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.

Managing drugs and devices in patients with permanent ventricular assist devices

Patients will be considered for destination mechanical circulatory support device (MCSD) implantation when all other organ-saving treatment options have failed and they are not eligible for heart transplantation. Current medical evidence suggests that only for those patients who are inotrope-dependent and therefore likely have a 1-year survival probability without MCSD implantation of less than 50%, MCSD intervention will add to survival and quality-of-life benefit. Suitable candidates for MCSD are those patients who have a high risk of dying from heart failure but acceptable noncardiac risk. Evaluation of patients for MCSD requires a systematic and critical review of all organ systems and of the psychosocial situation. Specifically, right ventricular function and risk of right ventricular failure should be evaluated before planning destination MCSD implantation. Treatment will focus on prompt recovery from MCSD implantation, maintaining optimal treatment for heart failure, and preventing/treating MCSD complications, including infection, bleeding, coagulopathy, right heart failure, and device dysfunction. MCSD programs should be organized as an advanced heart failure center directed by specialized heart failure cardiologists, surgeons expert at implant and management of MCSD, specialized nurses, social workers, psychologists, financial experts, and physical therapists. MCSD practice is based on a patient-centered theory, with an appropriate understanding of the respective roles of the physician and the patient during their iterative encounters in which the patient is an autonomous person making responsible personal health decisions while the health care team is providing continued expert and empathic counseling about various options, based on systematic outcomes research (eg, by participation in the Interagency Registry for Mechanically Assisted Circulatory Support - MCSD database ).

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

BACKGROUND

As acute cellular cardiac allograft rejection is a systemic process affecting the entire organism, we hypothesized that scores of a peripheral blood mononuclear cell gene expression profiling (GEP) test developed and validated to rule out International Society of Heart and Lung Transplantation (ISHLT) grade > or = 3A/2R acute cellular cardiac allograft rejection also reflects biologically plausible changes of the routinely assessed clinical parameters.

METHODS

We retrospectively analyzed 76 patients who underwent GEP testing, at the time of their routine clinical follow-up in our Institution between February 1, 2006 and January 31, 2007. Data were analyzed with t-test, nonparametric tests, bivariate Spearman's correlation, and multivariate linear regression modeling.

RESULTS

More activated GEP-score correlated with longer corrected QT (QTc)-interval (r = 0.377, p = 0.001, n = 63), longer QRS duration (r = 0.231, p = 0.03, n = 66), higher heart rate (r = 0.221, p = 0.037, n = 66), higher serum creatinine (r = 0.26, p = 0.01, n = 75), higher gamma-glutamyl transferase (GGT) GGT (r = 0.266, p = 0.037, n = 46), lower pulmonary artery oxygen saturation (r = -0.313, p = 0.003, n = 76), lower platelet count (r = -0.372, p = 0.001, n = 74), lower monocyte count (r = -0.208, p = 0.040, n = 72), and lower high-density lipoprotein (HDL) HDL level (r = -0.242, p = 0.041, n = 53). Multivariate analysis showed a significant amount of variance in the GEP score independently explained by the variability of QTc-interval (beta = 1.998, p = 0.001) and platelet count (beta = -1.540, p = 0.017). Post hoc analysis of the 11 individual GEP-classifier genes showed WDRA40 (p = 0.02) and ras homolog gene family, member U (RHOU) RHOU (p = 0.01) independently related to mixed venous O(2)Sat%.

CONCLUSION

A GEP test developed and validated to detect the absence of cardiac rejection correlates with electrocardiographic and hemodynamic cardiac parameters as well as renal, hepatic, bone marrow, and lipid metabolism parameters suggesting a complex relationship between rejection, leukocytes, and organ function within the continuum between alloimmunological quiescence and rejection.

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.

This study investigates the manner in which heart pumps become infected. Infections involving the driveline, the cord that connects the pump to its external power source, are a major complication of implantation of these devices. In this study, we examined why Staphylococcus epidermidis, a bacteria that is commonly found on the skin, is responsible for the majority of these infections. The ability of different surface molecules of S. epidermidis to attach to drivelines removed from patients undergoing transplantation was tested. SdrF, one of the S. epidermidis surface proteins studied, showed the highest adherence to the drivelines. This binding appeared to involve attachment of the B subunit of SdrF to collagen, a molecule that coats the driveline following implantation. SdrF also mediated attachment to the non-implanted Dacron material that is used to coat the drivelines. A mouse driveline infection model also demonstrated that SdrF was sufficient to initiate a driveline infection. Driveline infection can therefore be hypothesized to occur via: 1) skin colonization by S. epidermidis; 2) adherence of SdrF-positive S. epidermidis to the Dacron surface at the skin entry site; 3) migration of bacteria along the driveline; 4) adherence to the internal driveline via the collagen coating its surface; and 5) initiation of infection.