Leka, a New Platelet Antigen Absent in Glanzmann''s Thrombasthenia

The serum of a patient who developed a posttransfusion purpura contained antibodies directed against a previously undescribed platelet antigen Lek a. The antiplatelet activity was present in the IgG fraction and was detected by immunofluorescence, 51Cr lysis and 14C-serotonin release. The frequency of the Lek a phenotype in the French population is 98.18%. Lek a does not appear to be sex-linked and seems to be closely related to the Bak a antigen. The Lek a antigen is not expressed on thrombasthenic platelets but is found on platelets from patients with the Bernard-Soulier syndrome which suggests that this antigen is carried by platelet glycoproteins IIb and/or IIIa.     

A pilot study of 220 mg/m2 melphalan followed by autologous stem cell transplantation in patients with advanced haematological malignancies: pharmacokinetics and toxicity

We studied the pharmacokinetics and toxicity of 220 mg/m² melphalan (HDM 220) followed by autologous stem cell transplantation in 16 patients with advanced haematological malignancies. Pharmacokinetic parameters (mean values of steady-state volume of distribution 14.6 l/m², total body clearance 313 ml/min/m², elimination half-life 46 min) were the same as those of 140 or 200 mg/m² melphalan in previous reports. HDM 220 was feasible. Extramedullary toxicity was mainly W.H.O. grade 4 mucositis (13/16 patients). The median duration of 41 d (10, not reached) of thrombocytopenia <25 × 10⁹/l was long. In multiple myeloma the response rate was 89% in heavily pretreated patients, suggesting that HDM 220 could be considered earlier in the course of the disease as an alternative consolidation therapy.     

Discrepancy between simultaneous digital skin microvascular and brachial artery macrovascular post-occlusive hyperemia in systemic sclerosis

OBJECTIVE: Vascular impairment, a main feature of the pathogenesis of systemic sclerosis (SSc), involves both the macro- and the microvasculature. We compared and correlated simultaneously measured skin microvascular and brachial artery macrovascular post-occlusive hyperemia in 3 groups: patients with SSc, patients with primary Raynaud's phenomenon (RP), and healthy volunteers. METHODS: Thirty-three healthy volunteers, 36 patients with primary RP, and 42 patients with SSc were enrolled. For each subject, brachial artery flow-mediated dilation (FMD) and cutaneous post-occlusive reactive hyperemia (PORH) were simultaneously recorded after 5-minute occlusion of the brachial artery. Local thermal hyperemia, nitroglycerin-mediated dilation (NMD), intima-media thickness (IMT), and pulse wave velocity (PWV) were also assessed. RESULTS: Digital cutaneous peak PORH was altered in patients with primary RP and SSc compared to healthy controls, whereas FMD was not significantly different among all groups. We observed a correlation between digital peak cutaneous vascular conductance and brachial FMD in healthy controls (r = 0.49; p = 0.004), but not in patients with primary RP or SSc. Thermal hyperemia was altered only in patients with SSc. Brachial NMD, IMT, and PWV were not different among all groups. CONCLUSION: We observed a loss of the correlation between brachial FMD and digital cutaneous PORH in patients with SSc and primary RP. Microvascular function is impaired in SSc, whereas brachial artery endothelial function is normal.     

Anti-platelet antibodies in patients with systemic lupus erythematosus and the primary antiphospholipid antibody syndrome: their relationship with the observed thrombocytopenia

