Prevention of mucosal atrophy: role of glutamine and caspases in apoptosis in intestinal epithelial cells

Nutritional strategies to reduce intestinal cell apoptosis by alleviating oxidative stress

The gut barrier is the first line of defense against harmful substances and pathogens in the intestinal tract. The balance of proliferation and apoptosis of intestinal epithelial cells (IECs) is crucial for maintaining the integrity of the intestinal mucosa and its function. However, oxidative stress and inflammation can cause DNA damage and abnormal apoptosis of the IECs, leading to the disruption of the intestinal epithelial barrier. This, in turn, can directly or indirectly cause various acute and chronic intestinal diseases. In recent years, there has been a growing understanding of the vital role of dietary ingredients in gut health. Studies have shown that certain amino acids, fibers, vitamins, and polyphenols in the diet can protect IECs from excessive apoptosis caused by oxidative stress, and limit intestinal inflammation. This review aims to describe the molecular mechanism of apoptosis and its relationship with intestinal function, and to discuss the modulation of IECs' physiological function, the intestinal epithelial barrier, and gut health by various nutrients. The findings of this review may provide a theoretical basis for the use of nutritional interventions in clinical intestinal disease research and animal production, ultimately leading to improved human and animal intestinal health.

Dietary Glutamine Inclusion Regulates Immune and Antioxidant System, as Well as Programmed Cell Death in Fish to Protect against Flavobacterium columnare Infection

The susceptibility of animals to pathogenic infection is significantly affected by nutritional status. The present study took yellow catfish (Pelteobagrus fulvidraco) as a model to test the hypothesis that the protective roles of glutamine during bacterial infection are largely related to its regulation on the immune and antioxidant system, apoptosis and autophagy. Dietary glutamine supplementation significantly improved fish growth performance and feed utilization. After a challenge with Flavobacterium columnare, glutamine supplementation promoted il-8 and il-1β expression via NF-κB signaling in the head kidney and spleen, but inhibited the over-inflammation in the gut and gills. Additionally, dietary glutamine inclusion also enhanced the systematic antioxidant capacity. Histological analysis showed the protective role of glutamine in gill structures. Further study indicated that glutamine alleviated apoptosis during bacterial infection, along with the reduced protein levels of caspase-3 and the reduced expression of apoptosis-related genes. Moreover, glutamine also showed an inhibitory role in autophagy which was due to the increased activation of the mTOR signaling pathway. Thus, our study for the first time illustrated the regulatory roles of glutamine in the fish immune and antioxidant system, and reported its inhibitory effects on fish apoptosis and autophagy during bacterial infection.

Impacts of increasing challenge with Eimeria maxima on the growth performance and gene expression of biomarkers associated with intestinal integrity and nutrient transporters

This study was conducted to investigate the impacts of graded severity of Eimeria maxima infection on the growth performance and intestine health of broiler chickens. Four different levels of E. maxima-challenged treatments were used, including a non-challenged control group, a low challenge (12 500 oocysts), a medium challenge (25 000 oocysts), and a high challenge dose (50 000 oocysts). There were eight replicate cages per treatment, with 12 birds in each cage, and chickens in the challenged groups orally received sporulated oocysts on day 14. Gastrointestinal permeability was measured by fluorescein isothiocyanate dextran at 5 days post-infection (dpi), whereas intestinal morphology and gene expression of nutrient transporters and tight junction proteins were determined at 6 dpi. The results demonstrate a linear reduction in growth performance, jejunal villus height, and jejunal integrity with graded challenge doses of E. maxima (P < 0.01). Moreover, linear regulation of nutrient transporters and tight junction proteins was a consequence of increasing Eimeria infection levels (P < 0.01). The linear increase of Claudin 1, cationic amino acid transporter, glucose transporter 1, and L-type amino acid transporter genes was associated with increased severity of coccidiosis (P < 0.01). Furthermore, expression of nutrient transporters located at the brush border membrane were down-regulated (P < 0.01) with increasing E. maxima inoculation dose. In conclusion, growth performance and key intestinal integrity biomarkers in broiler chickens were adversely influenced in a dose-dependent manner by E. maxima infection.

Glutaminolysis Epigenetically Regulates Antiapoptotic Gene Expression in Idiopathic Pulmonary Fibrosis Fibroblasts

Fibrotic responses involve multiple cellular processes, including epigenetic changes. Epigenetic changes are sensitive to alterations in the tissue microenvironment such as the flux of tricarboxylic acid (TCA) cycle metabolites. TCA metabolites directly regulate epigenetic states, in part by regulating histone modification-related enzymes. Glutaminolysis is a critical metabolic process by which glutamine is converted to glutamate by glutaminase and then to α-ketoglutarate (α-KG), a TCA cycle metabolite. Idiopathic pulmonary fibrosis (IPF) is a disease characterized by aberrant metabolism, including enhanced glutaminolysis. IPF fibroblasts are apoptosis resistant. In this study, we explored the relationship between glutaminolysis and the resistance to apoptosis of IPF fibroblasts. Inhibition of glutaminolysis decreased expression of XIAP and survivin, members of the inhibitor of apoptosis protein (IAP) family. α-KG is a cofactor for JMJD3 histone demethylase, which targets H3K27me3. In the absence of glutamine, JMJD3 activity in fibroblasts is significantly decreased, whereas H3K27me3 levels are increased. Chromatin immunoprecipitation assays confirmed that JMJD3 directly interacts with XIAP and survivin promoter regions in a glutamine-dependent manner. Exogenous α-KG partially restores JMJD3 function and its interaction with the XIAP and survivin promoter regions under glutamine-deficient conditions. Interestingly, α-KG upregulates XIAP, but not survivin, suggesting differential α-KG-dependent and -independent mechanisms by which glutamine regulates these IAPs. Our data demonstrate a novel mechanism of metabolic regulation in which glutaminolysis promotes apoptosis resistance of IPF fibroblasts through epigenetic regulation of XIAP and survivin.

l-Glutamine Attenuates Apoptosis in Porcine Enterocytes by Regulating Glutathione-Related Redox Homeostasis

Background

Programmed cell death plays a fundamental role in intestinal development and mucosal homeostasis. Dysregulation of these processes is associated with an impaired intestinal-mucosal barrier, reduced nutrient absorption, and initiation and progression of intestinal diseases. 4-Hydroxy-2-nonenal (4-HNE), a product of lipid peroxidation, is commonly used to induce oxidative stress in cells. l-Glutamine is known to protect cells from apoptosis. However, the underlying mechanisms are largely unknown.

Objective

This study was conducted to test the hypothesis that l-glutamine attenuates 4-HNE-induced apoptosis by modulating glutathione (GSH) and thioredoxin (TXN) antioxidant systems and the expression of genes involved in 4-HNE metabolism in enterocytes.

Methods

Intestinal porcine epithelial cell line 1 (IPEC-1) cells were cultured with or without 4-HNE (30 μmol/L) in the presence of 0.05 or 0.25 mmol l-glutamine/L (a physiological concentration in the lumen of the small intestine) for indicated time periods. Cell viability, abundances of apoptotic proteins, mitochondrial membrane depolarization, production of reactive oxygen species (ROS) and GSH, and expression of genes involved in the biosynthesis of GSH, thioredoxin, and 4-HNE metabolism were determined.

Results

Compared with basal medium containing 0.05 mmol l-glutamine/L, 4-HNE enhanced apoptosis by 19.6% (P < 0.05) in a caspase-3-dependent manner. This effect was accompanied by elevated intracellular ROS production (39.5% and 85.3% for 2- and 4-h treatment, respectively), increased mitochondrial depolarization by 80%, and decreased intracellular GSH concentrations by 17.7%. These effects of 4-HNE were reduced by 0.25 mmol l-glutamine/L. Further study showed that the protective effect of l-glutamine was associated with the enhanced expression of genes involved in GSH production (including GCLC, GCLM, GSR, CBS, and CTH) by 3.9-14-fold, as well as genes involved in 4-HNE metabolism [e.g., glutathione S-transferase A (GSTA)1 and GSTA4] by 1.9-7.2-fold. The mRNA levels for ADH5, AKR1C1, AKR1A1, and TXNRD1 were enhanced 1.4-8.8-fold by 4-HNE but were not changed in cells co-treated with 4-HNE and l-glutamine.

