Expression and Function of ABC Proteins in Fish Intestine

Abstract

In fish, the intestine is fundamental for digestion, nutrient absorption, and other functions like osmoregulation, acid-base balance, and excretion of some metabolic products. These functions require a large exchange surface area, which, in turn, favors the absorption of natural and anthropogenic foreign substances (xenobiotics) either dissolved in water or contained in the food. According to their chemical nature, nutrients, ions, and water may cross the intestine epithelium cells’ apical and basolateral membranes by passive diffusion or through a wide array of transport proteins and also through endocytosis and exocytosis. In the same way, xenobiotics can cross this barrier by passive diffusion or taking advantage of proteins that transport physiological substrates. The entry of toxic substances is counterbalanced by an active efflux transport mediated by diverse membrane proteins, including the ATP binding cassette (ABC) proteins. Recent advances in structure, molecular properties, and functional studies have shed light on the importance of these proteins in cellular and organismal homeostasis. There is abundant literature on mammalian ABC proteins, while the studies on ABC functions in fish have mainly focused on the liver and, to a minor degree, on the kidney and other organs. Despite their critical importance in normal physiology and as a barrier to prevent xenobiotics incorporation, fish intestine’s ABC transporters have received much less attention. All the ABC subfamilies are present in the fish intestine, although their functionality is still scarcely studied. For example, there are few studies of ABC-mediated transport made with polarized intestinal preparations. Thus, only a few works discriminate apical from basolateral transport activity. We briefly describe the main functions of each ABC subfamily reported for mammals and other fish organs to help understand their roles in the fish intestine. Our study considers immunohistochemical, histological, biochemical, molecular, physiological, and toxicological aspects of fish intestinal ABC proteins. We focus on the most extensively studied fish ABC proteins (subfamilies ABCB, ABCC, and ABCG), considering their apical or basolateral location and distribution along the intestine. We also discuss the implication of fish intestinal ABC proteins in the transport of physiological substrates and aquatic pollutants, such as pesticides, cyanotoxins, metals, hydrocarbons, and pharmaceutical products.

Physiological Benefits of Dietary Lysophospholipid Supplementation in a Marine Fish Model: Deep Analyses of Modes of Action

“…Therefore, we demonstrate here for the first time a direct link between dietary LPLs and improved liver lipid metabolism. For instance, some of the proteins upregulated by dietary LPLs are relevant metabolic enzymes: long-chain fatty acid—CoA ligase 1 (ACSL1), which activates long-chain fatty acids for both the degradation via beta-oxidation and synthesis of cellular lipids [ 45 ]; cytochrome P450 1A1 (CYP1A1), which is involved in the oxidation of a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics [ 46 ]; fatty acid amide hydrolase 2 (FAAH2), which degrades bioactive fatty acid amides [ 47 ]; acyl-CoA desaturase (SCD), which plays an important role in regulating the expression of genes that are involved in regulating mitochondrial fatty acid oxidation [ 48 ]; ATP-binding cassette sub-family D member 3 (ABCD3), which is a probable transporter involved in the transport of branched-chain fatty acids and C27 bile acids into the peroxisome [ 49 ], the latter function being a crucial step in bile acid biosynthesis; and fatty-acid-binding protein (FABP2), which plays a role in the intracellular transport of long-chain fatty acids and their acyl-CoA esters [ 50 ]. FABP2 is probably involved in triglyceride-rich lipoprotein synthesis, favoring lipid release from the liver.…”

Impact of Pesticide Residues on the Gut-Microbiota–Blood–Brain Barrier Axis: A Narrative Review

“…Despite the apical distribution on enterocytes, little is known regarding how ABC transporters interact with the GM. Recent studies reported that their expression is influenced by gut microbes (pathogenic or otherwise) ( Figure 2 ) [ 74 ].…”

Factors Determining the Susceptibility of Fish to Effects of Human Pharmaceuticals

“…Marine teleost fish have a number of physiological features that may render them more susceptible to the uptake of APIs from the GIT than FW fish (Figure b). First of all, being hypo-osmotic to their environment, they consume large volumes of seawater for osmoregulatory purposes. , Second, cortisol stimulates cellular apoptosis in the GIT of fish acclimating to saltwater (SW), thereby making the epithelium more permeable than in FW fish . Substantial amounts of bicarbonate ions are also secreted into the intestines of marine fish, precipitating divalent cations such as calcium and thereby further promoting the absorption of water .…”