Triglyceride-rich Lipoproteins apoB-48 Research Articles

Dietary-Induced Elevations of Triglyceride-Rich Lipoproteins Promote Atherosclerosis in the Low-Density Lipoprotein Receptor Knockout Syrian Golden Hamster.

Elevated triglycerides are associated with an increased risk of cardiovascular disease (CVD). Therefore, it is very important to understand the metabolism of triglyceride-rich lipoproteins (TRLs) and their atherogenic role in animal models. Using low-density lipoprotein receptor knockout (LDLR−/−) Syrian golden hamsters, this study showed that unlike LDLR−/− mice, when LDLR−/− hamsters were fed a high cholesterol high-fat diet (HFD), they had very high plasma levels of triglycerides and cholesterol. We found that LDLR−/− hamsters exhibited increased serum TRLs and the ApoB100 and 48 in these particles after being fed with HFD. Treatment with ezetimibe for 2 weeks decreased these large particles but not the LDL. In addition, ezetimibe simultaneously reduced ApoB48 and ApoE in plasma and TRLs. The expression of LRP1 did not change in the liver. These findings suggested that the significantly reduced large particles were mainly chylomicron remnants, and further, the remnants were mainly cleared by the LDL receptor in hamsters. After 40 days on an HFD, LDLR−/− hamsters had accelerated aortic atherosclerosis, accompanied by severe fatty liver, and ezetimibe treatment reduced the consequences of hyperlipidemia. Compared with the serum from LDLR−/− hamsters, that from ezetimibe-treated LDLR−/− hamsters decreased the expression of vascular adhesion factors in vascular endothelial cells and lipid uptake by macrophages. Our results suggested that in the LDLR−/− hamster model, intestinally-derived lipoprotein remnants are highly atherogenic and the inflammatory response of the endothelium and foam cells from macrophages triggered atherosclerosis. The LDL receptor might be very important for chylomicrons remnant clearance in the Syrian golden hamster, and this may not be compensated by another pathway. We suggest that the LDLR−/− hamster is a good model for the study of TRLs-related diseases as it mimics more complex hyperlipidemia.

Plasma PCSK9 correlates with apoB-48-containing triglyceride-rich lipoprotein production in men with insulin resistance

Intestinal triglyceride (TG)-rich lipoproteins (TRLs) are important in the pathogenesis of atherosclerosis in insulin resistance (IR). We investigated the association of plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) concentrations with apoB-48-containing TRL metabolism in 148 men displaying various degrees of IR by measuring in vivo kinetics of TRL apoB-48 during a constant-fed state after a primed-constant infusion of L-[5,5,5-D3]leucine. Plasma PCSK9 concentrations positively correlated with TRL apoB-48 pool size (r = 0.31, P = 0.0002) and production rate (r = 0.24, P = 0.008) but not the fractional catabolic rate (r = -0.04, P = 0.6). Backward stepwise multiple linear regression analysis identified PCSK9 concentrations as a positive predictor of TRL apoB-48 production rate (standard β = +0.20, P = 0.007) independent of BMI, age, T2D/metformin use, dietary fat intake during the kinetic study, and fasting concentrations of TGs, insulin, glucose, LDL cholesterol, or C-reactive protein. We also assessed intestinal expression of key genes involved in chylomicron processing from duodenal samples of 71 men. Expression of PCSK9 and HMG-CoAR genes was positively associated (r = 0.43, P = 0.002). These results support PCSK9 association with intestinal secretion and plasma overaccumulation of TRL apoB-48 in men with IR.

Differential associations between plasma concentrations of insulin and glucose and intestinal expression of key genes involved in chylomicron metabolism.

