Safety,inhibition of platelet aggregation and pharmacokinetics of Fab'2 fragments of the anti-glycoprotein IIb-IIIa monoclonal antibody FRaMon in high-risk coronary angioplasty

The purpose of the study was to evaluate safety, effects on platelet aggregation and pharmacokinetics of F(ab')(2) fragments of anti-glycoprotein (GP) IIb-IIIa murine monoclonal antibody FRaMon (F(ab')(2) FRaMon) upon its intravenous administration in patients undergoing high-risk coronary angioplasty. Patients were treated before angioplasty with F(ab')(2) FRaMon at 0.2 mg/kg (n = 17) and 0.25 mg/kg (n = 12) bolus or with abciximab at 0.25 mg/kg bolus + 12 h infusion at 0.125 microg/kg per min (n = 29). F(ab')(2) FRaMon at both doses decreased platelet aggregation induced by 20 microM ADP to <10, <20, <40 and <70% of the predrug level at 1, 12, 24 and 72 h after injection, respectively. No significant differences were observed between F(ab')(2) FRaMon and abciximab antiaggregatory effects. In none of the patients did F(ab')(2) FRaMon cause allergic reactions, major bleedings or deep thrombocytopenia. Antibodies against F(ab')(2) FRaMon were detected in one patient. Free F(ab')(2) FRaMon was cleared from plasma within 12 h, while platelet-bound preparation occupied >95, 70-80 and 40-50% of GP IIb-IIIa at 1 and 12-24 h and 3 days after injection, respectively. Thrombotic complications within the first month after angioplasty in groups treated with F(ab')(2) FRaMon and abciximab were observed in one and two patients, respectively. The data obtained have shown that F(ab')(2) FRaMon at bolus administration to patients undergoing coronary angioplasty caused no serious side effects and at comparative dosage inhibited platelet aggregation with the same efficacy as abciximab at bolus + infusion administration.     

Annexin A2 mediates endothelial cell activation by antiphospholipid/anti-beta2 glycoprotein I antibodies

Patients with antiphospholipid antibodies (APLAs) are at increased risk for arterial and venous thrombosis. Many APLAs associated with these events react with beta2 glycoprotein I (beta2GPI), and endothelial cell reactive antibodies that activate endothelial cells in a beta2GPI-dependent manner occur commonly in these patients. We previously reported that beta2GPI binds with high affinity to annexin A2 on the endothelial surface, though the relevance of this interaction to APLA/anti-beta2GPI antibody-induced endothelial activation has not been determined. In this report, we confirm that anti-beta2GPI antibodies activate endothelial cells in the presence of beta2GPI, and demonstrate that anti-annexin A2 antibodies directly cause endothelial cell activation of a similar magnitude and with a similar time course. Moreover, bivalent anti-annexin A2 F(ab')2 fragments also caused endothelial cell activation, whereas monomeric Fab fragments not only did not cause activation, but blocked activation induced by anti-annexin A2 antibodies and F(ab')2 fragments, as well as that caused by anti-beta2GPI antibodies in the presence of beta2GPI. These observations suggest a novel pathway for endothelial activation induced by APLA/anti-beta2GPI antibodies that is initiated by cross-linking or clustering of annexin A2 on the endothelial surface.     

Augmentation of antitumor effects by NK cell inhibitory receptor blockade in vitro and in vivo

Subsets of natural killer (NK) cells are characterized by the expression of inhibitory and/or stimulatory receptors specific for major histocompatibility complex (MHC) class I determinants. In mice, these include the Ly49 family of molecules. One mechanism by which tumor cells may evade NK cell killing is by expressing the appropriate MHC class I and binding inhibitory Ly49 receptors. Therefore, the question of whether blocking the interaction between the Ly49 inhibitory receptors on NK and MHC class I cells on tumor cells augments antitumor activity was investigated. Blockade of Ly49C and I inhibitory receptors using F(ab')(2) fragments of the 5E6 monoclonal antibody (mAb) resulted in increased cytotoxicity against syngeneic tumors and decreased tumor cell growth in vitro. The effect of 5E6 F(ab')(2) was specific for the MHC of the tumor, as the use of F(ab')(2) of the mAb against Ly49G2 failed to increase NK activity. Treatment of leukemia-bearing mice with 5E6 F(ab')(2) fragments or adoptive transfer of NK cells treated ex vivo with the F(ab')(2) resulted in significant increases in survival. These results demonstrate that blockade of NK inhibitory receptors enhances antitumor activity both in vitro and in vivo, suggesting that NK inhibitory receptors can be responsible for diminishing antitumor responses. Therefore, strategies to block inhibitory receptors may be of potential use in increasing the efficacy of immunotherapy. (Blood. 2001;97:3132-3137)     

