Cholesterol esterase accelerates intestinal cholesterol absorption

Spray drying and ultrasonication processing of camel whey protein concentrate: Characterization and impact on bioactive properties

The production of whey protein concentrates (WPCs) from camel milk whey represents an effective approach to valorize this processing by-product. These concentrates harbor active ingredients with significant bioactive properties. Camel WPCs were spray-dried (SD) at inlet temperature of 170, 185 and 200°C, or Ultrasonicated (US) for 5, 10 and 15 min, then freeze-dried to obtain fine powder. The impact of both treatments on protein degradation was studied by sodium dodecyl sulfate-PAGE and reverse-phase ultraperformance liquid chromatography (RP-UPLC) techniques. Significantly enhanced protein degradation was observed after US treatment when compared with SD. Both SD and US treatments slightly enhanced the WPCs samples' antioxidant activities. The US exposure for 15 min exhibited highest 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) scavenging activity (12.12 mmol TE/g). Moreover, US treatment for 10 min exhibited the highest in vitro anti-diabetic properties (α-amylase and α-glucosidase inhibition), and dipeptidyl-peptidase-IV inhibitory activity among all samples. In addition, the ultrasonication for 10 min and SD at 170°C showed the lowest IC50 values for in vitro anti-hypercholesterolemic activities in terms of pancreatic lipase and cholesteryl esterase inhibition. Conclusively, these green techniques can be adapted in the preservation and processing of camel milk whey into active ingredients with high bioactive properties.

Nutritional Viewpoints on Eggs and Cholesterol

Although most current epidemiologic studies indicate no significant association between consuming one egg daily and blood cholesterol levels and cardiovascular risk, arguments still persist with a positive association. Since the diet is one of the most influential factors for this association, we illustrate characteristic features in Japanese people whose dietary pattern is distinct from that, for example, the US (United States) population. Available epidemiologic studies in healthy Japanese people show no association between consumption of one egg daily and blood cholesterol level, consistent with those observed in the US population. However, when consumption of major nutrients and food sources of cholesterol are compared to the US population, Japanese people may have an extra-reserve against the influence of eggs on cardiovascular risk markers, despite consuming relatively more eggs. Further discussion on the influence of nutrients contained in the egg and dietary pattern, including interaction with gut microbes, is necessary. In addition, special consideration at the personalized level is needed for judgment regarding dietary cholesterol not only for hypercholesterolemic patients but for hyper-responsive healthy persons. Although randomized controlled trials with long-term follow-up are required to evaluate the association between consumption of eggs and human health, available information, at least from the nutritional viewpoint, suggests that egg is a healthy and cost-efficient food worldwide.

Improvement of the Activity of a Fungal Versatile-Lipase Toward Triglycerides: An in silico Mechanistic Description

Some enzymes that belong to the Candida rugosa-like lipase family (abH03. 01) combine the activities of lipases and sterol esterases. Thus, they can act on water-insoluble carboxylic esters releasing long-chain fatty acids but also on sterol esters, although with different activity and affinity. The differences in the catalytic properties among the proteins of this family are explained by small changes in the hydrophobicity of some regions. One of such versatile enzymes is the sterol esterase/lipase from Ophiostoma piceae (OPE) that acts very efficiently on the two types of substrates. Structurally, OPE is characterized by the presence of a lid formed by a α-helix and two 3₁₀-helices rich in hydrophobic amino acids. In this study, the ope gene was modified by directed mutagenesis in order to change specific amino acids in the lid region to modify its structure with the aim of increasing its hydrophobicity. Several recombinant forms of OPE were heterologously produced in Pichia pastoris. In silico molecular dynamics simulations have been used to decipher the mechanistic principles behind the improvements in substrate catalysis. The analyses suggested that the enhanced activity toward hydrophobic substrates such as triglycerides could be due to a better stabilization of the substrate in the lid region as a result of an increased hydrophobicity and an improved topology. These results indicate that in silico simulations can be useful for the optimization of the activity of lipases from the C. rugose-like family for different biotechnological applications.

ω-Phthalimidoalkyl Aryl Ureas as Potent and Selective Inhibitors of Cholesterol Esterase

Cholesterol esterase (CEase), a serine hydrolase thought to be involved in atherogenesis and thus coronary heart disease, is considered as a target for inhibitor development. We investigated recombinant human and murine CEases with a new fluorometric assay in a structure-activity relationship study of a small library of ω-phthalimidoalkyl aryl ureas. The urea motif with an attached 3,5-bis(trifluoromethyl)phenyl group and the aromatic character of the ω-phthalimide residue were most important for inhibitory activity. In addition, an alkyl chain composed of three or four methylene groups, connecting the urea and phthalimide moieties, was found to be an optimal spacer for inhibitors. The so-optimized compounds 2 [1-(3,5-bis(trifluoromethyl)phenyl)-3-(3-(1,3-dioxoisoindolin-2-yl)propyl)urea] and 21 [1-(3,5-bis(trifluoromethyl)phenyl)-3-(4-(1,3-dioxoisoindolin-2-yl)butyl)urea] exhibited dissociation constants (K_i ) of 1-19 μm on the two CEases and showed either a competitive (2 on the human enzyme and 21 on the murine enzyme) or a noncompetitive mode of inhibition. Two related serine hydrolases-monoacylglycerol lipase and fatty acid amide hydrolase-were inhibited by ω-phthalimidoalkyl aryl ureas to a lesser extent.