The mechanisms underlying the oversecretion of apolipoprotein (apo)B-48-containing triglyceride-rich lipoproteins (TRL) in insulin-resistance (IR) states in humans remain to be fully understood. The objective of this study was to evaluate the association between the plasma levels of insulin and glucose and the intestinal expression of key genes involved in chylomicron metabolism in a large sample of nondiabetic men displaying various degrees of IR. Duodenal biopsies were obtained by gastroduodenoscopy in 127 men free of intestinal disease. Gene expression was measured using quantitative PCR in duodenal samples. Plasma insulin and glucose concentrations were measured in the fasting state. Postprandial TRL apoB-48 kinetics were measured using a primed-constant infusion of l-[5,5,5-D3]leucine for 12 h in a subgroup of 75 subjects maintained in a constant fed state. Plasma insulin levels were negatively associated with intestinal expression of ACS1 (standard β = -0.20, P = 0.007), DGAT1 (β = -0.18, P = 0.001), DGAT2 (β = -0.20, P = 0.02), and MTP (β = -0.27, P = 0.0005), whereas glucose levels were positively associated with MTP expression (β = 0.15, P = 0.04) independent of age, BMI, waist circumference, dietary intake, and duodenal expression of SREBP1c. Insulin levels, but not glucose concentrations, were positively correlated with postprandial TRL apoB-48 production rate ( r = 0.24, P = 0.04) and pool size ( r = 0.27, P = 0.03). In conclusion, plasma insulin and glucose levels are differentially associated with the expression of key genes involved in chylomicron metabolism. These results suggest that alterations in intestinal lipoprotein metabolism associated with IR may be regulated by plasma levels of both insulin and glucose concurrently and are therefore likely modified by the onset of insulin insufficiency. NEW & NOTEWORTHY We demonstrate that plasma insulin and glucose levels are differentially associated with the expression of key genes involved in chylomicron metabolism in men. For instance, intestinal expression of MTP is negatively associated with plasma insulin concentrations and positively associated with plasma glucose concentrations. Alterations in intestinal lipoprotein metabolism associated with insulin resistance may be regulated by plasma levels of both insulin and glucose concurrently and are therefore likely modified by the onset of insulin insufficiency.

Differential Effects of Estrogen and Progestin on Apolipoprotein B100 and B48 Kinetics in Postmenopausal Women.

The distinct effects of the estrogen and progestin components of hormonal therapy on the metabolism of apolipoprotein (apo) B-containing lipoproteins have not been studied. We enrolled eight healthy postmenopausal women in a placebo-controlled, randomized, double-blind crossover study. Each subject received placebo, conjugated equine estrogen (CEE, 0.625 mg/day) and CEE plus medroxyprogesterone acetate (MPA, 2.5 mg/day) for 8 weeks in a randomized order, with a 4-week washout between phases. Main outcomes were the fractional catabolic rate (FCR) and production rate (PR) of apo B100 in triglyceride-rich lipoproteins (TRL), intermediate-density lipoproteins (IDL) and low -density lipoprotein (LDL) and of apo B48 in TRL. Compared to placebo, CEE increased TRL apo B100 PR (p = 0.04). CEE also increased LDL apo B100 FCR (p = 0.02), but this effect was offset by a significant increase in LDL apo B100 PR (p = 0.04). Adding MPA to CEE negated the CEE effects resulting in no significant changes in TRL apo B100 PR and LDL apo B100 FCR and PR relative to placebo. Relative to placebo, during CEE there was a trend toward a reduction in plasma apo B48 concentrations and PR (p = 0.07 and p = 0.12, respectively). Compared with CEE, CEE + MPA significantly increased TRL apo B48 FCR (p = 0.02) as well as apo B48 PR (p = 0.01), resulting in no significant changes in apo B48 concentration. Estrogen and progestin have independent and opposing effects on the metabolism of the atherogenic apo B100- and apo B48-containing lipoproteins.

Effects of Intranasal Insulin on Triglyceride-Rich Lipoprotein Particle Production in Healthy Men.

Insulin administered directly into the brain acutely suppresses hepatic glucose production and triglyceride-rich lipoprotein (TRL) secretion in rodents. In addition, intranasally administered insulin, which selectively raises cerebrospinal fluid insulin concentration, suppresses hepatic glucose production in humans; however, its effect on TRL secretion in humans has not previously been examined. In this study, we examined whether intranasal insulin, administered at a dose that has previously been shown to suppress hepatic glucose production, modulates TRL particle secretion by the liver and intestine in humans. Nine healthy, normolipidemic, and normoglycemic men participated in a study consisting of 2 randomized study arms. Subjects received intranasal lispro insulin (40 IU) or placebo. Because intranasal insulin results in a rapid and transient increase in systemic insulin concentration after administration, we matched systemic insulin concentrations in the 2 study arms by infusing lispro insulin intravenously for 30 minutes together with intranasal placebo administration. Apo (apolipoprotein) B100-containing (hepatically derived) and apoB48-containing (intestinally derived) TRL lipoprotein particle turnover were measured for the ensuing 10 hours under pancreatic clamp conditions and constant fed state, using stable isotope enrichment techniques and multicompartmental modeling. Under these experimental conditions, no significant effects of intranasal insulin versus placebo on TRL apoB100 or B48 concentrations, fractional catabolic rates, or production rates were observed. Insulin delivered intranasally at a dose that has been shown to raise cerebrospinal fluid insulin concentration and suppress hepatic glucose production does not affect TRL particle production by the liver and intestine in healthy men. URL: http://www.clinicaltrials.gov. Unique identifier: NCT03141827.

