Increased activities of cathepsin B and other lysosomal hydrolases in fibroblasts and bone tissue cultured in the presence of cysteine proteinases inhibitors

Engineered arylsulfatase A with increased activity, stability and brain delivery for therapy of metachromatic leukodystrophy

A deficiency of human arylsulfatase A (hASA) causes metachromatic leukodystrophy (MLD), a lysosomal storage disease characterized by sulfatide accumulation and central nervous system (CNS) demyelination. Efficacy of enzyme replacement therapy (ERT) is increased by genetic engineering of hASA to elevate its activity and transfer across the blood-brain barrier (BBB), respectively. To further improve the enzyme's bioavailability in the CNS, we mutated a cathepsin cleavage hot spot and obtained hASAs with substantially increased half-lives. We then combined the superstabilizing exchange E424A with the activity-promoting triple substitution M202V/T286L/R291N and the ApoEII-tag for BBB transfer in a trimodal modified neoenzyme called SuPerTurbo-ASA. Compared with wild-type hASA, half-life, activity, and M6P-independent uptake were increased more than 7-fold, about 3-fold, and more than 100-fold, respectively. ERT of an MLD-mouse model with immune tolerance to wild-type hASA did not induce antibody formation, indicating absence of novel epitopes. Compared with wild-type hASA, SuPerTurbo-ASA was 8- and 12-fold more efficient in diminishing sulfatide storage of brain and spinal cord. In both tissues, storage was reduced by ∼60%, roughly doubling clearance achieved with a 65-fold higher cumulative dose of wild-type hASA previously. Due to its enhanced therapeutic potential, SuPerTurbo-ASA might be a decisive advancement for ERT and gene therapy of MLD.

Enzymes in the time of COVID-19: An overview about the effects in the human body, enzyme market, and perspectives for new drugs

The rising pandemic caused by a coronavirus, resulted in a scientific quest to discover some effective treatments against its etiologic agent, the severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2). This research represented a significant scientific landmark and resulted in many medical advances. However, efforts to understand the viral mechanism of action and how the human body machinery is subverted during the infection are still ongoing. Herein, we contributed to this field with this compilation of the roles of both viral and human enzymes in the context of SARS‐CoV‐2 infection. In this sense, this overview reports that proteases are vital for the infection to take place: from SARS‐CoV‐2 perspective, the main protease (M^pro) and papain‐like protease (PL^pro) are highlighted; from the human body, angiotensin‐converting enzyme‐2, transmembrane serine protease‐2, and cathepsins (CatB/L) are pointed out. In addition, the influence of the virus on other enzymes is reported as the JAK/STAT pathway and the levels of lipase, enzymes from the cholesterol metabolism pathway, amylase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and glyceraldehyde 3‐phosphate dehydrogenase are also be disturbed in SARS‐CoV‐2 infection. Finally, this paper discusses the importance of detailed enzymatic studies for future treatments against SARS‐CoV‐2, and how some issues related to the syndrome treatment can create opportunities in the biotechnological market of enzymes and the development of new drugs.

Dynamic Model of Protease State and Inhibitor Trafficking to Predict Protease Activity in Breast Cancer Cells

Introduction

Cysteine cathepsins are implicated in breast cancer progression, produced by both transformed epithelial cells and infiltrated stromal cells in tumors, but to date, no cathepsin inhibitor has been approved for clinical use due to unexpected side effects. This study explores cellular feedback to cathepsin inhibitors that might yield non-intuitive responses, and uses computational models to determine underlying cathepsin-inhibitor dynamics.

Methods

MDA-MB-231 cells treated with E64 were tested by multiplex cathepsin zymography and immunoblotting to quantify total, active, and inactive cathepsins S and L. This data was used to parameterize mathematical models of intracellular free and inhibited cathepsins, and then applied to a dynamic model predicting cathepsin responses to other classes of cathepsin inhibitors that have also failed clinical trials.

