Hemoglobin A1c Serum Level Predicts 5-year Mortality in Patients with Cognitive Impairment

Background

Subjective cognitive decline (SCD) and mild cognitive impairment (MCI) may occur as preclinical stages of Alzheimer's disease (AD), ultimately leading to dementia. Glycated hemoglobin A1c (HbA1c) is a diagnostic marker for diabetes mellitus and indicates mortality risk.

Objectives

This university-based, exploratory retrospective study examined the impact of HbA1c serum level on 5-year mortality among individuals with cognitive impairment.

Methods

Included were 1076 subjects aged at least 50 years who visited the Memory Outpatient Clinic of the Medical University of Vienna due to memory problems. Participants were diagnosed with SCD, MCI, or AD subsequent to neurological examination, standard laboratory blood tests, and neuropsychological testing. Survival was compared between diagnostic subgroups and with respect to HbA1c categories using log-rank tests based on Kaplan-Meier functions. The Neuropsychological Test Battery Vienna (NTBV) was dimensionally reduced, and a principal component analysis (PCA) was performed to further analyze results. Corresponding factor scores, HbA1c values, and baseline characteristics were included in Cox proportional hazards models to assess 5-year mortality risk.

Results

During the observation period, 323 patients (30%) died at a mean age comparable between diagnostic subgroups (SCD 84.2 ± 10.1, MCI 81.2 ± 8.3, AD 82.2 ± 7.4 years). Individuals with normal serum HbA1c levels had significant advantages in survival within the MCI (12.9 ± .3 vs. 10.0 ± .8 years) and the AD subgroups (8.2 ± .4 vs. 5.5 ± .6 years), and metric HbA1c predicted 5-year mortality (HR 1.24).

Conclusion

This study demonstrates an association between abnormal HbA1c serum levels and increased mortality.

Molecular Interactions of Cephalosporins with the Deep Binding Pocket of the RND Transporter AcrB

The drug/proton antiporter AcrB, part of the major efflux pump AcrABZ-TolC in Escherichia coli, is characterized by its impressive ability to transport chemically diverse compounds, conferring a multidrug resistance phenotype. However, the molecular features differentiating between good and poor substrates of the pump have yet to be identified. In this work, we combined molecular docking with molecular dynamics simulations to study the interactions between AcrB and two representative cephalosporins, cefepime and ceftazidime (a good and poor substrate of AcrB, respectively). Our analysis revealed different binding preferences of the two compounds toward the subsites of the large deep binding pocket of AcrB. Cefepime, although less hydrophobic than ceftazidime, showed a higher affinity than ceftazidime for the so-called hydrophobic trap, a region known for binding inhibitors and substrates. This supports the hypothesis that surface complementarity between the molecule and AcrB, more than the intrinsic hydrophobicity of the antibiotic, is a feature required for the interaction within this region. Oppositely, the preference of ceftazidime for binding outside the hydrophobic trap might not be optimal for triggering allosteric conformational changes needed to the transporter to accomplish its function. Altogether, our findings could provide valuable information for the design of new antibiotics less susceptible to the efflux mechanism.

Hepatitis E virus blood donor NAT screening: as much as possible or as much as needed?

BACKGROUND

The cost-benefit question of general screening of blood products for the hepatitis E virus (HEV) is currently being discussed. One central question is the need for individual nucleic acid amplification techniques (NAT) screening (ID-NAT) versus minipool NAT screening (MP-NAT) approaches to identify all relevant viremias in blood donors. Here, the findings of ID-NAT versus MP-NAT in pools of 96 samples were compared.

STUDY DESIGN AND METHODS

From November 2017 to January 2018, a total of 10,141 allogenic blood donations from 7650 individual German blood donors were screened for the presence of HEV RNA using MP-NAT (96 samples) (RealStar HEV RT-PCR Kit) compared to ID-NAT (cobas HEV assay) on the fully automated cobas 6800 platform.

RESULTS

Parallel screening of MP (n = 122, 96 samples/MP) using both methods detected seven reactive pools. After pool resolution, 8 HEV RNA-positive donations were identified by the in-house detection method, whereas 17 HEV RNA-positive donations were identified by ID-NAT with the cobas HEV assay. This resulted in an incidence of 1:1268 donations (0.079%) for MP-NAT screening and 1:597 donations (0.168%) for ID-NAT screening.

CONCLUSIONS

The detection frequency of HEV RNA was approximately 50% higher if ID-NAT was used compared to MP-NAT. However, viral loads of ID-NAT-only samples were below 25 IU/mL and will often not result in transfusion-transmitted HEV (TT-HEV) infection, taking into account the currently known infectious dose of 5.0E + 04 IU inevitably resulting in TT-HEV infection. The clinical relevance and need for identification of these low-level HEV-positive donors still require further investigation.

Identification and characterization of carbapenem binding sites within the RND-transporter AcrB

Understanding the molecular determinants for recognition, binding and transport of antibiotics by multidrug efflux systems is important for basic research and useful for the design of more effective antimicrobial compounds. Imipenem and meropenem are two carbapenems whose antibacterial activity is known to be poorly and strongly affected by MexAB-OprM, the major efflux pump transporter in Pseudomonas aeruginosa. However, not much is known regarding recognition and transport of these compounds by AcrAB-TolC, which is the MexAB-OprM homologue in Escherichia coli and by definition the paradigm model for structural studies on efflux pumps. Prompted by this motivation, we unveiled the molecular details of the interaction of imipenem and meropenem with the transporter AcrB by combining computer simulations with biophysical experiments. Regarding the interaction with the two main substrate binding regions of AcrB, the so-called access and deep binding pockets, molecular dynamics simulations revealed imipenem to be more mobile than meropenem in the former, while comparable mobilities were observed in the latter. This result is in line with isothermal titration calorimetry, differential scanning experiments, and binding free energy calculations, indicating a higher affinity for meropenem than imipenem at the deep binding pocket, while both sharing similar affinities at the access pocket. Our findings rationalize how different physico-chemical properties of compounds reflect on their interactions with AcrB. As such, they constitute precious information to be exploited for the rational design of antibiotics able to evade efflux pumps.

