Antibiotics Suppress Activation of Intestinal Mucosal Mast Cells and Reduce Dietary Lipid Absorption in Sprague-Dawley Rats.

Background & Aims: The gut microbiota affects intestinal permeability and mucosal mast cells (MMCs) responses. Activation of MMCs has been associated with absorption of dietary fat. We investigated whether the gut microbiota contributes to the fat-induced activation of MMCs in rats, and how antibiotics might affect this process.

The Increasing Use of Interesterified Lipids in the Food Supply and Their Effects on Health Parameters.

A variety of modified fats that provide different functionalities are used in processed foods to optimize product characteristics and nutrient composition. Partial hydrogenation results in the formation of trans FAs (TFAs) and was one of the most widely used modification processes of fats and oils. However, the negative effects of commercially produced TFAs on serum lipoproteins and risk for cardiovascular disease resulted in the Institute of Medicine and the 2010 US Dietary Guidelines for Americans both recommending that TFA intake be as low as possible.

Cholesterol Absorption and Metabolism.

Inhibitors of cholesterol absorption have been sought for decades as a means to treat and prevent cardiovascular diseases (CVDs) associated with hypercholesterolemia. Ezetimibe is the one clear success story in this regard, and other compounds with similar efficacy continue to be sought. In the last decade, the laboratory mouse, with all its genetic power, has become the premier experimental model for discovering the mechanisms underlying cholesterol absorption and has become a critical tool for preclinical testing of potential pharmaceutical entities.

Relative contributions of L-FABP, SCP-2/SCP-x, or both to hepatic biliary phenotype of female mice.

Both sterol carrier protein-2/sterol carrier protein-x (SCP-2/SCP-x) and liver fatty acid binding protein (L-FABP) have been proposed to function in hepatobiliary bile acid metabolism/accumulation. To begin to address this issue, the impact of ablating L-FABP (LKO) or SCP-2/SCP-x (DKO) individually or both together (TKO) was examined in female mice. Biliary bile acid levels were decreased in LKO, DKO, and TKO mice; however, hepatic bile acid concentration was decreased in LKO mice only.

Apolipoprotein A-V is present in bile and its secretion increases with lipid absorption in Sprague-Dawley rats.

Apolipoprotein (apo) A-V is a protein synthesized only in the liver that dramatically modulates plasma triglyceride levels. Recent studies suggest a novel role for hepatic apoA-V in regulating the absorption of dietary triglycerides, but its mode of action on the gut remains unknown. The aim of this study was to test for apoA-V in bile and to determine whether its secretion is regulated by dietary lipids.

ABCG5/G8 deficiency in mice reduces dietary triacylglycerol and cholesterol transport into the lymph.

The adenosine triphosphate-binding cassette (ABC) transporter G5/G8 is critical in protecting the body from accumulating dietary plant sterols. Expressed in the liver and small intestine, it transports plant sterols into the biliary and intestinal lumens, thus promoting their excretion. The extent to which G5/G8 regulates cholesterol absorption remains unclear.

Ablating L-FABP in SCP-2/SCP-x null mice impairs bile acid metabolism and biliary HDL-cholesterol secretion.

On the basis of their abilities to bind bile acids and/or cholesterol, the physiological role(s) of liver fatty acid-binding protein (L-FABP) and sterol carrier protein (SCP) 2/SCP-x (SCP-2/SCP-x) gene products in biliary bile acid and cholesterol formation was examined in gene-ablated male mice. L-FABP (LKO) or L-FABP/SCP-2/SCP-x [triple-knockout (TKO)] ablation markedly decreased hepatic bile acid concentration, while SCP-2/SCP-x [double-knockout (DKO)] ablation alone had no effect. In contrast, LKO increased biliary bile acid, while DKO and TKO had no effect on biliary bile acid levels.

Methods for studying rodent intestinal lipoprotein production and metabolism.

Lipid absorption begins with the digestion of dietary triacylglycerol and ultimately results in the secretion of triacylglycerol in chylomicrons into the lymphatics. Additionally, the intestine also secretes numerous proteins and peptides involved in lipid and lipoprotein metabolism in response to food. Ultimately, chylomicrons and these proteins, peptides, and hormones are found in lymph.

