Synthetic developmental biology: New tools to deconstruct and rebuild developmental systems.

Technological advances have driven many recent advances in developmental biology. Light sheet imaging can reveal single-cell dynamics in living three-dimensional tissues, whereas single-cell genomic methods open the door to a complete catalogue of cell types and gene expression states. An equally powerful but complementary set of approaches are also becoming available to define development processes from the bottom up. These synthetic approaches aim to reconstruct the minimal developmental patterns, signaling processes, and gene networks that produce the basic set of developmental operations: spatial polarization, morphogen interpretation, tissue movement, and cellular memory. In this review we discuss recent approaches at the intersection of synthetic biology and development, including synthetic circuits to deliver and record signaling stimuli and synthetic reconstitution of pattern formation on multicellular scales.

PROX1 Inhibits PDGF-B Expression to Prevent Myxomatous Degeneration of Heart Valves.

BACKGROUND: Cardiac valve disease is observed in 2.5% of the general population and 10% of the elderly people. Effective pharmacological treatments are currently not available, and patients with severe cardiac valve disease require surgery. PROX1 (prospero-related homeobox transcription factor 1) and FOXC2 (Forkhead box C2 transcription factor) are transcription factors that are required for the development of lymphatic and venous valves. We found that PROX1 and FOXC2 are expressed in a subset of valvular endothelial cells (VECs) that are located on the downstream (fibrosa) side of cardiac valves. Whether PROX1 and FOXC2 regulate cardiac valve development and disease is not known. METHODS: We used histology, electron microscopy, and echocardiography to investigate the structure and functioning of heart valves from Prox1ΔVEC mice in which Prox1 was conditionally deleted from VECs. Isolated valve endothelial cells and valve interstitial cells were used to identify the molecular mechanisms in vitro, which were tested in vivo by RNAScope, additional mouse models, and pharmacological approaches. The significance of our findings was tested by evaluation of human samples of mitral valve prolapse and aortic valve insufficiency. RESULTS: Histological analysis revealed that the aortic and mitral valves of Prox1ΔVEC mice become progressively thick and myxomatous. Echocardiography revealed that the aortic valves of Prox1ΔVEC mice are stenotic. FOXC2 was downregulated and PDGF-B (platelet-derived growth factor-B) was upregulated in the VECs of Prox1ΔVEC mice. Conditional knockdown of FOXC2 and conditional overexpression of PDGF-B in VECs recapitulated the phenotype of Prox1ΔVEC mice. PDGF-B was also increased in mice lacking FOXC2 and in human mitral valve prolapse and insufficient aortic valve samples. Pharmacological inhibition of PDGF-B signaling with imatinib partially ameliorated the valve defects of Prox1ΔVEC mice. CONCLUSIONS: PROX1 antagonizes PDGF-B signaling partially via FOXC2 to maintain the extracellular matrix composition and prevent myxomatous degeneration of cardiac valves.

Valvular Prostaglandins Are Elevated in Severe Human Aortic Valve Stenosis.

BACKGROUND: Aortic valve stenosis (AVS) is the most common valvular disease in the developed world. AVS involves the progressive fibrocalcific remodeling of the aortic valve (AV), which impairs function and can ultimately lead to heart failure. Due to gaps in our understanding of the underlying mechanisms of AVS, there are no pharmacological treatments or dietary interventions known to slow AVS progression. Recent studies have begun to suggest oxylipins-a class of bioactive lipids-may be dysregulated in the valves of patients with AVS. METHODS: We utilized high-performance liquid chromatography-tandem mass spectrometry to conduct a targeted oxylipin analysis on human AV tissue and plasma from a cohort of 110 patients undergoing AV surgery. RESULTS: We identified 36 oxylipins in human AV tissue with all showing significant increase in patients with severe AVS. A multivariate model including patient characteristics and valvular oxylipins identified the arachidonic acid-COX (cyclooxygenase) pathway-derived prostanoids to be the most associated with AVS severity. Plasma oxylipin levels were measured in a subset of AV surgery patients and compared with a control group of healthy participants, showing distinct oxylipin profiles between control and disease. CONCLUSIONS: Our comprehensive analysis of oxylipins in the human AV identified the inflammatory and osteogenic regulating prostanoids to be positively correlated with AVS severity. This elucidation of prostanoid dysregulation warrants further research into COX inhibition to mitigate AVS.

