Atrial fibrillation impairs ventricular function by altering excitation-contraction coupling in the human heart

 

Atrial fibrillation (AF) often co-exists in patients with heart failure (HF). Recent clinical evidence suggests that the arrhythmic component of AF alone may contribute to ventricular dysfunction. However, the pathophysiological effects of a non-tachycardic AF on the human ventricle are unknown. To investigate the effects of normofrequent AF on the human ventricle we investigated ventricular myocardium from patients with preserved ejection fraction with sinus rhythm (SR) or AF in the absence of HF (compensated hypertrophy, EF>50%, matched clinical characteristics). In histological analysis we detected no difference between SR (n=9) vs. AF (n=6) regarding the amount and distribution of fibrosis. For functional investigation, Ca-handling was studied (Fura-2 AM). While systolic Ca-transient amplitude was in trend reduced in isolated human ventricular AF cardiomyocytes, we found a significantly prolonged Ca-elimination time (n=17–22 cells/4 pat.). Using caffeine application, a decreased SR Ca-load in AF was detected, which may be explained by a significant decrease in SERCA2a activity (ksys-kCaff, n=10–12/4 pat.). Patch-clamp experiments revealed a prolonged action potential duration in AF cardiomyocytes (n=5/15 cells).

For the standardized evaluation of the mechanisms of persistent normofrequent arrhythmia, we simulated AF in vitro by using arrhythmic (1 Hz, 40% R-R-variability) or rhythmic (1 Hz) field stimulation. We performed contractility experiments using in-toto isolated human ventricular trabeculae from explanted human hearts. After 8h of pacing, arrhythmically stimulated human trabeculae showed a significantly reduced systolic force, an increase in diastolic tension and a prolonged relaxation (n=11–12 trabeculae/11 pat.). For studying the cellular effects of persistent normofrequent arrhythmia in a model suitable for chronic pacing (up to 7 days), we utilized human iPSC cardiomyocytes (iPSC-CM) from healthy donors (n=6). After 7 days, arrhythmic paced iPSC-CM showed a significantly reduced systolic Ca-transient amplitude, a prolonged Ca-elimination time (n=35/45 cells) as well as a reduced SR Ca-load and a trend towards a lower SERCA2a activity compared to control (n=11 cells). Confocal line-scans (Fluo-4 AM) showed an increased diastolic SR Ca-release, which might also explain the reduced SR Ca-content (n=45/35 cells). Moreover, in irregularly paced iPSC-CM we found significant increased levels of cytosolic Na (n=69 cells each) and in patch-clamp experiments a significantly prolonged action potential duration (n=14/11 cells/3 diff.).

This study demonstrates that a normofrequent arrhythmic ventricular excitation as it occurs in AF impairs human ventricular myocardial function by altering cardiomyocyte excitation-contraction coupling. Thus, this study provides the first translational mechanistic characterization and the potential negative impact of isolated AF in the absence of tachycardia on the human ventricle.

Funding Acknowledgement

Type of funding source: None

4967Effects of atrial fibrillation on the human ventricle

Background

The consequence of normofrequent atrial fibrillation (AF) on the ventricle remains largely unknown.

Methods and results

To elucidate the effects of arrhythmic excitation on human ventricular myocardium we performed contractility experiments using ventricular trabecula from patients with heart failure (HF). Normofrequent AF was simulated using arrhythmic (60 bpm, 40% R-R interval variability) or rhythmic field stimulation (60 bpm). Within 8h of arrhythmic stimulation, human specimen showed an impaired systolic force, while diastolic tension increased pathologically (n=5–7 each/7 HF patients, Fig. 1). The characterization of the ventricular (in-vivo) phenotype in patients with AF was performed by utilizing ventricular myocardium from patients with sinus rhythm (SR) and from patients with AF in the absence of HF (compensated hypertrophy, EF>50%, matched clinical characteristics, LV myocardium obtained from aortic valve replacement surgery). Histological investigation showed increased levels of interstitial fibrosis in myocardium from patients with AF compared to SR (n=10 patients each). Studies of cellular Ca-homeostasis (epifluorescence microscopy, Fura-2) were performed using isolated human ventricular cardiomyocytes. While systolic Ca-transient amplitude (0.5 Hz) was preserved in ventricular cardiomyocytes from patients with AF, we found a significantly prolonged Ca-elimination time (RT80) by 22.0±7.7% and a trend towards increased diastolic Ca-levels (n=17–23 cells/4 patients each). This finding may be explained by a decrease in SERCA2a activity (ksys-kCaff, n=10–12/4 each) and an enhanced phospholamban expression in Western Blot experiments (n=5 patients each). For the standardized investigation of the involved targets/mechanisms mediating the pathological changes upon arrhythmic excitation, we utilized human induced pluripotent stem cell cardiomyocytes (iPSC-CM) from healthy donors for chronic arrhythmic culture stimulation (24h). Arrhythmic paced iPSC-CM showed no changes in systolic Ca-transient amplitude (0.5 Hz), whereas diastolic Ca-levels were increased, which fits nicely to the finding of disturbed trabeculae diastolic function (n=15 cells each). In patch clamp experiments, arrhythmic paced cells showed no alterations of resting membrane potential, upstroke velocity, action-potential amplitude or -duration (n=7–9 cells each). Protein expression levels of key Ca-handling proteins in iPSC-CM as well as regulated genes are already under investigation.

