Lipid binding activities of the P2 protein in peripheral nerve myelin

Evaluation of AlphaFold3 for the fatty acids docking to human fatty acid-binding proteins

Human fatty acid-binding proteins (FABPs) are involved in many aspects of lipid metabolism, such as the uptake, transport, and storage of lipophilic molecules, as well as cellular functions. Understanding how FABPs recognize fatty acids (FAs) is crucial for identifying FABP function and applications, such as in inhibitor design or biomarker development. The recently developed AlphaFold3 (AF3) demonstrates significantly higher accuracy than other prediction tools, particularly in predicting protein-ligand interactions with state-of-the-art docking tools. Studies on whether AF3 can be used to identify the FAs of FABP are lacking. To assess the accuracy of FA docking to FABPs using AF3, models of FA docked into FABP generated using AF3 were compared with experimentally determined FA-bound FABP structures. FA ligands in AF3 structures docked reliably into the FA-binding pocket of FABPs; however, the detailed binding configuration of most FA ligands docked into FABPs and the interaction between FA and FABP determined using AF3 and experimentally differed. These results will aid in understanding FA docking to FABPs and other FA-binding proteins using AF3.

Intestinal fatty acid binding protein: A rising therapeutic target in lipid metabolism

Fatty acid binding proteins (FABPs) are key proteins in lipid transport, and the isoforms are segregated according to their tissue origins. Several isoforms, such as adipose-FABP and epidermal-FABP, have been shown to participate in multiple pathologic processes due to their ubiquitous expression. Intestinal fatty acid binding protein, also termed FABP2 or I-FABP, is specifically expressed in the small intestine. FABP2 can traffic lipids from the intestinal lumen to enterocytes and bind superfluous fatty acids to maintain a steady pool of fatty acids in the epithelium. As a lipid chaperone, FABP2 can also carry lipophilic drugs to facilitate targeted transport. When the integrity of the intestinal epithelium is disrupted, FABP2 is released into the circulation. Thus, it can potentially serve as a clinical biomarker. In this review, we discuss the pivotal role of FABP2 in intestinal lipid metabolism. We also summarize the molecular interactions that have been reported to date, highlighting the clinical prospects of FABP2 research.

Myelin Fat Facts: An Overview of Lipids and Fatty Acid Metabolism

Myelin is critical for the proper function of the nervous system and one of the most complex cell–cell interactions of the body. Myelination allows for the rapid conduction of action potentials along axonal fibers and provides physical and trophic support to neurons. Myelin contains a high content of lipids, and the formation of the myelin sheath requires high levels of fatty acid and lipid synthesis, together with uptake of extracellular fatty acids. Recent studies have further advanced our understanding of the metabolism and functions of myelin fatty acids and lipids. In this review, we present an overview of the basic biology of myelin lipids and recent insights on the regulation of fatty acid metabolism and functions in myelinating cells. In addition, this review may serve to provide a foundation for future research characterizing the role of fatty acids and lipids in myelin biology and metabolic disorders affecting the central and peripheral nervous system.

Enhanced axonal neuregulin-1 type-III signaling ameliorates neurophysiology and hypomyelination in a Charcot-Marie-Tooth type 1B mouse model

Charcot-Marie-Tooth (CMT) neuropathies are a group of genetic disorders that affect the peripheral nervous system with heterogeneous pathogenesis and no available treatment. Axonal neuregulin 1 type III (Nrg1TIII) drives peripheral nerve myelination by activating downstream signaling pathways such as PI3K/Akt and MAPK/Erk that converge on master transcriptional regulators of myelin genes, such as Krox20. We reasoned that modulating Nrg1TIII activity may constitute a general therapeutic strategy to treat CMTs that are characterized by reduced levels of myelination. Here we show that genetic overexpression of Nrg1TIII ameliorates neurophysiological and morphological parameters in a mouse model of demyelinating CMT1B, without exacerbating the toxic gain-of-function that underlies the neuropathy. Intriguingly, the mechanism appears not to be related to Krox20 or myelin gene upregulation, but rather to a beneficial rebalancing in the stoichiometry of myelin lipids and proteins. Finally, we provide proof of principle that stimulating Nrg1TIII signaling, by pharmacological suppression of the Nrg1TIII inhibitor tumor necrosis factor-alpha-converting enzyme (TACE/ADAM17), also ameliorates the neuropathy. Thus, modulation of Nrg1TIII by TACE/ADAM17 inhibition may represent a general treatment for hypomyelinating neuropathies.

