Cysteinyl Cathepsins Research Articles

A possible role of cystatin C in adipose tissue homeostasis may impact kidney function estimation in metabolic syndrome

The assessment of kidney function [1] serves two main purposes: one is to accurately diagnose kidney function impairment at a given—preferably early—point in time, and the other is to determine the slope of function decline by serial assessment. Kidney function is best measured as the glomerular filtration rate (GFR) by infusion of exogenous markers such as inulin, I-iothalamate or chromium–EDTA. Unfortunately, these gold standards are cumbersome, costly and often too time-consuming for clinical or epidemiological purposes. Current guidelines recommend the use of prediction equations based on a single serum creatinine concentration to estimate the GFR or to calculate the creatinine clearance from a 24-h urine sample. Many investigators have questioned the accuracy of these equations, particularly when used in the normal to elevated range of kidney function. Consequently, there has been much interest in the performance of alternative biomarkers such as cystatin C. Cystatin C, a low-molecular weight (13kD) protein and a member of the super-family of cysteine protease inhibitors, has been proposed to provide a more accurate estimation of the GFR than serum creatinine [2, 3]. In various populations, cystatin C was more sensitive in the identification of mild reductions in kidney function than serum creatinine [3]. Cystatin C is believed to be produced at a constant rate by a “housekeeping” gene that is present in all nucleated cells, and to be freely filtered across the glomerulus. Prediction equations based on serum cystatin C concentrations have been formulated [4], whereas 100/cystatin C visualizes function decline over time. Unlike creatinine, cystatin C does not undergo tubular secretion, but is catabolized by epithelial cells of the proximal tubulus, which prevents cystatin C from being used for calculating clearance. The rate of production of cystatin C was initially believed to be uninfluenced by changes in diet, muscle mass, age, gender and ethnicity. Yet various recent studies have shown that cystatin C concentrations are indeed affected by determinants other than kidney function: age, male gender, body mass index, fat mass, triglyceride concentrations, hypertension, uric acid, C-reactive protein and diabetes have all been associated with higher serum concentrations of cystatin C independent of kidney function (in some studies assessed using I-iothalamate and Chromium-EDTA) [5–7]. Intriguingly, all these factors cluster together in the metabolic syndrome [8], suggesting a yet ill-defined role of cystatin C in the pathophysiology of the metabolic syndrome. In this issue of NDT, Reutens et al. [9] report on an association between cystatin C and incident type-2 diabetes. The study involved a large cohort of participants included in the DESIR cohort, which comprises men and women of the French general population aged 36–71 years with relatively low prevalence of the metabolic syndrome (24%). The 3-year incidence of type 2 diabetes was only 2%. The authors confirmed recent literature that showed that cystatin C predicts incident diabetes independent of the estimated GFR (MDRD), waist circumference, insulin resistance and other risk factors for type-2 diabetes. More importantly, Reutens et al. showed that the impact of cystatin C on incident type-2 diabetes was dependent on the amount of adiposity. This finding sheds some interesting light on the possible role of cystatin C in obesity. Cystatin C’s main biological role is to be the endogenous inhibitor of the cysteine proteases cathepsins [10], which comprises a family of 11 human proteases (cathepsins B, C, H, F, K, L, O, S, V, W and Z) [11]. Of this family, cathepsins S, K and L have been shown to promote adipogenesis, often in conjunction with the degradation of extracellular matrix (ECM) [12–14]. Cysteinyl cathepsins, which have proteolytic activity, are known to degrade ECM components [11]. In addition, they are involved in the processing of antigen presentation [15], while inflammatory cells migrate into tissue in a cathepsin-dependent manner. In agreement, mouse models of cathepsin deficiencies typically display attenuated inflammation [16]. These are properties that may be of relevance to the remodelling of adipose tissue. Recent evidence suggests that impaired IN F O C U S

E64D DETERIORATES POST-MYOCARDIAL INFARCTION LEFT VENTRICULAR REMODELLING BY INHIBITING CATHEPSIN S-MEDIATED FIBROBLAST TRANS-DIFFERENTIATION

ObjectivesExtracellular matrix (ECM) turnover is a major process of left ventricular (LV) remodelling following myocardial infarction (MI). Cysteinyl cathepsins participate in ECM catabolism in human arterial diseases, but their functions...

