Biomedical subjects

Niren Angle

Publications and source records attributed to Niren Angle.

12 recordsLinked to original sources

PubMed2006

A novel fluorescence-based cellular permeability assay.

Vascular permeability is a pathologic process in many disease states ranging from metastatic progression of malignancies to ischemia-reperfusion injury. In order to more precisely study tissue, and more specifically cell layer permeability, our goal was to create a fluorescence-based assay which could quantify permeability without radioactivity or electrical impedance measurements. Human aortic endothelial cells were grown in monolayer culture on Costar-Transwell clear polyester membrane 6-well cell culture inserts. After monolayer integrity was confirmed, vascular endothelial growth factor (VEGF(165)) at varying concentrations with a fixed concentration of yellow-green fluorescent 0.04 microm carboxylate-modified FluoSpheres microspheres were placed in the luminal chamber and incubated for 24 h. When stimulated with VEGF(165) at 20, 40, 80, and 100 ng/ml, this assay system was able to detect increases in trans-layer flux of 8.2+/-2.4%, 16.0+/-3.7%, 41.5+/-4.9%, and 58.6+/-10.1% for each concentration, respectively. This represents the first fluorescence-based permeability assay with the sensitivity to detect changes in the permeability of a cell layer to fluid flux independent of protein flux; as well as being simpler and safer than previous radioactive-and impedance-based permeability assays. With the application of this in vitro assay to a variety of pathologic conditions, both the dynamics and physiology relating to cellular permeability can be more fully investigated.

Biophysics↗

PubMed2005

VEGF inhibits PDGF-stimulated calcium signaling independent of phospholipase C and protein kinase C.

INTRODUCTION: Despite advances in both open and endovascular techniques for treatment of arterial occlusive disease, restenosis because of neointimal hyperplasia continues to be a major cause of graft failure and restenosis. This phenomenon has been attributed to vascular smooth muscle cell (VSMC) activation by several potent mitogens including platelet derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) released at the site of injury. PDGF is known to stimulate calcium influx in VSMC that has been shown to be critical for VSMC migration and proliferation. We have previously shown that VEGF inhibits PDGF-stimulated VSMC proliferation. The objective of this set of experiments was to investigate whether VEGF modulated PDGF-stimulated Ca2+ influx in VSMC. MATERIALS AND METHODS: Primary cultured human aortic SMC were grown to subconfluency and assigned to the following groups: no stimulation, stimulation with PDGF-BB (20 ng/ml), stimulation with VEGF165 (40 ng/ml), or a combination of PDGF-BB + VEGF165. Ca2+ influx was measured using a Fura-2 fluorescence assay. The intracellular Ca2+ fraction was assayed with the Fura-2 assay by using Ca2+-free media. Phospholipase Cgamma1 (PLCgamma1), protein kinase C (PKC), and Akt phosphorylation was assessed with standard immunoblotting techniques at 1, 5, and 10 min time points. Ca2+-calmodulin kinase II (CaMKII) activity was extrapolated from the phosphorylation of Phospholamban B (PLB), a well-known protein substrate, at 1, 5, and 10 min time points. RESULTS: PDGF stimulation resulted in a 328 +/- 9 nm total calcium influx in VSMC. The combination of VEGF + PDGF resulted in a 273 +/- 21 nm total calcium influx, an amount significantly less than with PDGF alone (P < 0.04). PDGF stimulation resulted in a 72 +/- 35 nm intracellular calcium release. The addition of VEGF to PDGF resulted in an intracellular calcium release of only 15 +/- 11 nm, a significant decrease compared to PDGF alone (P < 0.01). The phosphorylation of PLCgamma1, PKC, and Akt was equivalent at 1, 5, and 10 min between the PDGF and the PDGF + VEGF treatment groups. There was an increase in CaMKII activity at 1 and 5 min time points in both the PDGF and PDGF + VEGF treatment groups suggesting that extracellular calcium influx is sufficient for CaMKII activation. CONCLUSION: VEGF inhibits PDGF-stimulated total calcium influx and, in particular, PDGF-stimulated intracellular calcium release in VSMC. The equivalent phosphorylation of PLCgamma1, PKC, and Akt suggests that the inhibitory mechanism by VEGF on calcium influx occurs downstream of these proximal mediators. The inhibition of intracellular calcium release did not inhibit CaMKII activity. VEGF may play an important role in modulating PDGF induced VSMC proliferation by specifically inhibiting intracellular calcium release in response to PDGF.

