The effect of lidocaine on apoptotic neurodegeneration in the developing mouse brain

The potential role of dexmedetomidine on neuroprotection and its possible mechanisms: Evidence from in vitro and in vivo studies

Neurological disorders following brain injuries and neurodegeneration are on the rise worldwide and cause disability and suffering in patients. It is crucial to explore novel neuroprotectants. Dexmedetomidine, a selective α2-adrenoceptor agonist, is commonly used for anxiolysis, sedation and analgesia in clinical anaesthesia and critical care. Recent studies have shown that dexmedetomidine exerts protective effects on multiple organs. This review summarized and discussed the current neuroprotective effects of dexmedetomidine, as well as the underlying mechanisms. In preclinical studies, dexmedetomidine reduced neuronal injury and improved functional outcomes in several models, including hypoxia-induced neuronal injury, ischaemic-reperfusion injury, intracerebral haemorrhage, post-traumatic brain injury, anaesthetic-induced neuronal injury, substance-induced neuronal injury, neuroinflammation, epilepsy and neurodegeneration. Several mechanisms are associated with the neuroprotective function of dexmedetomidine, including neurotransmitter regulation, inflammatory response, oxidative stress, apoptotic pathway, autophagy, mitochondrial function and other cell signalling pathways. In summary, dexmedetomidine has the potential to be a novel neuroprotective agent for a wide range of neurological disorders.

Naringenin Prevents Propofol Induced Neurodegeneration in Neonatal Mice Brain and Long-Term Neurocognitive Impacts on Adults

Background

Natural products have shown neuroprotective effects in neurodegenerative conditions. Naringenin is a natural flavonoid with various pharmacological activities especially antioxidant, anti-inflammatory and neuroprotective properties. We investigated the effects of naringenin on anesthetic propofol-induced impacts on neonatal mouse brain development and consequent long-term neurocognitive impacts during adulthood.

Materials and Methods

Female C57Bl/6 and male CD-1 mice and postnatal day 7 (P7) pups were exposed to propofol (2.5 mg/kg) and propofol with naringenin (50 mg/kg). Mice pups were allowed to grow until week 10 (adulthood), and memory and learning were assessed.

Results

Propofol caused neurodegeneration by inducing apoptosis in the neonatal mouse brains while naringenin administration prevented neuronal cell loss by preventing neuronal apoptosis in neonatal mouse brains. Propofol caused degenerative alterations in metabolic factors pH, PO₂, glucose and lactate, which were subsequently restored by naringenin treatment. Propofol-exposed mice, when developed into adults, showed long-term neuronal deficits, impaired neurocognitive functions, and memory and learning restrictions.

Conclusion

Administration of naringenin to propofol-exposed mice resulted in significant neuroprotective effects by restoring long-term neurocognitive functions. The molecular mechanism behind the effects of naringenin was mediated by suppressing apoptosis and preventing cellular inflammation. These findings suggest that propofol administration requires careful consideration and that naringenin may prevent neurodegeneration and neurocognitive functions.

Dexmedetomidine protects against lidocaine-induced neurotoxicity through SIRT1 downregulation-mediated activation of FOXO3a

Lidocaine, a typical local anesthetic, has been shown to directly induce neurotoxicity in clinical settings. Dexmedetomidine (DEX) is an alpha-2-adrenoreceptor agonist that has been used as anxiolytic, sedative, and analgesic agent which has recently found to protect against lidocaine-induced neurotoxicity. Nicotinamide adenine dinucleotide-dependent deacetylase sirtuin-1 (SIRT1)/forkhead box O3 (FOXO3a) signaling is critical for maintaining neuronal function and regulation of the apoptotic pathway. In the present study, we designed in vitro and in vivo models to investigate the potential effects of lidocaine and DEX on SIRT1 and FOXO3a and to verify whether SIRT1/FOXO3a-mediated regulation of apoptosis is involved in DEX-induced neuroprotective effects against lidocaine. We found that in both PC12 cells and brains of mice, lidocaine decreased SIRT1 level through promoting the degradation of SIRT1 protein. Lidocaine also increased FOXO3a protein level and increased the acetylation of SIRT1 through inhibiting SIRT1. Upregulation of SIRT1 or downregulation of FOXO3a significantly inhibited lidocaine-induced changes in both cell viability and apoptosis. DEX significantly inhibited the lidocaine-induced decrease of SIRT1 protein level and increase of FOXO3a protein level and acetylation of FOXO3a. Downregulation of SIRT1 or upregulation of FOXO3a suppressed DEX-induced neuroprotective effects against lidocaine. The data suggest that SIRT1/FOXO3a is a potential novel target for alleviating lidocaine-induced neurotoxicity and provide more theoretical support for the use of DEX as an effective adjunct to alleviate chronic neurotoxicity induced by lidocaine.

