Propofol inhibits proliferation and induces neuroapoptosis of hippocampal neurons in vitro via downregulation of NF-κB p65 and Bcl-2 and upregulation of caspase-3

Ganglioside GM1 Alleviates Propofol-Induced Pyroptosis in the Hippocampus of Developing Rats via the PI3K/AKT/NF-κB Signaling Cascade

In pediatric and intensive care units, propofol is widely used for general anesthesia and sedation procedures as a short-acting anesthetic. Multiple studies have revealed that propofol causes hippocampal injury and cognitive dysfunction in developing animals. As is known, GM1, a type of ganglioside, plays a crucial role in promoting nervous system development. Consequently, this study explored whether GM1 mitigated neurological injury caused by propofol during developmental stages and investigated its underlying mechanisms. Seven-day-old SD rats or PC12 cells were used in this study for histopathological analyses, a Morris water maze test, a lactate dehydrogenase release assay, Western blotting, and an ELISA. Furthermore, LY294002 was employed to explore the potential neuroprotective effect of GM1 via the PI3K/AKT signaling cascade. The results indicated that GM1 exerted a protective effect against hippocampal morphological damage and pyroptosis as well as behavioral abnormalities following propofol exposure by increasing p-PI3K and p-AKT expression while decreasing p-p65 expression in developing rats. Nevertheless, the inhibitor LY294002, which targets the PI3K/AKT cascade, attenuated the beneficial effects of GM1. Our study provides evidence that GM1 confers neuroprotection and attenuates propofol-induced developmental neurotoxicity, potentially involving the PI3K/AKT/NF-κB signaling cascade.

Dexmedetomidine Protects Cortical Neurons from Propofol-Induced Apoptosis via Activation of Akt-IKK-NF-κB Signaling Pathway by α2A-adrenoceptor

CONTEXT

Propofol can induce neuroapoptosis. It has been reported that dexmedetomidine (DEX) has a protective effect on propofol-induced neuroapoptosis, but the specific mechanism needs to be further explored to provide a theoretical basis for their combined use.

OBJECTIVE

We aimed to explore the neuroprotective effect of DEX on primary cortical neurons treated by propofol and to elucidate the underlying mechanistic pathways.

METHODS

Cortical neurons were isolated from fetal rats and treated with propofol. MTT assays were performed to detect cell viability, α-tubulin immunofluorescent assays were conducted to observe cell abnormalities, and c-caspase3 immunofluorescent assays and flow cytometry were performed to examine cell apoptosis. Further, neurons were cotreated with propofol and DEX to study DEX's neuroprotective effects on propofol-caused neuronal injuries. Finally, the α2A-adrenoceptor was knocked out and/or the Akt activator (SC-79) was added to cells co-treated with propofol and DEX. The expression levels of Akt-IKK-NF-κB pathway-related proteins were detected by western blot.

RESULTS

Propofol decreased cell viability in a dose-dependent manner, triggered apoptosis, caused morphological abnormalities and down-regulated the phosphorylation levels of Akt, IKK, NF-κB and IκB in cortical neurons. DEX ameliorated the decrease of cell viability, alleviated neuronal apoptosis and promoted the downregulated expression levels of p-Akt, IKK, NF-κB, and IκB proteins which had been induced by propofol treatment. Western blot findings following the transfection of α2A-siRNA and the addition of SC-79 suggested that DEX's neuroprotective functions arose from the stimulation of α2A-adrenoceptors to activate the Akt-IKK-NF-κB signal pathway.

CONCLUSION

DEX protected neurons against propofol-induced apoptosis via activation of the Akt-IKK-NF-κB signal pathway through α2A-adrenoceptors.

Downregulation of miR-138-5p alleviates propofol-induced neurotoxicity and autophagy by regulating SIRT1

BACKGROUND

Propofol, a commonly utilized anesthetic, has been shown to induce neurotoxicity in developing neurons. A previous study showed that microRNA (miR)-138-5p was dysregulated in hippocampus tissue of mice administrated with propofol. The current study aimed to investigate the functions of miR-138-5p and its target gene in propofol-induced neurotoxicity.

METHODS

SH-SY5Y neuronal cells were treated with increasing doses of propofol for indicated time to identify the optimal concentration and treatment time. MiR-138-5p and SIRT1 expression in SH-SY5Y neuronal cells stimulated with propofol were measured by RT-qPCR. Western blotting was performed to quantify protein levels of SIRT1 and autophagy markers. After interference of miR-138-5p and/or SIRT1 expression, the toxicity of SH-SY5Y neuronal cells was evaluated by cell counting kit-8 (CCK-8) assays and flow cytometry. The formation of autophagosomes was estimated by monodansylcadaverine staining.

RESULTS

Propofol induced neurotoxicity in a dose- or time-dependent manner. Propofol upregulated miR-138-5p while downregulating SIRT1 in SH-SY5Y neuronal cells. The propofol-stimulated neurotoxicity and autophagy was inhibited by miR-138-5p knockdown. Moreover, miR-138-5p bound to SIRT1 3'untranslated region. SIRT1 overexpression increased cell viability while inhibiting apoptosis and autophagy in the context of propofol. SIRT1 downregulation reversed the ameliorative effect of miR-138-5p inhibition on propofol-induced neurotoxicity and autophagy.