Association of elevated anti-sarcolemma, anti-idiotype antibody levels with the clinical and pathologic expression of chronic Chagas myocarditis

Antibody F(ab')2 fragments derived from the sera of four patients with histology-proven chronic Chagas myocarditis [cF(ab')2]-complexed antibody F(ab')2 fragments of children with acute Trypanosoma cruzi infection [aF(ab')2] in significantly higher molar ratios than those measured with F(ab')2 antibody fragments of normal subjects [nF(ab')2] from nonendemic areas (p less than 0.05). Anti-idiotype [cF(ab')2 X aF(ab')2] immune-complex formation was significantly blunted by preabsorption of cF(ab')2 with porcine heart atria sarcolemma (PAMs) immobilized on sepharose beads (inhibition, mean, 78.1 +/- 2.4%, n = 4). cF(ab')2 X nF(ab')2] immune-complex formation was also inhibited by pretreatment of cF(ab')2 with PAMs (inhibition, mean, 48.7 +/- 7.5%, n = 4). The sera of three groups of subjects from a geographic zone endemic for T. cruzi infection in the northeast of Brazil were assayed for free and immune-complexed IgG anti-acute T. cruzi infection F(ab')2. The indexed levels of free IgG anti-idiotype antibody activity and levels of IgG anti-idiotype immune complexes (IC') were markedly elevated in hospitalized patients with severe, decompensated chronic Chagas myocarditis (n = 23), and their IC' indexes were significantly higher than those measured in asymptomatic seropositive subjects from a nearby endemic village of the northeast of Brazil (Moniz Ferreira, n = 92, p less than 0.001) and in healthy seronegative villagers (n = 84, p less than 0.001). There exists a strong correlation between elevated IgG anti-sarcolemma, anti-idiotype activity levels and the clinical and pathologic expression of chronic Chagas myocarditis.     

Rapid and sustained coronary artery recanalization with combined bolus injection of recombinant tissue-type plasminogen activator and monoclonal antiplatelet GPIIb/IIIa antibody in a canine preparation

The effects of bolus injections of recombinant single-chain tissue-type plasminogen activator (rt-PA) and of F(ab')2 fragments of a murine monoclonal antibody (7E3) against the human platelet GPIIb/IIIa receptor [7E3-F(ab')2] on coronary arterial thrombolysis and reocclusion was studied in a canine preparation of coronary artery thrombosis superimposed on high-grade stenosis. Bolus intravenous injections of rt-PA at a dose of 0.45 mg/kg, repeated at 15 min intervals until reperfusion occurred (maximum of four injections) caused reperfusion in five of seven dogs within 100 min (33 +/- 15 min, mean +/- SD). Reperfusion was rapidly followed (generally within 10 min) by reocclusion and then by periods of cyclical reflow and reocclusion. A single intravenous injection of 7E3-F(ab')2 alone at 0.8 mg/kg caused reperfusion within 100 min in two of six dogs (19 and 37 min) without subsequent reocclusion. Single bolus injections of different amounts (0.1 to 0.8 mg/kg) of 7E3-F(ab')2 were then combined with bolus injections of 0.45 mg/kg of rt-PA. Stable reperfusion without reocclusion was accomplished with 0.8 or 0.6 mg/kg 7E3-F(ab')2 and a single injection of 0.45 mg/kg rt-PA within 6 +/- 3 min (n = 6, p less than .01) and 8 +/- 5 min (n = 5, p less than .02), respectively. None of these animals suffered reocclusion of the coronary artery. Lower doses (0.1 to 0.2 mg/kg) of 7E3-F(ab')2 did not significantly shorten the time to reperfusion and did not prevent reocclusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

A monoclonal antibody against the platelet glycoprotein IIb/IIIa receptor complex prevents platelet aggregation and thrombosis in a canine model of coronary angioplasty.

