Geetha Jeyabalan

HMGB1 release induced by liver ischemia involves Toll-like receptor 4–dependent reactive oxygen species production and calcium-mediated signaling

Ischemic tissues require mechanisms to alert the immune system of impending cell damage. The nuclear protein high-mobility group box 1 (HMGB1) can activate inflammatory pathways when released from ischemic cells. We elucidate the mechanism by which HMGB1, one of the key alarm molecules released during liver ischemia/reperfusion (I/R), is mobilized in response to hypoxia. HMGB1 release from cultured hepatocytes was found to be an active process regulated by reactive oxygen species (ROS). Optimal production of ROS and subsequent HMGB1 release by hypoxic hepatocytes required intact Toll-like receptor (TLR) 4 signaling. To elucidate the downstream signaling pathways involved in hypoxia-induced HMGB1 release from hepatocytes, we examined the role of calcium signaling in this process. HMGB1 release induced by oxidative stress was markedly reduced by inhibition of calcium/calmodulin-dependent kinases (CaMKs), a family of proteins involved in a wide range of calcium-linked signaling events. In addition, CaMK inhibition substantially decreased liver damage after I/R and resulted in accumulation of HMGB1 in the cytoplasm of hepatocytes. Collectively, these results demonstrate that hypoxia-induced HMGB1 release by hepatocytes is an active, regulated process that occurs through a mechanism promoted by TLR4-dependent ROS production and downstream CaMK-mediated signaling.

Noninvasive radiofrequency ablation of cancer targeted by gold nanoparticles

INTRODUCTION Current radiofrequency ablation (RFA) techniques require invasive needle placement and are limited by accuracy of targeting. The purpose of this study was to test a novel non invasive radiowave machine that uses RF energy to thermally destroy tissue. Gold nanoparticles were designed and produced to facilitate tissue heating by the radiowaves. METHODS A solid state radiowave machine consisting of a power generator and transmitting/receiving couplers which transmit radiowaves at 13.56 MHz was used. Gold nanoparticles were produced by citrate reduction and exposed to the RF field either in solutions testing or after incubation with HepG2 cells. A rat hepatoma model using JM-1 cells and Fisher rats was employed using direct injection of nanoparticles into the tumor to focus the radiowaves for select heating. Temperatures were measured using a fiber-optic thermometer for real-time data. RESULTS Solutions containing gold nanoparticles heated in a time- and power-dependent manner. HepG2 liver cancer cells cultured in the presence of gold nanoparticles achieved adequate heating to cause cell death upon exposure to the RF field with no cytotoxicity attributable to the gold nanoparticles themselves. In vivo rat exposures at 35 W using direct gold nanoparticle injections resulted in significant temperature increases and thermal injury at subcutaneous injection sites as compared to vehicle (water) injected controls. DISCUSSION These data show that non invasive radiowave thermal ablation of cancer cells is feasible when facilitated by gold nanoparticles. Future studies will focus on tumor selective targeting of nanoparticles for in vivo tumor destruction.

Increasing numbers of hepatic dendritic cells promote HMGB1-mediated ischemia-reperfusion injury

Endogenous ligands released from damaged cells, so‐called damage‐associated molecular pattern molecules (DAMPs), activate innate signaling pathways including the TLRs. We have shown that hepatic, warm ischemia and reperfusion (I/R) injury, generating local, noninfectious DAMPs, promotes inflammation, which is largely TLR4‐dependent. Here, we demonstrate that increasing dendritic cell (DC) numbers enhance inflammation and organ injury after hepatic I/R. High‐mobility group box 1 (HMGB1), a NF released by necrotic cells or secreted by stimulated cells, is one of a number of ligands promoting TLR4 reactivity. Augmentation of DC numbers in the liver with GM‐CSF hydrodynamic transfection significantly increased liver damage after I/R when compared with controls. TLR4 engagement on hepatic DC was required for the I/R‐induced injury, as augmentation of DC numbers in TLR4 mutant (C3H/HeJ) mice did not worsen hepatic damage. It is interesting that TLR4 expression was increased in hepatic DC following HMGB1 stimulation in vitro, suggesting a mechanism for the increased liver injury following I/R. It thus appears that functional TLR4 on DC is required for I/R‐induced injury. Furthermore, HMGB1 may direct the inflammatory responses mediated by DC, at least in part, by enhancing TLR4 expression and reactivity to it and other DAMPs.

Cutting Edge: High-Mobility Group Box 1 Preconditioning Protects against Liver Ischemia-Reperfusion Injury

High mobility group box 1 (HMGB1) is a NF released extracellularly as a late mediator of lethality in sepsis and as an early mediator of inflammation following injury. Here we demonstrate that in contrast to the proinflammatory role of HMGB1, preconditioning with HMGB1 results in protection following hepatic ischemia/reperfusion (I/R). Pretreatment of mice with HMGB1 significantly decreased liver damage after I/R. The protection observed in mice pretreated with HMGB1 was associated with a higher expression of IL-1R-associated kinase-M, a negative regulator of TLR4 signaling, compared with controls. We thus explored the possibility that HMGB1 preconditioning was mediated through TLR4 activation. HMGB1 preconditioning failed to provide protection in TLR4 mutant (C3H/HeJ) mice, but successfully reduced damage in TLR4 wild-type (C3H/HeOuj) mice. Our studies demonstrate that in contrast to the role of HMGB1 as an early mediator of inflammation and organ damage in hepatic I/R, HMGB1 preconditioning can be protective.

