Protective Effect of Ketamine on Ischemic Spinal Cord Injury in Rabbits

Ketamine; history and role in anesthetic pharmacology

Ketamine (Ket) was developed in 1962 as a less hallucinogenic and shorter acting agent than phencyclidine. It was given to humans for the first time in 1964. However, Ket produces several adverse reactions such as raised intracranial and blood pressures along with seizures, and patients still show low acceptance due to hallucinations. As new volatile and intravenous anesthetic agents with good emergence and favorable side effect profiles were developed, Ket use markedly decreased. In the 1990s, as the ultrashort-acting opioid remifentanil was developed, high dose opioid could be used to reduce surgical stress in highly invasive procedures. However, high dose opioids can produce hyperalgesia and acute tolerance. As Ket can exert anti-hyperalgesic actions, the clinical use of low dose Ket has been reconsidered. Other beneficial effects of Ket such as; analgesia, anti-shock in hemorrhagic and septic insults, anti-inflammatory effects, anti-tumor effects, brain and spinal cord neuroprotection, and bronchodilation, have all been reported. Moreover, this anesthetic agent at low dose has been recently recognized to possess anti-depressive actions. This diverse profile extends Ket far beyond anesthesia practice and the operating room.

S-ketamine alleviates carbon tetrachloride-induced hepatic injury and oxidative stress by targeting the Nrf2/HO-1 signaling pathway

The aim of the present study was to investigate the protective effect of S-ketamine (S-KET) against carbon tetrachloride (CCl4) - induced liver damage and oxidative stress, as well as to elucidate the related underlying mechanisms. Blood was collected to measure biochemical parameters (alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), total bilirubin (TB) and γ-glutamyltransferase (γ-GT)) and the liver was harvested for histopathological analysis of enzymes related to the antioxidant response (malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GSH-PX)). Liver cell apoptosis was evaluated using the TUNEL assay. In addition, the expression levels of apoptosis-related proteins and the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway were detected by Western blot analysis to explore potential mechanisms. S-KET protected the liver from CCl4-induced damage. The changes to the liver biochemical parameters (increased ALT, AST, ALP, TB, and γ-GT) and oxidative stress-related indicators (increased MDA; depleted SOD, GSH, and GSH-PX) induced by CCl4 were inhibited by S-KET. S-Ket also inhibited CCl4-induced cell apoptosis, the changes in expression of related proteins, and blocked CCl4-induced liver injury and oxidative stress via activation of the Nrf2/HO-1 signaling pathway. S-KET effectively protected the liver by inhibition of CCl4-induced damage via upregulation the Nrf2/HO-1 signaling pathway.

Effects of D‑Ala2, D‑Leu5‑Enkephalin pre‑ and post‑conditioning in a rabbit model of spinal cord ischemia and reperfusion injury

It has recently been revealed that during the aorta-clamped period, D-Ala², D-Leu⁵-Enkephalin (DADLE) infusion can protect the spinal cord against ischemia and reperfusion (I/R) injury. However, the protective effects of DADLE administration prior to ischemia or at the time of early reperfusion have not yet been investigated. Drug pre- or post-conditioning can serve as a more valuable clinical strategy. Therefore, the present study was designed to investigate the neuroprotective effect of DADLE infusion at different time intervals in order to determine the optimum time point for ischemic spinal cord protection. A total of 40 New Zealand white rabbits were randomly divided into 5 groups: Sham-operated (Sham), normal saline pre-conditioning (NS), DADLE per-conditioning (D_per), DADLE pre-conditioning (D_pre) and DADLE post-conditioning (D_post). All animals were subjected to spinal cord ischemia for 30 min followed by 48 h reperfusion. Hind limb motor functions were assessed according to the Tarlov criterion when the animals regained consciousness, 6, 24 and 48 h after reperfusion. Histological analysis and the number of viable α-motor neurons were also used to assess the extent of spinal cord injury. Compared with the NS group, the Tarlov scores and the number of normal neurons were significantly higher in the D_per group (P<0.05), which were consistent with the results of a previous study. In addition, the paraplegia rate and loss of normal motor neurons were lower in the DADLE per- and post-conditioning groups compared with the DADLE pre-conditioning; however, these were not statistically significant. DADLE 0.05 mg/kg administration at three time points all mitigated normal motor neuron injury in the anterior horn and decreased the paraplegia rates in rabbits. The therapeutic benefits appeared best in the post-conditioning group with DADLE, and worst in the pre-conditioning group.

