Sterols of Pneumocystis carinii hominis organisms isolated from human lungs

The opportunistic pathogen Pneumocystis carinii causes pneumonia (P. carini i pneumonia, or PCP) in immunocompromised individuals such as AIDS patients . Rat-derived P. carinii carinii organisms have distinct sterols which are not synthesized by mammals and not found in other microbes infecting mammal ian lungs. The dominant sterol present in the organism is cholesterol (whic h is believed to be scavenged from the host), but other sterols in P. carin ii carinii have an alkyl group at C-24 of the sterol side chain (C-28 and C -29 24-alkylsterols) and a double bond at C-7 of the nucleus. Recently, pne umocysterol (C-32), which is essentially lanosterol with a C-24 ethylidene group, was detected in lipids extracted from a formalin-fixed human P. cari nii-infected lung, and its structures were elucidated by gas-liquid chromat ography, mass spectrometry, and nuclear magnetic resonance spectrometry in conjunction with analyses of chemically synthesized authentic standards. Th e sterol composition of isolated P. carinii hominis organisms has yet to be reported. If P. carinii from animal models is to be used for identifying p otential drug targets and for developing chemotherapeutic approaches to cle ar human infections, it is important to determine whether the 24-alkylstero ls of organisms found in rats are also present in organisms in humans. In t he present study, sterol analyses of P. carinii hominis organisms isolated from cryopreserved human P. carinii-infected lungs and from bronchoalveolar lavage fluid were performed. Several of the same distinct sterols (e.g., f ungisterol and methylcholest-7-ene-3 beta-ol) previously identified in P. c arinii carinii were also present in organisms isolated from human specimens . Pneumocysterol was detected in only some of the samples.