Combination of CD34‐positive cell subsets with infarcted myocardium‐like matrix stiffness: a potential solution to cell‐based cardiac repair

Detection of the optimal cell transplantation strategy for myocardial infarction (MI) has attracted a great deal of attention. Commitment of engrafted cells to angiogenesis within damaged myocardium is regarded as one of the major targets in cell‐based cardiac repair. Bone marrow–derived CD34‐positive cells, a well‐characterized population of stem cells, might represent highly functional endothelial progenitor cells and result in the formation of new blood vessels. Recently, physical microenvironment (extracellular matrix stiffness) around the engrafted cells was found to exert an essential impact on their fate. Stem cells are able to feel and respond to the tissue‐like matrix stiffness to commit to a relevant lineage. Notably, the infarct area after MI experiences a time‐dependent stiffness change from flexible to rigid. Our previous observations demonstrated myocardial stiffness‐dependent differentiation of the unselected bone marrow–derived mononuclear cells (BMMNCs) along endothelial lineage cells. Myocardial stiffness (~42 kPa) within the optimal time domain of cell engraftment (at week 1 to 2) after MI provided a more favourable physical microenvironment for cell specification and cell‐based cardiac repair. However, the difference in tissue stiffness‐dependent cell differentiation between the specific cell subsets expressing and no expressing CD34 phenotype remains uncertain. We presumed that CD34‐positive cell subsets facilitated angiogenesis and subsequently resulted in cardiac repair under induction of infarcted myocardium‐like matrix stiffness compared with CD34‐negative cells. If the hypothesis were true, it would contribute greatly to detect the optimal cell subsets for cell therapy and to establish an optimized therapy strategy for cell‐based cardiac repair.     

Infarcted myocardium-like stiffness contributes to endothelial progenitor lineage commitment of bone marrow mononuclear cells

Optimal timing of cell therapy for myocardial infarction (MI) appears during 5 to 14 days after the infarction. However, the potential mechanism requires further investigation. This work aimed to verify the hypothesis that myocardial stiffness within a propitious time frame might provide a most beneficial physical condition for cell lineage specification in favour of cardiac repair. Serum vascular endothelial growth factor (VEGF) levels and myocardial stiffness of MI mice were consecutively detected. Isolated bone marrow mononuclear cells (BMMNCs) were injected into infarction zone at distinct time-points and cardiac function were measured 2 months after infarction. Polyacrylamide gel substrates with varied stiffness were used to mechanically mimic the infarcted myocardium. BMMNCs were plated on the flexible culture substrates under different concentrations of VEGF. Endothelial progenitor lineage commitment of BMMNCs was verified by immunofluorescent technique and flow cytometry. Our results demonstrated that the optimal timing in terms of improvement of cardiac function occurred during 7 to 14 days after MI, which was consistent with maximized capillary density at this time domains, but not with peak VEGF concentration. Percentage of double-positive cells for DiI-labelled acetylated low-density lipoprotein uptake and fluorescein isothiocyanate (FITC)-UEA-1 (ulex europaeus agglutinin I lectin) binding had no significant differences among the tissue-like stiffness in high concentration VEGF. With the decrease of VEGF concentration, the benefit of 42 kPa stiffness, corresponding to infarcted myocardium at days 7 to 14, gradually occurred and peaked when it was removed from culture medium. Likewise, combined expressions of VEGFR2(+) , CD133(+) and CD45(-) remained the highest level on 42 kPa substrate in conditions of lower concentration VEGF. In conclusion, the optimal efficacy of BMMNCs therapy at 7 to 14 days after MI might result from non-VEGF dependent angiogenesis, and myocardial stiffness at this time domains was more suitable for endothelial progenitor lineage specification of BMMNCs. The results here highlight the need for greater attention to mechanical microenvironments in cell culture and cell therapy.     

Matrix elasticity directs stem cell lineage specification

Microenvironments appear important in stem cell lineage specification but can be difficult to adequately characterize or control with soft tissues. Naive mesenchymal stem cells (MSCs) are shown here to specify lineage and commit to phenotypes with extreme sensitivity to tissue-level elasticity. Soft matrices that mimic brain are neurogenic, stiffer matrices that mimic muscle are myogenic, and comparatively rigid matrices that mimic collagenous bone prove osteogenic. During the initial week in culture, reprogramming of these lineages is possible with addition of soluble induction factors, but after several weeks in culture, the cells commit to the lineage specified by matrix elasticity, consistent with the elasticity-insensitive commitment of differentiated cell types. Inhibition of nonmuscle myosin II blocks all elasticity-directed lineage specification-without strongly perturbing many other aspects of cell function and shape. The results have significant implications for understanding physical effects of the in vivo microenvironment and also for therapeutic uses of stem cells.     