Role for Cysteine Protease Cathepsins in Heart Disease

The extracellular matrix (ECM) of the heart is composed largely of elastin and collagen and plays many roles in cardiac wall and valve homeostasis. Maintenance of a healthy cardiac system relies on controlled biosynthesis, maturation, function, and breakdown of ECM proteins. Dysregulation of proteolytic enzymes may disrupt these normal biological processes in myocardium-coronary-valve disease (CCVD). Substantial evidence supports the involvement of matrix metalloproteinase (MMP) and serine protease families in this process (reviewed elsewhere1,2). Cysteinyl proteases have received much less consideration in this regard, even though cardiovascular cells and macrophages with greatly expanded lysosomal compartments figure prominently in the pathogenesis of CCVD. Lysosomal cysteine proteases, generally known as cathepsins, were discovered in the second half of the 20th century. In the initial years after their discovery, cysteinyl cathepsins were shown to localize in lysosomes and endosomes and to function there to degrade unwanted intracellular or endocytosed proteins.3–5 However, the recent recognition of the inducible cathepsins F, K, S, B, and L led to the unraveling of their molecular functions in inflammatory and/or autoimmune diseases such as atherosclerosis,6–11 obesity,12–14 rheumatoid arthritis,15,16 cardiac repair,17 cardiomyopathy,18–20 and cancer.21 Most strikingly, we have now discovered that these cathepsins can be secreted into and function within the extracellular spaces. The observations of cathepsin expression and activity in failing cardiac tissues22–24 and valve tissues25–27 from humans and animals and in cultured media of cardiomyocytes,22,24 cardiac fibroblasts,22 vascular smooth muscle cells,28 endothelial cells,12 and macrophages6,10 have significantly broadened our understanding of their potential roles in cardiovascular pathogenesis. Furthermore, recent studies have shown that pharmacological cathepsin inhibition exhibits cardiovascular protective actions in animal models. …

Microarray-guided discovery of two-photon (2P) small molecule probes for live-cell imaging of cysteinyl cathepsin activities

A microarray immobilized with 105 aldehyde-containing small molecules was screened against mammalian cell lysates over-expressing cathepsin L to identify two potent inhibitors, which were subsequently converted into cell-permeable probes capable of live-cell imaging of endogenous cysteinyl cathepsin activities by two-photon fluorescence microscopy.

Cysteinyl Cathepsins: Multifunctional Enzymes in Cardiovascular Disease

Until recently, the role of lysosomal cysteine protease cathepsins in intracellular protein degradation was believed to be mainly restricted to scavenging. However, recent studies have revealed nontraditional roles for cysteine protease cathepsins in the extracellular space during the development and progression of cardiovascular disease. Although the precise mechanisms are unknown, data from animal studies suggest that members of the cathepsin family, like other extracellular proteases, contribute to extracellular matrix protein remodeling and interstitial matrix degradation, as well as to cell signaling and cell apoptosis in heart disease. Inflammatory cytokines and hormones regulate the expression and secretion of cathepsins in cultured cardiovascular cells and macrophages. Serum levels of cathepsins L, S, and K and their endogenous inhibitor cystatin C may be useful predictive biomarkers in patients with coronary artery disease and cardiac disease. Furthermore, in vivo pharmacological intervention with a synthetic cathepsin inhibitor and cardiovascular drugs (including statins and angiotensin II type 1 receptor antagonists) has the potential for pharmacologic targeting of cathepsins in cardiovascular disease. This review focuses on cathepsin biology (structure, synthesis, processing, activation, secretion, activity regulation, and function) and the involvement of cysteinyl cathepsins in the pathogenesis of several heart and vessel diseases, especially with respect to their potential application as diagnostic and prognostic markers and drug targets to prevent inappropriate proteolysis in cardiovascular disease.

