An analysis of 14 molecular markers for monitoring osteoarthritis: segregation of the markers into clusters and distinguishing osteoarthritis at baseline

OBJECTIVE

To investigate the relationships between serum and urinary molecular markers (MM) used to monitor osteoarthritis.

DESIGN

Forty osteoarthritis patients had blood and urine collected at baseline and 1, 3, 6 and 12 months later. Specimens from 20 controls were obtained twice at a one month interval. The concentration of 14 different markers was determined at each time point and the data were analyzed by statistical methodology.

RESULTS

The markers could be divided by the method of principal components analysis into five clusters of related markers: inflammation markers (C-reactive protein, tumor necrosis receptor type I and tumor necrosis receptor type II, interleukin 6, eosinophilic cationic protein), bone markers (bone sialoprotein, hydroxylysyl pyridinoline, lysyl pyridinoline), putative markers of cartilage anabolism (carboxypropeptide of type II procollagen, hyaluronan, epitope 846) and catabolism (keratan sulfate, cartilage oligomeric matrix protein), and transforming growth factor beta. Three markers (tumor necrosis factor receptor II, cartilage oligomeric matrix protein and epitope 846) from independent clusters discriminated osteoarthritis patients from controls. Inflammation was not a confounding factor in measurement, but a recognizable distinguishing factor in osteoarthritis.

CONCLUSIONS

The markers separated into rational groups on the basis of their covariance, a finding with independent biochemical support. The covariance of markers from the same cluster suggests the use of a representative marker from the cluster to reflect changes in osteoarthritis. If multiple markers are being measured within a single cluster, then the use of a weighted cluster 'factor' may be preferable to the separate use of individual markers.

Effect of prolonged administration of a urinary kinase inhibitor, ebelactone B on the development of deoxycorticosterone acetate-salt hypertension in rats

The effect of prolonged administration of a carboxypeptidase Y-like kininase inhibitor, ebelactone B (EB) (2-ethyl-3, 11-dihydroxy-4, 6, 8, 10, 12-pentamethyl-9-oxo-6-tetradecenoic 1, 3-lactone), on the development of deoxycorticosterone acetate (DOCA)-salt hypertension was tested. The systolic blood pressure (SBP) of non-treated 6-week-old Sprague-Dawley strain rats was gradually increased by DOCA-salt treatment from 137+/-2 mmHg (n=11) to 195+/-7 mmHg at 10 weeks of age. With daily oral administration of lisinopril (5 mg kg(-1), twice a day), which is an inhibitor of angiotensin converting enzyme, a major kininase in plasma, the development of hypertension was not suppressed. By contrast, administration of EB (5 mg kg(-1), twice a day), completely inhibited the development of hypertension (SBP: 146+/-1 mmHg, n=5, 10 weeks old). The reduced SBP at 10 weeks of age was equal to the SBP before any treatment (142+/-1 mmHg, n=5). Direct determination of mean blood pressure (MBP) in conscious, unrestrained rats confirmed that MBP elevation was completely inhibited by EB. Continuous subcutaneous infusion (5 mg kg(-1) day(-1)) of HOE140, a bradykinin B2 receptor antagonist, restored the elevation of SBP, which was suppressed by EB. The weights of left ventricle of DOCA-salt treated rats 10-weeks-old (0.36+/-0.02 g 100 g body weight(-1), n=11) was significantly reduced by EB (0.27+/-0.01, n=5), as were the sodium levels in serum, cerebrospinal fluid and erythrocyte. These findings suggested that EB is effective in preventing salt-related hypertension presumably by eliminating sodium retention.

Ebelactone B, an inhibitor of urinary carboxypeptidase Y-like kininase, prevents the development of deoxycorticosterone acetate-salt hypertension in rats

Kininogen-deficient Brown Norway Katholiek rats (BN-Ka) excrete little urinary kinin, compared with normal rats of the same strain (BN Kitasato rats (BN-Ki)). Deoxycorticosterone acetate-salt treatment increased systolic blood pressure in both rats, but much faster in BN-Ka than in BN-Ki. Daily subcutaneous administration of ebelactone B (15 and 5 mg/kg/day), a rat urinary carboxypeptidase Y-like kininase inhibitor, significantly reduced systolic blood pressure in BN-Ki, but not in BN-Ka. This treatment significantly increased urinary Na+ excretion and reduced Na+ concentration in the erythrocytes in BN-Ki, but not in BN-Ka. An angiotensin-converting enzyme inhibitor, lisinopril (5 mg/kg/day s.c.), did not reduce the systolic blood pressure in either BN-Ki or BN-Ka. These results suggested that ebelactone B has promise as a preventive agent for the development of hypertension acting through the inhibition of urinary kinin degradation.

