Major achievements in cardiology in the past century: influence on Dutch cardiovascular medicine

At the occasion of the 75th anniversary of the Netherlands Society of Cardiology, it is interesting to look back on the major scientific achievements in cardiovascular medicine of the last century and to pay attention to the impact of these achievements on Dutch Cardiology. It might be a nice opportunity not only to mention the ten great discoveries in Cardiology in the past century, but also to address the pioneering work in the Netherlands. When honouring and paying tribute to Dutch individuals, this special article only refers to emeriti-professors in cardiology (and some other closely-related retired experts), as this is a historical reflection rather than a cross-sectional view of current attainments. The practising pioneers of today will hopefully be remembered in 75 years from now. (Neth Heart J 2009;17:136–9.)     

Improvement of mouse cardiac function by hESC-derived cardiomyocytes correlates with vascularity but not graft size

Transplantation of human embryonic stem cell-derived cardiomyocytes (hESC-CM) has been shown to improve the function of the rodent heart 1 month after myocardial infarction (MI). However, the mechanistic basis and optimal delivery strategies are unclear. We investigated the influence of the number of injected cells, resulting graft size, and possible paracrine mechanisms in this process. MI was induced in NOD-SCID mice (n = 84) followed by injection of enriched hESC-CM at different dosages, hESC-non-CM derivatives, culture medium, or no injection. Cardiac function was monitored for 12 weeks with 9.4 T MRI (n = 70). Grafts were identified by epifluorescence of a transgenic GFP marker and characterized by immunofluorescence. Vascularity and paracrine effects were investigated immunohistochemically. Transplantation of differentiated hESCs improved short, mid-, and long-term cardiac performance and survival, although only cardiomyocytes formed grafts. A mid-term (4 weeks) cardiomyocyte-specific enhancement was associated with elevated vascular density around the graft and attenuated compensatory remodeling. However, increasing the number of hESC-CM for injection did not enhance heart function further. Moreover, we observed that small graft size was associated with a better functional outcome. HESC-CM increased myocardial vascularization and enhanced heart function in mice after MI, but larger graft size was associated with reduced functional improvement. Future studies should focus on advanced delivery strategies and mechanisms of action rather than increasing graft size.     

Oxygen uptake kinetics in chronic heart failure: clinical and physiological aspects

One of the hallmark symptoms of patients with chronic heart failure (CHF) is exercise intolerance. Therefore, exercise testing has become an important tool for the evaluation and monitoring of heart failure. Whereas the maximal aerobic capacity (peak VO₂) is a reliable indicator of the severity and prognosis of heart failure, submaximal exercise parameters may be more closely related to the ability to perform daily activities. As such, oxygen (O₂) uptake kinetics, describing the rate change of O₂ uptake during onset or recovery of submaximal constant-load exercise (O₂ onset and recovery kinetics, respectively), have been shown to be useful parameters for objectively evaluating the functional capacity of CHF patients. However, their evaluation in this population is not a routine part of daily clinical practice. Possible reasons for this include a lack of standardisation of the assessment methodology and a limited number of studies evaluating the clinical use of O₂ uptake kinetics in CHF patients. In addition, the pathophysiological mechanisms underlying the delay in O₂ uptake kinetics in these patients are not completely understood. This review discusses the current literature on the clinical potency and physiological determinants of O₂ uptake kinetics in CHF patients and provides directions for future research. (Neth Heart J 2009;17:238–44.)     

One-year clinical follow-up of a registry evaluating a percutaneous revascularisation strategy combining a pre-specified simple selection process with the use of a new thin-strut bare cobalt-chromium stent

Objectives. To evaluate clinical events in a specifically selected cohort of patients with obstructive coronary artery disease (CAD), using a new generation thin-strut bare cobalt-chromium coronary stent. Methods. Patients with single- or multi-vessel, stable or unstable CAD eligible for percutaneous implantation of at least one bare cobalt-chromium stent were evaluated in a single-centre registry. Prospective pre-specified criteria for bare cobalt-chromium stent implantation in our centre were: any acute ST-elevation myocardial infarction (MI), otherwise 1) de novo coronary lesion, and 2) lesion length <20 mm, and 3) reference vessel diameter >2.6 mm, and 4) no diabetes, unless reference vessel diameter >3.5 mm. Endpoints, retrospectively collected, were death, MI and clinically driven target-lesion revascularisation (TLR) and target-vessel revascularisation (TVR) after 12 months. Results. Between September 2005 and June 2007, 712 patients (48.7% one-vessel, 29.9% two-vessel, 20% three-vessel and 1.4% left main disease; 7.9% diabetics) were treated with 800 bare cobalt-chromium stents, for stable angina (40.9%), unstable angina (20.9%) or acute ST-elevation MI (38.2%). The procedural success rate was 99.3%. Peri-procedural MI rate was 2.2% in the semi-elective group. At 12 months there were 17 deaths (2.4%), of which nine non-cardiac, 20 (2.8%) MI, 19 (2.7%) TLR and 29 (4.1%) TVR. Early and late definite stent thrombosis occurred in four (0.6%) and three (0.4%) patients, respectively. Conclusion. A strategy aimed at minimising drug-eluting stent use and combining a pre-specified simple selection process with the use of a new thin-strut bare cobalt-chromium stent is safe and effective at one-year clinical follow-up. (Neth Heart J 2010;18:486-92.)     

