Natalie A. Drucker

Hydrogen Sulfide: A Potential Novel Therapy for the Treatment of Ischemia

ABSTRACT Hydrogen sulfide (H2S) is a novel signaling molecule most recently found to be of fundamental importance in cellular function as a regulator of apoptosis, inflammation, and perfusion. Mechanisms of endogenous H2S signaling are poorly understood; however, signal transmission is thought to occur via persulfidation at reactive cysteine residues on proteins. Although much has been discovered about how H2S is synthesized in the body, less is known about how it is metabolized. Recent studies have discovered a multitude of different targets for H2S therapy, including those related to protein modification, intracellular signaling, and ion channel depolarization. The most difficult part of studying hydrogen sulfide has been finding a way to accurately and reproducibly measure it. The purpose of this review is to: elaborate on the biosynthesis and catabolism of H2S in the human body, review current knowledge of the mechanisms of action of this gas in relation to ischemic injury, define strategies for physiological measurement of H2S in biological systems, and review potential novel therapies that use H2S for treatment.

Hydrogen sulfide improves intestinal recovery following ischemia by endothelial nitric oxide-dependent mechanisms

Hydrogen sulfide (H2S) is an endogenous gasotransmitter that has vasodilatory properties. It may be a novel therapy for intestinal ischemia-reperfusion (I/R) injury. We hypothesized that 1) H2S would improve postischemic survival, mesenteric perfusion, mucosal injury, and inflammation compared with vehicle and 2) the benefits of H2S would be mediated through endothelial nitric oxide. C57BL/6J wild-type and endothelial nitric oxide synthase knockout (eNOS KO) mice were anesthetized, and a midline laparotomy was performed. Intestines were eviscerated, the small bowel mesenteric root identified, and baseline intestinal perfusion was determined using laser Doppler. Intestinal ischemia was established by temporarily occluding the superior mesenteric artery. Following ischemia, the clamp was removed, and the intestines were allowed to recover. Either sodium hydrosulfide (2 nmol/kg or 2 µmol/kg NaHS) in PBS vehicle or vehicle only was injected into the peritoneum. Animals were allowed to recover and were assessed for mesenteric perfusion, mucosal injury, and intestinal cytokines. P values < 0.05 were significant. H2S improved mesenteric perfusion and mucosal injury scores following I/R injury. However, in the setting of eNOS ablation, there was no improvement in these parameters with H2S therapy. Application of H2S also resulted in lower levels of intestinal cytokine production following I/R. Intraperitoneal H2S therapy can improve mesenteric perfusion, intestinal mucosal injury, and intestinal inflammation following I/R. The benefits of H2S appear to be mediated through endothelial nitric oxide-dependent pathways.NEW & NOTEWORTHY H2S is a gaseous mediator that acts as an anti-inflammatory agent contributing to gastrointestinal mucosal defense. It promotes vascular dilation, mucosal repair, and resolution of inflammation following intestinal ischemia and may be exploited as a novel therapeutic agent. It is unclear whether H2S works through nitric oxide-dependent pathways in the intestine. We appreciate that H2S was able to improve postischemic recovery of mesenteric perfusion, mucosal integrity, and inflammation. The beneficial effects of H2S appear to be mediated through endothelial nitric oxide-dependent pathways.

Rationale and design of the Clinical and Histologic Analysis of Mesenchymal Stromal Cells in AmPutations (CHAMP) trial investigating the therapeutic mechanism of mesenchymal stromal cells in the treatment of critical limb ischemia

Objective: Currently, there are no accepted nonsurgical therapies that improve the delivery of blood‐derived nutrients to patients with critical limb ischemia. Here, we describe the ongoing phase 1/2 Clinical and Histologic Analysis of Mesenchymal Stromal Cells in AmPutations (CHAMP) trial, which will provide crucial evidence of the safety profile of mesenchymal stromal cells (MSCs) and explore their therapeutic mechanisms in the setting of critical limb ischemia requiring below‐knee amputation (BKA). Methods: In the CHAMP and the parallel marrowCHAMP trials (hereafter grouped together as CHAMP), a total of 32 extremities with rest pain or tissue loss requiring BKA will be enrolled to receive intramuscular injections of allogeneic MSCs (CHAMP; n = 16) or autogenous concentrated bone marrow aspirate (marrowCHAMP; n = 16) along the distribution of the BKA myocutaneous flap and proximal tibialis anterior. After treatment, subjects are randomized to BKA at four time points after injection (days 3, 7, 14, and 21). At the time of amputation, skeletal muscle is collected at 2‐cm increments from the tibialis injection site and used to determine proangiogenic cytokine description, MSC retention, quantification of proangiogenic hematopoietic progenitor cells, and histologic description. Clinical limb perfusion before and after treatment will be quantified using transcutaneous oximetry, toe‐brachial index, ankle‐brachial index, and indocyanine angiography. Additional clinical end points include all‐cause mortality, need for amputation revision, and gangrene incidence during the 6‐month post‐treatment follow‐up. Results: Enrollment is under way, with 10 patients treated per protocol thus far. We anticipate full conclusion of follow‐up within the next 24 months. Conclusions: CHAMP will be pivotal in characterizing the safety, efficacy, and, most important, therapeutic mechanism of allogeneic MSCs and autogenous concentrated bone marrow aspirate in ischemic skeletal muscle.