Metabolism and proteomics of large and small dense LDL in combined hyperlipidemia: effects of rosuvastatin

Small dense LDL (sdLDL) has been reported to be more atherogenic than large buoyant LDL (lbLDL). We examined the metabolism and protein composition of sdLDL and lbLDL in six subjects with combined hyperlipidemia on placebo and rosuvastatin 40 mg/day. ApoB-100 kinetics in triglyceride-rich lipoproteins (TRLs), lbLDL (density [d] = 1.019-1.044 g/ml), and sdLDL (d = 1.044-1.063 g/ml) were determined in the fed state by using stable isotope tracers, mass spectrometry, and compartmental modeling. Compared with placebo, rosuvastatin decreased LDL cholesterol and apoB-100 levels in TRL, lbLDL, and sdLDL by significantly increasing the fractional catabolic rate of apoB-100 (TRL, +45%; lbLDL, +131%; and sdLDL, +97%), without a change in production. On placebo, 25% of TRL apoB-100 was catabolized directly, 37% was converted to lbLDL, and 38% went directly to sdLDL; rosuvastatin did not alter these distributions. During both phases, sdLDL apoB-100 was catabolized more slowly than lbLDL apoB-100 (P < 0.01). Proteomic analysis indicated that rosuvastatin decreased apoC-III and apoM content within the density range of lbLDL (P < 0.05). In our view, sdLDL is more atherogenic than lbLDL because of its longer plasma residence time, potentially resulting in more particle oxidation, modification, and reduction in size, with increased arterial wall uptake. Rosuvastatin enhances the catabolism of apoB-100 in both lbLDL and sdLDL.

Effects of bariatric surgery on hepatic and intestinal lipoprotein particle metabolism.

Insulin resistance and type 2 diabetes, driven largely by obesity, are characterized by an increase in triglyceride-rich lipoproteins (TRLs) due to both reduced TRL clearance from the circulation and increased production by the liver (apoB-100 containing VLDLs) and intestine (apoB-48 containing chylomicrons). Bariatric surgery is the only treatment currently that leads to marked, sustained weight loss. Here, we will review the effects of bariatric surgery on circulating triglyceride/TRL and TRL production and clearance. Bariatric surgery leads to a marked reduction in fasting and postprandial plasma triglyceride. Only one study to date has assessed TRL kinetics after bariatric surgery and has reported a reduction in TRL apoB-100 concentration (i.e. the number of VLDL particles) due to reduced production and increased clearance and reduced TRL apoB-48 concentration (the number of chylomicron particles) due to reduced production. Some bariatric surgery studies have reported no/weak correlation between weight loss and improvements in triglyceride/TRL, suggesting that as yet unidentified factors beyond weight loss may contribute to the marked changes in TRL that occur postbariatric surgery. Available data suggest that bariatric surgery reduces triglyceride and intestinal and hepatic TRL production with increased clearance of hepatic TRL particles. These effects of bariatric surgery on TRL kinetics need to be confirmed with additional studies. Further studies are also needed to compare the effects of various bariatric surgery procedures on TRL kinetics and to elucidate underlying mechanisms.

Abstract 521: Impact of Insulin-resistance, Body Mass Index and Dietary Fat Intakes on Apolipoprotein B-48 Kinetic

Substantial evidence exists indicating that elevated plasma levels of apolipoprotein (apo) B-48-containing lipoproteins are associated with increased cardiovascular disease risk. Overaccumulation of apoB-48-containing lipoproteins of intestinal origin observed in patients with insulin-resistance (IR) is thought to be attributable to both elevated intestinal production and reduced clearance of these lipoproteins. The objective of this study was to assess the relative contribution of IR, anthropometry, and dietary fat content on triglyceride (TG)-rich lipoprotein (TRL) apoB-48 kinetic. The in vivo kinetic of TRL apoB-48 was measured in 131 men with primed-constant infusion of L-[5,5,5-D3]leucine. TRL apoB-48 production rate (PR) and fractional catabolism rate (FCR) were determined by multi-compartmental modeling, while TRL apoB-48 pool size (PS) was measured by ELISA. IR was defined by TG levels &gt; 1.5 mmol/L and Homeostasis Model Assessment of IR (HOMA-IR) &gt; 2.5. Age was inversely associated with TRL apoB-48 FCR (ρ=-0.21; P=0.02), while BMI was positively correlated with TRL apoB-48 PR (ρ=0.33; P=0.0001) and PS (ρ=0.44; P&lt;0.0001). Fat intake was associated with TRL apoB-48 PR (ρ=0.34; P&lt;0.0001) and PS (ρ=0.34; P&lt;0.0001). HOMA-IR was positively associated with TRL apoB-48 PR (ρ=0.26; P=0.005) and PS (ρ=0.35; P=0.0001). Furthermore, when adjusted for fat intake, TRL apoB-48 PR was significantly higher in IR subjects (n=73) than in insulin-sensitive subjects (Δ=+64%; P&lt;0.0001), and TRL apoB-48 FCR was lower (Δ=-13%; P=0.005). Multiple linear regression analysis showed that IR was the most significant constitutive predictor of TRL apo B-48 PR variance (6.6%; P=0.01), while age and BMI were not significantly associated with PR. In conclusion, these results suggest that IR is a major factor contributing to TRL apoB-48 overaccumulation, possibly through increased production and decreased clearance, independent of age, BMI and fat intake.

