INTRODUCTION
In modern society, the global prevalence of diabetes has increased dramatically[1]. Compared with traditional senile and postmenopausal osteoporosis, patients with diabetes and diabetic osteoporosis (DOP) face a more severe disability risk and significantly higher fracture incidence[2]. DOP not only increases the disability and mortality rates of patients with diabetes but also imposes a heavy economic burden on global healthcare systems.
The core pathological feature of DOP is high glucose-induced bone metabolic imbalance. Currently, clinical intervention for DOP is still dominated by Western medicine, including calcium supplements, vitamin D analogs, bisphosphonates, and anti-osteoporosis drugs such as recombinant human parathyroid hormone (teriparatide), parathyroid hormone-related protein analog (abaloparatide), and romosozumab[3]. However, these drugs have obvious limitations: Long-term use of bisphosphonates can cause gastrointestinal discomfort or muscle soreness[4], while romosozumab may increase the incidence of major adverse cardiovascular events[5]. Moreover, most Western medicines cannot simultaneously improve glucose metabolic disorders and bone metabolic imbalance in diabetes, making it difficult to block the pathological process of DOP. In contrast, traditional Chinese medicine (TCM), adhering to the core concepts of a holistic view and syndrome differentiation and treatment, has shown unique advantages in DOP treatment through various therapeutic methods. These methods include tonifying the kidney and replenishing essence, invigorating the spleen and replenishing qi, and promoting blood circulation to unblock collaterals. Its multicomponent, multitarget, and multipathway regulatory effects permit overall regulation of body metabolism and can address bone and glucose metabolism disorders, providing a new direction for DOP treatment.
Ferroptosis was first discovered and named by Dixon et al[6] in 2012. It is a regulated form of cell death triggered by iron-dependent lipid peroxidation, which is distinct from other cell death modalities such as apoptosis, pyroptosis, and autophagy. A high-glucose microenvironment induces ferroptosis in bone cells, and ferroptosis acts as a key molecular mechanism underlying high glucose-mediated bone cell dysfunction and bone metabolic imbalance[7]. In-depth investigation of the pathological mechanism of high glucose-induced ferroptosis in bone cells, and exploration of therapeutic strategies targeting ferroptosis, are of great significance for the prevention and treatment of DOP in patients with diabetes. Although an increasing number of studies have focused on TCM-mediated regulation of ferroptosis in DOP intervention, the correlation between TCM theory and the molecular mechanisms of ferroptosis requires further exploration.
This minireview focuses on the pathological high-glucose microenvironment-bone cell ferroptosis-DOP axis. We first clarify the core pathological relationship between high glucose and bone cell ferroptosis. Then, we systematically elaborate on the core mechanisms of ferroptosis and its regulatory pathways in osteoblasts, osteoclasts, and bone marrow mesenchymal stem cells (BMSCs). Finally, we focus on the key regulatory pathways through which TCM targets ferroptosis; and the mechanisms and potential application value of TCM in improving bone metabolism and treating DOP by inhibiting ferroptosis in the bone cells of patients with diabetes. This minireview aims to build a theoretical bridge between TCM theory and the molecular mechanisms of ferroptosis, and to provide new insights for further mechanistic research and clinical translation of TCM-based therapies for DOP in patients with diabetes.
PATHOLOGICAL ASSOCIATION BETWEEN HIGH-GLUCOSE MICROENVIRONMENT AND FERROPTOSIS IN BONE CELLS
DOP is a systemic metabolic bone disease induced by a high-glucose microenvironment, characterized by reduced bone mass, increased bone fragility, impaired bone microstructure, and consequently elevated fracture risk[8]. Osteoporosis in type 1 diabetes is mainly caused by bone metabolic disorders resulting from absolute insulin deficiency, hyperglycemia, osmotic diuresis, and decreased insulin-like growth factor 1 levels, accompanied by autoimmune-mediated bone injury and chronic inflammation[9]. Osteoporosis in type 2 diabetes presents with increased bone fragility and fracture risk, driven by a complex interactive network including high glucose, insulin resistance, bone marrow fat accumulation, non-enzymatic glycation of bone collagen, and skeletal effects of antidiabetic agents[10]. Among them, biguanides are neutral to bone health, while thiazolidinediones may impair bone metabolism, and sodium-glucose cotransporter 2 inhibitors have potential bone protective effects[11].