Cysteine Protease Cathepsins in Atherosclerosis-Based Vascular Disease and Its Complications

Atherosclerosis-based vascular disease is an inflammatory disease characterized by extensive remodeling of the extracellular matrix architecture of the arterial wall. Although matrix metalloproteinases and serine proteases participate in these pathological events, the discovery of cysteine protease cathepsins, such as cathepsins K, S, L, and B, and cystatin C, and their tissue distribution has suggested that at least some of them participate in cardiovascular disease. Studies on vascular cells have shown that atherosclerosis-associated inflammatory cytokines augment cysteinyl cathepsin expression and activity. Novel insight into cathepsin functions has been made possible by the generation and in-depth analysis of knockout and transgenic mice. These studies have provided direct evidence implicating cathepsins in atherosclerosis-based vascular disease through the activation, liberation, and modification of angiogenic growth factors, cytokines, and proteases associated with lipid metabolism, cell events (migration, invasion, proliferation, and apoptosis), angiogenesis, and matrix protein remodeling. Furthermore, evaluation of the feasibility of cathepsins as a diagnostic tool has revealed that the serum cathepsins S and L and the endogenous inhibitor cystatin C hold promise as biomarkers of coronary artery disease and aneurysm formation. The goal of this review is to summarize the available information regarding the mechanistic contributions of cathepsins in atherosclerosis-based vascular disease.

Cathepsin L Activity Is Essential to Elastase Perfusion–Induced Abdominal Aortic Aneurysms in Mice

The development of abdominal aortic aneurysms (AAA) requires extensive aortic wall matrix degradation. Human AAA lesions express high levels of cathepsin L (CatL), one of the most potent mammalian elastases. Whether this protease participates directly in AAA pathogenesis, however, is unknown. We generated experimental AAA with aortic elastase perfusion in mice and established an essential role of CatL in AAA formation. After 14 days postperfusion, most wild-type (Ctsl(+/+)) mice developed AAA, but none of the CatL-deficient (Ctsl(-/-)) mice did. AAA lesion macrophage contents, CD4(+) T cell numbers, CD31(+) and laminin-5 angiogenic fragment γ2(+) microvessel numbers, and elastin fragmentation were all significantly lower in Ctsl(-/-) mice than in Ctsl(+/+) mice. While lesions from Ctsl(-/-) mice contained fewer Ki67(+) proliferating cells than did Ctsl(+/+) mice, the absence of CatL did not affect lesion apoptotic cell contents or medial smooth-muscle cell loss significantly. Mechanistic studies indicated that the absence of CatL reduced lesion chemokine monocyte chemotactic protein-1 content, macrophage and T-cell in vitro transmigration, and angiogenesis, and altered the expression and activities of matrix metalloproteinases and other cysteinyl cathepsins in inflammatory cells, vascular cells, and AAA lesions. CatL contributes to AAA formation by promoting lesion inflammatory cell accumulation, angiogenesis, and protease expression.

Cathepsin K Deficiency Reduces Elastase Perfusion–Induced Abdominal Aortic Aneurysms in Mice

Cathepsin K (CatK) is one of the most potent mammalian elastases. We have previously shown increased expression of CatK in human abdominal aortic aneurysm (AAA) lesions. Whether this protease participates directly in AAA formation, however, remains unknown. Mouse experimental AAA was induced with aortic perfusion of a porcine pancreatic elastase. Using this experimental model, we demonstrated that absence of CatK prevented AAA formation in mice 14 days postperfusion. CatK deficiency significantly reduced lesion CD4(+) T-cell content, total lesion and medial cell proliferation and apoptosis, medial smooth muscle cell (SMC) loss, elastinolytic CatL and CatS expression, and elastin fragmentation, but it did not affect AAA lesion Mac-3(+) macrophage accumulation or CD31(+) microvessel numbers. In vitro studies revealed that CatK contributed importantly to CD4(+) T-cell proliferation, SMC apoptosis, and other cysteinyl cathepsin and matrix metalloproteinase expression and activities in SMCs and endothelial cells but played negligible roles in microvessel growth and monocyte migration. AAA lesions from CatK-deficient mice showed reduced elastinolytic cathepsin activities compared with those from wild-type control mice. This study demonstrates that CatK plays an essential role in AAA formation by promoting T-cell proliferation, vascular SMC apoptosis, and elastin degradation and by affecting vascular cell protease expression and activities.

