Epigenetic manipulation as a pathway to develop functional metabolites from fungi

• Main Authors: Yu-Ming Chung, 鐘鈺旻
• Other Authors: Fang-Rong Chang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/59424129982085972258

博士 === 高雄醫學大學 === 天然藥物研究所 === 101 === Microbial natural products continue to play a vital role in modern drug-based therapy of various diseases. Currently, we are eager to combine the concept of epigenetics with an efficient method for production of novel compounds with biological activities from microorganisms. Application of this method to screen thirty-three fungi from different resources led to the findings of five strains, including Cordyceps indigotica、Gibellula formosana、Isaria tenuipes、Aspergillus sydowii and Beauveria felina, which changed significantly compared to untreated control. After scale-up cultivation, 42 secondary metabolites including 17 new compounds were obtained from the five fungal strains and some of them were evaluated for their anti-diabetic and anti-inflammatory activities. Treatment of the potato-dextrose broth (PDB) of C. indigotica with 5-azacytidine, a DNA methyltransferase inhibitor, led to the isolation of eight compounds (CI-1~8). Among them, CI-1 and CI-2 are new aromatic polyketide glycosides. The addition of a DNA methyltransferase inhibitor, 5-azacytidine, to PDB medium of Aspergillus sydowii significantly changed its secondary metabolites profile. It led to the isolation of three new bisabolane-type sesquiterpenoids (AS-1~3) and one new dihydroxanthone (AS-4), along with eight known compounds (AS-5~12). Beauveria felina cultivated in the presence of the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), to the yeast-malt (YM) medium induced the production of secondary metabolites and resulted in the isolation of eight compounds, including three new cyclodepsipeptides (BF-1~3), along with five known cyclodepsipeptides compounds (BF-4~8). Interestingly, BF-3 possessing a cyclodepsipeptide ring with N-methyl-butyric acid is rare in natural peptides. The concomitant addition of a histone deacetylase inhibitor, SBHA, and a DNA methyltransferase inhibitor, RG-108, to the YM medium of Gibellula formosana, an entomopathogenic fungus, induced a significant increase in diversity of secondary metabolites. The culture media were further isolated and yielded two new highly oxidized ergosterols (GF-1~2), and five new isariotin analogs (GF-4~8), together with six known compounds (GF-3, GF-9~13). The side chains of (GF-1~3) contained cis-22,23-epoxide, which is rarely present in naturally occurring sterols and triterpenes. Based on the aforementioned research, we propose that there may be conserved similar gene clusters in the different fungi as they are able to produce the similar secondary metabolites when affected by DNMT or/and HDAC inhibitors. Thus, we try to survey the related literature about fungi which reported the same isariotin derivatives as G. formosana. According to the literature, isariotin derivatives were obtained from an entomopathogenic fungus, Isaria tenuipes. Therefore, application of this approach to the YM culture medium of I. tenuipes in the concomitant presence of a histone deacetylase and a DNA methyltransferase inhibitor led to the isolation of a novel skeletal polyketide (IT-1), together with C10 lactone derivatives (IT-2~3). Regarding the biological activities of isolates, the bisabolane-type sesquiterpenoids from A. sydowii did not only potentiate insulin-stimulated glucose consumption but also prevented lipid accumulation in 3T3-L1 adipocytes, especially for AS-6. The cyclodepsipeptides obtained from B. felina showed moderate anti-inflammatory activity on inhibiting superoxide anion generation and elastase release by FMLP/CB-induced human neutrophils. In summary, epigenetic approach is an efficient and powerful tool for trigging silent gene clusters of fungus in discovering of new compounds. In the future, we will continue to search functional secondary metabolites using this method and combine it with pharmaceutical assays to develop potent lead compounds that are helpful for the improvement of current medication.