Influence of short-chain fatty acids on ammonia absorption across the rumen wall in sheep.

The effects of short-chain fatty acids (SCFA) on ammonia net absorption from the sheep rumen in vivo and on ammonia transport across rumen wall mucosa in vitro were studied. Ammonia net absorption was directly, though in a non-linear manner, correlated with the SCFA concentration in the artificial rumen fluid. Almost 70% of total ammonia absorption was dependent upon the presence of SCFA when 12 mmol l-1 ammonia and 67.5 mmol l-1 SCFA were present. Lactic acid was ineffective. Incubation experiments showed that mucosal disappearance and serosal appearance of ammonia were reduced by 38% and 32%, respectively, when SCFA (63 mmol l-1) were replaced by lactic acid. The SCFA effect was independent of the type of SCFA used. In part of the experiments up to 54% of the ammonia taken up by the tissue was not recovered in the serosal incubation solution and must have been metabolized in the mucosa.     

Monocarboxylate Transporter 1 (MCT1) is an independent prognostic biomarker in endometrial cancer

Background

Endometrial cancer (EC) is a major health concern due to its rising incidence. Whilst early stage disease is generally cured by surgery, advanced EC has a poor prognosis with limited treatment options. Altered energy metabolism is a hallmark of malignancy. Cancer cells drive tumour growth through aerobic glycolysis and must export lactate to maintain intracellular pH. The aim of this study was to evaluate the expression of the lactate/proton monocarboxylate transporters MCT1 and MCT4 and their chaperone CD147 in EC, with the ultimate aim of directing future drug development.

Methods

MCT1, MCT4 and CD147 expression was examined using immunohistochemical analysis in 90 endometrial tumours and correlated with clinico-pathological characteristics and survival outcomes.

Results

MCT1 and MCT4 expression was observed in the cytoplasm, the plasma membrane or both locations. CD147 was detected in the plasma membrane and associated with MCT1 (p =?0.003) but not with MCT4 (p =?0.207) expression. High MCT1 expression was associated with reduced overall survival (p =?0.029) and remained statistically significant after adjustment for survival covariates (p =?0.017).

Conclusion

Our data suggest that MCT1 expression is an important marker of poor prognosis in EC. MCT1 inhibition may have potential as a treatment for advanced or recurrent EC.

     

Expression of monocarboxylate transporter (MCT) 1 and MCT4 in overloaded mice plantaris muscle

A number of studies have shown that changes in muscle contractile activity regulate the expression of monocarboxylate transporters (MCTs) in the skeletal muscle. The aim of this study was to investigate the effect of functional overload on MCT1 and MCT4 protein expression. Plantaris muscles were functionally overloaded for 15 days by ablation of the synergistic muscles. MCT1 and MCT4 mRNA abundance increased by 160–161% (p < 0.01) and 265–325% (p < 0.05), respectively, after 1–3 days of functional overload. MCT1 and MCT4 protein expression increased by 92 and 61%, respectively, after 12 days of functional overload (p < 0.05). AMP-activated protein kinase (AMPK) phosphorylation status [phospho-AMPK (Thr172)/total AMPK] was significantly elevated after 3–9 days of functional overload. Plasma testosterone concentration was elevated after 12 days of functional overload, while blood lactate concentration was not altered. Thus, the current study demonstrated that heavy mechanical loading induces increase in MCT1 and MCT4 protein expression in the muscles with increase in AMPK phosphorylation status and plasma testosterone concentration.     

Immunohistochemical evaluation and prognostic value of monocarboxylate transporter 1 (MCT1) and 4 (MCT4) in T-cell non-Hodgkin lymphoma

Clinical and Experimental Medicine - Tumor cells often exhibit the Warburg effect, wherein, they preferentially undergo glycolysis over oxidative phosphorylation for energy production....     