CONCLUSION

Downregulation of miR-138-5p alleviates propofol-induced neurotoxicity and autophagy via upregulation of SIRT1.

Propofol-Induced Developmental Neurotoxicity: From Mechanisms to Therapeutic Strategies

Propofol is the most commonly used intravenous general anesthetic in clinical anesthesia, and it is also widely used in general anesthesia for pregnant women and infants. Some clinical and preclinical studies have found that propofol causes damage to the immature nervous system, which may lead to neurodevelopmental disorders and cognitive dysfunction in infants and children. However, its potential molecular mechanism has not been fully elucidated. Recent in vivo and in vitro studies have found that some exogenous drugs and interventions can effectively alleviate propofol-induced neurotoxicity. In this review, we focus on the relevant preclinical studies and summarize the latest findings on the potential mechanisms and therapeutic strategies of propofol-induced developmental neurotoxicity.

Role of ferroptosis in hypoxic preconditioning to reduce propofol neurotoxicity

Background: An increasing number of studies have reported that neurotoxicity of propofol may cause long-term learning and cognitive dysfunction. Hypoxic preconditioning has been shown to have neuroprotective effects, reducing the neurotoxicity of propofol. Ferroptosis is a new form of death that is different from apoptosis, necrosis, autophagy and pyroptosis. However, it is unclear whether hypoxic preconditioning reduces propofol neurotoxicity associated with ferroptosis. Thus, we aimed to evaluate the effect of propofol on primary hippocampal neurons in vitro to investigate the neuroprotective mechanism of hypoxic preconditioning and the role of ferroptosis in the reduction of propofol neurotoxicity by hypoxic preconditioning. Methods: Primary hippocampal neurons were cultured for 8 days in vitro and pretreated with or without propofol, hypoxic preconditioning, agonists or inhibitors of ferroptosis. Cell counting kit-8, Calcein AM, Reactive oxygen species (ROS), Superoxide dismutase (SOD), Ferrous iron (Fe²⁺), Malondialdehyde (MDA) and Mitochondrial membrane potential assay kit with JC-1 (JC-1) assays were used to measure cell viability, Reactive oxygen species level, Superoxide dismutase content, Fe²⁺ level, MDA content, and mitochondrial membrane potential. Cell apoptosis was evaluated using flow cytometry analyses, and ferroptosis-related proteins were determined by Western blot analysis. Results: Propofol had neurotoxic effects that led to decreased hippocampal neuronal viability, reduced mitochondrial membrane potential, decreased SOD content, increased ROS level, increased Fe²⁺ level, increased MDA content, increased neuronal apoptosis, altered expression of ferroptosis-related proteins and activation of ferroptosis. However, hypoxic preconditioning reversed these effects, inhibited ferroptosis caused by propofol and reduced the neurotoxicity of propofol. Conclusion: The neurotoxicity of propofol in developing rats may be related to ferroptosis. Propofol may induce neurotoxicity by activating ferroptosis, while hypoxic preconditioning may reduce the neurotoxicity of propofol by inhibiting ferroptosis.

WIN55,212-2 Attenuates Cognitive Impairments in AlCl3 + d-Galactose-Induced Alzheimer's Disease Rats by Enhancing Neurogenesis and Reversing Oxidative Stress

Neurotransmission and cognitive dysfunctions have been linked to old age disorders including Alzheimer’s disease (AD). Aluminium is a known neurotoxic metal, whereas d-galactose (d-gal) has been established as a senescence agent. WIN55,212-2 (WIN), is a potent cannabinoid agonist which partially restores neurogenesis in aged rats. The current study aimed to explore the therapeutic potentials of WIN on Aluminium chloride (AlCl₃) and d-gal-induced rat models with cognitive dysfunction. Healthy male albino Wistar rats weighing between 200–250 g were injected with d-gal 60 mg/kg intra peritoneally (i.p), while AlCl₃ (200 mg/kg) was orally administered once daily for 10 consecutive weeks. Subsequently, from weeks 8–11 rats were co-administered with WIN (0.5, 1 and 2 mg/kg/day) and donepezil 1 mg/kg. The cognitive functions of the rats were assessed with a Morris water maze (MWM). Furthermore, oxidative stress biomarkers; malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) and neurogenesis markers: Nestin and glial fibrillary acidic protein (GFAP) were also evaluated, as well as the histology of the hippocampus. The results revealed that rats exposed to AlCl₃ and d-gal alone showed cognitive impairments and marked neuronal loss (p < 0.05) in their hippocampal conus ammonis 1 (CA1). Additionally, a significant decrease in the expressions of GFAP and Nestin was also observed, including increased levels of MDA and decreased levels of SOD and GSH. However, administration of WIN irrespective of the doses given reversed the cognitive impairments and the associated biochemical derangements. As there were increases in the levels SOD, GSH, Nestin and GFAP (p < 0.05), while a significant decrease in the levels of MDA was observed, besides attenuation of the aberrant cytoarchitecture of the rat’s hippocampi. The biochemical profiles of the WIN-treated rats were normal. Thus, these findings offer possible scientific evidence of WIN being an effective candidate in the treatment of AD-related cognitive deficits.

