Cholesterol Absorption: Mechanism & Treatment
Cholesterol absorption describes the uptake of cholesterol from the intestine into the body. It influences blood cholesterol levels and is a key target in the treatment of lipid metabolism disorders.
Things worth knowing about "Cholesterol absorption"
Cholesterol absorption describes the uptake of cholesterol from the intestine into the body. It influences blood cholesterol levels and is a key target in the treatment of lipid metabolism disorders.
What is Cholesterol Absorption?
Cholesterol absorption refers to the process by which cholesterol is taken up from the small intestine through the intestinal wall into the bloodstream. Cholesterol enters the small intestine from two sources: through the diet (exogenous cholesterol) and via bile secreted by the liver into the intestine (endogenous cholesterol). In healthy adults, approximately 40–60 % of the cholesterol present in the intestine is typically absorbed.
Mechanism of Cholesterol Absorption
The uptake of cholesterol in the small intestine occurs in several steps:
- Emulsification: Bile acids and phospholipids from bile emulsify dietary fat and cholesterol, forming micelles – tiny water-soluble carrier structures.
- Transport to the intestinal wall: Micelles transport cholesterol to the surface of intestinal cells (enterocytes).
- Active uptake: A specific transport protein called NPC1L1 (Niemann-Pick C1-Like 1) mediates the active uptake of cholesterol into enterocytes. This transporter is the most important molecular mechanism of intestinal cholesterol absorption.
- Packaging and transport: Inside enterocytes, cholesterol is esterified with fatty acids and packaged into chylomicrons. These lipoprotein particles are released into the lymphatic system and subsequently enter the bloodstream.
Regulation and Influencing Factors
The amount of cholesterol absorbed is influenced by various factors:
- Diet: A high intake of saturated fatty acids and cholesterol from animal products increases the supply available in the intestine. Dietary fiber, particularly soluble fibers such as beta-glucan and pectin, can bind bile acids and thereby reduce cholesterol absorption.
- Genetics: Individual variations in the NPC1L1 gene can lead to increased or decreased cholesterol absorption.
- Bile acid production: Reduced bile production, for example in liver disease, decreases emulsification and thus reduces the rate of absorption.
- Medications: Certain drugs can specifically inhibit cholesterol absorption (see Treatment section).
Clinical Relevance
Excessive cholesterol absorption can contribute to elevated LDL cholesterol levels in the blood and increase the risk of atherosclerosis, heart attack, and stroke. In individuals with genetically inherited familial hypercholesterolemia, cholesterol absorption plays a particularly important role. Targeted inhibition of intestinal cholesterol absorption is therefore a key therapeutic approach in managing lipid metabolism disorders.
Treatment: Inhibiting Cholesterol Absorption
The most well-known drug for targeted inhibition of cholesterol absorption is ezetimibe. It blocks the NPC1L1 transporter in the intestinal wall, preventing cholesterol from being taken up into enterocytes. This lowers LDL cholesterol levels by an average of 15–20 %.
Additional strategies to reduce cholesterol absorption include:
- Bile acid sequestrants (anion exchange resins) such as cholestyramine, which bind bile acids in the intestine and prevent their reabsorption
- Dietary measures with adequate soluble fiber, for example from oats, legumes, or psyllium husk
- Plant sterols and stanols, which are structurally similar to cholesterol and competitively inhibit its intestinal uptake
References
- Ge, L. et al. (2008): The cholesterol absorption inhibitor ezetimibe acts by blocking the sterol transporter NPC1L1. Cell, 130(2), 340–349. DOI: 10.1016/j.cell.2007.04.040
- Grundy, S.M. et al. (2018): 2018 AHA/ACC Guideline on the Management of Blood Cholesterol. Circulation, 139(25). DOI: 10.1161/CIR.0000000000000625
- World Health Organization (WHO): Cardiovascular diseases – Key facts. Available at: https://www.who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds)
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