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

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Propofol Induces the Expression of Nrf2 and HO-1 in Echinococcus granulosus via the JNK and p38 Pathway In Vitro

The purpose of this study was to establish the relationship between mitogen-activated protein kinase (MAPK) and Nrf2 signaling pathways in Echinococcus granulosus (E. granulosus). E. granulosus protoscoleces (PSCs) cultured in vitro were divided into different groups: a control group, PSCs were pretreated with various concentrations of propofol followed by exposure to hydrogen peroxide (H₂O₂), and PSCs were pretreated with MAPK inhibitors, then co-treated with propofol and incubated in the presence of H₂O₂. PSCs activity was observed under an inverted microscope and survival rate was calculated. Reactive oxygen species (ROS) was detected by fluorescence microscopy, western blotting was used to detect the expression of Nrf2, Bcl-2, and heme oxygenase 1 (HO-1) in the PSCs among different groups. Pretreatment of PSCs with 0-1 mM propofol for 8 h prevented PSCs death after exposure to 0.5 mM H₂O₂. PSCs were pretreated with PD98059, SB202190, or SP600125 for 2 h, co-treated with propofol for an additional 8 h, and then exposed to 0.5 mM H₂O₂ for 6 h. On day 6, the PSCs viability was 42% and 39% in the p38 and JNK inhibitor groups, respectively. Additionally, pretreatment with propofol significantly attenuated the generation of ROS following H₂O₂ treatment. Propofol increased the expression of Nrf2, HO-1, and BCL2 compared with that of the control group. Pretreatment PSCs with SP600125 or SB202190, co-incubation with propofol and H₂O₂, can reduce the expression of Nrf2, HO-1, and BCL2 (p < 0.05). These results suggest that propofol induces an upregulated expression of HO-1 and Nrf2 by activation of the JNK and p38 MAPK signaling pathways. This study highlights the cross role of metabolic regulation of ROS signaling and targeting signalling pathways that may provide a promising strategy for the treatment of E. granulosus disease.

Propofol alleviates inflammation and apoptosis in HCY‑induced HUVECs by inhibiting endoplasmic reticulum stress

Atherosclerosis is a chronic vascular inflammatory disease, and is associated with oxidative stress and endothelial dysfunction. Homocysteine (HCY) can cause damage to endothelial cells via the enhancement of the endoplasmic reticulum stress (ERS) pathway. Propofol has a protective effect on endothelial injury and can suppress inflammation and oxidation. The purpose of the present study was to investigate the protective effect of propofol on HCY-induced inflammation and apoptosis of human umbilical vein endothelial cells (HUVECs). HCY was used to establish the endothelial injury model. Cell Counting Kit-8 assays and flow cytometry were used to detect cell viability and apoptosis, respectively. Then, ELISA was performed to examine the expression levels of inflammatory cytokines, and the expression levels of proteins related to inflammation, apoptosis and ERS were determined via western blotting. Results showed that propofol increased cell viability, suppressed NF-κB signaling pathway activation and decreased the expression levels of inflammatory factors in HUVECs induced by HCY. Moreover, propofol could inhibit the expression of proteins involved in ERS, including ER chaperone BiP (Bip), C/EBP-homologous protein, protein kinase R-like ER kinase and inositol-requiring 1α, and reduce cell apoptosis of HCY-induced HUVECs. However, the overexpression of Bip could reactivate ERS and the NF-κB signaling pathway, as well as promote inflammation and cell apoptosis, when compared with HCY-treated groups. In conclusion, propofol can ameliorate inflammation and cell apoptosis of HUVECs induced by HCY via inhibiting ERS, which may provide a novel insight into the treatment of atherosclerosis.

Propofol inhibits the expression of Abelson nonreceptor tyrosine kinase without affecting learning or memory function in neonatal rats

OBJECTIVE

Propofol is one of the most commonly used intravenous drugs to induce and maintain general anesthesia. In vivo and in vitro studies have shown that propofol can affect neuronal growth, leading to apoptosis and impairing cognitive function. The Abelson nonreceptor tyrosine kinase (c-Abl) is associated with both neuritic plaques and neurofibrillary tangles in the brains of patients with Alzheimer's disease and other neurodegenerative diseases. This study aimed to explore the effect of propofol on apoptosis and neurocognition through its regulation of c-Abl expression in vivo and in vitro.