Fatty acids modulate the expression levels of key proteins for cholesterol absorption in Caco-2 monolayer

BACKGROUND

Fatty acids have been shown to modulate intestinal cholesterol absorption in cells and animals, a process that is mediated by several transporter proteins. Of these proteins, Niemann-Pick C1-Like 1 (NPC1L1) is a major contributor to this process. The current study investigates the unknown mechanism by which fatty acids modulate cholesterol absorption.

METHODS

We evaluated the effects of six fatty acids palmitic acid (PAM), oleic acid (OLA), linoleic acid (LNA), arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on cholesterol uptake and transport in human enterocytes Caco-2 cells, and on the mRNA expression levels of NPC1L1, others proteins (ABCG5, ABCG8, ABCA1, ACAT2, MTP, Caveolin 1, Annexin-2) involved in cholesterol absorption, and SREBP-1 and SREBP-2 that are responsible for lipid metabolism.

RESULTS

The polyunsaturated fatty acids (PUFAs), especially for EPA and DHA, dose-dependently inhibited cholesterol uptake and transport in Caco-2 monolayer, while saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) had no inhibitory effects. EPA and DHA inhibited cholesterol absorption in Caco-2 monolayer might be caused by down-regulating NPC1L1 mRNA and protein levels, which were associated with inhibition of SREBP-1/- 2 mRNA expression levels.

CONCLUSION

Results from this study indicate that functional food containing high PUFAs may have potential therapeutic benefit to reduce cholesterol absorption. Further studies on this topic may provide approaches to control lipid metabolism and to promote health.

Egg-Yolk Sphingomyelin and Phosphatidylcholine Attenuate Cholesterol Absorption in Caco-2 Cells

Phospholipids have been shown to modulate intestinal cholesterol absorption in cells and animals, a process that is regulated by several transporter proteins. Of these proteins, Niemann-Pick C1-Like 1 (NPC1L1) is a major contributor to this process. The mechanism by which phospholipids modulate cholesterol absorption remains unknown. Here, we evaluate the effects of egg-yolk phospholipids on cholesterol absorption and transport in human colon carcinoma cell line (Caco-2 cells) and on the expression of NPC1L1 and others proteins associated with cholesterol absorption (ABCG5, ABCG8, ABCA1, ACAT2, MTP, CAV-1, ANX-2). The roles of SREBP-1 and SREBP-2 in this process were also investigated. The results show that egg-yolk sphingomyelin (CerPCho) and phosphatidylcholine (PtdCho) inhibit cholesterol transport in the Caco-2 monolayer in a dose-dependent manner. These might be due to the decrease of the cholesterol solubility in micelles as well as to the increases in the micellar sizes and the bile acid-binding capacity. Furthermore, the treatments with egg-yolk CerPCho or PtdCho at 1.2 mmol/L reduced the expression levels of NPC1L1 protein to 21 or 22%, respectively, and its mRNA to 9 or 31% of that in the control group (p < 0.05). Moreover, there was a general inhibitory effect of egg-yolk PtdCho and CerPCho on the mRNA levels of SREBP-1, and SREBP-2. These results suggest that the inhibitory effect of egg-yolk CerPCho and PtdCho on cholesterol transport might be due to their interference with the physicochemical properties of micelles and their regulations on the expression of the NPC1L1 gene.

Identification of Lead Molecules in Garcinia mangostana L. Against Pancreatic Cholesterol Esterase Activity: An In Silico Approach

Hypercholesterolemia is one of the major risk factors for the development and progression of atherosclerosis. Hence, inhibitors of cholesterol absorption have been investigated for decades as a strategy to prevent and treat cardiovascular diseases associated with hypercholesterolemia. Cholesterol esterase (CEase) in pancreatic juice plays a vital role in the hydrolysis of dietary cholesterol esters to cholesterol and fatty acids. Since inhibition of CEase might lead to a reduction of cholesterol absorption, an attempt is made in this study to identify lead molecules of Garcinia mangostana by the in silico approach. The study employed software applications viz., AutoDock 4.2 and GOLD Suite of Programs 5.2. The study revealed the efficacy of three compounds viz., epicatechin, euxanthone, and 1,3,5,6-tetrahydroxy-xanthone, which exhibited least binding energy in AutoDock and moderate scoring in GOLD. The molecular properties as well as biological activity of these three compounds were predicted by molinspiration prediction tool. The results show the crucial role of polyphenolic compounds to limit the activity of CEase. The drug-likeness prediction revealed the prospects of the identified lead molecules as potential drug candidates.

Heating Has No Effect on the Net Protein Utilisation from Egg Whites in Rats

Egg whites (EW) are a good source of protein; however, they are typically heated prior to consumption. Therefore, we investigated the effects of different heating conditions on the protein utilisation rate of EW. Male Sprague-Dawley rats (n = 36, 198 ± 1 g) were divided into six groups and fed American Institute of Nutrition-76 chow containing unheated EW, soft-boiled EW, boiled EW, milk whey protein, soybean protein, or no protein over a 10-day period using pair-feeding. Urine and faeces were sampled daily beginning on day 5 to measure nitrogen content and the net protein utilisation (NPU) rate. The soybean protein group had a significantly lower level of food intake and was thus excluded from subsequent analyses. The NPU value was similar among the unheated, soft-boiled, and boiled EW groups (97.5 ± 0.4, 96.5 ± 0.1, and 96.5 ± 0.7, resp.). The EW group values were significantly higher than the whey group values (90.5 ± 1.0). These results show that EW serve as a good source of protein, irrespective of heating.

