Sterols of Pneumocystis carinii hominis Organisms Isolated from Human Lungs

Abstract

The opportunistic pathogen Pneumocystis carinii causes pneumonia (P. carinii pneumonia, or PCP) in immunocompromised individuals such as AIDS patients. Rat-derivedP. carinii carinii organisms have distinct sterols which are not synthesized by mammals and not found in other microbes infecting mammalian lungs. The dominant sterol present in the organism is cholesterol (which is believed to be scavenged from the host), but other sterols in P. carinii carinii have an alkyl group at C-24 of the sterol side chain (C28 and C2924-alkylsterols) and a double bond at C-7 of the nucleus. Recently, pneumocysterol (C32), which is essentially lanosterol with a C-24 ethylidene group, was detected in lipids extracted from a formalin-fixed human P. carinii-infected lung, and its structures were elucidated by gas-liquid chromatography, mass spectrometry, and nuclear magnetic resonance spectrometry in conjunction with analyses of chemically synthesized authentic standards. The 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 potential drug targets and for developing chemotherapeutic approaches to clear human infections, it is important to determine whether the 24-alkylsterols of organisms found in rats are also present in organisms in humans. In the present study, sterol analyses of P. carinii hominis organisms isolated from cryopreserved humanP. carinii-infected lungs and from bronchoalveolar lavage fluid were performed. Several of the same distinct sterols (e.g., fungisterol and methylcholest-7-ene-3β-ol) previously identified inP. carinii carinii were also present in organisms isolated from human specimens. Pneumocysterol was detected in only some of the samples.

A Molecular Window into the Biology and Epidemiology of Pneumocystis spp

“…Unexpectedly, Pneumocystis was found to be resistant to these drugs, presumably due to its absence of ergosterol, the major sterol in the cell membranes of most fungi (64,66). Instead of ergosterol, cholesterol was found to be the major sterol in Pneumocystis (64,67,68), though the metabolic pathways for both sterols remained poorly understood until the recent sequencing of Pneumocystis genomes. Based on genome analysis, Pneumocystis lacks several key enzyme genes involved in ergosterol biosynthesis (69).…”

Sterol metabolism in the opportunistic pathogen Pneumocystis: Advances and new insights

“…However, detailed genetic analysis of the P. jirovecii erg11 gene from putative wild-type and mutant organisms has yet to be performed; thus, it cannot be ruled out that other factors regulating gene expression or enzyme activity are responsible. The putative 14DM − phenotype has been observed in samples obtained from the United States and Europe (71,72). Thus, it appears that organisms of this phenotype have spread among different human populations, and it is possible that several putative erg11 mutants developed independently.…”

“…There was no obvious correlation between these two phenotypes and HIV/AIDS status, drug treatment, or other information available on patients' histories (71,72), but the effects of disease or therapy could not be ruled out at the time. It was proposed that the high ≥C 30 sterol phenotype resulted from low 14DM activity and that the sterols with compositions between the two extremes represented co-infections of the two genetically distinct organisms (72). However, one could not be absolutely sure that some patients might have taken drugs such as azoles that had not been prescribed for them, or that their diets might have included compounds that inhibit 14DM.…”

“…From the initial studies on P. jirovecii sterols, it was clear that the sterol composition of these organisms was more variable from sample to sample than those reported for P. carinii (71,72). It is expected that the biochemical nature of humanderived material would not be as uniform as that observed in laboratory animals kept under controlled conditions.…”

“…It was a specimen of the latter type containing high concentrations of pneumocysterol that provided the material needed to describe this rare sterol (73). There was no obvious correlation between these two phenotypes and HIV/AIDS status, drug treatment, or other information available on patients' histories (71,72), but the effects of disease or therapy could not be ruled out at the time. It was proposed that the high ≥C 30 sterol phenotype resulted from low 14DM activity and that the sterols with compositions between the two extremes represented co-infections of the two genetically distinct organisms (72).…”