BACKGROUND. The comparative effects of aspirin and F(ab')2 fragments of monoclonal antibody 7E3 against the platelet glycoprotein IIb/IIIa receptor on ex vivo platelet aggregation and in vivo thrombosis were studied in a canine coronary balloon angioplasty model. METHODS AND RESULTS. Three groups were studied. Group 1 (n = 8) was pretreated with saline placebo, group 2 (n = 8) was pretreated with 325 mg aspirin, and group 3 (n = 8) was pretreated with 0.8 mg/kg 7E3 F(ab')2. Coronary angioplasty was performed in the left anterior descending coronary artery of open-chest dogs under fluoroscopic control; serial measurements of basal and hyperemic coronary blood flows were then made for 2 hours after application of an external stenosis that decreased hyperemic flow by 50%. There were no significant differences in platelet counts or hemodynamic measurements during the experiments. Platelet aggregation was decreased by treatment: group 1, 64 +/- 13% versus 50 +/- 13% (p = NS); group 2, 57 +/- 4% versus 25 +/- 4% (p less than 0.001); and group 3, 77 +/- 5% versus 10 +/- 6% (p less than 0.0002). Compared with initial measurements, the 7E3 antibody was superior to aspirin in maintaining hyperemic coronary blood flow after release of the external stenosis: group 1, 177 +/- 14 versus 21 +/- 14 ml/min (p less than 0.0003); group 2, 189 +/- 9 versus 110 +/- 28 ml/min (p less than 0.008); and group 3, 194 +/- 12 versus 181 +/- 15 ml/min (p less than 0.02). In group 1, arterial occlusion developed in five dogs, and nonocclusive thrombus was seen in three dogs. In group 2, arterial occlusion developed in one dog, and nonocclusive thrombus was seen in five dogs. No thrombotic material was visualized in group 3 dogs treated with 7E3 F(ab')2. CONCLUSIONS. In this animal model, the 7E3 antiplatelet antibody is superior to aspirin in inhibiting platelet aggregation, thrombosis, and acute closure after deep arterial injury caused by coronary balloon angioplasty.     

Fc receptor-mediated inhibitory effect of immunoglobulin therapy on autoimmune giant cell myocarditis: concomitant suppression of the expression of dendritic cells

In the present study, the mechanisms and importance of the Fc portion of immunoglobulin in experimental giant cell myocarditis were examined. Giant cell myocarditis was induced in rats by immunization of porcine cardiac myosin. Human intact immunoglobulin (1 g. kg(-1). d(-1)) or F(ab')(2) fragments of human immunoglobulin (1 g. kg(-1). d(-1)) were administered intraperitoneally daily on days 1 to 21. Intact immunoglobulin administration significantly ameliorated myocarditis, but F(ab')(2) fragments did not. The ribonuclease protection assay revealed that therapy with intact immunoglobulin, but not F(ab')(2) fragments, suppressed the mRNA expressions of inflammatory and proinflammatory cytokines. Immunohistochemical analysis showed that therapy with intact immunoglobulin, but not F(ab')(2) fragments, suppressed dendritic cell (DC) expression during both the early and the subsequent fulminant phases. Moreover, the early treatment of intact immunoglobulin until the 11th day or 14th day, when the expression of DCs was completely suppressed, ameliorated myocarditis. However, the late treatment of intact immunoglobulin beginning on day 15, when the expression of DCs had already been completed, failed to ameliorate the condition. An in vitro study showed that intact immunoglobulin, but not F(ab')(2) fragments, suppressed the lipopolysaccharide-induced interleukin-1beta production associated with the downregulation of CD32 antigen (Fcgamma receptor II) expression. Thus, intact immunoglobulin therapy markedly suppressed myocarditis as a result of Fc receptor-mediated anti-inflammatory action, and the suppression of the disease was associated with the suppression of DCs, ie, the suppression of the initial antigen-priming process in experimental giant cell myocarditis.     

Comparative effects of aspirin, a synthetic thrombin inhibitor and a monoclonal antiplatelet glycoprotein IIb/IIIa antibody on coronary artery reperfusion, reocclusion and bleeding with recombinant tissue-type plasminogen activator in a canine preparation