Peripheral Demyelinating Diseases: From Biology to Translational Medicine

Demyelinating diseases represent a spectrum of disorders that impose significant burden on global economy and society. Generally, the prognosis of these diseases is poor and there is no available cure. In recent decades, research has shed some light on the biology and physiology of Schwann cells and its neuroprotective effects in the peripheral nervous system (PNS). Insults to the PNS by various infectious agents, genetic predisposition and immune-related mechanisms jeopardize Schwann cell functions and cause demyelination. To date, there are no effective and reliable biomarkers for PNS-related diseases. Here, we aim to review the following: pathogenesis of various types of peripheral demyelinating diseases such as Guillain-Barre syndrome, Chronic Inflammatory Demyelinating Polyradiculoneuropathy, Anti-Myelin Associated Glycoprotein Neuropathy, POEMS syndrome, and Charcot-Marie-Tooth disease; emerging novel biomarkers for peripheral demyelinating diseases, and Schwann cell associated markers for demyelination.

A role of peripheral myelin protein 2 in lipid homeostasis of myelinating Schwann cells

Peripheral myelin protein 2 (Pmp2, P2 or Fabp8), a member of the fatty acid binding protein family, was originally described together with myelin basic protein (Mbp or P1) and myelin protein zero (Mpz or P0) as one of the most abundant myelin proteins in the peripheral nervous system (PNS). Although Pmp2 is predominantly expressed in myelinated Schwann cells, its role in glia is currently unknown. To study its function in PNS biology, we have generated a complete Pmp2 knockout mouse (Pmp2(-/-) ). Comprehensive characterization of Pmp2(-/-) mice revealed a temporary reduction in their motor nerve conduction velocity (MNCV). While this change was not accompanied by any defects in general myelin structure, we detected transitory alterations in the myelin lipid profile of Pmp2(-/-) mice. It was previously proposed that Pmp2 and Mbp have comparable functions in the PNS suggesting that the presence of Mbp can partially mask the Pmp2(-/-) phenotype. Indeed, we found that Mbp lacking Shi(-/-) mice, similar to Pmp2(-/-) animals, have preserved myelin structure and reduced MNCV, but this phenotype was not aggravated in Pmp2(-/-) /Shi(-/-) mutants indicating that Pmp2 and Mbp do not substitute each other's functions in the PNS. These data, together with our observation that Pmp2 binds and transports fatty acids to membranes, uncover a role for Pmp2 in lipid homeostasis of myelinating Schwann cells.

Regional differences in myelination of chick vestibulocochlear ganglion cells

In vertebrates, vestibular and cochlear ganglion (VG and CG, respectively) cells are bipolar neurons with myelinated axons and perikarya. The time course of the myelination of the VG and CG cells during development of chick embryos was investigated. Chick VG and CG from embryonic day at 7-20 (E7-20) were prepared for a transmission electron microscopy, myelin basic protein immunohistochemistry, and real-time quantitative RT-PCR. In the VG cells, myelination was first observed on the peripheral axons of the ampullar nerves at E10, on the utricular and saccular nerves at E12, and on the lagenar and neglecta nerves at E13. In the VG central axons, myelination was first seen on the ampullar nerves at E11, on the utricular and saccular nerves at E13, and on the lagenar nerves at E13. In the CG cells, the myelination was first observed on the peripheral and central axons at E14. In both VG and CG, myelination was observed on the perikarya at E17. These results suggest that the onset of the axonal myelination on the VG cells occurred earlier than that on the CG cells, whereas the perikaryal myelination occurred at about the same time on the both types of ganglion cells. Moreover, the myelination on the ampullar nerves occurred earlier than that on the utricular and saccular nerves. The myelination on the peripheral axons occurred earlier than that on the central axons of the VG cells, whereas that on the central and peripheral axons of the CG cells occurred at about the same time. The regional differences in myelination in relation to the onset of functional activities in the VG and CG cells are discussed.