Results

E64 treated cells exhibited increased amounts of active cathepsin S and reduced amount of active cathepsin L, although E64 binds tightly to both. This inhibitor response was not unique to cancer cells or any one cell type, suggesting an underlying fundamental mechanism of E64 preserving activity of cathepsin S, but not cathepsin L. Computational models were able to predict and differentiate between inhibitor-bound, active, and inactive cathepsin species and demonstrate how different classes of cathepsin inhibitors can have drastically divergent effects on active cathepsins located in different intracellular compartments.

Conclusions

Together, this work has important implications for the development of mathematical model systems for protease inhibition in tissue destructive diseases, and consideration of preservation mechanisms by inhibitors that could alter perceived benefits of these treatment modalities.

A Mild Inhibition of Cathepsin K Paradoxically Stimulates the Resorptive Activity of Osteoclasts in Culture

Cathepsin K (CatK) inhibition allows reducing bone resorption with specific advantages compared to the existing anti-osteoporosis drugs. Its clinical use appears even more promising with the recent development of ectosteric inhibitors. A confusing observation, however, is that a low dose of the active site CatK inhibitor odanacatib (ODN) was reported to decrease bone mineral density and increase serum levels of the bone resorption marker carboxy-terminal collagen crosslinks (CTX). The present study provides a possible explanation for this paradox. The resorptive activity of human osteoclasts seeded on bone slices was inhibited when subjected to ODN at doses of 20 nM, but about 100-fold lower doses induced a significant increase in CTX levels and in eroded surface (12 repeats). This low-dose-induced stimulation was prevented by inhibition of non-CatK cysteine proteinases, thereby indicating that the stimulation results from an interplay between CatK and other cysteine proteinases. Effective interplay between these proteinases was also shown in enzymatic assays where the CatK-mediated degradation of collagen was enhanced upon addition of cathepsins B or L. Furthermore, extracts of osteoclasts subjected to a low dose of ODN showed higher levels of cathepsin B compared with extracts of control osteoclasts. In conclusion, the low-dose-induced stimulation of resorption observed in the clinical study can be reproduced in osteoclasts cultured in the absence of any other cell. Our data support an osteoclast-intrinsic mechanism where a mild inhibition of CatK results in increased levels of other proteinases contributing to the collagen degradation process.

Chemoproteomic profiling reveals that cathepsin D off-target activity drives ocular toxicity of β-secretase inhibitors

Inhibition of β-secretase BACE1 is considered one of the most promising approaches for treating Alzheimer's disease. Several structurally distinct BACE1 inhibitors have been withdrawn from development after inducing ocular toxicity in animal models, but the target mediating this toxicity has not been identified. Here we use a clickable photoaffinity probe to identify cathepsin D (CatD) as a principal off-target of BACE1 inhibitors in human cells. We find that several BACE1 inhibitors blocked CatD activity in cells with much greater potency than that displayed in cell-free assays with purified protein. Through a series of exploratory toxicology studies, we show that quantifying CatD target engagement in cells with the probe is predictive of ocular toxicity in vivo. Taken together, our findings designate off-target inhibition of CatD as a principal driver of ocular toxicity for BACE1 inhibitors and more generally underscore the power of chemical proteomics for discerning mechanisms of drug action.

Several β-secretase (BACE) inhibitors exhibit unexplained ocular toxicity in preclinical studies. Here the authors generate a clickable photoaffinity probe to interrogate off-targets in cells and animals, and identify inhibition of cathepsin D as a driver of ocular toxicity.

Differential cathepsin responses to inhibitor-induced feedback: E-64 and cystatin C elevate active cathepsin S and suppress active cathepsin L in breast cancer cells