Stem cell therapy in necrotizing enterocolitis: Current state and future directions

Stem cell therapy is a promising treatment modality for necrotizing enterocolitis. Among the many promising stem cells identified to date, it is likely that mesenchymal stem cells will be the most useful and practical cell-based therapies for this condition. Using acellular components such as exosomes or other paracrine mediators are promising as well. Multiple mechanisms are likely at play in the positive effects provided by these cells, and further research is underway to further elucidate these effects.

Fenestrated Aortic Endografts in the Last 3 Years: An Update

Purpose of ReviewFenestrated endovascular aortic aneurysm repair (FEVAR) is an accepted treatment option for patients who are not suitable for conventional endovascular aortic aneurysm repair or open surgical repair (OSR). Five years ago, the FDA approved the use of FEVAR in patients with inadequate infrarenal aortic seal zones (short necks). This procedural paradigm continues to gain in popularity compared to OSR for complex aortic disease. We seek to define the current state of fenestrated endovascular repair by reviewing relevant literature over the past 3 years.Recent FindingsFEVAR continues to prove to be efficacious with reasonable durability as a therapy for patients who are not candidates for OSR. As a second-line treatment, FEVAR is less morbid in the short-term with trade-off of high reintervention rates in the follow-up period. Mid- to long-term outcomes have proven to be comparable to OSR in selected patients with persistent excellent patency of the visceral target vessels. Recent publications have thrust FEVAR into consideration as the primary interventional modality in juxtarenal abdominal aortic aneurysms, a traditional indication for OSR.SummaryAs FEVAR continues to evolve from surgeon-modified devices to custom built and eventually off-the-shelf grafts, it is anticipated to be employed widely for managing complex aortic aneurysms. Compared to OSR, FEVAR carries a low risk of perioperative morbidity while demonstrating continued safety and durability in early to mid-term reports.

Description of human AAA by cytokine and immune cell aberrations compared to risk-factor matched controls

Background: The pathogenesis driving the formation of abdominal aortic aneurysms continues to be poorly understood. Therefore, we systemically define the cytokine and circulating immune cell environment observed in human abdominal aortic aneurysm compared with risk‐factor matched controls. Methods: From 2015 to 2017, a total of 274 patients donated blood to the Indiana University Center for Aortic Disease. Absolute concentrations of circulating cytokines were determined, using enzyme‐linked immunosorbent assays while the expression of circulating immune cell phenotypes were assayed via flow cytometric analysis. Results: Human abdominal aortic aneurysm is characterized by a significant depletion of the antigen‐specific, CD4+ Tr1 regulatory lymphocyte that corresponds to an upregulation of the antigen‐specific, inflammatory Th17 cell. We found no differences in the incidence of Treg, B10, and myeloid‐derived suppressor regulatory cells. Similarly, no disparities were noted in the following inflammatory cytokines: IL‐1&bgr;, C‐reactive protein, tumor necrosis factor &agr;, interferon &ggr;, and IL‐23. However, significant upregulation of the inflammatory cytokines osteopontin, IL‐6, and IL‐17 were noted. Additionally, no changes were observed in the regulatory cytokines IL‐2, IL‐4, IL‐13, TNF‐stimulated gene 6 protein, and prostaglandin E2, but we did observe a significant decrease in the essential regulatory cytokine IL‐10. Conclusion: In this investigation, we systematically characterize the abdominal aortic aneurysm–immune environment and present preliminary evidence that faulty immune regulation may also contribute to aneurysm formation and growth.