MATERIALS AND METHODS

In this study, primary hippocampal neurons were cultured and exposed to propofol at different concentrations. Protein expression was measured by Western blotting and coimmunoprecipitation. The c-Abl transcription level was verified by fluorescence quantitative PCR. Reactive oxygen species (ROS) levels were detected by flow cytometry. In addition, an animal experiment was conducted to assess neuronal apoptosis by immunofluorescence staining for caspase-3 and to evaluate behavioral changes by the Morris water maze (MWM) test.

RESULTS

The in vitro experiment showed that propofol significantly decreased c-Abl expression and ROS levels. In addition, propofol has no cytotoxic effect and does not affect cell activity. Moreover, in the animal experiment, intraperitoneal injection of 50 mg/kg propofol for 5 days obviously decreased the expression of c-Abl in the neonatal rat brain (p < .05) but did not significantly increase the number of caspase-3-positive cells. Propofol treatment did not significantly reduce the number of platform crossings (p > .05) or prolong the escape latency of neonatal rats (p > .05) in the MWM test.

CONCLUSIONS

The present data suggest that reduced expression of this nonreceptor tyrosine kinase through consecutive daily administration of propofol did not impair learning or memory function in neonatal rats.

Dapagliflozin rescues endoplasmic reticulum stress-mediated cell death

The new type 2 diabetes drug, dapagliflozin, reduces blood glucose levels and body weight by inhibiting sodium glucose transporter 2 (SGLT2) in proximal tubular cells. SGLT2 inhibitors might modulate glucose influx into renal tubular cells, thereby regulating the metabolic conditions that cause endoplasmic reticulum (ER) stress in the cells. In this study, we examined the effect of dapagliflozin on ER stress in the HK-2 proximal tubular cell line and in the kidney of db/db mice to characterise its function in diabetic nephropathy (DN). We found that dapagliflozin regulated ER stress-mediated apoptosis in vitro and in vivo. Only the elf2α-ATF4-CHOP pathway was regulated under these conditions. Notably, the drug rescued C2 ceramide-induced ER stress-mediated apoptosis and ER stress-mediated apoptosis, which might occur in DN, in db/db mice. Our study shows a novel role for dapagliflozin as an inhibitor of ER stress and suggests that dapagliflozin might be useful for the prevention of DN.

Phagosomal and mitochondrial alterations in RPE may contribute to KCNJ13 retinopathy

Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We examined the retina of kcnj13 mutant zebrafish (obelix^td15, c.502T > C p.[Phe168Leu]) to provide new insights into the pathophysiology underlying these conditions. Detailed phenotyping of obelix^td15 fish revealed a late onset retinal degeneration at 12 months. Electron microscopy of the obelix^td15 retinal pigment epithelium (RPE) uncovered reduced phagosome clearance and increased mitochondrial number and size prior any signs of retinal degeneration. Melanosome distribution was also affected in dark-adapted 12-month obelix^td15 fish. At 6 and 12 months, ATP levels were found to be reduced along with increased expression of glial fibrillary acidic protein and heat shock protein 60. Quantitative RT-PCR of polg2, fis1, opa1, sod1/2 and bcl2a from isolated retina showed expression changes consistent with altered mitochondrial activity and retinal stress. We propose that the retinal disease in this model is primarily a failure of phagosome physiology with a secondary mitochondrial dysfunction. Our findings suggest that alterations in the RPE and photoreceptor cellular organelles may contribute to KCNJ13-related retinal degeneration and provide a therapeutic target.

Impact of general anaesthesia on endoplasmic reticulum stress: propofol vs. isoflurane

Background: This study investigated the effects of propofol and isoflurane on endoplasmic reticulum (ER) stress in an animal model under general anaesthesia. Methods: Rats were randomly divided into Propofol and Isoflurane groups. Anaesthesia was maintained with propofol for Propofol group or isoflurane for Isoflurane group during 3 h. ER stress from lymphocytes in blood and tissues was evaluated between two groups after euthanasia. Reactive oxygen species (ROS) from lymphocytes in blood and tissues, and cytokines in blood were also checked. An immunohistochemical assay for ER stress marker from tissues was performed. Results: After anaesthesia, the levels of CCAAT-enhancer-binding protein homologous proteins (CHOP) in blood and liver were significantly higher in Isoflurane group, compared to Propofol group [blood, 31,499 ± 4,934 (30,733, 26,441-38,807) mean fluorescence intensity (MFI) in Isoflurane group vs. 20,595 ± 1,838 (20,780, 18,866-22,232) MFI in Propofol group, p = 0.002; liver, 28,342 ± 5,535 (29,421, 23,388-32,756) MFI in Isoflurane group vs. 20,004 ± 2,155 (19,244, 18,197-22,191) MFI in Propofol group, p = 0.020]. ROS in blood was significantly higher in Isoflurane group, compared to Propofol group. However, cytokines in blood and immunohistochemical assays in tissues were similar between groups. Conclusion: Significant higher of ER stress from blood and liver were observed in rats under anaesthesia with isoflurane, compared to those that received propofol. ROS from blood also showed significant higher under anaesthesia with isoflurane. However, these findings were not associated with any changes in cytokines in blood or immunohistochemical assay in tissues.

