Bone Cements Used in Vertebral Augmentation: A State-of-the-art Narrative Review

Vertebral compression fractures (VCFs) are common in osteoporotic patients, with a frequency projected to increase alongside a growing geriatric population. VCFs often result in debilitating back pain and decreased mobility. Cement augmentation, a minimally invasive surgical technique, is widely used to stabilize fractures and restore vertebral height. Acrylic-based cements and calcium phosphate cements are currently the two primary fill materials utilized for these procedures. Despite their effectiveness, acrylic bone cements and calcium phosphate cements have been associated with various intraoperative and postoperative incidents impacting VCF treatment. Over the past decade, discoveries in the field of biomedical engineering and material science have shown advancements toward addressing these limitations. This narrative review aims to assess the potential pitfalls and barriers of the various types of bone cements.

A Novel Port to Facilitate Magnetic Hyperthermia Therapy for Glioma

High-grade gliomas (HGG) are the most common primary brain malignancy and continue to be associated with a dismal prognosis (median survival rate of 15-18 months) with standard of care therapy. Magnetic hyperthermia therapy (MHT) is an emerging intervention that leverages the ferromagnetic properties of magnetic iron-oxide nanoparticles (MIONPs) to target cancer cells that are otherwise left behind after resection. We report a novel port device to facilitate localization, delivery, and temperature measurement of MIONPs within a target lesion for MHT therapy. We conducted an in-depth literature and intellectual property review to define specifications of the conceived port device. After setting the design parameters, a thorough collaboration with neurological surgeons guided the iterative modeling process. A prototype was developed using Fusion 360 (Autodesk, San Rafael, CA) and printed on a Form 3 printer (Formlabs, Medford, MA) in Durable resin. The prototype was then tested in a phantom skull printed on a Pro-Jet 660Pro 3D printer (3D Systems, Rock Hill, SC) and a brain model based on mechanical and electrochemical properties of native brain tissue. This phantom underwent MHT heating tests using an alternating magnetic field (AMF) sequence based on current MHT workflow. Successful localization, delivery, and temperature measurement were demonstrated. The purpose of this study was twofold: first, to create and validate the procedural framework for a novel device, providing the groundwork for an upcoming comprehensive animal trial and second, to elucidate a cooperative approach between engineers and clinicians that propels advancements in medical innovation.

3D reconstruction of murine mitochondria reveals changes in structure during aging linked to the MICOS complex

During aging, muscle gradually undergoes sarcopenia, the loss of function associated with loss of mass, strength, endurance, and oxidative capacity. However, the 3D structural alterations of mitochondria associated with aging in skeletal muscle and cardiac tissues are not well described. Although mitochondrial aging is associated with decreased mitochondrial capacity, the genes responsible for the morphological changes in mitochondria during aging are poorly characterized. We measured changes in mitochondrial morphology in aged murine gastrocnemius, soleus, and cardiac tissues using serial block-face scanning electron microscopy and 3D reconstructions. We also used reverse transcriptase-quantitative PCR, transmission electron microscopy quantification, Seahorse analysis, and metabolomics and lipidomics to measure changes in mitochondrial morphology and function after loss of mitochondria contact site and cristae organizing system (MICOS) complex genes, Chchd3, Chchd6, and Mitofilin. We identified significant changes in mitochondrial size in aged murine gastrocnemius, soleus, and cardiac tissues. We found that both age-related loss of the MICOS complex and knockouts of MICOS genes in mice altered mitochondrial morphology. Given the critical role of mitochondria in maintaining cellular metabolism, we characterized the metabolomes and lipidomes of young and aged mouse tissues, which showed profound alterations consistent with changes in membrane integrity, supporting our observations of age-related changes in muscle tissues. We found a relationship between changes in the MICOS complex and aging. Thus, it is important to understand the mechanisms that underlie the tissue-dependent 3D mitochondrial phenotypic changes that occur in aging and the evolutionary conservation of these mechanisms between Drosophila and mammals.

Three-dimensional mitochondria reconstructions of murine cardiac muscle changes in size across aging

With sparse treatment options, cardiac disease remains a significant cause of death among humans. As a person ages, mitochondria breakdown and the heart becomes less efficient. Heart failure is linked to many mitochondria-associated processes, including endoplasmic reticulum stress, mitochondrial bioenergetics, insulin signaling, autophagy, and oxidative stress. The roles of key mitochondrial complexes that dictate the ultrastructure, such as the mitochondrial contact site and cristae organizing system (MICOS), in aging cardiac muscle are poorly understood. To better understand the cause of age-related alteration in mitochondrial structure in cardiac muscle, we used transmission electron microscopy (TEM) and serial block facing-scanning electron microscopy (SBF-SEM) to quantitatively analyze the three-dimensional (3-D) networks in cardiac muscle samples of male mice at aging intervals of 3 mo, 1 yr, and 2 yr. Here, we present the loss of cristae morphology, the inner folds of the mitochondria, across age. In conjunction with this, the three-dimensional (3-D) volume of mitochondria decreased. These findings mimicked observed phenotypes in murine cardiac fibroblasts with CRISPR/Cas9 knockout of Mitofilin, Chchd3, Chchd6 (some members of the MICOS complex), and Opa1, which showed poorer oxidative consumption rate and mitochondria with decreased mitochondrial length and volume. In combination, these data show the need to explore if loss of the MICOS complex in the heart may be involved in age-associated mitochondrial and cristae structural changes.NEW & NOTEWORTHY This article shows how mitochondria in murine cardiac changes, importantly elucidating age-related changes. It also is the first to show that the MICOS complex may play a role in outer membrane mitochondrial structure.

Bibliometric Analysis of International Medical Graduates and Professorship Promotion in Neurosurgery

BACKGROUND

International medical graduates (IMGs) comprise ∼25% of physicians in the United States. Differences in promotion rates from assistant to associate to full professorship based on medical school location have been understudied. We aim to stratify odds of professional advancement by 3 categories: IMG with U.S. residency, IMG with international residency, and U.S. medical with U.S. residency training.

METHODS

We created and queried a database after exclusions of 1334 neurosurgeons including multiple demographic factors: academic productivity and promotion rates. Stratified logistic regression modeled odds of promotion including the variables: decades out of training, Scopus h-index, gender, and training location. Odds ratios (ORs) and 95% confidence intervals (CIs) for each variable were calculated.

RESULTS

Significant predictors of increased associate versus assistant professorship included decades out of training (OR = 2.519 [95% CI: 2.07-3.093], P < 0.0001) and Scopus h-index (OR = 1.085 [95% CI: 1.064-1.108], P < 0.0001) while international medical school with U.S. residency (OR = 0.471 [95% CI: 0.231-0.914], P = 0.0352) was associated with decreased promotion. Significant predictors of associate versus full professorship were decades out of training (OR = 2.781 [95% CI: 2.268-3.444], P < 0.0001) and Scopus h-index (OR = 1.064 [95% CI: 1.049-1.080], P < 0.0001). Attending medical school or residency internationally was not associated with odds of full professorship.

