Reversible inhibition of type 2 dengue virus by agar polysaccharide

Antiviral Strategies Using Natural Source-Derived Sulfated Polysaccharides in the Light of the COVID-19 Pandemic and Major Human Pathogenic Viruses

Only a mere fraction of the huge variety of human pathogenic viruses can be targeted by the currently available spectrum of antiviral drugs. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak has highlighted the urgent need for molecules that can be deployed quickly to treat novel, developing or re-emerging viral infections. Sulfated polysaccharides are found on the surfaces of both the susceptible host cells and the majority of human viruses, and thus can play an important role during viral infection. Such polysaccharides widely occurring in natural sources, specifically those converted into sulfated varieties, have already proved to possess a high level and sometimes also broad-spectrum antiviral activity. This antiviral potency can be determined through multifold molecular pathways, which in many cases have low profiles of cytotoxicity. Consequently, several new polysaccharide-derived drugs are currently being investigated in clinical settings. We reviewed the present status of research on sulfated polysaccharide-based antiviral agents, their structural characteristics, structure-activity relationships, and the potential of clinical application. Furthermore, the molecular mechanisms of sulfated polysaccharides involved in viral infection or in antiviral activity, respectively, are discussed, together with a focus on the emerging methodology contributing to polysaccharide-based drug development.

Potential Antiviral Properties of Industrially Important Marine Algal Polysaccharides and Their Significance in Fighting a Future Viral Pandemic

Over the decades, the world has witnessed diverse virus associated pandemics. The significant inhibitory effects of marine sulfated polysaccharides against SARS-CoV-2 shows its therapeutic potential in future biomedical applications and drug development. Algal polysaccharides exhibited significant role in antimicrobial, antitumor, antioxidative, antiviral, anticoagulant, antihepatotoxic and immunomodulating activities. Owing to their health benefits, the sulfated polysaccharides from marine algae are a great deal of interest globally. Algal polysaccharides such as agar, alginate, carrageenans, porphyran, fucoidan, laminaran and ulvans are investigated for their nutraceutical potential at different stages of infection processes, structural diversity, complexity and mechanism of action. In this review, we focus on the recent antiviral studies of the marine algae-based polysaccharides and their potential towards antiviral medicines.

Dextrin Sulphate and Fucoidan are Potent Inhibitors of HIV Infection in vitro

Two sulphated polysaccharides, fucoidan (a derivative of seaweed) and the newly synthesised dextrin sulphate, were tested for their ability to inhibit human immunodeficiency virus (HIV) infection in vitro in comparison to dextran sulphate and azidothymidine. They were found to be potent inhibitors of diverse strains of HIV-1 in a variety of human cell lines and in peripheral blood lymphocytes (PBL) using a range of assays, including cell-free and cell-to-cell spread of infection. The drugs did not adversely affect cell proliferation or protein metabolism of PBL. As dextrin sulphate is less potent than dextran sulphate in prolonging thrombin-induced fibrin clotting time, it merits further development as an antiviral agent.

Mode of Action of an Inhibitor from Agar on Growth and Hemagglutination of Group A Arboviruses

Colón, Julio I. (Fort Detrick, Frederick, Md.), Jane B. Idoine, Orville M. Brand, and Richard D. Costlow. Mode of action of an inhibitor from agar on growth and hemagglutination of group A arboviruses. J. Bacteriol. 90:172-179. 1965.-A polysaccharide obtained from agar, and having properties similar to a previously described sulfated polysaccharide, was observed to inhibit growth and hemagglutination of some group A arboviruses. The evidence presented confirms that the inhibitory activity, in part, is the result of direct interaction between the agar polysaccharide (AP) and free virus particles. Additional evidence indicates that inhibition of viral growth also occurs as the result of interaction between AP and the chick-fibroblast cells used for propagation of the virus. The possibility was considered, therefore, that at least two different inhibitors could be present in AP-one that reacts directly with the virus particle and another that reacts with host cells. AP does not induce the production of interferon in the test system used.