Targeted inhibition of p38 mitogen-activated protein kinase antagonizes cardiac injury and cell death following ischemia-reperfusion in vivo

The p38 branch of the mitogen-activated protein kinase (MAPK) signaling cascade has been implicated as a regulator of cardiomyocyte apoptosis in culture as well as in the adult heart. However, considerable disagreement persists as to the functional effects attributed to p38 signaling, given that both pro- and anti-apoptotic regulatory roles have been reported. To address this area of uncertainty in the literature, we investigated the cell death effects associated with p38 inactivation in both cultured neonatal cardiomyocytes and the adult heart. In vitro, adenoviral-mediated gene transfer of two different dominant-negative-encoding p38 vectors reduced apoptosis induced by 2-deoxyglucose treatment, whereas overexpression of wild-type p38alpha or an activated mitogen-activated protein kinase kinase (MKK)6 mutant each enhanced cell death. In vivo, transgenic mice expressing a dominant-negative MKK6 mutant or a dominant-negative p38alpha mutant were each significantly protected from ischemia-reperfusion injury, as assessed by infarct area measurements, DNA laddering, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, and functional assessment of ventricular performance. Similarly, transgenic mice overexpressing the p38-inactivating dual specificity phosphatase MAPK phosphatase-1 (MKP-1) were also partially protected, whereas MKP-1 gene-targeted mice showed greater injury after ischemia-reperfusion injury. Mechanistically, inhibition of p38 signaling promoted a dramatic up-regulation of Bcl-2 in the hearts of transgenic mice. In primary neonatal cardiomyocyte cultures, adenoviral-mediated gene transfer of a p38 inhibitory mutant up-regulated Bcl-2, whereas expression of an activated p38 mutant down-regulated Bcl-2 protein levels. Collectively, these results indicate that p38 functions as a pro-death signaling effector in both cultured myocytes as well as in the intact heart.     

Females of the sea urchin Strongylocentrotus purpuratus differ in the structures of their egg jelly sulfated fucans

The egg jelly coats of sea urchins contain sulfated fucans which bind to a sperm surface receptor glycoprotein to initiate the signal transduction events resulting in the sperm acrosome reaction. The acrosome reaction is an ion channel regulated exocytosis which is an obligatory event for sperm binding to, and fusion with, the egg. Approximately 90% of individual females of the sea urchin Strongylocentrotus purpuratus spawned eggs having only one of two possible sulfated fucan electrophoretic isotypes, a slow migrating (sulfated fucan I), or a fast migrating (sulfated fucan II) isotype. The remaining 10% of females spawned eggs having both sulfated fucan isotypes. The two sulfated fucan isotypes were purified from egg jelly coats and their structures determined by NMR spectroscopy and methylation analysis. Both sulfated fucans are linear polysaccharides composed of 1-->3-linked alpha-L-fucopyranosyl units. Sulfated fucan I is entirely sulfated at the O -2 position but with a heterogeneous sulfation pattern at O -4 position. Sulfated fucan II is composed of a regular repeating sequence of 3 residues, as follows: [3-alpha-L-Fuc p - 2,4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)- 1]n. Both purified sulfated fucans have approximately equal potency in inducing the sperm acrosome reaction. The significance of two structurally different sulfated fucans in the egg jelly coat of this species could relate to the finding that the sperm receptor protein which binds sulfated fucan contains two carbohydrate recognition modules of the C-type lectin variety which differ by 50% in their primary structure.      

Sequence variations in small-subunit ribosomal RNAs of Hartmannella vermiformis and their phylogenetic implications

Evidence of associations between free-living amoebas and human disease has been increasing in recent years. Knowledge about phylogenetic relationships that may be important for the understanding of pathogenicity in the genera involved is very limited at present. Consequently, we have begun to study these relationships and report here on the phylogeny of Hartmannella vermiformis, a free-living amoeba that can harbor the etiologic agent of Legionnaires' disease. Our analysis is based on studies of small-subunit ribosomal RNA genes (srDNA). Nucleotide sequences were determined for nuclear srDNA from three strains of H. vermiformis isolated from the United Kingdom, Germany, and the United States. These sequences then were compared with a sequence previously obtained for a North American isolate by J. H. Gunderson and M. L. Sogin. The four genes are 1,840 bp long, with an average GC content of 49.6%. Sequence differences among the strains range are 0.38%-0.76%. Variation occurs at 19 positions and includes 2 single-base indels plus 14 monotypic and 3 ditypic single-base substitutions. Variation is limited to eight helix/loop structures according to a current model for srRNA secondary structure. Parsimony, distance, and bootstrap analyses used to examine phylogenetic relationships between the srDNA sequences of H. vermiformis and other eukaryotes indicated that Hartmannella sequences were most closely related to those of Acanthamoeba and the alga Cryptomonas. All ditypic sites were consistent with a separation between European and North American strains of Hartmannella, but results of other tests of this relationship were statistically inconclusive.      

Cloning and characterization of SK2 channel from chicken short hair cells

In the inner ear of birds, as in mammals, reptiles and amphibians, acetylcholine released from efferent neurons inhibits hair cells via activation of an apamin-sensitive, calcium-dependent potassium current. The particular potassium channel involved in avian hair cell inhibition is unknown. In this study, we cloned a small-conductance, calcium-sensitive potassium channel (gSK2) from a chicken cochlear library. Using RT-PCR, we demonstrated the presence of gSK2 mRNA in cochlear hair cells. Electrophysiological studies on transfected HEK293 cells showed that gSK2 channels have a conductance of approximately 16 pS and a half-maximal calcium activation concentration of 0.74±0.17 M. The expressed channels were blocked by apamin (IC₅₀=73.3±5.0 pM) and d-tubocurarine (IC₅₀=7.6±1.0 M), but were insensitive to charybdotoxin. These characteristics are consistent with those reported for acetylcholine-induced potassium currents of isolated chicken hair cells, suggesting that gSK2 is involved in efferent inhibition of chicken inner ear. These findings imply that the molecular mechanisms of inhibition are conserved in hair cells of all vertebrates.