High density lipoproteins carriers

Meng QH, Hockerstedt A, Heinonen S et al. Antioxidant protection of lipoproteins containing estrogens in vitro evidence for low- and high-density lipoproteins as estrogen carriers. Biochim. Biophys. Acta 1439, 331-340, 1999. 

M. K. Bijsterbosch and T. J. C. Van Berkel, Lactosylated high density lipoprotein a potential carrier for the site-specific delivery of drugs to parenchymal liver cells, Mol. Pharmacol. 47 404-411 (1992). 

Lipids are the main component in lipoproteins known as carriers of cholesterol (2). HDL (high-density lipoprotein, which is the good cholesterol) transports cholesterol and its esters from cells to liver for recirculation, whereas LDL (low-density lipoprotein, which is the bad cholesterol) carries cholesterol and cholesterol esters to the cells. The ratio of the two carrier particles partly determines one s risk for diseases such as atherosclerosis, although the understanding and the overall view of the related issues is still incomplete in many ways. 

Cholesterol is transported to and from the cells by special carriers called lipoproteins. There are two types, low-density lipoprotein (LDL) and high-density lipoprotein (HDL). It is believed that excess LDL cholesterol can clog arteries, increasing risk of heart attack and stroke. Conversely, studies suggest that higher levels of HDL cholesterol reduce risk of heart attack. That is, the ratio of LDL to HDL appears to be important. The adverse effects of a prolonged (i.e., chronic) history of excess LDL relative to HDL is of much greater concern than acute exposures to cholesterol. 

Fig. 10. Polyunsaturated fatty acids (PUFA) modulate the effects of the APOA-IG-A polymorphism on high density lipoprotein (HDL)-cholesterol concentrations in a gender-specific manner [data from Ordovas etal. (115), reproduced with permission]. In women carriers of the A allele, higher PUFA intakes were associated with higher HDL cholesterol concentrations, whereas the opposite effect was observed in G/G women. Adjusted for age, body mass index, alcohol, smoking, intake of energy, saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. Interaction of G x PUFA, P< 0.005.

Some of the major risk factors for clinical cardiovascular disease (CVD) are increased plasma levels of low-density lipoprotein (LDL), decreased plasma levels of high-density lipoprotein (HDL), hypertension, cigarette smoking, male gender, age, and diabetes mellitus (Table I). LDL is the major carrier of cholesterol and... 

The main carriers of blood cholesterol are low-density lipoproteins (LDLs). LDLs, also called bad cholesterol, have a density of 1.04 g/cm. They are bad because they tend to deposit cholesterol on arterial walls, increasing the risk of stroke and heart attack. Cholesterol is also carried by high-density lipoproteins (HDLs). HDLs, also called good cholesterol, have a density of 1.13 g/cm. HDLs transport cholesterol to the liver for processing and excretion and therefore have a tendency to reduce cholesterol on arterial walls. Too low a level of HDLs (below 35 mg/100 mL) is considered a risk factor for heart disease. Exercise, along with a diet low in saturated fats, is believed to raise HDL levels in the blood while lowering LDL levels. 

Figure 8.10. GC eiution profiie of iow- and high-density lipoproteins of plasma from a patient with phytosteroiemia [527], A glass WCOT column (10 m x 0.25 mm i.d.), coated with SP-2330 , was maintained isothermally at 250°C with hydrogen as the carrier gas. Abbreviations c, cholesterol cam, campesterol s, p-sitosterol. (Reproduced by kind permission of the authors and oWpids, and redrawn from the original paper).

A better indication of a person s risk of heart disease comes from a measurement of blood lipoprotein levels. Lipoproteins are complex molecules with both lipid and protein parts that transport lipids through the body. They can be divided into three types according to density, as shown in Table 27.3. Very-low-density lipoproteins (VLDLs) act primarily as carriers of triglycerides from the intestines to peripheral tissues, whereas low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs) act as carriers of cholesterol to and from the liver. 

It is still difficult to reconcile completely the work of Ritter and Dempsey with that of Scallen s group on a non-catalytic carrier protein (sterol carrier protein or SCP) which is involved in the conversion of squalene into cholesterol by liver microsomes. Whereas the former workers have isolated a heat-stable protein which activates the microsomal enzymic steps for conversion of squalene into cholesterol, Scallen s group have reported a heat-labile protein with SCP properties. It has been reported that one of tlK two major apo-high-density lipoprotein peptides, apo-LP-gln II, can substitute specifically in... 

Because there were no pubUshed reports of the local effects of vitamin E on the periarticular tissue, it is necessary to determine local toxicity using animal studies. Tocopherols that are orally from food or supplements are transported across the gastrointestinal membrane by passive diffusion after solubilization by mixing with chyme and bile salts in the stomach and small intestine [8]. Tocopherols are then incorporated in chylomicrons, which are taken up by the liver. After secretion from the liver, low density lipoproteins (LDLs) and high density lipoproteins (HDLs) are the major carriers of tocopherols in humans [101]. 

Lipids are less dense than water. Consequently, because they are complexed with lipid, plasma lipoproteins tend to float when plasma is subjected to ultracentrifugation (Table I). In contrast, other blood proteins sediment in the centrifuge. Lipoproteins float at distinct buoyant densities and are named according to their flotation behavior. The lipoprotein classes are (Table II) chylomicrons, very-low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL). Chylomicrons and VLDL are primarily triglyceride carriers, white LDL and HDL are primarily cholesterol (mostly cholesterol ester) carriers. 

Cholesterol in blood plasma is conjugated with other fipid molecules and with carrier proteins. These fipoprotein complexes may form droplets called chylomicrons, but cholesterol is usually transported as part of a number of larger lipoproteins, including low density lipoprotein (LDL), which carries cholesterol from the fiver to muscle and other tissues, and high density fipoprotein (HDL), which carries cholesterol to the fiver for conversion to bile acids. Physicians are especially concerned when patients have high levels of LDL (the so-called bad cholesterol) in blood moderate exercise and... 

---