Endothelial injury in scleroderma. A protease mechanism

The mechanism of action of the previously reported serum ECA in patients with scleroderma has been studied. Gel filtration (Sephadex G-200) followed by ion exchange chromatography (DEAE-Sephadex A-50, Tris buffer, pH 8, 1.5M NaCl) yielded a 13-fold enriched fraction. ECA biological activity was abolished by preincubating the active fraction with several protease inhibitors (STI, aprotinin, TLCK, and PMSF); exposure of target cells to protease inhibitors did not inhibit ECA. ECA-rich fractions have esterolytic activity (3H-TAME), which was irreversibly inhibited by TLCK and PMSF in a time-, temperature-, concentration-, and pH-dependent fashion. In separate studies, functional protease inhibitor activity in scleroderma sera was determined by the capacity of serum to inhibit BAPNA hydrolysis by trypsin (TIC). TIC was 1.32 +/- 0.15 (milligrams of trypsin inhibited by 1 ml of serum +/- S.D.) in 20 control sera, and 0.54 +/- 0.18 (p less than 0.001) in 38 scleroderma sera. A positive correlation was found between TIC and percent inhibition of endothelial cell 3HTdR uptake induced by the same serum (r = 0.94, p less than 0.001). These studies suggest that ECA is mediated in vitro via a protease mechanism associated with a functional deficiency of protease inhibitors in scleroderma sera.

Demonstration of kallikrein-like protease activity in nonactivated plasma of patients with Cooley's anemia

Routine evaluation of 12 children with Cooley's anemia revealed that each one had a prolonged partial thromboplastin time. However, prothrombin time and thrombin time were within the normal range. Specific assays demonstrated low levels of the four contact factors: factors XI, XII, prekallikrein, and high molecular weight kininogen. Further investigation revealed activity against para-nitroanilide peptide substrates in unactivated plasma from all 12 patients. Following gel filtration on Sephadex G200, the activity emerged in one peak in the void volume, indicating a molecular weight of greater the 500,000. Activity was greatest against H-D-Pro-Phe-Arg-pNA, the substrate for plasma kallikrein, and was inhibited by diisopropyl fluorophosphate and trasolyl. It was unaffected by hirudin, soy bean trypsin inhibitor, and lima bean trypsin inhibitor. It was destroyed by heating at 56 degrees C. Specific antisera against human prekallikrein and human alpha-macroglobulin did not reduce the activity. It is concluded that a high molecular weight kallikrein-like protease, is present in the plasma of these patients. It is postulated that it is released into the circulation from tissue as a result of damage due to iron overload. It is further postulated that this protease brings about in vivo activation of the contrast factors, resulting in a fall in their circulating levels.

Pancreatitis with arthropathy and subcutaneous fat necrosis. Evidence for the pathogenicity of lipolytic enzymes

The occurrence of peripheral fat necrosis in exceptional cases of pancreatic disease is not well understood. We report studies on such a patient with arthropathy and subcutaneous nodules. Examination of serial serum samples demonstrated striking elevations of the pancreatic enzymes phospholipase A, 3-3.4 units/ml (normal 0.17-0.41); lipase, 7-39 Sigma-Tietz units/ml (normal less than 1); immunoreactive trypsin, 912-3,207 ng/ml (normal 12-41). The distinguishing characteristic of the patient's synovial fluid was a marked elevation of hydrolized fatty acids (680 mg/dl versus 19 +/- 19 in control inflammatory joint fluids). Synovial fluid fatty acid distribution was identical to values for tissue fat. In contrast, serum fatty acid levels and distribution were normal. No associated proteinase inhibitor or significant immunologic abnormality was detected. Certain properties of adipose cells and lipolytic enzymes may help explain the characteristically selective necrosis of fat cells observed in this syndrome.