Febuxostat Prevents the Cytotoxicity of Propofol in Brain Endothelial Cells

Background and purpose: A high risk of brain injury has been reported with the usage of general anesthetics such as propofol in infants. Experimental data indicated that oxidative stress and inflammation are involved in the neurotoxicity induced by propofol. Febuxostat is a novel anti-gout agent recently reported to exert an anti-inflammatory effect. The present study aims to investigate the protective property of febuxostat against the cytotoxicity of propofol in brain endothelial cells as well as the underlying preliminary mechanism. Methods: The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was utilized to screen the optimized incubation concentration of febuxostat. bEnd.3 brain endothelial cells were stimulated with 2% propofol in the presence or absence of febuxostat (10, 20 μM) for 24 h. The lactate dehydrogenase (LDH) release assay was conducted to detect cytotoxicity. The reactive oxygen species (ROS) levels were evaluated using dichloro-dihydro-fluorescein diacetate (DCFH-DA) staining, and the concentration of reduced glutathione (GSH) was determined using a commercial kit. The expressions of TNF-α, IL-6, IL-12, CXCL-1, PDPN, CXCL8, VCAM-1, and E-selectin were determined using a quantitative real-time polymerase chain reaction (qRT-PCR) and an enzyme-linked immunosorbent assay (ELISA). Western blot and qRT-PCR were utilized to determine the expressions of COX-2 and KLF6. The production of PGE2 was evaluated by ELISA. Results: First, increased LDH release induced by propofol was significantly suppressed by febuxostat. The oxidative stress (elevated ROS levels and decreased GSH level) induced by propofol was alleviated by febuxostat. Second, the upregulated inflammatory factors (TNF-α, IL-6, and IL-12), pro-inflammatory chemokines (CXCL-1, PDPN, and CXCL8), adhesion molecules (VCAM-1 and E-selectin), and inflammatory mediators (COX-2 and PGE2) induced by propofol were greatly downregulated by febuxostat. Lastly, the expression of KLF6 was significantly suppressed by propofol but greatly elevated by febuxostat. Conclusion: Febuxostat prevented the cytotoxicity of propofol in brain endothelial cells by alleviating oxidative stress and inflammatory response through KLF6.

RTA-408 protects against propofol-induced cognitive impairment in neonatal mice via the activation of Nrf2 and the inhibition of NF-κB p65 nuclear translocation

OBJECTIVE

To explore the effect of RTA-408 on the propofol-induced cognitive impairment of neonatal mice via regulating Nrf2 and NF-κB p65 nuclear translocation.

METHODS

C57BL/6 neonatal mice were randomized into intralipid, propofol, vehicle + propofol, and RTA-408 + propofol groups. The learning and memory ability was inspected by Morries water maze (MWM) test. TUNEL staining was performed to examine the apoptosis of neurons in hippocampus. The gene and protein expressions in hippocampus were detected by immunohistochemistry, qRT-PCR, or Western blotting. The activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) were tested by the corresponding kits.

RESULTS

Propofol prolonged escape latency of mice, decreased the times of crossing the platform, and shortened the time of staying in the target quadrant, while RTA-408 treatment improved the above-mentioned situation. Besides, Nrf2 protein in hippocampus of mice induced by propofol was decreased with the increased NF-κB p65 nuclear translocation, which was reversed by RTA-408. Meanwhile, RTA-408 decreased the apoptosis of neurons accompanying with the down-regulation of Caspase-3 and the up-regulations of neuronal-specific nuclear protein (NeuN), microtubule-associated protein 2 (Map2), Ca₂⁺ /Calmodulin-dependent Protein Kinase II (CaMKII), and parvalbumin (PV) immunostaining in hippocampus. Besides, propofol-induced high levels of proinflammatory cytokines and antioxidase activities in hippocampus were reduced by RTA-408.

CONCLUSION

RTA-408 improved propofol-induced cognitive impairment in neonatal mice via enhancing survival of neurons, reducing the apoptosis of hippocampal neurons, mitigating the inflammation and oxidative stress, which may be correlated with the activation of Nrf2 and the inhibition of NF-κB p65 nuclear translocation.

Propofol induces oxidative stress and apoptosis in vitro via regulating miR-363-3p/CREB signalling axis

