Mianserin, an antidepressant kills Leishmania donovani by depleting ergosterol levels

In the present study, we have investigated the antileishmanial potential of mianserin, an antidepressant. Mianserin was found to inhibit both the promastigote and amastigote forms of the parasite in a dose dependant manner. The IC50 values for promastigotes and amastigotes were 21 mu M and 46 mu M respectively. Interestingly, mianserin failed to inhibit THP-1 differentiated macrophages up to 100 mu M concentration thus, exhibiting parasite selectivity. When mianserin was incubated with recombinant Leishmania donovani 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) enzyme, it exhibited an IC50 value of 19.8 mu M. Inhibition kinetics revealed competitive mode of enzyme-inhibition as the K-m increased with no change in V-max. Further structural investigation of enzyme-inhibitor interaction revealed quenching of HMGR tryptophan intrinsic fluorescence with a K-sv, value of 3.025 +/- 0.37 M-1 and an apparent binding constant of 0.0954 mM. We further estimated ergosterol levels which is a major component of Leishmania cell membrane. It is synthesized by HMGR enzyme, the first rate limiting enzyme of the sterol biosynthetic pathway. Analysis of ergosterol levels by HPLC revealed similar to 2.5-fold depletion in mianserin treated promastigotes with respect to untreated parasites. This data was further validated by exogenous supplementation of mianserin treated cells with ergosterol and cholesterol. Reversal of growth inhibition was observed only upon ergosterol addition though it was refractory to cholesterol supplementation. Overall, our results demonstrate the possibility of repositioning of an antidepressant for the treatment of Visceral Leishmaniasis. (C) 2014 Published by Elsevier Inc.