STUDIES OF THREE VARIANTS OF MENGO ENCEPHALOMYELITIS VIRUS. II. INHIBITION OF INTERACTION WITH L CELLS BY AN AGAR INHIBITOR AND BY PROTAMINE

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.

Susceptibility of a line of dolphin kidney cell culture to several herpesviruses

A cell line was established from cell cultures of kidney cortex of a pantropical spotted dolphin, Stenella attenuate. The replication of 6 strains of herpesviruses was studied in the cells. Five strains of them, herpes simplex virus type I and type II, equine rhinopneumonitis virus, infectious bovine rhinotracheitis virus and Aujeszky's disease virus, were grown fairly well in showing clear cytopathic effects and plaques under agar overlay medium.

Electrostatic interactions in the early events of VSV infection

The importance of electrostatic interactions in the early phases of vesicular stomatitis virus (VSV) infection has been investigated in susceptible cells of different origin, human (HeLa) and avian (CER), by using some polyanions (heparin, polygalacturonic acid and mucin) and polycations (polymyxin B sulphate, poly-L-lysine, protamine, histone and polybrene). In HeLa cells, the attachment of VSV was enhanced by polymers having a positive charge and inhibited by those having a negative charge. In CER cells, all the polyanions tested reduced virus infection. Among the polycations, histone, polymyxin B sulphate and poly-L-lysine enhanced virus plaque formation while protamine and polybrene reduced virus attachment. The effect of polyions on VSV particles and on cell membrane receptors has also been investigated. The analysis of the results obtained suggest that, although electrostatic interactions play an essential role in the binding of VSV to the cell membrane, more specific structural features appear to be required for viral attachment to occur.

Polysaccharides as antiviral agents: antiviral activity of carrageenan

A number of polysaccharides showed good antiviral activity against several animal viruses. At 5 micrograms/ml, carrageenan prevented the cell monolayer from destruction by herpes simplex virus type 1 (HSV-1) growth. At 10 micrograms/ml, carrageenan reduced the formation of new infectious HSV-1 by almost five logs. No cytotoxic effects were detected with concentrations of carrageenan up to 200 micrograms/ml. When 10 micrograms of carrageenan per ml was added at the beginning of HSV-1 infection of HeLa cells, there was potent inhibition of viral protein synthesis, and the cells continued synthesizing cellular proteins. This did not occur if carrageenan was added 1 h after HSV-1 infection. The use of [35S]methionine-labeled virions to analyze the entry of HSV-1 or Semliki Forest virions into cells indicated that carrageenan had no effect on virus attachment or virus entry. Moreover, carrageenan did not block the early permeabilization of cells to the toxic protein alpha-sarcin. These results suggest that this sulfated polysaccharide inhibits a step in virus replication subsequent to viral internalization but prior to the onset of late viral protein synthesis.

Characterization of hybrids between bovine (MDBK) and mouse (L-cell) cell lines

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-deficient mutants of a bovine kidney cell line (MDBK) were selected following mutagenesis with ethylmethane sulfonate or ICR-170G. MDBK mutants were hybridized to thymidine kinase-deficient L cells and selected in HAT medium. Parental and hybrid cells were characterized for isozyme patterns of lactic dehydrogenase malate dehydrogenase, glucose-6-phosphate dehydrogenase, and glutamate oxalate transaminase. Chromosomes of MDBK can be distinguished from mouse L cells by configuration and by fluorescent staining with Hoechst 33-258 stain. Hybrid cells contained both MDBK and L-cell chromosomes and had elevated DNA content. MDBK cells are normally restrictive for mengovirus replication. Both permissive and restrictive hybrids were found. Our data indicate that there was preferential loss of MDBK chromosomes in the hybrid cell lines.

Enhancement by diethylamineothyl-dextran of the plaque-forming activity of foot-and-mouth disease virus-antibody complexes in pig kidney IB-RS-2 cells

Mixtures of foot-and-mouth disease (FMD) virus and homologous antibody, assayed for surviving plaque-forming units (PFU) in pig kidney IB-RS-2 cells, demonstrated an average ten-fold greater recovery of infectivity when diethylaminoethyl-dextran (DEAE-dextran) was included in the overlay medium. This enhancement, which was not detected in baby hamster kidney BHK21 cells, was due to the ability of the polycation to potentiate attachment of virus-antibody complexes to the IB-RS-2 cells. In some instances the effect was so pronounced that the plaque-forming activity of virus in the presence of homologous antibody exceeded that of virus alone.

Comparison of agar and agarose preparations for mengovirus plaque formation

An agarose overlay yielded mengovirus plaques earlier and in greater size and number than overlays of chemically undefined agars with or without enhancers. Marked variability in plaque-forming efficacy of commercial agarose preparations was noted.

Rapid plaque assay for encephalomyocarditis virus

A liquid overlay plaquing technique is described which offers a rapid and simple plaque assay system for small plaque variants of encephalomyocarditis virus.

