Acarbose, a low-MW synthetic tetrasaccide inhibitor of alpha-amylase, is one of the best-known prescription drugs used to reduce blood glucose and insulin levels among those diagnosed with diabetes as well as cardiovascular risk factors in metabolic syndrome patients.
Studies have demonstrated the ability of certain phytoconstituents and plant species to block a-amylase enzyme activity and block its digestion of starch; this is used as the foundation for many commercial anti-diabetic drugs to slow carb breakdown to mitigate postprandial blood glucose spikes.
Physico-Chemical Properties
Chemical analyses of alpha-amylase inhibitors (AAI) from taro root (Colocasia esculenta) and ragi (Eleusine coracana) seeds have revealed their chemical properties to be powerful alpha-amylase blockers. They bind directly to the active groove of alpha-amylase, inhibiting its function by binding to four of five sugar binding sites of its active groove, thus rendering substrate binding impossible.
AAI exhibits a knottin-like structure, consisting of three domains. The largest domain contains an eight-stranded parallel b-barrel with chloride binding sites while its wall. Meanwhile, another domain contains four antiparallel b-strands arranged helically that contain calcium binding sites against this wall of AAI’s large domain.
AAI interacts with an enzyme through hydrogen bonds, electrostatic forces and Van der Waals interactions. Hydrophobic interactions between the inhibitor and protein residues of -amylase are vital for its high inhibition activity; their C=C double bond increases this interaction significantly while simultaneously occupying hydrophobic regions within active grooves – essential features that allow AAI to exert potent inhibition activities.
Molecular Starch-Blocking Mechanism
Starch-guest complexes form due to physical forces and interactions between non-polar guest molecules and hydrophobic interiors of amylose helices. Techniques like size-exclusion chromatography, fluorescence-assisted capillary electrophoresis and high-performance anion-exchange chromatography can be used to assess starch CLD and molecular size distribution.
Due to their physical properties, inhibitor extracts offer great promise as potential ingredients to increase carbohydrate tolerance in diabetics and decrease energy intake to combat obesity; their specific efficacy depends on processing and extraction techniques used. These inhibitors have been found to decrease postprandial plasma glucose and insulin levels as a result of distal ileum enterocytes absorbing undigested starch that passes digestion sites (reference Brugge and Rosenfeld63-64; Jain, Boivin, Zinsmeister and DiMagno66-67; Kotaru Iwami Yeh and Ibuki73). Mice given inhibitors also displayed increased butyrate output when compared with controls (Reference Yoshikawa, Kotaru and Nishizawa74), possibly due to reduced gastric secretions like chymotrypsin and pepsin production.
Anti-Obesity and Anti-Diabetes Effects
Interrupting alpha-amylase has many health-related applications. One such benefit is to promote weight loss by slowing carbohydrate absorption, increasing feelings of satiety and suppressing appetite. Other potential applications of alpha-amylase inhibition include diabetes management; for instance lowering postprandial hyperglycemia can significantly decrease long-term complications like hypertension, high triglyceride levels (especially high triglycerides), nonalcoholic fatty liver disease, cardiovascular diseases and vascular problems.
Alpha-amylase inhibitors may also play an integral part in preventing dental caries by decreasing starch breakdown in the mouth, thus decreasing oral bacteria’s ability to produce acids which erode tooth enamel. Thus, finding natural plant extracts with anti-diabetic properties through alpha-amylase inhibition has become an active area of research.
At present, the best known artificial insulin is Acarbose – a low molecular weight synthetic tetrasaccide sold as a prescription drug to treat type-2 diabetes. Not only does it lower blood glucose levels but it improves insulin sensitivity as well as reduce risks of metabolic syndrome (a cluster of risk factors including elevated triglycerides, low HDL cholesterol levels and high blood pressure). Furthermore, postprandial hyperglycemia is prevented with Acarbose.
Safety of Extracts
Polyphenols have been demonstrated to exert significant a-amylase inhibitory activity. Their chemical structures vary, which affects their binding abilities at the active site of a-amylase; those containing three or more hydroxyl groups on their A rings of flavonols (such as 7-hydroxyflavone, chrysin, baicalein and apigenin) show the greatest affinity.
Proteinaceous a-amylase inhibitors work by creating interactions between a-amylase and its inhibitor, creating multiple hydrogen bonds, salt bridges, and electrostatic forces which prevent substrate from entering the enzyme-inhibitor complex and thus blocking activity of a-amylase enzymes. According to molecular weight and structural characteristics these interactions may also be classified as steric hindrance or electrostatic interaction; or hydrogen bonding.
Cytotoxicity of extracts was assessed through testing their impact on human lymphocyte proliferation. Results demonstrated that all botanical extracts tested (PAL, PUR, FRA, Rhamnus purshiana and Cassia senna) did not induce any toxicities at concentrations used for in vitro micronucleus testing.