Interactions between biliary lipid micelles and intestinal brush border membranes investigated by 1H and 31P nuclear magnetic resonance

Nutrients central to maintaining intestinal absorptive efficiency and barrier integrity with fowl

The small intestinal mucosa acts to recover nutrients from the lumen while providing a barrier against potential hazards. Its unstirred water layer (USWL) at the lumen interface involves membrane associated mucin linearly protruding from underlying microvilli that entangles secretory mucin released from local goblet cells. Both mucin sources are dominated by repetitive O-glycosylated areas dependant on threonine, serine, glycine, and proline. Secretory mucin differs from membrane attached mucin by further employing multiple cystines that interconnect these areas into a net-like molecular sieve. All of the glycosylated areas have ionizable acidic groups credited with reducing pH from that in the lumen to create a micro environment favoring enzymes finalizing digestion while optimizing nutrient terms for absorption. Erosion of the USWL and/or abuse of the membrane due to lumen threats require continuous repair. The aforementioned amino acids are necessary in substantial amounts while vitamin B6 collaborates with vitamin A as meaningful cofactors for mucin synthesis. Marginal inadequacies of these nutrients during inordinate demand are expected to impair mucin replacement. In turn, marginal increases in feed conversion likely occur while fostering the probability of necrotic enteritis together with gizzard erosions. Abuse of the absorptive membrane is of particular concern from fatty acid hydroperoxides because of their continual presence in feed and inability of the USWL to provide protection. These hydroperoxides threaten membrane integrity by their inclusion in micelles during digestive events with fat thereby permitting transit through the USWL. Once coalesced with membrane phospholipids, structural aberrations are visualized as interfering with nutrient recovery while enabling leakage of cell contents to potentiate wet excreta. Inclusion of dietary vitamin E along with vitamin A into micelles with fatty acid hydroperoxides provides relief by quenching further peroxidation. Assuring cystine, threonine, glycine, and serine that are directly available as such together with vitamins A, E, and B6 represents one approach toward optimizing maintenance of the intestinal mucosa.

Static and magic angle spinning (31)P NMR spectroscopy of two natural plasma membranes

Static and magic angle spinning (31)P NMR spectroscopy was used for the first time in natural plasma membranes from erythrocytes and skeletal muscle to study phospholipid arrangement and composition. Typical static powder-like spectra were obtained showing that phospholipids were in a bilayer arrangement. Magic angle spinning narrowed spectra into two components. The first one corresponded to phosphatidylcholine and the second one to the other phospholipids with intensities in agreement with the known phospholipid composition. These findings show that NMR data previously acquired using model membranes can be transposed to studies on phospholipids in their natural environment.