quercetin diglycoside biosynthesis (pollen ..

Notably, quercetin induced several genes belonging to carbohydrate metabolism, including metabolism of energy reserves, known to be repressed by glucose. Specifically, quercetin up regulated genes associated with gluconeogenesis, glycogenolysis, glucose uptake and trehalose biosynthesis, as well as IRA1 and IRA2 genes, which encode GTPase-activating proteins that negatively regulate the glucose-activated cAMP-dependent protein kinase signaling pathway . These metabolic alterations redirect carbohydrate metabolism towards the production of trehalose, whose levels increased 4-fold after exposure to quercetin. Trehalose-6-phosphate, one of the intermediates of this pathway, and Tps1p play a major role in restricting glucose influx into glycolysis . Trehalose is a disaccharide of glucose with stress-protectant functions . Our results indicate that the increase in trehalose production contributes to oxidative stress resistance of cells treated with quercetin, since inactivation of TPS1 gene decreased its protective effect. Interestingly, glycogen levels also decrease whereas trehalose levels remain unchanged in stationary phase (quiescent) cells, which display a high oxidative stress resistance phenotype. Under these conditions, trehalose also functions as an energy reserve used by yeast cells upon exit from the quiescent state .

The flavonoid biosynthetic pathway in plants: Function …

glucosylation step which completes the flavonol-3-O-glucosylgalactoside biosynthesis in ..

Biosynthesis of flavonoids—XVI: ..

Oxidative stress has been implicated in aging and age-related diseases. Mounting evidence suggests that natural compounds with antioxidant properties exert health beneficial effects. The antioxidant activities of polyphenols have been attributed to ROS scavenging. However, a number of recent studies suggest that they also act through modulation of cell signaling pathways that increase cellular defense mechanisms. This phenomenon, known as xenohormesis, refers to sensing in one organism (yeast in this study) of a compound produced in another specie (plant) in response to environmental stress, leading to the induction of a defense response that increases its chances of survival . We have previously shown that quercetin, the most common flavonol in the diet, increases oxidative stress resistance in yeast cells by scavenging free radicals, maintaining the redox homeostasis, and preventing protein carbonylation and lipid peroxidation . Aiming to characterize genome-wide changes in gene expression induced by quercetin in yeast, a microarray analysis was performed. The results obtained show that quercetin down regulated a significant number of genes belonging to RNA metabolism and ribosome biogenesis categories. This cellular adaptation has been observed in response to multiple stress conditions and is beneficial since it spares energy resources for cellular processes other than ribosome biosynthesis (the most energy consuming cellular process).


Increasing evidence supports the suggestion thatglucosamine induces the apoprosis of various cels, including ratmesangial cells () andpancreatic β cells (). Althoughlimited information is available describing the harmful effects ofglucosamine on macrophages, elevated glucose increases flux throughthe hexosamine biosynthetic pathway, which ultimately leads toincreased glucosamine concentrations (–).In a study investigating subjects with type 2 diabetes, increasedlevels of macrophage apoptosis were observed in theiratherosclerotic lesions, and this may be a risk factor of plaquedestabilization and acute clinical events (). In addition, Khan () detected increased O-GlcNAc staining,an indicator of intracellular glucosamine concentration (), in macrophage/foam cells of theatherosclerotic lesions in hyperglycemic ApoE−/− mice, comparedwith normoglycemic rice. As mentioned previously, quercetin hasbeen observed to prevent macrophages from apoptosis induction byhigh glucose (), ox-LDL() andHO ().However, whether quercetin inhibits glucosamine-induced macrophageapoptosis had not previously reported. The results of the presentstudy suggested that macrophages treated with 15 mM glucosamine for24 h exhibited increased apoptotic and necrotic rates, comparedwith cells in the vehicle control group. However, the addition ofquercetin to the glucosamine-treated macrophages significantlydecreased the apoptotic and necrotic rates of the cells.

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Flavonoid Biosynthesis Pathway | Carotenoid | Chloroplast

Putative flavonoid biosynthesis pathway related to …