Concentrations of dexmedetomidine and effect on biomarkers of cartilage toxicity following intra-articular administration in horses.

OBJECTIVE: The goal of this study was to determine plasma, urine, and synovial fluid concentrations and describe the effects on biomarkers of cartilage toxicity following intra-articular dexmedetomidine administration to horses. ANIMALS: 12 research horses. PROCEDURES: Horses received a single intra-articular administration of 1 µg/kg or 5 µg/kg dexmedetomidine or saline. Plasma, urine, and synovial fluid were collected prior to and up to 48 hours postadministration, and concentrations were determined. The effects on CS846 and C2C were determined in synovial fluid at 0, 12, and 24 hours postadministration using immunoassays. RESULTS: Plasma concentrations of dexmedetomidine fell below the limit of quantification (LOQ) (0.005 ng/mL) by 2.5 and 8 hours postadministration of 1 and 5 µg/kg, respectively. Synovial fluid concentrations were above the LOQ (0.1 ng/mL) of the assay at 24 hours in both dose groups. Drug was not detected in urine samples at any time postdrug administration. CS846 concentrations were significantly decreased relative to baseline at 12 hours postadministration in the saline group and significantly increased in the 5-µg/kg-dose group at 24 hours. Concentrations of C2C were significantly decreased at 12 and 24 hours postadministration in the saline treatment group. There were no significant differences in CS846 or C2C concentrations between dose groups at any time. CLINICAL RELEVANCE: Systemic concentrations of dexmedetomidine remained low, compared to synovial fluid concentrations. CS846, a marker of articular cartilage synthesis, increased in a dose-dependent fashion. Based on these findings, further dose titration and investigation of analgesic and adverse effects are warranted.

Combined Cardiopulmonary Assessments Using Impedance and Digital Implants in Conscious Freely Moving Cynomolgus Monkeys, Beagle Dogs, and Göttingen Minipigs: Pharmacological Characterization and Social Housing Effects.

Respiratory monitoring, using impedance with implanted telemetry in socially housed animals, was not possible until the recent development of digital signal transmission. The objective of this study was to evaluate digital telemetry monitoring of cardiopulmonary parameters (respiratory rate, tidal volume, minute volume, electrocardiography (DII), systemic arterial blood pressure, physical activity, and body temperature) in conscious, single-housed, non-rodent species commonly used in toxicology studies following administration of positive/negative controls (saline, dexmedetomidine, morphine, amphetamine, and doxapram), and also, the effects of various social housing arrangements in untreated female and/or male cynomolgus monkeys, Beagle dogs, and Göttingen minipigs (n = 4 per species). Aggressions were observed in socially housed male minipigs, however, which prevented pair-housed assessments in this species. All tested pharmacological agents significantly altered more than one organ system, highlighting important inter-organ dependencies when analyzing functional endpoints. Stress-related physiological changes were observed with single-housing or pair-housing with a new cage mate in cynomolgus monkeys and Beagle dogs, suggesting that stable social structures are preferable to limit variability, especially around dosing. Concomitant monitoring of cardiovascular and respiratory parameters from the same animals may help reduce the number of animals (3 Rs) needed to fulfill the S7A guidelines and allows for identification of organ system functional correlations. Globally, the data support the use of social housing in non-rodents for safety pharmacology multi-organ system (heart and lungs) monitoring investigations.

Dexmedetomidine does not compromise neuronal viability, synaptic connectivity, learning and memory in a rodent model.

Recent animal studies have drawn concerns regarding most commonly used anesthetics and their long-term cytotoxic effects, specifically on the nervous tissue. It is therefore imperative that the search continues for agents that are non-toxic at both the cellular and behavioural level. One such agent appears to be dexmedetomidine (DEX) which has not only been found to be less neurotoxic but has also been shown to protect neurons from cytotoxicity induced by other anesthetic agents. However, DEX's effects on the growth and synaptic connectivity at the individual neuronal level, and the underlying mechanisms have not yet been fully resolved. Here, we tested DEX for its impact on neuronal growth, synapse formation (in vitro) and learning and memory in a rodent model. Rat cortical neurons were exposed to a range of clinically relevant DEX concentrations (0.05-10 µM) and cellular viability, neurite outgrowth, synaptic assembly and mitochondrial morphology were assessed. We discovered that DEX did not affect neuronal viability when used below 10 µM, whereas significant cell death was noted at higher concentrations. Interestingly, in the presence of DEX, neurons exhibited more neurite branching, albeit with no differences in corresponding synaptic puncta formation. When rat pups were injected subcutaneously with DEX 25 µg/kg on postnatal day 7 and again on postnatal day 8, we discovered that this agent did not affect hippocampal-dependent memory in freely behaving animals. Our data demonstrates, for the first time, the non-neurotoxic nature of DEX both in vitro and in vivo in an animal model providing support for its utility as a safer anesthetic agent. Moreover, this study provides the first direct evidence that although DEX is growth permissive, causes mitochondrial fusion and reduces oxygen reactive species production, it does not affect the total number of synaptic connections between the cortical neurons in vitro.

