Effects Of Dexmedetomidine On Spinal Cord Ischemia-reperfusion Injury In Rabbits

BackgroundThe conception of spinal cord ischemia-reperfusion injury is that the spinal cord ischemia injury has not reduced but has aggravated, seriously may lead to the death of spinal cord neuronal and the paraplegia of the body in the case of removing the factors of spinal cord ischemia and restoring the blood supply of the spinal cord.In order to ensure the smooth progress of the operation, doctors often need to block the thoracic aorta and abdominal aorta in the operation in the case of major vascular surgery especially for thoracic and abdominal aortic aneurysm surgery.It is reported in the literature that the incidence of paraplegia caused by spinal cord ischemia-reperfusion injury after aortic aneurysm surgery is 5% to 40%.In addition,the patients of spinal deformity, spinal tumor and spinal stenosis also have the possibility of spinal cord ischemia-reperfusion injury because of the reperfusion of spinal cord in a short period of time caused by surgical decompression.Paraplegia not only causes the patients to lose the ability of work,even to lose the basic ability of life self-care. These bring great suffering to patients and their families, but also bring the burden of economic and medical to their families and the whole society.Therefore, it has been a difficult and hot spot in the medical research to seek effective methods and measures to reduce the spinal cord ischemia-reperfusion injury.In recent years, although there are some researchers using a variety of different measures of deep hypothermic circulatory arrest, cerebrospinal fluid drainage, vascular transplantation surgery to protect the spinal cord of ischemia-reperfusion, but the incidence of postoperative paraplegia still can not be avoided. These protective measures are complicated and may cause other serious complications.Therefore, these measures are not the best choice for the treatment of spinal cord injury in ischemic-reperfusion injury, and there are no applications in clinical practice. If we can find the drugs of protective effect on ischemia-reperfusion injury, it will be of great significance in clinical practice.Dexmedetomidine (DEX) is a highly selective a2-adrenoceptor agonist,which has widely used clinically in recent years. Dexmedetomidine given with adrenergic receptor α2, α1 adrenergic receptor binding ratio of 1620:1. Clonidine given with adrenergic receptor a2, al adrenergic receptor binding ratio of 220:1. Dexmedetomidine acts as a full agonist and has 8 times greater affinity than clonidine for the a2-adrenoceptor. Dexmedetomidine given in small doses can be observed its agonistic effect for the a2-adrenoceptor, in large doses can be observed its agonistic effect both for the a2-adrenoceptor and al-adrenoceptor.Dexmedetomidine not only has powerful sedative and hypnotic effects,but also has rapid onset, short half-life, short duration of action, slight inhibition of respiration, unique easy-to-wake-up features.In addition, dexmedetomidine can inhibit the excitability of sympathetic nerve, enhance the excitability of vagus nerve, but also has analgesic, anxiolytic, anti shivering and stable hemodynamic effect.Dexmedetomidine can also significantly reduce the incidence of postoperative restlessness, nausea and vomiting, and improve the safety of anesthesia recovery period after operation.Dexmedetomidine can enhance the analgesic effect of morphine and fentanyl opioid drugs, thereby reducing the dose of opioid drugs and its adverse reactions.Because there are these clear and effective pharmacological action, so dexmedetomidine is widely used for sedation and hypnosis of clinical anesthesia, minor surgery clinics, ICU sedation and auxiliary examination.In 1999, dexmedetomidine approved by the US Food and Drug Administration (FDA) can be applied to ICU sedation. In 2008, dexmedetomidine approved by the FDA can be applied to non-intubated patients sedation. In 2009, dexmedetomidine approved by the FDA can be applied to sedation in the period of endotracheal intubation and mechanical ventilation.In 2009, dexmedetomidine approved by China National Food and Drug Administration can be applied to sedation in general anesthesia induction and mechanical ventilation.With dexmedetomidine in clinical widely extensive use, researchers gradually found that it has obvious protective effects on the various organs of the body. Scholars at home and abroad through experiments found that dexmedetomidine can reduce cardiac myocardial infarction area of ischemia -reperfusion injury; it can reduce sepsis rats blood urea nitrogen and serum creatinine, protect renal function in rats; it can reduce congestion of lobular central vein in sepsis rats, reduce glutamic-pyruvic