Propofol, a generally used anaesthetic in patients care, has been proven to induce neurotoxicity. Studies have shown that miR-363-3p was closely related to neurological dysfunction, and the up-regulated miR-363-3p was recognized to be participate in propofol-induced neurotoxicity. However, the mechanisms and functions of miR-363-3p in propofol-induced neurotoxicity remain rarely reported. The aim of our research was to clarify the potential effects of miR-363-3p in neurotoxicity induced by propofol. SH-SY5Y cells were treated with propofol, miR-363-3p inhibitor or sh-CREB. quantitative real-time polymerase chain reaction and western blotting were applied to detect the expression of miR-363-3p, CREB, Bax, Bcl-2, cleaved caspase-9 and cleaved caspase-3 at the mRNA and/or protein level, respectively. The levels of lactate dehydrogenase (LDH), superoxide dismutase (SOD) and malondialdehyde (MDA) in cell supernatant were detected using different kits. Flow cytometry and MTT assay were applied for assessing the functions of miR-363-3p and CREB on cell ability in cellular activity and apoptotic rate. In addition, Bioinformatic analysis and luciferase assay verified the relationship between 3'-UTR of CREB and miR-363-3p. Our data indicated that the cell viability decreased with the increasing propofol concentration. Bioinformatic analysis and luciferase assay suggested that 3'-UTR of transcript of CREB might be a binding site of miR-363-3p, and miR-363-3p could negatively regulate the expression of CREB. The changes in reactive oxygen species, LDH, SOD and MDA suggested that propofol mediates oxidative stress and apoptosis via modulating miR-363-3p/CREB axis. Propofol induces oxidative stress and apoptosis via affecting miR-363-3p/CREB axis in SH-SY5Y cells, suggesting miR-363-3p down-regulation may act as a novel strategy to ameliorate the propofol-induced neurotoxicity. Significance of the study: The present study demonstrated that propofol induces oxidative stress and apoptosis via affecting miR-363-3p/CREB axis in SH-SY5Y cells, suggesting miR-363-3p down-regulation may act as a novel strategy to ameliorate the propofol-induced neurotoxicity.

Upregulation of miR-496 Rescues Propofol-induced Neurotoxicity by Targeting Rho Associated Coiled-coil Containing Protein Kinase 2 (ROCK2) in Prefrontal Cortical Neurons

OBJECTIVE

Early exposure to general anesthesia in children might be a potentially highrisk factor for learning and behavioral disorders. The mechanism of neurotoxicity induced by general anesthesia was not defined. miR-496 could regulate cerebral injury, while the roles of miR- 496 in neurotoxicity were not elucidated. Therefore, we aimed to investigate the effects of miR- 496 in neurotoxicity induced by propofol.

METHODS

Primary Prefrontal Cortical (PFC) neurons were isolated from neonatal rats and treated with propofol to induce neurotoxicity. Cell viability was detected by (3-(4,5-Dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and cell apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The target relationship of miR-496 and Rho Associated Coiled-Coil Containing Protein Kinase 2 (ROCK2) was explored using luciferase assays.

RESULTS

Propofol decreased cell viability, promoted cell apoptosis, and decreased the expression of miR-496 in PFC neurons in a dose-dependent manner. Overexpression of miR-496 attenuated neurotoxicity induced by propofol in PFC neurons. ROCK2 was a target of miR-496, and miR-496 oppositely modulated the expression of ROCK2. Besides, propofol increased the expression of ROCK2 through inhibiting miR-496 in PFC neurons. Overexpression of miR-496 attenuated propofol- induced neurotoxicity by targeting ROCK2 in PFC neurons.

CONCLUSION

miR-496 was decreased in PFC neurons treated with propofol, and overexpression of miR-496 attenuated propofol-induced neurotoxicity by targeting ROCK2. miR-496 and ROCK2 may be promising targets for protecting propofol-induced neurotoxicity.

Potential role of the cAMP/PKA/CREB signalling pathway in hypoxic preconditioning and effect on propofol‑induced neurotoxicity in the hippocampus of neonatal rats

Hypoxic preconditioning (HPC) is neuroprotective against ischaemic brain injury; however, the roles of potential anti‑apoptotic signals in this process have not been assessed. To elucidate the molecular mechanisms involved in HPC‑induced neuroprotection, the effects of HPC on the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element‑binding protein (CREB) signalling pathway and apoptosis in Sprague‑Dawley pups (postnatal day 7) treated with propofol were investigated. Western blot and histological analyses demonstrated that HPC exerts multiple effects on the hippocampus, including the upregulation of cAMP and phosphorylation of CREB. These effects were partially blocked by intracerebroventricular injection of the protein kinase antagonist H89 (5 µmol/5 µl). Notably, the level of cleaved caspase‑3 was significantly downregulated by treatment with the cAMP agonist Sp‑cAMP (20 nmol/5 µl). The results indicate that propofol increased the level of cleaved caspase‑3 and Bax by suppressing the activity of cAMP‑dependent proteins and Bcl‑2; thus, HPC prevents propofol from triggering apoptosis via the cAMP/PKA/CREB signalling pathway.

MicroRNA-25 aggravates Aβ1-42-induced hippocampal neuron injury in Alzheimer's disease by downregulating KLF2 via the Nrf2 signaling pathway in a mouse model

Recently, numerous microRNAs (miRNAs) have been considered as key players in the regulation of neuronal processes. The purpose of the present study is to explore the effect of miR-25 on hippocampal neuron injury in Alzheimer's disease (AD) induced by amyloid β (Aβ) peptide fragment 1 to 42 (Aβ1-42) via Kruppel-like factor 2 (KLF2) through the nuclear factor-E2-related factor 2 (Nrf2) signaling pathway. A mouse model of AD was established through Aβ1-42 induction. The underlying regulatory mechanisms of miR-25 were analyzed through treatment of miR-25 mimics, miR-25 inhibitors, or small interfering RNA (siRNA) against KLF2 in hippocampal tissues and cells isolated from AD mice. The targeting relationship between miR-25 and KLF2 was predicted using a target prediction program and verified by luciferase activity determination. MTT assay was used to evaluate the proliferative ability and flow cytometry to detect cell cycle distribution and apoptosis. KLF2 was confirmed as a target gene of miR-25. When the mice were induced by Aβ1-42, proliferation was suppressed while apoptosis was promoted in hippocampal neurons as evidenced by lower levels of KLF2, Nrf2, haem oxygenase, glutathione S transferase α1, glutathione, thioredoxin, and B-cell lymphoma-2 along with higher bax level. However, such alternations could be reversed by treatment of miR-25 inhibitors. These findings indicate that miR-25 may inhibit hippocampal neuron proliferation while promoting apoptosis, thereby aggravating hippocampal neuron injury through downregulation of KLF2 via the Nrf2 signaling pathway.

