Hemodynamic and permeability characteristics of acute experimental necrotizing enterocolitis

Feeding associated neonatal necrotizing enterocolitis (Primary NEC) is an inflammatory bowel disease

Neonatal necrotizing enterocolitis which develops after feeding preterm infants is characterized by severe intestinal inflammation and profound systemic metabolic acidosis. The fermentation of undigested dietary carbohydrate by colonic flora yields gases (CO₂ and H₂) and short chain organic acids. These organic acids can disrupt the intestinal mucosa and initiate inflammation driven predominantly by resident mast cells and by granulocytes which are recruited from blood. A systemic acidosis ensues derived from intestinal acids, not classic lactic acidosis produced from anaerobic metabolism. The systemic acidosis further compromises inflamed bowel leading to bowel necrosis.

Intestinal mucosa remodeling by recombinant human epidermal growth factor(1-48) in neonates with severe necrotizing enterocolitis

BACKGROUND AND AIMS

Neonatal necrotizing enterocolitis (NEC) is a common and serious acquired gastrointestinal tract condition. This clinical study assessed the potential clinical efficacy and microscopic effects of recombinant human epidermal growth factor 1-48 (EGF(1-48)) in neonates with NEC.

METHODS

This prospective, double-blind, randomized controlled study included 8 neonates with NEC. The study compared the effects of a 6-day continuous intravenous infusion of EGF(1-48) at 100 ng kg(-1) h(-1) against placebo. Clinical outcomes and morphological evaluation of serial rectal mucosal biopsies were assessed at baseline and 4, 7, and 14 days after starting EGF infusions.

RESULTS

There was no difference between the clinical safety outcomes recorded for EGF(1-48) or placebo patients. Quantitative morphologic differences in the rectal mucosa biopsies were noted with EGF(1-48) treatment compared with baseline or placebo and included a statistically significant increase in the number of mitoses per mucosal crypt on study day 4, significantly increased thickness of rectal mucosa from baseline on study days 4 and 7, and increased crypt surface area of rectal mucosa in parallel with increased mucosa thickness on day 14.

CONCLUSION

This study of EGF(1-48) in neonates with severe NEC showed that growth factor treatment was well tolerated and produced positive and measurable remodeling trophic effects on the gastrointestinal mucosa.

Mathematical modeling in necrotizing enterocolitis--a new look at an ongoing problem

Necrotizing enterocolitis (NEC) is the most common and lethal disease that affects the gastrointestinal (GI) tract of the premature infant. The etiology of NEC remains undefined. The only consistent epidemiological precursors for NEC are prematurity and enteral alimentation. Various inflammatory mediators, including tumor necrosis factor (TNF)-a, interleukin (IL)-1, IL-6, IL-8, IL-10, IL-18, platelet-activating factor (PAF), and nitric oxide (NO) have been implicated in the pathogenesis of NEC, but the kinetics and role of these agents are ill-defined. Currently, there are no biomarker predictors of NEC risk and severity. Sera or tissue from early time points in the development of the disease may help delineate early inflammatory events that predispose an individual to NEC, thus providing an interventional opportunity. We suggest that the lack of diagnostic and therapeutic modalities for NEC are due to the absence of a systems view of the disease, which in turn is hindered by a lack of sensitive physiological measurements that predict perturbations in the intestinal tissue compartment and an inability to reliably test serial samples for the presence of inflammatory mediators in small volumes and in a high-throughput manner. Computational modeling is a useful tool in the study of complex systems such as the inflammatory process. Computation models provide an "existence proof" for a given mechanism, uncover subtle inconsistencies between the underlying hypotheses and quantitative data, and force one to ask how much is known. We suggest that a properly validated and calibrated mathematical model of inflammation and its pathologic consequences in NEC will be useful for predicting the physiologic and biologic response in infants suffering from the disease.

