Nitric oxide and intestinal barrier failure

Redox Chemistry: Implications for Necrotizing Enterocolitis

Reduction-oxidation (redox) chemistry plays a vital role in human homeostasis. These reactions play critical roles in energy generation, as part of innate immunity, and in the generation of secondary messengers with various functions such as cell cycle progression or the release of neurotransmitters. Despite this cornerstone role, if left unchecked, the body can overproduce reactive oxygen species (ROS) or reactive nitrogen species (RNS). When these overwhelm endogenous antioxidant systems, oxidative stress (OS) occurs. In neonates, OS has been associated with retinopathy of prematurity (ROP), leukomalacia, and bronchopulmonary dysplasia (BPD). Given its broad spectrum of effects, research has started to examine whether OS plays a role in necrotizing enterocolitis (NEC). In this paper, we will discuss the basics of redox chemistry and how the human body keeps these in check. We will then discuss what happens when these go awry, focusing mostly on NEC in neonates.

Schizochytrium sp. and lactoferrin supplementation alleviates Escherichia coli K99-induced diarrhea in preweaning dairy calves

Calf diarrhea, a common disease mainly induced by Escherichia coli infection, is one of the main reasons for nonpredator losses. Hence, an effective nonantibacterial approach to prevent calf diarrhea has become an emerging requirement. This study evaluated the microalgae Schizochytrium sp. (SZ) and lactoferrin (LF) as a nutrient intervention approach against E. coli O101:K99-induced preweaning calve diarrhea. Fifty 1-d-old male Holstein calves were randomly divided into 5 groups (n = 10): (1) control, (2) blank (no supplement or challenge), (3) 1 g/d LF, (4) 20 g/d SZ, or (5) 1 g/d LF plus 20 g/d SZ (LFSZ). The experimental period lasted 14 d. On the morning of d 7, calves were challenged with 1 × 1011 cfu of E. coli O101:K99, and rectum feces were collected on 3, 12, 24, and 168 h postchallenge for the control, LF, SZ, and LFSZ groups. The rectal feces of the blank group were collected on d 14. Data were analyzed using the mixed procedure of SAS (version 9.4; SAS Institute Inc.). The E. coli K99 challenge decreased the average daily gain (ADG) and increased feed-to-gain ratio (F:G) and diarrhea frequency (control vs. blank). Compared with the control group, the LFSZ group had a higher ADG and lower F:G, and the LFSZ and SZ groups had lower diarrhea frequency compared with the control group. In addition, the LFSZ and SZ groups have no differences in diarrhea frequency compared with the blank group. Compared with the control group, the blank group had lower serum nitric oxide (NO), endothelin-1, d-lactic acid (D-LA), and lipopolysaccharide (LPS) concentrations, as well as serum IgG, IL-1β, IL-6, IL-10, and TNF-α levels on d 7 and 14. On d 7, compared with the control group, all treatment groups had lower serum NO level, the SZ group had a lower serum D-LA concentration, and the LF and LFSZ groups had lower serum LPS concentration. On d 14, compared with the control group, the fecal microbiota of the blank group had lower Shannon, Simpson, Chao1, and ACE indexes, the LFSZ group had lower Shannon and Simpson indexes, the SZ and LFSZ groups had a higher Chao1 index, and all treatment groups had a higher ACE index. In fecal microbiota, Bifidobacterium and Actinobacteria were negatively associated with IL-10 and d-lactate, while Akkermansia was negatively associated with endothelin-1 and positively correlated with LPS, fecal scores, and d-lactate levels. Our results indicated that LF and SZ supplements could alleviate E. coli O101:K99-induced calf diarrhea individually or in combination. Supplementing 1 g/d LF and 20 g/d SZ could be a potential nutrient intervention approach to prevent bacterial diarrhea in calves.

