lipolyse

Lipolyse, or lipolysis, is the enzymatic breakdown of lipids. In humans the principal form occurs in adipose tissue, where stored triglycerides are hydrolyzed into glycerol and free fatty acids (FFAs) that are released into the circulation to supply energy during fasting or physical activity. Lipolysis also plays a role in lipid remodeling in other tissues.

Biochemical mechanism and enzymes: Lipolysis proceeds through a sequence of three main steps catalyzed by distinct enzymes. Adipose triglyceride lipase (ATGL) initiates the process by converting triglycerides to diacylglycerol. Hormone-sensitive lipase (HSL) then cleaves diacylglycerol to monoacylglycerol, which monoacylglycerol lipase (MGL) finally hydrolyzes to glycerol and FFAs. Regulation is tightly controlled by hormonal signals. Catecholamines via β-adrenergic receptors raise cAMP and activate protein kinase A, stimulating lipases. Insulin inhibits lipolysis by lowering cAMP levels and promoting dephosphorylation of the enzymes. Other signals, such as glucagon and natriuretic peptides, can also modulate lipolysis in specific tissues.

Physiological role and clinical relevance: Lipolysis supplies energy during fasting and exercise and helps maintain lipid homeostasis. In obesity and insulin resistance, dysregulated lipolysis can elevate plasma FFAs, contributing to ectopic fat deposition and metabolic disturbances, including hepatic steatosis and impaired insulin signaling. Genetic defects affecting lipases (for example ATGL deficiency) can cause disorders of lipid mobilization and storage.

Cosmetic and clinical applications: In some contexts, lipolyse refers to injectable fat-dissolving treatments marketed for localized body fat reduction, often using phosphatidylcholine/deoxycholate formulations. Evidence for efficacy and safety varies, and such approaches should be considered carefully within medical supervision, not as a substitute for lifestyle modification or surgical options.