Role of cathepsin B in intracellular trypsinogen activation and the onset of acute pancreatitis

Endothelial nitric oxide synthase is protective in the initiation of caerulein-induced acute pancreatitis in mice

The effect of inhibiting nitric oxide (NO) synthase (NOS) or enhancing NO on the course of acute pancreatitis (AP) is controversial, in part because three NOS isoforms exist: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). We investigated whether inhibition or selective gene deletion of NOS isoforms modified the initiation phase of caerulein-induced AP in mice and explored whether this affected pancreatic microvascular blood flow (PMBF). We investigated the effects of nonspecific NOS inhibition with N(omega)-nitro-l-arginine (l-NNA; 10 mg/kg ip) or targeted deletion of eNOS, nNOS, or iNOS genes on the initiation phase of caerulein-induced AP in mice using in vivo and in vitro models. Western blot analysis was performed to assess eNOS phosphorylation status, an indicator of enzyme activity, and microsphere studies were used to measure PMBF. l-NNA and eNOS deletion, but not nNOS or iNOS deletion, increased pancreatic trypsin activity and serum lipase during the initiation phase of in vivo caerulein-induced AP. l-NNA and eNOS did not affect trypsin activity in caerulein-hyperstimulated isolated acini, suggesting that nonacinar events mediate the effect of NOS blockade in vivo. The initiation phase of AP in wild-type mice was associated with eNOS Thr(495) residue dephosphorylation, which accompanies eNOS activation, and a 178% increase in PMBF; these effects were absent in eNOS-deleted mice. Thus eNOS is the main isoform influencing the initiation of caerulein-induced AP. eNOS-derived NO exerts a protective effect through actions on nonacinar cell types, most likely endothelial cells, to produce greater PMBF.

Neuronal and microglial cathepsins in aging and age-related diseases

It has been long believed that cathepsins compensate for each other because of their overlapping substrate specificities. However, there is increasing evidence that disturbance of the normal balance of their enzymatic activities is the first insult in brain aging and age-related diseases. The imbalance of cathepsins may further cause age-related neuropathological changes such as accumulation of autophagic vacuoles and the formation of ceroid-lipofuscin leading to neuronal dysfunction and damage. Leakage of cathepsins due to the fragility of lysosomal membranes during aging also contributes to neurodegeneration. Furthermore, the deficiency of cathepsin D has been recently revealed to provoke a novel type of lysosomal storage disease associated with massive neurodegeneration. In these animals, microglia are activated to initiate inflammatory and cytotoxic responses by binding and phagocytosis of storage neurons. Activated microglia also release some members of cathepsins to induce neuronal death by degrading extracellular matrix proteins. Thus the microglial activation possibly through sensing neuronal storage may also be an important causative factor for neurodegeneration in lysosomal storage diseases and age-related diseases such as Alzheimer's disease. This review describes the pathological roles of neuronal and microglial cathepsins in brain aging and age-related diseases.

Pancreatitis in childhood

Inflammatory disease of the pancreas falls into two major classifications: acute and chronic. Acute pancreatitis is a reversible process, whereas chronic pancreatitis produces irreversible changes in the architecture and function of the pancreas. The recent finding that mutations in the gene encoding cationic trypsinogen are associated with hereditary pancreatitis, the identification of genes that increase the risk for developing chronic pancreatitis, and advances in cell biology have contributed greatly to our understanding of the molecular mechanisms leading to pancreatitis. Although pancreatitis is less common in children than in adults, it still occurs with regularity and should be considered in any child with acute or chronic abdominal pain. The major difference between pancreatitis in children and adults lies in the etiologies and outcome of acute pancreatitis and in the etiology of chronic pancreatitis. The treatment of acute and chronic pancreatitis is similar at all ages.

Lysosomes in cell death

For many years apoptosis research has focused on caspases and their putative role as sole executioners of programmed cell death. Accumulating information now suggests that lysosomal cathepsins are also pivotally involved in this process, especially in pathological conditions. In particular, the role of lysosomes and lysosomal enzymes in initiation and execution of the apoptotic program has become clear in several models, to the point that the existence of a 'lysosomal pathway of apoptosis' is now generally accepted. This pathway of apoptosis can be activated by death receptors, lipid mediators, and photodamage. Lysosomal proteases can be released from the lysosomes into the cytosol, where they contribute to the apoptotic cascade upstream of mitochondria. This review focuses on the players and the molecular mechanisms involved in the lysosomal pathway of apoptosis as well as on the importance of this pathway in development and pathology.

Nuclear factor-kappaB mediates up-regulation of cathepsin B by doxorubicin in tumor cells

Anthracyclines such as doxorubicin remain among the most effective agents for the treatment of solid tumors and hematological malignancies. To overcome dose-limiting side effects like cardiotoxicity, an intensive effort has been undertaken to develop promising doxorubicin prodrugs that are specifically activated at the tumor site. One approach is the application of peptide prodrugs of doxorubicin. The enzyme cathepsin B catalyzes the activation of these prodrugs, and hence, the regulation of cathepsin B by antitumor agents could influence the efficacy of peptide prodrugs using this protease. In the present investigation, the effects of doxorubicin on cathepsin B expression in the human cervix carcinoma cell line HeLa were examined. Exposure to doxorubicin induced a time- and dose-dependent up-regulation of cathepsin B expression on mRNA, protein, and activity levels. In the cathepsin B gene promoter region, a potential nuclear factor kappaB (NF-kappaB) binding site could be identified. Pretreatment of HeLa cells with specific NF-kappaB inhibitors abrogated the induction of cathepsin B expression. Doxorubicin-induced degradation of the inhibitory protein IkappaB could be prevented by pretreatment with a specific proteasome inhibitor, resulting in a significant reduction of the doxorubicin-induced cathepsin B expression. Finally, binding of NF-kappaB subunits p50 and p65 to the NF-kappaB binding site in the cathepsin B gene promoter region could be demonstrated by electrophoretic mobility shift assay. In summary, our data clearly indicate that doxorubicin induces cathepsin B expression and activity via NF-kappaB. These findings contribute to a better understanding of tumor targeting with peptide prodrugs and help to define a possible mechanism of doxorubicin toxicity in tumor cells.

Cysteine proteases as disease markers

This review comprises issues concerning cysteine cathepsins (CCs): human peptidases belonging to papain family (C1) of clan CA of cysteine proteases: cathepsins B, L, H, S, K, F, V, X, W, O and C. The involvement of these enzymes in physiological and pathological processes is described, especially with respect to their application as diagnostic and prognostic markers. They participate in precursor protein activation (including proenzymes and prohormones), MHC-II-mediated antigen presentation, bone remodeling, keratinocytes differentiation, hair follicle cycle, reproduction and apoptosis. Cysteine cathepsins upregulation has been demonstrated in many human tumors, including breast, lung, brain, gastrointestinal, head and neck cancer, and melanoma. Besides cancer diseases, they have been implied to participate in inflammatory diseases, such as inflammatory myopathies, rheumatoid arthritis, and periodontitis. Also, certain hereditary disorders are connected with mutations in CCs genes, what is observed in pycnodysostosis resulted from catK gene mutation and Papillon-Lefevre and Haim-Munk syndrome caused by catC gene defect. The potential application of cysteine cathepsins in diagnosis and/or prognosis is discussed in cancer diseases (breast, lung, head and neck, ovarian, gastrointestinal cancers, melanoma), as well as other disorders (periodontitis, rheumatoid arthritis, osteoarthritis).

