Characterization of type I and type II insulin-like growth factor receptors in an intestinal epithelial cell line.

Insulin-like growth factors (IGFs) and insulin stimulate DNA and protein synthesis in IEC-6 cells (an intestinal epithelial cell line) grown in a chemically defined medium. IGF-I stimulates proliferation of IEC-6 cells at a lower concentration (ED50 = 1.6 nM) than either insulin or IGF-II. To gain insight into the mechanisms by which IGFs stimulate IEC-6 cell growth, we have examined the characteristics of specific IGF receptors on IEC-6 cells. Binding of 125I-IGF-I and 125I-IGF-II to IEC-6 monolayers was analyzed by incubation with various concentrations (0.2 nM to 0.5 microM) of radiolabeled IGFs for 16 h at 3 C. Scatchard plots of 125I-IGF-I binding were linear, suggesting a single class of binding sites with KD = 3.1 +/- 0.35 nM and Bmax = 50.7 +/- 6 fmol/10(6) cells. IGF-II was potent in displacing 125I-IGF-I (KI = 8.1 +/- 0.85 nM), but insulin had little effect. Affinity cross-linking with 125I-IGF-I followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed three bands with Mr of 270,000, 245,000, and 133,000, and the major band was the 133,000 species. Labeling of the 133,000 and 270,000 bands was greater than or equal to 80% inhibited by 10(-7) M unlabeled IGF-I, less potently inhibited by IGF-II and not at all by insulin. These results suggest that the 133,000 band represents the alpha-subunit of the type I IGF receptor. Scatchard plots of 125I-IGF-II binding to IEC-6 cell monolayers were curvilinear, suggesting two classes of binding sites: high affinity, low capacity sites, KD = 0.87 +/- 0.08 nM and Bmax = 28 +/- 2.5 fmol/10(6) cells; low affinity, high capacity sites, KD = 60 = +/- 8.8 nM and Bmax = 1780 +/- 230 fmol/10(6) cells. Neither IGF-I nor insulin was effective in inhibiting 125I-IGF-II binding. Affinity cross-linking with 125I-IGF-II labeled predominantly a 245,000 band, suggesting that this species is the type II receptor. A band with Mr 131,000 was barely detectable with 125I-insulin. These results indicate that IEC-6 cells have abundant quantities of the type I and II IGF receptors and few insulin receptors, suggesting that the mitogenic effect of IGFs is mediated through the type I IGF receptor.

Secretion of insulin-like growth factor II (IGF-II) and IGF-binding protein-2 by intestinal epithelial (IEC-6) cells: implications for autocrine growth regulation.

To identify the factors regulating the proliferation of intestinal epithelium, we examined the effects of various growth factors on [3H] thymidine incorporation into the DNA of IEC-6 cells, an intestinal epithelial cell line derived from rat jejunal crypts. Insulin-like growth factor-I (IGF-I), IGF-II, and insulin stimulated the DNA and protein synthesis of IEC-6 cells in serum-free medium supplemented with transferrin, dexamethasone, and BSA (basal medium). Concentration-response experiments demonstrated that IGF-I is approximately 10 times more potent than IGF-II or insulin in producing 2- to 3-fold stimulations of DNA and protein synthesis by IEC-6 cells. In addition, IEC-6 cells proliferated slowly in the basal medium without any added growth factors. Analysis of medium conditioned by IEC-6 cells by gel filtration chromatography, RIA, HPLC, and N-terminal sequencing revealed that IEC-6 cells synthesize and secrete mature, 7,500 mo wt (M(r)) IGF-II as well as high M(r) forms of IGF-II. In addition, ligand blot, immunoblot, and N-terminal sequence analyses showed that IEC-6 cells produce the 34,000 M(r) IGF-binding protein-2 (IGFBP-2). To determine if IGFBP-2 modulates IGF responses in IEC-6 cells, the IGF-I analogs, Des-(1-3)-IGF-I and [Gln3,Ala4,Tyr15,Leu16]IGF-I, both of which have a reduced affinity for IGFBPs, were tested for their effects on IEC-6 cell proliferation. Both analogs exhibited 10-fold greater potency than IGF-I, presumably because endogenously secreted IGFBPs depress IGF-I binding to cell surface receptors. Finally, purified IGFBP-2 attenuated the DNA synthesis of IEC-6 cells in a dose-dependent manner. We conclude that IGFBP-2 secreted by intestinal epithelial cells is capable of limiting the mitogenic activity of both exogenous and endogenous IGFs by blocking the association of the growth factors with cell surface binding sites. These results further suggest that the growth of IEC-6 cells is modulated by autocrine mechanisms involving IGF-II and IGFBP-2.

