Formation and transport of chylomicrons by enterocytes to the lymphatics

Abstract

Digestion of triglyceride in the intestine results in the production of 2-monoglyceride and fatty acid. Phosphatidylcholine is hydrolyzed in the lumen to form lysophosphatidylcholine before its absorption. These digestion products are absorbed by the enterocytes through simple diffusion. In contrast, cholesterol absorption seems specific and is energy dependent. After entry into the enterocytes, these lipid digestion products migrate to the endoplasmic reticulum. Both fatty acid-binding protein and sterol carrier protein may be involved in the intracellular transport of fatty acid and cholesterol, respectively. Through predominantly the monoglyceride pathway, monoglycerides and fatty acids are resynthesized to form triglyceride in the endoplasmic reticulum. The lipid droplets, coated with cholesterol, phospholipid, and apolipoproteins, are then further processed in the Golgi apparatus before being released by the enterocytes through exocytosis. As yet, little is known of the factors regulating the formation and release of these chylomicrons by the enterocytes. Although apolipoprotein B is a prerequisite for the formation of chylomicrons, the question of whether its supply is rate limiting for chylomicron formation remains to be demonstrated. Other factors that may play a role in chylomicron formation are luminal phospholipid supply, Ca2+, and microtubules. Chylomicrons and very low-density lipoproteins are probably produced by the enterocytes via different pathways. For example, Pluronic L-81, a hydrophobic surfactant, affects only chylomicron formation and has little effect on very low-density lipoprotein production. The movement of chylomicrons from the intercellular space through the basement membrane to the lamina propria is not fully understood. Once inside the lamina propria, the movement of chylomicrons is probably by diffusion and is greatly facilitated by interstitial hydration; thus the lymphogogic effect of fat absorption may serve an important function for the transfer of chylomicrons from the enterocytes to the lacteal.

Development of the lymphatic system: new questions and paradigms

“…In addition, lymphatic vessels play an important role in immune surveillance in mammals, serving as the main conduit of antigens and antigen-presenting cells from the periphery to lymph nodes, thus allowing the initiation of the immune response (Alitalo and Carmeliet, 2002). Finally, the lymphatic system is crucial for the absorption of dietary fats (Tso and Balint, 1986).…”

Intravital imaging of intestinal lacteals unveils lipid drainage through contractility

“…More importantly, in vitro models inevitably possess artificial condi tions that are quite different from natural physiological conditions in the lamina propria of villi. Most in vivo methods use lymph (9,10) or vein (11) fistula from rats for collecting lipids assembled by enterocytes or a perfusion model (12) for the intestinal permeabil ity test, and these in vivo methods have provided only an indirect view of lipid absorption dynamics in the villi at the cellular level.…”

A possible role for rat intestinal surfactant-like particles in transepithelial triacylglycerol transport.

“…The difference in intercellular lipid packaging has been reinforced by experiments using the nonionic hydrophobic surfactant, Pluronic L-8 1. This compound, when given intraluminally by continuous infusion or by bolus injection, caused a decrease in chylomicron formation and transport (13). The formation and packaging of VLDL particles was not affected by Pluronic L-8 1 ( 14).…”