Protective effect of Centella asiatica against D-galactose and aluminium chloride induced rats: Behavioral and ultrastructural approaches

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder and the commonest cause of dementia among the aged people. _D-galactose (D-gal) is a senescence agent, while aluminium is a known neurotoxin linked to pathogenesis of AD. The combined administration of rats with d-gal and aluminium chloride (AlCl₃) is considered to be an easy and a cheap method to obtain an animal model of AD. The plant Centella asiatica (CA) is reported to exert neuroprotective effects both in vitro and in vivo. Therefore, this study explored the protective effects of CA on cognition and brain ultrastructure in d-gal and AlCl₃ induced rats.

MATERIALS AND METHODS

Rats were exposed to d-gal 60 mg/kg/b.wt/day + AlCl₃ 200 mg/kg/b.wt/day and CA (200, 400 and 800 mg/kg/b.wt/day) and 1 mg/kg/b.wt/day of donepezil for 70 days. Different cognitive paradigms viz. T maze spontaneous alternation, modified elevated plus maze and novel object recognition test, were used to evaluate full lesions of the hippocampus, spatial learning and memory and non-spatial learning and memory respectively. Nissl's staining was used to determine the survival of hippocampus CA1 pyramidal cells, while transmission electron microscopy was used to check the ultrastructural changes.

RESULTS

The results revealed that d-gal and AlCl₃ could significantly impair behavior and cognitive functions, besides causing damage to the hippocampal CA1 pyramidal neurons in rats. In addition, it also caused ultrastructural morphological alterations in rat hippocampus. Conversely, co-administration o;f CA, irrespective of the dosage used, alleviated the cognitive impairments and pathological changes in the rats comparable to donepezil.

CONCLUSION

In conclusion the results suggest that CA could protect cognitive impairments and morphological alterations caused by d-gal and AlCl₃ toxicity in rats. Biochemical and molecular studies are ongoing to elucidate the probable pharmacodynamics of CA.

Hypoxic preconditioning reduces propofol-induced neuroapoptosis via regulation of Bcl-2 and Bax and downregulation of activated caspase-3 in the hippocampus of neonatal rats

OBJECTIVE

 Evidence has shown that propofol may cause widespread apoptotic neurodegeneration. Hypoxic preconditioning (HPC) was previously demonstrated to provide neuroprotection and brain recovery from either acute or chronic neurodegeneration in several cellular and animal models. Therefore, the present study was designed to investigate the protective effects of hypoxic preconditioning on apoptosis caused by propofol in neonatal rats.

METHODS

Propofol (100 mg/kg) was given to 7-day-old (P7) Sprague Dawley pups. Before the propofol injection, hypoxic preconditioning was administered by subjecting rats to five cycles of 10 min of hypoxia (8% O2) and 10 min of normoxia (21% O2), then 2 h of room air. We detected neuronal structure changes and apoptosis by hematoxylin and eosin (HE) staining and TUNEL assay, respectively. Bcl-2, Bax and cleaved-caspase-3 levels were quantified using Western blotting and immunohistochemistry.

RESULT

 After treatment with propofol, Bcl-2 levels decreased and Bax and cleaved-caspase-3 levels increased. However, our results suggest that hypoxic preconditioning could reverse this change. Conclusion: Our results indicate that pretreatment with hypoxic preconditioning prevents propofol-induced neuroapoptosis by increasing the levels of Bcl-2 and decreasing the levels of Bax and cleaved-caspase-3.

Propofol, but not ketamine or midazolam, exerts neuroprotection after ischaemic injury by inhibition of Toll-like receptor 4 and nuclear factor kappa-light-chain-enhancer of activated B-cell signalling: A combined in vitro and animal study

BACKGROUND

Propofol, midazolam and ketamine are widely used in today's anaesthesia practice. Both neuroprotective and neurotoxic effects have been attributed to all three agents.

OBJECTIVE

To establish whether propofol, midazolam and ketamine in the same neuronal injury model exert neuroprotective effects on injured neurones in vitro and in vivo by modulation of the Toll-like receptor 4-nuclear factor kappa-light-chain-enhancer of activated B cells (TLR-4-NF-κB) pathway.

DESIGN AND SETTING

Cell-based laboratory (n = 6 repetitions per experiment) and animal (n = 6 per group) studies using a neuronal cell line (SH-SY5Y cells) and adult Sprague-Dawley rats.

INTERVENTIONS

Cells were exposed to oxygen-glucose deprivation before or after treatment using escalating, clinically relevant doses of propofol, midazolam and ketamine. In animals, retinal ischaemia (60 min) was induced followed by reperfusion and randomised treatment with saline or propofol.

