Spontaneous neurological recovery after stroke and the fate of the ischemic penumbra

We prospectively tested the hypothesis that early recovery after ischemic stroke depends on the ultimate survival of functionally impaired, critically ischemic (i.e., "penumbral") tissue. From a series of 26 consecutive patients studied with positron emission tomography within 18 hours of first-ever stroke in the middle cerebral artery territory, all 11 survivors to the 2-month end point who exhibited increased oxygen extraction fraction were declared eligible. The positron emission tomographic images were compared to ultimate infarction defined by computed tomography performed during the chronic stage. The penumbra (operationally defined by increased oxygen extraction fraction and divided outcome despite uniformly reduced cerebral blood flow) was individually detected in 10 of the 11 patients; cerebral blood flow ranged from 7 to 17 ml/100 gm x min, consistent with that found in monkey studies. The volume of the penumbra that escaped infarction was highly correlated with neurological recovery (p < 0.04 to p < 0.0001, depending on the scale used). This longitudinal study is the first to characterize the penumbra in humans and to document one mechanism strongly influencing recovery; the surviving penumbra may offer opportunities for secondary perifocal neuronal reorganization. Therapeutic measures to prevent infarction of the penumbra (up to 16 hours in this series) may have reduced residual neurological impairment. Mapping the extent of the penumbra, according to prospective criteria, may allow one to predict each patient's potential for recovery, and to select the most appropriate candidates for therapeutic trials.

Von Willebrand factor: molecular size and functional activity

Von Willebrand factor (vWF) is the largest protein found in plasma. It circulates in blood as a series of multimers ranging in size from 500 to 20,000 kDa. The variable molecular weight of vWF is due to differences in the number of subunits comprising the protein. vWF mediates platelet adhesion to subendothelium of the damaged blood vessel. Only the largest multimers are hemostatically active. Each vWF subunit contains binding sites for collagen and for platelet glycoproteins GPIb and GPIIb/IIIa. Multiple interactions of repeating binding sites in vWF multimers with adhesive protein(s) of the subendothelium and with receptors on the platelet surface lead to "irreversible" binding of platelets to the exposed subendothelium. Functional properties of vWF are typical of multisubunit proteins encoded by autosomal loci. The phenotype of von Willebrand disease is determined by the properties of the dysfunctional subunits which become incorporated into heteropolymeric forms of vWF. Absence of large vWF multimers, seen in type 2A von Willebrand disease and in myeloproliferative disorders, is associated with bleeding tendency. On the other hand, in patients with vWF multimers of supranormal size, as they occur in thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), there is an increased risk of thrombosis. Proteolytic enzyme(s) are involved in physiologic regulation of the polymeric size of vWF. We have purified from human plasma a protease cleaving vWF at the same peptide bond that is also cleaved in vivo. vWF was quite resistant against the protease in a physiologic buffer but was degraded at low salt concentration or in the presence of 1 M urea. It appears that a conformational change in the vWF molecule exposes the specific protease-sensitive peptide bond and thus enhances degradation of vWF multimers. In some variants of type 2A vWF, the cleavage site in the vWF subunit is more susceptible to proteolytic degradation than in normal vWF, whereas in patients with TTP or HUS the protease activity may be suppressed. vWF-degrading protease plays an important role in pathogenesis of congenital or acquired disorders of hemostasis and thrombosis.

Partial purification and characterization of a protease from human plasma cleaving von Willebrand factor to fragments produced by in vivo proteolysis

