BACKGROUND The hand, foot and mouth disease (HFMD) is a febrile and exanthematous childhood disease mainly caused by Enterovirus 71 (EV-A71). In severe HFMD, virulent EV-A71 strains can cause acute flaccid paralysis and cardiopulmonary edema leading to death. Currently, no FDA approved antiviral treatment or vaccine is available for EV-A71. Flavonoids such as silymarin and baicalein are known to possess in vitro antiviral properties against viruses. In this study, the cytotoxicity and antiviral activity of silymarin, baicalein and baicalin were investigated. METHODS The cytotoxic effects of three flavonoids towards rhabdomyosarcoma (RD) cells were first examined using cell proliferation MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay. Compounds found to be non-cytotoxic in RD cells were evaluated for their in vitro antiviral properties against the EV-A71 subgenotype B4 strain 41 (5865/SIN/000009) using antiviral assays. Viral infectivity was determined by reduction of the formation of plaques in RD cells. For the measurement of RNA copy number, the real time quantitative reverse transcription PCR (qRT-PCR) was used. The most potent compound was further evaluated to determine the mode of action of inhibition by time course, virus attachment and entry assays in Vero cells. RESULTS Silymarin was shown to exert direct extracellular virucidal effects against EV-A71 at 50% inhibitory concentration (IC50) of 15.2 ± 3.53 μg/mL with SI of 10.53. Similarly, baicalein exhibited direct extracellular virucidal effects against EV-A71 at a higher IC50 value of 30.88 ± 5.50 μg/mL with SI of 13.64. Besides virucidal activity, silymarin was shown to block both viral attachment and entry of EV-A71 to inhibit infection in Vero cells. CONCLUSIONS Silymarin has a stronger inhibition activity against EV-A71 in comparison to baicalein. It could serve as a promising antiviral drug to treat EV-A71 infections.

中文翻译：

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与黄ical素相比，水飞蓟素对EV-A71的抗病毒活性。

背景技术手足口病（HFMD）是主要由肠病毒71（EV-A71）引起的发热和发炎的儿童疾病。在严重的手足口病中，强毒的EV-A71株会引起急性弛缓性麻痹和心肺水肿，导致死亡。目前，尚无FDA批准的EV-A71抗病毒治疗或疫苗。已知诸如水飞蓟素和黄e苷的类黄酮具有体外抗病毒特性。在这项研究中，研究了水飞蓟素，黄ical素和黄ical素的细胞毒性和抗病毒活性。方法首先使用细胞增殖MTS [3-（4,5-二甲基噻唑-2-基）-5-（3-羧甲氧基苯基）-2-（4-磺基苯基）增殖法检测三种类黄酮对横纹肌肉瘤（RD）细胞的细胞毒性作用。 -2H-四唑鎓]测定。使用抗病毒测定法评估发现的在RD细胞中无细胞毒性的化合物针对EV-A71 B4亚型B4株（5865 / SIN / 000009）的体外抗病毒特性。通过减少RD细胞中噬斑的形成来确定病毒的感染性。为了测量RNA拷贝数，使用了实时定量逆转录PCR（qRT-PCR）。进一步评估了最有效的化合物，以通过时程，病毒附着和Vero细胞中的进入试验来确定抑制作用的模式。结果显示水飞蓟素在50％抑制浓度（IC50）为15.2±3.53μg/ mL，SI为10.53时，对EV-A71具有直接的杀细胞作用。同样，黄ical素对EV-A71表现出直接的杀细胞作用，IC50值为30.88±5。50μg/ mL，SI为13.64。除杀病毒活性外，水飞蓟素还可以阻止病毒附着和EV-A71进入，从而抑制Vero细胞感染。结论与黄ical素相比，水飞蓟素对EV-A71具有更强的抑制活性。它可以作为有前景的抗病毒药物来治疗EV-A71感染。