Activation of Human Pancreatic Proteolytic Enzymes: The Role of Enteropeptidase and Trypsin.

The role of enteropeptidase and trypsin in the process by which pancreatic proteolytic zymogens are converted into active enzymes has been investigated in the past, using purified enzymes and proenzymes of animal origin. In the present study, we wanted to study this process under conditions which come near to the physiological situation, which prevails in the human duodenum and upper small intestine. Patients and Methods: Duodenal contents were collected from 2 patients with intestinal enteropeptidase deficiency. The samples expressed no tryptic activity and were used as the source of zymogens. Enteropeptidase or trypsin was added to these samples and the process of zymogen activation was followed by measuring trypsin and chymotrypsin activities. Results: When exogenous trypsin was added to the duodenal contents of patients with enteropeptidase deficiency, having no tryptic activity, activation of intrinsic trypsinogen was not observed. When purified porcine or human enteropeptidase was added to the same samples of duodenal contents, this resulted in a rapid, dose-dependent activation of trypsinogen followed by the activation of chymotrypsinogen. Conclusion: The study underlines the key role of enteropeptidase in the cascade process, which leads to the presence of active proteolytic enzymes in the human small intestine. The results also explain why patients with congenital deficiency of enteropeptidase are unable to activate trypsinogen by alternative pathways and therefore suffer from a severe disturbance of protein digestion with failure to thrive at young age, hypoproteinemia, and anemia.

Bicarbonate in cystic fibrosis.

BACKGROUND: Cystic fibrosis (CF, mucoviscidosis) is caused by mutations in the gene encoding CF transmembrane conductance regulator (CFTR), which is a chloride and bicarbonate channel necessary for fluid secretion and extracellular alkalization. For a long time, research concentrated on abnormal Cl- and Na+ transport, but neglected bicarbonate as a crucial factor in CF. METHODS: The present short review reports early findings as well as recent insights into the role of CFTR for bicarbonate transport and its defects in CF. RESULTS: The available data indicate impaired bicarbonate transport not only in pancreas, intestine, airways, and reproductive organs, but also in salivary glands, sweat duct and renal tubular epithelial cells. Defective bicarbonate transport is closely related to the impaired mucus properties and mucus blocking in secretory organs of CF patients, causing the life threatening lung disease. CONCLUSIONS: Apart from the devastating lung disease, abrogated bicarbonate transport also leads to many other organ dysfunctions, which are outlined in the present review.

Reduced incidence of severe metabolic crisis or death in children with medium chain acyl-CoA dehydrogenase deficiency homozygous for c.985A>G identified by neonatal screening.

The incidence of severe metabolic crises in medium chain acyl-CoA dehydrogenase deficiency (MCADD) patients homozygous for the common c.985A>G mutation, who had been identified by neonatal screening, was assessed prospectively and compared to retrospective cohort data in unscreened patients with identical genotypes. Logrank test showed a significant reduction of severe metabolic crises in the screened cohort (p<0.01). Neonatal screening appears to reduce the rate of severe metabolic crisis or death in the most prevalent subset of MCADD.

Mutations in the proenteropeptidase gene are the molecular cause of congenital enteropeptidase deficiency.

Enteropeptidase (enterokinase [E.C.3.4.21.9]) is a serine protease of the intestinal brush border in the proximal small intestine. It activates the pancreatic proenzyme trypsinogen, which, in turn, releases active digestive enzymes from their inactive pancreatic precursors. Congenital enteropeptidase deficiency is a rare recessively inherited disorder leading, in affected infants, to severe failure to thrive. The genomic structure of the proenteropeptidase gene (25 exons, total gene size 88 kb) was characterized in order to perform DNA sequencing in three clinically and biochemically proved patients with congenital enteropeptidase deficiency who were from two families. We found compound heterozygosity for nonsense mutations (S712X/R857X) in two affected siblings and found compound heterozygosity for a nonsense mutation (Q261X) and a frameshift mutation (FsQ902) in the third patient. In accordance with the biochemical findings, all four defective alleles identified are predicted null alleles leading to a gene product not containing the active site of the enzyme. These data provide first evidence that proenteropeptidase-gene mutations are the primary cause of congenital enteropeptidase deficiency.

[Exocrine enzymes in the pancreatic rudiments of the chick embryo developing in association with homologous or heterologous mesenchyme]. / Développement des enzymes exocrines dans les bourgeons pancréatiques chez l'embryon de poulet en présence de mésenchymes homologues et hétérologues.

The aim of the present study was to investigate the development of enzymes in the chick pancreas and to study the influence of a heterologous mesenchyme (lung mesenchyme) on the differentiation of these enzymes. 1. The normal development of chymotrypsin, carboxypeptidase A, amylase, and lipase in the chick pancreas has been studied. The proteolytic activities as well as the amylase become detectable between day 14 and day 17. The total and specific activities of these enzymes remain rather low during about a week, and they show a spectacular rise just before hatching. In contrast to the proteolytic and amylolytic enzymes, lipase could not be detected before day 20 and showed a rapid increase just before and during hatching. 2. These enzymes have also been studied in the spleen and in the lung. Both organs show low and constant activities of chymotrypsin, carboxypeptidase A, and amylase. They are devoid of lipase. The latter enzyme appears to be strictly specific for the pancreas. 3. The specific activities of the various enzymes were measured in the various lobes of the pancreas; however, no significant differences were found. 4. All enzymatic activities were found in the organs obtained from an association of pancreatic epithelium with pulmonary mesenchyme and which developed in coelomic grafts. These activities were as high as in control organs where the pancreatic epithelium was not dissociated from its own mesenchyme. In conclusion it was found that the determined pancreatic epithelium, if it is associated with a pulmonary mesenchyme at the early embryonic stage, gives rise to biochemically normal exocrine pancreatic tissue.