Heart organoids and tissue models for modeling development and disease.

Organoids, or miniaturized organs formed in vitro, hold potential to revolutionize how researchers approach and answer fundamental biological and pathological questions. In the context of cardiac biology, development of a bona fide cardiac organoid enables study of heart development, function, and pathogenesis in a dish, providing insight into the nature of congenital heart disease and offering the opportunity for high-throughput probing of adult heart disease and drug discovery. Recently, multiple groups have reported novel methods for generating in vitro models of the heart; however, there are substantial conceptual and methodological differences. In this review we will evaluate recent cardiac organoid studies through the lens of the core principles of organoid technology: patterned self-organization of multiple cell types resembling the in vivo organ. Based on this, we will classify systems into the following related types of tissues: developmental cardiac organoids, chamber cardiac organoids, microtissues, and engineered heart tissues. Furthermore, we highlight the interventions which allow for organoid formation, such as modulation of highly conserved cardiogenic signaling pathways mediated by developmental morphogens. We expect that consolidation and categorization of existing organoid models will help eliminate confusion in the field and facilitate progress towards creation of an ideal cardiac organoid.

Noncanonical Notch signals have opposing roles during cardiac development.

The Notch pathway is an ancient intercellular signaling system with crucial roles in numerous cell-fate decision processes across species. While the canonical pathway is activated by ligand-induced cleavage and nuclear localization of membrane-bound Notch, Notch can also exert its activity in a ligand/transcription-independent fashion, which is conserved in Drosophila, Xenopus, and mammals. However, the noncanonical role remains poorly understood in in vivo processes. Here we show that increased levels of the Notch intracellular domain (NICD) in the early mesoderm inhibit heart development, potentially through impaired induction of the second heart field (SHF), independently of the transcriptional effector RBP-J. Similarly, inhibiting Notch cleavage, shown to increase noncanonical Notch activity, suppressed SHF induction in embryonic stem cell (ESC)-derived mesodermal cells. In contrast, NICD overexpression in late cardiac progenitor cells lacking RBP-J resulted in an increase in heart size. Our study suggests that noncanonical Notch signaling has stage-specific roles during cardiac development.

Use of Breast Milk and Other Feeding Practices Following Gastrointestinal Surgery in Infants.

OBJECTIVES: The aim of the study was to characterize the enteral feeding practices in infants after gastrointestinal surgery. METHODS: We performed a retrospective analysis of infants who underwent intestinal surgery at age <6 months who survived to be fed enterally between January 2012 and June 2017. Demographics, surgical characteristics, feeding practices, and growth-related outcomes during hospitalization, discharge, and follow-up (3, 6, and 12 months) were obtained from the electronic medical records. Descriptive statistics compared infants by their initial diagnosis. RESULTS: We reviewed 111 infants: necrotizing enterocolitis (NEC) = 21, gastroschisis = 28, atresia = 27, spontaneous intestinal perforation (SIP) = 18, and other diagnoses = 17. Most infants (77%) received mother's milk (MM) as the first postoperative feed, but this differed by diagnosis (P = 0.004). Donor milk was used in 11%, most commonly in infants with NEC and SIP. Infants with NEC were least likely to continue MM in the hospital (7%, P = 0.0014) and were more likely to receive elemental formula. Only 44% of infants received MM at discharge. After 1 year, 25% were fed MM. The majority of infants were discharged with feeding tubes (nasogastric: 35%, gastric: 23%). Although all groups had acceptable weights at discharge, infants with NEC (z score: -1.8) and SIP (z score: -1.1) showed growth failure at 3 months (z scores: -3.3, -3.2, respectively, P < 0.0001), but had appropriate gain by 1 year (z scores: -1.1, -1.7, respectively). CONCLUSIONS: Despite most infants receiving MM in the early postoperative period, <50% at discharge and only 33% at 1-year still received MM. Weight gain after discharge in infants with NEC and SIP warrants close monitoring.

Orthogonally induced differentiation of stem cells for the programmatic patterning of vascularized organoids and bioprinted tissues.

The generation of organoids and tissues with programmable cellular complexity, architecture and function would benefit from the simultaneous differentiation of human induced pluripotent stem cells (hiPSCs) into divergent cell types. Yet differentiation protocols for the overexpression of specific transcription factors typically produce a single cell type. Here we show that patterned organoids and bioprinted tissues with controlled composition and organization can be generated by simultaneously co-differentiating hiPSCs into distinct cell types via the forced overexpression of transcription factors, independently of culture-media composition. Specifically, we used such orthogonally induced differentiation to generate endothelial cells and neurons from hiPSCs in a one-pot system containing either neural or endothelial stem-cell-specifying media, and to produce vascularized and patterned cortical organoids within days by aggregating inducible-transcription-factor and wild-type hiPSCs into randomly pooled or multicore-shell embryoid bodies. Moreover, by leveraging multimaterial bioprinting of hiPSC inks without extracellular matrix, we generated patterned neural tissues with layered regions composed of neural stem cells, endothelium and neurons. Orthogonally induced differentiation of stem cells may facilitate the fabrication of engineered tissues for biomedical applications.

