Myocardial strain is associated with adverse cardiac events in patients treated with chimeric antigen receptor (CAR) T-cell therapy.

BACKGROUND: Cardiovascular events, including heart failure and arrhythmias, following chimeric antigen receptor (CAR) T-cell therapy are increasingly recognized. Although global longitudinal strain (GLS) has demonstrated prognostic utility for other cancer therapy-related cardiac dysfunction, less is known regarding the association of GLS with adverse cardiac events following CAR T-cell therapy. OBJECTIVES: To determine the association of baseline GLS with adverse cardiovascular events in adults receiving CAR-T cell therapy. METHODS: Patients who had an echocardiogram within 6 months prior to receiving CAR T-cell therapy were retrospectively identified. Clinical data and cardiac events were collected via chart review. Echocardiograms were analyzed offline for GLS, left ventricular ejection fraction, and Doppler parameters. Multivariable logistic regression was used to determine the association between adverse cardiovascular events and echocardiographic parameters. RESULTS: Among 75 CAR T-cell therapy patients (mean age 63.9, 34.7% female), nine patients (12%) experienced cardiac events (CEs) including cardiovascular death, new/worsening heart failure, and new/worsening arrhythmia within 1 year of treatment. In univariable models, higher baseline GLS (OR 0.78 [0.63, 0.96], p = .021) was associated with a lower risk of CE and higher baseline mitral E/e' (OR 1.40 [1.08, 1.81], p = .012) was associated with a higher risk of CE. After adjusting for age and LDH, higher baseline GLS (OR 0.65 [0.48-0.88], p = <.01) was associated with a lower risk of CE and higher baseline mitral E/e' (OR 1.56 [1.06, 2.29], p = .024) was associated with a higher risk of CE. CONCLUSION: Lower GLS and higher mitral E/e' on a baseline echocardiogram were associated with higher risk for CEs in patients receiving CAR T-cell therapy.

Don't judge a book by its cover: a case report of apolipoprotein A-IV cardiac amyloidosis.

Background: To date, at least 20 different amyloidogenic proteins have been documented. Growing evidence suggests that despite being part of the universal amyloid proteome, apolipoprotein A-IV can be amyloidogenic, accounting for less than 1% of cases. Case summary: A 75-year-old woman was admitted for paroxysmal nocturnal dyspnoea and intermittent exertional shortness of breath and was found to be in acute heart failure. The patient underwent intravenous diuretic therapy and was discharged after decongestion. She then underwent a battery of outpatient tests to determine aetiology of her heart failure. Cardiac magnetic resonance imaging showed severe concentric left ventricular hypertrophy and diffuse late gadolinium enhancement, concerning for amyloidosis, but serologic evaluation for amyloidogenic light chain (AL) amyloidosis was negative. Tc 99m pyrophosphate (PYP) scan showed Grade 2 uptake at 1 h that was only moderately suggestive of transthyretin (TTR) amyloidosis. She ultimately received a right heart catheterization and endomyocardial biopsy, which showed apolipoprotein A-IV amyloid deposition within Congo red-positive areas of the endomyocardial specimen. The patient continues to report dyspnoea on exertion but has avoided additional heart failure admissions with intensification of her diuretic regimen. Discussion: In this case, nuclear PYP scan to evaluate for TTR amyloidosis demonstrated focal PYP uptake, but endomyocardial biopsy demonstrated apolipoprotein A-IV deposition without evidence of TTR amyloidosis. Our case increases knowledge of this rare form of amyloidosis, suggests that it may result in false positive nuclear PYP results, and highlights the importance of its evaluation, particularly in circumstances in which investigations do not reveal definitive evidence of AL or TTR amyloidosis.

Single-cell profiling reveals inflammatory polarization of human carotid versus femoral plaque leukocytes.

Femoral atherosclerotic plaques are less inflammatory than carotid plaques histologically, but limited cell-level data exist regarding comparative immune landscapes and polarization at these sites. We investigated intraplaque leukocyte phenotypes and transcriptional polarization in 49 patients undergoing femoral (n = 23) or carotid (n = 26) endarterectomy using single-cell RNA-Seq (scRNA-Seq; n = 13), flow cytometry (n = 24), and IHC (n = 12). Comparative scRNA-Seq of CD45+-selected leukocytes from femoral (n = 9; 35,265 cells) and carotid (n = 4; 30,655 cells) plaque revealed distinct transcriptional profiles. Inflammatory foam cell-like macrophages and monocytes comprised higher proportions of myeloid cells in carotid plaques, whereas noninflammatory foam cell-like macrophages and LYVE1-overexpressing macrophages comprised higher proportions of myeloid cells in femoral plaque (P < 0.001 for all). A significant comparative excess of CCR2+ macrophages in carotid versus plaque was observed by flow cytometry in a separate validation cohort. B cells were more prevalent and exhibited a comparatively antiinflammatory profile in femoral plaque, whereas cytotoxic CD8+ T cells were more prevalent in carotid plaque. In conclusion, human femoral plaques exhibit distinct macrophage phenotypic and transcriptional profiles as well as diminished CD8+ T cell populations compared with human carotid plaques.