The comparative effects of intravenous aspirin, the synthetic thrombin inhibitor (2R,4R)-4-methyl-1-[N2-(3-methyl-1,2,3,4-tetrahydro-8- quinolinesulfonyl)-L-arginyl]-2-piperidinecarboxylic acid monohydrate (Argatroban) and F(ab')2 fragments of monoclonal antibody 7E3 against platelet glycoprotein IIb/IIIa (7E3-F[ab']2) on thrombolysis, reocclusion and bleeding associated with 0.45 mg/kg body weight bolus injections of recombinant tissue-type plasminogen activator (rt-PA) were studied in a canine coronary artery thrombosis model. Coronary patency was monitored for 2 h both by flow probe and by coronary angiography. Four groups were studied: Group I = pretreated with 17 mg/kg intravenous aspirin (n = 6), Group II = pretreated with 200 micrograms/kg per min intravenous Argatroban for 60 min (n = 5), Group III = pretreated with aspirin and Argatroban (n = 5) and Group IV = pretreated with 0.8 mg/kg intravenous 7E3-F(ab')2 (n = 5). In Group I, reflow occurred in four of six dogs, but did not persist; reflow was induced in Group II in four of five dogs, persisting in one; in Group III, reflow occurred in all five dogs, persisting in four; in Group IV reflow was achieved in four of five dogs, persisting in two. The frequency of persistent reflow in Group III was significantly higher than in the combined Groups I and II (p = 0.012), whereas the time to reflow was significantly shorter in the groups receiving Argatroban than in the aspirin group (median 25 versus 55 min, p = 0.04). There were no significant differences between Groups III and IV.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lysis of plasminogen activator-resistant platelet-rich coronary artery thrombus with combined bolus injection of recombinant tissue-type plasminogen activator and antiplatelet GPIIb/IIIa antibody

Resistance of coronary occlusive thrombus to thrombolytic therapy, found in some patients with acute myocardial infarction, may be due to the presence of platelet-rich coronary clot. Reperfusion therapy in such patients may require the development and evaluation of alternative strategies in animal models. Therefore, platelet-rich coronary artery thrombus was developed by excision, eversion (inside out) and reanastomosis of a 1 cm segment of the left circumflex coronary artery in anesthetized dogs maintained on heparin antiocoagulation. Blood flow was restored in 25 of 27 dogs. Thrombotic occlusion of the everted segment graft with primarily platelet-rich thrombus or thrombus containing platelet-rich and erythrocyte-rich zones, persisting for at least 30 min, occurred within 4.5 +/- 3.5 min (mean +/- SD) in 20 of these 25 dogs. In 5 of these 20 dogs (group I, control), stable occlusion, as monitored with an ultrasound flow probe and coronary angiography, was maintained during a 2 h observation period. In group II (n = 5), intravenous bolus injections of recombinant tissue-type plasminogen activator (rt-PA) at a dose of 0.45 mg/kg body weight at four 15 min intervals did not cause reperfusion in four dogs and produced cyclic reperfusion and reocclusion in one dog. In group III (n = 5), a single intravenous bolus injection of 0.8 mg/kg of the F(ab')2 fragment of a murine monoclonal antibody (7E3) against the human platelet GPIIb/IIIa receptor [7E3-F(ab')2] produced stable reperfusion in two of the five dogs, whereas occlusion persisted in the other three. In group IV (n = 5), injection of 7E3-F(ab')2 (0.8 mg/kg) followed by rt-PA (0.45 mg/kg) caused stable reperfusion without reocclusion in all dogs (p less than 0.05 versus rt-PA alone and p less than 0.01 versus control). This study confirms that platelet-rich occlusive coronary thrombus is very resistant to lysis with intravenous rt-PA. However, this resistance may be overcome by the combined use of a reduced dose of rt-PA and the antiplatelet GPIIb/IIIa receptor antibody 7E3. The results indicate that platelet-rich thrombus resistant to thrombolytic agents may be dispersed pharmacologically without resort to mechanical recanalization. The present dog model may be useful in investigating specific strategies for the dispersion of resistant platelet-rich coronary thrombus.     

Preparation and activity of conjugate of monoclonal antibody HAb18 against hepatoma F(ab')(2) fragment and staphylococcal enterotoxin A

