Studies designed to examine effects of weight reduction by dieting on total cholesterol (TC), low-density-lipoprotein cholesterol (LDL-C), high-density-lipoprotein cholesterol (HDL-C), very-low-density-lipoprotein cholesterol (VLDL-C), and triglycerides (TGs) have reported inconsistent results. The purpose of this study was to quantify effects of weight loss by dieting on lipids and lipoproteins through the review method of meta-analysis. Results from the 70 studies analyzed indicated that weight reduction was associated with significant decreases (P less than or equal to 0.001) and correlations (P less than or equal to 0.05) for TC (r = 0.32), LDL-C (r = 0.29), VLDL-C (r = 0.38), and TG (r = 0.32). For every kilogram decrease in body weight, a 0.009-mmol/L increase (P less than or equal to 0.01) in HDL-C occurred for subjects at a stabilized, reduced weight and a 0.007-mmol/L decrease (P less than or equal to 0.05) for subjects actively losing weight. Our results indicate that weight reduction through dieting can be a viable approach to help normalize plasma lipids and lipoproteins in overweight individuals.

OBJECTIVE

Steatosis in patients with nonalcoholic fatty liver disease (NAFLD) is due to an imbalance between intrahepatic triglyceride (IHTG) production and export. The purpose of this study was to evaluate TG metabolism in adipose tissue and liver in NAFLD.

METHODS

Fatty acid, VLDL-TG, and VLDL-apolipoprotein B-100 (apoB100) kinetics were assessed by using stable isotope tracers in 14 nondiabetic obese subjects with NAFLD (IHTG, 22.7% +/- 2.0%) and 14 nondiabetic obese subjects with normal IHTG content (IHTG, 3.4% +/- 0.4%), matched on age, sex, body mass index, and percent body fat.

RESULTS

Compared with the normal IHTG group, the NAFLD group had greater rates of palmitate release from adipose tissue into plasma (85.4 +/- 6.6 and 114.1 +/- 8.1 micromol/min, respectively; P = .01) and VLDL-TG secretion (11.4 +/- 1.1 and 24.3 +/- 3.1 micromol/min, respectively; P = .001); VLDL-apoB100 secretion rates were not different between groups. The increase in VLDL-TG secretion was primarily due to an increased contribution from "nonsystemic" fatty acids, presumably derived from lipolysis of intrahepatic and intra-abdominal fat and de novo lipogenesis. VLDL-TG secretion rate increased linearly with increasing IHTG content in subjects with normal IHTG but reached a plateau when IHTG content was>>/=10% (r = 0.618, P < .001).

CONCLUSIONS

Obese persons with NAFLD have marked alterations in both adipose tissue (increased lipolytic rates) and hepatic (increased VLDL-TG secretion) TG metabolism. Fatty acids derived from nonsystemic sources are responsible for the increase in VLDL-TG secretion. However, the increase in hepatic TG export is not adequate to normalize IHTG content.

Adiponectin circulates in human plasma mainly as a 180-kDa low molecular weight (LMW) hexamer and a high molecular weight (HMW) multimer of approximately 360 kDa. We comprehensively examined the relationships between circulating levels of total adiponectin, adiponectin multimers, and the relative distribution (i.e., ratio) of multimeric forms with key features of the metabolic syndrome. Total adiponectin (r = 0.45), HMW (r = 0.47), LMW (r = 0.31), and HMW-to-total adiponectin ratio (r = 0.29) were significantly correlated with insulin-stimulated glucose disposal rate. Similarly, total (r = -0.30), HMW (r = -0.38), and HMW-to-total adiponectin ratio (r = -0.34) were correlated with central fat distribution but not with total fat mass or BMI. Regarding energy metabolism, although there were no effects on resting metabolic rate, total (r = 0.41) and HMW (r = 0.44) were associated with increasing rates of fat oxidation. HMW-to-total adiponectin ratio increased as a function of total adiponectin, and it was HMW quantity (not total or HMW-to-total adiponectin ratio or LMW) that was primarily responsible for all of these relationships. Impact on nuclear magnetic resonance lipoprotein subclasses was assessed. HMW and total adiponectin were correlated with decreases in large VLDL (r = -0.44 and -0.41); decreases in small LDL (r = -0.41 and -0.36) and increases in large LDL (r = 0.36 and 0.30) particle concentrations accompanied by increased LDL particle size (r = 0.47 and 0.39); and increases in large HDL (r = 0.45 and 0.37) and HDL particle size (r = 0.53 and 0.47). Most of these correlations persisted after adjustment for metabolic covariables. In conclusion, first, serum adiponectin is associated with increased insulin sensitivity, reduced abdominal fat, and high basal lipid oxidation; however, it is HMW quantity, not total or HMW-to-total adiponectin ratio, that is primarily responsible for these relationships. Second, reduced quantities of HMW independently recapitulate the lipoprotein subclass profile associated with insulin resistance after correcting for glucose disposal rate and BMI. Finally, HMW adiponectin is an important factor in explaining the metabolic syndrome.

