Triptolide, a diterpene, inhibits osteoclastogenesis, induced by RANKL signaling and human cancer cells

Antitumor mechanisms and future clinical applications of the natural product triptolide

Triptolide (TPL) is a compound sourced from Tripterygium wilfordii Hook. F., a traditional Chinese medicinal herb recognized for its impressive anti-inflammatory, anti-angiogenic, immunosuppressive, and antitumor qualities. Notwithstanding its favorable attributes, the precise mechanism through which TPL influences tumor cells remains enigmatic. Its toxicity and limited water solubility significantly impede the clinical application of TPL. We offer a comprehensive overview of recent research endeavors aimed at unraveling the antitumor mechanism of TPL in this review. Additionally, we briefly discuss current strategies to effectively manage the challenges associated with TPL in future clinical applications. By compiling this information, we aim to enhance the understanding of the underlying mechanisms involved in TPL and identify potential avenues for further advancement in antitumor therapy.

Activities and Molecular Mechanisms of Diterpenes, Diterpenoids, and Their Derivatives in Rheumatoid Arthritis

Diterpenes and their derivatives have many biological activities, including anti-inflammatory and immunomodulatory effects. To date, several diterpenes, diterpenoids, and their laboratory-derived products have been demonstrated for antiarthritic activities. This study summarizes the literature about diterpenes and their derivatives acting against rheumatoid arthritis (RA) depending on the database reports until 31 August 2021. For this, we have conducted an extensive search in databases such as PubMed, Science Direct, Google Scholar, and Clinicaltrials.gov using specific relevant keywords. The search yielded 2708 published records, among which 48 have been included in this study. The findings offer several potential diterpenes and their derivatives as anti-RA in various test models. Among the diterpenes and their derivatives, andrographolide, triptolide, and tanshinone IIA have been found to exhibit anti-RA activity through diverse pathways. In addition, some important derivatives of triptolide and tanshinone IIA have also been shown to have anti-RA effects. Overall, findings suggest that these substances could reduce arthritis score, downregulate oxidative, proinflammatory, and inflammatory biomarkers, modulate various arthritis pathways, and improve joint destruction and clinical arthritic conditions, signs, symptoms, and physical functions in humans and numerous experimental animals, mainly through cytokine and chemokine as well as several physiological protein interaction pathways. Taken all together, diterpenes, diterpenoids, and their derivatives may be promising tools for RA management.

Evolving Roles of Natural Terpenoids From Traditional Chinese Medicine in the Treatment of Osteoporosis

Osteoporosis (OP) is a systemic metabolic skeletal disease which can lead to reduction in bone mass and increased risk of bone fracture due to the microstructural degradation. Traditional Chinese medicine (TCM) has been applied in the prevention and treatment of osteoporosis for a long time. Terpenoids, a class of natural products that are rich in TCM, have been widely studied for their therapeutic efficacy on bone resorption, osteogenesis, and concomitant inflammation. Terpenoids can be classified in four categories by structures, monoterpenoids, sesquiterpenoids, diterpenoids, and triterpenoids. In this review, we comprehensively summarize all the currently known TCM-derived terpenoids in the treatment of OP. In addition, we discuss the possible mechanistic-of-actions of all four category terpenoids in anti-OP and assess their therapeutic potential for OP treatment.

Effects and mechanisms of natural plant active compounds for the treatment of osteoclast-mediated bone destructive diseases

Bone-destructive diseases, caused by overdifferentiation of osteoclasts, reduce bone mass and quality, and disrupt bone microstructure, thereby causes osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis. Osteoclasts, the only multinucleated cells with bone resorption function, are derived from haematopoietic progenitors of the monocyte/macrophage lineage. The regulation of osteoclast differentiation is considered an effective target for the treatment of bone-destructive diseases. Natural plant-derived products have received increasing attention in recent years due to their good safety profile, the preference of natural compounds over synthetic drugs, and their potential therapeutic and preventive activity against osteoclast-mediated bone-destructive diseases. In this study, we reviewed the research progress of the potential antiosteoclast active compounds extracted from medicinal plants and their molecular mechanisms. Active compounds from natural plants that inhibit osteoclast differentiation and functions include flavonoids, terpenoids, quinones, glucosides, polyphenols, alkaloids, coumarins, lignans, and limonoids. They inhibit bone destruction by downregulating the expression of osteoclast-specific marker genes (CTSK, MMP-9, TRAP, OSCAR, DC-STAMP, V-ATPase d2, and integrin av3) and transcription factors (c-Fos, NFATc1, and c-Src), prevent the effects of local factors (ROS, LPS, and NO), and suppress the activation of various signalling pathways (MAPK, NF-κB, Akt, and Ca²⁺). Therefore, osteoclast-targeting natural products are of great value in the prevention and treatment of bone destructive diseases.

