Brad W. Warner

Epidermal growth factor enhances intestinal adaptation after massive small bowel resection

Epidermal growth factor (EGF) has documented trophic effects on several tissues, including small bowel (SB) mucosa. The purpose of this study was to determine the effect of EGF on intestinal adaptation after massive resection. Young Sprague-Dawley rats (weight, 154 +/- 8.6 g) underwent a 75% proximal SB resection, with primary reanastomosis, and were continuously infused with equivalent volumes of either saline or human recombinant EGF (6.25 micrograms/kg/h) via a subcutaneous osmotic pump. In other animals, the SB was transected and reanastomosed without resection and either saline or EGF was infused. The animals were allowed standard rat chow and water ad libitum and were killed after 28 days. SB was harvested and subjected to histological examination. Intestinal mucosa was analyzed for total DNA and protein contents. After massive SB resection, subcutaneous administration of EGF resulted in significantly increased animal weight (294.5 +/- 16 v 242.8 +/- 14g; P < .05), SB weight (52.8 +/- 7.0 v 37.2 +/- 6.0 cm; P < .05), SB length (14.0 +/- 1.3 v 7.4 +/- 1.6 g; P < .05), and mucosal thickness (1.04 +/- 0.2 v 0.68 +/- 0.2 mm; P < .05). DNA and protein analyses suggest that EGF may augment the mucosal hyperplasia response to massive SB resection. Administration of EGF after massive SB loss may be of nutritional benefit to the host through its enhancement of the normal postresection intestinal response.

Enterocyte apoptosis is increased following small bowel resection

The intestinal mucosa is in a steady state of turnover as the rate of cellular proliferation is balanced by the rate of cell death. Although it is accepted that adaptation after small bowel resection (SBR) results in increased proliferation, its effect on apoptosis is not known. The purpose of this study was to determine the effect of adaptation following SBR on rates of enterocyte apoptosis. Male ICR mice underwent either 50% proximal SBR or sham operation (bowel transection/reanastomosis). After 12 and 24 hours, and 3 and 7 days, rates of proliferation were measured in the ileum as the percentage of crypt cells incorporating bromodeoxyuridine. Apoptosis was quantitated by end labeling of DNA strand breaks and propidium iodide staining of the number of apoptotic bodies per crypt and villus. Significant increases in enterocyte proliferation (30% to 40%) as well as apoptosis (57% to 87%) occurred at all time points following SBR when compared with sham-operated mice. Adaptation following SBR increases both the rate of enterocyte proliferation and the rate of apoptosis. Understanding the pathophysiology of intestinal adaptation and therapeutic interventions designed to augment this important response will require complete characterization of their effects on both proliferation and apoptosis.

Diminished epidermal growth factor levels in infants with necrotizing enterocolitis

BACKGROUND/PURPOSE Because epidermal growth factor (EGF) is trophic to the intestinal mucosa, and neonatal necrotizing enterocolitis (NEC) is associated with a disrupted intestinal mucosal barrier, the authors sought to determine whether diminished levels of EGF were present in infants with NEC. METHODS Saliva, serum, and urine specimens were obtained from infants with NEC during a 3-year period (February 1995 to May 1998). Control patients without NEC were chosen based on similar postnatal age and birthweight. EGF levels were determined by enzyme-linked immunosorbent assay (ELISA). Differences between groups were compared using Mann-Whitney Rank sum test with P less than .05 considered significant. Results are presented as mean values +/-SEM. RESULTS Twenty-five infants with NEC were compared with 19 control patients. Birth weight (1,616+/-238 g control v. 1,271+/-124 g NEC) and postnatal age (23+/-6 days control v. 22+/-3 days NEC) were similar. Infants with NEC had significantly lower levels of EGF in both saliva (590+/-80 pg/mL control v. 239+/-41 pg/mL NEC; P<.001) and serum (35+/-8 pg/mL control v. 5.6+/-1.9 pg/mL NEC; P<.001). Urinary EGF was also lower in the NEC group, but was not statistically significant. CONCLUSIONS Premature infants with NEC have significantly diminished levels of salivary and serum EGF. Reduced levels of this growth factor may distinguish infants at risk for NEC and play a pivotal role in the pathogenesis of the perturbed intestinal mucosal barrier that is central to this condition.

