Necrostatin-1 treatment inhibits osteocyte necroptosis and trabecular deterioration in ovariectomized rats

Noncoding RNAs: the crucial role of programmed cell death in osteoporosis

Osteoporosis is the most common skeletal disease characterized by an imbalance between bone resorption and bone remodeling. Osteoporosis can lead to bone loss and bone microstructural deterioration. This increases the risk of bone fragility and fracture, severely reducing patients' mobility and quality of life. However, the specific molecular mechanisms involved in the development of osteoporosis remain unclear. Increasing evidence suggests that multiple noncoding RNAs show differential expression in the osteoporosis state. Meanwhile, noncoding RNAs have been associated with an increased risk of osteoporosis and fracture. Noncoding RNAs are an important class of factors at the level of gene regulation and are mainly involved in cell proliferation, cell differentiation, and cell death. Programmed cell death is a genetically-regulated form of cell death involved in regulating the homeostasis of the internal environment. Noncoding RNA plays an important role in the programmed cell death process. The exploration of the noncoding RNA-programmed cell death axis has become an interesting area of research and has been shown to play a role in many diseases such as osteoporosis. In this review, we summarize the latest findings on the mechanism of noncoding RNA-mediated programmed cell death on bone homeostasis imbalance leading to osteoporosis. And we provide a deeper understanding of the role played by the noncoding RNA-programmed cell death axis at the gene regulatory level of osteoporosis. We hope to provide a unique opportunity to develop novel diagnostic and therapeutic approaches for osteoporosis.

TNF-α promotes osteocyte necroptosis by upregulating TLR4 in postmenopausal osteoporosis

Postmenopausal osteoporosis (PMOP) is a common kind of osteoporosis that is associated with excessive osteocyte death and bone loss. Previous studies have shown that TNF-α-induced osteocyte necroptosis might exert a stronger effect on PMOP than apoptosis, and TLR4 can also induce cell necroptosis, as confirmed by recent studies. However, little is known about the relationship between TNF-α-induced osteocyte necroptosis and TLR4. In the present study, we showed that TNF-α increased the expression of TLR4, which promoted osteocyte necroptosis in PMOP. In patients with PMOP, TLR4 was highly expressed at skeletal sites where exists osteocyte necroptosis, and high TLR4 expression is correlated with enhanced TNF-α expression. Osteocytes exhibited robust TLR4 expression upon exposure to necroptotic osteocytes in vivo and in vitro. Western blotting and immunofluorescence analyses demonstrated that TNF-α upregulated TLR4 expression in vitro, which might further promote osteocyte necroptosis. Furthermore, inhibition of TLR4 by TAK-242 in vitro effectively blocked osteocyte necroptosis induced by TNF-α. Collectively, these results suggest a novel TLR4-mediated process of osteocyte necroptosis, which might increase osteocyte death and bone loss in the process of PMOP.

Ferroptosis inhibitor improves cardiac function more effectively than inhibitors of apoptosis and necroptosis through cardiac mitochondrial protection in rats with iron-overloaded cardiomyopathy

Iron overload cardiomyopathy (IOC) is the leading cause of death in cases of iron overload in patients. Previous studies demonstrated that iron overload led to cardiomyocyte dysfunction and death through multiple pathways including apoptosis, necroptosis and ferroptosis. However, the dominant cell death pathway in the iron-overloaded heart needs clarification. We tested the hypothesis that ferroptosis, an iron-dependent cell death, plays a dominant role in IOC, and ferroptosis inhibitor exerts greater efficacy than inhibitors of apoptosis and necroptosis on improving cardiac function in iron-overloaded rats. Iron dextran was injected intraperitoneally into male Wistar rats for four weeks to induce iron overload. Then, the rats were divided into 5 groups: treated with vehicle, apoptosis inhibitor (z-VAD-FMK), necroptosis inhibitor (Necrostatin-1), ferroptosis inhibitor (Ferrostatin-1) or iron chelator (deferoxamine) for 2 weeks. Cardiac function, mitochondrial function, apoptosis, necroptosis and ferroptosis were determined. The increased expression of apoptosis-, necroptosis- and ferroptosis-related proteins, were associated with impaired cardiac and mitochondrial function in iron-overloaded rats. All cell death inhibitors attenuated cardiac apoptosis, necroptosis and ferroptosis in iron-overloaded rats. Ferrostatin-1 was more effective than the other drugs in diminishing mitochondrial dysfunction and Bax/Bcl-2 ratio. Moreover, both Ferrostatin-1 and deferoxamine reversed iron overload-induced cardiac dysfunction as indicated by restored left ventricular ejection fraction and E/A ratio, whereas z-VAD-FMK and Necrostatin-1 only partially improved this parameter. These results indicated that ferroptosis could be the predominant form of cardiomyocyte death in IOC, and that inhibiting ferroptosis might be a potential novel treatment for IOC.

