Manuel von Bayern

SdrF, a Staphylococcus epidermidis surface protein, contributes to the initiation of ventricular assist device driveline-related infections.

Staphylococcus epidermidis remains the predominant pathogen in prosthetic-device infections. Ventricular assist devices, a recently developed form of therapy for end-stage congestive heart failure, have had considerable success. However, infections, most often caused by Staphylococcus epidermidis, have limited their long-term use. The transcutaneous driveline entry site acts as a potential portal of entry for bacteria, allowing development of either localized or systemic infections. A novel in vitro binding assay using explanted drivelines obtained from patients undergoing transplantation and a heterologous lactococcal system of surface protein expression were used to identify S. epidermidis surface components involved in the pathogenesis of driveline infections. Of the four components tested, SdrF, SdrG, PIA, and GehD, SdrF was identified as the primary ligand. SdrF adherence was mediated via its B domain attaching to host collagen deposited on the surface of the driveline. Antibodies directed against SdrF reduced adherence of S. epidermidis to the drivelines. SdrF was also found to adhere with high affinity to Dacron, the hydrophobic polymeric outer surface of drivelines. Solid phase binding assays showed that SdrF was also able to adhere to other hydrophobic artificial materials such as polystyrene. A murine model of infection was developed and used to test the role of SdrF during in vivo driveline infection. SdrF alone was able to mediate bacterial adherence to implanted drivelines. Anti-SdrF antibodies reduced S. epidermidis colonization of implanted drivelines. SdrF appears to play a key role in the initiation of ventricular assist device driveline infections caused by S. epidermidis. This pluripotential adherence capacity provides a potential pathway to infection with SdrF-positive commensal staphylococci first adhering to the external Dacron-coated driveline at the transcutaneous entry site, then spreading along the collagen-coated internal portion of the driveline to establish a localized infection. This capacity may also have relevance for other prosthetic device–related infections.

The Role of Staphylococcus aureus Adhesins in the Pathogenesis of Ventricular Assist Device–Related Infections

Ventricular assist devices (VADs) are an important form of therapy for end-stage congestive heart failure. However, infection of the VAD, which is often caused by Staphylococcus aureus, poses a major threat to survival. Using a novel in vitro binding assay with VAD membranes and a heterologous lactococcal system of expression, we identify 3 S. aureus proteins--clumping factor A (ClfA) and fibronectin binding proteins A and B (FnBPA and FnBPB) as the main factors involved in adherence to VAD polyurethane membranes. Adherence is greatly diminished by long implantation times, reflecting a change in topological features of the VAD membrane, and is primarily mediated by the FnBPA domains in the staphylococcal proteins. We also compare the adherence of S. aureus mutant strains and show that other staphylococcal components appear to be involved in adherence to VAD membranes. Finally, we demonstrate that ClfA, FnBPA, and FnBPB mediate bacterial infection of implanted murine intra-aortic polyurethane patches.

Gene Expression Profiles of Patients With Antibody-Mediated Rejection After Cardiac Transplantation

ntibody-mediated rejection (AMR) is characterized y interstitial edema, prominent endothelial cell damge, occasional inflammatory cells, donor-specific ntibodies and C4d deposition, and may cause acute raft loss after heart transplantation. Unfortuately, there is no non-invasive method to accurately redict or diagnose AMR. Peripheral blood mononuclear cell (PBMC) gene ignatures allow for identification of patients at risk of ejection. We conducted a pilot study to test the ypothesis that patients with AMR show specific PBMC ene expression profiles. We included all patients at our center who were part f the Cardiac Allograft Rejection Gene expression bservational (CARGO) study and evaluated with gene icroarrays. Gene probes with expression values resent in 70% of the samples were filtered retaining ,688 probes of the original 7,370. AMR was defined as ew-onset graft dysfunction in the absence of cellular ejection, with light-microscopic criteria of endothelial welling, requiring specific treatment according to our nstitutional practice. Repeat samples from the same atients were averaged. Candidate genes were identied by Significance Analysis of Microarrays (SAM). unctional analysis was performed with High Throughut GOminer (HTGM) and Gene Set Enrichment Analsis (GSEA). Clinical variables were compared using a -test or chi-square test when appropriate.

