Effect of surface and intracellular pH on hepatocellular fatty acid uptake

1996 ◽  
Vol 271 (6) ◽  
pp. G1067-G1073
Author(s):  
C. Elsing ◽  
A. Kassner ◽  
W. Stremmel
Keyword(s):  
Fatty Acids ◽  
Plasma Membrane ◽  
Fatty Acid ◽  
Intracellular Ph ◽  
Outer Surface ◽  
Fatty Acid Uptake ◽  
Proton Gradient ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Acid Transport

Fatty acids enter hepatocytes, at least in part, by a carrier-mediated uptake mechanism. The importance of driving forces for fatty acid uptake is still controversial. To evaluate possible driving mechanisms for fatty acid transport across plasma membranes, we examined the role of transmembrane proton gradients on fatty acid influx in primary cultured rat hepatocytes. After hepatocytes were loaded with SNARF-1 acetoxymethyl ester, changes in intracellular pH (pHi) under different experimental conditions were measured and recorded by confocal laser scanning microscopy. Fatty acid transport was increased by 45% during cellular alkalosis, achieved by adding 20 mM NH4Cl to the medium, and a concomitant paracellular acidification was observed. Fatty acid uptake was decreased by 30% during cellular acidosis after withdrawal of NH4Cl from the medium. Cellular acidosis activates the Na+/H+ antiporter to export excessive protons to the outer cell surface. Inhibition of Na+/H+ antiporter activity by amiloride diminishes pHi recovery and thereby accumulation of protons at the outer surface of the plasma membrane. Under these conditions, fatty acid uptake was further inhibited by 57% of control conditions. This suggests stimulation of fatty acid influx by an inwardly directed proton gradient. The accelerating effect of protons at the outer surface of the plasma membrane was confirmed by studies in which pH of the medium was varied at constant pHi. Significantly higher fatty acid influx rates were observed at low buffer pH. Recorded differences in fatty acid uptake appeared to be independent of changes in membrane potential, because BaCl2 did not influence initial uptake velocity during cellular alkalosis and paracellular acidosis. Moreover, addition of oleate-albumin mixtures to the NH4Cl incubation buffer did not change the observed intracellular alkalinization. In contrast, after cells were acid loaded, addition of oleate-albumin solutions to the recovery buffer increased pHi recovery rates from 0.21 +/- 0.02 to 0.36 +/- 0.05 pH units/min (P < 0.05), indicating that fatty acids further stimulate Na+/H+ antiporter activity during pHi recovery from an acid load. It is concluded that carrier-mediated uptake of fatty acids in hepatocytes follows an inwardly directed transmembrane proton gradient and is stimulated by the presence of H+ at the outer surface of the plasma membrane.

Fatty acid transport and metabolism in HepG2 cells

2006 ◽  
Vol 290 (3) ◽  
pp. G528-G534 ◽  
Author(s):  
Wen Guo ◽  
Nasi Huang ◽  
Jun Cai ◽  
Weisheng Xie ◽  
James A. Hamilton
Keyword(s):  
Fatty Acids ◽  
Plasma Membrane ◽  
Fatty Acid ◽  
Hepg2 Cells ◽  
Fatty Acid Uptake ◽  
Metabolic Inhibitors ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Triacsin C ◽  
Membrane Bound

The mechanism(s) of fatty acid uptake by liver cells is not fully understood. We applied new approaches to address long-standing controversies of fatty acid uptake and to distinguish diffusion and protein-based mechanisms. Using HepG2 cells containing an entrapped pH-sensing fluorescence dye, we showed that the addition of oleate (unbound or bound to cyclodextrin) to the external buffer caused a rapid (seconds) and dose-dependent decrease in intracellular pH (pHin), indicating diffusion of fatty acids across the plasma membrane. pHin returned to its initial value with a time course (in min) that paralleled the metabolism of radiolabeled oleate. Preincubation of cells with the inhibitors phloretin or triacsin C had no effect on the rapid pHin drop after the addition of oleate but greatly suppressed pHin recovery. Using radiolabeled oleate, we showed that its esterification was almost completely inhibited by phloretin or triacsin C, supporting the correlation between pHin recovery and metabolism. We then used a dual-fluorescence assay to study the interaction between HepG2 cells and cis-parinaric acid (PA), a naturally fluorescent but slowly metabolized fatty acid. The fluorescence of PA increased rapidly upon its addition to cells, indicating rapid binding to the plasma membrane; pHin decreased rapidly and simultaneously but did not recover within 5 min. Phloretin had no effect on the PA-mediated pHin drop or its slow recovery but decreased the absolute fluorescence of membrane-bound PA. Our results show that natural fatty acids rapidly bind to, and diffuse through, the plasma membrane without hindrance by metabolic inhibitors or by an inhibitor of putative membrane-bound fatty acid transporters.

