Is glutamine a unique fuel for small intestinal cells?

Medium-chain triglyceride-specific appetite is regulated by the β-oxidation of medium-chain fatty acids in the liver

Most studies on fat appetite have focused on long-chain triglycerides (LCTs) due to their obesogenic properties. Medium-chain triglycerides (MCTs), conversely, exhibit antiobesogenic effects; however, the regulation of MCT intake remains elusive. Here, we demonstrate that mice can distinguish between MCTs and LCTs, and the specific appetite for MCTs is governed by hepatic β-oxidation. We generated liver-specific medium-chain acyl-CoA dehydrogenase (MCAD)-deficient (MCADL-/-) mice and analyzed their preference for MCT and LCT solutions using glyceryl trioctanoate (C8-TG), glyceryl tridecanoate (C10-TG), corn oil, and lard oil in two-bottle choice tests conducted over 8 days. In addition, we used lick microstructure analyses to evaluate the palatability and appetite for MCT and LCT solutions. Finally, we measured the expression levels of genes associated with fat ingestion (Galanin, Qrfp, and Nmu) in the hypothalamus 2 h after oral gavage of fat. Compared with control mice, MCADL-/- mice exhibited a significantly reduced preference for MCT solutions, with no alteration in the preference for LCTs. Lick analysis revealed that MCADL-/- mice displayed a significantly decreased appetite for MCT solutions only while the palatability of both MCT and LCT solutions remained unaffected. Hypothalamic Galanin expression in control mice was elevated by oral gavage of C8-TG but not by LCTs, and this response was abrogated in MCADL-/- mice. In summary, our data suggest that hepatic β-oxidation is required for MCT-specific appetite but not for LCT-specific appetite. The induction of hypothalamic galanin upon MCT ingestion, dependent on hepatic β-oxidation, could be involved in the regulation of MCT-specific appetite.NEW & NOTEWORTHY Whether and how medium-chain triglyceride (MCT) intake is regulated remains unknown. Here, we showed that mice can discriminate between MCTs and LCTs. Hepatic β-oxidation participates in MCT-specific appetite, and hypothalamic galanin may be one of the factors that regulate MCT intake. Because of the antiobesity effects of MCTs, studying MCT-specific appetite may help combat obesity by promoting the intake of MCTs instead of LCTs.

Saturated fatty acids differently affect mitochondrial function and the intestinal epithelial barrier depending on their chain length in the in vitro model of IPEC-J2 enterocytes

Introduction: Maintenance of the intestinal barrier mainly relies on the mitochondrial function of intestinal epithelial cells that provide ATP through oxidative phosphorylation (OXPHOS). Dietary fatty acid overload might induce mitochondrial dysfunction of enterocytes and may increase intestinal permeability as indicated by previous in vitro studies with palmitic acid (C16:0). Yet the impact of other dietary saturated fatty acids remains poorly described. Methods: To address this question, the in vitro model of porcine enterocytes IPEC-J2 was treated for 3 days with 250 µM of lauric (C12:0), myristic (C14:0), palmitic (C16:0) or stearic (C18:0) acids. Results and discussion: Measurement of the transepithelial electrical resistance, reflecting tight junction integrity, revealed that only C16:0 and C18:0 increased epithelial permeability, without modifying the expression of genes encoding tight junction proteins. Bioenergetic measurements indicated that C16:0 and C18:0 were barely β-oxidized by IPEC-J2. However, they rather induced significant OXPHOS uncoupling and reduced ATP production compared to C12:0 and C14:0. These bioenergetic alterations were associated with elevated mitochondrial reactive oxygen species production and mitochondrial fission. Although C12:0 and C14:0 treatment induced significant lipid storage and enhanced fusion of the mitochondrial network, it only mildly decreased ATP production without altering epithelial barrier. These results point out that the longer chain fatty acids C16:0 and C18:0 increased intestinal permeability, contrary to C12:0 and C14:0. In addition, C16:0 and C18:0 induced an important energy deprivation, notably via increased proton leaks, mitochondrial remodeling, and elevated ROS production in enterocytes compared to C12:0 and C14:0.

Mitochondrial function in intestinal epithelium homeostasis and modulation in diet-induced obesity

Background

Systemic low-grade inflammation observed in diet-induced obesity has been associated with dysbiosis and disturbance of intestinal homeostasis. This latter relies on an efficient epithelial barrier and coordinated intestinal epithelial cell (IEC) renewal that are supported by their mitochondrial function. However, IEC mitochondrial function might be impaired by high fat diet (HFD) consumption, notably through gut-derived metabolite production and fatty acids, that may act as metabolic perturbators of IEC.