Proteolytic cleavage of von Willebrand factor (vWF) takes place in the circulating blood of healthy subjects and is increased in some patients with von Willebrand disease type 2A. The hemostatically active large vWF multimers are degraded to smaller less active forms. It has been suggested that the polypeptide subunit of vWF is cleaved at the peptide bond 842Tyr-843Met. We purified (approximately 10,000-fold) from human plasma a vWF-degrading protease, using chelating Sepharose, hydrophobic interaction chromatography, and gel filtration. The enzyme was found to be virtually absent in the platelet lysates obtained by repeated freezing and thawing. The proteolytic activity was associated with a high molecular weight protein (approximately 300 kD) as judged by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. vWF was resistant against the protease in a neutral buffer at physiological ionic strength but became degraded at low salt concentration or in the presence of 1 mol/L urea. No degradation of human fibrinogen, bovine serum albumin, of calf skin collagen by the purified protease was noted under the same experimental conditions. Proteolytic activity showed a pH optimum at 8 to 9 and was strongly inhibited by chelating agents, whereas only slow inhibition was observed with N-ethylmaleimide. There was no inhibition by iodoacetamide, leupeptin, or serine protease inhibitors. The best peptidyl diazomethyl ketone inhibitor was Z-Phe-Phe-CHN2. Activation by divalent metal ions was found to increase in the following order: Zn2+ approximately Cu2+ approximately CD2+ approximately Ni2+ approximately Co2+ <Mn2+ <Mg2+ <Ca2+ <Sr2+ <Ba2+. The observed properties of the vWF-degrading enzyme differ from those of all other hitherto described proteases. Purified vWF was incubated with the protease, and the degraded material subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis after disulfide reduction. The size, amino acid composition, and amino terminal sequence of the reduced fragments confirmed that the peptide bond 842Tyr-843Met had been cleaved, ie, the same bond that has been proposed to be cleaved in vivo.

Binding of calcium ions and their effect on clotting of fibrinogen Milano III, a variant with truncated A alpha-chains

Calcium ions are known to be required for normal polymerisation of fibrin monomers. Normal human fibrinogen has three high-affinity calcium binding sites. Two of these are located in the D-domains whereas the third binding site was tentatively assigned either to the E-domain or to the C-terminal part of the A alpha-chain. Furthermore, binding of calcium to the low-affinity binding sites (n > or = 10) facilitates fibrin monomer polymerisation. In several abnormally clotting fibrinogen variants, the polymerisation defect was partially normalised following addition of calcium ions. In this study, we show normal binding of calcium to fibrinogen Milano III, a homozygous fibrinogen variant with truncated A alpha-chains (A alpha 452 Gly-Pro-Asp-->Trp-Ser-Stop). These results confirm that the C-terminal parts of the A alpha-chains beyond residue 451 Ile are not involved in calcium binding. The thrombin time was severely prolonged and the final clot turbidity was strongly reduced in fibrinogen Milano III. Moreover, calcium ions did not significantly improve the abnormal clotting behavior of this dysfibrinogen. The polymerisation defect in fibrinogen Milano III appears to be due to truncated A alpha-chains as well as to the disulphide-linked albumin.

Early spontaneous hyperperfusion after stroke. A marker of favourable tissue outcome?

To clarify the relationships between early hyperperfusion (i.e. the hallmark of early, efficient recanalization in animal stroke models) and ultimate infarction, we have compared acute-stage perfusion PET images and chronic-stage CT scans in patients with middle cerebral artery (MCA) stroke. We used PET and the oxygen-15 (15O) equilibrium method to obtain cerebral blood flow (CBF), cerebral blood volume (CBV), oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen consumption (CMRO2) parametric images in 30 consecutive, still symptomatic, first-ever MCA territory stroke patients without sign of haemorrhage at admission CT scan. Each subject was studied twice, first within 5-18 h of stroke onset, and, in survivors, approximately 1 month later; a plain CT scan (co-registered with PET) was performed approximately 1 month after onset. Following initial screening based on acute-stage perfusion images, 10 survivors with focal hyperperfusion in the appropriate MCA territory confirmed by computer were declared eligible. In each patient, the topography and volume of both hyperperfusion and infarction (delineated on late CT scan) were recorded, and all PET parameters were obtained for both areas and both times. The hyperperfused areas affected the cortical MCA territory, often widely so and in a patchy fashion; they were topographically distinct from, and consistently larger than (P < 0.01, Wilcoxon sign test) the final infarcts, which were small and generally deep-seated. In none of the nine patients in whom it was successfully performed did transcranial Doppler reveal MCA stem occlusion. In the hyperperfused regions, the acute-stage perfusion, blood volume and oxygen consumption were significantly increased, and the OEF significantly reduced, while all these variables had significantly returned toward normality in the chronic-stage PET study. The ultimately infarcted area did not exhibit significant hyperperfusion in the acute stage. The areas with acute-stage hyperperfusion exhibited haemodynamic and metabolic abnormalities consistent with post-recanalization hyperperfusion, i.e. vasodilatation and "luxury perfusion'. Increased oxidative metabolism, previously reported only in animals, presumably reflects an overshoot of protein synthesis. The fact that the areas with hyperperfusion, though extensive, were topographically distinct from the infarcted region, suggests that spontaneous non-haemorrhagic hyperperfusion, when documented 5-18 h after onset, is a harmless and even perhaps beneficial phenomenon. These results have implications for clinical trials.

