Visualization of herpes simplex virus type 1 attachment to target cells using Staphylococcus aureus as a morphologic tag

Calcium spirulan derived from Spirulina platensis inhibits herpes simplex virus 1 attachment to human keratinocytes and protects against herpes labialis

BACKGROUND

Chronic infections with herpes simplex virus (HSV) type 1 are highly prevalent in populations worldwide and cause recurrent oral lesions in up to 40% of infected subjects.

OBJECTIVE

We investigated the antiviral activity of a defined Spirulina platensis microalga extract and of purified calcium spirulan (Ca-SP), a sulfated polysaccharide contained therein.

METHODS

The inhibitory effects of HSV-1 were assessed by using a plaque reduction assay and quantitative PCR in a susceptible mammalian epithelial cell line and confirmed in human keratinocytes. Time-of-addition and attachment experiments and fluorescence detection of the HSV-1 tegument protein VP16 were used to analyze the mechanism of HSV-1 inhibition. Effects of Ca-SP on Kaposi sarcoma-associated herpesvirus/human herpes virus 8 replication and uptake of the ORF45 tegument protein were tested in human retinal pigment epithelial cells. In an observational trial the prophylactic effects of topically applied Ca-SP were compared with those of systemic and topical nucleoside analogues in 198 volunteers with recurrent herpes labialis receiving permanent lip makeup.

RESULTS

Ca-SP inhibited HSV-1 infection in vitro with a potency at least comparable to that of acyclovir by blocking viral attachment and penetration into host cells. Ca-SP also inhibited entry of Kaposi sarcoma-associated herpesvirus/human herpes virus 8. In the clinical model of herpes exacerbation, the prophylactic effect of a Ca-SP and microalgae extract containing cream was superior to that of acyclovir cream.

CONCLUSION

These data indicate a potential clinical use of Ca-SP containing Spirulina species extract for the prophylactic treatment of herpes labialis and suggest possible activity of Ca-SP against infections caused by other herpesviruses.

Herpes simplex virus type 1 penetration initiates mobilization of cell surface proteins

Changes in membrane structure resulting from herpes simplex virus 1 (HSV-1) penetration were detected using fluorescence photobleaching recovery methods. The effect could be blocked by inhibitors of viral and cellular processes involved in virus penetration. A rapid mode of HSV-1 strain KOS penetration into VERO cells at 37 degrees C normally occurs after a 5 min lag period and is 90-95% complete within 20-30 min. Rates of cell surface protein diffusion increase 2-3-fold after 5 min and return to normal after 25-30 min, this return correlating temporally with the penetration of the virus. At pH 6.3 the lag period preceeding penetration of HSV is increased to 20 min and penetration proceeds much more slowly than at pH 7.4. Inhibition of virus penetration with cytochalasin B or with the antiherpes drug tromantadine also prevents the HSV-1-induced increase in cell surface protein mobility. Colchicine, which does not block HSV-1 penetration, prevents the recovery of the membrane following virus penetration. Therefore, the changes in membrane structure characterized by increased cell surface protein mobility seem to be caused by virus penetration. Cytoskeletal function and integrity are required for the initiation of, and cell recovery from, virus penetration. A pH-sensitive activity, likely to be a virion fusion glycoprotein, is also required.

2-deoxy-D-glucose inhibition of herpes simplex virus type-1 receptor expression

Growth of HEp-2 cells in 2-deoxy-D-glucose (2-DOG) supplemented media decreased the cells' binding capacity for herpes simplex virus type-1 KOS(HSV-1) but not vesicular stomatitis virus. HEp-2 cells tolerated up to 30 mM 2-DOG, but 2-DOG was toxic for Vero cells over 2 mM. The reduction in binding was maintained for at least 24 h even after careful removal of the inhibitor and growth in normal media. Complete regeneration of the receptor sites on HEp-2 cells was observed 8 h after mild trypsinization of cells grown in either normal or the 2-DOG supplemented media. Specific glycoprotein characteristics of the HSV-1 binding site were indicated by its inactivation upon trypsinization (0.1 mg per 5 X 10(5) cells for 30 s) and blocking by wheat germ agglutinin but not limulin. These results suggest that 2-DOG inhibits the proper expression of cell surface glycoprotein HSV-1 receptor sites on HEp-2 cells.