Glutamine transporter in crypts compensates for loss of villus absorption in bovine cryptosporidiosis

A New Murine Undernutrition Model Based on Complementary Feeding of Undernourished Children Causes Damage to the Morphofunctional Intestinal Epithelium Barrier

BACKGROUND

Complementary feeding is critical in establishing undernutrition. However, experimental undernourished diets do not represent the amount of nutrients in the complementary diets of undernourished children.

OBJECTIVES

To develop, validate, and evaluate the impact of a new murine model of undernutrition on the intestinal epithelium, based on the complementary diet of undernourished children from 7 countries with low-socioeconomic power belonging to the Malnutrition-Enteric Diseases (MAL-ED) cohort study.

METHODS

We used the difference in the percentage of energy, macronutrients, fiber and zinc in the complementary diet of children without undernutrition compared with stunting (height-for-age Z-score < -2) for the MAL-ED diet formulation. Subsequently, C57BL/6 mice were fed a control diet (AIN-93M diet) or MAL-ED diet for 28 d. Weight was measured daily; body composition was measured every 7 d; lactulose:mannitol ratio (LM) and morphometry were evaluated on days 7 and 28; the cotransport test and analysis of intestinal transporters and tight junctions were performed on day 7.

RESULTS

The MAL-ED diet presented -8.03% energy, -37.46% protein, -24.20% lipid, -10.83% zinc, +5.93% carbohydrate, and +45.17% fiber compared with the control diet. This diet rapidly reduced weight gain and compromised body growth and energy reserves during the chronic period (P < 0.05). In the intestinal epithelial barrier, this diet caused an increase in the LM (P < 0.001) and reduced (P < 0.001) the villous area associated with an increase in FAT/CD36 in the acute period and increased (P < 0.001) mannitol excretion in the chronic period.

CONCLUSIONS

The MAL-ED diet induced undernutrition in mice, resulting in acute damage to the integrity of the intestinal epithelial barrier and a subsequent increase in the intestinal area during the chronic period. This study introduces the first murine model of undernutrition for the complementary feeding phase, based on data from undernourished children in 7 different countries.

Impact of probiotic Limosilactobacillus reuteri DSM 17938 on amino acid metabolism in the healthy newborn mouse

We studied the effect of feeding a single probiotic Limosilactobacillus reuteri DSM 17938 (LR 17938) on the luminal and plasma levels of amino acids and their derivatives in the suckling newborn mouse, using gas chromatography and high-performance liquid chromatography. We found that LR 17938 increased the relative abundance of many amino acids and their derivatives in stool, while it simultaneously significantly reduced the plasma levels of three amino acids (serine, citrulline, and taurine). Many peptides and dipeptides were increased in stool and plasma, notably gamma-glutamyl derivatives of amino acids, following ingestion of the LR 17938. Gamma-glutamyl transformation of amino acids facilitates their absorption. LR 17938 significantly upregulated N-acetylated amino acids, the levels of which could be useful biomarkers in plasma and warrant further investigation. Specific fecal microbiota were associated with higher levels of fecal amino acids and their derivatives. Changes in luminal and circulating levels of amino acid derivatives, polyamines, and tryptophan metabolites may be mechanistically related to probiotic efficacy.

Mechanisms of Regulation of Transporters of Amino Acid Absorption in Inflammatory Bowel Diseases

Intestinal absorption of dietary amino acids/peptides is essential for protein homeostasis, which in turn is crucial for maintaining health as well as restoration of health from significant diseases. Dietary amino acids/peptides are absorbed by unique transporter processes present in the brush border membrane of absorptive villus cells, which line the entire length of the intestine. To date, the only nutrient absorptive system described in the secretory crypt cells in the mammalian intestine is the one that absorbs the amino acid glutamine. Majority of the amino acid transporters are sodium dependent and therefore require basolateral membrane Na-K-ATPase to maintain an efficient transcellular Na gradient for their activity. These transport processes are tightly regulated by various cellular and molecular mechanisms that facilitate their optimal activity during normal physiological processes. Malabsorption of amino acids, recently described in pathophysiological states such as in inflammatory bowel disease (IBD), is undoubtedly responsible for the debilitating symptoms of IBD such as malnutrition, weight loss and ultimately a failure to thrive. Also recently, in vivo models of IBD and in vitro studies have demonstrated that specific immune-inflammatory mediators/pathways regulate specific amino acid transporters. This provides possibilities to derive novel nutrition and immune-based treatment options for conditions such as IBD. © 2020 American Physiological Society. Compr Physiol 10:673-686, 2020.

