Triglyceride Transport Research Articles

Meta‐analysis of genome‐wide association studies for circulating phylloquinone (818.9)

Phylloquinone (PK) is the primary dietary and circulating form of vitamin K. Low circulating PK has been associated with abnormal calcification of soft tissue. Because few studies have assessed the genetic component influencing circulating PK, we sought to identify common genetic variants associated with circulating PK concentrations by conducting a genome‐wide association (GWA) meta‐analysis of circulating PK in two populations of European descent from the Cohorts of Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. Results from adjusted cohort‐specific GWA analyses were meta‐analyzed with inverse variance weights. No genome‐wide significant associations were observed in the meta‐analysis (n = 2,138). We found nominal associations (P<1×10−6) on five independent loci. These results suggest that the APOA1C3/A4/A5 gene cluster, involved in triglyceride transport, CYP4F2, involved in vitamin metabolism, COL22A1, a collagen gene, CTNAA2, a catenin gene, and CDO1, a cysteine dioxygenase gene, are candidate genes that may be associated with serum PK. Given the multiple determinants of circulating PK and small sample size of the current study, further investigation with a larger sample is warranted.

Epistatic Interactions between Apolipoprotein E and Hemoglobin S Genes in Regulation of Malaria Parasitemia

Apolipoprotein E is a monomeric protein secreted by the liver and responsible for the transport of plasma cholesterol and triglycerides. The APOE gene encodes 3 isoforms Ɛ4, Ɛ3 and Ɛ2 with APOE Ɛ4 associated with higher plasma cholesterol levels and increased pathogenesis in several infectious diseases (HIV, HSV). Given that cholesterol is an important nutrient for malaria parasites, we examined whether APOE Ɛ4 was a risk factor for Plasmodium infection, in terms of prevalence or parasite density. A cross sectional survey was performed in 508 children aged 1 to 12 years in Gabon during the wet season. Children were screened for Plasmodium spp. infection, APOE and hemoglobin S (HbS) polymorphisms. Median parasite densities were significantly higher in APOE Ɛ4 children for Plasmodium spp. densities compared to non-APOE Ɛ4 children. When stratified for HbS polymorphisms, median Plasmodium spp. densities were significantly higher in HbAA children if they had an APOE Ɛ4 allele compared to those without an APOE Ɛ4 allele. When considering non-APOE Ɛ4 children, there was no quantitative reduction of Plasmodium spp. parasite densities for HbAS compared to HbAA phenotypes. No influence of APOE Ɛ4 on successful Plasmodium liver cell invasion was detected by multiplicity of infection. These results show that the APOE Ɛ4 allele is associated with higher median malaria parasite densities in children likely due to the importance of cholesterol availability to parasite growth and replication. Results suggest an epistatic interaction between APOE and HbS genes such that sickle cell trait only had an effect on parasite density in APOE Ɛ4 children. This suggests a linked pathway of regulation of parasite density involving expression of these genes. These findings have significance for understanding host determinants of regulation of malaria parasite density, the design of clinical trials as well as studies of co-infection with Plasmodium and other pathogens.

High DHA dosage from algae oil improves postprandial hypertriglyceridemia and is safe for type-2 diabetics

Postprandial refers to diet induced changes in plasma concentrations of sugars, amino acids and fats be- tween 0 and 6 h following a meal. This review details the fat transport through lipoprotein particles and triglyceride frac- tions in the postprandial plasma. The long-chain omega-3 fatty acid docosahexaenoic acid (DHA) is more active in postprandial plasma and is more abundantly incorporated into the surface phospholipid fraction of lipoproteins. A survey of controlled clinical trials in the literature demon- strates that 1,000 mg to 2,000 mg DHA daily is effective to treat hypertriglyceridemia (HTG), mixed dyslipidemia and most effectively controls elevated postprandial triglycerides (TG). TG is a marker for total fat in circulation. Omega-3 fatty acids lower fasting and postprandial TG, an activity first discovered in 1971 in Greenlandic Inuits. Low TG and high DHA were coincident with the absence of type 2 diabetes. It is now known that DHA is the major structural and functional omega-3 component of lipoproteins in hu- man plasma. DHA is the omega-3 to most substantially increase by mass in the phospholipid fraction of very low- density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL). DHA is most effective at raising HDL levels and improves the omega-3 index in red blood cells (RBC). DHA intake also correlates with greater than 25 % reductions of fasting TG and greater than 40 % reductions in postprandial TG. Postprandial HTG is common in the type 2 diabetes; therefore, we considered the safety of DHA from Schizochytrium sp. algae oil and the evidence for risk reduction of coronary vascular disease (CVD) and type 2 diabetes. Recent clinical trials suggest high DHA intake from Chromista algae controls plasma TG, but does not appear to control glucocentric markers or cholesterol levels. DHA directly affects postprandial TG transport, but has little effect on insulin function and insulin resistance. Applications for use in South Asian diabetics are considered. 1,200 mg algae DHA daily over 3 months is an optimized program for direct control of postprandial HTG and is safe for type 2 diabetics.

