Orlistat

Overview

Orlistat is a semi-synthetic derivative of lipstatin, a natural product isolated from Streptomyces toxytricini. It is a potent and selective inhibitor of pancreatic and gastric lipases — the enzymes responsible for hydrolysing dietary triglycerides into absorbable monoglycerides and fatty acids. By blocking approximately one-third of dietary fat absorption, orlistat reduces caloric intake at the gastrointestinal level without affecting appetite centres or systemic metabolism. Marketed as Xenical (prescription) and Alli (OTC), it remains one of the longest-studied anti-obesity compounds with over 25 years of clinical data.

Mechanism of Action

Orlistat forms a covalent bond with the serine residue at the active site of pancreatic lipase, irreversibly inactivating the enzyme. This prevents hydrolysis of dietary triglycerides into absorbable free fatty acids and 2-monoacylglycerol. Approximately 30% of ingested dietary fat passes through the GI tract unabsorbed and is excreted. The mechanism is entirely peripheral — orlistat is minimally absorbed systemically (<1%), with its action confined to the intestinal lumen. This local mechanism produces weight reduction through caloric deficit rather than through central appetite suppression or metabolic rate changes.

Research Applications

• Pancreatic lipase inhibition and enzyme kinetics research
• Gastrointestinal lipid absorption pathway studies
• Peripheral vs central anti-obesity mechanism comparison
• Dietary fat metabolism and energy balance research
• Intestinal lipase structure-activity relationship studies