Lactoferrin in a Context of Inflammation-Induced Pathology

Much progress has been achieved to elucidate the function of lactoferrin (LTF), an iron-binding glycoprotein, in the milieu of immune functionality. This review represents a unique examination of LTF toward its importance in physiologic homeostasis as related to development of disease-associated pathology. The immunomodulatory nature of this protein derives from its unique ability to "sense" the immune activation status of an organism and act accordingly. Underlying mechanisms are proposed whereby LTF controls disease states, thereby pinpointing regions of entry for LTF in maintenance of various physiological pathways to limit the magnitude of tissue damage. LTF is examined as a first line mediator in immune defense and response to pathogenic and non-pathogenic injury, as well as a molecule critical for control of oxidative cell function. Mechanisms of interaction of LTF with its receptors are examined, with a focus on protective effects via regulation of enzyme activities and reactive oxygen species production, immune deviation, and prevention of cell apoptosis. Indeed, LTF serves as a critical control point in physiologic homeostasis, functioning as a sensor of immunological performance related to pathology. Specific mediation of tissue pathophysiology is described for maintenance of intestinal integrity during endotoxemia, elicited airway inflammation due to allergens, and pulmonary damage during tuberculosis. Finally, the role of LTF to alter differentiation of adaptive immune function is examined, with specific recognition of its utility as a vaccine adjuvant to control subsequent lymphocytic reactivity. Overall, it is clear that while the ability of LTF to both sequester iron and to direct reactive oxygen intermediates is a major factor in lessening damage due to excessive inflammatory responses, further effects are apparent through direct control over development of higher order immune functions that regulate pathology due to insult and injury. This culminates in attenuation of pathological damage during inflammatory injury.

Aminoguanidine pretreatment prevents methotrexate-induced small intestinal injury in the rat by attenuating nitrosative stress and restoring the activities of vital mitochondrial enzymes

BACKGROUND

One of the major toxic side effects of methotrexate (MTX) is enterocolitis, for which there is no efficient standard treatment. Nitric oxide overproduction has been reported to play an important role in MTX-induced mucositis. This study was designed to investigate whether pretreatment with aminoguanidine (AG) - a selective iNOS inhibitor - prevents MTX-induced mucositis in rats.

METHODS

Rats were pretreated with AG (30 and 50 mg/kg body weight) i.p. daily 1 h before MTX (7 mg/kg body weight) administration for 3 consecutive days. After the final dose of MTX, the rats were killed, and the small intestines were used for analysis.

RESULTS

The small intestines of MTX-treated rats showed moderate to severe injury. Pretreatment with AG had a dose-dependent protective effect on MTX-induced mucositis. AG pretreatment reduced iNOS protein levels, mucosal nitric oxide levels, and protein tyrosine nitration. AG pretreatment also restored the activities of electron transport chain (ETC) complexes, vital tricarboxylic acid (TCA cycle) enzymes, and mitochondrial antioxidant enzymes.

CONCLUSIONS

These findings suggest that AG is beneficial in ameliorating MTX-induced enteritis in rats.

Expression of PARK7 is increased in celiac disease

Recently, it has been suggested that the gene called Parkinson's disease 7 (PARK7) might be an upstream activator of hypoxia-inducible factor (HIF)-1α, which plays a major role in sustaining intestinal barrier integrity. Furthermore, PARK7 has been proposed to participate in the Toll-like receptor (TLR)-dependent regulation of the innate immune system. Our aim was to investigate the involvement of PARK7 in the pathogenesis of coeliac disease (CD). Duodenal biopsy specimens were collected from 19 children with untreated CD, five children with treated CD (maintained on gluten-free diet), and ten children with histologically normal duodenal biopsies. PARK7 mRNA expression and protein level were determined by real-time polymerase chain reaction (PCR) and Western blot, respectively. Localization of PARK7 was visualized by immunofluorescence staining. Protein level of PARK7 increased in the duodenal mucosa of children with untreated CD compared to children with treated CD or to control biopsies (p <0.03). We detected intensive PARK7 staining in the epithelial cells and lamina propria of the duodenal mucosa of children with untreated CD compared with that in control biopsies. Our finding that mucosal expression of PARK7 is increased suggests that PARK7 is involved in the pathogenesis of gastrointestinal diseases, notably CD. Our results suggest that PARK7 may alter processes mediated by HIF-1α and TLR4, which supports a role for PARK7 in the maintenance of epithelial barrier integrity, immune homeostasis, or apoptosis.