High-Dose Dexmedetomidine Promotes Apoptosis in Fetal Rat Hippocampal Neurons.

OBJECTIVE: Dexmedetomidine (DEX) is a potent a2-adrenoceptor agonist that has sedative, analgesic, and anxiolytic effects. Its primary clinical use is as an adjunct to general anesthesia to reduce anesthetic doses, provide analgesia and sedation in the preoperative and postoperative periods, it also used in intensive care units (ICUs). However, high concentrations of DEX may have toxic effects on neurons and cause neuronal apoptosis. This study aimed to evaluate the potential proapoptotic effects of DEX on fetal rat hippocampal neurons. METHODS: Primary hippocampal were cultured in vitro for 8 days and incubated with different DEX concentrations for 3 h. Cell viability was measured using cell counting kit-8 assays. Cell apoptosis was evaluated using flow cytometry. The expression of apoptosis-related proteins, such as cleaved caspase-3, caspase-9, Cyt-c, Bax, and Bcl-2, was measured by Western blotting. The mitochondrial ATP levels, Δψm, and ROS analyzed were conducted. RESULTS: High concentrations of DEX (≥100 µM) significantly reduced cell viability, induced neuronal apoptosis, upregulated the protein expression of cleaved caspase 3, Bax, cleaved caspase 9, and Cyt-c. DEX also considerably promoted the release of ROS. However, DEX (≥100 µM) downregulated the protein expression of Bcl-2, decreased the mitochondrial membrane potential (MTP), and reduced ATP synthesis. CONCLUSION: High concentrations of dexmedetomidine produced toxic effects on neurons and caused neuronal apoptosis.

Neurotoxicity of sub-anesthetic doses of sevoflurane and dexmedetomidine co-administration in neonatal rats.

BACKGROUND: Preclinical studies suggest that exposures of infant animals to general anesthetics cause acute neurotoxicity and affect their neurobehavioral development representing a potential risk to human infants undergoing anesthesia. Alternative or mitigating strategies to counteract such adverse effects are desirable. Dexmedetomidine (DEX) is a clinically established sedative with potential neuroprotective properties. DEX ameliorates experimental brain injury as well as neurotoxicity caused by anesthetic doses of sevoflurane (SEVO) or other general anesthetics in infant animals. However, it is unknown whether DEX also is beneficial when given together with lower doses of these drugs. Here we tested the hypothesis that DEX co-administration with a sub-anesthetic dose of SEVO reduces responsiveness to external stimuli while also protecting against SEVO-induced brain cell apoptosis. METHOD: Rats were exposed on postnatal day 7 for 6 h to SEVO 1.1, 1.8, or 2.5% and were given intraperitoneal injections of saline or DEX at different doses (1-25 µg/kg) three times during the exposure. Responsiveness to external stimuli, respiratory rates, and blood gases were assessed. Apoptosis was determined in cortical and subcortical brain areas by activated caspase-3 immunohistochemistry. RESULTS: Rats exposed to SEVO 1.1% alone were sedated but still responsive to external stimuli whereas those exposed to SEVO 1.8% reached complete unresponsiveness. SEVO-induced brain cell apoptosis increased dose-dependently, with SEVO 1.1% causing a small increase in apoptosis above that in controls. Co-administration of DEX at 1 µg/kg did not alter the responsiveness to stimuli nor the apoptosis induced by SEVO 1.1%. In contrast, co-administration of DEX at 5 µg/kg or higher with SEVO 1.1% reduced responsiveness but potentiated apoptosis. CONCLUSIONS: In the neonatal rat model, co-administration of a clinically relevant dose of DEX (1 µg/kg) with a sub-anesthetic dose of SEVO (1.1%) does not affect the neurotoxicity of the anesthetic while co-administration of higher doses of DEX with SEVO 1.1% potentiates it.

Dexmedetomidine Inhibits Neuroinflammation by Altering Microglial M1/M2 Polarization Through MAPK/ERK Pathway.