Interconnected Clinical and Social Risk Factors in Breast Cancer and Heart Failure.

Breast cancer and heart failure share several known clinical cardiovascular risk factors, including age, obesity, glucose dysregulation, cholesterol dysregulation, hypertension, atrial fibrillation and inflammation. However, to fully comprehend the complex interplay between risk of breast cancer and heart failure, factors attributed to both biological and social determinants of health must be explored in risk-assessment. There are several social factors that impede implementation of prevention strategies and treatment for breast cancer and heart failure prevention, including socioeconomic status, neighborhood disadvantage, food insecurity, access to healthcare, and social isolation. A comprehensive approach to prevention of both breast cancer and heart failure must include assessment for both traditional clinical risk factors and social determinants of health in patients to address root causes of lifestyle and modifiable risk factors. In this review, we examine clinical and social determinants of health in breast cancer and heart failure that are necessary to consider in the design and implementation of effective prevention strategies that altogether reduce the risk of both chronic diseases.

Pharmacogenomics of Hypertension in CKD: The CKD-PGX Study.

Background: Patients with CKD often have uncontrolled hypertension despite polypharmacy. Pharmacogenomic drug-gene interactions (DGIs) may affect the metabolism or efficacy of antihypertensive agents. We report changes in hypertension control after providing a panel of 11 pharmacogenomic predictors of antihypertensive response. Methods: A prospective cohort with CKD and hypertension was followed to assess feasibility of pharmacogenomic testing implementation, self-reported provider utilization, and BP control. The analysis population included 382 subjects with hypertension who were genotyped for cross-sectional assessment of DGIs, and 335 subjects followed for 1 year to assess systolic BP (SBP) and diastolic BP (DBP). Results: Most participants (58%) with uncontrolled hypertension had a DGI reducing the efficacy of one or more antihypertensive agents. Subjects with a DGI had 1.85-fold (95% CI, 1.2- to 2.8-fold) higher odds of uncontrolled hypertension, as compared with those without a DGI, adjusted for race, health system (safety-net hospital versus other locations), and advanced CKD (eGFR <30 ml/min). CYP2C9-reduced metabolism genotypes were associated with losartan response and uncontrolled hypertension (odds ratio [OR], 5.2; 95% CI, 1.9 to 14.7). CYP2D6-intermediate or -poor metabolizers had less frequent uncontrolled hypertension compared with normal metabolizers taking metoprolol or carvedilol (OR, 0.55; 95% CI, 0.3 to 0.95). In 335 subjects completing 1-year follow-up, SBP (-4.0 mm Hg; 95% CI, 1.6 to 6.5 mm Hg) and DBP (-3.3 mm Hg; 95% CI, 2.0 to 4.6 mm Hg) were improved. No significant difference in SBP or DBP change were found between individuals with and without a DGI. Conclusions: There is a potential role for the addition of pharmacogenomic testing to optimize antihypertensive regimens in patients with CKD.

Cigarette Smoking and Competing Risks for Fatal and Nonfatal Cardiovascular Disease Subtypes Across the Life Course.

