The effect of arachidonic acid on lipid metabolism and biofilm formation of two closely related Candida species

[摘要] English: Candida albicans and C. dubliniensis are two closely related pathogenic yeastspecies, sharing many phenotypic characteristics which make it difficult todifferentiate them, especially in clinical samples. As a result of the similaritiesbetween these species, identification techniques, based on phenotypiccharacteristics, have been developed. In this study some of these techniquesand virulence factors were used to characterise strains belonging to thesespecies and to select phenotypically dissimilar strains for further study. Thiswas performed to evaluate if the effect of arachidonic acid (20:4) on thesestrains were the same, even though they are phenotypically different. Candidaalbicans and C. dubliniensis can form biofilms which play an important roleduring infection. During C. albicans infection, 20:4, a long-chainpolyunsaturated fatty acid (PUFA), derived from the phospholipids (PLs) of theinfected host cell membrane, serves as carbon source and precursor foreicosanoid production. Conflicting results are presented in literature regardingthe effect of 20:4 on morphogenesis in C. albicans. In addition, the effect of20:4 on growth and morphology of C. dubliniensis is unknown. Microscopicexamination and enzyme activity assay indicated that 1 mM 20:4 had little tono effect on growth and metabolic activity of planktonic cells and biofilms, aswell as on the morphology and viability of the cells in the biofilms. The uptakeof PUFAs by yeasts is necessary for utilisation as metabolic fuels, cellularbuilding blocks and the production of signalling molecules. However, there areno definitive studies regarding the uptake and cellular metabolism of 20:4 bythese pathogenic yeasts. The uptake and incorporation of 20:4 by planktoniccells and biofilms of selected strains of C. albicans and C. dubliniensis wereevaluated by subjecting residual and cellular lipids from planktonic cells andbiofilms, grown in the presence and absence of 20:4, to gas chromatographyand gas chromatography-mass spectrometry. Strain specific variation in 20:4uptake and incorporation into different lipid fractions of planktonic cells andbiofilms were found. In addition, eicosanoids produced by biofilms in thepresence of 20:4 were extracted and it was found that biofilms of these strainswere capable of producing 3-hydroxy fatty acids from 20:4. Arachidonic acidcan be incorporated into the PLs of yeasts, influencing saturation in cellmembranes. It is suggested that the effectiveness of antifungals may dependupon the level of unsaturation and ergosterol content of the membrane,therefore the effect of 20:4 on the cell membrane and susceptibility of C.albicans and C. dubliniensis biofilms towards amphotericin Band clotrimazolewere also determined. This was performed by confocal laser scanningmicroscopy, determination of mitochondrial metabolism, unsaturation index ofthe PL fractions and ergosterol content of the membranes of biofilms grown inthe presence and absence of 20:4. The results indicated that 20:4 influencesPL unsaturation and ergosterol content of both C. albicans and C. dubliniensistype strains, increasing susceptibility to the antifungals. Pre-treatment ofbiofilms with PUFAs may result in the reduction in antifungal dose needed toinhibit biofilms.

[发布机构] University of the Free State