CONCLUSIONS

Time out of residency and Scopus h-index were associated with higher academic rank regardless of career level. Attending medical school internationally with U.S. residency was associated with lower odds of associate professorship promotion over 10 years. There was no relationship between IMG and full professorship promotion. IMGs who attended residency internationally did not have lower promotion rates. These findings suggest it may be harder for IMGs to earn promotion from assistant to associate professor in neurosurgery.

Surgical techniques for evacuation of chronic subdural hematoma: a mini-review

Chronic subdural hematoma is one of the most common neurosurgical pathologies with over 160,000 cases in the United States and Europe each year. The current standard of care involves surgically evacuating the hematoma through a cranial opening, however, varied patient risk profiles, a significant recurrence rate, and increasing financial burden have sparked innovation in the field. This mini-review provides a brief overview of currently used evacuation techniques, including emerging adjuncts such as endoscopic assistance and middle meningeal artery embolization. This review synthesizes the body of available evidence on efficacy and risk profiles for each critical aspect of surgical technique in cSDH evacuation and provides insight into trends in the field and promising new technologies.

Validation of a Temperature-Feedback Controlled Automated Magnetic Hyperthermia Therapy Device

We present in vivo validation of an automated magnetic hyperthermia therapy (MHT) device that uses real-time temperature input measured at the target to control tissue heating. MHT is a thermal therapy that uses heat generated by magnetic materials exposed to an alternating magnetic field. For temperature monitoring, we integrated a commercial fiber optic temperature probe containing four gallium arsenide (GaAs) temperature sensors. The controller device used temperature from the sensors as input to manage power to the magnetic field applicator. We developed a robust, multi-objective, proportional-integral-derivative (PID) algorithm to control the target thermal dose by modulating power delivered to the magnetic field applicator. The magnetic field applicator was a 20 cm diameter Maxwell-type induction coil powered by a 120 kW induction heating power supply operating at 160 kHz. Finite element (FE) simulations were performed to determine values of the PID gain factors prior to verification and validation trials. Ex vivo verification and validation were conducted in gel phantoms and sectioned bovine liver, respectively. In vivo validation of the controller was achieved in a canine research subject following infusion of magnetic nanoparticles (MNPs) into the brain. In all cases, performance matched controller design criteria, while also achieving a thermal dose measured as cumulative equivalent minutes at 43 °C (CEM43) 60 ± 5 min within 30 min.

Electrocardiogram metrics identify ionic current dysregulation relevant to atrial fibrillation

Background

Personalisation of pharmacological treatment for atrial fibrillation (AF) is challenging. Pharmacological ionic current blockers such as digoxin or flecainide are commonly used, with caution given possible cardiotoxicity and proarrhythmia. Moreover, patients are stratified based on their associated heart disease rather than individual electrophysiological substrate, in part due to the inability for its non-invasive characterisation. Here we hypothesise that the ECG may contain information on key ionic currents regulating AF initiation and sustenance, and which would enable personalisation of pharmacological treatments to increase safety and efficacy.

Purpose

To identify clinical ECG markers that reflect dysregulation of key ionic currents for AF using modelling and simulation in populations of whole-atria models without structural heart disease.

Methods

Experimental data obtained from human AF and control patients was used to develop a virtual population of 200 whole-atria models (Figure, organ-level) with individual ionic profiles (Figure 1, bottom-left), including electrophysiological regional inhomogeneities (Figure 1, bottom-right). Modified-limb 12 lead ECGs were computed during sinus rhythm (Figure 1, body-surface-level) and biomarkers were quantified for the P and Ta-waves, such as duration, time-to-peak, decay, dispersion, amplitude and P-wave terminal force.

Results

Simulated modified-limb ECG consistently reproduced the clinical ECG observed in human subjects, with an apparent Ta-wave inversion in lead II (Figure 1, body-surface-level). The inward rectified K+ current (IK1), known to be critical for AF, was the only ionic current associated with Ta-wave duration, showing an inversely proportional relationship (236±48 vs. 466±53 ms, IK1 up-regulation vs. down-regulation in lead V5; median ± interquartile range; P&lt;0.001). Elevated IK1 additionally yield Ta-wave inversion in lead V5 and a higher Ta-wave magnitude in lead II (0.15±0.03 vs. 0.07±0.04 mV, IK1 up-regulation vs. down-regulation; P&lt;0.001). However, Ta-wave magnitude showed a predominant relationship with the Na+/K+ pump (INaK), especially in the precordial leads (0.17±0.13 vs. 0.07±0.04 mV, INaK up-regulation vs. down-regulation in V5; P&lt;0.001). Thus, the up-regulation of both currents led to very short, high-amplitude Ta-waves. While elevated IK1 additionally increased the P-wave terminal force (1.58±0.37 vs. 1.31±0.33 mV ms, IK1 up-regulation vs. down-regulation; P&lt;0.001), a higher increase was observed for decreased fast Na+ current (INa) (1.35±0.17 vs. 1.86±0.30 mV ms, INa up-regulation vs. down-regulation; P&lt;0.001).

Conclusion

Ta-wave duration and amplitude are revealing of IK1 and INaK dysregulation, respectively, holding potential for improving cardiac safety and efficacy through a better stratification of AF patients for pharmacological treatment.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 860974

Modelling and in silico simulation of human induced pluripotent stem cell derived cardiomyocyte electro-mechanical properties

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): BHF

Background

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) enable accessible human data-based cardiology studies. However, a caveat in hiPSC-CM-based studies is their immature electrophysiological and contractile phenotype. One of the modifications occurring during hiPSC-CM maturation is the change in myofilament calcium sensitivity, an important indicator of cardiac muscle function [1, 2]. In silico hiPSC-CM investigations could help improve understanding of the hiPSC-CM-specific contractile behaviour and its changes during maturation. Considering the growing use of hiPSC-CM, it is vital to enable investigations of hiPSC-CM-specific contractile features.

Purpose

To address the need of hiPSC-CM model with integrated contractile element, our goal is to develop an electromechanical human data-based iPSC-CM computer model. We aim to use the model to investigate the effects of the changes in myofilament calcium sensitivity on hiPSC-CM electrophysiology and contractility.

Methods

We coupled a published hiPSC-CM electrophysiological model [3] with a model of the human adult cardiomyocyte contractile machinery [4] by linking intracellular calcium and calcium-bound troponin dynamics. The established electromechanical hiPSC-CM model was calibrated using experimental hiPSC-CM active tension data and its simulated electromechanical biomarkers were also evaluated against experimental action potential and calcium transient data. We conducted a sensitivity analysis to investigate the effects of changes in myofilament calcium sensitivity on the electrophysiology and contractility of the cell.