Scope of review

This review presents the current general knowledge on mitochondria, before focusing on IEC mitochondrial function and its role in the control of intestinal homeostasis, and featuring the known effects of nutrients and metabolites, originating from the diet or gut bacterial metabolism, on IEC mitochondrial function. It then summarizes the impact of HFD on mitochondrial function in IEC of both small intestine and colon and discusses the possible link between mitochondrial dysfunction and altered intestinal homeostasis in diet-induced obesity.

Major conclusions

HFD consumption provokes a metabolic shift toward fatty acid β-oxidation in the small intestine epithelial cells and impairs colonocyte mitochondrial function, possibly through downstream consequences of excessive fatty acid β-oxidation and/or the presence of deleterious metabolites produced by the gut microbiota. Decreased levels of ATP and concomitant O₂ leaks into the intestinal lumen could explain the alterations of intestinal epithelium dynamics, barrier disruption and dysbiosis that contribute to the loss of epithelial homeostasis in diet-induced obesity. However, the effect of HFD on IEC mitochondrial function in the small intestine remains unknown and the precise mechanisms by which HFD induces mitochondrial dysfunction in the colon have not been elucidated so far.

Differences in the Establishment of Gut Microbiota and Metabolome Characteristics Between Balb/c and C57BL/6J Mice After Proton Irradiation

Although proton irradiation is ubiquitous in outer space as well as in the treatment of human diseases, its effects remain largely unclear. This work aimed to investigate and compare the composition of gut microbiota composition of mice in different species exposed to high-dose radiation. Male Balb/c mice and C57BL/6J mice were irradiated at a high dose (5Gy). Fecal specimens before and after irradiation were subjected to high-throughput sequencing (HTS) for the amplification of 16S rRNA gene sequences. We observed substantial changes in gut microbial composition among mice irradiated at high doses compared to non-irradiated controls. The changes included both the alpha and beta diversities. Furthermore, there were 11 distinct alterations in the irradiation group compared to the non-radiation control, including the families Muribaculaceae, Ruminococcaceae, Lactobacillus, Lachnospiraceae_NK4A136, Bacteroides, Alistipes, Clostridiales, Muribaculum, and Alloprevotella. Such alterations in the gut microbiome were accompanied by alterations in metabolite abundances, while at the metabolic level, 32 metabolites were likely to be potential biomarkers. Some alterations may have a positive effect on the repair of intestinal damage. Simultaneously, metabolites were predicted to involve multiple signal pathways, such as Urea Cycle, Ammonia Recycling, Alpha Linolenic Acid and Linoleic Acid Metabolism, Ketone Body Metabolism, Aspartate Metabolism, Phenylacetate Metabolism, Malate-Aspartate Shuttle, Arginine and Proline Metabolism and Carnitine Synthesis. Metabolites produced by proton irradiation in the microbial region play a positive role in repairing damage, making this area worthy of further experimental exploration. The present work offers an analytical and theoretical foundation to investigate how proton radiation affects the treatment of human diseases and identifies potential biomarkers to address the adverse effects of radiation.

The Roles of Cytoplasmic Lipid Droplets in Modulating Intestinal Uptake of Dietary Fat

Dietary fat absorption is required for health but also contributes to hyperlipidemia and metabolic disease when dysregulated. One step in the process of dietary fat absorption is the formation of cytoplasmic lipid droplets (CLDs) in small intestinal enterocytes; these CLDs serve as dynamic triacylglycerol storage organelles that influence the rate at which dietary fat is absorbed. Recent studies have uncovered novel factors regulating enterocyte CLD metabolism that in turn influence the absorption of dietary fat. These include peroxisome proliferator-activated receptor α activation, compartmentalization of different lipid pools, the gut microbiome, liver X receptor and farnesoid X receptor activation, obesity, and physiological factors stimulating CLD mobilization. Understanding how enterocyte CLD metabolism is regulated is key in modulating the absorption of dietary fat in the prevention of hyperlipidemia and its associated metabolic disorders. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Characterization of cytoplasmic lipid droplets in each region of the small intestine of lean and diet-induced obese mice in response to dietary fat