Probiotics: future directions.

Clinical studies have shown that certain probiotics may be useful in treating a variety of diarrheal disorders, including rotavirus diarrhea, antibiotic-associated diarrhea, Clostridium difficile diarrhea, and traveler's diarrhea. New data suggest that probiotics might be useful in controlling inflammatory diseases, treating and preventing allergic diseases, preventing cancer, and stimulating the immune system, which may reduce the incidence of respiratory disease. Different modes of administering probiotics are currently being investigated, which may ultimately lead to the widespread use of probiotics in functional foods. It is important that such practices be directed by carefully controlled clinical studies published in peer-reviewed journals.

Hepatic protein synthesis and secretion after jejunoileal bypass in the rat.

The rat was used as an animal model to explore the mechanism responsible for the development of hepatomegaly and hypoproteinemia which commonly occur after jejunoileal bypass. Sprague-Dawley rats. 300 to 350 g, were divided into three groups of 12 animals. Six of the 12 rats per group served as study animals and six as controls. The first six were subjected to 90% jejunoileal bypass and the six controls were sham-operated and pair-fed. In the second group, six animals were subjected to 90% jejunoileal resection and six controls were sham-operated and pair-fed. Six animals in the third group were underfed so that their weights mimicked that of the bypassed animals and six controls were fed ad libitum. After 8 wk the animals were killed. Liver weights, hepatic protein content, and serum protein and triglycerides were determined. Synthesis and secretion of proteins and glycoproteins were measured using incorporation of 14C-leucine and 14C-glucosamine, respectively, into hepatic and medium proteins by liver slices. Bypassed animals demonstrated hepatomegaly, decreased serum proteins and triglycerides, and increased hepatic protein content. While both protein and glycoprotein synthesis remained normal, the secretion of these proteins into the medium appeared to be impared. Comparable changes did not occur after jejunoileal resection or after underfeeding. This study suggests that the impairment of glycoprotein and protein secretion may be a contributing factor in the increased liver weight and protein content in conjunction with decreased serum protein observed in the bypassed rat.

Effect of dietary menhaden oil on normal growth and development and on ameliorating mucosal injury in rats.

We evaluated the effects of menhaden oil on growth and development of the small intestinal mucosa in growing rats and on the progression and resolution of methotrexate-induced mucosal injury in the rats. One study compared effects of diets containing 10% safflower oil(SO), 9% SO and 1% menhaden oil (MO), 10% MO, or 9% MO and 1% SO on mucosal growth and development for 125 d. In another study, animals fed the 10% MO or the 10% SO diet for 5 wk were subjected to subcutaneous methotrexate injections for 3 consecutive days. Feeding rats a diet containing large amounts of menhaden oil resulted in lower prostaglandin E2 and leukotriene B4 synthesis and lower sucrase activities. Indicators of mucosal mass after methotrexate-induced injury were significantly improved in both the jejunum and ileum at 3 and 10 d after methotrexate administration. Our data suggest that dietary menhaden oil stimulates mucosal regeneration after methotrexate-induced injury.

Effect of zinc deficiency on mucosal hyperplasia following 70% bowel resection.

We evaluated the effect of zinc deficiency on the development of mucosal hyperplasia in male Sprague-Dawley rats following 70% small-bowel resection: 20 underwent 70% jejunoileal resection, another 20 were sham operated. Half of each group were made zinc deficient by force-feeding technique. Operations were then performed, and feedings were continued for another 9 days. While mucosal weight did not differ between zinc-deficient and zinc-replete animals, whether or not they underwent resection, mucosal protein and DNA levels were decreased in both resected and sham-operated, zinc-deficient animals. Functional indices were also affected. Maltase activities were decreased in zinc-deficient animals in the midileum. Mucosal zinc-dependent enzymes, alkaline phosphatase and leucine aminopeptidase, were likewise depressed in zinc-deficient animals. Findings suggest that zinc deficiency in short-bowel syndrome will likely impair mucosal hyperplasia.

Manometric diagnosis of lower esophageal sphincter incompetence in infants: use of a small, single-lumen perfused catheter.

