Sodium butyrate increases glucose transporter expression in LLC-PK1 cells

Dietary sodium acetate and sodium butyrate improve high-carbohydrate diet utilization by regulating gut microbiota, liver lipid metabolism, oxidative stress, and inflammation in largemouth bass (Micropterus salmoides)

BACKGROUND

Adequate level of carbohydrates in aquafeeds help to conserve protein and reduce cost. However, studies have indicated that high-carbohydrate (HC) diet disrupt the homeostasis of the gut-liver axis in largemouth bass, resulting in decreased intestinal acetate and butyrate level.

METHOD

Herein, we had concepted a set of feeding experiment to assess the effects of dietary sodium acetate (SA) and sodium butyrate (SB) on liver health and the intestinal microbiota in largemouth bass fed an HC diet. The experimental design comprised 5 isonitrogenous and isolipidic diets, including LC (9% starch), HC (18% starch), HCSA (18% starch; 2 g/kg SA), HCSB (18% starch; 2 g/kg SB), and HCSASB (18% starch; 1 g/kg SA + 1 g/kg SB). Juvenile largemouth bass with an initial body weight of 7.00 ± 0.20 g were fed on these diets for 56 d.

RESULTS

We found that dietary SA and SB reduced hepatic triglyceride accumulation by activating autophagy (ATG101, LC3B and TFEB), promoting lipolysis (CPT1α, HSL and AMPKα), and inhibiting adipogenesis (FAS, ACCA, SCD1 and PPARγ). In addition, SA and SB decreased oxidative stress in the liver (CAT, GPX1α and SOD1) by activating the Keap1-Nrf2 pathway. Meanwhile, SA and SB alleviated HC-induced inflammation by downregulating the expression of pro-inflammatory factors (IL-1β, COX2 and Hepcidin1) through the NF-κB pathway. Importantly, SA and SB increased the abundance of bacteria that produced acetic acid and butyrate (Clostridium_sensu_stricto_1). Combined with the KEGG analysis, the results showed that SA and SB enriched carbohydrate metabolism and amino acid metabolism pathways, thereby improving the utilization of carbohydrates. Pearson correlation analysis indicated that growth performance was closely related to hepatic lipid deposition, autophagy, antioxidant capacity, inflammation, and intestinal microbial composition.

CONCLUSIONS

In conclusion, dietary SA and SB can reduce hepatic lipid deposition; and alleviate oxidative stress and inflammation in largemouth bass fed on HC diet. These beneficial effects may be due to the altered composition of the gut microbiota caused by SA and SB. The improvement effects of SB were stronger than those associated with SA.

Salivary and Gut Microbiomes Play a Significant Role in in Vitro Oral Bioaccessibility, Biotransformation, and Intestinal Absorption of Arsenic from Food

The release of a toxicant from a food matrix during the gastrointestinal digestion is a crucial determinant of the toxicant's oral bioavailability. We present a modified setup of the human simulator of the gut microbial ecosystem (SHIME), with four sequential gastrointestinal reactors (oral, stomach, small intestine, and colon), including the salivary and colonic microbiomes. Naturally arsenic-containing rice, mussels, and nori seaweed were digested in the presence of microorganisms and in vitro oral bioaccessibility, bioavailability, and metabolism of arsenic species were evaluated following analysis by using HPLC/mass spectrometry. When food matrices were digested with salivary bacteria, the soluble arsenic in the gastric digestion stage increased for mussel and nori samples, but no coincidence impact was found in the small intestinal and colonic digestion stages. However, the simulated small intestinal absorption of arsenic was increased in all food matrices (1.2-2.7 fold higher) following digestion with salivary microorganisms. No significant transformation of the arsenic species occurred except for the arsenosugars present in mussels and nori. In those samples, conversions between the oxo arsenosugars were observed in the small intestinal digestion stage whereupon the thioxo analogs became major metabolites. These results expand our knowledge on the likely metabolism and oral bioavailabiltiy of arsenic during human digestion, and provide valuable information for future risk assessments of dietary arsenic.

