Descripción: This study demonstrated that the λ- and ι-carrageenans, sulfated polysaccharides containing linear chains of galactopyranosyl residues, are potent inhibitors of dengue virus type 2 (DENV-2) and 3 (DENV-3) multiplication in Vero and HepG2 cells, with values of effective concentration 50% from 0.14 to 4.1 μg/ml. This activity was assayed by plaque reduction, virus yield inhibition and antigen expression tests, and was independent of the input multiplicity of infection in the range 0.001-1. The inhibitory action of the λ-carrageenan, an heparan sulfate (HS)-imitative compound, was exerted by a dual interference with virus adsorption and internalization of nucleocapsid into the cytoplasm. Although virus particles may enter the cell when compound was added after DENV-2 adsorption, as shown by intracellular uptake of radiolabeled DENV-2 particles and quantitative RT-PCR, infectious center and virion uncoating assays have shown that carrageenan-treated virions cannot be released from the endosomes. Viral protein synthesis, the first step of macromolecular synthesis after DENV entry to the host cell, was not affected by the carrageenan. Furthermore, no inhibition of virus multiplication was detected when the entry process was bypassed through DENV-2 RNA transfection into the cell. The dual sites of action of an HS-like molecule suggest that, at least in monkey kidney and human hepatic cells, the HS residues in the cell membrane appear to act as mediators for DENV-2 entry, an interesting alternative target for flavivirus therapy. © 2007 Elsevier Inc. All rights reserved.

Descripción: The antiviral activity against dengue virus-2 (DENV-2) of carrageenans reported here has shown a differential susceptibility of C6/36 HT and Vero cells, taken as models of mosquito and mammalian cells, depending on the structural class of polysaccharides: all polysaccharides blocked DENV-2 infection in monkey Vero cells, but only iota-carrageenans were virus inhibitors in mosquito cells. However, iota-carrageenans were less effective in mosquito cells in comparison with mammalian cells with effective concentration 50% (EC50) values in C6/36 HT cells 4.9-17.5-fold higher than in Vero cells, as determined by virus yield reduction assay. The mode of action of iota-carrageenan in both cell types was strikingly different: in Vero cells the inhibitory activity was exerted only at the initiation of the cycle, affecting virion binding, whereas in mosquito cells DENV-2 adsorption was not affected and comparable levels of inhibition were obtained if the compound was added to cells together with the virus, after 8 h of infection or by cell pretreatment before infection. Furthermore, iota-carrageenans induced a subtle alteration in mosquito cells, detected by cell proliferation and protein synthesis analyses, suggesting that a probable cellular target may be responsible for the refractory state of mosquito cells to DENV-2 infection produced by this class of polysulfates. The failure of iota-carrageenan to block DENV-2 adsorption to mosquito cells appeared to be related to the low presence of adequate heparin sulfate (HS) in C6/36 HT cell surface and is indicative of a differential participation of HS residues for DENV-2 entry in both types of cells. © 2011 SGM.

Descripción: The polysaccharides from cystocarpic Iridaea undulosa, soluble and insoluble in 2M potassium chloride, Cs and Ci, respectively, were treated with alkali and fractionated by precipitation with increasing concentrations of KCl. They were later separated by ion-exchange chromatography, to yield fractions enriched in an α-(1→6)-glucan, agaroids and carrageenans.