Can 5-azacytidine convert the adult stem cells into cardiomyocytes? A brief overview

From the first report that bone marrow cells (BMC) have stem cells characteristics, several studies have debated the possibility of intervening in myocardial remodeling after injury, for example myocardial infarction, by using BMC. The goal of this paper is to review the concept of whether the demethylating agent 5-azacytidine influences the myogenic differentiation of bone marrow-derived cells. The existing data seem to indicate that in vitro treatment with 5-azacytidine, even if not enough to generate mature CMC, promotes the in vivo and in vitro commitment of BMC into cells that express muscle-specific proteins and genes and, at a very low rate, show spontaneous contractions. It is probable this treatment makes the cells less responsive to other inductive factors secreted by the microenvironment that might modulate the differentiation. These data suggest that this approach may be used to prime cells prior to their transplantation in an injury area in the heart.     

Intracoronary infusion of autologous bone marrow cells and left ventricular function after acute myocardial infarction: a meta-analysis

Recent clinical studies have demonstrated that intracoronary infusion of autologous bone marrow cells (BMC) in conjunction with standard treatment may improve left ventricular function after an acute myocardial infarction (AMI). However, the results of these studies remain controversial, as the studies were relatively small in size and partially differed in design. We reviewed primary controlled randomized clinical studies comparing intracoronary transfer of autologous non-mobilized BMC combined with standard therapy versus standard therapy alone in patients with AMI. We identified five randomized controlled clinical trials, three of which were also placebo- and bone marrow aspiration-controlled. Non-mobilized BMC were infused into the revascularized coronary target artery 6.6 +/- 6.1 days after AMI. The mean follow- up period of 5.2 +/- 1.1 months was completed by 482 patients, 241 of which received infusion of BMC. The effect of BMC on left ventricular ejection fraction (LVEF) as a major functional parameter was evaluated. Analyzing the overall effect on the change in LVEF between baseline and follow-up value revealed a significant improvement in the BMCtreated group as compared to the control group (P = 0.04). Thus, considering the increase in LVEF during follow-up, transplantation of BMC may be a safe and beneficial procedure to support treatment of AMI. However, the functional improvement observed with this form of therapy was altogether relatively moderate and the studies were heterogeneous in design. Hence, further efforts aiming at large-scale, double-blind, randomized and placebo-controlled multi-center trials in conjunction with better definition of patients, which benefit from BMC infusion, appear to be warranted.     

Extracellular High Mobility Group Box 1 Plays a Role in the Effect of Bone Marrow Mononuclear Cell Transplantation for Heart Failure

Transplantation of unfractionated bone marrow mononuclear cells (BMCs) repairs and/or regenerates the damaged myocardium allegedly due to secretion from surviving BMCs (paracrine effect). However, donor cell survival after transplantation is known to be markedly poor. This discrepancy led us to hypothesize that dead donor BMCs might also contribute to the therapeutic benefits from BMC transplantation. High mobility group box 1 (HMGB1) is a nuclear protein that stabilizes nucleosomes, and also acts as a multi-functional cytokine when released from damaged cells. We thus studied the role of extracellular HMGB1 in the effect of BMC transplantation for heart failure. Four weeks after coronary artery ligation in female rats, syngeneic male BMCs (or PBS only as control) were intramyocardially injected with/without anti-HMGB1 antibody or control IgG. One hour after injection, ELISA showed that circulating extracellular HMGB1 levels were elevated after BMC transplantation compared to the PBS injection. Quantitative donor cell survival assessed by PCR for male-specific sry gene at days 3 and 28 was similarly poor. Echocardiography and catheterization showed enhanced cardiac function after BMC transplantation compared to PBS injection at day 28, while this effect was abolished by antibody-neutralization of HMGB1. BMC transplantation reduced post-infarction fibrosis, improved neovascularization, and increased proliferation, while all these effects in repairing the failing myocardium were eliminated by HMGB1-inhibition. Furthermore, BMC transplantation drove the macrophage polarization towards alternatively-activated, anti-inflammatory M2 macrophages in the heart at day 3, while this was abolished by HMGB1-inhibition. Quantitative RT-PCR showed that BMC transplantation upregulated expression of an anti-inflammatory cytokine IL-10 in the heart at day 3 compared to PBS injection. In contrast, neutralizing HMGB1 by antibody-treatment suppressed this anti-inflammatory expression. These data suggest that extracellular HMGB1 contributes to the effect of BMC transplantation to recover the damaged myocardium by favorably modulating innate immunity in heart failure.     