Investigating cholesterol metabolism and ageing using a systems biology approach

CVD accounted for 27 % of all deaths in the UK in 2014, and was responsible for 1·7 million hospital admissions in 2013/2014. This condition becomes increasingly prevalent with age, affecting 34·1 and 29·8 % of males and females over 75 years of age respectively in 2011. The dysregulation of cholesterol metabolism with age, often observed as a rise in LDL-cholesterol, has been associated with the pathogenesis of CVD. To compound this problem, it is estimated by 2050, 22 % of the world's population will be over 60 years of age, in culmination with a growing resistance and intolerance to pre-existing cholesterol regulating drugs such as statins. Therefore, it is apparent research into additional therapies for hypercholesterolaemia and CVD prevention is a growing necessity. However, it is also imperative to recognise this complex biological system cannot be studied using a reductionist approach; rather its biological uniqueness necessitates a more integrated methodology, such as that offered by systems biology. In this review, we firstly discuss cholesterol metabolism and how it is affected by diet and the ageing process. Next, we describe therapeutic strategies for hypercholesterolaemia, and finally how the systems biology paradigm can be utilised to investigate how ageing interacts with complex systems such as cholesterol metabolism. We conclude by emphasising the need for nutritionists to work in parallel with the systems biology community, to develop novel approaches to studying cholesterol metabolism and its interaction with ageing.

Metabolic fate of poly-(lactic-co-glycolic acid)-based curcumin nanoparticles following oral administration

Purpose

Curcumin (CUR), the main polyphenol in turmeric, is poorly absorbed and rapidly metabolized following oral administration, which severely curtails its bioavailability. Poly-(lactic-co-glycolic acid)-based CUR nanoparticles (CUR-NP) have recently been suggested to improve CUR bioavailability, but this has not been fully verified. Specifically, no data are available about curcumin glucuronide (CURG), the major metabolite of CUR found in the plasma following oral administration of CUR-NP. Herein, we investigated the absorption and metabolism of CUR-NP and evaluated whether CUR-NP improves CUR bioavailability.

Methods

Following oral administration of CUR-NP in rats, we analyzed the plasma and organ distribution of CUR and its metabolites using high-performance liquid chromatography-tandem mass spectrometry. To elucidate the mechanism of increased intestinal absorption of CUR-NP, we prepared mixed micelles comprised of phosphatidylcholine and bile salts and examined the micellar solubility of CUR-NP. Additionally, we investigated the cellular incorporation of the resultant micelles into differentiated Caco-2 human intestinal cells.

Results

Following in vivo administration of CUR-NP, CUR was effectively absorbed and present mainly as CURG in the plasma which contained significant amounts of the metabolite compared with other organs. Thus, CUR-NP increased intestinal absorption of CUR rather than decreasing metabolic degradation and conversion to other metabolites. In vitro, CUR encapsulated in CUR-NP was solubilized in mixed micelles; however, whether the micelles contained CUR or CUR-NP had little influence on cellular uptake efficiency. Therefore, we suggest that the high solubilization capacity of CUR-NP in mixed micelles, rather than cellular uptake efficiency, explains the high intestinal absorption of CUR-NP in vivo.

Conclusion

These findings provide a better understanding of the bioavailability of CUR and CUR-NP following oral administration. To improve the bioavailability of CUR, future studies should focus on enhancing the resistance to metabolic degradation and conversion of CUR to other metabolites, which may lead to novel discoveries regarding food function and disease prevention.

Cholesterol metabolism: A review of how ageing disrupts the biological mechanisms responsible for its regulation

Cholesterol plays a vital role in the human body as a precursor of steroid hormones and bile acids, in addition to providing structure to cell membranes. Whole body cholesterol metabolism is maintained by a highly coordinated balancing act between cholesterol ingestion, synthesis, absorption, and excretion. The aim of this review is to discuss how ageing interacts with these processes. Firstly, we will present an overview of cholesterol metabolism. Following this, we discuss how the biological mechanisms which underpin cholesterol metabolism are effected by ageing. Included in this discussion are lipoprotein dynamics, cholesterol absorption/synthesis and the enterohepatic circulation/synthesis of bile acids. Moreover, we discuss the role of oxidative stress in the pathological progression of atherosclerosis and also discuss how cholesterol biosynthesis is effected by both the mammalian target of rapamycin and sirtuin pathways. Next, we examine how diet and alterations to the gut microbiome can be used to mitigate the impact ageing has on cholesterol metabolism. We conclude by discussing how mathematical models of cholesterol metabolism can be used to identify therapeutic interventions.

Heterologous expression of a fungal sterol esterase/lipase in different hosts: Effect on solubility, glycosylation and production

Ophiostoma piceae secretes a versatile sterol-esterase (OPE) that shows high efficiency in both hydrolysis and synthesis of triglycerides and sterol esters. This enzyme produces aggregates in aqueous solutions, but the recombinant protein, expressed in Komagataella (synonym Pichia) pastoris, showed higher catalytic efficiency because of its higher solubility. This fact owes to a modification in the N-terminal sequence of the protein expressed in Pichia pastoris, which incorporated 4-8 additional amino acids, affecting its aggregation behavior. In this study we present a newly engineered P. pastoris strain with improved protein production. We also produced the recombinant protein in the yeast Saccharomyces cerevisiae and in the prokaryotic host Escherichia coli, corroborating that the presence of these N-terminal extra amino acids affected the protein's solubility. The OPE produced in the new P. pastoris strain presented the same physicochemical properties than the old one. An inactive form of the enzyme was produced by the bacterium, but the recombinant esterase from both yeasts was active even after its enzymatic deglycosylation, suggesting that the presence of N-linked carbohydrates in the mature protein is not essential for enzyme activity. Although the yield in S. cerevisiae was lower than that obtained in P. pastoris, this work demonstrates the importance of the choice of the heterologous host for successful production of soluble and active recombinant protein. In addition, S. cerevisiae constitutes a good engineering platform for improving the properties of this biocatalyst.

