Influence of inhibitors of sterol biosynthesis on growth and sterol metabolism in Candida albicans

Candida albicans was treated with seven antifungal agents designed to inhibit ergosterol biosynthesis. Two types of inhibitors were studied based on their hypothetical mode of action: mechanism-based inactivators, containing either a sulfur or bromine in the sterol side chain and transition state mimics, which contain a nitrogen in the sterol side chain or in the nucleus. The sterol composition of cells treated with the various compounds was determined using three chromatographic techniques, thin-layer chromatography, reverse-phase high-performance liquid chromatography and gas chromatography-mass spectrometry. Additional characterization of the sterol identities was by proton nuclear magnetic resonance spectroscopy and ultra-violet spectroscopy. Ergosterol was found to be the major sterol in control cultures (69%). In treated cells, the dominant effect on sterol biosynthesis was a significant decrease in the amount of ergosterol. The influence of containing a heteroatom in the side chain on sterol methyl transferase activity was evident in aberrant cell morphology of treated cells and a reduction in ergosterol production. Disturbance of the 24-alkyl to 24-desaikyi ratio by as little as 10 % is sufficient to elicit a fimgistatic response. A second class of inhibitor represented by 3p-aminoianosteroi, designed to inhibit the C-4 demethyiation pathway, was found to inhibit growth by impairing lanosterol metabolism. The relationship between ergosterol biosynthesis inhibition action on fungal growth and ergosterol homeostasis is discussed.