# Fungal Pigments and Their Roles Associated with Human Health
## 2 Types of Fungal Pigments and Their Relevance to Human Health
### Polykeptides  
Many fungal pigments are polyketide-based compounds. This group of fungal pigments is abundantly produced by most ascomycetous fungi, including the filamentous ascomycete genera _Neurospora_ and _Monascus_[41]. Fungal polyketide pigments are made of tetraketides and octoketides which have eight C\({}_{2}\) units giving rise to the polyketide chain. Anthraquinones (including hydroxyanthraquinones), and naphthoquinones are representative classes which display an arsenal of various colors [42; 43]. The basic structure of the anthraquinone class of pigments is a polycyclic aromatic hydrocarbon which is derived from anthracene or phthalal anhydride, i.e., the merger of three benzene rings. Anthraquinone itself is highly insoluble and is generally used in the manufacture of dyes for the textile and pulp industries [44; 45]. However, other members of the anthraquinone class have been used in the pharmaceuticals industry. Approximately 700 representatives of anthraquinones have been found in fungi, plants, and lichens, conferring a yellow, orange, or brown color to the mycelium of microscopic fungi, the fruiting bodies of macroscopic fungi (mushroom), as well as lichens [46]. The variety of anthraquinones results from the presence of different substituents, like -OH, -CH\({}_{3}\), -OCH\({}_{3}\), -CH\({}_{2}\)OH, etc. as well as the reduction of carbonyl groups or double bonds in the benzene ring. Anthraquinones produce a yellow color, whereas the substituents produce various hues of the molecules ranging through yellow, orange, red, brown, and violet [47]. The most widely distributed variants found among fungi are 1, 8-dihydroxy and 1, 5, 8- or 1, 6, 8- trihydroxy anthraquinone derivatives [48]. However, substituents at other positions of the ring have been recently identified. For example, chrysophanol is a trihydroxyanthraquinone with a methyl substituent at C-3. It has shown antiviral and anti-inflammatory activities. Both chrysophanol and helminththosporin have shown inhibitory activity against cholinesterase with helminththosporin showing permeability across the blood-brain barrier [49]. Cholinesterase is a key enzyme involved in the development of Alzheimer's disease. Most anthraquinone-producing fungi produce a mixture of pigments of the quinone class. _Aspergillus crisfafus_, for instance, has been found to synthesize as many as 15 pigments related to anthraquinone. A strain of _Curvularis lunata_ has been characterized that produces a mixture of three anthraquinone derivatives: chrysophanol, helminththosporin, and cynodontin, with cynodontin (1, 4, 5, 8-tetrahydrooxy-3-methylanthraquinone) comprising more than 70% of the mixture and showing potential as a pharmaceutical with antifungal activity [44]. Chrysophanol, helminththosporin, and cynodontin are all hydroxyanthraquinone (HAQNs), derivatives of anthraquinone via the substitution of hydrogen atoms by hydroxyl groups plus the addition of other functional groups. Anthraquinones including HAQNs have been found to be produced by such fungi as _Aspergillus_ spp., _Eurotium_ spp., _Fusarium_ spp., _Dreschlera_ spp., _Penicillium_ spp., _Emericella purpurea_, _Culturalia lunata_, _Mycosphaerella rubella_, _Microsporum_ spp., etc. [48]. Filamentous fungi, such as _Penicillium_ and _Aspergillus_, synthesize HAQNs through the polykele pathway. This process has been employed for the production of natural food-grade colorants [50]. Apart from their usage as colorants in the food and cosme industries, they have been found to possess antiviral activities. For instance, emodin has been extracted from _Penicillium_, _P. islandcium_, _Aspergillus glaucus_ and _A. variecolor_[51, 52] and aloe-emodin from _Penicillium_[53]. Emodin and its congener aloe-emodin are known antiviral agents [54]. Aspergil0 H and I, HAQNs produced by _Aspergillus versicolor_, have been reported to have antiviral effects against HSV-1 [55].