The insulin resistance syndrome (IRS) is associated with dyslipidemia and increased cardiovascular disease risk. A novel method for detailed analyses of lipoprotein subclass sizes and particle concentrations that uses nuclear magnetic resonance (NMR) of whole sera has become available. To define the effects of insulin resistance, we measured dyslipidemia using both NMR lipoprotein subclass analysis and conventional lipid panel, and insulin sensitivity as the maximal glucose disposal rate (GDR) during hyperinsulinemic clamps in 56 insulin sensitive (IS; mean +/- SD: GDR 15.8 +/- 2.0 mg. kg(-1). min(-1), fasting blood glucose [FBG] 4.7 +/- 0.3 mmol/l, BMI 26 +/- 5), 46 insulin resistant (IR; GDR 10.2 +/- 1.9, FBG 4.9 +/- 0.5, BMI 29 +/- 5), and 46 untreated subjects with type 2 diabetes (GDR 7.4 +/- 2.8, FBG 10.8 +/- 3.7, BMI 30 +/- 5). In the group as a whole, regression analyses with GDR showed that progressive insulin resistance was associated with an increase in VLDL size (r = -0.40) and an increase in large VLDL particle concentrations (r = -0.42), a decrease in LDL size (r = 0.42) as a result of a marked increase in small LDL particles (r = -0.34) and reduced large LDL (r = 0.34), an overall increase in the number of LDL particles (r = -0.44), and a decrease in HDL size (r = 0.41) as a result of depletion of large HDL particles (r = 0.38) and a modest increase in small HDL (r = -0.21; all P < 0.01). These correlations were also evident when only normoglycemic individuals were included in the analyses (i.e., IS + IR but no diabetes), and persisted in multiple regression analyses adjusting for age, BMI, sex, and race. Discontinuous analyses were also performed. When compared with IS, the IR and diabetes subgroups exhibited a two- to threefold increase in large VLDL particle concentrations (no change in medium or small VLDL), which produced an increase in serum triglycerides; a decrease in LDL size as a result of an increase in small and a reduction in large LDL subclasses, plus an increase in overall LDL particle concentration, which together led to no difference (IS versus IR) or a minimal difference (IS versus diabetes) in LDL cholesterol; and a decrease in large cardioprotective HDL combined with an increase in the small HDL subclass such that there was no net significant difference in HDL cholesterol. We conclude that 1) insulin resistance had profound effects on lipoprotein size and subclass particle concentrations for VLDL, LDL, and HDL when measured by NMR; 2) in type 2 diabetes, the lipoprotein subclass alterations are moderately exacerbated but can be attributed primarily to the underlying insulin resistance; and 3) these insulin resistance-induced changes in the NMR lipoprotein subclass profile predictably increase risk of cardiovascular disease but were not fully apparent in the conventional lipid panel. It will be important to study whether NMR lipoprotein subclass parameters can be used to manage risk more effectively and prevent cardiovascular disease in patients with the IRS.

