Chylomicron Triglyceride Research Articles

Increased chylomicron triglyceride hydrolysis by connective tissue flow in perfused rat hindlimb: implications for lipid storage

AbstractSkeletal muscle has two circulatory routes, nutritive (in contact with muscle) and non-nutritive (part of which is located in the connective tissue), and the balance of flow between the two is controlled by neural input and circulating vasomodulators. The purpose of this study was to assess muscle triglyceride hydrolysis given that the two circuits may have a differing vascular distribution of hydrolytic activity. The isolated rat hindlimb was perfused with 6% Ficoll® and a radiolabeled chylomicron–lipid emulsion containing apolipoprotein C-II. Serotonin (0.5–1 μm), a model vasoconstrictor previously shown to preferentially increase connective tissue flow, inhibited hindlimb oxygen uptake (from 16.7 ± 0.6 to 10.2 ± 1.0, mean ± SE, n = 7 (P <0.001)) and stimulated [14C]-labeled fatty acid uptake into muscles (from 184 ± 28 to 602 ± 132, mean ± SE, n = 7 (P = 0.009)). These effects were reversed by the vasodilator carbamyl choline. Vasopressin resulted in increased oxygen consumption but no change in triglyceride hydrolysis. Cholesteryl oleate uptake (an indicator of endocytosis of the chylomicron or remnant particle) was unaltered by serotonin. It is concluded that chylomicron triglyceride hydrolysis is enhanced by vasoconstrictors that increase connective tissue flow in the perfused rat hindlimb. Increased hydrolysis appears to be primarily due to an increased access of triglyceride to hydrolytic enzymes, presumably lipoprotein lipase associated with the fat cells commonly observed interlaced amongst bundles of muscle fibers. —Clerk, L. H., M. E. Smith, S. Rattigan, and M. G. Clark. Increased chylomicron triglyceride hydrolysis by connective tissue flow in perfused rat hindlimb: implications for lipid storage. J. Lipid Res. 2000. 41: 329–335.

Pancreas transplantation modulates reverse cholesterol transport.

Hyperinsulinemia secondary to insulin resistance in type-II diabetes or in the metabolic syndrome is associated with the "atherogenetic lipoprotein phenotype": high triglycerides, small, dense low-density lipoprotein (LDL) cholesterol, and low high-density lipoprotein (HDL) cholesterol. In contrast, hyperinsulinemia in pancreas-kidney transplant recipients (PKT-R), secondary to systemic venous drainage of the heteropically implanted pancreas graft, leads to high lipoprotein lipase (LPL) activity and a presumably antiatherogenic lipoprotein profile with very attenuated postprandial lipemia, high HDL cholesterol, and a preponderance of large-sized HDL (HDL(2)) and large buoyant LDL particles. We interpret these findings to suggest that in PKT-R, peripheral hyperinsulinemia upregulates LPL activity in peripheral tissues, which induces rapid clearance of chylomicron triglycerides from plasma and, thus, attenuates postprandial lipemia. Low postprandial lipemia allows little net cholesteryl ester transfer from HDL to triglyceride-rich lipoproteins, keeping the levels of the antiatherogenic lipoprotein HDL high and potentially increasing, thereby reverse cholesterol transport. The type of lipoprotein metabolism and pattern present in PKT-R is associated with a low cardiovascular risk in the general population; it cannot be excluded, however, that hyperinsulinemia as found in PKT-R may contribute to atherosclerosis by effects unrelated to lipoprotein metabolism.