Neuroinflammation is critical in the pathogenesis of neurological diseases. Microglial pro-inflammatory (M1) and anti-inflammatory (M2) status determines the outcome of neuroinflammation. Dexmedetomidine exerts anti-inflammatory effects in many neurological conditions. Whether dexmedetomidine functions via modulation of microglia M1/M2 polarization remains to be fully elucidated. In the present study, we investigated the anti-inflammatory effects of dexmedetomidine on the neuroinflammatory cell model and explored the potential mechanism. BV2 cells were stimulated with LPS to establish a neuroinflammatory model. The cell viability was determined with MTT assay. NO levels were assessed using a NO detection kit. The protein levels of IL-10, TNF-α, iNOS, CD206, ERK1/2, and pERK1/2 were quantified using Western blotting. LPS significantly increased pro-inflammatory factors TNF-α and NO, and M1 phenotypic marker iNOS, and decreased anti-inflammatory factor IL-10 and M2 phenotypic marker CD206 in BV2 cells. Furthermore, exposure of BV2 cells to LPS significantly raised pERK1/2 expression. Pretreatment with dexmedetomidine attenuated LPS-elicited changes in p-ERK, iNOS, TNF-α, NO, CD206 and IL-10 levels in BV2 cells. However, co-treatment with dexmedetomidine and LM22B-10, an agonist of ERK, reversed dexmedetomidine-elicited changes in p-ERK, iNOS, TNF-α, NO, CD206 and IL-10 levels in LPS-exposed BV2 cells. We, for the first time, showed that dexmedetomidine increases microglial M2 polarization by inhibiting phosphorylation of ERK1/2, by which it exerts anti-inflammatory effects in BV2 cells.

Comparison of Cognitive Impairments After Intensive Care Unit Sedation Using Dexmedetomidine and Propofol Among Older Patients.

Despite the high prevalence of cognitive impairment among older adults, little is known about the association of the selection of dexmedetomidine and propofol on cognitive functions of patients after a critical illness. Patients aged ≥70 years who received intensive care unit (ICU) care from Cangzhou Central Hospital between 2013 and 2016 were enrolled and randomized into a dexmedetomidine group and a propofol group with matched demographic and clinical characteristics. At discharge from the ICU and 4 weeks later, the cognitive status of patients was assessed and compared using the Montreal Cognitive Assessment system. There were 164 patients included in the dexmedetomidine group and 159 patients in the propofol group. No significant difference was observed between the 2 groups in terms of age, female sex, body weight, educational level, ICU and hospital stay, comorbidities, and medications. Further, patients from the 2 groups at ICU discharge did not demonstrate significant difference on the Montreal Cognitive Assessment component scores, which showed significant differences between the 2 groups 4 weeks later (P < .05). Moreover, dexmedetomidine and propofol showed different levels of impacts on the cognitive function of patients discharged from the postanesthesia care unit, neurological ICU, and medical ICU. This study demonstrated that patients discharged from the ICU who received propofol for sedation showed less impairment on the cognitive functions when compared with patients who received dexmedetomidine during ICU care 4 weeks after discharge. Despite some limitations, this study provides insights to the decision-making process in the selection of appropriate sedation strategy, especially for the elderly patients.

Dexmedetomidine enhances ropivacaine-induced sciatic nerve injury in diabetic rats.

BACKGROUND: Previous studies suggest that dexmedetomidine has a protective effect against local anaesthetic-induced nerve injury in regional nerve blocks. Whether this potentially protective effect exists in the context of diabetes mellitus is unknown. METHODS: A diabetic state was established in adult male Sprague-Dawley rats with intraperitoneal injection of streptozotocin. Injections of ropivacaine 0.5%, dexmedetomidine 20 µg kg-1 (alone and in combination), or normal saline (all in 0.2 ml) were made around the sciatic nerve in control and diabetic rats (n=8 per group). The duration of sensory and motor nerve block and the motor nerve conduction velocity (MNCV) were determined. Sciatic nerves were harvested at post-injection day 7 and assessed with light and electron microscopy or used for pro-inflammatory cytokine measurements. RESULTS: Ropivacaine and dexmedetomidine alone or in combination did not produce nerve fibre damage in control non-diabetic rats. In diabetic rats, ropivacaine induced significant nerve fibre damage, which was enhanced by dexmedetomidine. This manifested with slowed MNCV, decreased axon density, and decreased ratio of inner to outer diameter of the myelin sheath (G ratio). Demyelination, axon disappearance, and empty vacuoles were also found using electron microscopy. An associated increase in nerve interleukin-1ß and tumour necrosis factor-α was also seen. CONCLUSIONS: Ropivacaine 0.5% causes significant sciatic nerve injury in diabetic rats that is greatly potentiated by high-dose dexmedetomidine. Although the dose of dexmedetomidine used in this study is considerably higher than that used in clinical practice, our data suggest that further studies to assess ropivacaine (alone and in combination with dexmedetomidine) use for peripheral nerve blockade in diabetic patients are warranted.

