Acta Tropica 116 (2010) 127–133 Contents lists available at ScienceDirect Acta Tropica journal homepage: www.elsevier.com/locate/actatropica Antifilarial activity in vitro and in vivo of some flavonoids tested against Brugia malayi V. Lakshmi a , S.K. Joseph b , S. Srivastava a , S.K. Verma b , M.K. Sahoo b , V. Dube b , S.K. Mishra a , P.K. Murthy b,∗ a Division of Medicinal and Process Chemistry, Central Drug Research Institute, Lucknow 226001, India b Division of Parasitology, Central Drug Research Institute, Lucknow 226001, India article info Article history: Received 9 June 2009 Received in revised form 20 June 2010 Accepted 27 June 2010 Available online 6 July 2010 Keywords: Lymphatic filariasis Brugia malayi Flavonoids Motility assay MTT assay Meriones unguiculatus Mastomys coucha abstract We evaluated the antifilarial activity of 6 flavonoids against the human lymphatic filarial parasite Brugia malayi using an in vitro motility assay with adult worms and microfilariae, a biochemical test for via- bility (3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT)-reduction assay), and two animal models, Meriones unguiculatus (implanted adult worms) and Mastomys coucha (natural infec- tions). In vitro, naringenin and hesperetin killed the adult worms and inhibited (>60%) MTT-reduction at 7.8 and 31.2 g/ml concentration, respectively. Microfilariae (mf) were killed at 250–500 g/ml. The half maximal inhibitory concentration (IC 50 ) of naringenin for motility of adult females was 2.5 g/ml. Flavone immobilized female adult worms at 31.2 g/ml (MTT > 80%) and microfilariae at 62.5 g/ml. Rutin killed microfilariae at 125 g/ml and inhibited MTT-reduction in female worms for >65% at 500 g/ml. Naringin had adulticidal effects at 125 g/ml while chrysin killed microfilariae at 250 g/ml. In vivo, 50 mg/kg of naringenin elimiated 73% of transplanted adult worms in the Meriones model, but had no effect on the microfilariae in their peritoneal cavity. In Mastomys, the same drug was less effec- tive, killing only 31% of the naturally acquired adult worms, but 51%, when the dose was doubled. Still, effects on the microfilariae in the blood were hardly detectable, even at the highest dose. In summary, all 6 flavonoids showed antifilarial activity in vitro, which can be classed, in a decreasing order: narin- genin > flavone = hesperetin > rutin > naringin > chrysin. In jirds, naringenin and flavone killed or sterilized adult worms at 50 mg/kg dose, but in Mastomys, where the parasite produces a patent infection, only naringenin was filaricidal. Thus naringenin and flavone may provide a lead for design and development of new antifilarial agent(s). This is the first report on antifilarial efficacy of flavonoids. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Human lymphatic filariasis (LF), caused by the nematode para- sites Brugia malayi, Brugia timori and Wuchereria bancrofti, affects 120 million people worldwide, of which 40 million people show the chronic disease manifestations: elephantiasis and hydrocele (http://www.globalnetwork.org; WHO, 2006). A further one bil- lion people (18% of the world’s population) are at risk of infection (http://www.globalnetwork.org). The disease is the second leading cause of permanent and long-term disability worldwide (Molyneux et al., 2003). The Global Programme to Eliminate Lymphatic Filar- iasis (GPELF) started using yearly doses of multi-drug regimen ∗ Corresponding author at: Division of Parasitology, Central Drug Research Insti- tute, Lucknow 226001, India. Tel.: +91 0522 2612412 18x4427; fax: +91 0522 2623405/2623938/2629504. E-mail addresses: drpkmurthy@yahoo.com, drpkmurthy@gmail.com, psr murthy@yahoo.com (P.K. Murthy). in a mass drug administration (MDA) program for at least five years (http://www.filariasis.org)(Molyneux and Zagaria, 2002) to interrupt transmission and reduce morbidity. However, it appears unlikely that the MDA regimen will be sufficient to eliminate LF in all endemic areas (Molyneux et al., 2003). Numerous technical challenges threaten the success of such eradication programmes (Dadzie et al., 2003; Molyneux et al., 2003), including limited effi- cacy of available drugs diethylcarbamazine (DEC) and ivermectin given alone or in combination, against adult filarial worms. Killing the adult worms or sterilizing the female worms is con- sidered to be one of the best strategies. The need for an adulticidal (macrofilaricidal) and or sterilizing agent was specially emphasized by WHO because: (a) a single female adult worm can produce thou- sands of microfilariae (mf), (b) in an infected host, adult worms are numerically fewer than the millions of mf; and (c) adult worms are considered responsible for some of the severe and debilitat- ing manifestations of the disease. There are however several other advantages associated with killing the adult worms like the slow release of host-protective antigens; similarly sterilizing the worms 0001-706X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2010.06.006