Differences in secretory granule content in pancreatic acinar cells from peri-insular and tele-insular regions

Temporal Analysis of Amylase Expression in Control, Autoantibody-Positive, and Type 1 Diabetes Pancreatic Tissues

Within the human pancreas, exocrine and endocrine cells control secretion of digestive enzymes and production of hormones to maintain metabolic homeostasis, respectively. While the vast majority of type 1 diabetes research efforts have focused on endocrine function and autoimmunity, recent studies identified a series of unique features (e.g., reduced weight and volume, increased density of leukocytes) within the exocrine pancreas in this disease, but the mechanisms underlying these aberrancies are unknown. Therefore, we histologically assessed amylase, insulin, glucagon, lipase, and/or trypsinogen in 78 organ donor pancreata from birth through adulthood in control subjects and those at various stages of type 1 diabetes. While amylase-positive (AMY⁺) acinar cells were detectable in pancreata from all study groups, tissues from individuals >2 years of age contained clusters of acinar cells devoid of amylase (AMY^-). A majority of these AMY^- cell clusters localized proximal to islets (i.e., peri-islet). Additionally, most AMY^- clusters were positive for the exocrine enzymes lipase and trypsinogen. Interestingly, type 1 diabetes pancreata displayed significant reductions in the frequency of these AMY^- cell clusters. These results support a contribution of the islet-acinar axis in pancreatic development and underscore a potential role for the exocrine pancreas in the pathogenesis of type 1 diabetes.

Evaluation of miR-216a and miR-217 as Potential Biomarkers of Acute Exocrine Pancreatic Toxicity in Rats

Detecting and monitoring exocrine pancreatic damage during nonclinical and clinical testing is challenging because classical biomarkers amylase and lipase have limited sensitivity and specificity. Novel biomarkers for drug-induced pancreatic injury are needed to improve safety assessment and reduce late-stage attrition rates. In a series of studies, miR-216a and miR-217 were evaluated as potential biomarkers of acute exocrine pancreatic toxicity in rats. Our results revealed that miR-216a and miR-217 were almost exclusively expressed in rat pancreas and that circulating miR-216a and miR-217 were significantly increased in rats following administration of established exocrine pancreatic toxicants caerulein (CL) and 1-cyano-2-hydroxy-3-butene (CHB) as well as in rats administered a proprietary molecule known to primarily affect the exocrine pancreas. Conversely, neither microRNA was increased in rats administered a proprietary molecule known to cause a lesion at the pancreatic endocrine–exocrine interface (EEI) or in rats administered an established renal toxicant. Compared with amylase and lipase, increases in miR-216a and miR-217 were of greater magnitude, persisted longer, and/or correlated better with microscopic findings within the exocrine pancreas. Our findings demonstrate that in rats, miR-216a and miR-217 are sensitive and specific biomarkers of acute exocrine pancreatic toxicity that may add value to the measurement of classical pancreatic biomarkers.

Immunolocalization of venom metalloproteases in venom glands of adult and of newborn snakes of Bothrops jararaca

Using immunoelectronmicroscopy we analyzed qualitative and quantitatively the intracellular distribution of bothropasin, hemorrhagic factor 2 (HF2) and hemorrhagic factor 3 (HF3) in the venom secretory cells from adult snakes in the active (7 days after venom extraction) and in the resting (without venom extraction for 40 days) stages of protein synthesis. Glands from the newborn Bothrops jararaca were also studied. The results lead to the conclusion that all the secretory cells and the secretory pathway in the cells are qualitatively alike in regard to their content of the three metalloproteases. Secretory cells from the resting glands, unlike the active ones and the newborn glands, did not present immunolabeling in the narrow intracisternal spaces of the rough endoplasmic reticulum (RER). The label intensity for bothropasin was greater than that for the other proteins in the adults. HF3 and HF2 labeling densities in the newborn were higher than in the adults and HF3 labeling was not different from that of bothropasin. Co-localization of the three metalloproteases was detected in the RER cisternae of the active gland secretory cells, implying that mixing of the proteases before co-packaging into secretory vesicles occurs at the beginning of protein synthesis in the RER cisternae.