Molecular Determinants of the Promiscuity of MexB and MexY Multidrug Transporters of Pseudomonas aeruginosa

Secondary multidrug transporters of the resistance-nodulation-cell division (RND) superfamily contribute crucially to antibiotic resistance in Gram-negative bacteria. Compared to the most studied transporter AcrB of Escherichia coli, little is known about the molecular determinants of distinct polyspecificities of the most important RND transporters MexB and MexY of Pseudomonas aeruginosa. In an effort to add knowledge on this topic, we performed an exhaustive atomic-level comparison of the main putative recognition sites (access and deep binding pockets) in these two Mex transporters. We identified an underlying link between some structural, chemical and dynamical features of the binding pockets and the physicochemical nature of the corresponding substrates recognized by either one or both pumps. In particular, mosaic-like lipophilic and electrostatic surfaces of the binding pockets provide for both proteins several multifunctional sites for diffuse binding of diverse substrates. Specific lipophilicity signatures of the weakly conserved deep pocket suggest a key role of this site as a selectivity filter as in Acr transporters. Finally, the different dynamics of the bottom-loop in MexB and MexY support its possible role in binding of large substrates. Our work represents the first comparative study of the major RND transporters in P. aeruginosa and also the first structure-based study of MexY, for which no experimental structure is available yet.

Vitamin D supplementation and bone turnover in advanced heart failure: the EVITA trial

Low vitamin D status is common in patients with heart failure and may influence bone health. A daily vitamin D dose of 4000 IU (moderately high dose) for 3 years had however no effect on parameters of bone metabolism, even in patients with very low vitamin D status.

INTRODUCTION

Low vitamin D status is common in patients with heart failure (HF) and has been related to disturbed bone turnover. The present study investigated the effect of a daily vitamin D₃ dose of 4000 IU on bone turnover markers (BTMs) in patients with advanced HF and 25-hydroxyvitamin D (25OHD) concentrations < 75 nmol/L.

METHODS

In this pre-specified secondary analysis of a randomized controlled trial, we assessed in 158 male HF patients (vitamin D group: n = 80; placebo group: n = 78) between-group differences in calciotropic hormones (25OHD, 1,25-dihydroxyvitamin D [1,25(OH)₂D], intact parathyroid hormone [iPTH]), and BTMs (cross-linked C-telopeptide of type I collagen, bone-specific alkaline phosphatase, undercarboxylated osteocalcin). Comparisons were performed at the end of a 3-year vitamin D supplementation period with adjustments for baseline values.

RESULTS

Compared with placebo, vitamin D increased 25OHD on average by 54.3 nmol/L. At study termination, 25OHD and 1,25(OH)₂D were significantly higher (P < 0.001 and P = 0.007, respectively), whereas iPTH tended to be lower in the vitamin D group than in the placebo group (P = 0.083). BTMs were initially within their reference ranges and did not differ significantly between groups at study termination, neither in the entire study cohort nor when data analysis was restricted to the subgroup of patients with initial 25OHD concentrations < 30 nmol/L (n = 54) or to patients with initial hyperparathyroidism (n = 65) (all P values > 0.05).

CONCLUSIONS

A daily vitamin D₃ dose of 4000 IU did not influence BTMs. Data indicate that vitamin D supplementation will not lower bone turnover in male patients with heart failure.

Molecular Rationale behind the Differential Substrate Specificity of Bacterial RND Multi-Drug Transporters

Resistance-Nodulation-cell Division (RND) transporters AcrB and AcrD of Escherichia coli expel a wide range of substrates out of the cell in conjunction with AcrA and TolC, contributing to the onset of bacterial multidrug resistance. Despite sharing an overall sequence identity of ~66% (similarity ~80%), these RND transporters feature distinct substrate specificity patterns whose underlying basis remains elusive. We performed exhaustive comparative analyses of the putative substrate binding pockets considering crystal structures, homology models and conformations extracted from multi-copy μs-long molecular dynamics simulations of both AcrB and AcrD. The impact of physicochemical and topographical properties (volume, shape, lipophilicity, electrostatic potential, hydration and distribution of multi-functional sites) within the pockets on their substrate specificities was quantitatively assessed. Differences in the lipophilic and electrostatic potentials among the pockets were identified. In particular, the deep pocket of AcrB showed the largest lipophilicity convincingly pointing out its possible role as a lipophilicity-based selectivity filter. Furthermore, we identified dynamic features (not inferable from sequence analysis or static structures) such as different flexibilities of specific protein loops that could potentially influence the substrate recognition and transport profile. Our findings can be valuable for drawing structure (dynamics)-activity relationship to be employed in drug design.

Establishment of a proficiency panel for an external quality assessment programme for the detection of bacterial contamination in platelet concentrates using rapid and cultural detection methods

BACKGROUND

Platelet concentrates (PCs) are the main focus regarding the residual risk of transfusion-transmitted bacterial infections. Rapid screening methods for bacterial detection in platelets have been optimized over the last decade, but their external evaluation represents a complicated process. We developed a new type of proficiency panel for bacterial detection in PCs using currently available screening methods (especially rapid methods) suitable for external quality assessment programmes (EQAP).