Conclusion

These findings indicate that l-glutamine attenuates 4-HNE-induced apoptosis by regulating GSH-related redox homeostasis and enhancing GSTA-mediated metabolism in enterocytes.

Glutamine metabolism in advanced age

Glutamine, reviewed extensively in the last century, is a key substrate for the splanchnic bed in the whole body and is a nutrient of particular interest in gastrointestinal research. A marked decrease in the plasma glutamine concentration has recently been observed in neonates and adults during acute illness and stress. Although some studies in newborns have shown parenteral and enteral supplementation with glutamine to be of benefit (by decreasing proteolysis and activating the immune system), clinical trials have not demonstrated prolonged advantages such as reductions in mortality or risk of infections in adults. In addition, glutamine is not able to combat the muscle wasting associated with disease or age-related sarcopenia. Oral glutamine supplementation initiated before advanced age in rats increases gut mass and improves the villus height of mucosa, thereby preventing the gut atrophy encountered in advanced age. Enterocytes from very old rats continuously metabolize glutamine into citrulline, which allowed, for the first time, the use of citrulline as a noninvasive marker of intestinal atrophy induced by advanced age.

Alanyl-glutamine attenuates 5-fluorouracil-induced intestinal mucositis in apolipoprotein E-deficient mice

Apolipoprotein E (APOE=gene, apoE=protein) is a known factor regulating the inflammatory response that may have regenerative effects during tissue recovery from injury. We investigated whether apoE deficiency reduces the healing effect of alanyl-glutamine (Ala-Gln) treatment, a recognized gut-trophic nutrient, during tissue recovery after 5-FU-induced intestinal mucositis. APOE-knockout (APOE-/-) and wild-type (APOE+/+) C57BL6J male and female mice (N=86) were given either Ala-Gln (100 mM) or phosphate buffered saline (PBS) by gavage 3 days before and 5 days after a 5-fluorouracil (5-FU) challenge (450 mg/kg, via intraperitoneal injection). Mouse body weight was monitored daily. The 5-FU cytotoxic effect was evaluated by leukometry. Intestinal villus height, villus/crypt ratio, and villin expression were monitored to assess recovery of the intestinal absorptive surface area. Crypt length, mitotic, apoptotic, and necrotic crypt indexes, and quantitative real-time PCR for insulin-like growth factor-1 (IGF-1) and B-cell lymphoma 2 (Bcl-2) intestinal mRNA transcripts were used to evaluate intestinal epithelial cell turnover. 5-FU challenge caused significant weight loss and leukopenia (P<0.001) in both mouse strains, which was not improved by Ala-Gln. Villus blunting, crypt hyperplasia, and reduced villus/crypt ratio (P<0.05) were found in all 5-FU-challenged mice but not in PBS controls. Ala-Gln improved villus/crypt ratio, crypt length and mitotic index in all challenged mice, compared with PBS controls. Ala-Gln improved villus height only in APOE-/- mice. Crypt cell apoptosis and necrotic scores were increased in all mice challenged by 5-FU, compared with untreated controls. Those scores were significantly lower in Ala-Gln-treated APOE+/+ mice than in controls. Bcl-2 and IGF-1 mRNA transcripts were reduced only in the APOE-/- -challenged mice. Altogether our findings suggest APOE-independent Ala-Gln regenerative effects after 5-FU challenge.

Control of late apoptotic events by the p38 stress kinase in L-glutamine-deprived mouse hybridoma cells

L-Glutamine (Gln) starvation rapidly triggers apoptosis in Sp2/0-Ag14 (Sp2/0) murine hybridoma cells. Here, we report on the role played by the stress-activated kinase p38 mitogen-activated protein kinase (MAPK) in this process. p38 activation was detected 2 h after Gln withdrawal and, although treatment with the p38 inhibitor SB203580 did not prevent caspase activation in Gln-starved cells, it reduced the occurrence of both nuclear condensation/fragmentation and apoptotic body formation. Similarly, transfection of Sp2/0 cells with a dominant negative p38 MAPK reduced the incidence of nuclear pyknosis and apoptotic body formation following 2 h of Gln starvation. Gln withdrawal-induced apoptosis was blocked by the overexpression of the anti-apoptotic protein Bcl-xL or by the caspase inhibitor Z-VAD-fmk. Interestingly, Bcl-xL expression inhibited p38 activation, but Z-VAD-fmk treatment did not, indicating that activation of this MAPK occurs downstream of mitochondrial dysfunction and is independent of caspases. Moreover, the anti-oxidant N-acetyl-l-cysteine prevented p38 phosphorylation, showing that p38 activation is triggered by an oxidative stress. Altogether, our findings indicate that p38 MAPK does not contribute to the induction of apoptosis in Gln-starved Sp2/0 cells. Rather, Gln withdrawal leads to mitochondrial dysfunction, causing an oxidative stress and p38 activation, the latter contributing to the formation of late morphological features of apoptotic Sp2/0 cells.

Glutamine supplementation in sick children: is it beneficial?

The purpose of this review is to provide a critical appraisal of the literature on Glutamine (Gln) supplementation in various conditions or illnesses that affect children, from neonates to adolescents. First, a general overview of the proposed mechanisms for the beneficial effects of Gln is provided, and subsequently clinical studies are discussed. Despite safety, studies are conflicting, partly due to different effects of enteral and parenteral Gln supplementation. Further insufficient evidence is available on the benefits of Gln supplementation in pediatric patients. This includes premature infants, infants with gastrointestinal disease, children with Crohn's disease, short bowel syndrome, malnutrition/diarrhea, cancer, severe burns/trauma, Duchenne muscular dystrophy, sickle cell anemia, cystic fibrosis, and type 1 diabetes. Moreover, methodological issues have been noted in some studies. Further mechanistic data is needed along with large randomized controlled trials in select populations of sick children, who may eventually benefit from supplemental Gln.

Alanyl-glutamine promotes intestinal epithelial cell homeostasis in vitro and in a murine model of weanling undernutrition

Alanyl-glutamine (Ala-Gln) has recently been shown to enhance catch-up growth and gut integrity in undernourished children from Northeast Brazil. We hypothesized that the intestinal epithelial effects of Ala-Gln in malnourished weanling mice and mouse small intestinal epithelial (MSIE) cells would include modulation of barrier function, proliferation, and apoptosis. Dams of 10-day-old suckling C57BL/6 pups were randomized to a standard diet or an isocaloric Northeast Brazil "regional basic diet," moderately deficient in protein, fat, and minerals. Upon weaning to their dam's diet on day of life 21, pups were randomized to Ala-Gln solution or water. At 6 wk of age, mice were killed, and jejunal tissue was collected for morphology, immunohistochemistry, and Ussing chamber analysis of transmucosal resistance and permeability. Proliferation of MSIE cells in the presence or absence of Ala-Gln was measured by MTS and bromodeoxyuridine assays. MSIE apoptosis was assessed by annexin and 7-amino-actinomycin D staining. Pups of regional basic diet-fed dams exhibited failure to thrive. Jejunal specimens from undernourished weanlings showed decreased villous height and crypt depth, decreased transmucosal resistance, increased permeability to FITC-dextran, increased claudin-3 expression, and decreased epithelial proliferation and increased epithelial apoptosis (as measured by bromodeoxyuridine and cleaved caspase-3 staining, respectively). Undernourished weanlings supplemented with Ala-Gln showed improvements in weight velocity, villous height, crypt depth, transmucosal resistance, and epithelial proliferation/apoptosis compared with unsupplemented controls. Similarly, Ala-Gln increased proliferation and reduced apoptosis in MSIE cells. In summary, Ala-Gln promotes intestinal epithelial homeostasis in a mouse model of malnutrition-associated enteropathy, mimicking key features of the human disease.