Dexmedetomidine promotes metastasis in rodent models of breast, lung, and colon cancers.

BACKGROUND: Perioperative strategies can significantly influence long-term cancer outcomes. Dexmedetomidine, an α2-adrenoceptor agonist, is increasingly used perioperatively for its sedative, analgesic, anxiolytic, and sympatholytic effects. Such actions might attenuate the perioperative promotion of metastases, but other findings suggest opposite effects on primary tumour progression. We tested the effects of dexmedetomidine in clinically relevant models of dexmedetomidine use on cancer metastatic progression. METHODS: Dexmedetomidine was given to induce sub-hypnotic to sedative effects for 6-12 h, and its effects on metastasis formation, using various cancer types, were studied in naïve animals and in the context of stress and surgery. RESULTS: Dexmedetomidine increased tumour-cell retention and growth of metastases of a mammary adenocarcinoma (MADB 106) in F344 rats, Lewis lung carcinoma (3LL) in C57BL/6 mice, and colon adenocarcinoma (CT26) in BALB/c mice. The metastatic burden increased in both sexes and in all organs tested, including lung, liver, and kidney, as well as in brain employing a novel external carotid-artery inoculation approach. These effects were mediated through α2-adrenergic, but not α1-adrenergic, receptors. Low sub-hypnotic doses of dexmedetomidine were moderately beneficial in attenuating the deleterious effects of one stress paradigm, but not of the surgery or other stressors. CONCLUSIONS: The findings call for mechanistic translational studies to understand these deleterious effects of dexmedetomidine, and warrant prospective clinical trials to assess the impact of perioperative dexmedetomidine use on outcomes in cancer patients.

Prolonged Duration Local Anesthesia Using Liposomal Bupivacaine Combined With Liposomal Dexamethasone and Dexmedetomidine.

BACKGROUND: The relatively short duration of effect of local anesthetics has been addressed by encapsulation in drug delivery systems. Codelivery with a single compound that produces an adjuvant effect on nerve block but without intrinsic local anesthetic properties can further prolong the nerve block effect. Here, we investigated whether codelivery of more than 1 encapsulated adjuvant compound can further enhance nerve blockade. METHODS: Liposomes loaded with bupivacaine (Bup), dexamethasone phosphate (DexP), or dexmedetomidine (DMED) were synthesized and its in vitro drug release profiles were determined. Animals (Sprague-Dawley rats) were injected with liposomal Bup (Lipo-Bup) and adjuvants at the sciatic nerve and underwent a modified hot plate test to assess the degree of nerve block. The duration of block was monitored and the tissue reaction was assessed. RESULTS: Coinjection of Lipo-Bup with liposomal DexP (Lipo-DexP) and liposomal DMED (Lipo-DMED) prolonged the duration of sciatic nerve block 2.9-fold compared to Lipo-Bup alone (95% confidence interval, 1.9- to 3.9-fold). The duration of the block using this combination was significantly increased to 16.2 ± 3.5 hours compared to Lipo-Bup with a single liposomal adjuvant (8.7 ± 2.4 hours with Lipo-DMED, P = .006 and 9.9 ± 5.9 hours with Lipo-DexP, P = .008). The coinjection of Lipo-Bup with liposomal adjuvants decreased tissue inflammation (P = .014) but did not have a significant effect on myotoxicity when compared to Lipo-Bup alone. Coinjection of Lipo-Bup with unencapsulated adjuvants prolonged the duration of nerve block as well (25.0 ± 6.3 hours; P < .001) however was accompanied by systemic side effects. CONCLUSIONS: Codelivery of Lipo-DexP and Lipo-DMED enhanced the efficacy of Lipo-Bup. This benefit was also seen with codelivery of both adjuvant molecules in the unencapsulated state, but with marked systemic toxicity.

Effects of ketamine, dexmedetomidine and propofol anesthesia on emotional memory consolidation in rats: Consequences for the development of post-traumatic stress disorder.