Acute pancreatitis and organ failure: pathophysiology, natural history, and management strategies

Acute pancreatitis is a common condition that carries a significant risk of morbidity and mortality. It is characterized by intra-acinar cell activation of digestive enzymes and a subsequent systemic inflammatory response governed by the release of proinflammatory cytokines. In 80% of patients the disease runs a self-limiting course, but in the rest, pancreatic necrosis and systemic organ failure carry a mortality rate of up to 40%. The key to management is early identification of the patients liable to have a severe attack and require treatment in a high-dependency or critical-care setting by a specialist team. In gallstone-induced pancreatitis, early removal of ductal calculi by endoscopic sphincterotomy is indicated. The use of prophylactic antibiotics to prevent the infection of pancreatic necrosis remains controversial, but once established, infected necrosis must be removed. Although a number of techniques to accomplish this end have been described, minimally invasive techniques are gaining in popularity.

Interaction between trypsinogen isoforms in genetically determined pancreatitis: mutation E79K in cationic trypsin (PRSS1) causes increased transactivation of anionic trypsinogen (PRSS2)

The human pancreas secretes two major trypsinogen isoforms, cationic and anionic trypsinogen. To date, 19 genetic variants have been identified in the cationic trypsinogen gene (PRSS1) of patients with hereditary, familial, or sporadic chronic pancreatitis. A common feature of cationic trypsinogen mutants studied so far is an increased propensity for autocatalytic activation (autoactivation). This is thought to lead to premature intrapancreatic digestive protease activation. In contrast, no pancreatitis-associated mutations have been found in the anionic trypsinogen gene (PRSS2), suggesting that this isoform might play a relatively unimportant role in pancreatitis. To challenge this notion, here we describe the unique properties of the E79K cationic trypsinogen mutation (c.235G>A), which was identified in three European families affected by sporadic or familial pancreatitis cases. In vitro analysis of recombinant wild-type and mutant enzymes revealed that catalytic activity of E79K trypsin was normal, and its inhibition by pancreatic secretory trypsin inhibitor was unaffected. Although the E79K mutation introduces a potential new tryptic cleavage site, autocatalytic degradation (autolysis) of E79K-trypsin was also unchanged. Furthermore, in contrast to previously characterized disease-causing mutations, E79K markedly inhibited autoactivation of cationic trypsinogen. Remarkably, however, E79K trypsin activated anionic trypsinogen two-fold better than wild-type cationic trypsin did, while the common pancreatitis-associated mutants R122H or N29I had no such effect. The observations not only suggest a novel mechanism of action for pancreatitis-associated trypsinogen mutations, but also highlight the importance of interactions between the two major trypsinogen isoforms in the development of genetically determined chronic pancreatitis.

ANP preconditioning does not increase protection against experimental pancreatitis, observed after general anesthesia and jugular vein catheterization

It has been widely shown that preconditioning, inducing heat shock proteins, can protect against experimentally induced pancreatitis. Solid evidence indicates that HSP70 plays a central role in this context, possibly by inhibition of premature intracellular trypsinogen activation. Current preconditioning protocols such as whole body hyperthermia are, however, quite strenuous and clinically not applicable. There is little data on other means to induce pancreatic HSPs such as pharmacologic pretreatment.However, in models of ischemic liver reperfusion injury, it has been demonstrated that atrial natriuretic peptide (ANP) can be used for such pharmacologic preconditioning. Evidence indicates that ANP exerts its protective effects via increased cGMP levels, activation of heat shock transcription factor (HSF) and, increased protein levels of HSP70. Pancreatic acinar cells express ANP receptors and respond to ANP treatment with increased cGMP levels. We have, therefore, investigated whether intravenous ANP pretreatment could be used to protect the pancreas against experimental pancreatitis. When given 20 minutes prior to pancreatitis induction, ANP pretreatment had no effect on cerulein-induced pancreatitis. In contrast, 24 hours after preconditioning, induction of HSP70 protein expression and protection against experimental pancreatitis were found. However, controls treated with NaCl without ANP showed a similar response. This indicates that stress caused by general anesthesia and jugular vein catheterization can be sufficient for preconditioning while ANP, in contrast to models of ischemic liver reperfusion injury, does not confer additional protection.

Pharmacological prevention of post-endoscopic retrograde cholangiopancreatography pancreatitis

The incidence of clinically significant pancreatitis after endoscopic retrograde cholangiopancreatography (ERCP) ranges from 1-13.5%. It is more common after therapeutic procedures such as sphincterotomy or balloon dilatation of the sphincter, and diagnostic procedures such as biliary or pancreatic manometry. The severity of post-ERCP pancreatitis may vary from very mild to extremely severe disease with multiple organ failure and fatal outcome. Several factors including papillary oedema, injection of hyperosmolar contrast-material, introduction of previously activated enzymes during repeated cannulation, bacterial contamination and thermal injury from endoscopic sphincterotomy have been implicated as triggering factors that initiate the sequential cascade of pancreatic autodigestion and release of proinflammatory cytokines leading to acute pancreatitis. Recovery from post-ERCP pancreatitis is usually rapid when the injury is confined to the pancreas. However, systemic production of inflammatory mediators may lead to the development of more serious manifestations including multiorgan failure.A wide range of pharmacological agents has been tested in experimental and clinical trials, but the results have been largely disappointing. Several drugs are discussed in this review, but only somatostatin and gabexate (gabexate mesilate) have consistently shown a moderate beneficial effect. In clinical trials, both gabexate and somatostatin appear equally effective in reducing the incidence of pancreatitis by two-thirds compared with controls. However, both drugs need to be given by continuous infusion for about 12 hours and this makes them less cost-effective than conventional treatment. One potential strategy is to reserve these drugs for high-risk patients undergoing ERCP. Preliminary studies have shown encouraging results with nitroglycerin, antibacterials and heparin. However, these observations need to be corroborated in a rigorous fashion in large, randomised, double-blind, controlled trials. If these drugs are found to be effective in further trials, it may become cost-effective to use them routinely for the prevention of post-ERCP pancreatitis. Despite the theoretical benefits, interleukin-10 has not shown a consistent benefit in clinical trials. It is probable that other cytokine inhibitors or modulators may become available for future trials to prevent pancreatitis or more probably, to reduce the severity of pancreatitis. Further research also should focus on developing newer molecules or the use of a combination of currently available drugs to prevent pancreatitis in high-risk patients undergoing therapeutic ERCP procedures.

Phosphatidylinositide 3-kinase gamma regulates key pathologic responses to cholecystokinin in pancreatic acinar cells

BACKGROUND & AIMS

Early events in the pancreatic acinar cell critical for development of pancreatitis include activation of the transcription factor nuclear factor kappa B (NF-kappa B), abnormal Ca(2+) responses, and trypsinogen activation. Mechanisms underlying these responses, which can be studied in isolated pancreatic acini stimulated with supraphysiologic doses of cholecystokinin (CCK-8), remain poorly understood. We here report that these responses are regulated by phosphatidylinositide 3-kinase (PI3K) gamma.

METHODS

To inactivate PI3K, we used mice deficient in the catalytic PI3K gamma subunit p110 gamma as well as the PI3K inhibitors LY294002 and wortmannin. We measured Ca(2+) responses by using Fura-2, NF-kappa B-binding activity by electromobility shift assay, I kappa B degradation by Western blotting, and trypsinogen activation by fluorogenic assay.

RESULTS

CCK-induced intracellular Ca(2+) mobilization, Ca(2+) influx, trypsinogen, and NF-kappa B activation were all diminished in pancreatic acini isolated from p110 gamma(-/-) mice. Both in mouse and rat acini, these responses were inhibited by the PI3K inhibitors. The Ca(2+) signal and trypsinogen activation were similarly reduced in acini isolated from p110 gamma(-/-) and p110 gamma(+/-) mice compared with wild-type mice. By contrast, NF-kappa B activation was inhibited in p110 gamma(-/-) acini but not in p110 gamma(+/-) acini. These differences indicate that the mechanism of NF-kappa B regulation by PI3K gamma differs from those for the Ca(2+) and trypsinogen responses. CCK-induced responses in p110 gamma(-/-) acini were all further inhibited by LY294002, indicating the involvement of other PI3K isoform(s), in addition to PI3K gamma.

