Aldose reductase is the first enzyme that reduces glucose into polyols (such as sorbitol), and its inhibition serves a therapeutic role in diabetes management, specifically diabetic retinopathy.[151] Reishi possesses aldose reductase activity, and appears to be one of the most potent mushrooms at doing so,[152] the ethanol extract has been shown in vivo to reduce polyol formation in the rat eye.[152] When looking at the IC50 values of Ganoderma acids (the more potent portion of the triterpenoids), 17 tested fragments have an IC50 value below 200uM whereas some are very potent at 22.8uM (ganoderic acid Df) and 43.8uM (ganoderic acid C2).[27] It appears the carboxyl group on the side-chain is critical for aldose reductase inhibition, and double bonds on C20-C22 as well as hydroxyl groups on C3,7,11, and 15 increase inhibition (this 'ideal' molecule is ganoderic acid C2).[27]
Aldose Reductase inhibition may underlie the ability of the ethanolic extract for alleviating some complications of diabetes
The first investigation on Reishi and diabetes came from a study injecting 100mg/kg bodyweight polysaccharides (Ganoderan A and B) into mice, which subsequently demonstrated a 50% reduction in blood glucose levels with some noticeable effect on blood glucose reduction for up to 24 hours after injection.[153] Ganoderan B
was later reported to increase insulin secretion and modulate glucose metabolism in liver tissue.[154] A related polysaccharide, Ganoderan C, also possesses hypoglycemic action via increasing insulin.[155] Polysaccharides can act on pancreatic beta-cells (where insulin is producted) where they induce Ca2+ influx into beta-cells to induce insulin secretion.[156] Ganoderma polysaccharides also exert an anti-oxidative protective effect on pancraetic beta-cells, and can reduce apoptosis while modulating biomarkers of apoptosis such as Bax/Bcl-2.[157][100][158]
Polysaccharides, if reaching the pancreas, may stimulate insulin release and subsequently reduce blood glucose levels
Ganoderma also appears to possess a proteoglycan (polysaccharide with amino acids) PTP1B competitive inhibitor, dubbed Fudan-Yueyang-Ganoderma Lucidum, possessing an IC50 value of 5.12+/-0.05 μg/mL.[159][160] This proteoglycan, called FYGL for short, contains 77+/-3% polysaccharide and 16.8+/-0.9% protein, and possesses a certain extraction process mentioned here.[159] Oral administration of FYGL can decreased blood glucose in type 1 diabetic mice, as well as both reducing serum insulin and increasing insulin sensitivity.[160] At oral doses of 50 and 150mg/kg bodyweight in mice over 4 weeks, improvements in glucose and insulin sensitivity are observed and the higher dose is comparable to 300mg/kg Metformin.[159] These effects have been observed in Type II diabetes as well, increasing the insulin sensitivity of skeletal muscle.[101] No toxicity of this particular extract was seen at up to 6g/kg daily.[159]
A proteoglycan from Ganoderma appears to act as a PTP1B inhibitor, and may prolong signalling through its receptor (which would reduce the rate of which the receptor desensitizes to insulin); it is moderately potent and has in vivo support for efficacy, but its IC50 value is weaker than other compounds such as ursolic acid or berberine
In diabetic mice, reductions in blood glucose have been seen and attributed to reduced hepatic expression of phosphoenolpyruvate carboxykinase (PEPCK) after 0.3g/kg oral ingestion for 4 weeks.[93] In vitro, activation of AMPK and increased glucose uptake have been noted with Reishi in fat cells as well.[161] Reductions in blood glucose after ingestion of 400mg/kg Ganoderma polysaccharides are roughly as potent as 30mg/kg Berberine, a potent hypoglycemic.[162]
Can reduce expression of PEPCK, and thus endogenous production of glucose in the liver; it is not as potent as Berberine, used as a reference compound
The Farnesoid X Receptor (FXR), a nuclear transcription activator, is induced by five triterpenpoids from the ethanolic fragment of Ganoderma Lucidum; ergosterol peroxide , lucidumol A, ganoderic acid TR, ganodermanontriol, and ganoderiol F.[163] General Lucidum extracts at 100ug/mL were able to induce FXR to 150% the level of the active control, CDCA (Chenodeoxycholic acid), whereas the 5 isolated triterpenoids at 10uM were similar in potency to CDCA at 25uM (with ganodermanontriol causing the highest increase, and erogsterol peroxide having the lowest EC50 of 0.85uM).[163] As the FXR monomer can activate GLUT4 vesicles,[164] this mechanism of action may play a role in the anti-diabetic effects of Ganoderma.
May activate FXR, which has potential relations to glucose uptake in cells