Azathioprine induction of tumors with microsatellite instability: Risk evaluation using a mouse model

Mismatch-repair (MMR)-deficient cells show increased in vitro tolerance to thiopurines because they escape apoptosis resulting from MMR-dependent signaling of drug-induced DNA damage. Prolonged treatment with immunosuppressants including azathioprine (Aza), a thiopurine prodrug, has been suggested as a risk factor for the development of late onset leukemias/lymphomas displaying a microsatellite instability (MSI) phenotype, the hallmark of a defective MMR system. We performed a dose effect study in mice to investigate the development of MSI lymphomas associated with long term Aza treatment. Over two years, Aza was administered to mice that were wild type, null or heterozygous for the MMR gene Msh2. Ciclosporin A, an immunosuppressant with an MMR-independent signaling, was also administered to Msh2^wt mice as controls. Survival, lymphoma incidence and MSI tumor phenotype were investigated. Msh2^+/− mice were found more tolerant than Msh2^wt mice to the cytotoxicity of Aza. In Msh2^+/− mice, Aza induced a high incidence of MSI lymphomas in a dose-dependent manner. In Msh2^wt mice, a substantial lifespan was only observed at the lowest Aza dose. It was associated with the development of lymphomas, one of which displayed the MSI phenotype, unlike the CsA-induced lymphomas. Our findings define Aza as a risk factor for an MSI-driven lymphomagenesis process.     

Postconditioning: from the bench to bedside

Infarct size is determined not only by the severity of ischemia but also by pathological processes initiated at reperfusion. Accumulating experimental evidence indicates that lethal reperfusion injury might account for up to half of the final size of the myocardial infarct. Ischemic postconditioning (brief repeated periods of ischemia-reperfusion applied at the onset of coronary reflow) has been recently described as a powerful cardioprotection mechanism that prevents lethal reperfusion injury. This is the first method proven to reduce the final infarct size by about 50% in several in vivo models and to be confirmed in recent preliminary human studies. The molecular pathways are incompletely mapped but they probably converge to a mitochondrial key target: the mitochondrial permeability transition pore (PTP) which opening during early reperfusion is an event that promotes myocardial cell death. In different animal models and experimental settings, pharmacological PTP inhibition at the onset of reperfusion reproduces all the cardioprotective effects of ischemic postconditioning. In a recent proof-of-concept trial, the administration (just before percutaneous coronary intervention) of cyclosporine A, a potent PTP inhibitor, was associated with smaller infarct size. This review will focus on the physiological preclinical data on both ischemic and pharmacological postconditioning that are relevant to their translation to clinical therapeutics.     

Postoperative control in deep brain stimulation of the subthalamic region: the contact membership concept

Object

In deep brain stimulation, the anatomic positions of electrode contact centers are used as the basis for analysis. We propose a new semi-quantitative approach (contact membership concept) considering patient’s individual anatomy, contact size, and extent of involvement of STN and neighboring structures.

Materials and methods

In ten bilaterally operated and improved Parkinsonian patients, effective contact positions (contacts used for monopolar stimulation) were analyzed. The position of the contact center (classical binary approach: each center assigned, 1, or not, 0, to a given structure) and of the contact in its dimension (contact membership concept: membership degree, ordinal values from 0 to 1, assigned to each anatomic structure according to extent of involvement) were compared for the whole patient group and, individually, for each patient.

Results

The membership concept revealed that for 13 out of 20 contacts, more than one structure was involved, where the classical binary approach assigned only one structure. For both approaches lateral STN, zona incerta and H1 (Forel’s Field) were the main structures involved, but their frequencies of appearance differed.

Conclusion

The membership concept allows detailed analysis of the anatomic contact position. In the future this approach could assist in correlating anatomy and clinical results for all electrode contacts (effective ones and clinically less efficient ones).     

Genetic and Biochemical Characterization of the First Extended-Spectrum CARB-Type ?-Lactamase,RTG-4, from Acinetobacter baumannii

