Inhibition of carnitine palmitoyltransferase in the rat small intestine reduces export of triacylglycerol into the lymph

Fatty acid metabolism and colon cancer protection by dietary methyl donor restriction

INTRODUCTION

A methyl donor depleted (MDD) diet dramatically suppresses intestinal tumor development in Apc-mutant mice, but the mechanism of this prevention is not entirely clear.

OBJECTIVES

We sought to gain insight into the mechanisms of cancer suppression by the MDD diet and to identify biomarkers of cancer risk reduction.

METHODS

A plasma metabolomic analysis was performed on Apc^Δ14/+ mice maintained on either a methyl donor sufficient (MDS) diet or the protective MDD diet. A group of MDS animals was also pair-fed with the MDD mice to normalize caloric intake, and another group was shifted from an MDD to MDS diet to determine the durability of the metabolic changes.

RESULTS

In addition to the anticipated changes in folate one-carbon metabolites, plasma metabolites related to fatty acid metabolism were generally decreased by the MDD diet, including carnitine, acylcarnitines, and fatty acids. Some fatty acid selectivity was observed; the levels of cancer-promoting arachidonic acid and 2-hydroxyglutarate were decreased by the MDD diet, whereas eicosapentaenoic acid (EPA) levels were increased. Machine-learning elastic net analysis revealed a positive association between the fatty acid-related compounds azelate and 7-hydroxycholesterol and tumor development, and a negative correlation with succinate and β-sitosterol.

CONCLUSION

Methyl donor restriction causes dramatic changes in systemic fatty acid metabolism. Regulating fatty acid metabolism through methyl donor restriction favorably effects fatty acid profiles to achieve cancer protection.

Early Postnatal Diets Affect the Bioregional Small Intestine Microbiome and Ileal Metabolome in Neonatal Pigs

Background: Breastfeeding is known to be protective against gastrointestinal disorders and may modify gut development. Although the gut microbiome has been implicated, little is known about how early diet affects the small intestine microbiome.Objective: We hypothesized that disparate early diets would promote unique microbial profiles in the small intestines of neonatal pigs.Methods: Male and female 2-d-old White Dutch Landrace pigs were either sow fed or provided dairy (Similac Advance powder; Ross Products Abbott Laboratories) or soy (Enfamil Prosobee Lipil powder; Mead Johnson Nutritionals) infant formulas until day 21. Bacterial ecology was assessed in the contents of the small intestine through the use of 16S ribosomal RNA sequencing. α-Diversity, β-diversity, and differential abundances of operational taxonomic units were assessed by ANOVA, permutational ANOVA, and negative binomial regression, respectively. Ileum tissue metabolomics were measured by LC-mass spectrometry and assessed by weighted correlation network analysis.Results: Greater α-diversity was observed in the duodena of sow-fed compared with formula-fed neonatal pigs (P < 0.05). No differences were observed in the ilea. Firmicutes represented the most abundant phylum across all diets in duodena (78.8%, 80.1%, and 53.4% relative abundance in sow, dairy, and soy groups, respectively), followed by Proteobacteria in sow (12.2%) and dairy (12.4%) groups and Cyanobacteria in soy-fed (36.2%) pigs. In contrast to those in the duodenum, Proteobacteria was the dominant phylum in the ileum, with >60% relative abundance in all of the groups. In the duodenum, 77 genera were altered by diet, followed by 48 in the jejunum and 19 in the ileum. Metabolomics analyses revealed associations between ileum tissue metabolites (e.g., acylcarnitines, 3-aminoisobutyric acid) and diet-responsive microbial genera.Conclusions: These results indicate that the neonatal diet has regional effects on the small intestine microbiome in pigs, with the most pronounced effects occurring in the duodena. Regional effects may be important factors when considering gut tissue metabolism and development in the postnatal period.

