Munir Mobassaleh

Maturational regulation of globotriaosylceramide, the Shiga-like toxin 1 receptor, in cultured human gut epithelial cells.

Differentiated villus intestinal epithelial cells express globotriaosylceramide, the Shiga-like toxin 1 (SLT-1) receptor, and are sensitive to toxin-mediated cytotoxicity, whereas undifferentiated crypt cells neither express Gb3 nor respond to toxin. To investigate if SLT-1 receptors are maturationally regulated in human intestinal cells, we examined the effect of butyrate, a known transcriptional regulator of differentiation genes in many cell types, using cultured colonic cancer-derived epithelial cell lines. Exposure to butyrate increased villus cell marker enzymes such as alkaline phosphatase, sucrase, and lactase, expression of toxin receptors, and sensitivity to SLT-1 in villus-like CaCo-2A and HT-29 cells. These effects were reversibly inhibited by preincubation of CaCo-2A cells with actinomycin D or cycloheximide. Butyrate-treated CaCo-2A cells unable to bind fluoresceinated SLT-1 B subunit were undifferentiated as assessed by alkaline phosphatase activity. HT-29 cells induced to differentiate by another signal, glucose deprivation, upregulated receptor content and response to toxin. Crypt-like T-84 cells responded to butyrate with a modest increase in alkaline phosphatase and toxin binding, but no induction of sucrase or lactase, and no change in sensitivity to toxin. The results demonstrate that expression of SLT-1 toxin receptors and toxin sensitivity are coregulated with cellular differentiation in cultured intestinal cells.

Efficacy of cimetidine for gastric acid suppression in pediatric patients

The efficacy of oral cimetidine for gastric acid suppression in pediatric patients was examined in a double-blind study. Twenty-seven patients with gastroesophageal reflux-related gastrointestinal symptoms, pulmonary symptoms, or both were given randomly determined doses of cimetidine. Response was evaluated by continuous intragastric monitoring with a pH probe. Twenty-three patients were given cimetidine doses of 5,7.5, and 10 mg/kg; eight of these patients were also given additional doses of 15 mg/kg. Four patients received only 10 and 15 mg/kg, because of previous poor clinical response to the lower dosages. The onset of gastric pH greater than 4 was delayed more than 2 hours in 50% of patients with responses to the 5 mg/kg dose. Of the patients with responses to the 10 mg/kg dose, 75% had showed a rise in gastric pH greater than 4 within 2 hours. With respect to the duration of gastric acid suppression, 70% of patients receiving 5 mg/kg doses and 52% of those receiving 7.5 mg/kg doses did not have a sustained a response for more than 2 hours, whereas 75% of patients receiving 10 mg/kg doses had gastric acid suppression for longer than 2 hours. Of the patients receiving 15 mg/kg doses, 75% had a response for more than 2 hours; 50% of these patients had a response for more than 3 hours. We conclude that recommended doses of cimetidine for children may not be optimal for adequate gastric acid suppression.

Histological esophagitis: clinical and histological response to omeprazole in children.

Many children with esophagitis demonstratehistological changes without gross evidence ofesophagitis by esophagoscopy. The effect of omeprazoleon the histological healing of esophagitis in childrenis unknown. Therefore, the aim of this study wasto determine the effect of omeprazole on refractoryhistological esophagitis in pediatric patients. Eighteenpatients with histological evidence of esophagitis and recurrent symptoms despite therapy withH2-receptor antagonists and prokinetic agentswere prospectively treated with omeprazole. Dosing wasadjusted by monitoring intragastric pH, andesophagoscopy was repeated after 8-12 weeks of omeprazoletreatment. Two patients did not complete the study dueto either worsening symptoms or hypergastrinemia. Of theremaining patients, 76% were asymptomatic with omeprazole treatment and 24% reportedimprovement in their symptoms. Approximately 40%demonstrated complete histological healing of theiresophagitis. Three patients (17%) had persistentelevations in serum gastrin levels while on omeprazoletreatment, which was associated with both youngerpatient age and higher omeprazole dosing; however, allelevated gastrin levels returned to normal afterdiscontinuation of the medication. All patients had recurrenceof their symptoms after completing a course ofomeprazole, even patients with complete histologicalhealing. Omeprazole is efficacious in treating children with esophagitis refractory toH2-receptor antagonist and prokinetic agents.However, none of the patients were able to discontinueacid suppressive therapy even after documented healingof their esophagitis.