METHODS

PC samples were inoculated with different bacteria at two concentrations (10E+03 CFU/ml, 10E+05 CFU/ml) and stored under temperature-controlled conditions (1-5 days). Bacterial growth was further prevented by the addition of 0-20 μg/ml cotrimoxazole. Samples were analysed prior to and after storage using rapid detection methods (Bactiflow (BF), bacteria-generic NAT) and cultural methods to determine the influence of storage and antibiotic treatment on bacterial counts and the result outcome. A pilot EQAP was performed with four participants.

RESULTS

Testing under the evaluated conditions demonstrated that bacterial counts remained constant prior to and after storage. The supplementation of 10 μg/ml cotrimoxazole did not influence bacterial detection using the two rapid detection methods BF and NAT. Furthermore, the detection of bacteria using cultural methods is still possible despite of antibiotic supplementation. The pilot EQAP confirmed these results. A storage time of up to 3 days proved practicable, showing no considerable influence on bacterial count and outcome of test results.

CONCLUSION

The established proficiency panel provided PC matrix-conform samples with stabilized bacterial counts which can be analysed in parallel by rapid and cultural detection methods.

A prospective clinical trial to assess lapatinib effects on cutaneous squamous cell carcinoma and actinic keratosis

BACKGROUND

Antiepidermal growth factor receptor (EGFR)-targeted therapy is widely used in many epithelial cancer types. We investigated lapatinib effects on cutaneous squamous cell carcinoma (cSCC) scheduled for resection and in coexisting precursor lesions (actinic keratosis (AK) and Bowen's disease (BD)) in a phase 2 mode of action clinical trial including a histological workup of the cSCC.

PATIENTS AND METHODS

We initiated a prospective single-centre, open-label, non-controlled clinical study with translational intentions to investigate changes in size and histopathological features in cSCC after a 14-day period of neoadjuvant lapatinib therapy at a dose of 1500 mg/day prior to surgery, to quantify the impact on AK and BD in the same patient after 56 days and to evaluate the tolerability in patients with cSCC and precursor lesions.

RESULTS

10 immunocompetent male patients were included with a mean age of 73 years (range 59-87). 8 patients were treated with the study medication lapatinib 1500 mg/day for a total duration of 56 days according to the protocol and were available for full analysis, whereas 2 patients had to discontinue treatment during the first 2 weeks because of adverse events (diarrhoea, pancreatitis). Tolerability was acceptable with only 1 related grade III adverse event. A reduction in tumour size of cSCC was documented in 2 of 8 evaluable patients after 14 days of treatment. The mean regression of captured precursor lesions was 30% after 56 days of treatment and 36% 28 days after therapy cessation.

CONCLUSIONS

Short-term lapatinib resulted in a cSCC tumour reduction in 2 of 8 patients. In addition, there was a clinically documented reduction of AK in 7 of 8 patients encouraging larger clinical trials, especially in high-risk patients with cSCC such as organ transplant recipients.

TRIAL REGISTRATION NUMBER

NCT0166431.

Interaction of antibacterial compounds with RND efflux pumps in Pseudomonas aeruginosa

Pseudomonas aeruginosa infections are becoming increasingly difficult to treat due to intrinsic antibiotic resistance and the propensity of this pathogen to accumulate diverse resistance mechanisms. Hyperexpression of efflux pumps of the Resistance-Nodulation-Cell Division (RND)-type multidrug efflux pumps (e.g., MexAB-OprM), chromosomally encoded by mexAB-oprM, mexCD-oprJ, mexEF-oprN, and mexXY (-oprA) is often detected in clinical isolates and contributes to worrying multi-drug resistance phenotypes. Not all antibiotics are affected to the same extent by the aforementioned RND efflux pumps. The impact of efflux on antibiotic activity varies not only between different classes of antibiotics but also between members of the same family of antibiotics. Subtle differences in physicochemical features of compound-pump and compound-solvent interactions largely determine how compounds are affected by efflux activity. The combination of different high-resolution techniques helps to gain insight into the functioning of these molecular machineries. This review discusses substrate recognition patterns based on experimental evidence and computer simulations with a focus on MexB, the pump subunit of the main RND transporter in P. aeruginosa.

Look-back study on recipients of Parvovirus B19 (B19V) DNA-positive blood components

BACKGROUND AND OBJECTIVES

To assess the relevance of Parvovirus B19 (B19V) DNA at low to intermediate concentrations in blood donors for the recipients of their blood components.

MATERIAL AND METHODS

We studied recipients of B19V DNA-positive blood components [red blood cell concentrates (RBCs), pooled platelet concentrates and fresh frozen plasma]. This included archived pretransfusion samples as well as follow-up samples investigated by ELISA or NAT and genome sequence analysis.

RESULTS

In 132 out of 424 recipients, we could detect no anti-B19V IgG before transfusion. In 67 out of 132 sero-negative recipients, a follow-up sample was available. Sixty-five of these received blood components from donors with <10(4) IU B19V DNA/ml plasma and had no evidence of transfusion-transmitted (TT)-B19V infection. Homology in genome sequences in donor and recipient provided evidence for a TT-B19V infection in two recipients. Both patients received RBC containing 3.4 × 10(6) and 1.8 × 10(4) IU B19V DNA/ml plasma, respectively. The anti-B19V IgG titres in the donors were 2 and 76 IU/ml plasma, respectively. The antibodies in the second donor were directed against capsid proteins and are thus considered as potential neutralizing antibodies.

CONCLUSIONS

TT-B19V infections through blood components with low (<10(4) IU/ml plasma) B19V DNA concentrations did not occur in our study. One of the TT-B19V infections occurred from RBC with intermediate B19V DNA concentration despite the presence of potential neutralizing antibodies in the donor, but its clinical significance was low.