ROS-mediated mitophagy and necroptosis regulate osteocytes death caused by TCP particles in MLO-Y4 cells

Our previous data have revealed TCP particles caused cell death of osteocytes, comprising over 95 % of all bone cells, which contribute to periprosthetic osteolysis, joint loosening and implant failure, but its mechanisms are not fully understood. Here, we reported that TCP particles inhibited cell viability of osteocytes MLO-Y4, and caused cell death. TCP particles caused mitochondrial impairment and increased expressions of LC-3 II, Parkin and PINK 1, accompanied by the elevation of autophagy flux and intracellular acidic components, the accumulation of LC-3II, PINK1 and Parkin in damaged mitochondria, and p62 reduction. The increased LC-3II expression and cell death extent were significantly enhanced by the autophagy inhibitor Baf A1, compared with Baf A1 (or TCP particles) alone, indicating that TCP particles increase autophagic flux and lead to cell even death of MLO-Y4 cells, closely associated with mitophagy. Furthermore, TCP particles induced propidium iodide (PI) uptake and the phosphorylation of RIP1, RIP3 and MLKL, thereby increasing necroptosis in MLO-Y4 cells. The pro-necroptotic effect was alleviated by the RIP1 inhibitor Nec-1 or the MLKL inhibitor NSA. Additionally, TCP particles promoted the production of intracellular reactive oxygen species (ROS) and mitochondrial ROS (mtROS), and increased TXNIP expression, but decreased protein levels of TRX1, Nrf2, HO-1 and NQO1, leading to oxidative stress. The ROS scavenger NAC remarkably reversed mitophagy and necroptosis caused by TCP particles, suggesting that ROS is responsible for mitophagy and necroptosis. Collectively, ROS-mediated mitophagy and necroptosis regulate osteocytes death caused by TCP particles in MLO-Y4 cells, which enhances osteoclastogenesis and periprosthetic osteolysis.

Protaetia brevitarsis seulensis larvae ethanol extract inhibits RANKL-stimulated osteoclastogenesis and ameliorates bone loss in ovariectomized mice

Modulation of osteoclast formation could be a therapeutic target for inhibiting pathological bone destruction. The receptor activator of nuclear factor (NF)-κB ligand (RANKL) is known to be an essential factor in osteoclast differentiation and activation inducers. However, whether Protaetia brevitarsis seulensis (P. brevitarsis) larvae-a traditional animal-derived medicine used in many Asian countries-can inhibit RANKL-induced osteoclast formation and prevent ovariectomy (OVX)-induced bone loss has not been evaluated. Here, we aimed to investigate the anti-osteoporotic effects of P. brevitarsis larvae ethanol extract (PBE) in RANKL-stimulated RAW264.7 cells and OVX mice. In vitro, PBE (0.1, 0.5, 1, and 2 mg/mL) decreased RANKL‑induced tartrate-resistant acid phosphatase (TRAP) activity and expression of osteoclastogenesis-associated genes and proteins. Furthermore, PBE (0.1, 0.5, 1, and 2 mg/mL) significantly inhibited the phosphorylation of p38 and NF-κB. Female C3H/HeN mice were divided into five groups (n = 5 per group), namely, sham-operated, OVX, OVX+PBEL (100 mg/kg, oral gavage), OVX+PBEH (200 mg/kg, oral gavage), and OVX+estradiol (0.03 μg/day, subcutaneous injection). High doses of PBE significantly increased femoral bone mineral density (BMD) and bone volume/tissue volume (BV/TV), whereas femoral bone surface/bone volume (BS/BV) and osteoclastogenesis-associated protein expression decreased compared to those in the OVX group. Moreover, PBE (200 mg/kg) significantly increased estradiol and procollagen type I N-terminal propeptide and decreased N-terminal telopeptide of type I collagen and C-terminal telopeptide of type I collagen compared to those in the OVX group. Our results suggest that PBE can be an effective therapeutic candidate for preventing or treating postmenopausal osteoporosis.