Biology of Schwann cells

The fundamental roles of Schwann cells during peripheral nerve formation and regeneration have been recognized for more than 100 years, but the cellular and molecular mechanisms that integrate Schwann cell and axonal functions continue to be elucidated. Derived from the embryonic neural crest, Schwann cells differentiate into myelinating cells or bundle multiple unmyelinated axons into Remak fibers. Axons dictate which differentiation path Schwann cells follow, and recent studies have established that axonal neuregulin1 signaling via ErbB2/B3 receptors on Schwann cells is essential for Schwann cell myelination. Extracellular matrix production and interactions mediated by specific integrin and dystroglycan complexes are also critical requisites for Schwann cell-axon interactions. Myelination entails expansion and specialization of the Schwann cell plasma membrane over millimeter distances. Many of the myelin-specific proteins have been identified, and transgenic manipulation of myelin genes have provided novel insights into myelin protein function, including maintenance of axonal integrity and survival. Cellular events that facilitate myelination, including microtubule-based protein and mRNA targeting, and actin based locomotion, have also begun to be understood. Arguably, the most remarkable facet of Schwann cell biology, however, is their vigorous response to axonal damage. Degradation of myelin, dedifferentiation, division, production of axonotrophic factors, and remyelination all underpin the substantial regenerative capacity of the Schwann cells and peripheral nerves. Many of these properties are not shared by CNS fibers, which are myelinated by oligodendrocytes. Dissecting the molecular mechanisms responsible for the complex biology of Schwann cells continues to have practical benefits in identifying novel therapeutic targets not only for Schwann cell-specific diseases but other disorders in which axons degenerate.

High-resolution structural model of porcine P2 myelin membrane protein with associated fatty acid ligand: fact or artifact?

Myelin membrane is a biological complex of glial cells origin; it is composed of 25% (w/w) proteins and 75% lipids, and more than 300 proteins are associated with central nervous system myelin (for peripheral nervous system myelin, such data are lacking). Myelin plays an important role in maintaining propagation of nerve signals. To uncover the nature of propagation phenomena, it is essential to study biochemistry of myelin proteins and lipids, myelin composition, and myelin structure. Nearly all myelin proteins are like antigens, causing clinically well-defined devastating diseases; multiple sclerosis and Guillain-Barré syndrome are two of them. In this article, a high-resolution study (1.8 Å) of porcine myelin P2 protein is presented. Myelin was purified from porcine intradural spinal roots, which were stored at -80°C for 10 years before myelin and P2 protein were purified (spinal roots were a gift of Prof. Kunio Kitamura, Saitama Medical School). The three-dimensional structural analysis uncovered embedded 18-carbons-long fatty acid. Some speculative interpretation is presented, to uncover how this ligand of fatty acid may form cholesterol ester and stabilize the myelin structure or form simple raft microdomain. Protein crystallography indicates that the ligand may be 18-carbons-long fatty acid. This is unlike previous work with mass spectrometry, in which three ligands were determined. In other protein crystallography-based studies of P2 (bovine), an oleic fatty acid was suggested, but, for recombinant (human) protein, palmitic acid was found. There is no fatty acid ligand in equine P2 protein.

Myelin basic protein and myelin protein 2 act synergistically to cause stacking of lipid bilayers

Saltatory conduction of nerve impulses along axonal membranes depends on the presence of a multilayered membrane, myelin, that wraps around the axon. Myelin basic protein (MBP) and myelin protein 2 (P2) are intimately involved in the generation of the myelin sheath. They are also implicated in a number of neurological diseases, including autoimmune diseases of both the central and peripheral nervous systems. Here, we have used atomic force microsopy (AFM) to study the effects of MBP and P2 on lipid bilayers. MBP in association with a mica substrate appeared unstructured, and tended to coat the mica surface in the form of a monolayer. In contrast, P2 appeared as discrete particles, with molecular volumes consistent with the formation of both monomers and dimers. Either MBP or P2, at micromolar concentrations, caused stacking of brain lipid bilayers. This stacking effect was significantly potentiated when both proteins were added together. Bilayers composed of phosphatidylcholine (PC) and phosphatidylserine (PS) were stacked by MBP, provided that cholesterol was also present; in contrast, P2 did not stack PC/PS/cholesterol bilayers. Hence, the bilayer stacking effects of the two proteins have different lipid requirements.

Structural and functional characterization of human peripheral nervous system myelin protein P2

The myelin sheath is a tightly packed multilayered membrane structure insulating selected axons in the central and the peripheral nervous systems. Myelin is a biochemically unique membrane, containing a specific set of proteins. In this study, we expressed and purified recombinant human myelin P2 protein and determined its crystal structure to a resolution of 1.85 A. A fatty acid molecule, modeled as palmitate based on the electron density, was bound inside the barrel-shaped protein. Solution studies using synchrotron radiation indicate that the crystal structure is similar to the structure of the protein in solution. Docking experiments using the high-resolution crystal structure identified cholesterol, one of the most abundant lipids in myelin, as a possible ligand for P2, a hypothesis that was proven by fluorescence spectroscopy. In addition, electrostatic potential surface calculations supported a structural role for P2 inside the myelin membrane. The potential membrane-binding properties of P2 and a peptide derived from its N terminus were studied. Our results provide an enhanced view into the structure and function of the P2 protein from human myelin, which is able to bind both monomeric lipids inside its cavity and membrane surfaces.