Nutrition modulation of gastrointestinal toxicity related to cancer chemotherapy: from preclinical findings to clinical strategy

Chemotherapy-induced gut toxicity is a major dose-limiting toxicity for many anticancer drugs. Gastrointestinal (GI) complications compromise the efficacy of chemotherapy, promote overall malnutrition, aggravate cancer cachexia, and may contribute to worsened prognosis. The GI tract is an attractive target for nutrition modulation, owing to its direct exposure to the diet, participation in uptake and metabolism of nutrients, high rate of cell turnover, and plasticity to nutrition stimuli. Glutamine, ω-3 polyunsaturated fatty acids, and probiotics/prebiotics are therapeutic factors that potentially modulate GI toxicity related to cancer treatments. Preclinical and clinical evidence are reviewed to critically define plausible benefits of these factors and their potential development into adjuncts to cancer chemotherapy. Mechanisms underlying the action of these nutrients are being unraveled in the laboratory. Optimal strategies to translate these findings into clinical care still remain to be elucidated. Key questions that remain to be answered include the following: which nutrient or combination of nutrients is selected for which patient and chemotherapy regimen? What mechanisms are responsible for modulation, and how are nutrient(s) administered in a clinically optimal manner? Research exploring interactions between different nutrients in GI protection is ongoing and demands further understanding. How nutrition preparations given to chemotherapy-treated patients are formulated in terms of component selection and dose optimization should be carefully studied and justified.

Glutamine protects against apoptosis via downregulation of Sp3 in intestinal epithelial cells

Glutamine plays a key role in intestinal growth and maintenance of gut function, and as we have shown protects the postischemic gut (Kozar RA, Scultz SG, Bick RJ, Poindexter BJ, Desoigne R, Weisbrodt NW, Haber MM, Moore FA. Shock 21: 433-437, 2004). However, the precise mechanisms of the gut protective effects of glutamine have not been well elucidated. In the present study, RNA microarray was performed to obtain differentially expressed genes in intestinal epithelial IEC-6 cells following either 2 mM or 10 mM glutamine. The result demonstrated that specificity protein 3 (Sp3) mRNA expression was downregulated 3.1-fold. PCR and Western blot confirmed that Sp3 expression was decreased by glutamine in a time- and dose-dependent fashion. To investigate the role of Sp3, Sp3 gene siRNA silencing was performed and apoptosis was assessed. Silencing of Sp3 demonstrated a significant increase in Bcl-2 and decrease in Bax protein expression, as well as a decrease in caspase-3, -8, and -9 protein expression and activity. The protein expression of apoptosis-related proteins after hypoxia/reoxygenation was similar to that of normoxia and correlated with a decrease in DNA fragmentation. Importantly, the addition of glutamine to Sp3-silenced cells did not further lessen apoptosis, suggesting that Sp3 plays a major role in the inhibitory effect of glutamine on apoptosis. This novel finding may explain in part the gut-protective effects of glutamine.

Dissemination of invasive Salmonella via bacterial-induced extrusion of mucosal epithelia

Salmonella enterica is an intracellular bacterial pathogen that resides and proliferates within a membrane-bound vacuole in epithelial cells of the gut and gallbladder. Although essential to disease, how Salmonella escapes from its intracellular niche and spreads to secondary cells within the same host, or to a new host, is not known. Here, we demonstrate that a subpopulation of Salmonella hyperreplicating in the cytosol of epithelial cells serves as a reservoir for dissemination. These bacteria are transcriptionally distinct from intravacuolar Salmonella. They are induced for the invasion-associated type III secretion system and possess flagella; hence, they are primed for invasion. Epithelial cells laden with these cytosolic bacteria are extruded out of the monolayer, releasing invasion-primed and -competent Salmonella into the lumen. This extrusion mechanism is morphologically similar to the process of cell shedding required for turnover of the intestinal epithelium. In contrast to the homeostatic mechanism, however, bacterial-induced extrusion is accompanied by an inflammatory cell death characterized by caspase-1 activation and the apical release of IL-18, an important cytokine regulator of gut inflammation. Although epithelial extrusion is obviously beneficial to Salmonella for completion of its life cycle, it also provides a mechanistic explanation for the mucosal inflammation that is triggered during Salmonella infection of the gastrointestinal and biliary tracts.

Proximal gut mucosal epithelial homeostasis in aged IL-1 type I receptor knockout mice after starvation

BACKGROUND

Previous studies have shown that starvation induces small bowel atrophy, and that atrophy diminishes with aging. In this experiment, we assessed whether starvation-induced atrophy of proximal gut mucosa is associated with the Interleukin-1 receptor (IL-1R) signaling pathway in aged mice.

MATERIALS AND METHODS

Thirty 26-month-old IL-1R knockout mice and age-matched wild-type C57BL/6 mice were randomly divided into two groups: ad libitum fed and fasted. Mice were euthanized 12 or 48 hours after starvation. The proximal small bowel was harvested for morphologic analysis. Gut epithelial cell proliferation was detected using immunohistochemical staining for proliferating cell nuclear antigen (PCNA), and apoptosis was identified using terminal deoxyuridine nick-end labeling (TUNEL) staining.

RESULTS

Aged IL-1R knockout mice were larger than aged-matched wild-type mice (P < 0.05). Proximal gut mucosal height and mucosal cell number were not different between aged IL-1R knockout and wild-type groups. The apoptosis index in gut epithelial cells was higher in fed IL-1R knockout versus wild-type mice (P < 0.05), while there was no significant difference in cell proliferation between both groups. Mucosal atrophy was induced in both aged IL-1R knockout and wild-type groups by starvation (P < 0.05), however, aged IL-1R knockout mice experienced greater loss in proximal gut weight, mucosal length, and corresponding cell number than did wild-type mice at the 12-h time point (P < 0.05). The apoptosis index in gut epithelial cells significantly increased in both groups after starvation (P < 0.05). Starvation decreased cell proliferation in IL-1R knockout mice (P < 0.05), but not in wild-type mice.

CONCLUSIONS

The response in aged IL-1R knockout mice differs from wild-type mice in that starvation increases atrophy and is associated with decreased cell proliferation rather than increased apoptosis.

Amino acid regulation of mammalian gene expression in the intestine

Some amino acids exert a wide range of regulatory effects on gene expression via the activation of different signalling pathways and transcription factors, and a number of cis elements were shown to respond to changes in amino acid concentration. Particular attention has been paid to the effects of glutamine and arginine, which modulate a number of cell functions through the activation of various pathways in different tissues. In the intestine, appropriate concentrations of both arginine and/or glutamine contribute to facilitate cell proliferation, to limit the inflammatory response and apoptosis, and to modulate intermediary metabolism through specific transcription factors. Particularly, besides its role as a major fuel for enterocytes, the regulatory effects of glutamine have been extensively studied and the molecular mechanisms involved appear diversified and complex. Indeed, in addition to a major role of NF-kappaB in its anti-inflammatory action and a stimulatory role of AP-1 in its growth-promoting action and cell survival, the involvement of some other transcription factors, such as PPAR-gamma or HSF-1, was shown to maintain intestinal cell integrity. The signalling pathways leading to the activation of transcription factors imply several kinases, particularly MAP kinases in the effect of glutamine and p70 S6 kinase for those of arginine, but in most cases the precise pathways from the entrance of the aminoacid into the cell to the activation of gene transcription has remained elusive.