Cholesterol and Plant Sterol Efflux from Cultured Intestinal Epithelial Cells Is Mediated by ATP-Binding Cassette Transporters

In this study we analyzed functions of ATP-binding cassette (ABC) transporters involved in sterol transport from Caco-2 cells. Treatment with a synthetic liver x receptor ligand elevated both mRNA and protein levels of ABCG5, G8, and ABCA1. The ligand stimulated cholesterol efflux, suggesting that ABC transporters are involved in it. To identify the acceptors of cholesterol, potential molecules such as apolipoprotein A-I, glycocholic acid, phosphatidylcholine, and bile acid micelles were added to the medium. Apo A-I, a known acceptor of cholesterol transported by ABCA1, elevated cholesterol efflux on the basal side, whereas the others raised cholesterol efflux on the apical side. Moreover, bile acid micelles preferentially augmented plant sterol efflux rather than cholesterol. Finally, in HEK293 cells stably expressing ABCG5/G8, bile acid micelle-mediated sterol efflux was significantly accelerated. These results indicate that ABCG5/G8, unlike ABCA1, together with bile acids should participate in sterol efflux on the apical surface of Caco-2 cells.

Hydrolysis of Micellar Phosphatidylcholine Accelerates Cholesterol Absorption in Rats and Caco-2 Cells

Lymphatic recovery of cholesterol infused into the duodenum as bile salt micelles containing phosphatidylcholine (PC) was accelerated by the co-administration of phospholipase A2 in bile and pancreatic juice diverted rats. Previously we observed that cholesterol esterase, which has the ability to hydrolyze PC, caused the same effect under a similar experimental condition (Ikeda et al., Biochim. Biophys. Acta, 1571, 34-44 (2002)). Accelerated cholesterol absorption was also observed when a part of micellar PC was replaced by lysophosphatidylcholine (LysoPC) and oleic acid. Phospholipase A2 facilitated the incorporation of micellar cholesterol into Caco-2 cells in a dose-dependent manner. There was a highly negative correlation between the incorporation of cholesterol into Caco-2 cells and the content of micellar PC remaining in the culture medium. The release of cholesterol as a monomer from bile salt micelles was enhanced when a part of micellar PC was replaced with LysoPC and oleic acid. These results strongly suggest that the release of monomer cholesterol from bile salt micelles is accelerated by hydrolysis of PC in bile salt micelles and hence that cholesterol absorption is enhanced.

Proteomic characterization of serine hydrolase activity and composition in normal urine

Background

Serine hydrolases constitute a large enzyme family involved in a diversity of proteolytic and metabolic processes which are essential for many aspects of normal physiology. The roles of serine hydrolases in renal function are largely unknown and monitoring their activity may provide important insights into renal physiology. The goal of this study was to profile urinary serine hydrolases with activity-based protein profiling (ABPP) and to perform an in-depth compositional analysis.

Methods

Eighteen healthy individuals provided random, mid-stream urine samples. ABPP was performed by reacting urines (n = 18) with a rhodamine-tagged fluorophosphonate probe and visualizing on SDS-PAGE. Active serine hydrolases were isolated with affinity purification and identified on MS-MS. Enzyme activity was confirmed with substrate specific assays. A complementary 2D LC/MS-MS analysis was performed to evaluate the composition of serine hydrolases in urine.

Results

Enzyme activity was closely, but not exclusively, correlated with protein quantity. Affinity purification and MS/MS identified 13 active serine hydrolases. The epithelial sodium channel (ENaC) and calcium channel (TRPV5) regulators, tissue kallikrein and plasmin were identified in active forms, suggesting a potential role in regulating sodium and calcium reabsorption in a healthy human model. Complement C1r subcomponent-like protein, mannan binding lectin serine protease 2 and myeloblastin (proteinase 3) were also identified in active forms. The in-depth compositional analysis identified 62 serine hydrolases in urine independent of activity state.

Conclusions

This study identified luminal regulators of electrolyte homeostasis in an active state in the urine, which suggests tissue kallikrein and plasmin may be functionally relevant in healthy individuals. Additional serine hydrolases were identified in an active form that may contribute to regulating innate immunity of the urinary tract. Finally, the optimized ABPP technique in urine demonstrates its feasibility, reproducibility and potential applicability to profiling urinary enzyme activity in different renal physiological and pathophysiological conditions.

Regulation of cholesterol homeostasis

Hypercholesterolemia is an important risk factor for cardiovascular disease. It is caused by a disturbed balance between cholesterol secretion into the blood versus uptake. The pathways involved are regulated via a complex interplay of enzymes, transport proteins, transcription factors and non-coding RNA's. The last two decades insight into underlying mechanisms has increased vastly but there are still a lot of unknowns, particularly regarding intracellular cholesterol transport. After decades of concentration on the liver, in recent years the intestine has come into focus as an important control point in cholesterol homeostasis. This review will discuss current knowledge of cholesterol physiology, with emphasis on cholesterol absorption, cholesterol synthesis and fecal excretion, and new (possible) therapeutic options for hypercholesterolemia.

