Organ-specific model of simulated ischemia/reperfusion and hyperglycemia based on engineered heart tissue

Here we aimed to establish an in vitro engineered heart tissue (EHT) co-morbidity mimicking model of ischemia-reperfusion injury and diabetes. EHTs were generated from primary neonatal rat cardiomyocytes. Hyperglycemic conditions or hyperosmolar controls were applied for one day to model acute hyperglycemia and for seven days to model chronic hyperglycemia. 120 min' simulated ischemia (SI) was followed by 120 min' reperfusion (R) and 1-day follow-up reperfusion (FR). Normoxic controls (N) were not subjected to SI/R. Half of the EHTs was paced, the other half was left unpaced. To assess cell injury, lactate-dehydrogenase (LDH) concentration was measured. Beating force and activity (frequency) were monitored as cardiomyocyte functional parameters. LDH-release indicated relevant cell injury after SI/N in each experimental condition, with much higher effects in the chronically hyperglycemic/hyperosmolar groups. SI stopped beating of EHTs in each condition, which returned during reperfusion, with weaker recovery in chronic conditions than in acute conditions. Acutely treated EHTs showed small LDH-release and ∼80% recovery of force during reperfusion and follow-up, while chronically treated EHTs showed a marked LDH-release, only ∼30% recovery with reperfusion and complete loss of beating activity during 24 h follow-up reperfusion. We conclude that EHTs respond differently to SI/R injury in acute and chronic hyperglycemia/hyperosmolarity, and that our EHT model is a novel in vitro combination of diabetes and ischemia-reperfusion.

Comprehensive analyses of the inotropic compound omecamtiv mecarbil in rat and human cardiac preparations

Omecamtiv mecarbil (OM), a myosin activator, was reported to induce complex concentration- and species-dependent effects on contractile function and clinical studies indicated a low therapeutic index with diastolic dysfunction at concentrations above 1 µM. To further characterize effects of OM in a human context and under different preload conditions, we constructed a setup that allows isometric contractility analyses of human induced pluripotent stem cell (hiPSC)-derived engineered heart tissues (EHTs). The results were compared to effects of OM on the very same EHTs measured under auxotonic conditions. OM induced a sustained, concentration-dependent increase in time-to-peak under all conditions (maximally 2-3 fold). Peak force, in contrast, was increased by OM only in human, but not rat EHTs and only under isometric conditions, varied between hiPSC lines and showed a biphasic concentration-dependency with maximal effects at 1 µM. Relaxation time tended to fall under auxotonic and strongly increase under isometric conditions, again with biphasic concentration-dependency. Diastolic tension concentration-dependently increased under all conditions. The latter was reduced by an inhibitor of the mitochondrial sodium calcium exchanger (CGP-37157). OM induced increases in mitochondrial oxidation in isolated cardiomyocytes, indicating that OM, an inotrope that does not increase intracellular and mitochondrial Ca²⁺, can induce mismatch between an increase in ATP and ROS production and unstimulated mitochondrial redox capacity. Taken together, we developed a novel setup well suitable for isometric measurements of EHTs. The effects of OM on contractility and diastolic tension are complex with concentration-, time-, species- and loading-dependent differences. Effects on mitochondrial function require further studies.

Translational investigation of electrophysiology in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) patients are at increased risk of ventricular arrhythmias and sudden cardiac death, which can occur even in the absence of structural changes of the heart. HCM mouse models suggest mutations in myofilament components to affect Ca²⁺ homeostasis and thereby favor arrhythmia development. Additionally, some of them show indications of pro-arrhythmic changes in cardiac electrophysiology. In this study, we explored arrhythmia mechanisms in mice carrying a HCM mutation in Mybpc3 (Mybpc3-KI) and tested the translatability of our findings in human engineered heart tissues (EHTs) derived from CRISPR/Cas9-generated homozygous MYBPC3 mutant (MYBPC3hom) in induced pluripotent stem cells (iPSC) and to left ventricular septum samples obtained from HCM patients.