CONCLUSIONS

The results show that key pathologic responses of the pancreatic acinar cell are regulated by PI3K gamma and suggest an important role for this PI3K isoform in pancreatitis.

Beneficial effect of iloprost on the course of acute taurocholate pancreatitis in rats and its limitation by antecedent acute ethanol intake

The effects of stable prostacyclin analogue iloprost on the trypsinogen activation, labilization of lysosomal membranes, lipolytic enzymes activities, histopathological and ultrastructural changes in the pancreas of rats with severe, taurocholate acute pancreatitis (AP), preceded for 6 h by acute ethanol intake have been investigated. Iloprost (1 microg/kg b.w., i.p.) was applied every 6 hours after inducing of taurocholate AP. The antecedent intragastric 40% ethanol intake (5 g/kg b.w.) increased an index of trypsinogen activation in AP lasting 18 h. Treatment with iloprost prevented this increase in the rats with AP given earlier alcohol, and limited the labilization of lysosomal membranes in nonalcoholized rats with AP. Phospholipase A2 and lipase activities were reduced by iloprost only in the rats not given ethanol. The additional damaging effect of acute ethanol abuse prior to AP could be dependent on augmented activation of trypsinogen. The protective effect of iloprost in AP seems to be dependent on the attenuation of trypsinogen activation, decrease of total potential trypsin and the decrease of lysosomal membranes labilization. Its protective effect could be limited in taurocholate acute pancreatitis preceded by acute ethanol intake as evidenced by the differences in the cathepsin B, phospholipase A2 and lipase activities and by histopathological and ultrastructural examination.

Signal transduction, calcium and acute pancreatitis

Evidence consistently suggests that the earliest changes of acute pancreatitis are intracellular, the hallmark of which is premature intracellular activation of digestive zymogens, accompanied by disruption of normal signal transduction and secretion. Principal components of physiological signal transduction include secretagogue-induced activation of G-protein-linked receptors, followed by generation of inositol 1,4,5-trisphosphate, nicotinic acid adenine dinucleotide phosphate and cyclic ADP-ribose. In response, calcium is released from endoplasmic reticulum terminals within the apical, granular pole of the cell, where calcium signals are usually contained by perigranular mitochondria, in turn responding by increased metabolism. When all three intracellular messengers are administered together, even at threshold concentrations, dramatic potentiation results in sustained, global, cytosolic calcium elevation. Prolonged, global elevation of cytosolic calcium is also induced by hyperstimulation, bile salts, alcohol and fatty acid ethyl esters, and depends on continued calcium entry into the cell. Such abnormal calcium signals induce intracellular activation of digestive enzymes, and of nuclear factor kappaB, as well as the morphological changes of acute pancreatitis. Depletion of endoplasmic reticulum calcium and mitochondrial membrane potential may contribute to further cell injury. This review outlines current understanding of signal transduction in the pancreas, and its application to the pathophysiology of acute pancreatitis.

Human mesotrypsin is a unique digestive protease specialized for the degradation of trypsin inhibitors

Mesotrypsin is an enigmatic minor human trypsin isoform, which has been recognized for its peculiar resistance to natural trypsin inhibitors such as soybean trypsin inhibitor (SBTI) or human pancreatic secretory trypsin inhibitor (SPINK1). In search of a biological function, two conflicting theories proposed that due to its inhibitor-resistant activity mesotrypsin could prematurely activate or degrade pancreatic zymogens and thus play a pathogenic or protective role in human pancreatitis. In the present study we ruled out both theories by demonstrating that mesotrypsin was grossly defective not only in inhibitor binding, but also in the activation or degradation of pancreatic zymogens. We found that the restricted ability of mesotrypsin to bind inhibitors or to hydrolyze protein substrates was solely due to a single evolutionary mutation, which changed the serine-protease signature glycine 198 residue to arginine. Remarkably, the same mutation endowed mesotrypsin with a novel and unique function: mesotrypsin rapidly hydrolyzed the reactive-site peptide bond of the Kunitz-type trypsin inhibitor SBTI, and irreversibly degraded the Kazal-type temporary inhibitor SPINK1. The observations suggest that the biological function of human mesotrypsin is digestive degradation of trypsin inhibitors. This mechanism can facilitate the digestion of foods rich in natural trypsin inhibitors. Furthermore, the findings raise the possibility that inappropriate activation of mesotrypsinogen in the pancreas might lower protective SPINK1 levels and contribute to the development of human pancreatitis. In this regard, it is noteworthy that the well known pathological trypsinogen activator cathepsin B exhibited a preference for the activation of mesotrypsinogen of all three human trypsinogen isoforms, suggesting a biochemical mechanism for mesotrypsinogen activation in pancreatic acinar cells.

p8 improves pancreatic response to acute pancreatitis by enhancing the expression of the anti-inflammatory protein pancreatitis-associated protein I

p8 is a transcription cofactor whose expression is strongly and rapidly activated in pancreatic acinar cells during the acute phase of pancreatitis. A p8-deficient mouse strain was generated as a tool to investigate its function. Upon induction of acute pancreatitis, myeloperoxidase activity in pancreas and serum concentrations of amylase and lipase were much higher and pancreatic lesions more severe in p8-deficient mice than in wild-type, indicating that p8 expression decreased pancreatic sensitivity to pancreatitis induction. The protective mechanism might involve the pancreatitis-associated protein (PAP I), whose strong induction during pancreatitis is p8-dependent, because administration of anti-PAP I antibodies to rats increased pancreatic inflammation during pancreatitis. In addition, 100 ng/ml PAP I in the culture medium of macrophages prevented their activation by tumor necrosis factor alpha, strongly suggesting that PAP I was an anti-inflammatory factor. Finally, PAP I was able to inhibit NFkappaB activation by tumor necrosis factor alpha, in macrophages and in the AR42J pancreatic acinar cell line. In conclusion, p8 improves pancreatic resistance to inducers of acute pancreatitis by a mechanism implicating the expression of the anti-inflammatory protein PAP I.

Alcohol and zymogen activation in the pancreatic acinar cell

Activation of zymogens within the pancreatic acinar cell is an early feature of acute pancreatitis. Supraphysiologic concentrations of cholecystokinin (CCK) cause intrapancreatic zymogen activation and pancreatitis. Supraphysiologic concentrations of CCK also cause zymogen activation in isolated pancreatic acini. This activation first occurs in a nonzymogen granule compartment that contains lysosomal markers. A low pH environment may also be needed for activation. To examine the ability of alcohols to sensitize the acinar cell to CCK, the conversion of zymogens to active enzymes in isolated acini was assayed. Alcohols, including 35 mmol/L ethanol, sensitized acini to CCK induced activation. The sensitization increased with chain length and was less in branched compared with unbranched alcohols. The relationship of alcohol's structure to sensitization may be related to the mechanism of sensitization.

