Lipid absorption: passing through the unstirred layers, brush-border membrane, and beyond

Area of Science:

• Gastroenterology and Nutritional Science
• Cell Biology
• Biochemistry

Background:

• Lipids are essential dietary components and cellular building blocks, influencing numerous physiological and pathological processes.
• Triglycerides, phospholipids, and cholesterol are key dietary lipids with critical roles in cell membranes and metabolic pathways.
• Lipid metabolism is implicated in brain development, inflammation, atherosclerosis, and aging.

Purpose of the Study:

• To review recent advances in understanding lipid digestion and absorption mechanisms in the gastrointestinal tract.
• To highlight the physicochemical factors governing lipid assimilation and transport.
• To explore the roles of microclimates, lipid-binding proteins, and intracellular trafficking in lipid uptake.

Main Methods:

• Analysis of enzymatic hydrolysis of dietary and biliary lipids in the duodenum.
• Investigation of lipid product passage across the intestinal unstirred water layer and brush-border membrane.
• Review of studies examining lipid absorption based on composition, chain length, and saturation.

Main Results:

• Lipid digestion relies on pancreatic enzymes and bile acid solubilization, forming mixed micelles.
• Passage across the unstirred water layer is rate-limiting for long-chain fatty acids and cholesterol.
• An acidic microclimate facilitates micellar dissociation and lipid monomer uptake by enterocytes.

Conclusions:

• Lipid absorption is a complex, multi-step process influenced by lipid properties and the intestinal environment.
• Recent research has shed light on microclimates, intracellular lipid handling, and distinct enterocyte lipid pools.
• Understanding these mechanisms is vital for addressing lipid-related health conditions and optimizing dietary interventions.