Effect of AMPK activation on monocarboxylate transporter (MCT)1 and MCT4 in denervated muscle

It is now evident that exercise training leads to increases in monocarboxylate transporter (MCT)1 and MCT4, but little is known about the mechanisms of coupling muscle contraction with these changes. The aim of this study was to investigate the effect of 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) induced activation of AMP-activated protein kinase (AMPK) on MCT1, MCT4, and GLUT4 in denervated muscle. Protein levels of MCT4 and GLUT4 after 10 days of denervation were significantly decreased in mice gastrocnemius muscle, while MCT1 protein levels were not altered. AICAR treatment for 10 days significantly increased MCT4, and GLUT4 protein levels in innervated muscle as shown in previous studies. We found that the MCT1 protein level was also increased in AICAR treated innervated muscle. AICAR treatment prevented the decline in MCT4 and GLUT4 protein levels in denervated muscle. Thus, the current study suggests that MCT1 and MCT4 protein expression in muscles, as well as GLUT4, may be regulated by AMPK-mediated signal pathways, and AMPK activation can prevent denervation-induced decline in MCT4 protein.     

The role of volume-sensitive CI channels in the stimulation of chloride absorption by short-chain fatty acids in the rat colon

The short-chain fatty acids acetate, propionate and butyrate induced a concentration-dependent decrease in short-circuit current (I_sc) of the rat colon in vitro. The decrease in I_sc, being more pronounced in the distal than in the proximal colon, was dependent on the presence of CI^- ions and partly on the presence of HCO^-₃. In the distal colon, the fall in I_sc could be inhibited by amiloride, indicating that the activity of the Na⁺/H⁺ exchanger is necessary for the induction of this response. The decrease in I_sc was diminished by the CI^- channel blocker, 5-nitro-2-(3-phenylpropylamino)-benzoate, and the lipoxygenase inhibitor, nordihydroguaiaretic acid. In contrast, inhibitors of the leukotriene pathway or a CI^- channel blocker did not affect the I_sc response in the proximal colon. Measurements of unidirectional fluxes revealed that butyrate caused a stimulation of the mucosa to serosa fluxes (J_ms) of Na⁺ and CI^- in the distal, but only of j_ms^Na in the proximal colon. Unidirectional Rb⁺ fluxes were not altered. The stimulation of j_ms^cl correlated with the degree of metabolism of the short-chain fatty acid. The increase in j_ms^cl was most pronounced for butyrate, smaller for acetate and not observed with the poorly metabolizable short-chain fatty acid, isobutyrate. Consequently, two factors seem to be responsible for the stimulation of CI^- absorption by short-chain fatty acids in the distal colon: (1) the intracellular production of HCO^-₃ during the oxidation of short-chain fatty acids as substrate for the apical Cr/HCO^-₃ exchanger, and (2) the activation of volume-sensitive basolateral CI^- channels.     

Correlation between local monocarboxylate transporter 1 (MCT1) and glucose transporter 1 (GLUT1) densities in the adult rat brain

Monocarboxylate transporters type 1 (MCT1) facilitate the transport of monocarboxylates across cell membranes of the blood-brain barrier and brain parenchymal cells. The present study had two aims: (1) to determine the local distribution of MCT1 in the brain; and (2) to compare the local densities of MCT1 with the local densities of the main nutritional transporters, glucose transporter GLUT1. Using immunoautoradiography of cryosections from rat brain, 32 brain structures were analyzed. (1) A heterogenous distribution pattern of MCT1 densities was observed throughout the brain. Compared to brain homogenate (100%), MCT1 densities ranged from 43 to 164% in the brain structures investigated. Local GLUT1 densities showed a comparable range (35-145%). (2) A close correlation was found between local MCT1 and local GLUT1 densities. As local GLUT1 densities reflect local glucose metabolism in the brain, we conclude that local MCT1 densities are adjusted to local glucose metabolism and transport.     