The absorptive cells of the small intestine, namely, enterocytes, contribute to postprandial blood lipid levels by secreting dietary triacylglycerol in chylomicrons. The rate and amount of dietary triacylglycerol absorbed vary along the length of the small intestine. Excess dietary triacylglycerol not immediately secreted in chylomicrons can be temporarily stored in cytoplasmic lipid droplets (CLDs) and repackaged in chylomicrons at later times. The characteristics of CLDs, including their size, number per cell, and associated proteins, may influence CLD metabolism and reflect differences in lipid processing or storage in each intestinal region. However, it is unknown whether the characteristics or proteomes of CLDs differ in enterocytes of each intestine region in response to dietary fat. Furthermore, it is unclear if obesity influences the characteristics or proteomes of CLDs in each intestine region. To address this, we used transmission electron microscopy and shotgun liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis to assess the characteristics and proteome of CLDs in the proximal, middle, and distal regions of the small intestine of lean and diet-induced obese (DIO) mice 2 h after an oil gavage. We identified differences in lipid storage along the length of the small intestine and between lean and DIO mice, as well as distinct CLD proteomes reflecting potentially unique roles of CLDs in each region. This study reveals differences in lipid processing along the length of the small intestine in response to dietary fat in lean and DIO mice and reflects distinct features of the proximal, middle, distal region of the small intestine.NEW & NOTEWORTHY This study reflects the dynamics of fat absorption along the length of the small intestine in lean and obese mice in the physiological response to dietary fat. We identified unique features of cytoplasmic lipid droplets (CLDs) in the proximal, middle, and distal regions of the small intestine of lean and obese mice that may contribute to regional differences in dietary fat processing, absorption, or CLD metabolism.

Lysophosphatidic Acid Increases Maturation of Brush Borders and SGLT1 Activity in MYO5B-deficient Mice, a Model of Microvillus Inclusion Disease

BACKGROUND & AIM

Myosin VB (MYO5B) is an essential trafficking protein for membrane recycling in gastrointestinal epithelial cells. The inactivating mutations of MYO5B cause the congenital diarrheal disease, microvillus inclusion disease (MVID). MYO5B deficiency in mice causes mislocalization of SGLT1 and NHE3, but retained apical function of CFTR, resulting in malabsorption and secretory diarrhea. Activation of lysophosphatidic acid (LPA) receptors can improve diarrhea, but the effect of LPA on MVID symptoms is unclear. We investigated whether LPA administration can reduce the epithelial deficits in MYO5B-knockout mice.

METHODS

Studies were conducted with tamoxifen-induced, intestine-specific knockout of MYO5B (VilCre^ERT2;Myo5b^flox/flox) and littermate controls. Mice were given LPA, an LPAR2 agonist (GRI977143), or vehicle for 4 days after a single injection of tamoxifen. Apical SGLT1 and CFTR activities were measured in Üssing chambers. Intestinal tissues were collected, and localization of membrane transporters was evaluated by immunofluorescence analysis in tissue sections and enteroids. RNA sequencing and enrichment analysis were performed with isolated jejunal epithelial cells.

RESULTS

Daily administration of LPA reduced villus blunting, frequency of multivesicular bodies, and levels of cathepsins in intestinal tissues of MYO5B-knockout mice compared with vehicle administration. LPA partially restored the brush border height and the localization of SGLT1 and NHE3 in small intestine of MYO5B-knockout mice and enteroids. The SGLT1-dependent short-circuit current was increased and abnormal CFTR activities were decreased in jejunum from MYO5B-knockout mice given LPA compared with vehicle.

CONCLUSIONS

LPA may regulate a MYO5B-independent trafficking mechanism and brush border maturation, and therefore be developed for treatment of MVID.

Glutamine Metabolism and Its Role in Immunity, a Comprehensive Review

In the body of an animal, glutamine is a plentiful and very useful amino acid. Glutamine consumption in the body of animals in normal or disease conditions is the same or higher than the glucose. Many in vivo as well as in vitro experiments have been conducted to evaluate the importance of glutamine. Glutamine is a valuable nutrient for the proliferation of the lymphocytes. It also plays a crucial role in the production of cytokines, macrophages, phagocytic, and neutrophil to kill the bacteria. Most of the metabolic organs like the liver, gut, and skeletal muscles control the circulation and availability secretion of glutamine. In catabolic and hypercatabolic conditions, glutamine can turn out to be essential and plays a vital role in metabolism; however, availability may be compromised due to the impairment of homeostasis in the inter-tissue metabolism of amino acids. This is why the supplementation of glutamine is commonly used in clinical nutrition and is especially recommended to immune-suppressed persons. Despite this, in catabolic and hyper-catabolic conditions, it is challenging due to the amino acid concentration in plasma/bloodstream and glutamine should be provided via either the oral, enteral or parenteral route. However, the effect of glutamine as an immune-based supplement has been previously recognized as many research studies conducted in vivo and in-vitro evaluated the beneficial effects of glutamine. Hence, the present study delivers a combined review of glutamine metabolism in essential organs of the cell immune system. In this review, we have also reviewed the metabolism and action of glutamine and crucial problems due to glutamine supplementation in catabolic conditions.

Nutritional Feeding Strategies in Pediatric Intestinal Failure

Intestinal failure is defined as a critical reduction of the gut mass or function, below the minimum needed to absorb nutrients and fluids. The ultimate goal in intestinal failure is to promote bowel adaptation and reach enteral autonomy while a healthy growth and development is maintained. The condition is heterogeneous and complex. Therefore, recommendations for the type and duration of parenteral, enteral, and oral nutrition are variable, with the child's age as an additional key factor. The aim of this review is to provide an overview of nutritional feeding strategies in this heterogeneous population. Different perspectives on nutritional management, nutrition and adaptation, and microbiome and nutrition will be discussed.