High Glucose-Induced Kidney Injury via Activation of Necroptosis in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes mellitus (DM) and is closely associated to programmed cell death. However, the complex mechanisms of necroptosis, an alternative cell death pathway, in DKD pathogenesis are yet to be elucidated. This study indicates that necroptosis is involved in DKD induced by high glucose (HG) both in vivo and in vitro. HG intervention led to the activation of RIPK1/RIPK3/MLKL signaling, resulting in renal tissue necroptosis and proinflammatory activation in streptozotocin/high-fat diet- (STZ/HFD-) induced diabetic mice and HG-induced normal rat kidney tubular cells (NRK-52E). We further found that in HG-induced NRK-52E cell, necroptosis might, at least partly, depend on the levels of reactive oxygen species (ROS). Meanwhile, ROS participated in necroptosis via a positive feedback loop involving the RIPK1/RIPK3 pathway. In addition, blocking RIPK1/RIPK3/MLKL signaling by necrostatin-1 (Nec-1), a key inhibitor of RIPK1 in the necroptosis pathway, or antioxidant N-acetylcysteine (NAC), an inhibitor of ROS generation, could effectively protect the kidney against HG-induced damage, decrease the release of proinflammatory cytokines, and rescue renal function in STZ/HFD-induced diabetic mice. Inhibition of RIPK1 effectively decreased the activation of RIPK1-kinase-/NF-κB-dependent inflammation. Collectively, we demonstrated that high glucose induced DKD via renal tubular epithelium necroptosis, and Nec-1 or NAC treatment downregulated the RIPK1/RIPK3/MLKL pathway and finally reduced necroptosis, oxidative stress, and inflammation. Thus, RIPK1 may be a therapeutic target for DKD.

Benzo[a]pyrene exposure promotes RIP1-mediated necroptotic death of osteocytes and the JNK/IL-18 pathway activation via generation of reactive oxygen species

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) of environmental pollutants, readily produced during the processing of petroleum and fatty foods. BaP exposure can cause skeletal deformities. However, whether BaP affects osteocytes, making up over 95% of all the bone cells, remains unknown. This study aimed to investigate the effect of BaP on osteocytes in vivo and in vitro, as well as explore the underlying mechanisms. The in vivo data showed that BaP (50mg/kg) exposure for 12 weeks could cause bone destruction, and increase osteocytes death in mouse cortical femur. Our in vitro results revealed that BaP (25-100 μmol/L) exposure inhibited cell viability of MLO-Y4 cells, and resulted in cell death in a dose-dependent manner. Furthermore, BaP exposure significantly triggered necroptosis of MLO-Y4 cells, as indicated by increased propidium iodide (PI)-positive cells and up-regulation of necroptosis-related protein expressions of receptor-interacting protein kinase 1 (RIP1), RIP3, and mixed lineage kinase domain-like protein (MLKL). This necrotic effect was reversed by the RIP1 inhibitor necrostatin-1 (Nec-1). Simultaneously, BaP activated the downstream c-Jun N-terminal kinase (JNK)/ interleukin (IL)-18 signaling pathway, which was suppressed after the JNK inhibitor SP600125 or Nec-1 treatment. In addition, BaP exposure promoted the production of intracellular reactive oxygen species (ROS), mitochondrial ROS (mtROS), and elevated malondialdehyde (MDA) levels; while BaP decreased superoxide dismutase (SOD) activity and antioxidant enzymes including nuclear factor E₂-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels, leading to oxidative damage. The ROS scavenger N-acetylcysteine (NAC) inhibited this necroptotic death and the JNK/IL-18 pathway activation. Collectively, BaP exposure may cause RIP1-mediated necroptotic death of osteocytes and activate the JNK/IL-18 pathway via ROS generation.

Targeting Cell Death: Pyroptosis, Ferroptosis, Apoptosis and Necroptosis in Osteoarthritis

New research has shown that the development of osteoarthritis (OA) is regulated by different mechanisms of cell death and types of cytokines. Therefore, elucidating the mechanism of action among various cytokines, cell death processes and OA is important towards better understanding the pathogenesis and progression of the disease. This paper reviews the pathogenesis of OA in relation to different types of cytokine-triggered cell death. We describe the cell morphological features and molecular mechanisms of pyroptosis, apoptosis, necroptosis, and ferroptosis, and summarize the current research findings defining the molecular mechanisms of action between different cell death types and OA.

