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

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.

Binding of Sindbis virus to cell surface heparan sulfate

Alphaviruses are arthropod-borne viruses with wide species ranges and diverse tissue tropisms. The cell surface receptors which allow infection of so many different species and cell types are still incompletely characterized. We show here that the widely expressed glycosaminoglycan heparan sulfate can participate in the binding of Sindbis virus to cells. Enzymatic removal of heparan sulfate or the use of heparan sulfate-deficient cells led to a large reduction in virus binding. Sindbis virus bound to immobilized heparin, and this interaction was blocked by neutralizing antibodies against the viral E2 glycoprotein. Further experiments showed that a high degree of sulfation was critical for the ability of heparin to bind Sindbis virus. However, Sindbis virus was still able to infect and replicate on cells which were completely deficient in heparan sulfate, indicating that additional receptors must be involved. Cell surface binding of another alphavirus, Ross River virus, was found to be independent of heparan sulfate.

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.

Methylcellulose media for plaque assay of murine leukemia virus

When ecotropic murine leukemia virus was assayed by a methylcellulose-XC cell procedure, plaque titers showed less test-to-test variation, more uniform dose-response curves, and larger plaque sizes, as compared with results of the conventional liquid overlay-XC cell test system. This assay therefore seems to be reliable and useful for the titration of ecotropic murine leukemia virus.

An attenuated variant of Eastern encephalitis virus: biological properties and protection induced in mice

Wild type Eastern equine encephalitis virus (E) was compared with a mutant (Em) derived from it. The latter was tested as an attenuated vaccine in mice. They differed in the following properties: Em formed smaller plaques on chick embryo (CE) cell monolayers and, unlike E, did not plaque on mouse embryo (ME) monolayers. Futher, Em had a longer latent period and attained a lower peak titer than E after infection of CE cells, was more senssitive than E to chick interferon, and was less virulent for mice (SC and IP routes) and hamsters (IP route) than E. Both viruses were similar in several other properties tested. The mutant was found to induce a gradient in the specificity of protection in mice against challenge by selected viruses after a single subcutaneous injection of living virus. The protection was best against autologous (Em) challenge, was next best against challenge by the virulent parent (E) virus, but was not demonstrable against cross challenge by Venezuelan encephalitis (V) virus. Conventional hemagglutination-inhibiting (HI), complement-fixing (F), and neutralizing (N) antibodies could not be detected in Em-immunized mice even when fresh monkey or guinea pig serum was included in Ntests to provide complement and/or accessory factor(s). However, N antibodies were detected in protected mice by an indirect antiglobulin test. Passive protection by serum or ascites fluids (a.f.) was characterized by a lower but otherwise similar protection gradient like that found after active immunization with virus as described above. Interferon was not detected in the a.f. used for passive protection, nor was heterologous interference evident in Em immunized mice challenged 18 days later with vaccinia or vesicular stomatitis virus. Immunized mice that survived autologous (Em) challenge showed broadened protection against a second challenge by parent E virus, and cross protection against V virus. This typical protection was associated with the presence of HI and conventional N antibodies, except for V which showed no detectable neutralizing antibodies by either a standard or antiglobulin technique.

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.

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.

Enhancement of St. Louis arbovirus plaque formation by neutral red

Experiments with St. Louis encephalitis (SLE) virus have shown that neutral red enhances the plaque size in duck embryo cell cultures. This may represent a new method for genetic studies of SLE virus population. In a mosquito pool specimen NR(+) and NR(-) particles were demonstrated. By intracerebral passage in mice, there is a selection of NR(+) particles. Similar effects were not shown for eastern, western, and California encephalitis viruses. Plaques formed by the latter virus, however, were significantly reduced in number by neutral red.

Properties of Venezuelan equine encephalomyelitis virus accompanying attenuation in vitro

Virus obtained during serial plaque passage of the virulent parent egg seed (PES) of the Trinidad strain of Venezuelan equine encephalomyelitis (VEE) virus produced only large plaques during either 3 serial plaque passages in chick fibroblasts or 10 plaque passages in L cells, and was lethal for mice by the intraperitoneal route. Virus showing these characteristics was designated the stable large-plaque (Ls) type. In contrast, virus obtained during serial plaque passage of the attenuated 9t strain in chick fibroblasts formed only very small plaques and was not lethal for mice by the intraperitoneal route. Virus showing these properties was designated the stable small-plaque (Ss) type. Under other passage conditions, however, large-plaque virus that yielded about 90% large and 10% small plaques was obtained; this virus was designated the unstable large or Lu type because it differed from the Ls type, which yielded only large plaques. The Lu type continued to yield the same ratio of large to small plaques for several plaque-to-plaque passages. In addition, small-plaque virus that yielded both large and small plaques and that showed a reduced capability to infect mice was also recovered. This virus was designated the unstable small or Su type because it differed from the Ss type in its higher level of virulence and in its plaque-forming properties. Thus, based upon the properties of virulence for mice and plaque size, four viral types could be discerned. The evidence suggests that serial passage in cell culture imposed environmental pressures that sequentially selected the following viral types: Ls, Lu, Su, and Ss.

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.