We observed higher arrhythmia susceptibility in contractility measurements of field-stimulated intact cardiomyocytes and ventricular muscle strips as well as in electromyogram recordings of Langendorff-perfused hearts from adult Mybpc3-KI mice than in wild-type (WT) controls. The latter only occurred in homozygous (Hom-KI) but not in heterozygous (Het-KI) mouse hearts. Both Het- and Hom-KI are known to display pro-arrhythmic increased Ca²⁺ myofilament sensitivity as a direct consequence of the mutation. In the electrophysiological characterization of the model, we observed smaller repolarizing K⁺ currents in single cell patch clamp, longer ventricular action potentials in sharp microelectrode recordings and longer ventricular refractory periods in Langendorff-perfused hearts in Hom-KI, but not Het-KI. Interestingly, reduced K⁺ channel subunit transcript levels and prolonged action potentials were already detectable in newborn, pre-hypertrophic Hom-KI mice. Human iPSC-derived MYBPC3hom EHTs, which genetically mimicked the Hom-KI mice, did exhibit lower mutant mRNA and protein levels, lower force, beating frequency and relaxation time, but no significant alteration of the force-Ca²⁺ relation in skinned EHTs. Furthermore, MYBPC3hom EHTs did show higher spontaneous arrhythmic behavior, whereas action potentials measured by sharp microelectrode did not differ to isogenic controls. Action potentials measured in septal myectomy samples did not differ between patients with HCM and patients with aortic stenosis, except for the only sample with a MYBPC3 mutation.

The data demonstrate that increased myofilament Ca²⁺ sensitivity is not sufficient to induce arrhythmias in the Mybpc3-KI mouse model and suggest that reduced K⁺ currents can be a pro-arrhythmic trigger in Hom-KI mice, probably already in early disease stages. However, neither data from EHTs nor from left ventricular samples indicate relevant reduction of K⁺ currents in human HCM. Therefore, our study highlights the species difference between mouse and human and emphasizes the importance of research in human samples and human-like models.

•

Sudden cardiac death is threatening hypertrophic cardiomyopathy (HCM) patients.

•

Arrhythmia mechanisms are not well understood.

•

Mouse HCM models showed relevant reduction in K⁺ currents.

•

Human iPSC-EHT model and HCM patient septal myectomies did not display this mechanism.

Sulforaphane exposure impairs contractility and mitochondrial function in three-dimensional engineered heart tissue

Sulforaphane (SFN) is a phytochemical compound extracted from cruciferous plants, like broccoli or cauliflower. Its isothiocyanate group renders SFN reactive, thus allowing post-translational modification of cellular proteins to regulate their function with the potential for biological and therapeutic actions. SFN and stabilized variants recently received regulatory approval for clinical studies in humans for the treatment of neurological disorders and cancer. Potential unwanted side effects of SFN on heart function have not been investigated yet. The present study characterizes the impact of SFN on cardiomyocyte contractile function in cardiac preparations from neonatal rat, adult mouse and human induced-pluripotent stem cell-derived cardiomyocytes. This revealed a SFN-mediated negative inotropic effect, when administered either acutely or chronically, with an impairment of the Frank-Starling response to stretch activation. A direct effect of SFN on myofilament function was excluded in chemically permeabilized mouse trabeculae. However, SFN pretreatment increased lactate formation and enhanced the mitochondrial production of reactive oxygen species accompanied by a significant reduction in the mitochondrial membrane potential. Transmission electron microscopy revealed disturbed sarcomeric organization and inflated mitochondria with whorled membrane shape in response to SFN exposure. Interestingly, administration of the alternative energy source l-glutamine to the medium that bypasses the uptake route of pyruvate into the mitochondrial tricarboxylic acid cycle improved force development in SFN-treated EHTs, suggesting indeed mitochondrial dysfunction as a contributor of SFN-mediated contractile dysfunction. Taken together, the data from the present study suggest that SFN might impact negatively on cardiac contractility in patients with cardiovascular co-morbidities undergoing SFN supplementation therapy. Therefore, cardiac function should be monitored regularly to avoid the onset of cardiotoxic side effects.

•

Sulforaphane has negative inotropic effects and increases diastolic tension.

•

Sulforaphane exposure increases lactate levels and mitochondrial ROS production and reduces mitochondrial membrane potential.

•

l-glutamine supplementation rescues the sulforaphane-mediated reduction in force development.

•

Sulforaphane plasma levels and cardiac function should be monitored to avoid unwanted cardiac side effects in patients.

