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Biomedical subjects

M Schapira

Publications and source records attributed to M Schapira.

At least 19 recordsLinked to original sources
PubMed1992

[Acute paraplegia and intramedullary cavitation in a patient with pulmonary tuberculosis].

This 42-year-old male patient voluntarily discontinued treatment for lung TBC and twenty days later developed acute paraplegia. Magnetic resonance imaging (MRI) demonstrated a large intramedullary cavity extending from T2 to the conus medullaris. Having resumed anti-TBC treatment, the patient progressed favourably, despite any change in cavity size. Tuberculous meningitis may be complicated by the appearance of intramedullary cavities by two distinct mechanisms: 1) adhesive arachnoiditis at the skull base with obstruction of Luschka and Magendie foramina, followed by hydrocephalus and hydromyelia; and 2) spinal cord arachnoiditis with the development of arachnoidal and intramedullary cysts. In either case, symptoms are of late presentation. To the best of our knowledge, this is the first report in the literature of lung tuberculosis associated with syringomyelia but without basal arachnoiditis. Acute clinical presentation with paraplegia is exceptional.

Acute Disease↗
PubMed1992

Structure and mechanism of action of serpins.

Serpins have a central role in regulating proteolysis in blood coagulation, fibrinolysis, and inflammation. Congenital serpin deficiencies cause specific clinical syndromes such as thrombosis with antithrombin III deficiency or emphysema with alpha 1-antitrypsin deficiency. Acquired serpin abnormalities have also been reported, for example, increased PAI-1, which is believed to represent a major risk factor for the development of thromboembolic complications. This article has reviewed the structure/function relationships of serpins and have presented ideas concerning their mechanism of action. The implications of this information for designing drugs that could interfere with serpin function has also been described, and mention has been made of the therapeutic potential of such compounds.

Humans↗
PubMed1991

Mechanism of serpin action: evidence that C1 inhibitor functions as a suicide substrate.

Serpins form a family of structurally related proteins, many of which function in plasma as inhibitors of serine proteases involved in inflammation, blood coagulation, fibrinolysis, and complement activation. To further characterize the mechanism by which serpins inhibit their target enzymes, we have studied the effect of temperature on the reaction of C1 inhibitor and the serine protease plasma kallikrein. At both 38 and 4 degrees C, C1 inhibitor (Mr 105,000) is cleaved by alpha-kallikrein (Mr 85,000 and 88,000) at position P1 (Arg444) of the reactive center, a reaction that leads to the formation of a covalent bimolecular enzyme-serpin complex (Mr 195,000) and cleaved but uncomplexed serpin (Mr 95,000). Between 38 and 4 degrees C, the product distribution is temperature-dependent, with more cleaved C1 inhibitor (Mr 95,000) formed at lower temperatures and correspondingly less Mr 195,000 complex. Studies employing intrinsic tryptophan fluorescence and 1H NMR spectroscopy show that this behavior is not caused by temperature-dependent conformational changes of kallikrein or C1 inhibitor. C1 inhibitor also behaves in this manner with the light chain of kallikrein and, to a lesser extent, with plasmin and C1s. These data are best explained by a branched reaction pathway, identical with the scheme describing the mechanism of action of suicide substrates. This scheme involves the formation of an enzyme-inhibitor intermediate, which can be stabilized into a covalent complex and/or dissociate into free enzyme and cleaved inhibitor, depending on the reaction conditions.

Complement C1 Inactivator Proteins↗
PubMed1991

Substrate properties of C1 inhibitor Ma (alanine 434----glutamic acid). Genetic and structural evidence suggesting that the P12-region contains critical determinants of serine protease inhibitor/substrate status.