Dietary L-glutamine supplementation improves growth performance, gut morphology, and serum biochemical indices of broiler chickens during necrotic enteritis challenge

Necrotic enteritis (NE) causes significant economic losses in the broiler chicken industry, especially in birds raised without in-feed antibiotics. L-glutamine (Gln) is an amino acid that may compensate for metabolic losses from infection and improve the intestinal development. This study investigated the effects of dietary Gln (10 g/kg) supplementation on growth performance, intestinal lesions, jejunum morphology, and serum biochemical indices of broiler chickens during NE challenge. The study employed a factorial arrangement of treatments with factors: NE challenge, no or yes; dietary Gln inclusion, 0 g/kg in starter (S), d 0 to 10, grower (G) d 10 to 24, and finisher (F) d 24 to 35; 10 g/kg in S, G, F, or 10 g/kg in S, G only. Each treatment was replicated in 6 floor pens with 17 birds per pen as the experimental unit for performance and 2 birds for other measurements. Challenge significantly reduced bird performance, increased incidence of intestinal lesions, and affected intestinal development and serum biochemical indices. Regardless of challenge, Gln supplementation increased gain (P < 0.05), feed intake (P < 0.05), and decreased FCR (P < 0.05) on d 24. On d 35, Gln improved gain (P < 0.05) and FCR (P < 0.001) whereas withdrawing Gln from finisher tended to diminish the beneficial effect on weight gain but not FCR. Dietary Gln reduced lesion scores in the jejunum (P < 0.01) and ileum (P < 0.01) in challenged birds. On d 16, Gln increased villus height to crypt depth ratio in unchallenged birds (P < 0.05) and reduced crypt depth of challenged birds on d 24 (P < 0.05). Regardless of challenge, supplementation with Gln reduced crypt depth on d 16 (P < 0.05), and increased villus height (P < 0.01) and the villus height to crypt depth ratio (P < 0.001) on d 24. Dietary Gln lowered serum uric acid level regardless of challenge (P < 0.05). The current study indicates that dietary Gln alleviates adverse effects of NE and may be useful in antibiotic-free diets.

The effect of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus challenge on growing pigs II: Intestinal integrity and function

The objective of this study was to determine if intestinal function and integrity is altered due to porcine reproductive and respiratory syndrome (PRRS) virus and porcine epidemic diarrhea (PED) virus infection in growing pigs. Forty-two gilts (16.8 ± 0.6 kg BW), naïve for PRRS and PED, were selected and randomly assigned to 1 of 4 treatments: 1) a control (CON; = 6), 2) PRRS virus challenge only (PRRS; = 12), 3) PED virus challenge only (; = 12), or 4) coinfection of PRRS + PED viruses (PRP; = 12). Treatments 2 and 4 were inoculated with a live field strain of PRRS virus on d 0 after inoculation. Treatments 3 and 4 were inoculated with PED virus on 14 d after inoculation (dpi) and all pigs were euthanized 7 d later (21 dpi). Infection with PRRS virus was determined by viremia and seroconversion. Fecal quantitative PCR was used to confirm PED virus infection. Control pigs remained PRRS and PED virus negative throughout the study. Compared with the CON, intestinal morphology was unaffected by PRRS. As expected, PED and PRP treatments resulted in duodenum, jejunum, and ileum villus atrophy compared with the CON treatment ( < 0.01). Ex vivo transepithelial electrical resistance (TER) did not differ between CON and PRRS pigs (P < 0.05) but was reduced by 40% in PED alone ( < 0.01). Interestingly, TER was increased ( < 0.01) in the PRP pigs. Active transport of glucose was increased in PRRS pigs over CON pigs ( < 0.01), whereas PED had pigs increased ( < 0.01) active glutamine transport over the CON pigs. Jejunum GLUT2 mRNA abundance and sucrase, maltase, and Na+/K+ adenosine triphosphatase activities tended to be increased in PRRS pigs compared with CON pigs ( < 0.06). The jejunum AA transporter, SLC6A14, and mucin 2 mRNA abundance tended to be increased in PED-only pigs ( < 0.10). These data suggest that PRRS infection supports a higher affinity for glucose uptake, whereas PED favors glutamine uptake. Interestingly, digestive machinery during PED challenge remained intact. Altogether, PED but not PRRS challenges alter intestinal morphology and integrity in growing pigs.

Cryptosporidium Priming Is More Effective than Vaccine for Protection against Cryptosporidiosis in a Murine Protein Malnutrition Model

Cryptosporidium is a major cause of severe diarrhea, especially in malnourished children. Using a murine model of C. parvum oocyst challenge that recapitulates clinical features of severe cryptosporidiosis during malnutrition, we interrogated the effect of protein malnutrition (PM) on primary and secondary responses to C. parvum challenge, and tested the differential ability of mucosal priming strategies to overcome the PM-induced susceptibility. We determined that while PM fundamentally alters systemic and mucosal primary immune responses to Cryptosporidium, priming with C. parvum (10⁶ oocysts) provides robust protective immunity against re-challenge despite ongoing PM. C. parvum priming restores mucosal Th1-type effectors (CD3⁺CD8⁺CD103⁺ T-cells) and cytokines (IFNγ, and IL12p40) that otherwise decrease with ongoing PM. Vaccination strategies with Cryptosporidium antigens expressed in the S. Typhi vector 908htr, however, do not enhance Th1-type responses to C. parvum challenge during PM, even though vaccination strongly boosts immunity in challenged fully nourished hosts. Remote non-specific exposures to the attenuated S. Typhi vector alone or the TLR9 agonist CpG ODN-1668 can partially attenuate C. parvum severity during PM, but neither as effectively as viable C. parvum priming. We conclude that although PM interferes with basal and vaccine-boosted immune responses to C. parvum, sustained reductions in disease severity are possible through mucosal activators of host defenses, and specifically C. parvum priming can elicit impressively robust Th1-type protective immunity despite ongoing protein malnutrition. These findings add insight into potential correlates of Cryptosporidium immunity and future vaccine strategies in malnourished children.

