Calcium spirulan derived from Spirulina platensis inhibits herpes simplex virus 1 attachment to human keratinocytes and protects against herpes labialis
(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 definedSpirulina platensis microalga extract and of purified calciumspirulan (Ca-SP), a sulfated polysaccharide contained therein.Methods: The inhibitory effects of HSV-1 were assessed byusing a plaque reduction assay and quantitative PCR in asusceptible mammalian epithelial cell line and confirmed inhuman keratinocytes. Time-of-addition and attachmentexperiments and fluorescence detection of the HSV-1 tegumentprotein VP16 were used to analyze the mechanism of HSV-1inhibition. Effects of Ca-SP on Kaposi sarcoma–associatedherpesvirus/human herpes virus 8 replication and uptake of theORF45 tegument protein were tested in human retinal pigmentepithelial cells. In an observational trial the prophylactic effectsof topically applied Ca-SP were compared with those ofsystemic and topical nucleoside analogues in 198 volunteers withrecurrent herpes labialis receiving permanent lip makeup.Results: Ca-SP inhibited HSV-1 infection in vitro with a potencyat least comparable to that of acyclovir by blocking viralattachment and penetration into host cells. Ca-SP also inhibitedentry of Kaposi sarcoma–associated herpesvirus/human herpesvirus 8. In the clinical model of herpes exacerbation, theprophylactic effect of a Ca-SP and microalgae extractcontaining cream was superior to that of acyclovir cream.Conclusion: These data indicate a potential clinical use of Ca-SPcontaining Spirulina species extract for the prophylactictreatment of herpes labialis and suggest possible activity of Ca-SP against infections caused by other herpesviruses.