reduce the cytotoxicity of Stx2

Screening and analysis of edible seaweeds in the ability to adsorb Shiga toxin

We screened edible seaweeds in the ability to adsorb Shiga toxin (Stx) by an equilibrated dialysis method. Although water insoluble fractions of fourteen dry seaweeds did not adsorb Stx, most water soluble fractions were found to adsorb it to one degree or another. Among the seaweed tested, the extract of the Ulva linza Linnaeus [Enteromorpha linza (Linnaeus) J. Agardh] was found to well adsorb both Stx1 and Stx2. We purified the Stx-adsorbing substance from the U. linza extract by DEAE-Toyopearl column chromatography and gel filtration with HiPrep 16/60 Sephacryl S-300 HR column. The purified substance showed an average molecular mass of about 800 kDa by polyacrylamide gel electrophoresis. Analyses of its components indicated that the substance was a highly rhamnose-containing polysaccharide with sulfate esters of 18%. Apparent dissociation constants (Kd) of the polysaccharide to Stx1 and Stx2 were calculated to be 1.9 and 3.5 μM, respectively. To our knowledge, this is the first report on Stx-adsorbing dietary fibers