Antiviral and Immunomodulatory Properties of Prunella vulgaris

Asian Journal of Traditional Medicineseffects, this review will focus on these novel propertiesand future therapeutic potential.Antiviral activities of Prunella vulgaris againstHIV-1, HSV-1 and HSV-2A number of antiviral studies of P. vulgaris extractshave been carried out and active compounds against HIVand HSV have been identified (Table 1), especially in itspolar fractions. A 10 kDa anionic sulfatedpolysaccharide called prunellin was found to inhibit thereplication of HIV-1 [16] . In addition, the extract of P.vulgaris demonstrated a significant inhibitory effect onHIV-1 replication with relatively low cytotoxicityin-vitro and it was able to arrest the cell-celltransmission of HIV-1, prevent syncytium formation andinterfere with both HIV-1 and purified gp120 bindingto CD4 receptors [21] . Similar results have been obtainedin further studies involving the inhibitory mechanism ofHIV-1 infection in vitro by a purified extract of P.vulgaris [25] . The polyphenols and tannins of P. vulgarishave been suggested to be the major inhibitors of HIV-1gp41 six-helix bundle formation which is a critical stepin the membrane fusion between the HIV and its targetcells [17] . Also, it has been reported that an aqueousextract of P. vulgaris inhibited HIV-1 integrase activity[26] .Previously, anti-HSV activity of the aqueous extractof P. vulgaris has been described [8] . Out of one hundredand forty two kinds of traditional medicines, it has beenfound that the hot aqueous extract of P. vulgarisselectively inhibited HSV-1 [9] . Xu and co-authorsreported that a water soluble polysaccharide componentin P. vulgaris, which could be extracted with hot water,precipitated in ethanol and then purified by gelpermeation column chromatography, exhibited potentanti-HSV activity. The 50% plaque reduction dose of thepolysaccharide for HSV-1 and HSV-2 was 10 mg/ml andsimilar inhibitory effects were also exhibited againstacyclovir-resistant(TK-deficient or polymerase-defective)strains of HSV-1 and HSV-2 [10] . Furthermore, a studyusing the polysaccharide fraction of P. vulgaris showed areduction in the expression of HSV-1 and HSV-2antigens in their host Vero cells. Interestingly, thepolysaccharide fraction of P. vulgaris was also shown tohave an inhibitory effect on an acyclovir-resistant strainof HSV-1, ranging from 24.8 to 92.6% at 25-100 mg/ml,and it was suggested to have a different mode ofanti-HSV action from that of acyclovir [28] .Immunomodulatory effects of P. vulgarisThe immunomodulatory effects of P. vulgaris havereceived increasing attention in recent years. The keypromising immunomodulatory effects of differentextracts and chemical constituents isolated from P.vulgaris have been demonstrated in different models andthese are summarized below (Table 2).Table 1Antiviral properties of Prunella vulgaris and its active componentsAntiviral actions Active components ReferencesInhibition of HIV replication Prunellin [16]Prevention of viral attachment to CD4 receptors Active component with a molecular weight of 10 kDa [21]Suppression of the replication of HIV-1(IC100=16 microgram/ml)Hot water extract [22]Inhibition of HSV-1 plaque formation Hot water extract [9]Inhibition of HIV-1 reverse transcriptase activity Aqueous extract [23]Suppression of HSV and acyclovir-resistant strains of HSV-1and HSV-2 by competing for cell receptors (50% plaquereduction=10 microgram/ml); and inhibitory effects at earlyand late stages of virus replicationInhibition of HIV-1 integrase activity(EC50=45 microgram/ml)Suppression of HIV-1 entry by disrupting the gp41 six-helixbundle formation (at 50 microgram/ml, 86.2% inhibition)Suppression of the expression of HSV-1 and HSV-2 antigensand also the acyclovir-resistant strain of HSV-1 (EC50 of theHSV-1 and HSV-2 antigens were 20.6 and 20.1microgram/ml, respectively)A polysaccharide with a molecular weight of 3,500Da[10]Tannin or polyphenols [26]Tannin or polyphenols [27]A polysaccharide fraction [28]2