Oridonin enhances phagocytosis of UV-irradiated apoptotic U937 cells

Oridonin from Rabdosia rubescens: An emerging potential in cancer therapy - A comprehensive review

Cancer incidences are rising each year. In 2020, approximately 20 million new cancer cases and 10 million cancer-related deaths were recorded. The World Health Organization (WHO) predicts that by 2024 the incidence of cancer will increase to 30.2 million individuals annually. Considering the invasive characteristics of its diagnostic procedures and therapeutic methods side effects, scientists are searching for different solutions, including using plant-derived bioactive compounds, that could reduce the probability of cancer occurrence and make its treatment more comfortable. In this regard, oridonin (ORI), an ent-kaurane diterpenoid, naturally found in the leaves of Rabdosia rubescens species, has been found to have antitumor, antiangiogenesis, antiasthmatic, antiinflammatory, and apoptosis induction properties. Extensive research has been performed on ORI to find various mechanisms involved in its anticancer activities. This review article provides an overview of ORI's effectiveness on murine and human cancer populations from 1976 to 2022 and provides insight into the future application of ORI in different cancer therapies.

Natural Compounds Oridonin and Shikonin Exhibit Potentially Beneficial Regulatory Effects on Select Functions of Microglia

Accumulating evidence indicates that the adverse neuroimmune activation of microglia, brain immunocytes that support neurons, contributes to a range of neuroinflammatory disorders, including Alzheimer's disease. Correcting the abnormal functions of microglia is a potential therapeutic strategy for these diseases. Nucleotide-binding domain leucine-rich repeat and pyrin domain-containing receptor (NLRP) 3 inflammasomes are implicated in adverse microglial activation and their inhibitors, such as the natural compounds oridonin and shikonin, reduce microglial immune responses. We hypothesized that some of the beneficial effects of oridonin and shikonin on microglia are independent of their suppression of NLRP3 inflammasomes. Murine and human microglia-like cells were stimulated with bacterial lipopolysaccharide (LPS) only, which did not induce NLRP3 inflammasome activation or the resulting secretion of interleukin (IL)-1β, allowing for the identification of other anti-inflammatory effects. Under these experimental conditions, both oridonin and shikonin reduced nitric oxide (NO) secretion and the cytotoxicity of BV-2 murine microglia towards HT-22 murine neuronal cells, but upregulated BV-2 cell phagocytic activity. Only oridonin inhibited the secretion of tumor necrosis factor (TNF) by stimulated BV-2 microglia, while only shikonin suppressed the respiratory burst response of human HL-60 microglia-like cells. This observed discrepancy indicates that these natural compounds may have different molecular targets in microglia. Overall, our results suggest that oridonin and shikonin should be further investigated as pharmacological agents capable of correcting dysfunctional microglia, supporting their potential use in neuroinflammatory disorders.

Oridonin and its derivatives for cancer treatment and overcoming therapeutic resistance

Cancer is one of the diseases with high morbidity and mortality on a global scale. Chemotherapy remains the primary treatment option for most cancer patients, including patients with progressive, metastatic, and recurrent diseases. To date, hundreds of chemotherapy drugs are used to treat various cancers, however, the anti-cancer efficacy and outcomes are largely hampered by chemotherapy-associated toxicity and acquired therapeutic resistance. The natural product (NP) oridonin has been extensively studied for its anti-cancer efficacy. More recently, oridonin has been shown to overcome drug resistance through multiple mechanisms, with yet-to-be-defined bona fide targets. Hundreds of oridonin derivative analogs (oridonalogs) have been synthesized and screened for improved potency, bioavailability, and other drug properties. Particularly, many of these oridonalogs have been tested against oridonin for tumor growth inhibition, potential for overcoming therapeutic resistance, and immunity modulation. This concise review seeks to summarize the advances in this field in light of identifying clinical-trial level drug candidates with the promise for treating progressive cancers and reversing chemoresistance.