Results

First, we demonstrated that the model successfully reproduces the hiPSC-CM contractile phenotype. Simulations showed a peak twitch tension of 0.44 kPa which takes 201 ms to peak and 164 ms to achieve 50% relaxation, which all agree with the experimental hiPSC-CM values. Simulated calcium transient and action potential biomarkers remain within the experimentally established ranges after electromechanical coupling. The sensitivity analysis of the hiPSC-CM model focused on the myofilament calcium sensitivity effects showed an increase in active tension amplitude with a decrease in calcium transient peaks upon increased myofilament calcium sensitivity. Large increases in myofilament calcium sensitivity result in depolarization failure with low amplitude fluctuations of membrane voltage, calcium transient and active tension. Altogether simulation results demonstrate the usability of the model for simulating and exploring not only physiological, but also pathological cardiac conditions.

Conclusions

We present a new electromechanical hiPSC-CM model for in silico hiPSC-CM-based studies. The model has been evaluated against experimental data and has demonstrated the capacity to generate key electrophysiological currents, active tension as well as myofilament calcium sensitivity-induced electromechanical abnormalities.

Correlates of psychological intimate partner violence with HIV care outcomes on patients in HIV care

Background

Among people living with HIV (PLWH), physical intimate partner violence (IPV) is associated with poor virologic, psychiatric, and behavioral outcomes. We examined non-physical, psychological intimate partner violence (psy-IPV) and HIV care outcomes using data from two U.S. consortia.

Methods

We conducted multivariable analyses with robust standard errors to compare patients indicating/not indicating psy-IPV.

Results

Among PLWH (n = 5950), 9.5% indicated psy-IPV; these individuals were younger (− 3; 95% CI [− 2,-4], p-value < 0.001), less likely to be on antiretroviral treatment (ART) (0.73 [0.55,0.97], p = 0.03), less adherent to ART (− 4.2 [− 5.9,-2.4], p < 0.001), had higher odds of detectable viral load (1.43 [1.15,1.78], p = 0.001) and depression (2.63 [2.18,3.18], p < 0.001), and greater use of methamphetamines/crystal [2.98 (2.30,3.87),p < 0.001], cocaine/crack [1.57 (1.24,1.99),p < 0.001], illicit opioids [1.56 (1.13,2.16),p = 0.007], and marijuana [1.40 (1.15,1.70), p < 0.001].

Conclusion

Psychological IPV, even in the absence of physical or sexual IPV, appears to be associated with HIV care outcomes and should be included in IPV measures integrated into routine HIV care.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-11854-x.

Human-based computational and experimental investigation of disease mechanisms in mutation-specific hypertrophic cardiomyopathy

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement 764738. British Heart Foundation Intermediate Basic Science Fellowship (FS/17/22/32644).

Background

The pathogenic TNNI3R21C/+ variant causes malignant hypertrophic cardiomyopathy (HCM) with high incidence of sudden cardiac death, even in individuals absent of hypertrophy. There is evidence to support a known biophysical defect in the protein, yet the cellular mechanisms that precipitate adverse clinical outcomes remain unclear.

Purpose

We aim to computationally model and map the TNNI3R21C/+ cellular phenotype observed in induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) to human disease, thereby explaining the key mechanisms driving HCM in TNNI3R21C/+ variant carriers. 

Methods

Wild-type (WT) and TNNI3R21C/+ iPSC-CMs were characterised by calcium transient analysis and direct sarcomere tracking to assess cellular contraction and relaxation. In-vitro data was used to inform the in-silico modelling of human cardiomyocytes. We constructed an in-silico population of WT adult cardiomyocytes and used it to transform the in-vitro data into corresponding adult phenotypes by means of a novel iPSC-to-adult data mapping. We tested the hypothesis that the abnormal TNNI3R21C/+ phenotype observed in iPSC-CMs would be explained by alterations in calcium affinity of troponin and increased myofilament calcium sensitivity. 

Results

Analysis of in-vitro iPSC-CM data showed that TNNI3R21C/+ cells exhibit increased contractility with slowed relaxation when compared to WT. They also exhibited a faster rise in the calcium transient with a slowed calcium decay in comparison to WT. The in-silico adult TNNI3R21C/+ phenotype from the iPSC-to-adult mapping replicated the abnormalities observed in iPSC-CMs. The WT in-silico population accurately covered the ranges of electromechanical biomarkers providing a representative cohort of physiological variability. The TNNI3R21C/+ calcium phenotype could be recovered by our in-silico mutant models. Simulation results suggest that calcium abnormalities in TNNI3R21C/+ are a direct consequence of abnormal calcium buffering by thin filaments, mediated by increases in calcium affinity of troponin and myofilament calcium sensitivity. The TNNI3R21C/+ phenotype could not be recovered if these two factors were considered in isolation. Corresponding contractility analyses of in-silico models showed that the calcium level changes caused by the TNNI3R21C/+ phenotype are associated with hypercontractility and diastolic dysfunction, well-known hallmarks of HCM, which were also observed in the iPSC-CM model of disease.

Conclusions

This study showcases human-based computational and experimental methodologies that unearth direct mechanistic explanations of phenotypes driven by the TNNI3R21C/+ HCM variant. We show that the TNNI3R21C/+ HCM-causing mutation exhibits multifactorial remodelling of troponin calcium affinity and myofilament calcium sensitivity. Unearthing mechanistic pathways in mutation-specific HCM will be key to develop effective pharmacological interventions for a wide variety of understudied variants.

Post myocardial infarction ionic remodelling promotes repolarisation dispersion and electrocardiogram abnormalities in acute and chronic stages

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Wellcome Trust

Background

Sudden cardiac death (SCD) occurs in both acute and chronic stages post myocardial infarction (MI), and the left ventricular ejection fraction (LVEF) and electrocardiogram (ECG) characteristics are important biomarkers for clinical decision making. While various ionic remodelling has been reported in literature at various stages post-MI, the effect of them on clinical biomarkers have not been fully explored.

Purpose

Evaluate the effects of cellular ionic remodelling in acute and chronic post myocardial infarction on ECG and LVEF biomarkers through computational modelling and simulations of human biventricular electromechanics.