Relevance of experimental paradigms of anesthesia induced neurotoxicity in the mouse

Routine general anesthesia is considered to be safe in healthy individuals. However, pre-clinical studies in mice, rats, and monkeys have repeatedly demonstrated that exposure to anesthetic agents during early post-natal periods can lead to acute neurotoxicity. More concerning, later-life defects in cognition, assessed by behavioral assays for learning and memory, have been reported. Although the potential for anesthetics to damage the neonatal brain is well-documented, the clinical significance of the pre-clinical models in which damage is induced remains quite unclear. Here, we systematically evaluate critical physiological parameters in post-natal day 7 neonatal mice exposed to 1.5% isoflurane for 2–4 hours, the most common anesthesia induced neurotoxicity paradigm in this animal model. We find that 2 or more hours of anesthesia exposure results in dramatic respiratory and metabolic changes that may limit interpretation of this paradigm to the clinical situation. Our data indicate that neonatal mouse models of AIN are not necessarily appropriate representations of human exposures.

Neurotoxicity of anesthetics: Mechanisms and meaning from mouse intervention studies

Volatile anesthetics are widely used in human medicine and generally considered to be safe in healthy individuals. In recent years, the safety of volatile anesthesia in pediatric patients has been questioned following reports of anesthetic induced neurotoxicity in pre-clinical studies. These studies in mice, rats, and primates have demonstrated that exposure to anesthetic agents during early post-natal periods can cause acute neurotoxicity, as well as later-life cognitive defects including deficits in learning and memory. In recent years, the focus of many pre-clinical studies has been on identifying candidate pathways or potential therapeutic targets through intervention trials. These reports have shed light on the mechanisms underlying anesthesia induced neurotoxicity as well as highlighting the challenges of pre-clinical modeling of anesthesia induced neurotoxicity in mice. Here, we summarize the data derived from intervention studies in neonatal mouse models of anesthetic exposure and provide an overview of mechanisms proposed to mediate anesthesia induced neurotoxicity in mice based on these reports. The majority of these studies implicate one of three mechanisms: reactive oxygen species (ROS) mediated stress and signaling, growth/nutrient signaling, or direct neuronal modulation.

Bioactive Compounds of Kimchi Inhibit Apoptosis by Attenuating Endoplasmic Reticulum Stress in the Brain of Amyloid β-Injected Mice

This study investigated the inhibitory effects of kimchi bioactive compounds against endoplasmic reticulum (ER) stress-induced apoptosis in amyloid beta (Aβ)-injected mice. Mice received a single intracerebroventricular injection of Aβ_25-35, except for the normal group. Mice were subjected to oral administration of 10 mg of capsaicin, 50 mg of 3-(4'-hydroxyl-3',5'-dimethoxyphenyl)propionic acid (HDMPPA), 50 mg of quercetin, 50 mg of ascorbic acid, or 200 mg of kimchi methanol extract (KME) per kilogram of body weight for 2 weeks ( n = 7 per group). In the in vitro blood-brain barrier (BBB) permeability test, all bioactive compounds penetrated the BBB except ascorbic acid. The protein expression level of APP, BACE, and p-Tau elevated by Aβ injection was decreased by kimchi bioactive compounds ( P < 0.05). Quercetin, HDMPPA, and KME decreased oxidative stress, as indicated by ROS and TBARS levels ( P < 0.05). The protein expression level of ER stress markers GRP78, p-PERK, p-eIF2α, XBP1, and CHOP and the proapoptotic molecules Bax, p-JNK, and cleaved caspases-3 and -9 decreased ( P < 0.05). In contrast, the protein expression level of antiapoptotic molecules Bcl2 and cIAP increased ( P < 0.05). These results were supported by histological analysis.

GNB2 is a mediator of lidocaine-induced apoptosis in rat pheochromocytoma PC12 cells

Lidocaine has been recognized to induce neurotoxicity. However, the molecular mechanism underlying this effect, especially the critical molecules in cells that mediated the lidocaine-induced apoptosis were unclear. In the present study, PC12 cells were administrated with lidocaine for 48h. Using MTT assay and flow cytometry, we found lidocaine significantly decreased the cell proliferation and S phases in PC12 cells with treatment concentrations, and significantly enhanced cell apoptosis with treatment concentrations. Two-dimensional gel electrophoresis (2-DE) analysis and LC-MS/MS were used to identification of protein biomarkers. Six proteins were identified. Among them, three were up-expressed including ANXA6, GNB2 and STMN1, other three were down-expressed including ubiquitin-linke protein 7 (UBL7), DDAH2 and BLVRB. Using qRT-PCR, we confirmed that lidocaine up-regulated the mRNA expression of STMN1, GNB2, ANXA6 and DDAH2, and found that the GNB2 had the largest change (about increased by 6.4 folds). The up-regulation of GNB2 by lidocaine was also validated by western blot. After transfected with 100μM GNB2-Rat-453 siRNA, the expression of GNB2 in PC12 cells was almost completely inhibited; and the cell proliferation and cells in S phases were significantly enhanced, cell apoptosis including both early apoptosis and later apoptosis were significantly reduced in the presence of 0.5mM lidocaine for 48h. Therefore, neuronal apoptosis was induced by lidocaine and this effect was mediated by GNB2. Further research is needed to assess the clinical relevance and exact mechanism of neuronal apoptosis caused by lidocaine.