Disorders of lipid transport--update 1983

The relationship of physical activity to high-density lipoprotein cholesterol level in a sample of community-dwelling older adults from Amazonas, Brazil

OBJECTIVES

(1) To study the relation of physical activity (PA) to high-density lipoprotein cholesterol (HDL-C) and (2) to investigate if the strength of these associations holds after adjustments for sex, age, and other key correlates.

METHODS

This study included 550 older adults from Amazonas. HDL-C was derived from fasting blood samples. PA at sport and leisure, smoking, alcohol consumption, and socioeconomic status (SES) were interviewed. Waist circumference (WACI) was assessed.

RESULTS

HDL-C was positively related to PA sport, PA leisure, and SES (0.22≤r≤0.34; p≤0.001) and negatively related to smoking and WACI (r≤-0.10; p<0.05). Controlling for sex and age did not affect these relationships. Hierarchical multiple regression analyses showed that the relation of HDL-C to PA sport and leisure remained significant when controlling for all other investigated correlates (0.14≤β≤0.24; p≤0.001).

DISCUSSION

In order to prevent low HDL-C in older adults, promoting PA seems to be an important additional component besides common recommendations concerning weight reduction.

Dietary prescription in atherosclerosis

Although the evidence that dietary intervention reduces blood lipid levels is strong, evidence linking hypercholesterolemia and heart disease in elderly persons is conflicting. Treatment through dietary intervention for secondary prevention of heart disease in all elderly individuals and for primary prevention in those less than 75 years with risk factors seems to be justified. A more flexible dietary approach should be adopted for primary prevention of heart disease in the persons over 75 years. "The most reasonable dietary advice in them would be moderation, balance and variety".

Effect of L-carnitine treatment on very low density lipoprotein kinetics in the hyperlipidemic rabbit

This study examined the hypolipidemic effect of 4 weeks of L-carnitine treatment (170 mg/kg b.w./day) in New Zealand White rabbits fed a high fat diet (5% corn oil/0.5% cholesterol). Specifically, [3H] glycerol and [125I] very low density lipoprotein (VLDL) turnover studies were conducted to examine the effect of treatment on VLDL kinetics. The masses of plasma VLDL-triglycerides (VLDL-TG) and VLDL-apoprotein B (VLDL-apoB) were significantly increased by the high-fat diet. Four weeks of treatment with L-carnitine significantly reduced these masses. Kinetic analysis indicated that fat feeding reduced the fractional catabolic rates (FCRs) of VLDL-TG and VLDL-apoB relative to chow-fed controls. The transport of these VLDL components was not altered by the diet. L-carnitine treatment had no effect on the FCRs of VLDL-TG and VLDL-apoB or on the transport of VLDL-apoB. Yet, treatment significantly lowered the transport of VLDL-TG. These data indicate that the lipid-lowering effect of L-carnitine in this animal model was due, in part, to a decrease in the transport and not due to an alteration in the fractional catabolic rate of VLDL-TG.

Interindividual variation in the partition of lipoprotein(a) into lipoprotein subfractions

In order to evaluate cardiovascular risk, we analyzed the lipid composition of HDL and the presence of lipoprotein(a) [Lp(a)] by both agarose gel electrophoresis and enzyme-linked immunoassay (ELISA). In 681 plasmas we found a close correspondence between the existence of a visible sinking pre-beta lipoprotein band and a concentration of Lp(a) higher than 300 mg/L. In the sinking pre-beta(+) samples, the HDL-cholesterol level obtained by differential ultracentrifugation was significantly higher than that obtained by precipitation with the MgCl2-phosphotungstic acid reagent; and the difference between these HDL-cholesterol values was linearly correlated with plasma Lp(a) concentration. Moreover, the other HDL lipid components and the lipid mass ratios of HDL isolated by ultracentrifugation were significantly different from those of HDL isolated by precipitation, and these changes were also correlated with plasma Lp(a). These differences are attributed to Lp(a) because it was detected in the 1.063-1.21 kg/L plasma fractions, whereas it was absent in the plasma supernates after precipitation with MgCl2-phosphotungstic acid. Although to a lesser extent, Lp(a) was also present in the LDL and VLDL density ranges and it directly depended on both the Lp(a) and the triglyceride plasma concentrations. The proportion of Lp(a) in HDL as related to that in LDL density fractions decreased as Lp(a) plasma levels increased, reflecting an interindividual variation of Lp(a) density species. Since 90% of our study population had detectable Lp(a) in plasma, the results reinforce the concept that the ultracentrifugation method is not equivalent to precipitation in most samples, and the contaminant effect of Lp(a) cannot be predicted because of Lp(a) partition into the different lipoprotein fractions.

