Simulation and in vivo experimentation predict AdamTS-A location of function during caudal visceral mesoderm migration in Drosophila.

BACKGROUND: Caudal visceral mesoderm (CVM) cells migrate as a loose collective along the trunk visceral mesoderm (TVM) and are surrounded by extracellular matrix (ECM). In this study, we examined how one extracellular protease, AdamTS-A, facilitates CVM migration. RESULTS: A comparison of mathematical simulation to experimental results suggests that location of AdamTS-A action in CVM cells is on the sides of the cell not in contact with the TVM, predominantly at the CVM-ECM interface. CVM migration from a top-down view showed CVM cells migrating along the outside of the TVM substrate in the absence of AdamTS-A. Moreover, overexpression of AdamTS-A resulted in similar, but milder, mis-migration of the CVM. These results contrast with the salivary gland where AdamTS-A is proposed to cleave connections at the trailing edge of migrating cells. Subcellular localization of GFP-tagged AdamTS-A suggests that this protease is not limited to functioning at the trailing edge of CVM cells. CONCLUSION: Using both in vivo experimentation and mathematical simulations, we demonstrated that AdamTS-A cleaves connections between CVM cells and the ECM on all sides not attached to the TVM. Clearly, AdamTS-A has a more expansive role around the entire cell in cleaving cell-ECM attachments in cells migrating as a loose collective.

Acute and subacute effects of irreversible electroporation on nerves: experimental study in a pig model.

PURPOSE: To evaluate whether irreversible electroporation (IRE) has the potential to damage nerves in a porcine model and to compare histopathologic findings after IRE with histopathologic findings after radiofrequency ablation (RFA). MATERIALS AND METHODS: This study was approved by the institutional animal care and use committee. Computed tomography (CT)-guided IRE of 11 porcine sciatic nerves was performed in nine pigs, and histopathologic analysis was performed on the day of ablation or 3, 6, or 14 days after ablation. In addition, acute RFA of six porcine sciatic nerves was performed in six pigs that were harvested on the day of ablation. All nerves and associated muscles and tissues were assessed for histopathologic findings consistent with athermal or thermal injury, respectively, such as axonal swelling, axonal fragmentation and loss, Wallerian degeneration, inflammatory infiltrates, Schwann cell proliferation, and coagulative necrosis. The percentage of fascicles affected was recorded. RESULTS: All nerves had an axonal injury. The percentage of affected nerve fascicles after IRE was 50%-100%. Axonal swelling and perineural inflammatory infiltrates were detectable at every time point after ablation. Axonal fragmentation and loss, macrophage infiltration, and Schwann cell proliferation were found 6 and 14 days after ablation. Distal Wallerian axonal degeneration was observed 14 days after ablation. The endoneurium and perineurium architecture remained intact in all cases. RFA specimens at the day of ablation revealed acute coagulative necrosis associated with intense basophilic staining of extracellular matrix, including collagen of the perineurium and epineurium consistent with thermal injury. CONCLUSION: IRE has the potential to damage nerves and may result in axonal swelling, fragmentation, and distal Wallerian degeneration. However, preservation of endoneurium architecture and proliferation of Schwann cells may suggest the potential for axonal regeneration. In contrast, RFA leads to thermal nerve damage, causing protein denaturation, and suggests a much lower potential for regeneration.

Percutaneous irreversible electroporation lung ablation: preliminary results in a porcine model.