Association between circulating 25-hydroxyvitamin D levels and medication use in patients scheduled for cardiac surgery

BACKGROUND AND AIM

Low vitamin D status, i.e. circulating 25-hydroxyvitamin D (25OHD) levels <50 nmol/l, is independently associated with increased CVD risk. Medication use may influence 25OHD levels. We therefore investigated the association of circulating 25OHD with medication use in patients scheduled for cardiac surgery.

METHODS AND RESULTS

A total of 11,256 patients were included in this cross-sectional study. We compared 25OHD levels of medication users (18 groups of continuously used and 5 groups of intermittently used medications) with levels of non-users. Moreover, we assessed variables (medications, demographic and clinical parameters) that were independently associated with 25OHD levels <50 nmol/l. The prevalence of 25OHD levels <50 nmol/l was 65.7%. The use of statins and immunosuppressive agents was significantly associated with higher 25OHD levels and lower odds ratios of 25OHD levels <50 nmol/l. The use of ACE-inhibitors, catecholamines and antibiotics was associated with lower 25OHD levels and higher odds ratios of 25OHD levels <50 nmol/l. However, only use of antibiotics, immunosuppressive agents and catecholamines showed clinically relevant differences in 25OHD levels, i.e. differences of more than +4 nmol/l or -4 nmol/l, compared with respective non-users. These medications were prescribed either intermittently (antibiotics, catecholamines) and/or infrequently (<2%; immunosuppressive agents, catecholamines) and/or its causal relationship with circulating 25OHD is questionable (antibiotics). Female sex and blood drawing during wintertime were associated with the highest odds ratios of 25OHD levels <50 nmol/l.

CONCLUSION

Data indicate that in patients with high cardiovascular risk profile medication use does not substantially contribute to 25OHD levels <50 nmol/l.

Vitamin D metabolites and fibroblast growth factor-23 in patients with left ventricular assist device implants: association with stroke and mortality risk

PURPOSE

Stroke and mortality risk in patients with left ventricular assist device (LVAD) implants continue to be high. Whether nonclassical cardiovascular risk markers such as vitamin D metabolites and fibroblast growth factor (FGF)-23 contribute to this risk remains to be studied, and this was the objective of our work.

METHODS

In 154 LVAD patients (91 HeartWare and 63 HeartMate II implants), we measured circulating 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), parathyroid hormone (PTH) and FGF-23 shortly before LVAD implantation and investigated their association with stroke and mortality risk during 1-year follow-up.

RESULTS

Of the study cohort, 34.4 and 92.2%, respectively, had deficient 25OHD (<25 nmol/l) and 1,25(OH)2D3 (<41 pmol/l) values, whereas 42.6 and 98.7%, respectively, had elevated PTH levels (>6.7 pmol/l) and FGF-23 values above the reference range (100 RU/ml). One-year freedom from stroke was 80.9 %, and 1-year survival was 64.3%. The multivariable-adjusted hazard ratio of stroke was 2.44 (95% CI: 1.09-5.45; P = 0.03) for the subgroup of 25OHD levels <25 nmol/l (reference group: 25OHD levels ≥25 nmol/l). The multivariable-adjusted hazard ratio of 1-year mortality was 2.78 (95% CI: 1.52-5.09; P = 0.001) for patients with 25OHD levels <25 nmol/l compared with patients with 25OHD levels ≥25 nmol/l. PTH, FGF-23 and 1,25(OH)2D3 were not associated with stroke or mortality risk.

CONCLUSIONS

In LVAD patients, deficient 25OHD levels are independently associated with high stroke and mortality risk. If confirmed in randomized controlled trials, preoperative correction of deficient vitamin D status could be a promising measure to reduce stroke and mortality risk in LVAD patients.

Recognition of imipenem and meropenem by the RND-transporter MexB studied by computer simulations

Basic understanding of the means by which multidrug efflux systems can efficiently recognize and transport drugs constitutes a fundamental step toward development of compounds able to tackle the continuous outbreak of new bacterial strains resistant to traditional antibiotics. We applied a series of computational techniques, from molecular docking to molecular dynamics simulations and free energy estimate methods, to determine the differences in the binding properties of imipenem and meropenem, two potent antibiotics of the carbapenem family, to MexB, the RND transporter of the major efflux system of Pseudomonas aeruginosa. We identified and characterized two affinity sites in the periplasmic domain of the transporter, sharing strong similarities with the distal and proximal binding pockets identified in AcrB, the homologue of MexB in Escherichia coli. According to our results, meropenem has a higher affinity to the distal binding pocket than imipenem while both compounds are weakly bound to the proximal pocket. This different behavior is mainly due to the hydration properties of the nonpharmacophore part of the two compounds, being that of imipenem less bulky and hydrophobic. Our data provide for the first time a rationale at molecular level for the experimental evidence indicating meropenem as a compound strongly affected by MexB contrary to imipenem, which is apparently poorly transported by the same pump.

Effect of vitamin D supplementation on testosterone levels in men

The male reproductive tract has been identified as a target tissue for vitamin D, and previous data suggest an association of 25-hydroxyvitamin D [25(OH)D] with testosterone levels in men. We therefore aimed to evaluate whether vitamin D supplementation influences testosterone levels in men. Healthy overweight men undergoing a weight reduction program who participated in a randomized controlled trial were analyzed for testosterone levels. The entire study included 200 nondiabetic subjects, of whom 165 participants (54 men) completed the trial. Participants received either 83 μg (3,332 IU) vitamin D daily for 1 year (n = 31) or placebo (n =2 3). Initial 25(OH)D concentrations were in the deficiency range (< 50 nmol/l) and testosterone values were at the lower end of the reference range (9.09-55.28 nmol/l for males aged 20-49 years) in both groups. Mean circulating 25(OH)D concentrations increased significantly by 53.5 nmol/l in the vitamin D group, but remained almost constant in the placebo group. Compared to baseline values, a significant increase in total testosterone levels (from 10.7 ± 3.9 nmol/l to 13.4 ± 4.7 nmol/l; p < 0.001), bioactive testosterone (from 5.21 ± 1.87 nmol/l to 6.25 ± 2.01 nmol/l; p = 0.001), and free testosterone levels (from 0.222 ± 0.080 nmol/l to 0.267 ± 0.087 nmol/l; p = 0.001) were observed in the vitamin D supplemented group. By contrast, there was no significant change in any testosterone measure in the placebo group. Our results suggest that vitamin D supplementation might increase testosterone levels. Further randomized controlled trials are warranted to confirm this hypothesis.