Contrasting effects of polycations on plaquing efficiency of encephalomyocarditis virus variants

Polycation treatment of L cell monolayers affected plaquing efficiency of both the r(+) and r variants of the encephalomyocarditis virus. Plaque formation by r(+) variant was decreased markedly by three structurally different types of synthetic basic polymers, diethylaminoethyl dextran, hexadimethrene (polybrene), and basic polyamino acids. In contrast, these same substances increased substantially the number of plaques formed by the r variant. The effect on the two variants was observed when polycations were applied to the cells before or simultaneously with the introduction of virus. The molar concentration and size of the polymer proved important. Thus, basic polyamino acids of low molecular weight were significantly more inhibitory for the r(+) variant than were those of high molecular weight. On the other hand, plaquing efficiency of the r variant was increased by relatively large polyamino acids, but not by polymers of small size. Basic polyamino acids inhibited r(+) plaque formation to a greater degree at low than at high pH values. However, plaquing efficiency of the r variant in polycation-treated cultures was not affected by changes in pH. Basic polymers appear to bind to cell membranes and affect either attachment or uptake of the viruses. The evidence suggests that the substances influence by different mechanisms the interaction of the r(+) and r variants with cells.

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.

Isolation of a series of Mengo virus variants differing in sensitivity to polyanions

The isolation of six distinct new plaque variants from pools of S- and M-Mengo (small- and medium-plaque variants respectively) is described. The size of plaques produced in L cell monolayers under nutrient agar by five of the six new variants is strongly inhibited by the addition to the overlay of dextran sulfate of molecular weight 500,000. The sixth, although similar to L-Mengo in its virulence to mice and in having plaques that are almost unaffected by the addition of protamine or dextran sulfate to the overlay, can be distinguished from the latter by the larger and more uniform plaques it produces. The marked heterogeneity in the size of plaques produced by L-Mengo appears to be an inherent property of this variant, since all attempts to isolate other plaque variants from L-Mengo pools have been unsuccessful.The intraperitoneal LD50's of all six new variants in 14- to 16-g mice was determined. There is no complete correlation between the virulence of these variants and their sensitivity to inhibition by dextran sulfate.

Effect of diethylaminoethyl dextran on the growth of Mycoplasma in agar

The growth of certain strains of Mycoplasma is inhibited by substances present in commercial agar preparations. The addition of diethylaminoethyl (DEAE) dextran (10 mg per 100 ml) to agar media appears to enhance the growth of some strains. Of eight strains initially tested, the presence of DEAE dextran grossly enhanced the growth of three strains. One strain appeared not to be affected, and a clearly enhancing effect was not evident with four strains. Quantitative studies revealed that growth enhancement varied from 10 colony-forming units (CFU) for M. hominis type II (strain Campo) to 10(3.3) CFU for M. pulmonis (strain 880). The growth-enhancing effect is probably due to the ability of DEAE dextran to bind the sulfated polysaccharide moieties in agar and not to the DEAE dextran, per se.

Effect of polyions on the infectivity of rabies virus in tissue culture: construction of a single-cycle growth curve

The infectivity of fixed rabies virus in a number of cell lines has been shown to be markedly enhanced by the addition of protamine or diethylaminoethyl dextran to the virus inoculum. The polycations appear to exert their influence at a very early stage (adsorption or penetration or both) of virus-cell interaction. Immune globulin blocked infection completely when added up to 5 min after exposure and almost completely when added 5 to 15 min after infection. Antibody had no effect on adsorption and penetration when added to the inoculum 30 min or more after cells were exposed to the virus. Irradiation of BHK/21 cell monolayers with ultraviolet light increased their sensitivity to rabies virus. The events occurring after synchronous infection of cells in both irradiated and nonirradiated cell monolayers were followed by means of fluorescent-antibody staining and by intracerebral titration in mice. Virus-specific fluorescent antigen first appeared between 8 and 9 hr after infection, and in irradiated cultures there was a further lag period of 3 hr before infectious virus was produced intracellularly. Virus was first detected in the medium 12 to 15 hr after infection, and maximal yield of infectious virus was observed 48 hr after exposure. In nonirradiated cultures, formation of infectious virus was delayed, and the final yield of virus was also reduced.

Antibiotic activity in the presence of agar

Agar has been shown to interfere with the activity of some antibiotics against Staphylococcus aureus. This interference has been observed as an increase in the minimal inhibitory concentration and in the diameter of the zone of inhibition. Purifying the agar with water extractions substantially reduced this adverse effect.

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 interferon on polymerization of single-stranded and double-stranded mengovirus ribonucleic acid

Gordon, Irving (University of Southern California, Los Angeles), Sara S. Chenault, Douglas Stevenson, and Jean D. Acton. Effect of interferon on polymerization of single-stranded and double-stranded mengovirus ribonucleic acid. J. Bacteriol. 91:1230-1238. 1966.-The effect of interferon on actinomycin-resistant mengovirus ribonucleic acid (RNA) replication in L cells was investigated to determine whether defective or partially polymerized RNA products were made and whether synthesis of any specific class of virus RNA was prevented. RNA labeled with uridine-C(14) was extracted in hot and cold phenol and analyzed by zonal sucrose density centrifugation. Both single- and double-stranded infectious RNA peaks were identified. Interferon treatment caused almost complete depression of uridine-C(14) incorporation throughout linear sucrose gradients except in the 4S region, and no infectivity was detectable in any fraction. These inhibitory effects are attributable to the action of interferon, because they were reversed when cultures were treated with actinomycin D simultaneously with interferon. The results, with those of other investigators, indicate that the step at which interferon interrupts virus multiplication is between the events immediately after uncoating and the formation of template "minus" strands; under the conditions of our experiments, no partially polymerized virus RNA products were made.