Emanuel Lebenthal

Isolated colonocyte metabolism of glucose, glutamine, n-butyrate, and β-hydroxybutyrate in malnutrition

The colonic mucosa may be especially vulnerable during starvation and malnutrition, as luminal nutrients make the greatest contribution to its energy production. To investigate possible metabolic changes in the colonic mucosa during nutrient restriction, we studied substrate utilization by colonocytes isolated from three groups of 6-wk-old rats: control, fasted (72 h), and chronically malnourished animals. Isolated colonocytes were incubated with nonlabeled and 14C-labeled substrates (glucose, glutamine, n-butyrate, or beta-hydroxybutyrate). Substrate oxidation and net increase of intermediary metabolites were reduced in fasted and malnourished animals. The effect of fasting on substrate oxidation was greater than that of chronic malnutrition for all substrates tested except n-butyrate. The total ketone body concentrations and beta-hydroxybutyrate to acetoacetate ratios were higher in the fasted and malnourished groups than in controls. The findings suggest that the colonic mucosa responds to nutrient deprivation by a general reduction of oxidative metabolism that is associated with an altered redox state.

Interaction of epidermal growth factor with specific binding sites of enterocytes isolated from rat small intestine during development

Isolated enterocytes from rat small intestine were characterized for their specific binding of epidermal growth factor (EGF). Intestinal epithelial cells were isolated at 4 degrees C to minimize the loss of receptor sites during the isolation procedure. 125I-labelled EGF binding to enterocytes from adult rats was found to be specific, saturable, temperature dependent and trypsin sensitive. Binding performed in the presence of a lysosomotropic agent (NH4Cl) increased the time required to reach maximal binding at 25 degrees C. NH4Cl had no significant effect on the time-course of EGF binding at 4 degrees C and 37 degrees C. A Scatchard plot showed a curvilinear relationship indicating that EGF binds to enterocytes with more than one binding site. Developmentally, enterocytes from fetuses and pups showed characteristic temperature dependence and trypsin sensitivity, but with different levels of binding to EGF. Specific EGF binding was demonstrably higher in enterocytes from small intestine of term fetuses. EGF binding to isolated enterocytes declined rapidly after birth, and the level stayed fairly constant thereafter. Pretreatment of enterocytes from fetal intestine with mature rat milk led to a dose-dependent decrease in EGF binding. These results suggest the presence of endogenous milk factors that modify EGF binding and account for, at least partly, the observed rapid decrease of EGF binding after birth.

Small intestinal glucoamylase deficiency and starch malabsorption: A newly recognized alpha-glucosidase deficiency in children

To determine the prevalence of short polymers of glucose and starch malabsorption caused by small intestinal glucoamylase deficiency in children with chronic diarrhea, we studied small bowel biopsy specimens from 511 children (aged 1 month to 9 years) with chronic diarrhea evaluated at 54 medical centers. Glucoamylase and disaccharidase (lactase, sucrase, maltase, and palatinase) enzyme assays were performed. Of the 511 children, 15 had glucoamylase deficiency. Six who had significant small intestinal mucosal injury and disaccharidase deficiencies were defined as having secondary glucoamylase deficiency; the other nine patients with normal mucosal morphologic features were defined as having primary glucoamylase deficiency. Secretin tests showed normal pancreatic amylase values for age in all seven children tested. Four of them had abnormal findings on tolerance tests for starch and short polymers of glucose (rise in blood glucose concentration: < 20 mg/dl) and reducing substances in stools, and three of these four had symptoms of intolerance (abdominal distention, flatulence, and diarrhea). All seven patients responded to a starch elimination diet. After reintroduction of a starch diet, diarrhea recurred in four patients; this was alleviated 48 hours after reelimination of starch. We conclude that intestinal glucoamylase deficiency is present in some patients with chronic diarrhea.