Prednisolone rescues Duchenne muscular dystrophy phenotypes in human pluripotent stem cell-derived skeletal muscle in vitro.

Duchenne muscular dystrophy (DMD) is a devastating genetic disease leading to degeneration of skeletal muscles and premature death. How dystrophin absence leads to muscle wasting remains unclear. Here, we describe an optimized protocol to differentiate human induced pluripotent stem cells (iPSC) to a late myogenic stage. This allows us to recapitulate classical DMD phenotypes (mislocalization of proteins of the dystrophin-associated glycoprotein complex, increased fusion, myofiber branching, force contraction defects, and calcium hyperactivation) in isogenic DMD-mutant iPSC lines in vitro. Treatment of the myogenic cultures with prednisolone (the standard of care for DMD) can dramatically rescue force contraction, fusion, and branching defects in DMD iPSC lines. This argues that prednisolone acts directly on myofibers, challenging the largely prevalent view that its beneficial effects are caused by antiinflammatory properties. Our work introduces a human in vitro model to study the onset of DMD pathology and test novel therapeutic approaches.

Species-specific oxylipins and the effects of ontogeny and predation on their emission from freshwater snails.

Chemical cues play important roles in mediating ecological interactions. Oxylipins, oxygenated metabolites of fatty acids, are one signalling molecule type that influences the physiology and function of species, suggesting their broader significance in chemical communication within aquatic systems. Yet, our current understanding of their function is restricted taxonomically and contextually making it difficult to infer their ecological significance. Snails and leeches are ubiquitous in freshwater ecosystems worldwide, yet little is known about their oxylipin profiles and the factors that cause their profiles to change. As snails and leeches differ taxonomically and represent different trophic groups, we postulated oxylipin profile differences. For snails, we hypothesized that ontogeny (non-reproductive vs reproductive) and predation (non-infested vs leech-infested) would affect oxylipin profiles. Oxylipins were characterized from water conditioned with the snail Planorbella duryi and leech Helobdella lineata, and included three treatment types (snails, leeches, and leech-infested snails) with the snails consisting of three size classes: small (5-6 mm, non-reproductive) and medium and large (13-14 and 19-20 mm, reproductive). The two species differed in the composition of their oxylipin profiles both in diversity and amounts. Further, ontogeny and predation affected the diversity of oxylipins emitted by snails. Our experimental profiles of oxylipins show that chemical cues within freshwater systems vary depending upon the species emitting the signals, the developmental stage of the species, as well as from ecological interactions such as predation. We also identified some candidates, like 9-HETE and PGE2, that could be explored more directly for their physiological and ecological roles in freshwater systems.

Reduced morbidity with early surgical ligation of patent ductus arteriosus in extremely low birth weight infants: a retrospective single-centre study.

INTRODUCTION: Failure of the patent ductus arteriosus to close is common among extremely low birth weight neonates and has been associated with increased morbidities. The objective of this study was to compare outcomes between early and late surgical ligation in extremely low birth weight patients. METHODS: This was a single-centre retrospective cohort study of infants who required surgical closure of patent ductus arteriosus between January 2017 and August 2022. RESULTS: A total of 43 neonates were identified with birth weight less than 1 kg that underwent surgical patent ductus arteriosus ligation. Compared to the late ligation group, the early ligation group experienced fewer total days of mechanical ventilation (43.9 days vs. 97.2 days, p < 0.05) and a shorter length of hospital stay (114.2 days vs. 169.0 days, p < 0.05). CONCLUSION: Early surgical ligation of haemodynamically significant patent ductus arteriosus in extremely low birth weight neonates may improve hospital morbidity, including improved ventilatory outcomes and a shorter length of stay.

Low-temperature polycrystalline silicon waveguides for low loss transmission in the near-to-mid-infrared region.

