Incidence of venous thromboembolism following adrenalectomy: A CESQIP analysis

BACKGROUND

We aim to evaluate the incidence of venous thromboembolism (VTE) following adrenalectomy.

METHODS

A retrospective analysis of the Collaborative Endocrine Surgery Quality Improvement Program was performed to assess incidence for VTE, including pulmonary embolism or deep vein thrombosis, in adults undergoing adrenalectomy (2014-2022).

RESULTS

2567 patients undergoing adrenalectomy were included. Surgical approach was 10% open and 90% minimally invasive. Pathology was 13% malignant and 87% benign; 19% had hypercortisolism. VTE developed in 0.27% at a median of 8 days from surgery. The incidence was higher in primary adrenal malignancy compared to benign or metastases to the adrenals, p ​< ​0.01. VTE was associated with longer hospital stay, longer operative time, readmission, and mortality. VTE rates were similar for hypercortisolism vs no hypercortisolism and between patients with clinical vs subclinical hypercortisolism.

CONCLUSION

Although VTE following adrenalectomy is rare, it is more common in cases of primary adrenal malignancy, those with longer operations, or those requiring prolonged hospitalization.

The effect of hormonal secretion on survival in adrenocortical carcinoma: A multi-center study

BACKGROUND

Current evidence suggests that cortisol secreting adrenocortical carcinoma has worse prognosis compared to non-secreting adrenocortical carcinoma. However, the effect of other secretory subtypes is unknown.

METHODS

This multicenter study within the American-Australian-Asian Adrenal Alliance included adults with adrenocortical carcinoma (1997-2020). We compared overall survival and disease-free survival among cortisol secreting, mixed cortisol/androgen secreting, androgen secreting, and non-secreting adrenocortical carcinoma.

RESULTS

Of the 807 patients (mean age 50), 719 included in the secretory subtype analysis: 24.5% were cortisol secreting, 13% androgen secreting, 28% mixed cortisol/androgen, 32.5% non-secreting, and 2% were mineralocorticoid secreting. Median overall survival and disease-free survival for the entire cohort were 60 and 9 months, respectively. Median overall survival was 36 months for cortisol, 30 for mixed, 60 for androgen secreting, and 115 for non-secreting adrenocortical carcinoma, P < .01. Median disease-free survival was 7 months for cortisol, 8 for mixed, 10 for androgen, and 12 for non-secreting adrenocortical carcinoma, P = .06. On multivariable analysis of age, sex, Ki67%, secretory subtype, stage, resection, and adjuvant therapy, predictors of worse overall survival were older age, higher Ki67%, stage IV, mixed secreting, R1, and no adjuvant therapy, P < .05. On subgroup analysis of R0 resection, predictors of worse overall survival included older age and higher Ki67%. Ki67% ≥40, stage III and cortisol secretion were associated with worse disease-free survival.

CONCLUSION

Mixed cortisol/androgen secreting adrenocortical carcinoma was associated with worse overall survival, while cortisol or androgen secreting alone were not. Notably, among patients after R0 resection, secretory subtype did not affect overall survival. Cortisol secreting adrenocortical carcinoma demonstrated worse disease-free survival. Ki67% remained a strong predictor of worse overall survival and disease-free survival independent of stage.

Ethanol Ablation for Benign Insulinoma: Intraoperative and Endoscopic Approaches

INTRODUCTION

Ethanol ablation can be utilized to manage insulinoma. We aimed to analyze our outcomes of endoscopic ultrasound (EUS) and intraoperative ultrasound (IOUS) guided Ethanol ablation of insulinoma.

METHODS

A single institution retrospective review of adults undergoing Ethanol ablation of benign pancreatic insulinoma (2007-2022) was performed. Outcomes were categorized as resolution of hypoglycemia, improvement, or no change at last follow-up.

RESULTS

A total of 16 patients underwent Ethanol ablation of benign insulinoma (N = 8 EUS, N = 8 IOUS): median age was 68 y, 8 (50%) were females, and 2 (12.5%) were associated with multiple endocrine neoplasia type-1. Median insulinoma size was 12 (range 7, 25) mm. Ethanol ablation was preferred over resection to avoid pancreaticoduodenectomy when it was not possible to enucleate the tumor in 10 (62.5%) patients while the rest underwent ablation due to being poor surgical candidates or because of a history of previous pancreatic resection. The median follow-up (interquartile range) was 43 (19.5, 81.5) mo. Resolution of hypoglycemia occurred in 11 patients (5 EUS, 6 IOUS), while the rest (3 EUS, 2 IOUS) experienced improvement in the severity and frequency of hypoglycemia. A single patient underwent resection following a previous ablation for symptomatic hypoglycemia 5 y after EUS guided ablation.