Recombinant sterol esterase from Ophiostoma piceae: an improved biocatalyst expressed in Pichia pastoris

BACKGROUND

The ascomycete Ophiostoma piceae produces a sterol esterase (OPE) with high affinity towards p-nitrophenol, glycerol and sterol esters. Its hydrolytic activity on natural mixtures of triglycerides and sterol esters has been proposed for pitch biocontrol in paper industry since these compounds produce important economic losses during paper pulp manufacture.

RESULTS

Recently, this enzyme has been heterologously expressed in the methylotrophic yeast Pichia pastoris, and the hydrolytic activity of the recombinant protein (OPE*) studied. After the initial screening of different clones expressing the enzyme, only one was selected for showing the highest production rate. Different culture conditions were tested to improve the expression of the recombinant enzyme. Complex media were better than minimal media for production, but in any case the levels of enzymatic activity were higher (7-fold in the best case) than those obtained from O. piceae. The purified enzyme had a molecular mass of 76 kDa, higher than that reported for the native enzyme under SDS-PAGE (60 kDa). Steady-state kinetic characterization of the recombinant protein showed improved catalytic efficiency for this enzyme as compared to the native one, for all the assayed substrates (p-nitrophenol, glycerol, and cholesterol esters). Different causes for this were studied, as the increased glycosylation degree of the recombinant enzyme, their secondary structures or the oxidation of methionine residues. However, none of these could explain the improvements found in the recombinant protein. N-terminal sequencing of OPE* showed that two populations of this enzyme were expressed, having either 6 or 8 amino acid residues more than the native one. This fact affected the aggregation behaviour of the recombinant protein, as was corroborated by analytical ultracentrifugation, thus improving the catalytic efficiency of this enzyme.

CONCLUSION

P. pastoris resulted to be an optimum biofactory for the heterologous production of recombinant sterol esterase from O. piceae, yielding higher activity levels than those obtained with the saprophytic fungus. The enzyme showed improved kinetic parameters because of its modified N-terminus, which allowed changes in its aggregation behaviour, suggesting that its hydrophobicity has been modified.

Generating ceramide from sphingomyelin by alkaline sphingomyelinase in the gut enhances sphingomyelin-induced inhibition of cholesterol uptake in Caco-2 cells

Background Sphingomyelin (SM) is present in dietary products and cell plasma membranes. We previously showed that dietary SM inhibited cholesterol absorption in rats. In the intestinal tract, SM is mainly hydrolyzed by alkaline sphingomyelinase (alk-SMase) to ceramide.Aims We investigated the influence of SM and its hydrolytic products ceramide and sphingosine on cholesterol uptake in intestinal Caco-2 cells.Methods Micelles containing bile salt, monoolein, and (14)C-cholesterol were prepared with or without SM, ceramide,or sphingosine. The micelles were incubated with Caco-2 cells, and uptake of radioactive cholesterol was quantified.Results We found that confluent monolayer Caco-2 cells expressed NPC1L1, and the uptake of cholesterol in the cells was inhibited by ezetimibe, a specific inhibitor of NPC1L1. Incorporation of SM in the cholesterol micelles inhibited cholesterol uptake dose-dependently; 38% inhibition occurred at an equal mole ratio of SM and cholesterol.The inhibition was further enhanced to 45% by pretreating the cholesterol/SM micelles with recombinant alk-SMase, which hydrolyzed SM in the micelles by 85%, indicating ceramide has stronger inhibitory effects on cholesterol uptake. To confirm this, we further replaced SM in the micelles with ceramide and sphingosine, and found that at equal mole ratio to cholesterol, ceramide exhibited stronger inhibitory effect (50% vs 38%) on cholesterol uptake than SM, whereas sphingosine only had a weak effect at high concentrations.Conclusion Both SM and ceramide inhibit cholesterol uptake, the effect of ceramide being stronger than that of SM. Alk-SMase enhances SM-induced inhibition of cholesterol uptake by generating ceramide in the intestinal lumen.

Differential expression of intestinal genes in opossums with high and low responses to dietary cholesterol

High and low responding opossums (Monodelphis domestica) differ in their plasma very low density lipoprotein and low density lipoprotein (VLDL+LDL) cholesterol concentrations when they consume a high cholesterol diet, which is due in part to absorption of a higher percentage of dietary cholesterol in high responders. We compared the expression of a set of genes that influence cholesterol absorption in high and low responders fed a basal or a high cholesterol and low fat (HCLF) diet. Up-regulation of the ABCG5, ABCG8, and IBABP genes by the HCLF diet in high and low responders may reduce cholesterol absorption to maintain cholesterol homeostasis. Differences in expression of the phospholipase genes (PLA2 and PLB) and phospholipase activity were associated with differences in cholesterol absorption when opossums were fed cholesterol-enriched diets. Higher PLA2 and PLB mRNA levels and higher phospholipase activity may increase cholesterol absorption in high responders by enhancing the release of cholesterol from bile salt micelles for uptake by intestinal cells.

Update on patented cholesterol absorption inhibitors

BACKGROUND

Atherosclerosis is one of the most life-threatening diseases primarily associated with hypercholesterolemia and is characterized by increased serum cholesterol level. Cholesterol originates from both its de novo synthesis within the hepatic cells and its absorption into the intestine in the form of dietary or bile cholesterol. Interventions influencing both of these processes are promising therapeutic options to lower the cholesterol level. Hydroxymethyl glutaryl-CoA reductase inhibitors, commonly known as statins, effectively block the rate determining step in the biosynthesis of cholesterol. Ezetimibe is the first new class of drugs used to treat hypercholesterolemia by inhibition of cholesterol absorption through Niemann Pick C1 Like 1 membrane of enterocytes. Therefore, combination therapy of ezetimibe and statins offers an efficacious new approach for the prevention and treatment of hypercholesterolemia.

