The effects of systemic hypothermia on a murine model of thoracic aortic ischemia reperfusion

Ethyl pyruvate modulates delayed paralysis following thoracic aortic ischemia reperfusion in mice

OBJECTIVE

Delayed paralysis is an unpredictable problem for patients undergoing complex repair of the thoracic/thoracoabdominal aorta. These experiments were designed to determine whether ethyl pyruvate (EP), a potent anti-inflammatory and antioxidant agent, might ameliorate delayed paralysis following thoracic aortic ischemia reperfusion (TAR).

METHODS

C57BL6 mice were subjected to 5 minutes of thoracic aortic ischemia followed by reperfusion for up to 48 hours. Mice received either 300 mg/kg EP or lactated ringers (LR) at 30 minutes before ischemia and 3 hours after reperfusion. Neurologic function was assessed using an established rodent scale. Spinal cord tissue was analyzed for markers of inflammation (keratinocyte chemoattractant [KC], interleukin-6 [IL-6]), microglial activation (ionized calcium-binding adapter molecule-1 [Iba-1]), and apoptosis (Bcl-2, Bax, and terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL] staining) at 24 and 48 hours after TAR. Nissl body stained motor neurons were counted in the anterior horns sections from L1-L5 segments.

RESULTS

Ninety-three percent of the LR mice developed dense delayed paralysis between 40 and 48 hours after TAR, whereas only 39% of EP mice developed delayed paralysis (P < .01). Bcl-2 expression was higher (P < .05) and Iba-1 expression was lower (P < .05) in the EP group only at 24 hours reperfusion. At 48 hours, the number of motor neurons was higher (P < .01) and the number and TUNEL-positive cells was lower (P < .001) in the EP-treated mice. EP decreased the expression of KC (P < .01) and IL-6 (P < .001) at 48 hours after TAR.

CONCLUSIONS

The protection provided by EP against delayed paralysis correlated with preservation of motor neurons, higher expression of antiapoptotic molecules, decreased microglial cell activation, and decreased spinal cord inflammation. EP may be a treatment for humans at risk for delayed paralysis.

Spinal Cord Inflammation: Molecular Imaging after Thoracic Aortic Ischemia Reperfusion Injury

Purpose To evaluate whether noninvasive molecular imaging technologies targeting myeloperoxidase (MPO) can reveal early inflammation associated with spinal cord injury after thoracic aortic ischemia-reperfusion (TAR) in mice. Materials and Methods The study was approved by the institutional animal care and use committee. C57BL6 mice that were 8-10 weeks old underwent TAR (n = 55) or sham (n = 26) surgery. Magnetic resonance (MR) imaging (n = 6) or single photon emission computed tomography (SPECT)/computed tomography (CT) (n = 15) studies targeting MPO activity were performed after intravenous injection of MPO sensors (bis-5-hydroxytryptamide-tetraazacyclododecane [HT]-diethyneletriaminepentaacetic acid [DTPA]-gadolinium or indium 111-bis-5-HT-DTPA, respectively). Immunohistochemistry and flow cytometry were used to identify myeloid cells and neuronal loss. Proinflammatory cytokines, keratinocyte chemoattractant (KC), and interleukin 6 (IL-6) were measured with enzyme-linked immunosorbent assay. Statistical analyses were performed by using nonparametric tests and the Pearson correlation coefficient. P < .05 was considered to indicate a significant difference. Results Myeloid cells infiltrated into the injured cord at 6 and 24 hours after TAR. MR imaging confirmed the presence of ischemic lesions associated with mild MPO-mediated enhancement in the thoracolumbar spine at 24 hours compared with the sham procedure. SPECT/CT imaging of MPO activity showed marked MPO-sensor retention at 6 hours (P = .003) that continued to increase at 24 hours after TAR (P = .0001). The number of motor neurons decreased substantially at 24 hours after TAR (P < .01), which correlated inversely with in vivo inflammatory changes detected at molecular imaging (r = 0.64, P = .0099). MPO was primarily secreted by neutrophils, followed by lymphocyte antigen 6 complex^high monocytes and/or macrophages. There were corresponding increased levels of proinflammatory cytokines KC (P = .0001) and IL-6 (P = .0001) that mirrored changes in MPO activity. Conclusion MPO is a suitable imaging biomarker for identifying and tracking inflammatory damage in the spinal cord after TAR in a mouse model. ^© RSNA, 2016 Online supplemental material is available for this article.