Methods

An electromechanical coupled biventricular model with ToR-ORd (Tomek 2019) human electrophysiology coupled with human excitation-contraction machinery (Land 2017) and orthotropic passive mechanics (Holzapfel 2009) was used as baseline model. The 12-lead ECG were simulated at standard body-surface electrode locations, and the biventricular pressure volume loop was simulated to quantify the simulated LVEF. A cardiac magnetic resonance (CMR) derived human biventricular geometry (Strocchi 2020) was used in combination with rigidly aligned torso geometry (Minchole 2019). An anterior sub-endocardial infarction was delineated with infarct, border zone (BZ) and remote zone (RZ) regions. For acute infarction, three types of BZ ionic remodelling from literature, and their effects on simulated LVEF and ECG characteristics were quantified. For chronic infarction, a single chronic BZ ionic remodelling was combine with two different models of RZ ionic remodelling from literature, and the effects of these remodelling on the simulated LVEF and ECG were quantified. The electromechanical properties of the sub-endocardial infarct region did not significantly affect simulated ECG or LVEF biomarkers.

Results

For the acute phase, simulations showed pre-cordial ECG abnormalities for all three BZ models, with T-wave inversion and QT prolongation (80 ms) in BZ1, ST-segment elevation with T-wave inversion in BZ2, and decreased T-wave amplitude in BZ3. Activation maps showed conduction block in BZ2 simulations, leading to ST-segment elevation. Repolarisation maps showed high dispersion in BZ1 simulations, leading to T-wave inversion. LVEF for BZ2 decreased by 4% (from 57% in control) due to conduction block in BZ and lack of contraction in that region, LVEF remained constant for BZ1 and BZ3 simulations. For the chronic phase, there was QT prolongation in both RZ1 (80 ms) and RZ2 (170 ms) as well as decreased T-wave amplitude, reflected by elevated repolarisation dispersion. LVEF was not significantly altered for either simulations.

Conclusions

Post-MI ionic remodelling at the acute and chronic stages cause varying degrees of dispersion of repolarisation and T-wave and ST-segment abnormalities, with minimal effect on mechanical function, except in the case of severe conduction abnormality. Abstract Figure.

Brief Report: Weight Gain Following ART Initiation in ART-Naïve People Living With HIV in the Current Treatment Era

OBJECTIVES

Evaluate differences in weight change by regimen among people living with HIV (PLWH) initiating antiretroviral therapy (ART) in the current era.

METHODS

Between 2012 and 2019, 3232 ART-naïve PLWH initiated ≥3-drug ART regimens in 8 Centers for AIDS Research Network of Integrated Clinical Systems sites. We estimated weight change by regimen for 11 regimens in the immediate (first 6 months) and extended (all follow-up on initial regimen) periods using linear mixed models adjusted for time on regimen, interaction between time and regimen, age, sex, race/ethnicity, hepatitis B/C coinfection, nadir CD4, smoking, diabetes, antipsychotic medication, and site. We included more recently approved regimens [eg, with tenofovir alafenamide fumarate (TAF)] only in the immediate period analyses to ensure comparable follow-up time.

RESULTS

Mean follow-up was 1.9 years on initial ART regimen. In comparison to efavirenz/tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC), initiating bictegravir/TAF/FTC {3.9 kg [95% confidence interval (CI): 2.2 to 5.5]} and dolutegravir/TAF/FTC [4.4 kg (95% CI: 2.1 to 6.6)] were associated with the greatest weight gain in the immediate period, followed by darunavir/TDF/FTC [3.7 kg (95% CI: 2.1 to 5.2)] and dolutegravir/TDF/FTC [2.6 kg (95% CI: 1.3 to 3.9)]. In the extended period, compared with efavirenz/TDF/FTC, initiating darunavir/TDF/FTC was associated with a 1.0 kg (95% CI: 0.5 to 1.5) per 6-months greater weight gain, whereas dolutegravir/abacavir/FTC was associated with a 0.6-kg (95% CI: 0.3 to 0.9) and dolutegravir/TDF/FTC was associated with a 0.6-kg (95% CI: 0.1 to 1.1) per 6-months greater gain. Weight gain on dolutegravir/abacavir/FTC and darunavir/TDF/FTC was significantly greater than that for several integrase inhibitor-based regimens.

CONCLUSIONS

There is heterogeneity between regimens in weight gain following ART initiation among previously ART-naïve PLWH; we observed greater gain among PLWH taking newer integrase strand transfer inhibitors (DTG, BIC) and DRV-based regimens.

Statistical control of processes applied to geometric uncertainties for CTV expansion margins determination in prostate cancer patients treated with VMAT: a prospective study in 57 patients

PURPOSE

To study the control graphs applicability for the geometric uncertainties of VMAT treatments in prostate cancer patients, and their use to verify the hypothesis of the data obtained randomness, to apply the margins of Van Herk expression.

MATERIAL AND METHODS

During the first 5 days of treatment, and then once a week, a Kv CBCT was performed, compared with the simulation CT and adjusted the displacements, to determine the inter-fraction errors. Immediately after radiation therapy, another CBCT was performed (for intra-fraction errors). With these data, the X, R position control charts have been made. The patients, not maintained the deviations within the charts control limits, were called "anomalies". Then, we compared the deviations and margins calculated with the van Herk expression for all patients and for those without anomalies.

RESULTS

The margins determined show appreciable differences if there were calculated for the total set of patients or for the set of them without anomalies in the control charts. For the overall set of patients, the lateral, longitudinal, and vertical margins were 0.45 cm, 0.52 cm, 0.56 cm, while for the set of patients without anomalies were 0.29 cm, 0.35 cm, and 0.38 cm.

CONCLUSIONS

The use of control charts allows tracking geometric deviations both inter and intra-fraction, variability real-time control and to detect situations in which it can change for non-random reasons, and require immediate investigation. Maintaining geometric deviations in the control state decreases the margins needed to administer a high dose to CTV in a high percentage of cancer prostate patients.

Clinical codes combined with procedure codes increase diagnostic accuracy of Crohn's disease in a US Military health record

Background and aims

Previous examinations of International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) codes to predict accuracy of diagnosis in inflammatory bowel disease have had limited chart review to confirm diagnosis. We aimed to evaluate using the ICD-9-CM for identifying Crohn’s disease (CD) in a large electronic health record (EHR) database.

Methods

This is a retrospective case-control study with a 3:1 allocation of EHRs of active duty service members diagnosed with CD from 1996 to 2012. Subjects were selected by having two ICD-9-CM codes for CD and none for ulcerative colitis during the study period. Gastroenterologists reviewed each chart and confirmed the diagnosis of CD by analysing medication history and clinical, endoscopic, histological, and radiographic exams.

Results

300 cases of CD were selected; 14 cases were discarded due to lack of data, limiting analysis to 284 subjects. Two diagnostic codes for CD had sensitivity and specificity of 1.0 and 0.53 respectively, for confirmed CD. If two or more encounters listing CD were with a gastroenterologist, the sensitivity and specificity was 0.71 and 0.87 respectively. If two encounters included a colonoscopy was performed at the same time as a CD code, sensitivity and specificity was 0.49 and 0.88 respectively.