Arterial Occlusive Diseases↗

PubMed2005

The two-stage brachial artery-brachial vein autogenous fistula for hemodialysis: an alternative autogenous option for hemodialysis access.

The optimal dialysis access for the patient with chronic renal failure is considered to be an autogenous fistula; this is reflected in the recommendations of the National Kidney Foundation-Disease Outcomes Quality Initiatives (NKF-DOQI). If adequate superficial veins at the wrist or the forearm are not available, the next option is usually a prosthetic arteriovenous graft. In this case series, we describe our experience with an autogenous fistula constructed using the brachial vein. There were 20 patients over a 14-month period who were operated on for dialysis access. In these patients, no adequate superficial veins were found at operation. Instead of using a prosthetic graft, we performed a brachial artery-brachial vein fistula in two stages. The first stage involved a forearm anastomosis and then subsequently, weeks later, this fistula was "superficialized." Twenty patients underwent a brachial artery-brachial vein fistula. Of these patients, all had successful maturation of their fistula and after a minimum waiting period of 12 weeks for maturation; all but one were able to be successfully dialyzed through their fistula. One patient developed arm swelling due to previously placed subclavian vein pacemaker wires. None of the other patients developed arm swelling or vascular steal. The brachial artery-brachial vein fistula is a feasible option for hemodialysis access and we suggest that this option be considered before a prosthetic arteriovenous graft is inserted. Arm swelling and steal have not been a problem, and all patients have been able to have full dialysis through the fistula after appropriate maturation times.

Adult↗

PubMed2005

Vascular endothelial growth factor stimulates a novel calcium-signaling pathway in vascular smooth muscle cells.

BACKGROUND: Vascular endothelial growth factor (VEGF) is a potent vascular mitogen that selectively stimulates vascular smooth muscle cell (VSMC) migration through an unknown mechanism while having no effect on VSMC proliferation. It is known that VSMC migration and proliferation are dependent on the second messenger Ca2+ and, in particular, mitogen-stimulated Ca2+ influx. We hypothesized that the selective effect of VEGF on VSMC migration versus proliferation was a result of differential VEGF-stimulated Ca2+ signaling pathways. METHODS: Primary cultured human aortic smooth muscle cells (VSMCs) were grown to subconfluency and assigned to the following experimental groups: no stimulation, stimulation with platelet-derived growth factor-BB (PDGF-BB) (20 ng/mL) as positive control, and stimulation with VEGF165 (40 ng/mL). Total increase in [Ca2+]cyt and intracellular calcium release was quantified with the use of a fura-2 fluorescence assay. Assays for the following receptors VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1) and PDGFR-beta were performed by immunoprecipitation, while PLCgamma1, Akt 1/2, and phospholamban B phosphorylation were assessed with Western immunoblotting. RESULTS: VSMCs stimulated with VEGF165 exhibited no intracellular Ca2+ release, compared with a 75 +/- 30 nmol/L intracellular calcium release after PDGF-BB stimulation, (P < .02) VEGF165-stimulated VSMCs in Ca2+-containing media exhibited 192 +/- 26 nmol/L increase in [Ca2+]cyt, compared with 354 +/- 54 nmol/L increase after PDGF-BB stimulation (P < .02). VEGF165 did not phosphorylate PLCgamma1 after 1, 5, or 10 minutes of treatment. VEGF165 treatment did not result in PI3-K/Akt activation at 1-, 5-, or 10-minute time points. Calmodulin-dependent kinase II (CaMKII) was activated by both VEGF165 and PDGF-BB after 1 and 5 minutes of stimulation. The presence of the receptors VEGFR-1, VEGFR-2, and PDGFR-beta was confirmed in all experimental groups. CONCLUSIONS: VEGF induces extracellular calcium influx but no intracellular calcium release in VSMCs. This lack of intracellular Ca2+ release stems from the inability of VEGF165 to activate the PLCgamma1 cascade and IP3 receptor-mediated Ca2+ release. The lack of PI3-K/Akt activation at these time points indicates a novel extracellular Ca2+ influx pathway sufficient to activate CaMKII. A paradigm relating extracellular Ca2+ influx to CaMKII activation and migration is suggested and may account for the selective effects of VEGF on VSMC migration.

