Correlation between circulating proteasome activity, total protein and c-reactive protein levels following burn in children

AIM OF THE STUDY

To characterize burn-induced changes following burn in children by analyzing circulating proteasome (c-proteasome) activity in the plasma in correlation with total protein and c-reactive protein levels in the plasma, and the severity of the burn.

METHODS

Fifty consecutive children scalded by hot water who were managed at the Department of Pediatric Surgery after primarily presenting with burns in 4-20% TBSA were included into the study. The children were aged 9 months up to 14 years (mean age 2.5±1 years). Patients were divided into groups according to the pediatric injury severity score used by American Burns Association. Plasma proteasome activity was assessed using Suc-Leu-Leu-Val-Tyr-AMC peptide substrate, 2-6 h, 12-16 h, 3 days, 5 days, and 7 days after injury. 20 healthy children consecutively admitted for planned inguinal hernia repair served as controls.

RESULTS

Statistically significant elevation of plasma c-proteasome activity was noted in all groups of burned children 12-16 h after the injury. We found a strong negative correlation of c-proteasome activity with total protein levels, and positive correlation with CRP levels 12-16 h after burn. We also found stronger correlation between c-proteasome activity and severity of burn, than CRP level and severity of burn 12-16 h, and 3 days after the burn. Correlations were statistically significant.

CONCLUSIONS

This study characterized circulating 20S proteasome activity levels after burn. C-proteasome activity elevate after burn and correlate negatively with plasma total protein level, thus plasma 20S proteasome activity could be additional biomarker of tissue damage in burn in pediatric population.

Cathepsin A-like activity is possibly the main acidic carboxypeptidase in human platelets

Human platelets were investigated for activity of the acidic carboxypeptidases: cathepsin A, lysosomal carboxypeptidase B and prolyl-carboxypeptidase. It was found that the main acidic carboxypeptidase in human platelets had cathepsin A activity. No activity of lysosomal carboxypeptidase B and prolyl-carboxypeptidase in human platelets was detectable using their specific substrates. Human platelet cathepsin A-type enzyme hydrolyzed at the highest rate Cbz-Phe-Ala, Cbz-Phe-Met and Cbz-Phe-Leu, did not require sulfhydryl activator and was inhibited by serine protease inhibitors (DFP, DCI) and inhibitors that react with the SH group (mersalyl acid, PCMS, PCMB, HgCl2). Cbz-Phe-Ala and Cbz-Glu-Tyr were hydrolyzed at a broad pH range with optimum at pH 5.0-6.0. The chromatographic analysis on Con A-Sepharose and DEAE-Sephacel showed different forms of Cbz-Phe-Ala-hydrolyzing enzyme in human platelets. The multiple forms of this enzyme were probably due to heterogeneity of carbohydrate moiety.

Changes in proteasome activity in the ischemic kidney of rat with experimental renovascular hypertension

A long-lasting renal ischemia, followed by the left renal artery clipping (two-kidney, one clip Goldblatt model in rats) led to a marked decrease in proteasome chymotrypsin-like activity in the ischemic kidney. This activity was, however, significantly raised upon the stimulation with an artificial 20S proteasome activator SDS (0.025%). No changes were observed in either the levels of the constitutive 20S proteasome subunit (alpha5) or of its protein activator, PA28alpha, in the kidneys by Western blot. These preliminary results indicate that an inhibition of proteasome activity may result from a dissociation of the active proteasome complexes into the inactive 20S proteasome and its endogenous activators after a long-lasting renal ischemia.

Pulmonary neuroendocrine cells in chronic renal failure

In patients with chronic renal failure, mechanical and haemodynamic changes could occur in the lungs without obvious pulmonary symptoms and findings, and their effects could pave the way to pulmonary functional disorders. Numerous studies have demonstrated that the respiratory system is a site of synthesis of many compounds, which play biological roles ascribed to hormones. The present article is an attempt to make a synthesis of current opinions and views, based on the world literature survey and on our own studies, concerning the effect of homeostatic dysfunction of the kidneys on the morphology and action of DNES cells in the lung.

Effects of ebelactone B on cathepsin A activity in intact platelets and on platelet activation

PURPOSE

Previous in vitro studies have demonstrated that a potent antihypertensive agent ebelactone B inhibits cathepsin A/deamidase activity. The aim of our studies was to assess the effects of this inhibitor on cathepsin A activity in intact platelets and on platelet activation events.