As the key pathological stimulus for the skeletal system in diabetes, the high-glucose microenvironment regulates bone cell ferroptosis through multiple pathways, disrupts bone homeostasis, induces bone injury, and forms a close pathological association with DOP. Heme oxygenase-1 (HO-1) activated in the high-glucose microenvironment catalyzes heme oxidation and releases massive amounts of free Fe2+ to trigger the Fenton reaction, causing excessive reactive oxygen species (ROS) accumulation and lipid peroxidation. This further activates bone cell ferroptosis and accelerates DOP progression[12]. During this process, the surge in ferrous ions serves as the initiating event, ROS accumulation acts as the central intermediate event, and lipid peroxidation represents the key molecular event ultimately leading to ferroptosis. These three events are interlocked and collectively mediate the toxic effects of high glucose on osteocytes. Zhang et al[13] also observed that high glucose induces osteoblast ferroptosis, accompanied by characteristic mitochondrial morphological changes, including increased membrane density and reduced or absent mitochondria. As the core organelle responsible for iron metabolism and ROS production, mitochondrial structural abnormality is not only a typical morphological marker of ferroptosis, but also suggests that high glucose may amplify ferroptosis by targeting mitochondrial dysfunction, resulting in a pathological feature of simultaneous impairment in both structure and function. In summary, the high-glucose microenvironment participates in DOP pathogenesis by inducing bone cell ferroptosis.
CORE REGULATORY PATHWAYS OF FERROPTOSIS AND THE MECHANISM OF BONE CELL FERROPTOSIS IN DOP
Core regulatory pathways of ferroptosis
Ferroptosis is an iron-dependent form of programmed cell death, which was first discovered and formally named by Dixon et al[6] in 2012. It is significantly different from previously discovered cell death pathways such as apoptosis, programmed necrosis, autophagy and pyroptosis, and its core feature is the abnormal accumulation of lipid ROS[14].
In terms of morphological characteristics, ferroptotic cells typically show mitochondrial shrinkage, increased mitochondrial membrane density, outer membrane rupture, and a reduction or even complete disappearance of mitochondrial cristae. From a biochemical perspective, intracellular iron ion overload is the core initiating factor triggering ferroptosis. Glutathione peroxidase (GPX) 4 is a core regulatory molecule in the process of ferroptosis, and inhibition of its activity directly weakens the function of the intracellular endogenous antioxidant defense system. As the final defense against lipid peroxides, decreased GPX4 activity directly compromises the cellular antioxidant capacity and constitutes a critical turning point in the onset of ferroptosis. In this state, the accumulated Fe2+ in cells can generate a large amount of ROS through the Fenton reaction, thereby inducing lipid peroxidation of polyunsaturated fatty acids (PUFAs). Sustained lipid peroxidation destroys the integrity of cell structure and function, and finally induces ferroptosis[15]. Recent studies have confirmed that ferroptosis plays a key regulatory role in the occurrence and development of various diseases, and has become a core direction and focus of attention in the field of current disease treatment strategy optimization and prognosis improvement research.
Of note, in DOP, the persistent high-glucose microenvironment serves as a key inducer, which disrupts the core regulatory network of ferroptosis in osteocytes and further disturbs bone metabolic homeostasis. High glucose can trigger iron metabolic disorder, lipid peroxidation, and dysfunction of the system Xc-/glutathione (GSH)/GPX4 pathway, thereby promoting ferroptosis in osteocytes and accelerating the progression of DOP. This regulatory pattern indicates that the induction of ferroptosis by high glucose is characterized by multiple targets and multiple pathways. Inhibition of a single pathway is often insufficient to completely block osteocyte damage, suggesting that interventions for DOP should be carried out from multiple aspects simultaneously.
Iron overload
Iron is an essential trace element in humans that is involved in key physiological processes such as oxygen transport and energy metabolism. Its distribution and content in the body maintain homeostasis through precise regulation. If the balance of iron intake, storage and output is disrupted, the susceptibility of cells to ferroptosis is significantly increased. Under iron overload, the intracellular redox balance is disrupted, and excessive Fe2+ and H2O2 generate a large amount of ROS through the Fenton reaction, causing intracellular oxidative damage, destroying the integrity and function of the cell membrane structure, and finally triggering ferroptosis[16].