Low-temperature deposited polycrystalline silicon waveguides are emerging as a flexible platform that allows for dense optoelectronic integration. Here, the optical transmission properties of poly-silicon waveguides have been characterized from the near-to-mid-infrared wavelength regime, extending the optical transmission well beyond previous reports in the telecom band. The poly-Si waveguides with a dimension of 3 µm × âˆ¼0.6 µm have been produced from pre-patterned amorphous silicon waveguides that are post-processed through laser melting, reflowing, and crystallization using a highly localized laser induced heat treatment at a wavelength of 532 nm. Low optical transmission losses (<3 dB cm-1) have been observed at 1.55 µm as well as across the wavelength range of 2-2.25 µm, aided by the relatively large waveguide heights that are enabled by the deposition process. The results demonstrate the suitability of low-temperature poly-silicon waveguides to find wide ranging applications within integrated mid-infrared systems.

Metasurfaces integrated with a single-mode waveguide array for off-chip wavefront shaping.

Integration of metasurfaces and SOI (silicon-on-insulator) chips can leverage the advantages of both metamaterials and silicon photonics, enabling novel light shaping functionalities in planar, compact devices that are compatible with CMOS (complementary metal-oxide-semiconductor) production. To facilitate light extraction from a two-dimensional metasurface vertically into free space, the established approach is to use a wide waveguide. However, the multi-modal feature of such wide waveguides can render the device vulnerable to mode distortion. Here, we propose a different approach, where an array of narrow, single-mode waveguides is used instead of a wide, multi-mode waveguide. This approach tolerates nano-scatterers with a relatively high scattering efficiency, for example Si nanopillars that are in direct contact with the waveguides. Two example devices are designed and numerically studied as demonstrations: the first being a beam deflector that deflects light into the same direction regardless of the direction of input light, and the second being a light-focusing metalens. This work shows a straightforward approach of metasurface-SOI chip integration, which could be useful for emerging applications such as metalens arrays and neural probes that require off-chip light shaping from relatively small metasurfaces.

Factors affecting variability in free oxylipins in mammalian tissues.

PURPOSE OF THE REVIEW: Along with the growing interest in oxylipins is an increasing awareness of multiple sources of variability in oxylipin data. This review summarizes recent findings that highlight the experimental and biological sources of variation in free oxylipins. RECENT FINDINGS: Experimental factors that affect oxylipin variability include different methods of euthanasia, postmortem changes, cell culture reagents, tissue processing conditions and timing, storage losses, freeze-thaw cycles, sample preparation techniques, ion suppression, matrix effects, use and availability of oxylipin standards, and postanalysis procedures. Biological factors include dietary lipids, fasting, supplemental selenium, vitamin A deficiency, dietary antioxidants and the microbiome. Overt, but also more subtle differences in health affect oxylipin levels, including during resolution of inflammation and long-term recovery from disease. Sex, genetic variation, exposure to air pollution and chemicals found in food packaging and household and personal care products, as well as many pharmaceuticals used to treat health conditions also affect oxylipin levels. SUMMARY: Experimental sources of oxylipin variability can be minimized with proper analytical procedures and protocol standardization. Fully characterizing study parameters will help delineate biological factors of variability, which are rich sources of information that can be used to probe oxylipin mechanisms of action and to investigate their roles in health.

The Effect of Increasing Concentrations of Omega-3 Fatty Acids from either Flaxseed Oil or Preformed Docosahexaenoic Acid on Fatty Acid Composition, Plasma Oxylipin, and Immune Response of Laying Hens.