A 700 MHz1H-NMR study reveals apoptosis-like behavior in human K562 erythroleukemic cells exposed to a 50 Hz sinusoidal magnetic field

PURPOSE

To study cell damage and possible apoptosis in K562 human erythroleukemic cells exposed for 2 h to an extremely low frequency (ELF) 50 Hz sinusoidal magnetic field with a magnetic induction of either 1 or 5 mT using high resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy.

MATERIALS AND METHODS

One-dimensional 1H-NMR spectra were obtained on whole K562 cells and perchloric acid extracts of these cells. In addition, two-dimensional 1H-NMR spectra were also acquired. Cell damage was examined by lactate dehydrogenase release and changes in cell growth were monitored by growth curve analyses, bromodeoxyuridine incorporation and Ki67 antigen localization. Cell death (necrosis and apoptosis) were also studied by using the chromatin dye Hoechst 33258.

RESULTS

The variations in numerous metabolites observed with 1H-NMR reveal apoptosis-like behavior in response of K562 cells to ELF fields.

CONCLUSION

1H-NMR can be extremely useful in studying the effects of ELF fields on cells. In particular, the variations in metabolites which suggest apoptosis-like behavior occur when the cells are not identifiable as apoptotic by more traditional techniques.

Control of mammalian gene expression by amino acids, especially glutamine

Molecular data rapidly accumulating on the regulation of gene expression by amino acids in mammalian cells highlight the large variety of mechanisms that are involved. Transcription factors, such as the basic-leucine zipper factors, activating transcription factors and CCAAT/enhancer-binding protein, as well as specific regulatory sequences, such as amino acid response element and nutrient-sensing response element, have been shown to mediate the inhibitory effect of some amino acids. Moreover, amino acids exert a wide range of effects via the activation of different signalling pathways and various transcription factors, and a number of cis elements distinct from amino acid response element/nutrient-sensing response element sequences were shown to respond to changes in amino acid concentration. Particular attention has been paid to the effects of glutamine, the most abundant amino acid, which at appropriate concentrations enhances a great number of cell functions via the activation of various transcription factors. The glutamine-responsive genes and the transcription factors involved correspond tightly to the specific effects of the amino acid in the inflammatory response, cell proliferation, differentiation and survival, and metabolic functions. Indeed, in addition to the major role played by nuclear factor-kappaB in the anti-inflammatory action of glutamine, the stimulatory role of activating protein-1 and the inhibitory role of C/EBP homology binding protein in growth-promotion, and the role of c-myc in cell survival, many other transcription factors are also involved in the action of glutamine to regulate apoptosis and intermediary metabolism in different cell types and tissues. The signalling pathways leading to the activation of transcription factors suggest that several kinases are involved, particularly mitogen-activated protein kinases. In most cases, however, the precise pathways from the entrance of the amino acid into the cell to the activation of gene transcription remain elusive.

Glutamine, arginine, and leucine signaling in the intestine

Glutamine and leucine are abundant constituents of plant and animal proteins, whereas the content of arginine in foods and physiological fluids varies greatly. Besides their role in protein synthesis, these three amino acids individually activate signaling pathway to promote protein synthesis and possibly inhibit autophagy-mediated protein degradation in intestinal epithelial cells. In addition, glutamine and arginine stimulate the mitogen-activated protein kinase and mammalian target of rapamycin (mTOR)/p70 (s6) kinase pathways, respectively, to enhance mucosal cell migration and restitution. Moreover, through the nitric oxide-dependent cGMP signaling cascade, arginine regulates multiple physiological events in the intestine that are beneficial for cell homeostasis and survival. Available evidence from both in vitro and in vivo animal studies shows that glutamine and arginine promote cell proliferation and exert differential cytoprotective effects in response to nutrient deprivation, oxidative injury, stress, and immunological challenge. Additionally, when nitric oxide is available, leucine increases the migration of intestinal cells. Therefore, through cellular signaling mechanisms, arginine, glutamine, and leucine play crucial roles in intestinal growth, integrity, and function.

Starvation-induced proximal gut mucosal atrophy diminished with aging

BACKGROUND

Starvation induces small bowel atrophy with increased intestinal epithelial apoptosis and decreased proliferation. The authors examined these parameters after starvation in aged animals.

METHODS

Sixty-four 6-week-old and 26-month-old C57BL/6 mice were randomly assigned to either an ad libitum fed or fasted group. The small bowel was harvested at 12, 48, and 72 hours following starvation. Proximal gut mucosal height was measured and epithelial cells counted. Apoptosis was identified by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Proliferation was determined by immunohistochemical staining for proliferating cell nuclear antigen. Comparison of fed vs fasted and adult vs old groups was done by one-way ANOVA with Tukey's test and unpaired Student's t test. Significance was accepted at P < .05.

RESULTS

Aged mice had higher proximal gut weights, mucosal heights, and cell numbers at baseline compared with the adult group (P < .05). The rate of apoptosis was lower in the aged (P < .05), but proliferation was not different between groups before starvation. After starvation, proximal gut wet weight decreased only in adult mice (P < .05). Gut mucosal height and mucosal cell number decreased more in adult than in aged mice (P < .05). This was related to decreased proliferation only in the adult group (P < .05). The fold of epithelial apoptosis that increased was higher in the aged group than in the adult group after starvation (P < .05).

CONCLUSIONS

Gut mucosal kinetics change with age and have lower rates of apoptosis and greater mucosal mass; the character of starvation-induced atrophy is diminished with aging.

Alanyl-glutamine and glutamine supplementation improves 5-fluorouracil-induced intestinal epithelium damage in vitro

In this study, we have examined the role of glutamine derivatives in reducing 5-fluorouracil (5-FU)-induced epithelial damage in an undifferentiated crypt intestinal cell line, IEC-6. In this model, we have investigated proliferation indirectly by detecting the enzyme-derived formazan dye from the tetrazolium salt WST-1 in viable cells at 24 and 48 h after 5-FU treatment. Migration was measured at 12 and 24 h after razor scraping of the cell monolayer. Cell death was measured by quantifying the percentage of apoptotic and necrotic figures by flow cytometry at 12 and 24 h following 5-FU challenge. Neither glutamine nor alanyl-glutamine prevented 5-FU-induced apoptosis and necrosis in IEC-6 cells at 12 and 24 h after 5-FU challenge. However, glutamine and alanyl-glutamine enhanced migration and proliferation when compared with 5-FU-treated controls (P < 0.05). These new findings support our earlier study on the benefit of oral glutamine in enhancing epithelial recovery after 5-FU challenge.

Intracellular redox status and oxidative stress: implications for cell proliferation, apoptosis, and carcinogenesis

Oxidative stress can be defined as the imbalance between cellular oxidant species production and antioxidant capability. Reactive oxygen species (ROS) are involved in a variety of different cellular processes ranging from apoptosis and necrosis to cell proliferation and carcinogenesis. In fact, molecular events, such as induction of cell proliferation, decreased apoptosis, and oxidative DNA damage have been proposed to be critically involved in carcinogenesis. Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular reactions. ROS can modify many intracellular signaling pathways including protein phosphatases, protein kinases, and transcription factors, suggesting that the majority of the effects of ROS are through their actions on signaling pathways rather than via non-specific damage of macromolecules; however, exact mechanisms by which redox status induces cells to proliferate or to die, and how oxidative stress can lead to processes evoking tumor formation are still under investigation.

