Hydrolysis by cathepsin B of fluorescent peptides derived from human prorenin

Quantitative Detection of Cathepsin B Activity in Neutral pH Buffers Using Gold Microelectrode Arrays: Toward Direct Multiplex Analyses of Extracellular Proteases in Human Serum

Proteases are critical signaling molecules and prognostic biomarkers for many diseases including cancer. There is a strong demand for multiplex bioanalytical techniques that can rapidly detect the activity of extracellular proteases with high sensitivity and specificity. This study demonstrates an activity-based electrochemical biosensor of a 3 × 3 gold microelectrode array for the detection of cathepsin B activity in human serum diluted in a neutral buffer. Proteolysis of ferrocene-labeled peptide substrates functionalized on 200 × 200 μm microelectrodes is measured simultaneously over the nine channels by AC voltammetry. The protease activity is represented by the inverse of the exponential decay time constant (1/τ), which equals to (k_cat/K_M)[CB] based on the Michaelis-Menten model. An enhanced activity of the recombinant human cathepsin B (rhCB) is observed in a low-ionic-strength phosphate buffer at pH = 7.4, giving a very low limit of detection of 8.49 × 10^-4 s^-1 for activity and 57.1 pM for the active rhCB concentration that is comparable to affinity-based enzyme-linked immunosorbent assay (ELISA). The cathepsin B presented in the human serum sample is validated by ELISA, which mainly detects the inactive proenzyme, while the electrochemical biosensor specifically measures the active cathepsin B and shows significantly higher decay rates when rhCB and human serum are activated. Analyses of the kinetic electrochemical measurements with spiked active cathepsin B in human serum provide further assessment of the protease activity in the complex sample. This study lays the foundation to develop the gold microelectrode array into a multiplex biosensor for rapid detection of the activity of extracellular proteases toward cancer diagnosis and treatment assessment.

Quantitative electrochemical detection of cathepsin B activity in complex tissue lysates using enhanced AC voltammetry at carbon nanofiber nanoelectrode arrays

The proteolytic activity of a cancer-related enzyme cathepsin B is measured with alternating current voltammetry (ACV) using ferrocene (Fc) labeled tetrapeptides attached to nanoelectrode arrays (NEAs) fabricated with vertically aligned carbon nanofibers (VACNFs). This combination enables the use of high AC frequencies (~1kHz) with enhanced electrochemical signals. The specific proteolysis of the Fc-peptide by cathepsin B produces decay in the ACV peak current versus the reaction time. The exponential component of the raw data can be extracted and defined as the "extracted proteolytic signal" which allows consistent quantitative analyses using a heterogeneous Michaelis-Menten model. A "specificity constant" kcat/KM = (3.68 ± 0.50) × 10(4)M(-1)s(-1) for purified cathepsin B was obtained. The detections of cathepsin B activity in different concentrations of whole lysate of human breast tissue, tissue lysate spiked with varied concentrations of cathepsin B, and the tissue lysate after immunoprecipitation showed that there is ~13.4 nM higher cathepsin B concentration in 29.1 µg mL(-1) of whole tissue lysate than the immunoprecipitated sample. The well-defined regular VACNF NEAs by e-beam lithography show a much faster kinetics for cathepsin B proteolysis with kcat/KM = 9.2 × 10(4)M(-1)s(-1). These results illustrate the potential of this technique as a portable multiplex electronic system for cancer diagnosis by rapid protease profiling of serum or blood samples.