FATP4 contributes as an enzyme to the basal and insulin-mediated fatty acid uptake of C2C12 muscle cells

2011 ◽  
Vol 301 (5) ◽  
pp. E785-E796 ◽  
Author(s):  
Margarete Digel ◽  
Simone Staffer ◽  
Friedrich Ehehalt ◽  
Wolfgang Stremmel ◽  
Robert Ehehalt ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Fatty Acid ◽  
Enzymatic Activity ◽  
Muscle Cells ◽  
Fatty Acid Uptake ◽  
Fatty Acid Transport ◽  
Synthetase Activity ◽  
Acid Uptake ◽  
Acid Transport ◽  
Short Term

The function of membrane proteins in long-chain fatty acid transport is controversial. The acyl-CoA synthetase fatty acid transport protein-4 (FATP4) has been suggested to facilitate fatty acid uptake indirectly by its enzymatic activity, or directly by transport across the plasma membrane. Here, we investigated the function of FATP4 in basal and insulin mediated fatty acid uptake in C2C12 muscle cells, a model system relevant for fatty acid metabolism. Stable expression of exogenous FATP4 resulted in a twofold higher fatty acyl-CoA synthetase activity, and cellular uptake of oleate was enhanced similarly. Kinetic analysis demonstrated that FATP4 allowed the cells to reach apparent saturation of fatty acid uptake at a twofold higher level compared with control. Short-term treatment with insulin increased fatty acid uptake in line with previous reports. Surprisingly, insulin increased the acyl-CoA synthetase activity of C2C12 cells within minutes. This effect was sensitive to inhibition of insulin signaling by wortmannin. Affinity purified FATP4 prepared from insulin-treated cells showed an enhanced enzyme activity, suggesting it constitutes a novel target of short-term metabolic regulation by insulin. This offers a new mechanistic explanation for the concomitantly observed enhanced fatty acid uptake. FATP4 was colocalized to the endoplasmic reticulum by double immunofluorescence and subcellular fractionation, clearly distinct from the plasma membrane. Importantly, neither differentiation into myotubes nor insulin treatment changed the localization of FATP4. We conclude that FATP4 functions by its intrinsic enzymatic activity. This is in line with the concept that intracellular metabolism plays a significant role in cellular fatty acid uptake.

A STUDY ON CLASSIFICATION OF INHIBITORS OF FATTY ACID TRANSPORT PROTEIN-2 IN CELL

2021 ◽  
pp. 58-60
Author(s):  
Anand Shanker Singh ◽  
G . Radhika ◽  
R . Praveen Kumar ◽  
Debarshi Jana
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
High Throughput ◽  
Hepg2 Cells ◽  
High Throughput Screening ◽  
Atypical Antipsychotics ◽  
Fatty Acid Uptake ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Acid Transport

Inhibition of uptake of fatty acids in non-adipose tissues seems an attractive mechanism for treatment of lipotoxicity, dyslipidemia and other elements related to metabolic syndrome and obesity. Fatty acid transport proteins (FATPs) are bifunctional proteins involved in the uptake and activation of fatty acids by esterication with coenzyme A. To date, only inhibitors specic to FATP1 and FATP4 have been identied. Here we characterize a FATP2-specic fatty acid uptake inhibitor, CB5. Identied in a high throughput screening in yeast transformed with humanFATP2, CB5 is effective in inhibiting the uptake of fatty acid at low micro-molar ranges in cell lines that are models for intestines, liver, muscle, pancreas and adipose tissue with varying potencies. Inhibition was also specic for long and very-long chain fatty acids and not for medium chain fatty acids, which are transported by diffusion. Finally, CB5 was effective in protecting the cell lines that are models for liver and pancreas and primary liver cells from lipotoxic effects of saturated fatty acid, palmitic acid. High throughput screening also identied clozapine and chlorpromazine, atypical antipsychotics drugs, as inhibitors of FATP2-mediated fatty acid uptake in yeast system. However, atypical antipsychotics were ineffective in inhibiting the uptake of FAanalog C1-BODIPY-C12 in HepG2 cells. They were also ineffective in protecting HepG2 cells from the lipotoxic effects generated by saturated fatty acid compared to CB5 that exhibited protection to the cells, demonstrating that they are not effective inhibitors of fatty acid transport compared with CB5.