Pathophysiology of alcohol-induced pancreatitis

Excessive ethanol consumption is a common risk factor for acute and chronic pancreatitis. Ethanol could lead to the onset of pancreatitis in a number of ways; the most recently discovered is its effect on intrapancreatic digestive enzyme activation, by either sensitizing acinar cells to pathologic stimuli or stimulating the release of a secretagogue (cholecystokinin) from duodenal I cells. Recent advances in cell biologic and molecular techniques have permitted us to address the intracellular events involved in digestive enzyme activation in a manner that was previously considered impossible. Investigations that used these novel techniques found that (a) trypsin is, in contrast to its role in the small intestine, not necessarily involved in the premature intracellular activation of other digestive proteases such as proelastase; (b) trypsinogen does not autoactivate intracellularly but is instead largely activated by the lysosomal hydrolase cathepsin B; and (c) the role of trypsin in the intrapancreatic protease cascade is most likely one that involves the degradation, rather than the activation, of active digestive proteases including trypsin itself. These studies, as well as investigations that have addressed the role of mutant trypsin in the disease onset of hereditary pancreatitis, suggest that trypsin may not be critical for triggering pancreatitis but might have a protective role against the action of some of the other digestive proteases. While the specific role of different digestive enzymes in initiating pancreatitis is still a matter of debate and the topic of ongoing investigations, experimental evidence suggests that ethanol can directly interfere with the processes involved in digestive zymogen activation.

Cathepsin B but not cathepsins L or S contributes to the pathogenesis of Unverricht-Lundborg progressive myoclonus epilepsy (EPM1)

The inherited epilepsy Unverricht-Lundborg disease (EPM1) is caused by loss-of-function mutations in the cysteine protease inhibitor, cystatin B. Because cystatin B inhibits a class of lysosomal cysteine proteases called cathepsins, we hypothesized that increased proteolysis by one or more of these cathepsins is likely to be responsible for the seizure, ataxia, and neuronal apoptosis phenotypes characteristic of EPM1. To test this hypothesis and to identify which cysteine cathepsins contribute to EPM1, we have genetically removed three candidate cathepsins from cystatin B-deficient mice and tested for rescue of their EPM1 phenotypes. Whereas removal of cathepsins L or S from cystatin B-deficient mice did not ameliorate any aspect of the EPM1 phenotype, removal of cathepsin B resulted in a 36-89% reduction in the amount of cerebellar granule cell apoptosis depending on mouse age. The incidence of an incompletely penetrant eye phenotype was also reduced upon removal of cathepsin B. Because the apoptosis and eye phenotypes were not abolished completely and the ataxia and seizure phenotypes experienced by cystatin B-deficient animals were not diminished, this suggests that another molecule besides cathepsin B is also responsible for the pathogenesis, or that another molecule can partially compensate for cathepsin B function. These findings establish cathepsin B as a contributor to the apoptotic phenotype of cystatin B-deficient mice and humans with EPM1. They also suggest that the identification of cathepsin B substrates may further reveal the molecular basis for EPM1.

Antidiabetic and antimalarial biguanide drugs are metal-interactive antiproteolytic agents

Various biguanide derivatives are used as antihyperglycemic and antimalarial drugs (e.g., 1,1-dimethyl biguanide (metformin), phenylethyl biguanide (phenformin), N-(4-chlorophenyl)-N'-(isopropyl)-imidodicarbonimidic diamide (proguanil)); however, no common mechanism has been suggested in these controversial therapeutic actions. Biguanides bind endogenous metals that inhibit cysteine proteases independently, e.g., Zn(2+), Cu(2+), Fe(3+). Here, various biguanide derivatives are reported to be metal-interactive inhibitors of cathepsin B from mammals and falcipain-2 from Plasmodium falciparum. Structural homologies were identified among the Phe-Arg protease substrate motif and the metal complexes of phenformin and proguanil. Molecular modeling revealed that the position of the scissile amide substrate bond corresponds to the biguanide-complexed inhibitory metal when the phenyl groups are homologously aligned. Binding of the phenformin-metal complex within the active site of human cathepsin B was modeled with computational docking. A major binding mode involved binding of the drug phenyl group at the protease S2 subsite, and the complexed inhibitory metal shared between the drug and the protease Cys29-His199 catalytic pair. Cysteine protease inhibition was assayed with carbobenzyloxy-PHE-ARG-7-aminomethylcoumarin substrate. In the absence of metal ions, phenformin was a weakly competitive protease inhibitor (apparent K(i) several microM); however, metformin was noninhibitory. In contrast, the metal complexes of both metformin and phenformin were protease inhibitors with potency at therapeutic concentrations. Biguanide-metal complexes were more potent cysteine protease inhibitors than either the biguanide or metal ions alone, i.e., synergistic. Similar to chloroquine, therapeutic extracellular concentrations of metformin, phenformin, and proguanil caused metal-interactive inhibition of lysosomal protein degradation as bioassayed in primary tissue using perfused myocardium. The biguanide moiety is identified as a past and future structural scaffold for synthesis of many protease inhibitors. Results are discussed in relation to Zn(2+)-interactive inhibition of insulin degradation in hormone target tissues, and Fe(3+)-interactive inhibition of hemoglobin degradation in parasite food vacuoles. Previous studies on insulin hypercatabolism and insulin resistance are speculatively reviewed in light of present findings.

Severe acute pancreatitis is related to increased early urinary levels of the activation Peptide of pancreatic phospholipase A(2)

BACKGROUND/AIM

In acute pancreatitis, it is believed that generalized activation of pancreatic zymogens leads to autodigestion of the pancreas and if excessive to systemic organ injury. Under physiological circumstances, secretory phospholipase A(2) type I (sPLA(2)-I) is activated by trypsinogen, but the extent of this activation in acute pancreatitis is unclear. The aim of this study was to assess time course and level of activation of sPLA(2)-I and trypsinogen in acute pancreatitis, relative to severity.

METHODS

246 patients were enrolled into a prospective European multicenter study. 137 patients had mild and 35 had severe acute pancreatitis, and there were 74 control patients. Urinary samples were taken on admission and at 6-hour intervals for 48 h, then every 12 h up to 72 h, and finally daily for at least 5 days for measurement of the activation peptide of sPLA(2)-I (pro-phosphatase A(2); PROP) and trypsinogen activation peptide.

RESULTS

The median maximum PROP values were significantly elevated 48 h after symptom onset in patients with severe acute pancreatitis [1.52 (95% CI 0.8-2.9) nmol/l] as compared with patients with mild acute pancreatitis [0.72 (0.55-1) nmol/l, p = 0.002] and controls [0.49 (0.22-1.2) nmol/l, p = 0.001], but not before or after this time point. The best cutoff point for urinary PROP to predict overall severity was >1 nmol/l < or =48 h after symptom onset (negative predictive value = 88%), but the PROP levels failed to predict the development of multi-organ dysfunction.

CONCLUSIONS

Activation of sPLA(2)-I is associated with the early pathogenesis of acute pancreatitis, but not in the development of distant organ damage. This observation raises questions as to the theory of generalized zymogen activation being a principle mechanism involved in the pathogenesis of distant organ damage in acute pancreatitis.

Acute experimental pancreatitis and NF-kappaB/Rel activation

Acute pancreatitis is a serious disease with a high morbidity and an overall mortality rate of about 10%. However, in its most severe form, which is characterized by pancreatic necrosis, 20-30% of the patients die. Death is often the result of multiorgan dysfunction, including acute respiratory, kidney, and hepatic failure as well as generalized diffuse capillary leak water retention, hypoxia, and acid/base disturbance. The mechanisms by which distant organ systems are involved still remain obscure, but several lines of evidence suggest the participation of cytokines (IL-1, IL-6, and TNF-alpha) as a response to local tissue damage. A series of studies have now shed new light on the pivotal pathogenic role of the transcription factor NF-kappaB/Rel that binds to the promoter regions of many proinflammatory genes and regulates their transcription.