Prolonged Local Hypothermia Has No Long-Term Adverse Effect on the Spinal Cord

Hypothermia is known to be neuroprotective and is one of the most effective and promising first-line treatments for central nervous system (CNS) trauma. At present, induction of local hypothermia, as opposed to general hypothermia, is more desired because of its ease of application and safety; fewer side effects and an absence of severe complications have been noted. Local hypothermia involves temperature reduction of a small and specific segment of the spinal cord. Our group has previously shown the neuroprotective effect of short-term, acute moderate general hypothermia through improvements in electrophysiological and motor behavioral assessments, as well as histological examination following contusive spinal cord injury (SCI) in rats. We have also shown the benefit of using short-term local hypothermia versus short-term general hypothermia post-acute SCI. The overall neuroprotective benefit of hypothermia can be categorized into three main components: (1) induction modality, general versus local, (2) invasive, semi-invasive or noninvasive, and (3) duration of hypothermia induction. In this study, a series of experiments were designed to investigate the feasibility, long-term safety, as well as eventual complications and side effects of prolonged, semi-invasive, moderate local hypothermia (30°C±0.5°C for 5 and 8 hours) in rats with uninjured spinal cord while maintaining their core temperature at 37°C±0.5°C. The weekly somatosensory evoked potential and motor behavioral (Basso, Beattie and Bresnahan) assessments of rats that underwent 5 and 8 hours of semi-invasive local hypothermia, which revealed no statistically significant changes in electrical conductivity and behavioral outcomes. In addition, 4 weeks after local hypothermia induction, histological examination showed no anatomical damages or morphological changes in their spinal cord structure and parenchyma. We concluded that this method of prolonged local hypothermia is feasible, safe, and has the potential for clinical translation.

Reproducable paraplegia by thoracic aortic occlusion in a murine model of spinal cord ischemia-reperfusion

BACKGROUND

Lower extremity paralysis continues to complicate aortic interventions. The lack of understanding of the underlying pathology has hindered advancements to decrease the occurrence this injury. The current model demonstrates reproducible lower extremity paralysis following thoracic aortic occlusion.

METHODS

Adult male C57BL6 mice were anesthetized with isoflurane. Through a cervicosternal incision the aorta was exposed. The descending thoracic aorta and left subclavian arteries were identified without entrance into pleural space. Skeletonization of these arteries was followed by immediate closure (Sham) or occlusion for 4 min (moderate ischemia) or 8 min (prolonged ischemia). The sternotomy and skin were closed and the mouse was transferred to warming bed for recovery. Following recovery, functional analysis was obtained at 12 hr intervals until 48 hr.

RESULTS

Mice that underwent sham surgery showed no observable hind limb deficit. Mice subjected to moderate ischemia for 4 min had minimal functional deficit at 12 hr followed by progression to complete paralysis at 48 hr. Mice subjected to prolonged ischemia had an immediate paralysis with no observable hind-limb movement at any point in the postoperative period. There was no observed intraoperative or post operative mortality.

CONCLUSION

Reproducible lower extremity paralysis whether immediate or delayed can be achieved in a murine model. Additionally, by using a median sternotomy and careful dissection, high survival rates, and reproducibility can be achieved.