Protective effects of oridonin on the sepsis in mice

This study aimed to investigate the protective effects of oridonin (ORI) on cecal ligation and puncture (CLP)-induced sepsis in mice. Male C57BL/6 mice weighing 22-30 g and aged 8-10 weeks were randomly assigned to three groups: Sham group, CLP group, or CLP plus ORI group. In the CLP group and ORI group, CLP was induced, and intraperitoneal injection of normal saline and oridonin (100 μg/kg) was conducted, respectively. The survival rate was determined within the following 7 days. The blood, liver, and lung were collected at 24 hours after injury. Hematoxylin-eosin staining of the lung, detection of lung wet-to-dry ratio, and serum cytokines (tumor necrosis factor [TNF]-α and interleukin [IL]-6), and examination of intraperitoneal and blood bacterial clearance were conducted to evaluate the therapeutic efficacy. Results showed that ORI treatment significantly reduced the lung wet-to-dry ratio, decreased serum TNF-α and IL-6, and improved liver pathology compared with the CLP group (p < 0.05). Moreover, the intraperitoneal and blood bacterial clearance increased markedly after ORI treatment (p < 0.05). The 7-day survival rate in the ORI group was also dramatically higher than in the CLP group (p < 0.05). Our findings indicate that ORI can attenuate liver and lung injuries and elevate bacterial clearance to increase the survival rate of sepsis mice.

Molecular Insight in the Multifunctional Effects of Oridonin

Oridonin has attracted considerable attention in the last decade because of its anti-cancer pharmacological properties. This ent-kaurane diterpenoid, isolated from the Chinese herb Rabdosia rubescens and some related species, has demonstrated great potential in the treatment profile of many diseases by exerting anti-tumor, anti-inflammatory, pro-apoptotic, and neurological effects. Unfortunately, the mechanisms via which oridonin exerts these effects remain poorly understood. This review provides an overview of the multifunctional effects of oridonin as well as the reasons for its potential for investigations in the treatment of many diseases other than cancer.

N‑acetyl‑L‑cysteine reduces arsenite‑induced cytotoxicity through chelation in U937 monocytes and macrophages

In the present study, in order to clarify the preventive mechanism of N‑acetyl‑L‑cysteine (NAC) on arsenite‑induced apoptosis in U937 cells, which lack functional p53, the cytotoxicity among U937 cells [monocytes and 12‑O‑tetradecanoylphorbol‑13‑acetate (TPA)‑treated macrophages] receiving NAC treatment at different times post arsenite treatment was examined. TPA‑treated macrophages were more resistant to arsenite‑induced apoptosis than monocytes, which may be associated with the induction of Bcl‑2 expression. Pretreatment with 20 mM NAC prior to arsenite exposure suppressed apoptosis up to 75% in the monocytes and 100% in the macrophages. However, 6‑h NAC pretreatment and subsequent washing out of NAC from the culture medium prior to arsenite treatment did not inhibit the arsenite‑induced apoptosis. Post‑treatment by NAC up to 1 h following arsenite exposure almost completely inhibited the cytotoxic effects of arsenite in U937 monocytes and macrophages. The results of the current study indicate that the preventive mechanism of NAC on arsenite‑induced apoptosis in U937 monocytes and macrophages mainly involves chelation of arsenite in culture medium.

Simultaneous determination of oridonin, ponicidin and rosmarinic acid from Herba Isodi Rubescentis extract by LC-MS-MS in rat plasma