No association of APC resistance with myocardial infarction

Resistance to activated protein C (APC resistance) due to the factor V mutation 506 Arg-->Gln (factor V Leiden) is the most prevalent inherited risk factor for venous thromboembolism. Its association with arterial thromboembolic disease, however, is still controversial. In the present study we found no difference between the prevalence of APC resistance (assessed by the ratio of the aPTT with and without added APC) in 134 non-anticoagulated survivors of myocardial infarction and that in 100 controls of similar age and sex distribution (2.2% and 2.0%, respectively). Patients showed a significantly higher median value for the aPTT ratio than controls (2.85 and 2.66, respectively), a fact we could not explain by our data.

Functional circulation images by angio-CT in the assessment of small deep cerebral infarctions

We analyzed circulation time (rABCT) and vascular volume density images obtained by angio-computerized tomography (angio-CT) in 63 patients with small deep cerebral infarctions. Abnormalities in the rABCT image were found in 88% of the patients and in the vascular volume image in 48%. Two groups with different clinical pictures were picked out by rABCT changes: one with major-vessel involvement, the other with small-vessel involvement. The perfusional changes found were mainly due to altered vascular canalization rather than to altered vasomotility. The hemodynamic theory could explain the spatial relations between perfusion changes and CT hypodense areas without needing assumptions linking blood flow and metabolism.

Improved detection of proteolytically cleaved high molecular weight kininogen by immunoblotting using an antiserum against its reduced 47 kDa light chain

Several ligand blotting or immunoblotting assays for the detection of single-chain and proteolytically cleaved two-chain high molecular weight kininogen (HK) in whole plasma have been described. Since they may suffer from poor sensitivity for the light chain species of cleaved HK on reduced blots, an antiserum against the reduced and alkylated 47 kDa light chain of HK was raised in rabbits allowing improved immunodetection of HK species on blots of reduced electropherograms. This immunoblotting method is highly specific and sensitive, permitting detection of 0.2 ng single-chain HK or the light chains of 2 ng proteolytically cleaved HK in whole plasma. Thus, this immunoblotting technique is at least 50-100 times more sensitive than ligand blotting with radiolabelled factor XI overlay. A similar cleavage pattern was observed following in vitro activation of normal human plasma by dextran sulphate and after plasma kallikrein-induced proteolysis of purified HK. However, bands of different molecular weights were generated after HK had been cleaved by purified leukocyte elastase. During acute attack in a patient with hereditary angioedema, high levels of in vivo cleaved HK were noticed, whereas concentration of cleaved HK in plasma samples and synovial fluids from patients suffering from various inflammatory conditions were not substantially higher than those in normal plasma. During in vitro cold activation of plasma samples of pregnant women concomitant HK cleavage and plasma kallikrein generation were observed.

Towards the specification of consecutive steps in macromolecular lignin assembly

When Pinus taeda cell suspension cultures are exposed to 8% sucrose solution, the cells undergo significant intracellular disruption, irregular wall thickening/lignification with concomitant formation of an 'extracellular lignin precipitate. However, addition of potassium iodide (KI), an H202 scavenger, inhibits this lignification response, while the ability to synthesize the monolignols, p-coumaryl and coniferyl alcohols, is retained. Lignin synthesis (i.e. polymerization) is thus temporarily correlated with H202 generation, strongly implying a regulatory role for the latter. Time course analyses of extracellular metabolites leading up to polymer formation reveal that coniferyl alcohol, but not p-coumaryl alcohol, undergoes substantial coupling reactions to give various lignans. Of these, the metabolites, dihydrodehydrodiconiferyl alcohol, shonanin (divanillyl tetrahydrofuran) and its apparent aryl tetralin derivative, cannot be explained simply on the basis of phenolic coupling. It is proposed that these moieties are the precursors of so-called reduced substructures in the lignin macromolecule. This adds a new perspective to the lignin assembly mechanism.