Cryotherapy in inflammatory rheumatic diseases: a systematic review

The aim of this article was to review current evidence about cryotherapy in inflammatory rheumatic diseases (therapeutic and biological effects). For therapeutic effects, we performed a systematic review (PubMed, EMBASE, Cochrane Library, LILACS databases, unpublished data) and selected studies including non-operated and non-infected arthritic patients treated with local cryotherapy or whole-body cryotherapy. By pooling 6 studies including 257 rheumatoid arthritis (RA) patients, we showed a significant decrease in pain visual analogic scale (mm) and 28-joint disease activity score after chronic cryotherapy in RA patients. For molecular pathways, local cryotherapy induces an intrajoint temperature decrease, which might downregulate several mediators involved in joint inflammation and destruction (cytokines, cartilage-degrading enzymes, proangiogenic factors), but studies in RA are rare. Cryotherapy should be included in RA therapeutic strategies as an adjunct therapy, with potential corticosteroid and nonsteroidal anti-inflammatory drug dose-sparing effects. However, techniques and protocols should be more precisely defined in randomized controlled trials with stronger methodology.

Development and treatments of inflammatory cells and cytokines in spinal cord ischemia-reperfusion injury

During aortic surgery, interruption of spinal cord blood flow might cause spinal cord ischemia-reperfusion injury (IRI). The incidence of spinal cord IRI after aortic surgery is up to 28%, and patients with spinal cord IRI might suffer from postoperative paraplegia or paraparesis. Spinal cord IRI includes two phases. The immediate spinal cord injury is related to acute ischemia. And the delayed spinal cord injury involves both ischemic cellular death and reperfusion injury. Inflammation is a subsequent event of spinal cord ischemia and possibly a major contributor to spinal cord IRI. However, the development of inflammatory mediators is incompletely demonstrated. And treatments available for inflammation in spinal cord IRI are insufficient. Improved understanding about spinal cord IRI and the development of inflammatory cells and cytokines in this process will provide novel therapeutic strategies for spinal cord IRI. Inflammatory cytokines (e.g., TNF-α and IL-1) may play an important role in spinal cord IRI. For treatment of several intractable autoimmune diseases (e.g., rheumatoid arthritis), where inflammatory cytokines are involved in disease progression, anti-inflammatory cytokine antagonist is now available. Hence, there is great potential of anti-inflammatory cytokine antagonist for therapeutic use of spinal cord IRI. We here review the mediators and several possibilities of treatment in spinal cord IRI.

Hypothermia for acute spinal cord injury--a review

OBJECTIVE

Spinal cord injury (SCI) is a catastrophic neurological event with no proven treatments that protect against its consequences. Potential benefits of hypothermia in preventing/limiting central nervous system injury are now well known. There has been an interest in its potential use after SCI. This article reviews the current experimental and clinical evidence on the use of therapeutic hypothermia in patients with SCI.

METHODS

Review of literature.

RESULTS

There are various mechanisms by which hypothermia is known to protect the central nervous system. Modest hypothermia (32°C-34°C) can deliver the potential benefits of hypothermia without incurring the complications associated with deep hypothermia. Several recent experimental studies have repeatedly shown that the use of hypothermia provides the benefit of neuroprotection after SCI. Although older clinical studies were often focused on local cooling strategies and demonstrated mixed results, more recent data from systemic hypothermia use demonstrate its safety and its benefits. Endovascular cooling is a safe and reliable method of inducing hypothermia.

CONCLUSIONS

There is robust experimental and some clinical evidence that hypothermia is beneficial in acute SCI. Larger, multicenter trials should be initiated to further study the usefulness of systemic hypothermia in SCI.

The evolution of chemokine release supports a bimodal mechanism of spinal cord ischemia and reperfusion injury

BACKGROUND

Paraplegia remains a devastating complication of thoracic aortic surgery. The mechanism of the antecedent spinal cord ischemia and reperfusion injury (IR) remains poorly described. IR involves 2 injuries, an initial ischemic insult and subsequent inflammatory amplification of the injury. This mechanism is consistent with the clinical phenomenon of delayed onset paraplegia. This study sought to characterize the inflammatory response in the spinal cord after IR and hypothesized that this would support a bimodal mechanism of injury.