Glucagon-Like Peptide-2 Regulates Release of Chylomicrons From the Intestine

The intestine efficiently incorporates and rapidly secretes dietary fat as chylomicrons (lipoprotein particles comprising triglycerides, phospholipids, cholesterol, and proteins) that contain the apolipoprotein isoform apoB-48. The gut can store lipids for many hours after their ingestion, and release them in chylomicrons in response to oral glucose, sham feeding, or unidentified stimuli. The gut hormone glucagon-like peptide-2 (GLP-2) facilitates intestinal absorption of lipids, but its role in chylomicron secretion in human beings is unknown. We performed a randomized, single-blind, cross-over study, with 2 study visits 4 weeks apart, to assess the effects of GLP-2 administration on triglyceride-rich lipoprotein (TRL) apoB-48 in 6 healthy men compared with placebo. Subjects underwent constant intraduodenal feeding, with a pancreatic clamp and primed constant infusion of deuterated leucine. In a separate randomized, single-blind, cross-over validation study, 6 additional healthy men ingested a high-fat meal containing retinyl palmitate and were given either GLP-2 or placebo 7 hours later with measurement of TRL triglyceride, TRL retinyl palmitate, and TRL apoB-48 levels. GLP-2 administration resulted in a rapid (within 30 minutes) and transient increase in the concentration of TRL apoB-48, compared with placebo (P = .03). Mathematic modeling of stable isotope enrichment and the mass of the TRL apoB-48 suggested that the increase resulted from the release of stored, presynthesized apoB-48 from the gut. In the validation study, administration of GLP-2 at 7 hours after the meal, in the absence of additional food intake, robustly increased levels of TRL triglycerides (P = .007), TRL retinyl palmitate (P = .002), and TRL apoB-48 (P = .04) compared with placebo. Administration of GLP-2 to men causes the release of chylomicrons that comprise previously synthesized and stored apoB-48 and lipids. This transiently increases TRL apoB-48 levels compared with placebo. Clinical trials number at www.clinicaltrials.gov: NCT 01958775.

Effect of sitagliptin therapy on triglyceride-rich lipoprotein kinetics in patients with type 2 diabetes.

To investigate the effects of sitagliptin therapy on the kinetics of triglyceride-rich lipoprotein (TRL) apolipoprotein (apo)B-48, VLDL apoB-100, apoE and apoC-III in patients with type 2 diabetes. Twenty-two subjects with type 2 diabetes were recruited in this double-blind crossover study, during which the subjects received sitagliptin (100 mg/day) or placebo for a 6-week period each. At the end of each phase of treatment, the in vivo kinetics of the different apolipoproteins were assessed using a primed-constant infusion of l-[5,5,5-D3]leucine for 12 h, with the participants in a constantly fed state. Sitagliptin therapy significantly reduced fasting plasma triglyceride (-15.4%, p = 0.03), apoB-48 (-16.3%, p = 0.03) and free fatty acid concentrations (-9.5%, p = 0.04), as well as plasma HbA1c (placebo: 7.0% ± 0.8 vs. sitagliptin: 6.6% ± 0.7, p < 0.0001) and plasma glucose levels (-13.5%, p = 0.001), without any significant effect on insulin levels. Kinetic results showed that treatment with sitagliptin significantly reduced the pool size of TRL apoB-48 by -20.8% (p = 0.03), paralleled by a reduction in the production rate of these particles (-16.0%, p = 0.03). The VLDL apoB-100 pool size was also significantly decreased by sitagliptin therapy (-9.3%, p = 0.03), mainly because of a reduction in the hepatic secretion of these lipoproteins, although this difference did not reach statistical significance (-9.2%, p = 0.06). Treatment with sitagliptin for 6 weeks reduced triglyceride-rich apoB-containing lipoprotein levels by reducing the synthesis of these particles.

Hepatic lipogenesis and a marker of hepatic lipid oxidation, predict postprandial responses of triglyceride-rich lipoproteins.

