High density lipoprotein metabolism.

Lipoproteins and their receptors in the central nervous system. Characterization of the lipoproteins in cerebrospinal fluid and identification of apolipoprotein B,E(LDL) receptors in the brain.

Animal lipoproteins: chemistry, structure, and comparative aspects.

The role of the human intestine has been explored as a site of synthesis of apoA-IV, a major apoprotein of human intestinal triglyceride-rich lipoproteins. Intestinal biopsies were performed on normal volunteers while fasting and after lipid ingestion. Indirect immunofluorescence demonstrated a marked increase in immunofluorescence for apoA-IV during lipid absorption consistent with an increased intracellular content. ApoA-IV comprised 10-13% of chylomicron apoprotein and 24-30% of intestinal very low density lipoprotein (VLDL) as assessed by densitometry of sodium dodecyl sulfate gels of lipoproteins from chylous urine (mesenteric lymphatic-urinary fistula) and thoracic duct lymph (postoperative fistula). After one subject with chyluria ingested 40 g of corn oil, triglyceride excretion in urine was accompanied by an increased excretion of apoA-IV. 11.5 g of triglyceride and 81 mg of apoA-IV were recovered in the urine. In chylous urine 56% of apoA-IV was in the triglyceride-rich lipoproteins (chylomicrons and intestinal VLDL) and 44% in the d > 1.006-g/ml fraction. Normal plasma apoA-IV was 15.7+/-0.9 mg/dl (n = 14) whereas four subjects with abetalipoproteinemia had reduced levels 1.2, 7.6, 9.6, and 8.3 mg/dl, respectively. Lipid feeding in normal volunteers resulted in a rise in plasma apoA-IV (16.1+/-0.7 mg/dl to 18.5+/-0.7 mg/dl, n = 5, P 1.21-g/ml fraction. In lipemic plasma, 10% of apoA-IV was associated with triglyceride-rich lipoproteins and 90% with the d > 1.21-g/ml fraction. Agarose column chromatography of fasting plasma confirmed that the bulk of plasma apoA-IV is free, unassociated with lipoproteins. These results demonstrate that apoA-IV is present in human intestinal epithelial cells and is secreted as a chylomicron and VLDL apoprotein. Within fasting plasma most of the apoA-IV is found free, unassociated with lipoproteins. After lipid ingestion apoA-IV is also found in plasma chylomicrons indicating that some apoA-IV remains associated with chylomicrons in plasma during chylomicron metabolism, although some may be transferred from the chylomicron surface.

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Human Apolipoprotein A-IV: INTESTINAL ORIGIN AND DISTRIBUTION IN PLASMA

Mechanisms and consequences of cellular cholesterol exchange and transfer

Composition of proteins of mesenteric lymph chylomicrons in the rat and alterations produced upon exposure of chylomicrons to blood serum and serum proteins.

Secretion of the arginine-rich and A-I apolipoproteins by the isolated perfused rat liver.

Apoprotein content of plasma lipoproteins of the rat separated by gel chromatography or ultracentrifugation.

Radioimmunoassay of arginine-rich apolipoprotein of rat serum.

Origin and transport of the A-I and arginine-rich apolipoproteins in mesenteric lymph of rats.

Menahem Fainaru

Papers

Composition of proteins of mesenteric lymph chylomicrons in the rat and alterations produced upon exposure of chylomicrons to blood serum and serum proteins.

Secretion of the arginine-rich and A-I apolipoproteins by the isolated perfused rat liver.

Apoprotein content of plasma lipoproteins of the rat separated by gel chromatography or ultracentrifugation.

Radioimmunoassay of arginine-rich apolipoprotein of rat serum.

Origin and transport of the A-I and arginine-rich apolipoproteins in mesenteric lymph of rats.