Cryptosporidium attributable morbidities in malnourished children are increasingly recognized. Exactly how malnutrition interferes with host mucosal immunity to diarrheal pathogens and mucosal vaccine responses remains unclear. Dissecting these interactions in an experimental model of cryptosporidiosis can uncover new insights into novel therapeutic approaches against a pathogen for which effective therapies and vaccines are currently unavailable. We demonstrate that although malnutrition diminishes baseline (primary) Th1-type mucosal immunity these deficits can be partially overcome via non-specific mucosal strategies (S. Typhi and CpG) and completely restored after a sub-clinical (low-dose) exposure to viable C. parvum. These results add insight into preventive strategies to help alleviate Cryptosporidium-specific diarrhea in children in low-resource settings and abrogate prolonged post-infection sequelae.

Inducible nitric oxide regulates intestinal glutamine assimilation during chronic intestinal inflammation

To facilitate assimilation of glutamine, different Na-dependent glutamine absorptive pathways are present in the rabbit small intestine, specifically B0AT1 in villus and SN2 in crypt cell brush border membrane. Further, both are uniquely regulated in the chronically inflamed intestine. B0AT1 is inhibited secondary to reduced number of brush border membrane (BBM) co-transporters while SN2 is stimulated secondary to an increased affinity for glutamine. These unique changes are reversible by treatment with a broad spectrum immune modulator such as glucocorticoids. However, whether inducible nitric oxide (iNO), known to be elevated in the mucosa of the chronically inflamed intestine, may be responsible for these co-transporter alterations is not known. In the present study, treatment of chronically inflamed rabbits with L-NIL, a selective inhibitor of iNO synthase, reversed the inhibition of B0AT1 in villus and the stimulation of SN2 in crypt cells. At the level of the co-transporter in the brush border membrane, inhibition of iNO production reversed the inhibition of villus B0AT1 by restoring the co-transporter numbers while the stimulation of crypt SN2 was reversed back to normal by restoring its affinity for glutamine. Western blot analyses of BBM proteins also confirmed the kinetic studies. Thus, L-NIL treatment restores the uniquely altered Na-glutamine co-transporters in the enterocytes of chronically inflamed intestine. All these data indicate that iNO functions as an upstream immune modulator directly regulating glutamine assimilation during chronic intestinal inflammation.

Effects of creep feeding and supplemental glutamine or glutamine plus glutamate (Aminogut) on pre- and post-weaning growth performance and intestinal health of piglets

BACKGROUND

Creep feeding is used to stimulate piglet post-weaning feed consumption. L-Glutamine (GLN) is an important source of fuel for intestinal epithelial cells. The objective of this study was to determine the impact of creep feeding and adding GLN or AminoGut (AG; containing glutamine + glutamate) to pre- and post-weaning diets on pig performance and intestinal health. Litters (N = 120) were allotted to four treatments during 14-21 d of lactation: 1) No creep feed (NC, n = 45); 2) creep fed control diet (CFCD, n = 45); 3) creep fed 1% GLN (CFGLN, n = 15); 4) creep fed .88% AG (CFAG, n = 15). After weaning, the NC and CFCD groups were sub-divided into three groups (n = 15 each), receiving either a control nursery diet (NC-CD, CFCD-CD) or a diet supplemented with either GLN (NC-GLN, CFCD-GLN) or with AG (NC-AG, CFCD-AG). Litters that were creep fed with diets containing GLN or AG also were supplemented with those amino acids in the nursery diets (CFGLN-GLN, CFAG-AG). Glutamine was added at 1% in all three post-weaning diet phases and AG was added at .88% in phase 1 and 2 and at .66% in phase 3.

RESULTS

Feed conversion (feed/gain) showed means among treatment means close to significance (P = 0.056) and Tukey's test for pairwise mean comparisons showed that Pigs in the CFGLN-GLN group had the best feed conversion (feed/gain) in the first three-week period post-weaning, exceeding (P = 0.044) controls (CFCD-CD) by 34%. The NC-AG group had (P = 0.02) the greatest feed intake in the last three week of the study, exceeding controls (CFCD-CD) by 12%. CFGLN-GLN, CFCD-GLN and sow reared (SR) pigs had the greatest (P = 0.049) villi height exceeding the CFCD-AG group by 18%, 20% and 19% respectively. The CFAG-AG group had the deepest (P = 0.001) crypts among all treatments. CFGLN-GLN, CFCD-GLN and SR groups had the greatest (P = 0.001) number of cells proliferating (PCNA) exceeding those in the NC-CD group by 43%, 54% and 63% respectively. Sow reared pigs showed the greatest (P = 0.001) intestinal absorption capacity for xylose and mannitol.

CONCLUSION

Supplementation of creep feed and nursery diets with GLN and/or AminoGut in the first three week improved feed conversion possibly due to improved intestinal health.

