Imen Ben Abdelmalek ¹ Tomather A A Alhmdi ¹ Abir Ben Bacha ^2* Najeh Krayem ³

• ¹ Department of Biology, College of Science, Qassim University, Qassim, Saudi Arabia
• ² King Saud University, Riyadh, Saudi Arabia
• ³ Laboratory of Biochemistry and Enzymatic Engineering of Lipases, ENIS, University of Sfax, Sfax, Tunisia

Regulating the catalytic activity of alpha-Amylase enzymes can decrease glucose production during the postprandial phase, potentially offering therapeutic benefits for diabetes. This research aimed to assess the inhibition of α-amylase using crude extracts from Saussurea costus, a medicinal plant traditionally used for treating diabetes and its associated complications. Two novel potent proteinaceous amylase inhibitors: ScAI-R and ScAI-L were purified and characterized from Saussurea costus roots and leaves. The pure inhibitors exhibited an apparent molecular weight of about 16 kDa and a high N-terminal sequence identity (81%) with the monomeric α-amylase inhibitors from Kengyili amelanthera and Triticum dicoccoides. In addition to their significant stability at extreme pH values (2.0 to 12.0) and temperatures (100 °C), the structural integrity of both inhibitors was remarkably enhanced in the presence of divalent cations such as Mg 2+ , Ca 2+ , and Hg 2+ at 5 mM. Interestingly, the half-maximal inhibitory concentrations of ScAI-R (IC50 = 23 µg/mL) or ScAI-L (IC50 = 28 µg/mL) against human salivary amylase against were comparable to that of the standard drug acarbose (IC50 = 23 µg/mL). Both purified inhibitors acted as non-competitive inhibitors with Ki values of 0.38 and 0.32 µM, respectively, and displayed the highest affinities towards human salivary and pancreatic α-amylases (up to 90% inhibitory activity) and, to a lesser extent, porcine pancreatic α-amylase (~70% inhibitory activity). Furthermore, these inhibitors exhibited efficient antimicrobial activities against Gram (-) and Gram (+) bacteria, as well as fungal strains. Cytotoxicity towards the human cancer colorectal cells LoVo and HCT-116 with an IC50 of up to 50 µg/mL was also observed. Thus, Saussurea costus α-amylase inhibitors could be potential candidates for hyperglycemic control in diabetic and colorectal cancer patients.