Acylcarnitines participate in developmental processes associated to lipid metabolism in plants

Plant acylcarnitines are present during anabolic processes of lipid metabolism. Their low contents relatively to the corresponding acyl-CoAs suggest that they are associated to specific pools of activated fatty acids. The non-proteinaceous amino acid carnitine exists in plants either as a free form or esterified to fatty acids. To clarify the biological significance of acylcarnitines in plant lipid metabolism, we have analyzed their content in plant extracts using an optimized tandem mass spectrometry coupled to liquid chromatography method. We have studied different developmental processes (post-germination, organogenesis, embryogenesis) targeted for their high requirement for lipid metabolism. The modulation of the acylcarnitine content was compared to that of the lipid composition and lipid biosynthetic gene expression level in the analyzed materials. Arabidopsis mutants were also studied based on their alteration in de novo fatty acid partitioning between the prokaryotic and eukaryotic pathways of lipid biosynthesis. We show that acylcarnitines cannot specifically be associated to triacylglycerol catabolism but that they are also associated to anabolic pathways of lipid metabolism. They are present during membrane and storage lipid biosynthesis processes. A great divergence in the relative contents of acylcarnitines as compared to the corresponding acyl-CoAs suggests that acylcarnitines are associated to very specific process(es) of lipid metabolism. The nature of their involvement as the transport form of activated fatty acids or in connection with the management of acyl-CoA pools is discussed. Also, the occurrence of medium-chain entities suggests that acylcarnitines are associated with additional lipid processes such as protein acylation for instance. This work strengthens the understanding of the role of acylcarnitines in plant lipid metabolism, probably in the management of specific acyl-CoA pools.

The Carnitine Palmitoyl Transferase (CPT) System and Possible Relevance for Neuropsychiatric and Neurological Conditions

The carnitine palmitoyl transferase (CPT) system is a multiprotein complex with catalytic activity localized within a core represented by CPT1 and CPT2 in the outer and inner membrane of the mitochondria, respectively. Two proteins, the acyl-CoA synthase and a translocase also form part of this system. This system is crucial for the mitochondrial beta-oxidation of long-chain fatty acids. CPT1 has two well-known isoforms, CPT1a and CPT1b. CPT1a is the hepatic isoform and CPT1b is typically muscular; both are normally utilized by the organism for metabolic processes throughout the body. There is a strong evidence for their involvement in various disease states, e.g., metabolic syndrome, cardiovascular diseases, and in diabetes mellitus type 2. Recently, a new, third isoform of CPT was described, CPT1c. This is a neuronal isoform and is prevalently localized in brain regions such as hypothalamus, amygdala, and hippocampus. These brain regions play an important role in control of food intake and neuropsychiatric and neurological diseases. CPT activity has been implicated in several neurological and social diseases mainly related to the alteration of insulin equilibrium in the brain. These pathologies include Parkinson's disease, Alzheimer's disease, and schizophrenia. Evolution of both Parkinson's disease and Alzheimer's disease is in some way linked to brain insulin and related metabolic dysfunctions with putative links also with the diabetes type 2. Studies show that in the CNS, CPT1c affects ceramide levels, endocannabionoids, and oxidative processes and may play an important role in various brain functions such as learning.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

The effect of clozapine on the AMPK-ACC-CPT1 pathway in the rat frontal cortex

Clozapine is an antipsychotic drug that has a greater efficacy than other medications in some contexts, especially for the treatment of treatment-resistant schizophrenia. However, clozapine induces more metabolic side-effects involving abnormality in lipid metabolism compared to other antipsychotics. AMP-activated protein kinase (AMPK) plays a central role in controlling lipid metabolism through modulating the downstream acetyl CoA carboxylase (ACC) and carnitine palmitoyl transferase 1 (CPT1) pathway. In this study, we investigated the effect of a single intraperitoneal injection of clozapine on the AMPK-ACC-CPT1 pathway in the rat frontal cortex, which has been implicated as a target site for this antipsychotic drug. At 2 h after injection, the clinically relevant dose of clozapine had activated AMPK, with increased phosphorylation of AMPKα at Thr(172), and had inactivated ACC, with increased phosphorylation of ACC at Ser(79). In addition, clozapine activated the brain-specific isoform of CPT1, CPT1c, whose activity is inhibited by unphosphorylated ACC, in the rat frontal cortex. Immunohistochemistry and immunofluorescence analysis showed that clozapine induced an increase in number of p-AMPKα (Thr(172))- and p-ACC (Ser(79))-positive cells among the neurons of the rat frontal cortex. Taken together, these results show that clozapine activated the AMPK-ACC-CPT1 pathway in the neurons of the rat frontal cortex. These findings indicate that the antipsychotic agent clozapine affects the lipid regulatory system of neurons in the brain.