Bone Marrow Mononuclear Cell Transplantation Restores Inflammatory Balance of Cytokines after ST Segment Elevation Myocardial Infarction

Background

Acute myocardial infarction (AMI) launches an inflammatory response and a repair process to compensate cardiac function. During this process, the balance between proinflammatory and anti-inflammatory cytokines is important for optimal cardiac repair. Stem cell transplantation after AMI improves tissue repair and increases the ventricular ejection fraction. Here, we studied in detail the acute effect of bone marrow mononuclear cell (BMMNC) transplantation on proinflammatory and anti-inflammatory cytokines in patients with ST segment elevation myocardial infarction (STEMI).

Methods

Patients with STEMI treated with thrombolysis followed by percutaneous coronary intervention (PCI) were randomly assigned to receive either BMMNC or saline as an intracoronary injection. Cardiac function was evaluated by left ventricle angiogram during the PCI and again after 6 months. The concentrations of 27 cytokines were measured from plasma samples up to 4 days after the PCI and the intracoronary injection.

Results

Twenty-six patients (control group, n = 12; BMMNC group, n = 14) from the previously reported FINCELL study (n = 80) were included to this study. At day 2, the change in the proinflammatory cytokines correlated with the change in the anti-inflammatory cytokines in both groups (Kendall’s tau, control 0.6; BMMNC 0.7). At day 4, the correlation had completely disappeared in the control group but was preserved in the BMMNC group (Kendall’s tau, control 0.3; BMMNC 0.7).

Conclusions

BMMNC transplantation is associated with preserved balance between pro- and anti-inflammatory cytokines after STEMI in PCI-treated patients. This may partly explain the favorable effect of stem cell transplantation after AMI.     

Combined transmyocardial revascularization and cell-based angiogenic gene therapy increases transplanted cell survival

We hypothesized that pretreatment of an infarcted heart by mechanical transmyocardial revascularization (TMR) before transplantation of bone marrow cells (BMCs) or BMC-expressing angiogenic growth factors would increase transplanted BMC survival and enhance myocardial repair. Female Lewis rats underwent coronary ligation 3 wk before creation of 10 needle TMR channels (3 groups) or no TMR (3 groups), followed by transplantation of 3 x 10(6) male donor BMCs, BMC transfected with vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and insulin-like growth factor-1 (IGF-1) (BMC + VBI), or medium alone. At 1, 3, and 7 days, we evaluated transplanted cell survival, vascular densities, and left ventricular (LV) function (N = 4 per group x 6 groups x 3 time points). At 3 days, vascular densities in the scar were increased by TMR + BMC + VBI and by BMC + VBI (P < 0.05), and at 7 days, vascular densities were greatest in rats receiving TMR + BMC + VBI (P < 0.05). Transplanted cell survival at 3 and 7 days was increased by TMR and by BMC + VBI. Combined therapy with TMR + BMC + VBI resulted in the greatest cell survival at 3 days (P < 0.05) versus BMC. After 7 days, LV ejection fraction (LVEF) was lowest in rats receiving neither BMC nor TMR and greatest in rats receiving TMR + BMC + VBI (P = 0.004). We concluded that mechanical pretreatment of infarcted myocardium by TMR enhances the effect of subsequent cell-based gene therapy on transplanted cell survival, angiogenesis, and LV function. Scar pretreatment with TMR combined with cell-based multigene therapy may maximize myocardial repair.     

Cell Therapy Attenuates Cardiac Dysfunction Post Myocardial Infarction: Effect of Timing,Routes of Injection and a Fibrin Scaffold

Background

Cell therapy approaches for biologic cardiac repair hold great promises, although basic fundamental issues remain poorly understood. In the present study we examined the effects of timing and routes of administration of bone marrow cells (BMC) post-myocardial infarction (MI) and the efficacy of an injectable biopolymer scaffold to improve cardiac cell retention and function.