Quantitation of the rabbit intestinal glycolipid receptor for Shiga toxin

Shiga toxin, produced by Shigella dysenteriae 1, causes enterotoxic, cytotoxic, and neurotoxic effects, which may be mediated by a glycolipid receptor, globotriaosylceramide, Gb3. To study the relationship of this receptor and toxin effects, globotriaosylceramide was quantitated and further characterized in rabbit small intestinal microvillus membranes at various ages. Glycolipids were extracted from rabbit microvillus membranes, purified on Unisil columns, and quantitated by high-performance liquid chromatography. The major glycolipid peaks were hydroxylated fatty acid-containing glucosylceramide, lactosylceramide, and globotriaosylceramide. There was a marked increase of globotriaosylceramide levels with age, ranging from 0.02 to 16.2 pmol/micrograms microvillus membrane protein in neonates and adults, respectively. The globotriaosylceramide peak was susceptible to alpha-galactosidase treatment, which produced an elevation in the lactosylceramide peak, but markedly reduced globotriaosylceramide content in 34-day-old rabbits. Binding of iodinated Shiga toxin to globotriaosylceramide was documented on high-performance thin-layer chromatography plates by autoradiography. The glycolipid receptor for Shiga toxin in rabbit microvillus membranes is thus a hydroxylated fatty acid-containing globotriaosylceramide. This moiety is virtually absent in neonates and gradually increases with age. Quantitative differences in globotriaosylceramide may be the underlying basis for the age-specific differences in functional responsiveness of rabbit intestinal tissue to Shiga toxin.

Developmental delay and growth failure caused by a peroxisomal disorder, dihydroxyacetonephosphate acyltransferase (DHAP‐AT) deficiency

We describe a 6 1/2-year-old-girl presenting with a unique phenotype and dihydroxyacetonephosphate acyltransferase (DHAP-AT) deficiency (1.6% of control activity in cultured fibroblasts), a peroxisomal enzyme deficiency which was reported previously to cause rhizomelic chondroplasia punctata (RCDP). Her phenotype is less severe than that seen in classical RCDP, and is notable for short stature, microcataracts, normal limbs, mild hypotonia, and severe mental retardation. Epiphyseal stippling is present. This patient illustrates the variability of peroxisomal disorders whereby a specific defect in peroxisomal plasmalogen synthesis may lead to several phenotypes. Her case also suggests that children presenting with deficient growth, developmental delay, and epiphyseal stippling should be screened carefully for peroxisomal disorders, with measurement of plasmalogens in addition to very long chain fatty acids.

THE EFFECT OF BUTYRATE ON THE REGULATORY ENZYMES OF THE SHIGA TOXIN RECEPTOR IN HUMAN CULTURED INTESTINAL CELLS. • 727

THE EFFECT OF BUTYRATE ON THE REGULATORY ENZYMES OF THE SHIGA TOXIN RECEPTOR IN HUMAN CULTURED INTESTINAL CELLS. • 727

700 EFFICACY OF GASTRIC ACID SUPPRESSION BY CIMETIDINE IN PEDIATRIC PATIENTS

The dose of cimetidine necessary to suppress gastric acid production in pediatric patients is not well established. Consequently, we studied 9 pts (mean age 7 yr, range 8m-10yr) with GI and/or pulmonary symptoms of gastroesophageal reflux, documented by abnormal overnight esophageal pH probe. The probe was then advanced into the stomach and gastric pH recorded before and after oral doses of cimetidine: 4 pts received randomized doses (5,7.5,and 10 mg/kg) at 8-hr intervals; 5 pts received 5 and 10 mg/kg at 4-hr intervals. Age-appropriate standardized meals were given starting 1 hr following administration of the initial dose. Efficacy of gastric acid suppression was defined as gastric pH >4.RESULTS:*One pt, unresponsive to all 3 doses, was treated with 14.3 mg/kg; gastric pH measured >4 for 1.4 hrs only.CONCLUSIONS: 1) Currently used cimetidine doses of 5 and 7.5 mg/kg fail to suppress gastric acid for >1 hr in some pts. 2) Two pts were unresponsive to doses as high as 10 mg/kg. 3) Documentation of gastric acid suppression is indicated in the management of pediatric patients with peptic related disease.