Acyl-CoA:diacylglycerol acyltransferase: molecular biology, biochemistry and biotechnology

Triacylglycerol (TG) is a storage lipid which serves as an energy reservoir and a source of signalling molecules and substrates for membrane biogenesis. TG is essential for many physiological processes and its metabolism is widely conserved in nature. Acyl-CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the final step in the sn-glycerol-3-phosphate pathway leading to TG. DGAT activity resides mainly in two distinct membrane bound polypeptides, known as DGAT1 and DGAT2 which have been identified in numerous organisms. In addition, a few other enzymes also hold DGAT activity, including the DGAT-related acyl-CoA:monoacylglycerol acyltransferases (MGAT). Progress on understanding structure/function in DGATs has been limited by the lack of detailed three-dimensional structural information due to the hydrophobic properties of theses enzymes and difficulties associated with purification. This review examines several aspects of DGAT and MGAT genes and enzymes, including current knowledge on their gene structure, expression pattern, biochemical properties, membrane topology, functional motifs and subcellular localization. Recent progress in probing structural and functional aspects of DGAT1 and DGAT2, using a combination of molecular and biochemical techniques, is emphasized. Biotechnological applications involving DGAT enzymes ranging from obesity therapeutics to oilseed engineering are also discussed.

Oleate metabolism in pig enterocytes is characterized by an increased oxidation rate in the presence of a high esterification rate within two days after birth

Oleate (OLE) is the principle fatty acid (FA) in mammalian colostrum, but its role in the energy supply in enterocytes after birth remains unknown. We investigated the metabolic fate of OLE in pig enterocytes at birth (d0) and after 2 d of suckling (d2). Cellular TG and phospholipids (PL) and FA composition were analyzed. Metabolic end-products of [1-¹⁴C]OLE were measured in enterocyte incubations. We characterized intestinal carnitine palmitoyltransferase 1 (CPT1), the key enzyme of mitochondrial FA oxidation. The TG content was 6.6-fold higher in enterocytes from pigs on d 2 than in those obtained on d 0, whereas the PL content did not differ. The level of OLE in TG and PL increased from 15 and 11% of total FA, respectively, in enterocytes from newborn piglets to 30 and 17%, respectively, in those from d2 pigs. The capacity for OLE utilization was 2.8-fold greater in d2 than in d0 pig enterocytes. The oxidation and esterification rates were enhanced in enterocytes from piglets on d 2 compared to those obtained on d 0, by 4- and 2.6-fold, respectively. The predominant OLE fate was the esterification pathway, representing >85% of OLE metabolized in both groups. The limited OLE oxidation observed at d 2 may result from the presence of a highly malonyl-CoA-sensitive CPT1A, because the half maximal inhibitory concentration for malonyl-CoA was 162 ± 25 nmol/L. This study highlighted the high esterification capacity for OLE in the newborn pig intestine, which may preserve this major colostrum FA for delivery to other tissues.