BACKGROUND: There is a lack of nutrition guidelines for the feeding of omega-3 polyunsaturated fatty acids (PUFA) to laying hens. Knowledge as to whether the type and concentrations of α-linolenic acid (ALA) and/or docosahexaenoic acid (DHA) in the diet can make a difference to the birds' immune responses when subjected to a lipopolysaccharide (LPS) challenge is limited. OBJECTIVES: The study was designed to determine the potential nutritional and health benefits to laying hens when receiving dietary omega-3 PUFA from either ALA or DHA. METHODS: A total of 80 Lohmann LSL-Classic (white egg layer, 20 wk old) were randomly assigned to 1 of 8 treatment diets (10 hens/treatment), provided 0.2%, 0.4%, 0.6%, or 0.8% of total dietary omega-3 PUFA, provided as either ALA-rich flaxseed oil or DHA-enriched algal biomass. After an 8-wk feeding period, the birds were challenged with Escherichia coli-derived LPS (8 mg/kg; i.v. injection), with terminal sample collection 4 h after challenge. Egg yolk, plasma, liver, and spleen samples were collected for subsequent analyses. RESULTS: Increasing dietary omega-3 supplementation yielded predictable responses in egg yolk, plasma, and liver fatty acid concentrations. Dietary intake of ALA contributed mainly to ALA-derived oxylipins. Meanwhile, eicosapentaenoic acid- and DHA-derived oxylipins were primarily influenced by DHA dietary intake. LPS increased the concentrations of almost all the omega-6 PUFA-, ALA-, and DHA-derived oxylipins in plasma and decreased hepatic mRNA expression of COX-2 and 5-LOX (P < 0.001) involved in the biosynthesis of oxylipins. LPS also increased mRNA expression of proinflammatory cytokine IFN-γ and receptor TLR-4 (P < 0.001) in the spleen. CONCLUSIONS: These results revealed that dietary intake of ALA and DHA had unique impacts on fatty acid deposition and their derived oxylipins and inflammatory responses under the administration of LPS in laying hens.

Increasing the margin of patient safety for periodontal and implant treatments: The role of human factors.

Early complications following periodontal and dental implant surgeries are typically attributed to technique or poor biological response, ignoring the possibility of the human element. Interestingly, significant experience is not correlated with increased success, whereas evidence supports the impact of clinical behavior on patient outcome. This is the result of errors, much like those scrutinized in other high-risk technical fields, such as aviation. What can be surprising is that those who make these errors are very well acquainted with best practices. Given this, how is it possible for the conscientious practitioner to fail to apply protocols that are nonetheless very well known? Recently, the concepts of human and organizational factors have been translated to medicine, though dentistry has been slow to recognize their potential benefit. This review lists specific human factor behaviors, such as use of checklists and crew resource management, which might improve postsurgical outcome.

A Critical Analysis of Possible Mechanisms for the Oxygen Effect in Radiation Therapy with FLASH.

The aim of this review is to stimulate readers to undertake appropriate investigations of the mechanism for a possible oxygen effect in FLASH. FLASH is a method of delivery of radiation that empirically, in animal models, appears to decrease the impact of radiation on normal tissues while retaining full effect on tumors. This has the potential for achieving a significantly increased effectiveness of radiation therapy. The mechanism is not known but, especially in view of the prominent role that oxygen has in the effects of radiation, investigations of mechanisms of FLASH have often focused on impacts of FLASH on oxygen levels. We and others have previously shown that simple differential depletion of oxygen directly changing the response to radiation is not a likely mechanism. In this review we consider how time-varying changes in oxygen levels could account for the FLASH effect by changing oxygen-dependent signaling in cells. While the methods of delivering FLASH are still evolving, current approaches for FLASH can differ from conventional irradiation in several ways that can impact the pattern of oxygen consumption: the rate of delivery of the radiation (40 Gy/s vs. 0.1 Gy/s), the time over which each fraction is delivered (e.g., <0.5 s. vs. 300 s), the delivery in pulses, the number of fractions, the size of the fractions, and the total duration of treatment. Taking these differences into account and recognizing that cell signaling is an intrinsic component of the need for cells to maintain steady-state conditions and, therefore, is activated by small changes in the environment, we delineate the potential time dependent changes in oxygen consumption and overview the cell signaling pathways whose differential activation by FLASH could account for the observed biological effects of FLASH. We speculate that the most likely pathways are those involved in repair of damaged DNA.

High-risk ankle fractures in high-risk older patients: to fix or nail?