An analytical method was developed for the simultaneous quantification of oridonin, ponicidin and rosmarinic acid in rat plasma using liquid chromatography-tandem mass spectrometry with electrospray ionization in positive and negative ion modes of operation. Multiple reaction monitoring was used for quantification using the precursor to product ion pairs of m/z 359.100 → 160.9 (rosmarinic acid), m/z 150.1 → 106.9 (acetaminophen as internal standard 1), m/z 365.1 → 347.3 (oridonin), m/z 363.3 → 345.2 (ponicidin) and m/z 258.3 → 201.0 (dextrorphan as internal standard 2). Optimum chromatographic separation was achieved with a BDS Hypersil C18 column (100 × 2.1 mm, 2.4 µm) and a mobile phase consisting of acetonitrile-5mM ammonium acetate containing 0.1% acetic acid (25:75, v/v). The analytes were extracted from rat plasma using a single liquid-liquid extraction technique and the calibration curve was linear within the concentration range of 2-1,000.0 ng/mL for three analytes. The extraction recovery was above 70%, the intra-day and inter-day precision of the quality control (QC) samples was less than 12.45% and the accuracy of the QC samples was 96.99-105.79% of the nominal values. The method was sensitive and reliable and was successfully applied to a pharmacokinetic and bioavailability study of Herba Isodi Rubescentis extract in rats.

Oridonin: targeting programmed cell death pathways as an anti-tumour agent

Oridonin, an active diterpenoid isolated from traditional Chinese herbal medicine, has drawn rising attention for its remarkable apoptosis- and autophagy-inducing activity and relevant molecular mechanisms in cancer therapy. Apoptosis is a well known type of cell death, whereas autophagy can play either pro-survival or pro-death roles in cancer cells. Accumulating evidence has recently revealed relationships between apoptosis and autophagy induced by oridonin; however, molecular mechanisms behind them remain to be discovered. In this review, we focus on highlighting updated research on oridonin-induced cell death signalling pathways implicated in apoptosis and autophagy, in many types of cancer. In addition, we further discuss cross-talk between apoptosis and autophagy induced by oridonin, in cancer. Taken together, these findings open new perspectives for further exploring oridonin as a potential anti-tumour agent targeting apoptosis and autophagy, in future anti-cancer therapeutics.

Ultraviolet B (UVB) irradiation-induced apoptosis in various cell lineages in vitro

Ultraviolet B (UVB) radiation acts as a strong apoptotic trigger in many cell types, in tumor and normal cells. Several studies have demonstrated that UVB-induced cell death occurs through the generation of reactive oxygen species. The consequent oxidative stress includes the impairment of cellular antioxidants, the induction of DNA damage and the occurrence of apoptosis. In this review, we investigated UVB apoptotic action in various cell models by using ultrastructural, molecular and cytofluorimetric techniques. Myeloid leukemia HL-60, T-lymphoblastoid Molt-4 and myelomonocytic U937 human cells, generally affected by apoptotic stimuli, were studied. Human chondrocytes and C2C12 skeletal muscle cells, known to be more resistant to damage, were also considered. All of them, when exposed to UVB radiation, revealed a number of characteristic apoptotic markers. Membrane blebbing, cytoplasm shrinkage and chromatin condensation were detected by means of electron microscopy. DNA cleavage, investigated by using agarose gel electrophoresis and TUNEL reaction, was observed in suspended cells. Differently, in chondrocytes and in skeletal muscle cells, oligonucleosomic DNA fragmentation did not appear, even if a certain TUNEL positivity was detected. These findings demonstrate that UVB radiation appears to be an ideal tool to study the apoptotic behavior.

Melanogenesis inhibitors from Rabdosia japonica

The effects of the four major ent-kaurene diterpenoids isolated from the aerial part of Rabdosia japonica (Labiatae) on murine B16-F10 melanoma cells were investigated. Among the compounds tested, oridonin and nodosin most significantly suppressed cellular melanin production when the cells were cultured with these diterpenoids. However, oridonin and nodosin exhibited cytotoxicity against the same melanoma cells with an IC(50) of 1.1 μM (0.40 μg/ml) and of 1.3 μM (0.47 μg/ml) and almost complete lethality was observed at 4.0 μM and at 8.0 μM, respectively, and therefore observed melanogenesis inhibition is mainly due to its melanocytotoxic effect. Morphological observation showed that oridonin or nodosin treated B16-F10 melanoma cells induced dendrite structure. Diterpenoids quickly formed adducts partly in Dulbecco's Modified Eagle's Medium (DMEM) containing 10% of fetal bovine serum (10% FBS-DMEM) before their application to the cells. Approximately 20% of oridonin formed adducts within the first 15 min. Notably, dihydronodosin exhibited inferior cytotoxicity (>85% cell viability at 100 μM) but still significantly suppressed melanogenesis (>55%) when murine B16-F10 melanoma cells were cultured with this diterpenoid derivatives. Hence, dihydronodosin can be a potential melanogenesis inhibitor.

