Ferroptosis inhibitors reduce celastrol toxicity and preserve its insulin sensitizing effects in insulin resistant HepG2 cells.

OBJECTIVE: Research has shown that celastrol can effectively treat a variety of diseases, yet when passing a certain dosage threshold, celastrol becomes toxic, causing complications such as liver and kidney damage and erythrocytopenia, among others. With this dichotomy in mind, it is extremely important to find ways to preserve celastrol's efficacy while reducing or preventing its toxicity. METHODS: In this study, insulin-resistant HepG2 (IR-HepG2) cells were prepared using palmitic acid and used for in vitro experiments. IR-HepG2 cells were treated with celastrol alone or in combination with N-acetylcysteine (NAC) or ferrostatin-1 (Fer-1) for 12, 24 or 48 h, at a range of doses. Cell counting kit-8 assay, Western blotting, quantitative reverse transcription-polymerase chain reaction, glucose consumption assessment, and flow cytometry were performed to measure celastrol's cytotoxicity and whether the cell death was linked to ferroptosis. RESULTS: Celastrol treatment increased lipid oxidation and decreased expression of anti-ferroptosis proteins in IR-HepG2 cells. Celastrol downregulated glutathione peroxidase 4 (GPX4) mRNA. Molecular docking models predicted that solute carrier family 7 member 11 (SLC7A11) and GPX4 were covalently bound by celastrol. Importantly, we found for the first time that the application of ferroptosis inhibitors (especially NAC) was able to reduce celastrol's toxicity while preserving its ability to improve insulin sensitivity in IR-HepG2 cells. CONCLUSION: One potential mechanism of celastrol's cytotoxicity is the induction of ferroptosis, which can be alleviated by treatment with ferroptosis inhibitors. These findings provide a new strategy to block celastrol's toxicity while preserving its therapeutic effects. Please cite this article as: Liu JJ, Zhang X, Qi MM, Chi YB, Cai BL, Peng B, Zhang DH. Ferroptosis inhibitors reduce celastrol toxicity and preserve its insulin sensitizing effects in insulin resistant HepG2 cells. J Integr Med. 2024; 22(3): 286-294.

Hyperglycemia exacerbates cerebral ischemia/reperfusion injury by up-regulating autophagy through p53-Sesn2-AMPK pathway.

Hyperglycemia exacerbates ischemic brain injury by up-regulating autophagy. However, the underlying mechanisms are unknown. This study aims to determine whether hyperglycemia activates autophagy through the p53-Sesn2-AMPK signaling pathway. Rats were subjected to 30-min middle cerebral artery occlusion (MCAO) with reperfusion for 1- and 3-day under normo- and hyperglycemic conditions; and HT22 cells were exposed to oxygen deprivation (OG) or oxygen-glucose deprivation and re-oxygenation (OGD/R) with high glucose. Autophagy inhibitors, 3-MA and ARI, were used both in vivo and in vitro. The results showed that, compared with the normoglycemia group (NG), hyperglycemia (HG) increased infarct volume and apoptosis in penumbra area, worsened neurological deficit, and augmented autophagy. after MCAO followed by 1-day reperfusion. Further, HG promoted the conversion of LC-3I to LC-3II, decreased p62, increased protein levels of aldose reductase, p53, P-p53ser15, Sesn2, AMPK and numbers of autophagosomes and autolysosomes, detected by transmission electron microscopy and mRFP-GFP-LC3 molecular probe, in the cerebral cortex after ischemia and reperfusion injury in animals or in cultured HT22 cells exposed to hypoxia with high glucose content. Finally, experiments with autophagy inhibitors 3-MA and aldose reductase inhibitor (ARI) revealed that while both inhibitors reduced the number of TUNEL positive neurons and reversed the effects of hyperglycemic ischemia on LC3 and p62, only ARI decreased the levels of p53, P-p53ser15. These results suggested that hyperglycemia might induce excessive autophagy to aggravate the brain injury resulted from I/R and that hyperglycemia might activate the p53-Sesn2-AMPK signaling pathway, in addition to the classical PI3K/AKT/mTOR autophagy pathway.

Selenium inhibits ferroptosis in hyperglycemic cerebral ischemia/reperfusion injury by stimulating the Hippo pathway.

