EVIDENCE FOR THE PRESENCE OF METABOLIC STEROLS IN PNEUMOCYSTIS - IDENTIFICATION AND INITIAL CHARACTERIZATION OF PNEUMOCYSTIS-CARINII STEROLS

Mixed life cycle stages of rat-derived Pneumocystis carinii were isola ted from host lungs and their sterols were compared with those present in lungs from normal and immunosuppressed uninfected rats. Gas-liquid chromatography consistently detected, resolved, and quantified 9, 10, and 20 sterol components in the total nonsaponifiable neutral lipid f raction of lungs from normal rats, lungs from immunosuppressed uninfec ted rats, and P. carinii preparations, respectively. In all samples, c holesterol was the most abundant sterol present, comprising 97%, 93%, and 78% of total sterols in lungs from normal rats, lungs from immunos uppressed uninfected rats, and P. carinii, respectively. Tentative ide ntifications of several rat lung and P. carinii minor sterols were mad e based on gas-liquid chromatogram retention times and fragmentation p atterns from mass spectral analyses. Campesterol (ergost-5-en-3-ol), c holest-5-en-3-one, and beta-sitosterol (stigmast-5-en-3-ol) were among the minor components present in both types of lung controls, and were also components of P. carinii sterols. In contrast to lung controls, the sterols of P. carinii were enriched in C-28 and C-29 sterols with one or two double bonds, and a hydroxyl group at C-3 (ergost-5-en-3-ol , ergost-7-en-3-ol, ergosta-dien-3-ol, stigmast-5-en-3-oI, stigmast-7e n-3-ol and stigmasta-dien-3-ol). Steryl esters of P. carinii, probably stored in cytoplasmic lipid droplets, were dominated by those present in the host lung. In separate studies, 3-hydroxy-3-methylglutaryl coe nzyme A activity, a key enzyme in the regulation of sterol biosynthesi s, was detected in purified P. carinii preparations and incorporation of radiolabeled squalene and mevalonate was observed. Together, these results suggest that the parasite readily takes up and incorporates ho st sterols, and that the organism synthesizes some of its own ''metabo lic sterols.''