Density gradient ultracentrifugation of low density lipoproteins (LDL) from 12 normal subjects showed multiple, distinct isopycnic bands. Densitometric scanning of the gradient tubes revealed that each band could be assigned to one of four density intervals and that the boundaries of these intervals were consistent among all the subjects. Analytic ultracentrifuge flotation (S(f)(0)) rates were assigned to the four density intervals, and there was a strong correlation between peak S(f)(0) rate and peak isopycnic banding position (R(f)) of the LDL in the 12 subjects. The S(f)(0) value corresponding to the boundary between the two most buoyant LDL density subgroups was 7.5. This value is close to that previously demonstrated to define two LDL subdivisions (S(f)(0) 0-7 and S(f)(0) 7-12) that were discriminated by differing concentrations in men and women, and differing statistical relationships with levels of HDL and VLDL in a normal population. Further delineation of distinct subspecies of LDL was afforded by electrophoresis in 2-16% gradient polyacrylamide gels. Densitometric scans of protein-stained gels revealed multiple peaks, and particle diameters were assigned to these peaks using calibration markers. Particles of diameter>>/= 280 A included both IDL and Lp(a), the latter defined by pre-beta mobility on agarose electrophoresis and density>> 1.050 g/ml. LDL particles with diameters 220-272 A could be grouped into seven size intervals defined by modes in the distribution of gradient gel electrophoretic peaks in LDL from a group of 68 healthy men and women. Particle diameters of the major peaks in each of seven density subfractions decreased with increasing density of the fractions. However, particles within each of the size groups were distributed across a range of densities. Use of a lipid-staining procedure allowed identification of electrophoretic bands in whole plasma which corresponded to those seen in isolated LDL, eliminating the possibility that ultracentrifugation was responsible for formation of the subspecies detected by the gradient gel procedure. The application of density gradient ultracentrifugation and gradient gel electrophoresis provides a means of characterizing LDL from normal humans in terms of multiple distinct subpopulations which may also prove to have differing metabolic and pathologic properties.-Krauss, R. M., and D. J. Burke. Identification of multiple subclasses of plasma low density lipoproteins in normal humans.

Hepatitis C virus (HCV) infection is a major cause of liver disease. HCV associates with host apolipoproteins and enters hepatocytes through complex processes involving some combination of CD81, claudin-1, occludin, and scavenger receptor BI. Here we show that infectious HCV resembles very low density lipoprotein (VLDL) and that entry involves co-receptor function of the low-density lipoprotein receptor (LDL-R). Blocking experiments demonstrate that beta-VLDL itself or anti-apolipoprotein E (apoE) antibody can block HCV entry. Knockdown of the LDL-R by treatment with 25-hydroxycholesterol or siRNA ablated ligand uptake and reduced HCV infection of cells, whereas infection was rescued upon cell ectopic LDL-R expression. Analyses of gradient-fractionated HCV demonstrate that apoE is associated with HCV virions exhibiting peak infectivity and dependence upon the LDL-R for cell entry. Our results define the LDL-R as a cooperative HCV co-receptor that supports viral entry and infectivity through interaction with apoE ligand present in an infectious HCV/lipoprotein complex comprising the virion. Disruption of HCV/LDL-R interactions by altering lipoprotein metabolism may therefore represent a focus for future therapy.

BACKGROUND

High fructose consumption is suspected to be causally linked to the epidemics of obesity and metabolic disorders. In rodents, fructose leads to insulin resistance and ectopic lipid deposition. In humans, the effects of fructose on insulin sensitivity remain debated, whereas its effect on ectopic lipids has never been investigated.

OBJECTIVE

We assessed the effect of moderate fructose supplementation on insulin sensitivity (IS) and ectopic lipids in healthy male volunteers (n = 7).

METHODS

IS, intrahepatocellular lipids (IHCL), and intramyocellular lipids (IMCL) were measured before and after 1 and 4 wk of a high-fructose diet containing 1.5 g fructose . kg body wt(-1) . d(-1). Adipose tissue IS was evaluated from nonesterified fatty acid suppression, hepatic IS from suppression of hepatic glucose output (6,6-2H2-glucose), and muscle IS from the whole-body glucose disposal rate during a 2-step hyperinsulinemic euglycemic clamp. IHCL and IMCL were measured by 1H magnetic resonance spectroscopy.