The genetic dyslipoproteinemias--nosology update 1990

The number of discrete disorders of lipid transport is growing. Concomitantly, the classification of the disorders is changing, from one based on altered concentrations of lipoproteins, to one based on current understanding of the genetics of the disorders and of lipoprotein biochemistry and physiology. Many disorders are now traceable to deficiencies of essential proteins such as apolipoproteins, enzymes, lipid transfer proteins and cellular receptors.

Comparative molecular properties of swine and human very low density lipoproteins-apoproteins E and C

1. By means of 2-dimensional gradient-gel electrophoresis, the very low density lipoproteins (VLDL) apoproteins E and C profiles from human and swine plasma were studied. 2. The molecular properties (isoelectric point and molecular weight) of the VLDL apoproteins and their isoforms were determined and showed many similarities between species. 3. It also appears evident that a previously unrecognized apoprotein (C-III) and several associated isoforms may exist in swine; however, it's mobility on 2-dimensional gradient gels is very similar to Apo C-II.

High-density lipoprotein cholesterol levels as a marker of reverse cholesterol transport

Dramatic advances have been made over the last decade in understanding the role of low-density lipoprotein (LDL) in atherosclerotic cardiovascular diseases and how to manage elevated levels of LDL cholesterol. Understanding the role of high-density lipoprotein (HDL) and how to intervene therapeutically in HDL action offers the possibility of even greater benefits. Epidemiologic studies have shown a strong inverse relation between HDL cholesterol and the risk of coronary artery disease (CAD). Whereas several subfractions of HDL can be identified, none convincingly offers better predictive value than total HDL cholesterol. Apolipoprotein A-I, the major apolipoprotein of HDL, also is inversely related to atherosclerotic risk. Unfortunately, measurements of HDL cholesterol or apolipoprotein A-I are considerably less precise and less accurate than measurements of total or LDL cholesterol. The biologic phenomena responsible for these epidemiologic relations are not yet clear. Moreover, several apparently contradictory observations and puzzling exceptions to the simplistic inverse relation of HDL cholesterol to CAD suggested by epidemiologic studies have created considerable confusion. The current confusion is not likely to be resolved until HDL metabolism and the cellular and molecular events responsible for the apparent protective effects of HDL are better understood. One current hypothesis that could explain the protective effects of HDL is that it mediates reverse cholesterol transport, the process by which cholesterol is removed from sites of deposition and delivered to the liver for excretion. From the standpoint of current therapy, each intervention that changes HDL cholesterol levels must be evaluated individually, on its own merit, in light of its effect on atherosclerosis and coronary events rather than on alterations in HDL cholesterol levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of metabolic control on very low density lipoprotein composition in hypertriglyceridemic type II diabetics. A study using heparin-sepharose chromatography

The composition and heparin-binding capacity of very low density lipoproteins (VLDL) from type II diabetics prone to develop secondary hypertriglyceridemia have been examined. Twelve diabetic patients whose triglyceride levels normalized during short-term treatment for hyperglycemia were studied. Normalization of triglyceride values reduced plasma levels of VLDL without modifying its relative lipid composition. There was, however, an increase in its relative apoprotein (apo) content, to which apo B made a greater percentage contribution. The calculated average particle diameter of posttreatment VLDL was reduced. The fraction of VLDL binding to heparin increased after treatment. Binding was strongly correlated to the apo B content and, to a lesser extent, to the apo E content. The data suggest that treatment of hyperglycemia favorably modified VLDL such that they more closely resemble VLDL from normolipidemic subjects, with potentially beneficial physiological consequences.