In the high-glucose microenvironment of DOP, iron metabolism in bone cells is disrupted. Iron overload and abnormal expression of ferroptosis-related proteins occur in the femoral tissue of DOP rat models[17]. Excessive Fe2+ undergoes the Fenton reaction, which directly damages biomacromolecules such as DNA, proteins, and lipid membranes, impairing the structural integrity and functional stability of cell membranes[18]. Compared with other factors, high glucose-induced iron overload is persistent and cumulative, maintaining a sustained high intracellular Fe2+ state that keeps Fenton reaction continuously activated and oxidative stress progressively amplified. Iron overload serves as a critical initiating condition for osteocyte ferroptosis in DOP and provides the basis for subsequent exacerbation of lipid peroxidation and oxidative stress. Once iron overload is established, the preexisting iron accumulation and oxidative damage in osteocytes can persist even after partial glycemic control, which constitutes an important reason why bone injury in DOP is difficult to reverse rapidly.
Lipid peroxidation
Lipid metabolism disorder is a core inducement of ferroptosis, and lipid peroxidation is an iconic event in ferroptosis. Due to the presence of highly reactive bis-allylic hydrogen atoms, PUFAs are prone to react with hydroxyl radicals to trigger lipid peroxidation, making them key substrates for ferroptosis[19]. Long-chain acyl-CoA synthetase (ACSL) 4 is a key regulatory enzyme for lipid peroxidation, which can activate PUFAs and regulate their transmembrane properties. PUFA-CoA generated by acyl-CoA synthetase long-chain family member 4 catalysis is converted into phospholipid-bound PUFAs under the action of lysophosphatidylcholine acyltransferase 3. Subsequently, lipoxygenases oxidize PUFA-phospholipid into lipid peroxides (LOOH), which directly induce ferroptosis[20]. More importantly, the ferroptosis process can enhance the catalytic activity of lipoxygenases, promote the oxidation of PUFA-phospholipid, form a positive feedback loop of lipid peroxidation-ferroptosis, and aggravate cell damage.
In DOP, high glucose induces iron overload and massive ROS release via the Fenton reaction[17], providing sufficient oxidative substrates for lipid peroxidation. Derivatives such as 4-hydroxynonenal and malondialdehyde produced during lipid peroxidation can further damage bone cells and serve as specific markers for detecting bone cell ferroptosis[21].
System Xc-/GSH/GPX4 pathway and p53
GPX4 is a core molecule in ferroptosis regulation and belongs to the GSH-dependent peroxidase family[22]. GSH is a tripeptide condensed from cysteine, glutamic acid and glycine, with strong reducibility. It can reduce cytotoxic lipid peroxides (LOOH) to harmless lipid alcohols under the catalysis of GPX4, thereby inhibiting lipid peroxidation[23].
The level of GSH is directly related to the function of system Xc-, which is a cystine/glutamate antiporter composed of solute carrier family 7 member 11 (SLC7A11, light chain) and solute carrier family 3 member 2 (heavy chain), and its core function is to mediate the uptake of extracellular cystine and the efflux of intracellular glutamate. Cystine is a key raw material for GSH synthesis. If the function of system Xc- is inhibited, the intracellular uptake of cystine is reduced, and GSH synthesis is blocked[24]. When GSH is depleted or the activity of GPX4 is reduced, LOOH cannot be effectively cleared, leading to the massive accumulation of intracellular ROS, intensified oxidative stress, and finally triggering ferroptosis.
Tumor suppressor p53 plays a key regulatory role in ferroptosis: Activated p53 can specifically bind to the flanking regulatory region of the SLC7A11 gene, inhibiting the expression of SLC7A11 at the transcriptional level; decreased expression of SLC7A11 leads to impaired function of system Xc-, indirectly inhibiting GSH synthesis, and finally promoting ferroptosis[25].
High glucose directly downregulates SLC7A11 expression in bone cells, reduces intracellular GSH levels, promotes lipid peroxide accumulation[26], and induces bone cell ferroptosis. High glucose exerts a direct inhibitory effect on SLC7A11, rapidly depleting intracellular GSH stores and causing osteocytes to quickly lose their antioxidant capacity. Meanwhile, high glucose can directly suppress GPX4 activity by elevating intracellular ROS levels, further disrupting the balance of the antioxidant defense system and ultimately promoting ferroptosis in osteocytes.