Ileal inducible nitric oxide synthase mRNA expression in response to stress is modified in Sprague-Dawley rats exposed to a previous intestinal inflammation

The ability of stress to initiate or reactivate an inflammatory process seems to depend on an individual's susceptibility to stressful stimuli. The aim of this study was to establish whether previous inflammation alters the response to stress in Sprague-Dawley rats, a strain not especially susceptible to stressful stimuli. Stress exposure was performed in rats treated with indomethacin, to induce cyclic intestinal inflammation, during the inactive phase of inflammation. Both control and indomethacin-treated rats submitted to stress showed a decrease in body weight gain and blood leukocyte levels, as well as an increase in fecal pellet output. The increase in intestinal mucosal mast cell count induced by stress was similar in both groups of animals. Moreover, no differences were observed between control and indomethacin-treated rats in the degree of bacterial translocation and myeloperoxidase levels after stress exposure. Despite these similarities, differences between groups were observed in inducible nitric oxide synthase (iNOS) mRNA expression. Although ileal iNOS mRNA expression was inhibited in healthy rats submitted to stress, stress failed to modify this parameter in indomethacin-treated rats. As iNOS is another inflammatory marker, our results may allow the possibility that a previous intestinal inflammation could change the intestinal susceptibility to stress. Whether these differences in ileal iNOS expression can be indicative of a possible change in the predisposition to develop an intestinal inflammatory reaction in response to stress in Sprague-Dawley rats remains to be elucidated.

Functional changes induced by psychological stress are not enough to cause intestinal inflammation in Sprague-Dawley rats

BACKGROUND

It is well known that stress contributes to the perpetuation of several gastrointestinal diseases. However, its role as a trigger of the inflammatory process in absence of other putative contributing factors remains controversial. Our aim was to elucidate whether stress per se can induce a primary gut inflammation in non-predisposed rats.

METHODS

Male Sprague-Dawley rats were divided in sham and stress groups. Chronic stress was induced by subjecting animals 1 h day(-1) to wrap restraint or water avoidance stress alternatively for five consecutive days, as a model of ongoing life stress.

KEY RESULTS

Chronic stress induced a significant decrease in body weight gain without changes in food intake and an increase in frequency of defecation. Electromiografic (EMG) study showed that the duration of the migrating motor cycles (MMCs), but not its frequency, was shortened in stressed animals compared with non-stress conditions. Moreover, stressful stimulus caused mucosal mast cell hyperplasia and a decrease of iNOS mRNA expression. Bacterial translocation observed in stressed animals was not related to changes in epithelial barrier function and was not enough to induce intestinal inflammation.

CONCLUSIONS & INFERENCES

Decreased MMC duration, mast cell hyperplasia and decreased mRNA iNOS expression, but not altered epithelial barrier function, could be factors implicated in bacterial translocation-induced by chronic stress. However, these changes are not sufficient to induce intestinal inflammation in stress non-susceptible strain of rats.

The study of the inhibition of the recombinant TACE prodomain to endotoxemia in mice

Objective:

To demonstrate the inhibitory function of the prodomain of tumor necrosis factor-α (TNF-α) converting enzyme (TACE) on TACE activity and to develop an approach to interfere with inflammation processes.

Methods:

The cDNA encoding the full-length ectodomain (T1300) and prodomain (T591) of TACE were amplified by RT-PCR. The expression plasmids (pET-28a (+)-T1300 and pET-28a (+)-T591) were constructed and transformed into E. coli BL21. After Ni²⁺-NTA resin affinity chromatography, the recombinant T591 protein was obtained and assayed. In order to detect its inhibiton of TACE activity, the mice in the LPS-induced endotoxemia model group were treated with the recombinant TACE prodomain protein prior to the injection of LPS. Murine peritoneal macrophages were isolated from mice abdominal cavity for FCM and the liver, kidney and lung were removed for traditionally histopathology sectioning.