Pomegranate (Punica granatum) peel is effective in a murine model of experimental Cryptosporidium parvum ultrastructural studies of the ileum

The current treatments for cryptosporidiosis are ineffective, and there is an urgent need to search for more effective and safer alternatives. One such alternative may be treatments derived from natural resources. The pomegranate peel has been used effectively in traditional medicine to cure diarrhea and dysentery. The purpose of this study was to examine the effectiveness of a Punica granatum (pomegranate) peel suspension as a treatment for Cryptosporidium parvum infection. In this study, the effects of this treatment on the ultrastructure of both the intestinal epithelial layer of infected nursling mice and the parasite were observed with a transmission electron microscope. The histological study focused on the examination of the microvilli, columnar epithelium, goblet cells, lamina propria, and crypts of Lieberkuhn. Examination of the ileums of infected mice that received the pomegranate peel suspension demonstrated that the general structure of the ileal tissue of these mice was similar to that of the control group. In the infected mice treated with the suspension, but not the infected/untreated mice, there was an improvement in all ultrastructure aspects at 28days post-inoculation. The study of the ultrastructure of the parasite (C. parvum) in mice treated with the suspension showed that there was decomposition in the parasite to the extent that in some cases we were unable to identify the stage of the parasite due to the severe degeneration. Significant decomposition of the nutrition organ was also observed. Additionally, microgamonte and macrogamonte were not observed in the suspension-treated group, explaining the disappearance of the sexual phases of the parasite in the lumens of this group. In all, this examination demonstrated the restoration of the normal structures of villi and the disappearance of acute symptoms in the suspension-treated mice and showed that the suspension directly affected the parasite at various stages of its development and led to its decomposition and death.

Regulation of sodium-glutamine cotransport in villus and crypt cells by glucocorticoids during chronic enteritis

BACKGROUND

Assimilation of the preferred nutrient of enterocytes is mediated primarily by sodium (Na)-dependent cotransport (NGct) in the intestine. The predominant NGcT in villus cells, B0AT1, is inhibited secondary to a decrease in cotransporter numbers during chronic intestinal inflammation. In contrast, NGcT mediated by SN2 in crypt cells is stimulated secondary to increased affinity of the cotransporter for glutamine during chronic ileitis. Glucocorticoid is a mainstay of treatment for inflammatory bowel disease. However, its effect on NGcT is not known.

METHODS

The inhibition of B0AT1 in villus cells during chronic intestinal inflammation was reversed back to normal by methylprednisolone (MP). This was secondary to the restoration of the cotransporter numbers in the brush border membrane rather than an alteration in the affinity. The stimulation of NGcT in crypt cells during chronic ileitis was also restored back to its normal levels by MP treatment. This reversal was secondary to the restoration of the altered affinity of the cotransporter SN2 for glutamine.

RESULTS

Kinetic studies and western blot analysis were consistent with functional studies for both cotransporters. Thus, glucocorticoids restore two uniquely altered Na-glutamine cotransporters, B0AT1 in villus and SN2 in crypt cells during chronic enteritis.

CONCLUSIONS

These data indicate that glucocorticoids function as an upstream broad spectrum immune modulator in the chronically inflamed intestine.

Protective effects of alanyl-glutamine supplementation against nelfinavir-induced epithelial impairment in IEC-6 cells and in mouse intestinal mucosa

PURPOSE

Human Immunodeficiency Virus (HIV) protease inhibitors (PI) remain a crucial component of highly active therapy (HAART) and recently have been demonstrated to have potent antitumor effect on a wide variety of tumor cell lines. However, discontinuation of therapy is an important issue, which may be related to various side-effects, especially diarrhea. The aim of this study was to evaluate the effects of nelfinavir (NFV), an HIV PI, and of alanyl-glutamine (AQ) supplementation, on intestinal cell migration, proliferation, apoptosis and necrosis, using IEC-6 cells and on intestinal crypt depth, villus length, villus area, mitotic index and apoptosis in Swiss mice.

METHODS

Migration was evaluated at 12 and 24 h after injury using a wound healing assay. Cellular proliferation was measured indirectly at 24 and 48 h using tetrazolium salt WST-1. Apoptosis and necrosis were measured by flow cytometry using the Annexin V assay. Intestinal morphometry and mitotic index in vivo were assessed following a seven-day treatment with 100 mg/kg of NFV, given orally. In vivo proliferation and apoptosis were evaluated by intestinal crypt mitotic index and immunohistochemistry, respectively.

RESULTS

In vitro, AQ supplementation enhanced IEC-6 cell migration and proliferation, following challenge with NFV. In vivo, AQ increased intestinal villus length, villus area, crypt depth and cell proliferation and cell migration, following treatment with NFV. AQ did not decrease cell death induced by NFV both in vivo and in vitro.

CONCLUSIONS

AQ supplementation is potentially beneficial in preventing the effects of PIs, such as NFV, in the intestinal tract.

