The chemical characterization and biological evaluation of selenium-enriched Agaricus bisporus mushroom organic selenium species
Year: 2014
Type: dissertation
Abstract: The research study was divided into two main objectives, the chemical characterization and speciation of organic selenium species in cultivated selenium-enriched Agaricus bisporus mushroom and the biological evaluation of the organic Se species using a rat model. The biological evaluation of the mushroom organic Se species determined the effect of dietary supplementation with mushroom Se on the colonic antioxidant selenoprotein status markers cytosolic glutathione peroxidase-1 (GPx-1), gastrointestinal tract glutathione peroxidase-2 (GPx-2), thioredoxin reductase-1 (TrxR-1) and selenoprotein P (SeP). Furthermore, dietary effects of the mushroom organic Se supplementation on gut physiological function, (ileal) mucosal permeability and antioxidant selenoenzymes status during heat induced oxidative stress in rats were evaluated. We also evaluated the effects of dietary Se supplementation with the mushroom Se and with or without additional α-tocopherol on the regulation of the expression of colonic selenoproteins GPx-1, GPx-2, TrxR-1 and SeP in hyperthermally induced oxidative stress in rat. Selenocystine (SeCys), selenomethionine (SeMet), and methyl-selenocysteine (MeSeCys) were separated, identified and quantified by liquid chromatography–electrospray ionisation-mass spectrometry from water solubilised and acetone precipitated proteins. Although all three selenoamino acids were detected for both the control and selenium-enriched mushrooms, significant increases of the selenoamino acids were observed for the selenium-enriched mushrooms. The most notable result was the much higher levels of SeCys accumulated by A. bisporus compared to SeMet and MeSeCys, for both control and selenium-enriched A. bisporus. The maximum selenoamino acids concentration recorded in caps and stalks of control/selenised mushrooms was 4.16/9.65µg/g dried weight (DW) for SeCys, 0.08/0.58µg/g DW for SeMet, and 0.031/0.10µg/g DW for MeSeCys, respectively. The protein bound selenocysteine rich mushroom Se fed to the rats was observed to up-regulate all colonic selenoproteins under study. Rats maintained under thermoneutral conditions and fed the mushroom Se in dietary supplementation at a 1µg Se/g feed showed a significant (P<0.05) fold increase in mRNA expression relative to the basal treatment (rats fed the control diet) of GPx-1 (2.98±0.82), GPx-2 (1.8±1.4), TrxR-1 (1.83±0.64) and SeP (2.77±0.92). However, supplementation with α-tocopherol alone under thermoneutral conditions only affected the expression of GPx-1 (1.83±0.82) and SeP (2.21±0.92) and no effect was observed with GPx-2 and TrxR-1. Rats exposed to heat stress and placed on the low Se control diet also showed a significant (P<0.05) fold increase in mRNA expression relative to the basal treatment for all colonic selenoproteins at GPx-1 (3.15±0.82), GPx-2 (1.6±1.4), TrxR-1 (1.55±0.64) and SeP (1.93±0.92). However, heat stressed rats on the mushroom Se diet displayed a much higher mRNA expression of GPx-2 (3.2±1.4) and SeP (4.23±0.92). Heat stressed rats placed on the α-tocopherol diet alone displayed the highest expression level of selenoproteins relative to all diets with TrxR-1 at 4.10±0.64 and SeP at 7.44±0.92 fold increase. In correlation with mRNA expression, GPx-1 activity was observed to increase in rats placed on the mushroom Se diet and maintained under thermoneutral conditions, however in contrast with mRNA expression, GPx-1 activity was not up-regulated by α-tocopherol alone. Heat stress was observed to have a negative impact on GPx-1 activity which was recovered by mushroom Se, but not by α-tocopherol, in the diet. Although supplementation with α-tocopherol to the mushroom Se diet also displayed an increase in GPx-1 activity under thermoneutral conditions and also restored GPx-1 activity during heat stress, α-tocopherol did not enhance the Se effect. Furthermore, dietary supplementation with Se-enriched A. bisporus mushroom (1 µg Se/g feed) reduced (P < 0.05) gut (ileum) permeability markers baseline short-circuit current (Isc) and epithelium conductance (Ge) during heat stress to 1.74 and 1.91 fold, respectively, indicating protection from heat stress-induced mucosal permeability increase and restoration of gut barrier function. Thus, Se-enriched A. bisporus mushroom presented an efficient source of functional organic Se with demonstrated beneficial biological effects of up-regulating gut antioxidant selenoproteins linked to anti-cancer and anti-inflammatory mechanisms and disease prevention and protection against heat induced oxidative stress and gut dysfunction and injury.
Author: Tebo Maseko
Language: English
Subfield: Nutrition and Dietetics
Field: Nursing
Domain: Health Sciences
Open Access status: green
Funder: University of Melbourne
OpenAlex ID: W1566522826