Molecular mechanisms contributing to glutamine-mediated intestinal cell survival

Glutamine, the most abundant amino acid in the bloodstream, is the preferred fuel source for enterocytes and plays a vital role in the maintenance of mucosal growth. The molecular mechanisms regulating the effects of glutamine on intestinal cell growth and survival are poorly understood. Here, we show that addition of glutamine (1 mmol/l) enhanced rat intestinal epithelial (RIE)-1 cell growth; conversely, glutamine deprivation increased apoptosis as noted by increased DNA fragmentation and caspase-3 activity. To delineate signaling pathways involved in the effects of glutamine on intestinal cells, we assessed activation of extracellular signal-related kinase (ERK), protein kinase D (PKD), and phosphatidylinositol 3-kinase (PI3K)/Akt, which are important pathways in cell growth and survival. Addition of glutamine activated ERK and PKD in RIE-1 cells after a period of glutamine starvation; inhibition of ERK, but not PKD, increased cell apoptosis. Conversely, glutamine starvation alone increased phosphorylated Akt; inhibition of Akt enhanced RIE-1 cell DNA fragmentation. The role of ERK was further delineated using RIE-1 cells stably transfected with an inducible Ras. Apoptosis was significantly increased following ERK inhibition, despite Ras activation. Taken together, these results identify a critical role for the ERK signaling pathways in glutamine-mediated intestinal homeostasis. Furthermore, activation of PI3K/Akt during periods of glutamine deprivation likely occurs as a protective mechanism to limit apoptosis associated with cellular stress. Importantly, our findings provide novel mechanistic insights into the antiapoptotic effects of glutamine in the intestine.

Influence of glutamine on intestinal inflammatory response, mucosa structure alterations and apoptosis following traumatic brain injury in rats

Traumatic brain injury (TBI) can induce a persistent inflammatory response, histopathological changes and apoptosis in the intestine. Glutamine has been shown to reduce bacterial translocation and maintain intestine mucosal integrity, but its effects on the inflammatory response, structural alterations and apoptosis in intestinal mucosa following TBI have not been previously investigated. Using the weight-drop method, a right parietal cortical contusion was induced in rats and, for the next 5 days, they were fed either chow alone or chow mixed with glutamine. Intestinal tissue samples were then removed for analysis. Following TBI, glutamine supplementation was found to: decrease intestinal concentrations of interleukin (IL) -1beta, tumour necrosis factor-alpha (TNF-alpha) and IL-6; downregulate intercellular adhesion molecule-1 (ICAM-1) expression; attenuate TBI-induced damage to the intestine structure; and reduce apoptosis. These results suggest that post-TBI glutamine administration could suppress intestinal inflammation, protect intestinal mucosal structure and reduce mucosal apoptosis.

Glutamine Regulates the Human Epithelial Intestinal HCT-8 Cell Proteome under Apoptotic Conditions

Glutamine plays a key role in the metabolism of rapidly dividing cells, including enterocytes and lymphocytes, which may contribute to its beneficial clinical effects. Gut mucosal homeostasis is achieved through a balance between cell proliferation and apoptosis. In T cells, glutamine up-regulates antiapoptotic proteins and down-regulates proapoptotic proteins. In gut mucosa, glutamine prevents apoptosis in rat epithelial cell lines, whereas glutamine starvation induces apoptosis through caspase activation. Finally glutamine specifically prevents tumor necrosis factor-alpha-related apoptosis in the human intestinal cell line HT-29. Comparative functional proteomics enables the characterization of each differentially expressed protein in intestinal cells in response to modifications of nutritional environment. The influence of glutamine on intestinal proteome expression in apoptotic conditions has not been studied and evaluated. This comparative proteomics study was performed in the human epithelial intestinal cell line HCT-8 under experimental apoptotic conditions to investigate the influence of glutamine on protein expression during apoptosis. The pharmaconutritional effects of glutamine were determined under 2 mm (physiological concentration) and 10 mm (pharmaconutritional concentration) conditions. About 1,800 protein spots were revealed in both conditions. Comparative assessments indicated that 28 proteins were differentially expressed significantly (i.e. at least 2-fold modulated and Student's t test with p </= 0.05) in response to an increase of glutamine concentration in the culture medium. Twenty-four proteins were identified by mass spectrometry and associated databases. From these proteins, 34% are involved in cell cycle and apoptosis mechanisms, 17% are involved in signal transduction, and 13% are involved in cytoskeleton organization. These data were integrated in a proposed schema of the interactome under apoptotic conditions. In conclusion, this study provides the first holistic picture of proteome modulation by glutamine in a human enterocytic cell line under apoptotic conditions and supports further evaluation of nutritional modulation of human intestinal proteome in various pathological conditions where apoptosis may be involved.

Identification of apoptotic genes mediating TGF-beta/Smad3-induced cell death in intestinal epithelial cells using a genomic approach

Transforming growth factor (TGF)-beta-dependent apoptosis is important in the elimination of damaged or abnormal cells from normal tissues in vivo. Previously, we have shown that TGF-beta inhibits the growth of rat intestinal epithelial (RIE)-1 cells. However, RIE-1 cells are relatively resistant to TGF-beta-induced apoptosis due to a low endogenous Smad3-to-Akt ratio. Overexpression of Smad3 sensitizes RIE-1 cells (RIE-1/Smad3) to TGF-beta-induced apoptosis by altering the Smad3-to-Akt ratio in favor of apoptosis. In this study, we utilized a genomic approach to identify potential downstream target genes that are regulated by TGF-beta/Smad3. Total RNA samples were analyzed using Affymetrix oligonucleotide microarrays. We found that TGF-beta regulated 518 probe sets corresponding to its target genes. Interestingly, among the known apoptotic genes included in the microarray analyses, only caspase-3 was induced, which was confirmed by real-time RT-PCR. Furthermore, TGF-beta activated caspase-3 through protein cleavage. Upstream of caspase-3, TGF-beta induced mitochondrial depolarization, cytochrome c release, and cleavage of caspase-9, which suggests that the intrinsic apoptotic pathway mediates TGF-beta-induced apoptosis in RIE-1/Smad3 cells.

Temporal Dynamics of1H-NMR-Visible Metabolites during Radiation-Induced Apoptosis in MG-63 Human Osteosarcoma Spheroids

The metabolic changes that occur as a function of time in MG-63 osteosarcoma three-dimensional tumor spheroids undergoing radiation-induced apoptosis were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of MG-63 spheroids collected at 24, 48 and 72 h after exposure to 5 Gy of ionizing radiation were compared to the spectra of their respective controls. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. Apoptosis was verified by both staining of spheroid DNA with the Hoechst 33258 dye and determination of caspase 3 enzyme activity at the three times examined. The results demonstrate that, as the percentage of apoptosis rises with time after exposure to ionizing radiation, the metabolic changes that take place in MG-63 spheroids follow very precise temporal dynamics. In particular, significant time-related increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis, were observed. In addition, temporal variations were also observed in choline-containing metabolites, reduced glutathione (GSH), glutamine/glutamate, taurine, alanine, creatine/phosphocreatine and lactate. These data show that in addition to CH(2) and CH(3) lipids, other metabolites can also be extremely useful in a deeper understanding of the temporal dynamics of radiation-induced apoptosis. This comprehension is particularly important in spheroids, a cell model of great complexity that resembles in vivo tumors much more closely than monolayer cultures. Ultimately, it is hoped that such studies can help to evaluate the outcome of radiotherapy protocols more accurately.

Effects of enteral glutamine supplement on endotoxin translocation and mucosal immune barrier in starved rats

AIM: To investigate the changes in intestinal structure and function as well as the effect of enteral glutamine (GLN) supplement on the endotoxin translocation and immunological function in starved rats.

METHODS: Ninety male Sprague Dawley rats were randomly divided into 3 groups: normal control group (n = 10), starved group (group A, n = 40) and GLN group (group B, n = 40). The rats were sacrificed 3, 5, 7 and 9 d after starvation, respectively. Blood samples were collected from portal vein for the detection of plasma endotoxin and tissue samples removed from ileocecum were observed under light microscope for morphological changes. A contrasting study on the expression of secretary immunoglobulin A (sIgA) and the numbers of CD4⁺, CD8⁺ T lymphocytes were also performed between control group and other groups by immunohistochemical staining method.