CONCLUSIONS

Ethanol ablation provides an alternative therapeutic option for patients with insulinoma. Both EUS and IOUS guided approaches are associated with a favorable resolution rate although EUS guided ablation may require multiple procedures to optimize outcomes.

Intraoperative Parathyroid Hormone Monitoring Is of Limited Usefulness in Guiding Autotransplantation in Reoperative or Subtotal Parathyroidectomy for Primary Hyperparathyroidism

INTRODUCTION

Patients with primary hyperparathyroidism (1HPT) undergoing reoperative or subtotal parathyroidectomy (PTX) may undergo autotransplantation (ATX) when the viability of remaining tissue is unknown. This study aims to identify whether intraoperative parathyroid hormone levels (IOPTH) can determine ATX candidacy.

METHODS

Patients with 1HPT who underwent PTX with ATX at our institution were identified. IOPTH and PTH values within 24 h, 2-4 weeks, and >1 month postoperative were analyzed. Patients were classified as either a candidate for ATX (low PTH after 2-4 weeks) or not a candidate based on postoperative PTH (normal PTH after 2-4 weeks). Associations of ATX candidate status with demographic and clinical attributes were studied.

RESULTS

268 had a reoperative (49%) or subtotal PTX with ATX. 151 had data for PTH analysis, and 21 (14%) were identified as candidates for ATX. The mean % decline in IOPTH from baseline to 20 min post-excision was 51% in noncandidates vs 73% in candidates (P = .002). The mean change in IOPTH from baseline to final was 52% in noncandidates and 83% in candidates (P = .009). A decrease in IOPTH from baseline to 20 min post-excision of 23.4% or greater or a final PTH of 52 pg/mL or less would be an indication for ATX. Of the 21 who needed an ATX, it failed in 10.

CONCLUSION

Parathyroid ATX is frequently unnecessary, and the viability is less than expected. While candidates for ATX have a greater IOPTH % decline at all points during surgery and a lower final IOPTH, the clinical practicality of using IOPTH to determine ATX candidacy is limited.

Disparities in Parathyroidectomy: Who Receives Appropriate Treatment for Primary Hyperparathyroidism?

INTRODUCTION

Parathyroidectomy is underperformed despite clear benefits in primary hyperparathyroidism (PHPT). We evaluated disparities in receipt of parathyroidectomy following PHPT diagnosis to explore barriers to care.

METHODS

Adults diagnosed with PHPT 2013-2018 at a health system were identified. Recommended indications for parathyroidectomy include age ≤50 y, calcium >11 mg/dL, or the presence of nephrolithiasis, hypercalciuria, nephrocalcinosis, decreased glomerular filtration rate, osteopenia, osteoporosis, or pathological fracture 1 y prior to diagnosis. Kaplan-Meier analysis assessed rates of parathyroidectomy within 12 mo following diagnosis as well as median time to parathyroidectomy, and multivariable Cox proportional hazards analyses assessed factors associated with undergoing parathyroidectomy.

RESULTS

Of 2409 patients, 75% were females, 12% aged ≤50 y, and 92% non-Hispanic White, while 52% had Medicaid/Medicare, 36% were commercial/self-pay or uninsured, and 12% unknown. Parathyroidectomy was performed within 1 y in 50% of patients. Within the 68% that met recommendations, parathyroidectomy was performed within 1 y in 54%; median time from diagnosis to surgery was shorter for males, patients aged ≤50 y, commercial/self-pay/no insurance patients (versus Medicaid/Medicare), and those with fewer comorbidities, P < 0.05. Multivariable analysis demonstrated non-Hispanic White patients and those with commercial/self-pay/uninsured were more likely to undergo parathyroidectomy after adjusting for comorbidity, age, and facility site. Among those strongly indicated, patients not on Medicare/Medicaid and aged ≤50 y were more likely to undergo parathyroidectomy after adjusting for race, comorbidity, and facility site.

