ABSTRACT
This study evaluated the potential toxicity and antiviral activity of fucoidan from Cladosiphon okamuranus against Newcastle disease virus (NDV), one of the most serious threats to the poultry industry in the world. Toxicity was assayed on chicken embryo fibroblast (CEF) secondary cultures at concentrations ranging from 0.1 to 1500 µg per mL culture medium, assessing the cell viability by the yellow tetrazolium MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) assay, and on 9-day-old embryonated chicken eggs by inoculation of 2 to 500 µg doses in the allantoic cavity, assessing the embryos morphology and liver histology. At 48 h post-inoculation, viability of CEF exposed to concentrations up to 10 µg/mL was not significantly affected, and the 50% cytotoxic concentration was estimated as of 1062 µg/mL; after exposure in ovo, some chick embryos showed liver steatosis when treated with fucoidan doses over 20 µg per egg (15 to 28% at 200 µg, 27 to 56% at 500 µg), but no change was detected in their size or aspect. Antiviral activity was tested by treating 9-day-old embryos via the allantoic route with 0.25 to 16 µg fucoidan doses that were applied at different times (-1, 0 and +1 h) relative to the inoculation of 10,000 folds the 50% Tissue Culture Infective Dose (TCID50) of the NDV, La Sota strain. At 72 h post infection, virus titration in the allantoic fluid by hemagglutination assay (HA) showed a considerable and significant inhibition of infectivity for all doses, the best result (a 90% decrease) being obtained in embryos treated with 1 µg fucoidan one hour before infection. Viral RNA semi-quantification in pooled liver and small intestine of embryos that had been treated with 4 and 16 µg fucoidan 1 h before the infection showed reductions of the virus replication by 60 and 99.8%, respectively. Since this high anti-NDV activity in ovo was obtained with quite innocuous doses, fucoidan from C. okamuranus could be a potential low-toxicity antiviral compound to be used in areas exposed to NDV.
