In Vivo; In Vitro Interaction of Silver Nanoparticles with Leucine Aminopeptidase from Human and Plasmodium falciparum

There is increasing requirement for the development of new drug protocols against malaria, a fatal disease caused by the lethal parasite Plasmodium falciparum. Leucine aminopeptidase (Pf LAP) of Plasmodium falciparum, is being pursued as a promising target for the discovery of novel anti-malarials. The effects of silver nanoparticles (AgNPs) against P. falciparum leucine amino-peptidase (Pf LAP) and the human homolog (HsLAP) were compared. Pf LAP and HsLAP were expressed in Escherichia coli, and AgNPs (3-10 nm) characterized by ultra-violet spectroscopy and transmission electron microscopy. Pf LAP indicated a K-m of 694 mu M towards leucine-p-nitroanilide and a V-max of 57.9 mu mol.ml(-1).min(-1) while HsLAP had a K-m of 1.6 mM and V-max of 119.6 mu mol.ml(-1).min(-1). On interaction with AgNPs (670 nM) Pf LAP was selectively inhibited (57.1%; K-i = 610 nM) relative to HsLAP (10.8%; K-i = 5.22 mu M). Structural differences between the enzyme variants, particularly the orientation and distance of surface Met(349) in Pf LAP and Met(306) in HsLAP to the zinc binding sites were significant and may allow for selective targeting of Pf LAP by AgNPs. The viability of P. falciparum parasites was decreased when exposed to silver nanoparticles, with an IC50 value of 6.96 mu M, compared to an IC50 value of 647.7 mu M for human HeLa cells.