Background Cigarette smoking is significantly associated with premature death related and not related to cardiovascular disease (CVD). Whether risk associated with smoking is similar across CVD subtypes and how this translates into years of life lost is not known. Methods and Results We pooled and harmonized individual-level data from 9 population-based cohorts in the United States. All participants were free of clinical CVD at baseline with available data on current smoking status, covariates, and CVD outcomes. We examined the association between smoking status and total CVD and CVD subtypes, including fatal and nonfatal coronary heart disease, stroke, congestive heart failure, and other CVD deaths. We performed (1) modified Kaplan-Meier analysis to estimate long-term risks, (2) adjusted competing Cox models to estimate joint cumulative risks for CVD or noncardiovascular death, and (3) Irwin's restricted mean to estimate years lived free from and with CVD. Of 106 165 adults, 50.4% were women. Overall long-term risks for CVD events were 46.0% (95% CI, 44.7-47.3) and 34.7% (95% CI, 33.3-36.0) in middle-aged men and women, respectively. In middle-aged men who reported smoking compared with those who did not smoke, competing hazard ratios (HRs) were higher for the first presentation being a fatal CVD event (HR, 1.79 [95% CI, 1.68-1.92]), with a similar pattern among women (HR,1.82 [95% CI, 1.68-1.98]). Smoking was associated with earlier CVD onset by 5.1 and 3.8 years in men and women. Similar patterns were observed in younger and older adults. Conclusions Current smoking was associated with a fatal event as the first manifestation of clinical CVD.

Bone marrow-derived AXL tyrosine kinase promotes mitogenic crosstalk and cardiac allograft vasculopathy.

Cardiac Allograft Vasculopathy (CAV) is a leading contributor to late transplant rejection. Although implicated, the mechanisms by which bone marrow-derived cells promote CAV remain unclear. Emerging evidence implicates the cell surface receptor tyrosine kinase AXL to be elevated in rejecting human allografts. AXL protein is found on multiple cell types, including bone marrow-derived myeloid cells. The causal role of AXL from this compartment and during transplant is largely unknown. This is important because AXL is a key regulator of myeloid inflammation. Utilizing experimental chimeras deficient in the bone marrow-derived Axl gene, we report that Axl antagonizes cardiac allograft survival and promotes CAV. Flow cytometric and histologic analyses of Axl-deficient transplant recipients revealed reductions in both allograft immune cell accumulation and vascular intimal thickness. Co-culture experiments designed to identify cell-intrinsic functions of Axl uncovered complementary cell-proliferative pathways by which Axl promotes CAV-associated inflammation. Specifically, Axl-deficient myeloid cells were less efficient at increasing the replication of both antigen-specific T cells and vascular smooth muscle cells (VSMCs), the latter a key hallmark of CAV. For the latter, we discovered that Axl-was required to amass the VSMC mitogen Platelet-Derived Growth Factor. Taken together, our studies reveal a new role for myeloid Axl in the progression of CAV and mitogenic crosstalk. Inhibition of AXL-protein, in combination with current standards of care, is a candidate strategy to prolong cardiac allograft survival.

Race- and Sex-Specific Population Attributable Fractions of Incident Heart Failure: A Population-Based Cohort Study From the Lifetime Risk Pooling Project.

BACKGROUND: Race- and sex-specific differences in heart failure (HF) risk may be related to differential burden and effect of risk factors. We estimated the population attributable fraction (PAF), which incorporates both prevalence and excess risk of HF associated with each risk factor (obesity, hypertension, diabetes, current smoking, and hyperlipidemia), in specific race-sex groups. METHODS: A pooled cohort was created using harmonized data from 6 US longitudinal population-based cohorts. Baseline measurements of risk factors were used to determine prevalence. Relative risk of incident HF was assessed using a piecewise constant hazards model adjusted for age, education, other modifiable risk factors, and the competing risk of death from non-HF causes. Within each race-sex group, PAF of HF was estimated for each risk factor individually and for all risk factors simultaneously. RESULTS: Of 38 028 participants, 55% were female and 22% Black. Hypertension had the highest PAF among Black men (28.3% [95% CI, 18.7%-36.7%]) and women (25.8% [95% CI, 16.3%-34.2%]). In contrast, PAF associated with obesity was the highest in White men (21.0% [95% CI, 14.6%-27.0%]) and women (17.9% [95% CI, 12.8%-22.6%]). Diabetes disproportionately contributed to HF in Black women (PAF, 16.4% [95% CI, 12.7%-19.9%]). The cumulative PAF of all 5 risk factors was the highest in Black women (51.9% [95% CI, 39.3%-61.8%]). CONCLUSIONS: The observed differences in contribution of risk factors across race-sex groups can inform tailored prevention strategies to mitigate disparities in HF burden. This novel competing risk analysis suggests that a sizeable proportion of HF risk may not be associated with modifiable risk factors.

Risk-Based Approach for the Prediction and Prevention of Heart Failure.

