Oxidative stress is a cardinal feature of the inflammatory process and is involved in various pathologies including atherosclerosis. One of the important mechanisms in which oxidative stress may play a role is activation of matrix metalloproteinases such as MMP-2, which are involved in plaque destabilization. We investigated the mechanisms by which oxidative stress induces MMP-2 activation in cultured human coronary artery smooth muscle cells. Using zymography and Western blot analysis, we showed that oxidized low-density lipoproteins activate MMP-2 through up-regulation of the expression and activation of a membrane-type 1 matrix metalloproteinase (MT1-MMP). A second mechanism of MMP-2 activation involves oxidative radicals generated by the xanthine/xanthine oxidase complex (X/Xo). Research on these two mechanisms of MMP activation could lead to the elaboration of new vascular therapies for the treatment of atheroma based on interruption of a specific oxidative stress pathway.

The 8-iso-prostaglandin F 2␣ , a prostanoid produced in vivo by cyclooxygenase-independent free-radical-catalyzed lipid peroxidation, acts as a partial agonist on the thromboxane receptor (TXA 2 R) and is a potent vasoconstrictor in the oxidatively stressed isolated perfused rat heart. We hypothesized that the response in the isolated heart may be due to augmentation of TXA 2 R density, which may be initiated by the presence of oxidative radicals. Previous studies have shown that TXA 2 R density is increased during atherosclerosis on both the medial and intimal smooth muscle layers in human coronary arteries. Here we describe the effect of oxidative stress on TXA 2 R. The thromboxane A 2 receptor ␤ isoform (TXA 2 R␤) was transiently expressed in COS-7 cells. (TXA 2 ) 1 is an unstable arachidonate metabolite, implicated as a mediator in diseases such as myocardial infarction, stroke, and bronchial asthma (1). Binding of TXA 2 to its receptor, a polytopic membrane-spanning protein, induces vasoconstriction and platelet aggregation, as well as mitogenesis and hypertrophy of vascular smooth muscle cells (2). Two TXA 2 receptor (TXA 2 R) isoforms have been identified, TXA 2 R␣ (343 amino acids), which is mainly located in the placenta, and TXA 2 R␤ (407 amino acids), located in the endothelium; these isoforms are generated by the alternative splicing of a single gene (3, 4). The TXA 2 R is part of the G proteincoupled receptor superfamily, and evidence suggests that TXA 2 -induced production of second messenger inositol polyphosphates results from the activation of the G q11 family of heterotrimeric G proteins (5).Isoprostanes are formed by free radical attack on membrane phospholipids during oxidative stress (6). They are found in increased concentration in patients with coronary heart disease and are potent vasoconstrictors (7). We have shown that one of these, the 8-iso-prostaglandin F 2␣ , is a potent coronary vasoconstrictor, and its effect is exerted via partial agonist action on the TXA 2 R (8). This mechanism of action on TXA 2 R, in vascular smooth muscle and in platelets, has been confirmed in a TXA 2 R knock-out mouse (9). Our data suggested that a critical determinant of the intrinsic activity of the isoprostane is the TXA 2 R reserve, and this has subsequently been supported by another study (10). We have shown that, in the normal rat heart perfused at constant pressure in the Langendoff mode, 8-iso-prostaglandin F 2␣ had no effect, even though U46619, a TXA 2 R agonist, produced a pronounced vasoconstriction. However, after an oxidative stress induced by 30 min of low flow and reperfusion or by a superoxide-generating system (i.e. xanthine and xanthine oxidase), 8-iso-prostaglandin F 2␣ became a potent vasoconstrictor, whereas the response to U46619 was unchanged (11). Responses to both agonists were inhibited by the TXA 2 R antagonist SQ29548, suggesting that they act upon the same receptor.The rapidity of the change in response suggests that this is unlikely to be due to alterations in gene expressio...