Liberation of immunoreactive somatomedin-C from its binding proteins by proteolytic enzymes and heparin

Most of the somatomedin in serum exists as a high molecular weight complex (approximately equal to 140,000) composed of binding protein subunits and small molecular weight somatomedin. These binding proteins may interfere with measurements of the somatomedins by various radioligand assays. In a companion paper, we reported that when serum is incubated at neutral pH the detectability of the somatomedin-C (Sm-C) is increased. Using gel chromatography, however, it was not possible to demonstrate release of free Sm-C from the macromolecular complex. In the studies reported here, incubation of heparinized plasma at pH 7.4 followed by gel chromatography in a heparin-containing buffer caused 70-80% of the immunoreactive Sm-C to shift from the gamma-globulin region to a molecular weight which approximates that of free Sm-C. This conversion is a time-dependent process which is inhibited by the proteolytic enzyme inhibitor antipain. Similar changes in the elution profile of Sm-C were observed when heparinized plasma was acidified and chromatographed in heparin. These findings suggest that 1) at neutral pH, serum proteolytic enzymes reduce the affinity between small molecular weight Sm-C and its binding proteins. 2) At acid pH, a similar effect is observed. 3) In the presence of heparin, reassociation of these components does not occur. These results suggest a possible mechanism whereby the somatomedin macromolecular complex could be disrupted so that small molecular weight somatomedin is made available to tissues.

Effect of in vitro action of serum proteases or exposure to acid on measurable immunoreactive somatomedin-C in serum

The proportion of immunoreactive somatomedin-C (IR-Sm-C) in blood that is available for measurement in the RIA is influenced by whether the sample is processed as serum or plasma, by how promptly the sample is chilled and frozen, by whether the reaction is carried out in glass or polystyrene tubes and by whether the incubation mixture contains protamine or heparin. Although protamine buffers and polystyrene tubes increase the availability of purified somatomedin-C (Sm-C), they decrease the detectability of Sm-C in serum. By incubating serum at neutral or acid pH, this IR-Sm-C can be made available for measurement, suggesting that incubation alters the nature of the linkage between Sm-C and its binding proteins or causes a conformational change in the binding protein, resulting in greater exposure of IR-Sm-C. The increment in measurable IR-Sm-C that occurs at neutral pH appears to be due to the action of proteolytic enzymes since it is time, temperature, and pH dependent and is inhibited by a variety of protease inhibitors and chelating agents. The increment which occurs at acid pH is not inhibited by chelating agents or elevated temperature and must be due in part to acid hydrolysis of Sm-C and its binding proteins. However, since the acid-induced increment is optimal within a narrow pH range and falls off sharply below pH 3.5, acid proteases may also be involved. These observations, which provide insight into the nature of the serum proteins with which Sm-C is associated, bear on the interpretation of results of serum somatomedin measurements carried out with different methods. They also may aid in delineating the mechanisms by which the somatomedin contained in the macromolecular complex in serum is made available to tissues.

Studies on the enzymatic degradation of beta-casomorphins

beta-Casomorphins (beta-CMs), although known to be highly resistant to proteolytic enzymes, are demonstrated to be rapidly degraded in bovine or rat plasma. Degradation of these peptides consisting of the amino acid sequence TYR-PRO-PHE-PRO-GLY-PRO-ILE and C-terminally shortened fragments thereof, may be due to an enzyme identical with or similar to the dipeptidyl-peptidase IV (DP IV) which is known to cleave dipeptide fragments from the N-terminus of peptides after proline residues. This assumption is compatible with the finding that beta-casomorphin (beta-CM) analogues in which the proline residue in position two has been replaced by D-alanine, seem to be completely resistant to enzymatic attack in the plasma.

Proteolytic activation of influenza WSN virus in cultured cells is performed by homologous plasma enzymes

The effect of chick embryo allantoic fluid, porcine plasma or canine plasma on virus progeny was studied in cultured chicken, porcine and canine cells infected with influenza WSN virus. Cells incubated either without plasma or with heterologous plasma produced virions which had uncleaved haemagglutinin and low infectivity. Cells incubated with homologous plasma produced highly infectious virions with cleaved haemagglutinin. Little increase of progeny virus infectivity was observed in canine cell-porcine plasma and porcine cell-canine plasma host systems. The addition of protease inhibitors to culture containing homologous plasma, in particular epsilon-amino-n-caproic acid (an inhibitor of plasminogen activation), suppressed cleavage of haemagglutinin, and virions which had uncleaved haemagglutinin and low infectivity were produced by the cells. It therefore follows that haemagglutinin cleavage and activation of influenza WSN virus infectivity in cultured cells is most efficiently performed by homologous plasma proteolytic enzyme(s). The mechanism of selective plasma-mediated influenza virus proteolytic activation in homologous cells is discussed.