Postprandial hypertriglyceridemia is an important risk factor for cardiovascular disease. The mechanisms are still unclear. Here it was tested if hepatic de novo lipogenesis (DNL) and lipid oxidation influence the postprandial responses of triglyceride-rich lipoproteins (TRL) in humans. The contribution of hepatic DNL to hepatic TRL production was analyzed in 67 men and women with a moderate range of BMI after a fat-rich meal. Also, lipase activities, liver fat, and 3-OH-butyrate were quantitated as an indicator of β-oxidation. Lipoproteins and metabolic markers were measured in fasting and postprandial blood samples. Postprandial DNL correlates with postprandial TG and apolipoprotein (apo) C-III responses in plasma and with TG, apoB48 and apoB100 responses in TRLs and their larger remnant particles. Fasting and 8-h postprandial DNL was inversely related to 3-OH-butyrate but not to liver fat content. Fasting apoC-III and 3-OH-butyrate, but not liver fat, independently predicted fasting DNL. The fasting and 8-h postprandial rate of DNL was inversely associated with the hepatic lipid oxidation in humans. DNL contributes significantly to the TG content in TRLs but not to the amount of liver fat, suggesting that an imbalance between DNL and fat oxidation contributes to postprandial atherogenic dyslipidemia.

Abstract 411: Effect of Sitagliptin Therapy on Triglyceride-Rich Lipoprotein Kinetics in Patients With Type 2 Diabetes

Postprandial hyperlipemia is a key metabolic feature of insulin-resistant states and an important risk factor for cardiovascular disease, due to the accumulation of atherogenic triglyceride (TG)-rich lipoproteins (TRL) from both hepatic and intestinal origin. Sitagliptin is a selective inhibitor of dipeptidyl peptidase-4 that has been shown to reduce fasting and postprandial glucose levels in patients with type 2 diabetes (T2D) presumably through incretin hormone-mediated improvements in islet function. The objective of the present study was to investigate the effects of sitagliptin therapy on the kinetics of TRL apolipoprotein (apo) B-48, VLDL apoB-100, apoE and apoC-III in patients with type 2 diabetes. Twenty two subjects with T2D (18 men and 4 postmenopausal women, mean age of 58.2±3.8 y) were recruited in this double-blind crossover study using sitagliptin 100 mg/d or placebo for a 6-week period each, with a 4-week washout period between the two phases. At the end of each phase of treatment, the in vivo kinetics of the different apolipoproteins were assessed using a primed-constant infusion of L-[5,5,5-D3]leucine for 12 h with the participants in a constantly fed state. Sitagliptin therapy vs. placebo significantly reduced concentrations of fasting plasma TG (-15.4%, 0.03), apoB-48 (-16.3%, P=0.03), free fatty acids (-9.5%, P= 0.04), HbA1C (placebo: 7.0%±0.8 vs sitagliptin: 6.6%±0.7, P&lt;0.0001), and plasma glucose (-13.5%, P=0.001) without any significant effect on insulin level. Treatment with sitagliptin significantly reduced the pool size of TRL apoB-48 by -20.8% (P=0.03), due to a reduction in the production rate of these particles (-16.0%, P=0.03). VLDL apoB-100 pool size was also significantly decreased by sitagliptin therapy (-9.3%, P=0.03), mainly due to a reduction in the hepatic secretion of these lipoproteins (-9.2%, P=0.06). Finally, sitagliptin treatment had no effect on VLDL apoC-III and apoE levels, but reduced both fractional catabolic and production rates of VLDL apoE (-10.6%, P=0.05 and -12.7%, P=0.04). In conclusion, treatment with sitagliptin for 6 weeks reduces TG-rich apoB-containing lipoproteins levels through a reduction in the synthesis of these particles in patients with T2D.

Abstract 247: Dipeptidyl Peptidase-4 Inhibition With Sitagliptin Acutely Inhibits Intestinal Lipoprotein Particle Secretion in Healthy Humans

Postprandial dyslipidemia, in part due to overproduction of triglyceride-rich lipoprotein (TRL) particles from the liver and the intestine, contributes to increased CVD risk. The DPP-4 inhibitor sitagliptin, an anti-diabetic agent, has been shown to reduce postprandial lipid excursion following a mixed meal. The underlying mechanism of this effect, however, has not been examined in humans. This study was designed to examine intestinal and hepatic TRL particle production and clearance in response to a single oral dose of sitagliptin. 15 lean, healthy male volunteers were studied in two occasions, 4-6 weeks apart, receiving sitagliptin (100 mg) or placebo in random order. Kinetics of TRL particles of intestinal and hepatic origin were measured using stable isotope tracer infusion techniques and with control of pancreatic hormone levels. Sitagliptin decreased TRL apoB-48 concentration (-32%, P&lt;0.05) by reducing production rate (sitagliptin 47.2+/- 11.0 vs placebo 93.9 +/- 25.2 ug/kg/d, P&lt;0.05). Fractional catabolic rate was not significantly affected. TRL apoB-100 concentration, production rate and fractional catabolic rate were not significantly different between sitagliptin and placebo. Plasma TG, free fatty acids, glucose, pancreatic hormones, and TRL TG were similar between treatments. In conclusion, sitagliptin acutely inhibits intestinal, but not hepatic, lipoprotein particle production, independent of changes in pancreatic hormones and circulating glucose and free fatty acids. This pleotropic effect of sitagliptin explains in part the reduction in postprandial lipemia seen in clinical trials and may provide metabolic benefits beyond glucose lowering.