Influence of astragaloside IV on pharmacokinetics of triptolide in rats and its potential mechanism

Context: It is common to combine two or more drugs in clinics in China. Triptolide (TP) has been used primarily for the treatment of inflammatory and autoimmune diseases. Astragaloside IV (AS-IV) has been applied with many other drugs, due to its various pharmacological effects. AS-IV and TP can be used together for the treatment of diseases in clinics in China.Objective: This study investigates the effects of astragaloside IV (AS-IV) on the pharmacokinetics of TP in rats and its potential mechanism.Materials and methods: The pharmacokinetics of orally administered triptolide (2 mg/kg) with or without AS-IV pre-treatment (100 mg/kg/day for 7 d) were investigated. Additionally, the effects of AS-IV on the transport of triptolide were investigated using the Caco-2 cell transwell model.Results: The results indicated that when the rats were pre-treated with AS-IV, the C_max of triptolide decreased from 418.78 ± 29.36 to 351.31 ± 38.88 ng/mL, and the AUC_0-t decreased from 358.83 ± 19.56 to 252.23 ± 15.75 μg/h/L. The Caco-2 cell transwell experiments indicated that AS-IV could increase the efflux ratio of TP from 2.37 to 2.91 through inducing the activity of P-gp.Discussion and conclusions: In conclusion, AS-IV could decrease the system exposure of triptolide when they are co-administered, and it might work through decreasing the absorption of triptolide by inducing the activity of P-gp.

The Study of Cellular Mechanism of Triptolide in the Treatment of Cancer, Bone Loss and Cardiovascular Disease and Triptolide's Toxicity

Triptolide (TPL), the active component of Tripterygium wilfordii Hook F (Twhf) has been used to treat cancer and bone loss conditions for over two hundred years in traditional Chinese medicine (TCM). In this paper, we reviewed the specific molecular mechanisms in the treatment of cancer, bone loss and cardiovascular disease. In addition, we analyze the toxicity of TPL and collect some optimized derivatives extracted from TPL. Although positive results were obtained in most cell culture and animal studies, further studies are needed to substantiate the beneficial effects of TPL.

Potential Advantages of Bioactive Compounds Extracted From Traditional Chinese Medicine to Inhibit Bone Destructions in Rheumatoid Arthritis

Bone destruction is an important pathological feature of rheumatoid arthritis (RA), which finally leads to the serious decline of life quality in RA patients. Bone metabolism imbalance is the principal factor of bone destruction in RA, which is manifested by excessive osteoclast-mediated bone resorption and inadequate osteoblast-mediated bone formation. Although current drugs alleviate the process of bone destruction to a certain extent, there are still many deficiencies. Recent studies have shown that traditional Chinese medicine (TCM) could effectively suppress bone destruction of RA. Some bioactive compounds from TCM have shown good effect on inhibiting osteoclast differentiation and promoting osteoblast proliferation. This article reviews the research progress of bioactive compounds exacted from TCM in inhibiting bone destruction of RA, so as to provide references for further clinical and scientific research.

Triptolide prevents bone loss via suppressing osteoclastogenesis through inhibiting PI3K-AKT-NFATc1 pathway