RESULTS

Fructose caused significant (P < 0.05) increases in fasting plasma concentrations of triacylglycerol (36%), VLDL-triacylglycerol (72%), lactate (49%), glucose (5.5%), and leptin (48%) without any significant changes in body weight, IHCL, IMCL, or IS. IHCL were negatively correlated with triacylglycerol after 4 wk of the high-fructose diet (r = -0.78, P < 0.05).

CONCLUSIONS

Moderate fructose supplementation over 4 wk increases plasma triacylglycerol and glucose concentrations without causing ectopic lipid deposition or insulin resistance in healthy humans.

The low-density lipoprotein (LDL) receptor (LDL-R) family consists of cell-surface receptors that recognize extracellular ligands and internalize them for degradation by lysosomes. The LDL-R is the prototype of this family, which also contains very-low-density lipoprotein receptors (VLDL-R), apolipoprotein E receptor 2, LRP, and megalin. The family members contain four major structural modules: the cysteine-rich complement-type repeats, epidermal growth factor precursor-like repeats, a transmembrane domain, and a cytoplasmic domain. Each structural module serves distinct and important functions. These receptors bind several structurally dissimilar ligands. It is proposed that instead of a primary sequence, positive electrostatic potential in different ligands constitutes a receptor binding domain. This family of receptors plays crucial roles in various physiologic functions. LDL-R plays an important role in cholesterol homeostasis. Mutations cause familial hypercholesterolemia and premature coronary artery disease. LDL-R-related protein plays an important role in the clearance of plasma-activated alpha 2-macroglobulin and apolipoprotein E-enriched lipoproteins. It is essential for fetal development and has been associated with Alzheimer's disease. Megalin is the major receptor in absorptive epithelial cells of the proximal tubules and an antigenic determinant for Heymann nephritis in rats. Mutations in a chicken homolog of VLDL-R cause female sterility and premature atherosclerosis. This receptor is not expressed in liver tissue; however, transgenic expression of VLDL-R in liver corrects hypercholesterolemia in experiment animals, which suggests that it can be a candidate for gene therapy for various hyperlipidemias. The functional importance of individual receptors may lie in their differential tissue expression. The regulation of expression of these receptors occurs at the transcriptional level. Expression of the LDL-R is regulated by intracellular sterol levels involving novel membrane-bound transcription factors. Other members of the family are not regulated by sterols. All the members are, however, regulated by hormones and growth factors, but the mechanisms of regulation by hormones have not been elucidated. Studies of these receptors have provided important insights into receptor structure-function and mechanisms of ligand removal and catabolism. It is anticipated that increased knowledge about the LDL-R family members will open new avenues for the treatment of many disorders.

OBJECTIVE

Apolipoprotein E (apoE) exerts potent antiinflammatory effects. Here, we investigated the effect of apoE on the functional phenotype of macrophages.

RESULTS

Human apoE receptors very-low-density lipoprotein receptor (VLDL-R) and apoE receptor-2 (apoERRAW264.7 mouse macrophages. In these cells, apoE downregulated markers of the proinflammatory M1 phenotype (inducible nitric oxide synthase, interleukin [IL]-12, macrophage inflammatory protein-1α) but upregulated markers of the antiinflammatory M2 phenotype (arginase I, SOCS3, IL-1 receptor antagonist [IL-1RA]). In addition, M1 macrophage responses (migration, generation of reactive oxygen species, antibody-dependent cell cytotoxicity, phagocytosis), as well as poly(I:C)- or interferon-γ-induced production of proinflammatory cytokines; cyclooxygenase-2 expression; and activation of nuclear factor-κB, IκB, and STAT1, were suppressed in VLDL-R- or apoERVLDL-R-deficient mice but not wild-type or low-density lipoprotein receptor-deficient mice. The modulatory effects of apoE on macrophage polarization were inhibited in apoE receptor-expressing RAW264.7 cells exposed to SB220025, a p38 mitogen-activated protein kinase inhibitor, and PP1, a tyrosine kinase inhibitor. Accordingly, apoE induced tyrosine kinase-dependent activation of p38 mitogen-activated protein kinase in VLDL-R- or apoERRA levels, and peritoneal macrophages of transplanted animals were shifted to the M2 phenotype (increased IL-1RA production and CD206 expression).