Abstract 2: Overexpression of Human Apolipoprotein C-III in Mice Decreases Intestinal Transport of Triglyceride Into Lymph

INTRODUCTION Apolipoprotein C-III (apoC-III), synthesized by the liver and intestine, is an inhibitor of LPL-mediated lipolysis and hepatic clearance of triglyceride-rich lipoproteins. ApoC-III overproduction is linked with hypertriglyceridemia and atherosclerosis. ApoC-III may also play an intracellular role in hepatic VLDL assembly/secretion. Little is known about the role of apoC-III in the intestine, although it is secreted on chylomicrons coincident with triglyceride absorption. HYPOTHESIS Given that overexpression of apoC-III results in high plasma triglyceride levels, we hypothesized that it might also stimulate intestinal triglyceride transport, thereby exacerbating plasma hypertriglyceridemia in human apoC-III transgenic (h-apoC-III tg) mice. METHODS 28-30 gram male h-apoC-III tg (on a C57BL/6J background) were fitted with both a mesenteric lymph cannula and a duodenal feeding tube, and received a continuous intraduodenal infusion of triglyceride (6 μmol of 3[H]-Triolein in 0.3ml of phosphate-buffered saline) for 6 hours with hourly lymph samples collected (n=11-12). At the end of the infusion period, luminal and mucosal contents and tissue samples were isolated. An advantage of this lymph fistula model is the ability to sample lymph continuously throughout the triglyceride infusion period while avoiding confounding effects of anesthesia and stomach emptying. RESULTS h-apoC-III tg mice had a decrease in lymph flow and a 43% reduction in lymphatic 3[H]-triglyceride transport compared to WT mice. The h-apoC-III tg mice had 10.0±2.3% of the total dose of 3[H]-triglyceride remaining in intestinal lumen; which was significantly higher than the 3.1±0.4% observed in WT mice. Thin layer chromatographic analysis of the luminal contents showed that h-apoC-III tg mice, as opposed to WT controls, had a significantly higher percentage of fatty acid. There were no significant differences in the luminal triglyceride, diglyceride, and monoglyceride composition between groups. CONCLUSION Our studies reveal a novel role for apoC-III in decreasing intestinal triglyceride transport distinct from its extracellular roles in plasma on lipoprotein lipase, and its intracellular role in hepatic VLDL synthesis and secretion.

Abstract 388: Apolipoprotein A-V Deficiency in Mice Results In Increased Triglyceride and Cholesterol Absorption

Elevated plasma triglycerides constitute an independent risk factor for coronary heart disease. Discovered in 2001, apolipoprotein A-V (apoA-V) was found inversely proportional to plasma triglycerides (TG). Synthesized only in the liver, apoA-V exists in very low concentrations in the plasma (~10,000 fold lower than apoA-I). While apoA-V is proposed to enhance hydrolysis and reduce hepatic production of TG-rich lipoproteins, the role of apoA-V on intestinal lipid absorption has not been investigated. The aim of this study is to examine the effects of apoA-V deficiency on intestinal lipid absorption in chow-fed mice. Since mice lacking functional apoA-V have drastically elevated plasma TG, we hypothesize that apoA-V deficiency in mice elevates the lymphatic output of TG after a lipid meal. Using apoA-V knockout (n=8) and wildtype (n=8) control mice, we employed the conscious lymph fistula model to examine the transport of dietary TG and cholesterol into the lymph during a continuous lipid infusion. Interestingly, apoA-V knockout mice displayed a 2-fold elevation in dietary TG (P<0.001) and a 3-fold elevation in dietary cholesterol (P<0.001) transport into the lymph compared to wildtype mice, suggesting that a loss of apoA-V enhances transport across the enterocyte. However, apoA-V knockout mice displayed a 2-fold reduction (P<0.05) in dietary TG accumulated in the intestinal mucosa while there was no difference in the mucosal accumulation of dietary cholesterol between apoA-V knockout and wildtype mice, suggesting that apoA-V affected TG and cholesterol transport in the enterocyte differently. We conclude apoA-V deficiency results in increased TG and cholesterol absorption in mice, and therefore plays a previously unknown role in intestinal lipid absorption.

Is apolipoprotein A-IV rate limiting in the intestinal transport and absorption of triglyceride?