OBJECTIVE: Irreversible electroporation (IRE) uses direct electrical pulses to create permanent "pores" in cell membranes to cause cell death. In contrast to conventional modalities, IRE has a nonthermal mechanism of action. Our objective was to study the histopathological and imaging features of IRE in normal swine lung. MATERIALS AND METHODS: Eleven female swine were studied for hyperacute (8 h), acute (24 h), subacute (96 h), and chronic (3 week) effects of IRE ablation in lung. Paired unipolar IRE applicators were placed under computed tomography (CT) guidance. Some applicators were deliberately positioned near bronchovascular structures. IRE pulse delivery was synchronized with the cardiac rhythm only when ablation was performed within 2 cm of the heart. Contrast-enhanced CT scan was performed immediately before and after IRE and at 1 and 3 weeks after IRE ablation. Representative tissue was stained with hematoxylin and eosin for histopathology. RESULTS: Twenty-five ablations were created: ten hyperacute, four acute, and three subacute ablations showed alveolar edema and necrosis with necrosis of bronchial, bronchiolar, and vascular epithelium. Bronchovascular architecture was maintained. Chronic ablations showed bronchiolitis obliterans and alveolar interstitial fibrosis. Immediate post-procedure CT images showed linear or patchy density along the applicator tract. At 1 week, there was consolidation that resolved partially or completely by 3 weeks. Pneumothorax requiring chest tube developed in two animals; no significant cardiac arrhythmias were noted. CONCLUSION: Our preliminary porcine study demonstrates the nonthermal and extracellular matrix sparing mechanism of action of IRE. IRE is a potential alternative to thermal ablative modalities.

Irreversible electroporation near the heart: ventricular arrhythmias can be prevented with ECG synchronization.

OBJECTIVE: Irreversible electroporation is a nonthermal ablative tool that uses direct electrical pulses to create irreversible membrane pores and cell death. The ablation zone is surrounded by a zone of reversibly increased permeability; either zone can cause cardiac arrhythmias. Our purpose was to establish a safety profile for the use of irreversible electroporation close to the heart. MATERIALS AND METHODS: The effect of unsynchronized and synchronized (with the R wave on ECG) irreversible electroporation in swine lung and myocardium was studied in 11 pigs. Twelve lead ECG recordings were analyzed by an electrophysiologist for the presence of arrhythmia. Ventricular arrhythmias were categorized as major events. Minor events included all other dysrhythmias or ECG changes. Cardiac and lung tissue was submitted for histopathologic analysis. Electrical field modeling was performed to predict the distance from the applicators over which cells show electroporation-induced increased permeability. RESULTS: At less than or equal to 1.7 cm from the heart, fatal (major) events occurred with all unsynchronized irreversible electroporation. No major and three minor events were seen with synchronized irreversible electroporation. At more than 1.7 cm from the heart, two minor events occurred with only unsynchronized irreversible electroporation. Electrical field modeling correlates well with the clinical results, revealing increased cell membrane permeability up to 1.7 cm away from the applicators. Complete lung ablation without intervening live cells was seen. No myocardial injury was seen. CONCLUSION: Unsynchronized irreversible electroporation close to the heart can cause fatal ventricular arrhythmias. Synchronizing irreversible electroporation pulse delivery with absolute refractory period avoids significant cardiac arrhythmias.

Renal tissue ablation with irreversible electroporation: preliminary results in a porcine model.

OBJECTIVES: To evaluate the histopathologic and computed tomography imaging features associated with irreversible electroporation (IRE) ablation performed in normal porcine kidneys. IRE is a nonthermal ablative tool that uses direct electrical pulses to create permanent "pores" in cell membranes and cell death. It does not affect the extracellular matrix. METHODS: Fifteen female swine were treated with IRE using acute (<24 hours), subacute (36 hours), and chronic (3 weeks) treatment settings. Unipolar IRE applicators were placed under CT guidance. The renal pelvis/calyx was included in 18 ablations. Imaging and histopathologic follow-up were performed. RESULTS: A total of 29 ablations (19 acute, 4 subacute, and 6 chronic) were created. Acute/subacute ablations showed complete cortical necrosis without intervening live cells. The pelvic epithelium was necrotic with urothelial sloughing; pelvic extracellular matrix was intact. Chronic ablations showed cortical fibrosis, regenerating renal pelvic epithelium and intact pelvic extracellular matrix. No thermal injury, renal pelvic, or blood vessel injury was seen. Immediate postprocedure CT imaging demonstrated a hypodense nonenhancing lesion that persisted at 1 week. Of the 6 chronic lesions, 4 showed complete resolution at 3 weeks on imaging. No collecting system damage was seen. CONCLUSIONS: This preliminary porcine study demonstrates the nonthermal and connective tissue sparing mechanism of action of IRE. These features may protect against collecting system damage after IRE ablation of renal tissue. IRE could therefore play an important role in ablation of centrally located renal tumors.