scholarly journals Lipid Accumulation and Chronic Kidney Disease

Nutrients ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 722 ◽  
Author(s):  
Zhibo Gai ◽  
Tianqi Wang ◽  
Michele Visentin ◽  
Gerd Kullak-Ublick ◽  
Xianjun Fu ◽  
...  
Keyword(s):  
Chronic Kidney Disease ◽  
Fatty Acids ◽  
Fatty Acid ◽  
Kidney Disease ◽  
Lipid Accumulation ◽  
Scavenger Receptor ◽  
Fatty Acid Uptake ◽  
Lipid Lowering ◽  
Fatty Acid Transport ◽  
Acid Uptake

Obesity and hyperlipidemia are the most prevalent independent risk factors of chronic kidney disease (CKD), suggesting that lipid accumulation in the renal parenchyma is detrimental to renal function. Non-esterified fatty acids (also known as free fatty acids, FFA) are especially harmful to the kidneys. A concerted, increased FFA uptake due to high fat diets, overexpression of fatty acid uptake systems such as the CD36 scavenger receptor and the fatty acid transport proteins, and a reduced β-oxidation rate underlie the intracellular lipid accumulation in non-adipose tissues. FFAs in excess can damage podocytes, proximal tubular epithelial cells and the tubulointerstitial tissue through various mechanisms, in particular by boosting the production of reactive oxygen species (ROS) and lipid peroxidation, promoting mitochondrial damage and tissue inflammation, which result in glomerular and tubular lesions. Not all lipids are bad for the kidneys: polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) seem to help lag the progression of chronic kidney disease (CKD). Lifestyle interventions, especially dietary adjustments, and lipid-lowering drugs can contribute to improve the clinical outcome of patients with CKD.

Insulin induces the translocation of the fatty acid transporter FAT/CD36 to the plasma membrane

2002 ◽  
Vol 282 (2) ◽  
pp. E491-E495 ◽  
Author(s):  
Joost J. F. P. Luiken ◽  
David J. Dyck ◽  
Xiao-Xia Han ◽  
Narendra N. Tandon ◽  
Yoga Arumugam ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Fatty Acid ◽  
Muscle Contraction ◽  
Kinase Inhibitor ◽  
Fatty Acid Uptake ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Hindlimb Muscles ◽  
Fatty Acid Transporter ◽  
Acid Transporter

It is well known that muscle contraction and insulin can independently translocate GLUT-4 from an intracellular depot to the plasma membrane. Recently, we have shown that the fatty acid transporter FAT/CD36 is translocated from an intracellular depot to the plasma membrane by muscle contraction (<30 min) (Bonen et al. J Biol Chem 275: 14501–14508, 2000). In the present study, we examined whether insulin also induced the translocation of FAT/CD36 in rat skeletal muscle. In studies in perfused rat hindlimb muscles, we observed that insulin increased fatty acid uptake by +51%. Insulin increased the rate of palmitate incorporation into triacylglycerols, diacylglycerols, and phospholipids ( P < 0.05) while reducing muscle palmitate oxidation ( P < 0.05). Perfusing rat hindlimb muscles with insulin increased plasma membrane FAT/CD36 by +48% ( P < 0.05), whereas concomitantly the intracellular FAT/CD36 depot was reduced by 68% ( P < 0.05). These insulin-induced effects on FAT/CD36 translocation were inhibited by the phosphatidylinositol 3-kinase inhibitor LY-294002. Thus these studies have shown for the first time that insulin can induce the translocation of FAT/CD36 from an intracellular depot to the plasma membrane.This reveals a previously unknown level of regulation of fatty acid transport by insulin and may well have important consequences in furthering our understanding of the relation between fatty acid metabolism and insulin resistance.