Value of computed tomography of the lung in the management of primary spontaneous pneumothorax

The treatment of patients with primary spontaneous pneumothorax remains controversial, since recurrence and the ultimate need for thoracotomy [corrected] cannot be predicted. In the current study, computed tomography (CT) of the lung was performed prospectively on 26 consecutive patients with primary spontaneous pneumothorax to determine whether the size and/or the number of apical blebs would correlate with recurrence and/or need for thoracotomy [corrected]. Both the number of blebs and the bleb score (calculated by the number of blebs multiplied by a numeric value assigned a range of bleb sizes) of the affected lung was significantly greater in patients with a history of recurrent pneumothorax and/or ultimate need for thoracotomy [corrected] as treatment. CT of the lung may be useful in predicting the natural history of pneumothorax.

Adaptation after small bowel resection is attenuated by sialoadenectomy: The role for endogenous epidermal growth factor ☆ ☆☆

BACKGROUND Epidermal growth factor (EGF) is likely involved during adaptation after small bowel resection (SBR) because some studies have shown enhanced adaptation by EGF administration. Because the major source of endogenous EGF in mice is the submandibular glands, we sought to determine the effect of submandibular gland excision (SAL) and luminal or systemic EGF replacement on adaptation after SBR. METHODS A 50% proximal SBR or Sham-SBR (bowel transection and reanastomosis) was performed on male C57BL/6 mice after either SAL or gland mobilization only. Additional mice underwent both SBR and SAL and then received daily EGF or saline solution by intraperitoneal or orogastric administration. At 1 week, adaptation was characterized in the ileum as changes in villus height, DNA, and protein content. RESULTS SAL significantly attenuated the increase in ileal villus height, total protein, and DNA content after SBR. Both systemic and oral EGF reversed these findings equally and significantly augmented all parameters of intestinal adaptation after SAL. CONCLUSIONS Submandibular EGF is important for the adaptive response to massive SBR. As both luminal and systemic EGF equally reversed the findings following SAL and SBR, the specific site of action for endogenous EGF during adaptation is either the luminal or basolateral surface of the enterocyte.

Epidermal growth factor is critical for intestinal adaptation following small bowel resection.

The loss of small intestinal mucosal surface area is a relatively common clinical situation seen in both the pediatric and adult population. The most frequent causes include mesenteric ischemia, trauma, inflammatory bowel disease, necrotizing enterocolitis, and volvulus. Following surgical resection, the remnant intestine compensates or adapts to the loss of native bowel by increasing its absorptive surface area and functional capacity. Unfortunately, many patients fail to adapt adequately, and are relegated to lifelong intravenous nutrition. Research into intestinal adaptation following small bowel resection (SBR) has evolved only recently from the gross and microscopic level to the biochemical and genetic level. As understanding of this process has increased, numerous therapeutic strategies to augment adaptation have been proposed. Epidermal growth factor (EGF) is an endogenous peptide that is secreted into the gastrointestinal tract and able to influence gut ontogeny, as well as mucosal healing. Early studies have demonstrated its ability to augment the adaptive process. Focusing on a murine model of massive intestinal loss, the morphological, structural, biochemical, and genetic changes that occur during the intestinal adaptive process will be reviewed. The role of EGF and its receptor as critical mediators of the adaptive process will be discussed. Additionally, the ability of EGF to augment intestinal proliferation and diminish programmed cell death (apoptosis) following SBR will be examined. Enhancing adaptation in a controlled manner may allow patients to transition off parenteral nutrition to enteral feeding and, thereby, normalize their lifestyle. Microsc. Res. Tech. 51:138–148, 2000.

Intestinal overexpression of EGF in transgenic mice enhances adaptation after small bowel resection

The effect of direct intestinal overexpression of epidermal growth factor (EGF) on postresection adaptation has been investigated by the production of transgenic mouse lines. A murine pro-EGF cDNA construct was produced, and expression of the EGF construct was targeted to the small intestine with the use of the rat intestinal fatty acid-binding protein promoter. An approximately twofold increase in intestinal EGF mRNA and protein was detected in heterozygous mice. No changes in serum EGF levels were noted. Except for a slightly shortened small intestine, no other abnormal phenotype was observed. Intestinal adaptation (increases in body weight, DNA, protein content, villus height, and crypt depth) was markedly enhanced after a 50% proximal small bowel resection in transgenic mice compared with nontransgenic littermates. This transgenic mouse model permits the study of intestinal adaptation and other effects of EGF in the small intestine in a more physiological and directed manner than has been previously possible. These results endorse a direct autocrine/paracrine mechanism for EGF on enterocytes as a means to enhance adaptation.