Differentiation of species of the Streptococcus bovis/equinus-complex by MALDI-TOF Mass Spectrometry in comparison to sodA sequence analyses

The Streptococcus bovis/equinus complex is a heterogeneous group within the group D streptococci with important clinical relevance regarding infective endocarditis, sepsis and colon carcinoma. The taxonomic identification of species and sub-species of this complex, by the standard methods remains difficult. In the present study, we compared the cluster analysis of 88 strains of species of the S. bovis/equinus complex by sequence analysis of the manganese-dependent superoxide dismutase gene (sodA) and by Matrix Assisted Laser Desorption/Ionization-Time Of Flight Mass Spectrometry (MALDI-TOF MS). We observed a high congruence of strain grouping by MALDI-TOF MS in comparison with sodA sequence analyses, demonstrating the accuracy and reliability of MALDI-TOF MS in comparison to DNA sequence-based method. By generating mass spectra for each species and sub-species, we were able to discriminate all members of the S. bovis/equinus complex. Furthermore, we demonstrated reliable identifications to the species level by MALDI-TOF MS, independently of cultivation conditions.

Crystallographic analysis of bacterial signal peptidase in ternary complex with arylomycin A2 and a beta-sultam inhibitor

Bacterial type I signal peptidase (SPase I), an essential membrane-bound endopeptidase with a unique Ser/Lys dyad mechanism, is being investigated as a potential novel antibiotic target. We present here binding and inhibition assays along with crystallographic data that shows that the lipohexapeptide-based natural product arylomycin A2 and the morpholino-beta-sultam derivative (BAL0019193) inhibit SPase I by binding to non-overlapping subsites near the catalytic center. The 2.0 A resolution crystal structure of the soluble catalytic domain of Escherichia coli SPase I (SPase I Delta2-75) in ternary complex with arylomycin A2 and BAL0019193 reveals the position of BAL0019193 adjacent to arylomycin A2 within the SPase I binding site. BAL0019193 binds in a noncovalent manner in close proximity to SPase I residues Ser88, Ser90, Lys145, Asn277, Ala279, and Glu307, as well as atom O45 of arylomycin A2. The binding mode of arylomycin A2 in this 2.0 A resolution ternary complex is compared to that seen in the previous 2.5 A resolution arylomycin A2-SPase cocrystal structure. This work contributes to our understanding of SPase I inhibitor/substrate recognition and should prove helpful in the further development of novel antibiotics based on the inhibition of SPase I.

Spore-forming organisms in platelet concentrates: a challenge in transfusion bacterial safety

Bacterial detection and pathogen reduction are widely used methods of minimizing the risk of transfusion-transmitted bacterial infection. But, bacterial spores are highly resistant to chemical and physical agents. In this study, we assessed the bacterial proliferation of spore-forming organisms seeded into platelet concentrates (PCs) to demonstrate that spores can enter the vegetative state in PCs during storage. In the in vitro study, PCs were inoculated with 1-10 spores mL(-1)of Bacillus cereus (n = 1), Bacillus subtilis (n = 2) and Clostridium sporogenes (n = 2). Sampling was performed during 6-day aerobic storage at 22 degrees C. The presence of bacteria was assessed by plating culture, automated culture and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Spores of the C. sporogenes do not enter the vegetative phase under PC storage conditions, whereas B. subtilis and B. cereus showed growth in the PC and could be detected using RT-PCR and automated culture. Depending on the species and inoculums, bacterial spores may enter the vegetative phase during PC storage and can be detected by bacterial detection methods.

Propionibacterium acnes lacks the capability to proliferate in platelet concentrates

BACKGROUND AND OBJECTIVES

Propionibacterium acnes is considered to be one of the most frequent contaminants of platelet concentrates (PCs) when anaerobic culture-based detection methods are used. But Propionibacteria are often detected too late when blood products have already been transfused. Therefore, its transfusion relevance is still demanding clarification because studies of the outcome of patients transfused with P. acnes-contaminated PCs are still uncommon. In this study, we monitored clinical effects in patients after transfusion of PCs, which were detected too late in sterility testing. Furthermore, we assessed the bacterial proliferation of Propionibacterium species seeded into PCs to clarify their significance for platelet bacteria screening.

MATERIALS AND METHODS

In the look-back process, we followed the route of the putative contaminated PC units from storage to transfusion. In the in vitro study, PCs were inoculated with 1-100 colony-forming unit (CFU)/ml of clinical isolates of Propionibacteria (n = 10). Sampling was performed during 10-day aerobic storage at 22 degrees C. The presence of bacteria was assessed by plating culture and automated BacT/Alert culture system.

RESULTS

Propionibacterium acnes shows slow or no growth under PC storage conditions. Clinical signs of adverse events after transfusion of potentially contaminated PC units were not reported.

CONCLUSION

Propionibacteria do not proliferate under PC storage conditions and therefore may be missed or detected too late when blood products have already been transfused.