Conclusion

This study demonstrates that arrhythmic ventricular excitation deteriorates human myocardial contractility early in HF. In biopsies from patients with preserved EF, chronic AF was associated with increased levels of interstitial fibrosis and pathological diastolic Ca-handling, which could be causally confirmed in chronically arrhythmic paced iPSC-CM. Therefore, this study provides first mechanistic characterization of AF mediated effects on the human ventricle.

The prognostic value of lymph node ratio and updated TNM classification in rectal cancer patients with adequate versus inadequate lymph node dissection

BACKGROUND

The aim of this study was to clarify whether the lymph node ratio (LNR) is superior to the updated TNM classification regarding the prognosis of stage III rectal cancer patients who have not undergone neoadjuvant therapy. The TNM system is based on the absolute number of lymph nodes involved, and the LNR takes into account involved and examined nodes.

METHODS

In 237 patients with stage III rectal cancer, we evaluated prognostic factors for 5-year overall survival (OS), disease-free survival (DFS), and risk of distant metastases (DM) using the Kaplan-Meier method, with patients divided based on adequate versus inadequate lymph node dissection (≥12 vs. <12 lymph nodes examined). The updated TNM divides patients into four groups (1, 2-3, 4-6, and ≥7 involved nodes), while LNR divides patients into quartiles. Multivariate Cox regression analyses were performed.

RESULTS

Among patients with adequate lymph node dissection, the distributions within the two systems were in agreement in 141/178 (79.2 %, kappa 0.721), and the predictive values for OS, DFS, and DM were similar. In patients with inadequate lymph node dissection, the classifications of both systems were concordant in only 13/59 (22 %, kappa 0.021). The pN system significantly under-staged patients, while the LNR classification was a better predictor of OS, DFS, and DM.

CONCLUSIONS

In patients with adequate lymph node dissection, LNR staging does not add substantial information to the predictions of updated TNM lymph node staging. However, in patients with inadequate lymph node harvesting, the LNR compensates for the under-staging of the TNM classification and provides a better estimation of prognosis than the updated TNM system.

Shift of C3 deposition from localization in the glomerulus into the tubulo-interstitial compartment in the absence of secreted IgM in immune complex glomerulonephritis

The role of secretory IgM in protecting kidney tissue from immune complex glomerulonephritis induced by 4 mg horse spleen apoferritin and 0.05 mg lipopolysaccharide has been investigated in mutant mice in which B cells do not secrete IgM, but are capable of expressing surface IgM and IgD and secreting other Ig isotypes. Glomerular size, number of glomeruli per cross-section, glomerular cellularity and urine content of protein and creatinine was comparable in treated secreted IgM (sIgM)-deficient and wild-type mice. Assessment of urinary proteins by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed a 30 kDa low molecular weight protein in treated sIgM-deficient animals only, reflecting dysfunction of proximal tubules. A shift of bound C3 from glomeruli to the tubulo-interstitial compartment in sIgM-deficient mice also suggests tubulo-interstitial damage. In contrast, local C3 synthesis within the kidney tissue did not differ between the two treated groups. Apoptosis physiologically present to maintain kidney cell homeostasis was increased slightly in treated wild-type mice. These results indicate that secretory IgM can protect the tubulo-interstitial compartment from immune complex-induced damage without having an effect on the glomerulus.

STRO-1+ mesenchymal precursor cells located in synovial surface projections of patients with osteoarthritis

OBJECTIVE

To investigate the presence of mesenchymal precursor cells (MPCs) in synovial surface projections of patients with osteoarthritis (OA), to characterize their phenotype and to show their localization.

METHODS

Progenitor cells in synovial surface projections were identified by immunohistochemistry, morphometric analysis and confocal laser scanning microscopy using the following phenotypic markers: STRO-1, CD34, and alpha smooth muscle actin (alpha-SMA).

RESULTS

In the synovial tissue of all 21 patients with OA MPCs were detected. Immunohistochemistry and subsequent morphometric analysis showed that approximately twice as many STRO-1+ cells/mm2 were observed in synovial tissue of patients with OA as compared to healthy organ donors and that number of STRO-1+ cells/mm2 correlated with total cell number/mm2. Interestingly, in the synovial tissue of patients with OA, twice as many STRO-1+ cells/mm2 were found in synovial surface projections as compared to the sublining area without villi. Using confocal laser scanning microscopy two populations of STRO-1+ MPCs could be detected in synovial surface projections. Single STRO-1+ cells that co-expressed alpha-SMA resemble a population of pericyte precursors required to stabilize the immature vasculature. The second STRO-1+ cell population that was found lacked alpha-SMA but co-expressed CD34 on their surface with low intensity.

CONCLUSION

Here we can show that in the synovial tissue of patients with OA twice as many STRO-1+ MPCs can be found in synovial surface projections as compared to the sublining area. These cells are preferentially located at the basis and in the protruding end of the synovial surface projection.