The serine protease inhibitor (serpin) C1 inhibitor inactivates enzymes involved in the regulation of vascular permeability. A patient from the Ma family with the genetic disorder hereditary angioedema inherited a dysfunctional C1 inhibitor allele. Relative to normal plasma, the patients's plasma contained an additional C1 inhibitor immunoreactive band, which comigrated with normal C1 inhibitor cleaved by plasma kallikrein, C1s, or factor XIIa. C1 inhibitor Ma did not react with a monoclonal antibody to a neoepitope that is present in complexed and cleaved normal C1 inhibitor, suggesting conformational differences between cleaved normal C1- inhibitor and cleaved C1 inhibitor Ma. Molecular cloning and sequencing of exon 8 of the C1 inhibitor Ma allele revealed a single C to A mutation, changing alanine 434 to glutamic acid. Ala 434 of C1 inhibitor aligns with the P12 residue of the prototypical serpin alpha 1-antitrypsin. The P12 amino acid of all inhibitory serpins is alanine, and it is present in a highly conserved region on the amino-terminal side of the serpin-reactive center loop. Whereas normal C1 inhibitor expressed by transfected COS-1 cells formed complexes with and was cleaved by kallikrein, fXIIa, and C1s, COS-1-expressed Ala434---Glu C1 inhibitor was cleaved by these enzymes but did not form complexes with them. These results, together with evidence from other studies, suggest that serpin protease inhibitor activity is the result of protein conformational change that occurs when the P12 region of a serpin moves from a surface location, on the reactive site loop of the native molecule, to an internal location within sheet A of the complexed inhibitor.

Amino Acid Sequence↗
PubMed1991

[Unexplained fever or inflammatory syndrome. Diagnostic value of liver puncture-biopsy].

The value of transcutaneous biopsy of the liver was assessed in a series of 110 cases of fever of unknown origin or of unexplained inflammatory syndrome. Liver histology was useful to the ultimate etiological diagnosis in 12 cases (11 per cent). The result of a transcutaneous biopsy of the liver was considered an essential aid to the ultimate diagnosis in 7 of these 12 cases. A hepatic lesion regarded as useless for the ultimate diagnosis was present in 16 cases (14.5 per cent). In the other cases, hepatic histology was normal or showed a non-specific reactive hepatitis. Unicteric cholestasis was present in 73 per cent of the cases but was of no predictive value for the detection of a useful hepatic lesion. On the other hand, serum transaminase levels were significantly higher when a useful lesion of the liver was observed.

Adolescent↗
PubMed1990

Reactivity of alpha 1-antitrypsin mutants against proteolytic enzymes of the kallikrein-kinin, complement, and fibrinolytic systems.

Increased extracellular proteolysis because of unregulated activation of blood coagulation, complement, and fibrinolysis is observed in thrombosis, shock, and inflammation. In the present study, we have examined whether the plasma kallikrein-kinin system, the classical pathway of complement, and the fibrinolytic system could be inhibited by alpha 1-antitrypsin reactive site mutants. Wild-type alpha 1-antitrypsin contains a Met residue at P1 (position 358), the central position of the reactive center. It did not inhibit plasma kallikrein, beta-factor XIIa, plasmin, tissue-type plasminogen activator (t-PA), or urokinase. In contrast, these serine proteases were inhibited by alpha 1-antitrypsin Arg358. For the inhibition of C1s, a double mutant having Arg358 and a Pro----Ala mutation at P2 (position 357) was required. This double modification was made because C1-inhibitor, the natural inhibitor of C1s, has Arg and Ala residues at positions P1 and P2. Plasminogen activator inhibitor 1, the natural inhibitor of t-PA, also has Arg and Ala residues at positions P1 and P2. In a purified system, alpha 1-antitrypsin Ala357-Arg358 was 150-fold less efficient against C1s than C1-inhibitor and 27,000-fold less efficient against t-PA than plasminogen activator inhibitor-1. In plasma, 2.3 microM alpha 1-antitrypsin Ala357-Arg358 reduced by 65% the formation of a complex between kallikrein and C1-inhibitor following activation of the intrinsic pathway of blood coagulation by kaolin. Furthermore, after supplementation by 2.0 microM alpha 1-antitrypsin Ala357-Arg358, zymographic analysis showed that the majority of the free t-PA of normal plasma formed a bimolecular complex with the double mutant. In contrast, 3.4 microM alpha 1-antitrypsin Ala357-Arg358 did not prevent the activation of the classical pathway of complement observed when normal serum is supplemented with anti-C1-inhibitor F(ab')2 fragment. These results demonstrate that alpha 1-antitrypsin Ala357-Arg358 has therapeutic potential for disorders with unregulated activation of the intrinsic pathway of blood coagulation and the fibrinolytic system; however, the double mutant is not an efficient inhibitor for the classical pathway of complement.

