Lipoproteins and their metabolism
Paul Durrington in Hyperlipidaemia 3Ed, 2007
The lipoproteins are macromolecular complexes of lipids and protein (Figure 2.1). Great diversity of composition and physical properties are possible, particularly in disease but also in health. As such, their classification and definition is particularly difficult. Each lipoprotein has a wide range of components, each with its own metabolic origin and fate. The components of lipoprotein undergo a complex metabolic interplay with receptors and with enzymes located on the lipoproteins, and on the capillary endothelium and between the circulating lipoproteins themselves, both in the vascular compartment and within the tissue fluid space. It is thus naive in the extreme to try to think of serum cholesterol or triglycerides in the same way as serum sodium or glucose, which are transported simply as solutes. The very existence of lipids within the circulation is dependent on lipoproteins.
Role of Lingual and Gastric Lipases in Fat Digestion and Absorption
Margit Hamosh in Lingual and Gastric Lipases: Their Role in Fat Digestion, 2020
This chapter discusses the specific function of the pancreatic digestive enzymes in both physiological and pathological pancreatic insufficiency; their role in fat digestion in normal conditions. Fat digestion and absorption in the absence of pancreatic lipase could be attributed to the activity of prepancreatic lipolytic enzymes. Further studies on the gastric hydrolysis of milk fat in rats were conducted by several groups of investigators in suckling rats at 10 to 14 d of age. Studies in rats (a species with lingual lipase as the main preduodenal digestive enzyme) have shown that marked changes occur in the stomach to the ingested milk fat. Studies on the mechanism of hydrolysis of milk fat by lingual lipase were conducted by S. Patton et al. using milk fat globules prepared from human milk and patially purified lingual lipase. The products of lingual lipase activity, protonated fatty acids and diglyceride, appear to remain dissolved in the triglyceride core of the milk fat globule.
Emulsifiers, fats and foams
Sharon Croxford, Emma Stirling in Understanding the Science of food, 2020
This chapter explains the process of tempering chocolate. It describes colloid systems and their properties and explains emulsions and foams and how they are formed. Fats and oils provide flavour and texture to food and influence melting points, facilitate heat transfer, add tenderness through shortening gluten in bakery products, form emulsions and add to foods’ appearance. Fats and oils exists in three major crystal forms, and the proportion of each form and the crystal network structure produced in a food determine the ultimate melting point, and this determines texture, stability, spreadability and mouthfeel. The nanostructure of fat crystal networks relates to the type of fatty acids, triglyceride structure and the formation of crystals. Food fats and oils are mixes of many different triglycerides and thus fatty acids. Australian extra virgin olive oil wins prizes around the world and is growing into a major global player.
Clinical Chemistry: Turnover of Plasma Total and Very Low Density Lipoprotein Triglyceride in Man
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 1975
Kekki, M. & Nikkilä, E. A. Turnover of Plasma Total and Very Low Density Lipoprotein Triglyceride in Man. Scand. J. clin. Lob. Invest. 35, 171–179, 1975. Basal plasma total triglyceride and very low density lipoprotein (VLDL) triglyceride turnover rates were determined in 110 subjects whose triglyceride concentrations ranged from low normal to markedly elevated values. The mean total triglyceride turnover rate was 13.7 mg. kg−l. hr−1, whereas the mean VLDL triglyceride turnover rate was 13.2 mg · kg−1. hr−1. A highly significant correlation was present between the two turnover rates (r = +0.75). The endogenous serum triglyceride transported in the other lipoproteins (LDL and HDL) may account for more than half of the circulating triglyceride mass, but its significance in the total triglyceride transport is small. In a selected subgroup of 31 healthy subjects the plasma VLDL triglyceride concentration did not exceed 160 mg/100 ml. The range of this group's triglyceride turnover rate was completely comparable with most data reported in the literature for total serum or VLDL triglyceride transport in normal human subjects. When the turnover rate was plotted against the VLDL triglyceride concentration, three kinetic subgroups could be separated in accordance with the earlier experience on total serum triglyceride transport kinetics.
Hypertriglyceridemia Associated with Decreased Post-Heparin Plasma Hepatic Triglyceride Lipase Activity in Hypoxic Rats
Published in Archives Of Physiology And Biochemistry, 2003
H. Muratsubaki, K. Enomoto, Y. Ichijoh, Y. Yamamoto
Exposure of sated rats to 45% N2 in air for 5 h increased serum triglyceride levels by 212% over the levels in normoxic rats. This increase in triglyceride levels was accompanied by a decrease in plasma triglyceride hydrolase activity after intravenous injection of heparin. Further fractionation of the activity by inhibition of lipoprotein lipase indicated that the low triglyceride hydrolase activity is mainly due to a reduction in hepatic triglyceride lipase, which is inversely correlated with the serum triglyceride level. The hypoxic exposure decreased the arterial blood [acetoacetate]/[β-hydroxybutyrate] ratio in the sated rats, which is believed to reflect the oxidation-reduction state in hepatic mitochondria, but did not affect the level of serum enzymes indicative of tissue damage. On the other hand, triglyceride levels did not change during hypoxic exposure in fasted rats. Thus, hypertriglyceridemia in sated rats following exposure to hypoxia may result from impaired removal of circulating triglycerides by hepatic triglyceride lipase located in the sinusoidal surface of the liver.
The Effect of Lipid Peroxide on the Lipid and Carbohydrate Metabolism in Rat Liver
Published in Agricultural and Biological Chemistry, 1973
Nobukazu Shibata, Toyosuke Kinumaki, Hiromichi Okuda, Setsuro Fujii
Feeding tests were carried out on rats to clarify the mechanisms of fatty liver formation induced by autoxidized methyl linoleate. Lipid peroxides prepared by autoxidation of highly purified methyl linoleate were given orally to rats. Triglyceride and glycogen contents in liver were determined and enzyme activities including triglyceride synthetase and α-glycerophosphate dehydrogenase were also examined. The following results were obtained. 1. Triglyceride accumulation in rat liver fed autoxidized methyl linoleate was observed. 2. Increase in triglyceride content in rat liver was soon followed by the decrease of hepatic glycogen. 3. When rats were starved prior to introduction of autoxidized methyl linoleate, hepatic triglyceride accumulation did not occur. 4. The activities of α-glycerophosphate dehydrogenase and triglyceride synthetase in liver, and those of glutamic oxalacetic transaminase and leucine aminopeptidase in plasma were practically similar among the rats of test groups fed fresh or autoxidized methyl linoleate and the control fed diet without methyl linoleate. 5. The addition of l-carnitine which is a stimulator of fatty acid oxidation retarded the accumulation of the hepatic triglyceride mentioned above.
Related Knowledge Centers
- Adipose Tissue
- Lipid
- Fatty Acid