Bone loss (osteopenia) is a common complication in human solid tumour. In addition, after surgical treatment of gynaecological tumour, osteoporosis often occurs due to the withdrawal of oestrogen. The major characteristic of osteoporosis is the low bone mass with micro-architectural deteriorated bone tissue. And the main cause is the overactivation of osteoclastogenesis, which is one of the most important therapeutic targets. Inflammation could induce the interaction of RANKL/RANK, which is the promoter of osteoclastogenesis. Triptolide is derived from the traditional Chinese herb lei gong teng, presented multiple biological effects, including anti-cancer, anti-inflammation and immunosuppression. We hypothesized that triptolide could inhibits osteoclastogenesis by suppressing inflammation activation. In this study, we confirmed that triptolide could suppress RANKL-induced osteoclastogenesis in bone marrow mononuclear cells (BMMCs) and RAW264.7 cells and inhibited the osteoclast bone resorption functions. PI3K-AKT-NFATc1 pathway is one of the most important downstream pathways of RANKL-induced osteogenesis. The experiments in vitro indicated that triptolide suppresses the activation of PI3K-AKT-NFATc1 pathway and the target point located at the upstream of AKT because both NFATc1 overexpression and AKT phosphorylation could ameliorate the triptolide suppression effects. The expression of MDM2 was elevated, which demonstrated the MDM-p53-induced cell death might contribute to the osteoclastogenesis suppression. Ovariectomy-induced bone loss and inflammation activation were also found to be ameliorated in the experiments in vivo. In summary, the new effect of anti-cancer drug triptolide was demonstrated to be anti-osteoclastogenesis, and we demonstrated triptolide might be a promising therapy for bone loss caused by tumour.

A review of the total syntheses of triptolide

Triptolide is a complex triepoxide diterpene natural product that has attracted considerable interest in the organic chemistry and medicinal chemistry societies due to its intriguing structural features and multiple promising biological activities. In this review, progress in the total syntheses of triptolide are systematically summarized. We hope to gain a better understanding of the field and provide constructive suggestions for future studies of triptolide.

Effects of triptolide on pharmacokinetics of amlodipine in rats by using LC-MS/MS

CONTEXT

Triptolide and amlodipine are often simultaneously used for reducing urine protein excretion after renal transplantation in China clinics.

OBJECTIVE

This study investigated the effects of triptolide on the pharmacokinetics of amlodipine in male Sprague-Dawley rats.

MATERIALS AND METHODS

The pharmacokinetics of amlodipine (1 mg/kg) with or without triptolide pre-treatment (2 mg/kg/day for seven days) were investigated using a sensitive and reliable LC-MS/MS method. Additionally, the inhibitory effects of triptolide on the metabolic stability of amlodipine were investigated using rat liver microsome incubation systems.

RESULTS

The results indicated that when the rats were pre-treated with triptolide, the Cmax of amlodipine increased from 13.78 ± 3.57 to 19.96 ± 4.56 ng/mL (p < 0.05), the Tmax increased from 4.04 ± 1.15 to 5.89 ± 1.64 h (p < 0.05), and the AUC0-t increased by approximately 104% (p < 0.05), which suggested that the pharmacokinetic behaviour of amlodipine was affected after oral co-administration of triptolide. Additionally, the metabolic half-life was prolonged from 22.5 ± 4.26 to 36.8 ± 6.37 min (p < 0.05) with the pre-treatment of triptolide.

CONCLUSIONS

In conclusion, these results indicated that triptolide could affect the pharmacokinetics of amlodipine, possibly by inhibiting the metabolism of amlodipine in rat liver when they are co-administered.

Icariin abrogates osteoclast formation through the regulation of the RANKL-mediated TRAF6/NF-κB/ERK signaling pathway in Raw264.7 cells

BACKGROUND

Icariin is pharmacologically active prenylated flavonoid glycoside that has various biologic effects such as antioxidant, anticancer, and anti-inflammatory activities. In addition, icariin has been used in Chinese medicine for thousands of years to treat osteoporosis and it is still being used today. However, direct mechanism of icariin in the treatment of bone disease is not understood.

PURPOSE

The purpose of this study is to investigate whether icariin influences RANKL-induced osteoclast formation in murine macrophages.

METHODS

Osteoclastogenesis was determined by TRAP staining and activity assay. Inhibition of signaling pathways and marker protein expression were evaluated by western blot analysis. The NF-κB (p65) nuclear localization was detected by immunofluorescence assay, and NF-κB/DNA-binding activity was detected by electrophoretic mobility shift assay (EMSA).

RESULTS

In our study, icariin inhibited the differentiation of pre-osteoclast cells into osteoclasts and suppressed expression of various genes involved in osteoclast formation and bone resorption. Also, icariin blocked the osteoclastogenesis induced by MCF7 and MDA-MB-231 breast cancer cells through inhibition of NF-κB activation. We found that icariin inhibited RANKL-stimulated TRAF-6 expression, and subsequently suppressed the phosphorylation of ERK, but icariin did not show an effect on p38, JNK, and Akt activation.