Proteinases and their inhibitors in the immune system

The most important roles of proteinases in the immune system are found in apoptosis and major histocompatibility complex (MHC) class II-mediated antigen presentation. A variety of cysteine proteinases, serine proteinases, and aspartic proteinases as well as their inhibitors are involved in the regulation of apoptosis in neutrophils, monocytes, and dendritic cells, in selection of specific B and T lymphocytes, and in killing of target cells by cytotoxic T cells and natural killer cells. In antigen presentation, endocytosed antigens are digested into antigenic peptides by both aspartic and cysteine proteinases. In parallel, MHC class II molecules are processed by aspartic and cysteine proteinases to degrade the invariant chain that occupies the peptide-binding site. Proteinase activity in these processes is highly regulated, particularly by posttranslational activation and the balance between active proteinases and specific endogenous inhibitors such as cystatins, thyropins, and serpins. This article discusses the regulation of proteolytic processes in apoptosis and antigen presentation in immune cells and the consequences of therapeutic interference in the balance of proteinases and their inhibitors.

Lysosomal cysteine proteases regulate antigen presentation

Antigen presentation by both classical MHC class II molecules and the non-classical MHC class I-like molecule CD1D requires their entry into the endosomal/lysosomal compartment. Lysosomal cysteine proteases constitute an important subset of the enzymes that are present in this compartment and, here, we discuss the role of these proteases in regulating antigen presentation by both MHC class II and CD1D molecules.

Family C1 cysteine proteases: biological diversity or redundancy?

Recent progress in the identification and partial characterization of novel genes encoding cysteine proteases of the papain family has considerably increased our knowledge of this family of enzymes. Kinetic data available to date for this large family indicate relatively broad, overlapping specificities for most enzymes, thus inspiring a growing conviction that they may exhibit functional redundancy. This is also supported in part by phenotypes of cathepsin knockout mice and suggests that several proteases can substitute for each other to degrade or process a given substrate. On the other hand, specific functions of one particular protease have also been documented. In addition, differences in cellular distribution and intracellular localization may contribute to defining specific functional roles for some of these proteases.

Thyroid functions of mouse cathepsins B, K, and L

Thyroid function depends on processing of the prohormone thyroglobulin by sequential proteolytic events. From in vitro analysis it is known that cysteine proteinases mediate proteolytic processing of thyroglobulin. Here, we have analyzed mice with deficiencies in cathepsins B, K, L, B and K, or K and L in order to investigate which of the cysteine proteinases is most important for proteolytic processing of thyroglobulin in vivo. Immunolabeling demonstrated a rearrangement of the endocytic system and a redistribution of extracellularly located enzymes in thyroids of cathepsin-deficient mice. Cathepsin L was upregulated in thyroids of cathepsin K(-/-) or B(-/-)/K(-/-) mice, suggesting a compensation of cathepsin L for cathepsin K deficiency. Impaired proteolysis resulted in the persistence of thyroglobulin in the thyroids of mice with deficiencies in cathepsin B or L. The typical multilayered appearance of extracellularly stored thyroglobulin was retained in cathepsin K(-/-) mice only. These results suggest that cathepsins B and L are involved in the solubilization of thyroglobulin from its covalently cross-linked storage form. Cathepsin K(-/-)/L(-/-) mice had significantly reduced levels of free thyroxine, indicating that utilization of luminal thyroglobulin for thyroxine liberation is mediated by a combinatory action of cathepsins K and L.

Early changes in pancreatic acinar cell calcium signaling after pancreatic duct obstruction

Intracellular Ca(2+)-changes not only participate in important signaling pathways but have also been implicated in a number of disease states including acute pancreatitis. To investigate the underlying mechanisms in an experimental model mimicking human gallstone-induced pancreatitis, we ligated the pancreatic duct of Sprague-Dawley rats and NMRI mice for up to 6 h and studied intrapancreatic changes including the dynamics of [Ca(2+)](i) in isolated acini. In contrast to bile duct ligation, pancreatic duct obstruction induced intra-pancreatic trypsinogen activation, leukocytosis, hyperamylasemia, and pancreatic edema and increased lung myeloperoxidase activity. Although resting [Ca(2+)](i) in isolated acini rose by 45% to 205 +/- 7 nmol, the acetylcholine- and cholecystokinin (CCK)-stimulated calcium peaks as well as the amylase secretion declined, but neither the [Ca(2+)](i)-signaling pattern nor the amylase output in response to the Ca(2+)-ATPase inhibitor thapsigargin nor the secretin-stimulated amylase release were impaired by pancreatic duct ligation. On the single cell level pancreatic duct ligation reduced the percentage of cells in which submaximal secretagogue stimulation was followed by a physiological response (i.e. Ca(2+) oscillations) and increased the percentage of cells with a pathological response (i.e. peak plateau or absent Ca(2+) signal). Moreover, it reduced the frequency and amplitude of Ca(2+) oscillation as well as the capacitative Ca(2+) influx in response to secretagogue stimulation. Serum pancreatic enzyme elevation as well as trypsinogen activation was significantly reduced by pretreatment of animals with the calcium chelator BAPTA-AM. These experiments suggest that pancreatic duct obstruction rapidly changes the physiological response of the exocrine pancreas to a Ca(2+)-signaling pattern that has been associated with premature digestive enzyme activation and the onset of pancreatitis, both of which can be prevented by administration of an intracellular calcium chelator.

Protection from pancreatitis by the zymogen granule membrane protein integral membrane-associated protein-1

Pancreatitis is a common disease with substantial morbidity and mortality. To better understand the mechanisms conferring sensitivity or resistance to pancreatitis, we have initiated the analysis of novel acinar cell proteins. Integral membrane-associated protein-1 (Itmap1) is a CUB (complement subcomponents C1r/C1s, sea urchin Uegf protein, bone morphogenetic protein-1) and zona pellucida (ZP) domain-containing protein we find prominently expressed in pancreatic acinar cells. Within the acinar cell, Itmap1 localizes to zymogen granule membranes. Although roles in epithelial polarity, granule assembly, and mucosal protection have been postulated for CUB/ZP proteins, in vivo functions for these molecules have not been proven. To determine the function of Itmap1, we generated Itmap1-deficient mice. Itmap1(-/-) mice demonstrate increased severity of secretagogue- and diet-induced pancreatitis in comparison to Itmap1(+/+) mice. In contrast to previous animal models exhibiting altered severity of pancreatitis, Itmap1 deficiency results in impaired activation of trypsin, an enzyme believed critical for initiating a cascade of digestive zymogen activation during pancreatitis. Itmap1 deficiency does not alter zymogen granule size, appearance, or the composition of zymogen granule contents. Our results demonstrate that Itmap1 plays an essential role in trypsinogen activation and that both impaired and augmented trypsinogen activation can be associated with increased severity of pancreatitis.

Cathepsin B mediates tumor necrosis factor-induced arachidonic acid release in tumor cells

Arachidonic acid (AA) generated by cytosolic phospholipase A2 (cPLA2) has been suggested to function as a second messenger in tumor necrosis factor (TNF)-induced death signaling. Here, we show that cathepsin B-like proteases are required for the TNF-induced AA release in transformed cells. Pharmaceutical inhibitors of cathepsin B blocked TNF-induced AA release in human breast (MCF-7S1) and cervix (ME-180as) carcinoma as well as murine fibrosarcoma (WEHI-S) cells. Furthermore, TNF-induced AA release was significantly reduced in cathepsin B-deficient immortalized murine embryonic fibroblasts. Employing cPLA2-deficient MCF-7S1 cells expressing ectopic cPLA2 or cPLA2-deficient immortalized murine embryonic fibroblasts, we showed that cPLA2 is dispensable for TNF-induced AA release and death in these cells. Furthermore, TNF-induced cathepsin B-dependent AA release could be dissociated from the cathepsin B-independent cell death in MCF-7S1 cells, whereas both events required cathepsin B activity in other cell lines tested. These data suggest that cathepsin B inhibitors may prove useful not only in the direct control of cell death but also in limiting the damage-associated inflammation.