Cathepsins are powerful proteases, once referred to as the lysosomal cysteine proteases, that have been implicated in breast cancer invasion and metastasis, but pharmaceutical inhibitors have suffered failures in clinical trials due to adverse side effects. Scientific advancement from lysosomotropic to cell impermeable cathepsin inhibitors have improved efficacy in treating disease, but off-target effects have still been problematic, motivating a need to better understand cellular feedback and responses to treatment with cathepsin inhibitors. To address this need, we investigated effects of E-64 and cystatin C, two broad spectrum cathepsin inhibitors, on cathepsin levels intra- and extracellularly in MDA-MB-231 breast cancer cells. Cathepsins S and L had opposing responses to both E-64 and cystatin C inhibitor treatments with paradoxically elevated amounts of active cathepsin S, but decreased amounts of active cathepsin L, as determined by multiplex cathepsin zymography. This indicated cellular feedback to selectively sustain the amounts of active cathepsin S even in the presence of inhibitors with subnanomolar inhibitory constant values. These differences were identified in cellular locations of cathepsins L and S, trafficking for secretion, co-localization with endocytosed inhibitors, and longer protein turnover time for cathepsin S compared to cathepsin L. Together, this work demonstrates that previously underappreciated cellular compensation and compartmentalization mechanisms may sustain elevated amounts of some active cathepsins while diminishing others after inhibitor treatment. This can confound predictions based solely on inhibitor kinetics, and must be better understood to effectively deploy therapies and dosing strategies that target cathepsins to prevent cancer progression.

Intracochlear perfusion of leupeptin and z-VAD-FMK: influence of antiapoptotic agents on gunshot-induced hearing loss

The therapeutic efficiency of cochlear infusion of two anti-apoptotic substances: a potent calpain inhibitor, leupeptin and a caspase inhibitor, z-VAD-FMK was evaluated in guinea pigs after a gunshot noise-induced trauma (170 dB SPL). A preliminary study showed that hair cell apoptosis appeared within 7 days of the noise trauma. For each animal, one of the cochleae was perfused directly starting 1 h after the trauma with leupeptin or z-VAD-FMK for 7 days via a mini-osmotic pump whereas the other cochlea was untreated. ABR threshold shifts were measured over a 14-day recovery period. The functional hearing study was supplemented by histological analysis. Two days after the trauma significant differences were observed between threshold shifts in the z-VAD-FMK-treated and the non-treated ears. Cochleograms showed that hair cell losses were significantly lower in z-VAD-FMK-treated ears. Regarding the leupeptin treatment, no significant difference between treated and non-treated ears was observed. This work indicates that early direct infusion of z-VAD-FMK into the cochlea accelerates hearing recovery and reduces hair cell loss after gunshot noise-induced trauma. These results suggest that the gunshot noise-induced trauma may involve the caspase pathway rather than the calpain pathway in the apoptotic process.

Cathepsin K inhibitors prevent matrix-derived growth factor degradation by human osteoclasts

The coupling between bone formation and resorption creates a therapeutic impasse in osteoporosis: antiresorptive therapy halts bone loss, but also inhibits bone formation, and therefore does not cure the condition. Surprisingly, recent preliminary reports suggest that inhibition of resorption by cathepsin K (CathK) inhibitors augments bone formation. Uniquely amongst resorption-inhibitors, CathK-inhibitors suppress degradation of the organic matrix of bone while allowing demineralization. We hypothesized that these unique characteristics might explain a capacity of CathK inhibitors to enhance bone formation: the inhibitors might prevent degradation not only of collagen, but also other proteins, including growth factors embedded in matrix. We tested this hypothesis using osteocalcin and insulin-like growth factor I (IGF-I) as examples of matrix-embedded proteins, and found that CathK-inhibitors, unlike other resorption-inhibitors, dramatically increased the concentrations of these matrix-derived proteins in supernatants of osteoclasts on bone, most likely through protection against intracellular degradation. We found that protons are both necessary and sufficient for the release of IGF-I from bone matrix, and that recombinant CathK can degrade both marker proteins. In the presence of a CathK-inhibitor, the amount of IGF-I released from matrix substantially exceeded the amount secreted by osteoclasts. CathK-inhibition similarly augmented bone morphogenetic protein (BMP)-2 release. Lastly, MC3T3-E1 numbers were greater after co-culture with osteoclasts on bone with versus without CathK-inhibitor, showing that, in the presence of CathK-inhibitor, osteoclasts release biologically-significant quantities of biologically-active matrix-derived growth factors. These results support a model in which osteoclastic secretion of protons demineralizes bone, causing release of growth factors from bone matrix. Normally these are largely degraded, with collagen, in the resorptive hemivacuole and during transcytosis to the basal surface of the osteoclast, but in the presence of CathK inhibitor they are released intact, and so might augment bone formation.