Association of Heparin Dose, Route, Timing, and Duration With Heparin-Induced Thrombocytopenia.

BACKGROUND: The prevalence of heparin-induced thrombocytopenia (HIT) varies by population and the type and duration of heparinoid exposure; however, the association with unfractionated heparin (UFH) dose, route, timing, and duration has not been evaluated in cardiac surgery patients. METHODS: A retrospective case-control study matched HIT-positive adult cardiac surgery patients (positive platelet factor 4 immunoglobulin G and serotonin release assays) 1:1 with HIT-negative controls. Total UFH dose, route, timing, and duration were compared between groups. RESULTS: The study included 124 patients, 92 male (74%), with mean age of 65 ± 11 years. Significantly more HIT-positive patients received intravenous UFH preoperatively or postoperatively compared with patients without HIT (55 [88.7%] vs 23 [37.1%]; P < .001). There were no significant differences regarding intraoperative or subcutaneous UFH dose or duration. When controlling for obesity and cardiopulmonary bypass duration using multivariable conditional logistic regression, the odds of HIT were increased 10-fold in patients who received preoperative or postoperative intravenous UFH continuous infusion (odds ratio 10.2, 95% confidence interval, 3.1 to 33.7; P < .001). Receiver-operating characteristic curves demonstrated that receiving preoperative or postoperative intravenous UFH infusion total dose greater than 32,000 units (sensitivity 82%, specificity 74%, area under the curve 0.78) or longer than 7 hours (sensitivity 87%, specificity 68%, area under the curve 0.77) was associated with HIT. CONCLUSIONS: Odds of HIT were increased 10-fold in adult cardiac surgery patients receiving preoperative or postoperative intravenous UFH infusion. Intraoperative UFH dose and subcutaneous route were not associated with HIT. Future study should evaluate incorporation of intravenous UFH administration, dose, and duration in HIT scoring tools for cardiac surgery patients.

The Strongest Risk Factor for Operative Mortality in Acute Type A Aortic Dissection is Acidosis: Validation of Risk Model.

Multiple risk factors for operative mortality in the setting of acute type A aortic dissection (ATAAD) have been described. Recently, the combination of severe acidosis and malperfusion was found to significantly impact operative mortality following surgery for ATAAD and a treatment algorithm was proposed. The purpose of this study is to validate these findings in our institution. A retrospective chart review was performed for patients who underwent ATAAD repair between Feb 1997 and Jan 2018. Preoperative nadir pH, bicarbonate, base deficit, organ malperfusion, and other relevant parameters were collected. Multivariable logistic regression was performed to evaluate operative mortality. A total of 298 patients underwent ATAAD repair. The highest operative mortality (18/49; 37%) was noted in patients with severe acidosis (base deficit ≤ -10). There were 96 patients (32%) with malperfusion. In patients with abdominal malperfusion, this trend is even more pronounced. Multivariable logistic regression showed that severe acidosis is associated with higher operative mortality, odds ratio of 13.9 (P = 0.001). The presence of diabetes and advanced age were also associated with higher operative mortality. These findings validate the previously reported findings that severe acidosis is a strong predictor of operative mortality, and risk increases with associated organ malperfusion. This supports the suggestion that base deficit, which is easily performed at the bedside, should be used clinically to predict operative mortality and should be collected in aortic dissection databases.

Biomanufacturing of organ-specific tissues with high cellular density and embedded vascular channels.

Engineering organ-specific tissues for therapeutic applications is a grand challenge, requiring the fabrication and maintenance of densely cellular constructs composed of ~108 cells/ml. Organ building blocks (OBBs) composed of patient-specific-induced pluripotent stem cell-derived organoids offer a pathway to achieving tissues with the requisite cellular density, microarchitecture, and function. However, to date, scant attention has been devoted to their assembly into 3D tissue constructs. Here, we report a biomanufacturing method for assembling hundreds of thousands of these OBBs into living matrices with high cellular density into which perfusable vascular channels are introduced via embedded three-dimensional bioprinting. The OBB matrices exhibit the desired self-healing, viscoplastic behavior required for sacrificial writing into functional tissue (SWIFT). As an exemplar, we created a perfusable cardiac tissue that fuses and beats synchronously over a 7-day period. Our SWIFT biomanufacturing method enables the rapid assembly of perfusable patient- and organ-specific tissues at therapeutic scales.

3D and 4D Bioprinting of the Myocardium: Current Approaches, Challenges, and Future Prospects.

3D and 4D bioprinting of the heart are exciting notions in the modern era. However, myocardial bioprinting has proven to be challenging. This review outlines the methods, materials, cell types, issues, challenges, and future prospects in myocardial bioprinting. Advances in 3D bioprinting technology have significantly improved the manufacturing process. While scaffolds have traditionally been utilized, 3D bioprinters, which do not require scaffolds, are increasingly being employed. Improved understanding of the cardiac cellular composition and multiple strategies to tackle the issues of vascularization and viability had led to progress in this field. In vivo studies utilizing small animal models have been promising. 4D bioprinting is a new concept that has potential to advance the field of 3D bioprinting further by incorporating the fourth dimension of time. Clinical translation will require multidisciplinary collaboration to tackle the pertinent issues facing this field.