The effect of L-asparaginase on lipid metabolism during induction chemotherapy of childhood lymphoblastic leukaemia

L-asparaginase is an effective antileukaemic drug and a potent inhibitor of hepatic protein synthesis. Its effect on lipid metabolism was studied in two cohorts of children with ALL, one of whom received L-asparaginase concomitantly with three other drugs (protocol BFM 79). In the second protocol (BFM 83) administration of L-asparaginase was arranged to follow the other three drugs in time sequence. The two major findings of this study were elevated serum levels of total cholesterol and a strong increase in serum triglycerides. The former change was due to an increase in alpha-cholesterol and could not be attributed to L-asparaginase because it was also found following protocol BFM 83 before the administration of the drug. Elevations of total triglycerides were due to high levels of exogenous chylomicron bound triglycerides and were limited in occurrence almost exclusively to the period of L-asparaginase monotherapy. Hypothyroidism was excluded as a possible pathogenetic mechanism. These changes in lipid metabolism induced by L-asparaginase during intensive remission induction chemotherapy are fully reversible.

Progression and regression of human coronary atherosclerosis. The role of lipoproteins, lipases and thyroid hormones in coronary lesion growth

Relations between lipoprotein fractions, lipoprotein lipase activities, thyroid hormones and coronary lesion growth were studied among 35 male patients with severe coronary atherosclerosis, who had participated in the lipid lowering, dietary Leiden Intervention Trial. Coronary arteriographies were performed at the beginning of the study and 2 years later at termination. The coronary anatomy was quantitated with a computer-based analysis system to assess the progression rate of coronary atherosclerosis on the basis of the absolute arterial dimensions in a patient's coronary tree; for these purposes an absolute coronary score was computed. On the basis of the absolute coronary scores, the entire group of patients could be divided into a no lesion growth group (14 patients) and a progression group (21 patients). Lipoprotein fractions, lipoprotein lipases and thyroid hormones were determined at the end of the trial. No significant difference was found between the no lesion growth and progression groups of patients for total cholesterol (TC) and LDL-cholesterol (LDL-C). The VLDL-cholesterol (VLDL-C) and triglycerides (TG) were significantly higher (P less than 0.05) and HDL-C was almost significantly lower (P less than 0.10) in the progression group. Hepatic lipase (HL) values were significantly higher in the no lesion growth group, as compared to the progression group, whereas lipoprotein lipase (LPL) values were not significantly different. Triiodothyronine (T3) was significantly lower (P less than 0.01) in the progression group. Multivariate regression analysis showed HL to be the most important determinant of changes in coronary atherosclerotic lesions. T3 and HDL were also independently inversely related to coronary atherosclerotic lesion growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoproteins in liver disease

Liver disease is associated with profound and characteristic changes in lipoprotein composition and metabolism. The most pronounced alterations are the formation of lipoprotein-X in intra- and extrahepatic cholestasis, the decrease of apolipoproteins A-I and A-II and the increase of apolipoprotein E. These alterations impair the activities of both lipoprotein lipase and lecithin: cholesterol acyltransferase. They are also responsible for an abnormal receptor mediated uptake of the lipoproteins from plasma. The abnormal lipid and apolipoprotein composition of the lipoproteins in liver disease appears to affect various important functions of cell membranes. The understanding of how these changes occur and their significance in the pathogenesis of other metabolic disturbances secondary to the abnormal lipid metabolism are important challenges for future research.