Aorta↗

PubMed2005

What are the skills that prepare vascular surgeons for carotid stenting?

Although it has been clearly established that in certain groups of patients, such as in patients with symptomatic high-grade carotid stenosis and in selected asymptomatic patients with high-grade stenosis, carotid endarterectomy offers significant protection from stroke compared with medical therapy, the role of carotid stenting in this patients versus carotid endarterectomy is undergoing a rapid evolution. The definitive evidence awaits the results of ongoing prospective, randomized trials such as CREST and others, but it is clear that carotid stenting will increasingly occupy a significant role in the therapy of carotid bifurcation disease. In that context, vascular surgeons, traditionally the experts on the management of this condition, face the specter of other disciplines intervening in its treatment. In addition, if vascular surgeons do not acquire the skills and the expertise necessary to perform carotid stenting, it is self-evident that they run the risk of being spectators rather retaining the mantle of expert in the management of carotid bifurcation disease. As such, it is the duty of vascular surgeons to acquire the skills with which to retain their rightful place in its management and treatment. The purpose of this article is to describe the skills necessary to become competent in the endovascular management of carotid disease, offer some thoughts and strategy by which one can gain experience and develop an armamentarium of skills necessary to perform carotid stenting, and offer a comprehensive array of options of management and treatment to the patient with carotid disease.

Angiography↗

PubMed2004

Open versus endovascular repair of abdominal aortic aneurysms: what does each really cost?

Endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) has emerged as an alternative to open repair (OR). The aim of this study was to compare the clinical outcomes and specific costs of these procedures since commercialization.A retrospective analysis of 119 consecutive infrarenal AAA repaired via an EVAR or an OR between July 2000 and September 2001 was performed. Patient charts were reviewed. Diagnostic-related group (DRG) classification and payer mix were identified. The hospital cost accounting system was accessed to obtain actual variable direct cost (AVDC) for the two groups. Percentages of the mean AVDC for the two groups were compared in the following cost categories: graft, operating room, radiology procedures and supplies, pharmacy, respiratory therapy, clinical laboratories, surgical floor, and monitored unit. Hospital profit margins were determined. Fifty-five patients underwent EVAR and 64 patients underwent OR. Mean aneurysm size was 5.5A cm (EVAR) and 6.1A cm (OR). Mean intensive care unit (ICU) stay was 0.09 days for EVAR vs. 3.5 days for OR ( p < 0.05). Mean length of stay (LOS) was 1.96 days for EVAR vs. 7.3 days for OR ( p < 0.05). Reimbursement was based on DRG 110, 47.3% in the EVAR and 79.7% in the OR group ( p < 0.05), and DRG 111, 50.9% in the EVAR group and 12.5% in the OR group ( p < 0.05). The payer mix showed no significant differences between the two groups. Mean AVDC for EVAR was 1.74 times that of OR. Significant differences in the distribution of costs were found in the following: graft costs (58% vs. 6.3%, p < 0.05), radiology procedures and supplies (3.9% vs. 0.1%, p < 0.05), pharmacy (1.9% vs. 10.5%, p < 0.05), and monitored unit (7.3% vs. 24.65%, p < 0.05) comparing EVAR vs. OR, respectively. Median cost of an endovascular graft was 22.4 times that of the standard graft for OR. Average hospital profit margins for an EVAR case was 49.5% vs. 88.6% for OR. Despite significant differences in monitored unit utilization, pharmacy services, and respiratory therapy services by the OR group, the cost of EVAR is appreciably more expensive. Furthermore, increased DRG reimbursement, and decreased ICU use and LOS do not compensate for the cost of EVAR. The main cost of EVAR is the cost of the graft itself. Hospital profit margins are acceptable with both the EVAR and OR procedures at this time; however, with proposed reductions in reimbursement, the ability to cover the cost of this new technology may be threatened.