Adjunctive visceral artery chimney in patients undergoing Zenith Fenestrated aortic repair

Objective: Visceral artery chimneys have been employed as an adjunct to endovascular aneurysm repair (EVAR) to treat short‐neck infrarenal and juxtarenal aortic aneurysms for more than two decades. With the widespread introduction of fenestrated endovascular aneurysm repair by the Food and Drug Administration‐approved Zenith Fenestrated endograft (ZFEN; Cook Medical, Bloomington, Ind) to the United States in 2012, clinicians gained the ability to apply the chimney technique to these custom devices for difficult anatomy. The purpose of this report was to demonstrate feasibility and to provide evidence on the performance of chimneys for the treatment of complex juxtarenal aneurysms that could not be adequately treated with ZFEN alone. Methods: A retrospective analysis was performed of a prospectively maintained institutional ZFEN database capturing 110 fenestrated endovascular aneurysm repairs from October 2012 to January 2018 to identify patients undergoing a concomitant visceral artery chimney. All patients with <12 months of follow‐up were excluded from further analysis. Demographic, anatomic, intraoperative, perioperative, and follow‐up characteristics were tabulated and analyzed. Results: Six patients met criteria and were included in this investigation. They were universally male with a mean age of 76.2 years at the time of ZFEN/chimney. Chimneys were placed in a total of six visceral arteries (n = 1 per patient) consisting of three renal arteries, two celiac arteries, and one accessory renal artery. Mean estimated blood loss and operative time were 283 mL and 298 minutes, respectively. Technical success was achieved in all cases. Two small type IA “gutter” endoleaks were detected early; both spontaneously resolved on follow‐up. We observed no instances of chimney migration, stenosis, or thrombosis perioperatively or on follow‐up. Two reinterventions were performed in these six patients; these consisted of a repeated renal stent for ostial stenosis at a main body fenestration and a common femoral artery endarterectomy and patch angioplasty for an access‐related common femoral artery occlusion. Conclusions: Use of ZFEN in conjunction with a singular chimney is safe, feasible, and durable in patients with difficult anatomy who do not meet instructions for use as demonstrated in this limited series.

Use of the Zenith Fenestrated platform to rescue failing endovascular and open aortic reconstructions is safe and technically feasible

Objective: Proximal neck dilation is a serious long‐term complication directly causing the failure of endovascular aneurysm repair (EVAR) and open surgical repair (OSR) of abdominal aortic aneurysms. However, the implantation of a fenestrated device presents the opportunity for proximal extension of the aortic reconstruction into a healthy segment while maintaining patency of the visceral vessels. The objective of this investigation was to report perioperative and follow‐up outcomes using the Zenith Fenestrated (ZFEN; Cook Medical, Bloomington, Ind) aortic stent system in salvaging previous aortic repairs undergoing type IA endoleak or aneurysmal degeneration of the proximal neck. Methods: We performed a retrospective review of a prospectively maintained institutional database capturing all fenestrated EVAR (FEVAR) cases with the ZFEN platform. Fenestrated cases were classified as primary FEVAR or reoperative FEVAR (rFEVAR) after previous EVAR or OSR. Cohort comparisons were performed using Fisher exact tests and Student t‐tests for categorical and continuous variables, respectively. Results: Between October 2012 and March 2017, a total of 103 patients diagnosed with abdominal aortic aneurysm with an inadequate proximal seal zone for traditional EVAR were treated with ZFEN. In 12 patients, FEVAR was performed as a reoperation after previous EVAR (n = 6) or OSR (n = 6). The indications for rFEVAR were proximal neck dilation (>55 mm) after OSR (n = 6), type IA endoleak after EVAR (n = 5), and proximal neck dilation after EVAR without endoleak (n = 1). No difference in ability to achieve technical success was observed between primary FEVAR and rFEVAR (97.8% vs 100%; P = 1.00). In addition, there were no differences in estimated blood loss (363 vs 500 mL; P = .25) and intraoperative use of contrast material (97.3 vs 104.0 mL; P = .55). However, a significant increase in fluoroscopy time (61.1 vs 79.8 minutes; P = .04), radiation exposure (415.9 vs 606.3 rad; P = .02), and operative time (228.4 vs 287.6 minutes; P = .03) in the rFEVAR cohort was observed. In the 30‐day perioperative period, there were no significant differences with regard to mortality (2.2% vs 0%; P = 1.0), major adverse cardiovascular events (5.5% vs 0%, P = 1.0), and stent‐related adverse events (2.2% vs 0%; P = 1.0). There were no differences in rates of perioperative (5.5% vs 0%; P = 1.0) or follow‐up reintervention after a mean follow‐up duration of 20.8 months (18.6% vs 25.0%; P = .70). Conclusions: FEVAR with the ZFEN platform of failed and failing aortic reconstructions due to disease progression is safe and feasible without increased morbidity and mortality in select patients. These preliminary results support the inclusion of ZFEN as a treatment option for aortic reintervention.