Apolipoprotein A-IV (apoA-IV) is synthesized by the intestine and secreted when dietary fat is absorbed and transported into lymph associated with chylomicrons. We have recently demonstrated that loss of apoA-IV increases chylomicron size and delays its clearance from the blood. There is still uncertainty, however, about the precise role of apoA-IV on the transport of dietary fat from the intestine into the lymph. ApoA-IV knockout (KO) mice do not have a gross defect in dietary lipid absorption, as measured by oral fat tolerance and fecal fat measurements. Here, using the in vivo lymph fistula mouse model, we show that the cumulative secretion of triglyceride (TG) into lymph in apoA-IV KO mice is very similar to that of wild-type (WT) mice. However, the apoA-IV KO mice do have subtle changes in TG accumulation in the intestinal mucosa during a 6-h continuous, but not bolus, infusion of lipid. There are no changes in the ratio of esterified to free fatty acids in the intestinal mucosa of the apoA-IV KO, however. When we extended these findings, by giving a higher dose of lipid (6 μmol/h) and for a longer infusion period (8 h), we found no effect of apoA-IV KO on intestinal TG absorption. This higher lipid infusion most certainly stresses the intestine, as we see a drastically lower absorption of TG (in both WT and KO mice); however, the loss of A-IV does not exacerbate this effect. This supports our hypothesis that apoA-IV is not required for TG absorption in the intestine. Our data suggest that the mechanisms by which the apoA-IV KO intestine responds to intestinal lipid may not be different from their WT counterparts. We conclude that apoA-IV is not required for normal lymphatic transport of TG.

Dietary spices as beneficial modulators of lipid profile in conditions of metabolic disorders and diseases

Spices are valued for their medicinal properties besides their use as food adjuncts to enhance the sensory quality of food. Dietary garlic, onion, fenugreek, red pepper, turmeric, and ginger have been proven to be effective hypocholesterolemics in experimentally induced hypercholesterolemia. The hypolipidemic potential of fenugreek in diabetic subjects and of garlic and onion in humans with induced lipemia has been demonstrated. Capsaicin and curcumin - the bioactive compounds of red pepper and turmeric - are documented to be efficacious at doses comparable to usual human intake. Capsaicin and curcumin have been shown to be hypotriglyceridemic, thus preventing accumulation of fat in the liver under adverse situations by enhancing triglyceride transport out of the liver. Capsaicin, curcumin, fenugreek, ginger, and onion enhance secretion of bile acids into bile. These hypocholesterolemic spices/spice principles reduce blood and liver cholesterol by enhancing cholesterol conversion to bile acids through activation of hepatic cholesterol-7α-hydroxylase. Many human trials have been carried out with garlic, onion, and fenugreek. The mechanism underlying the hypocholesterolemic and hypotriglyceridemic influence of spices is fairly well understood. Health implications of the hypocholesterolemic effect of spices experimentally documented are cardio-protection, protection of the structural integrity of erythrocytes by restoration of membrane cholesterol/phospholipid profile and prevention of cholesterol gallstones by modulation of the cholesterol saturation index in bile.

Longitudinal Analysis of Maternal Plasma Apolipoproteins in Pregnancy: A Targeted Proteomics Approach

Minimally invasive diagnostic tests are needed in obstetrics to identify women at risk for complications during delivery. The apolipoproteins fluctuate in complexity and abundance in maternal plasma during pregnancy and could be incorporated into a blood test to evaluate this risk. The objective of this study was to examine the relative plasma concentrations of apolipoproteins and their biochemically modified subtypes (i.e. proteolytically processed, sialylated, cysteinylated, dimerized) over gestational time using a targeted mass spectrometry approach. Relative abundance of modified and unmodified apolipoproteins A-I, A-II, C-I, C-II, and C-III was determined by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry in plasma prospectively collected from 11 gravidas with uncomplicated pregnancies at 4-5 gestational time points per patient. Apolipoproteins were readily identifiable by spectral pattern. Apo C-III(2) and Apo C-III(1) (doubly and singly sialylated Apo C-III subtypes) increased with gestational age (r(2)>0.8). Unmodified Apo A-II, Apo C-I, and Apo C-III(0) showed no correlation (r(2) = 0.01-0.1). Pro-Apo C-II did not increase significantly until third trimester (140 ± 13% of first trimester), but proteolytically cleaved, mature Apo C-II increased in late pregnancy (702 ± 130% of first trimester). Mature Apo C-II represented 6.7 ± 0.9% of total Apo C-II in early gestation and increased to 33 ± 4.5% in third trimester. A label-free, semiquantitative targeted proteomics approach was developed using LTQ-Orbitrap mass spectrometry to confirm the relative quantitative differences observed by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry in Apo C-III and Apo C-II isoforms between first and third trimesters. Targeted apolipoprotein screening was applied to a cohort of term and preterm patients. Modified Apo A-II isoforms were significantly elevated in plasma from mothers who delivered prematurely relative to term controls (p = 0.02). These results support a role for targeted proteomics profiling approaches in monitoring healthy pregnancies and assessing risk of adverse obstetric outcomes.