Mechanisms of ferroptosis in different bone cells in DOP
Core pathophysiological characteristics of DOP: As one of the most common types of secondary osteoporosis in clinical practice, DOP is a systemic metabolic bone disease characterized by progressive reduction of bone mass, destruction of bone microstructure and increased bone fragility. Its direct consequence is a significant increase in the risk of fracture in patients[8]. Under the pathological state of hyperglycemia, a characteristic of diabetes, homeostasis of bone metabolism is easily disturbed. When the body is exposed to a high-glucose microenvironment for a long time, the normal bone metabolism process is seriously interfered, eventually leading to the imbalance of the originally precisely regulated bone formation-resorption dynamic balance between osteoblasts and osteoclasts[27].
BMSCs are a type of adult stem cells with multidirectional differentiation potential. Under physiological conditions, they can accurately respond to the body’s regulatory signals and differentiate into functional cells of bone tissue such as osteoblasts and chondroblasts. They play an irreplaceable key role in the formation, homeostasis maintenance and post-injury reconstruction of bone tissue, and are the core cell population maintaining the balance of bone metabolism. However, under the long-term effect of the persistent high-glucose microenvironment in patients with diabetes, the biological characteristics and functions of BMSCs undergo significant abnormal changes. Specifically, cell viability decreases, osteogenic differentiation ability is inhibited while adipogenic differentiation tendency is enhanced, and their paracrine function is also significantly reduced. The above functional abnormalities eventually lead to the imbalance of bone turnover rate, reduction of bone strength, which significantly weaken the regeneration and repair ability of bone tissue[28].
Ferroptosis in osteoblasts: The high-glucose environment can disrupt the homeostasis of bone metabolism in multiple dimensions. On the one hand, it directly inhibits the activity of BMSC-derived bone cells[29], significantly downregulates the differentiation efficiency of BMSCs into osteoblasts[30], leading to reduced functional activity of osteoblasts, slowed bone mineralization process and maturation disorders, and finally blocks the normal progress of bone remodeling[31]. On the other hand, it can induce osteoblast ferroptosis by interfering with iron metabolism. Under iron overload, the expression of Runx2 and its downstream target genes ALP and osteocalcin in BMSCs and osteoblast precursor cells is significantly inhibited, directly hindering osteoblast differentiation[31]. High glucose can also activate the ASK1/p38 signaling pathway to induce osteoblast ferroptosis, inhibit the differentiation of preosteoblast MC3T3-E1 cells into osteoblasts and bone mineralization[32], or synergize with the nuclear factor-κB (NF-κB) signal to upregulate the expression of NADPH oxidase (NOX) 4, promote generation of ROS and accumulation of lipid peroxidation products, damage the structure and function of osteoblast mitochondria, and induce ferroptosis[33]. Regarding molecular biological mechanisms, high glucose can induce and upregulate the expression of activating transcription factor 3. After activating transcription factor 3 is upregulated, it can directly act on the expression regulatory region of the SLC7A11 gene, reducing its expression level. This leads to a decrease in the intracellular GSH level and extracellular glutamate concentration, mediating ferroptosis in osteoblasts by inhibiting the activity of system Xc-[34]. In a high-glucose environment, the expression status of the mitochondrial ferritin (FtMt) gene also plays a key role in osteoblast ferroptosis. When FtMt is overexpressed, it can effectively inhibit osteoblast ferroptosis. The inhibition of FtMt expression induces mitophagy by activating the ROS/PINK1/Parkin signaling pathway, ultimately exacerbating osteoblast ferroptosis[35]. Advanced glycation end products (AGEs) can also act to promote osteoblast ferroptosis[36], thereby affecting bone metabolic balance and accelerating DOP development.
Ferroptosis in osteoclasts: At the same time, the high-glucose environment has a significant impact on the differentiation, activity and bone resorption ability of osteoclasts[37]. The high-glucose environment can upregulate expression of NOX4 by activating the NF-κB signaling pathway, thereby activating receptor activator of NF-κB ligand (RANKL)-mediated osteoclast differentiation transcription factors, promoting osteoclast differentiation and enhancing its bone resorption ability[38]. As a key regulatory factor for osteoclast differentiation, RANKL can induce differentiation of bone marrow monocytes into osteoclasts, and upregulate expression of NOX4 mRNA to promote generation of ROS; in NOX4-gene-deficient mice, RANKL cannot induce expression of key transcription factors for osteoclast differentiation, eventually leading to increased bone mass and thickened trabecular bone in mice[39].