Mast Cell Tryptase Deficiency Attenuates Mouse Abdominal Aortic Aneurysm Formation

Mast cells (MCs) contribute to the formation of abdominal aortic aneurysms (AAAs) by producing biologically active mediators. Tryptase is the most abundant MC granule protein and participates in MC activation, protease maturation, leukocyte recruitment, and angiogenesis-all processes critical to AAA pathogenesis. To test the hypothesis that tryptase participates directly in AAA formation. Immunohistochemistry demonstrated enhanced tryptase staining in media and adventitia of human and mouse AAA lesions. Serum tryptase levels correlated significantly with the annual expansion rate of AAA before (r = 0.30, P = 0.003) and after (r = 0.29, P = 0.005) adjustment for common AAA risk factors in a patient follow-up study, and associated with risks for later surgical repair or overall mortality before (P = 0.009, P = 0.065) and after (P = 0.004, P = 0.001) the adjustment. Using MC protease-6-deficient mice (Mcpt6(-/-)) and aortic elastase perfusion-induced experimental AAAs, we proved a direct role of this tryptase in AAA pathogenesis. Whereas all wild-type (WT) mice developed AAA at 14 or 56 days postperfusion, Mcpt6(-/-) mice were fully protected. AAA lesions from Mcpt6(-/-) mice had fewer inflammatory and apoptotic cells, and lower chemokine levels, than did those from WT mice. MC from WT mice restored reduced AAA lesions and lesion inflammatory cell content in MC-deficient Kit(W-sh/W-sh) mice, but those prepared from Mcpt6(-/-) mice did not. Mechanistic studies demonstrated that tryptase deficiency affected endothelial cell (EC) chemokine and cytokine expression, monocyte transmigration, smooth-muscle cell apoptosis, and MC and AAA lesion cysteinyl cathepsin expression and activities. This study establishes the direct participation of MC tryptase in the pathogenesis of experimental AAAs, and suggests that levels of this protease can serve as a novel biomarker for abdominal aortic expansion.

Molecular imaging of macrophage protease activity in cardiovascular inflammation in vivo

Macrophages contribute pivotally to cardiovascular diseases (CVD), notably to atherosclerosis. Imaging of macrophages in vivo could furnish new tools to advance evaluation of disease and therapies. Proteolytic enzymes serve as key effectors of many macrophage contributions to CVD. Therefore, intravital imaging of protease activity could aid evaluation of the progress and outcome of atherosclerosis, aortic aneurysm formation, or rejection of cardiac allografts. Among the large families of proteases, matrix metalloproteinases (MMPs) and cysteinyl cathepsins have garnered the most interest because of their participation in extracellular matrix remodelling. These considerations have spurred the development of dedicated imaging agents for protease activity detection. Activatable fluorescent probes, radiolabelled inhibitors, and nanoparticles are currently under exploration for this purpose. While some agents and technologies may soon see clinical use, others will require further refinement. Imaging of macrophages and protease activity should provide an important adjunct to understanding pathophysiology in vivo, evaluating the effects of interventions, and ultimately aiding clinical care.

Expression of cathepsin S and its inhibitor stefin A in sinonasal inverted papilloma

Dysregulation of cysteinyl cathepsins and their inhibitors, cystatins (stefins), were implied in progression of tumorgenesis; nevertheless, their role in sinonasal inverted papilloma (IP) is still unrecognized. The differential expression of cathepsins and stefins in IP and normal tissues were revealed by data of human Affymetrix U133A gene chips, real-time polymerase chain reaction (PCR) and immunohistochemistry. Among the cathepsins and stefins family, expression of cathepsin S and stefin A were most differentially expressed (down- and up-regulated, respectively) in IP tissue as compared with normal tissues. Their expression levels were validated by real-time PCR, which showed the expression level of cathepsin S was significantly down-regulated, whereas the expression of stefin A was significantly up-regulated in IP tissue compared to normal sinus mucosa. Using immunohistochemistry, expression of cathepsin S was observed in stromal and epithelial area macrophages of normal sinus mucosa, but no obvious expression of cathepsin S was found in IP tissue. In contrast, over-expression of stefin A was present in nearly all layers of the proliferative squamous cells of IP, but expression of stefin A was only detected in a scattered area of normal sinus mucosa. Down-regulation of cathepsin S and up-regulation of its endogenous inhibitor, stefin A, were found in IP tissues as compared with their expression level in normal sinus mucosa tissues. The biological significance of inverse expression of both stefin A and cathepsin S in sinonasal IP need further investigation in the future.