Differential binding of triglyceride-rich lipoproteins to lipoprotein lipase

In comparison to very low density lipoprotein (VLDL), chylomicrons are cleared quickly from plasma. However, small changes in fasting plasma VLDL concentration substantially delay postprandial chylomicron triglyceride clearance. We hypothesized that differential binding to lipoprotein lipase (LPL), the first step in the lipolytic pathway, might explain these otherwise paradoxical relationships. Competition binding assays of different lipoproteins were performed in a solid phase assay with purified bovine LPL at 4°C. The results showed that chylomicrons, VLDL, and low density lipoprotein (LDL) were able to inhibit specific binding of 125I-labeled VLDL to the same extent (85.1% ± 13.1, 100% ± 6.8, 90.7% ± 23.2% inhibition, P = NS), but with markedly different efficiencies. The rank order of inhibition (Ki) was chylomicrons (0.27 ± 0.02 nm apoB) > VLDL (12.6 ± 3.11 nm apoB) > LDL (34.8 ± 11.1 nm apoB). By contrast, neither triglyceride (TG) liposomes, high density lipoprotein (HDL), nor LDL from patients with familial hypercholesterolemia were efficient at displacing the specific binding of 125I-labeled VLDL to LPL (30%, 39%, and no displacement, respectively). Importantly, smaller hydrolyzed chylomicrons had less affinity than the larger chylomicrons (Ki = 2.34 ± 0.85 nm vs. 0.27 ± 0.02 nm apoB respectively, P < 0.01). This was also true for hydrolyzed VLDL, although to a lesser extent. Chylomicrons from patients with LPL deficiency and VLDL from hypertriglyceridemic subjects were also studied.▪Taken together, our results indicate an inverse linear relationship between chylomicron size and Ki whereas none was present for VLDL. We hypothesize that the differences in binding affinity demonstrated in vitro when considered with the differences in particle number observed in vivo may largely explain the paradoxes we set out to study.—Xiang, S-Q., K. Cianflone, D. Kalant, and A. D. Sniderman. Differential binding of triglyceride-rich lipoproteins to lipoprotein lipase. J. Lipid Res. 1999. 40: 1655–1662.

Effect of dietary docosahexaenoic acid on desaturation and uptake in vivo of isotope-labeled oleic, linoleic, and linolenic acids by male subjects.

The effect of dietary docosahexaenoic acid (22:6n-3, DHA) on the metabolism of oleic, linoleic, and linolenic acids was investigated in male subjects (n = 6) confined to a metabolic unit and fed diets containing 6.5 or <0.1 g/d of DHA for 90 d. At the end of the diet period, the subjects were fed a mixture of deuterated triglycerides containing 18:1n-9[d6], 18:2n-6[d2], and 18:3n-3[d4]. Blood samples were drawn at 0, 2, 4, 6, 8, 12, 24, 48, and 72 h. Methyl esters of plasma total lipids, triglycerides, phospholipids, and cholesterol esters were analyzed by gas chromatography-mass spectrometry. Chylomicron triglyceride results show that the deuterated fatty acids were equally well absorbed and diet did not influence absorption. Compared to the low-DHA diet (LO-DHA), clearance of the labeled fatty acids from chylomicron triglycerides was modestly higher for subjects fed the high DHA diet (HI-DHA). DHA supplementation significantly reduced the concentrations of most n-6[d2] and n-3[d4] long-chain fatty acid (LCFA) metabolites in plasma lipids. Accumulation of 20:5n-3[d4] and 22:6n-3[d4] was depressed by 76 and 88%, respectively. Accumulations of 20:3n-6[d2] and 20:4n-6[d2] were both decreased by 72%. No effect of diet was observed on acyltransferase selectivity or on uptake and clearance of 18:1n-9[d6], 18:2n-6[d2], and 18:3n-3[d4]. The results indicate that accumulation of n-3 LCFA metabolites synthesized from 18:3n-3 in typical U.S. diets would be reduced from about 120 to 30 mg/d by supplementation with 6.5 g/d of DHA. Accumulation of n-6 LCFA metabolites synthesized from 18:2n-6 in U.S. diets is estimated to be reduced from about 800 to 180 mg/d. This decrease is two to three times the amount of n-6 LCFA in a typical U.S. diet. These results support the hypothesis that health benefits associated with DHA supplementation are the combined result of reduced accretion of n-6 LCFA metabolites and an increase in n-3 LCFA levels in tissue lipids.

The role of microsomal triglyceride transfer protein and dietary cholesterol in chylomicron production in diabetes.