Acinetobacter baumannii isolate KAR was uncommonly more resistant to cefepime and cefpirome than to ceftazidime and cefotaxime. Cloning and expression of the β-lactamase gene content of this isolate into Escherichia coli TOP10 identified ß-lactamase RTG-4 (or CARB-10), which corresponds to the first reported extended-spectrum CARB-type enzyme. RTG-4 is a plasmid-encoded Ambler class A β-lactamase whose sequence differs by 4 amino acid substitutions from the narrow-spectrum β-lactamase RTG-3. RTG-4 hydrolyzes cefepime and cefpirome and weakly hydrolyzes ceftazidime due to the single Ser-to-Thr substitution at Ambler position 69. RTG-4 is less susceptible to inhibition by tazobactam and sulbactam than RTG-3. Expression of β-lactamase RTG-4 in a wild-type A. baumannii reference strain showed that it conferred resistance to cefepime and cefpirome. The genetic environment of the bla_RTG-4 gene was made of a peculiar transposon located on a ca. 50-kb plasmid. ISAba9, located upstream of bla_RTG-4, may be responsible for its acquisition by recognizing a secondary right inverted repeat sequence, thus acting by a one-ended transposition process.Acinetobacter baumannii is an opportunistic pathogen that is an important source of nosocomial infections such as pneumonia, septicemia, urinary tract infections, and wound infections (2). Treatment of infections due to this microorganism is becoming a serious clinical concern since A. baumannii is frequently resistant to multiple classes of antibiotics (23, 37). The main mechanism of resistance to β-lactam molecules in A. baumannii is the production of β-lactamases. Resistance to carbapenems is mostly related to the production of metallo-β-lactamases or carbapenem-hydrolyzing oxacillinases (33), whereas resistance to expanded-spectrum cephalosporins mostly results from the overexpression of the natural AmpC-type enzyme (3) or from the acquisition of extended-spectrum β-lactamases (ESBLs). Those ESBLs may correspond to TEM or SHV derivatives but mostly correspond to β-lactamases of the VEB or PER type in A. baumannii (21). Carbenicillin-hydrolyzing β-lactamases (also named CARB enzymes) are narrow-spectrum class A penicillinases that share less than 50% amino acid identity with SHV and TEM β-lactamases (7). The 10 ß-lactamase variants of this family show similar hydrolytic properties but are divided into two subgroups, named the CARB and RTG subgroups, according to their amino acid sequences. The CARB subgroup includes CARB-1 (formerly PSE-4) (18), CARB-2 (formerly PSE-1) (18), CARB-3 (14), CARB-4 (26), Proteus mirabilis N29 β-lactamase (11), CARB-6 (6), CARB-7 (20), and CARB-9 (25). The RTG subgroup includes RTG-1 (P. mirabilis GN79 enzyme) (34), RTG-2 (CARB-5; described in Acinetobacter calcoaceticus var. anitratus [24]), and RTG-3 (CARB-8; identified from an Oligella urethralis clinical isolate [17]). Although those three RTG-type ß-lactamases possess low levels of amino acid identity with members of the CARB family (44%), they might be considered the ancestors of that enzymatic group, as proposed by Choury et al. (7).The carbenicillin-hydrolyzing enzymes belonging to the CARB group were first identified from Pseudomonas aeruginosa clinical isolates (38). The bla_CARB genes are now widespread among distantly related bacteria, including Vibrio spp. (19), because of their location on mobile genetic structures. Indeed, bla_CARB genes such as bla_CARB-1 (22), bla_CARB-2 (28), and bla_CARB-4 (36) were found as a form of gene cassettes of class 1 integrons. In contrast, little is known about the genetic environment of the bla_RTG genes.Analysis of the β-lactamase content of an A. baumannii clinical isolate exhibiting an atypical higher level of resistance to cefepime and cefpirome than to ceftazidime and cefotaxime allowed us to identify a novel plasmid-encoded ESBL-encoding gene belonging to the bla_RTG group.     

Chromosome-borne class A BOR-1 beta-Lactamase of Bordetella bronchiseptica and Bordetella parapertussis

A narrow-spectrum clavulanic acid-inhibited class A beta-lactamase, BOR-1, was identified in a Bordetella bronchiseptica clinical isolate. It shared 45% amino acid identity with L-2 from Stenotrophomonas maltophilia. An identical beta-lactamase gene was found in B. bronchiseptica and Bordetella parapertussis reference strains that may contribute only in part to their resistance phenotype.     

SARS-CoV-2 Transmission in Belgian French-Speaking Primary Schools: An Epidemiological Pilot Study

Schools have been a point of attention during the pandemic, and their closure one of the mitigating measures taken. A better understanding of the dynamics of the transmission of SARS-CoV-2 in elementary education is essential to advise decisionmakers. We conducted an uncontrolled non-interventional prospective study in Belgian French-speaking schools to describe the role of attending asymptomatic children and school staff in the spread of COVID-19 and to estimate the transmission to others. Each participant from selected schools was tested for SARS-CoV-2 using a polymerase chain reaction (PCR) analysis on saliva sample, on a weekly basis, during six consecutive visits. In accordance with recommendations in force at the time, symptomatic individuals were excluded from school, but per the study protocol, being that participants were blinded to PCR results, asymptomatic participants were maintained at school. Among 11 selected schools, 932 pupils and 242 school staff were included between January and May 2021. Overall, 6449 saliva samples were collected, of which 44 came back positive. Most positive samples came from isolated cases. We observed that asymptomatic positive children remaining at school did not lead to increasing numbers of cases or clusters. However, we conducted our study during a period of low prevalence in Belgium. It would be interesting to conduct the same analysis during a high prevalence period.     

The clinical course of interstitial lung disease in an adult patient with an ABCA3 homozygous complex allele under hydroxychloroquine and a review of the literature

Objective: The gene mutations responsible for ABCA3 protein deficiency are involved in respiratory distress of the newborn and much more rarely in adult interstitial lung diseases (ILD). An adult patient homozygous for a complex allele encompassing the p.Ala1027Pro likely pathogenic mutation and the p.Gly974Asp variation was followed for a late-onset and fibrotic ILD. The evolution was marked by progressive clinical and functional degradation despite corticosteroid pulses. The patient, who was first registered on the list for lung transplantation, was improved quickly and persistently for at least 6.5 years with hydroxychloroquine treatment, allowing removal from the transplant list.