Necrotising enterocolitis

Necrotising enterocolitis is one of the most common gastrointestinal emergencies in newborn infants. Here we review the epidemiology, clinical presentation, and pathophysiology of the disease, as well as strategies for diagnosis, management, and prevention. Necrotising enterocolitis is one of the most devastating and unpredictable diseases affecting premature infants. Despite decades of research, its pathogenesis remains unclear; diagnosis can be difficult; and treatment is challenging. We will need to improve our understanding of intestinal defences in premature infants, dietary and bacterial factors, and genetic effects that could predispose infants to necrotising enterocolitis before we can develop new strategies for prevention and treatment.

Rectosigmoid pHi monitoring during experimental necrotizing enterocolitis

BACKGROUND/PURPOSE

Gastric or rectosigmoid intramural pH (pHi) is considered a reliable indicator of splanchnic perfusion. The aim of this study was to evaluate whether rectosigmoid pHi reflects the severity of bowel damage in experimental necrotizing enterocolitis (NEC).

METHODS

A total of 36 neonatal piglets, (median age, 3; range, 1 to 11 days; median weight, 2.5; range, 1.2 to 3.8 kg), were anesthetized, ventilated mechanically, and had invasive monitoring of hemodynamics. A sigmoid tonometer was inserted into the rectosigmoid colon. Enterocolitis was induced in 27 piglets by intraluminal injection of casein-d-gluconate (16.0 mL/kg) into terminal 100 cm of the ileum. Nine control piglets received an equal amount of intraluminal saline. NEC was graded macroscopically as follows: 0, no changes; 1, mild; 2, moderate; and 3, severe. Histology was evaluated according to Chiu scale from 0 to 5.

RESULTS

The macroscopical bowel injury in caseine-injected piglets was as follows: grade 3 (n = 6), grade 2 (n = 9), grade 1 (n = 12). All control piglets showed macroscopically normal bowel (grade 0). All affected bowels showed histologic changes (Chiu's scale 2 to 4). All study animals had an initial drop of pHi after injection of casein or saline. In control piglets and those with mild NEC (grade 1) pHi tended to return to preinjection level. In animals with moderate or severe NEC (grade 2 to 3) the initial drop was deeper and the pHi continued to decrease significantly throughout the experiment (P < .05). In the arterial pH and mean blood pressure there were no statistically significant differences between piglets with no NEC and mild NEC, and these with moderate or severe NEC.

CONCLUSION

Drop in rectosigmoid pHi was the most sensitive and earliest sign of severe mucosal necrosis of ileum in this experimental NEC model.

Development of a protocol to provide prolonged general anesthesia to pregnant sows

This study was designed to determine whether a pregnant sow could be maintained under conditions of prolonged general anesthesia in order to provide access to prematurely delivered piglets for purposes of acute experimentation. Fifteen time-dated pregnant (90% of gestation) sows were preanesthetized with intramuscular xylazine (Rompun Mobay Pharmaceutical, Shawnee, KS)/ketamine (Aveco Pharmaceutical, Fort Dodge, IA). After anesthesia was induced with intravenous sodium thiopental, the animals underwent tracheotomy and mechanical ventilation. The electrocardiogram was monitored externally; systemic arterial pressure was supervised by the insertion of a brachial artery cannula; and urine output was determined by inserting a cystostomy tube. A surgical plane of anesthesia was achieved by the "balanced" technique: an inhalant, isoflurane, supplemented by intravenous doses of sufentanil citrate, propofol (Stuart Pharmaceuticals, Wilmington, DE), and vecuronium. Sows were maintained under general anesthesia for an average of 12 h; piglets were delivered, one or two at a time, by a modified cesarean section technique. No sows or piglets were lost to anesthetic complications. It is concluded that, with appropriate precautions, pregnant sows can be anesthetized for a prolonged period of time, and provide viable premature neonates for acute experimentation.