The aim of this study was to examine factors involved in chylomicron production in the streptozotocin diabetic rat, our hypothesis being that the synthesis of the chylomicron is abnormal in diabetes. Diabetic rats (n = 20) were paired with control rats (n = 20). Cholesterol emulsion was given by gavage and the lymph duct was cannulated. Lymph was collected for 4 h. Chylomicrons were prepared from the lymph by ultracentrifugation. Lymph apolipoprotein B48 was isolated by gradient gel electrophoresis and quantified by densitometric scanning. Intestinal microsomal triglycerol transfer protein mRNA was measured by solution hybridisation nuclease protection, using a rat specific [32P]-labelled cRNA probe. Serum triglyceride and cholesterol were greatly increased in diabetic compared with control animals (258 +/- 77 and 8.9 +/- 6.4 mg/ml vs 1.04 +/- 0.37 and 0.54 +/- 0.03 mg/ml, p < 0.0001). Lymph chylomicron triglyceride and cholesterol were also higher in diabetic rats (29.4 +/- 27.3 and 0.28 +/- 0.3 mg/h vs 16.8 +/- 10.6 and 0.18 +/- 0.09 mg/h, p < 0.05). Lymph chylomicron apo B48 was similar in the two groups. Intestinal microsomal triglycerol transfer protein mRNA was higher in the diabetic rats (12.6 +/- 3.2 vs 3.8 +/- 3.0 amol/microgram RNA, p < 0.0001) and there was a positive correlation between lymph triglyceride and microsomal triglycerol transfer protein mRNA in the whole group (r = 0.65, p < 0.01). The study shows that microsomal triglycerol transfer protein mRNA is raised in diabetes without an increase in apolipoprotein B48 in the lymph suggesting that microsomal triglycerol transfer protein regulates chylomicron triglyceride content but not particle number.

The Lipoprotein Lipase HindIII Polymorphism: Association with Total Cholesterol and LDL-Cholesterol, but not with HDL and Triglycerides in 342 Females

Lipoprotein lipase (LPL) is the rate-limiting enzyme in the hydrolysis of core triglycerides in chylomicrons and VLDL. We investigated the association between the HindIII polymorphism of the LPL gene and fasting glucose, lipid, and lipoprotein concentrations in 683 Caucasians. We first stabilized the study subjects, using an 8-day diet and exercise intervention program before obtaining blood samples. The use of this standardization period reduced the variance of all glucose and lipid concentrations. In our study, the HindIII allele frequencies for females and males were 0.29 and 0.34 for H- and 0.71 and 0.66 for H+, respectively. We found in females, but not in males, a significant association between the HindIII genotype and total cholesterol (P = 0.007) and LDL-cholesterol (P = 0.018), with females homozygous for the rare H- allele having the lowest, heterozygotes (H-/+) having intermediate, and women homozygous for the common H+ allele having the highest of each of these lipid traits. With regard to triglycerides, HDL-cholesterol, and glucose, no significant effect of the HindIII genotype was noted in either gender. These results suggest that in a gender-specific manner, the rare LPL HindIII H- allele has a cholesterol-lowering and, therefore, potentially cardioprotective effect compared with the common H+ allele.

Association of lipoprotein lipase gene polymorphisms with coronary artery disease

OBJECTIVESThe purpose of this study was to test whether the HindIII (+) and PvuII (−) or (+) restriction enzyme–defined alleles are associated with angiographic coronary artery disease (CAD).BACKGROUNDLipoprotein lipase (LPL) plays a central role in lipid metabolism, hydrolyzing triglyceride in chylomicrons and very low density lipoproteins. Polymorphic variants of the LPL gene are common and might affect risk of CAD.METHODSBlood was drawn from 725 patients undergoing coronary angiography. Leukocyte deoxyribonucleic acid segments containing the genomic sites were amplified by the polymerase chain reaction and digested, and polymorphisms were identified after electrophoresis in 1.5% agarose gel.RESULTSIn no-CAD control subjects (n = 168), HindIII (−) and (+) allelic frequencies were 28.6% and 71.4%, and (−) and (+) alleles were carried by 44.0% and 86.9% of subjects, respectively. Control PvuII (−) and (+) allelic frequencies were 41.7% and 58.3%, and (−) and (+) alleles were carried by 64.3% and 81.0%, respectively. In CAD patients (>60% stenosis; n = 483), HindIII (+) allelic carriage was increased (93.8% of patients, odds ratio [OR] = 2.28, confidence interval [CI] 1.27 to 4.00). Also, PvuII (−) allelic carriage tended to be more frequent in CAD patients (OR = 1.33, CI 0.92 to 1.93). Adjusted for six CAD risk factors and the other polymorphism, HindIII (+) carriage was associated with an OR = 2.86, CI 1.50 to 5.42, p = 0.0014, and PvuII (−) carriage, OR = 1.42, CI 0.95 to 2.12, p = 0.09. The two polymorphisms were in strong linkage disequilibrium, and a haplotype association was suggested.CONCLUSIONSThe common LPL polymorphic allele, HindIII (+), is moderately associated with CAD, and the PvuII (−) allele is modestly associated (trend). Genetic variants of LPL deserve further evaluation as risk factors for CAD.