Results:

The FCM results showed that the recombinant prodomain protein decreased the release of the sTNF-α, which mediated the accumulation of TNF-α on the surface of macrophage cells. HE staining proved that the recombinant protein can decrease the inflammatory response in internal organs of endotoxaemia mice.

Conclusions:

The recombinant prodomain of TACE has the ability to inhibit sTNF-α release, which indicates that prodomain is an effective antagonist of TACE and might be useful in the molecular design of anti-inflammatory drugs.

Overexpression of hepatic inducible nitric oxide synthase in biliary atresia

AIMS

Biliary atresia (BA) is a rare and serious liver disease in infants characterized by progressive inflammatory cholangiopathy. The aims of this study were to investigate hepatic expression of inducible nitric oxide synthase (iNOS) in BA and to associate the iNOS expression with their early therapeutic outcome.

METHODS

Hepatic iNOS expression was determined using immunohistochemistry from liver biopsies of 24 BA patients, and 16 non-BA patients whose liver tissues were needed in the treatment process. Six months after surgery, the BA patients were categorized into two groups;good and poor outcome. The iNOS expression of hepatocyte areas was evaluated based on its intensity using ImageJ software. Unpaired t-tests were used for the comparisons of iNOS expression between groups.

RESULTS

Hepatic iNOS expression of BA patients was significantly stronger than that of non-BA patients (P < 0.0001). The largest area of hepatic iNOS expression was the area of hepatocytes. Subgroup analysis of BA patients at 6 months post-op revealed that there was no difference in iNOS expression between the patients with good outcome and those with poor outcome (P = 0.732).

CONCLUSIONS

Overexpression of hepatic iNOS in BA patients was demonstrated. Within liver tissues, hepatocytes were the major source of hepatic iNOS production. However, the expression was not associated with the early therapeutic outcome. These results suggest that iNOS plays a role in the liver pathology of BA but its expression cannot be used as a predictor for therapeutic outcome.

Methotrexate-induced nitrosative stress may play a critical role in small intestinal damage in the rat

Methotrexate (MTX), a structural analogue of folic acid, is widely used as a chemotherapeutic agent for leukemia and other malignancies. One of the major toxic effects of MTX is intestinal injury and enterocolitis .The mechanism of gastrointestinal toxicity of methotrexate has not been investigated completely. Therefore cancer chemotherapy has to be accompanied by symptomatic therapy such as antibiotics and anti-diarrheal drugs. It is important to investigate the mechanism by which methotrexate induces intestinal damage in order to perform cancer chemotherapy effectively by preventing the side effects. This study aimed at investigating whether nitrosative stress plays a role in methotrexate induced small intestinal damage using a rat model. Adult male rats were administered methotrexate at the dose of 7 mg/kg body weight intraperitoneally for 3 consecutive days and sacrificed 12 or 24 h after the final dose of methotrexate. Vehicle treated rats served as control. The intestinal tissue was used for light microscopic studies and markers of nitrosative stress including tissue nitrite level and nitrotyrosine. Myeloperoxidase (MPO) activity, a marker of neutrophil infiltration was also measured in intestinal homogenates. The villi were damaged at 12 h and the damage progressed and became severe at 24 h after the final dose of MTX. Biochemically, tissue nitrate was elevated fivefold at 12 h and fourfold at 24 h after the final dose of MTX as compared with control. Nitrotyrosine, measured immunohistochemically was detected in all the parts of the small intestine. Duodenum stained the most for nitrotyrosine, followed by ileum and then jejunum. The staining for nitrotyrosine was more intense at 24 h as compared with 12 h after the final dose of methotrexate. There was marked neutrophil infiltration as evidenced by increase in MPO activity in the small intestines. In conclusion, the results of the present study reveal that nitrosative stress may play a critical role in methotrexate induced small intestinal damage. Intervention studies using nitric oxide synthase inhibitors is being carried out in order to confirm the role of nitrosative stress in methotrexate induced small intestinal damage.