Comparison of Necroptosis With Apoptosis for OVX-Induced Osteoporosis

As one common kind of osteoporosis, postmenopausal osteoporosis (PMOP) is associated with the death and excessive loss of osteocytes. Estrogen deficiency of PMOP can cause osteocyte death by regulating necroptosis and apoptosis, but their roles in POMP have not been compared. In the present study, ovariectomy (OVX)-induced rat and murine long bone osteocyte Y4 (MLO-Y4) cells were used to compare the influence of necroptosis and apoptosis on osteocyte death and bone loss. Benzyloxycarbonyl-Val-Ala-Asp (zVAD) and necrostatin-1 (Nec-1) were used to specifically block cell apoptosis and necroptosis, respectively. OVX rats and MLO-Y4 cells were divided into zVAD group, Nec-1 group, zVAD + Nec-1 group, vehicle, and control group. The tibial plateaus of the rat model were harvested at 8 weeks after OVX and were analyzed by micro–computed tomography, transmission electron microscopy (TEM), the transferase dUTP nick end labeling assay, and western blot. The death of MLO-Y4 was stimulated by TNF-α and was measured by flow cytometry and TEM. The results found that necroptosis and apoptosis were both responsible for the death and excessive loss of osteocytes, as well as bone loss in OVX-induced osteoporosis, and furthermore necroptosis may generate greater impact on the death of osteocytes than apoptosis. Necroptotic death of osteocytes was mainly regulated by the receptor-interacting protein kinase 3 signaling pathway. Collectively, inhibition of necroptosis may produce better efficacy in reducing osteocyte loss than that of apoptosis, and combined blockade of necroptosis and apoptosis provide new insights into preventing and treating PMOP.

Necroptosis: A new target for prevention of osteoporosis

Multiple causes may contribute to osteoporosis, characterized by a loss in bone mass and density as a consequence of the degradation of bone microstructure and a resultant rise in bone fragility. Recently, increasing attention has been paid to the role of necroptosis in the development of osteoporosis. Necroptosis is orchestrated by a set of proteins known as receptor-interacting protein kinase (RIPK)1, RIPK3, and mixed lineage kinase domain-like protein (MLKL). A necrosome is formed by MLKL, RIPK1, RIPK3, and RIPK3-RIPK3. A dissociated MLKL forms pores in the plasma membrane and eventually leads to necroptosis after translocating from the necrosome. In this review, we discuss a detailed understanding of necroptosis and its associated processes, a better understanding of its interactions with osteoclasts, osteoblasts, and osteocytes, and the associations between necroptosis and diabetic osteoporosis, steroid-induced osteoporosis, and postmenopausal osteoporosis. In addition, a variety of experimental medicines capable of modulating crucial necroptosis processes are highlighted. It's important to note that this is the first review paper to consolidate current data on the role of necroptosis in osteoporosis, and it offers fresh hope for the future treatment of this disease.

Biologic and pathologic aspects of osteocytes in the setting of medication-related osteonecrosis of the jaw (MRONJ)

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe, debilitating condition affecting patients with cancer and patients with osteoporosis who have been treated with powerful antiresorptives (pARs) or angiogenesis inhibitors (AgIs). Oral risk factors associated with the development of MRONJ include tooth extraction and inflammatory dental disease (e.g., periodontitis, periapical infection). In bone tissues, osteocytes play a bidirectional role in which they not only act as the "receiver" of systemic signals from blood vessels, such as hormones and drugs, or local signals from the mineralized matrix as it is deformed, but they also play a critical role as "transmitter" of signals to the cells that execute bone modeling and remodeling (osteoclasts, osteoblasts and lining cells). When the survival capacity of osteocytes is overwhelmed, they can die. Osteocyte death has been associated with several pathological conditions. Whereas the causes and mechanisms of osteocyte death have been studied in conditions like osteonecrosis of the femoral head (ONFH), few studies of the causes and mechanisms of osteocyte death have been done in MRONJ. The three forms of cell death that affect most of the different cells in the body (apoptosis, autophagy, and necrosis) have been recognized in osteocytes. Notably, necroptosis, a form of regulated cell death with "a necrotic cell death phenotype," has also been identified as a form of cell death in osteocytes under certain pathologic conditions. Improving the understanding of osteocyte death in MRONJ may be critical for preventing disease and developing treatment approaches. In this review, we intend to provide insight into the biology of osteocytes, cell death, in general, and osteocyte death, in particular, and discuss hypothetical mechanisms involved in osteocyte death associated with MRONJ.