The Role of Glutamine in the Complex Interaction between Gut Microbiota and Health: A Narrative Review

The scientific literature has demonstrated that glutamine is one of the main beneficial amino acids. It plays an important role in gut microbiota and immunity. This paper provides a critical overview of experimental studies (in vitro, in vivo, and clinical) investigating the efficacy of glutamine and its effect on gut microbiota. As a result of this review, we have summarized that glutamine could affect gut microbiota via different mechanisms including the reduction in the ratio of Firmicutes to Bacteroidetes, with the activation of NF-κB and PI3K-Akt pathways, reducing the intestinal colonization (Eimeria lesions) and bacterial overgrowth or bacterial translocation, increasing the production of secretory immunoglobulin A (SIgA) and immunoglobulin A+ (IgA+) cells in the intestinal lumen, and decreasing asparagine levels. The potential applications of glutamine on gut microbiota include, but are not limited to, the management of obesity, bacterial translocation and community, cytokines profiles, and the management of side effects during post-chemotherapy and constipation periods. Further studies and reviews are needed regarding the effects of glutamine supplementation on other conditions in humans.

Glucose transport across lagomorph jejunum epithelium is modulated by AMP-activated protein kinase under hypoxia

The gastrointestinal epithelium possesses adaptation mechanisms to cope with huge variations in blood flow and subsequently oxygenation. Since sufficient energy supply is crucial under hypoxic conditions, glucose uptake especially must be regulated by these adaptation mechanisms. Therefore, we investigated glucose transport under hypoxic conditions. Jejunal epithelia of rabbits were incubated in Ussing chambers under short-circuit current conditions. Hypoxia was simulated by gassing with 1% O₂ instead of 100% O₂. The activity of sodium-coupled glucose transporter-1 (SGLT-1) was assessed by measuring the increase of short circuit current ( I_sc) after the addition of 2 mM glucose to the mucosal buffer solution. We observed decreased activity of SGLT-1 after hypoxia compared with control conditions. To investigate underlying mechanisms, epithelia were exposed to agonists and antagonists of AMP-activated protein kinase (AMPK) before assessment of SGLT-1-mediated transport and the pAMPK/AMPK protein ratio. Preincubation with the antagonist restored SGLT-1 activity under hypoxic conditions to the level of control conditions, indicating an involvement of AMPK in the downregulation of SGLT-1 activity under hypoxia, which was confirmed in Western blot analysis of pAMPK/AMPK. Transepithelial flux studies using radioactively labeled glucose, ortho-methyl-glucose, fructose, and mannitol revealed no changes after hypoxic incubation. Therefore, we could exclude a decreased transepithelial glucose transport rate and increased paracellular conductance under hypoxia. In conclusion, our study hints at a decreased activity of SGLT-1 under hypoxic conditions in an AMPK-dependent manner. However, transepithelial transport of glucose is maintained. Therefore, we suggest other transport mechanisms, especially glucose transporter 1 and/or 2 to substitute SGLT-1 under hypoxia. NEW & NOTEWORTHY To our knowledge, this is the first approach to simulate hypoxia and study its effects in the jejunal epithelium using the Ussing chamber technique. We were able show that AMPK plays a role in the downregulation of SGLT-1 and that there seems to be an upregulation of other glucose transport mechanisms in the apical membrane of lagomorph jejunum epithelium under hypoxia, securing the epithelial energy supply and thus integrity.

A multicomponent nutrient bar promotes weight loss and improves dyslipidemia and insulin resistance in the overweight/obese: chronic inflammation blunts these improvements

This study determined if twice-daily consumption of a nutrient-dense bar intended to fill gaps in Western diets, without other dietary/lifestyle requirements, favorably shifted metabolic/anthropometric indicators of dysregulation in a healthy direction. Three 8-wk clinical trials in 43 healthy lean and overweight/obese (OW/OB) adults, who served as their own controls, were pooled for analysis. In less inflamed OW/OB [high-sensitivity C-reactive protein (hsCRP) <1.5], statistically significant decreases occurred in weight (-1.1 ± 0.5 kg), waist circumference (-3.1 ± 1.4 cm), diastolic blood pressure (-4.1 ± 1.6 mmHg), heart rate [HR; -4.0 ± 1.7 beats per minute (bpm)], triglycerides (-72 ± 38.2 mg/dl), insulin resistance (homeostatic model of insulin resistance) (-0.72 ± 0.3), and insulin (-2.8 ± 1.3 mU/L); an increase in HDL-2b (+303 ± 116 nM) and realignment of LDL lipid subfractions toward a less atherogenic profile [decreased small LDL IIIb (-44 ± 23.5 nM), LDL IIIa (-99 ± 43.7 nM), and increased large LDL I (+66 ± 28.0 nM)]. In the more inflamed OW/OB (hsCRP >1.5), inflammation was reduced at 2 wk (-0.66 mg/L), and HR at 8 wk (-3.4 ± 1.3 bpm). The large HDL subfraction (10.5-14.5 nm) increased at 8 wk (+346 ± 126 nM). Metabolic improvements were also observed in lean participants. Thus, favorable changes in measures of cardiovascular health, insulin resistance, inflammation, and obesity were initiated within 8 wk in the OW/OB by replacing deficiencies in Western diets without requiring other dietary or lifestyle modifications; chronic inflammation blunted most improvements.