Topological orientation of acyl-CoA:diacylglycerol acyltransferase-1 (DGAT1) and identification of a putative active site histidine and the role of the n terminus in dimer/tetramer formation

Acyl CoA:diacylglycerol acyltransferase (DGAT) is an integral membrane protein of the endoplasmic reticulum that catalyzes the synthesis of triacylglycerols. Two DGAT enzymes have been identified (DGAT1 and DGAT2) with unique roles in lipid metabolism. DGAT1 is a multifunctional acyltransferase capable of synthesizing diacylglycerol, retinyl, and wax esters in addition to triacylglycerol. Here, we report the membrane topology for murine DGAT1 using protease protections assays and indirect immunofluorescence in conjunction with selective permeabilization of cellular membranes. Topology models based on prediction algorithms suggested that DGAT1 had eight transmembrane domains. In contrast, our data indicate that DGAT1 has three transmembrane domains with the N terminus oriented toward the cytosol. The C-terminal region of DGAT1, which accounts for ∼50% of the protein, is present in the endoplasmic reticulum lumen and contains a highly conserved histidine residue (His-426) that may be part of the active site. Mutagenesis of His-426 to alanine impaired the ability of DGAT1 to synthesize triacylglycerols as well as retinyl and wax esters in an in vitro acyltransferase assay. Finally, we show that the N-terminal domain of DGAT1 is not required for the catalytic activity of DGAT1 but, instead, may be involved in regulating enzyme activity and dimer/tetramer formation.

The biogenesis of chylomicrons

The absorption of dietary fat is of increasing concern given the rise of obesity not only in the United States but throughout the developed world. This review explores what happens to dietary fat within the enterocyte. Absorbed fatty acids and monoacylglycerols are required to be bound to intracellular proteins and/or to be rapidly converted to triacylglycerols to prevent cellular membrane disruption. The triacylglycerol produced at the level of the endoplasmic reticulum (ER) is either incorporated into prechylomicrons within the ER lumen or shunted to triacylglycerol storage pools. The prechylomicrons exit the ER in a specialized transport vesicle in the rate-limiting step in the intracellular transit of triacylglycerol across the enterocyte. The prechylomicrons are further processed in the Golgi and are transported to the basolateral membrane via a separate vesicular system for exocytosis into the intestinal lamina propria. Fatty acids and monoacylglycerols entering the enterocyte via the basolateral membrane are also incorporated into triacylglycerol, but the basolaterally entering lipid is much more likely to enter the triacylglycerol storage pool than the lipid entering via the apical membrane.

Intestinal absorption of long-chain fatty acids: evidence and uncertainties

Over the two last decades, cloning of proteins responsible for trafficking and metabolic fate of long-chain fatty acids (LCFA) in gut has provided new insights on cellular and molecular mechanisms involved in fat absorption. To this systematic cloning period, functional genomics has succeeded in providing a new set of surprises. Disruption of several genes, thought to play a crucial role in LCFA absorption, did not lead to clear phenotypes. This observation raises the question of the real physiological role of lipid-binding proteins and lipid-metabolizing enzymes expressed in enterocytes. The goal of this review is to analyze present knowledge concerning the main steps of intestinal fat absorption from LCFA uptake to lipoprotein release and to assess their impact on health.

Development and physiological regulation of intestinal lipid absorption. II. Dietary lipid absorption, complex lipid synthesis, and the intracellular packaging and secretion of chylomicrons

Research in dietary fat absorption has developed urgency because of the widely recognized epidemic of obesity in the United States. Despite its clinical importance, many controversies exist over some of the basic aspects of this process from the mechanisms of fatty acid uptake to the control of triacylglycerol export in chylomicrons. Recent advances have included the identification of a number of fatty acid transporters, the discovery of families of acyl-CoA synthetase long chains and acyltransferases, a physiological function for liver-fatty acid binding protein, and the characterization of the prechylomicron transport vesicle transporting chylomicrons from the endoplasmic reticulum to the Golgi.

l-Carnitine increases liver α-tocopherol and lowers liver and plasma triglycerides in aging ovariectomized rats