Detecting ligands interacting with lipoprotein lipase.

AbstractThe primary role for lipoprotein lipase (LPL) is hydrolysis of triglycerides in chylomicrons and very low density lipoproteins (VLDL). This enzyme has also been implicated in the process of atherogenesis (for reviews see refs. 1 and 2). Additional enzymatic activities of LPL include retinyl ester hydrolysis and fatty acid ethyl ester synthesis (3,4). Recent studies from several laboratories suggest that LPL may have roles unrelated to its enzymatic activity. For example, LPL increases lipoprotein binding to matrix and lipoprotein binding and uptake by cells, a function that does not appear to require catalytic activity. Since LPL has domains that interact with lipid, apoB, and cell surface molecules, it has been suggested that LPL forms a bridge between lipoproteins and cell surfaces (see refs. in 2). This bridging function has been postulated to play a role in the accumulation of lipoproteins by cells in vivo.KeywordsHepatic LipaseHEPES Buffer SalineLigand BlottingImmobilon MembraneBenzamidine HydrochlorideThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Identification of a silencing element in the chicken lipoprotein lipase gene promoter: characterization of the silencer-binding protein and delineation of its target nucleotide sequence

Lipoprotein lipase (LPL) hydrolyzes triglycerides in chylomicrons and very low density lipoproteins (VLDL) and plays a central role in lipid metabolism. It is regulated tissue-specifically. By deletion analysis, a negative regulatory element was identified in the chicken LPL gene promoter at base pairs (bp) −263 to −241. This sequence contained two palindromic halves with a three nucleotide spacer. Either half was sufficient for full inhibitory function. A protein complex bound specifically to this element and a high correlation was found between binding of the complex and inhibition of transcription. Its molecular mass, evaluated by native gel electrophoresis and Ferguson plot analysis, was 120 kDa. UV cross-linking followed by SDS–PAGE revealed two protein subunits of 48 kDa and 44 kDa, respectively. This inhibitory protein complex may contribute to the tissue-specific regulation of LPL gene transcription. It was much more abundant in liver than in adipose tissue and heart. Our data showed that this negative element inhibited transcription even when placed at an upstream location (−666), but failed to function in the herpes simplex virus thymidine kinase promoter, indicating that it acted in conjunction with other element(s) in the chicken LPL gene to inhibit transcription.

Large-scale lipoprotein lipase purification from adipose tissue.

AbstractLipoprotein lipase (LPL) plays a central role in lipoprotein metabolism. LPL is the major enzyme responsible for the hydrolysis of triglycerides in VLDL and chylomicrons. Following hydrolysis of the triglyceride core of lipoproteins, some of the LPL molecules remain associated with chylomicron remnants and intermediate density lipoproteins (IDL) derived from VLDL. There is now accumulating evidence that these lipase molecules may play a role in the removal of chylomicron remnants and IDL by the liver and other tissues (1–4). This second function of LPL is independent of its catalytic activity.KeywordsWash BufferEquilibration BufferAcetone PowderIntermediate Density LipoproteinChylomicron RemnantThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Influence of obesity and body fat distribution on postprandial lipemia and triglyceride-rich lipoproteins in adult women.

We know that upper body obesity is associated with metabolic complications, but we don't know how regional body fat distribution influences postprandial lipemia in obese adults. Thus, this study explored the respective effects of android or gynoid types of obesity and fasting triglyceridemia on postprandial lipid metabolism and especially triglyceride-rich lipoproteins. Twenty-four obese and 6 lean normotriglyceridemic women (control), age 24-57 yr, were enrolled. Among obese women with an android phenotype, 9 exhibited normal plasma triglyceride levels (mean: 1.38 mmol/L) (NTAO), and 7 displayed a frank hypertriglyceridemia (mean: 2.40 mmol/L) (HTAO). The 8 patients with a gynoid phenotype had normal triglyceride levels (mean: 1.00 mmol/L) (GO). All were given a mixed test meal providing 40 g triglycerides. Serum and incremental chylomicron triglycerides 0-7 h areas under the curve (AUCs) as well as triglyceride levels in apoB-48-containing triglyceride-rich lipoprotein (TRLs) or chylomicrons were significantly higher in HTAOs and NTAOs than in GOs and controls postprandially. The size of chylomicron particles was bigger in controls and GOs than in HTAOs and NTAOs postprandially. Android obese subjects showed abnormally elevated fasting apoB-48 and apoB-100 triglyceride-rich lipoprotein (TRL) levels. Most abnormalities that were found correlated to plasma levels of insulin and apoC-III. In conclusion, an abnormal postprandial lipid pattern is a trait of abdominal obesity even without fasting hypertriglyceridemia.

