Identification of metabolites of importance in the pathogenesis of pulmonary cryptococcoma using nuclear magnetic resonance spectroscopy

Abstract

Primary lung infection with Cryptococcus neoformans is characterised by circumscribed lesions (cryptococcomas). To identify cryptococcal and/or host products of importance in pathogenesis, we applied proton nuclear magnetic resonance (NMR) spectroscopy, which identifies mobile compounds present in complex mixtures, to experimental pulmonary cryptococcomas from rats. Magnetic resonance experiments were performed on cryptococcomas ( n = 10) and healthy lungs ( n = 8). Signal assignment to key metabolites was confirmed by homo-nuclear and hetero-nuclear NMR correlation spectroscopy. Cryptococcal metabolites, dominating spectra from cryptococcomas included the stress protectants, trehalose and mannitol, acetate, and in some animals, ethanol. Glycerophosphorylcholine was also abundant in cryptococcomas, consistent with hydrolysis of phospholipids in vivo by the cryptococcal enzyme, phospholipase B (PLB). PLB has been identified by molecular studies as a cryptococcal virulence determinant. We propose that PLB secreted by cryptococci promotes tissue invasion by hydrolysing host phospholipids, such as dipalmitoyl phosphatidyl choline, which is abundant in pulmonary surfactant, and lung cell membrane phospholipids. Our results confirm the utility of NMR spectroscopy in studies of microbial pathogenesis.