INTRODUCTION: Optimal treatment of high-risk ankle fractures in older, comorbid patients is unknown. Results of open reduction internal fixation (ORIF) versus tibiotalocalcaneal (TTC) fusion nailing for the treatment of high-risk geriatric ankle fractures were investigated. MATERIALS AND METHODS: Results of ORIF versus TTC fusion nailing were evaluated via retrospective case-control cohort study of 60 patients over age 50 with an open ankle fracture or one with at least 50% talar subluxation and at least 1 high-risk comorbidity: diabetes mellitus (DM), peripheral vascular disease, immunosuppression, active smoking, or a BMI > 35. The primary outcome was reoperation rate within 1-year post-surgery. Secondary outcomes include infection, peri-implant fracture, malunion/nonunion, mortality, length of stay, disposition, and hospital acquired complications. RESULTS: Mean age was 71 (ORIF) and 68 (TTC). 12/47 (25.5%) ORIF cases were open fractures versus 4/14 (28.6%) with TTC. There were no significant differences between ORIF and TTC in 1-year reoperation rates (17% vs 21.4%), infection rates (12.8% vs 14.3%), or union rates (76.% vs 85.7%), respectively. One TTC patient sustained a peri-implant fracture treated nonoperatively. There were no significant differences in medical risk factors between groups other than a higher rate of DM in the TTC group, 42.6% vs 78.6%, p = 0.02. Incomplete functional outcome data in this challenging patient cohort precluded drawing conclusions. CONCLUSION: ORIF and TTC fusion nailing result in comparable and acceptable reoperation, infection, and union rates in treating high-risk ankle fractures in patients over 50 with at least 1 major comorbidity for increased complications; further study is warranted.

Evaluating sources of bias in pedigree-based estimates of breeding population size.

Applications of genetic-based estimates of population size are expanding, especially for species for which traditional demographic estimation methods are intractable due to the rarity of adult encounters. Estimates of breeding population size (NS ) are particularly amenable to genetic-based approaches as the parameter can be estimated using pedigrees reconstructed from genetic data gathered from discrete juvenile cohorts, therefore eliminating the need to sample adults in the population. However, a critical evaluation of how genotyping and sampling effort influence bias in pedigree reconstruction, and how these biases subsequently influence estimates of NS , is needed to evaluate the efficacy of the approach under a range of scenarios. We simulated a model system to understand the interactive effects of genotyping and sampling effort on error in genetic pedigrees reconstructed from the program COLONY. We then evaluated how errors in pedigree reconstruction influenced bias and precision in estimates of NS using three different rarefaction estimators. Results indicated that pedigree error can be minimal when adequate genetic data are available, such as when juvenile sample sizes are large and/or individuals are genotyped at many informative loci. However, even in cases for which data are limited, using results of the simulation analysis to understand the magnitude and sources of bias in reconstructed pedigrees can still be informative when estimating NS . We applied results of the simulation analysis to evaluate N ̂ $$ \hat{N} $$ S for a population of federally endangered Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) in the Delaware River, USA. Our results indicated that NS is likely to be three orders of magnitude lower compared with historic breeding population sizes, which is a considerable advancement in our understanding of the population status of Atlantic sturgeon in the Delaware River. Our analyses are broadly applicable in the design and interpretation of studies seeking to estimate NS and can help to guide conservation decisions when ecological uncertainty is high. The utility of these results is expected to grow as rapid advances in genetic technologies increase the popularity of genetic population monitoring and estimation.

Impact of Age, Menopause, and Obesity on Oxylipins Linked to Vascular Health.