Calvarial osteoclasts express a higher level of tartrate-resistant acid phosphatase than long bone osteoclasts and activation does not depend on cathepsin K or L activity

Bone resorption by osteoclasts depends on the activity of various proteolytic enzymes, in particular those belonging to the group of cysteine proteinases. Next to these enzymes, tartrate-resistant acid phosphatase (TRAP) is considered to participate in this process. TRAP is synthesized as an inactive proenzyme, and in vitro studies have shown its activation by cysteine proteinases. In the present study, the possible involvement of the latter enzyme class in the in vivo modulation of TRAP was investigated using mice deficient for cathepsin K and/or L and in bones that express a high (long bone) or low (calvaria) level of cysteine proteinase activity. The results demonstrated, in mice lacking cathepsin K but not in those deficient for cathepsin L, significantly higher levels of TRAP activity in long bone. This higher activity was due to a higher number of osteoclasts. Next, we found considerable differences in TRAP activity between calvarial and long bones. Calvarial bones contained a 25-fold higher level of activity than long bones. This difference was seen in all mice, irrespective of genotype. Osteoclasts isolated from the two types of bone revealed that calvarial osteoclasts expressed higher enzyme activity as well as a higher level of mRNA for the enzyme. Analysis of TRAP-deficient mice revealed higher levels of nondigested bone matrix components in and around calvarial osteoclasts than in long bone osteoclasts. Finally, inhibition of cysteine proteinase activity by specific inhibitors resulted in increased TRAP activity. Our data suggest that neither cathepsin K nor L is essential in activating TRAP. The findings also point to functional differences between osteoclasts from different bone sites in terms of participation of TRAP in degradation of bone matrix. We propose that the higher level of TRAP activity in calvarial osteoclasts compared to that in long bone cells may partially compensate for the lower cysteine proteinase activity found in calvarial osteoclasts and TRAP may contribute to the degradation of noncollagenous proteins during the digestion of this type of bone.

Leupeptin, a Calpain Inhibitor, Protects Inner Ear Hair Cells from Aminoglycoside Ototoxicity

Inner ear hair cells play a major role in the auditory pathway that converts sound stimulation into electrical signals, and then into a neural code. However this function is often lost by aminoglycoside ototoxicity. The injury of inner ear hair cells from aminoglycoside treatment is considered apoptosis, and caspase is an important participant in the apoptosis pathway in many organs. It has been reported that calpain, a calcium-dependent protease, is essential for mediation and promotion of cell death. The purpose of the present study was to investigate effects of caspase and calpain inhibitors on the inner ear hair cells after aminoglycoside treatment, and to explore the cell death pathway. Cochlea explant cultures were prepared from mice of postnatal 6 days, cultured with neomycin and/or protease inhibitors, and then stained with phalloidin-fluorescein isothiocyanate (phalloidin-FITC), which was used as a marker to identify surviving hair cells. We demonstrated that neomycin (0.1-1 mM) reduced the number of outer hair cells in a dose-dependent manner. Furthermore, we showed that leupeptin, a calpain inhibitor, significantly protects against the neomycin-induced loss of outer hair cells, whereas a caspase inhibitor was effective only against a lower concentration of neomycin (0.2 mM). Using the TdT-mediated dUTP-biotin nick and labeling method, we also found that a calpain inhibitor, but not a caspase inhibitor, prevents apoptotic DNA fragmentation after treatment with 1 mM neomycin. These results suggest that calpain, rather than caspase, may be responsible for apoptosis induced by aminoglycoside. Thus, leupeptin may prevent hearing loss from aminoglycoside ototoxity.

