Christopher P. Gayer

Acute lower gastrointestinal bleeding in 1,112 patients admitted to an urban emergency medical center.

BACKGROUND This study was performed to elucidate the etiology, effectiveness of diagnostic and therapeutic modalities, and outcomes in patients with acute lower gastrointestinal bleeding. METHODS A retrospective review of the medical records of 1,112 consecutive patients admitted to the surgical service of a single urban emergency hospital with lower gastrointestinal bleeding from 1988 to 2006. Two groups were compared: 1988-1997 and 1998-2006. RESULTS All patients underwent colonoscopy, 33.2% within 24 h of admission. Hematochezia was the most frequent presentation (55.5%), followed by maroon stool (16.7%) and melena (11.0%). Most patients, 690 (62.1%) also had upper endoscopy. Sixty-six patients subsequently had barium enemas. Eleven of 27 nuclide scans were positive. Arteriography was performed on 22 patients, with 11 positive results and 2 therapeutic. No statistical difference was found in procedures performed in our 2 time periods. Diverticulosis (33.5%), hemorrhoids (22.5%), and carcinoma (12.7%) were the most common etiologies with the diagnosis of diverticulosis more common in the 1998-2006 time period. The small bowel was the source in 14 total patients. Spontaneous cessation of the bleeding occurred in 863 (77.6%) patients. Endoscopic control increased from 1% in 1997-1998 to 4.4% in 1998-2006 (P < .05) with a corresponding decrease in the need for operative control from 22.6% to 16.6% in this same time period (P < .05). Furthermore, among elective operations, there was a decrease in right hemicolectomies from 31.6% of total elective cases to 13.9% (P < .05). Emergent operations were needed in 3.4% and 4.8% of patients. The readmission rate did not change over time and was 5.2% overall with >50% because of diverticular bleeding. CONCLUSION In this urban setting, diverticulosis, hemorrhoids, and carcinoma were the most common causes of severe acute lower gastrointestinal bleeding (LGIB) with diverticular bleed causing the highest recurrence. Colonoscopy allows for diagnosis in most patients with severe acute LGIB requiring hospitalization. Furthermore, it is now being used more effectively for hemostasis resulting in less operative intervention to control bleeding.

The effects of mechanical forces on intestinal physiology and pathology.

The epithelial and non-epithelial cells of the intestinal wall experience a myriad of physical forces including strain, shear, and villous motility during normal gut function. Pathologic conditions alter these forces, leading to changes in the biology of these cells. The responses of intestinal epithelial cells to forces vary with both the applied force and the extracellular matrix proteins with which the cells interact, with differing effects on proliferation, differentiation, and motility, and the regulation of these effects involves similar but distinctly different signal transduction mechanisms. Although normal epithelial cells respond to mechanical forces, malignant gastrointestinal epithelial cells also respond to forces, most notably by increased cell adhesion, a critical step in tumor metastasis. This review will focus on the phenomenon of mechanical forces influencing cell biology and the mechanisms by which the gut responds these forces in both the normal as well as pathophysiologic states when forces are altered. Although more is known about epithelial responses to force, information regarding mechanosensitivity of vascular, neural, and endocrine cells within the gut wall will also be discussed, as will, the mechanism by which forces can regulate epithelial tumor cell adhesion.

Clinical evaluation and management of caustic injury in the upper gastrointestinal tract in 95 adult patients in an urban medical center