Na-glutamine co-transporters B(0)AT1 in villus and SN2 in crypts are differentially altered in chronically inflamed rabbit intestine

Glutamine is a major nutrient utilized by the intestinal epithelium and is primarily assimilated via Na-glutamine co-transport (NGcT) on the brush border membrane (BBM) of enterocytes. Recently we reported that B(0)AT1 (SLC6A19) mediates glutamine absorption in villus while SN2 (SLC38A5) does the same in crypt cells. However, how B(0)AT1 and SN2 are affected during intestinal inflammation is unknown. In the present study it was shown that during chronic enteritis NGcT was inhibited in villus cells, however, it was stimulated in crypt cells. Our studies also demonstrated that the mechanism of inhibition of NGcT during chronic enteritis was secondary to a reduction in the number of B(0)AT1 co-transporters in the villus cell BBM without a change in the affinity of the co-transporter. In contrast, stimulation of NGcT in crypt cells was secondary to an increase in the affinity of SN2 for glutamine without an alteration in the number of co-transporters. Thus, glutamine assimilation which occurs via distinct transporters in crypt and villus cells is altered in the chronically inflamed intestine.

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.

Detection of differentially regulated genes in ischaemic equine intestinal mucosa

REASONS FOR PERFORMING STUDY

Colic is a serious disease syndrome in horses. Much of the mortality is associated with ischaemic-injured intestine during strangulating obstruction, yet there is limited understanding of the associated molecular events. Identification of differentially expressed genes during ischaemic injury should expand our understanding of colic and may lead to novel targeted therapeutic approaches in the future.

OBJECTIVE

To isolate and identify differentially expressed genes in equine jejunum following a 2 h ischaemic event compared to normally perfused jejunum.

METHODS

Suppressive subtractive hybridisation was used to clone genes that are differentially expressed in equine jejunum injured by 2 h of complete ischaemia as compared to time-matched control jejunal tissues. Expression of selected clones was further evaluated by northern blot analysis.

RESULTS

Of the 384 clones selected, 157 were confirmed to possess cDNAs corresponding differentially expressed genes by dot blot analysis. Two genes, fatty acid binding protein 2 and calcium-activated chloride channel 4 were further confirmed to be differentially expressed by northern blot analysis.

CONCLUSIONS

Suppressive subtractive hybridisation can be used to detect changes in expression of a broad array of genes, as confirmed by northern blot analysis of selected genes.

POTENTIAL RELEVANCE

These initial results have identified a pool of equine intestinal epithelial genes that are differentially expressed following a 2 h ischaemic event. In particular, genes indicative of deranged metabolic activity and those potentially involved in early repair events were identified and may ultimately provide clues as to the nature of epithelial ischaemic injury in horses.

Pathophysiology of diarrhea in calves

Infectious diarrhea in calves is most commonly associated with enterotoxigenic Escherichia coli, Cryptosporidium parvum, rotavirus, coronavirus, or some combination of these pathogens. Each of these agents leads to diarrhea through either secretion or malabsorption/maldigestion, though the specific mechanisms and pathways may differ. Specific pharmacologic control and treatment are dependent on gaining a greater understanding of the pathophysiology of these organisms.

Malnutrition as an enteric infectious disease with long-term effects on child development

Malnutrition is a major contributor to mortality and is increasingly recognized as a cause of potentially lifelong functional disability. Yet, a rate-limiting step in achieving normal nutrition may be impaired absorptive function due to multiple repeated enteric infections. This is especially problematic in children whose diets are marginal. In malnourished individuals, the infections are even more devastating. This review documents the evidence that intestinal infections lead to malnutrition and that malnutrition worsens intestinal infections. The clinical data presented here derive largely from long-term cohort studies that are supported by controlled animal studies. Also reviewed are the mechanisms by which enteric infections lead to undernutrition and by which malnutrition worsens enteric infections, with implications for potential novel interventions. Further intervention studies are needed to document the relevance of these mechanisms and, most importantly, to interrupt the vicious diarrhea-malnutrition cycle so children may develop their full potential.

Induction of arginase II by intestinal epithelium promotes the uptake of L-arginine from the lumen of Cryptosporidium parvum-infected porcine ileum

OBJECTIVES

To determine the specific transport system activities and expression of transporter genes responsible for uptake of L-arginine from the lumen of normal and Cryptosporidium parvum-infected neonatal porcine ileum and the influence of L-arginine catabolic pathways on L-arginine uptake.

METHODS

Intact sheets of ileal mucosa from control and C parvum-infected neonatal piglets were mounted in Ussing chambers and the uptake of 14C-L-arginine was determined under initial rate conditions and in the presence of transport system-selective inhibitors. Epithelial expression of L-arginine transporter genes was quantified by real-time reverse transcription polymerase chain reaction. L-Arginine catabolic enzyme expression was examined by immunoblotting epithelial lysates for arginase I and II. The role of intracellular catabolism in promoting the uptake of L-arginine was determined by pharmacological inhibition of nitric oxide synthase and arginase activities.

