Determination of cathepsin S abundance and activity in human plasma and implications for clinical investigation

Two SPRi biosensors for the determination of cathepsin S in blood plasma

Cathepsin S is an emerging marker for ovarian cancer. Two 'analytically specific' SPRi biosensors for the determination of Cath S have been developed. The reception part of one of the biosensors consists of the rat monoclonal antibody specific for cathepsin S attached to the gold surface via covalent bonds with cysteamine linker, while the second biosensor consists of the inhibitor LY3000328 attached via hydrophobic interaction with the 1-octadecanothiol linker. Under optimized conditions, in terms of pH and receptor concentration, both biosensors have linear response ranges between LOQ (0.14 ng mL^-1) and 2.5 ng mL^-1, which is suitable for the determination of Cath S in blood plasma samples of ovarian cancer patients and healthy individuals, after corresponding dilution with 0.15 M PBS buffer. Precision and recoveries are quite acceptable: below 7% and 98-101% respectively for the biosensor with antibody, and below 12% and 101-103% for the biosensor with inhibitor. The biosensors were validated by the determination of Cath S in series of plasma from ovarian cancer patients and healthy volunteers using both biosensors and ELISA, giving Pearson coefficients close to 1. Plasma Cath S concentration can be used as an ovarian cancer marker, in view of the highly elevated concentrations detected.

Cathepsin S Alters the Expression of Pro-Inflammatory Cytokines and MMP-9, Partially through Protease-Activated Receptor-2, in Human Corneal Epithelial Cells

Cathepsin S (CTSS) activity is increased in tears of Sjögren's syndrome (SS) patients. This elevated CTSS may contribute to ocular surface inflammation. Human corneal epithelial cells (HCE-T cells) were treated with recombinant human CTSS at activity comparable to that in SS patient tears for 2, 4, 8, and 24 h. Acute CTSS significantly increased HCE-T cell gene and protein expression of interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) from 2 to 4 h, while matrix metalloproteinase 9 (MMP-9), CTSS, and protease-activated receptor-2 (PAR-2) were increased by chronic CTSS (24 h). To investigate whether the increased pro-inflammatory cytokines and proteases were induced by CTSS activation of PAR-2, HCE-T cells were transfected with PAR-2 siRNA, reducing cellular PAR-2 by 45%. Cells with reduced PAR-2 expression showed significantly reduced release of IL-6, TNF-α, IL-1β, and MMP-9 into culture medium in response to acute CTSS, while IL-6, TNF-α, and MMP-9 were reduced in culture medium, and IL-6 and MMP-9 in cell lysates, after chronic CTSS. Moreover, cells with reduced PAR-2 expression showed reduced ability of chronic CTSS to induce gene expression of pro-inflammatory cytokines and proteases. CTSS activation of PAR-2 may represent a potential therapeutic target for amelioration of ocular surface inflammation in SS patients.

Increased Cathepsin S activity associated with decreased protease inhibitory capacity contributes to altered tear proteins in Sjögren's Syndrome patients

Cathepsin S (CTSS) activity is elevated in Sjögren's Syndrome (SS) patient tears. Here we tested whether protease inhibition and cystatin C (Cys C) levels are reduced in SS tears, which could lead to enhanced CTSS-driven degradation of tear proteins. CTSS activity against Cys C, LF and sIgA was tested in SS or healthy control tears. Tears from 156 female subjects (33, SS; 33, rheumatoid arthritis; 31, other autoimmune diseases; 35, non-autoimmune dry eye (DE); 24, healthy controls) were analyzed for CTSS activity and Cys C, LF, and sIgA levels. Cys C and LF showed enhanced degradation in SS tears supplemented with recombinant CTSS, but not supplemented healthy control tears. CTSS activity was significantly increased, while Cys C, LF and sIgA levels were significantly decreased, in SS tears compared to other groups. While tear CTSS activity remained the strongest discriminator of SS in autoimmune populations, combining LF and CTSS improved discrimination of SS beyond CTSS in DE patients. Reductions in Cys C and other endogenous proteases may enhance CTSS activity in SS tears. Tear CTSS activity is reconfirmed as a putative biomarker of SS in an independent patient cohort while combined LF and CTSS measurements may distinguish SS from DE patients.