Preserved cardiovascular homeostasis despite blunted acetylcholine-induced dilation in mice with endothelial muscarinic M3 receptor deletion

AIM

Muscarinic acetylcholine receptors (AChMR1-5) are fundamental for cellular responses upon release of the neurotransmitter acetylcholine (ACh) from parasympathetic nerve fibers. ACh is the prototypical agonist stimulating endothelium-dependent dilation, but most blood vessels lack parasympathetic innervation, raising the question as to the physiologic function of endothelial AChMR in vivo. Global deletion of AChM3R revealed a role in ACh-induced vasodilation in vitro and food uptake, but overall cardiovascular homeostasis has not been examined thoroughly.

METHODS

To characterize the function of endothelial AChM3R in vivo, we deleted AChM3R specifically in endothelial cells with an inducible or a non-inducible Cre-loxP system, driven by the endothelium-specific promoters VE-cadherin (indEC-M3R^-/- ) or TIE2 (tek2; EC-M3R^-/- ) and examined arteriolar dilation in the cremaster microcirculation, arterial pressure and cardiac function in these mice in vivo.

RESULTS

In both EC-M3R^-/- , ACh-induced dilation was strongly impaired in arterioles in vivo, while responses to other dilators were mostly preserved. However, arterial pressure (indEC-M3R^-/- ) and arteriolar tone as a surrogate for peripheral vascular resistance did not differ between EC-M3R^-/- and control mice. Aged EC-M3R^-/- mice (74-78 weeks) did not differ in body weight, heart weight, cardiac structure or contractile function from controls.

CONCLUSION

We conclude that AChM3R elicits the endothelium-dependent dilation upon ACh also in arterioles in vivo. Despite this prominent role, the endothelial deletion of AChM3R does not affect overall cardiovascular homeostasis. Thus, their physiologic function in endothelial cells remains obscure.

Surgical and intensive care needs of head-injured patients transferred to the University Hospital of the West Indies

A cross-sectional, descriptive study utilizing data collected in the 'Trauma Registry' of the Department of Surgery, Radiology, Anaesthesia and Intensive Care at the University Hospital of the West Indies (UHWI) was undertaken to document injury severity, surgical requirements and intensive care needs of head-injured patients transferred to the UHWI over a three-year period Of 144 patients studied, the majority (71%) were young males. Overall, injury tended to be mild Twenty-three patients (16.0%) had severe head injury and 27 patients (18.8%) were admitted to the intensive care unit. Concussion with (33%) or without (36%) skull fracture was the commonest neurological admission diagnosis. Associated non-neurological injuries in 33% were primarily fractures. Fifty-six patients (39%) required surgical intervention. Craniotomies and open reduction and internal fixation of fractures were the commonest procedures. The majority of patients (79.2%) were discharged home; 56 (39%) made a good Glasgow outcome score recovery. Seventeen patients (11.8%) died in hospital. As most of the transferred patients with head injuries in this study had only mild injury, most commonly concussions, and their prognosis was good, we recommend that appropriate educational and training programmes and transfer policies be implemented to minimize inappropriate transfers.

The prevalence of seat belt use in Kingston, Jamaica: a follow-up observational study five years after the introduction of legislation

An observational cross-sectional study conducted in Kingston in 2004 showed that seat belts were used by 81.2% of private motor vehicle drivers and 74.0% offront seat passengers. This was significantly improved compared to 21.1% and 13.6% respectively in 1996 before the introduction of legislation in 1999 (p < 0.001). Females were significantly more likely than males to wear seat belts, both when driving (92.5% vs 77.3%; p < 0. 001) and as front seat passengers (79.9% vs 66.3%; p < 0.001). Of the 2289 motor vehicles examined, all except one were equipped with seat belts. Rear passenger utilization of seat belts was not examined. Drivers of new vehicles were more likely than other drivers to use seat belts (p < 0.001). Male drivers, drivers of older vehicles and all passengers may require specific targeting in an educational and enforcement campaign if the maximum benefits of seat belt use are to be realized

Transfer of head-injured patients in Jamaica: is there a problem?