RESULTS

C parvum-infected ileum transported L-arginine at rates equivalent to uninfected epithelium despite profound villous atrophy. This was attributed to enhanced uptake of L-arginine by individual epithelial cells in the infection. There were no differences in L-arginine transport system activities (y(+) and B(0, +)) or level of transporter gene expression (CAT-1, CAT-2A, and ATB(0, +)) between uninfected and C parvum-infected epithelial cells. However, infected epithelia had induced expression of the L-arginine hydrolytic enzyme arginase II and lower concentrations of L-arginine. Furthermore, transport of L-arginine by the infected epithelium was significantly inhibited by pharmacological blockade of arginase.

CONCLUSIONS

Intracellular catabolism by arginase II, the induction of which has not been described previously for intestinal epithelium, facilitates uptake of L-arginine by infected epithelium using transport systems that do not differ from those of uninfected cells. Induction of arginase II may limit nitric oxide synthesis by competing with nitric oxide synthase for utilization of L-arginine or promote use of L-arginine for the synthesis of reparative polyamines.

Functional characterization, localization, and molecular identification of rabbit intestinal N-amino acid transporter

We have characterized the Na-glutamine cotransporter in the rabbit intestinal crypt cell brush border membrane vesicles (BBMV). Substrate specificity experiments showed that crypt cell glutamine uptake is mediated by system N. Real-time PCR experiments showed that SN2 (SLC38A5) mRNA is more abundant in crypt cells compared with SN1 (SLC38A3), indicating that SN2 is the major glutamine transporter present in the apical membrane of the crypt cells. SN2 cDNA was obtained by screening a rabbit intestinal cDNA library with human SN1 used as probe. Rabbit SN2 cDNA encompassed a 473-amino-acid-long open reading frame. SN2 protein displayed 87% identity and 91% similarity to human SN2. Functional characterization studies of rabbit SN2 were performed by using vaccinia virus-mediated transient expression system. Substrate specificity of the cloned transporter was identical to that of SN2 described in the literature and matched well with substrate specificity experiments performed using crypt cell BBMV. Cloned rabbit SN2, analogous to its human counterpart, is Li(+) tolerant. Hill coefficient for Li(+) activation of rabbit SN2-mediated uptake was 1. Taken together, functional data from the crypt cell BBMV and the cloned SN2 cDNA indicate that the crypt cell glutamine transport is most likely mediated by SN2.

Enteric infections, diarrhea, and their impact on function and development

Enteric infections, with or without overt diarrhea, have profound effects on intestinal absorption, nutrition, and childhood development as well as on global mortality. Oral rehydration therapy has reduced the number of deaths from dehydration caused by infection with an enteric pathogen, but it has not changed the morbidity caused by such infections. This Review focuses on the interactions between enteric pathogens and human genetic determinants that alter intestinal function and inflammation and profoundly impair human health and development. We also discuss specific implications for novel approaches to interventions that are now opened by our rapidly growing molecular understanding.

Oral delivery of L-arginine stimulates prostaglandin-dependent secretory diarrhea in Cryptosporidium parvum-infected neonatal piglets

OBJECTIVES

To determine if oral supplementation with L-arginine could augment nitric oxide (NO) synthesis and promote epithelial defense in neonatal piglets infected with Cryptosporidium parvum.

MATERIALS AND METHODS

Neonatal piglets were fed a liquid milk replacer and on day 3 of age infected or not with 10(8) C. parvum oocysts and the milk replacer supplemented with L-arginine or L-alanine. Milk consumption, body weight, fecal consistency, and oocyst excretion were recorded daily. On day 3 postinfection, piglets were euthanized and serum concentration of NO metabolites and histological severity of villous atrophy and epithelial infection were quantified. Sheets of ileal mucosa were mounted in Ussing chambers for measurement of barrier function (transepithelial resistance and permeability) and short-circuit current (an indirect measurement of Cl secretion in this tissue).

RESULTS

C. parvum-infected piglets had large numbers of epithelial parasites, villous atrophy, decreased barrier function, severe watery diarrhea, and failure to gain weight. L-Arginine promoted synthesis of NO by infected piglets, which was unaccompanied by improvement in severity of infection but rather promoted epithelial chloride secretion and diarrhea. Epithelial secretion by infected mucosa from L-arginine-supplemented piglets was fully inhibited by the cyclooxygenase inhibitor indomethacin, indicating that prostaglandin synthesis was responsible for this effect.

CONCLUSIONS

Results of these studies demonstrate that provision of additional NO substrate in the form of L-arginine incites prostaglandin-dependent secretory diarrhea and does not promote epithelial defense or barrier function of C. parvum-infected neonatal ileum.

Wasting and intestinal barrier function in children taking alanyl-glutamine-supplemented enteral formula

OBJECTIVE

We examined the effect of a diet supplemented with alanyl-glutamine (AG) or placebo glycine (G) on intestinal barrier function and growth in children in northeastern Brazil.

PATIENTS AND METHODS

One hundred seven children ages 7.9 to 82.2 months with a weight-for-age (WAZ), height-for-age (HAZ), or weight-for-height (WHZ) z-score less than -1 were studied. From July 2003 to November 2004, 51 study patients received AG (24 g/d) and 56 received G (25 g/d; isonitrogenic concentration) control for 10 days. Lactulose/mannitol excretion ratio was used as a measure of intestinal permeability and was performed on days 1 and 10 of nutritional supplementation. Weight and height were measured on days 1, 10, 30, and 120 of the protocol.