A frameshift mutation in Exon V of the A alpha-chain gene leading to truncated A alpha-chains in the homozygous dysfibrinogen Milano III

An inherited dysfunctional fibrinogen variant, denoted as fibrinogen Milano III, was found in a 13-year-old girl suffering from recurrent venous thrombosis. Plasma of the patient exhibited prolonged thrombin time and Reptilase time. Polymerization of fibrin monomers in the presence and absence of calcium ions was strongly impaired. SDS-polyacrylamide gel electrophoresis of reduced fibrinogen showed normal B beta- and gamma-chains, whereas no normal A alpha-chain was detected in the proposita. Immunoblot analysis with the monoclonal antibody Y18, detecting an epitope within the stretch of amino acids A alpha 1-51, revealed an A alpha-chain of about 50 kDa with an intact amino terminus. Immunoblotting with antibodies directed against serum albumin demonstrated the presence of albumin covalently linked to fibrinogen via a disulfide bridge. The structural defect of fibrinogen Milano III was determined by sequence analysis of a single-stranded fragment of genomic DNA amplified by polymerase chain reaction. An insertion of a thymine in the exon V of the A alpha-chain gene after the triplet ATT coding for IleA alpha 451 altered the reading frame and caused premature termination of the protein synthesis (Trp452(TGG)-Ser453(TCC)-Stop454(TGA)). In both parents, normal and mutant alleles were established, leading to duplication of the sequence pattern after the thymine insertion site, whereas the proposita is homozygous for the new mutation in the fibrinogen A alpha-chain gene.

A new substitution, gamma 358 Ser-->Cys, in fibrinogen Milano VII causes defective fibrin polymerization

Fibrinogen Milano VII is a hereditary fibrinogen variant detected in a woman with no clinical symptoms of bleeding or thrombosis. Thrombin and reptilase clotting times were prolonged in six family members from three generations. Release of fibrinopeptides A and B was normal. Fibrin polymerization was strongly delayed both in the presence and in the absence of calcium. The structural defect was determined by sequence analysis of a 290-bp fragment of genomic DNA amplified by polymerase chain reaction and cloned in M13mp19. The triplet TCT coding for the amino acid residue gamma 358 was found to be replaced by TGT, resulting in the substitution gamma 358 Ser-->Cys. Immunoblot analysis demonstrated the presence of covalently linked fibrinogen albumin and fibrinogen (albumin)2 complexes. Albumin was released from fibrinogen Milano VII by limited reduction with 2-mercaptoethanol. Fibrin polymerization was not normalized after removal of albumin from fibrinogen Milano VII, suggesting that the delayed clot formation is not due to steric hindrance caused by bound albumin but by substitution of gamma 358 Ser by Cys itself. Our results indicate that the residue gamma 358 Ser is essential for normal expression of the carboxy terminal polymerization site on the fibrinogen gamma-chain.

Coagulation factor XII Locarno: the functional defect is caused by the amino acid substitution Arg 353-->Pro leading to loss of a kallikrein cleavage site

The dysfunctional coagulation factor XII (FXII) Locarno was purified from 2 L of the proposita's plasma. Studies to identify the molecular defect responsible for the lack of amidolytic and proteolytic activity of this FXII variant were performed. Amino acid sequence analysis of peptides obtained from FXII Locarno on activation with either trypsin or plasma kallikrein and dextran sulfate showed an amino acid substitution of Arg 353 by Pro. Thereby, the kallikrein cleavage site at Arg 353-Val 354 is lost. Although trypsin-activated FXII Locarno was fully cleaved at Arg 334-Asn 335 and at Arg 343-Leu 344, neither amidolytic nor proteolytic activity was generated. We conclude that proteolytic cleavage at Arg 343 in the absence of cleavage at Arg 353 is not sufficient to expose the enzymatic active site in FXII Locarno.

