Investigations into the antiadhesive activity of herbal extracts against Campylobacter jejuni.

Campylobacter jejuni is one of the most common bacterial causes of diarrhoea in the industrialized world, being associated with the occurrence of Guillain-Barré Syndrome, and inducing diseases partially through intestinal adherence. With increasing reports of C. jejuni drug resistance against standard antibiotics, investigations into antiadhesive agents for the prevention of bacterial infection are highly significant. Given the consumer-driven development towards holistic and integrative healthcare, research into additional anti-Campylobacter effects of herbal medicines that are already used for their beneficial effects on bowel and digestive functions is important. Twenty-one herbal extracts were screened for antiadhesive activity against C. jejuni using modifications of previously published antiadhesion assays. Antiadhesion effects with IC(50) values <3 mg/mL were obtained for seven ethanol plant extracts, with Zingiber officinale (ginger), Capsicum annum (cayenne) and Glycyrrhiza glabra (licorice) displaying the highest antiadhesion activity against C. jejuni (IC(50) : <0.1 mg/mL, 0.29 mg/mL and 0.65 mg/mL, respectively). Differences in antiadhesion activity were found for two different Echinacea species, with E. purpurea displaying significantly higher and dose dependent antiadhesion activity than E. angustifolia. No significant antiadhesion activity (IC(50) values >35 mg/mL) was found for Agrimonia eupatoria (agrimony), Andrographis paniculata (andrographis), Matricaria recutita (chamomile), Foeniculum vulgare (fennel), Filipendula ulmaria (meadowsweet) and Artemisia absinthium (wormwood) extracts. This study provides evidence for additional beneficial effects of marketed herbal medicines in gastrointestinal disorders.

Sialic acid-specific lectins: occurrence, specificity and function.

Sialic acids consist of a family of acidic nine-carbon sugars that are typically located at the terminal positions of a variety of glycoconjugates. Naturally occurring sialic acids show an immense diversity of structure, and this reflects their involvement in a variety of biologically important processes. One such process involves the direct participation of sialic acids in recognition events through specific interactions with lectins, a family of proteins that recognise and bind sugars. This review will present a detailed overview of our current knowledge regarding the occurrence, specificity and function of sialic acid-specific lectins, particularly those that occur in viruses, bacteria and non-vertebrate eukaryotes.

A high-throughput assay for rat liver golgi and Saccharomyces cerevisiae-expressed murine CMP-N-acetylneuraminic acid transport proteins.

Rat liver Golgi and Saccharomyces cerevisiae-expressed CMP-Neu5Ac transport protein were reconstituted in phosphatidylcholine liposomes and transport of CMP-Neu5Ac into these proteoliposomes was determined. The separation of transported substrate from free substrate was performed using Multiscreen minicolumns loaded with Sephadex G-50 resin (fine). The CMP-Neu5Ac transport characteristics of the rat liver Golgi and S. cerevisiae-expressed transporters, determined using this separation system, were very similar to those previously reported. Inhibition studies, utilizing the above procedure, revealed that the main structural features required for recognition of glycosyl nucleosides by the rat liver Golgi CMP-Neu5Ac transport protein were the nature of the nucleoside base and the anomeric configuration of the associated carbohydrate. In general, pyrimidine-based glycosyl nucleosides were found to inhibit transport to a far greater extent than purine-based glycosyl nucleosides, an observation that is in good agreement with previous reports. These results indicate that the reconstitution procedure, in conjunction with Multiscreen minicolumns, is an effective high-throughput method for the determination of CMP-Neu5Ac transport.

Characterisation of the enzymatic 4-O-acetylation of sialic acids in microsomes from equine submandibular glands.

Microsomes prepared from equine submandibular glands and incubated with tritium-labelled AcCoA incorporated acid-insoluble radioactivity in a manner dependent on time, protein, membrane integrity and AcCoA concentration, with incorporation being optimal at 37 degrees C and pH 6.6. Under the experimental conditions used a K(M) of 32.1 microM for AcCoA and a V(max) of 1.2 pmol/mg protein x min was obtained. The incorporation of acid-insoluble radioactivity was also inhibited by CoA in a competitive manner (K(i)=240 microM), as well as by para-chloromercuribenzoate, 3'-dephospho-CoA, 5'-IDP, 5'-ADP, beta-NAD and 4,4'-diisothiocyanatostilbene-2,2'-disulfonate. We demonstrate here that this incorporation of radioactivity into endogenous sialic acid is due to the action of an AcCoA:sialate-4-O-acetyltransferase [EC 2.3.1.44]. Radio thin-layer chromatography analyses of propionic acid-released sialic acids showed that the incorporation of radioactivity correlated with the formation of a radiolabelled species that co-migrated with authentic Neu4,5Ac2. Saponification experiments using NaOH, mouse hepatitis virus strain S and Influenza C/JJ/50 virus also showed that the transfer of [3H]acetyl groups from [3H]AcCoA to endogenous sialic acid acceptors was occurring exclusively at carbon 4 of the pyranose ring.

Effect of substrate aglycon on enzyme mechanism in the reaction of sialidase from influenza virus.

The effect of substrate aglycon on enzyme mechanism of sialidase from influenza virus was investigated by kinetic isotope effects using the substrates 4-methylumbelliferyl-N-acetyl-alpha-D-neuraminic acid (Neu5Ac alpha 2MU) and p-nitrophenyl-N-acetyl-alpha-D-neuraminic acid (Neu5Ac alpha 2PNP). The kinetic isotope effect on Vmax (beta DV), at pH 6.0, as revealed by direct comparison of rates obtained with Neu5Ac alpha 2MU and the [3,3-2H]-substituted substrate analogue, was shown to be inverse. This indicates that sialidase-catalysed hydrolysis of Neu5Ac alpha 2MU proceeds with substantial positive charge development at the reaction centre in the transition state for the formation of the glycosyl cation-enzyme intermediate. However, no such inverse effect on Vmax at pH 6.0 was observed when using Neu5Ac alpha 2PNP and the [3,3-2H]-substituted substrate. A mechanism by which hydrolysis proceeds through an alpha-lactone intermediate has been proposed by Guo et al. [8]. We propose that the differences in beta DV for the substrates investigated are due primarily to the differing properties of the aglycon leaving groups, which may result in influenza virus sialidase catalysing substrate hydrolysis by a similar mechanism with alternative stabilisation of transition state.