Improved plaque assays for Rickettsia prowazekii in Vero 76 cells

Typhus group rickettsiae, including Rickettsia prowazekii and R. typhi, produce visible plaques on primary chick embryo fibroblasts and low-passage mouse embryo fibroblasts but do not form reproducible plaques on continuous cell culture lines. We tested medium overlay modifications for plaque formation of typhus group rickettsiae on the continuous fibroblast cell line Vero76. A procedure involving primary overlay with medium at pH 6.8, which was followed 2 to 3 days later with secondary overlay at neutral pH containing 1 microgram of emetine per ml and 20 micrograms of NaF per ml, resulted in visible plaques at 7 to 10 days postinfection. A single-step procedure involving overlay with medium containing 50 ng of dextran sulfate per ml also resulted in plaque formation within 8 days postinfection. These assays represent reproducible and inexpensive methods for evaluating the infectious titers of typhus group rickettsiae, cloning single plaque isolates, and testing the susceptibilities of rickettsiae to antibiotics.

Marine products as a source of antiviral drug leads

A survey is presented of the occurrence of organic compounds from aquatic organisms that have been reported to have antiviral activities. Studies of the chemical structures and antiviral properties of unusual metabolic products of aquatic life have demonstrated that marine organisms offer excellent prospects in the search for antiviral drugs.

Antiretroviral activity in a marine red alga: reverse transcriptase inhibition by an aqueous extract of Schizymenia pacifica

An aqueous extract from the marine red alga, Schizymenia pacifica has been tested in a cell free system for its effect on reverse transcriptase from avian retrovirus (avian myeloblastosis virus), and mammalian retrovirus (Rauscher murine leukemia virus). The extract inhibited reverse transcriptase from both these retroviruses but showed almost no effect, if any, on the activity of cellular DNA polymerase alpha and RNA polymerase II in vitro. Consequently it is unlikely to have an adverse effect on the growth of cultured cell. The inhibitory activity of the extract was stable over a relatively wide pH range (pH 1-11) and was not lost after pronase digestion. Inhibitory activity of the extract was lost after boiling at 100 degrees C in 0.67 N HCl, and after treatment with 100 mM NaIO4. The active principle in the extract has an apparent molecular weight in excess of 100,000 daltons. This new reverse transcriptase inhibitor is probably a polysaccharide.

Strain-specific aggregation of enterovirus by dextran sulfate

Dextran sulfate aggregates several enteroviruses depending not only on the pH, the ionic strength of the medium, but also on the protein content of the fluids and on strain specificities of the viruses. The aggregation effect was measured by filtration experiments, by sedimentation in the ultracentrifuge and by electron microscopy. The well known inhibiting effect of dextran sulfate on plaque formation may be due to its aggregating effect: A very strong inhibition of the release of matured virions from the infected cells is observed in medium containing dextran sulfate, whereas the adsorption process is inhibited much less compared with PBS controls. The maximal effect on virus aggregation, plaque size and virus release is observed at the same concentration of dextran sulfate.

Arbovirus identification by an agar-gel diffusion technique

A double diffusion-in-agar test was used to investigate precipitation reactions of 75 arboviruses. Specific reactions were regularly observed with members of arbovirus groups B, California, Simbu, Turlock, Hart Park, vesicular stomatitis, and several other arboviruses as well as with a member of the Tacaribe group and a herpesvirus. The results demonstrated the feasibility of applying this technique to the identification of arboviruses.