Effect of the fat composition of a single meal on the composition and cytotoxic potencies of lipolytically-releasable free fatty acids in postprandial plasma

Ingestion of a meal increases plasma levels of triglyceride (TG)-rich lipoproteins through the secretion of intestine-derived chylomcirons and liver-derived very low density lipoproteins (VLDL). We have determined the effects of the fat composition of a single meal on the composition of TG in TG-rich lipoproteins (VLDL+chylomicrons) and circulating and lipolytically-releasable free fatty acids (FFA) in postprandial (PP) plasma and on the cytotoxic potencies of the lipolytically-released FFA to cultured arterial wall cells. PP lipemia was induced by feeding fasted normolipidemic human subjects with a meal rich in saturated fat (SF) and another meal rich in polyunsaturated fat (PUF), or vice versa; each meal provided 65% of energy as fat, and polyunsaturated to saturated fatty acid ratios (P/S) of the SF and PUF in the meals were 0.40 and 2.49, respectively. The mean P/S of TG in TG-rich lipoproteins (1.43) and circulating FFA (1.46) in 4 h PP plasma of PUF were significantly higher than those in PP plasma of SF (0.44 and 0.59, respectively) in fasting plasma (0.52 and 0.53, respectively). In vitro lipolysis of fasting and PP serum by purified bovine milk lipoprotein lipase (LpL) resulted in a marked (8.8–12.3-fold) increase in the serum FFA level. The P/S of serum FFA in postlipolysis fasting and PP serum were consistently higher than that of FFA or that of TG associated with TG-rich lipoproteins in prelipolysis fasting and PP serum, indicating that polyunsaturated TG in VLDL and/or chylomicrons is more susceptible than saturated TG to lipolysis. When postlipolysis serum was interacted with cultured endothelial cells and mouse peritoneal macrophages (MPM), the lipolytically-released FFA in PP serum of SF and PUF disrupted the barrier function of endothelial cells and were cytotocxic to cultured MPM; FFA in postlipolysis fasting serum was not cytotoxic. FFA in postlipolysis PP serum of PUF were consistently more potent than that in postlipolysis PP serum of SF. Further study showed that all long-chain monounsaturated FFA and polyunsaturated FFA, but not saturated FFA, incorporated into lipoproteins (LDL) were cytotoxic to cultured MPM. In conclusion, despite the generally well-accepted belief that SF is more atherogenic than PUF, the present study provides in vitro evidence that the lipolytic remnant products of TG-rich lipoproteins produced after a meal rich in PUF are more injurious to arterial wall cells than those produced after a meal rich in SF.

Low and high responders to pharmacological doses of β-carotene: proportion in the population, mechanisms involved and consequences on β-carotene metabolism

The aim of this study was to assess the interindividual variability of chylomicron β-carotene response to a pharmacological load of β-carotene in the population, to identify the mechanisms responsible for this variability, and to evaluate its consequences on β-carotene status and metabolism. The variability, as estimated by the 3-h chylomicron β-carotene response to 120 mg β-carotene in 79 healthy male volunteers, was high (CV = 61“%), but it was unimodal and all the subjects had detectable chylomicron β-carotene. In 16 subjects randomly selected among the 79, the interindividual variability of the triglyceride-adjusted chylomicron (β-carotene + retinyl palmitate) response (0–12.5 h area under the curve) was high (CV = 54”%), suggesting that there is a high interindividual variability in the efficiency of intestinal absorption of β-carotene. The chylomicron β-carotene response was correlated (r = 0.50, P < 0.05) with the chylomicron triglyceride response. The β-carotene status, as assessed by β-carotene concentration in buccal mucosal cells, was correlated (r = 0.73, P < 0.05) with the triglyceride-adjusted chylomicron β-carotene response, i.e., with the ability to respond to β-carotene. The triglyceride-adjusted chylomicron retinyl-palmitate response was correlated (r = 0.55, P < 0.05) with the triglyceride-adjusted chylomicron β-carotene response. Plasma all-trans retinoic acid slightly, but significantly, increased (+40“%) 3 h after the β-carotene load, but this increase was not related to the triglyceride-adjusted β-carotene response. In conclusion, the ability to respond to β-carotene is highly variable, but there is probably a very small proportion of true non-responders to pharmacological doses of β-carotene in the healthy population. This variability is apparently mainly due to interindividual differences in the efficiency of intestinal absorption of β-carotene and in chylomicron metabolism. The ability to respond to β-carotene can affect the β-carotene status and the provitamin A activity of β-carotene, but it has apparently no effect on the amount of retinoic acid appearing in the plasma after the ingestion of a pharmacological dose of β-carotene. —Borel, P., P. Grolier, N. Mekki, Y. Boirie, Y. Rochette, B. Le Roy, M. C. Alexandre-Gouabau, D. Lairon, and V. Azais-Braesco. Low and high responders to pharmacological doses of β-carotene: proportion in the population, mechanisms involved, and consequences on β-carotene metabolism. J. Lipid Res. 1998. 39: 2250–2260.