Therapeutic Targets to Raise HDL in Patients at Risk or with Coronary Artery Disease

The plasma levels of high-density lipoprotein (HDL) cholesterol are inversely related to cardiovascular risk. Traditional HDL-raising therapies, like fibrates, PPAR-γ agonists, and nicacin, among others, are associated with undesirable side effects, limited efficacy, or have not yet been shown to improve morbidity and mortality on top of statins in clinical outcome trials. A novel pharmacological target for raising circulating HDL-C levels is the cholesterol ester transfer protein (CETP), an enzyme that facilitates the transport of cholesteryl esters and triglycerides between the lipoproteins. Four pharmacological small-molecule inhibitors of CETP, i.e. torcetrapib (Pfizer), dalcetrapib (JTT-705; Roche), anacetrapib (Merck), and evacetrapib (Eli Lilly) have been developed. Notwithstanding a marked increase in HDL, torcetrapib was associated with an increase in all-cause mortality in the ILLUMINATE trial and raised safety concerns related to the off-target effects of CETP inhibition. Most recently, development of dalcetrapib was abruptly stopped due to a lack of clinically meaningful efficacy. Thus, it will be of utmost importance to demonstrate that the remaining CETP inhibitors in development not only increase HDL-C levels in plasma, but also improve HDL-function in patients with coronary disease or an acute coronary syndrome.

Abstract 109: Role of ApoAIV in ApoB Lipoprotein Assembly and Triglyceride Transport

Apolipoprotein A-IV (apoAIV) is a lipid binding protein expressed primarily in mammalian intestine and also in rodent liver. While in vitro studies have suggested a role of apoAIV in lipoprotein formation and triglyceride (TG) transport, limited evidence supports such a function in vivo. To explore if hepatic apoAIV is uniformly regulated by increased hepatic TG levels, as is the case in the intestine, we studied three distinct mouse models of hepatic steatosis. These included high fat diet (HFD)-fed wild type mice, mice overexpressing a constitutive active form of SREBP-1a (SREBP-1aTg), and mice in which hepatic TG hydrolysis is blunted (mice treated with an anti-sense oligonucleotide (ASO) targeting knockdown of CGI-58/ABHD5). High fat diet-fed mice displayed a 4.5-fold increase in liver TG content and a 10-fold increase in apoAIV mRNA expression and protein mass. SREBP-1aTg mouse liver demonstrated an ∼35-fold increase in hepatic TG, apoAIV mRNA and apoAIV protein. A linear correlation was observed between hepatic TG content and apoAIV mRNA expression in the HFD fed wild type and SREBP-1aTg mice (r2 = 0.6852; p < 0.01). Interestingly, while the TG content of CGI-58/ABHD5 knockdown animals increased by 4-fold, no corresponding increase in apoAIV expression was observed. To determine if the increase in apoAIV expression in the steatotic livers of SREPB-1aTg mice plays a role in the secretion of TG-rich apoB-containing lipoproteins, we crossed these mice with apoAIV knock out mice (A4-KO). The SREBP1a-Tg/A4-KO mice did not demonstrate a change in liver to body weight ratio or a change in hepatic TG content. Despite the large induction of apoAIV in the livers of SREBP1a-Tg mice, no difference was observed in hepatic TG production rates or VLDL particle size when apoAIV was deficient (SREBP1a-Tg/A4-KO). These results indicate that hepatic apoAIV expression is upregulated under conditions of enhanced lipogenesis, but is not altered under condition of defective TG hydrolysis. Furthermore, even under conditions of a 35-fold induction, apoAIV does not exert a detectable impact on TG transport or VLDL particle characteristics in mouse liver.