Chylous ascites: total parenteral nutrition as primary therapeutic modality

A female infant with Down syndrome and congenital chylous ascites presented at birth with respiratory distress secondary to marked abdominal distension. Total parenteral nutrition (TPN) and paracentesis were the primary therapeutic modality. On hyperalimentation, however, ascites initially recurred, requiring additional paracenteses to improve respiratory distress. The chylous ascites, lymphopenia and hypoalbuminemia were relieved after 10 weeks of TPN administration. We recommend a long-term course (10 weeks) of TPN before an exploratory laparatomy and possible surgical intervention are considered.

Effects of graded alpha-glucosidase inhibition on sugar absorption in vivo.

The effect of inhibition of disaccharidases on the degree of absorption of glucose, lactose, and sucrose was examined utilizing an in vivomodel in the rat. Acarbose, a competitive αglucosidase inhibitor was utilized to selectively inhibit small intestinal mucosal enzymes. Adult rats (250–350 g body weight) were the subjects of intraduodenal bolus infusion experiments with either sugar alone or sugar plus acarbose. All sugars were infused at a dose of 0.5 g/kg body weight. Portal venous blood glucose was determined at 30-min intervals from 0 to 150 min. Glucose (monosaccharide) and lactose (β-galactoside) absorption were not altered by the presence of acarbose. In contrast, sucrose (α-glucosidase) absorption was significantly diminished in the presence of acarbose. Sucrose absorption in the presence of increasing acarbose doses (0.7–5.6 mg/kg body weight) was depressed in a dose-dependent fashion. Linear regression analysis revealed a high degree of correlation between residual sucrase activity and area under blood glucose curve (r=0.9837). Similar degrees of correlation were found between acarbose dose and area under blood glucose curve (r=−0.9322), and between residual sucrase activity and acarbose dose (r=−0.9695). These data confirm that acarbose is a selective α-glucosidase inhibitor that does not affect monosaccharidase transport. In the presence of acarbose, α-glucosidase absorption is diminished in a dosedependent fashion. Postprandial glucose rise following an α-glucosidase meal seems to be determined, in the presence of graded acarbose inhibition, by residual mucosal α-glucosidase activity.

Effect of difluoromethyl ornithine (DFMO) on small intestine of adult and weanling rats

Oral feeding ofdl-difluoromethyl ornithine (DFMO) (2% in waterad libitum) for 14 days has no detectable effect on the small intestine of adult rats.Similar feeding of DFMO to weanling rat pups caused diarrhea in three to four days accompanied by a decrease in food consumption and body weight compared to age-matched controls. Significant decreases in small intestinal mucosal weight, total protein, DNA, enterokinase, leucine amino peptidase, sucrase, and maltase contents were observed in the DFMO-treated group four days after treatment. Extending the treatment to seven days led to a more severe reduction in these parameters. Villous atrophy of the mucosa was demonstrable by light microscopy and morphometric measurements. The mucosa of the DFMO-treated rat pups showed a reduction in total thickness and villous height but no change in crypt depth. A significant reduction in villus-crypt ratio was also seen.Changes in small intestinal mucosal parameters were not due to a decrease in food intake since pair-fed, agematched rat pups showed no biochemical changes compared to control pups. DFMO-treated weanling rats showed less than 5% of ornithine decarboxylase (ODC) activity when compared to age-matched control animals. The effects observed on the small intestinal mucosa are presumably due to inhibition of ornithine decarboxylase activities by DFMO which prevents the proliferation, regeneration, and maturation of epithelial cells. The relative insensitivity of the adult rat small intestine to DFMO treatment suggests a lesser dependence of its intestinal mucosa to ODC activities.

Medium-chain acyl CoA dehydrogenase deficiency: Electron microscopic differentiation from Reye syndrome

Inborn errors involving the oxidative metabolism of fatty acids may present clinically with a Reye syndrome-like picture. This case report of a patient with medium-chain acyl CoA dehydrogenase (MCAD) deficiency illustrates that electron microscopy may help to differentiate this disorder from Reye syndrome even if a liver biopsy is performed in a patient who recovered from an acute metabolic decompensation. Together with this case, a review of the few reports in the literature of pathological findings in MCAD deficiency is given. Changes uncharacteristic for Reye syndrome are a largedroplet steatosis and the presence of distinctive mitochondrial abnormalities on electron microscopy. The detection of an electron dense mitochondrial matrix and a widened space of inner mitochondrial membranes rules out Reye syndrome and is suggestive of a disorder of mitochondrial fatty acid oxidation.

