In VivoInterference of Paromomycin with Mitochondrial Activity of Leishmania

Abstract

Paromomycin is an aminocyclitol aminoglycoside antibiotic used for the treatment of leishmaniasis. In view of the central role of mitochondria in cellular energetics and metabolism, its effect on in vivomitochondrial activities of Leishmania donovanipromastigotes—the parasite flagellate form—was investigated. The approach used flow cytometry, amperometric measure of O 2consumption, and, as a global estimate of mitochondrial dehydrogenases, thiazolyl blue reduction (MTT test); some in vitrocontrols were also made. When added to promastigote cultures for 24–72 h at 150–200 μ M(= LC 50), paromomycin doubled the generation time, inhibited respiration, and lowered its associated electric potential difference across mitochondrial membranes, as measured by rhodamine 123 fluorescence. The chemical analogue neomycin was ineffective. Furthermore, the in vivomitochondrial dehydrogenase activities were lower, seemingly because of the shortage of respiratory substrates. Indeed, succinate addition to paromomycin-treated cultures partly restored mitochondrial membrane potential. However, no immediate effect of paromomycin on respiration was observed, neither inhibition of redox chain nor increase of membrane permeability (uncoupling). It is proposed that paromomycin acts at a metabolic level upstream of the respiratory chain itself. This would have the observed delayed consequence because the cell energy supply would progressively decline since it depends upon the proton gradient—viz., membrane potential—generated by respiration. In conclusion, paromomycin is an antibiotic affecting the cell's energetic metabolism; the respiratory dysfunction it induces may be a crucial aspect of its action against Leishmaniaand possibly other cells.