BackgroundCaustic ingestion causes a wide spectrum of injuries; appropriate treatment varies according to the severity and extent of the injury. This retrospective study of adult patients with caustic injury presents the endoscopic findings, treatment regimen, and clinical outcome.MethodsOver a 28-year period, 95 consecutive adult patients admitted to an urban emergency hospital for ingestion of caustic materials were studied. Each patient underwent early endoscopy and the injury was graded for severity. There were 61 men and 34 women with an average age of 37.2 years (range 17 to 81). Ingestion was due to a suicide attempt in 49 patients and accidental in 46 patients.ResultsTen patients showed no mucosal damage. The remaining 85 patients had grade I superficial injury in 47 patients, grade II moderate injury in 25 patients, and deep grade III injury in 13 patients. The ingestion of strong acid or strong alkali often produced deep grade III changes while bleach, detergent, ammonia or other substances usually caused grade I injury. Operative interventions were required for 11 patients with grade III injury and 6 patients with grade II injury. Endoscopic grading was predictive for the onset of complications including late esophageal stricture. There were no complications due to endoscopy; one patient with grade III and multiple comorbidities died from multiple organ failure.ConclusionUpper gastrointestinal endoscopy after caustic ingestion should be performed early to define the extent of injury and guide appropriate therapy. Grade I injuries heal spontaneously. Grade II injuries may be treated conservatively but repeat endoscopy helps define when intervention is needed. Grade III injuries ultimately require surgical intervention.

Strain-induced Proliferation Requires the Phosphatidylinositol 3-Kinase/AKT/Glycogen Synthase Kinase Pathway

The intestinal epithelium is repetitively deformed by shear, peristalsis, and villous motility. Such repetitive deformation stimulates the proliferation of intestinal epithelial cells on collagen or laminin substrates via ERK, but the upstream mediators of this effect are poorly understood. We hypothesized that the phosphatidylinositol 3-kinase (PI3K)/AKT cascade mediates this mitogenic effect. PI3K, AKT, and glycogen synthase kinase-3β (GSK-3β) were phosphorylated by 10 cycles/min strain at an average 10% deformation, and pharmacologic blockade of these molecules or reduction by small interfering RNA (siRNA) prevented the mitogenic effect of strain in Caco-2 or IEC-6 intestinal epithelial cells. Strain MAPK activation required PI3K but not AKT. AKT isoform-specific siRNA transfection demonstrated that AKT2 but not AKT1 is required for GSK-3β phosphorylation and the strain mitogenic effect. Furthermore, overexpression of AKT1 or an AKT chimera including the PH domain and hinge region of AKT2 and the catalytic domain and C-tail of AKT1 prevented strain activation of GSK-3β, but overexpression of AKT2 or a chimera including the PH domain and hinge region of AKT1 and the catalytic domain and C-tail of AKT2 did not. These data delineate a role for PI3K, AKT2, and GSK-3β in the mitogenic effect of strain. PI3K is required for both ERK and AKT2 activation, whereas AKT2 is sequentially required for GSK-3β. Furthermore, AKT2 specificity requires its catalytic domain and tail region. Manipulating this pathway may prevent mucosal atrophy and maintain the mucosal barrier in conditions such as ileus, sepsis, and prolonged fasting when peristalsis and villous motility are decreased and the mucosal barrier fails.

Repetitive deformation activates Src-independent FAK-dependent ERK motogenic signals in human Caco-2 intestinal epithelial cells.

Repetitive deformation due to villous motility or peristalsis may support the intestinal mucosa, stimulating intestinal epithelial proliferation under normal circumstances and restitution in injured and inflamed mucosa rich in tissue fibronectin. Cyclic strain enhances Caco-2 and IEC-6 intestinal epithelial cell migration across fibronectin via ERK. However, the upstream mediators of ERK activation are unknown. We investigated whether Src and FAK mediate strain-induced ERK phosphorylation and migration in human Caco-2 intestinal epithelial cells on fibronectin. Monolayers on tissue fibronectin-precoated membranes were subjected to an average 10% repetitive deformation at 10 cycles/min. Phosphorylation of Src-Tyr 418, FAK-Tyr 397-Tyr 576-Tyr 925, and ERK were significantly increased by deformation. The stimulation of wound closure by strain was prevented by Src blockade with PP2 (10 micromol/l) or specific short interfering (si)RNA. Src inhibition also prevented strain-induced FAK phosphorylation at Tyr 397 and Tyr 576 but not FAK-Tyr 925 or ERK phosphorylation. Reducing FAK by siRNA inhibited strain-induced ERK phosphorylation. Transfection of NH2-terminal tyrosine phosphorylation-deficient FAK mutants Y397F, Y576F-Y577F, and Y397F-Y576F-Y577F did not prevent the activation of ERK2 by cyclic strain, but a FAK mutant at the COOH terminal (Y925F) prevented the strain-induced activation of ERK2. Although the Y397F-Y576F-Y577F FAK construct exhibited less basal FAK-Tyr 925 phosphorylation under static conditions, it nevertheless exhibited increased FAK-Tyr 925 phosphorylation in response to strain. These results suggest that repetitive deformation stimulates intestinal epithelial motility across fibronectin in a manner that requires both Src activation and a novel Src-independent FAK-Tyr 925-dependent pathway that activates ERK. This pathway may be an important target for interventions to promote mucosal healing in settings of intestinal ileus or fasting.