Elevation of circulating intestinal fatty acid binding protein in a luminal contents-initiated model of NEC

Necrotizing enterocolitis (NEC) continues to produce significant morbidity and mortality, due in part to the difficulty in detecting its initial manifestations at a stage when compromised intestine may potentially be salvaged. We have previously reported our findings that intestinal fatty acid binding protein (I-FABP) is a sensitive biochemical marker for early intestinal mucosal injury due to mesenteric ischemia. In this study we evaluated the potential of serum I-FABP as a marker for incipient NEC in a nonischemic model of NEC in the rat. Intraluminal instillation of a solution of casein (10 mg/mL) and calcium gluconate (50 mg/mL) in saline acidified to pH 4.0 with propionic acid resulted in a rapid and prolonged increase in serum I-FABP from a baseline of < or = 4.0 ng/mL to 171 +/- 40 ng/mL. Instillation of the same electrolyte solution with either casein or propionic acid alone resulted in a less dramatic elevation of serum I-FABP to 19 +/- 4 ng/mL and 76 +/- 30 ng/mL, respectively. In both cases baseline values of < or = 4.0 ng/mL were reached within 60 minutes. In control animals, which received saline alone, serum I-FABP was undetectable throughout the experiment. Simultaneously, we found that serum hexosaminidase, a putative biochemical marker for intestinal ischemia and NEC, was unchanged in all groups. Light microscopy of the intestinal specimens obtained three hours after instillation of casein and organic acid demonstrated superficial villus necrosis and villus blunting, but no areas of transmural necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide release in response to gut injury

We evaluated nitric oxide release in several models of intestinal inflammation through luminal nitrite concentrations. In anesthetized rabbits, piglets, and guinea pigs, luminal lavages were collected from loops of normal or injured small intestine. Lavages were analyzed spectrophotometrically for nitrite (Griess reagent) and protein. Myeloperoxidase (MPO) content of intestinal segments was used as an index of granulocyte infiltration and intestinal inflammation. Acute ileal inflammation was induced by luminal acetic acid + casein in rabbits and luminal deoxycholate in neonatal piglets and adult rabbits. Chronic ileitis was induced in guinea pigs by intraluminal trinitrobenzenesulfonic acid. In each model nitrite levels in ileal lavages were significantly greater than control loops/animals. Increased luminal protein and intestinal MPO activity paralleled the changes in nitrite levels. To determine whether nitric oxide production influenced mucosal repair, segments of ileum were perfused with the L-arginine antagonist NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/ml) after acute acetic acid + casein exposure. L-NAME administration reversed the decline in epithelial permeability characteristic of epithelial restitution, causing an increase in epithelial permeability which was readily reversible. These results suggest that nitrite production is a useful index of gut injury and that nitric oxide may contribute to the functional repair of the epithelial barrier under acute conditions.

Rabbit gut permeability in response to histamine chloramines and chemotactic peptide

Granulocyte-derived chlorinated amines and bacterial formyl peptides are thought to enhance epithelial permeability. In the current study, gut permeability to [51Cr]ethylenediaminetetraacetic acid (EDTA) was monitored in response to luminal formyl-methionyl-leucyl-phenylalanine (fMLP) and histamine monochloramine and dichloramine. Responses were determined in rabbits during states of basal and elevated permeability. Luminal fMLP had minimal effects of gut permeability in control and injured states. Histamine monochloramine or dichloramine enhanced epithelial permeability under basal conditions; this effect was exaggerated by a pre-existing injury. Both histamine monochloramine and dichloramine retained full histamine agonist properties, and a combination of antioxidant and antihistamine therapy was required to block this increase in gut permeability. Whereas histamine chloramines caused a dose-dependent cytotoxicity in rat-cultured enterocytes, marked histological changes to the mucosa were not evident, nor were mucosal glutathione levels depleted. As histamine chloramines retain the histaminergic and oxidizing potential of their precursors, they represent a unique form of inflammatory mediator, although their highly reactive nature precludes in vivo confirmation of their formation.