RESULTS: The atrophy of intestinal mucosa and villa were observed 3 d after starvation in group A, with the degeneration, necrosis, and shedding of partial mucosal epithelial cells. The changes were gradually deteriorated till the 9^th day after starvation. Those pathological changes were lighter in group B than those in group A on the 3^rd day after starvation and restored to normal on the 5^th day. As the starvation time prolonged, the atrophy, degeneration and necrosis of the mucosal epithelial cells appeared again in group B, but were still lighter than those in group A. The levels of endotoxin were significantly higher 3, 5, 7 and 9 d after starvation in both group A and B than those in the controls, and there were also marked differences between group B and A (322.4 ± 65.1, 389.4 ± 32.6, 464.4 ± 76.6, 413.7 ± 67.2 EU/L vs 527.1 ± 74.9, 546.3 ± 65.7, 623.9 ± 85.9, 587.5 ± 140.8 EU/L, all P < 0.01). The expression of sIgA and the numbers CD4⁺ and CD8⁺ T lymphocytes in intestinal mucosa were reduced significantly in group A and B, in compared with those in the controls (P < 0.05 or P < 0.01), and there were higher levels of sIgA and CD4⁺ and CD8⁺ T lymphocytes in group B than those in group A (P < 0.01).

CONCLUSION: The structure of intestinal mucosa is damaged in the earlier stage of starvation in rats, accompanied by endotoxin translocation and dysfunction of intestinal mucosal immune barrier. Early enteral nourishment of glutamine is helpful for inhibiting endotoxin translocation and improve immune function of intestinal mucosa.

Glutamine regulates the expression of proteins with a potential health-promoting effect in human intestinal Caco-2 cells

Glutamine is an essential amino acid for the enterocytes with respect to maintaining the gut mucosal integrity and function. This study was conducted to explore a molecular basis for the beneficial effects of glutamine on intestinal cells by searching for glutamine-dependent changes in the proteome. Caco-2 cells were exposed to different concentrations of L-glutamine with or without L-methionine sulfoximine, an inhibitor of the glutamine synthetase activity. 2-DE combined with MALDI-TOF-MS was used to identify proteins whose expression is changed by glutamine. To assess the relative protein synthesis rate, incorporation of L-[2H5]glutamine into individual proteins was monitored. The expression levels of 14 proteins changed significantly with the glutamine availability. Examples of differentially expressed proteins with potential health-promoting effects on the intestine are plasma retinol-binding protein, ornithine aminotransferase, apolipoprotein A-I, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, and acyl-CoA synthetase 5. Expression of these proteins was not changed by arginine deprivation. The differential change in the expression levels of the proteins was not correlated with their rate of synthesis, excluding an effect of glutamine depletion on general protein synthesis. Together, this study shows a gene-specific effect of glutamine on intestinal cells.

Increases in 1H-NMR mobile lipids are not always associated with overt apoptosis: evidence from MG-63 human osteosarcoma three-dimensional spheroids exposed to a low dose (2 Gy) of ionizing radiation

The metabolic changes that occur in MG-63 osteosarcoma three-dimensional tumor spheroids exposed to 2 Gy of ionizing radiation, a dose that is comparable to radiation therapy, were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of control and exposed MG-63 spheroids were compared. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. The spectra of whole MG-63 spheroids as well as the perchloric acid extracts of these systems were evaluated. Cell damage was also examined by lactate dehydrogenase release and changes in cell growth. No cell damage was observed, but numerous metabolic changes took place in spheroids after exposure to ionizing radiation. In particular, significant increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis and also present in MG-63 spheroids undergoing overt apoptosis, were observed in spheroids irradiated with 2 Gy. However, the chromatin dye Hoechst 33258 and DNA fragmentation assays showed no overt apoptosis up to 7 days after irradiation with this low dose. Thus it is evident that increases in mobile lipids do not always indicate actual cell death. A detailed analysis of the other metabolic changes observed appears to suggest that the cell death program was initiated but not completed. In fact, the completely different behavior of two important cellular defense mechanisms, reduced glutathione and taurine, in spheroids irradiated with 2 Gy and in those undergoing overt apoptosis seems to indicate that these systems are protecting spheroids from actual cell death. In addition, these data also suggest that (1)H-NMR can be used to examine the effects of low doses of ionizing radiation in spheroids, a cell model of great complexity that closely resembles tumors in vivo. The importance of this possibility in relation to reaching the ultimate goal of a better evaluation of the outcome of radiotherapy protocols should not be ignored.

Intestinal mucositis: the role of the Bcl-2 family, p53 and caspases in chemotherapy-induced damage

Intestinal mucositis occurs as a consequence of cytotoxic treatment through multiple mechanisms including induction of crypt cell death (apoptosis) and cytostasis. The molecular control of these actions throughout the gastrointestinal tract has yet to be fully elucidated; however, they are known to involve p53, the Bcl-2 family and caspases. This review will provide an overview of current research as well as identify areas where gaps in knowledge exist.

Oxidative stress is not required for the induction of apoptosis upon glutamine starvation of Sp2/0-Ag14 hybridoma cells

L-glutamine (Gln) withdrawal rapidly triggers apoptosis in the murine hybridoma cell line Sp2/0-Ag14 (Sp2/0). In this report, we examined the possibility that Gln deprivation of Sp2/0 cells triggers an oxidative stress which would contribute to the activation of apoptotic pathways. Gln withdrawal triggered an oxidative stress in Sp2/0 cells, as indicated by an increased accumulation of reactive oxygen species (ROS) and an increase in the intracellular content in protein carbonyl groups. Gln starvation also caused a decrease in the intracellular levels of glutathione (GSH). However, a decrease in GSH was not sufficient to induce Sp2/0 cell death since reducing GSH levels with DL-buthionine-[S,R]-sulfoximine did not affect cell viability. The antioxidant N-acetyl-L-cysteine (NAC), while effective in inhibiting ROS accumulation and oxidative stress, did not prevent the loss in cell viability or the processing and activation of caspase-3 triggered by Gln starvation. On the other hand, NAC did reduce the formation of apoptotic bodies in dying cells. Altogether these results indicate that in Sp2/0 cells, Gln deprivation leads to the induction of an oxidative stress which, while involved in the formation of apoptotic bodies, is not essential to the activation of the cell death program.

Stressing out over survival: glutamine as an apoptotic modulator

INTRODUCTION

The amino acid glutamine (GLN) has received considerable attention as a potential therapeutic adjuvant in critical illness and in improving postoperative clinical outcomes. Most studies on the role of GLN in cellular physiology have historically focused on its anabolic roles in specific cell types and its contribution to growth in cancer cells. However, an emerging body of work that examines the consequences of GLN deprivation on cellular survival and gene expression has constructed a new paradigm for this amino acid, namely, that limited extracellular GLN supplies modulate stress and apoptotic responses.

METHODS

A survey of the scientific literature was conducted on GLN in cell survival signaling and apoptosis. Work from our laboratory in liver cancer cells also was included in this review.

RESULTS

Most studies on this topic have used mammalian cell lines derived from the gut, immune system (including hybridomas), and various cancers. GLN limitation, even in the presence of an adequate glucose supply, impacts stress-related gene expression, differentially modulates receptor-mediated apoptosis, and directly elicits apoptosis through signaling mechanisms and caspase cascades that are specific to cell type. To date, GLN transporters, cellular hydration, glutaminyl-tRNA synthetase, ATP levels, mRNA stability, and glutathione economy have been variably implicated in GLN-dependent survival signaling.

CONCLUSION

The cell type-specific mechanisms underlying the regulatory role of GLN in cell survival continue to unfold at a steady pace through in vitro studies. These results have collectively provided testable hypotheses for further in vivo studies into their physiological relevance during GLN "nutritional pharmacology."