Amino Acid Sequence↗
PubMed1990

[Hypoxic hepatitis. Prospective, clinical and hemodynamic study of 45 cases].

The authors report 45 episodes of centrilobular liver cell necrosis, called ischemic hepatitis, in 43 cardiac patients. In 75 percent of the episodes, centrilobular liver cell necrosis was preceded by a period of progressive deterioration of myocardiac function. In 100 percent of the episodes, liver cell necrosis occurred after an acute clinical event inducing a transient fall of cardiac output. Shock was observed in only 47 percent of the episodes. The biological hallmarks of this centrilobular liver cell necrosis were a massive increase in serum aminotransferase levels and in 85 percent of the episodes, a decrease in the prothrombine time below 50 percent of control level. The mortality rate, 15 days after admission, was 42 percent. Prognosis was mainly related to cardiac function. The hemodynamic comparison between the 45 episodes of centrilobular liver cell necrosis and 22 cases of cardiogenic shock without liver cell necrosis showed that, besides hepatic ischemia, passive venous congestion of the liver and arterial hypoxemia were also involved in the onset of liver cell necrosis in these cardiac patients. Among these 45 episodes of liver cell necrosis of cardiac origin, a unique case of hepatic necrosis secondary to major hypoxemia and passive venous congestion, despite an high cardiac output was observed and is reported in detail. Accordingly, the appellation "hypoxic hepatitis" seems to be more appropriate than "ischemic hepatitis".

Adult↗
PubMed1989

Studies on the human plasma kallikrein-kinin system: alpha-kallikrein does not directly activate blood neutrophils.

alpha-Kallikrein was prepared using an improved purification protocol (Burger, D., Schleuning, W.-D. and Schapira, M. (1986) J. Biol. Chem. 261, 324-327) and was employed to reevaluate our previous observations indicating that kallikrein activates blood neutrophils by a mechanism requiring an uncleaved Mr 52,000 NH2-terminal heavy chain. Cellular activation was evaluated by measuring neutrophil aggregation, release of both vitamin B12 binding capacity and myeloperoxidase, and generation of superoxide anion. Whereas all these indicators were evoked by exposing neutrophils to f-Met-Leu-Phe, phorbol myristate acetate, zymosan activated serum, or the calcium ionophore A 23187, we show here that neutrophils incubated with alpha-kallikrein remained unactivated. Moreover, we demonstrate that this lack of activation is accompanied by an inability of neutrophils to specifically bind alpha-kallikrein.

Binding, Competitive↗
PubMed1989

Involvement of the kallikrein-kinin system in the antihypertensive effect of the angiotensin converting enzyme inhibitors.

1. Studies were performed in normal subjects and in rats to assess the effect of angiotensin converting enzyme (ACE) inhibition on the kallikrein-kinin system. As ACE is identical to kininase II, one of the enzymes physiologically involved in bradykinin degradation, bradykinin may be expected to accumulate during ACE inhibition. 2. A competitive antagonist of bradykinin was used to explore in unanaesthetized rats the contribution of circulating bradykinin to blood pressure control under ACE inhibition. 3. No evidence was found for a role of this vasodilating peptide in the blood pressure lowering effect of acute ACE inhibition. 4. The plasma activity of carboxypeptidase N (= kininase I), another pathway of bradykinin degradation, remained intact during a 1 week course of treatment with an ACE inhibitor in normal subjects. This therefore indicates that bradykinin formed during ACE inhibition can still be metabolized.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1989

Plasminogen activators in dextran sulfate-activated euglobulin fractions: a molecular analysis of factor XII- and prekallikrein-dependent fibrinolysis.