Nitric oxide augments oridonin-induced efferocytosis by human histocytic lymphoma U937 cells via autophagy and the NF-κB-COX-2-IL-1β pathway

We previously demonstrated that oridonin-induced autophagy enhanced efferocytosis (phagocytosis of apoptotic cells) by macrophage-like U937 cells through activation of the inflammatory pathways. In this study, exposure of U937 cells to 2.5 μM oridonin caused up-regulation of inducible nitric oxide synthase (iNOS) expression and continuous endogenous generation of nitric oxide (NO), which was reversed by pre-treatment with the inhibitors of nitric oxide synthase 1400 W (dihydrochloride) or L-NAME (hydrochloride). NO donor sodium nitroprusside (SNP) and efferocytosis irritant lipopolysaccharide (LPS) could also exert NO generation and iNOS expression. Moreover, oridonin-induced stimulation of efferocytosis was significantly suppressed by 1400 W or L-NAME. In addition, 1400 W or L-NAME impaired oridonin-induced autophagy. Inhibition of autophagy with 3-methyladenine (3MA) or Beclin-1 siRNA attenuated the uptake of apoptotic cells with a slight increase in the production of NO. The pro-inflammatory cytokine interleukin-1β (IL-1β) has been reported to be involved in oridonin-induced efferocytosis in U937 cells and interact with NO to contribute to inflammatory responses. 1400 W or L-NAME blocked the secretion of IL-1β and the activation of NF-κB and COX-2. Provision of SNP or LPS in place of oridonin resulted in the similar enhancement of efferocytosis, autophagy, the release of IL-1β and the expression of signal protein. NO augmented the oridonin-induced efferocytosis by mediating autophagy and activating the NF-κB-COX-2-IL-1β pathway. Inhibition of NF-κB or COX-2 in turn decreased the production of NO and the expression of iNOS. There exists a positive feedback loop between NO generation and NF-κB-COX-2-IL-1β pathway.

Differential control of growth, cell cycle progression, and expression of NF-κB in human breast cancer cells MCF-7, MCF-10A, and MDA-MB-231 by ponicidin and oridonin, diterpenoids from the chinese herb Rabdosia rubescens

Ponicidin and oridonin are novel diterpenoids isolated from Rabdosia rubescens. We tested their effects in MCF-7 and MDA-MB-231 cells, as representing low and high invasive breast carcinoma, with normal MCF-10A cells. Clonogenicity and proliferation in MCF-7 cells were inhibited more significantly by ponicidin than oridonin, while the reverse was observed in MCF-10A cells. Ponicidin and oridonin induced S/G2M arrest and G1/S block in MCF-7 cells. In MCF-10A cells treated with either diterpenoid, induction of apoptosis was observed. Moreover, oridonin almost completely blocked MCF-10A progression from S to G2/M phase; in contrast, ponicidin-treated MCF-10A cells showed no discernable changes in cell cycle phase distribution. Neither diterpenoid affected growth of MDA-MB-231 cells, at the dose range effective for MCF-7 or MCF-10A cells. Ponicidin-treated MCF-7 cells expressed reduced levels of cyclin B1, cdc2, transcription factor E2F, and Rb including phosphorylation at S780. Less pronounced effects were found in cells treated with oridonin. Neither compound altered cyclin D1 and cdk4 in MCF-7 cells. In MCF-10A cells, oridonin was more active than ponicidin in inhibiting the expression of cyclin B1, cdc2, S780-phosphorylated Rb, and E2F. To further investigate induction of apoptosis in MCF-10A cells, we measured changes in NF-kappaB. Decreases in p65 or p50 forms of NF-kappaB and its upstream regulator I-kappaB were found in oridonin-treated MCF-10A and not MCF-7 cells. Taken together, these results provide a mechanistic framework for the cellular effects of ponicidin and oridonin in different stage breast cancer cells.