AIM: To prepare the conjugate of staphylococcal enterotoxin A (SEA) protein which is a bacterial SAg and the F(ab')(2) fragment of mAb HAb18 against human hepatocellular carcinoma (HCC), and identify its activity in order to use SAg in the targeting therapy of HCC. METHODS: MAb HAb18 was extracted from the abdominal dropsy of Balb/c mice, and was purified through chromatography column SP 40HR with Fast protein liquid chromatography (FPLC) system. The F(ab')(2) fragment of mAb HAb18 was prepared by papainic digestion method. The conjugate of mAb HAb18 F(ab')(2) fragment and SEA was prepared with chemical conjugating reagent N succinimidyl 3 (2-pyridyldithio) propionate (SPDP) and purified through chromatography column Superose 12 with FPLC system. The molecular mass and purity of each collected peak were identified with SDS-PAGE assay. The protein content was assayed by Lowry's method. The antibody activity of HAb18 F(ab')(2) against HCC in the conjugate was identified by indirect immunocytochemical ABC method, and the activity of SEA in the conjugate to activate peripheral blood mononuclear cells (PBMC) was identified with MTT assay. RESULTS: The IgG mAb HAb18 was extracted, and purified successfully. Immunocytochemical staining demonstrated that it reacted with most of HHCC cells of human HCC cell line. There were two peaks in the process of purification of the prepared HAb18 F(ab')(2) SEA conjugate. SDS-PAGE assay demonstrated that the molecular mass of the first peak was about 130 ku, and the second peak was the mixture of about 45 ku and a little 100 ku proteins. The immunocytochemical staining was similar in HAb18 F(ab') (2) SEA conjugate and HAb18 F(ab') (2), i.e.the cytoplasm and/or cell membranes of most HHCC cells were positively stained. The MTT assay showed that the optical absorbance (A) value at 490 nm of HAb18 F(ab') (2) SEA conjugate was 0.182 +/- 0.012, that of negative control was 0.033 +/- 0.009, and there was significant difference between them (P < 0.05). CONCLUSION: SPDP is a good protein conjugating reagent and can be used in preparing protein conjugate. The conjugate of mAb HAb18 F(ab') (2) fragment and SEA protein was prepared successfully in present study and can be used in the experimental study of HCC targeting therapy with the conjugate of SAg and anti HCC mAbs or their fragments.     

Abolition of in vivo platelet thrombus formation in primates with monoclonal antibodies to the platelet GPIIb/IIIa receptor. Correlation with bleeding time, platelet aggregation, and blockade of GPIIb/IIIa receptors

We studied the dose-response effects of the F(ab')2 fragments of murine monoclonal antibodies to the platelet GPIIb/IIIa receptor (7E3 and 10E5) on in vivo platelet thrombus formation in a well-characterized monkey model in which the carotid artery is stenosed and thrombus formation is provoked and augmented by intimal damage and the infusion of subaggregating doses of epinephrine. Both antibodies abolished thrombus formation with a mean dose of -0.2 mg/kg. Ex vivo platelet aggregation was not always abolished at doses that abolished thrombus formation; similarly, bleeding times were only moderately prolonged (9.1 +/- 1.4 minutes) at these doses. Increasing the dose above that required to abolish thrombus formation consistently produced abolition of ex vivo platelet aggregation, marked prolongation of the bleeding time (14.2 +/- 1.5 minutes), and nearly quantitative blockade of GPIIb/IIIa receptors. We conclude that in a significant percentage of animals, the extent of GPIIb/IIIa blockade required to prevent vasoocclusive thrombus formation in this model is less than that required for abolition of platelet aggregation, and that the preservation of only a minority of functional GPIIb/IIIa receptors might be adequate to maintain a nearly normal bleeding time.     

Sustained limitation of myocardial reperfusion injury by a monoclonal antibody that alters leukocyte function

Pentobarbital anesthetized dogs were subjected to 90 minutes of left circumflex coronary artery (LCCA) occlusion followed by 72 hours of reperfusion. Control or anti-Mo1 (904) F(ab')2 fragments of monoclonal antibodies were administered intravenously at a dose of 1 mg/kg beginning 45 minutes after occlusion and at a dose of 0.5 mg/kg at 12, 24, 36, and 48 hours after reperfusion. Myocardial infarct size expressed as a percentage of the area at risk (IN/AR) measured postmortem after 72 hours of reperfusion was significantly reduced by 904 F(ab')2 (21.6 +/- 2.8%, n = 8) compared with control F(ab')2 (37.4 +/- 5.8%, n = 8; p less than 0.025). There were no significant differences between groups in heart rate, mean arterial blood pressure, rate-pressure product, or LCCA blood flow that could account for a reduced infarct size. Regional myocardial blood flow (RMBF) was determined with 15-microns radiolabeled microspheres. Transmural blood flows (ml/min/g) within the region of myocardium at risk were not statistically different between treatment groups. Infarct size in both groups was related to regional myocardial blood flow, and the relation was shifted downward in the group treated with the anti-Mo1 F(ab')2 antibody (analysis of covariance, p = 0.01). Thus, anti-Mo1 F(ab')2 produces a sustained limitation of myocardial infarct size compared with controls under similar hemodynamic conditions and a similar degree of myocardial ischemia as determined by RMBF. These data suggest that inhibition of neutrophil adhesive interactions (as suggested by the inhibitory effect of anti-Mo1 on canine neutrophil aggregation) may be an effective mechanism for protection against myocardial injury secondary to myocardial ischemia and reperfusion.     

