Leishmania amazonensis: acidic organelles in amastigotes
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J C Antoine1, C Jouanne, A Ryter
1Unité d'Immunophysiologie cellulaire de l'Institut Pasteur et du C.N.R.S. (UA 1113), Paris, France.
Abstract:
Leishmania amastigotes are intracellular protozoan parasites which exclusively invade cells of the macrophage series and multiply within phagolysosomes. Recent studies showed that intracellular and isolated amastigotes of L. amazonesis are killed by amino acid esters which appear to be trapped within as yet unidentified, possibly acidified, "lysosome-like" parasite compartments and cleaved by hydrolytic enzyme(s) (M. Rabinovitch, V. Zilberfarb, and C. Ramazeilles, 1986, Journal of Experimental Medicine 163, 520-535). In the present study, we have localized acidic compartments of Leishmania amastigotes using as a probe the weak base 3-(2,4 dinitroanilino)-3'-amino-N-methyldipropylamine (DAMP). This indicator, which can be detected within cells by light and electron microscopy using immunocytochemical immunocytochemical methods, mainly accumulates within megasomes and in dense inclusion vacuoles. With the help of quantitative assays to titrate cell-associated DAMP, it was found that (a) its uptake is temperature dependent and thus probably requires an energy supply, (b) the proton ionophore monensin partially inhibits the trapping of DAMP, and (c) monensin greatly increases its efflux from cells. These results, as well as those obtained by quantitative ultrastructural immunocytochemistry of cells incubated with DAMP in the absence or presence of monensin, show that megasomes and inclusion vacuoles have a low pH probably maintained by an active process. Furthermore, confirming the report of H. F. Hassan and G. H. Coombs (1987, Molecular and Biochemical Parasitology 23, 285-296) megasomes were found to display acid phosphatase activity at both light and electron microscope levels. This, together with the demonstration that megasomes are acidified, suggests that these organelles may be targets for amino acid derivatives.
Insights
Leishmania amastigotes contain acidic compartments, megasomes and inclusion vacuoles, which are crucial for parasite survival. These compartments are acidified by an active process, suggesting they are targets for therapeutic amino acid derivatives.
Area of Science:
- Parasitology
- Cell Biology
- Biochemistry
Background:
- Leishmania amastigotes are intracellular parasites that multiply within macrophages.
- Amino acid esters can kill Leishmania amastigotes by acting on unidentified parasite compartments.
- The nature and function of these compartments remain largely uncharacterized.
Purpose of the Study:
- To identify and characterize acidic compartments within Leishmania amastigotes.
- To investigate the mechanism of acidification in these compartments.
- To explore the potential of these compartments as therapeutic targets.
Main Methods:
- Utilized the weak base 3-(2,4 dinitroanilino)-3'-amino-N-methyldipropylamine (DAMP) as a pH probe.
- Employed light and electron microscopy with immunocytochemical methods to detect DAMP.
- Quantified DAMP uptake and efflux using cell-associated assays and monensin treatment.
- Assessed acid phosphatase activity in Leishmania compartments.
Main Results:
- DAMP accumulated in megasomes and dense inclusion vacuoles within Leishmania amastigotes.
- DAMP uptake was temperature-dependent, indicating an active, energy-requiring process.
- Monensin partially inhibited DAMP trapping and enhanced its efflux, confirming compartment acidification.
- Megasomes exhibited acid phosphatase activity and were confirmed to be acidified.
Conclusions:
- Leishmania amastigotes possess acidified compartments, specifically megasomes and inclusion vacuoles.
- The acidification of these compartments is likely maintained by an active proton pump.
- These acidified organelles represent potential targets for novel anti-Leishmania therapies using amino acid derivatives.