Phytochemicals of six selected herbal plants and their inhibitory activities towards free radicals and glycation

In type 2 diabetes mellitus patients, hyperglycaemia speed up the production of advanced glycation end products (AGEs), leading to oxidative stress and various diabetic complications. In order to identify natural products with potential antioxidant and antiglycative properties, six herbal plants, namely Musa acuminata (flower buds), Bletilla striata (rhizomes), Amomum villosum (dried nuts), Moghania philippinensis (roots), Minettia speciosa (rhizomes), and Spatholobus suberectus (stems) were assessed for their antioxidant and antiglycative properties. Among all the selected samples, both water and ethanolic extracts of S. suberectus possessed the highest phenolic, flavonoid and triterpenoid contents, ranging from three to six-fold higher than other plant extracts. In consistent with its phytochemical content, S. suberectus also showed the highest antioxidant activities which are comparable, if not higher than the known antioxidants, butylated hydroxytoluene, gallic acid, rutin, quercetin and ursolic acid. Similarly, S. suberectus also displayed the highest antiglycative activities among the six herbal plants measured by two glycation assays using bovine serum albumin-glucose and bovine serum albumin-methylglyoxal as model systems. HPLC-QTa-MS/MS analysis identified 48 polyphenols and 76 terpenoids, from the water and ethanolic extracts of S. suberectus, where 12 polyphenols and 9 terpenoids are common in both extracts. The results also suggested that S. suberectus contains compounds such as quercetin, luteolin, apigenin and saponin derivatives, which were reported to exert high antioxidant and antiglycative properties. The high antioxidant and antiglycative properties suggest the great potential of S. suberectus in preventing the formation of AGEs and oxidative stress seen in type 2 diabetes.