No abstract

No abstract

We have studied the antiproliferative effects of mevinolin (lovastatin), an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, on the protozoan parasite Trypanosoma (Schizotrypanum) cruzi and its ability to potentiate the action of specific ergosterol biosynthesis inhibitors, such as ketoconazole and terbinafine, both in vitro and in vivo. Against the epimastigote form in vitro, mevinolin produced a dose-dependent reduction of the growth rate up to 25 ,uM, but at 50 and 75 ,uM, complete growth arrest and cell lysis took place after 144 and 96 h, respectively. A systematic study of the effects of mevinolin combined with ketoconazole and terbinafine, which act at different points in the ergosterol biosynthesis pathway, on the proliferation of epimastigotes indicated a synergic action, as shown by concave isobolograms and fractional inhibitory concentration indexes ranging from 0.17 to 0.54. Analysis of the sterol composition and de novo sterol synthesis in control and treated cells by thin-layer and gas-liquid chromatographies showed that the antiproliferative effects of the drug alone and in combination were correlated with the depletion of the endogenous ergosterol pool and particularly with a critical (exogenous) cholesterol/endogenous 4-desmethyl sterol ratio in the cells. When we studied the effects of mevinolin on the amastigote form proliferating inside Vero cells in vitro, only very modest effects on the parasites were observed up to 0.75 ,M; above this concentration, significant deleterious effects on the host cells were found. However, when the same concentration of the drug was combined with ketoconazole, it was able to reduce by a factor of 10 the concentration of the azole required to eradicate the parasite (from 10 to 1 nM), again indicating a synergic action. On the other hand, a combination of mevinolin and terbinafine had only additive effects on amastigotes, but a ternary combination of mevinolin, ketoconazole, and terbinafine was again clearly synergistic. In vivo studies with a murine model of Chagas' disease showed that mevinolin can also potentiate the therapeutic effects of ketoconazole in this system; combined treatment with the two drugs at doses that alone offered only limited protection against the parasite was able to essentially eliminate circulating parasites and produce complete protection against death. These results confirm the synergic action against the proliferative stages of T. cruzi both in vitro and in vivo of combined ergosterol biosynthesis inhibitors that act at different points in the pathway and suggest that mevinolin combined with azoles, such as ketoconazole, can be used in the treatment of human Chagas' disease.

No abstract

Detailed analysis of the endogenous sterol content of purified Pneumocystis carinii preparations by gas-liquid chromatography coupled to mass spectrometry suggested that this parasite can both synthesize de novo steroid skeletons (to produce delta7 sterols) and take them from the infected host (leading to delta5 sterols). In both cases the final products are 24-alkyl sterols, resulting from the action of delta24(25) and delta24(24') sterol methyltransferases, enzymes not present in vertebrates. To investigate the physiological significance of these sterols, cultures of P. carinii in embryonic lung cells were exposed to 22,26-azasterol (20-piperidin-2-yl-5alpha-pregnan-3beta-20(R)-diol), a compound previously shown to inhibit both enzymes and to halt cell proliferation in fungi and protozoa. This compound produced a dose-dependent reduction in the parasite proliferation, with a 50% inhibitory concentration of 0.3 microM and 80% reduction of growth after 96 h at 10 microM. Correspondingly, parasites treated with the azasterol at 10 microM for 48 h accumulated 24-desalkyl sterols such as zymosterol (cholesta-8,24-dien-3beta-ol) and cholesta-8,14,24-trien-3beta-ol to ca. 40% of the total mass of endogenous sterols. This is the first report on the antiproliferative effects of a sterol biosynthesis inhibitor on P. carinii and indicate that sterol methyltransferase inhibitors could be the basis of a novel and specific chemotherapeutic approach to the treatment of P. carinii infections.