Differential regulation of genes for intestinal cholesterol flux by epigallocatechin gallate (EGCG) and resveratrol (RES) in Caco‐2 cells: Potential role of histone deacetylases and sirtuins in intestinal cholesterol metabolism

Despite well‐established cardio‐protective properties of phenolic compounds, their role in intestinal cholesterol metabolism is unclear. We investigated the effect of EGCG and RES on the transcriptional regulation of genes encoding intestinal cholesterol transporters and lipoprotein receptors in Caco‐2 cells. Cells treated with EGCG for 12 hr markedly increased ATP‐binding cassette transporter G5 (ABCG5) mRNA but decreased the expression of ABCA1, scavenger receptor class B type 1, Niemann‐Pick C1‐like 1 (NPC1L1), microsomal triglyceride transport protein and LDL receptor related protein 2 in a dose‐dependent manner (0–100 μM). In contrast, RES at 100 μM increased ABCA1 and NPClL1 mRNA. Of interest, EGCG significantly decreased the expression of all major histone deacetylase (HDAC), i.e., 1, 2, 3, 6, 7, 10, whereas RES had a minimal effect. Sirtuin (Sirt) 2–7 expression was also markedly repressed by EGCG but RES increased Sirt3, 4 and 5. The results indicate differential regulation of key transporters involved in intestinal cholesterol efflux by EGCG and RES. The over‐arching objective of this research will be to relate changes in the gene expression profile to the promotion of cholesterol flux from the basolateral to apical side of enterocytes. Importantly, this study suggests that expression of the aforementioned intestinal transporters may be linked the regulation of HDAC and Sirt in the intestine.Grant Funding Source: Supported by USDA Hatch fund

Rab2 plays a role in lipid metabolism in the intestine

Intestinal lipid metabolism is comprised of multi‐steps of vesicle trafficking. Rab2 is localized in pre‐Golgi intermediates and required for vesicle trafficking between the endoplasmic reticulum and the Golgi. The aim of the study was to investigate the role of Rab2 in the secretion of chylomicron in the intestine. Rab2 expression was suppressed by transfection of specific siRNA in Caco‐2 cells, an intestinal in vitro model, and lipid absorption and lipoprotein production were examined. Rab2 expression was efficiently depleted by siRNA transfection for 14 days without interrupting cell differentiation. Apolipoprotein (Apo) B100 secretion was significantly lower in Rab2 siRNA transfected cells in the basal condition, but it recovered when the cells were oil‐loaded. In the same way, triglyceride secretion was slightly decreased in the basal condition, but recovered by oil‐load. Expression of microsomal triglyceride transport protein (MTTP) was not affected by Rab2 disruption. Rab6 expression was significantly increased in Rab2 siRNA transfected cells. These data suggest that Rab2 and Rab6 are involved in chylomicron secretion in Caco‐2 cells, and compensate its role each other.Grant Funding Source : Alexander von Humboldt Foundation

Chronic Alcohol Exposure Stimulates Adipose Tissue Lipolysis in Mice: Role of Reverse Triglyceride Transport in the Pathogenesis of Alcoholic Steatosis

Alcohol consumption induces liver steatosis; therefore, this study investigated the possible role of adipose tissue dysfunction in the pathogenesis of alcoholic steatosis. Mice were pair-fed an alcohol or control liquid diet for 8 weeks to evaluate the alcohol effects on lipid metabolism at the adipose tissue-liver axis. Chronic alcohol exposure reduced adipose tissue mass and adipocyte size. Fatty acid release from adipose tissue explants was significantly increased in alcohol-fed mice in association with the activation of adipose triglyceride lipase and hormone-sensitive lipase. Alcohol exposure induced insulin intolerance and inactivated adipose protein phosphatase 1 in association with the up-regulation of phosphatase and tensin homolog (PTEN) and suppressor of cytokine signaling 3 (SOCS3). Alcohol exposure up-regulated fatty acid transport proteins and caused lipid accumulation in the liver. To define the mechanistic link between adipose triglyceride loss and hepatic triglyceride gain, mice were first administered heavy water for 5 weeks to label adipose triglycerides with deuterium, and then pair-fed alcohol or control diet for 2 weeks. Deposition of deuterium-labeled adipose triglycerides in the liver was analyzed using Fourier transform ion cyclotron mass spectrometry. Alcohol exposure increased more than a dozen deuterium-labeled triglyceride molecules in the liver by up to 6.3-fold. These data demonstrate for the first time that adipose triglycerides due to alcohol-induced hyperlipolysis are reverse transported and deposited in the liver.

Induction of microsomal triglyceride transfer protein expression is a candidate mechanism by which ezetimibe therapy might exert beneficial effects in patients with nonalcoholic steatohepatitis