OBJECTIVES

The present review focuses on updates on ezetimibe and patented profile of novel cholesterol absorption inhibitors followed by critical analysis of different targets such as cholesterol esterase inhibitors, bile acid transport inhibitors or phospholipase-A(2) inhibitors, etc.which play an important role in the lipid absorption.

CONCLUSION

The discovery of ezetimibe has opened a new door for the management of hyper-cholesterolemia in combination with statins. There are newer analogues that are under clinical trials, among which darapladib, FM-VP4 and A-002 are promising compounds.

Effect of ezetimibe on plasma cholesterol levels, cholesterol absorption, and secretion of biliary cholesterol in laboratory opossums with high and low responses to dietary cholesterol

Partially inbred lines of laboratory opossums differ in plasma low-density lipoprotein cholesterol concentration and cholesterol absorption on a high-cholesterol diet. The aim of the present studies was to determine whether ezetimibe inhibits cholesterol absorption and eliminates the differences in plasma cholesterol and hepatic cholesterol metabolism between high and low responders on a high-cholesterol diet. Initially, we determined that the optimum dose of ezetimibe was 5 mg/(kg d) and treated 6 high- and 6 low-responding opossums with this dose (with equal numbers of controls) for 3 weeks while the opossums consumed a high-cholesterol and low-fat diet. Plasma and low-density lipoprotein cholesterol concentrations decreased significantly (P < .05) in treated but not in untreated high-responding opossums. Plasma cholesterol concentrations increased slightly (P < .05) in untreated low responders but not in treated low responders. The percentage of cholesterol absorption was significantly higher in untreated high responders than in other groups. Livers from high responders with or without treatment were significantly (P < .01) heavier than livers from low responders with or without treatment. Hepatic cholesterol concentrations in untreated high responders were significantly (P < .05) higher than those in low responders with or without treatment (P < .001). The gall bladder bile cholesterol concentrations in untreated high responders were significantly (P < .05) lower than those in other groups. A decrease in biliary cholesterol in low responders treated with ezetimibe was associated with a decrease in hepatic expression of ABCG5 and ABCG8. These studies suggest that ezetimibe decreases plasma cholesterol levels in high responders mainly by decreasing cholesterol absorption and increasing biliary cholesterol concentrations. Because ezetimibe's target is NPC1L1 and NPC1L1 is expressed in the intestine of opossums, its effect on cholesterol absorption may be mediated by inhibiting NPC1L1 function in the intestine.

Isocoumarin-based inhibitors of pancreatic cholesterol esterase

Pancreatic cholesterol esterase (CEase), which is secreted from the exocrine pancreas, is a serine hydrolase that aids in the bile salt-dependent hydrolysis of dietary cholesteryl esters and contributes to the hydrolysis of triglycerides and phospholipids. Additional roles for CEase in intestinal micelle formation and in transport of free cholesterol to the enterocyte have been suggested. There also are studies that point to a pathological role(s) for CEase in the circulation where CEase accumulates in atherosclerotic lesions and triggers proliferation of smooth muscle cells. Thus, there is interest in CEase as a potential drug target. 4-Chloro-3-alkoxyisocoumarins are a class of haloenol lactones that inhibit serine hydrolases and serine proteases and have the potential to be suicide inhibitors. In the present study, we have developed 3-alkoxychloroisocoumarins that are potent inhibitors of CEase. These inhibitors were designed to have a saturated cycloalkane ring incorporated into a 3-alkoxy substituent. The size of the ring as well as the length of the tether holding the ring was found to be important contributors to binding to CEase. 4-Chloro-3-(4-cyclohexylbutoxy)isocoumarin and 4-chloro-3-(3-cyclopentylpropoxy)isocoumarin were demonstrated to be potent reversible inhibitors of CEase, with dissociation constants of 11nM and 19nM, respectively. The kinetic results are consistent with predictions from molecular modeling.

A semi-empirical computational model for the inhibition of porcine cholesterol esterase

Cholesterol esterase significantly contributes to cell membrane structure. It also facilitates transfer of cholesterol and phospholipids across membranes. Inhibition of this enzyme by a number of xenobiotics has been reported. This research sought to confirm if a widely used methacrylate monomer, bisphenol A dimethacrylate, inhibits porcine cholesterol esterase since this and other methacrylates are known to leach from various biomaterial preparations. A quantum mechanically developed computational chemistry model is presented. Specific chemical information linking potential mechanisms of cholesterol esterase inhibition to chemical structure is shown. Model chemical descriptors identified the importance of maximum oxygen valency and molecular shape/size to cholesterol esterase inhibition. A porcine cholesterol esterase inhibition mechanism is inherent in bisphenol A dimethacrylate which mimics chemical properties of reported cholesterol esterase inhibitors. This predictive semiempirical quantum mechanical model can be used to design new cholesterol esterase non-inhibitors for biocompatible biomaterials used in an aqueous environment.