Urinary nitrite and nitrate concentrations in patients with idiopathic persistent pulmonary hypertension of the newborn and effect of extracorporeal membrane oxygenation.

ABSTRACT: Persistent pulmonary hypertension of the newborn (PPHN) often requires extracorporeal membrane oxygenation (ECMO), during which time pulmonary vascular resistance gradually declines. Nitric oxide (NO) is a recently recognized pulmonary vasodilator, but its role in PPHN is unknown. We tested the hypothesis that the concentrations of the urinary metabolites of NO, i.e. nitrite and nitrate, are reduced in patients with PPHN and increase during ECMO as the PPHN resolves. Eight newborn infants with PPHN on ECMO were studied. Daily urinary concentrations of nitrite/nitrate were measured. We found that mean urinary concentrations of nitrite/nitrate were lower in patients with PPHN than in 47 controls without pulmonary disease (p < 0.005). Urinary nitrite/nitrate concentration showed an initial increase after initiation of ECMO. However, a decrease to concentrations still lower than controls occurred on the day before decannulation. We conclude that intrinsic NO production is significantly lower in patients with PPHN than in controls but increases with oxygenation. We speculate that decreased urinary NO metabolite concentrations imply a role for NO deficiency in the pathogenesis of PPHN.

Epidermal growth factor upregulates the expression of its own intestinal receptor after small bowel resection

BACKGROUND/PURPOSE Epidermal growth factor (EGF) binds to its enterocyte receptor and enhances intestinal adaptation after massive small bowel resection (SBR). To ascertain the mechanism for enhanced adaptation by EGF, we sought to determine the effect of EGF administration on in vivo expression of the intestinal EGF receptor after SBR. METHODS Male ICR mice underwent a 50% proximal SBR and then were assigned randomly to EGF (150 microg/kg/d) or saline by twice daily intraperitoneal injection. After 3 days, the ileum was harvested and total protein and DNA content were measured. Northern hybridization and a ribonuclease protection assay were used to detect qualitative and quantitative expression of EGF receptor mRNA. The remaining ileum was pooled for each group and Western blotting used to determine expression of EGF receptor protein. RESULTS EGF augmented adaptation after SBR as monitored by significant increases in ileal protein (2.7+/-0.08 saline versus 3.9+/-0.17 mg/cm EGF; P<.001) and DNA (55.8+/-1.6 saline versus 104+/-8.4 microg/cm EGF; P<.001) content. Northern blotting results showed a marked (>fivefold) increase in ileal EGF receptor mRNA, which was confirmed with the ribonuclease protection assay. Administration of EGF after SBR induced a similar expression of EGF receptor protein. CONCLUSIONS EGF enhanced intestinal adaptation after SBR. This augmented response is associated with increased ileal expression of EGF receptor mRNA and protein. Increased EGF receptor expression and subsequent enhanced ligand/ receptor activity may be one important mechanism for the beneficial effect of EGF administration during intestinal adaptation.

Effect of massive small bowel resection on the Bax/Bcl-w ratio and enterocyte apoptosis

Following small bowel resection (SBR), the remnant intestine undergoes adaptation. Enterocyte proliferation is increased and counterbalanced by increased rates of apoptosis. To elucidate a mechanism for increased enterocyte apoptosis, this study tested the hypothesis that the ratio between pro-apoptotic Bax and pro-survival Bcl- w correlates with the apoptosis that occurs following SBR. Mice (C57B1/6; n = 76) underwent a 50% proximal SBR or sham operation. After 12 hours and 1,2,3, and 7 days, the ileum was removed, the apoptotic index (apoptotic bodies/crypt) was recorded, and the messenger RNA and protein for Bax and Bcl-w were quantified. The apoptotic index was equivalent in the sham and SBR mice at 12 hours; however, it was significantly elevated following SBR at every other day measured. The ratio of Bax to Bcl-w messenger RNA relative to sham operation increased after SBR at 24 hours, decreased by day 3, and returned to baseline levels by 1 week. The protein ratio showed an increase by day 1, which remained elevated through day 7. An augmented ratio of Bax to Bcl-w messenger RNA and protein corresponded with the increase in enterocyte apoptosis. Alterations in the expression ratio of these genes may play a role in establishing a new homeostatic set point between proliferation and apoptosis during adaptation.