Cathepsin B inhibition prevents trypsinogen activation and reduces pancreatitis severity

Intrapancreatic activation of trypsinogen is believed to play a critical role in the initiation of acute pancreatitis, but mechanisms responsible for intrapancreatic trypsinogen activation during pancreatitis have not been clearly defined. In previous in vitro studies, we have shown that intra-acinar cell activation of trypsinogen and acinar cell injury in response to supramaximal secretagogue stimulation could be prevented by the cell permeant cathepsin B inhibitor E64d (Saluja A, Donovan EA, Yamanaka K, Yamaguchi Y, Hofbauer B, and Steer ML. Gastroenterology 113: 304-310, 1997). The present studies evaluated the role of intrapancreatic trypsinogen activation, this time under in vivo conditions, in two models of pancreatitis by using another highly soluble cell permeant cathepsin B inhibitor, L-3-trans-(propylcarbamoyl)oxirane-2-carbonyl-L-isoleucyl-L-proline methyl ester (CA-074me). Intravenous administration of CA-074me (10 mg/kg) before induction of either secretagogue-elicited pancreatitis in mice or duct infusion-elicited pancreatitis in rats markedly reduced the extent of intrapancreatic trypsinogen activation and substantially reduced the severity of both pancreatitis models. These observations support the hypothesis that, during the early stages of pancreatitis, trypsinogen activation in the pancreas is mediated by the lysosomal enzyme cathepsin B. Our findings also suggest that pharmacological interventions that inhibit cathepsin B may prove useful in preventing acute pancreatitis or reducing its severity.

From acinar cell damage to systemic inflammatory response: current concepts in pancreatitis

Acute pancreatitis represents a local inflammatory disorder with severe systemic consequences. Significant progress in understanding the pathophysiology of acute pancreatitis has been achieved in recent years. However, there is no clear concept about initialization and propagation of the disease both in experimental models and in humans. Furthermore, reliable strategies to evaluate prognosis and perform therapy are still missing. The review focuses on mechanisms originating from acinar cells leading to a systemic inflammatory response in experimental pancreatitis.

Cathepsin L and cathepsin B mediate reovirus disassembly in murine fibroblast cells

After attachment to receptors, reovirus virions are internalized by endocytosis and exposed to acid-dependent proteases that catalyze viral disassembly. Previous studies using the cysteine protease inhibitor E64 and a mutant cell line that does not support reovirus disassembly suggest a requirement for specific endocytic proteases in reovirus entry. This study identifies the endocytic proteases that mediate reovirus disassembly in murine fibroblast cells. Infection of both L929 cells treated with the cathepsin L inhibitor Z-Phe-Tyr(t-Bu)-diazomethyl ketone and cathepsin L-deficient mouse embryo fibroblasts resulted in inefficient proteolytic disassembly of viral outer-capsid proteins and decreased viral yields. In contrast, both L929 cells treated with the cathepsin B inhibitor CA-074Me and cathepsin B-deficient mouse embryo fibroblasts support reovirus disassembly and growth. However, removal of both cathepsin B and cathepsin L activity completely abrogates disassembly and growth of reovirus. Concordantly, cathepsin L mediates reovirus disassembly more efficiently than cathepsin B in vitro. These results demonstrate that either cathepsin L or cathepsin B is required for reovirus entry into murine fibroblasts and indicate that cathepsin L is the primary mediator of reovirus disassembly. Moreover, these findings suggest that specific endocytic proteases can determine host cell susceptibility to infection by intracellular pathogens.

CA-074, but not its methyl ester CA-074Me, is a selective inhibitor of cathepsin B within living cells

Studies using inhibitors that reportedly discriminate between cathepsin B and related lysosomal cysteine proteinases have implicated the enzyme in a wide range of physiological and pathological processes. The most popular substance to selectively inhibit cathepsin B in vivo is CA-074Me, the methyl ester of the E-64 derivative CA-074. However, we now have found that CA-074Me inactivates both cathepsin B and cathepsin L within murine fibroblasts. In contrast, exposure of these cells to the parental compound CA-074 leads to the selective inhibition of endogenous cathepsin B, while intracellular cathepsin L remains unaffected. These results indicate that CA-074 rather than CA-074Me should be used to specifically inactivate cathepsin B within living cells.

Cathepsin B cleavage of the trypsinogen activation peptide

BACKGROUND

Cathepsin B is thought to play a central role in intrapancreatic trypsinogen activation and the onset of pancreatitis. A recent investigation of the cathepsin B mediated activability of wildtype trypsinogen and their mutations N29I, N29T and R122H, which are associated to hereditary pancreatitis, revealed no differences. This action seems to be restricted to the K23-I24 peptide bond, which is the trypsinogen activation bond. Here we investigated the influence of the mutations D22G and K23R of the trypsinogen activation peptide on the cleavability by cathepsin B.

METHODS

To investigate the functional impact of the TAP mutations on cathepsin B mediated cleavage of the trypsinogen activating K23-I24 bond, the corresponding peptides pWT, APFDDDDKIVGG; pD22G, APFDDDGKIVGG; and pK23R, APFDDDDRIVGG were digested with cathepsin B for 30 min at pH 3.8 and 5.0, and the fragments were analysed by high-performance liquid chromatography.

RESULTS

Without cathepsin B, less than 1 % of the peptides were hydrolysed. After a 30-minute digestion with cathepsin B at pH 5, 96% of pWT, 48% of pK23R, but only 2.4% of pD22G were hydrolysed. At pH 3.8, the cathepsin B cleavage of pWT and pK23R was less than at pH 5, whereas the cleavage of pD22G was completely inhibited.

CONCLUSIONS

Cathepsin B mediated trypsinogen activation seems not to be a crucial pathogenic step in hereditary pancreatitis patients with the trypsinogen mutations D22G and K23R.

Presence of cathepsin B in the human pancreatic secretory pathway and its role in trypsinogen activation during hereditary pancreatitis

The lysosomal cysteine protease cathepsin B is thought to play a central role in intrapancreatic trypsinogen activation and the onset of experimental pancreatitis. Recent in vitro studies have suggested that this mechanism might be of pathophysiological relevance in hereditary pancreatitis, a human inborn disorder associated with mutations in the cationic trypsinogen gene. In the present study evidence is presented that cathepsin B is abundantly present in the secretory compartment of the human exocrine pancreas, as judged by immunogold electron microscopy. Moreover, pro-cathepsin B and mature cathepsin B are both secreted together with trypsinogen and active trypsin into the pancreatic juice of patients with sporadic pancreatitis or hereditary pancreatitis. Finally, cathepsin B- catalyzed activation of recombinant human cationic trypsinogen with hereditary pancreatitis-associated mutations N29I, N29T, or R122H were characterized. In contrast to a previous report, cathepsin B-mediated activation of wild type and all three mutant trypsinogen forms was essentially identical under a wide range of experimental conditions. These observations confirm the presence of active cathepsin B in the human pancreatic secretory pathway and are consistent with the notion that cathepsin B-mediated trypsinogen activation might play a pathogenic role in human pancreatitis. On the other hand, the results clearly demonstrate that hereditary pancreatitis-associated mutations do not lead to increased or decreased trypsinogen activation by cathepsin B. Therefore, mutation-dependent alterations in cathepsin B-induced trypsinogen activation are not the cause of hereditary pancreatitis.

