Jonathan E. Frank

Neurotensin-induced hypothermia improves neurologic outcome after hypoxic-ischemia

ObjectiveExternal cooling is commonly used to force induction of mild hypothermia but requires equipment, has a slow onset of action, and must be prolonged to provide permanent neurologic benefits after hypoxic-ischemia. It is unknown whether the method for inducing mild hypothermia affects neurologic outcome after near-drowning. The objective of the study was to induce mild hypothermia with neurotensin analog NT77 or external cooling in a rat model of near-drowning. We hypothesize that NT77 would be more effective for improving neurologic outcome than external cooling of the same duration. DesignRats were randomized to a normothermic control, neurotensin-induced hypothermia, brief external cooling, or prolonged external cooling group after asphyxial cardiac arrest. SettingLaboratory investigation. SubjectsForty-eight rats. InterventionsMild hypothermia was induced by external cooling for 4 hrs (brief external cooling) or 24 hrs (prolonged external cooling) or by neurotensin-induced hypothermia administration 30 mins after asphyxial cardiac arrest in rats. MeasurementsOutcome was assessed by a neurologic deficit score, the Morris water maze, and CA1 hippocampus histology 15 days after resuscitation. Main ResultsNeurologic deficit score at 72 hrs after asphyxial cardiac arrest was lower with neurotensin-induced hypothermia (score, 0) and prolonged external cooling (score, 0) vs. normothermic control (score, 20) and brief external cooling (score, 18; p < .05). Latency time in the Morris water maze 15 days after asphyxial cardiac arrest was decreased with neurotensin-induced hypothermia (14 ± 11 secs) and prolonged external cooling (18 ± 9 secs) vs. normothermic control (74 ± 17 secs) and brief external cooling (78 ± 18 secs, p < .05). There was less ischemic neuronal damage with neurotensin-induced hypothermia (28 ± 24%) and prolonged external cooling (21 ± 14%) vs. normothermic control (61 ± 32%) and brief external cooling (51 ± 32%). ConclusionsNeurotensin-induced hypothermia improved neurologic outcome after asphyxial cardiac arrest in rats vs. brief external cooling but was comparable to prolonged external cooling.

Regulated hypothermia reduces brain oxidative stress after hypoxic-ischemia.

UNLABELLED Regulated hypothermia produces a decrease in core temperature by lowering the brains temperature set-point while maintaining thermoregulation at that lower set point. In contrast, forced hypothermia lowers core temperature by overwhelming the bodys capacity to thermoregulate, but does not change the set-point. Regulated hypothermia has been shown to be cerebral protective in hibernating mammals. The effect of regulated hypothermia on the brain during reperfusion from hypoxic-ischemia has not been well studied. We induced regulated hypothermia with a neurotensin analogue (NT77) to determine whether it could reduce oxidative stress in the brain during reperfusion from asphyxial cardiac arrest (ACA) in rats. Mild hypothermia (32-34 degrees C) was induced by brief (4 h) external cooling (BC), NT77 or prolonged external cooling (24 h) (PC) 30 min after resuscitation from 8 min of ACA in rats. Malondialdehyde (MDA) levels in the brain were measured during reperfusion to quantitate oxidative stress. RESULTS MDA levels in the hippocampus were elevated at 16 h of normothermic reperfusion versus 48 h with BC reperfusion. There was no increase in hippocampal MDA levels in the NT77 and PC groups at 24-72 h of reperfusion. Regulated hypothermia induced by NT77 reduced oxidative stress in the hippocampus during reperfusion from hypoxic-ischemia in comparison to forced brief external cooling of the same duration. In addition, the duration of external cooling after resuscitation also alters oxidative stress in the brain during reperfusion.

Spatiotemporal Uptake Characteristics of [18]F-2-Fluoro-2-Deoxy-d-Glucose in a Rat Middle Cerebral Artery Occlusion Model