Effect of kefir and low-dose aspirin on arterial blood pressure measurements and renal apoptosis in unhypertensive rats with 4 weeks salt diet

Abstract We aim to study the effect of low-dose aspirin and kefir on arterial blood pressure measurements and renal apoptosis in unhypertensive rats with 4 weeks salt diet. Forty adult male Sprague-Dawley rats were divided into five groups: control, high-salt (HS) (8.0% NaCl), HS+aspirin (10 mg/kg), HS+kefir (10.0%w/v), HS+aspirin +kefir. We measured sistolic blood pressure (SBP), mean arterial pressure (MAP), diastolic pressure, pulse pressure in the rats. Cathepsin B, L, DNA fragmentation and caspase-3 activities were determined from rat kidney tissues and rats clearance of creatinine calculated. Although HS diet increased significantly SBP, MAP, diastolic pressure, pulse pressure parameters compared the control values. They were not as high as accepted hypertension levels. When compared to HS groups, kefir groups significantly decrease Cathepsin B and DNA fragmentation levels. Caspase levels were elevated slightly in other groups according to control group. While, we also found that creatinine clearance was higher in HS+kefir and HS+low-dose aspirin than HS group. Thus, using low-dose aspirin had been approximately decreased of renal function damage. Kefir decreased renal function damage playing as Angiotensin-converting enzyme inhibitor. But, low-dose aspirin together with kefir worsened rat renal function damage. Cathepsin B might play role both apoptosis and prorenin-processing enzyme. But not caspase pathway may be involved in the present HS diet induced apoptosis. In conclusion, kefir and low-dose aspirin used independently protect renal function and renal damage induced by HS diet in rats.

Electrochemical Protease Biosensor Based on Enhanced AC Voltammetry Using Carbon Nanofiber Nanoelectrode Arrays

We report an electrochemical method for measuring the activity of proteases using nanoelectrode arrays (NEAs) fabricated with vertically aligned carbon nanofibers (VACNFs). The VACNFs of ~150 nm in diameter and 3 to 5 μm in length were grown on conductive substrates and encapsulated in SiO2 matrix. After polishing and plasma etching, controlled VACNF tips are exposed to form an embedded VACNF NEA. Two types of tetrapeptides specific to cancer-mediated proteases legumain and cathepsin B are covalently attached to the exposed VACNF tip, with a ferrocene (Fc) moiety linked at the distal end. The redox signal of Fc can be measured with AC voltammetry (ACV) at ~1 kHz frequency on VACNF NEAs, showing distinct properties from macroscopic glassy carbon electrodes due to VACNF's unique interior structure. The enhanced ACV properties enable the kinetic measurements of proteolytic cleavage of the surface-attached tetrapeptides by proteases, further validated with a fluorescence assay. The data can be analyzed with a heterogeneous Michaelis-Menten model, giving "specificity constant" kcat /Km as (4.3 ± 0.8) × 104 M-1s-1 for cathepsin B and (1.13 ± 0.38) × 104 M-1s-1 for legumain. This method could be developed as portable multiplex electronic techniques for rapid cancer diagnosis and treatment monitoring.

Activation of the Nipah virus fusion protein in MDCK cells is mediated by cathepsin B within the endosome-recycling compartment

Proteolytic activation of the fusion protein of the highly pathogenic Nipah virus (NiV F) is a prerequisite for the production of infectious particles and for virus spread via cell-to-cell fusion. Unlike other paramyxoviral fusion proteins, functional NiV F activation requires endocytosis and pH-dependent cleavage at a monobasic cleavage site by endosomal proteases. Using prototype Vero cells, cathepsin L was previously identified to be a cleavage enzyme. Compared to Vero cells, MDCK cells showed substantially higher F cleavage rates in both NiV-infected and NiV F-transfected cells. Surprisingly, this could not be explained either by an increased F endocytosis rate or by elevated cathepsin L activities. On the contrary, MDCK cells did not display any detectable cathepsin L activity. Though we could confirm cathepsin L to be responsible for F activation in Vero cells, inhibitor studies revealed that in MDCK cells, cathepsin B was required for F-protein cleavage and productive replication of pathogenic NiV. Supporting the idea of an efficient F cleavage in early and recycling endosomes of MDCK cells, endocytosed F proteins and cathepsin B colocalized markedly with the endosomal marker proteins early endosomal antigen 1 (EEA-1), Rab4, and Rab11, while NiV F trafficking through late endosomal compartments was not needed for F activation. In summary, this study shows for the first time that endosomal cathepsin B can play a functional role in the activation of highly pathogenic NiV.