Ethnic minorities with critical limb ischemia derive equal amputation risk reduction from autologous cell therapy compared with whites

Objective: Ethnic minorities (nonwhites) with critical limb ischemia (CLI) have historically performed worse compared with whites with regard to major amputation risk reduction and amputation‐free survival (AFS) after peripheral vascular intervention. This post hoc analysis was completed to determine whether this precedent also extended to treatment of CLI without a suitable revascularization option with intramuscular injections of concentrated bone marrow aspirate (cBMA). Methods: The treatment arm of the randomized, double‐blind, multicenter MarrowStim PAD Kit for the Treatment of Critical Limb Ischemia in Subjects with Severe Peripheral Arterial Disease (MOBILE) trial was stratified by ethnicity and evaluated for demographics, comorbidities, and outcomes. The primary and therapeutic end point was 1‐year AFS and major amputation, respectively. Noninferiority analysis was performed with the margin set at historically reported hazard ratios. Results: Thirty‐seven minority (African American, Hispanic, other) CLI patients (9 placebo, 28 cBMA) with no suitable revascularization option were randomized to cBMA or placebo at a 3:1 ratio during the MOBILE trial. At 1‐year follow‐up for the treatment group, overall AFS was 80%. Of the 28 minority patients randomized to cBMA intervention, an 89% AFS rate was observed compared with 77% in whites. Specifically, 22 of 24 (92%) African Americans survived amputation free at 1‐year follow‐up. Noninferiority testing confirmed no difference between whites and the ethnic minority treated with cBMA with respect to major amputation reduction; however, noninferiority could not be confirmed with regard to AFS. No significant differences favoring whites treated with cBMA were noted in the secondary end points of vascular quality of life, limb pain, ankle‐brachial index, toe‐brachial index, transcutaneous oximetry, and 6‐minute walk testing. Conclusions: This post hoc analysis of the MOBILE trial demonstrates noninferiority of cBMA intervention in minorities with no‐option CLI for the therapeutic end point of major amputation prevention. cBMA represents a novel treatment paradigm and should be explored for minorities with poor revascularization options who face impending amputation secondary to progressive CLI.

Long-term outcomes after pediatric peripheral revascularization secondary to trauma at an urban level I center

Objective The purpose of this investigation was to determine our limb‐related contemporary pediatric revascularization perioperative and follow‐up outcomes after major blunt and penetrating trauma. Methods A retrospective review was performed of a prospectively maintained pediatric trauma database spanning January 2010 to December 2017 to capture all level I trauma activations that resulted in a peripheral arterial revascularization procedure. All preoperative, intraoperative, and postoperative continuous variables are reported as a mean ± standard deviation; categorical variables are reported as a percentage of the population of interest. Results During the study period, 1399 level I trauma activations occurred at a large‐volume, urban childrens hospital. The vascular surgery service was consulted in 2.6% (n = 36) of these cases for suspected vascular injury based on imaging or physical examination. Our study population included only patients who received an arterial revascularization, which was performed in 23 of the 36 consultations (1.6% of total traumas; median age, 11 years). These injuries were localized to the upper extremity in 60.9% (n = 14), lower extremity in 30.4% (n = 7), and neck in 8.7% (n = 2). The mean Injury Severity Score in the revascularized cohort was 14.0 (±7.6). Bone fractures were associated with 39.1% of the vascular injuries (90% of blunt injuries). Restoration of in‐line flow was achieved by an endovascular solution in one patient and open surgery in the remainder, consisting of arterial bypass in 59.1% and direct repair in 40.9%. Within 30 days of the operation, we observed no deaths, no infections of the arterial reconstruction, and no major amputations. One patient required perioperative reintervention by the vascular team secondary to the development of a superficial seroma without evidence of graft involvement. Mean follow‐up in our cohort was 43.3 (±35.4) months. During this phase, no additional deaths, amputations, chronic wounds, or limb length discrepancies were observed. All vascular repairs were patent, and all but one patient reported normal function of the affected limb at the latest clinic visit. Conclusions Traumatic peripheral vascular injury is rare in the pediatric population but is often observed secondary to a penetrating force or after long bone fracture. However, contemporary perioperative and long‐term outcomes after surgical revascularization are excellent as demonstrated in this institutional case series.