The physiological function of osteoclasts is closely related to iron metabolism, and their differentiation and bone resorption process are highly dependent on iron. Therefore, iron metabolism disorders or iron overload are more likely to trigger osteoclast ferroptosis. Ni et al[38] found that during the osteoclast differentiation stage, under the synergistic effect of RANKL stimulation and transferrin receptor 1 (TfR1) overexpression, ferroptosis was significantly activated. During osteoclast maturation, a large amount of iron needs to be taken up through the TfR1-mediated transferrin endocytosis mechanism to meet energy needs, while excessive iron accelerates ferroptosis. In the late stage of type 2 diabetes, accumulated AGEs in the body can enhance bone resorption by stimulating osteoclast activity and expanding the bone resorption area[40], while triggering oxidative stress reactions.
Ferroptosis mechanism in BMSCs: BMSCs play a key regulatory role in bone metabolism by participating in bone tissue remodeling, and oxidative stress mediated by iron overload is an important factor damaging their physiological functions[41]. The increased level of ROS caused by iron overload can produce toxic effects on BMSCs, cause mitochondrial dysfunction, and finally damage the mineralization ability and osteogenic differentiation potential of BMSCs.
Mechanistically, iron overload can induce ferroptosis of BMSCs by inhibiting the Wnt signaling pathway of BMSCs and downregulating expression of Runx2[42]. The nuclear factor-erythroid 2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) signaling pathway plays an important role in BMSC ferroptosis. Erastin-induced ferroptosis of BMSCs can lead to upregulation of Nrf2 expression, downregulation of Keap1 expression, accompanied by increased expression of TfR1/ferroportin 1 (FPN1) and decreased expression of GPX4 and SLC7A11[43]. The regulatory mechanisms of ferroptosis in bone metabolism and its related signaling pathways are intuitively presented in Figure 1.
Figure 1 Ferroptosis-related signaling pathways regulate bone cell fate and bone metabolism imbalance.
BMSC: Bone marrow mesenchymal stem cell; ROS: Reactive oxygen species; OBs: Osteoblasts; OCs: Osteoclasts; FtMt: Ferritin mitochondrial; HG: High glucose; Trf1: Transferrin receptor 1; RANKL: Receptor activator of nuclear factor κB ligand; RUNX2: Runt-related transcription factor 2; Nrf2: Nuclear factor erythroid 2-related factor 2; Keap1: Kelch-like ECH-associated protein 1; TFR: Transferrin receptor; FPN: Ferroportin; GPX4: Glutathione peroxidase 4; SLC7A11: Solute carrier family 7 member 11; PUFA: Polyunsaturated fatty acids; ACSL4: Acyl-CoA synthetase long-chain family member 4; LPCAT3: Lysophosphatidylcholine acyltransferase 3; PUFA-PL: Polyunsaturated fatty acid-containing phospholipids; LOXs: Lipoxygenases; LIP: Labile iron pool; DMT1: Divalent metal transporter 1; ZIP8/14: Zrt/Irt-like protein 8/14.
Therapeutic effects of inhibiting ferroptosis on DOP
As a core molecular mechanism mediating the occurrence and progression of DOP induced by high glucose, targeted inhibition of ferroptosis is an effective therapeutic strategy for DOP[44]. Inhibiting ferroptosis in bone cells through various means can improve the bone metabolic disorders of DOP at multiple levels. First, inhibiting ferroptosis in osteoblasts can restore their proliferation and differentiation abilities, enhance bone mineralization function, improve bone formation efficiency, and compensate for insufficient bone mass[45]. Second, inhibiting ferroptosis in osteoclasts can reduce their dysfunction and simultaneously regulate their differentiation activity. These effects inhibit excessive bone resorption and restore the dynamic balance between bone resorption and bone formation[46]. Third, inhibiting ferroptosis in BMSCs can restore their multi-directional differentiation potential, promote osteoblast regeneration, improve the bone marrow microenvironment, and enhance the repair and regeneration ability of bone tissue[47]. Fourth, inhibiting ferroptosis in bone cells can negatively regulate the high-glucose microenvironment by downregulating oxidative stress and improving insulin resistance[48]. This in turn improves bone metabolism and glucose metabolism, blocking the pathological process of DOP.