Aged↗

PubMed2004

Cost analysis of carotid endarterectomy: is age a factor?

Carotid endarterectomy (CEA) has been demonstrated to be safe and effective in elderly patients. Our aim was to analyze and compare outcome and cost of CEA in both elderly and younger patient groups. A total of 125 consecutive patients who underwent CEA were examined retrospectively and grouped according to age (<80 years old, n = 95; and >or=80 years old, n = 30). The actual total costs and itemized costs were analyzed, and diagnosis-related group (DRG) code payor mix were identified. Patient demographics and risk factors were similar except for a greater incidence of coronary artery disease (CAD) in the >or=80 group than in these <80 (43.3% vs. 21.1%, p < 0.05). Patients had similar minor complication rates; however, the >or=80 group had higher perioperative major complications (16.7% vs. 1.1%, p < 0.01). There were no deaths and there was one perioperative stroke, which occurred in the <80 group. Mean length of stay (LOS), intensive care unit (ICU) LOS, and ICU admissions were greater in the >or=80 group. Cost figures were normalized to a base value of 10 US dollars to maintain proprietary data. Actual total costs of CEA were 131.50 US dollars for the >or=80 group and $100 for the <80 group (p < 0.001). Significant cost differences were found in ICU room costs, and costs for clinical laboratory, radiology imaging, other specialty consults, operating room, and ancillary services in the >or=80 group compared with the <80 group. These results show that the cost of CEA in the elderly is significantly greater than that for younger patients. This difference can be attributed to a greater number of major complications in the more elderly group, who require increased ICU stay, and thus require more clinical laboratory, radiology imaging, and specialty consult service resources. Consideration should be given for a DRG modifier code to increase hospital reimbursement for increased associated costs in elderly patients undergoing CEA.

Adult↗

PubMed2003

Vascular endothelial growth factor inhibits mitogen-induced vascular smooth muscle cell proliferation.

INTRODUCTION: Delivery of vascular endothelial growth factor (VEGF) protein or gene transfer has been shown to accelerate re-endothelialization and attenuate neointimal hyperplasia in various arterial injury models, including balloon injury, stent implantation, and vein grafts. In addition to stimulating re-endothelialization, we hypothesize that VEGF has further vascular protective functions to prevent neointimal hyperplasia by directly inhibiting mitogen-induced proliferation of vascular smooth muscle cells (VSMCs) via the mitogen-activated protein kinase pathway. MATERIALS AND METHODS: Human aortic VSMCs were seeded and serum starved for 24 h. The cells were then stimulated with a mitogen, recombinant human platelet derived growth factor at 20 ng/mL together with 0, 10, 20, 30, 40, 50 ng/mL recombinant human VEGF. A proliferation assay was used to quantitate bromodeoxyuridine uptake into newly synthesized DNA. Western immunoassay was used to quantify extracellular signal-regulated kinase (ERK) 2 protein and phosphorylation of retinoblastoma and ERK 1/2 protein. RESULTS: VEGF inhibited bromodeoxyuridine incorporation into mitogen-induced VSMC in a dose-dependent manner, reaching statistical significance at concentrations of 30 (P < 0.05), 40 (P < 0.05), and 50 ng/mL (P < 0.01). Densitometry of western immunoblots revealed an inhibition of phosphorylation of retinoblastoma at VEGF concentrations of 40 and 50 ng/mL and ERK 1/2 phosphorylation at concentrations of 30, 40 and 50 ng/mL. CONCLUSION: In addition to stimulating re-endothelialization, VEGF appears to have a vascular protective function by directly inhibiting VSMC proliferation. This effect occurs in the absence of endothelial cells and via the mitogen-activated protein kinase pathway. VEGF may serve as an important modulator of mitogen-induced VSMC proliferation after vascular injury.