Chylomicron β-Carotene and Retinyl Palmitate Responses Are Dramatically Diminished When Men Ingest β-Carotene with Medium-Chain Rather than Long-Chain Triglycerides

The effect of the ingestion of β-carotene with medium-chain triglycerides (MCT) or long-chain triglycerides (LCT) on the bioavailability and the provitamin A activity of β-carotene was investigated in humans. Sixteen healthy young men ingested, on two different days, a test meal containing 120 mg β-carotene incorporated into 40 g LCT (LCT meal) or 40 g MCT (MCT meal). This meal was followed 6 h later by a β-carotene–free meal containing 40 g LCT. Chylomicron β-carotene, retinyl palmitate and triglycerides were measured every hour for 12.5 h after the first meal. No significant increase in chylomicron triglycerides was detected for the 6 h after the MCT meal intake, whereas a significant increase in chylomicron triglycerides was observed after the LCT meal intake. The chylomicron β-carotene and retinyl palmitate responses to the MCT meal (0–6 h area under the curves, AUC) were significantly (P < 0.05) lower [AUC = 68.1 ± 26.8 and 43.4 ± 10.4 nmol/(L⋅h), for β-carotene and retinyl palmitate, respectively] than those obtained after the LCT meal [301.4 ± 64.0 and 166.0 ± 29.0 nmol/(L⋅h), respectively]. The chylomicron β-carotene and retinyl palmitate responses obtained after the β-carotene–free meal (6–12.5 h AUC) were also significantly lower when the first meal provided MCT rather than LCT. The chylomicron (retinyl palmitate/β-carotene) ratios were constant during the postprandial periods, whatever the meal ingested. We conclude that the chylomicron β-carotene response is markedly diminished when β-carotene is absorbed with MCT instead of LCT. This phenomenon is apparently due to the lack of secretion of chylomicrons in response to MCT; however, a lower intestinal absorption of β-carotene or a higher transport of β-carotene via the portal way in the presence of MCT cannot be ruled out. Finally, the data obtained show that MCT do not affect the rate of intestinal conversion of β-carotene into vitamin A.

Effects of an acute raw resistant potato starch supplement on postprandial glycemia, insulinemia, lipemia in healthy adults

The purpose of this study was to evaluate the lipid and glucose response after an acute intake of raw resistant potato starch. Ten healthy volunteers (6 males and 4 females, aged 19–27 years old, a body mass index of 22.4±0.8 kg·m −2) participate in the study after giving their written consent. They ingested on separate days a low fiber-low resistant starch meal (27 g proteins, 54 g carbohydrates, 24 g lipids and 390 mg cholesterol) supplemented (RSsup) or not (NoRS) with 30 g raw potato starch as a source of resistant starch. Fasting and postprandial blood data were analyzed for free fat acids, glucose, insulin, triglyceride, cholesterol, chylomicron triglyceride and cholesterol, and retinyl palmitate, during seven hours. The chylomicron was isolated and plasma retinyl palmitate (RP) was used as a tracer of chylomicron remnants clearance. The significant results, p<0.05, were: area under the curve of plasma glucose (AUC, mean normalized area against zero time) for NoRS=−32 and for RSsup=102 mmol·7h·L −1; AUC plasma retinyl palmitate NoRS=407 and RSsup=250 mg·7h·L −1; and AUC chylomicron-triglyceride NoRS=52 and RSsup=40 mmol·7h·L −1. The AUC for insulin, free fat acid, plasma triglyceride, cholesterol and chylomicron-cholesterol did not show statistical difference after both diets. The response over time for FFA was characterized by a delay insulin-driven fall with the RSsup that is an unexpected result. Sporadic intakes of potato raw resistant starch did not improve post prandial blood glucose. This unexpected conclusion must be considered with caution as the resistant starch used in this study is probably more digestible as suggested by in vitro study. However, the decrease of postprandial plasma triglycerides rich lipoprotein concentration due to a resistant starch supplement was related to an increase in the clearance of chylomicron. This finding is of interest in the coronary artery disease prevention. Sponsorship: EEC Flair program EURESTA, French Ministery of Agriculture, Danone and FAPESP-BR.