Conclusions

The relatively poor specificity of ICD-9-CM codes in making the diagnosis of CD should be taken into consideration when interpreting results and when conducting research using such codes. Limiting these codes to patients given this diagnosis by a gastroenterologist, or to those who had a colonoscopy at the time of a diagnosis, increases the specificity, although at cost of sensitivity, especially for colonoscopy.

Sensitivity analysis of a strongly-coupled human-based electromechanical cardiac model: Effect of mechanical parameters on physiologically relevant biomarkers

The human heart beats as a result of multiscale nonlinear dynamics coupling subcellular to whole organ processes, achieving electrophysiologically-driven mechanical contraction. Computational cardiac modelling and simulation have achieved a great degree of maturity, both in terms of mathematical models of underlying biophysical processes and the development of simulation software. In this study, we present the detailed description of a human-based physiologically-based, and fully-coupled ventricular electromechanical modelling and simulation framework, and a sensitivity analysis focused on its mechanical properties. The biophysical detail of the model, from ionic to whole-organ, is crucial to enable future simulations of disease and drug action. Key novelties include the coupling of state-of-the-art human-based electrophysiology membrane kinetics, excitation-contraction and active contraction models, and the incorporation of a pre-stress model to allow for pre-stressing and pre-loading the ventricles in a dynamical regime. Through high performance computing simulations, we demonstrate that 50% to 200% - 1000% variations in key parameters result in changes in clinically-relevant mechanical biomarkers ranging from diseased to healthy values in clinical studies. Furthermore mechanical biomarkers are primarily affected by only one or two parameters. Specifically, ejection fraction is dominated by the scaling parameter of the active tension model and its scaling parameter in the normal direction ( k ort 2 ); the end systolic pressure is dominated by the pressure at which the ejection phase is triggered ( P ej ) and the compliance of the Windkessel fluid model ( C ); and the longitudinal fractional shortening is dominated by the fibre angle ( ϕ ) and k ort 2 . The wall thickening does not seem to be clearly dominated by any of the considered input parameters. In summary, this study presents in detail the description and implementation of a human-based coupled electromechanical modelling and simulation framework, and a high performance computing study on the sensitivity of mechanical biomarkers to key model parameters. The tools and knowledge generated enable future investigations into disease and drug action on human ventricles.

Anemia risk factors among people living with HIV across the United States in the current treatment era: a clinical cohort study

Background

Anemia is common among people living with HIV infection (PLWH) and is associated with adverse health outcomes. Information on risk factors for anemia incidence in the current antiretroviral therapy (ART) era is lacking.

Methods

Within a prospective clinical cohort of adult PLWH receiving care at eight sites across the United States between 1/2010–3/2018, Cox proportional hazards regression analyses were conducted among a) PLWH free of anemia at baseline and b) PLWH free of severe anemia at baseline to determine associations between time-updated patient characteristics and development of anemia (hemoglobin < 10 g/dL), or severe anemia (hemoglobin < 7.5 g/dL). Linear mixed effects models were used to examine relationships between patient characteristics and hemoglobin levels during follow-up. Hemoglobin levels were ascertained using laboratory data from routine clinical care. Potential risk factors included: age, sex, race/ethnicity, body mass index, smoking status, hazardous alcohol use, illicit drug use, hepatitis C virus (HCV) coinfection, estimated glomerular filtration rate (eGFR), CD4 cell count, viral load, ART use and time in care at CNICS site.

Results

This retrospective cohort study included 15,126 PLWH. During a median follow-up of 6.6 (interquartile range [IQR] 4.3–7.6) years, 1086 participants developed anemia and 465 participants developed severe anemia. Factors that were associated with incident anemia included: older age, female sex, black race, HCV coinfection, lower CD4 cell counts, VL ≥400 copies/ml and lower eGFR.

Conclusion

Because anemia is a treatable condition associated with increased morbidity and mortality among PLWH, hemoglobin levels should be monitored routinely, especially among PLWH who have one or more risk factors for anemia.

Acute liver failure in a military recruit treated with valproic acid and harboring a previously unrecognized POLG-1 mutation

Patients with mutations in the POLG-1 gene often are afflicted with drug-resistant seizures at an early age and have an increased risk of valproic acid-induced acute liver failure. Severe valproate hepatotoxicity most commonly arises in children within the first 3 months of treatment with an overall estimated incidence of 1 in 40,000 treated patients. Due to high mortality rates among transplanted children, many experts consider valproic acid-induced acute liver failure in patients with mitochondrial disorders to be a contraindication to liver transplant. We report the successful use of liver transplantation in a young man with valproic acid-associated acute liver failure harboring a previously unrecognized POLG-1 mutation.

•

Patients with mutations in the POLG-1 gene often have an increased risk of valproic acid (VPA) induced acute liver failure.

•

Severe valproate hepatotoxicity most commonly arises in children within the first 3 months of treatment.

•

Many experts consider VPA induced acute liver failure with mitochondrial disorders a contraindication to liver transplant.

•

We report a case of acute liver failure associated with VPA treated successfully with a liver transplant

28Impact of non-invasive rapid cardiac magnetic resonance for the assessment of cardiomyopathies in developing countries

Background

Cardiovascular mortality is higher in developing countries. Part of that is suboptimal testing. Cardiac magnetic resonance (CMR) is the gold standard for measuring structure, function of the heart and adds incremental value by imaging scarring and to assess iron level. Despite the existence of MRI units, CMR is identified as a complex test, with poor training and availability in developing countries.

Purpose

To assess the potential impact of a faster CMR protocol at a multicentre level in developing countries; implementing it with an education program, for the assessment cardiomyopathies.

Methods

An international partnership. A rapid CMR protocol for the evaluation of cardiac volumes, function and tissue characterization (Cardiac Iron T2* and LGE for scar) Figure 1a. We deployed the protocol as a multicentre study: Argentina, Peru, India and South Africa accompanied by a program of education. Pre-scan clinical information, scanning data: complications, image quality and post-scan follow-up of participants for the assessment on impact, between 3 to 24 months.

Results

510 scans (4 countries, 6 cities, 12 centres) were performed with the rapid CMR protocol. Contrast studies in 378 (74%). There were no scan-related complications. Quality of the studies was maintained in a high level as an average of 89%. 97% of studies responded referral's question. All patients with contrast CMR scan have had at least one 2D echocardiogram before CMR. Average scan duration was 21±6 mins for contrast studies and 12±3 for non-contrast T2* protocol. The most common underlying diagnoses were non-ischaemic cardiomyopathy in 73% of participants (including cardiac iron level assessment in 26%, HCM in 17%, DCM in 15%), 27% for ischaemic cardiomyopathy and 15% for other pathologies. 4 of the 12 participant centres started to incorporate CMR for the first time. Findings impacted management in 60% of patients, including new diagnosis in 21% of participants. See table 1, figure 1b. For just cardiac iron assessment: 1/3 of participants had iron deposited in the heart with 14% of patients in severe levels.