Ultrastructural analysis of pancreatic acinar cells from mice fed on genetically modified soybean

No direct evidence that genetically modified (GM) food may represent a possible danger for health has been reported so far; however, the scientific literature in this field is quite poor. Therefore, we investigated the possible effects of a diet containing GM soybean on mouse exocrine pancreas by means of ultrastructural, morphometrical and immunocytochemical analyses. Our observations demonstrate that, although no structural modification occurs in pancreatic acinar cells of mice fed on GM soybean, quantitative changes of some cellular constituents take place in comparison to control animals. In particular, a diet containing significant amount of GM food seems to influence the zymogen synthesis and processing.

Roles of molecular chaperones in pancreatic secretion and their involvement in intestinal absorption

This review focuses on the contribution of molecular chaperones in the secretory process of digestive enzymes and their interaction with enterocytes. By using biochemistry and immunocytochemistry, we have shown that Grp94, Cpn10, Cpn60, and protein disulfide isomerase (PDI) are present all along the rough endoplasmic reticulum-Golgi-granule secretory pathway of the pancreatic acinar cells and are secreted into the acinar lumen. Two other molecular chaperones, Grp78 and the Hsp70, appear to be restricted to the rough endoplasmic reticulum and the trans-Golgi apparatus, respectively. We have found that chaperones can be associated with pancreatic enzymes along the secretory pathway. Indeed, double immunogold and immunocoprecipitation revealed an association between Cpn60 and the colipase-dependent lipase (CDL) and between Grp94 and the bile salt-dependent lipase (BSDL). These complexes are secreted into the acinar lumen and diverted to the duodenal lumen. These findings led us to investigate these enzyme-chaperone complexes in intestinal tissue. Grp94, Cpn60, and PDI are present on microvilli and on the endosomal compartment of enterocytes. Furthermore, we have shown that the Grp94-BSDL complexes are internalized by enterocytes through classical endocytosis. Upon dissociation of the BSDL-Grp94 complex in the late endosome, BSDL is transferred to the basolateral membrane. We propose that Grp94 interacts with specific receptors and/or could force the associated protein to adopt a specific conformation that allows its binding to corresponding membrane receptors and its internalization by enterocytes. These two hypotheses need not to be exclusive. The existence of such a pancreatic secretion-intestinal absorption link speaks in favor of a coordinated functional connection between these two entities, through molecular chaperones, in order to optimize intestinal activities.

Hydrocortisone induces an increase of amylase content in individual zymogen granules from rat pancreas

This study was performed to evaluate the effects of different doses of hydrocortisone (1, 10 and 25 mg/kg/day) administered for 1, 3 and 8 days on pancreatic enzyme storage in rats. The enzyme content in both pancreas homogenates and in individual isolated zymogen granules (ZGs) was measured using standard biochemical assays and flow cytometry, respectively. Hydrocortisone did not alter the total amount of pancreatic DNA but increased the pancreas enzyme content in a time-dose-dependent way. Amylase activity was significantly increased after hydrocortisone administration at day +8 when 10 mg/kg/day was used, and from the first day of treatment when 25 mg/kg/day was administered. A significant increase in trypsin activity was also observed in response to 25 mg/kg/day of hydrocortisone but only from the third day of treatment onwards. As compared with control rats, chronic administration of either 1 or 10 mg/kg/day of hydrocortisone did not alter significantly either the size or the percentage of the two ZG subpopulations (Z1 and Z2) identified in the pancreas by flow cytometry; in addition, no significant changes were observed in the mean amylase content per individual granule, although its mean concentration increased in rats treated with 10 mg/kg/day for 3 and 8 days. Nevertheless, when 25 mg/kg/day of hydrocortisone were administered for 1 and 3 days, a significant increase in the proportion of Z1 ZGs was observed, which may be related to the formation of new and smaller ZGs. When a very high dose of hydrocortisone (25 mg/kg/day) was used, an overall increase in the pancreatic enzyme content related to an increase in the mean amylase content per individual ZG was observed; this effect was apparent from the first day of treatment in the Z1 subset of ZGs and from day +3 in the Z2 subpopulation. Only a high concentration of hydrocortisone was able to alter the enzyme storage process in individual zymogen granules, but they maintain a normal enzyme load at lower hydrocortisone doses.

