Identification and characterization of new potent inhibitors of dengue virus NS5 proteinase from Andrographis paniculata supercritical extracts on in animal cell culture and in silico approaches

Abstract

Ethnopharmacological relevance: About 2.5 billion peoples are at risk of dengue virus and the majority of people, use traditional plant-based medicines to combat dengue. The whole plant of Andrographis paniculata used traditionally over past decades for health promotion. Andrographolide isolated from Andrographis paniculata is used as natural remedy for the treatment of various diseases in different parts of the world. Andrographolide has been reported to have antiviral activity against hepatitis B virus, hepatitis C virus, herpes simplex virus, influenza virus, chikungunya virus, dengue virus 2 and 4.

Aim of the study: The aim of the present study to isolate the andrographolide from the A. paniculata by supercritical fluid extraction technique and to characterize the isolated compound along with it anti-dengue activity against DENV-2 in vitro and in silico methods.

Materials and methods: Supercritical extraction condition for A. paniculata was standardised to isolate andrographolide compound at definite temperature and pressure on the basis of previous study. The andrographolide was identified by using Ultraviolet-Visible Spectroscopy (UV-VIS), Fourier-Transform Infrared Spectroscopy (FT-IR) and High Performance Thin Layer Chromatography (HPTLC) and Proton Nuclear Magnetic Resonance (¹HNMR). The maximum non-toxic dose of isolated andrographolide was detected by MTT assay using a micro plate reader at 595 nm. One hundred (100) copies/ml of the DENV-2 virus was used for antiviral assay in C6/36 cells lines and inhibition of virus due to andrographolide was determined by real-time PCR assay. The purity of isolated andrographolide was determined by Differential Scanning Calorimetry (DSC). The dengue NS5 receptor protein was docked with andrographolide and evaluated on the basis of the total energy and binding affinity score by Auto Dock (V4.2.6) software.

Results: Andrographolide, a diterpene lactone was isolated from the A. paniculata supercritical extract at 40 °C temperature and 15 Mpa pressure. UV spectrophotometer analysis revealed that the curve of andrographolide plant extract was overlapped with reference compound at 228 nm and the similar bands were detected from FT-IR spectroscopy analysis at 3315, 2917, 2849, 1673, 1462 and 1454 cm^-1 in isolated and standard andrographolide. HPTLC analysis shows the retention factor (R_f) of A. paniculata extract at 0.74 ± 0.06 as similar to standard andrographolide R_f values. The purity of isolated andrographolide was 99.76%. The maximum non-toxic dose of isolated andrographolide was found as 15.62 μg/ml on the C6/36 cell line calculated by using MTT assay. The andrographolide showed the 97.23% anti-dengue activity against the dengue-2 virus in C6/36 cell lines. Results of molecular docking showed that the interaction between andrographolide and NS5 of dengue protein with the maximum binding energy as -7.35 kcal/mol.

Conclusions: It is concluded that isolated andrographolide from the A. paniculata possess anti-dengue activity against dengue-2 virus as revealed from in vitro and in silico method. Due to lack of the vaccine and anti-viral agents, andrographolide extracted from A. paniculata play a major role to inhibit the dengue replication. Hence, it could be a source for drug design and help to reduce the dengue infection.

Keywords: Andrographolide; Antiviral assay; Dengue virus; HPTLC; Molecular docking.