Fibrinogen Milano V: a congenital dysfibrinogenaemia with a gamma 275 Arg-->Cys substitution

An abnormal fibrinogen was discovered in a clinically asymptomatic woman from Italy. Routine coagulation studies revealed prolonged thrombin and reptilase clotting times and a discrepancy between the plasma fibrinogen levels determined by the clotting assay and electroimmunoassay. Release of fibrinopeptides A and B from fibrinogen Milano V by thrombin was normal. Fibrin polymerization was strongly delayed in the presence of EDTA and was partially corrected at physiological calcium concentration. Normal migration of mercaptolysed polypeptide chains was observed in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. Moreover, there was no apparent abnormality in the charge of the reduced chains of the variant fibrinogen, as judged by two-dimensional gel electrophoresis. A fragment of the gamma-chain gene coding for the amino acids 259-350 was amplified and cloned. The amino acid gamma 275 arginine was found to be substituted by cysteine. Immunoblotting analysis with a rabbit antiserum against human serum albumin indicated that albumin was not linked to the odd sulphydryl group of fibrinogen Milano V. Treatment of fibrinogen Milano V with cysteamine, that is surmised to convert the mutant cysteine to a positively charged lysine analogue, did not improve the clotting properties of fibrinogen Milano V.

Functional perfusion and blood-brain barrier permeability images in the diagnosis of cerebral tumors by Angio CT

We performed rapid sequential CT scanning following iv injection of a bolus of contrast medium and generated three functional images relating to intravascular circulation time (rABCT), vascular volume (Vv) density and blood-brain barrier (BBB) unidirectional constant uptake rate (Ki), respectively. This was accomplished by calculating the first mathematical moment of the monitored time-density curves about the injection time and from the multiple time graph analysis described by Patlack and co-workers. A satisfactory resolution was achieved, allowing separate appreciation of changes in rABCT both in large vessels and in tissue small vessels. Combined evaluation of rABCT and Vv images allowed us to differentiate between tumors.

Functional circulation and blood-brain permeability images by Angio CT in the assessment of cerebral ischemia

We performed rapid sequential computerized tomography (CT) scanning following i.v. injection of a bolus of contrast medium, and generated three functional images related, respectively, to intravascular circulation time (rABCT), vascular volume density (Vv) and blood-brain barrier (BBB) unidirectional constant uptake rate (Ki). This was accomplished by calculating the first mathematical moment of the monitored time-density curves about the injection time, and by the multiple time graph analysis described by Patlack and coworkers. A satisfactory resolution was achieved, allowing separate appreciation of changes in rABCT both at large vessels and at tissue small vessels. Combined evaluation of rABCT and Vv images allowed us to draw qualitative conclusions about blood flow and perfusion reserve.

Binding of alpha-thrombin to fibrin depends on the quality of the fibrin network

Binding of human alpha-thrombin to fibrin was studied in a purified system at pH 7.35, I 0.08 and 37 degrees C. Binding experiments with active thrombin resulted in fibrin clots of variable quality, depending on the thrombin concentration: opaque gels composed of 'coarse' network were produced at low thrombin concentrations, while increasing concentrations of thrombin led to more translucent 'fine' gels. Scatchard analysis showed a non-linear dependence of thrombin binding to fibrin, suggesting the existence in fibrin(ogen) of multiple classes of binding sites for thrombin. Binding of catalytic-site-inhibited thrombin was investigated in clots of defined quality produced with three different concentrations of a thrombin-like enzyme, batroxobin (EC 3.4.21.29). Straight lines of different slopes were established by Scatchard analysis of binding data at each fixed batroxobin concentration. These results favour a model according to which binding affinity for thrombin depends on the thickness of fibrin bundles. Labelled active-site-inactivated thrombin incorporated in batroxobin-induced clots was only sparingly released during incubation for 24 h in the presence of a 200-fold excess of unlabelled thrombin, indicating that thrombin binding to fibrin is not reversible and that Scatchard analysis is not appropriate for quantification of binding parameters. Irreversible binding of thrombin appears to reflect trapping of thrombin molecules within fibrin fibres. The amount of trapped thrombin depends on the quality of the fibrin fibres, which in turn is determined by the concentration of the clotting enzyme.