scholarly journals New insights into long-chain fatty acid uptake by heart muscle: a crucial role for fatty acid translocase/CD36

2002 ◽  
Vol 367 (3) ◽  
pp. 561-570 ◽  
Author(s):  
Joep F.F. BRINKMANN ◽  
Nada A. ABUMRAD ◽  
Azeddine IBRAHIMI ◽  
Ger J. vanderVUSSE ◽  
Jan F.C. GLATZ
Keyword(s):  
Plasma Membrane ◽  
Fatty Acid ◽  
Heart Muscle ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Membrane Fatty Acid ◽  
Acid Transport ◽  
Fatty Acid Binding ◽  
Fatty Acid Translocase ◽  
Long Chain

Long-chain fatty acids are an important source of energy for several cell types, in particular for the heart muscle cell. Three different proteins, fatty acid translocase (FAT)/CD36, fatty acid transport protein and plasma membrane fatty acid binding protein, have been identified as possible membrane fatty acid transporters. Much information has been accumulated recently about the fatty acid transporting function of FAT/CD36. Several experimental models to study the influence of altered FAT/CD36 expression on fatty acid homoeostasis have been identified or developed, and underscore the importance of FAT/CD36 for adequate fatty acid transport. These models include the FAT/CD36 null mouse, the spontaneously hypertensive rat and FAT/CD36-deficient humans. The fatty acid transporting role of FAT/CD36 is further demonstrated in mice overexpressing muscle-specific FAT/CD36, and in transgenic mice generated using a genetic-rescue approach. In addition, a wealth of information has been gathered about the mechanisms that regulate FAT/CD36 gene expression and the presence of functional FAT/CD36 on the plasma membrane. Available data also indicate that FAT/CD36 may have an important role in the aetiology of cardiac disease, especially cardiac hypertrophy and diabetic cardiomyopathy. This review discusses our current knowledge of the three candidate fatty acid transporters, the metabolic consequences of alterations in FAT/CD36 levels in different models, and the mechanisms that have been identified for FAT/CD36 regulation.

Protein-mediated fatty acid uptake: regulation by contraction, AMP-activated protein kinase, and endocrine signals

2007 ◽  
Vol 32 (5) ◽  
pp. 865-873 ◽  
Author(s):  
James G. Nickerson ◽  
Iman Momken ◽  
Carley R. Benton ◽  
James Lally ◽  
Graham P. Holloway ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Fatty Acid ◽  
Protein Kinase ◽  
Acid Oxidation ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Acid Transport ◽  
Fatty Acid Binding ◽  
Mitochondrial Fatty Acid ◽  
Amp Activated Protein Kinase

Fatty acid transport into heart and skeletal muscle occurs largely through a highly regulated protein-mediated mechanism involving a number of fatty acid transporters. Chronically altered muscle activity (chronic muscle stimulation, denervation) alters fatty acid transport by altering the expression of fatty acid transporters and (or) their subcellular location. Chronic exposure to leptin downregulates while insulin upregulates fatty acid transport by altering concomitantly the expression of fatty acid transporters. Fatty acid transport can also be regulated within minutes, by muscle contraction, AMP-activated protein kinase activation, leptin, and insulin, through induction of the translocation of fatty acid translocase (FAT)/CD36 from its intracellular depot to the plasma membrane. In insulin-resistant muscle, a permanent relocation of FAT/CD36 to the sarcolemma appears to account for the excess accretion of intracellular lipids that interfere with insulin signaling. Recent work has also shown that FAT/ CD36, but not plasma membrane associated fatty acid binding protein, is involved, along with carnitine palmitoyltransferase, in regulating mitochondrial fatty acid oxidation. Finally, studies in FAT/CD36 null mice indicate that this transporter has a key role in regulating fatty acid metabolism in muscle.

scholarly journals Endogenous Peroxisome Proliferator-Activated Receptor-γ Augments Fatty Acid Uptake in Oxidative Muscle