In vitro efficacy of new antifolates against trimethoprim-resistant Bacillus anthracis

Bacillus anthracis is innately resistant to trimethoprim (TMP), a synthetic antifolate that selectively inhibits several bacterial dihydrofolate reductases (DHFRs) but not human DHFR. Previously, we were able to confirm that TMP resistance in B. anthracis (MIC > 2,048 microg/ml) is due to the lack of selectivity of TMP for the B. anthracis DHFR (E. W. Barrow, P. C. Bourne, and W. W. Barrow, Antimicrob. Agents Chemother. 48:4643-4649, 2004). In this investigation, 24 2,4-diaminopyrimidine derivatives, representing a class of compounds with dihydrophthalazine side chains, were screened for their in vitro effects on B. anthracis Sterne and their selectivities for the B. anthracis DHFR. MICs were obtained by a colorimetric (Alamar blue) broth microdilution assay. Purified human recombinant DHFR (rDHFR) and B. anthracis rDHFR were used in a validated enzyme assay to determine the 50% inhibitory concentrations (IC(50)s) and the selectivity ratios of the derivatives. The MICs ranged from 12.8 to 128 microg/ml for all but nine compounds, for which the MICs were > or =128 microg/ml. The IC(50) values for B. anthracis rDHFR ranged from 46 to 600 nM, whereas the IC(50) values for human rDHFR were >16,000 nM. This is the first report on the in vitro inhibitory actions of this class of antifolates against TMP-resistant B. anthracis isolates. The selective inhibition of B. anthracis rDHFR and the in vitro activity against B. anthracis demonstrate that members of this class of compounds have the potential to be developed into clinically important therapeutic choices for the treatment of infections caused by TMP-resistant bacteria, such as B. anthracis.

Detection of bacteria in platelet concentrates prepared from spiked single donations using cultural and molecular genetic methods

Bacteria show differences in their growth kinetics depending on the type of blood component. On to storage at 22 degrees C, platelet concentrates (PCs) seem to be more prone to bacterial multiplication than red cell concentrates. Knowledge of the potential for bacterial proliferation in blood components, which are stored at a range of temperatures, is essential before considering implementation of a detection strategy. The efficacy of bacterial detection was determined, using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), following bacterial growth in blood components obtained from a deliberately contaminated whole-blood (WB) unit. Cultivation was used as the reference method. WB was spiked with 2 colony-forming units mL(-1)Staphylococcus epidermidis or Klebsiella pneumoniae, kept for 15 h at room temperature and component preparation was processed. Samples were drawn, at intervals throughout the whole separation process, from each blood component. Nucleic acids were extracted using an automated high-volume extraction method. The 15-h storage revealed an insignificant increase in bacterial titre. No bacterial growth was detected in red blood cell or plasma units. K. pneumoniae showed rapid growth in the pooled PC and could be detected immediately after preparation using RT-PCR. S. epidermidis grew slowly and was detected 24 h after separation. These experiments show that sampling is indicative at 24 h after preparation of PCs at the earliest to minimize the sampling error.

Alanine aminotransferase cut-off values for blood donor screening using the new International Federation of Clinical Chemistry reference method at 37 degrees C

BACKGROUND AND OBJECTIVES

Serum alanine aminotransferase (ALT) determination is recommended, or even required by law, in the screening of blood donors in many countries, and donors with an increased catalytic activity of ALT are excluded from blood donation. In most countries, the ALT cut-off value for blood donor screening for men and women is twice the upper limit of the normal range. The introduction, in 2002, of the new International Federation of Clinical Chemistry (IFCC) reference method, performed at 37 degrees C, required new ALT reference values to be established for healthy individuals and a new cut-off point to be determined for blood donor screening.

MATERIALS AND METHODS

We compared ALT values of donor blood units using the previous German standard method, which measures ALT values at 25 degrees C, and the new IFCC reference procedure, where ALT levels are measured at 37 degrees C.

RESULTS

We found a linear correlation between the ALT values obtained by the method at 25 degrees C and the new IFCC reference method (37 degrees C) (r = 0.983), and a gender- and age-independent ratio of 0.523. Using this ratio we calculated the new ALT cut-off for blood donations and now propose a new upper limit of 132 U/l (2.20 microkat/l) for men and 86 U/l (1.43 microkat/l) for women. Only 220 of 151 678 blood donations collected over a period of 5 years showed an ALT value higher than the cut-off. None were hepatitis C virus (HCV) positive in serological or nucleic acid amplification technology (NAT) assays. Only 0.006% of all blood donations were positive for antibody to HCV and thus excluded.

CONCLUSIONS

With the implementation of the new IFCC reference method for ALT determination at 37 degrees C, we propose a new ALT cut-off for blood donor screening, which, for men, is about three times the upper limit of the normal range and for women about 2.5 times. Our results show that a lower cut-off would probably not yield a higher safety of blood products in terms of detecting viral infections, but would result in a loss of approximately 0.75% of suitable blood donors.

Low-level viraemia of hepatitis B virus in an anti-HBc- and anti-HBs-positive blood donor

summary In many countries, screening of hepatitis B virus (HBV) in blood donors is limited to HBsAg testing. However, if anti-HBc testing and sensitive HBV nucleic acid amplification testing (NAT) for routine screening are not prescribed, HBV viraemia might remain unrecognized. A clinically inconspicuous HBsAg-negative 35-year-old female blood donor was detected with anti-HBc antibodies following the introduction of anti-HBc screening of donors. Based on her history, she had seroconverted to anti-HBs positive (titre >7000 IU/L) after vaccination. Blood donations were routinely tested HBV-DNA negative by minipool NAT. The individual donor samples were reinvestigated by an ultrasensitive NAT with a lower detection limit of 3.8 IU/mL. Intermittent HBV viraemia was detected over a 7-year period from this donor, with a concentration ranging from 8 to 260 IU/mL. In the subsequent donor-directed lookback study, no post-transfusion hepatitis was detected. Low-level HBV viraemia in simultaneous anti-HBc- and anti-HBs-positive blood donors could only be identified with enhanced sensitivity individual polymerase chain reaction assays and is not detectable by pool HBV NAT.