CONCLUSIONS

Disparities in parathyroidectomy for PHPT were observed. Insurance type was associated with undergoing parathyroidectomy; patients on governmental insurance were less likely to undergo surgery and waited longer for surgery despite strong indications. Barriers to referral and access to surgery should be investigated and addressed to optimize all patients' access to care.

Pediatric primary hyperparathyroidism: Surgical pathology and long-term outcomes in sporadic and familial cases

BACKGROUND

Primary Hyperparathyroidism (PHPT) is rare in pediatric patients. Data regarding surgical outcomes are scarce.

METHODS

Single-center retrospective review (1994-2020) of patients ≤21 years undergoing surgery for PHPT.

RESULTS

66 patients were identified (61% female, 17 ± 3 years). 71% of patients were symptomatic at diagnosis. 32% of patients had known familial syndromes, most commonly MEN-1. 23% of patients without a known mutation had genetic testing, 22% positive. 56% of the total and 19% of the familial cohort underwent focused exploration. Single gland disease was found in 19% of familial vs 85% of sporadic cases, p < 0.00001. Persistence was 9%, all in the sporadic group, p = 0.11. Recurrence was 15%: 38% in the familial vs 2% in the sporadic groups, p=0.0004. Time to recurrence was 59 months (Q1-38, Q3-95), familial 61 vs 124 months sporadic, p=0.001.

CONCLUSION

Pediatric PHPT is frequently sporadic, although 5% of apparent sporadic cases are secondary to syndromes. Familial cases have higher rates of recurrence, requiring closer follow-up.

Clinical course and imaging characteristics of benign adrenal cysts: a single-center study of 92 patients

OBJECTIVE

Benign adrenal cysts are rare lesions of the adrenal glands. Limited data are available to guide management. We aimed to describe the presentation and outcomes of patients with benign adrenal cysts.

DESIGN

Retrospective longitudinal cohort study.

METHODS

Consecutive patients with histologically or radiologically confirmed adrenal cysts between 1995 and 2021 were identified. Pheochromocytomas and malignancy were excluded.

RESULTS

Benign adrenal cysts were diagnosed in 92 patients (53, 57% women) at a median age of 45 years. Mode of discovery was incidental on imaging in 81 (88%), symptoms of mass effect in 9 (9.8%), and others in 2 (2.2%). Majority (89, 97%) of patients had unilateral cysts (45 right, 44 left) with a median size of 48 mm (range 4-200) at diagnosis. On imaging, most cysts were round/oval (85.4%), homogenous (83.2%) lesions with calcifications (64.0%) and no vascular enhancement (97.7%). During a median follow-up of 65 months (range 7-288), adrenal cysts demonstrated minimal enlargement (median size change 6 mm, median growth rate 2 mm/year). On hormonal evaluation, 10% (5/50 tested) had an abnormal overnight dexamethasone suppression test, and 9.5% (4/42 tested) had an abnormal case detection testing for primary aldosteronism. Patients treated with adrenalectomy (46, 50%) were younger (36.9 years vs 50.8 years, P = 0.0009) and had more rapidly enlarging cysts (median growth rate 5.5 mm/year vs 0.4 mm/year, P = 0.0002).

CONCLUSION

Benign adrenal cysts are usually incidentally discovered, non-functional, homogenous lesions without vascular enhancement that demonstrate minimal growth. Adrenalectomy should be reserved for patients with heterogeneous lesions, abnormal hormonal evaluation, or those with mass effect symptoms.

Informing therapeutic lymphadenectomy: Location of regional metastatic lymph nodes in adrenocortical carcinoma

BACKGROUND

The anatomic boundaries of lymphadenectomy for adrenocortical carcinoma (ACC) are not defined.

METHODS

Adults undergoing resection of ACC were included. Locations were categorized based on positive LN locations on final pathology.

RESULTS

Of 231 resected ACC, 6% had positive LN during initial resection. Positive LN in left ACC (n = 7) were: 2 para-aortic, 2 left renal-hilar, 1 para-aortic and left renal-hilar and 1 unknown, while for right ACC (n = 7): 2 para-caval, 1 para-caval and right renal-hilar, 1 inter-aortocaval, 1 celiac, 1 para-aortic, and 1 unknown. Of 55 resections for recurrent ACC, positive LN in left ACC (n = 2) were: 1 para-aortic, and 1 para-aortic with left renal-hilar, while LN for right ACC (n = 7): 2 inter-aortocaval, 2 right renal-hilar, 2 para-caval and one retrocrural.