Abstract P270: Niacin Lowers Triglyceride-Rich Lipoprotein Apolipoprotein B-48 Secretion in Statin-Treated Type 2 Diabetics

Background: Type 2 diabetic subjects often have hypertriglyceridemia and an increased concentration of apolipoprotein B-48 (apoB-48) in circulation, particularly during the postprandial period. There is an accumulating body of evidence to suggest that apoB-48 plays a central role in the development of atherosclerosis. Statins are the frontline therapy to reduce cardiovascular risk, however, a large residual risk still remains. This residual risk suggests that additional therapeutic interventions may be required to further reduce CVD risk. Aim: To investigate the effect of niacin on the metabolism of triglyceride-rich lipoprotein (TRL) apoB-48 in men with type 2 diabetes on background statin therapy. Methods: Twelve type 2 diabetic men were recruited for this randomized, cross-over design study. Patients required a statin-treated low density lipoprotein (LDL) cholesterol of less than 2.5 mmol/L to enter the trial. Patients were then randomized to rosuvastatin alone or rosuvastatin plus niacin (titrated up from 1 to 2 g daily) for a period of 12 weeks and then were crossed over to the alternate therapy with a 3 week washout period in between. Metabolic studies were performed at the end of each treatment period. A bolus intravenous infusion of D3-leucine was administered as subjects consumed a standardised high-fat liquid meal. Blood samples were collected over 24 hours and TRL apoB-48 tracer/tracee ratios were measured using gas chromatography-mass spectrometry. Kinetic parameters, including fractional catabolic rate (FCR) and production rate (PR), were derived using a multicompartmental model. Results: Niacin significantly reduced triglyceride, plasma cholesterol, LDL cholesterol and apoB (all p&lt;0.005). TRL apoB-48 concentration was lower with niacin (8.24 ± 1.98 vs 5.48 ± 1.14 mg/L, p=0.03). ApoB-48 FCR was not altered with niacin (8.78 ± 1.04 vs 9.17 ± 1.26 pools/day; p=0.79). Basal apoB-48 PR (3.21 ± 0.34 vs 2.50 ± 0.31 mg/kg/day; p=0.04) and postprandial apoB-48 PR were significantly lower (1.35 ± 0.19 vs 0.84 ± 0.12 mg/kg; p=0.02) on niacin. Conclusion: Niacin reduces TRL apoB-48 concentration by lowering basal and postprandial apoB-48 PR. This effect on apoB-48 metabolism may be beneficial for reducing atherogenic postprandial TRL particles and may provide CVD risk benefit to patients with type 2 diabetes.

Key intestinal genes involved in lipoprotein metabolism are downregulated in dyslipidemic men with insulin resistance

Insulin resistance (IR) is associated with elevated plasma levels of triglyceride-rich lipoproteins (TRLs) of intestinal origin. However, the mechanisms underlying the overaccumulation of apolipoprotein (apo)B-48-containing TRLs in individuals with IR are not yet fully understood. This study examined the relationships between apoB-48-containing TRL kinetics and the expression of key intestinal genes and proteins involved in lipid/lipoprotein metabolism in 14 obese nondiabetic men with IR compared with 10 insulin-sensitive (IS) men matched for waist circumference. The in vivo kinetics of TRL apoB-48 were assessed using a primed-constant infusion of L-[5,5,5-D₃]leucine for 12 h with the participants in a constantly fed state. The expression of key intestinal genes and proteins involved in lipid/lipoprotein metabolism was assessed by performing real-time PCR quantification and LC-MS/MS on duodenal biopsy specimens. The TRL apoB-48 pool size and production rate were 102% (P < 0.0001) and 87% (P = 0.01) greater, respectively, in the men with IR versus the IS men. On the other hand, intestinal mRNA levels of sterol regulatory element binding factor-2, hepatocyte nuclear factor-4α, and microsomal triglyceride transfer protein were significantly lower in the men with IR than in the IS men. These data indicate that IR is associated with intestinal overproduction of lipoproteins and significant downregulation of key intestinal genes involved in lipid/lipoprotein metabolism.