Propofol inhibits parthanatos via ROS-ER-calcium-mitochondria signal pathway in vivo and vitro

Parthanatos is a new form of programmed cell death. It has been recognized to be critical in cerebral ischemia–reperfusion injury, and reactive oxygen species (ROS) can induce parthanatos. Recent studies found that propofol, a widely used intravenous anesthetic agent, has an inhibitory effect on ROS and has neuroprotective in many neurological diseases. However, the functional roles and mechanisms of propofol in parthanatos remain unclear. Here, we discovered that the ROS–ER–calcium–mitochondria signal pathway mediated parthanatos and the significance of propofol in parthanatos. Next, we found that ROS overproduction would cause endoplasmic reticulum (ER) calcium release, leading to mitochondria depolarization with the loss of mitochondrial membrane potential. Mitochondria depolarization caused mitochondria to release more ROS, which, in turn, contributed to parthanatos. Also, we found that propofol inhibited parthanatos through impeding ROS overproduction, calcium release from ER, and mitochondrial depolarization in parthanatos. Importantly, our results indicated that propofol protected cerebral ischemia–reperfusion via parthanatos suppression, amelioration of mitochondria, and ER swelling. Our findings provide new insights into the mechanisms of how ER and mitochondria contribute to parthanatos. Furthermore, our studies elucidated that propofol has a vital role in parthanatos prevention in vivo and in vitro, and propofol can be a promising therapeutic approach for nerve injury patients.

Autophagy decreases alveolar macrophage apoptosis by attenuating endoplasmic reticulum stress and oxidative stress

To study the impact of autophagy on alveolar macrophage apoptosis and its mechanism in the early stages of hypoxia, we established a cell hypoxia-reoxygenation model and orthotopic left lung ischemia-reperfusion model. Rat alveolar macrophages stably expressing RFP-LC3 were treated with autophagy inhibitor (3-methyladenine, 3-MA) or autophagy promoter (rapamycin), followed by hypoxia-reoxygenation treatment 2 h, 4 h or 6 h later. Twenty Sprague-Dawley male rats were randomly divided into four different groups: no blocking of left lung hilum (model group), left lung hilum blocked for 1h with DMSO lavage (control group), left lung hilum blocked for 1 h with 100 ml/kg 3-MA (5 μmol/L) lavage (3-MA group), and left lung hilum blocked for 1 h with 100 ml/kg rapamycin (250 nmol/L) lavage (rapamycin group). Rapamycin decreased the unfolded protein response, which reduced endoplasmic reticulum stress-mediated apoptosis in the presence of oxygen deficiency. Rapamycin increased superoxide dismutase activities and decreased malondialdehyde levels, whereas 3-MA decreased superoxide dismutase activities and increased malondialdehyde levels. Thus, autophagy decreases alveolar macrophage apoptosis by attenuating endoplasmic reticulum stress and oxidative stress in the early stage of hypoxia in vitro and in vivo. This could represent a new approach to protecting against lung ischemia-reperfusion injury.

Inhibition of Starvation-Triggered Endoplasmic Reticulum Stress, Autophagy, and Apoptosis in ARPE-19 Cells by Taurine through Modulating the Expression of Calpain-1 and Calpain-2

Age-related macular degeneration (AMD) is a complex disease with multiple initiators and pathways that converge on death for retinal pigment epithelial (RPE) cells. In this study, effects of taurine on calpains, autophagy, endoplasmic reticulum (ER) stress, and apoptosis in ARPE-19 cells (a human RPE cell line) were investigated. We first confirmed that autophagy, ER stress and apoptosis in ARPE-19 cells were induced by Earle’s balanced salt solution (EBSS) through starvation to induce RPE metabolic stress. Secondly, inhibition of ER stress by 4-phenyl butyric acid (4-PBA) alleviated autophagy and apoptosis, and suppression of autophagy by 3-methyl adenine (3-MA) reduced the cell apoptosis, but the ER stress was minimally affected. Thirdly, the apoptosis, ER stress and autophagy were inhibited by gene silencing of calpain-2 and overexpression of calpain-1, respectively. Finally, taurine suppressed both the changes of the important upstream regulators (calpain-1 and calpain-2) and the activation of ER stress, autophagy and apoptosis, and taurine had protective effects on the survival of ARPE-19 cells. Collectively, this data indicate that taurine inhibits starvation-triggered endoplasmic reticulum stress, autophagy, and apoptosis in ARPE-19 cells by modulating the expression of calpain-1 and calpain-2.