Conclusions

CMR can be delivered faster and easier. When this abbreviated protocol is enabled with education, it can be implemented in developing countries with existing technology. This protocol shows high quality exam, with an important impact on patient's management.

Characteristics and impact on management Contrast studies Non-contrast studies All patients (%) 378 (74) 132 (36) Age, mean (range) years 54 (16–93) 24 (13–41) Male (%) 151 (39) 64 (48) Pre-echocardiography exam (%) 370 (98) 42 (32) Scanning duration mean (SD) 21 (6) 12 (3) Good quality exam (%) 329 (87) 120 (91) Impact on management Total All patients (%) 510 (100) Completely new diagnosis (%) 105 (21) Change/Addition of Medication (%) 128 (25) Intervention/ Surgery (%) 31 (6) Invasive angiography/biopsy (%) 25 (5) Hospital discharge/admission (%) 15 (3) TOTAL 306 (60%) SD: Standard Deviation.

Acknowledgement/Funding

Global Engagement UCL, UK Foreign & Commonwealth Office and The Peruvian Scientific, Technological Development and Technological Innovation (FONDECYT)

Improving the clinical understanding of hypertrophic cardiomyopathy by combining patient data, machine learning and computer simulations: A case study

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In this paper, we present how, by combining electrocardiogram and imaging data, machine learning and high performance computing simulations, we identified four phenotypes in hypertrophic cardiomyopathy (HCM), with differences in arrhythmic risk, and provided two distinct possible mechanisms that may explain the heterogeneity of HCM manifestation.

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This led to a better HCM patient stratification and understanding of the underlying disease mechanisms, providing a step further towards tailored HCM patient management and treatment.

Most patients with hypertrophic cardiomyopathy (HCM), the most common genetic cardiac disease, remain asymptomatic, but others may suffer from sudden cardiac death. A better identification of those patients at risk, together with a better understanding of the mechanisms leading to arrhythmia, are crucial to target high-risk patients and provide them with appropriate treatment. However, this currently remains a challenge. In this paper, we present a successful example of implementing computational techniques for clinically-relevant applications. By combining electrocardiogram and imaging data, machine learning and high performance computing simulations, we identified four phenotypes in HCM, with differences in arrhythmic risk, and provided two distinct possible mechanisms that may explain the heterogeneity of HCM manifestation. This led to a better HCM patient stratification and understanding of the underlying disease mechanisms, providing a step further towards tailored HCM patient management and treatment.

Loss of Dnmt3a Immortalizes Hematopoietic Stem Cells In Vivo

Somatic mutations in DNMT3A are recurrent events across a range of blood cancers. Dnmt3a loss of function in hematopoietic stem cells (HSCs) skews divisions toward self-renewal at the expense of differentiation. Moreover, DNMT3A mutations can be detected in the blood of aging individuals, indicating that mutant cells outcompete normal HSCs over time. It is important to understand how these mutations provide a competitive advantage to HSCs. Here we show that Dnmt3a-null HSCs can regenerate over at least 12 transplant generations in mice, far exceeding the lifespan of normal HSCs. Molecular characterization reveals that this in vivo immortalization is associated with gradual and focal losses of DNA methylation at key regulatory regions associated with self-renewal genes, producing a highly stereotypical HSC phenotype in which epigenetic features are further buttressed. These findings lend insight into the preponderance of DNMT3A mutations in clonal hematopoiesis and the persistence of mutant clones after chemotherapy.

3' UTR shortening represses tumor-suppressor genes in trans by disrupting ceRNA crosstalk

Widespread mRNA 3' UTR shortening through alternative polyadenylation ¹ promotes tumor growth in vivo ² . A prevailing hypothesis is that it induces proto-oncogene expression in cis through escaping microRNA-mediated repression. Here we report a surprising enrichment of 3'UTR shortening among transcripts that are predicted to act as competing-endogenous RNAs (ceRNAs) for tumor-suppressor genes. Our model-based analysis of the trans effect of 3' UTR shortening (MAT3UTR) reveals a significant role in altering ceRNA expression. MAT3UTR predicts many trans-targets of 3' UTR shortening, including PTEN, a crucial tumor-suppressor gene ³ involved in ceRNA crosstalk ⁴ with nine 3'UTR-shortening genes, including EPS15 and NFIA. Knockdown of NUDT21, a master 3' UTR-shortening regulator ² , represses tumor-suppressor genes such as PHF6 and LARP1 in trans in a miRNA-dependent manner. Together, the results of our analysis suggest a major role of 3' UTR shortening in repressing tumor-suppressor genes in trans by disrupting ceRNA crosstalk, rather than inducing proto-oncogenes in cis.

Brain tumor-induced neuronal stress orchestrates adaptive immune surveillance through fractalkine

Tissue damage contributes to initiation and modulation of an immune response. Tumor progression generally causes distress to the surrounding tissue. However, how tumor-induced parenchymal damage regulates anti-tumor immune response remains to be understood. We found that tumors that invaded brain parenchyma compressed the surrounding neurons causing increased expression of the neuronal chemokine CX3CL1/fractalkine in the peritumoral margin. Intravital two-photon microscopy revealed perivascular recruitment of monocyte-derived CD11c+ dendritic cells and T cells that interacted and killed individual cancer cells in tumor margins. Immune surveillance of brain tumors became inefficient in mice lacking the receptor for fractalkine, CX3CR1, resulting in more aggressive tumor progression. Our results identify tissue stress and associated chemokine signaling as a potential target to orchestrate anti-tumor immune surveillance in the brain.

Slow Adaptation of Ventricular Repolarization as a Cause of Arrhythmia?

Introduction: This article is part of the Focus Theme of Methods of Information in Medicine on “Biosignal Interpretation: Advanced Methods for Studying Cardiovascular and Respiratory Systems”.

Background: Adaptation of the QT-interval to changes in heart rate reflects on the body-surface electrocardiogram the adaptation of action potential duration (APD) at the cellular level. The initial fast phase of APD adaptation has been shown to modulate the arrhythmia substrate. Whether the slow phase is potentially proarrhythmic remains unclear.

Objectives: To analyze in-vivo human data and use computer simulations to examine effects of the slow APD adaptation phase on dispersion of repolarization and reentry in the human ventricle.

Methods: Electrograms were acquired from 10 left and 10 right ventricle (LV/RV) endocardial sites in 15 patients with normal ventricles during RV pacing. Activation-recovery intervals, as a surrogate for APD, were measured during a sustained increase in heart rate. Observed dynamics were studied using computer simulations of human tissue electrophysiology.

Results: Spatial heterogeneity of rate adaptation was observed in all patients. Inhomogeneity in slow APD adaptation time constants (ΔTs) was greater in LV than RV (ΔTs LV = 31.8 ± 13.2, ΔTs RV = 19.0 ± 12.8 s, P < 0.01). Simulations showed that altering local slow time constants of adaptation was sufficient to convert partial wavefront block to block with successful reentry.