Ischemia reperfusion injury, preconditioning and critical illness

The purpose of this review is to describe in more detail ischemia reperfusion injury and preconditioning, and to speculate on the potential role of preconditioning in the care of critically ill patients. Current hemodynamic treatment of hypotension and hypoperfusion in critically ill patients is directed at ensuring essential organ perfusion by maintaining intravascular volume and cardiac output, and ensuring adequate oxygen delivery by maintaining arterial oxygen partial pressure and hemoglobin levels. However, morbidity and mortality remain high and new approaches to critically ill patients are required. Treatments are needed that can protect against organ ischemia during periods of low blood flow. In recent years, there has been a growing appreciation of the importance of ischemia reperfusion injury. Ischemia associated with reperfusion may result in greater injury than ischemia alone. Ischemic preconditioning is used to describe the protective effect of short periods of ischemia to an organ or tissue against longer periods of ischemia. Although first described in the myocardium, there is now evidence that this phenomenon occurs in a wide variety of organs and tissues, including the brain and other nervous tissue such as the retina and spinal cord, liver, stomach, intestines, kidney, and the lungs. Preconditioning therapy may offer a new avenue of treatment in critically ill patients. Both traditional preconditioning methods and pharmacologic agents that mimic or induce such preconditioning may be used in the future. Clinical trials of pharmacologic agents are underway in patients with coronary artery disease. Further trials of such methods and agents are needed in critically ill patients suffering from sepsis or multiorgan system failure.

Interaction between enteric epithelial cells and Peyer’s patch lymphocytes in response to Shigella lipopolysaccharide: Effect on nitric oxide and IL-6 release

AIM: To investigate the effect of interaction between enteric epithelial cells and lymphocytes of Peyer’s patch on the release of nitric oxide (NO) and IL-6 in response to Shigella lipopolysaccharide (LPS).

METHODS: Human colonic epithelial cells (Caco-2) were mixed cocultured with lymphocytes of Peyer’s patch from wild-type (C57 mice) and inducible NO synthase knockout mice, and challenged with Shigella F2a-12 LPS. Release of NO and mIL-6 was measured by Griess colorimetric assay and enzyme-linked immunosorbent assay (ELISA), respectively.

RESULTS: In the absence of LPS challenge, NO was detected in the culture medium of Caco-2 epithelial cells but not in lymphocytes of Peyer’s patch, and the NO release was further up-regulated in both cocultures with lymphocytes from either the wild-type or iNOS knockout mice, with a significantly higher level observed in the coculture with iNOS knockout lymphocytes. After Shigella F2a-12 LPS challenge for 24-h, NO production was significantly increased in both Caco-2 alone and the coculture with lymphocytes of Peyer’s patch from the wild-type mice but not from iNOS knockout mice. LPS was found to stimulate the release of mIL-6 from lymphocytes, which was suppressed by coculture with Caco-2 epithelial cells. The LPS-induced mIL-6 production in lymphocytes from iNOS knockout mice was significantly greater than that from the wild-type mice.

CONCLUSION: Lymphocytes of Peyer’s patch maintain a constitutive basal level of NO production from the enteric epithelial cell Caco-2. LPS-induced mIL-6 release from lymphocytes of Peyer’s patch is suppressed by the cocultured epithelial cells. While no changes are detectable in NO production in lymphocytes from both wild-type and iNOS knockout mice before and after LPS challenge, NO from lymphocytes appears to play an inhibitory role in epithelial NO release and their own mIL-6 release in response to LPS.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Enteropathogenic Escherichia coli (EPEC) effector-mediated suppression of antimicrobial nitric oxide production in a small intestinal epithelial model system