The objective of this study was to determine whether dietary L-carnitine can influence the status of alpha-tocopherol, retinol and selected lipid parameters in aging ovariectomized rats, an animal model for the menopausal state. Fourteen Fisher-344 female rats 18 months old were acclimated for 4 weeks and ovarectomized. Seven rats per treatment were assigned to either a control group fed ad libitum AIN-93M diet or a carnitine group fed the same diet supplemented with L-carnitine. After an 8-week feeding period, blood and selected tissues were taken for analyses. No differences were noted in food intake, body weight, or organ weights due to L-carnitine. Dietary carnitine significantly increased liver alpha-tocopherol and tended to increase plasma alpha-tocopherol (P<.09). No changes in alpha-tocopherol were observed in other tissues including the brain, lungs and retroperitoneal fat. Retinol levels in plasma and tissues were not affected by supplemental L-carnitine. Significant decreases in liver and plasma triglyceride (TG) levels were noted, suggesting increased utilization of fatty acids. No differences were observed in the fatty acid profile of tissues. The results provide evidence that dietary supplementation of L-carnitine enhances the alpha-tocopherol status and improves the utilization of fat leading to lowering of the liver and plasma levels of TG in aging ovariectomized rats. Whether supplemental L-carnitine may be of benefit to postmenopausal women in lowering plasma TG and improving the antioxidant status remains to be studied.

Synergistic role of specificity proteins and upstream stimulatory factor 1 in transactivation of the mouse carboxylesterase 2/microsomal acylcarnitine hydrolase gene promoter

Mouse carboxylesterase 2 (mCES2), a microsomal acylcarnitine hydrolase, is thought to play some important roles in fatty acid (ester) metabolism, and it is therefore thought that the level of transcription of the mCES2 gene is under tight control. Examination of the tissue expression profiles revealed that mCES2 is expressed in the liver, kidney, small intestine, brain, thymus, lung, adipose tissue and testis. When the mCES2 promoter was cloned and characterized, it was revealed that Sp1 (specificity protein 1) and Sp3 could bind to a GC box, that USF (upstream stimulatory factor) 1 could bind to an E (enhancer) box, and that Sp1 could bind to an NFkappaB (nuclear factor kappaB) element in the mCES2 promoter. Co-transfection assays showed that all of these transcription factors contributed synergistically to transactivation of the mCES2 promoter. Taken together, our results indicate that Sp1, Sp3 and USF1 are indispensable factors for transactivation of the mCES2 gene promoter. To our knowledge, this is the first study in which transcription factors that interact with a CES2 family gene have been identified. The results of the present study have provided some clues for understanding the molecular mechanisms regulating mCES2 gene expression, and should be useful for studies aimed at elucidation of physiological functions of mCES2.

CD36 deficiency impairs intestinal lipid secretion and clearance of chylomicrons from the blood

CD36 mediates the transfer of fatty acids (FAs) across the plasma membranes of muscle and adipose cells, thus playing an important role in regulating peripheral FA metabolism in vivo. In the proximal intestine, CD36 is localized in abundant quantities on the apical surface of epithelial cells, a pattern similar to that of other proteins implicated in the uptake of dietary FAs. To define the role of CD36 in the intestine, we examined FA utilization and lipoprotein secretion by WT and CD36-null mice in response to acute and chronic fat feeding. CD36-null mice given a fat bolus by gavage or fed a high-fat diet accumulated neutral lipid in the proximal intestine, which indicated abnormal lipid processing. Using a model in which mice were equipped with lymph fistulae, we obtained evidence of defective lipoprotein secretion by directly measuring lipid output. The secretion defect appeared to reflect an impaired ability of CD36-null enterocytes to efficiently synthesize triacylglycerols from dietary FAs in the endoplasmic reticulum. In the plasma of intact mice, the reduced intestinal lipid secretion was masked by slow clearance of intestine-derived lipoproteins. The impaired clearance occurred despite normal lipoprotein lipase activity and likely reflected feedback inhibition of the lipase by FAs due to their defective removal from the plasma. We conclude that CD36 is important for both secretion and clearance of intestinal lipoproteins. CD36 deficiency results in hypertriglyceridemia both in the postprandial and fasting states and in humans may constitute a risk factor for diet-induced type 2 diabetes and cardiovascular disease.