MATERIAL AND METHODS

PRP or washed human platelets from healthy volunteers were pre-incubated with different concentrations of ebelactone B (1-10 microM) for 10-60 min. Cathepsin A activity in platelets was assayed colorimetrically using Cbz-Phe-Ala at pH 5.5. Expression of platelet activation markers GpIIb/IIIa and P-selectin on non-activated or agonist-activated platelets (ADP, TRAP) was measured by flow cytometry.

RESULTS

Pre-treatment of platelets for up to 60 minutes with 10 mumol/l ebelactone B, that effectively inhibits cathepsin A activity in platelet lysate, did not affect this activity in intact platelets. Exposure of PRP to 10 mumol/l ebelactone B alone, or before platelet activation with ADP or TRAP caused only a small but non-significant increase in P-selectin and GpIIb/IIIa expression on the platelet surface, as demonstrated by flow cytometry analysis.

CONCLUSIONS

The lack of cathepsin A inhibition by ebelactone B in intact platelets indicates that this inhibitor does not enter cells. Therefore, a potential antihypertensive significance of this compound may be through the inhibition of cathepsin A/deamidase released from activated or damaged cells. In vitro ebelactone B seems to exert no effect on platelet activation. Further studies are underway to determine whether ebelactone B administration affects platelet activation events in experimental model of hypertension in rats.

Chymotrypsin-like activity in rat tissues in experimental acute pancreatitis

PURPOSE

Increase in intracellular chymotrypsin activity was reported during acute pancreatitis. Beside chymotrypsin, there are at least two enzymes with chymotrypsin-like activity: proteasome and lysosomal cathepsin A. Until now it is not known whether and to what extent they contribute to increases in chymotrypsin activity in acute pancreatitis. Our aim was to study organ chymotrypsin-like activities during experimental acute pancreatitis.

MATERIAL AND METHODS

Rat cerulein model of acute pancreatitis was used. The chymotrypsin-like activities were assessed in pancreas, liver, lung, heart, spleen and kidney using highly selective synthetic substrates of the proteasome and the cathepsin A, at neutral and acidic pH. Determinations after addition of selective inhibitor were also performed.

RESULTS

During acute pancreatitis we found in the pancreas an increase only in neutral chymotrypsin-like activity, as compared to the control animals. In other organs neutral chymotrypsin-like activity did not increase, and in kidney it even decreased. There were no changes in acidic chymotrypsin-like activity in any of organs studied. The studies using the inhibitor of the proteasome showed that the neutral chymotrypsin-like activity in the pancreas of the rats with acute pancreatitis should not be attributed to the proteasome activity, but rather to the chymotrypsin.

CONCLUSIONS

Our results did not confirm any significant contribution of proteasome or cathepsin A to increased chymotrypsin-like activity in acute pancreatitis. We showed a decrease in neutral chymotrypsin-like activity of proteasome in the kidney, but the significance of this finding remains to be established.

Lactacystin inhibits cathepsin A activity in melanoma cell lines

We describe the inhibitory effect of the proteasome inhibitor, lactacystin, on cathepsin A activity in murine melanoma cell lines. In vitro lactacystin metabolite, beta-lactone, at a concentration of 1 microM, significantly suppressed cathepsin A activity in B78 melanoma cell lysates by about 50%. Exposure of three murine melanoma cell lines with different metastatic potential to lactacystin at a concentration of 5 microM for 6 h caused a significant reduction in the carboxypeptidase activity of this enzyme, while the inhibitory activity remained unchanged for at least 12 h. Other proteasome-specific inhibitors, e.g. epoxomicin and N-benzyloxycarbonyl-Ile-Glu(O-tert-Bu)-Ala-leucinal (PSI) at a concentration of 1 microM did not affect cathepsin A activity in melanoma cell line lysates. These data support our previous proposal that lactacystin is not a specific inhibitor of the proteasome. Since cathepsin A is also a tumor-associated enzyme, further research is needed to clarify its role and the significance of its inhibition by lactacystin in tumor biology.

Separation of cathepsin A-like enzyme and the proteasome: evidence that lactacystin/beta-lactone is not a specific inhibitor of the proteasome

