Özet:
Sphingolipids are essential cell compounds, mostly found in membranes and participated in cell events such as cell signaling, proliferation and apoptosis. Sphingolipid biosynthesis pathways have recently been highlighted as a promising target for therapeutic intervention against pathogens, including parasites. Giardia lamblia is a common cause of diarrhea in humans and other mammals throughout the world. Currently available anti-G. lamblia drugs cause serious in vivo side effects, often in the gastrointestinal tract, which frequently necessitate treatment interruption. Recently, it has been shown that the inhibition of the activity of glucosylceramide (GlcCer) synthase by PPMP (1-phenyl-2- palmitoylamino-3-morpholino-1-propanol) inhibitor prevented the proliferation and differentiation of G. lamblia in a dose dependent manner (Sonda et al., 2008). This result indicated that as-yet-uncharacterized sphingolipid biosynthetic pathways are potential drug targets for the development of anti-G.lamblia agents. In the present study, a metabolic model for the G.lamblia sphingolipid metabolism was developed and by the application of flux balance analysis (FBA) in silico gene deletion simulations were performed to gain insight about the metabolic consequences of drug actions on candidate enzymes. An experimental study was also conducted with wild type and DPP1 deletion mutant of S.cerevisiae and the effects of gene deletions on the sphingolipid metabolism were investigated. It was observed that the production of D-Cer was increased in the DPP1 mutant strain and a distinct increase in dihydrosphingosine favoring the increase of ceramide production was also noted. Other complex sphingolipids, MIPC and M(IP)2C, were similarly found to increase. When the in silico deletion mutants of G. lamblia simulating the anti-Giardia drug effects were investigated by FBA, the inhibitions of the enzymes encoded by the genes of Ugcg or DPP1 resulted in higher fluxes of ceramide synthesis. These increases are around 2 to 10 % of those of the wildtype strain. One can conclude that the results of the present simulation study agree well with the experimental findings reported in literature.