Targeted prevention of heart failure (HF) remains a critical need given the high prevalence of HF morbidity and mortality. Similar to risk-based prevention of atherosclerotic cardiovascular disease, optimal HF prevention strategies should include quantification of risk in the individual patient. In this review, we discuss incorporation of a quantitative risk-based approach into the existing HF staging landscape and the clinical opportunity that exists to translate available data on risk estimation to help guide personalized decision making. We first summarize the recent development of key HF risk prediction tools that can be applied broadly at a population level to estimate risk of incident HF. Next, we provide an in-depth description of the clinical utility of biomarkers to personalize risk estimation in select patients at the highest risk of developing HF. We also discuss integration of genomics-enhanced approaches (eg, Titin [TTN]) and other risk-enhancing features to reclassify risk with a precision medicine approach to HF prevention. Although sequential testing is very likely to identify low and high-risk individuals with excellent accuracy, whether or not interventions based on these risk models prevent HF in clinical practice requires prompt attention including randomized placebo-controlled trials of candidate therapies in risk-enriched populations. We conclude with a summary of unanswered questions and gaps in evidence that must be addressed to move the field of HF risk assessment forward.

Association of the V122I Transthyretin Amyloidosis Genetic Variant With Cardiac Structure and Function in Middle-aged Black Adults: Coronary Artery Risk Development in Young Adults (CARDIA) Study.

IMPORTANCE: The variant V122I is commonly enriched in the transthyretin (TTR) gene in individuals of African ancestry and associated with greater risk of heart failure (HF) in older adulthood, after age 65 years. Prevention of HF may be most effective earlier in life, but whether screening with echocardiography can identify subclinical cardiac abnormalities during middle age to risk-stratify individuals appears to be unknown. OBJECTIVE: To examine the association between the V122I TTR variant and cardiac structure and function during middle age in those without prevalent HF. DESIGN, SETTING, AND PARTICIPANTS: This serial cross-sectional study of 875 Black participants in the Coronary Artery Risk Development in Young Adults (CARDIA) cohort was conducted at 4 urban sites across the US. Recruiting was completed in 1985-1986, and follow-up examinations occurred 25 and 30 years later. A subset of Black adults from the CARDIA cohort who underwent TTR genotyping was included. Data analysis was completed from January 2020 to October 2020. EXPOSURES: The V122I TTR genotype. MAIN OUTCOMES AND MEASURES: Echocardiographic left ventricular (LV) circumferential and longitudinal systolic strain and LV structure, measured at years 25 and 30 of follow-up. The analyses were adjusted for age, sex, echocardiography quality, genetic ancestry, and field center. RESULTS: Among the 875 Black adults (mean [SD] age, 49.4 [3.8] years at year 25; 543 women [62.1%]), there were 31 individuals who were heterozygous and 1 who was homozygous for the V122I TTR variant. Of the adults who had an echocardiogram at year 25, rates of hypertension (312 [46%]), diabetes (102 [15%]), and current smoking (128 [19%]) were not significantly different between those who did and did not carry V122I TTR. At year 25, there was no difference in LV circumferential strain, longitudinal strain, or LV structure between those who did vs did not carry V122I TTR. At year 30, those who carried V122I TTR had significantly lower absolute LV circumferential strain (mean [SD], 12.4 [4.2] percentage units) compared with those who did not carry the variant (mean [SD], 14.5 [3.7] percentage units). Those who carried V122I TTR also had significantly higher LV mass index values (mean [SD], 97.5 [34.1] g/m2) compared with those who did not (mean [SD], 83.7 [22.6] g/m2) at year 30. CONCLUSIONS AND RELEVANCE: Carrier status for the V122I TTR variant is associated with subclinical cardiac abnormalities in middle age (worse LV systolic function and higher LV mass) that have been associated with increased risk of incident HF. Midlife screening of individuals who carry V122I TTR with echocardiography may prognosticate risk of symptomatic HF and inform prevention strategies.

Carnitine Is Associated With Atherosclerotic Risk and Myocardial Infarction in HIV -Infected Adults.