MTP gene polymorphisms and postprandial lipemia in familial combined hyperlipidemia: Effects of treatment with atorvastatin

BackgroundThe microsomal triglyceride transfer protein (MTP) is involved in hepatic and intestinal apoB secretion. We studied the effect of the functional MTP−493G/T polymorphism on fasting and postprandial lipoproteins in patients with familial combined hyperlipidemia (FCH) before and after treatment with atorvastatin. MethodsEight FCH heterozygote carriers of the rare −493T allele were compared to 9 matched FCH homozygotes for the wild-type allele in a pilot study. Oral fat loading tests were carried out to measure triglycerides (TG) and apo B48 and B100 in the different fractions of triglyceride-rich lipoproteins (TRLs) before and after treatment with atorvastatin. ResultsBefore treatment, TG were similar between the −493T allele carriers and non-carriers. In the T-allele carriers, a trend was observed for increased postprandial apo B48 and B100 concentrations in Sf >400 and Sf 60–400 compared to non-carriers. After treatment, fasting and postprandial TG were significantly lowered in carriers of the T allele, but atorvastatin had no effect on postprandial TG in non-carriers. Atorvastatin resulted in similar reductions of apo B48 and B100 in TRLs in both groups. ConclusionThe MTP-493G/T polymorphism modulates postprandial apo B48 and apo B100 of TRLs in FCH. Atorvastatin decreases postprandial TG in T-allele carriers with FCH.

Abstract 167: Dietary Medium-chain Triglyceride Supplementation Has No Effect on Apolipoprotein B-48 and Apolipoprotein B-100 Kinetics in Insulin-resistant Males

Medium-chain triglyceride (MCT) supplements are used by clinicians to treat patients with severe hypertriglyceridemia at risk for pancreatitis. However, the potential mechanisms underlying the triglyceride-lowering effects of MCT have not been thoroughly examined yet in human. This double-blind crossover study compared the impact of a 4-week supplementation with MCT oil 20 g/d vs corn oil 20 g/d on the intravascular kinetics of apolipoprotein (apo) B-48-containing triglyceride-rich lipoproteins (TRL) and apoB-100-containing VLDL as well as on the expression of key intestinal genes involved in lipid metabolism in 28 obese insulin-resistant males. In vivo kinetics of TRL apoB-48 and VLDL apoB-100 were assessed using a primed-constant infusion of L-[5,5,5-D3]leucine for 12h in the fed state. Expression of key intestinal genes involved in lipid metabolism was assessed in a subgroup of participants (n=16) by real-time PCR quantification in duodenal biopsy performed at the end of each phase of the supplementation in the fasted state. Compared with corn oil, MCT supplement had no significant effect on plasma lipoprotein profile and the TRL apoB-48 and VLDL apoB-100 kinetics. There were significant positive correlations at the end of the MCT supplementation between expression of SREBP-2 and expression of HNF-4α (r=0.51; P&lt;0.05), HMGCoAR (r=0.75; P&lt;0.001), ACAT-2 (r=0.51; P&lt;0.05), NPC1L1 (r=0.66; P&lt;0.05), ACS-1 (r=0.74; P&lt;0.001), LDL receptor (r=0.67; P&lt;0.05) and PCSK-9 (r=0.60; P&lt;0.05) in intestinal tissue. However, MCT supplement had no significant impact on the expression of those key lipid and fatty acid regulation genes compared with corn oil. These data indicate that 4-week supplementation with MCT in obese insulin resistant men has no effect on TRL apoB-48 and VLDL apoB-100 kinetics and on the intestinal expression of genes involved in lipid and fatty acid metabolism.

Abstract 290: Key Intestinal Genes Involved in Lipoprotein Metabolism Are Downregulated in Insulin-Resistant Males

