| Tartary buckwheat (Fagopyrum tataricum), as a unique food medicine dual-use cerealcrop, which health benefits have been reported in many China traditional medicine books.And modern medical researches have also shown its many pharmacological activities such asantiinflammation, antioxidant, antidiabetes, antihyperlipidemia, antihypertension andantitumor et al. By the year2020, reportedly, cardiovascular disease (CVD) will become thefirst cause of death in the first time in the global scope. Metabolic disorder is a commonpathological basis of CVD. Metabolic syndrome (MS) is the general term that describes anumber of metabolic disorders, and characterized by insulin resistance (IR). MS is not asingle disease, but in fact it is a unity of a series of pathologic physiology phenomenon, suchas obesity, type2diabetes, hyperlipidemia, hypertension and coronary heart disease et al.Therefore, MS is also referred to as insulin resistance syndrome. As a matter of fact, IR is asub-health state of a body with gradually development. Early and long-term prevention aregood ways to prevent IR, and it is in keeping with application characteristics of functionalfood. People have been paying more attention on the application of tartary buckwheat in foodand medical fields. Tartary buckwheat is rich in polyphenols with a wide array of bioactivitiesimplicated in cardiovascular protection, and polyphenols are a group important functionalsubstance in tartary buckwheat. This study aims to establish the link between the polyphenolantioxidants and their metabolites of ameliorating insulin resistance and further elucidateunderlying mechanism. Determination of the functional substances and verification of theirbeneficial regulation of insulin sensitivity should contribute to further applications of tartarybuckwheat in the management of metabolic syndrome and diabetes insulin resistanceinvolved.This research incorporated plant organic chemistry, modern chromatography analysisand molecular biology. And the composition, antioxidant activity and regulation of insulinaction of flavonoids and phenolic acids of tartary buckwheat were researched using HPLC,NMR, Elisa and Western blot methods, and free radicals and anti-oxidation, structure-activityand insulin resistance theories. The objectives of present study were the following:(1) toanalysis the influencing factors of phenolics and antioxidant activity of tartary buckwheat;(2)to look for the pure antioxidant substance;(3) to investigate the molecular mechanism ameliorating insulin resistance of pure antioxidant substance (quercetin) and its metabolite(quercetin-3-O-glucuronide). The results will provide a theoretical basis for the application oftartary buckwheat in the prevention and treatment of MS.The main conclusions of this study are as follows:(1) The majority (76%-95%) of phenolic compounds of tartary buckwheat was presentin the free form and the distinction between free and bound phenolics helps to understand thepotential benefit of tartary buckwheat consumption.(2) Phenolic acids in tartary buckwheat seed included p-hydroxybenzoic, ferulic,protocatechuic, p-coumaric, gallic, caffeic, vanillic, syringic and chlorogenic acids. Andp-hydroxybenzoic, protocatechuic and ferulic acids were the prominent phenolic acids intartary buckwheat seed.(3) The variety and growing environment and the interaction between variety andenvironment may contribute more to individual antioxidant properties and phenolics oftartary buckwheat. Environmental parameter such as higher altitudes may also have anincreasing effect on rutin and phenolic acids content of tartary buckwheat. The results alsoshow the possibility of increasing the content of natural antioxidants by optimizing thegrowing conditions of a selected variety.(4) The milling fractions of tartary buckwheat influenced their phenolics and antioxidantproperties. Protocatechuic acid was the dominant phenolic acid of the hull. p-Hydroxybenzoicacid was the dominant phenolic acid of bran and light flour. The orders of total phenoliccontent and DPPH· and ABTS·+scavenging activities of milling fractions were bran> hull> light flour. The orders of total reducing power of milling fractions was hull> bran> lightflour. The results indicate that the antioxidants including phenolic acids are concentrated inthe outer layers of tartary buckwheat. These results suggest that the use of bran fractionationto reduce the particle size can help in developing grain-based products with increasednutritional and functional potential. Therefore, hull and fine bran have the potential to be usedas functional food ingredients and may increase the added value of tartary buckwheat.(5) The ethyl acetate fraction of tartary buckwheat bran ethanol extract had higherphenolic and flavonoid contents and showed stronger antioxidant activity than n-butanol andaqueous fractions. Therefore, ethyl acetate is excellent solvent concentrated tartarybuckwheat flavonoids.(6) Quercetin, p-hydroxybenzoic acid and daucosterol were identified as the mainantioxidant constituents in the ethanol extracts of tartary buckwheat bran following abioguided chromatographic strategy. p-Hydroxybenzoic acid was isolated from buckwheatgrain for the first time. The result will contribute to the understanding of the health benefits and the novel utilization of tartary buckwheat bran in the health food and medical industries,improving the potential to add value of tartary buckwheat.(7) Quercetin and quercetin-3-O-glucuronide inhibited ROS overproduction andeffectively restored Δψm, demonstrating their chemorpotection of mitochondrial functionthrough antioxidative actions. Also, quercetin and quercetin-3-O-glucuronide inhibitedROS-associated inflammation by inhibition of IL--6and TNF-α production with suppressionof IKKβ/NF-κB phosphorylation.(8) Inflammation and ROS impaired insulin PI3K signaling and reducedinsulin-mediated NO production. Quercetin and quercetin-3-O-glucuronide facilitated PI3Ksignaling by positive regulation of serine/tyrosine phosphorylation of IRS-1and restorationof downstream Akt/eNOS activation, leading to an increased insulin-mediated NO level.(9) Quercetin and quercetin-3-O-glucuronide inhibited ROS-associated inflammation byblocking IKKβ/NF-κB activation and effectively facilitated insulin signaling transductionalong IRS-1/Akt/eNOS pathway in the endothelium. Because quercetin is rapidlymetabolized during absorption, by methylation, glucuronidation and sulfation, parallelinvestigation of effects of quercetin and its metabolite on insulin sensitivity in theendothelium should be beneficial for us to get more information about quercetin in themanagement of endothelial dysfunction involved in insulin resistance.In this study, the results provided evidences of application of tartary buckwheat inprevention and treatment of MS in terms of structure effect model and signal transductionpathways. Meanwhile, the functionality of tartary buckwheat would be promoted to a newhigh. |
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