Endocrinology ◽  
2008 ◽  
Vol 149 (11) ◽  
pp. 5374-5383 ◽  
Author(s):  
Andrew W. Norris ◽  
Michael F. Hirshman ◽  
Jianrong Yao ◽  
Niels Jessen ◽  
Nicolas Musi ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Uptake ◽  
Transport Protein ◽  
Fatty Acid Transport ◽  
Peroxisome Proliferator ◽  
Acid Uptake ◽  
Acid Transport ◽  
Peroxisome Proliferator Activated Receptor ◽  
Nonesterified Fatty Acids ◽  
Fatty Acid Transport Protein

In the setting of insulin resistance, agonists of peroxisome proliferator-activated receptor (PPAR)-γ restore insulin action in muscle and promote lipid redistribution. Mice with muscle-specific knockout of PPARγ (MuPPARγKO) develop excess adiposity, despite reduced food intake and normal glucose disposal in muscle. To understand the relation between muscle PPARγ and lipid accumulation, we studied the fuel energetics of MuPPARγKO mice. Compared with controls, MuPPARγKO mice exhibited significantly increased ambulatory activity, muscle mitochondrial uncoupling, and respiratory quotient. Fitting with this latter finding, MuPPARγKO animals compared with control siblings exhibited a 25% reduction in the uptake of the fatty acid tracer 2-bromo-palmitate (P &lt; 0.05) and a 13% increase in serum nonesterified fatty acids (P = 0.05). These abnormalities were associated with no change in AMP kinase (AMPK) phosphorylation, AMPK activity, or phosphorylation of acetyl-CoA carboxylase in muscle and occurred despite increased expression of fatty acid transport protein 1. Palmitate oxidation was not significantly altered in MuPPARγKO mice despite the increased expression of several genes promoting lipid oxidation. These data demonstrate that PPARγ, even in the absence of exogenous activators, is required for normal rates of fatty acid uptake in oxidative skeletal muscle via mechanisms independent of AMPK and fatty acid transport protein 1. Thus, when PPARγ activity in muscle is absent or reduced, there will be decreased fatty acid disposal leading to diminished energy utilization and ultimately adiposity.

Common mechanisms of monoacylglycerol and fatty acid uptake by human intestinal Caco-2 cells

2001 ◽  
Vol 281 (4) ◽  
pp. C1106-C1117 ◽  
Author(s):  
Shiu-Ying Ho ◽  
Judith Storch
Keyword(s):  
Plasma Membrane ◽  
Fatty Acid ◽  
Monomer Concentration ◽  
Protein S ◽  
Fatty Acid Uptake ◽  
Fatty Acid Transport ◽  
Acid Uptake ◽  
Fatty Acid Binding ◽  
Bound Lipids ◽  
Kinetics Of

Free fatty acids (FFA) and sn-2-monoacylglycerol ( sn-2-MG), the two hydrolysis products of dietary triacylglycerol, are absorbed from the lumen into polarized enterocytes that line the small intestine. Intensive studies regarding FFA transport across the brush-border membrane of the enterocyte are available; however, little is known about sn-2-MG transport. We therefore studied the kinetics of sn-2-MG transport, compared with those of long-chain FFA (LCFA), by human intestinal Caco-2 cells. To mimic postprandial luminal and plasma environments, we examined the uptake of taurocholate-mixed lipids and albumin-bound lipids at the apical (AP) and basolateral (BL) surfaces of Caco-2 cells, respectively. The results demonstrate that the uptake of sn-2-monoolein at both the AP and BL membranes appears to be a saturable function of the monomer concentration of sn-2-monoolein. Furthermore, trypsin preincubation inhibits sn-2-monoolein uptake at both AP and BL poles of cells. These results suggest that sn-2-monoolein uptake may be a protein-mediated process. Competition studies also support a protein-mediated mechanism and indicate that LCFA and LCMG may compete through the same membrane protein(s) at the AP surface of Caco-2 cells. The plasma membrane fatty acid-binding protein (FABPpm) is known to be expressed in Caco-2, and here we demonstrate that fatty acid transport protein (FATP) is also expressed. These putative plasma membrane LCFA transporters may be involved in the uptake of sn-2-monoolein into Caco-2 cells.

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