Previous studies have described a human platelet cathepsin A-like enzyme with a number of similarities to the "acidic" and "neutral" chymotrypsin-like activities of the proteasome. This includes its strong inhibition by the highly specific proteasome inhibitor Lactacystin/beta-lactone, suggesting that either the Cbz-Phe-Ala-hydrolyzing activity attributed to cathepsin A was due to the chymotrypsin-like activity of the proteasome or that lactacystin was not a specific inhibitor of the proteasome. In the present study we discard the first possibility on the basis of the following findings: (a) human platelet cathepsin A, unlike proteasome, binds to concanavalin A, and does not bind to Heparin-Sepharose at pH 7.4; (b) neither the chymotrypsin-like activity of the proteasome, nor proteasome antigens are detected in the cathepsin A preparation; (c) purified proteasome does not exhibit Cbz-Phe-Ala-hydrolyzing activity; (d) Z-lle-Glu-(Ot-Bu)Ala-leucinal (PSI), a compound that selectively inhibits the chymotrypsin-like activity of the proteasome at a concentration of 10 microM has no inhibitory effect on the carboxypeptidase activity of cathepsin A; (e) cathepsin A, free of the proteasome, is completely inhibited by micromolar concentrations of lactacystin/beta-lactone. It is therefore concluded that lactacystin/beta-lactone is not a specific inhibitor of the proteasome.

Cathepsin A activity in primary and metastatic human melanocytic tumors

Several lysosomal proteases including cathepsins B, D, H and L have been found to play a role in the metastasis of tumor cells. However, up to now no information on the role of cathepsin A, a lysosomal multifunctional peptidase, in the proliferative, invasive, and metastatic potential of malignant tumors has been available. In the present study we compared the activity of cathepsin A in lysates of 34 human melanocytic tumors: primary (n = 12) and metastatic (n = 5) malignant melanoma, dysplastic pigmented nevi (n = 6) and pigmented nevi without evidence of dysplastic melanocytes (n = 11). The carboxypeptidase activity of cathepsin A was assayed at pH 5.0 with its specific substrate Cbz-Phe-Ala. The amount of released C-terminal alanine was measured by the ninhydrin method. We found that lysates of primary malignant melanoma lesions exhibited significantly higher cathepsin A activity than lysates of dysplastic and normal pigmented nevi. The cathepsin A activity in lysates of metastatic lesions of malignant melanoma was significantly higher than in primary focus lysates. It seems that cathepsin A may play a role in malignant transformation and metastatic dissemination of malignant melanoma.

[The role of proteolytic enzymes in apoptosis]

The literature review dealing with participation of proteolytic enzymes in initiation and execution of apoptosis was done. Cysteine proteases with Asp-X cleavage specificity, called caspases, play the main role in this process. The other proteases such calpains and proteasomes take also part in apoptosis. The proteases degrade proteins of cytoskeleton and structural proteins of nucleus, they also activate proendonucleases.

Cellular serine carboxypeptidases

The literature on serine carboxypeptidases of cells is reviewed. These proteases occur in the vacuoles of fungi and higher plants and in the lysosomes of animals and man cells. Physico-chemical properties, chemical structure, catalytic mechanism and substrate specificity of these enzymes are presented.

Activity of lysosomal and nonlysosomal proteases of fibrosarcoma induced by methylcholanthrene

Activity of lysosomal (cathepsins A,B,C,D and E) and nonlysosomal proteases (cathepsin G, elastase, collagenase, prolidase, prolinase) was evaluated in fibrosarcoma induced in rats by methylcholanthrene. No differences were found in the activity of the examined proteases in tumours of different size in the external, intermediate and central spheres of these tumours. Activity of cathepsins A,B,C,D,E and G, prolidase and prolinase was higher in the fibrosarcoma and activity of collagenase and elastase was lower than in the rat skin.

Activity and tissue localization of cathepsin G in non small cell lung cancer

Activity and tissue localization of cathepsin G were examined in tumors deriving from 73 patients with non small cell lung cancer. Activity of cathepsin G was highest in adenocarcinoma, lower in planoepitheliale cancer, the lowest in macrocellular cancer. In all histological types of tumors cathepsin G activity in supernatants was lower than in sediments. The enzyme immunohistochemically was localized in neutrophils. There is evident correlation between neutrophil numbers and cathepsin G activity in examined cancer types. Result of our examinations indicate a relationship between cathepsin G activity, grade of tumor differentiation and particular clinical stages of disease.

Activity and tissue localization of cathepsin D in non small cell lung cancer

Activity and tissue localization of cathepsin D were examined in tumors deriving from 80 patients with non small cell lung cancer. Activity of the enzyme was higher in sediments and supernatants of tumors than in non invaded lung parenchyma. In all histological types of tumors cathepsin D activity in sediments was three times lower and in lung parenchyma five times lower than in supernatants. The immunohistochemical technique was used for enzyme localization. We observed seemingly the lack of correlation between activity of cathepsin D examined in tumors and immunohistochemical reaction intensity in neoplasm cells. Different numbers of macrophages and quantity of tumor stroma could explain this effect in examined histological types of cancer. Results of our explanations indicates for relations between cathepsin D activity versus histological type and degree of tumor differentiation. We did not observe correlation between cathepsin D activity versus lymph node metastases and clinical stages.

