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Intraluminal and Mucosal Starch Digestion in Congenital Deficiency of Intestinal Sucrase and Isomaltase Activities

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Intraluminal and Mucosal Starch Digestion in Congenital Deficiency of Intestinal Sucrase and Isomaltase Activities Pediat. Res. 6: 832-839 (1972) Congenital enzyme deficiencies isomaltase digestion starch intestine sucrase Intraluminal and Mucosal Starch Digestion in Congenital Deficiency of Intestinal Sucrase and Isomaltase Activities S. AURIGCHIO'481, F. CICCIMARRA, L. MOAURO, F. REY, J. JOS, AND J. REY Gruppo di Ricerca in Gastroenterologia del Consiglio Nazionale delle Ricerche, Clinica Pediatrica II, Universita di Napoli, Naples, Italy, and Unite de Recherches de Genetique Medicale, Hopital des Enfants Malades, Paris, France Extract Ten patients affected by congenital deficiency of intestinal sucrase and isomaltase activities were studied. The intraluminal a-amylolysis of amylopectin was found to be normal in these patients. It is incomplete during the 1st year of life, both in pa- tients and in controls, as a consequence of the lower a-amylase activity in this age group. Maltotriose was well tolerated in two normal controls ages 32 and 3 months and in one 31-month-old patient: in these subjects an oral tolerance test with the trisaccha- ride was followed by a rapid increase of blood glucose (46-58 mg/100 ml) and did not cause diarrhea. However, in a 6-month-old patient fermentative diarrhea and low increase of blood glucose (24 mg/100 ml) followed oral load with maltotriose. In all patients, enzyme assays on intestinal biopsy specimens showed that the glucamylase activity of the heat-resistant maltase(s) was normal, while that of the sucrase-iso- maltase complex was decreased. These results suggest that starch malabsorption in congenital sucrose and isomal- tose intolerance results from deficiency of the enzymatic activities of the sucrase-iso- maltase complex involved in starch digestion. Speculation Malabsorption of starch can be expected to result from: (/) deficiency of pancreatic amylase; (2) congenital or acquired deficiency of the glucosidase activities of the brush border; (3) glucose malabsorption; (4) higher intestinal flow rate. The results in this study show that one particular form of starch malabsorption is a consequence of congenital deficiency of the activities of the sucrase-isomaltase complex involved in starch digestion. The methods used here should prove to be useful also in the investi- gation of other forms of starch malabsorption. Introduction the intestinal lumen, salivary and pancreatic amylases Starch digestion results from the combined action of split starch into a mixture of maltose, maltotriose, and enzymes in the intestinal lumen and of enzymes of the branched dextrins [4, 8] (a-amylase limit products). brush border surface of the intestinal epithelial cell. In At the brush border surface of the enterocyte, the fol- 832 Starch digestion in sucrase-isomaltase deficiency 833 lowing compounds are hydrolyzed into glucose by the Table I. Intestinal glycosidase activities involved in starch heat-resistant maltase(s) and by the sucrase-isomaltase digestion complex [12, 31]: (/) the a-amylase limit products of Enzymes Substrates starch digestion [21, 22, 28, 31]; (2) the intermediary products of the a-amylolysis of starch, such as malto- Sucrase-isomaltase Maltose [31] complex (destroyed Mahotiiose [22, 28] tetraose and higher linear and branched oligosaccha- by heating at 56°) Isomaltos: [31] rides [1, 29]; and (3) starch and glycogen [1, 6, 13, 14, Low molecular weight branched 30, 32] (Table I). dextrins [21] It is well known that on ingestion of starch patients Low molecular weight fractions of soluble starch (glucamylase ac- with congenital deficiency of intestinal sucrase and tivity1) [3, 6] isomaltase activities get fermentative diarrhea of a Heat-resistant malt- Maltose [31] considerably milder degree than upon ingestion of ase(s) (resistant to Maltotriose [22, 28] sucrose [7, 9, 27, 33]. Actually, the intestinal mucosa of heating at 56°) Isomaltose [31] these patients was found to be deficient not only in Low and high molecular weight fractions of soluble starch; glyco- sucrase and isomaltase [2, 10], but also in maltase [10], gen (glucamylase activity') [1, 6, maltotriase [22], and glucamylase [15] activities. 