Cellular uptake of proMMP-2:TIMP-2 complexes by the endocytic receptor megalin/LRP-2.

Matrix metalloproteinases (MMPs) are regulated at multiple transcriptional and post-transcriptional levels, among which receptor-mediated endocytic clearance. We previously showed that low-density lipoprotein receptor-related protein-1 (LRP-1) mediates the clearance of a complex between the zymogen form of MMP-2 (proMMP-2) and tissue inhibitor of metalloproteinases, TIMP-2, in HT1080 human fibrosarcoma cells. Here we show that, in BN16 rat yolk sac cells, proMMP-2:TIMP-2 complex is endocytosed through a distinct LRP member, megalin/LRP-2. Addition of receptor-associated protein (RAP), a natural LRP antagonist, caused accumulation of endogenous proMMP-2 and TIMP-2 in conditioned media. Incubation with RAP also inhibited membrane binding and cellular uptake of exogenous iodinated proMMP-2:TIMP-2. Moreover, antibodies against megalin/LRP-2, but not against LRP-1, inhibited binding of proMMP-2:TIMP-2 to BN16 cell surface. BIAcore analysis confirmed direct interaction between the complex and megalin/LRP-2. Conditional renal invalidation of megalin/LRP-2 in mice resulted in accumulation of proMMP-2 and TIMP-2 in their urine, highlighting the physiological relevance of the binding. We conclude that megalin/LRP-2 can efficiently mediate cell-surface binding and endocytosis of proMMP-2:TIMP-2 complex. Therefore megalin/LRP-2 can be considered as a new actor in regulation of MMP-2 activity, an enzyme crucially involved in many pathological processes.

Diagnostic Efficiency of Serum and Urine Procathepsin B and Cathepsin B in Patients with Carcinoma of the Urinary Bladder.

BACKGROUND: The aim of the study was to evaluate the diagnostic efficiency of cathepsins B (cathepsin B and procathepsin B) in patients with transient cell carcinoma of the urinary bladder. METHODS: Serum and urine concentrations of cathepsin B and procathepsin B were measured by two commercially available enzymatic immunoassays in a group of 125 patients with bladder cell carcinoma without metastases and in a group of 72 healthy individuals. Concentrations in urine were adjusted to creatinine. RESULTS: Concentrations of both cathepsin B and procathepsin B in serum and urine were significantly elevated in patients with bladder cell carcinoma (p < 0.0001 for U-procathepsin B, U-procathepsin B/creatinine, and U-cathepsin B/creatinine, p = 0.0001 for U-cathepsin B, p = 0.0002 for S-procathepsin B and p = 0.02 for S-cathepsin B). Comparison of all diagnostic efficiencies of cathepsin B and procathepsin B in serum and in urine showed the best diagnostic accuracy for procathepsin B in urine (AUC = 0.81 vs. 0.50). The ratio of U-procathepsin B/creatinine was also more efficient than the ratio of U-cathepsin B/creatinine (AUC = 0.81 vs. AUC = 0.70). The diagnostic efficiencies of both parameters in serum were low (S-procathepsin B: AUC = 0.50, S-cathepsin B: AUC = 0.60). U-procathepsin B and U-procathepsin B/creatinine ratio show significantly better diagnostic efficiency in patients with invasive bladder tumors than other parameters (S-procathepsin B, S-cathepsin B, U-cathepsin B and U-Cathepsin B/creatinine; U-procathepsin B: AUC = 0.82, U-procathepsin B/creatinine: AUC = 0.86, S-procathepsin B and cathepsin B: AUC = 0.51 - 0.68). CONCLUSIONS: Procathepsin B concentration in urine is a valuable diagnostic marker in patients with bladder cell carcinoma.

Methodologic issues in the measurement of urinary renin.