To elucidate the mechanism by which activation of the contact system of blood coagulation leads to expression of fibrinolytic activity, we have determined the molecular characteristics of the plasminogen activators present in dextran sulfate-treated euglobulin fractions by electrophoretic-zymographic analysis and specific immunoadsorption. In addition to free and protease inhibitor-bound tissue-type plasminogen activator (t-PA), dextran sulfate precipitates of euglobulins contained the complex formed between plasma kallikrein and C1-inhibitor, an indicator of prekallikrein activation. These precipitates also contained substantial fibrinolytic activity related to urinary-type plasminogen activator (u-PA). Autoradiographic analysis was then used to evaluate the cleavage of 125I-single-chain u-PA (prourokinase) in dextran sulfate euglobulins as well as after exposure to kallikrein or beta-factor XIIa. This analysis supported the conclusion that plasma kallikrein-mediated cleavage and activation of single-chain u-PA is the mechanism operative for the development of lytic activity in euglobulin precipitates following activation of the contact system.

Blood Proteins↗
PubMed1988

A prospective study of platelets and plasma proteolytic systems during the early stages of Rocky Mountain spotted fever.

We prospectively examined early changes in platelets and plasma proteolytic systems in 12 vaccinated and 6 unvaccinated volunteers in whom Rocky Mountain spotted fever developed after challenge with Rickettsia rickettsii. The platelet counts declined while the plasma concentration of beta-thromboglobulin and the ratio of beta-thromboglobulin to platelet factor 4 increased, indicating in vivo activation of platelets. Plasma levels of antithrombin III decreased and levels of fibrinopeptide A increased, indicating in vivo activation of the coagulation system. Plasma fibrinogen levels peaked at 24 hours and gradually declined; this is consistent with the behavior of fibrinogen as an acute-phase reactant. Prolongation of the prothrombin time and a decrease in plasma levels of factor VII in the absence of evidence of liver injury suggested possible activation of the extrinsic pathway of coagulation. A decline in plasma prekallikrein levels with an increase in plasma C1-inhibitor-kallikrein complexes suggested activation of kallikrein, probably through the intrinsic coagulation system. Elevations in levels of plasma fibrin-degradation products and alpha 2-antiplasmin-plasmin complexes with declines in plasminogen and alpha 2-antiplasmin levels provided evidence of activation of the fibrinolytic system. Elevated plasma levels of tissue plasminogen activator and von Willebrand factor reflected endothelial stimulation. Thus, even early in the course of Rocky Mountain spotted fever that is treated promptly, there is activation of platelets, coagulation pathways, and the fibrinolytic system. These changes may be related to endothelial perturbation, a major pathogenetic mechanism in the disorder.

Antithrombin III↗
PubMed1988

Fibronectin degradation products containing the cytoadhesive tetrapeptide stimulate human neutrophil degranulation.

We investigated whether adhesive glycoproteins, such as fibronectin or fibrinogen, could function to provide a nidus for neutrophil degranulation. Elastase release in recalcified plasma was normal in afibrinogenemic plasma, but 73% less in plasma depleted of fibronectin. Proteolytic digests of fibronectin, but not intact fibronectin (50-1,000 micrograms/ml), induced a concentration-dependent release of neutrophil elastase and lactoferrin. MAbs N293, which recognized the mid-molecule of fibronectin, N294, which was directed toward the 11-kD cell adhesive fragment, and N295, generated against the amino terminal of the 11-kD fragment, inhibited the release of elastase by 7, 24, and 60%, respectively. The cytoadhesive tetrapeptide portion of fibronectin, Arg-Gly-Asp-Ser (250-1,000 micrograms/ml), released 1.94 +/- 0.10 micrograms/ml of elastase from 10(7) neutrophils, in contrast to the lack of release by the control hexapeptide, Arg-Gly-Tyr-Ser-Leu-Gly. Plasmin appeared to be the enzyme responsible for fibronectin cleavage, since neutrophil elastase release in plasma that had been depleted of plasminogen was decreased and reconstitution of plasminogen-deficient plasma with purified plasminogen corrected the abnormal release. Plasmin cleaved fibronectin to multiple degradation products, each less than 200 kD. This fibronectin digest released 1.05 microgram/ml of elastase from 10(7) neutrophils. We suggest that the activation of plasminogen leads to the formation of fibronectin degradation products capable of functioning as agonists for neutrophils.

Antibodies, Monoclonal↗