transaminase, protect the liver function of rats; it alleviate pulmonary edema and pleural effusion in rat of acute lung injury,inhibit the inflammatory reaction of lung, protect the lung of rats; it can prevent testicular torsion testicular ischemia-reperfusion injury in mice.Dexmedetomidine not only has protective effects on some organs ischemia-reperfusion injury., many scholars found that it also has obvious protective effects on the nervous system in recent years.In cerebral ischemia-reperfusion injury model, dexmedetomidine pretreatment group can reduce the area of infarction of cerebral cortex and striatum, whose protective mechanism may be that reduce the levels of TNF-a and NO, improve the activity of superoxide dismutase, reduce the generation of free radicals.Subsequently, some experiments confirmed the protective effect of dexmedetomidine on the brain is in a dose-dependent manner. Now the protective effect and mechanism of it mainly concentrated in both anti-inflammatory effect on the organization and inhibition of oxidative stress.Inflammatory reaction is one of the main mechanisms of spinal cord injury after ischemia reperfusion.The function of spinal microvascular endothelial disorders, spinal cord edema, blood spinal cord barrier is damaged in the case of spinal cord ischemia-reperfusion.Various immune cells and antibodies will enter the spinal cord, causing strong inflammatory response.After spinal cord ischemia-reperfusion injury,there will be up of the expression of tumor necrosis factor-α (TNF-a) and interleukin-rise-1β (IL-1β) in the organization.TNF-α is a kind of cytokine which is secreted by monocytes and macrophages. It has a wide range of biological functions.It is an important mediator of inflammation in the central nervous system.It acts as a promoter of other inflammatory cytokines in the inflammatory response, which is able to induce the production of other inflammatory cytokines, such as interleukin IL-1β and other inflammatory cytokines, which can induce and produce inflammatory cascade reactions and related injuries.In addition, TNF-a of overexpression can act directly on vascular endothelial cells, changing its permeability.It is with the IL-1β synergistic effects on endothelial cells, leading to injury endothelial cells start the coagulation reaction, promote thrombosis.TNF-a was able to cause the leukocyte migration, attachment, aggregation and microvascular obstruction, microvascular blood flow reduced or disappeared, which further aggravate the ischemia -reperfusion injury.IL-1β is the main component of IL-1,and that is an important proinflammatory cytokine.The expression of IL-1β in the central nervous system is very normal trace, but the expression up to several times after the injury (such as trauma, ischemia, infection, etc). Many studies proved that IL-1β is activated by a large number in the period of spinal cord ischemia-reperfusion. IL-1β can activate nuclear transcription factor (NF- nuclear factor kappa B),which can activate many kinds of inflammatory factors.These lead to inflammatory cascade reaction, so that the spinal cord ischemia and reperfusion injury aggravated.The spinal cord and brain belong to the nervous system, and the structure and the physiological and pathological processes of the spinal cord have strong homology and similarity.The research about the protective effect of dexmedetomidine on ischemia reperfusion injury of the spinal cord is little.Effect of dexmedetomidine on ischemia reperfusion injury of the spinal cord, whether as its on cerebral ischemia reperfusion injury,has protective effect.If there is a protective effect, whether there is dose dependent. The specific protection mechanism is produced by what way, whether with dexmedetomidine will inhibit the inflammatory reaction of key cytokines TNF-α and IL-1β and inhibition of oxidative stress on these problems are worth us to study and explore.Therefore, in order to study the above problems, this study divided into two parts. The first part investigate the effects of dexmedetomidine on spinal cord ischemia-reperfusion injury in rabbits and pro inflammatory factor TNF-α and IL-1β expression. The second part investigate the comparison of different doses of dexmedetomidine on spinal cord ischemia-reperfusion injury in rabbits.Experiment 1. Effects of dexmedetomidine on spinal cord ischemia-reperfusion injury in rabbits and proinflammatory cytokine TNF-α, IL-1β expressionObjective To investigate the effects of dexmedetomidine(Dex) on the expression of inflammatory factor tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β) after spinal cord ischemia-reperfusion in rabbit.Methods Twenty-four New Zealand white rabbit, which 4-5 months old,weighed 2-2.5 kg, were divided into three groups (n= 8) by the method