CONCLUSION

These results indicate that icariin is likely to be a candidate for bone-related disease treatment and that icariin provides insights into the molecular mechanisms that influence RANKL-induced osteoclast differentiation.

The protective effects of triptolide on age-related bone loss in old male rats

BACKGROUND

Previous studies have showed that triptolide have a critical role in inhibiting osteoclast formation, bone resorption and attenuating regional osteoporosis. However, the protective role of triptolide on age-related bone loss has not been investigated. In the study, we assessed the effect of triptolide supplementation on bone microstructure and bone remolding in old male rat lumbars.

METHODS

Fifty-two 22-month-old male Sprague-Dawley rats were randomly assigned to either triptolide treatment group or control group. Triptolide (15 μg/kg/d) or normal saline was administered to the rats of assigned group for 8 weeks. Lumbar bone mineral density (BMD) and bone microstructure were analyzed by micro-CT. Fluorochrome labeling of the bones was performed to measure the mineral apposition rate (MAR) and bone formation rate (BFR). Osteoclast number was also measured by TRAP staining. Plasma level of osteocalcin and tartrate-resistant acid phosphatase 5b (Tracp 5b) was also analyzed.

RESULTS

Micro-CT results revealed that triptolide-treated rats had significant higher BMD, bone volume over total volume (BV/TV), trabecular thickness (Tb.Th), bone trabecular number (Tb.N), and lower trabecular separation (Tb.Sp) compared to the control group. Although fluorochrome labeling result showed no significant difference in MAR and BFR between the groups, triptolide decreased osteoclast number in vivo. In addition, a significant higher level of plasma Tracp 5b was observed in the triptolide-treated rats. Furthermore, triptolide also reduced the expression of receptor for activation of NF-κB ligand (RANKL) and increased osteoprotegerin (OPG) expression in the lumbars.

CONCLUSION

These results suggested that triptolide had a protective effect on age-related bone loss at least in part by reducing osteoclast number in elder rats. Therefore, triptolide might be a feasible therapeutic approach for senile osteoporosis.

Triptolide inhibits proliferation, differentiation and induces apoptosis of osteoblastic MC3T3‑E1 cells

Ankylosing spondylitis (AS) is characterized by the formation of bony spurs. Treatment of the resulting ankylosis, excessive bone formation and associated functional impairment, remain the primary therapeutic aims in research regarding this condition. Triptolide is the primary active component of the perennial vine Tripterygium wilfordii Hook. f., and has previously been demonstrated to exert anti-tumor activities including inhibition of cell growth and the induction of apoptosis, however, the effect of triptolide on osteoblasts remains to be elucidated. In the present study, the MC3T3-E1 mouse osteoblast cell line was treated with differing concentrations of triptolide for various intervals. Cell proliferation was detected using the bromodeoxyuridine assay, cell cycle and apoptosis were measured by flow cytometry, nuclear apoptosis was observed by Hoechst staining and associated proteins were determined via western blot analysis. The cells were then further incubated with osteogenic induction medium supplemented with triptolide for 7 or 12 days and the differentiation to osteoblasts was examined by picrosirius staining, observation of alkaline phosphatase activity and a calcium deposition assay. It was demonstrated that treatment with triptolide significantly inhibited osteoblast proliferation and induced cell cycle arrest and apoptosis of the osteoblasts. Furthermore, treatment with triptolide reduced collagen formation, alkaline phosphatase activity and calcium deposition. The present study demonstrated an inhibitory effect of triptolide on osteoblast proliferation and differentiation, and therefore suggests a potential therapeutic agent for the treatment of AS in the future.

Fabrication of novel vesicles of triptolide for antirheumatoid activity with reduced toxicity in vitro and in vivo

