Inhibiting gastrointestinal α-amylases, α-glucosidases and glucose transporters can alleviate postprandial hyperglycaemia, a major risk factor for metabolic diseases. Orally administered antihyperglycemic agents (OHAs), like acarbose, help manage diabetes but are associated with numerous side effects, especially gastrointestinal, and are unsuitable for patients with irritable bowel syndrome or organ dysfunction1. Therefore, there is interest in food-based compounds with similar but milder effects to reduce metabolic disease risk and the adverse effects of OHAs in the management of diabetes.
We developed a complete in vitro protocol to accurately assess human carbohydrate digestive enzyme activities2 and glucose transport3 with high sensitivity and reliability. Sugars in enzyme assays (substrates and products) and cell transport assays, and any endogenous sugars in the test compounds/extracts, are quantified directly and simultaneously by specialised ion chromatography. We use commercially-available human α-amylases to assess starch hydrolysis and brush border α-glucosidases derived from differentiated human intestinal Caco-2/TC7 cells to assess disaccharide hydrolysis, while 2-deoxy-D-glucose transport is measured across Caco-2/TC7 cell monolayers.
We have successfully used this approach to screen for potential inhibitors and uncover specific mechanisms of action and structure-function relationships. For example, we confirmed that quercetagetin, a polyphenol in spinach, blocks human salivary α-amylase by binding to both starch and the enzyme4, while also inhibiting human α-glucosidase activities5. Methoxylated anthocyanidins found in berries directly inhibit pancreatic α-amylase6, while polyphenols found in walnut inhibit both salivary and pancreatic α-amylases and intestinal glucose transport3.
Our method will benefit researchers involved in the discovery and development of novel agents for the prevention and management of diabetes. Notably, we have identified several inhibitors that may be useful in regulating postprandial glycaemia in vivo, but with lesser gut symptoms than OHAs. We also exploit this technique to measure skeletal muscle glucose uptake in vitro and assess intestinal epithelial permeability using sugar probes in vivo7.