Research Article - Asian Journal of Biomedical and Pharmaceutical Sciences (2017) Volume 7, Issue 60

Azaphilones: Their Role in Various Biological Activities

Nikhil Khurana¹, Suman Bala Sharma^1*, Aiman Abbas Jafri¹ and Akash M Sharma²

¹Depatment of Biochemistry, University College of Medical Sciences, Delhi, India

²Era Medical College, Lucknow, U.P, India

*Corresponding Author:

Suman Bala Sharma
Depatment of Biochemistry
University College of Medical Sciences, Delhi, India
E-mail: drsbs08@hotmail.com

Accepted on February 15, 2017

Abstract

Azaphilones which can be isolated from various natural resources like fungi and plant have range of potent biological activities that can be exploited against various diseases. Structure of numerous azaphilones has already been described. The present review talks about activities of azaphilones like anti cancerous, anti HIV, anti nematicidal, anti-bacterial, antifungal which have been extensively explored and efforts are going on to use azaphilones in drug formulation. This review is an effort to shift focus from complex synthetic products to natural products which are known to have to less toxicity and have less side effect for the treatment of various diseases

Keywords

Fungi; Penicillium; Immunosuppression; Antifungal; Natural Products.

Introduction

Natural products, produced by sources present in nature like plants, fungi, algae etc., have been used to cure diseases from the ancient time. In ancient literature like that of charka and various other literature available one can easily found how extracts from leaves, seeds and various other parts of the plant were utilized to treat various diseases and for healing of the wounds. Early ayurvedic practices and even today these natural products either in extracted or as in some cases whole plant or leaves are applied to the wounds. These natural products, even in today’s world are contributing lot for fight against diseases. Traditionally natural products have been employed for discovery of drugs and laid the foundation of early medicines but unfortunately with advent of new technologies and procedure for drug discovery like rational drug designing, crystallography, NMR’s results into the shifting of focus from natural products. Despite of all of these discoveries there is still a shortage of medicines in the field like oncology, immunosuppression and various metabolic diseases where natural products can play a vital role.

Fungi which have been considered as a potent source of various biologically active compounds and have been used to produce some valuable compounds that are still the active component of lots medicines. Various different chemical compounds have been identified in fungi these includes organic acids, polyynes, polyketides, polysaccharides etc.

The role of fungi in producing biological active compounds have been widely spread and is known to be use in medicinal purposes in Africa and Asia [1,2]. Our knowledge for fungi is very limited as of about 1.5 million species of fungi we know only about 7% of the total population and out of 7% of the population very few of these species have been cultivated and screened for drug production. The contribution of fungi is extraordinarily in managing human and animal diseases. Fungi are being explored for secondary metabolites for clinical applications and compounds extracted through them are active ingredients of modern drugs including antifungal agents and stains. Due to their wide spread uses many publications have focused on novel active compounds [3-6].

One such interesting set of secondary metabolites is azaphilones. Azaphilones are natural products belongs to structurally diverse family having an oxygenated bicyclic core and quaternary center. They possess large groups of pyranoquinon and have chromophoric properties. Their colour depends upon their chemical structure and they got their name from the reaction with ammonia which led to the formation of gamma pyradone derivatives. To classify as azaphilone both pyrone-quinone structure and quaternary center is necessary. For most of azaphilones their absorption spectrum lies within the visible range. They have been identified in various filamentous fungi well known producers of these compounds include the genera Manascus, Penicillium and Chaetomium. They are also identified in Aspergillus, Cochlioboluslunata and Emericellafalconensis.

Many secondary metabolites are being produced by fungi and which sorts out the fungi into different groups on the basis of the secondary metabolites and different chemicals produced. Some of the secondary metabolites follows certain combinatorial chemistry and are synthesized by combination of biosynthetic pathways. Genes involved in the production of enzymes of secondary metabolites are nucleic acids to form red or purple vinylogous c-pyridones due to the exchange of pyrane oxygen for nitrogen [7-9]. This appears to be a characteristic reaction. It can take place both with ammonia alone as found in the case of monascorubramine and rubropunctamine [10,11] and the side chain of a macrocyclic polypeptide as discovered for chlorofusin [12,13]. They possess large groups of pyrano-quinone and have chromophoric properties. Their colour depends upon the chemical pyradonederivatives. To classify azaphilones both pyronequinone structure and quaternary center is necessary. For most of azaphilones their absorption spectrum lies within the visible range. They have been identified in various filaments fungi (Manascus, Penicillium and Chaetomium). They are also identified in Aspergillus, Colchlioboluslumata and Emericellafalconensis.