of random number table:sham operation group (S group), ischemia reperfusion group (I/R group), dexmedetomidine treatment group (D group). Classic Zivin method is adopted to establish the rabbit model of spinal cord ischemia reperfusion,D group 30 minutes before ischemia start intravenous 2.5 ug/(kg · h) dexmedetomidine until reperfusion. At the same time period S group and I/R group is pumped into the same amount of saline solution. On awake immediately and 6,12,24,48 hours after reperfusion, Tarlov method is used to evaluate rabbit hind limbs motor function. And at the same time detect the expression of TNF-α, IL-1βin each group before the operation and 6,12,24,48 hours after reperfusion.Take the rabbit spinal cord after 48 hours, and detect the expression level of TNF-α, IL-1β, SOD and MDA,HE staining to observe the pathological changes.Results Compared with S group, I/R group and D group all time points Tarlov scores have decreased, the expression of TNF-α,IL-1β in serum and spinal cord have increased, the expression of MDA in spinal have increased, the expression of SOD in spinal cord have decreased, HE staining pathological damage has aggravated Compared with I/R group, group D all time points Tarlov scores have increased, and the expression of TNF-α,IL-1β in serum and spinal cord have decreased, the expression of MDA in spinal have decreased, the expression of SOD in spinal cord have increased, HE staining pathological damage has alleviated.Conclusion Dexmedetomidine can alleviate the rabbit spinal cord ischemia reperfusion injury, its mechanism may be associated with proinflammatory factor and reduce the lipid peroxidation reaction in spinal cord tissue.Experiment 2 Comparison of different doses of dexmedetomidine on rabbit spinal cord ischemia reperfusion injuryObjective Through the observation of different doses of dexmedetomidine in rabbit spinal cord ischemia reperfusion injury, study whether protective effect of dexmedetomidine on spinal cord is in a dose dependent manner and the optimal dose is how much.Methods Twenty-four New Zealand white rabbit, which 4-5 months old,weighed 2-2.5 kg, were divided into three groups (n= 8) by the method of random number table:low dose dexmedetomidine group(D1 group), middle dose dexmedetomidine group(D2 group), high dose dexmedetomidine group(D3 group). Classic Zivin method is adopted to establish the rabbit model of spinal cord ischemia reperfusion, D1 group 30 minutes before ischemia start intravenous 2.5 (kg · h)dexmedetomidine until reperfusion. At the same time period D2 group is pumped into 10ug/(kg · h) dexmedetomidine,D3 group is pumped into 40 ug/(kg · h) dexmedetomidine. Tarlov method is used to evaluate rabbit hind limbs motor function at 48 hours after reperfusion.Take the rabbit spinal cord after 48 hours, and detect the expression level of SOD and MDA,HE staining to observe the pathological changes.Results Compared with Dl group, D2 group Tarlov scores have increased, the difference was statistically significant (P<0.05);D3 group Tarlov scores have no obvious change, the difference was not statistically significant (P> 0.05). Compared with D2 group, D3 group Tarlov scores have decreased, the difference was statistically significant (P<0.05). Compared with Dl group, D2 group normal motor neurons in the anterior horn have increased, the difference was statistically significant (P<0.05);D3 group normal motor neurons in the anterior horn have no obvious change, the difference was not statistically significant (P> 0.05). Compared with D2 group, D3 group normal motor neurons in the anterior horn have decreased, the difference was statistically significant (P<0.05). Compared with D1 group, D2 group SOD activity of spinal cord have increased, the difference was statistically significant (P<0.05);D3 group SOD activity of spinal cord have no obvious change, the difference was not statistically significant (P> 0.05). Compared with D2 group, D3 group SOD activity of spinal cord have decreased, the difference was statistically significant (P<0.05). Compared with D1 group, D2 group MDA content of spinal cord have decreased, the difference was statistically significant (P<0.05);D3 group Tarlov scores have no obvious change, the difference was not statistically significant (P> 0.05). Compared with D2 group, D3 group MDA content of spinal cord have increased, the difference was statistically significant (P<0.05).Conclusion The protective effect of dexmedetomidine on spinal cord ischemia-reperfusion injury in rabbits with dose increasing increase in a certain range. Its optimal dose is 10 ug/(kg · h). When the dose was increased to 40 ug/(kg· h), there is dramatic effects on the hemodynamics of rabbits, and it would aggravate spinal cord injury and decrease the protective effect.