Glutamine inhibits cytokine-induced apoptosis in human colonic epithelial cells via the pyrimidine pathway

Glutamine (Gln) prevents apoptosis in intestinal epithelial cells, but the mechanism(s) remain unknown. Gln-derived metabolites include ammonia, glutamate (Glu), glutathione (GSH), and nucleotides. We previously showed that Gln potently inhibited apoptosis in cytokine-treated human colonic HT-29 cells; this effect was specific to Gln, unaffected by Glu, and unrelated to intracellular GSH. The current research examines mechanism(s) for Gln-induced antiapoptotic effects in HT-29 cells treated with TNF-alpha-related apoptosis-inducing ligand (TRAIL). Proliferating cells were treated with Gln or selected Gln metabolites for 24 h. Cells were then treated with TRAIL and Gln or its downstream metabolites, and apoptosis was assessed at 8 h after treatment. The purine and pyrimidine precursors inosine and orotate inhibited TRAIL-induced apoptosis. However, inhibition of purine synthesis with azaserine did not alter the potent antiapoptotic effect of Gln. In contrast, the pyrimidine synthesis inhibitor, acivicin, completely prevented this response. Supplementation with the pyrimidine uracil or the pyrimidine precursor orotate rescued the acivicin-induced blockade of Gln antiapoptotic action. Removal of bicarbonate, a substrate for pyrimidine synthesis, also inhibited the antiapoptotic effects of Gln. Uracil and thymine alone also significantly decreased TRAIL-induced apoptosis. The antiapoptotic effects of Gln were independent of DNA/RNA synthesis as measured by flow cytometry and bromodeoxyuridine incorporation. In conclusion, Gln prevents TRAIL-induced apoptosis in HT-29 cells through a mechanism involving the pyrimidine pathway. Our data also demonstrate the novel antiapoptotic effects of pyrimidine bases and their precursor orotate in these human intestinal cells.

Differentiation stage-dependent preferred uptake of basolateral (systemic) glutamine into Caco-2 cells results in its accumulation in proteins with a role in cell-cell interaction

Glutamine is an essential amino acid for enterocytes, especially in states of critical illness and injury. In several studies it has been speculated that the beneficial effects of glutamine are dependent on the route of supply (luminal or systemic). The aim of this study was to investigate the relevance of both routes of glutamine delivery to in vitro intestinal cells and to explore the molecular basis for proposed beneficial glutamine effects: (a) by determining the relative uptake of radiolabelled glutamine in Caco-2 cells; (b) by assessing the effect of glutamine on the proteome of Caco-2 cells using a 2D gel electrophoresis approach; and (c) by examining glutamine incorporation into cellular proteins using a new mass spectrometry-based method with stable isotope labelled glutamine. Results of this study show that exogenous glutamine is taken up by Caco-2 cells from both the apical and the basolateral side. Basolateral uptake consistently exceeds apical uptake and this phenomenon is more pronounced in 5-day-differentiated cells than in 15-day-differentiated cells. No effect of exogenous glutamine supply on the proteome was detected. However, we demonstrated that exogenous glutamine is incorporated into newly synthesized proteins and this occurred at a faster rate from basolateral glutamine, which is in line with the uptake rates. Interestingly, a large number of rapidly labelled proteins is involved in establishing cell-cell interactions. In this respect, our data may point to a molecular basis for observed beneficial effects of glutamine on intestinal cells and support results from studies with critically ill patients where parenteral glutamine supplementation is preferred over luminal supplementation.

Clostridium difficile toxin A induces intestinal epithelial cell apoptosis and damage: role of Gln and Ala-Gln in toxin A effects

The aim of this study was to investigate the effect of Clostridium difficile toxin A (TxA) on intestinal epithelial cell migration, apoptosis, and transepithelial resistance and to evaluate the effect of glutamine (Gln) and its stable derivative, alanyl-glutamine (Ala-Gln), on TxA-induced damage. Migration was measured in rat intestinal epithelial cells (IEC-6) 6 and 24 hr after a razor scrape of the cell monolayer. Cell proliferation was indirectly measured utilizing the tetrazolium salt WST-1. The cells were incubated with TxA (1-100 ng/ml) in medium without Gln or medium containing Gln or Ala-Gln (1-30 mM). Apoptosis was quantified in IEC-6 cells using annexin V assay. Transepithelial resistance was measured using an epithelial voltohmmeter across T84 cells seeded on a transwell filter. TxA-induced a dose-dependent reduction of migration and also caused dose and time-dependent apoptosis in IEC-6 cells. Gln and Aln-Gln significantly enhanced IEC-6 cell migration and proliferation. Gln and Ala-Gln also prevented the inhibition of migration, apoptosis, and the initial drop in transepithelial resistance induced by TxA. In conclusion, both peptides reduced toxin-induced epithelial damage and thus might play an adjunctive role in C. difficile-induced colitis therapy.

Extracellular thiols and thiol/disulfide redox in metabolism

Many proteins present on cell surfaces and located in extracellular fluids contain cysteine and methionine residues that are subject to oxidation. These proteins, which include transporters, receptors, and enzymes, respond to variations in the extracellular thiol/disulfide redox environment. Changes in activity of these proteins can alter the ability of organs to function normally and influence processes such as nutritional absorption, secretory function, neurotransmission, and susceptibility to toxicants. In addition, extracellular redox can regulate tissue homeostasis through effects on cell proliferation, differentiation, apoptosis, and immune function. Consequently, extracellular redox can have important influences on health status and disease states and thus could be a target for nutritional interventions.

Mesna ameliorates intestinal mucosa damage after ifosfamide administration in the rabbit at a dose-Related manner

BACKGROUND

Cancer chemotherapy may lead to mucositis, a serious dose-limiting side effect. The alkylating agent ifosfamide is used in the treatment of various forms of cancer in combination with the uroprotective thiol mesna (2-mercaptoethane-sulfonate). The aims of this study were to assess the dose response intestinal mucosa damage of ifosfamide and to investigate the potential protective effect of mesna on rabbit intestinal epithelium.

MATERIALS AND METHODS

Fifty New Zealand White rabbits were randomly assigned to 10 groups of five animals each and received intravenously every week for 10 weeks either normal saline, ifosfamide, mesna, or ifosfamide plus mesna at three escalating dose levels (ifosfamide: 30, 45, or 60 mg/kg; mesna: 12, 18, or 24 mg/kg divided into two equal doses administered 4 h apart). Intestinal mucosa damage was assessed on the basis of crypt cell apoptosis and proliferation as well as intestinal morphometry. Apoptosis was detected by agarose gel electrophoresis and quantified by the DNA fragmentation assay and a standard terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling (TUNEL) method by which the percentage of fragmented DNA and the apoptotic index were determined, respectively. The mitotic index and the crypt-villus (c/v) unit height were also measured in histological sections.

RESULTS

Ifosfamide caused a dose-related increase of crypt cell apoptosis and shortening of c/v unit, while it had a steady antimitotic effect. Mesna as a sole agent had no apoptotic or trophic effect on intestinal mucosa and hence no effect on intestinal morphometry. However, mesna, when administered concurrently with ifosfamide, ameliorated apoptosis, hypoproliferation, and mucosal atrophy at a dose-related manner.

CONCLUSIONS

Ifosfamide causes intestinal mucosa damage, which may be ameliorated in a dose-related manner by coadministration of mesna.

Dose related effects of ifosfamide on enterocyte apoptosis in different sites of the rabbit intestine

OBJECTIVE

We investigated the potential dose related apoptotic effect of subchronic administration of the alkylating chemotherapeutic agent ifosfamide in different sites of the small and large rabbit intestine.