Direct demonstration that receptor crosslinking or aggregation is important in insulin action

Exposure of adipocytes to antibodies to the insulin receptor results in a blockade of (125)I-labeled insulin binding, stimulation of glucose oxidation, and many more insulin-like effects. Allowing for differences in purity, antireceptor antibody is equipotent with insulin on a molar basis. Both the bivalent F(ab')(2) and monovalent Fab' fragments of the antireceptor antibody are fully active in inhibiting (125)I-labeled insulin binding. Bivalent F(ab')(2) also retains its insulin-like effects. In contrast, the monovalent Fab' loses almost all ability to stimulate glucose oxidation and acts as a competitive antagonist of insulin-stimulated glucose oxidation. Addition of anti-F(ab')(2) antisera, which crosslink the Fab'-receptor complexes, results in a restoration of the insulin-like activity of the antibody. Similarly, when cells are exposed to submaximal doses of insulin, addition of anti-insulin antibodies at low concentration enhances the biological activity of insulin. These data suggest that receptor occupancy by ligand is not sufficient for signal generation and that the insulin-like effects of antireceptor antibody (and perhaps insulin itself) require receptor aggregation or clustering. This aggregation, however, appears to be independent of microfilaments or microtubules because the insulin-like effects of antireceptor antibody, and in fact, of insulin itself, are unaffected by agents that are known to disrupt these structures.     

Antiplatelet antibody [7E3 F(ab')2] prevents rethrombosis after recombinant tissue-type plasminogen activator-induced coronary artery thrombolysis in a canine model

Coronary artery rethrombosis can complicate initially effective thrombolytic therapy. Platelets interacting with injured vascular endothelium in a region along the coronary artery with reduced luminal cross-sectional area contribute to rethrombosis. The purpose of this study was to investigate the potential of the F(ab')2 fragment of the murine monoclonal antibody 7E3 [7E3 F(ab')2] to prevent rethrombosis after intracoronary clot lysis with recombinant tissue-type plasminogen activator (rt-PA) in an experimental model. The 7E3 F(ab')2 binds to the platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa), thereby preventing platelet-fibrinogen interaction and intravascular thrombus formation. Experimental coronary artery thrombosis was produced in the anesthetized dog by application of direct anodal current to the intimal surface of the left circumflex coronary artery in the region of an external stenosis. Lysis of the established intracoronary thrombus was achieved with the intravenous administration of rt-PA (25 mg) after which the animals were randomized into two groups. Group 1 (n = 10) served as the control, receiving the saline diluent, and group 2 (n = 9) received 7E3 F(ab')2, given as a single intravenous injection (0.8 mg/kg). The times required for occlusive thrombus formation, rt-PA-induced thrombolysis, and rethrombosis (if it occurred) were similar in the animals treated with saline and those treated with 7E3 F(ab')2. The initial left circumflex coronary artery blood flow was similar in both groups but decreased to a negligible level in group 1. In group 2, left circumflex coronary artery blood flow declined modestly (24 +/- 2 to 10 +/- 2 ml/min). Rethrombosis occurred in all animals in group 1 but in only two of nine animals in group 2 (p less than 0.05). Oscillations in coronary blood flow preceded rethrombosis in group 1, whereas 7E3 F(ab')2 stabilized left circumflex coronary artery blood flow patterns during the course of teh experimental protocol (5.2 +/- 0.9 vs. 0.7 +/- 0.4 oscillations, respectively; p less than 0.05). Thrombus mass recovered from the left circumflex coronary artery at the conclusion of each experiment was greater in group 1 as compared with group 2 (7.0 +/- 2.3 vs. 1.5 +/- 0.7 mg, respectively; p less than 0.05). The area of left ventricle at risk for infarction was similar in both groups but infarct size, infarction/at risk assessed histochemically, was larger in group 1 than group 2 (35 +/- 9% vs. 6 +/- 4%, respectively; p less than 0.05). Platelet aggregation induced by ADP and arachidonic acid was similar at baseline for all of the animals.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antiplatelet monoclonal F(ab')2 antibody directed against the platelet GPIIb/IIIa receptor complex prevents coronary artery thrombosis in the canine heart