Methodology/Principal Findings

^99mTc-labeled BMC (6×10⁶ cells) were injected by 4 different routes in adult rats: intravenous (IV), left ventricular cavity (LV), left ventricular cavity with temporal aorta occlusion (LV⁺) to mimic coronary injection, and intramyocardial (IM). The injections were performed 1, 2, 3, or 7 days post-MI and cell retention was estimated by γ-emission counting of the organs excised 24 hs after cell injection. IM injection improved cell retention and attenuated cardiac dysfunction, whereas IV, LV or LV* routes were somewhat inefficient (<1%). Cardiac BMC retention was not influenced by timing except for the IM injection that showed greater cell retention at 7 (16%) vs. 1, 2 or 3 (average of 7%) days post-MI. Cardiac cell retention was further improved by an injectable fibrin scaffold at day 3 post-MI (17 vs. 7%), even though morphometric and function parameters evaluated 4 weeks later displayed similar improvements.

Conclusions/Significance

These results show that cells injected post-MI display comparable tissue distribution profile regardless of the route of injection and that there is no time effect for cardiac cell accumulation for injections performed 1 to 3 days post-MI. As expected the IM injection is the most efficient for cardiac cell retention, it can be further improved by co-injection with a fibrin scaffold and it significantly attenuates cardiac dysfunction evaluated 4 weeks post myocardial infarction. These pharmacokinetic data obtained under similar experimental conditions are essential for further development of these novel approaches.     

Enhanced mobilization of the bone marrow-derived circulating progenitor cells by intracoronary freshly isolated bone marrow cells transplantation in patients with acute myocardial infarction

Autologous bone marrow cell transplantation (BMCs-Tx) is a promising novel option for treatment of cardiovascular disease. We analysed in a randomized controlled study the influence of the intracoronary autologous freshly isolated BMCs-Tx on the mobilization of bone marrow-derived circulating progenitor cells (BM-CPCs) in patients with acute myocardial infarction (AMI). Sixty-two patients with AMI were randomized to either freshly isolated BMCs-Tx or to a control group without cell therapy. Peripheral blood (PB) concentrations of CD34/45(+) - and CD133/45(+)-circulating progenitor cells were measured by flow cytometry in 42 AMI patients with cell therapy as well as in 20 AMI patients without cell therapy as a control group on days 1, 3, 5, 7, 8 and 3, 6 as well as 12 months after AMI. Global ejection fraction (EF) and the size of infarct area were determined by left ventriculography. We observed in patients with freshly isolated BMCs-Tx at 3 and 12 months follow up a significant reduction of infarct size and increase of global EF as well as infarct wall movement velocity. The mobilization of CD34/45(+) and CD133/45(+) BM-CPCs significantly increased with a peak on day 7 as compared to baseline after AMI in both groups (CD34/45(+): P < 0.001, CD133/45(+): P < 0.001). Moreover, this significant mobilization of BM-CPCs existed 3, 6 and 12 months after cell therapy compared to day 1 after AMI. In control group, there were no significant differences of CD34/45(+) and CD133/45(+) BM-CPCs mobilization between day 1 and 3, 6 and 12 months after AMI. Intracoronary transplantation of autologous freshly isolated BMCs by use of point of care system in patients with AMI may enhance and prolong the mobilization of CD34/45(+) and CD133/45(+) BM-CPCs in PB and this might increase the regenerative potency after AMI.     

Transplantation of microencapsulated Schwann cells and mesenchymal stem cells augment angiogenesis and improve heart function

Because of their plasticity and availability, bone-marrow-derived mesenchymal stem cells (MSC) are a potential cell source for treating ischemic heart disease. Schwann cells (SC) play a critical role in neural remodeling and angiogenesis because of their secretion of cytokines such as vascular endothelial growth factor (VEGF). Cell microencapsulation, surrounding cells with a semipermeable polymeric membrane, is a promising tool to shelter cells from the recipient's immune system. We investigated whether transplantation of microencapsulated SC (MC-SC) and MSC together could improve heart function by augmenting angiogenesis in acute myocardial infarction (AMI). Sprague-Dawley rats with ligation of the left anterior descending artery to induce AMI were randomly divided for cell transplantation into four groups-MC-SC+MSC, MC+MSC, MSC, MC-SC, and controls. Echocardiography was performed at 3 days and 2 and 4 weeks after AMI. Rat hearts were harvested on day 28 after transplantation and examined by immunohistochemistry and western blot analysis. Echocardiography revealed differences among the groups in fractional shortening and end-systolic and end-diastolic dimensions (P < 0.05). The number of BrdU-positive cells was greater with MC-SC+MSC transplantation than the other groups (P < 0.01). The vessel density and VEGF level in the infarcted zone was significantly increased with MC-SC+MSC transplantation (P < 0.05). These results show that transplanting a combination of MC-SC and MSC could augment angiogenesis and improve heart function in AMI.     