Dear Editor Park and colleagues have reported that ezetimibe therapy improves the histological abnormalities of nonalcoholic fatty liver disease (NAFLD) [1]. In their study, while no significant difference was observed in the fibrosis stage, significant improvements of the steatosis grade, necroinflammatory grade, ballooning score, and NAFLD activity score (NAS) were observed after treatment with ezetimibe (10 mg/day) for 24 months. Ezetimibe, a potent inhibitor of cholesterol absorption, has been shown to inhibit Niemann-Pick C1 Like 1 (NPC1L1)-dependent cholesterol transport at the brush border of the intestine and the liver [2]. Therefore, ezetimibe has been considered as a noteworthy candidate agent for the treatment of metabolic syndrome, including nonalcoholic steatohepatitis (NASH). In several experimental rodent models, drugs antagonizing mechanisms such as sterol regulatory element-binding protein-1c (SREBP-1c) induction, carbohydrate responsive binding protein (ChREBP) induction, and endoplasmic reticulum (ER) stress have been reported as candidate mechanisms for the improvement of hepatic steatosis [3, 4]. However, unlike in rodents, in which NPC1L1 is mainly expressed in the intestine, in humans high levels of expression of NPC1L1 mRNA are observed in both the small intestine and the liver; therefore, ezetimibe would inhibit not only dietary and biliary cholesterol absorption in the small intestine, but also biliary cholesterol absorption in the liver [2]. Therefore, the mechanism by which ezetimibe might improve the changes of NASH in humans remains unknown. We conducted a 6-month pilot study to investigate the effect of ezetimibe in patients with NASH [5]. To investigate the mechanism of action of ezetimibe treatment in human NASH patients, we analyzed the hepatic mRNA expression of SREBP1c, ChREBP, and ER stress in 8 NASH patients before and after ezetimibe treatment. We found no significant changes in SREBP1c expression, ChREBP expression, or ER stress (Glucose-regulated protein 78, C/EBP-homologous protein) in this study. Secondly, we examined microsomal triglyceride transfer protein (MTTP) expression, which is a key factor for triglyceride (TG) transport in the liver, because we had previously found that the hepatic expression of MTTP mRNA was impaired in NASH patients as compared with that in patients with simple steatosis [6]. After ezetimibe treatment, a significant increase of hepatic MTTP mRNA expression was observed as compared with that before ezetimibe treatment (p = 0.0052). We suggest, therefore, that the induction of MTTP expression is an important candidate mechanism by which ezetimibe therapy might exert beneficial effects against NAFLD in humans.

Changes in hepatic lipid parameters and hepatic messenger ribonucleic acid expression following estradiol administration in laying hens (Gallus domesticus)

Fatty liver hemorrhagic syndrome (FLHS) is characterized by increased hepatic triacylglycerol content associated with liver hemorrhages and results in a sudden decline in egg production. Genetic, environmental, nutritional, and hormonal factors have all been implicated in the etiology of FLHS, but the exact cause of FLHS is still unknown. Estrogens have been implicated in the development of excess fat content of the liver and in the etiology of FLHS. This study investigated estradiol (E2) administration in hens and its effect on lipid metabolism. Hy-Line Brown laying hens were intramuscularly injected with E2 on a daily basis for 3 wk. The dosages were 0, 0.5, and 1.0 mg/kg of BW, with corn oil injections used as a control. Egg production and quality were measured among the groups, with no significant difference seen in egg production. Liver weights of hens treated with E2 were greater than those of control hens, but the increase was not statistically significant. Serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase activities and E2 plasma concentrations increased in a dose-dependent manner, with plasma concentration of E2 increasing from 6,900 to 19,000 pg/mL. No significant differences in free cholesterol or phospholipids were observed, but there was a significant increase in hepatic triacylglycerol levels. Injection with E2 showed an increased expression of mRNA for peroxisome proliferator-activated receptor γ (23-fold), but not for peroxisome proliferator-activated receptor α. A statistically significant increase was seen for fatty acid synthase, apolipoprotein B, and adenosine triphosphate citrate lyase, but not for acetyl coenzyme A carboxylase, apolipoprotein VLDL-II, microsomal triglyceride transport protein, or malic enzyme. For proteins involved in the oxidation of E2, only cytochrome P450 3A37 showed a statistically significant increase. The present results suggest that E2 upregulates the synthesis of fatty acids and triacylglycerols and the accumulation of hepatic lipids by increasing mRNA expression related to lipid metabolism, and that excess E2 in the blood leads to activation of E2 catabolic metabolism (cytochrome P450 3A37)-related mRNA expression.