Arginase blockade protects against hepatic damage in warm ischemia-reperfusion.

BACKGROUND Liver ischemia reperfusion (I/R) injury is associated with profound arginine depletion due to arginase release from injured hepatocytes. Nitric oxide (NO), shown to have protective effects in I/R, is produced by nitric oxide synthase (NOS) from the substrate arginine. The purpose of this study was to determine if nor-NOHA, a novel arginase inhibitor, would be able to increase circulating arginine levels and decrease hepatic damage following warm I/R. METHODS C57BL/6 mice underwent partial liver warm I/R and were treated intraperitoneally with either nor-NOHA (100mg/kg) or saline. Serum and tissue samples were collected to measure liver enzyme levels, amino acids, and inflammatory mediators. The agent nor-NOHA (100mg/kg) was administered 15 min before ischemia and immediately after reperfusion. Serum amino acid analysis was performed using HPLC. RESULTS Arginase activity after hepatic I/R peaked at 3-6h after reperfusion and resulted in a 10-fold drop in circulating arginine levels. Treatment with nor-NOHA inhibited arginase activity and reversed the arginine depletion after I/R while simultaneously increasing serum nitric oxide. In addition, circulating citrulline, a product of NOS activity, was increased in nor-NOHA-treated animals compared to controls. Inhibition of arginase also resulted in protection from hepatic I/R-induced damage in association with markedly lower hepatic TNF, IL-6, and inducible NOS mRNA levels compared to controls. CONCLUSION Arginase blockade represents a potentially novel strategy to combat liver injury under conditions of arginine deficiency. This protection may be mediated through the arginine-NO pathway.

Technical Challenges and Utility of Anterior Exposure for Thoracic Spine Pathology

BACKGROUND Thoracic surgeons are frequently called upon to provide exposure to the anterior cervicothoracic, thoracic, and proximal lumbar spine. We reviewed our surgical experience and the perioperative outcomes of these spinal approaches. Relevant technical and anatomic considerations of each procedure are highlighted. METHODS A total of 213 patients (116 female, 97 male) undergoing anterior thoracic spinal exposures over an 11-year period at a single institution were analyzed. Primary endpoints include morbidity, mortality, and perioperative outcomes. RESULTS Mean age was 53.7 years. Surgical approaches were determined based on the location and length of spinal involvement, and included cervicothoracic (5), thoracotomy (117), and thoracoabdominal (91) techniques. Malignant etiologies were associated with the highest perioperative mortality (6.7%, p = 0.08). Procedures for infection were associated with a significantly higher complication rate (p = 0.041) and length of stay (p = 0.033). Correction of scoliosis required longer operative times (p < 0.001) and resulted in a trend toward higher blood loss (p = 0.16). Thoracoabdominal approaches were associated with increased operative times (386 vs 316 minutes) and length of stay (8 vs 6 days) compared with thoracotomy. CONCLUSIONS The increased use of anterior approaches to spinal pathology necessitates greater involvement by thoracic surgeons. Familiarity with the anatomic and technical features of the anterior spinal exposure is required by thoracic surgeons to optimize surgical outcomes.

Late collapse of a thoracic endoprosthesis

Thoracic stent graft collapse is a rare complication of thoracic endovascular aortic repair that is mostly asymptomatic and occurs ≤ 3 months of the procedure. We describe the case of a 36-year-old man who presented with symptomatic endograft collapse 38 months after an initial thoracic endovascular aortic repair that was performed for traumatic aortic transection. He had sudden and complete loss of bilateral lower extremity motor and sensory functions (spinal cord ischemia) and anal sphincter tone. The patient was successfully treated with redo thoracic endovascular aortic repair, followed by open conversion and device explantation.

Comparison of modern open infrarenal and pararenal abdominal aortic aneurysm repair on early outcomes and renal dysfunction at one year