CONCLUSION

The most common LN metastases are para-caval for right, and para-aortic and left renal-hilar for left ACC. Further studies are necessary to determine the boundaries of lymphadenectomy in ACC resection.

Medullary thyroid cancer: What is the optimal management of the lateral neck in a node negative patient at index operation?

BACKGROUND

Medullary thyroid cancer is a neuroendocrine malignancy that can occur sporadically or as the result of genomic rearranged during transfection mutations. Medullary thyroid cancer has a higher rate of metastasis than well-differentiated thyroid cancer. Lateral neck dissection is often performed, and its prophylactic use is controversial.

METHODS

Single-center, retrospective review (2000-2017) of patients undergoing primary surgical treatment for medullary thyroid cancer who had negative lateral neck imaging preoperatively. Demographics, genetic associations, clinical, and imaging findings were analyzed. Locoregional recurrence, overall recurrence, and overall survival were examined.

RESULTS

A total of 110 patients were identified, of which 18 underwent prophylactic lateral neck dissection and 92 did not. Age, sex distribution, preoperative calcitonin levels, and follow-up were similar among groups. Overall recurrence was 20% for no prophylactic lateral neck dissection and 39% for prophylactic lateral neck dissection (P = .46). Most recurrences were locoregional recurrence, 7.6% for no prophylactic lateral neck dissection versus 22% for prophylactic lateral neck dissection (P = .08), half of it being to the lateral neck in both groups. A total of 7 patients from the no prophylactic lateral neck dissection group required treatment for recurrences versus 4 patients in prophylactic lateral neck dissection group (P = .57). Overall survival at 5 years was similar, 43% the no prophylactic lateral neck dissection group and 31% for prophylactic lateral neck dissection group (P = .52).

CONCLUSION

Lateral neck dissection has no effect in decreasing locoregional or overall recurrences in medullary thyroid cancer and has no effect in overall survival when performed prophylactically at index surgical intervention.

Stimulation of Caveolin-1 Signaling Improves Arteriovenous Fistula Patency

Objective- Arteriovenous fistulae (AVF) are the most common access created for hemodialysis; however, many AVF fail to mature and require repeated intervention, suggesting a need to improve AVF maturation. Eph-B4 (ephrin type-B receptor 4) is the embryonic venous determinant that is functional in adult veins and can regulate AVF maturation. Cav-1 (caveolin-1) is the major scaffolding protein of caveolae-a distinct microdomain that serves as a mechanosensor at the endothelial cell membrane. We hypothesized that Cav-1 function is critical for Eph-B4-mediated AVF maturation. Approach and Results- In a mouse aortocaval fistula model, both Cav-1 mRNA and protein were increased in the AVF compared with control veins. Cav-1 KO (knockout) mice showed increased fistula wall thickening ( P=0.0005) and outward remodeling ( P<0.0001), with increased eNOS (endothelial NO synthase) activity compared with WT (wild type) mice. Ephrin-B2/Fc inhibited AVF outward remodeling in WT mice but not in Cav-1 KO mice and was maintained in Cav-1 RC (Cav-1 endothelial reconstituted) mice (WT, P=0.0001; Cav-1 KO, P=0.7552; Cav-1 RC, P=0.0002). Cavtratin-a Cav-1 scaffolding domain peptide-decreased AVF wall thickness in WT mice and in Eph-B4 het mice compared with vehicle alone (WT, P=0.0235; Eph-B4 het, P=0.0431); cavtratin also increased AVF patency (day 42) in WT mice ( P=0.0275). Conclusions- Endothelial Cav-1 mediates Eph-B4-mediated AVF maturation. The Eph-B4-Cav-1 axis regulates adaptive remodeling during venous adaptation to the fistula environment. Manipulation of Cav-1 function may be a translational strategy to enhance AVF patency.

