EGCG является сильным антиоксидантным, что ранее было показано, чтобы уменьшить число ВИЧ бляшек в культуре ткани (Williamson et al. 2006). Модификация зеленого чая полифенол эпигаллокатехин галлат (EGCG) с пальмитат повышает эффективность EGCG в качестве противовирусного агента. Palmitoyl-EGCG (p-EGCG) представляет интерес, поскольку она может быть наружно наносится на кожу, одной из основных тканей, инфицированные вирусом простого герпеса. Здесь мы покажем, что p-EGCG является более мощным ингибитором вируса простого герпеса 1 (HSV-1), чем EGCG и что p-EGCG не токсичен для клеток Vero в культуре клеток жизнеспособность и пролиферацию клеток анализов. Существенно, p-EGCG было обнаружено, ингибируют HSV-1 адсорбции клеток Vero. Таким образом, p-EGCG может обеспечить романе лечение ВПГ-1 инфекции.
Although infection with HSV-1 or -2 is typically asymptomatic, viral activation results in epithelial lesions that are painful, recurrent, ulcerative, and infectious. HSV-1 causes cold sores and lesions of the mouth and lip, as well as herpes keratitis, a leading cause of corneal blindness in the United States. HSV-1 is also emerging as an inducer of genital herpes in developing countries (Xu et al. 2006), although HSV-2 is the primary cause of most cases of genital herpes. In rare cases, HSV-2 can also cause encephalitis (Stanberry et al. 2000; Xu et al. 2006). Frequent HSV outbreaks can have major psychological and social impacts on infected individuals. Further, HSV lesions provide a facile route for HIV infection during sexual activity (Van de Perre et al. 2008; Wald and Link 2002). HSV-1 and -2 are enveloped, double stranded DNA viruses with ~152 Kb genomes and have capsids of ~200 nm in diameter (Garner 2003). The virion consists of three major structures, an outer portion called the envelope, which includes 11 glycoproteins, a tegument layer composed of 15 proteins, and an icosahedral capsid enclosing the viral DNA (Foster et al. 1998; Garner 2003; Willard 2002). The tegument proteins connect the capsid to the viral envelope.
HSV infection is initiated by envelope glycoprotein C binding to cell surface proteoglycan heparin sulfate on epithelial cells and glycoprotein D binding to one of three entry receptors; this results in strong virion attachment to the host cell (Akhtar and Shukla 2009; Carfi et al. 2001; Shukla and Spear 2001; Spear et al. 2006). Glycoproteins B, D, H and L form a complex that results in fusion of the viral envelope with the host cell membrane, allowing the virus to enter the cell. The viral capsid is transported to the nucleus where the viral DNA content is released. Persistent lifetime infection is maintained by the virus infecting and becoming latent in the cell bodies of neurons. Activation (e.g., by other viral infections, stress or injury) and axonal transport can lead to reinfection of epithelial cells and a recurrence of lesions.
Although many efforts have been made, there is currently no effective vaccine against HSV infection, which successfully evades the immune system during latent infections (Belshe et al. 2012; Bernstein and Stanberry 1999; Toka et al. 2004). Nucleotide analogs targeting viral replication represent the primary treatment for infection, but they do not provide a cure (Brady and Bernstein 2004; Fatahzadeh and Schwartz 2007; Morfin and Thouvenot 2003). Moreover, the virus can develop resistance due to mutations in the DNA polymerase gene (Brady and Bernstein 2004; Frobert et al. 2008; Lebel and Boivin 2006; Piret and Boivin 2011). Therefore, new medications are required to block infection and to prevent viral shedding by an infected individual (Morfin and Thouvenot 2003). EGCG has been reported to lack marked cytotoxic effects on non-cancerous cells (Babich et al. 2005; Weisburg et al. 2004). Data presented here indicate that both EGCG and p-EGCG have similar cytotoxicity towards African green monkey kidney-derived Vero cells at concentrations up to 75 µM. Pilot studies with 100 µM of EGCG and p-EGCG have shown no increase in toxicity. Cellular metabolism retains 90% of its normal activity, suggesting that EGCG and p-EGCG are not toxic at the concentrations used in this study. EGCG is unstable in aqueous solution and readily oxidizes, resulting in a loss of activity (Chen et al. 2009; Chen et al. 2003). Therefore, aqueous topical solutions must be prepared fresh, making it unsuitable for the preparation of medications. Several experimental approaches used here demonstrated that palmitoyl-EGCG, and to a lesser extent EGCG, had a powerful inhibitory effect on the HSV-1 lytic cycle, consistent with a previous report for the effects of EGCG (Isaacs et al. 2008). Treatment of virions for 1 hour with 50 µM EGCG and p-EGCG and removed after 1 hour absorption caused a 92% and >99% respectively, reduction in infectivity as measured by plaque formation. Unlike the effect of p-EGCG on Vero cell metabolism, the effect on HSV-1 was dose-dependent (Figure 8). Moreover, p-EGCG treatment caused a >99% reduction in the amount of HSV-1 genome DNA synthesized 12 hours after infection, whereas EGCG caused a 95% reduction.
In this study, the EGCG or p-EGCG was removed after one hour of viral adsorption, but still resulted in a significant inhibition of viral production by Vero cells. One potential mechanism for this inhibitory effect of EGCG and p-EGCG on the HSV-1 lytic cycle is by blocking virion entry into cells, which was observed for the effect of EGCG on HIV and influenza virus infection (Song et al. 2005; Williamson et al. 2006). Alternatively (or in addition), the virion particles could be damaged, as has been observed previously for the effect of EGCG on HSV (Isaacs et al. 2008). While these may be the dominant mechanism(s), some HSV-1 DNA persisted after infection of Vero cells with EGCG or p-EGCG treated virions serving as effective PCR templates for HSV-1 genes, suggesting some viral particles enter the cells and the genomes are replicated although no detectable plaques are formed. Therefore, p-EGCG may also affect intracellular genome trafficking, and/or virion assembly to form viable virus particles. Further work will be required to test these possibilities and further clarify the mechanisms of action. Collectively, the results from this study demonstrate that lipophilic p-EGCG is a potent inhibitor of HSV-1 infection of epithelial cells in vitro at non-toxic doses. The fatty acid derivative is stable to air exposure, vaginal pH (Isaacs et al. 2008; Lambert et al. 2006; Sang et al. 2005; Zhu et al. 1997), and is a more effective antiviral agent against HSV-1 than EGCG. Palmitoyl-EGCG therefore offers a potentially useful approach to prevent infection by topical application on epithelial tissues. A case study has been reported recently that the topical application of lipophilic EGCG could be a potential effective treatment for HSV (Zhao et al. 2012). Use of p-EGCG could have significant public health benefits, and warrants further study in appropriate models.