In vivo studies with the mouse-specific member of the attaching and effacing (A/E) family of pathogens raised the possibility that these non-invasive enteric pathogens can specifically inhibit inducible nitric oxide synthase (iNOS) expression to prevent the production of antimicrobial nitric oxide (NO). In this study we use polarized Caco-2 cells, a model of human small intestinal epithelia, to (i) demonstrate conclusively that an A/E member, human specific enteropathogenic Escherichia coli (EPEC), can inhibit cytokine-induced iNOS expression, (ii) show that this activity is dependent on the delivery of effector molecules into host cells and (iii) investigate the mechanism of inhibition. Analysis of the level of iNOS-related mRNA, protein and NO production demonstrated that EPEC can inhibit iNOS expression at the transcriptional, by direct and indirect mechanisms, and post-transcriptional levels. This transcriptional block was linked to the failure of the iNOS-related transcriptional factor NF-kappaB, but not STAT1, to undergo phosphorylation-associated activation. A selective pressure to prevent iNOS production was evidenced by the finding that iNOS activity had a potent antimicrobial effect on adherent but not non-adherent bacteria. Moreover, given the central role NF-kappaB plays in transcribing genes associated with early host immune responses, this inhibitory mechanism presumably represents an important role in pathogenesis. Our study also provides insights into the nature of NO production in response to bacterial infection as well as the role of the locus of enterocyte effacement (LEE)-encoded effector molecules in inhibiting iNOS expression.

Astrovirus-induced synthesis of nitric oxide contributes to virus control during infection

Astrovirus is one of the major causes of infant and childhood diarrhea worldwide. Our understanding of astrovirus pathogenesis trails behind our knowledge of its molecular and epidemiologic properties. Using a recently developed small-animal model, we investigated the mechanisms by which astrovirus induces diarrhea and the role of both the adaptive and innate immune responses to turkey astrovirus type-2 (TAstV-2) infection. Astrovirus-infected animals were analyzed for changes in total lymphocyte populations, alterations in CD4(+)/CD8(+) ratios, production of virus-specific antibodies (Abs), and macrophage activation. There were no changes in the numbers of circulating or splenic lymphocytes or in CD4(+)/CD8(+) ratios compared to controls. Additionally, there was only a modest production of virus-specific Abs. However, adherent spleen cells from infected animals produced more nitric oxide (NO) in response to ex vivo stimulation with lipopolysaccharide. In vitro analysis demonstrated that TAstV-2 induced macrophage production of inducible nitric oxide synthase. Studies using NO donors and inhibitors in vivo demonstrated, for the first time, that NO inhibited astrovirus replication. These studies suggest that NO is important in limiting astrovirus replication and are the first, to our knowledge, to describe the potential role of innate immunity in astrovirus infection.

Mechanisms of immune resolution

Initially after injury, the innate/proinflammatory and some aspects of the acquired immune response are up-regulated to maintain a defense against foreign pathogens, clear tissue debris present at the wound site, and orchestrate aspects of tissue remodeling, cell proliferation and angiogenic process, associated with the wound response. However, for proper wound healing to progress, this initial inflammatory response has to be regulated or shut down so as to allow for the reestablishment of matrix, recellularization, and tissue remodeling. Inability to properly resolve the extent of innate/acquired response at a site of injury can lead to poor wound healing, immune suppression, and recurrent infectious episodes. This review attempts to summarize information on regulatory mechanisms that are thought to be involved in controlling/resolving innate or acquired immune responses so as to provide a framework for use in thinking about the impact these processes and their manipulation may have on wound healing and its potential management.

Differential effects of prophylactic, concurrent and therapeutic lactoferrin treatment on LPS-induced inflammatory responses in mice