Diuretic and natriuretic effect of ebelactone B in anesthetized rats by inhibition of a urinary carboxypeptidase Y-like kininase

Ebelactone B (EB) (10(-7)-10(-5) M) inhibited dose-dependently carboxypeptidase (CP) Y-like exopeptidase, one of the major kininases separated from rat urine, whereas it inhibited neither CPA, CPB or neutral endopeptidase (NEP). Degradation of bradykinin (BK) to BK-(1-8) in rat urine was completely inhibited by EB (10(-5) M) with the increased generation of BK-(1-7). Intraduodenal administration of EB (3 mg/kg) to anesthetized rats caused marked diuresis (by 110%) and natriuresis (130%), in parallel with the increase in urinary kinin levels (110%). Intravenous infusion of a BK antagonist, Hoe140 (3 mg/kg/hr), strongly blocked both EB-induced diuresis and natriuresis. EB may be a novel type of diuretic and natriuretic agent that acts by increasing urinary kinin levels.

Angiotensin carboxypeptidase activity in urine from normal subjects and patients with kidney damage

Angiotensin carboxypeptidase (ACP) activity has been detected in urine samples from normal subjects and patients with hypertension and diabetes by determining the enzyme's ability to convert angiotensin I to des-Leu angiotensin I. Gel filtration chromatography of a concentrated urine sample indicated that about equal amounts of the enzyme exist as 100 kDa and 500 kDa molecular weight forms, respectively. This ACP activity co-eluted with activity that cleaved histidine from des-Leu angiotensin I to form angiotensin II and activity that cleaved tyrosine from benzyloxycarbonyl-glutamyl-tyrosine (ZGT). These results suggest that the urinary ACP activity is due to cathepsin A as we have reported previously for the porcine kidney enzyme. Analysis of sequential urine samples from a single individual over a 6-day period revealed as much as a 6-fold fluctuation in creatinine-normalized ACP activity. Of five male healthy adult subjects, the creatinine-normalized urinary ACP activity ranged from 1.7 to 3.7 mU/mL with a mean of 2.8 mU/mL. However, five male patients with renovascular hypertension had elevated levels of ACP activity with a mean of 11.6 mU/mL. Of five male patients with diabetic nephropathy, all had elevated ACP activity levels with a mean of 21.0 mU/mL. It is concluded that ACP activity in the urine is due to cathepsin A probably derived from kidney tissue, and that the release is increased in patients with kidney damage. We suggest that urinary ACP activity should be evaluated further for a possible relationship to renal hypertension and as a potentially early marker for diabetic nephropathy.

Carboxypeptidase activity in human urine from healthy subjects and renal disease patients

We have attempted to estimate the carboxypeptidase activity in unconcentrated human urine by means of a colorimetric method in which Bz-Gly-Lys is employed as a substrate. Upon addition of both 1.6 mmol/l CoCl2 and 0.18 g/l bovine serum albumin to the assay solution at pH 5.6, the carboxypeptidase activity in human urine can be evaluated. Using our method, the daily excretion of carboxypeptidase in both healthy subjects and patients with renal diseases has been examined. The level is increased in patients with nephrotic glomerulonephritis (24.9 +/- 14.9 (SD) U/day; n = 8) and patients with nephritic glomerulonephritis (11.4 +/- 7.55 (SD) U/day; n = 14) as compared to that in healthy subjects (5.10 +/- 1.88 (SD) U/day; n = 18). However, it is decreased in patients with chronic renal failure (2.70 +/- 2.13 (SD) U/day; n = 12).

A sensitive method for differential determination of kininase I, II and neutral endopeptidase (NEP) in human urine

In order to clarify the significance of NEP in human renal kallikrein-kinin system, an assay system was developed for the simultaneous determination of kininase I, II and NEP activities in human. Each kininase activity was determined by measuring the hydrolysis of bradykinin in the presence of specific inhibitors of kininase I (2-mercaptomethyl-3-guanidinoethylthiopropanoic acid), kininase II (captopril) and NEP (phosphoramidon) in 8 normal subjects. The effects of the different assay buffers on kininase activities were also investigated by using a phosphate buffer. Total kininase, kininase I, II and NEP activities were 499 +/- 65 ng/min/ml (mean +/- S.E.), 55 +/- 8, 141 +/- 21 and 299 +/- 42, respectively in our method using a tris buffer, while a phosphate buffer brought about activities of 358 +/- 43, 45 +/- 5, 156 +/- 21 and 135 +/- 25 ng/min/ml. The relative contributions of kininase I, II and NEP to total kininase activity were 11, 29 and 59% in our assay system, while they were 13, 44 and 35% when a phosphate buffer was used. From these results it was suggested that 1) phosphate may inhibit urinary NEP activity, so that a tris buffer should be used as the incubation buffer, 2) NEP is the major component of human urinary kininases, and 3) NEP may play an important role in the renal kallikrein-kinin system.

Kallikrein and kininase excretion in football players after psychophysical stress

In eleven football players and in four football-reserve players urinary kallikrein and kininase activities were determined before and after an official match. The results showed a significant reduction of kallikrein after the match in football players when the football-reserve players were used for comparison (p less than 0.01). Kininase activity appears increased in football players after the match, but not significantly. The Kininase/Kallikrein ratio after the match resulted significantly increased in football players (p less than 0.05) and very significantly compared to the football-reserve players (p less than 0.01).