Short bowel syndrome in infants: the critical role of luminal nutrients in a management program

Short bowel syndrome develops when the remnant mass of functioning enterocytes following massive resections cannot support growth or maintain fluid–electrolyte balance and requires parenteral nutrition. Resection itself stimulates the intestine’s inherent ability to adapt morphologically and functionally. The capacity to change is very much related to the high turnover rate of enterocytes and is mediated by several signals; these signals are mediated in large part by enteral nutrition. Early initiation of enteral feeding, close clinical monitoring, and ongoing assessment of intestinal adaptation are key to the prevention of irreversible intestinal failure. The length of the functional small bowel remnant is the most important variable affecting outcome. The major objective of intestinal rehabilitation programs is to achieve early oral nutritional autonomy while maintaining normal growth and nutrition status and minimizing total parenteral nutrition related comorbidities such as chronic progressive liver disease. Remarkable progress has been made in terms of survivability and quality of life, especially in the context of coordinated multidisciplinary programs, but much work remains to be done.

Comparative aspects of tissue glutamine and proline metabolism

The cellular metabolism of glutamine and proline are closely interrelated, because they can be interconverted with glutamate and ornithine via the mitochondrial pathway involving pyrroline-5-carboxylate (P5C). In adults, glutamine and proline are converted via P5C to citrulline in the gut, then citrulline is converted to arginine in the kidney. In neonates, arginine is a semiindispensable amino acid and is synthesized from proline completely in the gut; because of low P5C synthase activity, glutamine is not an important precursor for neonatal arginine synthesis. Thus, splanchnic metabolism of glutamine and proline is important, because both amino acids serve as key precursors for arginine synthesis with some developmental differences. Studies investigating splanchnic extraction demonstrate that about two-thirds of dietary glutamine and almost all dietary glutamate are extracted on first pass and the vast majority is oxidized in the gut. This capacity to extract glutamine and glutamate appears to be very large, so diets high in glutamine or glutamate probably have little impact on circulating concentrations and consequent potential toxicity. In contrast, it appears that very little proline is extracted by the gut and liver, at least in the neonate, which may result in hyperprolinemia and potential toxicity. Therefore, the upper limits of safe dietary intake for glutamine and proline, and other amino acids, appear to be substantially different depending on the extent of first-pass splanchnic extraction and irreversible catabolism.

Na+-dependent neutral amino acid transporter ASCT2 is downregulated in seriously traumatized human intestinal epithelial cells

OBJECTIVE

Serious trauma to the body often is associated with changes in protein metabolism in multiple organs and tissues. Clinically, the catabolic response results in a generalized negative nitrogen balance. Nutrition support has been an important component of the care of seriously traumatized patients. However, during states of severe trauma, enterocyte transport function remains unclear. This study aims to quantitate the Na+-dependent neutral amino acid transport and expression of its transporter in traumatically injured Caco-2 cell lines.

MATERIALS AND METHODS

Transport and transporter of Na+-dependent neutral amino acid in Caco-2 cell lines were characterized. Then the cell lines were cultured under hypoxic, nutrient-deprived, and ischemic conditions for 1, 2, 4, and 6 hours. After severe trauma was performed, we investigated the transport of Na+-dependent neutral amino acids and the expression of transporter protein and mRNA in apical membrane vesicles.

RESULTS

Among the neutral amino acid transporters, only ASCT2 mRNA was amplified successfully. Under nutrient-deprived and ischemic conditions, transport of L-alanine and L-glutamine decreased significantly compared with control (P < 0.01), whereas hypoxia had no significant effect. The changes were associated with a decrease in maximum transport velocity without an influence on transport affinity. Expression of relative transporter proteins and mRNA decreased significantly compared with control (P < 0.01).

CONCLUSIONS

Na+-dependent neutral amino acid transport and its key transporter are differently regulated during state of traumatic injury. It may be of use to provide some strategies targeting the special nutrient requirements and transport capabilities of seriously traumatized patients.