Physiological factors controlling release of enterokinase from rat enterocytes

The quantitative release of enterokinase from isolated rat enterocytes following treatment with taurocholate-taurodeoxycholate, papain, chymotrypsin, elastase, carbamylcholine, and cholecystokinin-octapeptide was examined. Alkaline phosphatase and lactate dehydrogenase activities were evaluated simultaneously to check for specificity. Bile salts promoted a concentration-dependent release of all enzymes. Concomitantly, bile salts also led to cell destruction in proportion to the amount of enzymes released. Proteases caused the release of enterokinase and alkaline phosphatase with no concomitant increase of lactate dehydrogenase or cell lysis. At equal concentrations, papain released more enzymes than chymotrypsin and elastase. Chymotrypsin and elastase, however, led to higher ratios of enterokinase to alkaline phosphatase found in the media and suggested a selective release of enterokinase (EK) over that of alkaline phosphatase. Bile salts and pancreatic proteases together seem to have an additive effect of the release of EK. Carbamylcholine and cholecystokinin-octapeptide had no effect on enzyme release. These results suggested that pancreatic proteases are involved in the release of enterokinase by a selective action. Bile salts may also play a role through a nonselective detergent effect.

Hydrolysis and absorption of glucose polymers from rice compared with corn in chronic diarrhea of infancy

Because rice remains the most available carbohydrate in developing countries, where chronic diarrhea is most prevalent, we compared the in vitro hydrolysis and clinical tolerance of rice glucose polymer with those of corn glucose polymer. Rice glucose polymer hydrolysis to D-glucose and short-chain polymers (polymers with two to four glucose units and those with five or more units) was similar to that for corn glucose polymers during incubation with saliva or duodenal aspirates. However, rice glucose polymers yielded more short-chain products than corn glucose polymers during incubation with pooled mucosal homogenates (p less than 0.01). In vivo tolerance testing of 16 infants with chronic diarrhea confirmed that rice glucose polymers were well tolerated and, compared with corn glucose polymers, achieved a higher maximal increase of serum glucose concentration (36.6 +/- 7.3 vs 27.6 +/- 10.3 mg/dl; p less than 0.02), a shorter time to peak serum glucose concentration (34.0 +/- 10.2 vs 52.5 +/- 25.7 minutes; p less than 0.02), and a greater area under the serum glucose response curve at 30 minutes (538 +/- 131 vs 1035 +/- 501 cm; p less than 0.02). We conclude that rice glucose polymers are rapidly hydrolyzed in vitro and in vivo and are more rapidly absorbed than are corn glucose polymers in children with chronic diarrhea.

Oral feeding of isolated lectins from red kidney bean stimulates rat small intestinal mucosal DNA synthesis and crypt cell division

A lectin preparation containing enterokinase inhibitor purified or partially purified from red kidney bean (RKB) when fed to weanling rats was shown to cause small intestinal hyperplasia. To see if this hyperplastic effect on the rat small intestine was due to the mitogenic properties of the isolated lectin, male weanling rats were fed a chow containing 0.1% of the isolated lectin for six days. Age-matched control rats were fed regular chow. Both control and lectin-fed rats were sacrificed at one, two, three, four, and six days after the start of lectin feeding. The proximal small intestinal mucosa of rats fed lectin showed gradual increases in protein and DNA contents throughout the experimental period. Morphological studies showed marked increases in crypt depth from days I through 6 in these rats with essentially no change in mucosal thickness or villous height. DNA synthetic activity peaked at day 2, but was higher than control throughout the experimental period. Labeling index was 0.36±0.03 in duodenum of controls as compared to 0.45±0.02 in duodenum of weanling rats fed lectin for two days. These results demonstrate that RKB lectin stimulates overall DNA synthetic activity and increases crypt cell proliferation on the small intestine of weanling rats. The observed mucosal hyperplasia is probably due to increases in crypt cell population as shown by the increase in crypt depth.