METHODS AND RESULTS

Male C57Bl/6 mice were subjected to 5 minutes of aortic arch and left subclavian occlusion with subsequent reperfusion to generate spinal cord ischemia. Functional outcomes were scored at 12-hour intervals. Spinal cords were harvested after 0, 6, 12, 18, 24, 36, and 48 hours of reperfusion. Cytokine levels were analyzed using a mouse magnetic bead-based multiplex immunoassay. Inflammatory chemokine concentrations (interleukin [IL]-1β, IL-6, keratinocyte-derived cytokine, macrophage inflammatory protein-1α, monocyte chemotactic protein-1, RANTES, and tumor necrosis factor-α) peaked at 6 hours and 36 to 48 hours after reperfusion. Functional scores reflected initial gain in function with subsequent decline, inversely proportional to cytokine levels. Immunofluorescent staining demonstrated microglia activation at 12 and 48 hours.

CONCLUSIONS

Spinal cord ischemia and reperfusion injury occurs in 2 phases, correlating to increases in inflammatory chemokines release and microglial activation. These observations chronologically parallel the too-common clinical syndrome of delayed-onset paraplegia. Understanding the molecular pathogenesis of this injury may allow future intervention to prevent this devastating complication.

Role of induced hypothermia in thoracoabdominal aortic aneurysm surgery

For more than 50 years, hypothermia has been used in aortic surgery as a tool for neuroprotection. Hypothermia has been introduced into thoracoabdominal aortic aneurysm (TAAA) surgery by many cardiovascular centers to protect the body's organs, including the spinal cord. Numerous publications have shown that hypothermia can prevent immediate and delayed motor dysfunction after aortic cross-clamping. Here, we reviewed the historical application of hypothermia in aortic surgery, role of hypothermia in preclinical studies, cellular and molecular mechanisms by which hypothermia confers neuroprotection, and the role of systemic and regional hypothermia in clinical protocols to reduce and/or eliminate the devastating consequences of ischemic spinal cord injury after TAAA repair.

Facts and fiction: the impact of hypothermia on molecular mechanisms following major challenge

Numerous multiple trauma and surgical patients suffer from accidental hypothermia. While induced hypothermia is commonly used in elective cardiac surgery due to its protective effects, accidental hypothermia is associated with increased posttraumatic complications and even mortality in severely injured patients. This paper focuses on protective molecular mechanisms of hypothermia on apoptosis and the posttraumatic immune response. Although information regarding severe trauma is limited, there is evidence that induced hypothermia may have beneficial effects on the posttraumatic immune response as well as apoptosis in animal studies and certain clinical situations. However, more profound knowledge of mechanisms is necessary before randomized clinical trials in trauma patients can be initiated.

Ultrafast and whole-body cooling with total liquid ventilation induces favorable neurological and cardiac outcomes after cardiac arrest in rabbits

BACKGROUND

In animal models of cardiac arrest, the benefit afforded by hypothermia is closely linked to the rapidity of the decrease in body temperature after resuscitation. Because total liquid ventilation (TLV) with temperature-controlled perfluorocarbons induces a very rapid and generalized cooling, we aimed to determine whether this could limit the post-cardiac arrest syndrome in a rabbit model. We especially focused on neurological, cardiac, pulmonary, liver and kidney dysfunctions.

METHODS AND RESULTS

Anesthetized rabbits were submitted to either 5 or 10 minutes of untreated ventricular fibrillation. After cardiopulmonary resuscitation and resumption of a spontaneous circulation, the animals underwent either normothermic life support (control) or therapeutic hypothermia induced by TLV. The latter procedure decreased esophageal and tympanic temperatures to 32°C to 33°C within only 10 minutes. After rewarming, the animals submitted to TLV exhibited an attenuated neurological dysfunction and decreased mortality 7 days later compared with control. The neuroprotective effect of TLV was confirmed by a significant reduction in brain histological damages. We also observed limitation of myocardial necrosis, along with a decrease in troponin I release and a reduced myocardial caspase 3 activity, with TLV. The beneficial effects of TLV were directly related to the rapidity of hypothermia induction because neither conventional cooling (cold saline infusion plus external cooling) nor normothermic TLV elicited a similar protection.

CONCLUSIONS

Ultrafast cooling instituted by TLV exerts potent neurological and cardiac protection in an experimental model of cardiac arrest in rabbits. This could be a relevant approach to provide a global and protective hypothermia against the post-cardiac arrest syndrome.