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Pancreatic necroses are a major challenge in the treatment of patients with pancreatitis, causing high morbidity. When indicated, these lesions are usually drained endoscopically using plastic or metal stents. However, data on factors associated with the occurrence of failure or adverse events during stent therapy are scarce. We retrospectively analyzed all adverse events and their associated features which occurred in patients who underwent a first-time endoscopic drainage of pancreatic necrosis from 2009 to 2019. During the observation period, a total of 89 eligible cases were identified. Adverse events occurred in 58.4% of the cases, of which 76.9% were minor (e.g., stent dislocation, residual lesions, or stent obstruction). However, these events triggered repeated interventions (63.5% vs. 0%, p < 0.001) and prolonged hospital stays (21.0 [11.8–63.0] vs. 14.0 [7.0–31.0], p = 0.003) compared to controls without any adverse event. Important factors associated with the occurrence of adverse events during endoscopic drainage therapy were positive necrosis cultures (6.1 [2.3–16.1], OR [95% CI], p < 0.001) and a larger diameter of the treated lesion (1.3 [1.1–1.5], p < 0.001). Superinfection of pancreatic necrosis is the most significant factor increasing the likelihood of adverse events during endoscopic drainage. Therefore, control of infection is crucial for successful drainage therapy, and future studies need to consider superinfection of pancreatic necrosis as a possible confounding factor when comparing different therapeutic modalities.
Inflammation is part of the body's immune response in order to remove harmful stimuli—like pathogens, irritants or damaged cells—and start the healing process. Recurrent or chronic inflammation on the other side seems a predisposing factor for carcinogenesis and has been found associated with cancer development. In chronic pancreatitis mutations of the cationic trypsinogen (PRSS1) gene have been identified as risk factors of the disease. Hereditary pancreatitis (HP) is a rare cause of chronic pancreatic inflammation with an early onset, mostly during childhood. HP often starts with recurrent episodes of acute pancreatitis and the clinical phenotype is not very much different from other etiologies of the disease. The long-lasting inflammation however generates a tumor promoting environment and represents a major risk factor for tumor development This review will reflect our knowledge concerning the specific risk of HP patients to develop pancreatic cancer.
Pancreatitis is an inflammatory disorder of the pancreas with a mortality rate of 5% and severe negative effects on the quality of life. Of all non-malignant gastrointestinal diseases, it is the most common reason for hospitalization. Pancreatitis is a disease of multiple etiologies with different underlying pathomechanisms. Due to the diversity of mechanisms by which homeostasis within the exocrine pancreas can be disrupted, finding appropriate therapeutic approaches is challenging. Current treatment options are inadequate and are mostly limited to supportive treatment like fluid administration, bowel rest, antibiotics and pain control. Although significant advancements have been achieved in recent decades, the mortality rate for pancreatitis has not decreased. Furthermore, progress is slow due to limited patient sample availability and lack of an appropriate cell model. Taking samples from a human pancreas is typically avoided, because damaging the pancreatic tissue can itself induce pancreatitis. Additionally, while it is possible to keep individual acini in culture, it is not possible to grow pancreatic acinar cells. Thus, less appropriate cell models, often derived from pancreatic cancer samples, have to be used. The most common animal model for pancreatitis is mice, with caerulein administration being the most common method of inducing pancreatitis. However, the use of animal models has significant drawbacks, as they are time-consuming, costly, and pose ethical questions. Furthermore, exposing the pancreas to appropriate stimuli in animal models is difficult. For example, alcohol is the leading cause of pancreatitis in humans, but is typically avoided by animals. Thus, alcohol feeding methods had to be developed to overcome the natural aversion of rodents to alcohol. Results obtained from animal models are also often not transferable into clinical trials and outcomes in humans remain largely unpredictable. Due to the lack of experimental models, our understanding of this highly complex disease is still limited and significant progress is required for the development of effective therapy options.
In this dissertation recombinantly expressed trypsin isoforms and variants of the serine protease inhibitor Kazal-type 1 (SPINK1) inhibitor are used to investigate mechanisms, by which tryptic activity is regulated in pancreatic acinar cells. With premature tryptic activity in the exocrine pancreas being the common focal point of most etiologies connected to pancreatitis, trypsin represents by far the most promising target for treating pancreatitis. Understanding the mechanisms by which the pancreas protects itself and rationalizing mutations that can undermine these protective mechanisms, are important steps towards developing effective therapies.
(1) The serine protease inhibitor Kazal type 1 (SPINK1) inhibits trypsin activity in zymogen granules of pancreatic acinar cells. Several mutations in the SPINK1 gene are associated with acute recurrent pancreatitis (ARP) and chronic pancreatitis (CP). The most common variant is SPINK1 p.N34S. Although this mutation was identified two decades ago, the mechanism of action has remained elusive. (2) SPINK1 and human cationic trypsin (TRY1) were expressed in E. coli, and inhibitory activities were determined. Crystals of SPINK1–TRY1 complexes were grown by using the hanging-drop method, and phases were solved by molecular replacement. (3) Both SPINK1 variants show similar inhibitory behavior toward TRY1. The crystal structures are almost identical, with minor differences in the mutated loop. Both complexes show an unexpected rotamer conformation of the His63 residue in TRY1, which is a member of the catalytic triad. (4) The SPINK1 p.N34S mutation does not affect the inhibitory behavior or the overall structure of the protein. Therefore, the pathophysiological mechanism of action of the p.N34S variant cannot be explained mechanistically or structurally at the protein level. The observed histidine conformation is part of a mechanism for SPINK1 that can explain the exceptional proteolytic stability of this inhibitor.