Neuronal loss and brain atrophy in mice lacking cathepsins B and L

Cathepsins B and L are widely expressed cysteine proteases implicated in both intracellular proteolysis and extracellular matrix remodeling. However, specific roles remain to be validated in vivo. Here we show that combined deficiency of cathepsins B and L in mice is lethal during the second to fourth week of life. Cathepsin B(-/-)/L(-/-) mice reveal a degree of brain atrophy not previously seen in mice. This is because of massive apoptosis of select neurons in the cerebral cortex and the cerebellar Purkinje and granule cell layers. Neurodegeneration is accompanied by pronounced reactive astrocytosis and is preceded by an accumulation of ultrastructurally and biochemically unique lysosomal bodies in large cortical neurons and by axonal enlargements. Our data demonstrate a pivotal role for cathepsins B and L in maintenance of the central nervous system.

Evolution of placentally expressed cathepsins

Species and strain variants of a family of placentally expressed cathepsins (PECs) were cloned and sequenced in order to identify evolutionary conserved structural characteristics of this large family of cysteine proteases. Cathepsins M, P, Q, and R, are conserved in mice and rats but homologs of these genes are not found in human or rabbit placenta, showing that this family of proteases are probably restricted to rodents. Species-specific gene duplications have given rise to variants of cathepsin M in mice, and cathepsin Q in rats. Although the PECs have diverged at a greater rate than the other lysosomal cathepsins, residues around the specificity sub-sites of the individual enzymes are conserved. Strain-specific polymorphisms show that the evolutionary rate of divergence of cathepsins M and 3, the most recently duplicated pair of mouse genes, is even higher than the other PECs. In human placenta, critical functions of the PECs are probably performed by broader specificity proteases such as cathepsins B and L.

New laboratory tests in acute pancreatitis

Acute pancreatitis (AP) is a common disease with wide variation of severity. The diagnosis of AP is usually based on high serum amylase or lipase values but the accuracy of these methods is considered unsatisfactory. One in five of the patients develops a severe disease and carries a considerable risk of development of organ failure and high mortality. Early detection of patients with severe AP and especially those with increased risk of organ failure is importance since such patients seem to benefit from treatment in an intensive care unit started as soon as possible after presentation. In addition to enzymological methods, increasing interest has been focused on laboratory markers reflecting the level of inflammatory response in AP. At present, in routine clinical work the most commonly used severity marker is serum C-reactive protein, the concentration of which rises too slowly to be used for early prediction of severity. New therapies aiming at modifying the course of systemic inflammation in AP are being developed and therefore monitoring the patient's immune inflammatory status is needed. In this review article we present the current knowledge of laboratory tests, which has been evaluated for diagnostic and prognostic purposes in AP.

Human cationic trypsinogen. Arg(117) is the reactive site of an inhibitory surface loop that controls spontaneous zymogen activation

Mutation of Arg(117), an autocatalytic cleavage site, is the most frequent amino acid change found in the cationic trypsinogen (Tg) of patients with hereditary pancreatitis. In the present study, the role of Arg(117) was investigated in wild-type cationic Tg and in the activation-resistant Lys(15) --> Gln mutant (K15Q-Tg), in which Tg-specific properties of Arg(117) can be examined selectively. We found that trypsinolytic cleavage of the Arg(117)-Val(118) bond did not proceed to completion, but due to trypsin-catalyzed re-synthesis an equilibrium was established between intact Tg and its cleaved, two-chain form. In the absence of Ca(2+), at pH 8.0, the hydrolysis equilibrium (K(hyd) = [cleaved Tg]/[intact Tg]) was 5.4, whereas 5 mm Ca(2+) reduced the rate of cleavage at Arg(117) at least 20-fold, and shifted K(hyd) to 0.7. These observations indicate that the Arg(117)-Val(118) bond exhibits properties analogous to the reactive site bond of canonical trypsin inhibitors and suggest that this surface loop might serve as a low affinity inhibitor of zymogen activation. Consistent with this notion, autoactivation of cationic Tg was inhibited by the cleaved form of K15Q-Tg, with an estimated K(i) of 80 microm, while no inhibition was observed with K15Q-Tg carrying the Arg(117) --> His mutation. Finally, zymogen breakdown due to other trypsinolytic pathways was shown to proceed almost 2000-fold slower than cleavage at Arg(117). Taken together, the findings suggest two independent, successively functional trypsin-mediated mechanisms against pathological Tg activation in the pancreas. At low trypsin concentrations, cleavage at Arg(117) results in inhibition of trypsin, whereas high trypsin concentrations degrade Tg, thus limiting further zymogen activation. Loss of Arg(117)-dependent trypsin inhibition can contribute to the development of hereditary pancreatitis associated with the Arg(117) --> His mutation.

Hereditary pancreatitis caused by a novel PRSS1 mutation (Arg-122 --> Cys) that alters autoactivation and autodegradation of cationic trypsinogen

Hereditary pancreatitis has been found to be associated with germline mutations in the cationic trypsinogen (PRSS1) gene. Here we report a family with hereditary pancreatitis that carries a novel PRSS1 mutation (R122C). This mutation cannot be diagnosed with the conventional screening method using AflIII restriction enzyme digest. We therefore propose a new assay based on restriction enzyme digest with BstUI, a technique that permits detection of the novel R122C mutation in addition to the most common R122H mutation, and even in the presence of a recently reported neutral polymorphism that prevents its detection by the AflIII method. Recombinantly expressed R122C mutant human trypsinogen was found to undergo greatly reduced autoactivation and cathepsin B-induced activation, which is most likely caused by misfolding or disulfide mismatches of the mutant zymogen. The K(m) of R122C trypsin was found to be unchanged, but its k(cat) was reduced to 37% of the wild type. After correction for enterokinase activatable activity, and specifically in the absence of calcium, the R122C mutant was more resistant to autolysis than the wild type and autoactivated more rapidly at pH 8. Molecular modeling of the R122C mutant trypsin predicted an unimpaired active site but an altered stability of the calcium binding loop. This previously unknown trypsinogen mutation is associated with hereditary pancreatitis, requires a novel diagnostic screening method, and, for the first time, raises the question whether a gain or a loss of trypsin function participates in the onset of pancreatitis.

Identification and characterization of a dense cluster of placenta-specific cysteine peptidase genes and related genes on mouse chromosome 13

Genes encoding novel murine cysteine peptidases of the papain family C1A and related genes were cloned and mapped to mouse chromosome 13, colocalizing with the previously assigned cathepsin J gene. We constructed a <460-kb phage artificial chromosome (PAC) contig and characterized a dense cluster comprising eight C1A cysteine peptidase genes, cathepsins J, M, Q, R, -1, -2, -3, and -6; three pseudogenes of cathepsins M, -1, and -2; and four genes encoding putative cysteine peptidase inhibitors related to the proregion of C1A peptidases (trophoblast-specific proteins alpha and beta and cytotoxic T-lymphocyte-associated proteins 2alpha and -beta). Because of sequence homologies of 61.9-72.0% between cathepsin J and the other seven putative cysteine peptidases of the cluster, these peptidases are classified as "cathepsin J-like". The absence of cathepsin J-like peptidases and related genes from the human genome suggests that the cathepsin J cluster arose by partial and complete gene duplication events after the divergence of primate and rodent lineages. The expression of cathepsin J-like peptidases and related genes in the cluster is restricted to the placenta only. Clustered genes are induced at specific time points, and their expression increases toward the end of gestation. The specific expression pattern and high expression level suggest an essential role of cathepsin J-like peptidases and related genes in formation and development of the murine placenta.