Intensive Care Unit (ICU) or emergency care patients, exposed to traumatic events, are at increased risk for Post-Traumatic Stress Disorder (PTSD) development. Commonly used sedative/anesthetic agents can interfere with the mechanisms of memory formation, exacerbating or attenuating the memory for the traumatic event, and subsequently promote or reduce the risk of PTSD development. Here, we evaluated the effects of ketamine, dexmedetomidine and propofol on fear memory consolidation and subsequent cognitive and emotional alterations related to traumatic stress exposure. Immediately following an inhibitory avoidance training, rats were intraperitoneally injected with ketamine (100-125mg/kg), dexmedetomidine (0.3-0.4mg/kg) or their vehicle and tested for 48h memory retention. Furthermore, the effects of ketamine (125mg/kg), dexmedetomidine (0.4mg/kg), propofol (300mg/kg) or their vehicle on long-term memory and social interaction were evaluated two weeks after drug injection in a rat PTSD model. Ketamine anesthesia increased memory retention without altering the traumatic memory strength in the PTSD model. However, ketamine induced a long-term reduction of social behavior. Conversely, dexmedetomidine markedly impaired memory retention, without affecting long-lasting cognitive or emotional behaviors in the PTSD model. We have previously shown that propofol anesthesia enhanced 48h memory retention. Here, we found that propofol induced an enduring traumatic memory enhancement and anxiogenic effects in the PTSD model. These findings provide new evidence for clinical studies showing that the use of ketamine or propofol anesthesia in emergency care and ICU might be more likely to promote the development of PTSD, while dexmedetomidine might have prophylactic effects.

Dexmedetomidine Combined with Therapeutic Hypothermia Is Associated with Cardiovascular Instability and Neurotoxicity in a Piglet Model of Perinatal Asphyxia.

The selective α2-adrenoreceptor agonist dexmedetomidine has shown neuroprotective, analgesic, anti-inflammatory, and sympatholytic properties that may be beneficial in neonatal encephalopathy (NE). As therapeutic hypothermia is only partially effective, adjunct therapies are needed to optimize outcomes. The aim was to assess whether hypothermia + dexmedetomidine treatment augments neuroprotection compared to routine treatment (hypothermia + fentanyl sedation) in a piglet model of NE using magnetic resonance spectroscopy (MRS) biomarkers, which predict outcomes in babies with NE, and immunohistochemistry. After hypoxia-ischaemia (HI), 20 large White male piglets were randomized to: (i) hypothermia + fentanyl with cooling to 33.5°C from 2 to 26 h, or (ii) hypothermia + dexmedetomidine (a loading dose of 2 µg/kg at 10 min followed by 0.028 µg/kg/h for 48 h). Whole-brain phosphorus-31 and regional proton MRS biomarkers were assessed at baseline, 24, and 48 h after HI. At 48 h, cell death was evaluated over 7 brain regions by means of transferase-mediated d-UTP nick end labeling (TUNEL). Dexmedetomidine plasma levels were mainly within the target sedative range of 1 µg/L. In the hypothermia + dexmedetomidine group, there were 6 cardiac arrests (3 fatal) versus 2 (non-fatal) in the hypothermia + fentanyl group. The hypothermia + dexmedetomidine group required more saline (p = 0.005) to maintain blood pressure. Thalamic and white-matter lactate/N-acetylaspartate did not differ between groups (p = 0.66 and p = 0.21, respectively); the whole-brain nucleotide triphosphate/exchangeable phosphate pool was similar (p = 0.73) over 48 h. Cell death (TUNEL-positive cells/mm2) was higher in the hypothermia + dexmedetomidine group than in the hypothermia + fentanyl group (mean 5.1 vs. 2.3, difference 2.8 [95% CI 0.6-4.9], p = 0.036). Hypothermia + dexmedetomidine treatment was associated with adverse cardiovascular events, even within the recommended clinical sedative plasma level; these may have been exacerbated by an interaction with either isoflurane or low body temperature. Hypothermia + dexmedetomidine treatment was neurotoxic following HI in our piglet NE model, suggesting that caution is vital if dexmedetomidine is combined with cooling following NE.

Global reduction of information exchange during anesthetic-induced unconsciousness.

During anesthetic-induced unconsciousness (AIU), the brain undergoes a dramatic change in its capacity to exchange information between regions. However, the spatial distribution of information exchange loss/gain across the entire brain remains elusive. In the present study, we acquired and analyzed resting-state functional magnetic resonance imaging (rsfMRI) data in rats during wakefulness and graded levels of consciousness induced by incrementally increasing the concentration of isoflurane. We found that, regardless of spatial scale, the functional connectivity (FC) change (i.e., ∆FC) was proportionally dependent on the FC strength at the awake state across all connections. This dependency became stronger at higher doses of isoflurane. In addition, the relative FC change at each anesthetized condition (i.e., ∆FC normalized to the corresponding FC strength at the awake state) was exclusively negative across the whole brain, indicating a global loss of meaningful information exchange between brain regions during AIU. To further support this notion, we showed that during unconsciousness, the entropy of rsfMRI signal increased to a value comparable to random noise while the mutual information decreased appreciably. Importantly, consistent results were obtained when unconsciousness was induced by dexmedetomidine, an anesthetic agent with a distinct molecular action than isoflurane. This result indicates that the observed global reduction in information exchange may be agent invariant. Taken together, these findings provide compelling neuroimaging evidence suggesting that the brain undergoes a widespread disruption in the exchange of meaningful information during AIU and that this phenomenon may represent a common system-level neural mechanism of AIU.