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Thromboxane A 2 (TXA 2 ) is a key mediator of platelet aggregation and smooth muscle contraction. Its action is mediated by its G protein-coupled receptor of which two isoforms, termed TP␣ and TP␤, occur in humans. TXA 2 has been implicated in pathologies such as cardiovascular diseases, pulmonary embolism, atherosclerosis, and asthma. This study describes the pharmacological characterization of BM-613 [N-n-pentyl-NЈ-[2-(4Ј-methylphenylamino)-5-nitrobenzenesulfonyl]urea], a new combined TXA 2 receptor antagonist and TXA 2 synthase inhibitor. It exhibits a strong affinity for human platelet TP receptors (IC 50 ϭ 1.4 nM), TP␣ and TP␤ expressed in COS-7 cells (IC 50 ϭ 2.1 and 3.1 nM, respectively), and TPs expressed in human coronary artery smooth muscle cells (IC 50 ϭ 29 M). BM-613 shows a weak ability to prevent contraction of isolated rat aorta (ED 50 ϭ 1.52 M) and guinea pig trachea (ED 50 ϭ 2.5 M) induced by TXA 2 agonist U-46619 (9.11-dideoxy-9.11-methanoepoxy-prostaglandin F 2 ). Besides, BM-613 antagonizes TP␣ (IC 50 ϭ 0.11 M) and TP␤ (IC 50 ϭ 0.17 M) calcium mobilization induced by U-46619 and inhibits human platelet aggregation induced by U-46619 (ED 50 ϭ 0.278 M), arachidonic acid (ED 50 ϭ 0.375 M), and the second wave of ADP. BM-613 also dose dependently prevents TXA 2 production by human platelets (IC 50 ϭ 0.15 M). In a rat model of ferric chloride-induced thrombosis, BM-613 significantly reduces weight of formed thrombus by 79, 49, and 28% at 5, 2, and 1 mg/kg i.v., respectively. In conclusion, BM-613 is a dual and potent TP receptor antagonist and TXA 2 synthase inhibitor characterized by a strong antiplatelet and antithrombotic potency. These results suggest that BM-613 could be a potential therapeutic drug for thrombotic disorders.Thromboxane A 2 (TXA 2 ) is a key lipid mediator characterized by several implications in physiological homeostasis, including platelet aggregation and vascular and bronchial smooth muscle constriction (Hamberg et al., 1975;Moncada and Vane, 1978). An overproduction of TXA 2 has been associated with many pathological states such as myocardial infarction, thrombosis and thrombotic disorders, unstable angina, pulmonary embolism, shock, atherosclerosis, preeclampsia, and asthma (Dogné et al., 2004a).TXA 2 is a metabolite of arachidonic acid (AA), a 20-carbon

To the Editor: Rituximab, a chimeric murine-human monoclonal anti CD20 antibody, is approved for the treatment of relapsed or refractory, CD20(+) B-cell, low-grade or follicular non-Hodgkin's lymphoma (NHL). This antibody is also being used and evaluated against other CD20-expressing hematological malignancies and autoimmune disorders [1]. Recently, D'Arcy and Mannick [2] reported the first case of serum sickness occurring 10 days after the patient started a protocol of 4 weekly infusions of rituximab for refractory autoimmune polyneuropathy. The patient presented with fever, polyarthritis, and transient decrease of C3 and C4 levels. IgG antibodies directed to the murine FabЈ fragments of the rituximab were found [2]. We observed a similar clinical presentation in a 48-year-old woman with refractory immune thrombocytopenia (anti-nuclear factor negative). Six days after the second course of rituximab on a weekly protocol, the patient was admitted because of fever (38.5°C), malaise, symmetric polyarthritis of large and small joints, and a morbilliform skin eruption. At the same time, her platelet count dropped to 2,000, and she was treated with methylprednisolone 500 mg (i.v.) for 2 days. The patient responded favorably to the treatment, and less than 48 h after the treatment was started the symptoms and the signs of serum sickness resolved.Although rituximab is a chimeric murine-human antibody, only 3 patients out of more than 300 patients who were treated with rituximab and were tested for human anti-chimeric antibodies showed detectable antibodies levels [3]. None of them was reported to develop serum sickness. This is the second case reported of rituximab-induced serum sickness; both cases occurred a few days after the second course of rituximab for an autoimmune disorder, and both of them responded favorably to glucosteroid treatment. We believe that with increasing clinical experience with rituximab more cases of serum sickness will occur; therefore, the clinicians should be aware of this adverse effect. YAIR HERISHANU Effective Treatment With Recombinant Factor VIIa of Severe Bleeding Due to Acquired Factor VIII Inhibitor and Acquired ThrombocytopathyTo the Editor: Acquired hemophilia is a rare, severe hemorrhagic diathesis in nonhemophiliac patients [1]. Moreover, the appearance of a coagulation factor VIII inhibitor and alteration in the platelet function are exceptional. Activated recombinant factor VII (rVIIa) has been used recently in the antihemorrhagic treatment of patients with factor VIII inhibitors and thrombopathies [2]. We present, to the best of our knowledge, the first case of a nonhemophiliac patient, with acquired hemophilia and thrombopathy secondary to a malignant hemopathy, who was treated satisfactorily with rVIIa.A 65-year-old nonhemophiliac man presented a large hematoma of his right arm following extraction for arterial gasometry test. The activated partial thromboplastin time was 118 sec (control 25-40 sec), which was not corrected by normal fresh plasma; factor VIII:C 3%; factor V...

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