MAIN OUTCOME MEASURES

Neuronal cell death was determined using flow-cytometry (mitochondrial membrane potential) and lactate dehydrogenase (LDH) release. Nuclear factor NF-κB and hypoxia-inducible factor 1 α-activity were analysed by DNA-binding ELISA, expression of NF-κB-dependent genes and TLR-4 by luciferase-assay and flow-cytometry, respectively. In animals, retinal ganglion cell density, caspase-3 activation and gene expression (TLR-4, NF-κB) were used to determine in vivo effects of propofol. Results were compared using ANOVA (Analysis of Variance) and t test. A P value less than 0.05 was considered statistically significant.

RESULTS

Post-treatment with clinically relevant concentrations of propofol (1 to 10 μg ml) preserved the mitochondrial membrane potential in oxygen-glucose deprivation-injured cells by 54% and reduced LDH release by 21%. Propofol diminished TLR-4 surface expression and preserved the DNA-binding activity of the protective hypoxia-inducible factor 1 α transcription factor. DNA-binding and transcriptional NF-κB-activity were inhibited by propofol. Neuronal protection and inhibition of TLR-4-NF-κB signalling were not consistently seen with midazolam or ketamine. In vivo, propofol treatment preserved rat retinal ganglion cell densities (cells mm, saline 1504 ± 251 vs propofol 2088 ± 144, P = 0.0001), which was accompanied by reduced neuronal caspase-3, TLR-4 and NF-κB expression.

CONCLUSION

Propofol, but neither midazolam nor ketamine, provides neuroprotection to injured neuronal cells via inhibition of TLR-4-NF-κB-dependent signalling.

Dexmedetomidine attenuates the propofol-induced long-term neurotoxicity in the developing brain of rats by enhancing the PI3K/Akt signaling pathway

BACKGROUND

Propofol induces short- and long-term neurotoxicity. Our previous study showed that dexmedetomidine (Dex) can attenuate the propofol-induced acute neurotoxicity in rodents by enhancing the PI3K/Akt signaling. However, whether treatment of young rats with Dex could protect them from long-term neurotoxicity induced by propofol is unclear.

MATERIALS AND METHODS

Seven-day-old male Sprague Dawley rats were randomized and injected intraperitoneally with saline (100 μL, NS), propofol (100 mg/kg), Dex (75 μg/kg), propofol (100 mg/kg) plus Dex (25, 50 or 75 μg/kg), 10% dimethyl sulfoxide (DMSO, 100 μL) or TDZD-8 (a GSK3β inhibitor, 1 mg/kg), or intracerebroventricularly with DMSO (5 μL) or LY294002 (a PI3K inhibitor, 25 μg/5 μL DMSO). Other rats in the experimental group were injected with the same doses of propofol, Dex and LY294002 or TDZD-8. All the rats were monitored until they were 9 weeks old. Their spatial learning and memory were tested by Morris water maze. The neuronal apoptosis, expression of PSD₉₅, expression and phosphorylation of Akt and GSK3β and synaptic ultrastructures were determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, immunohistochemistry, Western blot and transmission electron microscopy assays, respectively.

RESULTS

Compared with the NS control group, young rats injected with intralipid, Dex, TDZD-8, LY294002 or DMSO alone did not show any significant change as they aged. Propofol significantly increased the escape latency time, hippocampal neuroapoptosis and synaptic ultrastructural changes but decreased the relative levels of PSD₉₅ expression, and Akt and GSK3β phosphorylation in the developing hippocampus of the rats. The neuronal toxic effects of propofol were significantly mitigated by the pretreatment with a higher dose of Dex. The neuroprotective effect of Dex was enhanced by the treatment with TDZD-8, but was completely abrogated by the treatment with LY294002.

CONCLUSION

Our results indicated that the pretreatment of young rats with Dex attenuated the propofol-induced long-term neurotoxicity in their developing hippocampus by enhancing the PI3K/Akt signaling.

Insufficient Astrocyte-Derived Brain-Derived Neurotrophic Factor Contributes to Propofol-Induced Neuron Death Through Akt/Glycogen Synthase Kinase 3β/Mitochondrial Fission Pathway

BACKGROUND

Growing animal evidence demonstrates that prolonged exposure to propofol during brain development induces widespread neuronal cell death, but there is little information on the role of astrocytes. Astrocytes can release neurotrophic growth factors such as brain-derived neurotrophic factor (BDNF), which can exert the protective effect on neurons in paracrine fashion. We hypothesize that during propofol anesthesia, BDNF released from developing astrocytes may not be sufficient to prevent propofol-induced neurotoxicity.

METHODS

Hippocampal astrocytes and neurons isolated from neonatal Sprague Dawley rats were exposed to propofol at a clinically relevant dose of 30 μM or dimethyl sulfoxide as control for 6 hours. Propofol-induced cell death was determined by propidium iodide (PI) staining in astrocyte-alone cultures, neuron-alone cultures, or cocultures containing either low or high density of astrocytes (1:9 or 1:1 ratio of astrocytes to neurons ratio [ANR], respectively). The astrocyte-conditioned medium was collected 12 hours after propofol exposure and measured by protein array assay. BDNF concentration in astrocyte-conditioned medium was quantified using enzyme-linked immunosorbent assay. Neuron-alone cultures were treated with BDNF, tyrosine receptor kinase B inhibitor cyclotraxin-B, glycogen synthase kinase 3β (GSK3β) inhibitor CHIR99021, or mitochondrial fission inhibitor Mdivi-1 before propofol exposure. Western blot was performed for quantification of the level of protein kinase B and GSK3β. Mitochondrial shape was visualized through translocase of the outer membrane 20 staining.