Chronic Ethanol Consumption Induces Osteopenia via Activation of Osteoblast Necroptosis

Chronic high-dose alcohol consumption impairs bone remodeling, reduces bone mass, and increases the risk of osteoporosis and bone fracture. However, the mechanisms underlying alcohol-induced osteoporosis are yet to be elucidated. In this study, we showed that excess intake of ethyl alcohol (EtOH) resulted in osteopenia and osteoblast necroptosis in mice that led to necrotic lesions and reduced osteogenic differentiation in bone marrow mesenchymal stem cells (BMMSCs). We found that EtOH treatment led to the activation of the RIPK1/RIPK3/MLKL signaling, resulting in increased osteoblast necroptosis and decreased osteogenic differentiation and bone formation both in vivo and in vitro. We further discovered that excessive EtOH treatment-induced osteoblast necroptosis might partly depend on reactive oxygen species (ROS) generation; concomitantly, ROS contributed to necroptosis of osteoblasts through a positive feedback loop involving RIPK1/RIPK3. In addition, blocking of the RIPK1/RIPK3/MLKL signaling by necrostatin-1 (Nec-1), a key inhibitor of RIPK1 kinase in the necroptosis pathway, or antioxidant N-acetylcysteine (NAC), an inhibitor of ROS, could decrease the activation of osteoblast necroptosis and ameliorate alcohol-induced osteopenia both in vivo and in vitro. Collectively, we demonstrated that chronic high-dose alcohol consumption induced osteopenia via osteoblast necroptosis and revealed that RIPK1 kinase may be a therapeutic target for alcohol-induced osteopenia.

Necrostatin-1 and necroptosis inhibition: Pathophysiology and therapeutic implications

Necrostatin-1 (Nec-1) is a RIP1-targeted inhibitor of necroptosis, a form of programmed cell death discovered and investigated in recent years. There are already many studies demonstrating the essential role of necroptosis in various diseases, including inflammatory diseases, cardiovascular diseases and neurological diseases. However, the potential of Nec-1 in diseases has not received much attention. Nec-1 is able to inhibit necroptosis signaling pathway and thus ameliorate necroptotic cell death in disease development. Recent research findings indicate that Nec-1 could be applied in several types of diseases to alleviate disease development or improve prognosis. Moreover, we predict that Nec-1 has the potential to protect against the complications of coronavirus disease 2019 (COVID-19). This review summarized the effect of Nec-1 in disease models and the underlying molecular mechanism, providing research evidence for its future application.

Necrostatin-1 Mitigates Cognitive Dysfunction in Prediabetic Rats With No Alteration in Insulin Sensitivity

Previous studies showed that 12 weeks of high-fat diet (HFD) consumption caused not only prediabetes but also cognitive decline and brain pathologies. Recently, necrostatin-1 (nec-1), a necroptosis inhibitor, showed beneficial effects in brain against stroke. However, the comparative effects of nec-1 and metformin on cognition and brain pathologies in prediabetes have not been investigated. We hypothesized that nec-1 and metformin equally attenuated cognitive decline and brain pathologies in prediabetic rats. Rats (n = 32) were fed with either normal diet (ND) or HFD for 20 weeks. At week 13, ND-fed rats were given a vehicle (n = 8) and HFD-fed rats were randomly assigned into three subgroups (n = 8/subgroup) with vehicle, nec-1, or metformin for 8 weeks. Metabolic parameters, cognitive function, brain insulin receptor function, synaptic plasticity, dendritic spine density, microglial morphology, brain mitochondrial function, Alzheimer protein, and cell death were determined. HFD-fed rats exhibited prediabetes, cognitive decline, and brain pathologies. Nec-1 and metformin equally improved cognitive function, synaptic plasticity, dendritic spine density, microglial morphology, and brain mitochondrial function and reduced hyperphosphorylated Tau and necroptosis in HFD-fed rats. Interestingly, metformin, but not nec-1, improved brain insulin sensitivity in those rats. In conclusion, necroptosis inhibition directly improved cognition in prediabetic rats without alteration in insulin sensitivity.

Autophagy as a decisive process for cell death

Autophagy is an intracellular catabolic pathway in which cellular constituents are engulfed by autophagosomes and degraded upon autophagosome fusion with lysosomes. Autophagy serves as a major cytoprotective process by maintaining cellular homeostasis and recycling cytoplasmic contents. However, emerging evidence suggests that autophagy is a primary mechanism of cell death (autophagic cell death, ACD) and implicates ACD in several aspects of mammalian physiology, including tumor suppression and psychological disorders. However, little is known about the physiological roles and molecular mechanisms of ACD. In this review, we document examples of ACD and discuss recent progress in our understanding of its molecular mechanisms.