OBJECTIVE This study was conducted to review contemporary results of elective open infrarenal abdominal aortic aneurysm (IAAA) and pararenal abdominal aortic aneurysm (PAAA) repairs and determine predictors of death and acute and 1-year renal dysfunction (RD). METHODS A retrospective review identified 432 consecutive patients undergoing open IAAA (233 patients) or PAAA (184 patients) repair between January 2000 and December 2007. Demographic, preoperative, intraoperative, and postoperative variables were collected. RD was defined as an increase in creatinine of ≥ 0.5 mg/dL from baseline. Multiple logistic regression models were used to identify predictors of mortality and RD. RESULTS Mortality rates were similar between the groups (3.9% IAAA and 6.0% PAAA). Preoperative coronary artery disease (CAD), postoperative myocardial infarction, or pulmonary complications were all strong predictors of operative mortality in patients undergoing repair of PAAAs and IAAAs. However, neither PAAA nor baseline renal insufficiency was an independent predictor of death. Postoperative RD occurred in 32% of patients after PAAA repairs compared with 13% of patients after IAAA repairs (P < .001). The presence of PAAA, baseline hypertension, and hyperlipidemia all correlated positively with postoperative RD, while a trend was noted with baseline renal insufficiency (P = .09). At the 1-year follow-up, 5.1% of patients in the PAAA group had RD compared with none in the IAAA group. Similarly, the serum creatinine level was significantly higher in the PAAA group (1.4 mg/dL vs 1.2 mg/dL, PAAA and IAAA, respectively; P = .02) at 1 year. However, there were no instances of new-onset hemodialysis dependence at 1 year. Mean follow-up was 2.2 years overall. CONCLUSION Open PAAA repair can be performed without a significant increase in mortality compared to open IAAA repair. Although the incidence of renal function deterioration after open PAAA repairs remains higher than with open IAAA repairs, the overall incidence remains low at 1-year follow-up.

Bradyarrhythmias during Rheolytic Pharmacomechanical Thrombectomy for Deep Vein Thrombosis

Purpose: To explore possible mechanisms of bradycardia occurring during rheolytic pharmacomechanical thrombectomy (PMT) for deep venous thrombosis (DVT) and to propose a treatment algorithm for this phenomenon. Methods: Intraoperative anesthesia records, operative notes, and hospital records of 57 patients treated with the AngioJet rheolytic thrombectomy device for DVT over a 3-year period were retrospectively reviewed. Of the 57 patients, 7 (12.3%) patients (5 women; mean age 67 years, range 23–78) experienced bradyarrhythmias: 2 had a brief period of asystole and 5 patients experienced sinus bradycardia, 4 of which had >1 episode. All patients were in normal sinus rhythm (NSR) preoperatively, and only 2 had underlying coronary disease. Results: The AngioJet device was located in the infrarenal inferior vena cava in over half of the patients and in other peripheral venous beds in the others when the bradyarrhythmias occurred. Five of 7 patients reverted to NSR with cessation of the device alone, while 2 required a dose of atropine in addition. External pacing was not required, and all patients did well postoperatively. Since sinus bradycardia resolved immediately upon cessation of the device in all cases, the theory that adenosine (a product of hemolysis affecting conduction) plays an important role is called into question. Stretch receptor activation in the right heart from cyclical high-pressure gradients generated by the device may play a more important role mechanistically. Conclusion: The occurrence of bradyarrhythmias during peripheral venous use of the AngioJet device is poorly described in the literature. Routine pre-treatment with various agents is not recommended during use of the device in peripheral venous beds as the incidence of bradyarrhythmias appears to be very low, with no defined mechanism of onset.

Inflow thrombosis does not adversely affect thrombolysis outcomes of symptomatic iliofemoral deep vein thrombosis

OBJECTIVE The presence of popliteal or tibial vein clot is thought to adversely affect thrombolysis for iliofemoral deep vein thrombosis (DVT). We examined the effect of inflow thrombosis on functional and anatomic outcomes. METHODS Data for 44 patients treated for symptomatic iliofemoral DVT between 2006 and 2009 were retrospectively reviewed. All patients were treated by pharmacomechanical thrombectomy with local lytic therapy. Catheter-directed lysis and vena cava filters were used sparingly. Univariate and multivariate logistic regression analyses were used. The independent variable used in the logistic regression model was symptom relief. RESULTS Forty-four patients (mean age, 52.1 ± 15.8 years) presented with symptoms averaging 13.4 ± 9.9 days in duration. Twenty (45.4%) had symptoms for >14 days. Seventeen patients were treated in one session, but 27 patients required lytic infusion for residual thrombus. Iliac stenting was required in 49% of limbs. Successful lysis (>50%) was achieved in 91% of patients, and symptom resolution or improvement in 91%. All patients became ambulatory, with no or minimal limitation. No major systemic bleeding complications occurred. Freedom from DVT recurrence and reintervention was 84% at 24 months by life-table analysis. Preoperative ultrasound imaging showed 89% had popliteal and tibial clots. A thrombosed popliteal vein was accessed for treatment and was corroborated by venographic findings. One patient required simultaneous tibial lysis. At a mean follow up of 8.7 ± 6.3 months, 41 patients (93%) had no symptom recurrence, 82% had preserved valve function and no reflux on duplex imaging, with a mean CEAP class of 1.4 and Villalta score of 3.3. Inflow thrombus had no adverse effect on symptom relief, treatment duration, patency, CEAP class, or valve reflux. Interestingly, 90% of patients with initial popliteal thrombus had a patent popliteal vein on postlysis ultrasound imaging, and the presence of tibial thrombus on presentation was predictive of symptom relief with thrombolysis (odds ratio, 13.03; 95% confidence interval, 1.02-165.58; P = .048). CONCLUSIONS Inflow thrombosis is common and does not preclude successful thrombolysis of iliofemoral DVT. Valve function is preserved on midterm follow-up, with maintained CEAP class and symptom relief.