[Activity of peptide hydrolases and trypsin inhibitor in psoriasis]

Distinct activation of alkaline and trypsinlike proteinases, leucine aminopeptidase as well as inhibition of the antitryptic activity (ATA) occurred in the area of impaired skin and in peripheral blood of patients with psoriasis as shown by clinico-laboratory examinations. These data suggest the epidermal origin of the substance inhibiting the enzymatic activity. After administration into animals of homogenates of impaired skin obtained from the patients an increase in BAEE-esterase activity and a decrease in the ATA were observed in blood serum. A reverse correlation was found between the ATA of parakeratotic layer and amount of eosinophils in peripheric blood.

Tubulin tyrosinolation in human polymorphonuclear leukocytes: studies in normal subjects and in patients with the Chediak-Higashi syndrome

We have recently reported a specific dose-dependent stimulation of posttranslational incorporation of tyrosine into tubulin alpha-chains of rabbit peritoneal leukocytes as induced by the synthetic peptide chemoattractant formyl-methionyl-leucyl-phenylalanine (FMLP). The present study reports a similar, specific stimulation of tubulin tyrosinolation in human polymorphonuclear leukocytes (PMN). When compared to normal PMN, both the resting and FMLP-stimulated levels of posttranslational tyrosine incorporation were two- to threefold higher in PMN of three patients with the Chediak-Higashi syndrome (CHS). The concentration of cellular tubulin and the specific activity of tubulin tyrosine ligase were similar in PMN of CHS patients and normal donors and resembled that of other non-neuronal cells. The high levels of tyrosine incorporation in PMN of CHS patients were normalized by the administration of ascorbate, both in vitro and in in vivo experiments. In vitro addition of ascorbate also inhibited the FMLP-induced stimulation of tyrosine incorporation in both normal and CHS cells. Normalization of higher levels of tyrosine incorporation in PMN of CHS patients and the inhibition of FMLP-induced stimulation of tubulin tyrosinolation in normal and CHS cells as observed with ascorbate could also be affected by other reducing agents such as reduced glutathione, cysteine, or dithiothreitol. These results suggest a possible relationship between cellular redox and tubulin tyrosinolation in PMN.

Systematic study of the hydrolysis of 4-methylumbelliferylguanidinobenzoate in plasma from patients with cystic fibrosis and controls

In contrast to the original reports by others, the hydrolysis of 4-methylumbelliferylguanidinobenzoate ((MUGB), and active-site titrant of serine proteases, was found not to be significantly different in plasma samples from patients with cystic fibrosis (CF), obligate heterozygotes, and normal controls. Since the steady-state turnover of substrate is the dominant term of MUGB hydrolysis, the assay in its present form does not meet the requirements of an active-site titration. The reproducibility and reliability of the assay are hampered by (1) high blank values due to non-specific hydrolysis, (2) the absence of a defined endpoint of the incubation, (3) the non-linearity of the assay with respect to plasma concentration, (4) the temperature-dependent evolution of esterase activity during incubation, and (5) most importantly the loss of activity during storage of plasma samples. Cleavage of MUGB catalysed by the imidazole ring of histidine accounts for a significant portion of the activity in plasma.

[Acid-stable protein proteinase inhibitors of mammals. Structure, properties, biological role]

The literary and experimental data on some new natural proteinase inhibitors derived from their precursor, plasma inter-alpha-trypsin inhibitor, or synthesized by secretory glands and mucous membranes of various mammalian organs and referred to as "acid-stable inhibitors" are discussed. The physico-chemical properties, primary structure, specificity and biological functions of these inhibitors are described. The mechanism of interaction of the acid-stable inhibitors with human granulocyte proteinases is discussed in terms of their pathophysiological importance. The antiinflammatory role of locally synthesized acid-stable inhibitors from genital and respiratory tracts and the role of these inhibitors in fertilization are discussed. The barrier function of the acid-stable inhibitors which, similar to that of the plasma labile inhibitors (alpha 1-antitrypsin, alpha 2-macroglobulin, etc.), restricts the destructive action of leukocyte proteinases under normal and pathological conditions is considered.