Cocaine induces a mixed lysosomal lipidosis in cultured fibroblasts, by inactivation of acid sphingomyelinase and inhibition of phospholipase A1

This paper reports that cocaine may induce a lysosomal storage disorder. Indeed, culture of Rat-1 fibroblasts with 250-500 microM cocaine induced after 2-3 days a major accumulation in lysosomes of electron-dense lamellar structures. By subcellular fractionation, this was reflected by a selective decrease of the buoyant density of several lysosomal enzymes, indicating lysosomal lipid overload. Biochemical analysis confirmed an increased cellular content of major phospholipids and sphingomyelin, but not of cholesterol. Cocaine, a membrane-permeant weak base, is concentrated by acidotropic sequestration, because its accumulation was abrogated by the proton ionophore, monensin and the vacuolar ATPase inhibitor, bafilomycin A1. At its estimated lysosomal concentration, cocaine almost completely inhibited phospholipase A1 activity on liposomes. Cell incubation with cocaine, but not with its inactive metabolite, benzoylecgonine, rapidly inactivated acid sphingomyelinase, as reflected by a 10-fold decrease in Vmax with identical Km. Acid sphingomyelinase inactivation was fully prevented by the thiol proteinases inhibitors, leupeptin and E64, indicating that cocaine induces selective sphingomyelinase proteolysis. Upon cocaine removal, acid sphingomyelinase activity was rapidly restored, pointing to its fast turnover. In contrast, the cellular content of several other lysosomal hydrolases was increased up to 2-fold. Together, these data show that acidotropic accumulation of cocaine in lysosomes rapidly inhibits acid phospholipase A1 and inactivates acid sphingomyelinase, which can explain induction of a mixed lysosomal lipidosis.

Matrix metalloproteinases (MMP) and cathepsin K contribute differently to osteoclastic activities

The best established proteolytic event of osteoclasts is bone matrix solubilization by the cysteine proteinase cathepsin K. Here, however, we draw the attention on osteoclastic activities depending on matrix metalloproteinases (MMPs). We discuss the observations supporting that MMPs contribute significantly to bone matrix solubilization in specific areas of the skeleton and in some developmental and pathological situations. Our discussion takes into account (1) the characteristics of the bone remodeling persisting in the absence of cathepsin K, (2) the ultrastructure of the resorption zone in response to inactivation of MMPs and of cathepsin K in different bone types, (3) bone resorption levels in MMP knockout mice compared to wild-type mice, (4) the identification of MMPs in osteoclasts and surrounding cells, and (5) the effect of different bone pathologies on the serum concentrations of specific collagen fragments believed to discriminate between cathepsin K and MMP cleavage. Next, we provide evidence that MMPs are very critical for osteoclast migration, thereby controlling also the cell-matrix interactions required for cell attachment/detachment. The evidence supporting this role is based on a model of osteoclast recruitment in primitive long bones, an assay of osteoclast invasion through collagen gel, and the effect of proteinase inhibitors/knockouts in these models. Furthermore, we mention observations indicating a role of MMPs in initiation of bone resorption. Finally, we emphasize the many distinct ways MMPs may alter focally the extracellular environment thereby regulating the osteoclast behavior. Although the understanding of MMPs in osteoclast biology is rapidly expanding, it is suspected that important roles remain to be discovered.

Leupeptin protects cochlear and vestibular hair cells from gentamicin ototoxicity

Calpains, a family of calcium-activated proteases that breakdown proteins, kinases, phosphatases and transcription factors, can promote cell death. Since leupeptin, a calpain inhibitor, protected against hair cell loss from acoustic overstimulation, we hypothesized that it might protect cochlear and vestibular hair cells against gentamicin (GM) ototoxicity. To test this hypothesis, mouse organotypic cultures from the cochlea, maculae of the utricle and the crista of the semicircular canal (P1-P3) were treated with different doses of GM (0.1-3 mM) alone or in the presence of leupeptin (0.1-3 mM). The percentage of outer hair cells (OHCs) and inner hair cells (IHCs) decreased with increasing doses of GM between 0.1 and 3 mM. The addition of 1 mM of leupeptin significantly reduced GM-induced damage to IHCs and OHCs; this protective effect was dose-dependent. GM also significantly reduced hair cell density in the crista and utricle in a dose-dependent manner between 0.1 and 3 mM. The addition of 1 mM of leupeptin significantly reduced hair cell loss in the crista and utricle for GM concentrations between 0.1 and 3 mM. These results suggest that one of the early steps in GM ototoxicity may involve calcium-activated proteases that lead to the demise of cochlear and vestibular hair cells.