RESULTS

The patients were similar on admission with regard to age, sex, birth weight, nutritional status, lactulose/mannitol ratio, and serum concentrations of glutamine and arginine. The percentage of lactulose urinary excretion significantly improved (decreased) in children receiving AG for 10 days but not in those receiving glycine controls. AG significantly increased cumulative change over 120 days in WHZ and WAZ scores but not HAZ scores after adjustment for age and season in comparison with the placebo glycine group.

CONCLUSIONS

Children tolerated AG-supplemented enteral formula well, and it significantly improved cumulative WHZ and WAZ over 120 days in comparison with children in the placebo glycine group. The data also suggested a beneficial effect of AG in the barrier function paracellular pathway, albeit with reduced mannitol excretion. Thus, although the effect of AG on reduced mannitol concentration requires clarification, AG appears to improve nutrition and barrier function.

Severe cryptosporidiosis in a seven-year-old renal transplant recipient: case report and review of the literature

Cryptosporidium is an intracellular protozoa that can cause gastroenteritis in humans. In immunocompromised hosts, infection can be severe, leading to life-threatening persistent diarrhea. There is limited experience in treating this infection in solid organ transplants. Although newer drugs active against Cryptosporidium exist, they are only licensed in the USA for treatment of immunocompetent hosts. Here we describe a seven-year-old renal transplant recipient with severe cryptosporidiosis. He had a protracted course of diarrhea of up to 2 L/day. He was successfully managed with combination antimicrobial therapy including nitazoxanide, paromomycin, and azithromycin. In conjunction with this regimen, he had a reduction in immunosuppression and complete bowel rest. His stool pattern normalized in four weeks and he has had no recurrence after six months of follow up.

A Phase II Trial of Irinotecan, 5-Fluorouracil and Leucovorin Combined with Celecoxib and Glutamine as First-Line Therapy for Advanced Colorectal Cancer

OBJECTIVES

Preclinical and clinical data indicate that cyclooxygenase-2 (COX-2) is a bona fide molecular target for colorectal cancer (CRC). Glutamine may decrease chemotherapy-associated diarrhea. This study was designed to address whether the addition of celecoxib, a COX-2 inhibitor, and glutamine would improve the efficacy and decrease the toxicities of the irinotecan, fluorouracil and leucovorin (IFL) regimen.

METHODS

All patients received the original IFL regimen plus celecoxib (400 mg, po, every 12 h continuously while on trial) and glutamine (10 g, po, every 8 h continuously while on chemotherapy).

RESULTS

Of the 41 patients enrolled, 40 patients received between 1 and 6 cycles of treatment. This regimen was associated with significant toxicities: 45.0% had grade 3 diarrhea, 35.0% grade 3/4 neutropenia, 22.5% hospitalization, 10.0% deep vein thrombosis and 2 treatment-related deaths. The overall response rate was 47.2%. The median progression-free survival was 6.7 months. The median overall survival was 16.3 months. The 12-month overall survival rate was 54.8%. COX-2 expression was present in 63.2% of the specimens evaluated. There was no significant correlation between COX-2 expression and response to chemotherapy (p = 0.739).

CONCLUSION

The addition of celecoxib and glutamine appears not to improve the efficacy or decrease the toxicities of IFL for the treatment of metastatic CRC.

Effect of glutamine on water and sodium absorption in human jejunum at baseline and during PGE1-induced secretion

Glutamine, a major fuel for enterocytes, stimulates water and sodium absorption in animal models of secretory diarrhea, but data in humans are still limited. The aim of this study was to investigate the effect of glutamine on jejunal absorption during hypersecretion in humans. In six healthy adults, the effects of glutamine on jejunal absorption were assessed with a triple-lumen tube on two occasions, at baseline and during PGE1-induced hypersecretion (0.1 μg·kg−1·min−1) in a random order. Isoosmolar solutions containing polyethylene glycol 4000 as nonabsorbable marker were infused in the jejunum at 10 ml/min over 1-h periods: saline (sodium chloride 308 mmol/l), glucose-mannitol 45:45 mM, glucose 90 mM, alanine-glucose 45:45 mM, glutamine-glucose 45:45 mM, and glutamine 90 mM. Net absorptive and secretory fluxes were measured at steady state. At baseline, glutamine- and alanine-containing solutions induced a threefold increase of water and sodium absorption ( P < 0.05); 90 mM glutamine stimulated water absorption more than 90 mM glucose (3.6 ± 0.6 vs. 1.9 ± 0.3 ml·min−1·30 cm−1, P < 0.05). PGE1-induced hypersecretion was reduced ( P < 0.05) by solutions of alanine-glucose, glutamine-glucose, and glutamine 90 mM ( P < 0.05) and reversed to absorption by alanine-glucose and glutamine-glucose. Glutamine and alanine absorption was nearly complete and was not influenced by PGE1. In conclusion, glutamine stimulates water and electrolyte absorption in human jejunum, even during experimental hypersecretion. In addition to the metabolic effects of glutamine, these results support the evaluation of glutamine-containing solutions for the rehydration and the nutritional support of patients with secretory diarrhea.