OBJECTIVE: Cardiovascular disease, a major cause of mortality and morbidity, exhibits sexual dimorphism since the onset of cardiovascular disease occurs later in women than in men. The loss of cardioprotection in older women may be due to an increase in arterial stiffness after menopause. Free fatty acid metabolites of polyunsaturated fatty acids, called oxylipins, are known to impact vessel function and may be responsible for the vascular benefits of polyunsaturated fatty acids. The objectives of this study were to compare the plasma oxylipin profiles of young females (20-55 years), older females (55+), and older males (55+) and to identify associations between oxylipins and cardiovascular disease risk factors, such as obesity and arterial stiffness. Approach and Results: We quantified plasma oxylipins by high-performance liquid chromatography-tandem mass spectrometry in archived samples taken from completed clinical trials. We identified 3 major 12-lipoxygenase products, 12-hydroxy-eicosatetraenoic acid, 12-hydroxy-eicosapentaenoic acid, and 14-hydroxy-docosahexaenoic acid, that are present at high levels in young females compared with older females and males. These oxylipins also decreased with obesity and displayed robust negative associations with arterial stiffness as assessed by brachial-ankle pulse wave velocity. According to multiple linear regression modeling, these associations were maintained even after correcting for body mass index category combined with either age, menopausal status, or estradiol levels. Using linear discriminant analysis, the combination of these 3 oxylipins effectively distinguished participants according to both brachial-ankle pulse wave velocity risk group and age. CONCLUSIONS: Higher 12-lipoxygenase oxylipin plasma concentrations associated with lower arterial stiffness in premenopausal females may be an important contributing factor to sex differences in cardiovascular disease. Registration: URL: https://www.clinicaltrials.gov; Unique identifiers: NCT01661543, NCT01562171, NCT01890330, NCT02571114 and NCT02317588.

Use of synchronous kidney and lung extracorporeal support for severe COVID-19: A single-center retrospective study.

BACKGROUND: Infection with severe acute respiratory syndrome coronavirus disease 2019 (COVID-19) has been associated with both kidney and respiratory failure. During the early phase of the coronavirus disease pandemic, patients often required the use of mechanical assistance to provide adequate kidney and lung function. In this paper we describe the clinical outcomes of patients who required synchronous kidney and lung extracorporeal support for COVID-19. MATERIALS AND METHODS: All patients admitted to Baylor University Medical Center, Dallas, between February 1, 2020, to April 23, 2021, with COVID-19 who required both extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT) were retrospectively analyzed. Patients who were on hemo- or peritoneal dialysis prior to admission or who required veno-arterial (VA) ECMO were excluded. RESULTS: 35 patients with COVID-19 required ECMO and CRRT support. Four patients (11%) were excluded, 2 due to being on dialysis prior to admission and 2 due to the requirement of VA-ECMO. The median time on CRRT was 33 days (IQR 13 - 51). The median time on ECMO was 28 days (IQR 10.5 - 59.5). At 90 days, 9 patients had died (29%), 4 patients remained hospitalized, and 18 patients had been discharged: 10 to long-term acute care, 2 to inpatient rehabilitation, and 6 to home. CONCLUSION: Patients with severe COVID-19 requiring concurrent ECMO and CRRT in this institution had a 29% mortality at 90 days.

Association of the COVID-19 pandemic with increased adherence among prevalent hemodialysis patients.

BACKGROUND: During the COVID-19 pandemic, there has been a reduction in emergency department visits and hospital admissions. We hypothesized that hemodialysis patients were decreasing their hospital visits and increasing their dialysis adherence during the COVID-19 pandemic. MATERIAL AND METHODS: This is a retrospective analysis of hemodialysis patients treated in the seven American Renal Associates (ARA) dialysis centers in the Dallas-Fort Worth metropolitan area. We conducted a "before-and-after" study using existing clinical data to examine patient adherence with hemodialysis between January 1 and March 14, 2020 (pre-COVID) and March 15 to May 18, 2020 (COVID) time periods. Data points included missed treatments, shortened treatments, post-dialysis weight, and hospital visits. Finally, we conducted an anonymous survey in which patients reported their hemodialysis adherence. RESULTS: Data analysis was performed on 556 patients. Significantly fewer patients missed a single treatment in the COVID vs. pre-COVID time periods (44.1 vs. 58.6%; p < 0.001). Significantly fewer patients finished their treatment with a post-dialysis weight more than 1 kg above their estimated dry weight in the COVID vs. pre-COVID time periods (31.7 vs. 38.9%, p = 0.01). Finally, there was a reduction in total hospital visits during the COVID vs. pre-COVID periods (12.6 vs. 19.4%; p = 0.002). The anonymous survey showed patients reporting increased adherence with hemodialysis and restriction of salt and water intake. CONCLUSION: The COVID time period was associated with increased adherence with hemodialysis and decreased hospital visits, and patients were conscious of these changes.

