Abstract
Naturally occurring anti-glycation compounds have drawn much interest in recent years as they show potential in reducing or preventing the risk of chronic complications for diabetic patients. In this study, annotation of the genome–transcriptome data from tiger milk mushroom (Lignosus rhinocerus, syn. Lignosus rhinocerotis) to PlantCyc enzymes database identified transcripts that are related to anti-diabetic properties, and these include genes that are involved in carotenoid and abscisic acid biosynthesis as well as genes that code for glyoxalase I, catalase-peroxidases, and superoxide dismutases. The existence of these genes suggests that L. rhinocerus may contain bioactive compound(s) with anti-glycation properties that can be exploited for management of diabetic complications. A medium-molecular-weight (MMW) fraction which was obtained from a combination of cold water extraction and Sephadex® G-50 (fine) gel filtration chromatography of L. rhinocerus sclerotia powder was demonstrated to exhibit potent anti-glycation activity. The fraction specifically inhibited the formation of N𝜀-(carboxymethyl)lysine, pentosidine, and other advanced glycation end-product (AGE) structures in a human serum albumin-glucose system, with an IC50 value of 0.001 mg/ml, almost 520 times lower than that of the positive control, aminoguanidine hydrochloride (IC50 = 0.52 mg/ml). Its ability to suppress protein glycation may be partly associated with its strong superoxide anion radical scavenging activity (10.16 ± 0.12 mmol TE/g). Our results suggest that the MMW fraction of L. rhinocerus shows potential to be developed into a potent glycation inhibitor for preventing AGE-mediated diabetic complications.
Highlights
The Polyporale tiger milk mushroom [Lignosus rhinocerus (Cooke) Ryvarden; syn
This was not unexpected, as previous study on L. rhinocerus transcriptome analysis revealed a few highly expressed gene clusters that encode for sesquiterpene synthases which may be responsible for the production of several sesquiterpene alcohols (C15H26O), including cadinols and germacrene D-4-ol (Yap et al, 2015a, 2017)
In addition to the number of transcripts involved in carotenoids synthesis, L. rhinocerus has genes that are able to reduce the oxidative damage in cells through the superoxide radical degradation pathway by acting as catalase (CAT)-peroxidases and/or superoxide dismutases (SODs)
Summary
The Polyporale tiger milk mushroom [Lignosus rhinocerus (Cooke) Ryvarden; syn. Lignosus rhinocerotis] is an important medicinal mushroom that has been used as a remedy to treat various health problems including wounds, fever, whooping cough, asthma, food poisoning, chronic hepatitis, gastric ulcers, and cancer (Jones et al, 2007; Wong and Cheung, 2009). Traditional consumption of its sclerotium (the part with medicinal value) is usually in the form of cold water extract. The sclerotium has been reported to be sliced, boiled, and consumed in the form of a decoction (Chang and Lee, 2004; Azliza et al, 2012). The sclerotial extracts of L. rhinocerus have been reported to exhibit anti-hypertensive, anti-inflammatory, anti-proliferative, neurite outgrowth, and antimicrobial activities along with the enhancement of immunomodulatory activity (Lai et al, 2008; Wong et al, 2011; Eik et al, 2012; Lee et al, 2012; Shopana et al, 2012). We have demonstrated that the cold water extract of L. rhinocerus TM02 cultivar’s sclerotia exhibited strong superoxide anion radical (O2−) scavenging activity with potency comparable to rutin (Yap et al, 2013). Yeast-based genome mining guided by transcriptomics approach which has been reported recently has enabled the discovery of several bioactive sesquiterpenoids, namely (+)-torreyol and α-cadinol from this mushroom (Yap et al, 2017)
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