Focus On The Preparation And Bioavailability Of Epigallocatechin-3-gallate (EGCG)-dispersed Selenium Nanoparticles

Bovine serum albumin dispersed selenium nanoparticles (B-Se) has beendemonstrated to be a novel selenium source with reduced toxicity but withoutcompromised bioavailability relative to organic selenium compounds in use, such asmethyl selenocysteine (Se-MSC) and selenomethionine (Se-Met). Thereafter, othersubstances such as melatonin, polyethylene glycol, adenosine triphosphate, andpolysaccharides were found to be effective dispersers of selenium nanoparticles; however,in view of bioavailability in terms of elevating selenoenzyme activities, none of theseselenium nanoparticles was evaluated. The current work demonstrated epigallocatechin-3-gallate (EGCG), a major functional ingredient of green tea, has been employed as stabilizerfor fabricating single-walled carbon nanotubes and gold nanoparticles, in conjunction withthe present finding that EGCG is able to disperse selenium nanoparticles, and confer theEGCG-dispersed materials or nanoparticles the particular features due to the property ofEGCG itself, such as the antioxidate activity, the targeting therapy owing to the specificbinding to67LR of EGCG.It has been well demonstrated that pH value has a tremendous impact on theprotonation status and consequent electron-donating ability of EGCG. At strong acidic pHconditions, the3′,4′,4′′-phenolic hydroxyl groups of EGCG have no electron-donatingability. At neutral to alkaline pH conditions, the3′,4′,4′′-phenolic hydroxyl groups aretransformed through deprotonation into phenolic anions with a strong electron-donatingability. EGCG in the form of phenolic anions with a strong electron-donating ability atneutral to alkaline pH condition, was able to effectively control the formation of seleniumnanoparticles, but massive aggregation of EGCG-dispersed selenium nanoparticles(referred to as E-Se) occurred while pH was adjusted to strong acidic conditionphysiologically relevant to gastric juice wherein EGCG, in the form of protonatedphenolic hydroxyl groups, has no electron-donating ability, thereby suggestingdeprotonated phenolic anions of EGCG play an important role in maintaining E-Sestability and E-Se would suffer from reduced oral bioavailability. To validate thisconjecture, size-equivalent E-Se and B-Se whose physicochemical properties were notaltered at pH1.0were orally administered to selenium-deficient mice for7days, comparedto B-Se at the same dose of80μg Se/kg, E-Se showed significantly reduced capacity ofincreasing hepatic and renal activities of glutathione peroxidase as well as hepatic seleniumlevel (p all <0.01). When they were intraperitoneally injected to selenium-deficient mice for7days, compared to B-Se at the same dose of50μg Se/kg, E-Se showed the matchedcapacity of increasing hepatic and renal activities of glutathione peroxidase as well ashepatic selenium level (p all>0.05). The current results suggest that size-equivalentselenium nanoparticles prepared by different dispersers do not necessarily guarantee anequal oral bioavailability.