Biliary excretion of enterokinase in rats: studies in alcoholic rats with fatty liver

Isolated ventral pancreatitis in an alcoholic with pancreas divisum

An alcoholic with no history of clinical pancreatitis was found to have pancreas divisum and marked changes of chronic pancreatitis isolated to the ventral pancreas. Pancreas divisum has been suggested to cause recurrent pancreatitis in some patients. Gross and histologic changes of pancreatitis in only the dorsal pancreas of surgically resected specimens from patients with pancreas divisum is thought to support the concept that obstruction at the minor papilla produces dorsal pancreatitis. Alternative explanations for the occurrence of segmental pancreatitis and the possible synergistic role of ethanol and bile are reviewed.

A differential effect between the acute and chronic administration of ethanol on the endocytotic rate constant, ke, for the internalisation of asialoglycoproteins by hepatocytes

The endocytotic rate constant, ke, originally described for the quantification of epidermal growth factor by fibroblasts (Wiley, H.S. and Cunningham, D.D. (1982) J. Biol. Chem. 257, 4222-4229) has been adapted to measure receptor-mediated endocytosis of asialoglycoproteins by hepatocytes. A ke value of 0.21 min-1 was obtained for the internalisation of beta-D-galactosyl bovine serum albumin by freshly isolated hepatocytes. The addition of ethanol to the incubation medium had a biphasic effect on ke. The value of ke was increased by up to 30% by low concentrations of ethanol, whereas higher concentrations progressively decreased ke and in 500 mM ethanol the ke value was 0.1 min-1. The amount of ligand bound to the cell surface was independent of the extracellular concentration of ethanol and the changes in ke were exclusively due to changes in the amount of internalised ligand. There was a progressive decrease in the value of ke in hepatocytes prepared from rats that were maintained on an ethanol-impregnated liquid diet for up to 20 days. The decrease was already apparent by day 2 when blood alcohol levels were only 50 mg%, indicating that the effect of chronic alcoholism on endocytosis are manifested at an early stage.

The generation of lysolecithin by enterokinase in trypsinogen prophospholipase A2 lecithin mixtures, and its relevance to the pathogenesis of acute necrotising pancreatitis

The cascade enterokinase-trypsinogen-prophospholipase A2 lecithin, generating trypsin, phospholipase A2 and lysolecithin, respectively, was studied in vitro using a novel phospholipase A2 assay. The rate of enterokinase catalysed activation of trypsinogen was maximal at 4 mmol/1 glycodeoxycholic acid; higher concentrations of bile salt progressively inhibited enterokinase activity. Net phospholipase A2 activity in reaction mixtures was critically dependent on the trypsin/prophospholipase A2 molar ratio. Lecithin hydrolysis by phospholipase A2 was dependent on the bile salt/lecithin molar ratio and was optimal at 1.25 to 1. The addition of enterokinase to lecithin and bile salt mixtures, containing trypsinogen and prophospholipase A2 at presumed pathophysiological concentrations, resulted in the generation of concentrations of lysolecithin lytic for pancreatic acinar cells within 5 min. These findings would support the concept that the entry of bile containing active enterokinase into the pancreatic duct system in vivo may in some cases be involved in the initiation of necrotising acute pancreatitis in man.

A rational approach to the specific chemotherapy of pancreatitis

Oedematous pancreatitis is pancreatic acinar cell damage with leakage into the peritoneal cavity and circulation of the inactive zymogens of digestive enzymes and active amylase and lipase. Pancreatic oedema and intra-abdominal fat necrosis occur. Necrotising pancreatitis is pancreatic acinar cell damage accompanied by the specific conversion of trypsinogens to trypsins, at a rate, and on a scale, sufficient to overwhelm local defences. Rapid release of the whole spectrum of activated pancreatic enzymes leads to necrosis of parts of the pancreas and blood vessels, and the disseminated enzyme-mediated damage which characterises the molecular pathology of the established severe disease. Chronic pancreatitis, although less well understood, is also associated with trypsinogen activation within the gland. Two mechanisms have emerged as initiators of trypsinogen activation, lysosomal cathepsins and bile-borne enterokinase. Chemotherapeutic strategies against disease initiation include preparation of synthetic enterokinase and Cathepsin B inhibitors. Chemotherapeutic strategies against second-stage mediation of multi-organ damage in the disease, include oligopeptide or organic functionalities with novel catalytic site-directed moieties (such as fluoromethyl ketones) suitable for in vivo use and the specific inhibition of the relevant range of enzymes in complex with alpha 2-macroglobulin. Interference with pancreatic enzyme biosynthesis using proteolysis-resistant constructs mimicking receptor-binding domains of inhibitor peptide hormones as well as inhibitors of pancreatic signal peptidase are promising additional chemotherapeutic approaches worthy of active investigation.

Displacement of endogenous enterokinase into portal venous blood and bile following luminal perfusion of proximal small intestine in guinea pigs

The displacement of endogenous enterokinase into portal venous blood or bile was studied in conscious guinea pigs both with the small intestine undisturbed and during gentle, intermittent luminal perfusion of a 25-cm segment of duodenum and proximal jejunum. Perfusates tested included water, 150 mM saline, 5% (v/v) ethanol, 0.2% (w/v) lysolecithin, and mixtures of ethanol and lysolecithin. Enterokinase activity was absent from portal venous blood of control guinea pigs with the intestine undisturbed but perfusion with luminal saline or water was consistently associated with substantial levels of active enterokinase in portal venous blood. Similar concentrations of enterokinase in portal blood were also detected in response to luminal ethanol and lysolecithin. The capacity of the normal liver rapidly to clear the enzyme from portal blood was demonstrated. Of the estimated total endogenous enterokinase displaced, 0.2-0.4% was recovered in catalytically active form from the pooled bile of luminally perfused but not control animals. The readiness with which enterokinase was displaced into the circulation in the absence of mucosal damage raises the unexpected possibility that the event may be physiological. Induced penetration of the mucosa and absorption of luminal components is clearly different from the release into portal venous blood of endogenous mucosal macromolecules.

Catalytically active enterokinase in human bile

Enterokinase activates trypsinogen very rapidly and is itself resistant to proteolysis and endogenous inhibitors in blood and pancreas. Using a novel one-stage specific catalytic assay capable of detecting enterokinase in the presence of trypsin inhibitors, we have positively identified catalytically active enterokinase in human bile in each of 14 patients studied. Since the presence of active enterokinase in human bile was not explicable by duodeno-biliary reflux, enterokinase must have followed the pathway from gut to blood to liver to bile, previously identified in greater detail experimentally. We suggest that entry into the pancreatic duct system of bile-borne active enterokinase from the common bile duct may trigger necrotising acute pancreatitis.