Eph-B4 regulates adaptive venous remodeling to improve arteriovenous fistula patency

Low rates of arteriovenous fistula (AVF) maturation prevent optimal fistula use for hemodialysis; however, the mechanism of venous remodeling in the fistula environment is not well understood. We hypothesized that the embryonic venous determinant Eph-B4 mediates AVF maturation. In human AVF and a mouse aortocaval fistula model, Eph-B4 protein expression increased in the fistula vein; expression of the arterial determinant Ephrin-B2 also increased. Stimulation of Eph-B-mediated signaling with Ephrin-B2/Fc showed improved fistula patency with less wall thickness. Mutagenesis studies showed that tyrosine-774 is critical for Eph-B4 signaling and administration of inactive Eph-B4-Y774F increased fistula wall thickness. Akt1 expression also increased in AVF; Akt1 knockout mice showed reduced fistula diameter and wall thickness. In Akt1 knockout mice, stimulation of Eph-B signaling with Ephrin-B2/Fc showed no effect on remodeling. These results show that AVF maturation is associated with acquisition of dual arteriovenous identity; increased Eph-B activity improves AVF patency. Inhibition of Akt1 function abolishes Eph-B-mediated venous remodeling suggesting that Eph-B4 regulates AVF venous adaptation through an Akt1-mediated mechanism.

CD44 Promotes Inflammation and Extracellular Matrix Production During Arteriovenous Fistula Maturation

OBJECTIVE

Arteriovenous fistulae (AVF) remain the optimal conduit for hemodialysis access but continue to demonstrate poor patency and poor rates of maturation. We hypothesized that CD44, a widely expressed cellular adhesion molecule that serves as a major receptor for extracellular matrix components, promotes wall thickening and extracellular matrix deposition during AVF maturation.

APPROACH AND RESULTS

AVF were created via needle puncture in wild-type C57BL/6J and CD44 knockout mice. CD44 mRNA and protein expression was increased in wild-type AVF. CD44 knockout mice showed no increase in AVF wall thickness (8.9 versus 26.8 μm; P=0.0114), collagen density, and hyaluronic acid density, but similar elastin density when compared with control AVF. CD44 knockout mice also showed no increase in vascular cell adhesion molecule-1 expression, intercellular adhesion molecule-1 expression, and monocyte chemoattractant protein-1 expression in the AVF compared with controls; there were also no increased M2 macrophage markers (transglutaminase-2: 81.5-fold, P=0.0015; interleukin-10: 7.6-fold, P=0.0450) in CD44 knockout mice. Delivery of monocyte chemoattractant protein-1 to CD44 knockout mice rescued the phenotype with thicker AVF walls (27.2 versus 14.7 μm; P=0.0306), increased collagen density (2.4-fold; P=0.0432), and increased number of M2 macrophages (2.1-fold; P=0.0335).

CONCLUSIONS

CD44 promotes accumulation of M2 macrophages, extracellular matrix deposition, and wall thickening during AVF maturation. These data show the association of M2 macrophages with wall thickening during AVF maturation and suggest that enhancing CD44 activity may be a strategy to increase AVF maturation.

Patch Angioplasty in the Rat Aorta or Inferior Vena Cava

Pericardial patches are commonly used in vascular surgery to close vessels. To facilitate studies of the neointimal hyperplasia that forms on the patch, we developed a rat model of patch angioplasty that can be used in either a vein or an artery, creating a patch venoplasty or a patch arterioplasty, respectively. Technical aspects of this model are discussed. The infra-renal IVC or aorta are dissected and then clamped proximally and distally. A 3 mm venotomy or arteriotomy is performed in the infrarenal inferior vena cava or aorta of 6 to 8 week-old Wistar rats. A bovine pericardial patch (3 mm x 1.5 mm x 0.6 mm) is then used to close the site using a 10-0 nylon suture. Compared to arterial patches, venous patches show increased neointimal thickness on postoperative day 7. This novel model of pericardial patch angioplasty can be used to examine neointimal hyperplasia on vascular biomaterials, as well as to compare the differences between the arterial and venous environments.

Pericardial patch venoplasty heals via attraction of venous progenitor cells

Pericardial patches are commonly used during cardiovascular surgery to close blood vessels. In arteries, patches accumulate arterial progenitor cells; we hypothesized that venous patches would accumulate venous progenitor cells, in the absence of arterial pressure. We developed a novel rat inferior vena cava (IVC) venotomy model and repaired it with a pericardial patch. Cells infiltrated the patch to form a thick neointima by day 7; some cells were CD34⁺/VEGFR2⁺ and CD31⁺/Eph‐B4⁺ consistent with development of venous identity in the healing patch. Compared to arterial patches, the venous patches had increased neointimal thickness at day 7 without any pseudoaneurysms. Addition of an arteriovenous fistula (AVF) to increase blood flow on the patch resulted in reduced patch neointimal thickness and proliferation, but neointimal thickness was not reversible with AVF ligation. These results show that rat patch venoplasty is a novel model of aggressive venous neointimal hyperplasia.