Delineating the signals by which repetitive deformation stimulates intestinal epithelial migration across fibronectin

Repetitive strain stimulates intestinal epithelial migration across fibronectin via focal adhesion kinase (FAK), Src, and extracellular signal-related kinase (ERK) although how these signals act and interact remains unclear. We hypothesized that PI3K is central to this pathway. We subjected Caco-2 and intestinal epithelial cell-6 cells to 10 cycles/min deformation on flexible fibronectin-coated membranes, assayed migration by wound closure, and signaling by immunoblots. Strain stimulated PI3K, AKT, glycogen synthase kinase (GSK), and p38 phosphorylation. Blocking each kinase prevented strain stimulation of migration. Blocking PI3K prevented strain-stimulated ERK and p38 phosphorylation. Blocking AKT did not. Downstream, blocking PI3K, AKT, or ERK inhibited strain-induced GSK-Ser9 phosphorylation. Upstream of AKT, reducing FAK or Rac1 by siRNA blocked strain-stimulated AKT phosphorylation, but inhibiting Src by PP2 or siRNA did not. Transfection with FAK point mutants at Tyr397, Tyr576/577, or Tyr925 demonstrated that only FAK925 phosphorylation is required for strain-stimulated AKT phosphorylation. Myosin light chain activation by strain required FAK, Rac1, PI3K, AKT, GSK, and ERK but not Src or p38. Finally, blebbistatin, a nonmuscle myosin II inhibitor, blocked the motogenic effect of strain downstream of myosin light chain. Thus strain stimulates intestinal epithelial migration across fibronectin by a complex pathway including Src, FAK, Rac1, PI3K, AKT, GSK, ERK, p38, myosin light chain, and myosin II.

Bile acids regulate intestinal cell proliferation by modulating EGFR and FXR signaling

Bile acids (BAs) are synthesized in the liver and secreted into the intestine. In the lumen, enteric bacteria metabolize BAs from conjugated, primary forms into more toxic unconjugated, secondary metabolites. Secondary BAs can be injurious to the intestine and may contribute to disease. The epidermal growth factor receptor (EGFR) and the nuclear farnesoid X receptor (FXR) are known to interact with BAs. In this study we examined the effects of BAs on intestinal epithelial cell proliferation and investigated the possible roles for EGFR and FXR in these effects. We report that taurine-conjugated cholic acid (TCA) induced proliferation, while its unconjugated secondary counterpart deoxycholic acid (DCA) inhibited proliferation. TCA stimulated phosphorylation of Src, EGFR, and ERK 1/2. Pharmacological blockade of any of these pathways or genetic ablation of EGFR abrogated TCA-stimulated proliferation. Interestingly, Src or EGFR inhibitors eliminated TCA-induced phosphorylation of both molecules, suggesting that their activation is interdependent. In contrast to TCA, DCA exposure diminished EGFR phosphorylation, and pharmacological or siRNA blockade of FXR abolished DCA-induced inhibition of proliferation. Taken together, these results suggest that TCA induces intestinal cell proliferation via Src, EGFR, and ERK activation. In contrast, DCA inhibits proliferation via an FXR-dependent mechanism that may include downstream inactivation of the EGFR/Src/ERK pathway. Since elevated secondary BA levels are the result of specific bacterial modification, this may provide a mechanism through which an altered microbiota contributes to normal or abnormal intestinal epithelial cell proliferation.