Hyperglycemia can exacerbate cerebral ischemia/reperfusion (I/R) injury, and the mechanism involves oxidative stress, apoptosis, autophagy and mitochondrial function. Our previous research showed that selenium (Se) could alleviate this injury. The aim of this study was to examine how selenium alleviates hyperglycemia-mediated exacerbation of cerebral I/R injury by regulating ferroptosis. Middle cerebral artery occlusion (MCAO) and reperfusion models were established in rats under hyperglycemic conditions. An in vitro model of hyperglycemic cerebral I/R injury was created with oxygen-glucose deprivation and reoxygenation (OGD/R) and high glucose was employed. The results showed that hyperglycemia exacerbated cerebral I/R injury, and sodium selenite pretreatment decreased infarct volume, edema and neuronal damage in the cortical penumbra. Moreover, sodium selenite pretreatment increased the survival rate of HT22 cells under OGD/R and high glucose conditions. Pretreatment with sodium selenite reduced the hyperglycemia mediated enhancement of ferroptosis. Furthermore, we observed that pretreatment with sodium selenite increased YAP and TAZ levels in the cytoplasm while decreasing YAP and TAZ levels in the nucleus. The Hippo pathway inhibitor XMU-MP-1 eliminated the inhibitory effect of sodium selenite on ferroptosis. The findings suggest that pretreatment with sodium selenite can regulate ferroptosis by activating the Hippo pathway, and minimize hyperglycemia-mediated exacerbation of cerebral I/R injury.

Oxymatrine Alleviates Hyperglycemic Cerebral Ischemia/Reperfusion Injury via Protecting Microvessel.

Hyperglycemia aggravates cerebral ischemia/reperfusion (I/R) injury via vascular injury. There is still a lack of effective pharmaceutical preparations for cerebral I/R injury under hyperglycemia. This study aimed to investigate the effects of oxymatrine (OMT) on hyperglycemia-exacerbated cerebral I/R injury in vitro and in vivo. The middle cerebral artery occlusion (MCAO) and reperfusion was established in the rats under hyperglycemia. Meanwhile, oxygen-glucose deprivation and reoxygenation (OGD/R) with high glucose was used as an in vitro model of hyperglycemic cerebral I/R injury. The results showed that the neurological deficit score, mortality, infarct volume and penumbra apoptosis in hyperglycemia group were significantly higher than those in normal glucose group. OMT pre-treated obviously reduced the degree of neurological deficit, mortality, infarct volume, improve cerebral blood flow after I/R in rats with hyperglycemia, and increase the survival rate of human brain microvascular endothelial cells (HBMECs) in high glucose and OGD/R group. OMT significantly improved the ultrastructure changes of endothelial cells, and maintain the migration and angiogenesis potency of HBMECs in high glucose and OGD/R group. OMT obviously alleviated the down-regulating CD31 and CD105 expression in cerebral microvessels caused by hyperglycemia. It is concluded that OMT treatment might alleviate cerebral I/R injury under hyperglycemia via protecting microvessels.

Network pharmacology suggests biochemical rationale for treating COVID-19 symptoms with a Traditional Chinese Medicine.

Chinese herbal formulas including the lung-cleaning and toxicity-excluding (LCTE) soup have played an important role in treating the ongoing COVID-19 pandemic (caused by SARS-CoV-2) in China. Applying LCTE outside of China may prove challenging due to the unfamiliar rationale behind its application in terms of Traditional Chinese Medicine. To overcome this barrier, a biochemical understanding of the clinical effects of LCTE is needed. Here, we explore the chemical compounds present in the reported LCTE ingredients and the proteins targeted by these compounds via a network pharmacology analysis. Our results indicate that LCTE contains compounds with the potential to directly inhibit SARS-CoV-2 and inflammation, and that the compound targets proteins highly related to COVID-19's main symptoms. We predict the general effect of LCTE is to affect the pathways involved in viral and other microbial infections, inflammation/cytokine response, and lung diseases. Our work provides a biochemical basis for using LCTE to treat COVID-19 and its main symptoms.

In silico screening of Chinese herbal medicines with the potential to directly inhibit 2019 novel coronavirus.

OBJECTIVE: In this study we execute a rational screen to identify Chinese medical herbs that are commonly used in treating viral respiratory infections and also contain compounds that might directly inhibit 2019 novel coronavirus (2019-nCoV), an ongoing novel coronavirus that causes pneumonia. METHODS: There were two main steps in the screening process. In the first step we conducted a literature search for natural compounds that had been biologically confirmed as against sever acute respiratory syndrome coronavirus or Middle East respiratory syndrome coronavirus. Resulting compounds were cross-checked for listing in the Traditional Chinese Medicine Systems Pharmacology Database. Compounds meeting both requirements were subjected to absorption, distribution, metabolism and excretion (ADME) evaluation to verify that oral administration would be effective. Next, a docking analysis was used to test whether the compound had the potential for direct 2019-nCoV protein interaction. In the second step we searched Chinese herbal databases to identify plants containing the selected compounds. Plants containing 2 or more of the compounds identified in our screen were then checked against the catalogue for classic herbal usage. Finally, network pharmacology analysis was used to predict the general in vivo effects of each selected herb. RESULTS: Of the natural compounds screened, 13 that exist in traditional Chinese medicines were also found to have potential anti-2019-nCoV activity. Further, 125 Chinese herbs were found to contain 2 or more of these 13 compounds. Of these 125 herbs, 26 are classically catalogued as treating viral respiratory infections. Network pharmacology analysis predicted that the general in vivo roles of these 26 herbal plants were related to regulating viral infection, immune/inflammation reactions and hypoxia response. CONCLUSION: Chinese herbal treatments classically used for treating viral respiratory infection might contain direct anti-2019-nCoV compounds.