Transplantation of neural stem cells into the spinal cord after injury

Thanks to advances in the stem cell biology of the central nervous system (CNS), the previously inconceivable regeneration of the damaged CNS is approaching reality. The availability of signals to induce the appropriate differentiation of the transplanted and/or endogenous neural stem cells (NSCs) as well as the timing of the transplantation are important for successful functional recovery of the damaged CNS. Because the immediately post-traumatic microenvironment of the spinal cord is in an acute inflammatory stage, it is not favorable for the survival and differentiation of NSC transplants. On the other hand, in the chronic stage after injury, glial scars form in the injured site that inhibit the regeneration of neuronal axons. Thus, we believe that the optimal timing of transplantation is 1-2 weeks after injury.     

Differential Migration of Mesenchymal Stem Cells to Ischemic Regions after Middle Cerebral Artery Occlusion in Rats

To evaluate the optimal timing of mesenchymal stem cell (MSC) transplantation following stroke, rats were transplanted with MSCs at 1 (D1), 4 (D4), and 7 days (D7) after middle cerebral artery occlusion (MCAo). Rats in the D1 group showed a better functional recovery than those in the D4 or D7 groups after MCAo. MSCs preferentially migrated to the cortex in the D1 group, while the MSCs in the D4 or D7 groups preferentially migrated to the striatum. Interestingly, the level of monocyte chemotactic protein-1 (MCP-1) in the cortex was highest at 1 day after MCAo, while the level of stromal cell-derived factor-1 (SDF-1) in the striatum was lowest at 1 day after MCAo and then increased over time. The pattern of MCP-1 and SDF-1 level changes according to the time after MCAo was consistent with in vivo and in vitro migration patterns of MSCs. The results suggest that an earlier MSC transplantation is associated with a better functional recovery after stroke, which could be explained by the preferential migration of MSCs to the cortex in the early transplantation group. The time-dependent differential expression of MCP-1 and SDF-1 between ischemic regions seemed to mediate the differential migration of MSCs. Highest level of MCP-1 at one day of stroke may induce preferential migration of MSCs to the cortex, then better functional improvement.     

Transplantation of brain cells assembled around a programmable synthetic microenvironment

Cell therapy is a promising method for treatment of hematopoietic disorders, neurodegenerative diseases, diabetes, and tissue loss due to trauma. Some of the major barriers to cell therapy have been partially addressed, including identification of cell populations, in vitro cell proliferation, and strategies for immunosuppression. An unsolved problem is recapitulation of the unique combinations of matrix, growth factor, and cell adhesion cues that distinguish each stem cell microenvironment, and that are critically important for control of progenitor cell differentiation and histogenesis. Here we describe an approach in which cells, synthetic matrix elements, and controlled-release technology are assembled and programmed, before transplantation, to mimic the chemical and physical microenvironment of developing tissue. We demonstrate this approach in animals using a transplantation system that allows control of fetal brain cell survival and differentiation by pre-assembly of neo-tissues containing cells and nerve growth factor (NGF)-releasing synthetic particles.     

Role of patient chronotype on circadian pattern of myocardial infarction: a pilot study

Population-based studies indicate the risk of acute myocardial infarction (AMI) is greatest in the morning, during the initial hours of diurnal activity. The aim of this pilot study was to determine whether chronotype, i.e., morningness and eveningness, impacts AMI onset time. The sample comprised 63 morning- and 40 evening-type patients who were classified by the Horne-?stberg Morningness-Eveningness Questionnaire (MEQ) in the hospital after experiencing the AMI. The average wake-up and bed times of morning types were ~2?h earlier than evening types. Although the lag in time between waking up from nighttime sleep and AMI onset during the day did not differ between the two chronotypes, the actual clock-hour time of the peak in the 24-h AMI pattern did. The peak in AMI of morning types occurred between 06:01 and 12:00?h and that of the evening types between 12:01 and 18:00?h. Although the results of this small sample pilot study suggest one's chronotype influences the clock time of AMI onset, larger scale studies, which also include assessment of 24-h patterning of events in neither types, must be conducted before concluding the potential influence of chronotype on the timing of AMI onset.     