BACKGROUND AND OBJECTIVES: Alge et al. recently reported that urinary renin may be a prognostic biomarker for AKI after cardiac surgery. However, their urinary renin levels far exceeded published plasma renin levels, whereas normally, urinary renin is <10% of plasma renin. This result raises questions about the specificity of the new Quantikine Renin ELISA Kit used in the work by Alge et al., which is claimed to detect total renin (i.e., renin and prorenin). Therefore, this study tested this assay. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Plasma and urine from 30 patients with hypertension, diabetes, or preeclampsia and 10 healthy pregnant women (randomly selected from sample sets obtained earlier to investigate urinary renin-angiotensin system components) were used to compare the ELISA with a validated renin immunoradiometric assay and an in-house enzyme kinetic assay. Measurements were performed before and after in vitro prorenin activation, representing renin and total renin, respectively. RESULTS: Total renin measurements by ELISA, immunoradiometric assay, and enzyme kinetic assay were highly correlated. However, ELISA results were consistently ≥10-fold higher. The ELISA standard yielded low to undetectable levels in the immunoradiometric assay and enzyme kinetic assay, except after prorenin activation, when the results were ≥10-fold lower than the ELISA results. In plasma, prorenin activation increased ELISA results by 10%-15%. Urine contained no detectable prorenin. CONCLUSIONS: The ELISA renin kit standard is prorenin, and its immunoreactivity and enzymatic activity after conversion to renin do not match the International Reference Preparation of human renin that has been used to validate previous immunoradiometric assays and enzyme kinetic assays; in fact, they are at least 10-fold lower, and thus, any measurements obtained with this ELISA kit yield levels that are at least 10-fold too high. The ELISA antibodies detect both renin and prorenin, with a preference for the former. Given these inconsistencies, urinary renin levels should be measured by established renin assays.

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.

Development of a peptide-based sandwich ELISA for human tissue prokallikrein with no cross-reactivity from mature kallikrein.

Human tissue prokallikrein is the enzymatically inactive zymogen of a serine proteinase involved in the liberation of vasoactive kinin peptides, and it is supposed that an impaired prokallikrein-to-kallikrein conversion is closely related to certain hypertensive and inflammatory disorders. Progress in understanding the biological role of the proenzyme has been limited by the absence of an accurate assay for the kallikrein precursor. We describe a sandwich enzyme-linked immunosorbent assay to measure human tissue prokallikrein using monospecific anti-peptide antibodies raised against propeptide derivatives. This method could detect a minimum concentration of 60 pg/ml prokallikrein and displayed no cross-reactivity or interference with mature tissue kallikrein. The intra- and inter-assay precision varied from 8-15%, respectively, indicating a reasonable reproducibility of the method. The level of prokallikrein was defined in different human urine samples, and the corresponding dilution curves showed good linearity. The mean recovery of added zymogen was 104%. Prokallikrein immunoassay is the first reported tool for the direct and sensitive quantification of the precursor of tissue kallikrein and should facilitate the precise determination of prokallikrein levels in a variety of biological specimen.

Activation peptide of carboxypeptidase B in serum and urine in acute pancreatitis.

BACKGROUND: The pathophysiology of acute pancreatitis involves activation of the pancreatic proenzymes. Levels of the trypsinogen activation peptide in urine in acute pancreatitis has been shown to correlate with the severity of disease. However, this peptide is unstable in urine and, because of its low molecular mass, difficult to measure. Procarboxypeptidase B has a larger activation peptide which could be more suitable for analysis in serum and urine. AIMS: To study the presence of the activation peptide from procarboxypeptidase B (CAPAP) in serum and urine in acute pancreatitis. PATIENTS: Urine and serum samples were obtained within 48 hours of admittance from 40 patients with acute pancreatitis. Severity was classified retrospectively according to levels of C-reactive protein and clinical course. Thirty four patients with abdominal pain from other causes were studied as controls. METHODS: CAPAP was purified from human pancreatic juice. Specific antibodies were obtained and a radioimmunoassay was developed. RESULTS: Levels of CAPAP in serum and urine in acute pancreatitis correlate with the severity of the attack. CAPAP is very stable, and urine contains only CAPAP whereas, in serum, cross reacting procarboxypeptidase B is found together with CAPAP. CONCLUSIONS: CAPAP could be a valuable tool in the diagnosis and early determination of severity in acute pancreatitis.

Characterization of a tissue-type plasminogen activator from porcine urine.

Porcine urine, unlike human urine, does not contain detectable amounts of urokinase-type plasminogen activator (u-PA). The plasminogen activator present in porcine urine is of tissue-type (t-PA) as identified by the following criteria. (1) Porcine urine PA exhibits an Mr of 65,000 similar to the Mr of human t-PA (64-70,000) but distinct from the Mr of human u-PA (55,000). (2) Antibodies against human t-PA bind and inhibit crude and purified porcine urine PA, while human u-PA-specific antibodies do not react with porcine urine PA. (3) Plasminogen activation by porcine urine PA is markedly stimulated in the presence of fibrinogen fragments. (4) Porcine urine PA activity is not affected by concentration of amiloride substantially suppressing human u-PA activity.