Evaluating the diagnostic and prognostic value of circulating cathepsin S in gastric cancer

To evaluate whether serum Cathepsin S (Cat S) could serve as a biomarker for the diagnosis and prognosis of gastric cancer (GC), Enzyme-linked immuno sorbent assay (ELISA) was used to detect serum Cat S in 496 participants including healthy controls and patients with benign gastric diseases, gastric cancer, esophageal cancer, liver cancer, colorectal cancer, nasopharyngeal cancer and lung cancer. The levels of serum Cat S were significantly increased in cancer patients, especially in GC patients. The qRT-PCR, Western blotting, and immunohistochemical staining revealed the overexpression of Cat S in GC cell lines and tissues. The diagnostic value of serum Cat S for GC patients from controls resulted in an AUC of 0.803 with a sensitivity of 60.7% and a specificity of 90.0%. Moreover, the levels of serum Cat S were associated with GC tumor volume, lymphoid nodal status, metastasis status, and stages. Moreover, the patients with high levels of serum Cat S had a poorer overall survival. Univariate analysis revealed Cat S expression was a prognostic factor. The knockdown of Cat S significantly suppressed the migration and invasion of GC cells. This study suggested serum Cat S may be a potential biomarker for the diagnosis and prognosis of GC.

Symbiotic gut commensal bacteria act as host cathepsin S activity regulators

Cathepsin S (CTSS) is a lysosomal protease whose activity regulation is important for MHC-II signaling and subsequent activation of CD4⁺ T cell mediated immune responses. Dysregulation of its enzymatic activity or enhanced secretion into extracellular environments is associated with the induction or progression of several autoimmune diseases. Here we demonstrate that commensal intestinal bacteria influence secretion rates and intracellular activity of host CTSS and that symbiotic bacteria, i.e. Bacteroides vulgatus mpk, may actively regulate this process and help to maintain physiological levels of CTSS activities in order to prevent from induction of pathological inflammation. The symbiont-controlled regulation of CTSS activity is mediated by anticipating reactive oxygen species induction in dendritic cells which, in turn, maintains cystatin C (CysC) monomer binding to CTSS. CysC monomers are potent endogenous CTSS inhibitors. This Bacteroides vulgatus caused and CysC dependent CTSS activity regulation is involved in the generation of tolerant intestinal dendritic cells contributing to prevention of T-cell mediated induction of colonic inflammation. Taken together, we demonstrate that symbionts of the intestinal microbiota regulate host CTSS activity and secretion and might therefore be an attractive approach to deal with CTSS associated autoimmune diseases.

Prognostic and predictive biomarkers of abdominal aortic aneurysm growth rate

OBJECTIVES

To test the utility of clinical and circulating biomarkers to predict abdominal aortic aneurysm (AAA) growth rate and response to doxycycline therapy.

METHODS

Plasma samples were obtained in the Pharmaceutical Aneurysm Stabilization Trial that tested the effect of doxycycline (n = 44) vs. placebo (n = 49) in patients with a 35-50 mm AAA. Approximately 200 biomarkers were evaluated in a candidate approach that included markers of matrix turnover and cathepsin S activity and a broad-based approach of predominantly inflammation-related and clinical biomarkers.

RESULTS

In a recursive partitioning based analysis, total cholesterol, baseline AAA size, and apolipoprotein B were prognostic of AAA growth in the placebo group whereas elastin and biglycan degradation products were predictive of AAA growth with doxycycline treatment. Univariate analysis of these biomarkers showed that baseline total cholesterol (r = 0.38, unadjusted P = 0.011), apolipoprotein B (r = 0.41, unadjusted P = 0.005), and baseline AAA size (r = 0.35, unadjusted P = 0.013) correlated with AAA growth in the placebo but not the doxycycline group. Elastin fragments were associated with 18 month AAA growth (r = 0.33, unadjusted P = 0.031) in the doxycycline group.