Effect of training and detraining on monocarboxylate transporter (MCT) 1 and MCT4 in Thoroughbred horses

The aim of this study was to investigate the effects of training and detraining on the monocarboxylate transporter (MCT) 1 and MCT4 levels in the gluteus medius muscle of Thoroughbred horses. Twelve Thoroughbred horses were used for the analysis. For 18 weeks, all the horses underwent high-intensity training (HIT), with running at 90-110% maximal oxygen consumption (VO2 max ) for 3 min, 5 days week(-1). Thereafter, the horses either underwent detraining for 6 weeks by either 3 min of moderate-intensity training (MIT) at 70% VO2 max, 5 days week(-1) (HIT-MIT group) or stall rest (HIT-SR group). The horses underwent an incremental exercise test, VO2 max was measured and resting muscle samples were obtained from the middle gluteus muscle at 0, 18 and 24 weeks. The content of MCT1 and MCT4 proteins increased after 18 weeks of HIT. At the end of this period, an increase was noted in the citrate synthase activity, while phosphofructokinase activity remained unchanged. After 6 weeks of detraining, all these indexes returned to the pretraining levels in the HIT-SR group. However, in the HIT-MIT group, the increase in the MCT1 protein content and citrate synthase activity was maintained after 6 weeks of MIT, while the MCT4 protein content decreased to the pretraining value. These results suggest that the content of MCT1 and MCT4 proteins increases after HIT in Thoroughbred horses. In addition, the increase in the MCT1 protein content and oxidative capacity induced by HIT can be maintained by MIT of 70% VO2 max, but the increase in the MCT4 protein content cannot be maintained by MIT.     

Histochemical demonstration of a Na(+)-coupled transporter for short-chain fatty acids (slc5a8) in the intestine and kidney of the mouse

Short-chain fatty acids in the intestinal lumen affect colonic cell proliferation as well as function as an energy source for intestinal epithelial cells. A novel transporter of monocarboxylates, Slc5a8, is expressed abundantly in the colon, where it may participate in the Na(+)-coupled absorption of short-chain fatty acids produced by bacterial fermentation of dietary fiber. The present study examined the cellular localization of Slc5a8 in the murine gastrointestinal tract and kidney by in situ hybridization and immunohistochemistry. The hybridization signals were recognized in the terminal ileum and whole length of the large intestine, and were especially intense in the distal colon and rectum. The immunoreactivity of Slc5a8 was restricted to the striated border (the brush border) of enterocytes, and was not present in goblet cells, Paneth cells, or lamina propria cells. In the kidney, proximal tubules of both the cortex and the outer stripe of the outer medulla intensely expressed Slc5a8 mRNA, while the distal portions, including the loop of Henle, lacked the signals. The renal Slc5a8 immunoreactivity was localized only in the brush border of proximal tubules, not along the basolateral membrane. Thyroid follicular cells were immunoreactive for Slc5a8, with predominant labeling on the apical membrane. No other organs, including the esophagus, stomach, liver, pancreas, and salivary glands contained any notable signals of Slc5a8. These findings on the cellular and subcellular localization of Slc5a8 under normal conditions are helpful for understanding the physiological and pathological roles of Slc5a8.     

Regulatory role of cAMP in transport of Na+, Cl- and short-chain fatty acids across sheep ruminal epithelium

Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short-chain fatty acids (SCFAs). However, regulation of ruminal Na+, Cl-, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodium-coupled transport mechanisms in short-circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mM) or theophylline in combination with forskolin (0.1 mM) significantly reduced mucosal-to-serosal sodium transport, leading to a reduction of net transport. The theophylline- or theophylline-forskolin-induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short-chain fatty acids stimulated Na+ transport but their stimulatory effect was almost completely blocked by theophylline-forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mM amiloride on sodium transport was strongly reduced after theophylline-forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 microM) led to a theophylline-sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride-sensitive Na+-H+ exchange and/or basolateral Na+-K+-ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions.     

Natural caprine herpesvirus 1 (CpHV-1) infection in kids

Twenty-seven kids aged 5-7 days from a flock of 200 goats in which a high rate of abortion occurred died over a 2-month period. All showed hyperthermia, abdominal pain and anorexia. Two of the kids were examined post mortem. Ulcerative and necrotic lesions affected the whole intestine, and macroscopical changes were also observed in the lungs, urinary bladder and liver. Histologically, a severe necrotizing enteritis as well as thickening of the alveolar septa and necrotic bronchiolo-alveolitis were detected. Prominent microscopical lesions were also present in the liver, urinary bladder, spleen, thymus, mesenteric lymph nodes and kidney. Macrophages containing eosinophilic intranuclear inclusion bodies appeared to be the main inflammatory cell in all the organs examined. Ultrastructurally, herpesvirus particles were evident. Characteristic morphological features of type-A capsids (empty), type-C capsids (large core), and type-B capsids were observed. A virus was isolated in cell culture from all organs examined in the two kids. Cytopathogenic effects (rounding cells, syncytia, vacuoles, cell lysis) and acidophilic intranuclear inclusions typical of herpesvirus infection were observed. The virus was identified as caprine herpesvirus 1 (CpHV-1) by the polymerase chain reaction (PCR) technique and by serum neutralization Copyright 2000 Harcourt Publishers Ltd.     