CONCLUSIONS

ApoE signaling via <em>VLDL</em>-<em>R</em> or apoE<em>R</em>2 promotes macrophage conversion from the proinflammatory M1 to the antiinflammatory M2 phenotype. This effect may represent a novel antiinflammatory activity of apoE.

BACKGROUND

The APOE gene and its protein product is associated with a number of plasma proteins like very-low density lipoprotein (VLDL), high density lipoprotein (HDL) chylomicrons, chylomicron remnants, and plays a crucial role in lipid metabolism. The APOE gene is polymorphic and common alleles (*E2, *E3 and *E4) have been associated with a number of common and complex diseases in different populations. Due to their crucial role in metabolism and clinical significance, it is imperative that allelic variation in different populations is analysed to evaluate the usage of APOE in an evolutionary and clinical context.

OBJECTIVE

We report allelic variation at the APOE locus in three European and four Indian populations and evaluate global patterns of genetic variation at this locus. The large, intricate and unexpected heterogeneity of this locus in its global perspective may have insightful consequences, which we have explored in this paper.

METHODS

Apolipoprotein E genotypes were determined in four population groups (Punjabi Sikhs, Punjabi Hindus, Maria Gonds and Koch, total individuals = 497) of India and three regionally sub-divided British populations (Nottinghamshire, East Midlands and West Midlands, total individuals = 621). The extent and distribution of APOE allele frequencies were compared with 292 populations of the world using a variety of multivariate methods.

RESULTS

Three alleles, APOE*E2, APOE*E3 and APOE*E4, were observed with contrasting variation, although *E4 was absent in the tribal population of Koch. Higher heterozygosities (>43%) in British populations reflected their greater genetic diversity at this locus. The overall pattern of allelic diversity among these populations is comparable to many European and Indian populations. At a global level, higher frequencies of the *E2 allele were observed in Africa and Oceania (0.099 +/- 0.083 and 0.111 +/- 0.052, respectively). Similarly, *E4 allele averages were higher in Oceania (0.221 +/- 0.149) and Africa (0.209 +/- 0.090), while Indian and Asian populations showed the highest frequencies of *E3 allele. The coefficient of gene differentiation was found to be highest in South America (9.6%), although the highest genetic diversity was observed in Oceania (48.7%) and Africa (46.3%). APOE*E2 revealed a statistically significant decreasing cline towards the north in Asia (r = -0.407, d.f. = 70, p < 0.05), which is not compatible with the coronary heart disease statistics in this continent. APOE*E4 showed a significant increasing cline in North European populations. Spatial autocorrelation analysis shows that the variation at this locus is influenced by 'isolation by distance' with a strong positive correlation for lower distances up to 1313 km.

CONCLUSIONS

Overall APOE allelic variation in UK and Indian populations is comparable to previous studies but in tribal populations *E4 allele frequency was very low or absent. At a global level allelic variation shows that geography, isolation by distance, genetic drift and possibly pre-historical selection are responsible for shaping the spectrum of genetic variation at the APOE gene. Overall, APOE is a good anthropogenetic and clinical diagnostic marker.