Structural properties of proteins specific to the myelin sheath

The myelin sheath is an insulating membrane layer surrounding myelinated axons in vertebrates, which is formed when the plasma membrane of an oligodendrocyte or a Schwann cell wraps itself around the axon. A large fraction of the total protein in this membrane layer is comprised of only a small number of individual proteins, which have certain intriguing structural properties. The myelin proteins are implicated in a number of neurological diseases, including, for example, autoimmune diseases and peripheral neuropathies. In this review, the structural properties of a number of myelin-specific proteins are described.

Crystals of P2 myelin protein in lipid-bound form

The P2 protein of peripheral nervous system myelin induces experimental allergic neuritis in rats, a model of Guillain-Barré syndrome in humans. Previous purification procedures have used acid extraction to obtain the protein in lipid-free form (LF-P2). Here, we have purified the P2 protein in lipid-bound form (LB-P2) by extracting myelin with the detergent CHAPS, followed by Cu(2+)-affinity column chromatography. All myelin lipids were present in the preparation as shown by high-performance thin-layer chromatography and mass spectrometry. The LB-P2 preparation, which differs from LF-P2 in solubility and in the secondary-structure composition, was dialyzed to remove unbound lipids and excess detergent and crystallized using the hanging-drop vapor diffusion technique. Crystals of lipid-bound P2 appeared usually very reproducibly within 2 weeks at pH 5.7 in polyethylene glycol 6000 (PEG6000) at concentrations of 20-30% (w/v), and larger crystals were obtained by additional sitting-drop crystallization. X-ray diffraction showed reflections up to 2.7A. The crystallization conditions (25-30% PEG6000, pH 5.0) and the unit cell dimensions (a = 94.5A, b = 94.5A, c=74.2A, alpha = beta = 90 degrees, gamma = 120 degrees ) of LB-P2 were different from those earlier described for LF-P2 (10% PEG4000, pH 3, and unit cell dimensions a = 91.8A, b = 99.5A, c = 56.5A, alpha = beta = gamma = 90.0 degrees ). It is important that P2 has been crystallized with specifically bound lipids; therefore, solving this new crystal structure will reveal details of this protein's behavior and role in the myelin sheath.

Identification of genes that are downregulated in the absence of the POU domain transcription factor pou3f1 (Oct-6, Tst-1, SCIP) in sciatic nerve

Despite the importance of myelinating Schwann cells in health and disease, little is known about the genetic mechanisms underlying their development. The POU domain transcription factor pou3f1 (Tst-1, SCIP, Oct-6) is required for the normal differentiation of myelinating Schwann cells, but its precise role requires identification of the genes that it regulates. Here we report the isolation of six genes whose expression is reduced in the absence of pou3f1. Only one of these genes, the fatty acid transport protein P2, was known previously to be expressed in Schwann cells. The LIM domain proteins cysteine-rich protein-1 (CRP1) and CRP2 are expressed in sciatic nerve and induced by forskolin in cultured Schwann cells, but only CRP2 requires pou3f1 for normal expression. pou3f1 appears to require the claw paw gene product for activation of at least some of its downstream effector genes. Expression of the novel Schwann cell genes after nerve injury suggests that they are myelin related. One of the genes, tramdorin1, encodes a novel amino acid transport protein that is localized to paranodes and incisures. Our results suggest that pou3f1 functions to activate gene expression in the differentiation of myelinating Schwann cells.

The mammalian fatty acid-binding protein multigene family: molecular and genetic insights into function

Intracellular fatty acid-binding proteins associate with fatty acids and other hydrophobic biomolecules in an internal cavity, providing for solubilization and metabolic trafficking. Analyses of their in vivo function by molecular and genetic techniques reveal specific function(s) that fatty acid-binding proteins perform with respect to fatty acid uptake, oxidation and overall metabolic homeostasis.

New gene targets related to schizophrenia and other psychiatric disorders: enzymes, binding proteins and transport proteins involved in phospholipid and fatty acid metabolism

Phospholipids make up about 60% of the brain's dry weight. In spite of this, phospholipid metabolism has received relatively little attention from those seeking genetic factors involved in psychiatric and neurological disorders. However, there is now increasing evidence from many quarters that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. To date the possible specific proteins and genes involved have been relatively ill-defined. This paper reviews the main pathways of phospholipid metabolism, emphasizing the roles of phospholipases of the A2 and C series in signal transduction processes. It identifies some likely protein candidates for involvement in psychiatric and neurological disorders. It also reviews the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.