Expression of cathepsin S and its inhibitor stefin A in sinonasal inverted papilloma

Background: Dysregulation of cysteinyl cathepsins and their inhibitors, cystatins (stefins), were implied in progression of tumorgenesis; nevertheless, their role in sinonasal inverted papilloma (IP) is still unrecognized. Methods: The differential expression of cathepsins and stefins in IP and normal tissues were revealed by data of human Affymetrix U133A gene chips, real-time polymerase chain reaction (PCR) and immunohistochemistry. Results: Among the cathepsins and stefins family, expression of cathepsin S and stefin A were most differentially expressed (down- and up-regulated, respectively) in IP tissue as compared with normal tissues. Their expression levels were validated by real-time PCR, which showed the expression level of cathepsin S was significantly down-regulated, whereas the expression of stefin A was significantly up-regulated in IP tissue compared to normal sinus mucosa. Using immunohistochemistry, expression of cathepsin S was observed in stromal and epithelial area macrophages of normal sinus mucosa, but no obvious expression of cathepsin S was found in IP tissue. In contrast, over-expression of stefin A was present in nearly all layers of the proliferative squamous cells of IP, but expression of stefin A was only detected in a scattered area of normal sinus mucosa. Conclusion: Down-regulation of cathepsin S and up-regulation of its endogenous inhibitor, stefin A, were found in IP tissues as compared with their expression level in normal sinus mucosa tissues. The biological significance of inverse expression of both stefin A and cathepsin S in sinonasal IP need further investigation in the future.

Cystatin C Deficiency Promotes Inflammation in Angiotensin II–Induced Abdominal Aortic Aneurisms in Atherosclerotic Mice

An imbalance between cysteinyl cathepsins and their principal endogenous inhibitor cystatin C (CystC) may favor proteolysis in the pathogenesis of human abdominal aortic aneurysms (AAA), yet a direct role of CystC in AAA remains unproven. This study used CystC and apolipoprotein E (ApoE) compound mutant (CystC(-/-)ApoE(-/-)) mice to examine directly the role of cysteine protease/protease inhibitor imbalance in AAA formation in angiotensin II-induced AAA. CystC-deficiency increased lumenal diameter and lesion size compared with control mice. CystC(-/-) ApoE(-/-) lesions also demonstrated enhanced inflammatory cell accumulation, more severe elastin fragmentation, and fewer smooth muscle cells in the tunica media. Macrophage content, measured as percent positive area (23.2 +/- 1.4% versus 11.2 +/- 1.4%; P = 0.0003) and number of the CD4(+) T cells (ninefold; P = 0.048), increased significantly in CystC(-/-)ApoE(-/-) lesions. CystC deficiency increased cathepsin activity (5.5 fold; P = 0.001) in AAA, yielding greater elastin degradation and proangiogenic laminin-5 gamma2 peptide production, which may account for increased microvascularization in CystC(-/-)ApoE(-/-) compared with ApoE(-/-) lesions. Increased leukocyte adhesion molecule VCAM-1 expression and leukocyte proliferation might also promote inflammation in CystC-deficient AAA. These data indicate that CystC contributes to experimental AAA pathogenesis and that enhanced cysteine protease activity, due to the lack of CystC, favors inflammation in AAA lesions induced in atherosclerotic mice by promoting microvascularization and smooth muscle cell apoptosis as well as leukocytes adhesion and proliferation.

Usefulness of Serum Cathepsin L as an Independent Biomarker in Patients With Coronary Heart Disease

