Triglyceride-Rich Lipoproteins and Plasma Lipid Transport

Abstract

Abstract-This memoir provides a history of the triglyceride-rich lipoproteins of blood plasma over the last half-century.As precursors of low-density lipoproteins and in their own right, triglyceride-rich lipoproteins are essential to the formation of atherosclerotic plaques and to consequent ischemic vascular disease. The author recounts research at the National Heart Institute during 1953 to 1956 and continuing thereafter at the University of California San Francisco. Emphasis is placed on key insights arising from investigations of human disease, the interplay of fatty acid and triglyceride-transport involving the liver, small intestine, adipose tissue and muscle, and the role of the liver in the synthesis and catabolism of atherogenic lipoproteins. (Arterioscler Thromb Vasc Biol. 2010;30:9-19.)Key Words: chylomicrons Ⅲ very low-density lipoproteins Ⅲ apolipoproteins Ⅲ lipoprotein receptors Ⅲ atherosclerosis I n 1951, I was one of 8 residents at East Coast medical schools recruited by James Shannon to the National Heart Institute as Clinical Associates to provide care for patients in the Clinical Center of the National Institutes of Health (NIH). At the time, many house officers were being drafted into the U.S. Army for service in Korea. To obviate loss to a "mash" unit, we immediately joined the U.S. Public Health Service. Owing to delays in opening the Clinical Center, I was able to finish my residency at New York Hospital/Cornell Medical Center, arriving in Bethesda in 1953, where by chance I admitted the first inpatient on July 1. In addition to caring for patients our group was expected to engage in research. We were advised to "look around" and select a basic science laboratory to join. During planning for the Clinical Center, Shannon, aware that virtually no NHI scientists were doing "heart" research, asked laboratory heads to suggest appropriate disease-related areas. Christian B. Anfinsen, a protein chemist (and later Nobel laureate for his work on proteinfolding), perused the literature and suggested two topics related to plasma lipids. The first was to investigate the lipemia "clearing factor." At the University of Rochester, Paul Hahn had made a serendipitous observation: in dogs given intravenous heparin, the opalescence of blood plasma occurring postprandially rapidly disappeared. 1 Anfinsen suspected that a protein might be released into the blood by heparin. The second was to investigate the plasma lipoproteins recently described by John Gofman and his students at the University of California Berkeley. They discovered that lipoproteins can be separated from serum by ultracentrifugation and quantified in an analytic ultracentrifuge; and they had reported that a low-density group of these giant macromolecules are risk markers for coronary heart disease. 2 As a result, Anfinsen was asked to organize a new Section in the Laboratory of Metabolism in 1951. Of the 8 who arrived in 1953, Donald Fredrickson, Robert Gordon, and I joined this Section. Research at the National Heart Institute (1953 to 19...

Lipidomic profiling reveals protective function of fatty acid oxidation in cocaine-induced hepatotoxicity

“…With regard to the metabolic events associated with decreased fatty acid oxidation, one interesting observation in this study was the lack of change in serum TAG level on day 3 of cocaine treatment in contrast to the dramatic change in hepatic TAG level ( Fig. 1C, D ), since fatty acids not used for oxidative metabolism in the liver were usually incorporated into TAG and then secreted into the blood via very low density lipoprotein (VLDL) ( 56 ). It has been shown that microsomal TAG transfer protein (MTP), which is responsible for assembling VLDL, is inhibited by other known inhibitors of mitochondrial ␤ -oxidation ( 57 ).…”

Recent advances in physiological lipoprotein metabolism

“…As the chylomicron circulates, the core triglyceride undergoes hydrolysis by endothelial bound LPL with entry of fatty acids into muscle for energy production and adipocytes for storage. In the two-step model, the remaining relatively triglyceride-depleted chylomicron 'remnant' particles which are enriched in cholesteryl ester (from both dietary-and HDLderived cholesteryl ester) and apoE enriched can interact with receptors on hepatocytes and be removed from the circulation [69]. All CMs usually disappear from the circulation within 12-14 h after a meal [70].…”

Genetic determinants of plasma triglycerides

“…These results were generated based on the HTG subject cohort reported in the GLGC ( 19 ) ( 31,62 ). The APOC2 mutations were fi rst defi nitively shown to cause HTG after they were characterized at the amino acid level ( 40 ). Rare heterozygous LPL mutations also accumulate in patients with late-onset HTG ( 32 ) and were observed in ‫ف‬ 6.4% of these patients ( 53 ).…”