Upregulation of scavenger receptor class B type I expression by activation of FXR in hepatocyte

Objective The farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, has been proposed to play an important role in the pathogenesis of cardiovascular diseases by regulating the metabolism and transport of cholesterol and triglyceride. Scavenger receptor class B type I (SR-BI), a high-density lipoprotein receptor, plays an important role in decreasing lipid metabolism-associated cardiovascular diseases by regulating reverse cholesterol transport. Recent studies have shown that SR-BI expression is upregulated by several nuclear receptors. However, the role of FXR in the regulation of SR-BI expression is not well known. In the present study, we investigate the regulation of SR-BI by FXR in hepatocyte and the corresponding mechanism. Methods and results Treatment of human hepatoma cell line HepG2 with FXR ligands resulted in upregulation of SR-BI at the levels of both mRNA and protein. Reporter assays showed that activation of FXR significantly enhanced the SR-BI promoter activity. Electrophoretic mobility shift and chromatin immunoprecipitation assays indicated that FXR induced SR-BI expression by binding to a novel FXR element (FXRE), a directed repeat DNA motif, DR8 (−703 AGGCCAcgttctagAGCTCA −684). The in vivo experiment demonstrated that gavaging mice with a natural ligand of FXR increased SR-BI expression in liver tissues. Conclusions FXR can directly upregulate SR-BI expression in hepatocyte, and DR8 is a likely novel FXRE that is involved in SR-BI regulation. FXR may serve as a novel molecular target for manipulating SR-BI expression in hepatocyte.

고지방식이 비만쥐의 지방관련 단백질의 변화

과체중과 비만은 당뇨병, 고혈압, 고지혈증과 같은 신진 대사 질환의 발병과 강력하게 연관되어 있다. 비만의 원인은 여러가지가 있겠지만, 고지방식이는 비만의 원인 중 가장 중요한 요소 중 하나이다. 본 연구에서는 C57BL/6 생쥐에게 22주간의 고지방 식이를 주었으며, 이를 통해 비만과 고혈당을 유도하였다. 22주 후에 고지방식이를 한 생쥐들에서 체중과 혈장 포도당 수준이 정상 식이를 한 생쥐들에 비해 크게 증가함을 관찰하였다. 복막 내 당 부하 검사(IPGTT)에서도 고지방 식이를 한 생쥐들은 정상 식이를 한 생쥐들에 비해서 당 내성 이상 반응을 보여주었다. 이러한 결과들은 고지방식이가 C57BL/6 생쥐에서 비만 및 고혈당을 유도한다는 사실을 확인시켜 주었다. 고지방식이군 생쥐들에서는 정상식이군의 생쥐들에 비해 혈장의 중성지방과 총 콜레스테롤의 양이 증가됨이 관찰되었다. 간에서의 중성지방 및 총 콜레스테롤의 수준도 역시 증가하였다. 따라서, 간에서의 지질대사가 어떻게 변하였는지를 알기 위해, 지질대사에 관련된 단백질들의 변화를 관찰하였다. 지방 합성과 관련된 효소들 중 FAS와 GPAT가 고지방식이 군에서 의미있게 증가 되어있었으며, 지방 수송에 관련하는 단백질 중에서도 ApoB 및 MTP의 큰 증가가 고지방식이군에서 관찰되었다. 흥미롭게도, 대사 조절 인자로 알려진 AMPK의 단백질의 양과 인산화 정도는 정상식이군에 비해 고지방식이군에서 의미있게 증가되었음이 관찰되었다. 결론적으로, 본 연구에서 우리는 고지방식이가 지질 합성과 지질 수송과정을 생리학적으로 증가시키지만, 역설적으로 AMPK의 활성화를 유발한다는 것을 확인하였다. Obesity and being overweight are strongly associated with the development of metabolic disease such as diabetes, hypertension, dyslipidemia. High-fat diet (HFD) is one of the most important factors which cause obesity. In this study, C57BL/6 mice were treated with a HFD for 22 weeks in order to induce obesity and hyperglycemia. Twenty-two weeks later, body weight and plasma glucose level of the HFD group were significantly increased, compared with the normal diet (ND) group. Intra-peritoneal glucose tolerance test (IPGTT) showed glucose intolerance in the HFD group compared with the ND group. These results confirmed that a HFD induced obesity and hyperglycemia in C57BL/6 mice. Plasma levels of triglyceride (TG) and total cholesterol (TC) were increased in the HFD group compared with the ND group. Hepatic levels of TG and TC were also increased by a HFD. To investigate the alteration of lipid metabolism in liver, proteins which are related to lipid metabolism were observed. Among lipid synthesis related enzymes, fatty acid synthase (FAS) and glycerol phosphate acyl transferase (GPAT) were significantly increased in the HFD group. Apolipoprotein B (apoB) and microsomal triglyceride transport protein (MTP), which are related to lipid transport, were significantly increased in the HFD group. Interestingly, protein level and phosphorylation of AMP-activated protein kinase (AMPK), which is known as a metabolic regulator, were significantly increased in the HFD group compared with the ND group. In the present study we suggest that HFD may physiologically increase the proteins which are related with lipid synthesis and lipid transport, but that HFD may paradoxically induce the activation of AMPK.

Hypertriglyceridemia in obese subjects: Caused by reduced apolipoprotein A5 plasma levels?