Interactions between platelets with injured vascular endothelium contribute to thrombotic occlusion. A murine monoclonal antibody [7E3 F(ab')2] to the platelet GPIIb/IIIa receptor complex was used to inhibit platelet aggregation in an experimental model of coronary artery thrombosis. Prevention of thrombotic occlusion by 7E3 F(ab')2 (0.8 mg/kg bolus i.v.) was studied in dogs with direct current induced intimal injury (100 microA for 5 h) and critical stenosis of the left circumflex coronary artery (LCCA). Baseline LCCA blood flow (CBF) was similar in 7E3 F(ab')2 and control groups, but decreased in the controls [24 +/- 2 ml/min to 0 +/- 0 ml/min, n = 13 (mean +/- S.E.M.)] due to thrombotic occlusion in each case (time to thrombosis 136 +/- 15 min). In the group treated with 7E3 F(ab')2, CBF did not change significantly (27 +/- 3 ml/min to 22 +/- 3 ml/min, n = 6) and thrombotic occlusion did not occur during the 5-h observation period in which intimal injury was produced in the LCCA (P less than 0.001). Oscillations in CBF preceded thrombosis in the control group, but did not occur with 7E3 F(ab')2 treatment (2.2 +/- 0.7 vs. 0 +/- 0, P less than 0.05). The thrombus mass recovered from the LCCA 30 min after occlusion was 8.8 +- 1.3 mg in the controls compared to 2.2 +/- 1.2 mg determined 5 h after administration of 7E3 F(ab')2 (P less than 0.05). When studied ex vivo, before the administration of the test agents, platelets from both groups of dogs aggregated in response to ADP and arachidonic acid. However, after treatment, the ex vivo aggregation of platelets from 7E3 F(ab')2 animals was inhibited whereas platelets from the control animals continued to aggregate ex vivo throughout the period of the experimental protocol (P less than 0.05). The labeling of platelets with 111indium showed accumulation of radioactivity within the thrombus and upon the vascular endothelium which was less in 7E3 F(ab')2 treated dogs as compared to the control group (P less than 0.05). The murine monoclonal antibody 7E3 F(ab')2 did not affect hemodynamic values or the circulating platelet count during the experimental protocol. In conclusion, antibody to platelet GPIIb/IIIa receptors: (1) prevented thrombotic LCCA occlusion, (2) inhibited ex vivo platelet aggregation, (3) minimized platelet deposition on injured vascular endothelium and within formed thrombi, and (4) stabilized CBF during 5 h of continuous direct current induced intimal injury of the LCCA.     

A non-immunological phospholipid-dependent coagulation inhibitor associated with IgGlambda-type multiple myeloma

We investigated the rare case of a patient with IgGlambda multiple myeloma for whom both prothrombin time and APTT were significantly prolonged. The IgG inhibited coagulation reactions upstream from prothrombin when coagulation was initiated by mRVVT, but not by FXa, as indicated by a chromogenic substrate for FXa. The mPT and the mAPTT showed inhibition of FXa generation in both the intrinsic and extrinsic pathways. The IgG inhibited both protein C (indicated by APTT) and FX (indicated by RVV) but not amidolysis for either activated protein C or FXa. The addition of excess phospholipid significantly shortened the prolonged RVVT of the patient. It inhibited the coagulation reactions of normal plasma and was dependent on decreasing the PS concentration in the APTT reagent. It was suggested that the IgG showed lupus anticoagulant (LA)-like activity that inhibited phospholipid-dependent coagulation reactions in the intrinsic, extrinsic, and common pathways. However, the IgG did not bind cardiolipin-beta2GPI complex, beta2GPI, or prothrombin in ELISA assays. The IgG did not bind to either PS or phospholipid complexes in the presence or absence of prothrombin, FX, or FXa. Interestingly, the IgG lost its LA like-activity when it was degraded to F(ab')2 and Fc fragments by pepsin. We suspected that the IgG might inhibit the interaction between coagulation factors and acid phospholipid non-immunologically and that this process requires an intact IgG conformation, although the reaction mode is still not clear.     

Antithrombotic effect of a monoclonal antibody to the platelet glycoprotein IIb/IIIa receptor in an experimental animal model

A murine monoclonal antibody directed at the platelet glycoprotein IIb/IIIa complex, which blocks platelet aggregation ex vivo, was tested for its antithrombotic effects in an established animal model of acute platelet thrombus formation in partially stenosed arteries. Infusion of 0.7 to 0.8 mg/kg of the F(ab')2 fragment of the antibody completely blocked new thrombus formation despite multiple provocations, making it the most potent antithrombotic agent tested in this model.     

