Faculty Bibliography

Acute HIV-1 infection depletes CD4(+) T cells in gut-associated lymphoid tissue (GALT). The failure of containment of local viral replication, and consequent CD4(+) T cell depletion, might be due to delayed mobilization of effector CD8(+) T cells or absence of functioning HIV-1-specific CD8(+) T cell effectors within GALT. No studies have addressed human intestinal HIV-1-specific CD8(+) T cell functions. We sought to determine whether functional HIV-1-specific CTL were present in GALT and whether the repertoire differed from HIV-1-specific CTL isolated from peripheral blood mononuclear cells. From three HIV-1-infected subjects, we isolated HIV-1-specific CD8(+) T cells expressing the mucosal lymphocyte integrin CD103 from GALT. These antigen-specific effector cells could be expanded in vitro and lysed target cells in an MHC class I-restricted manner. HIV-1-specific CTL could be isolated from both duodenal and rectal GALT sites, indicating that CD8(+) effectors were widespread through GALT tissue. The breadth and antigenic specificities of GALT CTL appeared to differ from those in peripheral blood in some cases. In summary, we found HIV-1-specific CD8(+) effector T cells in GALT, despite HIV-1-induced CD4(+) T cell lymphopenia. This suggests that HIV-1-specific CTL in gut tissue can be maintained with limited CD4(+) T cell help

This presentation reviews the role of cholecystokinin (CCK) as a contributory factor for the development and progression of acute pancreatitis (AP) and the perspective of CCK receptor antagonists for treatment of AP. High, supraphysiological concentrations of CCK induce AP in various species including man. There is also evidence that physiological increases in plasma CCK deteriorates AP in several animal models. The latter findings support the hypothesis that CCK plays a contributory or permissive role for the development of AP. The majorities of experimental studies show that the prophylactic and therapeutic use of CCK antagonists ameliorates AP. The latter effects were clearly shown for models of biliary AP in which plasma CCK is increased due to a feedback mechanism. However, CCK antagonists also had beneficial effects in models in which plasma CCK is not increased. In animal strains which do not have a CCK-A-receptor due to a genetic abnormality AP induced by a certain noxious factor does not develop to the same severity when compared to animals with a normal CCK-A-receptor. Thus, CCK acts as a permissive or contributory factor for the development and progression of AP. There is also evidence that CCK antagonists have a potential therapeutic benefit. Clinical studies will evaluate their therapeutic potential for patients with AP.

CONCLUSION/CONCLUSIONS:In models of biliary acute pancreatitis, which might resemble the situation in humans, premature activation of trypsinogen inside the pancreas ("autodigestion") occurs and is correlated with the extent of ductal and parenchymal injury. It is accompanied by a critical spending of protease inhibitors and glutathione, compromising important acinar cell defense and maintenance mechanisms. BACKGROUND:Premature activation of pancreatic digestive enzymes and profound changes of levels of certain biochemical compounds have been implicated in the pathophysiology of acute pancreatitis. Hitherto, little information on their role in biliary acute pancreatitis has been available. METHODS:Three types of injury to the pancreaticobiliary duct system of various severity were induced in rats--ligation of the common bile-pancreatic duct, retrograde infusion of electrolyte, or retrograde infusion of taurocholate solution--and were compared to sham-operated animals. Trypsin, trypsin inhibitory capacity (TIC), reduced glutathione (GSH), and other compounds were measured in pancreatic tissue. Histopathology, as well as serum amylase, lipase, and gamma-glutamyl transferase (gamma GT) were assessed. RESULTS:Histopathology and elevated activity of gamma GT in the serum revealed increasing severity of pancreatic injury from sham operation through retrograde duct infusion with taurocholate. GSH was diminished even in macroscopically normal-appearing tissue, but significantly lower in altered (hemorrhagic)-looking sections. Conversely, tissue levels of trypsin were significantly increased. TIC was elevated only in the duct obstruction model, whereas it was reduced in the retrograde duct infusion models.

The pathological activation of zymogens within the pancreatic acinar cell plays a role in acute pancreatitis. To identify the processing site where activation occurs, antibodies to the trypsinogen activation peptide (TAP) were used in immunofluorescence studies using frozen sections from rat pancreas. Saline controls or animals receiving caerulein in amounts producing physiological levels of pancreatic stimulation demonstrated little or no TAP immunoreactivity. However, after caerulein hyperstimulation (5 micrograms. kg-1. h-1) for 30 min and the induction of pancreatitis, TAP immunoreactivity appeared in a vesicular, supranuclear compartment that demonstrated no overlap with zymogen granules. The number of vesicles and their size increased with time. After 60 min of hyperstimulation with caerulein, most of the TAP reactivity was localized within vacuoles >/=1 micrometer that demonstrated immunoreactivity for the granule membrane protein GRAMP-92, a marker for lysosomes and recycling endosomes. Pretreatment with the protease inhibitor FUT-175 blocked the appearance of TAP after hyperstimulation. These studies provide evidence that caerulein hyperstimulation stimulates trypsinogen processing to trypsin in distinct acinar cell compartments in a time-dependent manner.

