Re-evaluation of Quercus Lusitanica Extract as an Inhibitory Agent against Viability of Dengue Virus Type 2

The aim of this study was the reconfirmation of Quercus lusitanica extract as an antiviral compound against dengue virus type 2 (DV2) using conventional plaque assay technique. In vitro antiviral activity of Q. lusitanica extract was assessed in C6/36 cells employing virus inhibition assay. The result showed that Q. lusitanica extract, at its maximum nontoxic concentration of 0.25 mg/ml, completely inhibited 10-1,000 TCID 50 of virus as indicated by the absence of cytopathic effect (CPE). The low dose of Q. lusitanica (0.032mg/ml) showed 100% inhibition with 10 TCID 50 of virus, but only 50% and 25% inhibition with 100 and 1,000 TCID 50 , respectively. The plaque assay result for the viral control at 10 TCID 50 of DV2 gave 13x10 pfu/ml. After treatment, 0.032 mg/ml of this extract yielded 3.5 x 10 pfu/ml, while 0.063 mg/ml of this extract gave 1.5x10 pfu/ml. The results showed that Q. lusitanica extract has a good inhibitory effect on viability of DV2, whether by post genomic technique or conventional method. poses a threat to more than 2.5 billion people (Guzman and Kouri, 2003). The more severe forms of the disease, dengue hemorrhagic fever and dengue shock syndrome (DSS), have been reported in up to 5-10% of secondary infections, with case fatality rates as high as 10% (Halstead, 1988; Rigan-Perez et al, 1998; WHO, 2000; Shuenn-Jue et al, 2001). Dengue virus is a positive-polarity RNA virus in the family Flaviviridae, and there are four antigenically related serotypes of dengue viruses (DV1, DV2, DV3, and DV4) (Lindenbach and Rice, 2001). A primary infection with any of the four serotypes of dengue viruses usually results in subclinical or self-limited febrile disease (Shuenn-Jue et al, 2001). Despite the antigenic relatedness of dengue viruses, two or more serotypes may sequentially infect one host (Alvarez et al, 2005). In a previous study, it was demonstrated the in vitro inhibitory effect of Quercus lusitanica seed extract on the replication of DV2 through the NS1 protein expression of infected C6/36 cells using proteomics technique (Muliawan et al, 2006). The results showed the downregulation of NS1 protein expression of infected C6/36 cells after treatment with this extract. The NS1 is a glycoprotein present in all flaviviruses and appears to be essential for virus viability. The INTRODUCTION Dengue fever (DF) or dengue hemorrhagic fever (DHF) has emerged as a public health problem worldwide (Gubler, 2002; Guzman and Kouri, 2003; Guzman et al, 2004). Dengue viruses are among the most important arboviruses because of the high morbidity they cause among humans who inhabit urban communities in the tropical and subtropical regions of the world (Gubler, 1998; Guzman and Kouri, 2002). It is estimated that two billion people live in areas at-risk for dengue virus transmission, and that as many as 100 million infections (Rigan-Perez et al, 1998; WHO, 2000; Shuenn-Jue et al, 2001), 500,000 hospitalizations, and 25,000-30,000 deaths occur annually, mostly among children (Gubler, 1999, 2002; Dussart et al, 2006). It is now endemic in more than 100 countries (the Americas, the Eastern Mediterranean, Southeast Asia, and the Western Pacific) and Correspondence: Dr Sylvia Y Muliawan, Department of Microbiology, Faculty of Medicine, Trisakti University, Jakarta 11440, Indonesia. Tel. (62)(21)-567231, -5655786; Fax. (62)(21)-5660706 E-mail: [email protected]