Diarrhea and reduced levels of antiretroviral drugs: improvement with glutamine or alanyl-glutamine in a randomized controlled trial in northeast Brazil

The effects of therapy with glutamine and alanyl-glutamine on diarrhea and antiretroviral drug levels in patients with acquired immune deficiency syndrome (AIDS) were examined in a randomized, double-blinded, placebo-controlled study in northeast Brazil. Patients with AIDS and with diarrhea and/or wasting were randomized into 4 groups to determine the efficacy of glutamine or high- or low-dose alanyl-glutamine given for 7 days, compared with isonitrogenous glycine given to control subjects. All patients in whom baseline antiretroviral drug levels were determined had low levels 2 h after dosing. Gastrointestinal symptom scores improved with receipt of high-dose alanyl-glutamine (P<.05) or glutamine (P<.01). Antiretroviral drug levels increased in patients given alanyl-glutamine (P=.02) or glutamine (P=.03) by 113% (P=.02) and 14% (P=.01), respectively. Antiretroviral drug resistance mutations were common in all groups. The dose-related efficacy of alanyl-glutamine and glutamine in treating diarrhea and in increasing antiretroviral drug levels shows that these supplements may help to improve therapy for patients with AIDS who have diarrhea and/or wasting in developing, tropical areas.

Cholera, diarrhea, and oral rehydration therapy: triumph and indictment

Cholera drove the sanitary revolution in the industrialized world in the 19th century and now is driving the development of oral rehydration therapy (ORT) in the developing world. Despite the long history of cholera, only in the 1960s and 1970s was ORT fully developed. Scientists described this treatment after the discovery of the intact sodium-glucose intestinal cotransport in patients with cholera. This new understanding sparked clinical studies that revealed the ability of ORT to reduce the mortality associated with acute diarrheal disease. Despite the steady reductions in mortality due to acute dehydrating diarrheal diseases achieved by ORT, the costly morbidity due to these diseases remains, the result of a failure to globalize sanitation and to control the developmental impact of diarrheal diseases and their associated malnutrition. New advances in oral rehydration and nutrition therapy and new methods to recognize its costs are discussed in this review.

Glutamine Analogues As Adjunctive Therapy for Infectious Diarrhea

Glutamine is the major fuel for the gut as well as for many cells in the immune system that becomes conditionally essential during catabolic states. Glutamine supplementation improves intestinal mucosal repair and function. Glutamine, even at high doses, is without side effects and is well tolerated. Though unstable in solution, this is overcome by creating stable dipeptides such as alanyl-glutamine. In HIV-positive patients with wasting, glutamine enhances intestinal absorptive function and weight gain. Glutamine enhances sodium and water absorption in a rabbit model of cholera and Cryptosporidium-infected piglet intestine. Both glutamine and alanyl-glutamine have recently proven effective in a bovine model of Cryptosporidium as well. Finally, a rat model of cholera toxin-induced diarrhea also showed that alanyl-glutamine enhanced water and electrolyte intestinal absorption even better than the traditional glucose solutions. Clearly glutamine and its stabler derivatives hold promise for enhancing repair of mucosal injury by a wide range of infections or toxic agents, and hence have great potential as a new oral rehydration and nutrition therapy for patients with enteric infection, malnutrition, or chemotherapy- or radiation-induced enteritis.

Cyclooxygenase blockade and exogenous glutamine enhance sodium absorption in infected bovine ileum

We have previously shown that prostanoids inhibit electroneutral sodium absorption in Cryptosporidium parvum-infected porcine ileum, whereas glutamine stimulates electroneutral sodium absorption. We postulated that glutamine would stimulate sodium absorption via a cyclooxygenase (COX)-dependent pathway. We tested this hypothesis in C. parvum-infected calves, which are the natural hosts of cryptosporidiosis. Tissues from healthy and infected calves were studied in Ussing chambers and analyzed via immunohistochemistry and Western blots. Treatment of infected tissue with selective COX inhibitors revealed that COX-1 and -2 must be blocked to restore electroneutral sodium absorption, although the transporter involved did not appear to be the expected Na(+)/H(+) exchanger 3 isoform. Glutamine addition also stimulated sodium absorption in calf tissue, but although this transport was electroneutral in healthy tissue, sodium absorption was electrogenic in infected tissue and was additive to sodium transport uncovered by COX inhibition. Blockade of both COX isoforms is necessary to release the prostaglandin-mediated inhibition of electroneutral sodium uptake in C. parvum-infected calf ileal tissue, whereas glutamine increases sodium uptake by an electrogenic mechanism in this same tissue.

Cryptosporidiosis: an update

Cryptosporidiosis was recognised in human beings in 1976, and was prominent in the 1980s and 1990s as a cause of severe diarrhoeal illness in patients with AIDS. It is now additionally recognised as a major cause of waterborne diarrhoeal illness in developed regions, and as a pathogen with long-term effect on childhood growth and development in impoverished areas. This update focuses on recent changes in our understanding of the taxonomy of cryptosporidium, its epidemiology, effects, pathogenesis, diagnosis, and treatment.