Different doses of dexmedetomidine reduce plasma cytokine production, brain oxidative injury, PARP and caspase expression levels but increase liver oxidative toxicity in cerebral ischemia-induced rats.

Cerebral ischemia-induced progression of brain, liver, and erythrocyte oxidative injuries might be modulated by dexmedetomidine (DEX) as a potent antioxidant and anti-inflammatory drug. The present study was conducted to explore whether two different doses of DEX protect against plasma cytokine and brain, liver and erythrocyte oxidative toxicity and apoptosis in cerebral ischemia-induced rats. Forty-two rats were equally divided into 7 groups. The first and second groups were used as untreated and sham controls, respectively. The third (DEX4) and fourth (DEX40) groups received 4mg/kg and 40mg/kg DEX treatments. The fifth, sixth and seventh group were operated on to induce cerebral ischemia. The fifth, sixth and seventh groups are used to represent cerebral ischemia, cerebral ischemia+DEX4, and cerebral ischemia+DEX40, respectively. DEX was intraperitoneally given to the DEX groups at the 3rd, 24th and 48th hour. Brain and erythrocyte lipid peroxidation (MDA) levels and plasma IL-1ß and TNF-α levels were high in the cerebral ischemia group although they were low in the DEX4 and DEX40 groups. Decreased glutathione peroxidase (GSH-Px) and reduced glutathione (GSH) values in the brain and erythrocyte of the cerebral ischemia group were increased by the DEX treatments, although PARP, and the caspase 3 and 9 expressions in the brain were further decreased. Conversely, the cerebral ischemia-induced decrease in the liver vitamin A, vitamin E, GSH, and GSH-Px were further decreased by the DEX treatments, although MDA level, PARP, and caspase 3 and 9 expressions were further increased by the DEX treatments. In conclusion, DEX induced protective effects against cerebral ischemia-induced brain and erythrocyte oxidative injuries through regulation of the antioxidant level and cytokine production. However, both doses of DEX induced oxidative toxicity and apoptotic effects in the rats' livers.

Comparison of histopathological effects of perineural administration of bupivacaine and bupivacaine-dexmedetomidine in rat sciatic nerve.

Injection of a variety of drugs such as local anesthetics (LAs) for peripheral nerve block has been shown to cause damage to peripheral nerves. Bupivacaine is a local anesthetic widely used in surgical procedures. The aim of this study was to evaluate the neurotoxicity of LAs including Bupivacaine and dexmedetomidine (DEX)-Bupivacaine on sciatic nerve tissue at histopathological level. In addition, we investigated whether perineural administration of DEX can attenuate Bupivacaine-induced neurotoxicity. Twenty adult Sprague Dawley rats received unilateral sciatic nerve blocks with either 0.2ml of 0.5% bupivacaine (n=8) or 0.5% bupivacaine plus 0.005% DEX (n=8) or normal saline (0.9%, as control group) (n=4) in the left hind extremity. Sciatic nerves were harvested at 14days post-injection and analyzed for nerve damage using ultrastructure and histopathologic analysis. Histopathology of sciatic nerve at day 14 post-injection showed a variable degree of neuronal injury associated with perineural inflammation in each treatment group and was classified as none or mild, intermediate or severe. Administration of both LAs resulted in a significant decrease in the total number of myelinated fibers per nerve (95% CI for group difference: Bupivacaine, P=0.001, DEX-Bupivacaine, P=0.036) compared to the saline control group. Animals that received these perineural local anesthetics (LAs) injections showed increased severity of injury compared to the control group. Animals in the DEX-Bupivacaine group had higher perineural inflammation and nerve damage than those of the saline control group and less than those of the Bupivacaine group at day 14 post-injection. Quantitatively, average total nerve fiber per nerve and average myelinated nerve fiber density in the injured region of the Bupivacaine-treated group was less than that of the DEX-Bupivacaine-treated group. LAs injection into the nerve causes peripheral nerve damage and remains an important clinical danger. Bupivacaine is associated with considerable histopathological changes, including edema of the perineurium and myelin degeneration with Wallerian degeneration, when injected perineurally. Perineural DEX added to a clinical concentration of bupivacaine attenuates the Bupivacaine-induced injuries.