Mechanism of enhancement of virus plaques by cationic polymers

It has been assumed that plaque enhancement by cationic polymers is due to their binding of sulfated polysaccharides in agar. However, viruses that are enhanced by cationic polymers, diethylaminoethyl-dextran, and protamine were found not to be inhibited by polyanions in agar under the usual overlay conditions. In the case of adenovirus, enhancement by protamine seems to be due to the protamine serving as a source of arginine; enzymes released from the cultured cells digest the protamine and provide a reservoir of arginine for the cells. Other viruses (herpes and echovirus types 3, 4, 5, and 6) known to be susceptible to agar inhibitors were found to be enhanced by cationic polymers even under starch gel and methylcellulose overlays, which are free of polyanions. Since cationic polymers enhance the diffusion of virus through agar or starch gel, plaque enhancement seems to be the result of the gel becoming positively charged so that viruses can move effectively through them. The observation that starch gel and methylcellulose enhance plaque formation with viruses known to be inhibited under agar was also reinvestigated. When the consistency of the agar gel was reduced to the same viscosity of starch gel and methylcellulose overlays, the same plaque counts and sizes were observed under all three overlays.

Plaque enhancement of enteroviruses by magnesium chloride, cysteine, and pancreatin

Wallis, Craig (Baylor University College of Medicine, Houston, Tex.), Fred Morales, Joycelyn Powell, and Joseph L. Melnick. Plaque enhancement of enteroviruses by magnesium chloride, cysteine, and pancreatin. J. Bacteriol. 91:1932-1935. 1966.-Plaque formation of 21 echoviruses (types 1-6, 9, 13, 15-19, 23-26, 29-32) and 8 coxsackieviruses (B1-6, A7, and A9) was enhanced by increased concentrations of MgCl(2), l-cysteine, and pancreatin in agar overlay medium. In most cases, cationic and anionic polymers (diethylaminoethyl dextran, dextran sulfate, or protamine sulfate) were ineffective. All strains of poliovirus and group B coxsackieviruses were enhanced under agar by MgCl(2). Five of the eight coxsackieviruses tested were also enhanced by cysteine or pancreatin. Certain enteroviruses, which have been difficult to assay by plaque method, can now be quantified effectively by incorporation of additives such as MgCl(2), cysteine, or pancreatin into the overlay medium.

Effect of different commercial agar preparations on the inhibitory activities of phenols

The minimal inhibitory concentrations of 11 phenolic inhibitors were compared in five commercial agars and in nutrient broth. It was found that the brand of agar affected the end point obtained for a particular inhibitor, and that the degree of antagonism varied with each compound studied. The results indicate that there are at least two deleterious factors present in agar, one of which is water-soluble and one which is not. The major portion of the total antagonism was due to the water-soluble factor, which could be removed by washing the agar in warm distilled water prior to use in the test medium.

COLORADO TICK FEVER VIRUS IN CELL CULTURE I

Trent, Dennis W. (University of Oklahoma School of Medicine, Oklahoma City) and L. Vernon Scott . Colorado tick fever virus in cell culture. I. Cell-type susceptibility and interaction with L cells. J. Bacteriol. 88: 702–708. 1964.—Colorado tick fever (CTF) virus was serially propagated in monolayer cultures of L and FL cells. Early passages of virus in FL cells yielded viral titers 10 4 -fold greater than did the corresponding L-cell passages. During L-cell passage number 4, there was a 10 3 -fold increase in the amount of infectious virus produced as compared with virus cultured earlier in this cell line. Viruses from L-cell passages 8 and 12 were identified with specific immune serum to be CTF viruses which were antigenically similar, if not identical, to the mouse-adapted virus. Parallel titrations of mouse-, L cell-, and FL cell-adapted viruses were performed in mice and replicate monolayers of L, FL, HeLa, KB, chick embryo, and cotton rat kidney cells. Cytopathic effects and viral replication were noted in all cultures except HeLa and cotton rat kidney. Cultures of L, FL, and chick embryo cells were as sensitive to infection as were suckling or weanling mice. KB cells were the least susceptible of those cell types examined. In L-cell cultures, 90% of the input virus was adsorbed to the cells during the first 30 min of incubation. The latent period lasted 10 to 12 hr, and was followed by rapid viral synthesis for the next 10 to 24 hr, depending upon the multiplicity of infection. Curves describing exponential increase in cell-associated and cell-released virus were separated by 4 hr. When the maximal total virus titers were reached, 80 to 90% of the virus was released from the cell.