Lower esophageal sphincter (LES) pressure is frequently measured to diagnose LES incompetence in adults. The multilumen perfused catheters with large diameters that are used for ths purpose are not suitable for small infants. We measured LES pressure in ten normal newborns with a small, single-lumen perfused catheter and compared our values with those obtained with the standard adult apparatus. Higher pressures were recorded with the single-lumen catheter. Chloral hydrate sedation had no effect on LES pressure. Two-day-old infants had LES pressures comparable to those of adults and older children. The technique was applied to the diagnosis of LES incompetence in 23 infants. Infants with LES incompetence (chalasia) were correctly separated from infants with chronic vomiting secondary to all other causes. Single-lumen manometric studies provide a simple, reliable, and safe method of assessing LES incompetence in small infants.

Elevated plasma aluminum levels in normal infants receiving antacids containing aluminum.

Aluminum toxicity is a documented cause of encephalopathy, anemia, and osteomalacia. Excretion is primarily renal; therefore, patients with renal insufficiency are at risk for aluminum accumulation and toxicity. This has been demonstrated in uremic children treated with aluminum-containing antacids. The purpose of this study was to determine whether plasma aluminum levels were elevated in infants with normal renal function during prolonged aluminum-containing antacid use. Ten study infants (mean age = 5.8 months), who had been receiving antacids for at least 1 week, were compared with 16 control infants (mean age = 9.8 months) not receiving antacids. The study patients consumed 123 +/- 16 mg/kg per day (mean +/- SEM) of elemental aluminum for an average of 4.7 weeks. Their plasma aluminum level (37.2 +/- 7.13 micrograms/L) was significantly greater than that of the control group (4.13 +/- 0.66 micrograms/L) (P less than .005). It is concluded that plasma aluminum levels may become elevated in infants with normal renal function who are consuming high doses of aluminum-containing antacids. The safety of antacids containing aluminum should not be assumed and they should be used judiciously in infants, with careful monitoring of the aluminum dose and plasma level.

Preliminary experience with intestinal transplantation in infants and children.

OBJECTIVE: This report discusses the preliminary experience with intestinal transplantation in children at the University of Nebraska Medical Center. PATIENTS: During the past 4 years, 16 intestinal transplants have been performed in infants and children. Thirteen have been combined liver and bowel transplants, and the reminder were isolated intestinal transplants. Nearly half of the patients were younger than 1 year of age at the time of surgery, and the vast majority were younger than 5 years of age. All but one had short bowel syndrome. RESULTS: The 1-year actuarial patient and graft survival rates for recipients of liver and small bowel transplants were 76% and 61%, respectively. Eight of 13 patients who received liver and small bowel transplants remain alive at the time of this writing, with a mean length of follow-up of 263 (range, 7 to 1223) days. Six patients are currently free of total parenteral nutrition. All three patients receiving isolated intestinal transplants are alive and free of parenteral nutrition. The mean length of follow-up is 384 (range, 330 to 450) days. Major complications have included severe infections and rejection. Lymphoproliferative disease, graft-versus-host disease, and chylous ascites have not been major problems. CONCLUSIONS: Although intestinal transplantation is in its infancy, these preliminary results suggest combined liver and bowel transplants and isolated intestinal transplantation may be viable options for some patients with intestinal failure caused by short bowel syndrome or other gastrointestinal disease in whom long-term total parenteral nutrition is not an attractive option.

Nitrogen balance in adult hospitalized patients with the use of a pediatric amino acid model.

Normalization of plasma amino acid patterns and that relationship to improved nitrogen balance was studied using a pediatric-specific amino acid solution in 21 adults requiring total parenteral nutrition therapy. There was a significantly positive correlation between improved nitrogen balance and the amino acids cystine, tyrosine, total cysteine/cystine, and ornithine. When additional cysteine was added to the solution of 11 subjects, taurine also correlated with nitrogen balance. Despite higher amounts of histidine in solution, plasma amino acid levels were not normalized. These amino acids, heretofore considered nonessential, may be required in specific molar ratios in stress. The use of a 30% branched-chain pediatric-balanced amino acid solution resulted in near normalization of plasma amino acid levels and group mean positive nitrogen balance.

On the importance of cholecystokinin in neonatal pancreatic growth and secretory development in guinea pigs.