Atherogenic oxidized low-density lipoprotein/beta2-glycoprotein I (oxLDL/beta2GPI) complexes in patients with systemic lupus erythematosus and antiphospholipid syndrome

Oxidized low-density lipoprotein (oxLDL) interacts in vitro with beta2-glycoprotein I (beta2GPI) via LDL-derived specific ligands forming oxLDL/beta2GPI complexes. Circulating oxLDL/beta2GPI complexes have been demonstrated in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). Autoimmune vascular inflammation and oxidative stress contribute to oxLDL/beta2GPI complex formation. Immunohistochemical staining of atherosclerotic lesions suggest that these complexes are formed in the arterial wall and released into circulation. The demonstration of antibodies to oxLDL/beta2GPI complexes indicates that these complexes are immunogenic, and the coexistence of complexes and antibodies suggest an active pro-thrombotic/pro-atherogenic role in the development of autoimmune vascular complications. Circulating oxLDL/beta2GPI complexes can be measured by ELISA using a monoclonal antibody specific to complexed human beta2GPI to capture beta2GPI bound to oxLDL. An enzyme-conjugated monoclonal antibody to human Apo B 100 allows the specific detection of oxLDL/beta2GPI complexes. OxLDL/beta2GPI complexes were common in SLE and APS patients suggesting an underlying process of inflammation and oxidation. Using oxLDL/beta2GPI complexes as capture antigen, antibodies to oxLDL/beta2GPI can be measured by ELISA. Serum levels of IgG anti-oxLDL/beta2GPI antibodies were significantly higher in SLE patients with APS compared to SLE controls without APS. Further, high titers of these IgG antibodies were observed in APS patients with a history of arterial thrombosis. The presence of circulating oxLDL/beta2GPI complexes and IgG antibodies to these complexes indicates significant vascular injury and oxidative stress as well as an active role in autoimmune-mediated atherothrombosis.     

Inhibition of human platelet function in vivo with a monoclonal antibody. With observations on the newly dead as experimental subjects

The F(ab')2 fragment of a monoclonal antibody to the platelet glycoprotein IIb/IIIa receptor (7E3) is a potent inhibitor of both in-vitro platelet aggregation and in-vivo platelet thrombus formation in animal studies. As a first step in assessing the potential of 7E3-F(ab')2 as an antithrombotic agent for use in humans, we administered 7E3-F(ab')2 intravenously at increasing doses to a person who had just died and was being maintained on a respirator (neomort). At 0.1 and at 0.2 mg/kg body weight, 74% and 92% of the glycoprotein IIb/IIIa receptors were blocked, respectively; adenosine-diphosphate-induced platelet aggregation was inhibited by 84% and 100% at these same doses. Platelet glycoprotein Ib function remained intact, even at 0.6 mg/kg. Acute hemodynamic or hemorrhagic toxicity was not noted. This antibody fragment, a potent, immediate-acting inhibitor of platelet aggregation, may be of benefit in vaso-occlusive and thromboembolic disorders.     

Anti-beta2 glycoprotein I-beta2 glycoprotein I] immune complexes in patients with antiphospholipid syndrome and other autoimmune diseases

Antiphospholipid syndrome (APS) is defined by the presence of aPL antibodies in patients with thromboembolic phenomena. Some antiphospholipid (aPL) antibodies, such as those directed against beta2-glycoprotein I (beta2GPI), are associated with thromboembolism, possess Lupus Anticoagulant (LA) activity and recognize their target antigen only when bound to specific surfaces or to phospholipids (PL). To ascertain whether both free and antibody-bound beta2GPI circulate in APS, we set up an ELISA to detect [IgG anti-beta2GPI-beta2GPI] immune complexes. In this system, rabbit anti-human beta2GPI antibodies were adsorbed onto plastic plates, incubated with patient plasma, and bound complexes were detected by means of alkaline phosphatase-labeled goat anti-human IgG; each assay was stopped when positive controls consisting of in vitro generated immune complexes reached an Optical Density (OD) of 0.5 at 405 nm. Plasma from 16 patients with APS showed a mean OD405 of 0.291 (range 0.115-0.558), not statistically different from the mean obtained for 15 age- and sex-matched healthy volunteers (mean OD405 = 0.169, range 0.066-0.264). Surprisingly, levels of immune complexes in 14 patients with other autoimmune diseases and no circulating anti-beta2GPI antibodies were statistically higher (mean OD405 = 0.552, range 0.204-0.991) than those of healthy subjects and patients with APS. These data indicate that while autoantibodies to beta2GPI are mainly unbound in plasma of patients with APS, they are complexed with their antigen in patients with other autoimmune diseases, possibly reflecting a higher binding affinity.