Background and Purpose— Alterations of cerebral glucose metabolism are well anticipated during cerebral ischemia. However, detailed spatiotemporal characteristics of disturbed cerebral glucose metabolism during acute ischemia remain largely elusive. This study aims to delineate spatiotemporal distributions of [18]F-2-fluoro-2-deoxy-D-glucose (FDG) uptake using positron emission tomography imaging, particularly at the peri-ischemic zone, and its correlation with tissue outcome. Methods— The intraluminal suture middle cerebral artery occlusion model was used to induce focal cerebral ischemia in rats (n=48). All animals underwent sequential MRI and FDG positron emission tomography imaging at different times (30–150 minutes) after middle cerebral artery occlusion. MR and positron emission tomography images were coregistered. FDG uptake in the peri-ischemic zone was assessed in relation to middle cerebral artery occlusion duration, cerebral blood flow, apparent diffusion coefficient, and 24-hour T2 lesions. Results— Elevated FDG uptake was consistently observed at the peri-ischemic zone surrounding the presumed ischemic core with low FDG uptake. Both the spatial volume and the uptake level of the hyper-uptake region were inversely correlated with the duration of middle cerebral artery occlusion. The hyper-uptake regions exhibited a mild reduction of cerebral blood flow (28.2±3.2%) and apparent diffusion coefficient (9.1±1.4%) when compared with that in the contralateral hemisphere. Colocalization analysis revealed that, with reperfusion, an average of 12.1±1.7% of the hyper-uptake volume was recruited into final infarction. Conclusions— Elevated FDG uptake at the peri-ischemic zone is consistently observed during acute cerebral ischemia. The region with elevated FDG uptake likely reflects viable tissues that can be salvaged with reperfusion. Therefore, acute FDG positron emission tomography imaging might hold promise in the management of patients with acute stroke.

Treating Brain Tumor with Microbeam Radiation Generated by a Compact Carbon-Nanotube-Based Irradiator: Initial Radiation Efficacy Study

Microbeam radiation treatment (MRT) using synchrotron radiation has shown great promise in the treatment of brain tumors, with a demonstrated ability to eradicate the tumor while sparing normal tissue in small animal models. With the goal of expediting the advancement of MRT research beyond the limited number of synchrotron facilities in the world, we recently developed a compact laboratory-scale microbeam irradiator using carbon nanotube (CNT) field emission-based X-ray source array technology. The focus of this study is to evaluate the effects of the microbeam radiation generated by this compact irradiator in terms of tumor control and normal tissue damage in a mouse brain tumor model. Mice with U87MG human glioblastoma were treated with sham irradiation, low-dose MRT, high-dose MRT or 10 Gy broad-beam radiation treatment (BRT). The microbeams were 280 μm wide and spaced at 900 μm center-to-center with peak dose at either 48 Gy (low-dose MRT) or 72 Gy (high-dose MRT). Survival studies showed that the mice treated with both MRT protocols had a significantly extended life span compared to the untreated control group (31.4 and 48.5% of life extension for low- and high-dose MRT, respectively) and had similar survival to the BRT group. Immunostaining on MRT mice demonstrated much higher DNA damage and apoptosis level in tumor tissue compared to the normal brain tissue. Apoptosis in normal tissue was significantly lower in the low-dose MRT group compared to that in the BRT group at 48 h postirradiation. Interestingly, there was a significantly higher level of cell proliferation in the MRT-treated normal tissue compared to that in the BRT-treated mice, indicating rapid normal tissue repairing process after MRT. Microbeam radiation exposure on normal brain tissue causes little apoptosis and no macrophage infiltration at 30 days after exposure. This study is the first biological assessment on MRT effects using the compact CNT-based irradiator. It provides an alternative technology that can enable widespread MRT research on mechanistic studies using a preclinical model, as well as further translational research towards clinical applications.

Effect of a pharmacologically induced decrease in core temperature in rats resuscitated from cardiac arrest

AIM Hypothermia is recommended by international guidelines for treatment of unconscious survivors of cardiac arrest to improve neurologic outcomes. However, temperature management is often underutilized because it may be difficult to implement. The present study evaluated the efficacy of pharmacologically induced hypothermia on survival and neurological outcome in rats resuscitated from cardiac arrest. METHODS Cardiac arrest was induced for 10 min in 120 rats. Sixty-one rats were resuscitated and randomized to normothermia, physical cooling or pharmacological hypothermia 5 min after resuscitation. Pharmacological hypothermia rats received a combination of ethanol, vasopressin and lidocaine (HBN-1). Physical hypothermia rats were cooled with intravenous iced saline and cooling pads. Rats in the pharmacological hypothermia group received HBN-1 at ambient temperature (20 °C). Normothermic rats were maintained at 37.3 ± 0.2 °C. RESULTS HBN-1 (p < 0.0001) shortened the time (85 ± 71 min) to target temperature (33.5 °C) versus physical hypothermia (247 ± 142 min). The duration of hypothermia was 17.0 ± 6.8h in the HBN-1 group and 17.3 ± 7.5h in the physical hypothermia group (p = 0.918). Survival (p = 0.034), neurological deficit scores (p < 0.0001) and Morris Water Maze performance after resuscitation (p = 0.041) was improved in the HBN-1 versus the normothermic group. HBN-1 improved survival and early neurological outcome compared to the physical hypothermia group while there was no significant difference in performance in the Morris water maze. CONCLUSION HBN-1 induced rapid and prolonged hypothermia improved survival with good neurological outcomes after cardiac arrest suggesting that pharmacologically induced regulated hypothermia may provide a practical alternative to physical cooling.