Triptolide (TP) displays a strong immunosuppression function in immune-mediated diseases, especially in the treatment of rheumatoid arthritis. However, in addition to its medical and health-related functions, TP also exhibits diverse pharmacological side effects, for instance, liver and kidney toxicity and myelosuppression. In order to reduce the side effects, a nano drug carrier system (γ-PGA-l-PAE-TP [PPT]), in which TP was loaded by a poly-γ-glutamic acid-grafted l-phenylalanine ethylester copolymer, was developed. PPT was characterized by photon scattering correlation spectroscopy and transmission electron microscopy, which demonstrated that the average diameter of the drug carrier system is 98±15 nm, the polydispersity index is 0.18, the zeta potential is −35 mV, and the TP encapsulation efficiency is 48.6% with a controlled release manner. The methylthiazolyldiphenyl-tetrazolium bromide assay and flow cytometry revealed that PPT could decrease toxicity and apoptosis induced by free TP on RAW264.7 cells, respectively. The detection of reactive oxygen species showed that PPT could decrease the cellular reactive oxygen species induced by TP. Compared with the free TP-treated group, PPT improved the survival rate of the mice (P<0.01) and had no side effects or toxic effects on the thymus index (P>0.05) and spleen index (P>0.05). The blood biochemical indexes revealed that PPT did not cause much damage to the kidney (blood urea nitrogen and creatinine), liver (serum alanine aminotransferase and aspartate aminotransferase), or blood cells (P>0.05). Meanwhile, hematoxylin and eosin staining and terminal-deoxynucleotidyl transferase dUTP nick-end labeling staining indicated that PPT reduced the damage of free TP on the liver, kidney, and spleen. Our results demonstrated that PPT reduced free TP toxicity in vitro and in vivo and that it is a promising fundamental drug delivery system for rheumatoid arthritis treatment.

Natural products for treatment of bone erosive diseases: The effects and mechanisms on inhibiting osteoclastogenesis and bone resorption

Excessive bone resorption plays a central role on the development of bone erosive diseases, including osteoporosis, rheumatoid arthritis, and periodontitis. Osteoclasts, bone-resorbing multinucleated cells, are differentiated from hemopoietic progenitors of the monocyte/macrophage lineage. Regulation of osteoclast differentiation is considered an effective therapeutic target to the treatment of pathological bone loss. Natural plant-derived products, with potential therapeutic and preventive activities against bone-lytic diseases, have received increasing attention in recent years because of their whole regulative effects and specific pharmacological activities, which are more suitable for long-term use than chemically synthesized medicines. In this review, we summarized the detailed research progress on the active compounds derived from medical plants with potential anti-resorptive effects and their molecular mechanisms on inhibiting osteoclast formation and function. The active ingredients derived from natural plants that are efficacious in suppressing osteoclastogenesis and bone resorption include flavonoids, terpenoids (sesquiterpenoids, diterpenoids, triterpenoids), glycosides, lignans, coumarins, alkaloids, polyphenols, limonoids, quinones and others (steroid, oxoxishhone, fatty acid). Studies have shown that above natural products exert the inhibitory effects via regulating many factors involved in the process of osteoclast differentiation and bone resorption, including the essential cytokines (RANKL, M-CSF), transcription factors (NFATc1, c-Fos), signaling pathways (NF-κB, MAPKs, Src/PI3K/Akt, the calcium ion signaling), osteoclast-specific genes (TRAP, CTSK, MMP-9, integrin β3, OSCAR, DC-STAMP, Atp6v0d2) and local factors (ROS, LPS, NO). The development of osteoclast-targeting natural products is of great value for the prevention or treatment of bone diseases and for bone regenerative medicine.

Absorption and Metabolism Characteristics of Triptolide as Determined by a Sensitive and Reliable LC-MS/MS Method

In this research, a sensitive and reliable LC-MS/MS method was developed and applied to determine the concentration of triptolide in rat plasma, microsomes, and cell incubation media. The absolute oral bioavailability of triptolide is 63.9% at a dose of 1 mg·kg⁻¹. In vitro, the bidirectional transport of triptolide across Caco-2 cells was studied. A markedly higher transport of triptolide across Caco-2 cells was observed in the basolateral-to-apical direction and was abrogated in the presence of the P-gp inhibitor, verapamil. The result indicated that P-gp might be involved in the absorption of triptolide in intestinal. The metabolic stability was also investigated using human liver microsome incubation systems in vitro. In HLMs, incubations with an initial triptolide concentration of 1 μM resulted in an 82.4% loss of substrate over 60 min, and the t_1/2 was 38 min, which indicated that triptolide was easily metabolized in human liver microsomes. In conclusion, the absolute oral bioavailability of triptolide in plasma, transport across Caco-2 cell monolayers, and metabolic stability in human liver microsomes were systematically investigated by using a sensitive and reliable LC-MS/MS method.