Background People living with HIV ( PLWH ) have an increased risk of myocardial infarction ( MI ). Changes in the gut microbiota that occur with chronic HIV infection could play a role in HIV -associated atherosclerosis. Choline, carnitine, betaine, and trimethylamine N-oxide are small molecules that are, in part, metabolized or produced by the gut microbiome. We hypothesized that these metabolites would be associated with carotid artery intima-media thickness and MI in PLWH . Methods and Results Carotid artery intima-media thickness was measured at baseline and at a median interval of 4 years in 162 PLWH from the SCOPE (Study of the Consequences of the Protease Inhibitor Era) cohort in San Francisco, CA . Separately, 105 PLWH (36 cases with type I adjudicated MI and 69 controls without MI ) were selected from the Center for AIDS Research Network of Integrated Clinical Systems, a multicenter clinic-based cohort. Controls were matched by demographics, CD 4 cell count, and duration of viral suppression. In the SCOPE cohort, higher carnitine levels had a significant association with presence of carotid plaque and greater baseline and progression of mean carotid artery intima-media thickness after adjusting for traditional cardiovascular disease risk factors. In the treated and suppressed subgroup, these associations with carnitine remained significant after adjustment for cardiovascular disease risk factors. In the Center for AIDS Research Network of Integrated Clinical Systems cohort, the risk of MI was significantly increased in subjects with carnitine levels in the highest quartile after adjustment for cardiovascular disease risk factors. Conclusions In PLWH , including the treated and suppressed subgroup, carnitine is independently associated with carotid artery intima-media thickness, carotid plaque, and MI in 2 separate cohorts. These results emphasize the potential role of gut microbiota in HIV -associated atherosclerosis and MI , especially in relation to carnitine metabolism.

Coronary Artery Disease Manifestations in HIV: What, How, and Why.

Understanding why persons with human immunodeficiency virus (HIV) have accelerated atherosclerosis and its sequelae, including coronary artery disease (CAD) and myocardial infarction, is necessary to provide appropriate care to a large and aging population with HIV. In this review, we delineate the diverse pathophysiologies underlying HIV-associated CAD and discuss how these are implicated in the clinical manifestations of CAD among persons with HIV. Several factors contribute to HIV-associated CAD, with chronic inflammation and immune activation likely representing the primary drivers. Increased monocyte activation, inflammation, and hyperlipidemia present in chronic HIV infection also mirror the pathophysiology of plaque rupture. Furthermore, mechanisms central to plaque erosion, such as activation of toll-like receptor 2 and formation of neutrophil extracellular traps, are also abundant in HIV. In addition to inflammation and immune activation in general, persons with HIV have a higher prevalence than uninfected persons of traditional cardiovascular risk factors, including dyslipidemia, hypertension, insulin resistance, and tobacco use. Antiretroviral therapies, although clearly necessary for HIV treatment and survival, have had varied effects on CAD, but newer generation regimens have reduced cardiovascular toxicities. From a clinical standpoint, this mix of risk factors is implicated in earlier CAD among persons with HIV than uninfected persons; whether the distribution and underlying plaque content of CAD for persons with HIV differs considerably from uninfected persons has not been definitively studied. Furthermore, the role of cardiovascular risk estimators in HIV remains unclear, as does the role of traditional and emerging therapies; no trials of CAD therapies powered to detect clinical events have been completed among persons with HIV.

Role of T-Cell Dysfunction, Inflammation, and Coagulation in Microvascular Disease in HIV.

BACKGROUND: Compared to uninfected adults, HIV-infected adults on antiretroviral therapy are at increased risk of cardiovascular disease. Given the increase in T-cell dysfunction, inflammation, and coagulation in HIV infection, microvascular dysfunction is thought to contribute to this excess cardiovascular risk. However, the relationships between these variables remain undefined. METHODS AND RESULTS: This was a cross-sectional study of 358 HIV-infected adults from the SCOPE cohort. Macrovascular endothelial function was assessed using flow-mediated dilation of the brachial artery and microvascular function by reactive hyperemia. T-cell phenotype was determined by flow cytometry. Plasma markers of inflammation (tumor necrosis factor-α, interleukin-6, high-sensitivity C-reactive protein, sCD14) and coagulation (fibrinogen, D-dimer) were also measured. In all HIV+ subjects, markers of inflammation (tumor necrosis factor-α, high-sensitivity C-reactive protein), coagulation (D-dimer) and T-cell activation (CD8+PD1+, CD4+interferon+cytomegalovirus-specific) were associated with worse reactive hyperemia after adjusting for traditional cardiovascular risk factors and co-infections. In treated and suppressed subjects, tumor necrosis factor-α and CD8+PD1+ cells remained associated with worse reactive hyperemia after adjustment. Compared to the untreated subjects, CD8+PD1+ cells were increased in the virally suppressed group. Reactive hyperemia was predictive of flow-mediated dilation. CONCLUSIONS: CD8+PD1+ cells and tumor necrosis factor-α were associated with microvascular dysfunction in all HIV+ subjects and the treated and suppressed group. Additionally, D-dimer, high-sensitivity C-reactive protein, sCD-14, and interleukin-6 were associated with microvascular dysfunction in all HIV+ subjects. Although T-cell dysfunction, inflammation, and microvascular dysfunction are thought to play a role in cardiovascular disease in HIV, this study is the first to look at which T-cell and inflammatory markers are associated with microvascular dysfunction in HIV-infected individuals.