Apolipoprotein E2-Christchurch (136 Arg----Ser). New variant of human apolipoprotein E in a patient with type III hyperlipoproteinemia

The primary structure of apolipoprotein E (apo E) was investigated in seven type III hyperlipoproteinemic patients with the apo E-2/2 phenotype. Six of the patients had identical two-dimensional tryptic peptide maps. These differed from the normal apo E3 map by the altered mobility of a single peptide. Amino acid analysis and sequencing showed that apo E2 in these patients had a substitution of 158 Arg----Cys. The presence of this mutation in six of the seven type III patients confirms that this is the most common form of apo E2. The seventh type III patient had a unique map with a new peptide resulting from a substitution of 136 Arg----Ser. He was heterozygous for this and for the more common apo E2 (158 Arg----Cys) variant. His very low-density lipoprotein contained approximately five times more apo E2 (136 Arg----Ser) than apo E2 (158 Arg----Cys), as determined by cysteamine treatment and peptide mapping. This new apo E2 mutant thus appears to contribute significantly to the patient's hyperlipidemia.

Mitogenic activity in human atherosclerotic lesions

Focal smooth muscle cell proliferation is a key event in atherogenesis, but the stimulating factors are unknown, and there is little information on the occurrence of growth promoting factors in the arterial wall. We have tested extracts of human aortic intima for stimulation of DNA synthesis, using the chick chorioallantoic membrane (CAM) assay in an attempt to avoid artifacts arising with cultured cells. Consistently high levels of stimulation were obtained with early proliferative (gelatinous) lesions (mean DNA synthesis 188% of control, n = 6) and slightly more advanced transitional lesions (mean 160%, n = 4); results with mature fibrous plaques were variable (range 120-182%, n = 3). Significant stimulation was also given by four of eleven samples of apparently lesion-free intima. Intima contains fibrinogen and a range of fibrinogen and fibrin degradation products (FRA) and preliminary fractionation experiments suggest that activity may reside in the FRA fraction. Serum does not stimulate DNA synthesis in the CAM; extract activity was retained in FRA-containing fractions after removal of most serum proteins by affinity chromatography, but was mainly lost from serum protein-containing fractions after removal of FRA.

The chromogenicity and quantitation of apoB-100 and apoB-48 of human plasma lipoproteins on analytical SDS gel electrophoresis

ApoB-100 and apoB-48 may be readily resolved in 3.3% sodium dodecyl sulphate-polyacrylamide gels. This study has characterized the relative chromogenicities (staining intensity/micrograms protein) of human apoB-100 and apoB-48 in various lipoprotein classes with Coomassie Brilliant Blue (R250) upon SDS-PAGE. The relation between dye uptake and the mass of each apoB species in any lipoprotein preparation, was linear at least within the concentration range of total apoprotein B which is optimally resolved in these gels (20-50 micrograms total apoprotein B), and was a function of the density of the particular lipoprotein fraction under investigation. There was a constant and characteristic difference between the chromogenicity for apoB-100 and that for apoB-48 as determined from the slopes of their respective chromogenicity curves. The slope of the lines describing staining intensity vs. protein mass for both apoB-100 and apoB-48 decreased as the density of the lipoprotein fraction increased. The slope of the line for apoB-100 was steeper than that for apoB-48 (i.e. chromogenicity apoB-100 greater than apoB-48) in all lipoprotein fractions where both were present. The relationship between the slopes of the lines for apoB-100 and apoB-48 was constant regardless of the density of the lipoprotein fraction. The chromogenicity curves for apoB-100 and for apoB-48 obtained when lipoprotein samples were applied to gels in concentrations conventionally used for this technique (i.e. 20-100 micrograms total apoB/gel) did not extrapolate to the same point on the ordinate, which precludes the use of a simple ratio or "chromogenicity factor" to describe their relative chromogenicities over this concentration range, Hence, a novel approach was developed to determine the relative mass of apoB-100/apoB-48 in lipoprotein samples, based on their staining characteristics in SDS-PAGE.

