FABP1

Official Full Name

fatty acid binding protein 1

Organism

Homo sapiens

GeneID

2168

Background

This gene encodes the fatty acid binding protein found in liver. Fatty acid binding proteins are a family of small, highly conserved, cytoplasmic proteins that bind long-chain fatty acids and other hydrophobic ligands. This protein and FABP6 (the ileal fatty acid binding protein) are also able to bind bile acids. It is thought that FABPs roles include fatty acid uptake, transport, and metabolism. [provided by RefSeq, Mar 2011]

Synonyms

FABPL; L-FABP;

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Detailed Information

The role of FABP1 in tetrahydrocannabinol (THC) biotransformation and metabolism

Brain-expressed fatty acid-binding proteins (FABPs) can function as intracellular delivers for THC and cannabidiol (CBD). However, mammals express ten unique FABP subtypes in different tissues, and none of the FABP isoforms that are found in the brain are also present in liver. Two members of the FABPs are found in hepatic cells; liver-type FABP (FABP1) and intestinal-type FABP (FABP2). FABP1 is more likely to facilitate cytoplasmic THC delivery because of a wide range of structurally diverse lipophilic ligands, including synthetic cannabinoids and endocannabinoids. FABP2 is present at only trace levels in liver and could play a subordinate role in facilitating phytocannabinoid transport. Recently mouse FABP1 was found to interact with phytocannabinoids with high affinities in vitro. Furthermore, FABP1 plays an important role in THC induced hepatocyte accumulation of endocannabinoids, likely indicating competition for FABP1-mediated cellular uptake. FABP1 plays a major role in governing THC metabolism and biotransformation via facilitating its cytoplasmic transport to hepatic CYP450 enzymes (see Fig. 1 for schematic).

Figure 1. Schematic of FABP1-mediated transport of THC for subsequent metabolism by intracellular CYP450 enzymes. (Elmes et al. 2019)

Human and murine FABP1 enhance long chain fatty acids (LCFA) uptake

While there have been no researches of absolute loss of FABP1 in humans, the effect of human and murine FABP1 expression has been examined in a great diversity of tumor cell lines including cloned human HepG2 hepatocarcinoma cells, transfected 'Chang liver' cells overexpressing human FABP1, and transfected L-cell fibroblasts overexpressing FABP1. Rat FABP1 overexpression in cultured mouse L-cell fibroblasts stimulates fatty acid absorption and delivering. Similarly, the expression of human FABP1 in human HepG2 cells relevant directly with uptake of radiolabeled monounsaturated LCFA. Overexpression of human FABP1 in 'Chang liver' cells also irritates absorption of LCFA. On the contrary, the effect of absolute loss of FABP1 has been researched widely in mouse FABP1 gene ablated models. FABP1 gene ablation estrains uptake of multitudinous fluorescent saturated fatty acids (NBD-stearic acid, C18:0; BODIPY-C16) and/or branched-chain saturated (phytanic acid), radiolabeled saturated fatty acids (C18:0) and monounsaturated fatty acids (C18:1) in vivo and in cultured primary mouse hepatic cells. Concomitantly, FABP1 ablation reduced liver cytoplasmic LCFA binding capacity >80% in vivo and decreased cytoplasmic transport/diffusion 2-fold. LCFA are membrane-bound, and cytoplasm is 10-fold more sticky than aqueous because of organelles, cytoskeleton and proteins. FABP1 overcomes these barriers by releasing membrane-bound LCFA into the cytoplasm and decreasing 'tortuosity' of diffusional paths. It should be noted that FABP1 gene ablation was not compensated for by up-regulation of other liver cytosol LCFA binding proteins (FABP2, SCP-2, FABP7, FABP3, CRABP2, FABP5, CRABP1, FABP4) or membrane LCFA transport proteins.

FABP1 may be a biomarker to detect for kidney dysfunction

Fatty acid-binding protein 1 (FABP1) is a 14 kDa small molecule, which is expressed in the proximal tubules of the human kidney and participates in fatty acid metabolism. The circulated FABP1 is filtered by the glomeruli and then reabsorbed in the proximal renal tubules, which indicates the increase of its expression in the urine when proximal tubule cell is injury. Numerous animal studies about kidney disease have suggested a higher level of the human FABP1 gene in the kidneys, and that stress can induce upregulation in the urinary excretion of human FABP1, such as tubular ischemia, urinary protein overload, hyperglycemia, tubular stretch, toxins and hypertension. In addition, a clinical study showed relationships between the urinary excretion of FABP1 and the seriousness of tubulointerstitial injury and rate of chronic kidney disease (CKD) progression in patients with non-diabetic CKD. These researches suggest that FABP1 in urine may be a biomarker to detect for kidney dysfunction and identify patients who are vulnerable to experience deterioration in renal function in the future.

References:

Tsai, I. T., Wu, C. C., Hung, W. C., Lee, T. L., Hsuan, C. F., Wei, C. T., Lu, Y. C., Yu, T. H., Chung, F. M., Lee, Y. J., & Wang, C. P. (2020). FABP1 and FABP2 as markers of diabetic nephropathy. International journal of medical sciences, 17(15), 2338–2345.
Elmes, M. W., Prentis, L. E., McGoldrick, L. L., Giuliano, C. J., Sweeney, J. M., Joseph, O. M., Che, J., Carbonetti, G. S., Studholme, K., Deutsch, D. G., Rizzo, R. C., Glynn, S. E., & Kaczocha, M. (2019). FABP1 controls hepatic transport and biotransformation of Δ9-THC. Scientific reports, 9(1), 7588.
Schroeder, F., McIntosh, A. L., Martin, G. G., Huang, H., Landrock, D., Chung, S., Landrock, K. K., Dangott, L. J., Li, S., Kaczocha, M., Murphy, E. J., Atshaves, B. P., & Kier, A. B. (2016). Fatty Acid Binding Protein-1 (FABP1) and the Human FABP1 T94A Variant: Roles in the Endocannabinoid System and Dyslipidemias. Lipids, 51(6), 655–676.

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