TCM regulating ferroptosis for treatment of DOP
DOP is one of the common complications of diabetes and is characterized by disruption of bone metabolism balance under high-glucose conditions, manifested as an imbalance between decreased bone formation and increased bone resorption. From the perspective of TCM, DOP is mainly related to the spleen and kidney. TCM theory holds that “the kidney governs bone and produces marrow, serving as the congenital foundation; the spleen governs muscles and nourishes the limbs, acting as the acquired foundation”. Physiologically, the “congenital and acquired foundations” mutually support and benefit each other; pathologically, they often interact and cause each other. Deficiency of kidney essence leads to bone withering and marrow emptiness, while dysfunction of the spleen in transportation results in insufficient production of qi and blood, and the tendons, muscles and bones lose nourishment, leading to “bone atrophy”[49]. The ferroptosis discovered by modern medicine - a form of programmed cell death driven by iron-dependent lipid peroxidation - is exactly the key molecular bridge connecting the TCM pathological state of “spleen and kidney disharmony” with DOP bone cell damage, providing a new target and theoretical support for TCM intervention in DOP.
In terms of regulating ferroptosis for the treatment of DOP, TCM has the unique advantage of being multicomponent, multitarget and multipathway. TCM can balance intracellular iron homeostasis by regulating iron-metabolism-related proteins (such as FPN1 and hepcidin), reduce the accumulation of free iron, and inhibit initiation of ferroptosis from the source. For oxidative stress, TCM can activate the Nrf2/Keap1 signaling pathway, promote synthesis of GSH, upregulate activity of superoxide dismutase (SOD), enhance the antioxidant capacity of cells, and reduce lipid peroxidation damage. In addition, TCM can regulate signaling pathways such as phosphoinositide 3-kinases (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin, Wnt/β-catenin and osteoprotegerin (OPG)/RANKL, which inhibit the lipid peroxidation cascade reaction related to ferroptosis, and promote the proliferation and differentiation of osteoblasts, inhibit the activity of osteoclasts, and restore the balance of bone metabolism.
TCM can also improve the hyperglycemia status of patients with diabetes and enable bone cells to escape from the high-glucose microenvironment. These effects reduce ferroptosis, treating both the symptoms and root causes of DOP. Compared with Western medicine, TCM for DOP has advantages such as high-cost effectiveness, mild toxicity and side effects, and good patient tolerance. TCM is expected to become a key strategy for the comprehensive management of DOP.
Single TCM herbs
Baicalein, derived from the roots of Scutellaria baicalensis Georgi, is a flavonoid compound with multiple pharmacological effects such as free radical scavenging, anti-inflammation, antioxidation, anticancer and antitumor. Baicalein regulates ferroptosis mainly through two pathways. First, it activates the Nrf2 pathway, induces the biosynthesis of GSH, enhances the antioxidant capacity of cells, prevents degradation of Nrf2 induced by erastin, inhibits oxidative damage, and reduces ferroptosis caused by oxidative stress[50]. Baicalein can block the initiation of ferroptosis by activating the Nrf2 pathway and inhibiting oxidative damage, thereby preventing cells from undergoing iron-dependent programmed cell death and promoting cell survival. Second, it regulates fatty acid metabolism, inhibits expression of acyl-CoA synthetase long-chain family member 4 and increases expression of acyl-CoA synthetase long chain family member 3, thereby altering fatty acid metabolism, reducing production of peroxidized lipids, and inhibiting ferroptosis[51]. A study in the ferroptosis model of MC3T3-E1 cells (a mouse osteoblast cell line) found that an appropriate concentration of baicalein could increase the expression of GPX4 and β-catenin proteins, enhance cell proliferation and inhibit ferroptosis. The mechanism may be achieved by upregulating GPX4 through the Wnt/β-catenin signaling pathway[52]. Wei et al[53] reported that baicalein can reduce the level of oxidative stress in the pancreatic tissue of rats, thereby improving blood glucose levels.
Quercetin is a natural flavonoid compound present in many Chinese herbal medicines. It can inhibit the accumulation of lipid peroxides and ROS in BMSCs, reduce cell death, and enhance cell proliferation and differentiation[54]. Quercetin provides sufficient cell sources for bone tissue repair, supplementing the functional cells required for bone formation and preventing bone loss. It can also mediate the PI3K/AKT/mammalian target of rapamycin signaling pathway, upregulate expression of osteogenic markers and antioxidant genes, downregulate ROS level, inhibit ferroptosis and promote osteogenesis, exerting an antiosteoporosis effect[41].