Heart-type fatty acid binding protein - involvement in growth inhibition and differentiation

Fatty acid binding proteins (FABPs) comprise a well-established family of cytoplasmic hydrophobic ligand binding proteins and are thought to be involved in lipid metabolism by binding and intracellular transport of long-chain fatty acids. However, from other studies role for FABPs in cell signalling, growth inhibition and differentiation has also been implied. In particular, the heart-type (H-FABP) is abundantly expressed in differentiated mammary gland and its relationship with a very homologous (95%) mammary derived growth inhibitor (MDGI) was disputed. Here we give a survey on the experimental evidence for the existence of such protein with growth inhibitory function. After cloning of the bovine adipocyte-type (A-)FABP cDNA from mammary gland we conclude that the reported MDGI sequence actually represents a mixture of bovine H- and A-FABP and that the MDGI function is exerted by H-FABP. We also monitored the H-FABP level during differentiation of C2C12 muscle cells from myoblasts to multiply nucleated myotubes. H-FABP expression is clearly detected after that of the transcription factor myogenin which is upregulated immediately upon onset of differentiation and after that of the typical muscle enzyme creatine kinase. This argues against an active role of H-FABP in muscle development unlike the situation in the mammary gland.

Congenital hypomyelination neuropathy: decreased expression of the P2 protein in peripheral nerve with normal DNA sequence of the coding region

Congenital hypomyelination neuropathy (Lyon type) is characterized by a non-progressive clinical course and a histopathological formation of atypical onion-bulb. We have studied the immunohistochemical expression of the major peripheral myelin proteins including P0 protein, myelin basic protein (MBP) and P2 protein in three such patients. No significant difference was observed between the patients and the controls, as to the P0 and MBP staining. In contrast, P2 protein antiserum scarcely stained the patients' nerve fibers except for a few scattered adequately myelinated fibers. Assuming the pathogenetic contribution of the extremely decreased P2 protein to the disease, we investigated P2 protein gene by sequencing all coding regions but failed to detect any change in the nucleotide sequence. Further investigation including the analysis of promoter region of P2 protein gene is needed to elucidate the mechanism of congenital hypomyelination neuropathy.

The expression pattern of a novel gene encoding brain-fatty acid binding protein correlates with neuronal and glial cell development

Fatty acid binding proteins (FABPs) are a multigene family of small intracellular proteins that bind hydrophobic ligands. In this report we describe the cloning and expression pattern of a novel member of this gene family that is specifically expressed in the developing and adult nervous system and thus was designated brain (B)-FABP. B-FABP is closely related to heart (H)-FABP with 67% amino acid identity. B-FABP expression was first detected at mouse embryonic day 10 in neuroepithelial cells and its pattern correlates with early neuronal differentiation. Upon further development, B-FABP was confined to radial glial cells and immature astrocytes. B-FABP mRNA and protein were found in glial cells of the peripheral nervous system such as satellite cells of spinal and cranial ganglia and ensheathing cells of the olfactory nerve layer from as early as embryonic day 11 until adulthood. In the adult mouse brain, B-FABP was found in the glia limitans, in radial glial cells of the hippocampal dentate gyrus and Bergman glial cells. These findings suggest a function of B-FABP during neurogenesis or neuronal migration in the developing nervous system. The partially overlapping expression pattern with that of cellular retinoid binding proteins suggests that B-FABP is involved in the metabolism of a so far unknown hydrophobic ligand with potential morphogenic activity during CNS development.

Isolation and sequence determination of cDNA encoding P2 protein of human peripheral myelin

A full length cDNA of P2 protein of peripheral myelin has been isolated from a cDNA library of human fetus spinal cord. The clone is 2150 base pairs (bp) in length and contains a 393 bp open reading frame encoding a polypeptide of 131 residues. The deduced amino acid sequence is highly homologous to P2 protein from other species.