Recent experience with human immunodeficiency virus transmission by cellular blood products in Germany: antibody screening is not sufficient to prevent transmission

BACKGROUND AND OBJECTIVES

A case of transfusion-related human immunodeficiency virus-1 (HIV-1) transmission was not detected by standard HIV antibody screening.

MATERIALS AND METHODS

In a look-back procedure, the preceding donations were extensively analyzed by nucleic acid amplification technology (NAT) screening and alternative serological tests.

RESULTS

The chain of infection could be demonstrated by the analysis of HIV-specific amplicon sequences from the donor and the recipient.

CONCLUSION

This case report clearly indicates that the remaining risk of transfusion-related transmission of HIV could be severely reduced, not only by the use of NAT screening but even by HIV antigen screening or more sensitive HIV antibody assays.

Direct influence of S9 liver homogenate on fluorescence signals: impact on practical applications in a bacterial genotoxicity assay

Assays based on the bacterial SOS-response offer the possibility of automatization of genotoxicity testing for screening of large compound libraries. While existing assays use colorimetric detection or luminescence read-out, we describe here the use of a fluorescence-based system to achieve high sensitivity of detection required for assay miniaturization. Three commonly used fluorophores--fluorescein, DDAO and resorufin--are evaluated. Experimental evidence is given that S9 liver homogenate contains a heat-labile, reversible fluorophore-binding activity and therefore, significantly reduces fluorescence intensities. We have worked out simple solutions to overcome the S9 related interference in order to be able to establish a robust bacterial genotoxicity assay.

Malonyl-CoA:ACP transacylase from Streptomyces coelicolor has two alternative catalytically active nucleophiles

Fatty acids and polyketides are synthesized by mechanistically and evolutionarily related multienzyme systems. Their carbon chain backbones are synthesized via repeated decarboxylative condensations of alpha-carboxylated building blocks onto a growing acyl chain. These alpha-carboxylated building blocks are transferred from the corresponding coenzyme A thioesters onto the phosphopantetheine arm of an acyl carrier protein (ACP) by acyl transferases, which operate by a ping-pong mechanism involving an acyl-O-serine intermediate. In the course of our studies on the malonyl-CoA:ACP transacylase (MAT) from Streptomyces coelicolor, we observed that an active-site Ser (97) --> Ala mutant retains activity as well as the ability to be covalently labeled by (14)C malonyl-CoA. Here we demonstrate that an alternative, catalytically competent nucleophile exists in the active site of this enzyme. Next to the active-site serine is a histidine residue that is conserved in some, but not all acyl transferases. The H96A mutant is also active and can be labeled, but an H96A/S97A double mutant is inactive and cannot be labeled. The ability of H96 to form a malonyl-imidazole adduct was confirmed by proteolysis, followed by radio-HPLC and mass spectrometric analysis of the S97A mutant enzyme. Kinetic analysis revealed that the k(cat) of the S97A mutant was within 10-fold that of the wild-type enzyme, whereas the K(M)s of the two enzymes were comparable. Sequence comparison with the E. coli MAT (whose X-ray structure is known) led to the identification of H201 as the putative base in the serine-histidine catalytic dyad of the S. coelicolor enzyme. The absence of MAT activity in the H201A mutant and the detection of weak activity in the H201Q mutant was consistent with this proposal. The implications of this unexpected finding are discussed.

Rapid elimination of GB virus C (hepatitis G virus) in the mosquito Aedes aegypti

The transmissibility of the GB virus C (hepatitis G virus; HGV), a member of the Flaviviridae, by a typical flavivirus vector was investigated. Female mosquitoes of the species Aedes aegypti were fed with HGV-infected human blood and assayed 1, 24, 48, 72 and 96 h after the blood meal for viral RNA, human glyceraldehyde-3-phosphate dehydrogenase mRNA, human beta-actin DNA and A. aegypti actin mRNA by total nucleic acid extraction, reverse transcription and PCR. Viral RNA had already disappeared from nucleic acid extracts 1 h after the blood meal and was not detectable throughout the observation period. Aedes-specific mRNA served as an internal control and was detected in all nucleic acid extracts, whereas human mRNA had disappeared after 24 h, indicating digestion of human cells. From these results we conclude that GB virus C (HGV) cannot replicate in A. aegypti, which is a widespread and competent vector of several other flaviviruses.

The endo-beta-1,4-glucanase CelA of Clavibacter michiganensis subsp. michiganensis is a pathogenicity determinant required for induction of bacterial wilt of tomato

The phytopathogenic bacterium Clavibacter michiganensis subsp. michiganensis NCPPB382, which causes bacterial wilt and canker of tomato, harbors two plasmids, pCM1 (27.35 kb) and pCM2 (72 kb), encoding genes involved in virulence (D. Meletzus, A. Bermpohl, J. Dreier, and R. Eichenlaub, 1993, J. Bacteriol. 175:2131-2136; J. Dreier, D. Meletzus, and R. Eichenlaub, 1997, Mol. Plant-Microbe Interact. 10:195-206). The region of pCM1 carrying the endoglucanase gene celA was mapped by deletion analysis and complementation. RNA hybridization identified a 2.4-knt (kilonucleotide) transcript of the celA structural gene and the transcriptional initiation site was mapped. The celA gene encodes CelA, a protein of 78 kDa (746 amino acids) with similarity to endo-beta-1,4-glucanases of family A1 cellulases. CelA has a three-domain structure with a catalytic domain, a type IIa-like cellulose-binding domain, and a C-terminal domain. We present evidence that CelA plays a major role in pathogenicity, since wilt induction capability is obtained by endoglucanase expression in plasmid-free, nonvirulent strains and by complementation of the CelA- gene-replacement mutant CMM-H4 with the wild-type celA gene.

