Spirulina now named Arthrospira is a cyanobacteria that belongs to kingdom Mon-era and division Cyanophyta. Cyanobacterias also know as blue-green alga, have been consumed as a food for many centuries. Traditionally it was used by Mexicans during the Aztec civilization, and it is currently used by the natives in the Lake Chad area.1'2 The most commonly used species of Spirulina for nutritional supplements are Spirulinaplatensis and Spirulina maxima. They are produced commercially and sold as food supplement in health food stores around the world. Early interest in Spirulina was focused mainly on its potential as a source of protein, vitamins, especially vitamin B12 and provitamin A (fi-carotene), and essential fatty acids like Y-linolenic acid (GLA). Recently more attention has been given to the study of its therapeutic effects, which include reduction of cholesterol and nephrotoxicity by heavy metals, anticancer properties, protection against radiation, and enhancement of the immune system.3 Spirulina also possesses other biological functions such as antiviral, antibacterial, antifungal, and antiparasite activities.4-6,1

Actinomycetes have been the most prolific producers of new bioactive metabolites, and at the present time, yield known compounds at a rate in excess of 95% of all active leads discovery in primary screening. Therefore, the interest in identifying naturally occurring molecules with antiviral properties has been largely intensified, mainly searching for new sources of cultivable microorganisms. A high priority has been given for new antiviral drugs against human immunodeficiency virus type 1 (HIV-1), which has caused the most important pandemic disease, the acquired immunodeficiency syndrome (AIDS), since 1981.

Cyanophytes or cyanobacterias are widely distributed in nature, and relatively little systematic screening for antiviral activity had been done. In 1987 Patterson et al., started the screening of extracts of cultured cyanophytes for antiviral activity. Their goal was to examine the distribution of antiviral compounds among blue-green alga and determine whether particular geographic or physical sites are especially likely to yield active leads. They analyzed lipophilic and hydrophilic extracts from 694 strains of cultured cyanophytes, representing 334 species. The extracts were evaluated for antiviral activity against three human pathogenic viruses: herpes simplex type 2 (HSV-2), as representative of double stranded DNA viruses with a nuclear cell cycle; the respiratory syncytial virus (RSV) as representative of single-stranded RNA viruses, with a cellular cytoplasm cycle; and HIV-1, as representative of retroviruses. Approximately 10% of the extracts exhibited antiviral activity against HSV-2 and HIV-1, whereas 2% had activity against RSV. The antiviral activity was more commonly associated with lipophilic extracts than hydrophilic extracts. This survey of blue-green alga for the presence of antiviral activities showed that this biological activity is widely distributed among cyanophytes, and the order Chroococcales proved to be the most prolific producer of antiviral compounds. The substratum from which the organisms were collected showed little correlation with the presence of antiviral compounds. And there was not any relation among the conditions of cultivation of the organisms and the presence of antiviral activity.7

Another study published by Gustafson et al., 1989, showed that after the screening of extracts from cultured cyanobacterias (blue-green alga) by using a tetrazolium-based microculture many of these were remarkably active against HIV-1. The microculture assay used to guide the fractionation and purification process revealed a new class of HIV-1 inhibitory compounds, the sulfonic acid-containing glycolipids. These pure compounds were active against HIV-1 in different human lymphoblastoid cells.8

In another primary screening of aqueous extracts from terrestrial plants, cyanobacteria, marine invertebrates, and alga, approximately 15% of them showed anti-HIV activity, and this activity was found to be associated to anionic polysaccharides.9

Specific screening for inhibitors of reverse transcriptase (RT) from two retroviruses: avian myeloblastosis virus (AMV) and HIV-1, using the lipophilic and hydrophilic extracts of approximately 900 strains of cultured blue-green alga showed that 2% of the aqueous extracts have an anti-RT activity for both viruses. This inhibitory activity could not be attributed entirely to the degradation of transcript DNA, template RNA, or enzyme protein in the reaction mixture. The inhibition of the RT was associated to sulfolipids extracted from cyanobacterias.10

These studies on cyanobacterias clearly show the enormous potential of these organisms to produce antiviral compounds which have new targets in the viral replication cycles.

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