Cholesterol metabolism and aging

Changes occur in lipid and lipoprotein concentrations with age that increase the risk of developing atherosclerotic disease. In children and young adults (less than 20 years of age), the plasma total cholesterol concentration decreases between the ages of 10 and 20 years. After age 20, the plasma total cholesterol concentration increases progressively, and in men reaches a plateau between the ages of 50 and 60 years, whereas in women, it reaches a peak between 60 and 70 years of age. The low-density lipoprotein cholesterol concentration increases progressively in men and women after age 20, but more rapidly in men, accounting for most of the overall gender difference in total cholesterol. The rate at which the low-density lipoprotein cholesterol concentration increases in women begins to accelerate between 40 and 50 years of age, and the concentration exceeds that in men by 55 to 60 years. High-density lipoprotein cholesterol concentrations decrease in males during puberty and early adulthood, and thereafter remain lower than those in women at all comparable ages. The high-density lipoprotein cholesterol concentrations remain constant in women throughout their lifetime. Beyond 30 years of age, women taking estrogen preparations have higher high-density lipoprotein cholesterol concentrations than women who are not taking estrogens. The triglyceride concentration increases progressively in men, reaching peak values between 40 and 50 years of age, and then declining slightly thereafter. In women, the triglyceride concentration increases throughout their lifetime, but is always higher in those using estrogens. Whether these changes in lipoprotein concentrations merely accompany the increasing prevalence of atherosclerotic vascular disease that occurs with age, or contribute to it, is unknown at this time.

The association of increased levels of intermediate-density lipoproteins with smoking and with coronary artery disease

Studies were undertaken to determine whether there is an association between elevated levels of intermediate-density lipoproteins (IDL) (Sf 12-60 lipoproteins) and coronary artery disease. Forty-five to sixty-five-year-old men with objectively documented coronary artery disease (n = 58) who were free of known risk factors (diabetes, hypertension, obesity, hyperuricemia, and hypercholesterolemia) were compared with similar men who were free of coronary artery disease (n = 52). Smokers could not be excluded. The coronary artery disease group had a higher rate of cigarette smoking (NS, due to large variations); higher concentrations of triglycerides in their plasma (p = .003) and higher levels of very low-density lipoproteins (VLDL) (p = .007), IDL (p = .016), and low-density lipoproteins (LDL) (p = .04); as well as somewhat lower levels of high-density lipoprotein (HDL) cholesterol (p = .04). Chi-squared analysis demonstrated a strong association between coronary artery disease and IDL apolipoprotein (apo) B (p = .006), coronary artery disease and IDL triglyceride (p = .032), and coronary artery disease and IDL apo B times IDL triglyceride (p = .006) when the top quintile of the population was compared with the bottom quintile for each of these variables. Stepwise logistic regression analysis resulted in rejection of an association between coronary artery disease and HDL cholesterol, plasma triglyceride, VLDL triglyceride, or LDL triglyceride. However, it did show that coronary artery disease was most strongly associated with smoking and that the second strongest association was with IDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of the apolipoprotein B-containing lipoproteins

This chapter was designed to describe the approaches one can take to study the metabolism of the apoB-containing particles in vivo. The focus has been to blend (1) what is the current tracer kinetics analysis methodology and (2) what are the current experimental protocols being used into a total picture so that the experimentalist wishing to perform such studies may have a better perspective of the strong points and pitfalls of this important experimental tool. Hence, these points have been summarized from the point of view of what caveats are associated with each methodology. Recognition of these is essential to avoid reaching potentially erroneous conclusions. More important, attention has been focused on the realization that certain methodologies can be chosen depending upon what questions are being asked. Finally, areas where future development is needed in order to proceed to the next level of understanding are pointed out in the context of using tracer kinetic analysis as an integral part of a total experimental design.