Engineering the embryoid body microenvironment to direct embryonic stem cell differentiation

Embryonic stem cells (ESCs) are pluripotent cells capable of differentiating into all somatic and germ cell types. The intrinsic ability of pluripotent cells to generate a vast array of different cells makes ESCs a robust resource for a variety of cell transplantation and tissue engineering applications, however, efficient and controlled means of directing ESC differentiation is essential for the development of regenerative therapies. ESCs are commonly differentiated in vitro by spontaneously self‐assembling in suspension culture into 3D cell aggregates called embryoid bodies (EBs), which mimic many of the hallmarks of early embryonic development, yet the 3D organization and structure of EBs also presents unique challenges to effectively direct the differentiation of the cells. ESC differentiation is strongly influenced by physical and chemical signals comprising the local extracellular microenvironment, thus current methods to engineer EB differentiation have focused primarily on spatially controlling EB size, adding soluble factors to the media, or culturing EBs on or within natural or synthetic extracellular matrices. Although most such strategies aim to influence differentiation from the exterior of EBs, engineering the microenvironment directly within EBs enables new opportunities to efficiently direct the fate of the cells by locally controlling the presentation of morphogenic cues. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Evaluating a new graphical ordinal logit method (GOLDminer) in the diagnosis of myocardial infarction utilizing clinical features and laboratory data

OBJECTIVE: We used a new graphical ordinal logit method (GOLDminer) to assess a single cardiac troponin T (cTnT) analysis at the time of admission (first generation monoclonal; Roche BMC Corp., Indianapolis, Indiana), the character of chest pain, and electrocardiographic (ECG)findings in predicting the likelihood of acute myocardial infarction (AMI) in patients presenting with suspected myocardial ischemia. The final diagnosis of AMI was based on serial ECG findings and evolution of CKMB isoenzyme levels in conjunction with clinical findings. SUBJECTS: The study population consisted of 293 consecutive patients who presented at a mean of six hours after onset of chest pain or associated symptoms warranting a "rule-out" for AMI assessment to a university-affiliated community hospital. RESULTS: The odds-ratio for an elevated cTnT (> 0. 1 ng/ml) in AMI was 22.2:1. There was an association between typical chest pain and cTnT (chi square = 78.23, p < .0001) and between abnormal ECG findings and cTnT (chi square = 108, p < .0001). The cTnT yielded diagnostic benefit in addition to chest pain characteristics and ECG findings in AMI. We present the odds-ratios for the combined features in GOLDminer plots. CONCLUSION: We demonstrate how the odds-ratios for AMI are obtained after scaling continuous to ordinal the values for a single cTnT determination alone and with other features in patients presenting with chest pain.     

Neovascularization derived from cell transplantation in ischemic myocardium

Myocardial ischemia triggers a limited angiogenic response, part of the remodeling process that is insufficient to avoid further functional impairment. Several strategies have been evaluated to regenerate myocardial vascularization after ischemic injury such as transmyocardial laser revascularization and gene therapy. Attention has recently been focused on the potential of cell therapy to induce angiogenesis. Enhancing myocardial neovascularization is a major goal of myocardial cell transplantation because it would provide patients, who cannot undergo conventional revascularization, with an alternative therapy. Additionally, neovascularization would provide the implanted cells with adequate microenvironment to enhance survival and function. This short review gives an overview of the effect of various cell transplantation strategies on myocardial neovascularization. It suggests that in order to optimize myocardial neovascularization induced by cell therapy, future experiments should focus on the contribution of exogenous and endogenous stem cells to new vessels formation, and on the identification of the molecular pathways involved in the process.     

Role of Patient Chronotype on Circadian Pattern of Myocardial Infarction: A Pilot Study

Population-based studies indicate the risk of acute myocardial infarction (AMI) is greatest in the morning, during the initial hours of diurnal activity. The aim of this pilot study was to determine whether chronotype, i.e., morningness and eveningness, impacts AMI onset time. The sample comprised 63 morning- and 40 evening-type patients who were classified by the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) in the hospital after experiencing the AMI. The average wake-up and bed times of morning types were ～2?h earlier than evening types. Although the lag in time between waking up from nighttime sleep and AMI onset during the day did not differ between the two chronotypes, the actual clock-hour time of the peak in the 24-h AMI pattern did. The peak in AMI of morning types occurred between 06:01 and 12:00?h and that of the evening types between 12:01 and 18:00?h. Although the results of this small sample pilot study suggest one's chronotype influences the clock time of AMI onset, larger scale studies, which also include assessment of 24-h patterning of events in neither types, must be conducted before concluding the potential influence of chronotype on the timing of AMI onset. (Author correspondence: dryavuzselvi@yahoo.com).