Emodin plays an interventional role in epileptic rats via multidrug resistance gene 1 (MDR1)

Objective: To observe the interventional effects of emodin in epileptic rats and elucidate its possible mechanism of action. Methods: Thirty-six female Wistar rats were randomly divided into normal control group, model group (intraperitoneal injection of kainic acid) and emodin group (intraperitoneal injection of kainic acid + emodin intervention). The rat epilepsy model was confirmed by behavioral tests and electroencephalography. The protein levels of P-glycoprotein and N-methyl-D-aspartate (NMDA) receptor in cerebral vascular tissue were analyzed by western blotting, and mRNA levels of multidrug resistance gene 1 (MDR1) and cyclooxygenase-2 (COX-2) were analyzed by real-time PCR. COX-2 and P-glycoprotein levels in the brains were detected by immunohistochemical assay. Results: The seizures were relieved in emodin group. Laser scanning confocal microscopy showed P-glycoprotein fluorescence increased significantly after seizures, indicating that epilepsy can induce overexpression of P-glycoprotein. Compared with control group, protein levels of P-glycoprotein and NMDA receptor in cerebral vascular tissue were significantly higher in model group, and mRNA levels of MDR1 and COX-2 were also significantly increased. Compared with model group, P-glycoprotein and NMDA receptor levels in cerebral vascular tissue were significantly decreased in emodin group (P < 0.05), and the levels of MDR1 and COX-2 were down-regulated (P < 0.05). In the rat brain, seizures could significantly increase COX-2 and P-glycoprotein levels, while emodin intervention was able to significantly reduce the levels of both. Discussion: These findings suggest that epileptic seizures are tightly associated with up-regulated MDR1 gene, and emodin shows good antagonistic effects on epileptic rats, possibly through inhibition of MDR1 gene and its associated genes.     

Dimerization of human pS2 (TFF1) plays a key role in its protective/healing effects

Human pS2 (trefoil factor family 1, TFF1), a 60-amino acid member of the trefoil peptide family, forms dimers via Cys⁵⁸ and may stimulate gut repair. The effects of dimeric pS2-TFF1 and monomeric pS2-TFF1 (Cys⁵⁸ replaced by Ser⁵⁸) were compared in models of wound healing. Rats given dimeric pS2-TFF1 at 25 and 50 μg/kg per h had 50 per cent and 70 per cent reduction in gastric damage induced respectively by indomethacin (20 mg/kg subcutaneously) and restraint (P<0·01). Monomeric pS2-TFF1, at the same doses, was significantly less effective at reducing injury (about half the amount of protection, P<0·01 vs. same doses of dimeric). The rate of migration of cells at the leading edge of wounded monolayers of the human colonic cell line HT29 was increased by addition of dimeric or monomeric forms of pS2-TFF1 (0·65–325 μg/ml). Dimeric pS2-TFF1 had a greater effect than the monomeric form at all doses tested (P<0·05). Cell migration induced by pS2-TFF1 was blocked by a pS2-TFF1 antibody, but not by a transforming growth factor β neutralizing antibody. pS2-TFF1 did not influence cell proliferation as assessed by thymidine incorporation. The increased biological effects of dimeric pS2-TFF1 might be due to direct interaction of Cys⁵⁸ with a putative trefoil receptor or, more likely, dimerization of pS2-TFF1 might stabilize the interaction with its receptor. This may involve a bivalent interaction of residues on the surfaces of the two trefoil domains. © 1998 John Wiley & Sons, Ltd.