Kininase one-an'-a-half: the newest member of the kininase family

A kininase I-like enzyme (carboxypeptidase) was purified to homogeneity from human urine and compared to the 48,000 mol. wt. (48K) active subunit of carboxypeptidase N. The urinary carboxypeptidase had a mol. wt. of 73,000 in gel filtration and 76,000 in SDS-polyacrylamide gel electrophoresis. It had a pH optimum of 7.0 and differed from the 48K subunit in stability, susceptibility to trypsin, and enzymatic activity. The urinary enzyme did not cross-react with antibody to carboxypeptidase N in "Western blotting". Urine from a patient genetically deficient in plasma carboxypeptidase N (21% of normal) contained normal levels of urinary carboxypeptidase with similar properties to that from pooled human urine. Membrane fractions from several tissues contained a similar carboxypeptidase activity. The activity was highest in a microvillous membrane fraction from human placenta (65 nmol/min/mg with Bz-Gly-Lys as substrate). High specific activities were also found in membrane fractions of human kidney (18 nmol/min/mg) and lung (8 nmol/min/mg). The membrane-bound enzyme was distinguished from lysosomal and catheptic carboxypeptidases as well as "enkephalin convertase" by the use of specific inhibitors. These results show that urine contains a carboxypeptidase capable of cleaving arginine or lysine from the C-terminus of peptides. The enzyme does not arise from plasma carboxypeptidase N, but may be released into the urine from the renal brush border.

Kallikrein and kininase activities excretion in newborns affected by jaundice

In a homogeneous group of 30 newborns, aging between 10 hours--10 days, and affected by jaundice, urinary kallikrein and kininase activities were determined. The variable considered were: sex, time of life, weight and gestational age. Urinary samples were taken at the beginning and at the end of phototherapy.

Urinary excretions of kininase I and kininase II activities in essential hypertension. A sensitive and simple method for its kinin-destroying capacity

To further clarify the role of the renal kallikrein-kinin system in essential hypertension, a sensitive and simple method for the determination of both human urinary kininase I and kininase II was established, and the system components were determined in patients. In the measurement of kininase activity, desalted urine samples were incubated with synthetic bradykinin, and the reaction was terminated with kininase inhibitors, ethylene diamine tetraacetic acid and phenanthroline. Thus, kininase activity was determined as the kinin-destroying capacity. Moreover, the specific inhibitor for kininase II, SQ14225, was applied for the separation of kininase I and kininase II activities. Daily urinary excretions of total kininase and kininase I activities were significantly higher in essential hypertensive patients than those in normotensive subjects, whereas no difference was observed in kininase II activity. As reported previously, daily excretions of urinary kallikrein and kinin simultaneously determined in these patients were significantly lower than excretions in normotensive subjects. From these results, it was suggested that not only decreased renal kallikrein, but also increased kininase activity, may play an important role in the suppression of the renal kallikrein-kinin system through the reduction of active kinin level in essential hypertension.

Purification of a human urinary carboxypeptidase (kininase) distinct from carboxypeptidases A, B, or N

A carboxypeptidase which cleaves basic C-terminal amino acids from peptides was purified from concentrated human urine by a three-step procedure: chromatography on Affi-Gel Blue, arginine-Sepharose affinity chromatography, and gel filtration by HPLC on a TSK-G3000SW column. Urinary carboxypeptidase was purified 406-fold with an 11% yield and a specific activity of 49 mumol/min/mg with benzoylglycylargininic acid as substrate. It migrated as a single band of Mr 75,700 in polyacrylamide gel electrophoresis with sodium dodecyl sulfate. It cleaved benzoylglycylarginine, benzoylglycyllysine, benzoylglycylargininic acid, benzoylalanyllysine, and benzoylphenylalanyllysine at different relative rates than human plasma carboxypeptidase N, the Mr 48,000 active subunit of carboxypeptidase N or human pancreatic carboxypeptidase B. Urinary carboxypeptidase did not hydrolyze benzoylglycylphenylalanine, a substrate of carboxypeptidase A, but readily cleaved bradykinin with a Km of 46 microM and a Kcat of 32 min-1. Its activity was enhanced by CoCl2 and inhibited by cadmium acetate, o-phenanthroline, or DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid. The enzyme had a pH optimum of 7.0 and its activity dropped at pH 6.0 by 60%. It was stable for at least 2 h at 37 degrees C (pH 8.0) but was unstable at room temperature below pH 4.5. The molecular weight, electrophoretic mobility, and activity of urinary carboxypeptidase was not affected by trypsin. The effect of pH and stability further distinguished the urinary carboxypeptidase from other human carboxypeptidases. Urinary carboxypeptidase was immunologically distinct from carboxypeptidase N when analyzed by the "Western blot" technique. Thus, human urine contains a basic carboxypeptidase, different from known carboxypeptidases, which may be released into the urine by the kidney. Here it could inactivate kinins and other peptides containing a basic C-terminal amino acid.