Histamine is a transient marker of small intestinal injury induced by luminal acetic acid and casein

We compared the time course of histamine release with other markers of intestinal injury in a rabbit model of necrotizing enterocolitis. Injury was induced by luminal acetic acid (200 mM) and casein (10 mg/ml) and experiments terminated after 45 min or 3 hr. Compared to saline controls there was a significant elevation of epithelial permeability (51Cr-EDTA clearance) and luminal protein levels at both time points. Luminal fluid histamine levels were approximately 120-fold greater than saline controls at 45 min but were indistinguishable from control values at 3 hr. We conclude that although mast cell activation is a characteristic of this model, elevations in histamine levels are transient.

Misoprostol attenuates acetic acid-induced damage in rabbit distal small intestine

The influence of misoprostol pretreatment (100 micrograms/loop intraluminally) on small intestinal damage induced by acetic acid was evaluated in anesthetized rabbits. In this model injury was induced by intraluminal administration into loops of distal small intestine, of a solution of calcium gluconate (50 mg/ml) and acetic (200 mM). After 3 hr damage was associated with increase in loop fluid volume, loop fluid protein levels and epithelial permeability to 51Cr-EDTA, all of which were attenuated by misoprostol pretreatment. Similar protective effects were noted 45 min after the insult, suggesting that misoprostol may be therapeutically useful in conditions where the epithelial barrier is compromised.

Acute intestinal injury induced by acetic acid and casein: prevention by intraluminal misoprostol

Acute injury was established in anesthetized rabbits by intraluminal administration of acetic acid with and without bovine casein, into loops of distal small intestine. Damage was quantified after 45 minutes by the blood-to-lumen movement of 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) and fluorescein isothiocyanate-tagged bovine serum albumin as well as luminal fluid histamine levels. The amount of titratable acetic acid used to lower the pH of the treatment solutions to pH 4.0 was increased by the addition of calcium gluconate. Luminal acetic acid caused a 19-fold increase in 51Cr-EDTA accumulation over saline controls; casein did not modify this effect. In saline controls, loop fluid histamine levels bordered on the limits of detection (1 ng/g) but were elevated 19-fold by acetic acid exposure and markedly increased (118-fold) by the combination of acid and casein. Intraluminal misoprostol (3 or 30 micrograms/mL), administered 30 minutes before acetic acid, significantly attenuated the increase in epithelial permeability (luminal 51Cr-EDTA, fluorescein isothiocyanate-bovine serum albumin accumulation) and histamine release (P less than 0.05). Diphenhydramine, alone or in combination with cimetidine, and indomethacin (5 mg/kg IV) were not protective. It is concluded that exposure of the epithelium to acetic acid promotes the transepithelial movement of casein leading to enhanced mast cell activation and mucosal injury. Damage to the epithelial barrier can be prevented by misoprostol.

Exaggerated intestinal histamine release by casein and casein hydrolysate but not whey hydrolysate

Loops of rabbit distal small intestine received luminal acetic acid (pH 4.0) alone or in combination with bovine casein, casein hydrolysate, or whey hydrolysate. Blood-to-lumen movement of 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) (an index of epithelial permeability) and loop fluid histamine levels were quantified after 45 min. Luminal acetic acid caused a marked increase in 51Cr-EDTA accumulation which was not modified by the addition of bovine casein or hydrolysates by of casein or whey. However, acetic acid-induced histamine release was potentiated by casein and casein hydrolysate (six- and four-fold respectively) but was not altered by whey hydrolysate. Casein hydrolysate-dependent histamine release was evident in naloxone-pretreated rabbits, suggesting that beta-casomorphins were not solely responsible. We conclude that luminal casein or casein hydrolysate, but not whey hydrolysate. can activate intestinal mast cells under conditions of enhanced epithelial permeability. This effect appears to involve components other than beta-casomorphins.