Blood elastolytic activity in patients with aortic aneurysm

The question of why obstruction of the aorta (Leriche's syndrome) develops in some patients with severe atherosclerosis of the abdominal aorta while an abdominal aortic aneurysm occurs in others was examined. Significant differences in age, height, weight, mortality, and subsequent operative treatment were found between 335 patients with Leriche's syndrome and 103 patients with abdominal aortic aneurysm. Almost all in both groups smoked and demonstrated leukocytosis. In smokers with aneurysm, circulating serum elastolytic activity and leukocytic granular elastolytic activity were significantly increased, whereas serum antiproteolytic capacity was reduced. These results indicate that the development of abdominal aortic aneurysm in patients who smoke correlates with an abnormal homeostasis between proteolytic and antiproteolytic activity.

Intracellular protease activity in glucocorticoid-mediated thymolysis

The effect of dexamethasone on rat thymus protease activity was tested by following hydrolysis of 14C-labeled globin. Most of the proteolytic activity was located in the cytoplasmic fraction obtained from either whole thymus homogenates or isolated thymic lymphocytes. The protease showed an acid pH optimum and was inhibited by pepstatin and leupeptin. The particulate fractions exhibited only a negligible proteolytic activity throughout the pH range tested. The administration of dexamethasone (9 alpha-fluoro-11 beta, 17,21-trihydroxy-16 alpha-methylpregna-1,4-diene-3,20-dione; 1 mg/kg, ip) to adrenalectomized castrated rats caused a marked increase in the acid protease activity assayed in the cytosol of whole thymus or thymic lymphocytes, with no change in the particular enzyme activity. The sensitivity of the cytosolic enzyme to several protease inhibitors was unchanged after glucocorticoid treatment. Minimal effective dexamethasone doses for thymic involution and increases in protease activity were 0.01 and 0.1 mg/kg BW, respectively. The half-maximal thymolytic effect was obtained at 0.05 mg/kg dexamethasone, while the half-maximal effect on the protease was observed only at 0.30 mg/kg dexamethasone. In contrast, in vitro exposure of isolated thymic lymphocytes to 8.3 X 10(-6) M dexamethasone failed to affect the acid protease activity in the cytosol, but produced a marked time-dependent cytolytic response. These observations suggest that glucocorticoid-induced cytolysis in rat thymic lymphocytes is not mediated by a direct effect of the hormone on endogenous proteases.

Amino acid-p-nitroanilide and -beta-naphthylamide cleaving activities in rat serum

Determination of proteolytic activities gains increasing importance for the diagnosis of various pathologic conditions. Many questions can only be solved with the aid of experiments with animals. In preparation of such studies the pattern of the enzymatic hydrolysis of 20 amino acid-p-nitroanilides and one -beta-naphthylamide by normal rat serum was measured. The pH dependences of the single reactions are reported as well as their sensitivity to the action of ethylenediaminetetraacetic acid, dithioerithrol, and puromycin. Additionally, it is shown that collecting of the blood by cardiac puncture and preparation of the native plasma is the best way to get reproducible results.

Nonspecific protease and elastase activities in rat leukocytes

Extracts were prepared from rat peritoneal leukocytes obtained 4 h after glycogen injection and assayed for proteolytic enzyme activities against various substrates. The substrates used included acid-denatured bovine hemoglobin, bovine serum albumin, a partially purified preparation of rat pulmonary basement membrane, bovine neck ligament elastin, and an artificial substrate with elastase specificity. A high level of activity was observed when hemoglobin was used as the substrate. The serum albumin and basement membrane preparation were also readily hydrolyzed by the leukocyte extract. In contrast, the native elastin and synthetic elastase substrate were much more resistant. Although the leukocyte extract demonstrated little intrinsic elastase activity, when it was mixed with a commercial hog pancreatic elastase preparation, it greatly potentiated the elastolytic activity, suggesting the activation of a latent enzyme.