Accumulation of chylomicron remnants in homozygous subjects with familial hypercholesterolaemia.

Post-prandial lipoprotein kinetics were investigated in subjects who lack functioning low-density lipoprotein (LDL) receptors [homozygous familial hypercholesterolaemia (FH)]. An oral fat load was given, and chylomicron plasma kinetics was determined by monitoring the clearance of triglyceride, retinyl palmitate and apolipoprotein B48, calculated as the area under the curve, for 7.5 h. In addition, the binding and uptake of chylomicron remnants by fibroblasts of FH and control subjects were assessed in vitro. Based on the plasma kinetics of chylomicron triglyceride, retinyl palmitate and apolipoprotein B48 after a lipid meal, chylomicron clearance was found to be substantially delayed compared with normolipidaemic control subjects. Consistent with involvement of the LDL receptor in chylomicron clearance, binding and uptake of chylomicron remnants by fibroblasts of FH subjects was found to be substantially less than in cells from control subjects. This study shows that, in addition to LDL, chylomicron metabolism is severely impaired in FH and that the LDL receptor is significantly involved in the clearance of post-prandial lipoproteins. Moreover, this study raises the possibility that in FH, and in other disorders in which LDL receptor expression is reduced, atherogenesis might be a post-prandial disease.

Lipoprotein lipase mass and activity in post-heparin plasma from subjects with intra-abdominal visceral fat accumulation.

The purpose of this study was to investigate the possibility of impaired lipolysis of triglyceride-rich lipoproteins in patients with abdominal visceral fat accumulation by assessing two major lipolytic enzymes in the plasma, lipoprotein lipase (LPL) and hepatic lipase (HL). A total of 31 patients [20 men, 11 women, age 50 +/- 7 years old, body mass index (BMI) 26 +/- 2 kg/m2 (mean +/- sd)] were analyzed. Visceral fat and subcutaneous fat areas were evaluated using a computerized tomographic (CT) method at the level of the umbilicus. Total lipolytic activity in the postheparin plasma (PHP) was measured using Triton X-100-emulsified triolein and LPL activity was calculated as the activity in whole plasma inhibited by the 5D2 monoclonal antibody for LPL. LPL enzyme mass was determined by a sandwich enzyme immunoassay. The visceral fat area was found to be negatively correlated with LPL mass (V vs LPL mass, r = -0.37, P = 0.04) in PHP and had a tendency toward negative correlation with the LPL activity in the PHP (V vs LPL activity, r = -0.29, P = 0.12). Subcutaneous fat area, on the other hand, did not show any correlation with LPL activity (r = 0.13, P = 0.49) or mass (r = 0.22, P = 0.25) in the PHP. The visceral fat area was found to be positively correlated with fasting serum insulin levels (r = 0.67, P < 0.01). Body mass index (BMI) was not correlated with LPL mass or activity in the PHP. Multi-regressional analysis showed that abdominal visceral fat could be correlated with LPL mass in the PHP, independently of fasting serum insulin. The HL activity from PHP of the patients did not show significant correlation with visceral fat area, subcutaneous fat area or body mass index. Fat distribution affects LPL mass and activity, either directly or via another metabolic abnormality such as insulin resistance, leading to impaired hydrolysis of triglycerides in chylomicrons and very low density lipoproteins (VLDL) in these subjects.

In vitro measurement of lipoprotein and hepatic lipases.