It is necessary, however, to note that azaphilones are not the only structural class reacting with primary amines. Thus, fluorones isolated from Echinodontumtinctorium and Pyroformesalbomarginatus also change their colour on exposure to ammonia [14]. However, they are not azaphilones and should not be mistakenly included in the azaphilone class. However, they are not azaphilones and should not be mistakenly included in the azaphilones class. Azaphilones exhibit a wide range of interesting biological activities, such as anticancerous, antimicrobial, inhibitory effects on HIV-1 replication and gp120-CD4 activity, antifungal, nematicidal and anti-inflammatory activities. Several secondary metabolites from microbial origin inhibit 15-lipoxgyenase (15- LOX) [15,16]. More recently the fungal pigment, (+)- sclerotiorin [1], was found to inhibit lipoxygenase-1, also known as 15-LOX [17]. Geumsanols were isolated from Penicillium sp. KCB11A109, a fungus derived from ginseng field. The isolates were evaluated for their anti-cancer, anti-bacterial, anti-malarial activities in zebrafish development [18]. Endophytic fungus Colletotrichum sp. secondary metabolites showed anti-bacterial activities against two commonly dispersed environmental strains of Escherichia coli and Bacillus subtilis, as well as against two human pathogenic clinical strains of Staphylococcus aureus and Pseudomonas aeruginosa [19]. The potent nonselective biological activities of azaphilones may be related to their production of vinylogousc-pyridones [20]. Azaphilones were also found to be a new class of heat shock protein Hsp90 inhibitors [21], and more recently, Paranjape et al. reported that azaphilones inhibit tau aggregation and dissolve tau aggregates [22]. A. nidulans secondary metabolites were tested for their ability to inhibit tau aggregation in vitro and it was found that several were active inhibitors at micromolar concentrations, although they did not have tau disaggregation properties [23].

Materials and Methods

PUBMED database, MEDLINE database, Google Scholar and other online journals such as Journal of Natural Products Nat, Mycological Research and others were searched with no date restrictions for published articles using keywords azaphilones, secondary metabolite, and natural products. Some additional articles of interest were selected from reference lists of included articles. Only those articles were eligible to be included which showed azaphilones having numerous biological activities and can be isolated from natural resources like plant and fungi. Screening of the literature was also done on the same basis. Literature search began in January 2013 and ended in January 2016. The prime focus of the literature search was to screen the literature on the basis of eligibility criteria. Publications only in English were used and there was not any limitation on date of publication. Data extraction was based on which secondary metabolite can be isolated from natural resources and further incorporated into drug formulation. If many separate studies were present with similar conclusions, then only those were selected to be included which were most relevant to the objectives of the study and research question. No unpublished study was used or included (Tables 1 and 2).

Table 1. Azaphilones showing anti- cancerous activity.

Table 2. Azaphilones showing inhibitory effects on HIV-1 replication and gp120-CD4 activity.

Role of Azaphilones in anticancer activity

Sclerotiorin and azaphilone was found to be potent anti-proliferative against different cancer cells and found to be involved in different pathways. It activates BAX which induces apoptosis in colon cancer (HCT-116) and it involved in the down regulation of BCL-2, and which leads to the activated cleaved caspase-3 causing apoptosis of cancer cells. Enzyme K-Ras is activated in many colon cancers. The enzyme Ras protein farnesyltransfersae (PFTase), which catalyze the initial step of RAS signalling, has been reviewed as a potential target for cancer therapy [35]. Sclerotiorin have been identified to exhibit PFTase inhibitory activity. Its role in RAS inhibitor in time and dose dependent caspase mediated apoptosis in cells has been reported earlier [36]. Screening for anticancer activity was done with cell proliferation assay and LDH release assay. Sclerotiorin showed IC50 in the range of 0.63 to 2.1 mM in different cancer cell lines viz. ACHN, Panc-1, Calu-1, HCT-116 having IC50 of 0.63 ± 0.08, and H460 along with the normal breast epithelial cell (MCF10A) having IC50 of >10 Mm [26]. Seco-chaetomugilin D exhibited significant cytotoxic activity against the murine P388 leukemia cell line, the human HL-60 leukemia cell line, the murine L1210 leukemia cell line, and the human KB epidermoid carcinoma cell line [37]. Harziphilone demonstrated cytotoxicity at 38 μM against the murine tumor cell. Chaetomugilins are similar to some of azophilones, the compound which shows significant cytotoxic activity against P388 and HL-60 cell lines have the double bond between C-2 and C-3 intetracyclic ring systems [38].