Dexmedetomidine-Induced Neuroapoptosis Is Dependent on Its Cumulative Dose.

BACKGROUND: Dexmedetomidine (DEX) has inherent neuroprotective properties that have been attributed to the activation of prosurvival kinases. However, the impact of supraclinical doses of DEX on neuroapoptosis and neuronal viability has not been determined. METHODS: Rat pups and primary neuronal cells were treated with DEX or ketamine (KET) alone or in combination. Neuroapoptosis was measured by cleaved-caspase-3 expression and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining in brain sections. Expression of prosurvival kinases was measured by Western blot. We measured the impact of DEX with and without α1-adrenergic receptor blockade on the viability of primary neuronal cell cultures. RESULTS: Increasing the cumulative dose of DEX resulted in elevated levels of neuroapoptosis in vivo. Low doses increased, whereas high dose decreased phosphorylation of the prosurvival kinases. KET alone and in combination with DEX produced a greater degree of apoptosis and reductions in expression of these protein kinases than DEX alone. Increasing concentrations of DEX decreased, while coadministration of an α1-adrenergic receptor blocker preserved neuronal viability in vitro. CONCLUSIONS: Although DEX is neuroprotective at clinical doses, high cumulative doses and concentrations induce neuroapoptosis, in vivo and in vitro, respectively. Because the current dosing schedules used in humans yield plasma levels that are substantially below concentrations that induce neurotoxicity, low-dose DEX should not be neurotoxic and has the potential to be a neuroprotective adjuvant.

Histological and biochemical effects of dexmedetomidine on liver during an inflammatory bowel disease.

Inflammation in the liver is an extraintestinal manifestation that is frequently seen during inflammatory bowel diseases (IBD). The authors investigated histopathologycal, ultrastructural and antioxidant effects of dexmedetomidine (Dex) on liver during trinitrobenzene sulfonic acid (TNBS)-induced inflammatory bowel disease. Thirty-two BALB/c mice were divided (n = 8) as follows: control; Dex (dexmedetomidine) (30 µg/kg) for 6 days; TNBS 150 µL, TNBS + ethanol (50% w/v) intrarectally; TNBS + Dex. The histopathological and ultrastructural changes were evaluated. The levels of malondialdehyde (MDA), activity of antioxidant enzymes (GPx and SOD) were measured in liver tissue. Induction of colitis induced histopathological and ultrastructural changes of damage in liver. Those changes were markedly reduced in the TNBS + Dex group and that reduction was even significant in comparison to the TNBS group. MDA levels were significantly higher in the TNBS group and dexmedetomidine significantly elevated SOD levels in the TNBS + Dex group. These results suggest that the administration of dexmedetomidine reduces the histopathological and ultrastructural damage and increases the defense capacity against oxidative damage on liver in this IBD mice model.

Neurotoxic effects of dexmedetomidine in fetal cynomolgus monkey brains.

The neuroprotective effects of dexmedetomidine have been reported by many investigators; however its underlying mechanism to reduce neuronal injury during a prolonged anesthesia remains unclear. In this study, we investigated the neurotoxic effects of dexmedetomidine in fetal monkey brains. In the present study, we compare the neurotoxic effects of dexmedetomidine and ketamine, a general anesthetic with a different mechanism of action, in fetal cynomolgus monkeys. Twenty pregnant monkeys at approximate gestation day 120 were divided into 4 groups: non-treatment controls (Group 1); ketamine at 20 mg/kg intramuscularly followed by a 12-hr infusion at 20-50 mg/kg/hr (Group 2); dexmedetomidine at 3 µg/kg intravenously (i.v.) over 10 min followed by a 12-hr infusion at the human equivalent dose (HED) of 3 µg/kg/hr (Group 3); and dexmedetomidine at 30 µg/kg i.v. over 10 min followed by a 12-hr infusion at 30 µg/kg/hr, 10 times HED (Group 4). Blood samples from both dams and fetuses were measured for concentration of dexmedetomidine. Each fetus was perfusion-fixed, serial sections were cut through the frontal cortex, and stained to detect for apoptosis (activated caspase 3 and TUNEL) and neurodegeneration (silver stain). In utero treatment with ketamine resulted in marked apoptosis and degeneration primarily in layers I and II of the frontal cortex. In contrast, fetal brains from animals treated with dexmedetomidine showed none to minimal neuroapoptotic or neurodegenerative lesions at both low- and high-dose treatments. Plasma levels confirmed systemic exposure of dexmedetomidine in both dams and fetuses. In conclusion, these results demonstrate that dexmedetomidine at both low-dose (HED) and high-dose (10 times HED) does not induce apoptosis in the frontal cortex (layers I, II, and III) of developing brain of cynomolgus monkeys.

