A natural sulfated polysaccharide, calcium spirulan, isolated from Spirulina platensis: in vitro and ex vivo evaluation of anti-herpes simplex virus and anti-human immunodeficiency virus activities

Anti-HIV activity of extracts and compounds from algae and cyanobacteria

The human immunodeficiency virus (HIV) is the retrovirus that causes the acquired immune deficiency disease syndrome (AIDS). This review discusses the anti-HIV activity of extracts and compounds isolated from freshwater and marine algae, and cyanobacteria (formerly called "blue-green algae"). Compounds and extracts with anti-HIV activity are also active against other retroviruses such as herpes simplex virus (HSV), but the amount of antiviral activity varies with the compound and the virus. Most of the research has focused on sulfated homopolysaccharides and heteropolysaccharides. Sulfoglycolipids, carrageenans, fucoidan, sesquiterpene hydroquinones, and other classes of compounds with anti-HIV activity that have been isolated from algae have received less attention. Most studies have used in vitro test systems, but a few in vivo studies have been carried out using compounds isolated from algae or analogs produced synthetically or isolated from other natural sources. Sulfated homopolysaccharides are more potent than sulfated heteropolysaccharides. The presence of the sulfate group is necessary for anti-HIV activity, and potency increases with the degree of sulfation. Studies using nonsulfated and sulfated homo- and heteropolysaccharides isolated from algae or other natural sources, or synthesized, have revealed the mechanisms of binding of drugs to the virion, and the mechanisms of viral binding to host cells. However, given the few classes of compounds investigated, most of the pharmacopeia of compounds in algae and cyanobacteria with antiretroviral activity is probably not known.

Oligomeric modeling and electrostatic analysis of the gp120 envelope glycoprotein of human immunodeficiency virus

The human immunodeficiency virus envelope glycoproteins, gp120 and gp41, function in cell entry by binding to CD4 and a chemokine receptor on the cell surface and orchestrating the direct fusion of the viral and target cell membranes. On the virion surface, three gp120 molecules associate noncovalently with the ectodomain of the gp41 trimer to form the envelope oligomer. Although an atomic-level structure of a monomeric gp120 core has been determined, the structure of the oligomer is unknown. Here, the orientation of gp120 in the oligomer is modeled by using quantifiable criteria of carbohydrate exposure, occlusion of conserved residues, and steric considerations with regard to the binding of the neutralizing antibody 17b. Applying similar modeling techniques to influenza virus hemagglutinin suggests a rotational accuracy for the oriented gp120 of better than 10 degrees. The model shows that CD4 binds obliquely, such that multiple CD4 molecules bound to the same oligomer have their membrane-spanning portions separated by at least 190 A. The chemokine receptor, in contrast, binds to a sterically restricted surface close to the trimer axis. Electrostatic analyses reveal a basic region which faces away from the virus, toward the target cell membrane, and is conserved on core gp120. The electrostatic potentials of this region are strongly influenced by the overall charge, but not the precise structure, of the third variable (V3) loop. This dependence on charge and not structure may make electrostatic interactions between this basic region and the cell difficult to target therapeutically and may also provide a means of viral escape from immune system surveillance.

Structural analysis of calcium spirulan (Ca-SP)-derived oligosaccharides using electrospray ionization mass spectrometry

Detailed structural analyses of calcium spirulan (Ca-SP)-derived oligosaccharides were performed by ESI-MS and collision-induced dissociation tandem mass spectrometry. This study indicates that Ca-SP is composed of two types of disaccharide repeating units, O-rhamnosyl-acofriose and O-hexuronosyl-rhamnose (aldobiuronic acid).

Pseudovitamin B(12) is the predominant cobamide of an algal health food, spirulina tablets

The vitamin B(12) concentration of an algal health food, spirulina (Spirulina sp.) tablets, was determined by both Lactobacillus leichmannii ATCC 7830 microbiological and intrinsic factor chemiluminescence methods. The values determined with the microbiological method were approximately 6-9-fold greater in the spirulina tablets than the values determined with the chemiluminescence method. Although most of the vitamin B(12) determined with the microbiological method was derived from various vitamin B(12) substitutive compounds and/or inactive vitamin B(12) analogues, the spirulina contained a small amount of vitamin B(12) active in the binding of the intrinsic factor. Two intrinsic factor active vitamin B(12) analogues (major and minor) were purified from the spirulina tablets and partially characterized. The major (83%) and minor (17%) analogues were identified as pseudovitamin B(12) and vitamin B(12), respectively, as judged from data of TLC, reversed-phase HPLC, (1)H NMR spectroscopy, ultraviolet-visible spectroscopy, and biological activity using L. leichmannii as a test organism and the binding of vitamin B(12) to the intrinsic factor.

A new sulfated beta-galactan from clams with anti-HIV activity

A new polysaccharide composed of galactan sulfate with a beta-(1-->3)-glycosidic linkage has been isolated from the marine clam species Meretrix petechialis. The polysaccharide was homogeneous in its composition containing D-galactose. The glycosidic linkage was examined by 2D DQF-COSY and 2D NOESY spectroscopy. The coupling constant of anomeric proton was 7.8 Hz, suggesting a beta-galacto configuration. The downfield shift of H-2 of galactose residue demonstrated the presence of 2-O-sulfonate group. TQF-COSY confirmed that the C-6 position was substituted with a sulfonate group. The anti-HIV activity of the polysaccharides has been evaluated by the inhibition of syncytia formation. The fusion index and percentage fusion inhibition of sulfated galactan were 0.34 and 56% at 200 micrograms/mL.

Further purification and structural analysis of calcium spirulan from Spirulina platensis

An antiviral sulfated polysaccharide, calcium spirulan (Ca-SP), isolated from Spirulina platensis, was subjected to further purification. Ca-SP was found to be composed of rhamnose, 3-O-methylrhamnose (acofriose), 2,3-di-O-methylrhamnose, 3-O-methylxylose, uronic acids, and sulfate. The backbone of Ca-SP consisted of 1,3-linked rhamnose and 1,2-linked 3-O-methylrhamnose units with some sulfate substitution at the 4-position. The polymer was terminated at the nonreducing end by 2,3-di-O-methylrhamnose and 3-O-methylxylose residues.

Inhibition of HIV-1 replication by an aqueous extract of Spirulina platensis (Arthrospira platensis)

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 microg/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.