Lymphatic absorption and deposition of various plant sterols in stroke-prone spontaneously hypertensive rats, a strain having a mutation in ATP binding cassette transporter G5

ATP binding cassette transporter G5 (ABCG5) and ATP binding cassette transporter G8 (ABCG8) have been suggested to transport absorbed plant sterols and cholesterol from enterocytes to the intestinal lumen and from hepatocytes to bile. It has been thought that mutations of ABCG5 or ABCG8 cause the deposition of plant sterols in the body. In the present study, lymphatic absorption of various plant sterols and their deposition in various tissues was investigated in stroke-prone spontaneously hypertensive rats (SHRSP), having a mutation in Abcg5 and depositing plant sterols in the body. The order of lymphatic 24-h recovery of plant sterols was as follows: campesterol > sitosterol > brassicasterol > stigmasterol = sitostanol. When SHRSP were fed a diet containing one of the plant sterols, the depositions of campesterol and sitosterol were comparatively higher than those of brassicasterol, stigmasterol and sitostanol. Highly positive correlations were obtained between lymphatic recovery of plant sterols and their levels in plasma, liver, adipose tissue and heart. The tendency of differential absorption of plant sterols to the lymph in SHRSP was similar to that in normal Wistar rats previously reported by us (Hamada et al. Lipids 41:551-556, 2006). These observations suggest that differential absorption of various plant sterols is kept in SHRSP in spite of a mutation in Abcg5.

Solubility in and affinity for the bile salt micelle of plant sterols are important determinants of their intestinal absorption in rats

Intestinal absorption of various plant sterols was investigated in thoracic duct-cannulated normal rats. Lymphatic recovery was the highest in campesterol, intermediate in brassicasterol and sitosterol, and the lowest in stigmasterol and sitostanol. Higher solubility in the bile salt micelle was observed in sitosterol, campesterol, and sitostanol than in brassicasterol and stigmasterol. The solubility of the latter two sterols was extremely low. When the affinity of plant sterols for the bile salt micelle was compared in an in vitro model system, which assessed sterol transfer from the micellar to the oil phase, the transfer rate was the highest in brassicasterol, intermediate in campesterol and stigmasterol, and lowest in sitosterol and sitostanol. Although no significant correlations between lymphatic recovery of plant sterols and their micellar solubility or transfer rate from the bile salt micelle were observed, highly positive correlation was obtained between the lymphatic recovery and the multiplication value of the micellar solubility and the transfer rate. These observations strongly suggest that both solubility in and affinity for the bile salt micelle of plant sterols are important determinants of their intestinal absorption in rats.

Hydrolysis of zeaxanthin esters by carboxyl ester lipase during digestion facilitates micellarization and uptake of the xanthophyll by Caco-2 human intestinal cells

Zeaxanthin (Zea) and lutein are the only dietary carotenoids that accumulate in the macular region of the retina and lens. It was proposed that these carotenoids protect these tissues against photooxidative damage. Few plant foods are enriched in Zea, and information about the bioavailability of Zea from these foods and its accumulation in ocular tissues is limited. The amounts of free Zea and its mono- and diesters were measured for several plant foods that have relatively high concentrations of this xanthophyll. Wolfberry had the greatest concentration of Zea with a diester that accounts for 95% of the total. Free, mono-, and diesters of Zea were present in orange and red peppers, whereas only Zea monoesters were detected in squash. Zea esters were partially hydrolyzed by carboxyl ester lipase (CEL) during simulated digestion. The efficiency of micellarization was dependent on speciation with combined means of free Zea, Zea monoesters, Zea diesters from the digested foods of 81 +/- 8, 44 +/- 5, and 11 +/- 4%, respectively. When exposed to micelles generated during digestion of the test foods, Zea uptake by Caco-2 cells was proportional to the medium content (11-14%). Free Zea was the most abundant form in Caco-2 cells, although Zea monoesters also were detected (<8 +/- 0.7% vs. free Zea). CEL enhanced Zea uptake from micelles (12.3-fold; P < 0.05) by hydrolyzing Zea esters. After cell uptake, concentrations of free and monoesterified Zea remained relatively stable. These data suggest that dietary Zea esters are hydrolyzed by CEL during the small intestinal phase of digestion and that this conversion enhances Zea bioavailability.

The clinical and nutritional implications of lipid-lowering drugs that act in the gastrointestinal tract

PURPOSE OF REVIEW

A new class of cholesterol-lowering therapy that reduces intestinal sterol absorption has recently been introduced. This increases the number of classes of lipid-lowering agents that directly affect gastrointestinal function and raises questions concerning the overall effect of these agents on absorption and nutritional status.

RECENT FINDINGS

A recent assessment notes a paucity of information concerning the factors that affect the bioavailability and intestinal absorption of lipophilic nutrients. By contrast, the specificity of the mechanisms of action of new drugs acting on the gastrointestinal tract may circumvent some of the detrimental effects on nutrient and drug bioavailability that have been noted with older forms of treatment.

SUMMARY

The clinical imperative for aggressive control of lipid and metabolic risk factors makes widespread use, alone or in combination, of lipid-lowering agents that affect the gastrointestinal tract seem increasingly likely. Whilst the opportunity for therapeutic synergy is attractive, care will be required to avoid interference with intestinal absorptive function.

Enteral administration of soybean phosphatidylcholine enhances the lymphatic absorption of lycopene, but reduces that of alpha-tocopherol in rats