Drawing networks of rejection - a systems biological approach to the identification of candidate genes in heart transplantation

Technological development led to an increased interest in systems biological approaches to characterize disease mechanisms and candidate genes relevant to specific diseases. We suggested that the human peripheral blood mononuclear cells (PBMC) network can be delineated by cellular reconstruction to guide identification of candidate genes. Based on 285 microarrays (7370 genes) from 98 heart transplant patients enrolled in the Cardiac Allograft Rejection Gene Expression Observational study, we used an information‐theoretic, reverse‐engineering algorithm called ARACNe (algorithm for the reconstruction of accurate cellular networks) and chromatin immunoprecipitation assay to reconstruct and validate a putative gene PBMC interaction network. We focused our analysis on transcription factor (TF) genes and developed a priority score to incorporate aspects of network dynamics and information from published literature to supervise gene discovery. ARACNe generated a cellular network and predicted interactions for each TF during rejection and quiescence. Genes ranked highest by priority score included those related to apoptosis, humoural and cellular immune response such as GA binding protein transcription factor (GABP), nuclear factor of κ light polypeptide gene enhancer in B‐cells (NFκB), Fas (TNFRSF6)‐associated via death domain (FADD) and c‐AMP response element binding protein. We used the TF CREB to validate our network. ARACNe predicted 29 putative first‐neighbour genes of CREB. Eleven of these (37%) were previously reported. Out of the 18 unknown predicted interactions, 14 primers were identified and 11 could be immunoprecipitated (78.6%). Overall, 75% (n= 22) inferred CREB targets were validated, a significantly higher fraction than randomly expected (P < 0.001, Fisher’s exact test). Our results confirm the accuracy of ARACNe to reconstruct the PBMC transcriptional network and show the utility of systems biological approaches to identify possible molecular targets and biomarkers.

Relationship between a validated molecular cardiac transplant rejection classifier and routine organ function parameters

Cadeiras M, Shahzad K, John MM, Gruber D, von Bayern M, Auerbach S, Sinha A, Latif F, Unniachan S, Memon S, Mital S, Restaino S, Marboe CC, Addonizio LJ, Deng MC. Relationship between a validated molecular cardiac transplant rejection classifier and routine organ function parameters.
Clin Transplant 2010: 24: 321–327.

Development of a murine ventricular assist device transcutaneous drive-line model.

Mechanical circulatory support devices (MCSD) are a major form of therapy for congestive heart failure. However, MCSD have been associated with a high incidence of infections. The most common of these infections involves the transcutaneous driveline 1–4. Here, we describe a murine driveline model developed to study MCSD-related infections.

Destination therapy: an alternative for end-stage heart failure patients not eligible for heart transplantation

Purpose of reviewEvidence on survival and quality-of-life benefit from destination mechanical circulatory support has been available since the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure trial and the database of the International Society of Heart and Lung Transplantation is continuously providing information on outcomes. Limited survival, resource allocation, and expanding indications should prompt careful identification of patients most likely to benefit and list program requirements to reconcile patient outcomes with a public health rationale. Recent findingsSuitable candidates should be identified early and referred to centers experienced in all aspects of terminal heart failure care. Extensive studies on pulsatile and nonpulsatile devices are needed, including randomized clinical trials. Coagulopathies are still common early after device implantation whereas infections increase linearly, limiting 1-year survival. Right-sided heart failure should be identified and accurately evaluated, especially in the older population. Arrhythmias unlikely complicate outcomes and improvements in device design can reduce device-related complications. SummaryIndication for destination mechanical circulatory support devices is rapidly increasing and benefit will most likely be obtained if evaluation is systematic and complications are foreseen. Assessment and prediction of organ dysfunction recovery are challenging and several new innovative risk tools might help aid clinical algorithms. Advanced age, renal failure, and right-sided heart failure are related to worst survival, and first consensus guidelines for evaluation and decision-making algorithms have been outlined. Innovative translational medical research, including use of high-throughput genomics, will potentially improve patient selection and might ensure a better survival.