Considerable controversy exists over the purported role of obesity in causing hyperglycemia, hyperlipemia, hyperinsulinemia, and insulin resistance; and the potential beneficial effects of weight reduction remain incompletely defined. Hypertriglyceridemia is one of the metabolic abnormalities proposed to accompany obesity, and in order to help explain the mechanisms leading to this abnormality we have proposed the following sequential hypothesis: insulin resistance ->> hyperinsulinemia ->> accelerated hepatic triglyceride(TG) production ->> elevated plasma TG concentrations. To test this hypothesis and to gain insight into both the possible role of obesity in causing the above metabolic abnormalities and the potential benefit of weight reduction we studied the effects of weight loss on various aspects of carbohydrate and lipid metabolism in a group of 36 normal and hyperlipoproteinemic subjects. Only weak to absent correlations (r = 0.03 - 0.46) were noted between obesity and the metabolic variables measured. This points out that in our study group obesity cannot be the sole, or even the major, cause of these abnormalities in the first place. Further, we have observed marked decreases after weight reduction in fasting plasma TG (mean value: pre-weight reduction, 319 mg/100 ml; post-weight reduction, 180 mg/100 ml) and cholesterol (mean values: pre-weight reduction, 282 mg/100 ml; post-weight reduction, 223 mg/100 ml) levels, with a direct relationship between the magnitude of the fall in plasma lipid values and the height of the initial plasma TG level. We have also noted significant decreases after weight reduction in the insulin and glucose responses during the oral glucose tolerance test (37% decrease and 12% decrease, respectively). Insulin and glucose responses to liquid food before and after weight reduction were also measured and the overall post-weight reduction decrease in insulin response was 48% while the glucose response was relatively unchanged. In a subgroup of patients we studied both the degree of cellular insulin resistance and the rate of hepatic very low density (VLDL) TG production before and after weight reduction. These subjects demonstrated significant decreases after weight reduction in both degree of insulin resistance (33% decrease) and VLDL-TG production rates (40% decrease). Thus, weight reduction has lowered each of the antecedent variables (insulin resistance, hyperinsulinemia, and VLDL-TG production) that according to the above hypothesis lead to hypertriglyceridemia, and we believe the overall scheme is greatly strengthened. Furthermore, the consistent decreases in plasma TG and cholesterol levels seen in all subjects lead us to conclude that weight reduction is an important therapeutic modality for patients with endogenous hypertriglyceridemia.

BACKGROUND

Autism is a severe neurodevelopmental disorder with genetic and environmental etiologies. Recent genetic linkage studies implicate Reelin glycoprotein in causation of autism. To further investigate these studies, brain levels of Reelin protein and mRNA and mRNAs for VLDLR, Dab-1, and GSK3 were investigated.

METHODS

Postmortem superior frontal, parietal, and cerebellar cortices of age, gender, and postmortem interval-matched autistic and control subjects were subjected to SDS-PAGE and Western blotting of Reelin protein. Quantitative reverse transcriptase polymerase chain reaction analysis of Reelin, VLDL-R, Dab-1, and GSK3 mRNA species in superior frontal and cerebellar cortices of autistic and control subjects were also performed.

RESULTS

Reelin 410, 330, and 180 kDa/beta-actin values were reduced significantly in frontal and cerebellar, and nonsignificantly in parietal, areas of autistic brains versus control subjects, respectively. The mRNAs for Reln and Dab-1 were reduced significantly whereas the mRNA for Reln receptor VLDLR was elevated significantly in superior frontal and cerebellar areas of autistic brains versus control brains, respectively.

CONCLUSIONS

Reductions in Reelin protein and mRNA and Dab 1 mRNA and elevations in Reln receptor VLDLR mRNA demonstrate impairments in the Reelin signaling system in autism, accounting for some of the brain structural and cognitive deficits observed in the disorder.

A previous study has shown that serum levels of the active vitamin D metabolite 1,25-(OH)2-vitamin D were inversely related to blood pressure levels while the prohormone 25-OH-vitamin D was found to be related to insulin metabolism. Also other clinical and experimental data support the view that vitamin D metabolism is involved in blood pressure regulation and other metabolic processes. The present study was conducted in order to see if the above mentioned relationships between the vitamin D endocrine system and blood pressure, as well as other cardiovascular risk factors, could be found in a cross-section population-based study. Serum levels of 1,25-(OH)2-vitamin D, 25-OH-vitamin D, and blood pressure were therefore measured in 34 middle-aged men and metabolic cardiovascular risk factors were evaluated by means of intravenous glucose and fat tolerance tests, euglycemic hyperinsulinemic clamp, lipoprotein measurements, and lipoprotein lipase activity determinations. Serum levels of 1,25-(OH)2-vitamin D were found to be inversely correlated to the blood pressure (r = -0.42, P < .02), VLDL triglycerides (r = -0.47, P < .005), and to triglyceride removal at the intravenous fat tolerance test (r = 0.34, P < .05), while serum levels of 25-OH-vitamin D were correlated to fasting insulin (r = -0.35, P < .05), insulin sensitivity during clamp (r = 0.54, P < .001), and lipoprotein lipase activity both in adiposal tissue (r = 0.48, P < .005) and skeletal muscle (r = 0.38, P < .03).(ABSTRACT TRUNCATED AT 250 WORDS)

