The Problem and Therapeutic Approach
In diabetes mellitus, the body faces a state of persistent, chronic elevation in blood glucose. A particularly challenging issue is postprandial hyperglycemia—a sharp spike in blood sugar concentrations that occurs immediately following the ingestion of carbohydrate-rich meals.
To control this condition, drugs such as acarbose are utilized. Chemically, this compound is a pseudotetrasaccharide. The primary function of acarbose is to act as an inhibitor of the enzymes responsible for carbohydrate digestion in the gastrointestinal tract.
Normal Carbohydrate Digestion Pathway
To understand the mechanism of action of these inhibitors, it is necessary to review the normal biochemical cascade of carbohydrate hydrolysis in the intestine. The process occurs in several steps involving specific enzymes:
- Polysaccharide breakdown: Starch and glycogen are broken down by pancreatic alpha-amylase into shorter fragments—dextrins, as well as disaccharides (maltose and isomaltose).
- Maltose hydrolysis: The disaccharide maltose is split into two free glucose molecules by the enzyme maltase.
- Isomaltose hydrolysis: Isomaltose is likewise cleaved into two glucose molecules by isomaltase.
- Sucrose hydrolysis: The enzyme sucrase cleaves sucrose into glucose and fructose.
- Lactose hydrolysis: Under the influence of lactase, milk sugar (lactose) is broken down into glucose and galactose.
Mechanism of Action of Acarbose
Acarbose acts via competitive inhibition. This means that the drug molecule is structurally very similar to the natural substrate (oligosaccharide). Because of this structural similarity, acarbose binds to the active sites of the enzymes, blocking access for dietary carbohydrates.
The primary target of the drug is the alpha-glucosidase complex, which is localized on the brush border of enterocytes (small intestinal epithelial cells). The enzymes most sensitive to the drug include:
- Glucoamylase
- Sucrase
- Maltase
To a somewhat lesser extent, the drug can also inhibit the activity of pancreatic alpha-amylase. As a result, the enzymatic breakdown of poly- and oligosaccharides in the lumen of the small intestine is reliably blocked.
Biochemical and Clinical Outcome
Blocking the brush-border enzymes triggers a sequential chain of favorable biochemical changes. Because complex carbohydrates cannot be rapidly broken down into monosaccharides, the release of free glucose from the food bolus is delayed.
Consequently, the rate of glucose absorption into the bloodstream drops significantly. Clinically, this means that the peak blood glucose concentration is blunted, effectively reducing postprandial hyperglycemia. The body avoids sharp glycemic spikes after meals, which is critical for the management of diabetes mellitus.