THERAPEUTIC HYPOTHERMIA AND TEMPERATURE MANAGEMENT Volume 1, Number 1, 2011 ª Mary Ann Liebert, Inc. DOI: 10.1089/ther.2010.0007
Neuroprotection of Selective Brain Cooling After Penetrating Ballistic-like Brain Injury in Rats Guo Wei, Xi-Chun M. Lu, Deborah A. Shear, Xiaofang Yang, and Frank C. Tortella
Induced hypothermia has been reported to provide neuroprotection against traumatic brain injury. We recently developed a novel method of selective brain cooling (SBC) and demonstrated its safety and neuroprotection efficacy in a rat model of ischemic brain injury. The primary focus of the current study was to evaluate the potential neuroprotective efficacy of SBC in a rat model of penetrating ballistic-like brain injury (PBBI) with a particular focus on the acute cerebral pathophysiology, neurofunction, and cognition. SBC (348C) was induced immediately after PBBI, and maintained for 2 hours, followed by a spontaneous re-warming. Intracranial pressure (ICP) and regional cerebral blood flow were monitored continuously for 3 hours, and the ICP was measured again at 24 hours postinjury. Brain swelling, blood–brain barrier permeability, intracerebral hemorrhage, lesion size, and neurological status were assessed at 24 hours postinjury. Cognitive abilities were evaluated in a Morris water maze task at 12–16 days postinjury. Results showed that SBC significantly attenuated PBBI-induced elevation of ICP (PBBI ¼ 33.2 10.4; PBBI + SBC ¼ 18.8 6.7 mmHg) and reduced brain swelling, blood–brain barrier leakage, intracerebral hemorrhage, and lesion volume by 40%–45% for each matrix, and significantly improved neurologic function. However, these acute neuroprotective benefits of SBC did not translate into improved cognitive performance in the Morris water maze task. These results indicate that 348C SBC is effective in protecting against acute brain damage and related neurological dysfunction. Further studies are required to establish the optimal treatment conditions (i.e., duration of cooling and/or combined therapeutic approaches) needed to achieve significant neurocognitive benefits.
tially invokes systemic side effects. For example, systemic hypothermia decreases the enzymatic activity of clotting factors when body temperature drops below 338C, increasing the risk of coagulopathy and ensuing hypotension (Shiozaki et al., 2001; Milhaud et al., 2005; Liu et al., 2006; Hemmen and Lyden, 2007). It also dampens the immune response and poses an increased risk of infectious pneumonia in TBI patients (Bernard et al., 2002; Alderson et al., 2004). These adverse effects of whole-body cooling have raised serious concerns for its clinical application in treating TBI patients, especially for patients suffering severe hemorrhage (Romlin et al., 2007; Tieu et al., 2007). Therefore, a method to rapidly and selectively cool the brain may offer a viable alternative to achieve the beneficial effects of hypothermia while minimizing potentially serious adverse effects during the treatment of severe TBI (Milhaud et al., 2005; Hemmen and Lyden, 2007). We recently developed a novel method of selective brain cooling (SBC) in rats using extraluminal bilateral common carotid artery (CCA) cooling cuffs that can achieve rapid and sustained reductions in brain temperature while maintaining normal (378C) body temperature. This method has been
Introduction
T
herapeutic hypothermia has been well established at the experimental level as a neuroprotective strategy for treating traumatic brain injury (TBI), showing significant and consistent beneficial effects in different TBI models across laboratories (Fingas et al., 2007; Wei et al., 2008a; Dietrich and Bramlett, 2010). In contrast, clinical trials have not yielded consistent results establishing hypothermia therapy for severe TBI. Although individual cases and clinical trials conducted at single institutions have generally demonstrated a benefit from hypothermic treatment, results from a comprehensive, multicenter, phase III trial (National Acute Brain Injury Study: Hypothermia, NABISH-I) failed to show significant effects of hypothermic treatment on patient outcome after severe TBI (Clifton et al., 2001b). However, those investigators later acknowledged that the variability in management between multiple centers and delays in the initiation of cooling likely contributed to the failure of this trial (Clifton et al., 2001a). Clinically induced therapeutic hypothermia is usually achieved by whole-body cooling techniques, which poten-
Department of Applied Neurobiology, Walter Reed Army Institute of Research, Silver Spring, Maryland.