The role of cholecystokinin (CCK) in pancreatic growth and secretory development in fetal and neonatal guinea pigs was investigated by CCK receptor blockade. For the last 20 days of gestation, sows received the CCKA receptor antagonist, MK329 (25 nmol/kg/h) by continuous subcutaneous infusion. Alternatively, neonates from untreated females received an MK329 infusion for the first 4 or 15 days following birth. Pancreatic weight, DNA, RNA, protein, and amylase content per 100 g body weight and secretory responses to CCK, carbamylcholine, and phorbol ester were determined at birth and 4 days in animals receiving MK329 in utero and were measured at 4 and 15 days in neonatally infused animals. No significant changes in pancreatic growth parameters were seen in MK329-treated animals compared to controls, except for a small (14%; p < 0.02) decrease in weight after 15 days of neonatal exposure. Enhanced amylase secretion in response to CCK and carbamylcholine was seen in all groups receiving MK329 (all p values < 0.00001). Pancreatic growth and secretion were not inhibited by CCKA receptor blockade, which suggests that the effects of CCK mediated by the CCKA receptor are not essential for growth or development of the pancreatic amylase secretory response in the neonatal guinea pig.

Enteral nutrition in short bowel syndrome.

Enteral nutrition in pediatric short bowel syndrome is a key component in facilitating a child's growth and development. In addition, aggressive use of enteral nutrition is not only one of the most important factors in promoting intestinal adaptation; it as well avoids the numerous complications associated with long-term parenteral nutrition. This manuscript will review the appropriate enteral nutrition for a child with short bowel syndrome. Issues to be addressed include appropriate enteral formula selection, solid food intake, enteral administration routes, and devices. Information presented is based on current research as well as experience with a large population of pediatric short bowel syndrome patients.

Immunonutrition: the role of carbohydrates.

The major role for carbohydrates in the diet is for the provision of energy. Most non-energy-related effects of carbohydrates can be related to short-chain fatty acid production or other effects of bacterial fermentation in the colon. More complex or slowly absorbed carbohydrates may also reduce glycemic index and insulin production and therefore may have a less profound effect on modification of lipid metabolism. Certain carbohydrates may promote fermentation in the colon, increasing short-chain fatty acid production and may alter bacterial flora in the small bowel and colon. Increased insoluble fiber will increase fecal bulk. Further immunomodulary effects of carbohydrates have had little attention in the literature. This would be a potential opportunity for further investigation.

Effect of high percentage medium-chain triglyceride diet on mucosal adaptation following massive bowel resection in rats.

Patients undergoing massive small bowel resection for a variety of conditions develop severe nutrient malabsorption which gradually improves through mucosal hyperplasia in the remaining small intestine. Following massive small bowel resection, patients are generally fed elemental diets, often containing high concentrations of medium-chain triglycerides. We evaluated the effect of high percentage medium-chain triglyceride feeding on mucosal adaptation following massive small bowel resection in rats. Twenty 150-g Sprague-Dawley rats were subjected to 60% jejunoileal resection. Another 20 animals received sham operations. One-half of each group were fed a diet containing 83% of the fat as medium-chain triglycerides, the remainder were fed a diet containing 40% medium-chain triglycerides. Animals were pair-fed for 2 wk and subsequently killed. The remaining bowel was removed and unidirectional glucose and leucine uptake were measured using isolated sacs. Mucosal wet weight, protein, and sucrase content were determined. Animals fed medium-chain triglycerides demonstrated decreased mucosal weight in the proximal bowel, decreased mucosal sucrase activity in the proximal bowel, and decreased mucosal leucine uptake in the distal bowel. While medium-chain triglycerides offer an advantage to patients with short bowel syndrome because they are easily absorbed, they may not stimulate the same degree of mucosal adaptation following resection as long-chain triglyceride feedings.

The role of eicosanoids in the process of adaptation following massive bowel resection in the rat.

BACKGROUND: Long chain polyunsaturated fatty acids (LCPUFAs) such as arachidonic acid (AA) and eicosapentaenoic acid (EPA) stimulate intestinal adaptation. Prostaglandins also enhance intestinal adaptation. The purpose of this study was to determine by which eicosanoid pathway dietary arachidonic acid enhances intestinal adaptation. Cyclo-oxygenase or lipoxygenase were selectively inhibited to determine whether either of them enhanced or inhibited adaptation. METHODS: Sixty Sprague-Dawley rats were divided into 2 groups, one receiving an 80% small bowel resection and the other receiving a sham operation. Rats were further divided into groups receiving either a placebo, a general lipoxygenase inhibitor (nordihydroguaiaretic acid [NDGA] at 40 mg/kg per day), or a cyclo-oxygenase-2 inhibitor (Etodolac at 3 mg/kg per day). Rats were pair-fed a diet containing 30% kcal from fat, primarily consisting of AA. RESULTS: After 14 days, mucosal mass, protein, DNA, and disaccharidase activity were measured in the remaining small intestine. There was a significant decrease in ileal mucosal mass in rats receiving Etodolac and a significant increase in mucosal mass in the duodenum in rats receiving NDGA (both p < .001). Mucosal DNA, protein, and disaccharidase data showed similar trends. CONCLUSIONS: These findings suggest that after small bowel resection, dietary arachidonic acid may facilitate the adaptation process by acting as a substrate for the synthesis of prostaglandins, and not through the derivatives of lipoxygenase such as leukotrienes or thromboxanes.

