Chylomikronien

Chylomikronien are the largest class of lipoproteins, which are complex particles consisting of lipids and proteins. They are assembled in the cells of the small intestine and are primarily responsible for transporting dietary fats, such as triglycerides and cholesterol, from the intestine to various tissues throughout the body. Specifically, they deliver these fats to muscle and adipose tissue for energy or storage.

The formation of chylomikronien begins after a meal rich in fats. Inside the intestinal cells, absorbed fatty acids and monoglycerides are reassembled into triglycerides and then packaged with cholesterol, phospholipids, and apolipoproteins into nascent chylomikronien. The main apolipoprotein associated with chylomikronien is apolipoprotein B-48 (ApoB-48), which is crucial for their assembly and secretion.

Once secreted into the lymphatic system, chylomikronien bypass the portal vein and enter the bloodstream indirectly through the thoracic duct. In the circulation, they undergo several transformations. They acquire other apolipoproteins, such as ApoC and ApoE, from high-density lipoproteins (HDL). Enzymes like lipoprotein lipase (LPL), found on the surface of capillary endothelial cells, hydrolyze the triglycerides within the chylomikronien, releasing free fatty acids that are then taken up by surrounding tissues.

As triglycerides are removed, the chylomikronien shrink and become chylomicron remnants. These remnants, enriched in cholesterol, are eventually cleared from the circulation by the liver through receptors that recognize ApoE. The liver then processes the cholesterol and other components. Disruptions in chylomikron metabolism can lead to the accumulation of fats in the blood, a condition known as hypertriglyceridemia, and can be associated with various health issues.