Urinary excretion of inactive renin during blockade of the renal tubular protein reabsorption with lysine.

The purpose was to study whether the kidneys eliminate inactive renin from the circulation of mice. The urinary concentration, excretion rate and clearance of inactive renin were very low during basal conditions. After blockade of the reabsorption of proteins in the renal tubules with the basic amino acid lysine, the urinary concentration, excretion rate and clearance of inactive renin increased very markedly. This finding indicates that inactive plasma renin is subjected to glomerular ultrafiltration followed by reabsorption in the renal tubules by mechanisms which are most likely the same as for active renin and other filtered proteins. The urinary clearance of inactive renin after blockade of the renal tubular protein reabsorption was 13% of that of active renin. Our findings demonstrate that glomerular ultrafiltration is a route of elimination from the circulation for inactive renin.

Fibrin activatable urokinase (FA-UK): a latent form of UK found in urine related to a complex with an inhibitor/fibrin-interacting cofactor.

In order to investigate the binding of pro-urokinase (pro-UK) in urine to fibrin/Celite, the property which led to its discovery, the effect of fibrin on the plasminogen activator activity of urine was studied. The plasminogen activator activity in urine was found to be consistently about 2-fold higher when measured by fibrin plate assay than by amidolytic substrate (S-2444), when normalized against the UK reference standard. When the amidolytic activity measurement was preceded by incubation of urine with soluble fibrin, a 2-fold increase in amidolytic activity was also found. Fibrin similarly increased plasmin generation in urine enriched with Glu- or Lys-plasminogen as determined by synthetic substrate S-2251. The observed promoting effect was common to several forms of soluble fibrin and was dose dependent, whereas fibrinogen had little effect. The promoting effect of fibrin was not expressed in the presence of pro-UK or two-chain UK (TC-UK) in buffer and therefore was attributed to another constituent of urine. Since the activity was inhibited by antibodies to UK but not to t-PA, it was called fibrin activatable UK (FA-UK). Gel filtration (Sephacryl-200) of urine revealed FA-UK activity in fractions eluting at a molecular weight of approximately 100K. A 100 K band of activity was also consistently seen when concentrated urine was subjected to zymography. Treatment of concentrated urine with hydroxylamine (1 M) eradicated both these activities and was associated with an increase in baseline amidolytic activity in the urine sample indicative of the release of UK from an inhibitor complex. Moreover, passage of urine over insolubilized monoclonal antibody against UK-inhibitor (PAI-3) complexes resulted in loss of FA-UK activity and of the 100 K band on the zymogram suggesting that the complex responsible for FA-UK was related to a PAI-3 complex. Since the FA-UK activity appeared to bind to fibrin/Celite, attempts were made to investigate complexation with pro-UK. Unfortunately, due to the instability of pro-UK in urine, no reliable data were obtained. It was concluded that PAI-3 may serve as a fibrin-interacting co-factor of UK, and therefore may play a role in fibrinolysis.

Immunological identification of rat urinary inactive kallikrein as a proform of tissue kallikrein.

Antibody was raised against a synthetic undecapeptide (PS 11) which corresponds to the prosegment of the rat tissue kallikrein precursor. The potential to recognize rat urinary active or inactive kallikrein was assessed by an enzyme immunoassay method for PS 11, using beta-D-galactosidase as the labeling enzyme. The active kallikrein failed to compete with the enzyme-labeled PS 11 in binding to the antibody. The inactive kallikrein displaced the enzyme-labeled PS 11 in this enzyme immunoassay, and the displacement curve was in parallel with that of PS 11. These results indicate that rat urinary inactive kallikrein contains a prosequence recognized by the antibody to PS 11. This inactive kallikrein is probably a proform of tissue kallikrein.

Reactivities of human urinary prokallikrein and kallikrein toward rabbit antibodies with special reference to enzyme immunoassay.