Serial perioperative cell-free DNA levels in donors and recipients undergoing living donor liver transplantation

BACKGROUND

Effect of anaesthesia and surgery on cell-free DNA (cfDNA) is not known. Given that surgical stress augments inflammation and injury, we hypothesized that levels of cfDNA will fluctuate during perioperative period. Therefore, in this study serial perioperative cfDNA concentration was measured in donors and recipients undergoing living donor liver transplantation (LDLT).

METHODS

Baseline, post-induction, intraoperative and post-operative plasma cfDNA levels were evaluated in 21 donors and recipients each, by Sytox green method. In addition, qPCR was performed in a subset of samples.

RESULTS

Baseline cfDNA levels were higher in recipients (37.62 ng/ml) than in donors (25.49 ng/ml). A decrease in cfDNA was observed following anaesthesia induction in both recipients (11.90 ng/ml) and donors (10.75 ng/ml). When the kinetics of the cfDNA was monitored further, an increase was noted intraoperatively in donors (46.18 ng/ml) and recipients (anhepatic phase: 56.25 ng/ml, reperfusion phase: 54.36 ng/ml). cfDNA levels remained high post-operatively. One recipient who developed post-operative sepsis had the highest cfDNA level (94.72 ng/ml).

CONCLUSION

Plasma cfDNA levels are high in recipients indicative of liver injury. Lower cfDNA levels following induction may be attributed to the subduing effect of anaesthetic agents on cell death. High cfDNA levels seen in intra- and post-operative phases reflect cellular trauma and inflammation. This similar pattern of fluctuation of cfDNA level in donors and recipients is suggestive of its possible utility as a surgical stress marker. In addition, comparable cfDNA levels in anhepatic and reperfusion phase reflect less ischemia reperfusion injury during LDLT.

Valproate Attenuates Endoplasmic Reticulum Stress-Induced Apoptosis in SH-SY5Y Cells via the AKT/GSK3β Signaling Pathway

Endoplasmic reticulum (ER) stress-induced apoptosis plays an important role in a range of neurological disorders, such as neurodegenerative diseases, spinal cord injury, and diabetic neuropathy. Valproate (VPA), a typical antiepileptic drug, is commonly used in the treatment of bipolar disorder and epilepsy. Recently, VPA has been reported to exert neurotrophic effects and promote neurite outgrowth, but its molecular mechanism is still unclear. In the present study, we investigated whether VPA inhibited ER stress and promoted neuroprotection and neuronal restoration in SH-SY5Y cells and in primary rat cortical neurons, respectively, upon exposure to thapsigargin (TG). In SH-SY5Y cells, cell viability was detected by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, and the expression of ER stress-related apoptotic proteins such as glucose‑regulated protein (GRP78), C/EBP homologous protein (CHOP), and cleaved caspase-12/-3 were analyzed with Western blot analyses and immunofluorescence assays. To explore the pathway involved in VPA-induced cell proliferation, we also examined p-AKT, GSK3β, p-JNK and MMP-9. Moreover, to detect the effect of VPA in primary cortical neurons, immunofluorescence staining of β-III tubulin and Anti-NeuN was analyzed in primary cultured neurons exposed to TG. Our results demonstrated that VPA administration improved cell viability in cells exposed to TG. In addition, VPA increased the levels of GRP78 and p-AKT and decreased the levels of ATF6, XBP-1, GSK3β, p-JNK and MMP-9. Furthermore, the levels of the ER stress-induced apoptosis response proteins CHOP, cleaved caspase-12 and cleaved caspase-3 were inhibited by VPA treatment. Meanwhile, VPA administration also increased the ratio of Bcl-2/Bax. Moreover, VPA can maintain neurite outgrowth of primary cortical neurons. Collectively, the neurotrophic effect of VPA is related to the inhibition of ER stress-induced apoptosis in SH-SY5Y cells and the maintenance of neuronal growth. Collectively, our results suggested a new approach for the therapeutic function of VPA in neurological disorders and neuroprotection.