Future research directions to improve fistula maturation and reduce access failure

With the increasing prevalence of end-stage renal disease, there is a growing need for hemodialysis. Arteriovenous fistulae (AVF) are the preferred type of vascular access for hemodialysis, but maturation and failure continue to present significant barriers to successful fistula use. AVF maturation integrates outward remodeling with vessel wall thickening in response to drastic hemodynamic changes in the setting of uremia, systemic inflammation, oxidative stress, and pre-existent vascular pathology. AVF can fail due to both failure to mature adequately to support hemodialysis and development of neointimal hyperplasia that narrows the AVF lumen, typically near the fistula anastomosis. Failure due to neointimal hyperplasia involves vascular cell activation and migration and extracellular matrix remodeling with complex interactions of growth factors, adhesion molecules, inflammatory mediators, and chemokines, all of which result in maladaptive remodeling. Different strategies have been proposed to prevent and treat AVF failure based on current understanding of the modes and pathology of access failure; these approaches range from appropriate patient selection and use of alternative surgical strategies for fistula creation, to the use of novel interventional techniques or drugs to treat failing fistulae. Effective treatments to prevent or treat AVF failure require a multidisciplinary approach involving nephrologists, vascular surgeons, and interventional radiologists, careful patient selection, and the use of tailored systemic or localized interventions to improve patient-specific outcomes. This review provides contemporary information on the underlying mechanisms of AVF maturation and failure and discusses the broad spectrum of options that can be tailored for specific therapy.

Abstract 172: Arteriovenous Fistula Adaptation Requires Caveolin1 Signaling

Background: Arteriovenous fistula (AVF) is the preferred access for hemodialysis. However, many AVFs fail to mature and require intervention, showing a need to improve AVF maturation. Caveolin1 (Cav1) is the major scaffolding protein of caveolae, a distinct microdomain that serves as a flow activated mechanosensor at the membrane of endothelial cells. We have previously shown that stimulation of embryonic venous determinant EphB4 associates with Cav1, mediating vessel remodeling in the murine vein graft model. Since Cav1 is a mechanism of EphB4 mediated vein graft adaptation, we examined the role of Cav1 in mediating AVF maturation, a different and distinct hemodynamic and molecular conditions from vein graft. We hypothesized that Cav1 function is critical for AVF maturation.

Methods: We used a mouse aortocaval fistula model; the venous AVF limb and control (sham) inferior vena cava of wild type (WT) C57BL/6 mice were analyzed and compared for Cav1 expression. Vessel remodeling was assessed in WT and Cav1 knockout (KO) mice by serial ultrasound measurements of the IVC/AVF diameter. AVF were harvested at day 21 and examined with histology; IVC wall thickness was measured using computerized morphometry.

Results: Both Cav1 mRNA and protein were increased in the fistula veins compared to control veins (Figure A; mRNA: *p=0.019, ANOVA, n=8; protein: *p=0.005, t-test, n=5). Cav1 KO mice had increased fistula vein diameter compared with WT mice (Figure B; *p<0.0001, ANOVA, n=7-10). The fistula vein wall thickness was increased in Cav1 KO mice as compared with WT mice (Figure B; 15.6 vs 30.9μm, *p=0.0005, t-test, n=7, bar 50μm).

Conclusions: Cav1 expression is increased during AVF maturation, and loss of Cav1 leads to increased fistula vein diameter and wall thickness, similar to the function of Cav1 during vein graft adaptation. These results suggest that Cav1 is a regulator of AVF maturation and manipulation of Cav1 function may enhance venous adaptation to the arterial environment.

Delivery of mesenchymal stem cells in biomimetic engineered scaffolds promotes healing of diabetic ulcers

AIM

We hypothesized that delivery of mesenchymal stem cells (MSCs) in a biomimetic collagen scaffold improves wound healing in a diabetic mouse model.