Trypsin activity is not involved in premature, intrapancreatic trypsinogen activation

A premature and intracellular activation of digestive zymogens is thought to be responsible for the onset of pancreatitis. Because trypsin has a critical role in initiating the activation cascade of digestive enzymes in the gut, it has been assumed that trypsin also initiates intracellular zymogen activation in the pancreas. We have tested this hypothesis in isolated acini and lobules from rat pancreas. Intracellular trypsinogen activation was induced by supramaximal secretagogue stimulation and measured using either specific trypsin substrates or immunoreactivity of the trypsinogen activation peptide (TAP). To prevent a trypsin-induced trypsinogen activation, we used the cell-permeant, highly specific, and reversible inhibitor Nalpha-(2-naphthylsulfonyl)-3-amidinophenylalanine-carboxymethylpiperazide (S124), and to prevent cathepsin-induced trypsinogen activation, we used the cysteine protease inhibitor E-64d. Incubation of acini or lobules in the presence of S124 completely prevented the generation of trypsin activity in response to supramaximal caerulein but had no effect whatsoever on the generation of TAP. Conversely, when trypsin activity was recovered at the end of the experiment by either washout of S124 from acini or extensive dilution of lobule homogenates, it was up to 400% higher than after caerulein alone and corresponded, in molar terms, to the generation of TAP. Both trypsin activity and TAP release were inhibited in parallel by E-64d. We conclude that caerulein-induced trypsinogen activation in the pancreas is caused by an E-64d-inhibitable mechanism such as cathepsin-induced trypsinogen activation, and neither involves nor requires intracellular trypsin activity. Specific trypsin inhibition, on the other hand, prevents 80% of trypsin inactivation or autodegradation in the pancreas.

S2' substrate specificity and the role of His110 and His111 in the exopeptidase activity of human cathepsin B

The ability of the lysosomal cysteine protease cathepsin B to function as a peptidyldipeptidase (removing C-terminal dipeptides) has been attributed to the presence of two histidine residues (His(110) and His(111)) present in the occluding loop, an extra peptide segment located in the primed side of the active-site cleft. Whereas His(111) is unpaired, His(110) is present as an ion pair with Asp(22) on the main body of the protease. This ion pair appears to act as a latch to hold the loop in a closed position. The exopeptidase activity of cathepsin B, examined using quenched fluorescence substrates, was shown to have a 20-fold preference for aromatic side chains in the P2' position relative to glutamic acid as the least favourable residue. Site-directed mutagenesis demonstrated that His(111) makes a positive 10-fold contribution to the exopeptidase activity, whereas His(110) is critical for this action with the Asp(22)-His(110) ion pair stabilizing the electrostatic interaction by a maximum of 13.9 kJ/mol (3.3 kcal/mol). These studies showed that cathepsin B is optimized to act as an exopeptidase, cleaving dipeptides from protein substrates in a successive manner, because of its relaxed specificity in P2' and its other subsites.

Thermal stress-induced HSP70 mediates protection against intrapancreatic trypsinogen activation and acute pancreatitis in rats

BACKGROUND & AIMS

Prior thermal stress induces heat shock protein 70 (HSP70) expression in the pancreas and protects against secretagogue-induced pancreatitis, but it is not clear that this thermal stress-induced protection is actually mediated by HSP70 since thermal stress may have other, non-HSP related, effects.

METHODS

In the present study, we have administered antisense (AS) oligonucleotides, which prevent pancreatic expression of HSP70 to rats, in vivo, to evaluate this issue. In a separate series of experiments, designed to examine the role of pancreatitis-induced HSP70 expression in modulating the severity of pancreatitis, rats not subjected to prior thermal stress were given AS-HSP70 before cerulein administration, and trypsinogen activation as well as the severity of pancreatitis were evaluated.

RESULTS

Hyperthermia induced HSP70 expression, prevented intrapancreatic trypsinogen activation, and protected against cerulein-induced pancreatitis. Administration of AS-HSP70 but not sense-HSP70 reduced the thermal stress-induced HSP70 expression, restored the ability of supramaximal cerulein stimulation to cause intrapancreatic trypsinogen activation, and abolished the protective effect of prior thermal stress against pancreatitis. In non-thermally stressed animals, pretreatment with AS-HSP70 before the induction of pancreatitis exacerbated all the parameters associated with pancreatitis.

CONCLUSIONS

These findings lead us to conclude that HSP70 induction, rather than some other thermal stress-related phenomenon, mediates the thermal stress-induced protection against pancreatitis and that it protects against pancreatitis by preventing intrapancreatic activation of trypsinogen. The worsening of pancreatitis, which occurs when non-thermally stressed animals are given AS-HSP70 before cerulein, suggests that cerulein-induced HSP70 expression in nontreated animals acts to limit the severity of pancreatitis.

Cathepsin B knockout mice are resistant to tumor necrosis factor-alpha-mediated hepatocyte apoptosis and liver injury: implications for therapeutic applications

Tumor necrosis factor-alpha (TNF-alpha) contributes to liver injury by inducing hepatocyte apoptosis. Recent evidence suggests that cathepsin B (cat B) contributes to TNF-alpha-induced apoptosis in vitro. The aim of the present study was to determine whether cat B contributes to TNF-alpha-induced hepatocyte apoptosis and liver injury in vivo. Cat B knockout (catB(-/-)) and wild-type (catB(+/+)) mice were first infected with the adenovirus Ad5I kappa B expressing the I kappa B superrepressor to inhibit nuclear factor-kappa B-induced survival signals and then treated with murine recombinant TNF-alpha. Massive hepatocyte apoptosis with mitochondrial release of cytochrome c and activation of caspases 9 and 3 was detected in catB(+/+) mice 2 hours after the injection of TNF-alpha. In contrast, significantly less hepatocyte apoptosis and no detectable release of cytochrome c or caspase activation occurred in the livers of catB(-/-) mice. By 4 hours after TNF-alpha injection, only 20% of the catB(+/+) mice were alive as compared to 85% of catB(-/-) mice. Pharmacological inhibition of cat B in catB(+/+) mice with L-3-trans-(propylcarbamoyl)oxirane-2-carbonyl-L-isoleucyl-L-proline (CA-074 Me) also reduced TNF-alpha-induced liver damage. The present data demonstrate that a cat B-mitochondrial apoptotic pathway plays a pivotal role in TNF-alpha-induced hepatocyte apoptosis and liver injury.

Inhibition of trypsin-like cysteine proteinases (gingipains) from Porphyromonas gingivalis by tetracycline and its analogues

Extracellular cysteine proteinases, referred to as gingipains, are considered important virulence factors for Porphyromonas gingivalis, a bacterium recognized as a major etiologic agent of chronic periodontitis. We investigated the effect of tetracycline and its analogues, doxycycline and minocycline, on the enzymatic activities of gingipains. Tetracyclines at 100 microM totally inhibited the amidolytic activity of arginine-specific gingipains (HRgpA and RgpB). In contrast, inhibition of Kgp was less efficient and required a somewhat higher concentration of the antibiotic to achieve the same effect. Among tetracycline derivatives, the most potent gingipain inhibitor was doxycycline, followed by tetracycline and minocycline. RgpB was inhibited by doxycycline in an uncompetitive and reversible manner with a 50% inhibitory concentration of 3 microM. Significantly, inhibition was unaffected by calcium, excluding the chelating activity of tetracyclines as the mechanism of gingipain inactivation. In contrast, the inhibitory activities of the tetracyclines were reduced by cysteine, a reducing agent, suggesting an interference of the drug at the oxidative region with the catalytic system of the enzyme. Doxycycline, at 10 microM, significantly inhibited the RgpB-mediated production of vascular permeability-enhancing activity from human plasma, thus proving an effective inhibition of gingipain in vivo. These results indicate a new activity of tetracyclines as cysteine proteinase inhibitors and may explain the therapeutic efficiency of these antibiotics in the treatment of periodontitis.