Higher levels of cysteinyl cathepsin L were detected in human atherosclerotic lesions than in healthy aortas. However, a link between human coronary heart disease (CHD) and systemic cathepsin L levels remains unknown. A total of 137 volunteers with diagnosed acute and previous myocardial infarction (MI) and stable and unstable angina pectoris in addition to 48 controls were asked to undergo coronary angiography. Serum cathepsin L, high-sensitivity C-reactive protein, fasting glucose, and lipid protein profiles were measured. Serum cathepsin L levels were significantly higher in patients with CHD than in those without CHD (p <0.001). The significance persisted after adjusting for most major confounders. Patients with unstable angina pectoris had higher serum cathepsin L levels than those with stable angina pectoris (p = 0.02). Of patients with acute coronary syndrome, those with acute MI had higher serum cathepsin L levels than those with unstable angina pectoris (p <0.05) and patients with previous MI had the highest levels. Importantly, serum cathepsin L associated positively with number of coronary branch luminal narrowings (R = 0.38, p <0.001), Gensini scores (R = 0.44, p <0.001), high-sensitivity C-reactive protein (R = 0.32, p <0.001), fasting glucose (R = 0.16, p <0.03), and cigarette smokers (R = 0.27, p <0.001), but inversely with high-density lipoprotein (R = -0.23, p = 0.002) and apolipoprotein A1 (R = -0.19, p = 0.01) in all subjects. In conclusion, after adjusting for these confounders, we found that serum cathepsin L correlated positively and independently with Gensini score, suggesting that serum cathepsin L serves as a novel and independent biomarker for CHD.

New Insights into the Roles of Endolysosomal Cathepsins in the Pathogenesis of Alzheimers Disease: Cathepsin Inhibitors as Potential Therapeutics

Endolysosomal proteases such as cysteinyl and aspartyl cathepsins play diverse roles in inflammatory autoimmune diseases, cancers, and neurodegenerative diseases. Cysteinyl cathepsin B and aspartyl cathepsin D levels are markedly elevated in a variety of neurological disorders including Alzheimer's disease (AD), a leading cause of dementia in the elderly. Studies have also shown an increased cathepsin activity in AD patients where senile plaques and neuronal loss are marked features of the disease. Senile plaques contain amyloid-beta (Abeta) peptide, which is produced by proteolytic cleavage of the amyloid precursor protein (APP) by the proteases. In this article, we present the current knowledge of cysteinyl and aspartyl cathepsins in cellular and molecular events that lead to formation of senile plaques in AD. This article also focused on the role of cathepsin inhibitors as disease-modifying treatment strategies that could halt, or even prevent, this devastating neurological disorder.

Digesting the Remodeled Heart

Of the many proteinases present in the myocardium, members of the matrix metalloproteinase (MMP) family have received most attention. However, the cysteine proteases and their inhibitors have now been implicated in the pathogenesis of cardiac remodeling in the hypertrophied and failing heart. Cathepsins, cysteine proteases of the papain family, are optimally active in the acidic pH of lysosomes and are responsible for the physiological digestive turnover of cellular molecules and organelles. We now know that the levels of cathepsins and their endogenous inhibitors, cystatins, can be regulated by a number of signaling molecules, and cathepsins can be released from lysosomes into the extracellular space. Cysteine proteinases may degrade extracellular matrix proteins, such as elastin and fibrillar collagens.1 Nonlysosomal cathepsin targets include degradation of matrix and bone via elastinolytic/collagenolytic activity, activation of pro-MMP, induction of anoikis-dependent apoptosis via matrix degradation, activation of caspases, and cleavage of focal adhesion kinases. A decade ago, measurement of cathepsin activity in heart tissue of different pathologies was used as a measure of lysosomal activity and …

Prolonged seizures and cellular injury: Understanding the connection

Status epilepticus (SE)-induced neuronal death is morphologically necrotic and is initiated by excessive glutamate release, which activates postsynaptic N-methyl- d-aspartate (NMDA) receptors and triggers receptor-mediated calcium influx (excitotoxicity). This results in activation of intracellular proteases and neuronal nitric oxide synthase, with generation of free radicals, and damage to cellular membranes, structural proteins, and essential enzymes. Programmed cell death mechanisms, such as p53 activation, activation of cell death-promoting Bcl-2 family members, and endonuclease-induced DNA laddering, occur in SE-induced neuronal death. Caspase-independent excitotoxic mechanisms, such as NMDA-induced calpain I activation, with activation and translocation of the cell death-promoting Bcl-2 family member Bid from cytoplasm to mitochondria, and subsequent translocation of apoptosis-inducing factor and endonuclease G to nuclei (which cause large-scale and internucleosomal DNA cleavage, respectively), may be triggered by SE. Poly(ADP-ribose) polymerase-1 (PARP-1) activation and cysteinyl cathepsin and DNase II release from lysosomes may occur following SE as well, but these events await future investigation. In the future, rational combinations of central nervous system-penetrable neuroprotective agents, based on our knowledge of excitotoxic mechanisms, may be useful in refractory human SE.

