Inhibition of oxidative stress and advanced glycation end-product formation in purified BSA/glucose glycation system by polyphenol extracts of selected nuts from Pakistan

Pistachio green hull and pomegranate peel extracts as two natural antiglycation agents

Advanced glycation end products (AGEs) are formed in the final step of the nonenzymatic Maillard reaction, which can contribute to various health problems such as diabetes mellitus, renal failure, and chronic inflammation. Bioactive compounds with antiglycation properties have the potential to inhibit AGE-related diseases. This study investigated the antiglycation potential of pistachio green hull (PGH) and pomegranate peel (PP) extracts, which are polyphenol-rich agro-residues, against fluorescent AGE formation and compared the results with pyridoxine (vitamin B6), metformin, and EDTA (as usual chemical antiglycation agents). The results showed that PGH and PP effectively inhibited the formation of AGEs in bovine serum albumin-glucose (BSA-Glu) and BSA-fructose (BSA-Fru) with antiglycation activities ranging from 92% to 97%. PP extract (with an IC50 of 94 mg ml-1) had a greater antiglycation ability than PGH extract (with an IC50 of 142 mg ml-1). Also, results indicated that the antiglycation activities of the extracts were comparable to that of pyridoxine, and higher than metformin and EDTA. These findings suggest that the two studied extracts can be used for sustainable production of high-added-value food products with a positive effect on consumers' health.

Novel Fluorometric Assay of Antiglycation Activity Based on Methylglyoxal-Induced Protein Carbonylation

Advanced glycation end products (AGEs), which can have multiple structures, are formed at the sites where the carbonyl groups of reducing sugars bind to the free amino groups of proteins through the Maillard reaction. Some AGE structures exhibit fluorescence, and this fluorescence has been used to measure the formation and quantitative changes in carbonylated proteins. Recently, fluorescent AGEs have also been used as an index for the evaluation of compounds that inhibit protein glycation. However, the systems used to generate fluorescent AGEs from the reaction of reducing sugars and proteins used for the evaluation of antiglycation activity have not been determined through appropriate research; thus, problems remain regarding sensitivity, quantification, and precision. In the present study, using methylglyoxal (MGO), a reactive carbonyl compound to induce glycation, a comparative analysis of the mechanisms of formation of fluorescent substances from several types of proteins was conducted. The analysis identified hen egg lysozyme (HEL) as a protein that produces stronger fluorescent AGEs faster in the Maillard reaction with MGO. It was also found that the AGE structure produced in MGO-induced in HEL was argpyrimidine. By optimizing the reaction system, we developed a new evaluation method for compounds with antiglycation activity and established an efficient evaluation method (HEL-MGO assay) with greater sensitivity and accuracy than the conventional method, which requires high concentrations of bovine serum albumin and glucose. Furthermore, when compounds known to inhibit glycation were evaluated using this method, their antiglycation activities were clearly and significantly measured, demonstrating the practicality of this method.