RESULTS

Propofol increased cell death in neurons by 1.8-fold (% of PI-positive cells [PI%] = 18.6; 95% confidence interval [CI], 15.2-21.9, P < .05) but did not influence astrocyte viability. The neuronal death was attenuated by a high ANR (1:1 cocultures; fold change [FC] = 1.17, 95% CI, 0.96-1.38, P < .05), but not with a low ANR [1:9 cocultures; FC = 1.87, 95% CI, 1.48-2.26, P > .05]). Astrocytes secreted BDNF in a cell density-dependent way and propofol decreased BDNF secretion from astrocytes. Administration of BDNF, CHIR99021, or Mdivi-1 significantly attenuated the propofol-induced neuronal death and aberrant mitochondria in neuron-alone cultures (FC = 0.8, 95% CI, 0.62-0.98; FC = 1.22, 95% CI, 1.11-1.32; FC = 1.35, 95% CI, 1.16-1.54, respectively, P < .05) and the cocultures with a low ANR (1:9; FC = 0.85, 95% CI, 0.74-0.97; FC = 1.08, 95% CI, 0.84-1.32; FC = 1.25, 95% CI, 1.1-1.39, respectively, P < .05). Blocking BDNF receptor or protein kinase B activity abolished astrocyte-induced neuroprotection in the cocultures with a high ANR (1:1).

CONCLUSIONS

Astrocytes attenuate propofol-induced neurotoxicity through BDNF-mediated cell survival pathway suggesting multiple neuroprotective strategies such as administration of BDNF, astrocyte-conditioned medium, decreasing mitochondrial fission, or inhibition of GSK3β.

Recent Insights Into Molecular Mechanisms of Propofol-Induced Developmental Neurotoxicity: Implications for the Protective Strategies

Mounting evidence has demonstrated that general anesthetics could induce developmental neurotoxicity, including acute widespread neuronal cell death, followed by long-term memory and learning abnormalities. Propofol is a commonly used intravenous anesthetic agent for the induction and maintenance of anesthesia and procedural and critical care sedation in children. Compared with other anesthetic drugs, little information is available on its potential contributions to neurotoxicity. Growing evidence from multiple experimental models showed a similar neurotoxic effect of propofol as observed in other anesthetic drugs, raising serious concerns regarding pediatric propofol anesthesia. The aim of this review is to summarize the current findings of propofol-induced developmental neurotoxicity. We first present the evidence of neurotoxicity from animal models, animal cell culture, and human stem cell-derived neuron culture studies. We then discuss the mechanism of propofol-induced developmental neurotoxicity, such as increased cell death in neurons and oligodendrocytes, dysregulation of neurogenesis, abnormal dendritic development, and decreases in neurotrophic factor expression. Recent findings of complex mechanisms of propofol action, including alterations in microRNAs and mitochondrial fission, are discussed as well. An understanding of the toxic effect of propofol and the underlying mechanisms may help to develop effective novel protective or therapeutic strategies for avoiding the neurotoxicity in the developing human brain.

Dexmedetomidine attenuates propofol-induce neuroapoptosis partly via the activation of the PI3k/Akt/GSK3β pathway in the hippocampus of neonatal rats

Recent studies have demonstrated that propofol causes neurodegeneration in developing brains. Evidence has shown that dexmedetomidine has neuroprotective effects. However, whether dexmedetomidine can reduce propofol-induced neuroapoptosis and by what mechanisms it acts remain unclear. We investigated whether dexmedetomidine can attenuate propofol-induced neuroapoptosis by disturbing the PI3K/Akt/GSK3β pathway during brain development. Seven-day-old rats were randomly exposed to 100mg/kg propofol and 100mg/kg propofol plus different doses of dexmedetomidine or 100mg/kg propofol and 75μg/kg dexmedetomidine plus PI3K inhibitor LY294002 or GSK3β inhibitor TDZD-8. TEM and TUNEL were used to detect neuronal structure changes and apoptosis. The expression of phospho-Akt, phospho-GSK3β, Akt and GSK3β were quantified using western blots and immunofluorescence. Pretreatment with different doses of dexmedetomidine protected against propofol-induced neuroapoptosis. Furthermore, propofol decreased the levels of phospho-Akt and phospho-GSK3β, whereas dexmedetomidine partially reversed this inhibition. In addition, treatment with LY294002 inhibited the neuroprotection of dexmedetomidine, whereas TDZD-8 enhanced neuroprotection. Our results indicate that dexmedetomidine prevents propofol-induced neuroapoptosis by increasing the levels of phospho-Akt and phospho-GSK3β.