Mice injected with endotoxin develop endotoxaemia and endotoxin-induced death, accompanied by the oxidative burst and overproduction of inflammatory mediators. Lactoferrin, an iron binding protein, provides a natural feedback mechanism to control the development of such metabolic imbalance and protects against deleterious effects of endotoxin. We investigated the effects of intraperitoneal administration of human lactoferrin on lipopolysaccharide (LPS)-induced release of tumour necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), interleukin 10 (IL-10) and nitric oxide (NO) in vivo. Lactoferrin was administered as a prophylactic, concurrent or therapeutic event relative to endotoxic shock by intravenous injection of LPS. Inflammatory mediators were measured in serum at 2, 6 and 18 h post-shock induction. Administration of lactoferrin 1 h before LPS resulted in a rather uniform inhibition of all mediators; TNF by 82%, IL-6 by 43%, IL-10 by 47% at 2 h following LPS injection,and reduction in NO (80%) at 6 h post-shock. Prophylactic administration of lactoferrin at 18 h prior to LPS injection resulted in similar decreases in TNF-alpha (95%) and in NO (62%), but no statistical reduction in IL-6 or IL-10. Similarly, when lactoferrin was administered as a therapeutic post-induction of endotoxic shock, significant reductions were apparent in TNF-alpha and NO in serum, but no significant effect was seen on IL-6 and IL-10. These results suggest that the mechanism of action for lactoferrin contains a component for differential regulation of cellular immune responses during in vivo models of sepsis.

Heparin-binding EGF-like growth factor (HB-EGF) decreases oxygen free radical production in vitro and in vivo

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been shown to protect intestinal epithelial cells from anoxia/reoxygenation in vitro, and to protect the intestines from ischemia/reperfusion (I/R) injury in vivo. The goal of the present study was to determine whether the cytoprotective effects of HB-EGF were due, in part, to its ability to decrease reactive oxygen species (ROS) production. Human whole blood, polymorphonuclear leukocytes, and monocytes, as well as rat intestinal epithelial cells, were exposed to stimuli designed to produce an oxidative burst in these cells. Treatment of the cells with HB-EGF led to a significant decrease in oxidative burst production. In vivo, total midgut I/R injury in rats led to increased ROS production, which was markedly decreased by HB-EGF treatment. Histochemically, I/R injury led to increased ROS production, which was significantly decreased with HB-EGF treatment. HB-EGF cytoprotection is due, in part, to its ability to decrease ROS production. Future studies will determine the mechanisms by which HB-EGF exerts these effects.

Ultrastructural characteristics of distal duodenum mucosa in patients with cirrhosis

OBJECTIVES

Morphological abnormalities observed by light microscopy, such as oedema or vasodilatation, have been described in intestinal mucosa of patients with cirrhosis, but no information is available regarding the ultrastructural characteristics of the intestinal epithelial layer. The aim of this observational study was to investigate the ultrastructural characteristics of the intestinal epithelial layer of duodenum mucosa in patients with cirrhosis.

METHODS

Six patients with advanced cirrhosis and six control patients without liver disease were included in the study. Biopsies were obtained from the distal duodenum during upper diagnostic endoscopy, and ultrastructural characteristics were studied by means of electron microscopy.

RESULTS

A distended interenterocyte space with intestinal epithelial cells closely attached by morphologically intact tight junctions has been observed in cirrhotic patients, together with shorter and wider microvilli than in the control subjects.

CONCLUSIONS

The epithelial layers from cirrhotic patients show ultrastructural abnormalities. However, it is not known if the observed alterations are related to the presence of increased intestinal permeability or to bacterial translocation, which are frequently found in these patients.

Heparin-binding EGF-like growth factor down regulates proinflammatory cytokine-induced nitric oxide and inducible nitric oxide synthase production in intestinal epithelial cells