Cloning of a pig homologue of the human lactoferrin receptor: expression and localization during intestinal maturation in piglets

The presence of a small intestinal lactoferrin receptor (SI-LfR) has been suggested in the pig, but remains to be identified. LfR has been suggested to play a key role in the internalization of lactoferrin (Lf) and to facilitate absorption of iron bound to Lf. The aim of this study was to identify the pig SI-LfR cDNA, determine its mRNA and protein expression during different stages of intestinal development. The coding region of the pig LfR cDNA was cloned by PCR using conserved sequences among species. LfR mRNA expression and protein abundance were measured in proximal small intestine from piglets at 1 week (pre-weaning), 3 weeks (weaning) and 6 months (post-weaning) of age by quantitative real-time PCR (Q-PCR) and Western blot, respectively. Intestinal brush border membrane vesicles (BBMV) were also isolated to examine LfR abundance on the apical membrane. We determined the pig SI-LfR open reading frame (ORF) consists of 972 bp, resulting in a protein with a molecular mass approximately 135 kD and approximately 35 kD under non-reducing and reducing conditions, respectively. Using Q-PCR, we determined LfR expression significantly increased with age in the duodenum and reciprocally decreased in the jejunum. Intestinal LfR protein expression was maintained at all timepoints in the jejunum; however, in the duodenum LfR abundance reached maximum levels at 6 months. In BBMV fractions, LfR abundance significantly increased with age. Taken together our findings demonstrate the presence of a human SI-LfR homologue in pig, with mRNA and protein expression concomitantly regulated in the duodenum and inversely regulated in the jejunum. These findings suggest a mechanism by which pig Lf can be internalized in the intestine.

Experimental small bowel preservation using Polysol: A new alternative to University of Wisconsin solution, Celsior and histidine-tryptophan-ketoglutarate solution?

AIM: To evaluate the potential of Polysol, a newly developed preservation solution, in cold storage of small bowel grafts, compared with the current standards, University of Wisconsin solution (UW), Celsior and histidine-tryptophan-ketoglutarate solution (HTK).

METHODS: Male Wistar rats were used as donors. Small bowels were retrieved, flushed and then stored in the respective 4 solutions for 18 h at 4°C. Functional integrity of the grafts was evaluated by isolated reperfusion with oxygenated Krebs-Henseleit buffer at 37°C for 30 min in all 4 groups.

RESULTS: Polysol preservation exhibited the highest tissue ATP concentration and the lowest release of LDH. Malondialdehyde, an index for tissue lipid peroxidation, was also the lowest in Polysol. Tissue oxygen consumption was significantly higher in Polysol than in the others. Of interest, UW-storage promoted 10-fold higher apoptosis than in the others. Moreover, electron microscopy revealed that the mucosal villi/micro-villi formation and the cell organelles, including mitochondria, were both significantly better preserved in Polysol, while deleterious alterations were apparent in the others, most notably in UW. Although Celsior and HTK exhibited the better trend of results than UW in some parameters, but could not reach the over-all superiority to UW.

CONCLUSION: Cold storage using Polysol resulted in significantly better integrity and function of small bowel grafts than UW. Hence, Polysol may be a novel alternative for the small bowel preservation.

Glutamine transporter ASCT2 was down-regulated in ischemic injured human intestinal epithelial cells and reversed by epidermal growth factor

BACKGROUND

Clinically, nutrition support has been an important component of the care of the hypoperfusion traumatized patient who is unable to accept complete volitional nutrition. However, enterocyte transport function during states of intestinal hypoperfusion remains unclear. Glutamine is essential for the viability and growth of intestine epithelial cells, and the Na(+)-dependent neutral amino acid transporter ASCT2 is thought to mainly mediate glutamine transport. This study aims to quantify the change of glutamine transporter ASCT2 expression in ischemic injured Caco-2 cell lines and the regulatory action of epidermal growth factor (EGF) on glutamine transport and its transporter.

METHODS

Cells were cultured under ischemic conditions for 2 hours. After ischemia was performed, Caco-2 cells were incubated with or without EGF (100 microg/mL) for 0-8 hours. Then we studied the cell membrane l-glutamine transport, the expression of ASCT2 protein, and mRNA.

RESULTS

After ischemia was performed, Caco-2 cell membrane glutamine transport decreased significantly (p < .01), and the expression of ASCT2 proteins decreased significantly compared with control (p < .01). Under ischemic conditions, expression of ASCT2 mRNA was down-regulated by a real-time polymerase chain reaction (PCR) method. After EGF incubation for 1-2 hours, the proteins and mRNA of ASCT2 were reversed to normal levels (p > .05).

