Activity of andrographolide against chikungunya virus infection.

Chikungunya virus (CHIKV), an arthropod-borne virus, is the member of genus Alphavirus, family Togaviridae and is the causative agent of chikungunya fever (CHIKF). CHIKV has recently re-emerged and caused large epidemics in Africa, India and Southeast Asia between 2004 and 20101,2,3,4 and more recently in the Americas starting from 20145,6. CHIKV is an approximately 70 nm enveloped virus with an icosahedral nucleocapsid. The genome is an 11.8 kb positive single stranded RNA, containing a 5′-methylguanylate cap and a 3′-poly A tail with two open reading frames encoding for four nonstructural proteins (nsP1-nsP4) in the first, 5′ open reading frame and three structural proteins (capsid, E1 and E2) and two protein of unidentified function (E3 and 6 K) in the second, 3′ reading frame7. CHIKV is transmitted to humans by the bite of infected Aedes (Ae.) mosquitoes and it was first isolated in Tanzania, Africa during an outbreak in 19528,9. Subsequently, CHIKV was identified as the causative agent in other febrile disease outbreaks in Africa and elsewhere, and phylogenic analysis identified three CHIKV lineages, the East, Central and South African (ECSA) lineage, the West African lineage and the Asian lineage10. In 2004, an outbreak of CHIKV occurred in Kenya, and the causative virus of the ECSA lineage subsequently spread to the islands of the Indian Ocean and then to India and Southeast Asia3,11. In outbreaks in the Indian Ocean island of Reunion, and subsequently in India, it was observed that while the initial wave of infections was driven by transmission in Ae. aegypti mosquitoes, later, more severe waves of transmission were driven by transmission in Ae. albopictus12,13. It was subsequently shown14,15 that transmission in Ae. albopictus mosquitoes was facilitated by the emergence of strains of CHIKV with the substitution of a valine instead of the normal alanine at position 226 of the CHIKV E1 protein (E1 A226V). Remarkably, the E1 A226V substitution was shown to have occurred independently several times14,16. CHIKV infected patients develop symptoms within 3–7 days of being bitten by an infected mosquito7. The clinical symptoms of infection where manifested show great similarity with dengue fever, and include a sudden febrile illness, rash, headache, edema of the extremities, gastrointestinal complaints and myalgia17. Additionally polyarthralgia, which frequently persists for two or more months, is considered a hallmark of CHIKV infection18. There is currently no specific treatment for CHIKV infection, and treatment is primarily symptomatic. Chikungunya fever is seldom fatal, although increased neurological involvement19,20 and occasional fatalities have been reported21,22. However the disease, and particularly the persistent arthralgia can have long term impact on an infected person’s quality of life, particularly through disruption of their ability to work23. Specific antivirals that could reduce or eliminate CHIKV, either as a treatment or as a prophylactic in epidemic situations, are urgently required. Andrographis paniculata (Burm. f.) Nees (also known as the “king of bitters”) is a traditional medicinal plant used to treat infections and other disorders24. It is originally believed to be native to India and Sri Lanka, but is now commonly found and cultivated around much of Southern and Southeastern Asia. Andrographolide, a bicyclic diterpenoid lactone is believed to be the main bioactive ingredient with potential anti-inflammatory and hepatoprotective effects25. Given the traditional usage of Andrographis paniculata to treat infections, this study sought to determine whether the principal bioactive ingredient (andrographolide) possessed detectable anti-CHIKV activities. The cell line selected for investigation was the liver cell line HepG2 which has been shown to be highly susceptible to CHIKV26 and liver involvement in the disease has been shown in mouse27 and non human primate model systems28. In addition a non-relevant cell line previously used in evaluating anti-CHIKV compounds29, BHK-21, was investigated. Remarkably, andrographolide showed good potency in inhibiting CHIKV replication with no marked cytotoxicity in a cell culture system. These results suggest that andrographolide has significant potential for further development as an anti-CHIKV agent.