Inhibitory actions of selected natural substances on formation of advanced glycation endproducts and advanced oxidation protein products

Ewa Grzebyk, Agnieszka Piwowar

Advanced glycation endproducts (AGE) and advanced oxidation protein products (AOPP) arise as a result of excessive glycation and oxidation processes of proteins in hyperglycemia and oxidative stress conditions respectively, both in vivo and in vitro. In vivo these processes are especially intensified in patients with diabetes, and the adverse effects of AGE and AOPP are particularly unfavorable for the pathogenesis and aggravate the biochemical disturbances and clinical complications of diabetes. Total AGE and AOPP (T-AGE and T-AOPP) are heterogeneous groups of compounds, and they can be divided into two main fractions: high- and low-molecular-weight, i.e. HMW-AGE and HMW-AOPP as well as LMW-AGE and LMW-AOPP. Therefore it is important to find natural substances that will prevent formation of total AGE and AOPP and their high- and low-molecular-weight fractions and thereby reduce their adverse effects on tissues and organs. Selected natural substances and dietary supplements such as vitamin C, aminoguanidine, quercetin and green tea as well as the multicompound formulations Padma Circosan and Padma 28 were tested in an in vitro model using bovine serum albumin (BSA). Fluorescence of T-, HMW- and LMW-AGE and concentration of T-, HMW- and LMW-AOPP were measured after incubation with these substances. In the examined concentrations quercetin showed the greatest degree of inhibition for T-AGE (60.5 %) as well as for HMW-AGE (79.5 %), while in the case of LMW-AGE the greatest degree of glycation inhibition was shown by Padma Circosan (74.9 %). T-AOPP and HMW-AOPP were best inhibited by vitamin C (87.3 and 89.1 % respectively). The results obtained for LMW-AOPP are atypical, but the lowest concentration was observed in a sample with Padma 28. The results show that all tested natural compounds have inhibitory activity towards the formation of total and low- and high-molecular-weight forms of AGE and AOPP in vitro. That suggest a possible role in the prevention of diabetic complications, especially the multiherbal compound Padma preparations, which are especially effective in lowering the most dangerous, i.e. LMW fractions.