An aqueous extract of the blue-green filamentous algae Arthrospira platensis (previously called Spirulina platensis) inhibited HIV-1 replication in human T-cell lines, peripheral blood mononuclear cells (PBMC) and Langerhans cells (LC). Extract concentrations ranging between 0.3 and 1.2 mcg/ml reduced viral production by approximately 50% (50% effective concentration [EC50] in PBMCs). The 50% inhibitory concentration (IC50) of extract for PBMC growth ranged between 0.8 and 3.1 mg/ml. Depending on the cell type used, therapeutic indices ranged between 200 and 6000. The extract inactivated HIV-1 infectivity directly when preincubated with virus before addition to human T-cell lines. Fractionation of the extract revealed antiviral activity in the polysaccharide fraction and also in a fraction depleted of polysaccharides and tannins. We conclude that aqueous A platensis extracts contain antiretroviral activity that may be of potential clinical interest.
Key Words: Arthrospira platensis extract - HIV-1 replication inhibition - Primary cells.

Bioactivity-directed fractionation of a hot H2O extract from a blue-green-alga Spirulina platensis led to the isolation of a novel sulfated polysaccharide named Calcium Spirulan (Ca-SP) as an antiviral principle. This polysaccharide was composed of rhamnose, ribose, mannose, fructose, galactose, xylose, glucose, glucuronic acid, galacturonic acid, sulfate and calcium. Ca-SP was found to inhibit the replication of several enveloped viruses, including Herpes simplex virus type 1, human cytomegalovirus, measles virus, mumps virus, influenza A virus and HIV-1. It was revealed that Ca-SP selectively inhibited the penetration of virus into host cells. Retention of molecular conformation by chelation of calcium ion with sulfate groups was suggested to be indispensible to its antiviral effect.

The water soluble extract of spirulina achieved a dose-dependent inhibition of the replication of herpes simplex virus type 1 (HSV-1) in HeLa cells within the concentration range of 0.08-50 mg/mL. This extract proved to have no virucidal activity and did not interfere with adsorption to host cells. However, the extract affected viral penetration in a dose-dependent manner. At 1 mg/ml the extract was found to inhibit virus-specific protein synthesis without suppressing host cell protein synthesis if added to the cells 3 hours before hamsters at doses of 100 and 500 mg/kg per day.

Lipophilic and hydrophilic extracts from approximately 600 strains of cultured cyanophytes, representing some 300 species, were examined for antiviral activity against three pathogenic viruses. Approximately 10% of the cultures produced substances that caused significant reduction in cytopathic effect normally associated with viral infection. The screening program identified Chroocococcales as commonly producing antiviral agents. Key index words: antiviral, cyanobacteria, cyanophyte, herpes virus, HIV-1, HIV-2, human immunodeficiency virus, natural products, pharmaceutical, respiratory syncytical virus.

Sulfoglycolipids from blue-green algae exhibit strong antiviral properties. Helper T-cells exposed to blue-green algae-sulfoglycolipids were protected from HIV-1 infection in in vitro studies.