Mechanistic analysis of a type II polyketide synthase. Role of conserved residues in the beta-ketoacyl synthase-chain length factor heterodimer

Type II polyketide synthases (PKSs) are a family of multienzyme systems that catalyze the biosynthesis of polyfunctional aromatic natural products such as actinorhodin, frenolicin, tetracenomycin, and doxorubicin. A central component in each of these systems is the beta-ketoacyl synthase-chain length factor (KS-CLF) heterodimer. In the presence of an acyl carrier protein (ACP) and a malonyl-CoA:ACP malonyl transferase (MAT), this enzyme synthesizes a polyketide chain of defined length from malonyl-CoA. We have investigated the role of the actinorhodin KS-CLF in priming, elongation, and termination of its octaketide product by subjecting the wild-type enzyme and selected mutants to assays that probe key steps in the overall catalytic cycle. Under conditions reflecting steady-state turnover of the PKS, a unique acyl-ACP intermediate is detected that carries a long, possibly full-length, acyl chain. This species cannot be synthesized by the C169S, H309A, K341A, and H346A mutants of the KS, all of which are blocked in early steps in the PKS catalytic cycle. These four residues are universally conserved in all known KSs. Malonyl-ACP alone is sufficient for kinetically and stoichiometrically efficient synthesis of polyketides by the wild-type KS-CLF, but not by heterodimers that carry the mutations listed above. Among these mutants, C169S is an efficient decarboxylase of malonyl-ACP, but the H309A, K341A, and H346A mutants are unable to catalyze decarboxylation. Transfer of label from [(14)C]malonyl-ACP to the nucleophile at position 169 in the KS can be detected for the wild-type enzyme and for the C169S and K341A mutants, but not for the H309A mutant and only very weakly for the H346A mutant. A model is proposed for decarboxylative priming and extension of a polyketide chain by the KS, where C169 and H346 form a catalytic dyad for acyl chain attachment, H309 positions the malonyl-ACP in the active site and supports carbanion formation by interacting with the thioester carbonyl, and K341 enhances the rate of malonyl-ACP decarboxylation via electrostatic interaction. Our data also suggest that the ACP and the KS dissociate after each C-C bond forming event, and that the newly extended acyl chain is transferred back from the ACP pantetheine to the KS cysteine before dissociation can occur. Chain termination is most likely the rate-limiting step in polyketide biosynthesis. Within the act CLF, neither the universally conserved S145 residue nor Q171, which aligns with the active site cysteine of the ketosynthase, is essential for PKS activity. The results described here provide a basis for a better understanding of the catalytic cycle of type II PKSs and fatty acid synthases.

Novel twelve-generation kindred of fatal familial insomnia from germany representing the entire spectrum of disease expression

We present a novel large German kindred of fatal familial insomnia (FFI) consisting of three branches and comprising more than 800 individuals of 12 generations, the largest pedigree of any familial prion disease known today. There is a wide spectrum of clinical presentations leading to misdiagnoses of Olivo-Ponto-Cerebellar Atrophy (OPCA), Parkinson's or Alzheimer's disease in addition to Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler-Scheinker (GSS) syndrome. Molecular genetic analysis of the prion protein gene (PRNP) confirmed the mutation D178N segregating with methionine at the polymorphic codon 129 of PRNP in all 7 patients examined. This polymorphism at codon 129 is supposed to discriminate between familial CJD (fCJD) and FFI; the 129M allele determines FFI and 129V fCJD. Furthermore, heterozygosity at this site appears to induce prolonged disease duration as compared to the homozygous condition. The variability of the clinical and pathological findings documented for our patients indicates the difficulty in establishing the diagnosis of FFI on clinical and on pathological grounds alone. In three cases (IX-97, XI-21, V-2) followed up by us prospectively insomnia was an early and severe symptom; however, in case notes analyzed retrospectively this symptom was frequently missed. In contrast to previous reports and in agreement with recent studies we cannot confirm a clear relationship between the status of the M/V polymorphism at codon 129 and the age-of-onset of this disease.

Kinetic analysis of the actinorhodin aromatic polyketide synthase

Type II polyketide synthases (PKSs) are bacterial multienzyme systems that catalyze the biosynthesis of a broad range of natural products. A core set of subunits, consisting of a ketosynthase, a chain length factor, an acyl carrier protein (ACP) and possibly a malonyl CoA:ACP transacylase (MAT) forms a "minimal" PKS. They generate a poly-beta-ketone backbone of a specified length from malonyl-CoA derived building blocks. Here we (a) report on the kinetic properties of the actinorhodin minimal PKS, and (b) present further data in support of the requirement of the MAT. Kinetic analysis showed that the apoACP is a competitive inhibitor of minimal PKS activity, demonstrating the importance of protein-protein interactions between the polypeptide moiety of the ACP and the remainder of the minimal PKS. In further support of the requirement of MAT for PKS activity, two new findings are presented. First, we observe hyperbolic dependence of PKS activity on MAT concentration, saturating at very low amounts (half-maximal rate at 19.7 +/- 5.1 nM). Since MAT can support PKS activity at less than 1/100 the typical concentration of the ACP and ketosynthase/chain length factor components, it is difficult to rule out the presence of trace quantities of MAT in a PKS reaction mixture. Second, an S97A mutant was constructed at the nucleophilic active site of the MAT. Not only can this mutant protein support PKS activity, it is also covalently labeled by [(14)C]malonyl-CoA, demonstrating that the serine nucleophile (which has been the target of PMSF inhibition in earlier studies) is dispensible for MAT activity in a Type II PKS system.