High glucose concentration stimulates intracellular renin activity and angiotensin II generation in rat mesangial cells

Increased intrarenal renin-angiotensin system activity contributes to diabetic nephropathy. ANG II generation in mesangial cells (MC) is increased by high-glucose (HG) exposure. This study assessed the mechanisms involved in the glucose-induced ANG II generation in rat MC. Under basal conditions, MC mainly secreted prorenin. HG decreased prorenin secretion and induced a striking 30-fold increase in intracellular renin activity. After 72 h of HG exposure, only the mRNA levels for angiotensinogen and angiotensin-converting enzyme (ACE) were significantly elevated. However, after shorter periods of 24 h of HG stimulation the mRNA levels of the enzymes prorenin and cathepsin B, besides that for ACE, were significantly increased. The results suggest that the HG-induced increase in ANG II generation in MC results from an increase in intracellular renin activity mediated by at least three factors: a time-dependent stimulation of (pro)renin gene transcription, a reduction in prorenin enzyme secretion, and an increased rate of conversion of prorenin to active renin, probably mediated by cathepsin B. The increase in angiotensinogen mRNA in parallel to increased renin activity indicates that HG also increased the availability of the renin substrate. The consistent upregulation of ACE mRNA suggests that, besides renin, ACE is directly involved in the increased mesangial ANG II generation induced by HG.

The relationship between active renin concentration and plasma renin activity in Type 1 diabetes

AIMS

Circulating activity of the renin-angiotensin-aldosterone system (RAAS) can be assessed by measuring plasma active renin concentration (ARE), as well as by measuring plasma renin activity (PRA). We aimed to assess the relationships between ARE and PRA in Type 1 diabetic compared with non-diabetic control subjects. We also assessed concentrations of the active renin precursor, prorenin.

PATIENTS AND METHODS

Thirty-five Type 1 diabetic subjects and 34 non-diabetic control subjects were assessed. Groups had similar ages, sex distributions, body mass indices, systolic and diastolic blood pressures. PRA was measured by radioimmunoassay of angiotensin I generation from endogenous substrate. ARE and total renin concentration (TRE) were measured by immunoradiometric assay (Nichols Institute Diagnostics, USA). Prorenin concentration was calculated as the difference between ARE and TRE.

RESULTS

PRA was significantly lower in Type 1 diabetic than in control subjects (0.8 (0.4-1.1) vs. 1.1 (0.9-1.9) pmol/ml per h; P < 0.005), while ARE was similar (17 (9-33) vs. 18 (15-25) mU/l; P = 0.548). PRA (loge transformed) correlated strongly with ARE in diabetic (r = 0.49; P = 0.003) and control subjects (r = 0.59; P = 0.0002), but there was significant vertical separation of the regression lines for the two groups (P < 0.0001). Prorenin concentrations were significantly higher in Type 1 diabetic subjects (249 (170-339) vs. 171 (153-219) mU/l; P = 0.005). Diabetic subjects with high prorenin concentrations (> 400 mU/l (control mean + 3 SD)) were more likely to have microalbuminuria (P = 0.027) and peripheral neuropathy (P = 0.049).

CONCLUSIONS

Type 1 diabetes is associated with an altered relationship between ARE and PRA, such that ARE is higher for a given PRA compared with non-diabetic control subjects. Both ARE and PRA are used to assess circulating RAAS activity. The altered relationship between the two in Type 1 diabetic subjects suggests that neither parameter alone is necessarily an adequate and reliable index of such activity. Higher prorenin concentrations, particularly in association with microvascular complications, were confirmed in the Type 1 diabetic subjects. Diabet. Med. 18, 451-458 (2001)