Effects of Low-dose Triamcinolone Acetonide on Rat Retinal Progenitor Cells under Hypoxia Condition

BACKGROUND

Retinal degenerative diseases are the leading causes of blindness in developed world. Retinal progenitor cells (RPCs) play a key role in retina restoration. Triamcinolone acetonide (TA) is widely used for the treatment of retinal degenerative diseases. In this study, we investigated the role of TA on RPCs in hypoxia condition.

METHODS

RPCs were primary cultured and identified by immunofluorescence staining. Cells were cultured under normoxia, hypoxia 6 h, and hypoxia 6 h with TA treatment conditions. For the TA treatment groups, after being cultured under hypoxia condition for 6 h, RPCs were treated with different concentrations of TA for 48-72 h. Cell viability was measured by cell counting kit-8 (CCK-8) assay. Cell cycle was detected by flow cytometry. Western blotting was employed to examine the expression of cyclin D1, Akt, p-Akt, nuclear factor (NF)-κB p65, and caspase-3.

RESULTS

CCK-8 assays indicated that the viability of RPCs treated with 0.01 mg/ml TA in hypoxia group was improved after 48 h, comparing with control group (P < 0.05). After 72 h, the cell viability was enhanced in both 0.01 mg/ml and 0.02 mg/ml TA groups compared with control group (all P < 0.05). Flow cytometry revealed that there were more cells in S-phase in hypoxia 6 h group than in normoxia control group (P < 0.05). RPCs in S and G2/M phases decreased in groups given TA, comparing with other groups (all P < 0.05). There was no significant difference in the total Akt protein expression among different groups, whereas upregulation of p-Akt and NF-κB p65 protein expression and downregulation of caspase-3 and cyclin D1 protein expression were observed in 0.01 mg/ml TA group, comparing with hypoxia 6 h group and control group (all P < 0.05).

CONCLUSION

Low-dose TA has anti-apoptosis effect on RPCs while it has no stimulatory effect on cell proliferation.

Prolonged Treatment with Propofol Transiently Impairs Proliferation but Not Survival of Rat Neural Progenitor Cells In Vitro

Neurocognitive dysfunction is common in survivors of intensive care. Prolonged sedation has been implicated but the mechanisms are unclear. Neurogenesis continues into adulthood and is implicated in learning. The neural progenitor cells (NPC) that drive neurogenesis have receptors for the major classes of sedatives used clinically, suggesting that interruption of neurogenesis may partly contribute to cognitive decline in ICU survivors. Using an in vitro system, we tested the hypothesis that prolonged exposure to propofol concentration- and duration-dependently kills or markedly decreases the proliferation of NPCs. NPCs isolated from embryonic day 14 Sprague-Dawley rat pups were exposed to 0, 2.5, or 5.0 μg/mL of propofol, concentrations consistent with deep clinical anesthesia, for either 4 or 24 hours. Cells were assayed for cell death and proliferation either immediately following propofol exposure or 24 hours later. NPC death and apoptosis were measured by propidium iodine staining and cleaved caspase-3 immunocytochemistry, respectively, while proliferation was measured by EdU incorporation. Staurosporine (1μM for 6h) was used as a positive control for cell death. Cells were analyzed with unbiased high-throughput immunocytochemistry. There was no cell death at either concentration of propofol or duration of exposure. Neither concentration of propofol impaired NPC proliferation when exposure lasted 4 h, but when exposure lasted 24 h, propofol had an anti-proliferative effect at both concentrations (P < 0.0001, propofol vs. control). However, this effect was transient; proliferation returned to baseline 24 h after discontinuation of propofol (P = 0.37, propofol vs. control). The transient but reversible suppression of NPC proliferation, absence of cytotoxicity, and negligible effect on the neural stem cell pool pool suggest that propofol, even in concentrations used for clinical anesthesia, has limited impact on neural progenitor cell biology.

Propofol Decreases Endoplasmic Reticulum Stress-Mediated Apoptosis in Retinal Pigment Epithelial Cells

Age-related macular degeneration (AMD) is the major cause of loss of sight globally. There is currently no effective treatment available. Retinal pigment epithelial (RPE) cells are an important part of the outer blood-retina barrier and their death is a determinant of AMD. Propofol, a common clinically used intravenous anesthetic agent, has been shown to act as an efficacious neuroprotective agent with antioxidative and anti-inflammatory properties in vivo and in vitro. However, little is known about its effects on RPE cells. The purpose of our research was to investigate whether propofol could protect RPE cells from apoptosis through endoplasmic reticulum (ER) stress–dependent pathways. To this end, prior to stimulation with thapsigargin (TG), ARPE-19 cells were pretreated with varying concentrations of propofol. A protective effect of propofol in TG-treated ARPE-9 was apparent, TUNEL and flow cytometric assays showed decreased apoptosis. We further demonstrated that propofol pretreatment attenuated or inhibited the effects caused by TG, such as upregulation of Bax, BiP, C/EBP homologous protein (CHOP), active caspase 12, and cleaved caspase 3, and downregulation of Bcl2. It also decreased the TG-induced levels of ER stress–related molecules such as p-PERK, p-eIF2α, and ATF4. Furthermore, it downregulated the expression of nuclear factor κB (NF-κB). This study elucidated novel propofol-induced cellular mechanisms for antiapoptotic activities in RPE cells undergoing ER stress and demonstrated the potential value of using propofol in the treatment of AMD.