MATERIALS & METHODS

Rolled collagen scaffolds containing MSCs were implanted or applied topically to diabetic C57BL/6 mice with excisional wounds.

RESULTS

Rolled scaffolds were hypoxic, inducing MSC synthesis and secretion of VEGF. Diabetic mice with wounds treated with rolled scaffolds containing MSCs showed increased healing compared with controls. Histologic examination showed increased cellular proliferation, increased VEGF expression and capillary density, and increased numbers of macrophages, fibroblasts and smooth muscle cells. Addition of laminin to the collagen scaffold enhanced these effects.

CONCLUSION

Activated MSCs delivered in a biomimetic-collagen scaffold enhanced wound healing in a translationally relevant diabetic mouse model.

Membrane-mediated regulation of vascular identity

Vascular diseases span diverse pathology, but frequently arise from aberrant signaling attributed to specific membrane-associated molecules, particularly the Eph-ephrin family. Originally recognized as markers of embryonic vessel identity, Eph receptors and their membrane-associated ligands, ephrins, are now known to have a range of vital functions in vascular physiology. Interactions of Ephs with ephrins at cell-to-cell interfaces promote a variety of cellular responses such as repulsion, adhesion, attraction, and migration, and frequently occur during organ development, including vessel formation. Elaborate coordination of Eph- and ephrin-related signaling among different cell populations is required for proper formation of the embryonic vessel network. There is growing evidence supporting the idea that Eph and ephrin proteins also have postnatal interactions with a number of other membrane-associated signal transduction pathways, coordinating translation of environmental signals into cells. This article provides an overview of membrane-bound signaling mechanisms that define vascular identity in both the embryo and the adult, focusing on Eph- and ephrin-related signaling. We also discuss the role and clinical significance of this signaling system in normal organ development, neoplasms, and vascular pathologies.

Eph-B4 mediates vein graft adaptation by regulation of endothelial nitric oxide synthase

OBJECTIVE

Vein graft adaptation is characterized by loss of expression of the tyrosine kinase receptor Eph-B4, the embryonic determinant of venous identity, without increased expression of its ligand ephrin-B2, the embryonic determinant of arterial identity. Endothelial nitric oxide synthase (eNOS) is an important mediator of vessel remodeling. We hypothesized that the mechanism of action of Eph-B4 during vein graft adaptation might be through regulation of downstream eNOS activity.

METHODS

Mouse lung endothelial cells were stimulated with ephrin-B2/Fc, without and with preclustering, without and with the eNOS inhibitor N_ω-nitro-l-arginine methyl ester hydrochloride or the Eph-B4 inhibitor NVP-BHG712, and assessed by Western blot and immunofluorescence for eNOS and Eph-B4 phosphorylation. Nitric oxide (NO) production was assessed using an NO-specific chemiluminescence analyzer. Cell migration was assessed using a Transwell assay. Human and mouse vein graft specimens were examined for eNOS activity by Western blot, and vessel remodeling was assessed in vein grafts in wild-type or eNOS knockout mice.

RESULTS

Ephrin-B2/Fc stimulated both Eph-B4 and eNOS phosphorylation in a bimodal temporal distribution (n = 4; P < .05), with preclustered ephrin-B2/Fc causing prolonged peak Eph-B4 and eNOS phosphorylation as well as altered subcellular localization (n = 4; P < .05). Ephrin-B2/Fc increased NO release (n = 3; P < .01) as well as increased endothelial cell migration (n = 6; P < .05) in an eNOS-dependent fashion. Both human and mouse vein grafts showed increased eNOS phosphorylation compared with normal veins (n = 3; P < .05). Vein grafts from eNOS knockout mice showed less dilation and less wall thickening compared with wild-type vein grafts (n = 7; P < .05).

CONCLUSIONS

eNOS is a mediator of vein graft adaptation to the arterial environment. Eph-B4 stimulates eNOS phosphorylation in vitro and may mediate vein graft adaptation by regulation of eNOS activity in vivo.