Recent evidence from a collaborative analysis demonstrates gain, that genetic variations in the A1-C3-A4-A5-Locus resultng in increased circulating triglyceride (TG) levels are associated ith coronary heart disease [1]. Therefore, it is of great interest o unravel the underlying pathophysiological mechanisms leading o elevated TG concentrations. Intestinal chylomicrons and livererived VLDL represent the two classes of lipoproteins that are esponsible for the transport of triglycerides to various body cells. n the bloodstream these triglyceride-rich lipoproteins (TRL) are ydrolysed by the action of lipoprotein lipase (LPL) and the fatty cids released are taken up by peripheral organs such as adipose issue and muscle for storage or energy production, respectively. PL mediated hydrolysis is crucially dependent on the essential ofactor apolipoprotein C2 (apoC2). The lipolytic process is augented by the presence of another apolipoprotein, apoA5 [2,3] and nhibited by apoC3 [4]. Under normal conditions, the remaining holesterol-rich remnant particles are then rapidly cleared by the iver via lipoprotein receptor-mediated endocytosis [5]. Both dysunctional vascular TRL processing and impaired hepatic remnant ptake can lead to hypertriglyceridemia. Hypertriglyceridemia is a characteristic of obesity associated etabolic abnormalities evolving from insulin resistance. Several f the molecular mechanisms leading to impaired TG clearance n insulin resistant patients can be explained by reduced insulin ensitivity in different organs as liver and adipose tissue. The roduction of large triglyceride-rich VLDL-1 particles in insulin esistant patients contributes to elevated triglyceride levels in he postprandial phase, since these VLDL are less hydrolysable nd may compete with chylomicrons [6]. Hepatic LDL receptor

Bioavailability of lycopene in the rat: the role of intestinal lymphatic transport

As a natural antioxidant derived from dietary sources, lycopene has attracted considerable attention as a potent chemopreventative agent. Lycopene is an extremely lipophilic compound and absorption from dietary sources is estimated to be low and highly variable. As a result, plasma lycopene concentrations are poorly correlated with dietary intake of lycopene rich food stuffs. The development of an oral formulation remains a challenge that requires a better understanding of the mechanisms involved in the intestinal absorption of this compound. The solubility of lycopene in simulated physiological fluids and bile salt mixed micelle formulations was determined. The extent of intestinal lymphatic transport and the absolute bioavailability of lycopene from a range of biorelevant media was evaluated in a mesenteric lymph duct cannulated anaesthetised rat model. The absolute bioavailability of lycopene after 8 h was 1.85 +/- 0.39%. The overall extent of the intestinal lymphatic transport was in the range of 0.6-3.4% of the administered dose. A strong positive correlation (r(2) > 0.9) between intestinal lycopene levels and intestinal triglyceride levels was demonstrated. The intestinal lymphatic route is the major uptake mechanism of lycopene from the gastrointestinal tract. Lycopene transport in intestinal lymph was closely associated with triglyceride transport in the lymph. Formulation strategies designed to promote intestinal lymphatic uptake, such as lipid-based formulations containing long-chain fatty acids (LCFA) or lecithin, may serve to enhance oral bioavailability of lycopene.

The Role of the Intestinal Lymphatics in the Absorption of Two Highly Lipophilic Cholesterol Ester Transfer Protein Inhibitors (CP524,515 and CP532,623)

To evaluate the potential role of intestinal lymphatic transport in the absorption and oral bioavailability of members of an emerging class of anti-atherosclerosis drugs (CETP inhibitors). CP524,515 and CP532,623 are structurally related with eLogD(7.4) >5; however, only CP524,515 (and not CP532,623) had sufficient solubility (>50 mg/g) in long-chain triglyceride (LCT) to be considered likely to be lymphatically transported. CP524,515 and CP532,623 were administered intravenously and orally to fasted or fed lymph-cannulated or non-cannulated dogs. Oral bioavailability and lymphatic transport of drug (and triglyceride) was subsequently quantified. Both CETP inhibitors were substantially transported into the lymphatic system (>25% dose) in fed and fasted dogs. Food enhanced oral bioavailability (from 45 to 83% and 44 to 58% for CP524,515 and CP532,623, respectively) and the proportion of the absorbed dose transported via the lymph (from 61 to 86% and from 68 to 83%, respectively). Lymphatic triglyceride transport was significantly lower in fed dogs administered CP532,623. Intestinal lymphatic transport is the major absorption pathway for CP524,515 and CP532,623, suggesting that a LCT solubility >50 mg/g is not an absolute requirement for lymphatic transport. The effect of CP532,623 on intestinal lipid transport may suggest a role in the activity/toxicity profiles of CETP inhibitors.