Physically well-trained people generally have lower VLDL-triglyceride and higher HDL-cholesterol levels than sedentary subjects. To examine the underlying mechanisms of this lipoprotein pattern, we measured the lipoprotein lipase (LPL) activity in needle biopsy specimens of adipose tissue and skeletal muscle of competitive runners and of body weight-matched, physically less-active controls. The active sportsmen were either sprinters, whose training program consisted mainly of athletics of short duration or long distance runners undergoing a strenuous endurance exercise program. In sprinters (all males) the serum lipid and lipoprotein concentrations did not differ significantly from those of controls and the mean LPL activities in muscle and adipose tissue were also similar in these two groups. The long distance runners (both sexes), on the other hand, had higher means levels of HDL-cholesterol than the respective controls. The LPL-activity of both adipose tissue (p less than 0.05) and skeletal muscle (p less than 0.01) was significantly higher in male long distance runners than in control males. Female runners had higher muscle LPL activity than controls (p less than 0.01) but in adipose tissue the difference in LPL activity was not significant. Rough estimates calculated for LPL activity present in whole body adipose tissue and skeletal muscle indicated that total LPL activity was 2.3 times higher in male long distance runners and 1.5 times higher in female long distance runners than in the respective controls. In combined groups of male runners and controls, there was a highly significant positive correlation between the serum HDL-cholesterol level and the LPL activity of adipose tissue expressed per tissue weight (r = +0.72, p less than 0.001) or per whole body fat (r = +0.62, p less than 0.001). The group means of HDL-cholesterol and adipose tissue LPL activity in the five cohorts studied (male sprinters, distance runners and controls and female distance runners and controls) were also positively correlated (r = +0.94). It is concluded that endurance training is associated with an adaptive increase of LPL activity not only in skeletal muscle but also in adipose tissue. These changes are not observed in sprinters who are trained by exercises of shorter duration. The high HDL-cholesterol levels of physically well-trained people are probably accounted for, at least partly, by the increased LPL activity and the concomitant rapid turnover or triglyceride-rich lipoproteins.

BACKGROUND

Insulin resistance and obesity are associated with a dyslipidemia composed of high levels of triglycerides (TG), low levels of high-density lipoprotein cholesterol (HDL-C), and no change in level of low-density lipoprotein cholesterol (LDL-C). We examined the association of insulin resistance and adiposity with lipoprotein particle size, concentration, and subclass concentrations.

METHODS

The Insulin Resistance Atherosclerosis Study is a multicenter cohort study of middle-aged men and women. Lipoprotein lipid concentrations were determined using standard methods. Lipoprotein size, particle concentration, and subclass concentrations were determined using nuclear magnetic resonance technology. Insulin resistance (SI) was determined based on the frequently sampled intravenous glucose tolerance test and the MINMOD program. A higher SI represents less insulin resistance. Fasting insulin, body mass index, waist circumference, and waist/hip ratio were assessed.

RESULTS

Among the 1371 participants were 754 women and 617 men; 459 Hispanics, 383 African Americans, and 529 non-Hispanic whites; 437 with type 2 diabetes, 301 with impaired glucose tolerance, and 633 with normal glucose tolerance. The mean (SD) age was 55.5 (8.5) years, body mass index was 29.3 (5.8) kg/m2 , and SI was 1.6 (1.8) units. Adjusted for age, sex, and ethnicity, SI was not associated with LDL-C (r = 0.01); however, S I was associated with LDL size (r = 0.34, P < .001), LDL particle concentration (r = -0.28, P < .001), small LDL (r = -0.34, P < .001), intermediate LDL (r = -0.37, P < .001), and large LDL (r = 0.21, P < .001). In addition, S I was associated with TG (r = -0.36, P < .001), VLDL particles (r = -0.08, P < .01), large VLDL (r = -0.32, P < .001), VLDL size (r = -0.38, P < .001), HDL-C (r = 0.37, P < .001), HDL particles (r = 0.09, P < .001), large HDL (r = 0.31, P < .001), and HDL size (r = 0.33, P < .001). A factor analysis revealed a factor that accounted for 41.4% of the variance across the lipoprotein measures and that was correlated with SI (r = -0.33, P < .001). Similar results of opposing direction were observed for analyses of lipoprotein measures with fasting insulin and adiposity.