Human urinary prokallikrein and kallikrein have been analyzed by means of solid phase enzyme immunoassay (EIA) using rabbit antibodies. The anti-kallikrein antibody-immobilized EIA detected both kallikrein and prokallikrein. However, only kallikrein was detectable at concentrations below 20 micrograms/1. The anti-prokallikrein antibody-immobilized EIA detected both kallikrein and prokallikrein, but the binding maximum for kallikrein was about one-third less than that for prokallikrein. Similar difference in reactivity of kallikrein and prokallikrein toward each antibody was observed with immunoaffinity column chromatography and single radial immunodiffusion. The results show that immunochemical properties of human urinary prokallikrein and kallikrein differ distinctly, and conflicting results on detectability of kallikrein and prokallikrein in human urine with EIA or radioimmunoassay using the anti-kallikrein antibody was due to the difference in reactivity of the two forms of kallikrein toward the immobilized antibody.

Tryptase and kinin generation: tryptase from human mast cells does not activate human urinary prokallikrein.

The effect of tryptase, a neutral protease released from human lung mast cell secretory granules, on the tissue prokallikrein present in human urine was examined. Tryptase has been shown previously to lack activity against plasma prokallikrein. Purified tryptase was incubated with a concentrated preparation of urinary prokallikrein. No increase in kallikrein-like enzymatic activity or immunoreactive tissue kallikrein was detected. Activation of urinary prokallikrein with trypsin served as a positive control. Furthermore, preincubation of urinary prokallikrein with tryptase did not diminish the subsequent activation of urinary prokallikrein by trypsin. Therefore, tryptase neither activates nor destroys human tissue or plasma prokallikreins.

Monoclonal antibodies against human high molecular weight urinary urokinase: application for affinity purification of urinary prourokinase.

Monoclonal antibodies against urinary urokinase were obtained by immunizing mice with purified human high molecular weight urokinase. Five antibodies were selected and denominated MPW1UK, MPW2UK, MPW3UK, MPW4UK, and MPW5UK, respectively. All selected antibodies reacted with high and low molecular weight urokinase. Cleavage of the low molecular weight paranitroanilide substrate pyro-Glu-Gly-Arg-pNA by urokinase was not inhibited by the antibodies and only one antibody (MPW5UK) inhibited plasminogen activation by urokinase. The ability of MPW5UK to bind to coated urokinase was 100-fold higher than that of the other antibodies. MPW5UK was used to prepare an immunosorbent for the purification of urokinase antigen from freshly voided crude urine. One-chain prourokinase was separated from two-chain urokinase by chromatography of the urokinase antigen containing mixture on agmatine Sepharose. As judged by SDS gel electrophoresis one-chain prourokinase as well as two-chain urokinase were purified to apparent homogeneity by this two-step procedure; the yields were 18% and 47% for single-chain prourokinase and two-chain urokinase, respectively, as calculated from total urokinase antigen contained in the starting material.

Activation of urinary inactive kallikrein by an extract from the rat kidney cortex.

Activation of purified urinary inactive kallikrein by an extract from the rat kidney cortex was investigated. The extract produced a dose-dependent activation of the inactive kallikrein and the optimum pH for this activation was 5.0. Marked depression of the activation was observed when the extract was pre-incubated with E-64, p-CMB and iodoacetate, but not with DFP, PMSF or pepstatin A. The molecular weight of the inactive kallikrein (Mr 44,000) was reduced to 38,000 by treatment with the extract, this molecular weight value being identical with that of urinary active kallikrein. These results indicate that the rat kidney cortex contains a protease catalyzing conversion of urinary inactive kallikrein into its active form, and that the protease has properties compatible with those of a thiol protease, but not of trypsin which has been used as a tool for the activation of urinary inactive kallikrein. The thiol protease is probably one of regulators of the kallikrein-kinin system in the kidney.

Fibrin-binding urokinase (or precursor form of urokinase) with a molecular weight of about 100,000 in fresh human urine.