Roles of Ras and extracellular signal-regulated kinase-dependent IkappaBalpha degradation in oridonin-enhanced phagocytosis of apoptotic cells by human macrophage-like U937 cells

Rapid recognition and ingestion of apoptotic cells by phagocytes are important for the prevention of toxic intracellular contents release, thereby attenuate inflammation and autoimmune diseases such as systemic lupus erythematosus (SLE). We have reported that oridonin isolated from Rabdosia rubescens enhanced phagocytosis of apoptotic U937 cells by macrophage-like U937 cells through TNFalpha and IL-1beta release. In this study, the molecular mechanisms involved in this phagocytic process are investigated. Inhibitors of Ras and Raf1 kinase significantly reduced oridonin-induced phagocytic stimulation as well as extracellular signal-regulated kinase (ERK) phosphorylation. Simultaneously, oridonin-enhanced engulfment was partially blocked by a nuclear factor (NF)-kappaB inhibitor PDTC or proteasome inhibitor MG132. Further studies revealed that oridonin induced IkappaBalpha degradation, which was prevented by Ras inhibitor manumycin A, ERK inhibitor PD98059, but not prevented by c-Jun N-terminal kinase (JNK) MAPK inhibitor SP600125, and up-regulated expression of IL-1beta precursor. These results demonstrate that Ras/Raf1/ERK signaling pathway-dependent IkappaBalpha degradation, resulting in NF-kappaB activation, participates in regulation of oridonin-enhanced phagocytosis, and one of its effector functions is to induce synthesis of IL-1beta, which partially contribute to phagocytic activity of oridonin.

Activation of Phosphoinositide 3-Kinase, Protein Kinase C, and Extracellular Signal-Regulated Kinase Is Required for Oridonin-Enhanced Phagocytosis of Apoptotic Bodies in Human Macrophage-Like U937 Cells

Our previous study showed that oridonin isolated from Rabdosia rubescens enhanced phagocytosis of apoptotic cells by macrophage-like U937 cells through tumor necrosis factor (TNF) alpha and interleukin (IL)-1beta release. In this study, we further investigated signaling events involved in oridonin-augmented phagocytosis. Phagocytic stimulation was significantly suppressed by inhibitors, including a phosphoinositide 3-kinases (PI3K) inhibitor (wortmannin), a protein kinase C (PKC) inhibitor (stauroporine), and a phospholipase C (PLC) inhibitor (U73122). Exposure of U937 cells to oridonin caused an increase in PKC activity time- dependently, which was prevented by pretreatment with inhibitors of PI3K and PLC. Simultaneously, the activation of protein kinase B (PKB/Akt) and the increased expression of PLCgamma2 were also blocked by wortmannin. In addition, an extracellular signal-regulated kinase (ERK) MAPK inhibitor, PD98059, suppressed oridonin-augmented phagocytosis, whereas the p38 MAPK inhibitor (SB203580) and c-Jun N-terminal kinase (JNK) MAPK inhibitor (SP98059) had no inhibitory effect. Furthermore, pretreatment of U937 cells with anti-TNFalpha and anti-IL-1beta antibodies blocked oridonin-induced phagocytic stimulation as well as phosphorylation of ERK, but did not block the activation of PKC, indicating that these signaling events are triggered by oridonin, whereas secreted TNFalpha or IL-1beta only activate the ERK-dependent pathway. Taken together, oridonin is suggested to enhance phagocytosis of apoptotic bodies by activating PI3K, PKC, and ERK-dependent pathways.