Disturbed shear stress reduces Klf2 expression in arterial-venous fistulae in vivo

Laminar shear stress (SS) induces an antiproliferative and anti-inflammatory endothelial phenotype and increases Klf2 expression. We altered the diameter of an arteriovenous fistula (AVF) in the mouse model to determine whether increased fistula diameter produces disturbed SS in vivo and if acutely increased disturbed SS results in decreased Klf2 expression. The mouse aortocaval fistula model was performed with 22, 25, or 28 gauge needles to puncture the aorta and the inferior vena cava. Duplex ultrasound was used to examine the AVF and its arterial inflow and venous outflow, and SS was calculated. Arterial samples were examined with western blot, immunohistochemistry, and immunofluorescence analysis for proteins and qPCR for RNA. Mice with larger diameter fistulae had diminished survival but increased AVF patency. Increased SS magnitudes and range of frequencies were directly proportional to the needle diameter in the arterial limb proximal to the fistula but not in the venous limb distal to the fistula, with 22-gauge needles producing the most disturbed SS in vivo. Klf2 mRNA and protein expression was diminished in the artery proximal to the fistula in proportion to increasing SS. Increased fistula diameter produces increased SS magnitude and frequency, consistent with disturbed SS in vivo. Disturbed SS is associated with decreased mRNA and protein expression of Klf2. Disturbed SS and reduced Klf2 expression near the fistula are potential therapeutic targets to improve AVF maturation.

Thermodynamics and folding pathway of tetraloop receptor-mediated RNA helical packing

Little is known about the thermodynamic forces that drive the folding pathways of higher-order RNA structure. In this study, we employ calorimetric [isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC)] and spectroscopic (NMR and UV) methods to characterize the thermodynamics of the GAAA tetraloop-receptor interaction, utilizing a previously described bivalent construct. ITC studies indicate that the bivalent interaction is enthalpy driven and highly stable, with a binding constant (K(obs)) of 5.5x10(6) M(-1) and enthalpy (DeltaH(obs)(o)) of -33.8 kcal/mol at 45 degrees C in 20 mM KCl and 2 mM MgCl(2). Thus, we derive the DeltaH(obs)(o) for a single tetraloop-receptor interaction to be -16.9 kcal/mol at these conditions. UV absorbance data indicate that an increase in base stacking quality contributes to the enthalpy of complex formation. These highly favorable thermodynamics are consistent with the known critical role for the tetraloop-receptor motif in the folding of large RNAs. Additionally, a significant heat capacity change (DeltaC(p,obs)(o)) of -0.24 kcal mol(-1) K(-1) was determined by ITC. DSC and UV-monitored thermal denaturation experiments indicate that the bivalent tetraloop-receptor construct follows a minimally five-state unfolding pathway and suggest the observed DeltaC(p,obs)(o) for the interaction results from a temperature-dependent unbound receptor RNA structure.

Role of metal ions in the tetraloop-receptor complex as analyzed by NMR

Metal ions are critical for the proper folding of RNA, and the GAAA tetraloop-receptor is necessary for the optimal folding and function of many RNAs. We have used NMR to investigate the role of metal ions in the structure of the tetraloop-receptor in solution. The NMR data indicate native tertiary structure is formed under a wide range of ionic conditions. The lack of conformational adaptation in response to very different ionic conditions argues against a structural role for divalent ions. Nuclear Overhauser effects to cobalt hexammine and paramagnetic relaxation enhancement induced by manganese ions were used to determine the NMR structures of the tetraloop receptor in association with metal ions, providing the first atomic-level view of these interactions in the solution state. Five manganese and two cobalt hexammine ions could be localized to the RNA surface. The locations of the associated metal ions are similar, but not identical to, those of previously determined crystal structures. The sites of association are in general agreement with nonlinear Poisson-Boltzmann calculations of the electrostatic surface, emphasizing the general importance of diffusely associated ions in RNA tertiary structure.

Experimental infections of the musculoskeletal system: evaluation with MR imaging and Tc-99m MDP and Ga-67 scintigraphy

Acute osteomyelitis, soft-tissue infection, or both were experimentally produced in 38 New Zealand white rabbits, and three-phase technetium-99m methylene diphosphonate, gallium-67, and magnetic resonance (MR) images were obtained 7 or 14 days after infection. There was no significant difference between radionuclide studies and MR images in the detection of osteomyelitis, but MR imaging was significantly more sensitive (100% vs. 69%; P less than .01) in the detection of soft-tissue infection. In addition, cellulitis could not be distinguished from soft-tissue abscess on radionuclide studies, whereas MR imaging was 92% accurate in depicting soft-tissue abscesses. Further research is necessary to determine how to relate these findings to true human clinical situations.