Fresh human urine was found to contain at least three different molecular forms of fibrin-binding urokinase (UK) or its precursor, all of which were absorbed on a fibrin/Celite column at neutral pH, and could be eluted with 0.3-1.0 mol/l NaCl in phosphate buffer, followed by 0.2 mol/l, Arg, 2 mol/l KSCN, and 2 mol/l urea, respectively. The main molecular form isolated revealed a molecular weight (MW) of approximately 100,000 (UK-100), and the minor ones were estimated to have MW of 150,000-200,000 and 45,000. In contrast, commercially obtained UK preparations contained mostly active enzymes with MW of 53,000 and 32,000, respectively, and the remaining high molecular forms represented less than 2.0% of the total amount. Rabbit monospecific antibody (IgG) against UK subcomponent (active heavy chain; H-chain UK) reacted and inhibited the fibrinolytic activity of all the active UK molecules. The UK-100 isolated was relatively stable in solution at neutral pH and resistant to mild reduction, without molecular change. Although the preparation had a very low specific activity (ca. 300 IU/mg protein), both the pyro-Glu-Gly-Arg-pNA amidolytic and plasminogen activating activities could be partially enhanced by the addition of trace amounts of plasmin. In this process, the appearance of two additional active enzymes of MW 53,000 and 32,000 was also confirmed by zymography.

Isolation and characterization of a precursor form of lysosomal alpha-glucosidase from human urine.

A two-step procedure is described for the isolation of lysosomal alpha-glucosidase from human urine. In the second step, affinity chromatography on Sephadex G-100, two fractions with acid alpha-glucosidase activity were obtained. Fraction I contained alpha-glucosidase of Mr 109000, whereas fraction II contained components of Mr 76000 and 70000. alpha-Glucosidase in fraction I had an Mr similar to that of the precursor of alpha-glucosidase detected in the medium of fibroblasts after labelling with [14C]leucine. The components in fraction II had Mr identical to those of the mature forms of alpha-glucosidase found in placenta or cultured human skin fibroblasts. alpha-Glucosidase in fraction I contained mannose 6-phosphate (3.5 mol/mol polypeptide). No mannose 6-phosphate was present in the components in fraction II. Fraction I, but not fraction II, was avidly endocytosed by alpha-glucosidase-deficient cultured human skin fibroblasts. Endocytosis of fraction I was inhibited by mannose 6-phosphate. The pH optimum and Km values for p-nitrophenyl alpha-glucoside, maltose and glycogen of fractions I and II alpha-glucosidase were almost identical. However, the activity with glycogen relative to that of either p-nitrophenyl alpha-glucoside or maltose was lower in fraction I than in fraction II. It is concluded that fraction I consists of the precursor form of alpha-glucosidase and fraction II of the mature forms of the enzyme. The importance of urine as a source of precursors of lysosomal enzymes is discussed.

Molecular forms of beta-hexosaminidase and cathepsin D in serum and urine of healthy subjects and patients with elevated activity of lysosomal enzymes.

A procedure is described that allows the characterization of the molecular forms of beta-hexosaminidase and cathepsin D in controls and pathological specimens of human serum and human urine. The following observations were made. (1) In human serum, beta-hexosaminidase (alpha- and beta-chain) and cathepsin D are present predominantly in their high-molecular-weight precursor forms. In human urine, these enzymes exist as both precursor and mature forms. (2) Cathepsin D precursor from serum and urine differs in the number of oligosaccharides that are sensitive to endo-beta-N-acetylglucosaminidase H. Therefore the urine enzyme is not likely to originate from the serum. (3) The presence exclusively of precursors of beta-hexosaminidase and of cathepsin D in the sera of patients with hepatitis suggests that in hepatitis secretion of lysosomal enzymes is elevated, rather than the enzymes leaking from damaged cells. (4) In the urine of patients with nephrotic syndrome, beta-hexosaminidase and cathepsin D are present in grossly elevated amounts, but do not differ in the polypeptide patterns from controls. (5) In urine from a patient with mucolipidosis II, the elevated activity of beta-hexosaminidase is accounted for mainly by the precursor forms. Mature beta-chain of beta-hexosaminidase is lacking, and incompletely processed beta-hexosaminidase polypeptides are present. Both the precursor and the mature forms of cathepsin D are increased. They contain only complex oligosaccharides.

Active and inactive renins in human urine.

Urinary excretions of active and inactive renin were studied in normal subjects and in patients with hypertensive or renal disease. Excessive excretion of active and inactive renins was observed in some patients with no significant correlation to their plasma levels or the degree of proteinuria. Inactive renin excretion correlated to active renin excretion, but the clearance was lower than that of the active form. No correlation was found between the urinary kallikrein excretion and the active/inactive renin ratio in the urine or the plasma. Urinary renin activity was increased by acidification and by trypsin treatment, but not by cold exposure. Both active and inactive renins in the urine showed multiple peaks corresponding to molecular weights between 45,000 and 64,000 by gel filtration.