Cathepsin A-like activity in thrombin-activated human platelets. Substrate specificity, pH dependence, and inhibitory profile

Cathepsin A-like enzyme released from human platelets by thrombin hydrolyzed at the highest rate Cbz-Phe-Ala, Cbz-Phe-Met and Cbz-Phe-Leu, did not require activators and was inhibited by DFP, DCI and mercurial compounds (mersalyl acid, PCMS, PCMB and HgCl2). The optimum activity of secreted enzyme was at pH 5.0-6.0. Cbz-Glu-Tyr was also hydrolyzed at lower pH with optimum at pH 3.5. These enzymatic properties are the same as those of cathepsin A solubilized from whole platelets and purified from other mammalian cells and tissues. High specific activity of secreted cathepsin A, and a broad pH range of activity may have a significance in extracellular proteolysis in local sites of ischemia. Large portion of cathepsin A-like activity was not secretable by high concentration of thrombin and was sedimented with platelet aggregates. No activity of lysosomal carboxypeptidases B and prolylcarboxypeptidase was detectable in supernatants and pellets of thrombin-stimulated platelets.

Lactacystin, a specific inhibitor of the proteasome, inhibits human platelet lysosomal cathepsin A-like enzyme

Lactacystin, the most specific inhibitor of the proteasome, strongly inhibited at pH 5.5 the activity of human platelet lysosomal cathepsin A-like enzyme. At a concentration as low as 1-5 microM it almost completely decreased the hydrolysis rate of cathepsin A specific substrates: Cbz-Phe-Ala and FA-Phe-Phe. This inhibition was probably due to the lactacystin intermediate beta-lactone formed during 10 min hydrolysis at pH 8.0 since nonhydrolyzed inhibitor did not affect cathepsin A activity. Basing on similarities in the inhibitor sensitivity, pH optimum, and substrate preferences it is suggested that the cathepsin A-like activity may be involved in chymotrypsin-like activity of the proteasome.

Activity of lysosomal and nonlysosomal proteases and contents of protein and its degradation products in the blood serum of rats with fibrosarcoma induced by methylcholanthrene

Activity of lysosomal and nonlysosomal proteases and contents of protein and its degradation products in the blood serum of rats with methylcholantrene fibrosarcoma were evaluated. Activity of lysosomal proteases and prolidase and prolinase as well in the blood serum of rats with methylcholanthrene tumour did not differ from the activity of these enzymes in the blood serum of control rats. Only the activity of elastase and collagenase in the blood serum of rats with methylcholanthrene tumour especially with tumour of intermediate and big mass was increased. Content of total protein was decreased in the blood serum of rats with tumour of intermediate and big mass and contents of glycoproteins and alfa-amin nitrogen were increased in comparison to the blood serum of control rats.

Inhibition of human platelet cathepsin A by non-steroidal anti-inflammatory drugs--in vitro study

Since the lysosomal proteases appear at site of inflammation they may be a target for non-steroidal anti-inflammatory drugs (NSAIDs). In in vitro study the inhibition of human platelet cathepsin A by NSAIDs was found. Indomethacin, phenacetin and aminophenazone were the most potent inhibitors of cathepsin A. Acetylsalicylic acid added to platelet lysate inhibited cathepsin A in the same extent as salicylate. The inhibition was time-dependent and reversed after dialysis. Mixed type of inhibition by salicylate was shown.

Pig platelet acidic carboxypeptidases

Pig platelet acidic carboxypeptidases hydrolyzed only N-blocked dipeptides with bulky aromatic and aliphatic hydrophobic amino acids. The optimum hydrolysis of these substrates was at pH 5.0. The main acidic carboxypeptidase in pig platelet lysate was lysosomal carboxypeptidase A (1CPA), which hydrolyzed Cbz-Phe-Ala at the highest rate. A lower activity of this enzyme was found on Cbz-Glu-Tyr and Cbz-Glu-Phe. 1CPA also hydrolyzed Cbz-Glu-Tyr at pH 3.5. No activity of lysosomal carboxypeptidase B in platelet lysate was detectable using Bz-Gly-Arg. Pig platelet acidic carboxypeptidase hydrolyzed Cbz-Pro-Phe and Cbz-Pro-Ala, which are specific substrates of lysosomal prolylcarboxypeptidase, more slowly. The incubation of platelet lysate with plasma did not influence the rate of hydrolysis of Cbz-Glu-Tyr, whereas no hydrolysis of Cbz-Pro-Phe was observed.