Dietary phosphatidylcholine (PC) increases the lymphatic absorption of triglyceride (TG). This result suggests that dietary PC might also enhance the absorption of other fat-soluble nutrients. We examined the effects of PC on lycopene and alpha-tocopherol absorption in male rats fitted with a thoracic lymph cannula. The lymphatic output was collected after administration of 1 mL of emulsified test oils containing lycopene and/or alpha-tocopherol in 3 separate experiments. The sodium taurocholate-emulsified test oils contained soybean oil (SO; 113 micromol triglyceride), SO containing soybean PC (SPC; 82.5 micromol SO plus 30.5 micromol purified soybean PC) or SO containing egg PC (EPC; 82.5 micromol SO plus 30.5 micromol purified egg PC) with both lycopene and alpha-tocopherol (Expt. 1) or SO, SPC, or EPC with lycopene (Expt. 2) or alpha-tocopherol alone (Expt. 3). In rats administered SPC or EPC, the lymphatic outputs of TG and lycopene were higher, and that of alpha-tocopherol was lower compared with rats administered SO (Expt. 1). The absorption rate for lycopene increased from 0.59% (SO group) to 2.16 and 1.28% in the SPC and EPC groups (P < 0.05), respectively, whereas the corresponding rates for tocopherol were 21.5% for the SO, 14.8% for the SPC, and 12.9% for the EPC groups. The increase in lycopene, but not in triglyceride absorption, was higher in the SPC than in the EPC groups. The promotive effects of SPC and EPC were decreased when lycopene alone was added to the test lipids (Expt. 2), and the inhibitory effects of PC were reduced when alpha-tocopherol alone was added to the test lipids (Expt. 3). Dietary PC increased the lymphatic output of lycopene and TG and decreased that of alpha-tocopherol, suggesting that differences exist between lycopene and alpha-tocopherol in the absorptive mechanisms. The present results also show that the promotive effects of PC on lycopene absorption are influenced by the type of fatty acids in PC.

Cholesterol absorption and hepatic acyl-coenzyme A:cholesterol acyltransferase activity play major roles in lipemic response to dietary cholesterol and fat in laboratory opossums

Partially inbred lines of laboratory opossums differ considerably in their low-density lipoprotein (LDL) cholesterol responses to dietary cholesterol and fat. Genetic analysis suggested that a single major gene is responsible for the variation in LDL cholesterol on the high cholesterol and high fat (HCHF) diet. We measured cholesterol absorption and acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity in intestine and liver to narrow the search for the major gene. We measured plasma lipoproteins and percent cholesterol absorption by the fecal isotope ratio method in high and low responding lines of opossums on basal and HCHF diets. We also measured lipids in liver and ACAT activity in liver and intestine on the HCHF diet. High and low lines exhibited no differences in percent cholesterol absorption on the basal diet. However, high responding opossums had significantly higher percent cholesterol absorption, hepatic free and esterified cholesterol, and hepatic ACAT activity than low responding opossums on the HCHF diet. Hepatic ACAT activity but not the intestinal ACAT activity was associated with hepatic cholesterol concentration and percent cholesterol absorption. Cholesterol absorption is a major determinant of diet-induced hyperlipidemia in opossums. Hepatic ACAT activity but not the intestinal ACAT may also play a role in diet-induced hyperlipidemia in opossums.

Inhibition of pancreatic cholesterol esterase reduces cholesterol absorption in the hamster

BACKGROUND

Pancreatic cholesterol esterase has three proposed functions in the intestine: 1) to control the bioavailability of cholesterol from dietary cholesterol esters; 2) to contribute to incorporation of cholesterol into mixed micelles; and 3) to aid in transport of free cholesterol to the enterocyte. Inhibitors of cholesterol esterase are anticipated to limit the absorption of dietary cholesterol.

RESULTS

The selective and potent cholesterol esterase inhibitor 6-chloro-3-(1-ethyl-2-cyclohexyl)-2-pyrone (figure 1, structure 1) was administered to hamsters fed a high cholesterol diet supplemented with radiolabeled cholesterol ester. Hamsters were gavage fed 3H-labeled cholesteryl oleate along with inhibitor 1, 0-200 micromoles. Twenty-four hours later, hepatic and serum radioactive cholesterol levels were determined. The ED50 of inhibitor 1 for prevention of the uptake of labeled cholesterol derived from hydrolysis of labeled cholesteryl oleate was 100 micromoles. The toxicity of inhibitor 1 was investigated in a 30 day feeding trial. Inhibitor 1, 100 micromoles or 200 micromoles per day, was added to chow supplemented with 1% cholesterol and 0.5% cholic acid. Clinical chemistry urinalysis and tissue histopathology were obtained. No toxicity differences were noted between control and inhibitor supplemented groups.

CONCLUSIONS

Inhibitors of cholesterol esterase may be useful therapeutics for limiting cholesterol absorption.

Carboxyl ester lipase: structure-function relationship and physiological role in lipoprotein metabolism and atherosclerosis

Carboxyl ester lipase (CEL), previously named cholesterol esterase or bile salt-stimulated (or dependent) lipase, is a lipolytic enzyme capable of hydrolyzing cholesteryl esters, tri-, di-, and mono-acylglycerols, phospholipids, lysophospholipids, and ceramide. The active site catalytic triad of serine-histidine-aspartate is centrally located within the enzyme structure and is partially covered by a surface loop. The carboxyl terminus of the protein regulates enzymatic activity by forming hydrogen bonds with the surface loop to partially shield the active site. Bile salt binding to the loop domain frees the active site for accessibility by water-insoluble substrates. CEL is synthesized primarily in the pancreas and lactating mammary gland, but the enzyme is also expressed in liver, macrophages, and in the vessel wall. In the gastrointestinal tract, CEL serves as a compensatory protein to other lipolytic enzymes for complete digestion and absorption of lipid nutrients. Importantly, CEL also participates in chylomicron assembly and secretion, in a mechanism mediated through its ceramide hydrolytic activity. Cell culture studies suggest a role for CEL in lipoprotein metabolism and oxidized LDL-induced atherosclerosis. Thus, this enzyme, which has a wide substrate reactivity and diffuse anatomic distribution, may have multiple functions in lipid and lipoprotein metabolism, and atherosclerosis.