Conclusions: Using electrophysiological data acquired in-vivo in human and computer simulations, we identify heterogeneity in the slow phase of APD adaptation as an important component of arrhythmogenesis.

δ-cells and β-cells are electrically coupled and regulate α-cell activity via somatostatin

Key points

We used a mouse expressing a light‐sensitive ion channel in β‐cells to understand how α‐cell activity is regulated by β‐cells.

Light activation of β‐cells triggered a suppression of α‐cell activity via gap junction‐dependent activation of δ‐cells.

Mathematical modelling of human islets suggests that 23% of the inhibitory effect of glucose on glucagon secretion is mediated by β‐cells via gap junction‐dependent activation of δ‐cells/somatostatin secretion.

Abstract

Glucagon, the body's principal hyperglycaemic hormone, is released from α‐cells of the pancreatic islet. Secretion of this hormone is dysregulated in type 2 diabetes mellitus but the mechanisms controlling secretion are not well understood. Regulation of glucagon secretion by factors secreted by neighbouring β‐ and δ‐cells (paracrine regulation) have been proposed to be important. In this study, we explored the importance of paracrine regulation by using an optogenetic strategy. Specific light‐induced activation of β‐cells in mouse islets expressing the light‐gated channelrhodopsin‐2 resulted in stimulation of electrical activity in δ‐cells but suppression of α‐cell activity. Activation of the δ‐cells was rapid and sensitive to the gap junction inhibitor carbenoxolone, whereas the effect on electrical activity in α‐cells was blocked by CYN 154806, an antagonist of the somatostatin‐2 receptor. These observations indicate that optogenetic activation of the β‐cells propagates to the δ‐cells via gap junctions, and the consequential stimulation of somatostatin secretion inhibits α‐cell electrical activity by a paracrine mechanism. To explore whether this pathway is important for regulating α‐cell activity and glucagon secretion in human islets, we constructed computational models of human islets. These models had detailed architectures based on human islets and consisted of a collection of >500 α‐, β‐ and δ‐cells. Simulations of these models revealed that this gap junctional/paracrine mechanism accounts for up to 23% of the suppression of glucagon secretion by high glucose.

We used a mouse expressing a light‐sensitive ion channel in β‐cells to understand how α‐cell activity is regulated by β‐cells.

Light activation of β‐cells triggered a suppression of α‐cell activity via gap junction‐dependent activation of δ‐cells.

Mathematical modelling of human islets suggests that 23% of the inhibitory effect of glucose on glucagon secretion is mediated by β‐cells via gap junction‐dependent activation of δ‐cells/somatostatin secretion.

Sparse conserved under-methylated CpGs are associated with high-order chromatin structure

BACKGROUND

Whole-genome bisulfite sequencing (WGBS) is the gold standard for studying landscape DNA methylation. Current computational methods for WGBS are mainly designed for gene regulatory regions with multiple under-methylated CpGs (UMCs), such as promoters and enhancers.

RESULTS

To reliably predict the functional importance of single isolated UMCs across the genome, which is usually not achievable using traditional methods, we develop a multi-sample-based method. We identified 9421 sparse conserved under-methylated CpGs (scUMCs) from 31 high-quality methylomes, which are enriched in distal interacting anchor regions co-occupied by multiple chromatin-loop factors and are flanked by highly methylated CpGs. Moreover, cell lineage-specific scUMCs are associated with essential developmental genes, regulators of cell differentiation, and chromatin remodeling enzymes. Dynamic methylation levels of scUMCs correlate with the intensity of chromatin interactions and binding of looping factors as well as patterns of gene expression.

CONCLUSIONS

We introduce an innovative computational method for the identification of scUMCs, which are novel epigenetic features associated with high-order chromatin structure, opening new directions in the study of the inter-relationships between DNA methylation and chromatin structure.

Risk Factors of Recurrence of Diabetic Nephropathy in Renal Transplants

BACKGROUND

Renal transplantation has been established as the treatment of choice for end-stage renal disease (ESRD) due to diabetic nephropathy. This study aimed to investigate the risk factors for recurrence of diabetic nephropathy (RDN) in renal allografts.

METHODS

We studied 1,011 renal transplant patients from 1986 to 2003, of which 95 had ESRD due to diabetic nephropathy. We retrospectively analyzed the clinical characteristics and outcomes of RDN after renal transplantation.

RESULTS

Of the 95 recipients with ESRD due to diabetic nephropathy, 41 developed RDN and 11 of those 41 underwent graft biopsy. The mean durations from transplantation to RDN and to renal replacement therapy was 81.58 months (range, 54-120 mo), and 109.66 months (range, 27-188.4 mo), respectively. At 5 years, treatment on statins and renin-angiotensin-aldosterone system (RAAS) blockers were associated with a higher survival free from RND (82.2% vs 63.2% [P = .070] and 100% vs 80% vs 0.6% [P = .013], respectively). Compared with cyclosporine, tacrolimus was associated with a higher risk for RND (odds ratio [OR], 4.27; 95% confidence interval [CI], 1.75-5.13; P = .047). High doses of prednisone (>0.06 mg/kg) were also associated with a higher risk of RDN (OR, 3.03; 95% CI, 1.19-8.30; P = .029). The combination of calcineurin inhibitor and mammalian target of rapamycin inhibitor (mTORi) demonstrated the highest risk of RDN (OR, 14.08; 95% CI, 3.72-53.29; P < .01).

CONCLUSIONS

Treatment with tacrolimus and mTORi is the most diabetogenic immunosuppressive regimen. Treatment with tacrolimus entails a greater risk of RDN than with cyclosporine. The administration of statins or RAAS blockers could delay the progression of RDN.

DNMT3A Loss Drives Enhancer Hypomethylation in FLT3-ITD-Associated Leukemias

DNMT3A, the gene encoding the de novo DNA methyltransferase 3A, is among the most frequently mutated genes in hematologic malignancies. However, the mechanisms through which DNMT3A normally suppresses malignancy development are unknown. Here, we show that DNMT3A loss synergizes with the FLT3 internal tandem duplication in a dose-influenced fashion to generate rapid lethal lymphoid or myeloid leukemias similar to their human counterparts. Loss of DNMT3A leads to reduced DNA methylation, predominantly at hematopoietic enhancer regions in both mouse and human samples. Myeloid and lymphoid diseases arise from transformed murine hematopoietic stem cells. Broadly, our findings support a role for DNMT3A as a guardian of the epigenetic state at enhancer regions, critical for inhibition of leukemic transformation.