Hepatic deficiency of low density lipoprotein receptor-related protein-1 reduces high density lipoprotein secretion and plasma levels in mice.

The low density lipoprotein receptor-related protein-1 (LRP1) is known to serve as a chylomicron remnant receptor in the liver responsible for the binding and plasma clearance of apolipoprotein E-containing lipoproteins. Previous in vitro studies have provided evidence to suggest that LRP1 expression may also influence high density lipoprotein (HDL) metabolism. The current study showed that liver-specific LRP1 knock-out (hLrp1(-/-)) mice displayed lower fasting plasma HDL cholesterol levels when compared with hLrp1(+/+) mice.

Reverse cholesterol transport is elevated in carboxyl ester lipase-knockout mice.

Mechanisms to increase reverse cholesterol transport (RCT) and biliary sterol disposal are currently sought to prevent atherosclerosis. Previous work with HepG2 cells and primary hepatocytes showed that carboxyl ester lipase (CEL), a broad-spectrum lipase secreted by pancreas and liver, plays an important role in hydrolysis of high-density lipoprotein (HDL) cholesteryl esters (CEs) after selective uptake by hepatocytes. The effect of CEL on RCT of HDL cholesterol was assessed by measuring biliary and fecal disposal of radiolabeled HDL-CE in control and Cel(-/-) mice.

Effect of ezetimibe on incretin secretion in response to the intestinal absorption of a mixed meal.

Ezetimibe is a potent inhibitor of cholesterol absorption by enterocytes. Although ezetimibe minimally affects the absorption of triglyceride, it is unknown whether ezetimibe affects the secretion of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). It has been shown that ezetimibe-treated mice are protected from diet-induced insulin resistance.

Cholesterol absorption and metabolism.

Inhibitors of cholesterol absorption have been sought for decades as a means to treat and prevent cardiovascular diseases associated with hypercholesterolemia. Ezetimibe is the one clear success story in this regard, and other compounds with similar efficacy continue to be sought. In the last decade, the laboratory mouse, with all its genetic power, has become the premier experimental model for discovering the mechanisms underlying cholesterol absorption and has become a critical tool for preclinical testing of potential pharmaceutical entities.

Reduced absorption of saturated fatty acids and resistance to diet-induced obesity and diabetes by ezetimibe-treated and Npc1l1-/- mice.

The impact of NPC1L1 and ezetimibe on cholesterol absorption are well documented. However, their potential consequences relative to absorption and metabolism of other nutrients have been only minimally investigated. Thus studies were undertaken to investigate the possible effects of this protein and drug on fat absorption, weight gain, and glucose metabolism by using Npc1l1(-/-) and ezetimibe-treated mice fed control and high-fat, high-sucrose diets.

Development and physiological regulation of intestinal lipid absorption. III. Intestinal transporters and cholesterol absorption.

Intestinal cholesterol absorption is modulated by transport proteins in enterocytes. Cholesterol uptake from intestinal lumen requires several proteins on apical brush-border membranes, including Niemann-Pick C1-like 1 (NPC1L1), scavenger receptor B-I, and CD36, whereas two ATP-binding cassette half transporters, ABCG5 and ABCG8, on apical membranes work together for cholesterol efflux back to the intestinal lumen to limit cholesterol absorption. NPC1L1 is essential for cholesterol absorption, but its function as a cell surface transporter or an intracellular cholesterol transport protein needs clarification.

The central melanocortin system directly controls peripheral lipid metabolism.

Disruptions of the melanocortin signaling system have been linked to obesity. We investigated a possible role of the central nervous melanocortin system (CNS-Mcr) in the control of adiposity through effects on nutrient partitioning and cellular lipid metabolism independent of nutrient intake. We report that pharmacological inhibition of melanocortin receptors (Mcr) in rats and genetic disruption of Mc4r in mice directly and potently promoted lipid uptake, triglyceride synthesis, and fat accumulation in white adipose tissue (WAT), while increased CNS-Mcr signaling triggered lipid mobilization.

Carboxyl ester lipase deficiency exacerbates dietary lipid absorption abnormalities and resistance to diet-induced obesity in pancreatic triglyceride lipase knockout mice.