Inhibition of receptor-interacting protein kinase 1 improves experimental non-alcoholic fatty liver disease

BACKGROUND & AIMS

In non-alcoholic fatty liver disease (NAFLD), hepatocytes can undergo necroptosis: a regulated form of necrotic cell death mediated by the receptor-interacting protein kinase (RIPK) 1. Herein, we assessed the potential for RIPK1 and its downstream effector mixed lineage kinase domain-like protein (MLKL) to act as therapeutic targets and markers of activity in NAFLD.

METHODS

C57/BL6J-mice were fed a normal chow diet or a high-fat diet (HFD). The effect of RIPA-56, a highly specific inhibitor of RIPK1, was evaluated in HFD-fed mice and in primary human steatotic hepatocytes. RIPK1 and MLKL concentrations were measured in the serum of patients with NAFLD.

RESULTS

When used as either a prophylactic or curative treatment for HFD-fed mice, RIPA-56 caused a downregulation of MLKL and a reduction of liver injury, inflammation and fibrosis, characteristic of non-alcoholic steatohepatitis (NASH), as well as of steatosis. This latter effect was reproduced by treating primary human steatotic hepatocytes with RIPA-56 or necrosulfonamide, a specific inhibitor of human MLKL, and by knockout (KO) of Mlkl in fat-loaded AML-12 mouse hepatocytes. Mlkl-KO led to activation of mitochondrial respiration and an increase in β-oxidation in steatotic hepatocytes. Along with decreased MLKL activation, Ripk3-KO mice exhibited increased activities of the liver mitochondrial respiratory chain complexes in experimental NASH. In patients with NAFLD, serum concentrations of RIPK1 and MLKL increased in correlation with activity.

CONCLUSION

The inhibition of RIPK1 improves NASH features in HFD-fed mice and reverses steatosis via an MLKL-dependent mechanism that, at least partly, involves an increase in mitochondrial respiration. RIPK1 and MLKL are potential serum markers of activity and promising therapeutic targets in NAFLD.

LAY SUMMARY

There are currently no pharmacological treatment options for non-alcoholic fatty liver disease (NAFLD), which is now the most frequent liver disease. Necroptosis is a regulated process of cell death that can occur in hepatocytes during NAFLD. Herein, we show that RIPK1, a gatekeeper of the necroptosis pathway that is activated in NAFLD, can be inhibited by RIPA-56 to reduce not only liver injury, inflammation and fibrosis, but also steatosis in experimental models. These results highlight the potential of RIPK1 as a therapeutic target in NAFLD.

AT1 and AT2 receptors modulate renal tubular cell necroptosis in angiotensin II-infused renal injury mice

Abnormal renin-angiotensin system (RAS) activation plays a critical role in the initiation and progression of chronic kidney disease (CKD) by directly mediating renal tubular cell apoptosis. Our previous study showed that necroptosis may play a more important role than apoptosis in mediating renal tubular cell loss in chronic renal injury rats, but the mechanism involved remains unknown. Here, we investigate whether blocking the angiotensin II type 1 receptor (AT1R) and/or angiotensin II type 2 receptor (AT2R) beneficially alleviates renal tubular cell necroptosis and chronic kidney injury. In an angiotensin II (Ang II)-induced renal injury mouse model, we found that blocking AT1R and AT2R effectively mitigates Ang II-induced increases in necroptotic tubular epithelial cell percentages, necroptosis-related RIP3 and MLKL protein expression, serum creatinine and blood urea nitrogen levels, and tubular damage scores. Furthermore, inhibition of AT1R and AT2R diminishes Ang II-induced necroptosis in HK-2 cells and the AT2 agonist CGP42112A increases the percentage of necroptotic HK-2 cells. In addition, the current study also demonstrates that Losartan and PD123319 effectively mitigated the Ang II-induced increases in Fas and FasL signaling molecule expression. Importantly, disruption of FasL significantly suppressed Ang II-induced increases in necroptotic HK-2 cell percentages, and necroptosis-related proteins. These results suggest that Fas and FasL, as subsequent signaling molecules of AT1R and AT2R, might involve in Ang II-induced necroptosis. Taken together, our results suggest that Ang II-induced necroptosis of renal tubular cell might be involved both AT1R and AT2R and the subsequent expression of Fas, FasL signaling. Thus, AT1R and AT2R might function as critical mediators.