33
34 shown to be safe and efficient for inducing SBC in normal animals and in animals with ischemic brain injury. More importantly, we have demonstrated that SBC (348C for 2 hours) provides significant neuroprotection against ischemic brain injury in a rat model of middle cerebral artery occlusion (Wei et al., 2008a). The primary focus of this study was to evaluate the potential therapeutic efficacy of SBC in an experimental model of TBI. The penetrating ballistic-like brain injury (PBBI) rat model reproduces clinically relevant pathophysiological aspects of a severe, penetrating brain injury caused by a low- or high-velocity bullet/fragment wound to the head (Williams et al., 2005a), including elevated intracranial pressure (ICP) and reductions in regional cerebral blood flow (rCBF) and brain oxygen tension (Bramlett and Dietrich, 2004; Williams et al., 2005a; Wei et al., 2008b; Murakami et al., 2009). Since timing and duration of treatment are critically important factors for effective management of severe TBI, a major advantage of our CCA cooling method of SBC is that therapeutic brain temperature levels can be rapidly achieved, within 20–30 minutes after induction of SBC. Several hours of cooling is sufficient to produce significant neuroprotection in TBI models (Clifton et al., 1991; Lyeth et al., 1993; Dietrich et al., 1994), and based on our previous success in applying SBC (348C for 1.5 hours) initiated 30 minutes post-middle cerebral artery occlusion in rats (Wei et al., 2008a), we hypothesized that early initiation of SBC during the acute postinjury period would provide significant neuroprotection. For this purpose, SBC (348C) was induced immediately after PBBI and maintained for 2 hours, followed by spontaneous rewarming. Physiological measures included ICP and rCBF monitored continuously for 3 hours and ICP was measured again at 24 hours postinjury. Brain swelling formation, blood–brain barrier (BBB) permeability, intracerebral hemorrhage (ICH), lesion size, and neurological status were assessed at 24 hours postinjury, whereas spatial learning abilities were assessed in a Morris water maze (MWM) task at 12–16 days postinjury. Materials and Methods Animals All research procedures were approved by the Walter Reed Army Institute of Research Institutional Animal Care and Use Committee and were conducted in compliance with the Animal Welfare Act and Guide for the Care and Use of Laboratory Animals (National Research Council). Male Sprague Dawley rats (Charles River Laboratories, Raleigh, VA) weighing 275–325 g were used. During all surgical procedures, rats were anesthetized by isoflurane (5% for induction and 1.5% for maintenance) delivered in a mixture of 30% oxygen and 70% air. PBBI model Unilateral, frontal 10% PBBI was induced in rats as described previously (Williams et al., 2005a). Briefly, the head of the anesthetized rat was secured in a stereotaxic frame and a cranial window (4 mm diameter) was created on the dorsal surface of the skull (4.5 mm anterior and 2.0 mm lateral to the bregma) to expose the right frontal pole. A specially designed PBBI probe was manually advanced through the cranial window along the axis (angled 508 from the vertical axis and
WEI ET AL. 258 counter-clockwise from the midline), penetrating the right frontal hemisphere to a distance of 1.2 cm from dura. The ballistic component of the injury was induced by a rapid (
Neuroprotection of Selective Brain Cooling After Penetrating Ballistic-like Brain Injury in Rats Guo Wei, Xi-Chun M. Lu, Deborah A. Shear, Xiaofang Yang, and Frank C. Tortella
Induced hypothermia has been reported to provide neuroprotection against traumatic brain injury. We recently developed a novel method of selective brain cooling (SBC) and demonstrated its safety and neuroprotection efficacy in a rat model of ischemic brain injury. The primary focus of the current study was to evaluate the potential neuroprotective efficacy of SBC in a rat model of penetrating ballistic-like brain injury (PBBI) with a particular focus on the acute cerebral pathophysiology, neurofunction, and cognition. SBC (348C) was induced immediately after PBBI, and maintained for 2 hours, followed by a spontaneous re-warming. Intracranial pressure (ICP) and regional cerebral blood flow were monitored continuously for 3 hours, and the ICP was measured again at 24 hours postinjury. Brain swelling, blood–brain barrier permeability, intracerebral hemorrhage, lesion size, and neurological status were assessed at 24 hours postinjury. Cognitive abilities were evaluated in a Morris water maze task at 12–16 days postinjury. Results showed that SBC significantly attenuated PBBI-induced elevation of ICP (PBBI ¼ 33.2 10.4; PBBI + SBC ¼ 18.8 6.7 mmHg) and reduced brain swelling, blood–brain barrier leakage, intracerebral hemorrhage, and lesion volume by 40%–45% for each matrix, and significantly improved neurologic function. However, these acute neuroprotective benefits of SBC did not translate into improved cognitive performance in the Morris water maze task. These results indicate that 348C SBC is effective in protecting against acute brain damage and related neurological dysfunction. Further studies are required to establish the optimal treatment conditions (i.e., duration of cooling and/or combined therapeutic approaches) needed to achieve significant neurocognitive benefits.
