The Urtica Dioica Agglutinin Prevents Rabies Virus Infection in a Muscle Explant Model

Infection with the rabies virus (RABV) causes fatal encephalitis and paralysis in humans and animals. Post-exposure prophylaxis (PEP) consists of vaccination and the injection of anti-rabies immunoglobulins (RIGs) around the (bite) wound. This is 100% effective in preventing disease if administered in a timely manner. However, the costs, the required cold chain for storage and transport and the limited availability of RIGs makes the treatment challenging. Cheaper and easier to produce alternatives are urgently needed. To aid in the discovery and development of such alternative therapeutics, we developed a physiological relevant infection model. Strips of freshly dissected swine skeletal muscle were placed under tension in culture medium and infected with RABV. Viral antigens were produced in the muscle explants and the virus production increased significantly over time, indicating that RABV infects and replicates in the muscle explants. Subsequently, in a search for inhibitors of RABV entry in muscle cells, we first screened a panel of 34 different lectins in a RABV / BHK-21J cell assay. The Urtica Dioica (stinging nettle) Agglutinin (UDA; a N-acetyl-D-glucosamine specific agglutinin) was found to be able to completely inhibit infection of cells with the RABV (EC50 8.2 μg/mL) by preventing binding of the virus to the host cell. When the infection of the muscle strips was carried out in the presence of UDA, infection of the tissue was completely prevented. We thus developed a physiological relevant RABV muscle infection model and identified an easy to produce component that (i) may serve as a reference for further studies and (ii) holds promise as an alternative for RIGs in PEP.

Thermodynamic Analysis of Chitooligosaccharide Binding to Urtica dioica agglutinin by Isothermal Titration Calorimetry

UDA (Urtica dioica agglutinin) contains two hevein like domains with two non-identical interacting sites and is specific for chitooligosaccharides. The binding of chitooligosaccharides to UDA was studied by Isothermal Titration Calorimetry. Each site is composed of three subsites, each binding to a sugar residue. Thermodynamic parameters obtained show that while chitobiose has two independent non-interacting sites, chitotriose, chitotetrose and chitopentose have two interacting sites on each monomer of UDA. Values of binding enthalpy (ΔH) increase almost by a factor of 7 in going from chitobiose to chitotriose indicating the existence of three subsites in the combining site of UDA. The binding constant for chitotetrose and chitopentose increase without any further enhancement in the values of ΔH indicating that for oligomers larger than chitotriose interaction is favoured entropically.