Diabetes, lipoproteins, and atherosclerosis

Certain lipoproteins are deemed to be atherogenic because (a) they are found in plasmas of patients with various dyslipoproteinemias who also have atherosclerosis, (b) they appear in plasmas and arterial walls of animals during the experimental induction of atherosclerosis, and (c) they convert cultured macrophages and arterial smooth muscle cells into lipid-laden foam cells such as are found in atherosclerotic lesions. These lipoproteins are low-density lipoproteins (LDL), very low density lipoproteins (VLDL), and the alpha-VLDL of hypertriglyceridemic patients. Low levels or the absence of high-density lipoproteins (HDL) in patients is also associated with atherosclerosis. Poorly controlled diabetics may have higher levels of VLDL and/or LDL and lower levels of HDL than are found in well-controlled diabetics. These quantitative changes place poorly controlled patients into higher coronary risk categories. Several qualitative alterations of lipoprotein also may be present that may make them more atherogenic, among these, glycosylation of apoprotein could be very important.

Relative contribution of triglyceride-rich lipoprotein particle size and number to plasma triglyceride concentration

These studies were undertaken to determine whether differences in plasma triglyceride concentrations reflected differences in the number or in the size of the triglyceride-rich lipoprotein particles in the circulation. A population of 122 men and women, composed of normotriglyceridemic individuals and individuals with endogenous hypertriglyceridemia (plasma triglyceride concentration from 60 mg/dl to 1400 mg/dl), was studied by one of four independent experimental procedures. Rates of triglyceride production and particle (as reflected by apolipoprotein B) production were simultaneously determined. The data suggest that 71% of any increase in triglyceride production was due to an increase in the production of particles, and only 29% was due to an increase in the amount of triglyceride carried per particle. Direct measurement of the triglyceride-rich lipoprotein particle size by electron microscopy demonstrated that for a fivefold difference in triglyceride borne by the Sf 12-400 lipoproteins (from 100 mg to 500 mg triglyceride/dl plasma), the mean particle size rose by only 29%. Hence, 71% of this difference was due to an increase in particle number. The same results were obtained when triglyceride levels were related to the number of triglyceride-rich lipoproteins in the plasma. The number of particles for these studies was either estimated from apo B concentration or by calculations based on the chemical composition of ultracentrifugal subfractions. These studies have used four different approaches to show that changes of plasma triglyceride concentration primarily reflected a change in the number, not the size, of triglyceride-rich lipoprotein particles. Our studies also demonstrated that 75% to 80% of the triglyceride-rich lipoproteins in both normotriglyceridemic and hypertriglyceridemic subjects were in the Sf 12-60 or intermediate density lipoprotein subfraction.

Treatment of common lipoprotein disorders

The pathogenesis of arteriosclerosis is not yet fully understood. The growing body of scientific information strongly indicates that the plasma lipoproteins are playing a crucial role in the development of this disease. We now have conclusive information that dietary cholesterol can produce arteriosclerosis in animals and its removal from the diet can result in regression of these lesions. Most importantly, we know that reducing plasma cholesterol in humans will prevent mortality and morbidity related to the clinical sequelae of arteriosclerosis. A diet can be prescribed that can produce profound reductions in lipoprotein levels in many individuals. The rate of success in achieving modifications that reduce plasma cholesterol is very high. Most patients over time find a diet with reduced cholesterol and saturated fat to be quite palatable. As food suppliers become more active in emphasizing low fat, low cholesterol products, and as restaurants see a demand for healthier entrees, the task for the physician and nutritionist will become much easier. Achieving sustained weight reduction is a much more difficult problem, but this too can be accomplished in many patients if the health professionals maintain a hopeful supportive approach. Ultimately, it is the patient's responsibility to bring about these lifestyle changes. It is the physician's and nutritionist's job to monitor the process and provide sound information and encouragement. For individuals with severe lipoprotein disorders such as familial hypercholesterolemia where diet therapy is helpful but not adequate, the use of medications is now indicated (bile acid binding resins and nicotinic acid). Other medications that promise additional effectiveness and safety are under development (Compactin, Mevinolin). It is our belief that control of coronary heart disease and stroke requires appropriate treatment of lipoprotein disorders and the methods for a strong beginning in this endeavor are at hand.