Enhanced Uptake of Glycerol by Butyrate Treatment in HCT-15 Human Colon Cancer Cell Line

The HCT-15 human colon cancer cell line has a Na(+)-dependent carrier-mediated transport system for the uptake of glycerol. A similar transport system has been suggested to be present also in the small intestine and is of interest with regard to its role in the absorption of glycerol and possibly some structurally related compounds. To help clarifying functional characteristics of such glycerol transport systems, we examined the effect of butyrate, an agent known to facilitate the differentiation of cells, on glycerol uptake in HCT-15 cells. The uptake of glycerol (0.4 microM) was found to be about 5-fold greater in HCT-15 cells pretreated with butyrate (2 mM) for 24 h than in those untreated. The increase in the uptake by the butyrate treatment was due to an increase in the maximum transport rate. The effect of butyrate was almost completely suppressed when actinomycin D, an inhibitor of gene transcription, and cycloheximide, an inhibitor of protein synthesis, were added to the medium during the butyrate treatment. These results support the suggestion that a specific carrier protein is involved in glycerol uptake by HCT-15 cells and the carrier protein is one of those inducible by butyrate-induced cell differentiation.

Real-time analysis of the transcriptional regulation of HIV and hCMV promoters in single mammalian cells

The regulation of human cytomegalovirus (hCMV) and human immunodeficiency virus (HIV) gene expression has been studied in single intact mammalian cells. Viral promoters were placed upstream of the firefly luciferase reporter gene and the resulting hybrid reporter constructs were stably integrated into the HeLa cell genome. A highly sensitive photon-counting camera system was used to study the level of gene expression in single intact cells. Luciferase expression was studied in the absence of activators of viral gene expression, in the presence of the HIV-1 TAT transactivator protein, or in the presence of sodium butyrate, a non-viral activator of gene expression. In the absence of any activator of gene expression, while expression was undetectable in most cells, significant levels of basal luciferase activity were observed in a few cells, indicating heterogeneity in gene expression in the cell population. In the presence of the general activator of viral gene expression, sodium butyrate, transcriptional activation from the viral promoters gave rise to significant and relatively homogeneous levels of luciferase expression in a majority of cells. The luciferase imaging technology was used for the real-time analysis of changes of gene expression within a single cell. This non-invasive reporter assay should become important for studies of the temporal regulation of gene expression in single cells.

Facilitative glucose transporters

Facilitative glucose transport is mediated by members of the Glut protein family that belong to a much larger superfamily of 12 transmembrane segment transporters. Six members of the Glut family have been described thus far. These proteins are expressed in a tissue- and cell-specific manner and exhibit distinct kinetic and regulatory properties that reflect their specific functional roles. Glut1 is a widely expressed isoform that provides many cells with their basal glucose requirement. It also plays a special role in transporting glucose across epithelial and endothelial barrier tissues. Glut2 is a high-Km isoform expressed in hepatocytes, pancreatic beta cells, and the basolateral membranes of intestinal and renal epithelial cells. It acts as a high-capacity transport system to allow the uninhibited (non-rate-limiting) flux of glucose into or out of these cell types. Glut3 is a low-Km isoform responsible for glucose uptake into neurons. Glut4 is expressed exclusively in the insulin-sensitive tissues, fat and muscle. It is responsible for increased glucose disposal in these tissues in the postprandial state and is important in whole-body glucose homeostasis. Glut5 is a fructose transporter that is abundant in spermatozoa and the apical membrane of intestinal cells. Glut7 is the transporter present in the endoplasmic reticulum membrane that allows the flux of free glucose out of the lumen of this organelle after the action of glucose-6-phosphatase on glucose 6-phosphate. This review summarizes recent advances concerning the structure, function, and regulation of the Glut proteins.

Regulation of glucose transporters in LLC-PK1 cells: effects of D-glucose and monosaccharides

Regulation of D-glucose transport in the porcine kidney epithelial cell line LLC-PK1 was examined. To identify the sodium-coupled glucose transporter (SGLT), we cloned and sequenced several partial cDNAs homologous to SGLT1 from rabbit small intestine (M. A. Hediger, M. J. Coady, T. S. Ikeda, and E. M. Wright, Nature (London) 330:379-381, 1987). The extensive homology of the two sequences leads us to suggest that the high-affinity SGLT expressed by LLC-PK1 cells is SGLT1. SGLT1 mRNA levels were highest when the D-glucose concentration in the culture medium was 5 to 10 mM. Addition of D-mannose or D-fructose, but not D-galactose, in the presence of 5 mM D-glucose suppressed SGLT1 mRNA levels. SGLT1 activity, measured by methyl alpha-D-glucopyranoside uptake, paralleled message levels except in cultures containing D-galactose. Therefore, SGLT1 gene expression may respond either to the cellular energy status or to the concentration of a hexose metabolite(s). By isolating several cDNAs homologous to rat GLUT-1, we identified the facilitated glucose transporter in LLC-PK1 cells as the erythroid/brain type GLUT-1. High-stringency hybridization of a single mRNA transcript to the rat GLUT-1 cDNA probe and failure to observe additional transcripts hybridizing either to GLUT-1 or to GLUT-2 probes at low stringency provide evidence that GLUT-1 is the major facilitated glucose transporter in this cell line. LLC-PK1 GLUT-1 mRNAs were highest at medium D-glucose concentrations of less than or equal to 2 mM. D-Fructose, D-mannose, and to a lesser extent D-galactose all suppressed GLUT-1 mRNA levels. Since the pattern of SGLT1 and GLUT-1 expression differed, particularly in low D-glucose or in the presence of D-galactose, we suggest that the two transporters are regulated independently.

