In vitro pharmacological studies on the bioavailability of flavonoid compounds and on AGEs formation

Free radicals and reactive oxygen species (ROS) are responsible for the oxidative stress which causes damage to cellular membranes, proteins, and DNA, affecting many human tissues. Thus, oxidative stress is involved in the genesis of several pathological conditions like vascular alterations, diabetes complications, inflammatory diseases and so on. Furthermore, advanced glycation end-products (AGEs) are well-known contributors to the pathophysiology of these complications, because glycated proteins in vivo may in turn promote the formation of free radicals; hence, glycation and oxidative stress are intimately interrelated. A role in prevention of chronic diseases is given to antioxidant compounds, among these, natural phenolic compounds and flavonoids have received attention for their biological effects, such as antioxidant and antiglycative activities. Despite the health claims of flavonoids, it is known that the bioavailability of flavonoids is generally low and can vary dramatically among different flavonoid classes as well as individual compounds in a particular class. In fact, the effects of these polyphenols and their in vivo circulating forms will ultimately depend on the extent to which they associate with cells, either by interactions at the membrane or more importantly by their cellular uptake. The aim of this research was to evaluate the antiglycative activity of several flavonoid compounds and to investigate their uptake by intestinal cells, in order to have a preview on their in vivo properties. The flavonoids studied were baicalein, eupatorin, galangin, myricetin, and silibinin, which are well known plant-derived polyphenols widely used in traditional medicine. Advanced glycation end-products (AGEs) were determined using bovine serum albumin (BSA) as protein substrate and glucose, ribose or glyoxal as glicative agents. Glucose and ribose are sugars found in vivo in physiological conditions, while glyoxal is a highly reactive dialdehyde, a metabolite produced during the autoxidation of glucose. To assess the cellular uptake of flavonoids, we used as experimental model the human colon carcinoma (HT29) cells which were incubated for three hours with the flavonoid compounds (1-5 μM). The flavonoid content of the cells was analyzed by high performance liquid chromatography (HPLC) equipped with a UV diode array detector. The results showed that flavonoid compounds possess antiglycative activity in the BSA-sugar assay in comparison with aminoguanidine as positive control. Further, the data on the cellular flavonoids uptake showed that these compounds are partially taken up by HT29 cells. Others studies are in progress to determine the cellular uptake and antiglycative activity of the flavonoid compounds.