Short bowel syndrome in children and small intestinal transplantation.

This article discusses the management of short bowel syndrome from the time of intestinal resection until the patient either recovers free of supplemental parenteral and enteral nutrition or progresses to the point of needing intestinal transplantation. The importance of aggressive use of enteral feedings is emphasized, especially in relation to the process of intestinal adaptation. An approach to the various complications of short bowel syndrome, especially small bowel bacterial overgrowth, is discussed. Surgical options short of transplantation also are described. Intestinal transplantation and its present and future roles in the management of patients with short bowel syndrome are discussed.

Juvenile polysaccharidosis with cardioskeletal myopathy.

Polysaccharidoses with ultrastructural features reminiscent of glycogenosis type IV, but without enzymatic correlation, have been observed in several adolescent and adult patients. Little is known of the clinical, pathologic, or biochemical nature of these disorders. We describe a patient with ultrastructural characteristics consistent with glycogenosis type IV, but with normal brancher enzyme activity in dermal fibroblasts and cardiac muscle. During life and at autopsy, electron microscopy revealed amylopectin-like polysaccharide deposits present in a wide variety of tissues. The polysaccharidosis of our patient and similar patients may be a variant of glycogenosis type IV with a yet to be defined enzymatic defect.

Short bowel syndrome.

This article discusses the management of short bowel syndrome during the neonatal period. It includes information regarding etiology and pathophysiology and parenteral and enteral nutrition therapy. Finally, a discussion of the role of intestinal transplantation in the treatment of short bowel syndrome is included.

Experience with intestinal lengthening for the short-bowel syndrome.

Patients with the short-bowel syndrome frequently develop dilated intestinal segments that may lead to impaired motility and malabsorption. Although intestinal tapering alone improves motility, the intestine can be lengthened as well. We reviewed our experience with six children undergoing intestinal lengthening to improve intestinal absorption secondary to the short-bowel syndrome. The procedure was performed by dissecting the vessels along the mesenteric border and dividing the intestine longitudinally with a stapler. Five patients were receiving total parenteral nutrition (TPN) and one was becoming malnourished with enteral feedings alone. Bacterial overgrowth was documented in four patients and abnormal liver function in three patients. The intestinal segments were dilated up to 10 cm in diameter and remnant length ranged from 15 to 79 cm. Segments 5 to 25 cm in length were divided, resulting in an average increase in length of 52%. Necrosis of one of the divided limbs necessitated resection in one patient. Follow-up ranged from 2 to 84 months. TPN has been discontinued in four patients and avoided in another. Symptomatic improvement occurred in all patients. We feel the tapering and lengthening procedure should be considered in patients with symptomatic, dilated intestinal segments in whom the need for TPN may potentially be obviated.

A jejunoileal bypass rat model for rapid study of the effects of vitamin malabsorption.

Jejunoileal bypass operation was originally done to promote weight loss for treatment of morbid obesity. We used such a model to determine if dietary vitamin absorption is compromised by such an operation. Six rats were subjected to a jejunoileal bypass, 6 control rats were pair-fed to bypassed rats; and 6 were fed ad libitum. Vitamin content of folic, B6, riboflavin, nicotinate, pantothenate, thiamin, biotin, B12, vitamins A, E, and carotene in blood and liver was determined after 8 postoperative weeks. Aside from riboflavin, blood vitamin levels were significantly depressed in bypassed rats. The deepest depression was seen for B12, carotene and vitamin E. Liver vitamin stores of folate, riboflavin, thiamin, B12, clearly were significantly depressed in the bypassed animals compared to the pair-fed and ad libitum-fed controls. This model can serve for rapidly studying micronutrient depletion due to malabsorption without dietary manipulation or antibiotics for gut sterilization.