Fibrin glue in surgery: frequent development of inhibitors of bovine thrombin and human factor V

We report on a 34-year-old woman whose plasma showed a marked prolongation of thrombin time (TT) (> 200 s) using bovine thrombin. The patient had previously been exposed twice to topical bovine thrombin contained in fibrin glue during cardiac surgery. TT was normal when human thrombin was used as reagent. The patient's purified IgG reacted with bovine prothrombin and bovine thrombin in immunoblotting studies but showed virtually no cross-reaction with human thrombin. In addition, following surgery, factor V clotting activity (FV:C) was reduced to 9% of normal. The inhibitor of bovine thrombin persisted over a period of more than a year, while the level of FV:C progressively returned to normal within this time period. Development of thrombin and FV:C inhibitors was also investigated in plasma of 34 consecutive patients who had undergone either cardiac surgery or neurosurgery with use of fibrin glue containing bovine thrombin. Eleven of 24 patients after cardiac surgery and two of 10 patients after neurosurgery presented with TT > or = 25 s (normal plasma 15 s). Two patients had been re-exposed to fibrin glue during cardiac re-operation and showed markedly prolonged TT (> 60 s). All 13 patients who had acquired a thrombin inhibitor also had low FV:C activity (10-60% of normal plasma), whereas FV:C activity remained in the normal range in the 21 patients with normal TT. Our findings indicate that development of inhibitors of bovine thrombin as well as co-immunization to factor V occurs frequently and is associated with the amount of applied fibrin glue and with the type of operation. Re-exposure to fibrin glue seems to enhance formation of inhibitors of bovine thrombin and human factor V.

Fibrinogen Bern I: substitution gamma 337 Asn-->Lys is responsible for defective fibrin monomer polymerization

An inherited fibrinogen variant, fibrinogen Bern I, was isolated from plasma of an asymptomatic woman. Routine coagulation studies showed prolonged thrombin and reptilase clotting times. Fibrinogen concentration was diminished when determined by a functional assay, but was normal by the heat precipitation method. The release of fibrinopeptides A and B was not delayed. Two-dimensional gel electrophoresis of mercaptolyzed fragments D of fibrinogen, obtained by digestion with plasmin, showed an abnormal electrophoretic mobility in the gamma-chain remnants of fragments D1 and D2 from fibrinogen Bern I, whereas conversion of D2 to D3 by plasmin resulted in the loss of the abnormal charge, suggesting that the structural abnormality in this variant is located in the region gamma 303 through 356. The molecular defect in fibrinogen Bern I was identified by sequence analysis of genomic DNA amplified by polymerase chain reaction and cloned in M13mp19. The triplet AAC coding for asparagine at position gamma 337 was found to be substituted by AAA coding for lysine. We conclude that the substitution gamma 337 Asn-->Lys in fibrinogen Bern I is responsible for defective polymerization of fibrin monomers and for impaired protection by calcium against plasmic degradation.

Functional characterization of a variant prekallikrein (PK Zürich)

The plasma of a 68-year-old man with cross reacting material (CRM)-positive prekallikrein (PK) deficiency was studied. PK clotting activity was < 0.01 U/ml, and PK antigen was 0.1 U/ml. No circulating anticoagulant against PK was detectable. The abnormal PK molecule, denoted as prekallikrein Zürich, was partially characterized by immunological and functional studies on the propositus' plasma. Immunoblotting analysis showed the abnormal PK being a single chain molecule of the same M(r) (80 kDa) as normal PK. Dextran sulfate activation of the propositus' plasma did not lead to proteolytic cleavage of the variant PK molecule, in contrast to dextran sulfate activation of a mixture of 1 volume normal plasma and 9 volumes CRM-negative PK deficient plasma. Agarose gel electrophoresis followed by immunoblotting demonstrated that PK Zürich was complexed with high molecular weight kininogen similarly to PK in normal plasma. Incubation of the propositus' plasma with purified beta-FXIIa resulted in impaired cleavage of PK Zürich when compared with PK hydrolysis in a mixture of 10% normal plasma and 90% CRM-negative PK deficient plasma. Moreover, proteolytically cleaved PK Zürich showed no enzymatic activity against factor XII and high molecular weight kininogen. These studies show that the functional defect of prekallikrein Zürich is due to an impaired cleavage by activated factor XII and probably the lack of enzymatic activity of the cleaved variant molecule.