Regulation of glucose transporters in LLC-PK1 cells: effects of D-glucose and monosaccharides

Regulation of D-glucose transport in the porcine kidney epithelial cell line LLC-PK1 was examined. To identify the sodium-coupled glucose transporter (SGLT), we cloned and sequenced several partial cDNAs homologous to SGLT1 from rabbit small intestine (M. A. Hediger, M. J. Coady, T. S. Ikeda, and E. M. Wright, Nature (London) 330:379-381, 1987). The extensive homology of the two sequences leads us to suggest that the high-affinity SGLT expressed by LLC-PK1 cells is SGLT1. SGLT1 mRNA levels were highest when the D-glucose concentration in the culture medium was 5 to 10 mM. Addition of D-mannose or D-fructose, but not D-galactose, in the presence of 5 mM D-glucose suppressed SGLT1 mRNA levels. SGLT1 activity, measured by methyl alpha-D-glucopyranoside uptake, paralleled message levels except in cultures containing D-galactose. Therefore, SGLT1 gene expression may respond either to the cellular energy status or to the concentration of a hexose metabolite(s). By isolating several cDNAs homologous to rat GLUT-1, we identified the facilitated glucose transporter in LLC-PK1 cells as the erythroid/brain type GLUT-1. High-stringency hybridization of a single mRNA transcript to the rat GLUT-1 cDNA probe and failure to observe additional transcripts hybridizing either to GLUT-1 or to GLUT-2 probes at low stringency provide evidence that GLUT-1 is the major facilitated glucose transporter in this cell line. LLC-PK1 GLUT-1 mRNAs were highest at medium D-glucose concentrations of less than or equal to 2 mM. D-Fructose, D-mannose, and to a lesser extent D-galactose all suppressed GLUT-1 mRNA levels. Since the pattern of SGLT1 and GLUT-1 expression differed, particularly in low D-glucose or in the presence of D-galactose, we suggest that the two transporters are regulated independently.

Butyrate induces an ectoMg2(+)-ATPase activity in Li-7A human hepatoma cells

The human hepatoma cell line (Li-7A) possesses a high concentration of epidermal growth factor (EGF) receptors and exhibits ectoATPase activity in the presence of either MgATP or CaATP (Knowles: J. Cell. Physiol., 134:109-116, 1988). Growth for 96 hours in the presence of both EGF and cholera toxin or another cyclic AMP elevating agent induced an ectoATPase activity which was more active with CaATP and resistant to inhibition by the sulfydryl reagent, p-chloromercuriphenylsulfonate (pCMPS) (Knowles: Arch. Biochem. Biophys., 263: 264-271, 1988). In contrast, treatment of cells with butyrate, a short chain organic acid which can be derived from the analogue, dibutyryl cyclic AMP, resulted in a 4-7-fold increase of an ectoATPase which was more active with MgATP and highly sensitive to pCMPS inhibition. Maximal induction by butyrate required 48 hours and was dependent on butyrate concentration, but was independent of EGF and cyclic AMP elevating agents. Of six organic acids tested, butyrate was most effective in the induction of the ectoMg2(+)-ATPase. The increase in the ectoMg2(+)-ATPase activity could be prevented with actinomycin D and cycloheximide, indicating that both transcription and translation were necessary for induction. In addition to the induction of the ectoMg2(+)-ATPase, butyrate induced alkaline phosphatase activity, but had no effect on a third ectoenzyme 5'-nucleotidase. These data further support our proposal that two distinct ectoATPases exist in the plasma membrane of Li-7A hepatoma cells.