Although it is widely accepted that trypsinogen activation is an initiating event in the development of acute pancreatitis, its location inside the pancreas is not known. In our studies, acute edematous pancreatitis was induced in rats by one or two intraperitoneal injections of 50 microg cerulein/kg body weight. The pancreas was removed for examination 1 or 2 h after the first and the second cerulein injection, respectively. The cleavage product of trypsinogen activation, trypsinogen activation peptide, was specifically labeled on pancreatic tissue sections by a corresponding antibody, the signal enhanced by a biotin-avidin conjugate, and the site then visualized by coupled peroxidase activity on diaminobenzidine. The sections were examined by light microscopy. Trypsinogen activation peptide, reflecting activation of the pancreatic digestive enzyme trypsinogen, was detected inside pancreatic acinar cells in this animal model of acute pancreatitis. As early as 1 h after the first injection of cerulein, protease activation was seen within the apical pole of acinar cells. Protease activation was increased 2 h after the latter of two injections of cerulein and more evenly distributed within the cells. For the first time morphologic evidence confirms that the activation originates within the acinar cell, rather than from the interstitium or the duct lumen. The location of this activation at the apical site of the acinar cell indicates its origin from subcellular compartments involving the late steps in the secretory pathway.

BACKGROUND & AIMS/OBJECTIVE:Disturbances of the thiol metabolism of acinar cells may play a role in the pathophysiology of acute pancreatitis. Cerulein-induced pancreatitis causes depletion of glutathione. The entire pancreatic thiol status was assessed in this model. The potential benefit of augmentation of pancreatic glutathione by L-2-oxothiazolidine-4-carboxylate (OTC) for the course of pancreatitis was determined. METHODS:Mice were treated with cerulein (50 microg/kg) and with or without administration of OTC (6.5 and 20 mmol/kg, respectively). Pancreatic tissue was analyzed for reduced and oxidized glutathione, nonprotein thiol, mixed disulfide, protein thiol, and protein disulfide. Histopathology and serum amylase were also assessed. RESULTS:Levels of all thiol compounds were altered profoundly at a different rate during pancreatitis. OTC caused an increase of 60% in pancreatic glutathione. Its administration at 20 mmol/kg attenuated the decrease of pancreatic glutathione and protein thiol until 8 hours and blunted the cerulein-induced increase in amylase activity and histopathologic damage. At 6.5 mmol/kg, OTC failed to show effects on all parameters. CONCLUSIONS:OTC administered in a prophylactic protocol dose-dependently exerted beneficial effects in cerulein-induced pancreatitis in mice despite only transient influence on pancreatic thiol compounds. Thiols (e.g., reduced glutathione) and their corresponding disulfides are critically involved in the pathophysiology of cerulein-induced pancreatitis.

Stimulation of the exocrine pancreas with cholecystokinin analogues leads to a variety of intraacinar processes, many coupled to energy consumption. It was hypothesized that extensive ATP depletion could play a role in the pathophysiology of acute pancreatitis, especially in the hyperstimulation (cerulein) model. Mice received seven intraperitoneal injections of cerulein at hourly intervals, at doses ranging from physiological (0.1 micrograms/kg) to pharmacological (50 micrograms/kg). A single dose of cerulein induced a 28-33% decrease in ATP, whereas a complete course of injections led to a nadir as low as 45% of the control value. The overall pattern of ATP tissue content during the observed time course was surprisingly similar in all four groups and statistically not different at any time point. Until 12 h, ATP levels in all groups remained below the control value. In contrast, serum amylase and light microscopy reflected a degree of pancreatitis in a close dose-response pattern to the administered cerulein dose. These findings suggest that ATP depletion--although probably facilitating acinar damage--does not seem to play a causal or primary role in the pathophysiology of acute pancreatitis.

BACKGROUND & AIMS/OBJECTIVE:Subcellular redistribution of lysosomal enzymes into the zymogen-enriched fraction (cosedimentation) in pancreatic homogenates occurs after different pancreatic injuries and has been proposed to be the trigger event for acute pancreatitis. This phenomenon is now studied in models of biliary pancreatitis. METHODS:The bile-pancreatic duct in rats was either obstructed or retrogradely infused at different degrees of pressure and with solutions of various injurious potential. Controls were untreated or sham operated. Six hours later, the pancreas was analyzed for the total activity of cathepsin B and beta-galactosidase and their distribution among subcellular fractions. RESULTS:In control animals, 17% and 29%, respectively, of these lysosomal enzymes were found in the zymogen fraction. Redistribution occurred after all duct manipulations, including obstruction. In contrast to sham operation and duct obstruction, all modes of duct infusion resulted in marked increases in the total activity of lysosomal enzymes. CONCLUSIONS:Increased lysosomal activity in models of biliary pancreatitis might contribute to acinar injury or represent a cellular repair mechanism. Cosedimentation at a certain extent is a physiological event. Redistribution reflects a uniform response to a range of perturbations, some of which do not cause pancreatitis. Thus, it seems unlikely that redistribution is the trigger event for acute pancreatitis.

Octreotide is an effective therapeutic option in controlling secretory diarrhea of varied etiology. However, marked patient-to-patient differences in the antidiarrheal effects necessitate titration of octreotide dose in individual patients to achieve optimal symptom control. A consensus development panel established guidelines for octreotide dose titration in patients with secretory diarrhea. Overall, the panel recommended an aggressive approach in selecting the initial octreotide dose and in making subsequent dose escalations in patients with secretory diarrhea due to gastrointestinal tumors (eg, carcinoids, VIPomas), AIDS, dumping syndrome, short bowel syndrome, radiotherapy, or chemotherapy. To avoid hypoglycemia in patients with diabetes mellitus-associated secretory diarrhea, the panel recommended a low initial octreotide dose and a conservative titration regimen with close monitoring a blood glucose levels. The end point of therapy should focus on a reduction in diarrhea (frequency of bowel movements or stool volume) rather than normalization of hormonal profile. Overall, octreotide is well tolerated; principal side effects are transient injection site pain and gastrointestinal discomfort. For many patients with secretory diarrhea, octreotide therapy is expected to improve the overall health and quality of life and in the long run will lessen health care costs.