We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) protects intestinal epithelial cells (IEC) from necrosis and apoptosis in vitro and from intestinal ischemia/reperfusion injury in vivo; however, the mechanisms of HB-EGF cytoprotection are unclear. Overproduction of iNOS and NO have been implicated in the pathogenesis of several forms of ischemia/reperfusion injury. We therefore studied whether HB-EGF could down-regulate proinflammatory cytokine-induced iNOS and NO production in intestinal epithelial cells in vitro. DLD-1 human intestinal epithelial cells were exposed to the proinflammatory cytokines interleukin-1beta (IL-1beta) (20 ng/ml) and interferon-gamma (IFN-gamma) (10 ng/ml) to stimulate iNOS induction and NO production. Cells were treated with HB-EGF (0-100 ng/ml) either before or with cytokine exposure, and cells and supernatants were harvested 24 and 48 h later. Accumulated NO was measured in supernatants by chemiluminescence. Total RNA was extracted from cell lysates for iNOS mRNA quantification using real-time reverse transcription-polymerase chain reaction (RT-PCR), and total protein was extracted from cell lysates for detection of iNOS protein. HB-EGF significantly decreased cytokine-induced NO production in a dose dependent manner, and NO reduction was associated with iNOS suppression at both the mRNA and protein levels. While cytokine exposure resulted in a significant increase in iNOS mRNA expression in these cells (109 plus minus 9 fold), HB-EGF reduced iNOS expression by 5.7-fold (P < 0.05). These results suggest that HB-EGF may exert its cytoprotective effects, in part, by down-regulating iNOS and NO production, and provides further rationale for additional testing of the effects of HB-EGF in the treatment of intestinal ischemia/reperfusion injury in vivo.

Heparin-binding EGF-like growth factor decreases inducible nitric oxide synthase and nitric oxide production after intestinal ischemia/reperfusion injury

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been shown to protect intestine from ischemia/reperfusion (I/R) injury in vivo and to down-regulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production in intestinal epithelial cells in vitro. The present study was undertaken to investigate whether HB-EGF could modulate the iNOS/NO axis after total midgut I/R injury in rats. I/R injury induced a significant increase in iNOS gene expression (quantified by real-time RT-PCR) and protein production (detected by western blots), as well as elevation of serum NO levels (measured by chemiluminescence assay). Nitrotyrosine (NT) and iNOS production colocalized immunohistochemically, with positive staining found mainly in villous and crypt epithelial cells, as well as ganglion cells. Intraluminal administration of HB-EGF 45 min after the start of a 90-min ischemic interval significantly decreased I/R-induced iNOS gene expression and protein production, as well as serum NO levels. Immunohistochemically, HB-EGF administration led to elimination of iNOS and NT staining in crypt epithelial cells and ganglion cells, with only weak staining that remained in villous epithelial cells. Thus, HB-EGF protects the intestine from I/R injury, at least partially, through down-regulation of the iNOS/NO/NT pathway, a mechanism that is central to I/R injury in multiple organ systems.

Heparin-binding EGF-like growth factor decreases apoptosis in intestinal epithelial cells in vitro

BACKGROUND/PURPOSE

The production of heparin-binding EGF-like growth factor (HB-EGF) is upregulated during organ injury and has a cytoprotective effect during hypoxic stress in intestinal epithelial cells in vitro and intestinal ischemia-reperfusion injuries in vivo. The purpose of this study was to determine if HB-EGF-related cytoprotection is manifested through alterations in apoptosis.

METHODS

Human intestinal epithelial cell monolayers (DLD-1 and Caco-2) were stimulated with interleukin (IL)-1 (20 ng/mL), tumor necrosis factor (TNF)-alpha (40 ng/mL), and interferon (IFN)-gamma (10 ng/mL) with or without HB-EGF (1, 10 or 100 ng/mL) and analyzed for rates of apoptosis utilizing a Cell Death Detection ELISA and flow cytometry.

RESULTS

ELISA results showed a 3-fold increase in the level of apoptosis during stimulation with cytokines compared with nonstimulated cells (P <.05). Relative levels of cytokine induced apoptosis were reduced after 12 hours of HB-EGF exposure (P <.05) in a dose-dependent fashion. Results of flow cytometric analysis also showed a reduction in apoptosis at 6 hours when cell monolayers were stimulated with cytokines in conjunction with HB-EGF compared with cytokines alone (P <.05).

CONCLUSIONS

HB-EGF downregulated apoptosis in intestinal epithelial cells exposed to proinflammatory cytokines in vitro. The results of this study suggest that alterations in apoptosis may represent a possible mechanism by which this growth factor exerts its cytoprotective effect at the mucosal level during the proinflammatory state.