MATERIALS AND METHODS

Twenty New Zealand White rabbits received intravenously every week, for 10 weeks, 0 (group S, controls, n = 5), 30 (group A, n = 5), 45 (group B, n = 5) or 60 mg/kg ifosfamide (group C, n = 5). One day after the end of the treatment period, segments of jejunum, ileum, cecum, proximal and distal colon were excised. Intestinal mucosa apoptosis was detected by agarose gel electrophoresis and quantified by DNA fragmentation and standard terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-biotin nick-end labelling (TUNEL) assays by which the percentage of fragmented DNA and the ratio of apoptotic cells per crypt (apoptotic index) were determined, respectively.

RESULTS

At low dose (group A), ifosfamide had minor apoptotic effect on enterocytes, which was enhanced mainly in the small intestine when the dose was increased (group B); at the highest dose tested (group C), this effect was extended to the large intestine. In all groups of animals, the observed crypt cell apoptosis was maximal in the ileum, while minimal in the proximal colon.

CONCLUSIONS

Our results show a dose and intestinal site-dependent induction of enterocyte apoptosis after subchronic ifosfamide administration in the rabbit.

Inducible antisense RNA targeting amino acid transporter ATB0/ASCT2 elicits apoptosis in human hepatoma cells

Amino acid transporter B(0)/ASC transporter 2 (ATB(0)/ASCT2) is responsible for most glutamine uptake in human hepatoma cells. Because this transporter is not expressed in normal hepatocytes, we hypothesized that its expression is necessary for growth of human liver cancer cells. To test this hypothesis, Sloan Kettering hepatoma (SK-Hep) cells were stably transfected with an inducible 1.3-kb ATB(0)/ASCT2 antisense RNA expression plasmid under the transcriptional control of mifepristone, a synthetic steroid. Induced antisense RNA expression in monolayer cultures decreased ATB(0)/ASCT2 mRNA levels by 73% and glutamine transport rates by 65% compared with controls after 24 h, leading to a 98% decrease in cell number after 48 h. Cellular death was attributable to apoptosis based on cellular blebbing, caspase-3 activation, vital dye and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, and poly-(ADP-ribose) polymerase (PARP) cleavage. Transporter knockdown also markedly increased activities of caspases-2 and -9, marginally enhanced caspase-8 activity, and dramatically increased ASCT1 mRNA levels, presumably as a futile compensatory response. Apoptosis elicited via transporter silencing was not attributable to the double-stranded RNA-dependent protein kinase R (PKR) pathway. For comparison, glutamine deprivation also caused apoptotic cell death but with slower temporal kinetics, stimulated caspases-2 and -3 but not caspases-8 or -9 activities, and led to considerable PARP cleavage. Thus ASCT2 suppression exerts proapoptotic effects transcending those of glutamine starvation alone. We conclude that ATB(0)/ASCT2 expression is necessary for SK-Hep cell growth and viability and suggest that it be further explored as a selective target for human hepatocellular carcinoma.

Glutamine Prevents Cytokine-Induced Apoptosis in Human Colonic Epithelial Cells

Epithelial cell apoptosis is an important regulator of normal gut mucosal turnover; however, excessive apoptosis may inhibit mucosal restitution during pathophysiologic states. Apoptosis is induced by oxidative stress and cytokines, but regulation by specific nutrients has been infrequently studied under these conditions. Glutamine (Gln) is an important metabolic fuel for intestinal epithelial cells and a precursor to the antioxidant glutathione (GSH), which has antiapoptotic effects. In cultured intestinal epithelial cells, Gln depletion increases oxidant-induced apoptosis. This study examined whether Gln protects against apoptosis induced by the cytokine tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) in the human colon carcinoma cell line, HT-29. TRAIL-induced apoptosis in HT-29 cells was characterized by an increase in the percentage of cells in the sub-G1 fraction by flow cytometry, nuclear condensation and the activation of caspase-8 and caspase-3. TRAIL-induced apoptosis was completely prevented by Gln, but not inhibited by other amino acids, including the GSH constituents, glutamate, cysteine and glycine. Similar antiapoptotic effects of Gln occurred when apoptosis was induced by a combination of tumor necrosis factor-alpha and interferon-gamma. Cellular GSH was oxidized during TRAIL-induced apoptosis. This effect was completely blocked by Gln, however, inhibition of GSH synthesis with buthionine sulfoximine did not alter Gln antiapoptotic effects. Furthermore, glutamate prevented GSH oxidation in response to TRAIL but did not protect against TRAIL-induced apoptosis. These results show that Gln specifically protects intestinal epithelial cells against cytokine-induced apoptosis, and that this occurs by a mechanism that is distinct from the protection against oxidative stress mediated by cellular GSH.

Effects of immunonutrition on intestinal mucosal apoptosis, mucosal atrophy, and bacterial translocation in head injured rats

BACKGROUND

Immunonutrition has been demonstrated to modulate gut function, reduce infectious complications, hospital stay, and ventilator days in the critical patients.

AIM OF THE STUDY

We assessed the effect of immunonutrition for the prevention of intestinal mucosal atrophy, apoptosis, and bacterial translocation in head injured rats.

METHODS

Thirty five rats were randomised into 5 groups. Following moderate closed head injury, in Group 1; Standard Enteral Nutrition, Group 2; Immunonutrition, Group 3; TPN, Group 4; pe. saline were applied. Group 5 was control group (chow-fed). The rats were sacrificed and segments of the ileum were removed for histologic examination, and samples of tissues taken for microbiologic evaluation.

RESULTS

Both intestinal apoptosis and mucosal atrophy were significantly lower in Group 2 and Group 5 (p<0.008). Bacterial translocation was significantly lower in Group 2 than Group 1 (p<0.008).

CONCLUSION

The enteral immunonutrition prevents intestinal barrier function in brain injured rats.

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.

The role of caspases in methotrexate-induced gastrointestinal toxicity

BACKGROUND

Enterocolitis is the major toxicity of methotrexate-based cancer chemotherapy, which limits its clinical applications. Methotrexate induces gut mucosal apoptosis in vivo; however, little is known about the molecular mechanism involved. The effectors of apoptosis include the caspase family of proteases, which are selectively activated in a stimulus-specific and tissue-specific fashion. The aims of this study were (1) to establish an in vitro model of methotrexate-induced gut apoptosis and (2) to determine the role of caspases in methotrexate-induced apoptosis in intestinal epithelial cells.

METHODS

Rat intestinal epithelial cells (RIE-1) were treated with methotrexate in the absence or presence of ZVAD-fluoromethyl ketone, a general caspase inhibitor. Apoptosis was quantified by means of deoxyribonucleic acid (DNA) fragmentation assays and Hoechst nuclear staining. Caspase activation was measured with the use of fluorogenic substrates.

RESULTS

Methotrexate induced apoptosis and decreased cell number in RIE-1 cells. DNA fragmentation was preceded by the sequential activation of caspases 9, 2, and 3, whereas caspases 1 and 8 remained inactive. ZVAD-fluoromethyl ketone inhibited methotrexate-induced caspase activation, DNA fragmentation, and nuclear condensation.

CONCLUSIONS

These results indicate that methotrexate activates specific caspases and induces apoptosis in RIE-1 cells. Furthermore, caspases may play an important role in methotrexate-induced apoptosis in RIE-1 cells and may be potential therapeutic targets to attenuate methotrexate-induced enterocolitis.

Molecular and cellular biology of small-bowel mucosa

Study of the molecular and cellular biology of the small-intestinal mucosa is providing insights into the remarkable properties of this unique tissue. With its structured pattern of cell proliferation, differentiation, and apoptosis, and its ability to adapt following exposure to luminal nutrients or injury from surgery or pathogens, it functions in a regulated but responsive manner. We review recent publications on factors affecting development, gene expression, cell turnover, and adaptation.