CONCLUSIONS

The dyslipidemia associated with insulin resistance and obesity includes effects on lipoprotein metabolism that are missed when traditional lipoprotein cholesterol and total TG are examined. Lipoprotein size and subclasses should be examined in studies investigating the roles of insulin resistance and obesity in the pathogenesis and prevention of atherosclerosis.

BACKGROUND

High-carbohydrate (HC) diets increase de novo lipogenesis (DNL), but effects on stearoyl-CoA desaturase (SCD) are not so well studied.

OBJECTIVE

The objective was to investigate DNL and SCD in liver and adipose tissue by using fatty acid ratios after short-term dietary intervention.

METHODS

Eight subjects consumed isoenergetic 3-d HC (10% fat; 75% carbohydrates) or higher fat (HF; 40% fat; 45% carbohydrates) diets (sugar to starch ratio: 60:40 for both) in a crossover study. Blood was taken from an artery and a vein draining subcutaneous adipose tissue. DNL and SCD activity were investigated by using the ratios of 16:0 to 18:2n-6 and of 16:1n-7 to 16:0, respectively. A test meal, including [U-(13)C]palmitate was given to trace dietary fatty acid incorporation into VLDL-triacylglycerol (TG). The conversion of intravenously infused [(2)H(2)]palmitic acid to [(2)H(2)]palmitoleic acid in VLDL-TG was quantified as a specific marker of hepatic SCD activity.

RESULTS

The VLDL-TG 16:0/18:2n-6 ratio, which reflects hepatic DNL, was greater after the HC diet than after the HF diet (P = 0.02). With the HC diet, increased plasma TG concentrations correlated with 16:0/18:2n-6 ratios (r = 0.76, P = 0.028). Plasma VLDL-TG and adipose venous nonesterified fatty acid (NEFA) 16:1n-7/16:0 ratios were higher after the HC diet (fasting: P = 0.01 and P = 0.05, respectively; postprandial: P = 0.03 and P = 0.05, respectively). Changes in fasting VLDL-TG 16:0/18:2n-6 and 16:1n-7/16:0 ratios were associated (P = 0.06). The contribution of total fatty acids from splanchnic sources (including DNL) was higher after the HC diet (P = 0.02). Expression of lipogenic genes in subcutaneous adipose tissue was not significantly affected by diet.

CONCLUSIONS

Parallel activation of DNL and SCD was found after a short period of HC feeding.

The relations between triglyceride-rich lipoproteins, alimentary lipaemia and coronary heart disease (CHD) have remained obscure and much debated. We studied the basal and postprandial plasma levels of chylomicron remnants and very low density lipoproteins (VLDL) of varying particle size in 32 male postinfarction patients (mean (S.D.) age 48.8 (3.2) years) and in 10 age-matched control men. The selective quantification of postprandial intestinal and hepatic lipoproteins was accomplished by determining apolipoproteins B-48 and B-100 in lipoprotein subfractions of Svedberg flotation (Sf) rates>> 12 before and 3, 6 and 12 h after an oral fat load. Since all patients had undergone two coronary angiographies with an intervening time interval of around 5 years, lipoprotein fractions were examined in relation to the global severity as well as the rate of progression of coronary lesions. The postprandial plasma levels of small chylomicron remnants (Sf 20-60 apolipoprotein B-48) were found to relate distinctly to the rate of progression of coronary lesions between the angiographies (r = 0.51, P = 0.01). Adjustment for the possible confounding effect of the HDL cholesterol and dense LDL apolipoprotein B concentrations did not substantially alter the strength of this association. Neither the increment of plasma triglyceride during the postprandial period nor the concentrations of other lipoprotein fractions closely reflected the amount of small chylomicron remnants in the circulation or correlated with progression of coronary lesions. Our data suggest that small chylomicron remnants are implicated in the progression of coronary artery disease.