Permeabilization of enterocytes induced by absorption of dietary fat

Abstract

Absorption of dietary fat in the small intestine involves epithelial exposure to potentially harmful molecules such as bile salts and free fatty acids. We used organ culture of porcine jejunal explants incubated with a pre-digested mixture of fat (plant oil), bile and pancreatin to mimick the physiological process of dietary fat absorption, and short exposures to the fat mixture caused fat droplet accumulation within villus enterocytes. Lucifer yellow (LY), a fluorescent membrane-impermeable polar tracer was included to monitor epithelial integrity. Both in controls and during fat absorption LY penetrated the epithelium and accumulated in the basal lamina and the lamina propria. LY was also seen in the paracellular space, whereas villus enterocytes were generally only weakly labeled except for small amounts taken up by apical endocytosis. In the crypts, however, fat absorption induced cell permeabilization with LY accumulating in the cytosol and nucleus. Morphologically, both apical and basolateral membranes appeared intact, indicating that the leakiness was caused by minor lesions in the membrane. Albeit to a lesser extent, bile alone was capable of permeabilizing crypt cells, implying that the surfactant properties of bile salts are involved in the process. In addition to LY, crypt enterocytes also became permeable for albumin, ovalbumin and insulin. In conclusion, during fat absorption the permeability of the gut epithelium is increased mainly in the crypts. A possible explanation is that cell membranes of immature crypt cells, lacking detergent-resistant lipid raft microdomains, are less resistant to the deleterious effects of bile salts and free fatty acids.

Keywords::

• Dietary fat absorption
• small intestine
• Lucifer yellow

Acknowledgements

The study was supported by grants from Augustinus Fonden (Grant number 11-0253), Aase og Ejnar Danielsens Fond (Grant number 1´0-000128), Brødrene Hartmanns Fond (Grant number A11481), Fonden til Lægevidenskabens Fremme (Grant number 10-58), and Hørslev Fonden (Grant number 203866-MIA). E.M.D. planned and supervised the study and wrote the manuscript. G.H.H. participated in designing the experiments, discussion of results and drafting of the manuscript. K.R. and L.-L. N.-C. performed the major part of the experimental work and participated in the discussion of the results.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.