Data on biodistribution and radiation absorbed dose profile of a novel 64Cu-labeled high affinity cell-specific peptide for positron emission tomography imaging of tumor vasculature

New peptide-based diagnostic and therapeutic approaches hold promise for highly selective targeting of cancer leading to more precise and effective diagnostic and therapeutic modalities. An important feature of these approaches is to reach the tumor tissue while limiting or minimizing the dose to normal organs. In this context, efforts to design and engineer materials with optimal in vivo targeting and clearance properties are important. This Data In Brief article reports on biodistribution and radiation absorbed dose profile of a novel high affinity radiopeptide specific for bone marrow-derived tumor vasculature. Background information on the design, preparation, and in vivo characterization of this peptide-based targeted radiodiagnostic is described in the article “Synthesis and comparative evaluation of novel 64Cu-labeled high affinity cell-specific peptides for positron emission tomography of tumor vasculature” (Merrill et al., 2016) [1]. Here we report biodistribution measurements in mice and calculate the radiation absorbed doses to normal organs using a modified Medical Internal Radiation Dosimetry (MIRD) methodology that accounts for physical and geometric factors and cross-organ beta doses.

Independence of brain and trunk temperature during hypothermic preconditioning in rats.

UNLABELLED Hypothermic preconditioning is rapid cooling and warming to induce tolerance to ischemia. The purpose of the study was to examine differences in brain and trunk temperature during hypothermic preconditioning. METHODS Rats (n=18) were implanted with telemetric probes for simultaneous measure of brain and trunk temperature. Hypothermic preconditioning was produced by exposing rats to cool and warm environments that produced rapid cooling to 30 degrees C and warming to 35 degrees C. RESULTS Brain temperature was warmer (37.56+/-0.45 degrees C) than trunk (37.17+/-0.29 degrees C) temperature in unanesthetized, free roaming rats at room temperature (t-test p=0.04). The brain cooled (0.59+/-0.1 degrees C/min) quicker than the trunk (0.44+/-0.19 degrees C/min) during cooling cycles of hypothermic preconditioning and the brain (0.28+/-0.04 degrees C/min) warmed quicker than the trunk (0.18+/-0.07 degrees C/min) during the warming cycle of hypothermic preconditioning (t-test p<0.0001). When the trunk temperature probe was designated to reach the target temperature of 35 degrees C during warming, the brain temperature (38.1+/-0.44 degrees C) was warmer than trunk temperature (34.95+/-0.16 degrees C) during the peak of warming (t-test p<0.0001). CONCLUSION The brain cools and warms quicker than the trunk during hypothermic preconditioning. Failure to anticipate these differences could lead to unrecognized brain hyperthermia during warming. Appreciation of differences in rates of change between brain and trunk temperature may be important when designing hypothermic preconditioning experiments.

Thrombolysis enhanced by dual-frequency highintensity focused ultrasound

It has been demonstrated that high-intensity focused ultrasound can be an efficient method to induce thrombolysis. Excessive thermal effect on neighboring tissue is however a concern. The goal of this work is to test the efficacy of dual-frequency ultrasound-induced thrombolysis, with the aim to reduce the acoustic power required to achieve the same lysis rate (mass loss of blood clots over time) as single-frequency ultrasound. In vitro clots of mouse blood were prepared and placed at the focus of two piezoelectric ultrasound transducers (center frequencies were 0.95 MHz and 1.5 MHz, respectively). 0.65 W ultrasound waves with 10% duty cycle were employed in both single- and dual-frequency ultrasound exposures. The mass losses of the clots were recorded to obtain the lysis rate after each test. It was found that dual-frequency results in more efficient thrombolysis. Cavitation bubble modeling was also conducted for both single- and dual-frequency ultrasound to explain the experimental founding.