Celastrol Reverses Palmitic Acid-Induced Insulin Resistance in HepG2 Cells via Restoring the miR-223 and GLUT4 Pathway.

OBJECTIVES: The natural triterpenoid compound celastrol ameliorates insulin resistance (IR) in animal models, but the underlying molecular mechanism is unclear. In this study, we investigated how celastrol regulates IR. METHODS: The HepG2 cellular IR model was initially established with palmitic acid (PA). The expression and activity of glucose transporter 4 (GLUT4), insulin receptor substrate-1 (IRS1) and 9 microRNAs (miRNAs) (miR-7, -34a, -96, -113, -126, -145, -150, -223 and -370) were detected before and after celastrol treatment using the PA-induced HepG2 IR model. RESULTS: The results showed that 250 µM PA for ≥2 days was optimal for inducing IR in HepG2 cells; 600 nM celastrol significantly attenuated the PA-induced IR in HepG2 cells. The PA-induced GLUT4 and IRS1 downregulation and Ser307 phosphorylation on IRS1 was reversed by subsequent treatment with 600 nM celastrol for 6 h. We next investigated which IR-related miRNAs were possible upstream regulators of celastrol-mediated reversal of PA-induced HepG2 IR. Two miRNAs, miR-150 and -223, were significantly downregulated by PA and were re-raised by subsequent celastrol treatment; and miR-223 was upstream of miR-150. Moreover, knocking down miR-223 abolished celastrol's anti-IR effects in the PA-induced model. CONCLUSIONS: Collectively, our results demonstrated that celastrol reverses PA-induced IR-related alterations, in part via miR-223 in HepG2 cells. Further investigation is warranted for establishing the clinical potential of celastrol in treating IR-related disorders.

Celastrol reverses palmitic acid (PA)-caused TLR4-MD2 activation-dependent insulin resistance via disrupting MD2-related cellular binding to PA.

Elevated plasma statured fatty acids (FFAs) cause TLR4/MD2 activation-dependent inflammation and insulin tolerance, which account for the occurrence and development of obesity. It has been confirmed that statured palmitic acid (PA) (the most abundant FFA) could bind MD2 to cause cellular inflammation. The natural compound celastrol could improve obesity, which is suggested via inhibiting inflammation, yet the detailed mechanism for celastrol is still unclear. As celastrol is reported to directly target MD2, we thought disrupting the binding between FFAs and MD2 might be one of the ways for celastrol to inhibit FFAs-caused inflammation and insulin resistance. In this study, we found evidence to support our hypothesis: celastrol could reverse PA-caused TLR4/MD2 activation-dependent insulin resistance, as determined by glucose-lowering ability, cellular glucose uptake, insulin action-related proteins and TLR4/MD2/NF-κB activation. Bioinformatics and cellular experiments showed that both celastrol and PA could bind MD2, and that celastrol could expel PA from cells. Finally, celastrol could reverse high fat diet caused hyperglycemia and obesity, and liver NF-kB activations. Taking together, we proved that celastrol could reverses PA-caused TLR4-MD2 activation-dependent insulin resistance via disrupting PA binding to MD2.

Mutations Y493G and K546D in human HSP90 disrupt binding of celastrol and reduce interaction with Cdc37.

Celastrol, a natural compound derived from the Chinese herb Tripterygium wilfordii Hook F, has been proven to inhibit heat shock protein 90 (HSP90) activity and has attracted much attention because of its promising effects in cancer treatment and in ameliorating degenerative neuron diseases. However, the HSP90 structure involved in celastrol interaction is not known. Here, we report a novel celastrol-binding pocket in the HSP90 dimer, predicted by molecular docking. Mutation of the two key binding pocket amino acids (Lys546 and Tyr493) disrupted the binding of celastrol to HSP90 dimers, as detected by isothermal titration calorimetry (ITC). Interestingly, such mutations also reduced binding between HSP90 and the cochaperone Cdc37, thus providing a new explanation for reported findings that celastrol shows more obvious effects in disrupting binding between HSP90 and Cdc37 than between HSP90 and other cochaperones. In short, our work discloses a novel binding pocket in HSP90 dimer for celastrol and provides an explanation as to why celastrol has a strong effect on HSP90 and Cdc37 binding.