[Comparison of dexmedetomidine and midazolam on neurotoxicity in neonatal mice].

Dexmedetomidine and midazolam have been widely used in clinical anesthesia and intensive care unit sedation. These two drugs differ in sedative mechanism. We hypothesized that the neurotoxicity of repeated exposure to dexmedetomidine or midazolam for neonatal mice might be different. Twenty four mice of postnatal day 8 were randomly divided into control (n=8), dexmedetomidine (n=8) and midazolam group (n=8) respectively. In the three groups, saline(10mL/kg), dexmedetomidine(10microg/kg) or midazolam(40mg/kg) was injected intraperitoneally once a day, in the next five days, respectively. Then the brains of the mice in the three qroups were removed and cryosectioned. Apoptotic neural cell in hippocampus region was detected with terminal deoxynucleotydyl transferase -mediated dUTP nick end labeling(TUNEL). Bcl2 and Bax protein expression level in the hippocampus were determined by immunofluorescent staining. In the present study, the number of TUNEL-positive cells from midazolam group ((20 +/-3) /mm2) was larger than that from dexmedetomidine group ((15+/-2) /mm2, P<0. 05) and control group((13+/-3) /mm2, P<0. 05); Bcl-2 protein quantity in hippocampus from control group((790+/-103)/mm2)was significantly lower than that in midazolam group((1187+/- 162)/mm2, P<0.05)and dexmedetomidine group((890+/-125)/mm2, P<0. 05). Bax protein level in control group((942+/-104)/mm2) was also significantly lower than that in midazolam group((1839+/-160)/mm2, P<0. 05)and dexmedetomidine group((1143+/-125)/mm2, P<0. 05); Bax/Bcl-2 ratio in midazolam group(0. 64+/-0. 13) was significantly lower than that in dexmedetomidine group(0. 78 +/-0. 14, P<0. 05) and control group(0. 84+/-0. 15, P<0. 05). Our results suggest that dexmedetomidine has lower neurotoxicity than midazolam for neonatal mice.

Molecular mechanisms underlying the analgesic property of intrathecal dexmedetomidine and its neurotoxicity evaluation: an in vivo and in vitro experimental study.

BACKGROUND: Dexmedetomidine (DEX) has been used under perioperative settings as an adjuvant to enhance the analgesic property of local anesthetics by some anesthesiologists. However, the analgesic mechanisms and neurotoxicity of DEX were poorly understood. This study examined the effect of DEX alone on inflammatory pain, and it also examined the underlying molecular mechanisms of DEX in the spinal cord. Furthermore, in vivo and in vitro experiments were performed to investigate the neurotoxicity of DEX on the spinal cord and cortical neurons. METHODS: This study used adult, male Kunming mice. In the acute inflammatory model, the left hind-paws of mice were intradermally injected with pH 5.0 PBS while chronic constrictive injury (CCI) of the sciatic nerve was used to duplicate the neuropathic pain condition. Thermal paw withdrawal latency and mechanical paw withdrawal threshold were tested with a radiant heat test and the Von Frey method, respectively. Locomotor activity and motor coordination were evaluated using the inverted mesh test. Western blotting examined spinal ERK1/2, p-ERK1/2, caspase-3 and ß-actin expressions, while spinal c-Fos protein expression was realized with immunohistochemical staining. Hematoxylin eosin (HE) staining was used to examine the pathological impacts of intrathecal DEX on the spinal cord. DAPI (4',6-diamidino-2-phenylindole) staining was used to observe cell death under an immunofluorescence microscope. RESULTS: Intra-plantar pH 5.0 PBS-induced acute pain required spinal ERK1/2 activation. Inhibition of spinal ERK1/2 signaling by intrathecal injection of DEX displayed a robust analgesia, via a α2-receptor dependent manner. The analgesic properties of DEX were validated in CCI mice. In vivo studies showed that intrathecal DEX has no significant pathological impacts on the spinal cord, and in vitro experiments indicated that DEX has potential protective effects of lidocaine-induced neural cell death. CONCLUSION: Intrathecal injection of DEX alone or as an adjuvant might be potential for pain relief.