Gushukang inhibits osteocyte apoptosis and enhances BMP-2/Smads signaling pathway in ovariectomized rats

BACKGROUND

Traditional herbal formula Gushukang (GSK) has been clinically applied to treat primary osteoporosis, which can stimulate osteoblastogenesis and improve calcium homeostasis. However, it remains unknown the mechanism that GSK against ovariectomized (OVX) induced damage.

PURPOSE

The aim of this study was to investigate the effect of GSK on BMP-2/Smsds signaling pathway and osteocyte apoptosis which has been reported to play a central role in bone remodeling.

STUDY DESIGN

OVX in rat was established and GSK was administered.

RESULTS

BMP-2/Smsds signaling pathway was inhibited and the number of apoptotic osteocytes was increased in OVX rats. Treatment with GSK significantly enhanced BMP-2/Smsds signaling pathway by up-regulating the expression of BMP-2, p-Smad1 and p-Smad5, Osterix and Runx2, and inhibited osteocyte apoptosis by up-regulating Bcl-xl and down-regulating Bak, which were consistent with histological changes revealed by ALP, Trap and TUNEL staining. GSK treatment improved bone mass and micro-structure of trabecular bone at distal femur in OVX rats shown by BMD, micro-CT measurement and HE staining.

CONCLUSION

These data suggest that GSK exhibited protective effects on promoting bone formation and precluding osteocyte apoptosis. The underlying mechanism may be attributed to its regulation on BMP-2/Smads signaling pathway and Bcl2 family.

Chitosan gold nanoparticles induce different ROS-dependent cell death modalities in leukemic cells

BACKGROUND

Nanotechnology proposes the use of gold nanoparticles (AuNPs) for drug delivery, diagnosis, and treatment of cancer. Leukemia is a type of hematopoietic cancer that results from the malignant transformation of white blood cells. Chitosan-coated AuNPs (CH-AuNPs) are cell death inductors in HeLa and MCF-7 cancer cells without affecting peripheral blood mononuclear cells (PBMC). Considering the selectivity and versatile cytotoxicity of CH-AuNPs, we evaluated whether their selectivity is due to the cell lineage or the characteristics of the cancer cells, by assessing its cytotoxicity in leukemic cells. Moreover, we further examined the cell death mechanism and assessed the implication of nuclear damage, autophagosome formation, and the cell death mechanism induced in leukemic cells.

MATERIALS AND METHODS

We synthesized CH-AuNPs by chemical methods and analyzed their cell death capacity in a T-acute lymphocytic leukemia cell line (CEM), in a chronic myeloid leukemia cell line (K562), and in healthy cells from the same lineage (PBMC and bone marrow, BM, cells). Then, we assessed ROS generation and mitochondrial and nuclear damage. Finally, we evaluated whether cell death occurred by autophagy, apoptosis, or necroptosis, and the role of ROS in this mechanism.

RESULTS

We found that CH-AuNPs did not affect PBMC and BM cells, whereas they are cytotoxic in a dose-dependent manner in leukemic cells. ROS production leads to mitochondrial and nuclear damage, and cell death. We found that CH-AuNPs induce apoptosis in CEM and necroptosis in K562, both undergoing autophagy as a pro-survival mechanism.

CONCLUSION

CH-AuNPs are selective cell death inductors in hematologic cancer cells, without affecting their healthy counterparts. Cell death induced by CH-AuNPs is independent of the cancer cell type; however, its mechanism is different depending on the type of leukemic cells.

Sterile particle-induced inflammation is mediated by macrophages releasing IL-33 through a Bruton's tyrosine kinase-dependent pathway

Initiation of the innate sterile inflammatory response that can develop in response to microparticle exposure is little understood. Here, we report that a potent type 2 immune response associated with the accumulation of neutrophils, eosinophils and alternatively activated (M2) macrophages was observed in response to sterile microparticles similar in size to wear debris associated with prosthetic implants. Although elevations in interleukin-33 (IL-33) and type 2 cytokines occurred independently of caspase-1 inflammasome signalling, the response was dependent on Bruton's tyrosine kinase (BTK). IL-33 was produced by macrophages and BTK-dependent expression of IL-33 by macrophages was sufficient to initiate the type 2 response. Analysis of inflammation in patient periprosthetic tissue also revealed type 2 responses under aseptic conditions in patients undergoing revision surgery. These findings indicate that microparticle-induced sterile inflammation is initiated by macrophages activated to produce IL-33. They further suggest that both BTK and IL-33 may provide therapeutic targets for wear debris-induced periprosthetic inflammation.