Celastrol targets IRAKs to block Toll-like receptor 4-mediated nuclear factor-κB activation.

OBJECTIVE: Celastrol has been established as a nuclear factor-κB (NF-κB) activation inhibitor; however, the exact mechanism behind this action is still unknown. Using text-mining technology, the authors predicted that interleukin-1 receptor-associated kinases (IRAKs) are potential celastrol targets, and hypothesized that targeting IRAKs might be one way that celastrol inhibits NF-κB. This is because IRAKs are key molecules for some crucial pathways to activate NF-κB (e.g., the interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) superfamily). METHODS: The human hepatocellular cell line (HepG2) treated with palmitic acid (PA) was used as a model for stimulating TLR4/NF-κB activation, in order to observe the potential effects of celastrol in IRAK regulation and NF-κB inhibition. The transfection of small interfering RNA was used for down-regulating TLR4, IRAK1 and IRAK4, and the Western blot method was used to detect changes in the protein expressions. RESULTS: The results showed that celastrol could effectively inhibit PA-caused TLR4-dependent NF-κB activation in the HepG2 cells; PA also activated IRAKs, which were inhibited by celastrol. Knocking down IRAKs abolished PA-caused NF-κB activation. CONCLUSION: The results for the first time show that targeting IRAKs is one way in which celastrol inhibits NF-κB activation.

Celastrol Ameliorates EAE Induction by Suppressing Pathogenic T Cell Responses in the Peripheral and Central Nervous Systems.

Multiple sclerosis (MS) is the prototypical inflammatory demyelinating disease of the central nervous system (CNS), and MS results in physical and cognitive impairments, such as fatigue, pain, depression and bladder dysfunction. Though many therapies for MS have been developed, the safety profile and effectiveness of these therapies still need to be defined. Thus, new therapies for MS must be explored. Celastrol, a quinonemethide triterpene, is a pharmacologically active compound present in Thunder God Vine root extracts used to treat inflammatory and autoimmune diseases. Molecular studies have identified several molecular targets, which are mostly centered on the inhibition of IKK-NF-κB signaling. The animal model of experimental autoimmune encephalomyelitis (EAE) has been widely used in MS studies; thus, we tried to explore the role of celastrol in EAE development in this study. We demonstrated that the intraperitoneal injection of celastrol significantly attenuated EAE disease. Th17 cell responses in the peripheral lymph nodes in EAE mice were also inhibited by celastrol. We determined that celastroldownregulated cytokine production in bone-marrow derived dendritic cells (BMDCs). Accordingly, T cells that were co-cultured with either BMDCs pre-treated with celastrolor splenic DCs and then collected on day 7 after EAE immunizationshowed that Th17 cell polarization is suppressed in the above two situations. Moreover, celastrol was required for tissue-infiltrating DCs to sustain Th17 responses in the central nervous system (CNS). Taken together, the results of our study demonstrate that celastrol ameliorates EAE development by suppressing pathogenic Th17 responses; this finding offers a better understanding of the role of celastrol in EAE development as well as new proposals for clinical interventions.

Celastrol inhibits lung infiltration in differential syndrome animal models by reducing TNF-α and ICAM-1 levels while preserving differentiation in ATRA-induced acute promyelocytic leukemia cells.

All-trans retinoic acid (ATRA) is a revolutionary agent for acute promyelocytic leukemia (APL) treatment via differentiation induction. However, ATRA treatment also increases cytokine, chemokine, and adhesive molecule (mainly ICAM-1) expression, which can cause clinical complications, including a severe situation known as differentiation syndrome (DS) which can cause death. Therefore, it is of clinical significance to find a strategy to specifically blunt inflammatory effects while preserving differentiation. Here we report that the natural compound, celastrol, could effectively block lung infiltrations in DS animal models created by loading ATRA-induced APL cell line NB4. In ATRA-treated NB4 cells, celastrol could potently inhibit ICAM-1 elevation and partially reduce TNF-α and IL-1ß secretion, though treatment showed no effects on IL-8 and MCP-1 levels. Celastrol's effect on ICAM-1 in ATRA-treated NB4 was related to reducing MEK1/ERK1 activation. Strikingly and encouragingly, celastrol showed no obvious effects on ATRA-induced NB4 differentiation, as determined by morphology, enzymes, and surface markers. Our results show that celastrol is a promising and unique agent for managing the side effects of ATRA application on APL, and suggest that hyper-inflammatory ability is accompanied by, but not necessary for, APL differentiation. Thus we offered an encouraging novel strategy to further improve differentiation therapy.