tially invokes systemic side effects. For example, systemic hypothermia decreases the enzymatic activity of clotting factors when body temperature drops below 338C, increasing the risk of coagulopathy and ensuing hypotension (Shiozaki et al., 2001; Milhaud et al., 2005; Liu et al., 2006; Hemmen and Lyden, 2007). It also dampens the immune response and poses an increased risk of infectious pneumonia in TBI patients (Bernard et al., 2002; Alderson et al., 2004). These adverse effects of whole-body cooling have raised serious concerns for its clinical application in treating TBI patients, especially for patients suffering severe hemorrhage (Romlin et al., 2007; Tieu et al., 2007). Therefore, a method to rapidly and selectively cool the brain may offer a viable alternative to achieve the beneficial effects of hypothermia while minimizing potentially serious adverse effects during the treatment of severe TBI (Milhaud et al., 2005; Hemmen and Lyden, 2007). We recently developed a novel method of selective brain cooling (SBC) in rats using extraluminal bilateral common carotid artery (CCA) cooling cuffs that can achieve rapid and sustained reductions in brain temperature while maintaining normal (378C) body temperature. This method has been
Introduction
T
herapeutic hypothermia has been well established at the experimental level as a neuroprotective strategy for treating traumatic brain injury (TBI), showing significant and consistent beneficial effects in different TBI models across laboratories (Fingas et al., 2007; Wei et al., 2008a; Dietrich and Bramlett, 2010). In contrast, clinical trials have not yielded consistent results establishing hypothermia therapy for severe TBI. Although individual cases and clinical trials conducted at single institutions have generally demonstrated a benefit from hypothermic treatment, results from a comprehensive, multicenter, phase III trial (National Acute Brain Injury Study: Hypothermia, NABISH-I) failed to show significant effects of hypothermic treatment on patient outcome after severe TBI (Clifton et al., 2001b). However, those investigators later acknowledged that the variability in management between multiple centers and delays in the initiation of cooling likely contributed to the failure of this trial (Clifton et al., 2001a). Clinically induced therapeutic hypothermia is usually achieved by whole-body cooling techniques, which poten-
Department of Applied Neurobiology, Walter Reed Army Institute of Research, Silver Spring, Maryland.
33
34 shown to be safe and efficient for inducing SBC in normal animals and in animals with ischemic brain injury. More importantly, we have demonstrated that SBC (348C for 2 hours) provides significant neuroprotection against ischemic brain injury in a rat model of middle cerebral artery occlusion (Wei et al., 2008a). The primary focus of this study was to evaluate the potential therapeutic efficacy of SBC in an experimental model of TBI. The penetrating ballistic-like brain injury (PBBI) rat model reproduces clinically relevant pathophysiological aspects of a severe, penetrating brain injury caused by a low- or high-velocity bullet/fragment wound to the head (Williams et al., 2005a), including elevated intracranial pressure (ICP) and reductions in regional cerebral blood flow (rCBF) and brain oxygen tension (Bramlett and Dietrich, 2004; Williams et al., 2005a; Wei et al., 2008b; Murakami et al., 2009). Since timing and duration of treatment are critically important factors for effective management of severe TBI, a major advantage of our CCA cooling method of SBC is that therapeutic brain temperature levels can be rapidly achieved, within 20–30 minutes after induction of SBC. Several hours of cooling is sufficient to produce significant neuroprotection in TBI models (Clifton et al., 1991; Lyeth et al., 1993; Dietrich et al., 1994), and based on our previous success in applying SBC (348C for 1.5 hours) initiated 30 minutes post-middle cerebral artery occlusion in rats (Wei et al., 2008a), we hypothesized that early initiation of SBC during the acute postinjury period would provide significant neuroprotection. For this purpose, SBC (348C) was induced immediately after PBBI and maintained for 2 hours, followed by spontaneous rewarming. Physiological measures included ICP and rCBF monitored continuously for 3 hours and ICP was measured again at 24 hours postinjury. Brain swelling formation, blood–brain barrier (BBB) permeability, intracerebral hemorrhage (ICH), lesion size, and neurological status were assessed at 24 hours postinjury, whereas spatial learning abilities were assessed in a Morris water maze (MWM) task at 12–16 days postinjury. Materials and Methods Animals All research procedures were approved by the Walter Reed Army Institute of Research Institutional Animal Care and Use Committee and were conducted in compliance with the Animal Welfare Act and Guide for the Care and Use of Laboratory Animals (National Research Council). Male Sprague Dawley rats (Charles River Laboratories, Raleigh, VA) weighing 275–325 g were used. During all surgical procedures, rats were anesthetized by isoflurane (5% for induction and 1.5% for maintenance) delivered in a mixture of 30% oxygen and 70% air. PBBI model Unilateral, frontal 10% PBBI was induced in rats as described previously (Williams et al., 2005a). Briefly, the head of the anesthetized rat was secured in a stereotaxic frame and a cranial window (4 mm diameter) was created on the dorsal surface of the skull (4.5 mm anterior and 2.0 mm lateral to the bregma) to expose the right frontal pole. A specially designed PBBI probe was manually advanced through the cranial window along the axis (angled 508 from the vertical axis and
WEI ET AL. 258 counter-clockwise from the midline), penetrating the right frontal hemisphere to a distance of 1.2 cm from dura. The ballistic component of the injury was induced by a rapid (