Dietary L-carnitine enhances the lymphatic absorption of fat and alpha-tocopherol in ovariectomized rats

This study was conducted to determine whether the feeding of dietary L-carnitine (CN) improves the intestinal absorption of fat and alpha-tocopherol (alphaTOH) in ovariectomized (OX) rats. OX adult rats were weight-matched and assigned to 2 groups fed a modified AIN-93G diet containing alphaTOH-stripped soybean oil without (-CN) or with (+CN) supplemental CN at 150 mg/kg diet. At 5 wk, each rat with a lymph cannula was infused intraduodenally at 3.0 mL/h with a lipid emulsion consisting of 565 micromol triolein labeled with (14)C ((14)C-OA), 3.6 micromol alphaTOH, and 396 micromol sodium taurocholate in 24 mL PBS buffer. Lymph was collected hourly for 8 h and analyzed for lipids. The lymphatic absorption of alphaTOH for 8 h in +CN rats (899 +/- 201 nmol) was higher (P < 0.05) than in -CN rats (587 +/- 92 nmol). The absorption of (14)C-OA in +CN rats (53.5 +/- 4.0% dose/8 h) also was increased (P < 0.05) compared with -CN rats (47.6 +/- 5.0% dose/8 h). Lymph flow did not differ between the groups. When bile was diverted but with infusion of sodium taurocholate, the lymphatic absorption of lipids did not differ. The present study provides evidence that dietary CN enhances the rates and amounts of lymphatic absorption of alphaTOH and fat in OX rats. Our findings suggest that dietary CN may influence the process of lipid packaging and absorption by the enterocyte in OX rats, and may explain in part the increased status of alphaTOH in CN-fed animals.

Etomoxir, a fatty acid oxidation inhibitor, increases food intake and reduces hepatic energy status in rats

Etomoxir, an inhibitor of fatty acid oxidation, increases food intake and reported hunger in humans. Work with animal models suggests that other inhibitors of fatty acid oxidation stimulate feeding behavior by acting on the liver. In the following study, we assessed whether etomoxir would increase food intake in rats and to what degree the effects of etomoxir on feeding were associated with changes in hepatic energy status. The effects of etomoxir on hepatic energy status were assessed by measuring liver ATP, ADP, phosphorylation potential, and glycogen content. Blood glucose, free fatty acids, and ketone bodies were also measured to determine the availability of circulating fuels following etomoxir treatment. Etomoxir and methyl palmoxirate (MP; another inhibitor of fatty acid oxidation) increased food intake. Etomoxir, like MP, also reduced hepatic ATP/ADP ratio and phosphorylation potential. In combination with 2,5-anhydro-D-mannitol (an analogue of fructose that produces an increase in feeding by action on the liver), etomoxir synergistically increased food intake and reduced hepatic ATP/ADP ratio. In summary, etomoxir increased food intake and decreased hepatic energy status in the rat. This suggests that etomoxir stimulates feeding by action on the liver.

Expression of three carnitine palmitoyltransferase-I isoforms in 10 regions of the rat brain during feeding, fasting, and diabetes

Inhibition of carnitine palmitoyltransferase-I (CPT-I) activity in the brain has been shown to decrease food intake in rats. We examined the expression of mRNA encoding all three known CPT-I isoforms (alpha, beta, and gamma in 10 different major regions of the rat brain in normal, chow-fed rats, in fasting rats, and in insulin-dependent diabetic rats. Compared with the effects of fasting and diabetes on CPT-I mRNA in the liver and heart, there was either less effect or no effect depending on the particular brain region examined. These results suggest that the regulation of CPT-I mRNA levels is different in the brain than in other tissues. A surprising result of this study was the discovery of very high, unique expression of CPT-Ibeta (the muscle isoform) in the cerebellum.