Enzyme changes in zymogen granules and in pancreatic secretion throughout long-term CCK treatment

Pancreatic enzyme storage and secretion were studied in rats treated twice daily with s.c. injections (5 micrograms/kg) of CCK-8 for 3, 7, and 15 days. Isolated zymogen granules were analyzed by flow cytometry to determine their FSC (forward scatter), SSC (side scatter), and amylase and trypsinogen contents. DNA content, pancreatic weight, and both basal and stimulated pancreatic secretion under i.v. CCK infusion (1.25 micrograms/kg/h) were also studies. Two subsets of zymogen granules were identified by flow cytometry in both control and CCK-treated rats on the basis of FSC and SSC parameters: Z1 (smaller and less complex) and Z2. Both subsets displayed a high degree of heterogeneity with respect to their enzyme content per zymogen granule. During the first 7 days of CCK treatment, hyperplasia and hypertrophy developed in the rats together with changes in the zymogen granules, reflected by a significantly decreased FSC, and increased SSC, and an increase in the mean trypsinogen/amylase ratio per granule. A rise in pancreatic enzyme secretion, especially of trypsin, was observed. After 15 days of CCK administration, a simultaneous decrease in amylase content and increase in trypsinogen content per zymogen granule was observed. A desensitization of the pancreas to CCK happened after 15 days of CCK administration, reflected by a reduction of all the pancreatic functions that had been increased at shorter CCK administration periods. Nevertheless, trypsinogen appeared resistant to desensitization because its secretion significantly increased in response to an i.v. infusion of CCK. CCK treatment displayed a differential packaging of the enzymes in individual zymogen granules; the trypsinogen/amylase ration was significantly higher in Z2 zymogen granules than in Z1 subset throughout the treatment.

Amazing pancreas: specific regulation of pancreatic secretion of individual digestive enzymes in rats

We investigated the effects of somatostatin (SMS)-201-995, atropine, and MK-329 on the role of cholinergic- and cholecystokinin-related systems and on the secretory relationship between five pancreatic digestive enzymes in rats. Animals kept in restraint cages and provided with pancreatic, biliary, duodenal, and jugular vein cannulas were treated as follows: 1) 0.25 micrograms.kg-1.h-1 caerulein alone, 2) both 0.25 micrograms.kg-1.h-1 caerulein and 100 micrograms.kg-1.h-1 atropine, 3) both caerulein and 5 micrograms.kg-1.h-1 SMS, 4) 91.3 micrograms.kg-1.h-1 carbachol alone, 5) both carbachol and 0.5 mg.kg-1.h-1 MK-329, and 6) both carbachol and 5 micrograms.kg-1.h-1 SMS, respectively. Food, but not water, was denied rats starting 10 h before the experiment and throughout the 6-h experimental period. The secretory patterns over the 6-h experimental period showed noticeably independent regulation of pancreatic secretion of individual digestive enzymes. The relationship between paired enzymes significantly varied according to the treatment. The correlation between chymotrypsinogen and the other enzymes was markedly modulated by MK-329. Our results suggest that SMS is a major "gate-keeper" in the regulation of exocrine pancreatic secretion and that the secretion of each digestive enzyme is individually regulated. Furthermore, they suggest that cholecystokinin and acetylcholine and their respective agonists are essentially initiators of secretory processes of the pancreas. Therefore, the paradigms of the regulation of pancreatic secretion heretofore accepted should be reexamined.

Separation and analysis of pig pancreatic zymogen granules with free flow electrophoresis and lectins

Purified pig pancreatic zymogen granules were subjected to free flow electrophoresis (FFE) in an acetate buffer system (acetic acid/NaOH, pH 5.5) to detect the presence or absence of more than one population or zymogen granules. Pig pancreatic zymogen granules were purified by differential and density gradient centrifugation and subjected to FFE. Fractions were analyzed for protein, alpha-amylase (EC 3.2.1.1) and 5'-nucleotidase (EC 3.1.3.5) as marker enzymes for zymogen granule content and membranes, respectively. Only one distinct peak, with coincident alpha-amylase and 5'-nucleotidase activity, and most protein was detected, which reflects the presence of a single population of intact zymogen granules. This was confirmed by electron microscopy. When the granules were incubated with different lectins before FFE, the one distinct peak representing intact zymogen granules was shifted towards the cathode in the case of concanavalin A (Con A) and Ricinus communis agglutinin 120 (RCA 120). No splitting of the peak occurred. Our results do not support the hypothesis of a coexistence of more than one distinct population of zymogen granules.