Recent studies indicate that insulin-resistance (IR) is associated with elevated levels of triglyceride-rich lipoproteins (TRL), including apoB-48-containing TRL of intestinal origin, in both the fasted and post-prandial states. This is of interest because elevated levels of intestine-derived lipoproteins are associated with increased cardiovascular disease risk. However, the mechanisms underlying the overaccumulation of apoB-48-containing TRL in IR have not been fully characterized in human. Therefore, the objective of this study was to examine the relationships between apoB-48-containing TRL kinetics and expression of key intestinal genes involved in lipid and lipoprotein metabolism in nondiabetic, IR males compared with insulin-sensitive (IS) males matched for age and waist circumference. A total of 30 nondiabetic caucasian males were chosen for extremes of insulin sensitivity (14 IR and 16 IS subjects) and matched for age and waist circumference. In vivo kinetics of TRL apoB-48 were assessed using a primed-constant infusion of L-[5,5,5-D3]leucine for 12h in the fed state in all subjects. Expression of key intestinal genes involved in lipid and lipoprotein metabolism was compared by real-time PCR quantification in duodenal biopsy specimens from IR and IS participants taken in the fasted state. TRL apoB-48 pool size (PS) and production rate (PR) were increased by 105% (P&lt;0.0001) and 45% (P=0.03), respectively in IR subjects compared with IS subjects. Expression of the nuclear transcription factors SREBP-2, SREBP1-C and HNF4α was significantly reduced by 31%, 28% and 25%, respectively in IR subjects. Similarly, many key genes involved in cholesterol, fatty acid, triglyceride and lipoprotein metabolism were significantly downregulated in IR individuals. In IR participants, intestinal expression of HMG CoAR, ACC1, SCD1, DGAT2, apoB and MTP was significantly reduced compared with IS subjects. Intestinal MTP expression was inversely correlated with TRL apoB-48 PS (r=-0.50, P=0.005) and PR (r=-0.32, P=0.07). These data suggest that IR is associated with intestinal overproduction of lipoproteins and downregulation of key intestinal genes involved in lipid/lipoprotein metabolism. Downregulation of these genes in the fasted state could represent an adaptive response to IR state.

Effects of ezetimibe and simvastatin on apolipoprotein B metabolism in males with mixed hyperlipidemia

Sixteen hyperlipidemic men were enrolled in a randomized, placebo-controlled, double-blind, cross-over study to evaluate the effect of ezetimibe 10 mg and simvastatin 40 mg, coadministered and alone, on the in vivo kinetics of apolipoprotein (apo) B-48 and B-100 in humans. Subjects underwent a primed-constant infusion of a stable isotope in the fed state. The coadministration of simvastatin and ezetimibe significantly reduced plasma concentrations of cholesterol (-43.0%), LDL-C (-53.6%), and triglycerides (-44.0%). Triglyceride-rich lipoproteins (TRL) apoB-48 pool size (PS) was significantly decreased (-48.9%) following combination therapy mainly through a significant reduction in TRL apoB-48 production rate (PR) (-38.0%). The fractional catabolic rate (FCR) of VLDL and LDL apoB-100 were significantly increased with all treatment modalities compared with placebo, leading to a significant reduction in the PS of these fractions. We also observed a positive correlation between changes in TRL apoB-48 PS and changes in TRL apoB-48 PR (r = 0.85; P < 0.0001) with combination therapy. Our results indicate that treatment with simvastatin plus ezetimibe is effective in reducing plasma TRL apoB-48 levels and that this effect is most likely mediated by a reduction in the intestinal secretion of TRL apoB-48. Our study also indicated that the reduction in LDL-C concentration following combination therapy is mainly driven by an increase in FCR of apoB-100 containing lipoproteins.

Both Intestinal and Hepatic Lipoprotein Production Are Stimulated by an Acute Elevation of Plasma Free Fatty Acids in Humans

Hepatic lipoprotein production has been shown previously to be regulated by free fatty acid (FFA) flux to the liver, whereas intestinal lipoprotein production is stimulated mainly by ingested fat absorbed from the intestinal lumen. Emerging evidence indicates that intestinal lipoprotein production is increased in insulin resistance and type 2 diabetes mellitus, conditions that are associated with increased levels of circulating FFAs. Here we investigated whether short-term elevation of plasma FFAs stimulates intestinal apolipoprotein (apo) B-48- and hepatic apoB-100-containing triglyceride-rich lipoprotein (TRL) production in humans in the fed state. TRL apoB-48 and apoB-100 metabolism were examined in 12 healthy men during a constant fed state. The studies were as follows, respectively: (1) Intralipid/heparin was infused intravenously immediately before and during the kinetics study to induce an approximately 3-fold difference in plasma FFA compared with the saline study; (2) saline was infused intravenously as a control. ApoB-48- and apoB-100-containing TRL production and clearance were determined with a 12-hour primed constant infusion of [D3]L-leucine and multicompartmental kinetic modeling. TRL apoB-48 production rate was 69% higher in the Intralipid/heparin study than in the saline control (5.95+/-1.13 versus 3.53+/-0.58 mg/kg per day; P=0.027), and there was no significant difference in TRL apoB-48 clearance. TRL apoB-100 concentrations were also increased (P<0.001) and TRL apoB-100 production rate was 35% higher in the Intralipid/heparin study compared with saline (28+/-4 versus 21+/-3 mg/kg per day; P=0.020). This is the first study to demonstrate that intestinal TRL apoB-48 production is increased after short-term elevation of plasma FFAs in humans in the fed state, similar to the well-described stimulation of hepatic TRL apoB100-containing particles by FFAs.