Head-injured patients are often transferred to the University Hospital of the West Indies (UHWI) for tertiary care. There is no standardized, agreed protocol governing their transfer. During the three-year period January 1998 to December 2000, 144 head injured patients were transferred to the UHWI from other institutions. They were 70% male, had a mean age of 34 years and spent a mean of 13 days in hospital. Eighteen per cent were admitted to the Intensive Care Unit, where they spent a mean of nine days. On arrival, mean pulse rate was 92 +/- 22 beats/minute, mean systolic blood pressure was 130 +/- 27 mmHg and mean diastolic was 76 +/- 19mmHg. Twenty-eight per cent of patients had a pulse rate above 100/min on arrival and 13.8% had systolic blood pressure below 60 mmHg. The Glasgow Coma Scale score was unrecorded at the referring institution in 70% of cases and by the receiving officers at the UHWI in 23% of cases. Intubation was done on only half of those who were eligible. Junior staff members initiated and carried out transfers whenever this was documented. The types of vehicles and monitoring equipment used could not be determined in most instances. Fifty-eight per cent of patients had minor head injuries, 12%, severe injury and 33%, associated injuries requiring a variety of surgical procedures by multiple specialties. Most patients (80.6%) were discharged home but 11.8% died in hospital. Transfer of head-injured patients, many with multiple injuries is not being performed in a manner consistent with modern medical practice. There is urgent need for implementation of a standardized protocol for the transfer of such patients in Jamaica.

Cancer of the colon and rectum in a Jamaican population: diagnostic implications of the changing frequency and subsite distribution

The aim of this study was to examine the clinical and pathological characteristics of colorectal cancer in Jamaica, to determine whether there was a change in the anatomic distribution and clinical presentation and to discuss the options for diagnosis and management. A comprehensive retrospective review of patients newly diagnosed with colorectal carcinoma was conducted at The University Hospital of the West Indies by reviewing both patient records and pathological data. These data were compared with previous reports of patients with colorectal cancer seen in Jamaica. One hundred and forty-seven patients were studied There were 85 females and 62 males with a female to male ratio of 1.37:1. The median age was 65.5 years (range 19 to 94 years). The predominant symptoms were abdominal pain in 91 patients, change in bowel habit in 77 patients and rectal bleeding in 74 patients. Sixty patients presented with weight loss and 28 with a rectal mass. The most common tumours were right-sided colonic cancers in 42 patients (28.5%) followed by sigmoid colon in 30 (20.4%) rectum in 34 (23.1%) and left and transverse colon accounting for 16 and 10 cases respectively. Most of the tumours were well or moderately differentiated adenocarcinomas. Only eight patients presented with Dukes' A disease, 50 with Dukes'B, 53 with Dukes'C disease and 34 with advanced disease. The findings showed that sigmoid and rectal tumours accounted for 43.5% of cancers. The colon/rectum ratio in this series was 3.3:1 indicating a significant proximal shift of colorectal cancers in this population in keeping with recent reports. The results of the current study suggest that the sub-site location of colorectal cancers seen is similar to that reported in high incidence countries such as the United States of America and parts of Europe but differs from the African continent which has a high proportion of rectal tumours. This right-sided preponderance also differs from previous studies in Jamaica, which report a higher incidence of rectal lesions The detection of early colorectal carcinoma will require screening at a stage when the disease is asymptomatic in order to improve the chance for cure. The data presented here imply that screening programmes should allow evaluation of the entire colon rather than the distal 25 cm.

The challenge of designing a database for auditing surgical in-patients

Surgical audit is imperative in modern practice, particularly in the developing world where resources are limited and efficient allocation important. The structure, process and outcome of surgical care can be determined for quality assurance or for research. Improved efficiency and reduction of morbidity and mortality are additional goals which may be accomplished. However, computerization, medical staff cooperation and the availability of dedicated staff are among the hurdles which may be encountered. We report the challenge of designing and establishing a database for auditing surgical inpatients in a developing country and the difficulties which were encountered.

The prevalence of seat belt use in Jamaica. An observational study

An observational cross-sectional survey showed that 21.1% of private motor vehicle drivers and 13.5% of front seat passengers voluntarily wore seat belts in Kingston, Jamaica, where there is no law requiring this. Rear passenger utilisation was not examined. Compared to males, females were significantly more likely to wear seat belts when driving but not as front seat passengers. Of all motor vehicles examined, 10.1% were not equipped with seat belts. The oldest group of vehicles were mostly not fitted with seat belts. Drivers of older vehicles were significantly less likely to use seat belts even when the vehicles were equipped with belts. Implementation of legislation can reduce mortality, morbidity and costs from road traffic accidents which are relatively frequent in Jamaica. Male drivers, drivers of older vehicles and all passengers may require specific targeting in an educational and enforcement campaign should legislation, which is highly desirable, be implemented.