CONCLUSIONS

In ischemic injured Caco-2 cells, ASCT2 protein expression and mRNA transcription were involved in the down-regulation of Na(+)-dependent glutamine transport. The decrease of glutamine transport and its transporter under ischemic conditions could be reversed by EGF action. These findings may help in the choice of the nutrition support manner and clinical therapy of ischemia-damaged intestinal epithelial cells.

Glutamine: do the data support the cause for glutamine supplementation in humans?

This review examines the preclinical rationale for using glutamine supplements and reviews the prospective randomized trials using glutamine to improve outcomes in patients. A special role for glutamine in gut physiology and in management of a variety of serious illnesses has been suggested, because it is the most abundant extracellular amino acid, and is used at high rates by the gut, liver, central nervous system, and immune cells. A state of relative Gln deficiency has been postulated in humans based on the decrease in plasma Gln in acute critical illness, but the decrease in plasma Gln is not specific for that amino acid, predicts only poorer outcome, and has not been validated to identify a deficiency state. Current evidence does not necessarily predict a special need or role for Gln in critical illness. Clinical efficacy of supplemental Gln has been difficult to demonstrate, possibly related to the lack of a Gln deficiency state, the wide range of end points used that reflect the lack of certainty of the predicted effect of supplementation, the heterogeneous patient populations studied, the lack of stable clinical course during the study, the lack of adequate power, and the relatively short follow-up period. Prospective randomized clinical trials of Gln supplementation were reviewed in patients with short-bowel syndrome, during cancer chemotherapy and in bone marrow transplantation, and in surgical, burn, and intensive care unit patients. No firm recommendation can be made at this time. Future studies should seek to develop a more standard and stable design for intervention in sufficiently powered studies.

Short time L-glutamine supplementation of malnourished rats

OBJETIVE: Considering that in malnourished patients supplemented with L-glutamine the negativity of the nitrogen balance tends to decrease, the present study aimed to determine whether malnourished Wistar rats supplemented with L-glutamine would show lower urinary nitrogen excretion, a greater deposition of nitrogen content in different tissues, and/or an alteration in the plasma amino acid levels. METHODS: The rats were divided into groups: 1) protein-energy malnutrition, 2) protein malnutrition and 3) normally nourished group. The urinary and tissue nitrogen contents were determined by the Kjeldahl method and plasma amino acids by liquid chromatography. RESULTS: Weight, urinary and tissue nitrogen accumulation were significantly reduced in the group with protein-energy malnutrition, but did not improve with L-glutamine supplementation supplied for a short time. The plasma amino acid concentrations showed no special pattern with L-glutamine supplementation. CONCLUSION: It was concluded that it was not possible to detect any positive effect of L-glutamine supplementation on the tissue and urinary nitrogen metabolism in malnourished rats.

Atrofia mucosa/translocação bacteriana na sepse experimental em ratos Wistar

OBJETIVO: Avalizar a relação entre lesão mucosa e translocação bacteriana. MÉTODO: Utilizou-se 50 ratos distribuídos em 5 grupos: 1.Controle: injeção de inóculo padrão de Pseudomonas aeruginosa, 2.Dreno: injeção do inóculo padrão e drenagem da cavidade abdominal, após 6 horas, 3.Lavado: injeção do inóculo padrão e lavagem da cavidade abdominal, após 6 horas, 4.Lavado + dreno: injeção do inóculo padrão e após 6 horas, drenagem e lavagem da cavidade, 5.Normal: avaliação histológica da parede intestinal normal. Após o óbito, realizou-se hemocultura e cultura peritoneal. Realizou-se medida da espessura total da parede do jejuno e da camada mucosa em vilosidades seccionadas de forma longitudinal. RESULTADOS: Na hemocultura, houve crescimento de Pseudomonas aeruginosa e Escherichia coli em 90% e 52,5% dos animais. Na cultura peritoneal, houve crescimento de P. aeruginosa, E. coli e Klebsiella sp em 87,5%, 85% e 5% dos animais. Quanto a altura da camada mucosa e da parede intestinal, não houve alteração estatisticamente significativa entre os 5 grupos. CONCLUSÃO: A sepse aguda não causou alteração na camada mucosa do intestino delgado e a translocação ocorrida não pode ser considerada como decorrente de uma lesão da mucosa intestinal.