LIMITATIONS

Limitations of this study include small sample size, a retrospective growth analysis, and translatability of the method used to measure the analytes.

CONCLUSIONS

This study implies that total cholesterol, baseline AAA size, and apolipoprotein B are predictors of AAA growth. Levels of elastin and biglycan fragments are predictive of doxycycline effects on AAA growth and provide a clue towards this unexpected negative effect.

Cathepsin S Cleavage of Protease-Activated Receptor-2 on Endothelial Cells Promotes Microvascular Diabetes Complications

Endothelial dysfunction is a central pathomechanism in diabetes-associated complications. We hypothesized a pathogenic role in this dysfunction of cathepsin S (Cat-S), a cysteine protease that degrades elastic fibers and activates the protease-activated receptor-2 (PAR2) on endothelial cells. We found that injection of mice with recombinant Cat-S induced albuminuria and glomerular endothelial cell injury in a PAR2-dependent manner. In vivo microscopy confirmed a role for intrinsic Cat-S/PAR2 in ischemia-induced microvascular permeability. In vitro transcriptome analysis and experiments using siRNA or specific Cat-S and PAR2 antagonists revealed that Cat-S specifically impaired the integrity and barrier function of glomerular endothelial cells selectively through PAR2. In human and mouse type 2 diabetic nephropathy, only CD68(+) intrarenal monocytes expressed Cat-S mRNA, whereas Cat-S protein was present along endothelial cells and inside proximal tubular epithelial cells also. In contrast, the cysteine protease inhibitor cystatin C was expressed only in tubules. Delayed treatment of type 2 diabetic db/db mice with Cat-S or PAR2 inhibitors attenuated albuminuria and glomerulosclerosis (indicators of diabetic nephropathy) and attenuated albumin leakage into the retina and other structural markers of diabetic retinopathy. These data identify Cat-S as a monocyte/macrophage-derived circulating PAR2 agonist and mediator of endothelial dysfunction-related microvascular diabetes complications. Thus, Cat-S or PAR2 inhibition might be a novel strategy to prevent microvascular disease in diabetes and other diseases.

Pharmacokinetics and pharmacodynamics of the cathepsin S inhibitor, LY3000328, in healthy subjects

AIM

The aim of this study was to assess the safety and tolerability, pharmacokinetics and pharmacodynamics of LY3000328 when administered as single escalating doses to healthy volunteers.

METHODS

This was a phase 1, placebo-controlled, dose escalation study with LY3000328 in 21 healthy male volunteers. Subjects were administered escalating LY3000328 doses up to 300 mg with food in this single dose study. Blood samples were collected at set times post-dose for the assessment of LY3000328 pharmacokinetics and the measurement of cathepsin S (CatS) activity, CatS mass and calculated CatS specific activity.

RESULTS

All doses of LY3000328 were well tolerated, with linear pharmacokinetics up to the 300 mg dose. The pharmacodynamic activity of LY3000328 was measured ex vivo showing a biphasic response to LY3000328, where CatS activity declines, then returns to baseline, and then increases to a level above baseline. CatS mass was also assessed post-dose which increased in a dose-dependent manner, and continued to increase after LY3000328 had been cleared from the body. CatS specific activity was additionally calculated to normalize CatS activity for changes in CatS mass. This demonstrated the increase in CatS activity was attributable to the increase in CatS mass detected in plasma.

CONCLUSION

A specific inhibitor of CatS which is cleared quickly from plasma may produce a transient decrease in plasma CatS activity which is followed by a more prolonged increase in plasma CatS mass which may have implications for the future clinical development of inhibitors of CatS.