Chronic renal disease progression: treatment strategies and potassium intake.

Disordered potassium homeostasis is a common complication of chronic kidney disease and traditional management focuses on restricting potassium intake to avoid hyperkalemia. Permissive potassium intake carries the risk of hyperkalemia and hyperphosphatemia, and possibly may contribute to the development of uremic neuropathy. Excessive potassium restriction and removal by dialysis carries the risk of worsened chronic hypertension, intradialytic hypotension, renal fibrosis and cyst formation, and ventricular arrhythmias. Cohort studies have associated both hypokalemia and hyperkalemia with increased mortality in CKD. A single study of potassium intake in hemodialysis patients found increased intake associated with increased mortality despite adjustment for serum potassium concentration. We recommend avoiding mandatory potassium restriction in early chronic kidney disease. We endorse routine potassium restriction in advanced chronic kidney disease requiring hemodialysis and close monitoring of serum potassium concentration in any patients receiving renin-angiotensin-aldosterone system blockers.

Accuracy of stress myocardial perfusion imaging to diagnose coronary artery disease in end stage liver disease patients.

Patients with end-stage liver disease (ESLD) who also have underlying coronary artery disease (CAD) may be at increased risk for undergoing hemodynamically challenging orthotopic liver transplantation. Noninvasive single-photon emission computed tomographic (SPECT) imaging is often used to determine whether a patient with ESLD has unsuspected CAD. The objective of this study was to determine the accuracy of SPECT imaging for detection of CAD in patients with ESLD. Patients with ESLD who underwent coronary angiography and SPECT imaging before orthotopic liver transplantation were analyzed retrospectively. The predictive accuracy of clinical risk factors was calculated and compared to the results of SPECT imaging. There were 473 SPECT imaging studies. Adenosine SPECT imaging had a sensitivity of 62%, specificity of 82%, positive predictive value of 30%, and negative predictive value of 95% for diagnosing severe CAD. Regadenoson SPECT imaging had a sensitivity of 35%, specificity of 88%, positive predictive value of 23%, and negative predictive value of 93% for diagnosing severe CAD. The accuracy of a standard risk factor analysis showed no statistical difference in predicting CAD compared with adenosine (sensitivity McNemar's p = 0.48, specificity McNemar's p = 1.00) or regadenoson (sensitivity McNemar's p = 0.77, specificity McNemar's p = 1.00) SPECT studies. In conclusion, the 2 pharmaceutical agents had low sensitivity but high specificity for diagnosing CAD. However, because the sensitivity of the test is low, the chances of missing patients with ESLD with CAD is high, making SPECT imaging an inaccurate screening test. A standard risk factor analysis as a predictor for CAD in patients with ESLD is less expensive, has no radiation exposure, and is as accurate as SPECT imaging.

The role of oxygen during fracture healing.

Oxygen affects the activity of multiple skeletogenic cells and is involved in many processes that are important for fracture healing. However, the role of oxygen in fracture healing has not been fully studied. Here we systematically examine the effects of oxygen tension on fracture healing and test the ability of hyperoxia to rescue healing defects in a mouse model of ischemic fracture healing. Mice with tibia fracture were housed in custom-built gas chambers and groups breathed a constant atmosphere of 13% oxygen (hypoxia), 21% oxygen (normoxia), or 50% oxygen (hyperoxia). The influx of inflammatory cells to the fracture site, stem cell differentiation, tissue vascularization, and fracture healing were analyzed. In addition, the efficacy of hyperoxia (50% oxygen) as a treatment regimen for fracture nonunion was tested. Hypoxic animals had decreased tissue vascularity, decreased bone formation, and delayed callus remodeling. Hyperoxia increased tissue vascularization, altered fracture healing in un-complicated fractures, and improved bone repair in ischemia-induced delayed fracture union. However, neither hypoxia nor hyperoxia significantly altered chondrogenesis or osteogenesis during early stages of fracture healing, and infiltration of macrophages and neutrophils was not affected by environmental oxygen after bone injury. In conclusion, our results indicate that environmental oxygen levels affect tissue vascularization and fracture healing, and that providing oxygen when fractures are accompanied by ischemia may be beneficial.