Aorta↗

PubMed2002

The evolution of the axillofemoral bypass over two decades.

To determine if the indications and numbers of the axillofemoral bypass have changed, a retrospective analysis was performed of all patients undergoing axillofemoral bypass over the past two decades. Group A (1980-89) and group B (1990-99) were compared using demographics, comorbid illness, perioperative outcomes, and indications for operation. There were 33 extraanatomic bypasses performed in group A and 24 extraanatomic bypasses in group B. The average age in both group A and group B was 69 years. Males comprised a higher percentage in group B (75%) than in group A (55%). The percentage of smokers was roughly equivalent (group A 76%, group B 71%). Coronary artery disease was more prevalent in group A (85%) than in group B (63%). Diabetes mellitus was also more common in group A (33%) than in group B (21%). All of the grafts in group B were composed of PTFE and there were 2 early (30 day) failures (6%). There were no perioperative deaths, strokes, or myocardial infarctions. At our institution, the axillofemoral bypass is now reserved almost exclusively for the treatment of graft infections and rarely for primary limb ischemia. This evolution is a reflection of the increase in interventional techniques used to improve inflow in high-risk patients who require revascularization.

Adult↗

PubMed2002

A comparison of antegrade and retrograde mesenteric bypass.

Mesenteric artery bypass originating from the supraceliac aorta (antegrade bypass) has been the standard orientation of visceral artery bypass grafts. Retrograde bypass, in which the bypass originates from the iliac arteries, has not been as widely accepted. The purpose of our study was to compare the results of these two types of bypass in a similar population. We retrospectively reviewed the records of patients undergoing mesenteric artery bypass at two tertiary care medical centers (UCLA Medical Center, Beth Israel Deaconess Medical Center). Between February 1992 and January 2001, 37 patients underwent 39 mesenteric bypass procedures. The choice of bypass orientation (antegrade versus retrograde) was determined by the individual surgeon. Chart review, duplex ultrasonography, and/or telephone interviews were used to assess symptom-free survival. Actuarial analysis was completed using Kaplan-Meier survival estimates. From this assessment we were able to determine that symptom-free survival of patients undergoing retrograde mesenteric bypass is similar to that seen in antegrade bypass. Primary retrograde bypass is a valid option for patients undergoing mesenteric bypass.

Aged↗

PubMedDate not supplied

Mycotic aneurysm of the internal carotid artery--a case report.

Extracranial internal carotid artery (ICA) mycotic aneurysms are rare entities that may result in significant neurologic morbidity and mortality. Several operative techniques have been described in the literature for the management of this difficult condition. This case report describes a contained ruptured mycotic aneurysm of the extracranial ICA associated with Proteus mirabilis infection successfully treated by an end-to-end spatulated interposition saphenous vein graft.

Aged↗

PubMedDate not supplied

Occluded infrainguinal bypass graft: potential source of limb-threatening emboli.

Surgical bypass represents one of the chief treatment modalities for peripheral arterial occlusive disease. Despite improving techniques, graft occlusion accounts for the majority of these bypass failures. Once occluded, however, these grafts are thought to rarely pose a threat for future ischemic events. This report describes two patients with previously thrombosed grafts who subsequently presented with limb-threatening ischemia owing to peripheral embolization from the graft. Two patients with occluded grafts presented with ipsilateral limb-threatening acute ischemia. Both of these patients developed severe acute limb-threatening ischemia weeks to months after known graft thrombosis. Arteriography revealed peripheral embolization in each case. Both patients were operated on for disconnection of the thrombosed graft from the native circulation and have been free of recurrent symptoms. The occluded graft, although generally innocuous, can be a source of peripheral emboli, resulting in peripheral embolization and acute limb ischemia. Both patients in this report developed limb-threatening ischemia owing to embolization from the cul-de-sac of occluded prosthetic grafts. Due to the rarity of the condition and its associated morbidity and mortality, awareness and recognition of this phenomenon are critical. Operative disconnection is recommended if the embolism occurs downstream of the graft and no other embolic source can be identified.

Acute Disease↗