It has been reported that Isochromophilone I and Isochromophilone II isolated from Penicillium multicolor FO-2338 showed inhibitory activity against gp120-CD4 binding. Though the strain FO-3216 also produced Isochromophilone I and II with Isochromophilone III & VI, the inhibitory activity of Isochromophilone III & VI against gp120-CD4 binding was weaker than that of Isochromophilone I and II [20]. The novel 5-bromo-derivative 9, showed the most potent inhibition with an IC50 value of 2.5 μM [30] (Tables 3 and 4).

Table 3. Inhibitory activities of azaphilones against gp120-CD4 binding [30].

Table 4. Anti-HIV activities of Phomouephorbins A and Phomouephorbins C

Azaphilones showing Anti-HIV activity

Phomoeuphorbin A and Phomoeuphorbin Cisolated from cultures of Phomopsiseuphorbiae,an endophytic fungus isolated from Trewianudiflora were tested for in vitro inhibitory effects against HIV replication in C8166 cells. Phomoeuphorbin A and Phomoeuphorbin C both exerted minimal cytotoxicity against C8166 cells (CC50>200 μg/mL) and each showed anti-HIV activity with EC50=79 μg/mL and 71 μg/mL [44] (Tables 4 and 5).

Table 5. Azaphilones showing Anti-inflammatory.

Role of Azaphilones (Harziphilone and Fleephilone) as two new HIV REV/ RRE binding inhibitors produced by Trichodermaharzianum

Azaphilones (Falconensins) showing inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate-induced inflammatory ear edema in mice

Falconensin have found to be having anti-inflammatory activity induced by TPA. Falconensins anti-inflammatory activity was tested using 12-O-tetradecanoylphorbol-13-acetate (TPA) induced inflammatory ear edema in mice. Their ID50 value of 526 μg/ear and 1.09 μmol/ear is a clear indication of its effectiveness as an anti-inflammatory agent [50] (Tables 6 and 7).

Table 6. 12-O-tetradecanoylphorbol-13-acetate (TPA) induced inflammatory ear edema in mice with ID50 values and confidence intervals [50].

Table 7. Azaphilones showing Nematicidal activity.

Two new azaphilones metabolites, named Pseudohalonectrin A (1) and B (2), wereisolated from the culture of the aquatic fungus Pseudohalonectriaadversaria YMF1.01019, originally separated from submerged wood in Yunnan Province,China. The nematicidal activity of pseudohalonectrin A and B was measured and the results revealed that of pseudohalonectrin A and B displayed moderatenematicidal activity against B. xylophilus [55] (Table 8).

Table 8. Azaphilones showing antibacterial activity.

Azaphilones anti-microbial activity

The antimicrobial activity of RP-1551-1, RP-1551-6, RP-1551- M1, RP-1551-3, RP-1551-4, RP-1551-5 was measured and the results revealed that they showed weak anti-microbial activity against activity Bacillus subtilis, Enterococcus faecium, and Staphylococcus aureus [66]. The two major components were used Deflectins A (1b) and B (2a), for the evaluation of the biological activities of the Deflectins. Both compounds showed antibacterial and weak antifungal activity with minimum inhibitory concentrations (MIC) ranging from less than 1 μg/ml to 150 μg/ml, depending on the medium. In synthetic media the MIC's were 20~100 fold lower than in complex media. Bacillus brevis and B. subtilis were the most sensitive organisms. Deflectin B was slightly more active than Deflectin A. Besides the inhibitory effects on the growth of bacteria and fungi, these compounds showed lytic activity towards bacteria and erythrocytes and cytotoxic activity towards cells of the ascitic form of Ehrlich carcinoma of mice.

Conclusion

Fungi have been used for medical purposes for a long time. Fungal kingdom appears to be very rich and diverse in area of secondary metabolites. Fungi have evolved its secondary metabolic pathways in such a way producing various compounds having diverse array of biological activities. The chemical composition and biochemical activity of many fungi has not been yet studied in detail. Identification of novel herbal compounds and further to explore its wide range potential secondary metabolite has become a trend in the last decade. Speaking of that, more and more novel azaphilones are being identified and is being used in drug formulation. Azaphilones has shown a wide spectrum of biological activities against various target organisms, including bacteria, fungi, and nematodes including the anti-cancerous and anti-HIV activity, lipogenase activity and recently it has been reported that reported that azaphilones inhibit tau aggregation and dissolve tau aggregates. Concerning the pharmaceutical science, finding new secondary metabolites enriches the possibilities of new drug discovery.

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