Alterações da mucosa intestinal em ratos: estudo morfométrico em três diferentes tratamentos após indução experimental de sepse abdominal aguda

OBJETIVO: Verificar as possíveis alterações morfológicas da parede intestinal provocadas pela contaminação de uma monocultura bacteriana na cavidade abdominal de ratos, após tratamento por drenagem, lavagem e a combinação destes dois processos. MÉTODOS: Foram utilizados 50 ratos fêmeas da linhagem Wistar, foram distribuídos em 5 subgrupos: grupo Controle (C) - recebeu um inóculo padrão com 1,2.10(9) de Pseudomonas aeruginosa, intraperitonial, sem nenhum tipo de tratamento; grupo Dreno (D) - inóculo padrão e realizada a drenagem da cavidade abdominal; grupo Lavado (L) - inóculo e realizada a lavagem da cavidade abdominal com solução salina; grupo L+D - inóculo e submetido aos dois tipos de tratamentos; grupo Normal (N) sem nenhum tipo de inoculação ou tratamento. Realizou-se a análise morfométrica das lâminas coradas por H.E da mucosa intestinal e hemocultura. RESULTADOS: Não houve diferenças estatisticamente significantes na espessura da mucosa intestinal entre os 5 subgrupos de ratos analisados no período de 24 horas após a injeção do inóculo. 37 animais que receberam o inóculo evoluíram para o óbtito entre 5,83 e 28 horas, com 2 animais do grupo L sobrevivendo por um período de 28 horas. CONCLUSÃO: A sepse aguda não causou alterações morfológicas mensuráveis através desta metodologia na parede intestinal.

The nutritional management of gastrointestinal tract disorders in companion animals

Dietary protein, carbohydrates, fats and fibre have marked influences on gastrointestinal tract function and dysfunction. This article reviews the nutritional management of common gastrointestinal disorders in companion animals and introduces some of the current areas of research including probiotics, prebiotics, protein-hydrolysate diets, immunonutrition and dietary fibre. Nutritional management of oesophageal disease revolves around varying the consistency of the diet and feeding the animal from an elevated container. Provision of bowel rest remains the mainstay of the management of acute gastroenteritis but food-based oral rehydration solutions are a useful adjunct. The recommended diet for chronic small bowel diarrhoea is a highly digestible, hypoallergenic, gluten-free, low-lactose and low-fat diet with modest amounts of fermentable fibre. The use of probiotics in the management of diarrhoea in companion animals has not yet been shown to be beneficial. It is likely that prebiotics will prove more effective than probiotics in the prevention of enteropathogenic infections. Approximately 50% of cats in New Zealand that suffer from chronic idiopathic vomiting or diarrhoea will respond to a novel-protein-elimination diet and approximately 30% meet the diagnostic criteria for food sensitivity. Growing evidence supports the use of protein-hydrolysate diets in the management of inflammatory bowel disease and further advances in immunonutrition are expected. The dietary management of colitis should include a hypoallergenic diet with a fermentable fibre source. Manipulation of the diet provides clinicians a powerful therapeutic strategy to be used alone or concurrently with drug therapy in the management of gastrointestinal disorders.

Immune-enhancing diets for stressed patients with a special emphasis on arginine content: analysis of the analysis

PURPOSE OF REVIEW

After two decades of intensive research, whether arginine-enriched diets for oral/enteral administration are beneficial or harmful for stressed patients remains uncertain. An American consensus and a meta-analysis provide divergent conclusions. The main goal of the present review is to analyze these documents.

RECENT FINDINGS

The so-called immune-enhancing diets have been found to be beneficial to postoperative patients. Nothing proves, however, that arginine is responsible for these beneficial effects since immune-enhancing diets contain other pharmacologically active components (e.g. omega3 free fatty acids, RNAs, antioxidant vitamins). In fact, arginine-enriched diets may be harmful in hemodynamically unstable patients and those presenting with multiple organ failure.

SUMMARY

In light of the current doubts and until convincing data are produced, immune-enhancing diets should not be used in unstable critically ill patients.

Enteral feeding and gut atrophy

PURPOSE OF REVIEW

Because of the hypothesis that enteral feeding prevents intestinal mucosal atrophy and bacterial translocation, when fasting or malnutrition is present, nutrition support by the enteral route is usually preferred, if it is available. If nutrients are provided only parenterally intestinal mucosal mass falls dramatically in rats, but the relevance of this finding to humans has not been documented. This article reviews findings in the last 2 years relating to this dilemma.

RECENT FINDINGS

Most work continues to be done in rats and pigs, two species that demonstrate mucosal atrophy with fasting. The earlier demonstration of effects of administration of hormones and glutamine have been corroborated, but proper controls for hormones (related peptides) or glutamine (most importantly glutamate) have usually not been included. In humans mucosal atrophy does not occur except modestly (approximately 10% decrease in thickness) in some reports during catabolic conditions, such as in critical-care units. Even so, no evidence for reversal by enteral feeding has as yet been provided. On the other hand, evidence for specific gene adaptation with or without mucosal atrophy has begun to appear in animals and humans.

SUMMARY

The focus on mucosal atrophy has obscured the adaptation that may occur simultaneously to minimize the atrophy. Attention to gene adaptation during fasting and malnutrition may provide evidence, in future, for appropriate therapeutic interventions.