Hypothermic preconditioning but not ketamine reduces oxygen and glucose deprivation induced neuronal injury correlated with downregulation of COX-2 expression in mouse hippocampal slices

Hypothermic preconditioning is an effective treatment for limiting ischemic injury, but the mechanism is poorly understood. This study was aimed to explore the effect of hypothermic and ketamine preconditioning on oxygen and glucose deprivation (OGD) induced neuronal injury in mouse hippocampal slices, and to investigate its possible mechanism. The population spike (PS) was recorded in the CA1 region of mouse hippocampal slices using extracellular recordings, Na⁺/K⁺ ATPase activity in slices was determined by spectrophotometer and the expression of Cyclooxygenase-2 (COX-2) was measured by Western blot. Ten min of OGD induced a poor recovery of PS in slices after reoxygenation. Hypothermic (33 °C) preconditioning delayed the appearance of transient recovery (TR) of PS and improved the recovery amplitude of PS after reoxygenation. Hypothermic preconditioning also decreased the expression of COX-2 and increased Na⁺/K⁺ ATPase activity in slices. Pretreatment of ketamine, a non-competitive NMDA receptor antagonist at a subanesthetic dose has no effect on OGD induced neuronal injury. Moreover, the protection of hypothermic preconditioning was not added by ketamine. The downregulation of COX-2 expression and the increase of Na⁺/K⁺ ATPase activity may be associated with the effectiveness of hypothermic preconditioning in increasing tolerance to an OGD insult.

Current and emerging treatment options for spinal cord ischemia

Spinal cord infarction (SCI) is a rare but disabling disorder caused by a wide spectrum of conditions. Given the lack of randomized-controlled trials, contemporary treatment concepts are adapted from guidelines for cerebral ischemia, atherosclerotic vascular disease, and acute traumatic spinal cord injury. In addition, patients with SCI are at risk for several potentially life-threatening but preventable systemic and neurologic complications. Notably, there is emerging evidence from preclinical studies for the use of neuroprotection in acute ischemic injury of the spinal cord. In this review, we discuss the current state of the art for the therapy and prevention of SCI and highlight potential emerging treatment concepts awaiting translational adoption.

Dose-effects of aorta-infused clenbuterol on spinal cord ischemia-reperfusion injury in rabbits

Background

The β₂ adrenergic receptor (β₂AR) plays an important role in ischemia-reperfusion (I/R) injury in various organs. Recently, a selective β₂AR agonist clenbuterol was suggested to protect against cerebral I/R injury. This study was designed to investigate changes of β₂ARs after spinal cord I/R injury and dose-effects of aorta-infused clenbuterol on spinal cord I/R injury in rabbits.

Methods

Spinal cord ischemia was induced in New Zealand white rabbits by infrarenal abdominal aortic occlusion with a balloon catheter for 30 minutes except the sham group. During occlusion, nothing (I/R group), normal saline (NS group) or clenbuterol at different doses of 0.005, 0.01, 0.05, 0.1, 0.5, or 1 mg/kg (C_0.005, C_0.01, C_0.05, C_0.1, C_0.5, and C₁ groups) was infused into the occluded aortic segments. The hemodynamic data, blood glucose and serum electrolytes were measured during experimental period. Neurological function was assessed according to the modified Tarlov scales until 48 hours after reperfusion. After that, the lumbar spinal cord was harvested for β₂AR immunohistochemistry and histopathologic evaluation in the anterior horns.

Results

The β₂AR expression in the anterior horns of the spinal cord was significantly higher in the I/R group than in the sham group. Tarlov scores and the number of viable α-motor neurons were higher in C_0.01-C_0.5 groups than in the NS group, C_0.005 and C₁ groups and were highest in the C_0.1 group. Hypotension and hyperglycemia were found in the C₁ group.

Conclusion

β₂ARs in the anterior horn were upregulated after spinal cord I/R injury. Aortic-infused clenbuterol (0.01–0.5 mg/kg) can attenuate spinal cord I/R injury dose-dependently during the ischemic period. The Optimal dosage was 0.1 mg/kg. Activation of β₂AR could be a new therapeutic strategy for the treatment of spinal cord I/R injury.