The role of antiphospholipid antibodies in the pathogenesis of the thrombocytopenia observed during primary antiphospholipid antibody syndrome (APAS) and systemic lupus erythematosus (SLE) remains controversial. We have used the MAIPA test to examine the frequency and specificity of anti-platelet antibodies directed against the major platelet membrane glycoproteins (GP IIb–IIIa, GP Ib–IX, GP Ia–IIa and GP IV) in patients where SLE and APAS were associated or not with thrombocytopenia. Results were compared with a series of 26 ITP patients, 46% of whom were shown to possess anti-platelet antibodies directed against one or more of the platelet surface glycoproteins. When APAS was associated with thrombocytopenia, 7/10 patients possessed antibodies against GP IIb–IIIa and/or GP Ib–IX. For SLE patients with thrombocytopenia, 6/10 patients were shown to have antiplatelet antibodies against GP IIb–IIIa, GP Ib–IX or GP IV. In contrast, for APAS ( n =11) and SLE patients ( n =11) without thrombocytopenia, only one patient had an antibody directed against GP IIb–IIIa and one patient had an antibody to GP IV. Our results suggest that antibodies directed against major platelet membrane glycoproteins may play a role in the thrombocytopenia that is seen during SLE and APAS.     

Atrial septal pacing to prevent atrial fibrillation in patients with sinus node dysfunction: results of a randomized controlled study

Background

In order to assess the preventive effects of right atrial septal pacing on atrial fibrillation (AF) in patients with sinus node dysfunction, we conducted a prospective randomized controlled study in patients requiring atrial pacing.

Methods

The inclusion criterion was the presence of a sinus node dysfunction with or without episodes of AF. Pacing sites were randomized to either the right atrial septum or appendage. Patients with permanent AF or with atrioventricular (AV) block without sinus node dysfunction were excluded. Patients were discharged at a pacing rate of 65 beats per minute after setting of the optimal AV delay. The antiarrhythmic therapy remained unchanged until the first recurrence of AF. Sequential analyses were performed with the triangular test.

Results

Mean baseline characteristics were not different between the septum (n = 57) and the appendage (n = 67) groups. The triangular test evidenced a lack of effect of septal pacing at the last sequential analysis. The rates of AF-free survival were not different between the septum and the appendage group (65% vs 64%, P = .28).In the subgroup of patients with at least 1 episode of AF 3 months before pacing, AF-free survival was increased by atrial septal pacing (70% vs 40%, P = .018). The mean follow-up was 16 ± 13 months (range, 1-54).

Conclusions

Atrial septal pacing does not have a preventive effect on the occurrence of AF in patient requiring atrial pacing for sinus node dysfunction. Subgroup analysis suggests that atrial septal pacing may benefit patients with ≥1 episode of AF in the 3 months preceding pacing.     

Hydrolysis of Clavulanate by Mycobacterium tuberculosis β-Lactamase BlaC Harboring a Canonical SDN Motif

Combinations of β-lactams with clavulanate are currently being investigated for tuberculosis treatment. Since Mycobacterium tuberculosis produces a broad spectrum β-lactamase, BlaC, the success of this approach could be compromised by the emergence of clavulanate-resistant variants, as observed for inhibitor-resistant TEM variants in enterobacteria. Previous analyses based on site-directed mutagenesis of BlaC have led to the conclusion that this risk was limited. Here, we used a different approach based on determination of the crystal structure of β-lactamase Bla_MAb of Mycobacterium abscessus, which efficiently hydrolyzes clavulanate. Comparison of Bla_MAb and BlaC allowed for structure-assisted site-directed mutagenesis of BlaC and identification of the G¹³²N substitution that was sufficient to switch the interaction of BlaC with clavulanate from irreversible inactivation to efficient hydrolysis. The substitution, which restored the canonical SDN motif (SDG→SDN), allowed for efficient hydrolysis of clavulanate, with a more than 10⁴-fold increase in k_cat (0.41 s⁻¹), without affecting the hydrolysis of other β-lactams. Mass spectrometry revealed that acylation of BlaC and of its G¹³²N variant by clavulanate follows similar paths, involving sequential formation of two acylenzymes. Decarboxylation of the first acylenzyme results in a stable secondary acylenzyme in BlaC, whereas hydrolysis occurs in the G¹³²N variant. The SDN/SDG polymorphism defines two mycobacterial lineages comprising rapidly and slowly growing species, respectively. Together, these results suggest that the efficacy of β-lactam–clavulanate combinations may be limited by the emergence of resistance. β-Lactams active without clavulanate, such as faropenem, should be prioritized for the development of new therapies.