This study evaluated the contributions of carboxyl ester lipase (CEL) and pancreatic triglyceride lipase (PTL) in lipid nutrient absorption. Results showed PTL deficiency has minimal effect on triacylglycerol (TAG) absorption under low fat dietary conditions. Interestingly, PTL(-)(/)(-) mice displayed significantly reduced TAG absorption compared with wild type mice under high fat/high cholesterol dietary conditions (80.

Class B type I scavenger receptor is responsible for the high affinity cholesterol binding activity of intestinal brush border membrane vesicles.

Recent studies have documented the importance of Niemann-Pick C1-like 1 protein (NPC1L1), a putative physiological target of the drug ezetimibe, in mediating intestinal cholesterol absorption. However, whether NPC1L1 is the high affinity cholesterol binding protein on intestinal brush border membranes is still controversial. In this study, brush border membrane vesicles (BBMV) from wild type and NPC1L1-/- mice were isolated and assayed for micellar cholesterol binding in the presence or absence of ezetimibe.

Molecular mechanisms of cholesterol absorption and transport in the intestine.

Many enzymes and transport proteins participate in cholesterol absorption. This review summarizes recent results on several proteins that are important for each step of the cholesterol absorption pathway, including the important roles of: (i) pancreatic triglyceride lipase (PTL), carboxyl ester lipase (CEL), and ileal bile acid transporter in determining the rate of cholesterol absorption; (ii) ATP binding cassette (ABC) transporters and the Niemann-Pick C-1 like-1 (NPC1L1) protein as intestinal membrane gatekeepers for cholesterol efflux and influx; and (iii) intracellular membrane vesicles and transport proteins in lipid trafficking through intracellular compartments prior to lipoprotein assembly and secretion to plasma circulation.

Carboxyl ester lipase cofractionates with scavenger receptor BI in hepatocyte lipid rafts and enhances selective uptake and hydrolysis of cholesteryl esters from HDL3.

Cholesteryl esters are selectively removed from high density lipoproteins by hepatocytes and steroidogenic cells through a process mediated by scavenger receptor BI. In the liver this cholesterol is secreted into bile, primarily as free cholesterol. Previous work showed that carboxyl ester lipase enhanced selective uptake of cholesteryl ether from high density lipoprotein by an unknown mechanism.

Rate of gastric emptying influences dietary cholesterol absorption efficiency in selected inbred strains of mice.

This study compared the physiological process of cholesterol absorption in different strains of inbred mice with the goal of identifying novel mechanism(s) by which cholesterol absorption can be controlled. The rate and amount of cholesterol absorption were evaluated based on [14C]cholesterol appearance in plasma after feeding a meal containing [14C]cholesterol and by the percentage of [14C]-cholesterol absorbed over a 24 h period. Results showed that the rate of [14C]cholesterol appearance in plasma was slower in 129P3/J mice than in SJL/J mice.

Pancreatic triglyceride lipase deficiency minimally affects dietary fat absorption but dramatically decreases dietary cholesterol absorption in mice.

This study generated pancreatic triglyceride lipase (PTL)-null mice to test the hypothesis that PTL-mediated hydrolysis of dietary triglyceride is necessary for efficient dietary cholesterol absorption. The PTL-/- mice grew normally and displayed similar body weight as their PTL+/+ littermates. Plasma lipid levels between animals of various PTL genotypes were similar when they were maintained on either a basal low fat diet or a western-type high fat/high cholesterol diet.

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-stimulated carboxyl ester lipase influences lipoprotein assembly and secretion in intestine: a process mediated via ceramide hydrolysis.

Bile salt-stimulated carboxyl ester lipase (CEL), also called cholesterol esterase, is one of the major proteins secreted by the pancreas. The physiological role of CEL was originally thought to be its mediation of dietary cholesterol absorption. However, recent studies showed no difference between wild type and CEL knockout mice in the total amount of cholesterol absorbed in a single meal.

Evaluating a Model of an NRE Mediated Tissue-Specific Expression of Murine Renin Genes.

-We have used comparative sequence analysis to evaluate a putative silencer element that has been proposed to be involved in the differential tissue-expression of the murine renin genes: Ren-1 and Ren-2. In the mouse, these genes share a similar pattern of tissue-specific renin expression. One significant difference is seen in the submandibular gland (SMG) where renin expression from the Ren-2 locus is 100-fold greater than the expression from the Ren-1 locus.