IP-FCM platform detects the existence and regulator-caused dissociation of components in naturally assembled HSP90 complex.

Flow cytometry, in conjunction with immunoprecipitation (IP-FCM), is suggested to have some advantages to conventional IP-western blot technology in analyzing protein complexes. In this paper, to further examine its practicability, we test the use of IP-FCM in detecting the HSP90 complex, which has gained importance in drug research and development and involves more than a dozen components. We found that IP-FCM could effectively detect HSP70, p23, Cdc37, and Cdk6 components in the HSP90 complex naturally formed in U937 cells when this complex was captured by anti-HSP90 antibody-coated polystyrene microspheres. IP-FCM could also detect alteration in components caused by treating cells with HSP90 inhibitors. In a cell-free environment, IP-FCM could detect the direct effects of ATP and/or HSP90 inhibitors (17-N-allylamino-17-demethoxygeldanamycin or celastrol) in causing component dissociation and the time- and dose-effects of inhibitor-caused dissociation. IP-FCM is a practical and powerful platform for analyzing HSP90 complex components, and is thus a useful tool in studying HSP90 complex function and screening inhibitors.

[Tripterine inhibits all-trans retinoic acid-caused adhesion between leukemia cells and endothelial cells].

OBJECTIVE: Increasing of adhesion between leukemia cells and endothelial cells during all-trans retinoic acid (ATRA) treatment plays an important role in retinoic acid syndrome. This work observed the effects of tripterine on this ATRA-caused increasing in adhesion. METHODS: The effects of tripterine on ATRA-induced expressions of adhesive molecules in acute promyelocytic leukemia cell line NB4 and human umbilical vascular endothelial cells (HUVEC) were detected by flow cytometry. The effects of tripterine on adhesion between ATRA-treated NB4 and HUVEC were determined by adhesive assays. RESULTS: ATRA caused remarkable elevation of intercellular adhesion molecule-1 (ICAM-1) in NB4 cells, which could be significantly reduced by tripterine (P<0.01). The expressions of E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and ICAM-1 in HUVEC were elevated by conditioned medium from ATRA-induced NB4 (ATRA-NB4-CM) (P<0.01), and inhibited by tripterine with inhibition rates being 25.3%, 42.4% and 61.0% respectively. ATRA increased the adhesion between NB4 and HUVEC, which was reversed completely by tripterine. CONCLUSION: Tripterine can inhibit ATRA-caused adhesion between leukemia cells and endothelial cells, and it might be a potential agent for treating retinoic acid syndrome.

Tripterine inhibits the expression of adhesion molecules in activated endothelial cells.

Cell adhesion molecules (CAM) expressed by vascular endothelium in response to cytokine stimulation play a key role in leukocyte adhesion to endothelium during the inflammatory response. Tripterine, a chemical compound of the Chinese plant Tripterygium wilfordii Hook f, displays anti-inflammatory properties in several animal models. However, mechanisms of its action are poorly understood. In the present study, we show that in inflammatory conditions, mimicked by tumor necrosis factor alpha (TNF-alpha) stimulation, pretreatment for 6 h with tripterine at nontoxic concentrations of 20-200 nM inhibits the expression of E-selectin, vascular cell adhesion molecule (CAM)-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) in human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. Tripterine (200 nM) almost completely inhibits expression of VCAM-1 [50% inhibitory concentration (IC50) = 52 nM] and ICAM-1 (IC50 = 51 nM) and 73% of E-selectin (IC50 = 94 nM). This inhibition effect is prominent, compared with that of dexamethasone, ibuprofen, methotrexate, or probucol, which revealed a much weaker inhibition at doses as high as 1 mM. Effects on endothelial CAM of other proinflammatory cytokines, such as interleukin-1beta and interferon-gamma, were also inhibited significantly by tripterine. Moreover, significant inhibition was equally observable in postincubation experiments. In addition, tripterine inhibited adhesion of human monocytes and T lymphocytes to TNF-alpha-stimulated HUVEC. Finally, tripterine inhibited TNF-alpha-driven CAM mRNA transcription and nuclear factor-kappaB nuclear (NF-kappaB) translocation. Hence, we describe a new mechanism of tripterine's anti-inflammatory action obtained at nanomolar concentrations, owing to the negative regulation of cytokine-induced adhesion molecule expression and adhesiveness in human endothelium.