Glioblastoma-infiltrated innate immune cells resemble M0 macrophage phenotype

Glioblastomas are highly infiltrated by diverse immune cells, including microglia, macrophages, and myeloid-derived suppressor cells (MDSCs). Understanding the mechanisms by which glioblastoma-associated myeloid cells (GAMs) undergo metamorphosis into tumor-supportive cells, characterizing the heterogeneity of immune cell phenotypes within glioblastoma subtypes, and discovering new targets can help the design of new efficient immunotherapies. In this study, we performed a comprehensive battery of immune phenotyping, whole-genome microarray analysis, and microRNA expression profiling of GAMs with matched blood monocytes, healthy donor monocytes, normal brain microglia, nonpolarized M0 macrophages, and polarized M1, M2a, M2c macrophages. Glioblastoma patients had an elevated number of monocytes relative to healthy donors. Among CD11b⁺ cells, microglia and MDSCs constituted a higher percentage of GAMs than did macrophages. GAM profiling using flow cytometry studies revealed a continuum between the M1- and M2-like phenotype. Contrary to current dogma, GAMs exhibited distinct immunological functions, with the former aligned close to nonpolarized M0 macrophages.

En Bloc Multivisceral and Kidney Transplantation in an HIV Patient: First Case Report

The continual improvement in outcome with highly active antiretroviral therapy (HAART) for human immunodeficiency virus (HIV) infection and visceral transplantation for gut failure stimulated our interest in lifting HIV infection as a contraindication for intestinal and multivisceral transplantation. This report is the first to describe visceral transplantation in a patient with HIV infection. A HAART regimen was introduced in the setting of short-gut syndrome with successful suppression of HIV viral load. The indication for en bloc multivisceral and kidney transplantation was end-stage liver failure with portomesenteric venous thrombosis and chronic renal insufficiency. The underlying hepatic pathology was alcoholic and home parenteral nutrition-associated cirrhosis. Surgery was complicated due to technical difficulties with excessive blood loss and long operative time. The complex posttransplant course included multiple exploratory laparotomies due to serious intra-abdominal and systemic infections. Heavy immunosuppression was required to treat recurrent episodes of severe allograft rejection. Posttransplant oral HAART successfully sustained undetectable viral load. Unfortunately, the patient succumbed to sepsis 3 months posttransplant. With new insights into the biology of gut immunity, mechanisms of allograft tolerance, and HIV-associated immune dysregulation, successful outcome is anticipated, particularly in patients who are in need of isolated intestinal and less-organ-contained visceral allografts.

Human induced pluripotent stem cell-derived versus adult cardiomyocytes: an in silico electrophysiological study on effects of ionic current block

Background and Purpose

Two new technologies are likely to revolutionize cardiac safety and drug development: in vitro experiments on human‐induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) and in silico human adult ventricular cardiomyocyte (hAdultV‐CM) models. Their combination was recently proposed as a potential replacement for the present hERG‐based QT study for pharmacological safety assessments. Here, we systematically compared in silico the effects of selective ionic current block on hiPSC‐CM and hAdultV‐CM action potentials (APs), to identify similarities/differences and to illustrate the potential of computational models as supportive tools for evaluating new in vitro technologies.

Experimental Approach

In silico AP models of ventricular‐like and atrial‐like hiPSC‐CMs and hAdultV‐CM were used to simulate the main effects of four degrees of block of the main cardiac transmembrane currents.

Key Results

Qualitatively, hiPSC‐CM and hAdultV‐CM APs showed similar responses to current block, consistent with results from experiments. However, quantitatively, hiPSC‐CMs were more sensitive to block of (i) L‐type Ca²⁺ currents due to the overexpression of the Na⁺/Ca²⁺ exchanger (leading to shorter APs) and (ii) the inward rectifier K⁺ current due to reduced repolarization reserve (inducing diastolic potential depolarization and repolarization failure).

Conclusions and Implications

In silico hiPSC‐CMs and hAdultV‐CMs exhibit a similar response to selective current blocks. However, overall hiPSC‐CMs show greater sensitivity to block, which may facilitate in vitro identification of drug‐induced effects. Extrapolation of drug effects from hiPSC‐CM to hAdultV‐CM and pro‐arrhythmic risk assessment can be facilitated by in silico predictions using biophysically‐based computational models.

Broad H3K4me3 is associated with increased transcription elongation and enhancer activity at tumor-suppressor genes

Tumor suppressors are mostly defined by inactivating mutations in tumors, yet little is known about their epigenetic features in normal cells. Through integrative analysis of 1,134 genome-wide epigenetic profiles, mutations from >8,200 tumor-normal pairs and our experimental data from clinical samples, we discovered broad peaks for trimethylation of histone H3 at lysine 4 (H3K4me3; wider than 4 kb) as the first epigenetic signature for tumor suppressors in normal cells. Broad H3K4me3 is associated with increased transcription elongation and enhancer activity, which together lead to exceptionally high gene expression, and is distinct from other broad epigenetic features, such as super-enhancers. Genes with broad H3K4me3 peaks conserved across normal cells may represent pan-cancer tumor suppressors, such as TP53 and PTEN, whereas genes with cell type-specific broad H3K4me3 peaks may represent cell identity genes and cell type-specific tumor suppressors. Furthermore, widespread shortening of broad H3K4me3 peaks in cancers is associated with repression of tumor suppressors. Thus, the broad H3K4me3 epigenetic signature provides mutation-independent information for the discovery and characterization of new tumor suppressors.

ECG-based estimation of dispersion of APD restitution as a tool to stratify sotalol-induced arrhythmic risk

Background

Increased spatial dispersion of restitution properties has been associated to arrhythmic risk. An ECG-based index quantifying restitution dispersion, DRest, is evaluated in patients who experienced Torsades de Pointes (TdP) under sotalol challenge and compared with the response in healthy subjects.

Methods and Results

ECG recordings were analyzed for quantification of DRest and QTc, among others biomarkers. DRest provides improved discrimination following sotalol administration between TdP and healthy subjects ([min–max]: [0.18–0.22] vs [0.02–0.12]), compared to other biomarkers including QTc ([436–548 ms] vs [376–467 ms]). Results in healthy subjects are in agreement with simulations of sotalol effects on a human tissue electrophysiological model.

Conclusions

This case study supports the potential of DRest for improved arrhythmia risk stratification even with QTc values below 450 ms.

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Several rate-dependent ECG-based biomarkers were evaluated in three patients who develop Torsades des Pointes after sotalol intake and in twenty five healthy volunteers who do not.

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Dispersion of restitution quantified from the ECG, DRest, identified better drug-induced cardiotoxicity than the conventionally used QTc.

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Neither DRest nor QTc shows sotalol-induced changes in subjects who do not develop TdP.

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Computer simulations corroborate the results of the ECG analysis and suggest that DRest is able to quantify the arrhythmogenic substrate in patients at risk of developing drug-induced arrhythmias.