Objective: The pathophysiological mechanisms underlying chronic pancreatitis (CP) are still poorly understood. Human cationic (TRY1) and anionic (TRY2) trypsins are the two major trypsin isoforms and their activities are tightly regulated within pancreatic acinar cells. Typically, they exist in a molar ratio of 2:1 (cationic:anionic). This ratio is reversed during chronic alcohol abuse, pancreatic cancer, or pancreatitis due to selectively upregulated expression of TRY2, causing anionic trypsin to become the predominant isoform. The involvement of TRY2 in pancreatitis is considered limited due to the absence of disease-causing mutations and its increased prevalence for autoproteolysis. However, exacerbated pancreatitis in TRY2 overexpressing mice was recently demonstrated. Here, we aim to elucidate the molecular structure of human anionic trypsin and obtain insights into the autoproteolytic regulation of tryptic activity.
Methods: Trypsin isoforms were recombinantly expressed in E. coli, purified and refolded. Enzymatic activities of all trypsin isoforms were determined and crystals of TRY2 were grown using the vapor-diffusion method. The structure was solved by molecular replacement and refined to a resolution of 1.7 Å. Equilibration molecular dynamics simulations were used to generate the corresponding TRY1–TRY1 model.
Results: All trypsin isoforms display similar kinetic properties. The crystal structure of TRY2 reveals that the enzyme crystallized in the autoproteolytic state with Arg122 placed in the S1 binding pocket and the corresponding loop cleaved. The TRY2–TRY2 dimer confirms a previously hypothesized autoinhibitory state with an unexpectedly large binding interface.
Conclusion: We provide a structure of TRY2, which is the predominant trypsin isoform in chronic pancreatitis and pancreatic cancer. A proposed autoinhibition mode was confirmed and the structural basis of the autoproteolytic failsafe mechanism elucidated.
Für die Therapie von Pankreaserkrankungen, insbesondere für fortgeschrittene Pankreasadenokarzinome gibt es kaum suffiziente Behandlungsmethoden. Durch chirurgische Interventionen kann der Tumor häufig nicht vollständig entfernt werden und eine pharmakologische Radiochemotherapie führt zu Nebenwirkungen, durch die die Lebensqualität der Patienten deutlich eingeschränkt wird. Durch den Einsatz von Prodrugs könnte dieses Problem gelöst werden. Bei Prodrugs handelt es sich um zunächst inaktive Pharmaka, die durch eine auf den Wirkort beschränkte enzymatische Spaltung aktiviert werden. Bei der humanen β–Glukuronidase handelt es sich um ein solches Enzym. Aufgrund ihrer extrazellulären Lokalisation und verstärkten Expression im Tumorgewebe verschiedenen Ursprungs ist sie für eine Prodrug-Therapie geeignet. Für einen erfolgreichen Einsatz der β–Glukuronidase in der Therapie von Pankreaserkrankungen sind Untersuchungen über die genaue Lokalisation im gesunden und pathologisch veränderten Pankreasgewebe wichtig. Ziel der vorliegenden Arbeit war es deshalb, die mRNA und das Protein in gesundem Pankreasgewebe, im akut und chronisch entzündeten Pankreasgewebe und in unterschiedlich weit entwickelten Pankreaskarzinomen zu lokalisieren und mittels densitometrischer und molekularbiologischer Analysen in diesen Präparaten zu quantifizieren. Mittels in situ Hybridisierung und Immunhistochemie konnte die β–Glukuronidase im gesunden Pankreasgewebe in exokrinen und gering schwächer in endokrinen Zellen lokalisiert werden. Im akut entzündeten Pankreasgewebe (Pankreatitis) wurde die β-Glukuronidase in exokrinen Zellen und in den pankreatischen Ausführungsgängen detektiert. Ebenfalls im exokrinen Pankreasgewebe aber nicht in den Ausführungsgängen konnte bei chronischer Pankreatitis die β-Glukuronidase nachgewiesen werden. Für die genaue Lokalisation der β-Glukuronidase-mRNA und -Proteins in Pankreastumoren standen Gewebeproben verschiedener „Tumor-Grading-Stufen“ zur Verfügung. Im G1, -G2- und G3-Tumorgewebe konnte die β-Glukuronidase in malignen exokrinen Drüsenzellen und im nekrotischen Gewebe lokalisiert werden. Außerdem konnte in der vorliegenden Arbeit bei Präparaten von chronischer Pankreatitis die β-Glukuronidase-Aktivität mittels enzymhistochemischer Methoden in pankreatischen Ausführgängen, exokrinen Drüsenzellen und in endokrinen Inselzellen detektiert werden. Im Zweiten Teil der Arbeit wurde die Expression der β-Glukuronidase im Pankreasgewebe untersucht. Die Untersuchungen zeigten die höchste Expression der β-Glukuronidase-mRNA im Karzinomgewebe im Vergleich zu normalem Gewebe. Dabei wurde in G1-Tumoren eine geringere β-Glukuronidase-mRNA-Expression als in G2- und G3-Pankreaskarzinomen nachgewiesen. Im Gegensatz dazu konnte der höchste β-Glukuronidase-Proteinlevel bei chronischer Pankreatitis nachgewiesen werden, gefolgt von G2- und G3-Pankreaskarzinomen. Die Ergebnisse dieser Arbeit zeigen ein verstärktes Vorkommen der β-Glukuronidase in pathologisch verändertem Pankreasgewebe. Da aber gleichzeitig ein Nachweis in gesundem Pankreasgewebe und in verschiedenen anderen Zellen, wie z.B. Leukozyten erfolgte, könnte dies ein Problem in der Therapie spezifischer Pankreaserkrankungen mit β-Glukuronidase Prodrugs darstellen. Auf einen Einsatz von β-Glukuronidase Prodrugs in der Behandlung von Pankreaserkrankungen sollte deshalb verzichtet werden.