Two genetically related lipases perform the hydrolysis of fatty acids from triglycerides and phosphohpids in plasma lipoproteins; lipoprotein lipase (LPL) and hepatic lipase (HL) (). The former catabolizes the hydrolysis of triglycerides in chylomicrons and very low-density lipoproteins (VLDL) producing the so-called remnant particles. The later, with higher affinity for phospholipids, may modify the conformation of lipoproteins acting on the surface of intermediate-density lipoproteins (IDL) and high-density lipoprotein (HDL) particles. Both enzymes have a high affinity for the proteoglycans that anchor the lipases to the endothelial surface, their resident site. LPL has a peripheral distribution being more abundant in tissues in which fatty acids are stored (adipose tissue) or predominantly used as metabolic fuel (muscle), whereas HL is confined to the endothelia of the liver. When an heparin bolus is injected into the blood stream, a release of lipases from their anchors to the circulation is observed because lipases have higher affinity for heparin than for proteoglycans. After heparin injection, the amount of LPL and HL circulating in plasma is increased several hundred folds and the amount of lipases in postheparin plasma is taken as an indirect measure of the lipase content in the individual ().

Suppressive Effect of Globin Digest on Postprandial Hyperlipidemia in Male Volunteers1,2

We have reported previously that various edible protein digests inhibit dietary hyperlipidemia in mice, rats, pigs and dogs. Of the various digests tested, globin digest had the most potent inhibitory activity, and a tetrapeptide extracted from globin digest, Val-Val-Tyr-Pro, had activity 7000-fold greater than that of the parent digest. In this clinical study, we investigated the influence of globin digest on serum chylomicron triglyceride concentrations as an indicator of the effect of globin digest on fat absorption and catabolism in humans. Parallel and crossover trials were conducted in which men consumed a control high fat diet (25 g fat, 7.6 g carbohydrate, 1.9 g protein and 0.7 g sodium chloride) or the same diet supplemented with globin digest. The supplemented dosages were 1 and 4 g globin digest. In the parallel trial, 22 men were divided into three groups: control, globin digest 1 g and globin digest 4 g. The increases in chylomicron triglyceride concentrations at 1 h after ingestion of 1 or 4 g globin digest were significantly lower (P< 0.05) compared with the control group. The crossover trial involved six subjects who consumed the control high fat diet and the same diet supplemented with 4 g globin digest. Serum chylomicron triglyceride levels increased in both groups at 1 and 2 h after ingestion, but when subjects consumed 4 g globin digest the increases were suppressed to 75 (P< 0.05) and 42% (P< 0.05) of the increases in controls at the corresponding times, respectively. The areas under the curves of chylomicron and serum total triglyceride concentrations during the 4 h after ingestion of 4 g globin digest were 46 (P< 0.05) and 34% (P< 0.05) lower, respectively, than when the men consumed the high fat control diet. In these trials, globin digest reduced the increase in serum chylomicron triglyceride concentrations as a result of the ingestion of a high fat diet. This hypotriglyceridemic effect of globin digest may be valuable for preventing obesity and in lowering the incidence of cardiovascular diseases.

Hepatic uptake of chylomicron remnants

Chylomicrons are formed in the intestine and transport dietary triglyceride to peripheral tissues and cholesterol to the liver. The enzyme lipoprotein lipase, with apolipoprotein (apo)C-II as a co-factor, hydrolyzes chylomicron triglyceride allowing the delivery of free fatty acids to muscle and adipose tissue. As a result, a new particle called a chylomicron remnant is formed. This particle is enriched in cholesteryl ester and fat-soluble vitamins and contains apoB-48 and apoE. It is rapidly removed from the circulation by the liver. ApoE is the moiety required for rapid hepatic removal. Its activity is inhibited by C apolipoproteins, especially apoC-I. Hepatic removal appears to be accomplished by several overlapping mechanisms. The particle must first achieve a size that allows it to be "sieved" through the endothelial fenestre allowing entrance into the space of Disse. Here, it may 1) be removed directly by LDL receptors; 2) acquire additional apoE that is secreted free into the space, and then be removed directly by the LDL receptor-related protein (LRP); or 3) it may be sequestered in the space. Sequestration occurs by binding of apoE to heparan sulfate proteoglycans and/or binding of apoB to hepatic lipase. Sequestered particles may be further metabolized allowing apoE, and lysophospholipid enrichment, followed by transfer to one of the above receptors for hepatic uptake. The above formulation is based upon animal studies. In humans, delayed removal of chylomicron remnants has been documented in diabetes, renal failure, and familial combined hyperlipemia and is the abnormality resulting in type III hyperlipidemia. Case control studies have identified delayed remnant removal as an independent risk factor for atherosclerotic cardiovascular disease. Thus, understanding the further details of the processes, and how it can be regulated in humans, is an important challenge for the future.