title: Role of heme in the antifungal activity of the azaoxoaporphine alkaloid sampangine.
abstract: Sampangine, a plant-derived alkaloid found in the Annonaceae family, exhibits strong inhibitory activity against the opportunistic fungal pathogens Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. In the present study, transcriptional profiling experiments coupled with analyses of mutants were performed in an effort to elucidate its mechanism of action. Using Saccharomyces cerevisiae as a model organism, we show that sampangine produces a transcriptional response indicative of hypoxia, altering the expression of genes known to respond to low-oxygen conditions. Several additional lines of evidence obtained suggest that these responses could involve effects on heme. First, the hem1Delta mutant lacking the first enzyme in the heme biosynthetic pathway showed increased sensitivity to sampangine, and exogenously supplied hemin partially rescued the inhibitory activity of sampangine in wild-type cells. In addition, heterozygous mutants with deletions in genes involved in five out of eight steps in the heme biosynthetic pathway showed increased susceptibility to sampangine. Furthermore, spectral analyses of pyridine extracts indicated significant accumulation of free porphyrins in sampangine-treated cells. Transcriptional profiling experiments were also performed with C. albicans to investigate the response of a pathogenic fungal species to sampangine. Taking into account the known differences in the physiological responses of C. albicans and S. cerevisiae to low oxygen, significant correlations were observed between the two transcription profiles, suggestive of heme-related defects. Our results indicate that the antifungal activity of the plant alkaloid sampangine is due, at least in part, to perturbations in the biosynthesis or metabolism of heme.
authors.affiliation: National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA. aagarwal@olemiss.edu
authors.forename: Ameeta K
authors.initials: AK
authors.lastname: Agarwal
authors.forename: Tao
authors.initials: T
authors.lastname: Xu
authors.forename: Melissa R
authors.initials: MR
authors.lastname: Jacob
authors.forename: Qin
authors.initials: Q
authors.lastname: Feng
authors.forename: Michael C
authors.initials: MC
authors.lastname: Lorenz
authors.forename: Larry A
authors.initials: LA
authors.lastname: Walker
authors.forename: Alice M
authors.initials: AM
authors.lastname: Clark
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology; D002176:Candida albicans / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D015687:Cell Hypoxia; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects*; D006418:Heme / Q000378:metabolism*; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D009287:Naphthyridines; D020411:Oligonucleotide Array Sequence Analysis; D010100:Oxygen / Q000378:metabolism; D011725:Pyridines / Q000378:metabolism; D012331:RNA, Fungal; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D000470:Alkaloids; D000935:Antifungal Agents; D006576:Heterocyclic Compounds, 4 or More Rings; D009287:Naphthyridines; D011725:Pyridines; D012331:RNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; D006418:Heme; C121572:sampangine; C023666:pyridine; D010100:Oxygen