Nutritional regulation of proteases involved in fetal rat insulin secretion and islet cell proliferation

Epidemiological studies have indicated that malnutrition during early life may programme chronic degenerative disease in adulthood. In an animal model of fetal malnutrition, rats received an isoenergetic, low-protein (LP) diet during gestation. This reduced fetal beta-cell proliferation and insulin secretion. Supplementation during gestation with taurine prevented these alterations. Since proteases are involved in secretion and proliferation, we investigated which proteases were associated with these alterations and their restoration in fetal LP islets. Insulin secretion and proliferation of fetal control and LP islets exposed to different protease modulators were measured. Lactacystin and calpain inhibitor I, but not isovaleryl-L-carnitine, raised insulin secretion in control islets, indicating that proteasome and cysteinyl cathepsin(s), but not mu-calpain, are involved in fetal insulin secretion. Insulin secretion from LP islets responded normally to lactacystin but was insensitive to calpain inhibitor I, indicating a loss of cysteinyl cathepsin activity. Taurine supplementation prevented this by restoring the response to calpain inhibitor I. Control islet cell proliferation was reduced by calpain inhibitor I and raised by isovaleryl-L-carnitine, indicating an involvement of calpain. Calpain activity appeared to be lost in LP islets and not restored by taurine. Most modifications in the mRNA expression of cysteinyl cathepsins, calpains and calpastatin due to maternal protein restriction were consistent with reduced protease activity and were restored by taurine. Thus, maternal protein restriction affected cysteinyl cathepsins and the calpain-calpastatin system. Taurine normalised fetal LP insulin secretion by protecting cysteinyl cathepsin(s), but the restoration of LP islet cell proliferation by taurine did not implicate calpains.

Peptidic 1-cyanopyrrolidines: synthesis and SAR of a series of potent, selective cathepsin inhibitors

1-Cyanopyrrolidines have previously been reported to inhibit cysteinyl cathepsins (Falgueyret, J.-P. et al., J. Med. Chem. 2001, 44, 94). In order to optimize binding interactions for a given cathepsin and simultaneously reduce interactions with the other closely related enzymes, small peptidic substituents were introduced to the 1-cyanopyrrolidine scaffold, either at the 2-position starting with proline or at the 3-position of aminopyrrolidines. The resulting novel compounds proved to be micromolar inhibitors of cathepsin B (Cat B) but nanomolar to picomolar inhibitors of cathepsins K, L, and S (Cat K, Cat L, Cat S). Several of the compounds were >20-fold selective versus the other three cathepsins. SAR trends were observed, most notably the remarkable potency of Cat L inhibitors based on the 1-cyano- d-proline scaffold. The selectivity of one such compound, the 94 picomolar Cat L inhibitor 12, was demonstrated at higher concentrations in DLD-1 cells. Although none of the compounds in the proline series that was tested proved to be submicromolar in the in vitro bone resorption assay, two Cat K inhibitors in the 3-substituted pyrrolidine series, 24 and 25 were relatively potent in that assay.

Peptidyl sulfonium salts. A new class of protease inhibitors.

The possibility has been examined that peptidylmethyl sulfonium salts might affinity label proteases by an alkyl transfer from sulfur to an active center residue. The synthesis of a number of agents of this type is described as well as initial results of their effect on cysteinyl proteases, papain and cathepsin B. These are readily inactivated by reagents in which the peptidyl portion contains features that promote binding to the proteases such as a penultimate phenylalanine residue. Irreversible inactivation ensues by transfer of the peptidyl portion, not methyl groups. Peptidylmethyl sulfonium salts lose a proton to form an ylide structure which may be the prevalent form at physiological pH values. The ylide may also be the active affinity labeling form of the reagent since the rate of inactivation of cathepsin B increases with pH. In contrast, the action of another affinity labeling reagent for cathepsin B, benzyloxycarbonyl-Phe-AlaCHN2, a diazomethyl ketone, is relatively independent of pH.