Structure of the mouse myelin P2 protein gene

Myelin P2 protein is a small (14,800 Da) protein found in peripheral and central nervous system myelin. To investigate the regulation of expression of this myelin protein, a mouse genomic library was screened with a rabbit P2 cDNA (pSN2.2-2), and a single positive phage clone containing a 20-kb insert was obtained. This insert contained a single internal SalI restriction site and several EcoRI sites. The EcoRI fragments from this insert were subcloned into Bluescript. The rabbit P2 cDNA (pSN2.2-2) hybridized with a 4-kb EcoRI fragment, and this 4-kb fragment was then sequenced after the creation of nested deletions. The mouse gene contained four exons: exon 1 coded for amino acids 1-24, exon 2 for amino acids 24-81, exon 3 for amino acids 82-115, and exon 4 for amino acids 116-131. The three introns were 1.2 kb, 150 bp, and 1.3 kb in length. Primer extension analysis revealed two transcription start sites at +1 and +47, consistent with the presence of two P2 mRNAs, with the larger transcript appearing more abundant. The amino acid sequences predicted from the mouse DNA indicate that the mouse protein differs from the rabbit protein at 16 different positions, with most of the differences located in exon 3. When the gene structure of fatty acid binding protein (FABP) genes were compared, the P2 gene had the same overall structure as others in the FABP family, suggesting a common ancestral gene for members of this family. The 5'-flanking region contains candidate TATA and CAAT sequences, as well as two AP-1 binding sites that may be important in modulation of the expression of this gene.

Functions of fatty acid binding proteins

Cytosolic fatty acid binding proteins (FABP) belong to a gene family of which eight members have been conclusively identified. These 14-15 kDa proteins are abundantly expressed in a highly tissue-specific manner. Although the functions of the cytosolic FABP are not clearly established, they appear to enhance the transfer of long-chain fatty acids between artificial and native lipid membranes, and also to have a stimulatory effect on a number of enzymes of fatty acid metabolism in vitro. These findings, as well as the tissue expression, ligand binding properties, ontogeny and regulation of these proteins provide a considerable body of indirect evidence supporting a broad role for the FABP in the intracellular transport and metabolism of long-chain fatty acids. The available data also support the existence of structure- and tissue-specific specialization of function among different members of the FABP gene family. Moreover, FABP may also have a possible role in the modulation of cell growth and proliferation, possibly by virtue of their affinity for ligands such as prostaglandins, leukotrienes and fatty acids, which are known to influence cell growth activity. FABP structurally unrelated to the cytosolic gene family have also been identified in the plasma membranes of several tissues (FABPpm). These proteins have not been fully characterized to date, but strong evidence suggest that they function in the transport of long-chain fatty acids across the plasma membrane.

Possible role of rat fatty acid-binding proteins in the intestine as carriers of phenol and phthalate derivatives

Fatty acid-binding proteins of hepatic and intestinal type and gastrotropin-like protein (GTLP) were purified from rat intestinal cytosol by Sephadex G-75 gel filtration and DEAE-cellulose, CM-cellulose, and hydroxylapatite chromatographies. In addition to fatty acids, butylated hydroxytoluene (BHT), phthalate dibutyl, and di(2-ethylhexyl) esters (DBP and DEHP) were identified by gas liquid chromatography and mass spectrometry as endogenous ligands from the extract of either fatty acid-binding protein superfamily. These protein families in the intestine may have an important role as carriers in the initial step of arresting these exogenous pollutants.

Functional studies of newly synthesized benzoic acid derivatives: identification of highly potent retinoid-like activity

Three newly synthesized benzoic acid derivatives (terephthalic acid anilides, chalcone carboxylic acid, and azobenzene carboxylic acid), with a certain structural similarity to retinoic acid, were examined for their retinoid-like bioactivity and their capacity to bind to cellular retinoid binding proteins. Two in vitro systems were used to evaluate their retinoid-like bioactivity: inhibition of adipose conversion of ST 13 murine preadipose cells and growth promotion of murine sarcoma virus (MSV)-transformed 3T3 cells in serum-free culture. All three compounds tested inhibited ST 13 adipose conversion at nanomolar concentrations in a manner similar to classical retinoids such as retinoic acid. The growth-stimulating activity of these compounds on MSV-transformed 3T3 cells was one to two orders of magnitude greater than that of retinoic acid. Simultaneous treatment with these compounds and retinoic acid produced only a barely detectable additive effect, suggesting a common mechanism of action, whereas unrelated mitogens, thrombin, and insulin worked synergistically in combination with retinoic acid. None of the compounds competed with retinol for binding to cellular retinol binding protein. However, two of the three competed with retinoic acid for binding to cellular retinoic acid binding protein. This study provides evidence that the newly synthesized compounds should be included among the retinoids and that their strong biological activity will undoubtedly contribute to the biological and medical application of retinoids.