14, 30, 32] This paper describes in vivo and in vitro studies on 1 digestion of starch in children with congenital deficiency Glucamylase enzymes are able to hydrolyze starch and glyco- of sucrase and isomaltase activities and in normal con- gen directly into glucose. trols. The intraluminal a-amylolytic digestion of starch was studied by analyzing the carbohydrates which measurement of the average degree of polymerization accumulate in the proximal jejunum after a test meal (DP) of total carbohydrates, and fractionation of the containing amylopectin. Some aspects of mucosal starch carbohydrates on Sephadex G-50 [39] and on a char- digestion were also investigated by performing malto- coal-celite column [40, 41] were carried out according triose tolerance tests and by assaying the glucamylase to methods previously described [8]. The only modifica- tions concern the chromatography on charcoal: follow- activity in bioptic specimens of intestinal mucosa. ing deactivation with HC1, charcoal was treated with a 2.5% solution of stearic acid in absolute ethanol; fur- Material and Methods thermore, elution of the sugars in the 1 to 4 DP range Ten patients affected by congenital deficiency of in- was achieved by a water to 10% tertiary butanol gradi- testinal sucrase and isomaltase activities [27] were ent [18]; the column was subsequently washed with investigated. At the time of the first investigation, pa- 20 % tertiary butanol in water, in order to elute the tients 1 and 4, ages 4 and 6 months, respectively, were remaining dextrins. These modifications improved re- kept on a starch- and sucrose-free diet; the only sugars covery of branched dextrins from the column. fed to them were glucose and lactose. The remaining Oral tolerance tests were done in two patients and patients were also kept on a sucrose-free diet, but they in two controls with 50 g/m2 of amylopectin [37], mal- received a small amount of starch. The control group was tose [38], and maltotriose given as 15% watery solution. fed a diet containing sucrose and starch. In every case Glucose was determined in capillary blood by the glu- informed consent for the intubation was obtained from cose-oxidase method [20] before and 10-180 min after the parents. ingestion of the test solution. Stools were collected during Intubation studies using a single-lumen tube were the 24-hr period preceding and the 72-hr period carried out in five patients and in three controls after following oral administration of the test substance: in oral administration of a test meal containing amylo- each stool sample, pH [9], lactic acid [33], glucose, and pectin [37], casein [38], and oil. Details on the compo- starch [5] were determined. Carbohydrates in stool were sition of the test meal were previously given [8]. The separated and detected by thin layer chromatography intestinal juice was continuously collected from the [34] after treatment of feces with acetone [17]. Malto- proximal 20-cm segment of jejunum for 1- to 3-hr peri- triose was prepared in our laboratory according to the ods [8]. Collection was made directly into a vessel which procedure described in the appendix to this paper. was maintained in a freezing solution of Dry Ice and The disaccharidase activities were assayed according acetone. At the end of collection, the juice was rapidly to Auricchio et al. [11]. The enzymatic activity hydro- homogenized at +4°. Assay of pancreatic enzymes, lyzing soluble starch directly into glucose (i.e., glucamyl- 834 AuRICCHIO ET AL. ase activity) was assayed: (i) as "total glucamylase," crase and isomaltase activities were in the same range as after tryptic inactivation of the a-amylase; and (2) as controls (Table II). Furthermore, the intestinal content "heat-resistant glucamylase" after heat inactivation of of glucose, oligosaccharides, and dextrins of three pa- the a-amylase and of the sucrase-isomaltase complex tients and one control, all older than 1 year, was not [3, 6, 30]. significantly different. The average degree of polymeri- For tryptic inactivation, a 2%, w/v, homogenate in zation (DP) of total carbohydrates was 2.15 in the distilled water was added, volume by volume, to 0.2 M control and ranged between 2.42 and 2.53 in the pa- sodium maleate buffer, pH 5.8, containing ethylenedia- tients. Dextrins with DP larger than 7 were 8 % of total minetetraacetate (EDTA, 4 ^moles/ml) and twice carbohydrates in the control and ranged between 11 and crystallized trypsin [42] (1 mg/ml); the mixture was 15% in the patients. Most carbohydrates had DP incubated at 37° for 30 min. For heat inactivation, the smaller than 7; these were branched dextrins with DP 2 % homogenate was diluted with the same volume of between 5.11 and 5.85, as well as maltotriose, maltose, 0.01 M sodium phosphate buffer, pH 6.9, containing and glucose. No maltotetraose was found in this age 0.01 M EDTA and was heated at 56° for 30 min. After group (Table III). tryptic digestion or heat inactivation, glucamylase ac- Two patients and two controls, ages from 6 to 13 tivity was determined as follows: 20 jj enzyme solution months, displayed quite low levels of a-amylase activity (0.02-0.1 unit enzyme activity per ml 0.1 M sodium in intestinal juice (Table IV). In these subjects, the a- maleate buffer, pH 5.8) were added to 20 /A 2% soluble amylolysis of amylopectin was less extensive, at least in starch solution [43] in distilled water and were incubated the proximal part of jejunum. Indeed, dextrins with DP at 37° for 0 min, 30 min, and 60 min. The reaction was larger than 7 were present in larger amounts as compared stopped by heating in a boiling water bath for 2 min; to older subjects (24 and 26 % of total carbohydrates in then 280 jj water and 40 Ml of both 10% ZnSO4- 7 H2O the controls and 27 and 40.4% in the patients) and the .and 0.6 N NaOH were added to the test tubes.
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