A Radiation Biological Analysis of the Oxygen Effect as a Possible Mechanism in FLASH.

The delivery of radiation at an ultra-high dose rate (FLASH) is an important new approach to radiotherapy (RT) that appears to be able to improve the therapeutic ratio by diminishing damage to normal tissues. While the mechanisms by which FLASH improves outcomes have not been established, a role involving molecular oxygen (O2) is frequently mentioned. In order to effectively determine if the protective effect of FLASH RT occurs via a differential direct depletion of O2 (compared to conventional radiation), it is essential to consider the known role of O2 in modifying the response of cells and tissues to ionising radiation (known as 'the oxygen effect'). Considerations include: (1) The pertinent reaction involves an unstable intermediate of radiation-damaged DNA, which either undergoes chemical repair to restore the DNA or reacts with O2, resulting in an unrepairable lesion in the DNA, (2) These reactions occur in the nuclear DNA, which can be used to estimate the distance needed for O2 to diffuse through the cell to reach the intermediates, (3) The longest lifetime that the reactive site of the DNA is available to react with O2 is 1-10 µsec, (4) Using these lifetime estimates and known diffusion rates in different cell media, the maximal distance that O2 could travel in the cytosol to reach the site of the DNA (i.e., the nucleus) in time to react are 60-185 nm. This calculation defines the volume of oxygen that is pertinent for the direct oxygen effect, (5) Therefore, direct measurements of oxygen to determine if FLASH RT operates through differential radiochemical depletion of oxygen will require the ability to measure oxygen selectively in a sphere of <200 nm, with a time resolution of the duration of the delivery of FLASH, (6) It also is possible that alterations of oxygen levels by FLASH could occur more indirectly by affecting oxygen-dependent cell signalling and/or cellular repair.

Staged unifocalization revisited.

BACKGROUND: A staged thoracotomy unifocalization approach has not been the dominant option over the past 20 years primarily due to the introduction of midline one-stage complete unifocalization. METHODS: In this issue of the Journal of Cardiac Surgery, van de Woestijne et al. publish their experience over the past 30 years in 39 consecutive patients with "consistent" staged unifocalization through a lateral thoracotomy in patients with pulmonary atresia, ventricular septal defect, and major aortopulmonary collateral arteries (PA/VSD/MAPCA). RESULTS: They report definitive repair completion in 76.3% of the patients and an overall survival after definitive repair of 96% at 20 years despite the study period ranging from 1989 to the present. CONCLUSION: Given the multiple variations one could have with PA/VSD/MPACA, a midline unifocalization approach may not always be possible. Surgeons should be familiar with the lateral thoracotomy unifocalization staged approach to PA/VSD/MAPCA.

Sinus of Valsalva aneurysm: Defining the optimal approach.

Sinus of Valsalva aneurysm (SVA) is relatively rare, especially in Western countries, and reports on long-term results after surgical SVA repair in a sizable patient cohort are scarce. In this issue of the Journal of Cardiac Surgery, Chaganti and colleagues publish their surgical experience over the past 30 years in 216 patients with SVA. SVAs were closed via a dual approach, with (1) patch closure (80%) or direct closure (20%) of the base of the fistula through aortotomy and (2) direct closure of the ruptured tip through the chamber of rupture. Aortic valve replacement (9.7%) or repair (6.5%) was performed for moderate to severe aortic regurgitation (AR). There was no hospital mortality. During a mean follow-up of 10 years, no patient had residual/recurrent shunting. The actual survival at 10 years was 99%, with only two deaths. Freedom from moderate or severe AR was 98.5% at 10 years. Early and long-term results after surgical repair of SVA were excellent in their 216 patients with a mean follow-up of 10 years. Their dual approach for SVA was effective in preventing residual/recurrent shunting. The need for AVR in 10% of the patients speaks to the importance of follow-up. The current report provides strong support for surgical repair being the preferred management for SVA.