ERK regulates strain‐induced migration and proliferation from different subcellular locations

Repetitive deformation like that engendered by peristalsis or villous motility stimulates intestinal epithelial proliferation on collagenous substrates and motility across fibronectin, each requiring ERK. We hypothesized that ERK acts differently at different intracellular sites. We stably transfected Caco‐2 cells with ERK decoy expression vectors that permit ERK activation but interfere with its downstream signaling. Targeting sequences constrained the decoy inside or outside the nucleus. We assayed proliferation by cell counting and migration by circular wound closure with or without 10% repetitive deformation at 10 cycles/min. Confocal microscopy confirmed localization of the fusion proteins. Inhibition of phosphorylation of cytoplasmic RSK or nuclear Elk confirmed functionality. Both the nuclear‐localized and cytosolic‐localized ERK decoys prevented deformation‐induced proliferation on collagen. Deformation‐induced migration on fibronectin was prevented by constraining the decoy in the nucleus but not in the cytosol. Like the nuclear‐localized ERK decoy, a Sef‐overexpressing adenovirus that sequesters ERK in the cytoplasm also blocked the motogenic and mitogenic effects of strain. Inhibiting RSK or reducing Elk ablated both the mitogenic and motogenic effects of strain. RSK isoform reduction revealed isoform specificity. These results suggest that ERK must translocate to the nucleus to stimulate cell motility while ERK must act in both the cytosol and the nucleus to stimulate proliferation in response to strain. Selectively targeting ERK within different subcellular compartments may modulate or replace physical force effects on the intestinal mucosa to maintain the intestinal mucosal barrier in settings when peristalsis or villous motility are altered and fibronectin is deposited into injured tissue. J. Cell. Biochem. 109: 711–725, 2010. Published in 2010 Wiley‐Liss, Inc.

Supraphysiologic extracellular pressure inhibits intestinal epithelial wound healing independently of luminal nutrient flow

BACKGROUND Luminal pressure may injure the gut mucosa in obstruction, ileus, or inflammatory bowel disease. METHODS We formed Roux-en-Y anastomoses in 19 mice, creating proximal and defunctionalized partially obstructed limbs and a distal limb to vary luminal pressure and flow. We induced mucosal ulcers by serosal acetic acid, and assessed proliferation (proliferating cell nuclear antigen) and ERK (immunoblotting). Parallel studies compared Caco-2 enterocyte migration and proliferation after pressure and/or ERK blockade. RESULTS At 3 days, anastomoses were probe-patent, proximal and distal limbs contained chyme, and defunctionalized limbs were empty. The proximal and defunctionalized limbs showed increased pressure and slower healing despite increased proliferation, ERK protein, and ERK activation. In vitro, pressure decreased Caco-2 migration across collagen or fibronectin, stimulated proliferation, and activated ERK. However, ERK blockade did not prevent pressure effects. CONCLUSIONS Luminal pressure during obstruction or ileus may impair mucosal healing independently of luminal flow despite increased mitosis and ERK activation.

Advances in paediatric gastroenterology

Recent developments in paediatric gastrointestinal surgery have focused on minimally invasive surgery, the accumulation of high-quality clinical evidence, and scientific research. The benefits of minimally invasive surgery for common disorders like appendicitis and hypertrophic pyloric stenosis are all supported by good clinical evidence. Although minimally invasive surgery has been extended to neonatal surgery, it is difficult to establish its role for neonatal disorders such as oesophageal atresia and biliary atresia through clinical trials because of the rarity of these disorders. Advances in treatments for biliary atresia and necrotising enterocolitis have been achieved through specialisation, multidisciplinary management, and multicentre collaboration in research; similarly robust clinical evidence for other rare gastrointestinal disorders is needed. As more neonates with gastrointestinal diseases survive into adulthood, their long-term sequelae will also need evidence-based multidisciplinary care. Identifying cures for long-term problems of a complex developmental anomaly such as Hirschsprungs disease will rely on unravelling its pathogenesis through genetics and the development of stem-cell therapy.