Discovery of a tetrazolyl β-carboline with in vitro and in vivo osteoprotective activity under estrogen-deficient conditions

β-Carbolines have been assessed for osteoclastogenesis. However, their effect on osteoblasts during estrogen deficiency is still unclear. Here, a series of novel piperazine and tetrazole tag β-carbolines have been synthesized and examined for osteoblast differentiation in vitro. In vitro data suggest that compound 8g is the most promising osteoblast differentiating agent that was evaluated for in vivo studies. Compound 8g promoted osteoblast mineralization, stimulated Runx2, BMP-2 and OCN expression levels, increased BrdU incorporation and inhibited generation of free radicals as well as nitric oxide. Since a piperazine group is involved in bone repair activity and β-carboline in IκB kinase (IKK) inhibition, compound 8g inhibited tumor necrosis factor α (TNFα) directed IκBα phosphorylation, preventing nuclear translocation of NF-κB thereby alleviating osteoblast apoptosis. In vivo studies show that compound 8g was able to restore estrogen deficiency-induced bone loss in ovariectomized rats without any toxicity, thus signifying its potential in bone-protection chemotherapy under postmenopausal conditions.

Necrostatin-1 attenuates lipopolysaccharide-induced acute lung injury in mice

AIM OF THE STUDY

Receptor-interacting protein (RIP) kinase family members are involved in several biological processes. However, their role in acute lung injury (ALI) is still unclear. In the present study, we aim to determine the expression and function of RIP kinase family in ALI.

MATERIALS AND METHODS

In the present study, ALI was induced in BALB/c male mice by intravenously injecting lipopolysaccharide (LPS). The expression levels of the RIP kinase family in ALI mice were determined using western blotting and immunohistochemical staining. The specific RIP-1 inhibitor, necrostatin-1, was used to treat LPS-induced ALI mice, followed by survival time recording, as well as histopathological and immunohistochemical staining of lung tissues, western blotting, myeloperoxidase (MPO) assay and enzyme-linked immunosorbent assay (ELISA) of related cytokines and downstream target expression.

RESULTS

We found that RIP-1 expression was upregulated in the lung of ALI mice and inhibition of RIP-1 by necrostatin-1 significantly prolonged the survival time of mice, which was accompanied by less serve lung injury. Furthermore, lower expression of pro-inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor [TNF]-α, IL-8, cyclooxygenase [COX]-2, monocyte chemoattractant protein [MCP]-1, and IL-1β), MPO and nuclear factor (NF)-κB activation were found in bronchoalveolar lavage fluid (BALF) and lung tissues of necrostatin-1-treated ALI mice. Necrostatin-1 also attenuated LPS-induced pro-inflammatory cytokine expression and NF-κB activation in RAW 264.7 cells.

CONCLUSIONS

In summary, necrostatin-1 protected against LPS-induced ALI in mice by inhibiting inflammation and pulmonary NF-κB activation. Thus, necrostatin-1 could be a novel therapeutic strategy for ALI.

Quantitative analysis of necrostatin-1, a necroptosis inhibitor by LC-MS/MS and the study of its pharmacokinetics and bioavailability

Necrostatin-1 (Nec-1) is known as a specific and potent inhibitor of non-apoptotic cell death. In this study, a rapid and sensitive LC-MS/MS method that was developed for the determination of Nec-1 levels in plasma. Meanwhile, it has been used to explore pharmacokinetics and bioavailability of Nec-1 among rats. The m/z 260.1→131 was selected as the optimal MRM transition in analyzing Nce-1. The chromatographic separation was performed with SB-C18 analytical column using the optimized gradient elution mode. The extraction recoveries of Nec-1 ranged from 85.40% to 98.25% and the matrix effects were between 94.73% and 99.26%. Both the intra- and inter-day precision did not exceed 10.0%, respectively. Moreover, it is found that Nec-1 remained stable in plasma despite different processing and storage environment. The plasma concentration of Nec-1 was successfully determined among rats who received single dose via intravenous and oral route (5mg/kg), respectively. A two-compartment model was fitted the concentration-time profile of the Nec-1 with C_max 1733μgL^-1 and t_1/2 1.8h for intravenous route, and C_max 648μgL^-1 and t_1/2 1.2h for oral route, respectively. The results showed that absolute bioavailability of Nec-1 was 54.8%. It is promising that the study is helpful to understand in vivo behaviors of Nec-1 and facilitate the future investigations of the compound.