Icariin is the active ingredient of Epimedium brevicornu Maxim. It has multiple functions such as anti-inflammation, anti-free radical and antiosteoporosis. In terms of regulating ferroptosis for the prevention and treatment of osteoporosis, it can inhibit the overexpression of FPN1 protein in osteoblasts, reduce accumulation of intracellular iron ions, lower expression of ROS, and alleviate the damage of oxidative stress to cells[55]. At the same time, icariin can increase expression of GPX4, Runx and ALP proteins, promote dissociation of Nrf2 from Keap1 and its translocation to the nucleus, activate antioxidant genes, inhibit the NF-κB pathway[56], and inhibit mitochondrial oxidative stress and ferroptosis.
Astragalus polysaccharide is one of the main active components of Astragalus membranaceus. It can prevent accumulation of mitochondrial ROS and significantly inhibit cell apoptosis and senescence caused by iron overload induced by ferric ammonium citrate. In the prevention and treatment of osteoporosis, astragalus polysaccharide can inhibit the reduction of proliferation and pluripotency of BMSCs, regulate processes related to ferroptosis, maintain bone metabolic balance and play a protective role in bone health[57].
Puerarin is the active ingredient of Pueraria lobata. Research has confirmed that puerarin can inhibit ferroptosis of osteoblasts induced by high glucose, and its mechanism of action is closely related to the regulation of the SLC7A11/GPX4 signaling pathway. The results show that 100 μmol/L puerarin can significantly alleviate the inhibitory effect of high glucose on cell proliferation and enhance the osteogenic differentiation ability of cells. At the same time, this concentration of puerarin can reduce the levels of intracellular ROS and malondialdehyde, increase the content of GSH and activity of SOD, and upregulate expression of SLC7A11 and GPX4 proteins. Therefore, puerarin is expected to become a potential drug component for the treatment of DOP[26].
TCM compound prescriptions
Qing’e Pill, first recorded as being composed of Eucommia ulmoides Oliv., Psoralea corylifolia L., Juglans regia L., and Allium sativum L. Research has found that it can alleviate oxidative damage and inhibit the ferroptosis of osteoblasts by mediating the AKT/PI3K signaling pathway in vitro[58], exert an antiosteoporosis effect and provide an effective treatment plan for osteoporosis. Rao and Huang[59] found that Qing’e Pill can also regulate the expression of bone formation-related genes through the Wnt1/β-catenin pathway, improve bone mineral density and microstructure in DOP mice, and delay diabetes progression.
Zuogui Pill is a representative formula of the kidney-tonifying method in TCM. It can reduce the iron ion level in the liver tissue of ovariectomized osteoporosis model rats, increase the level of hepcidin, and correct the iron overload state. At the same time, it intervenes in cell iron overload by regulating the OPG/RANKL signaling pathway, increases the expression of OPG protein, reduces expression of RANKL protein, inhibits activity of osteoclasts, promotes bone formation, and thus exerts an antiosteoporosis effect[60]. Zuogui Pill may reduce lipid peroxidation and inhibit ferroptosis by activating the SLC7A11/GPX4 pathway[61].
Taohong Siwu Decoction is a classic prescription for promoting blood circulation and removing blood stasis in TCM. It may inhibit ferroptosis by activating the Nrf2/Keap1/HO-1 signaling pathway. Research has found that in the KOA rat model, Taohong Siwu Decoction can significantly upregulate protein expression of Nrf2, HO-1, GPX4 and SLC7A11, which are significantly downregulated in the model control group, and simultaneously downregulate protein expression of Keap1 and P53[62]. Among them, as a key factor in ferroptosis, upregulation of GPX4 expression can reduce lipid peroxidation and inhibit the ferroptosis of chondrocytes.
Electroacupuncture
Electroacupuncture can regulate expression of bone-formation-related genes, upregulate expression of genes related to bone formation, and downregulate expression of proteins that inhibit the bone formation pathway, thereby promoting bone formation and achieving the effect of treating osteoporosis[63]. Geng et al[64] showed that electroacupuncture reduced the Fe2+ level in the ovarian tissue of mice, and at the same time regulated expression of GSH, antisuperoxide activity and SOD, thereby significantly inhibiting the oxidative stress response and ferroptosis process in the ovarian tissue of mice. In view of the close pathological connection between premature ovarian failure and osteoporosis, this result suggests that electroacupuncture has potential application in regulating ferroptosis, providing experimental evidence for subsequent electroacupuncture intervention in ferroptosis-related bone metabolism diseases. Similarly, Ding et al[65] found that pulsed magnetic therapy inhibited osteoblast ferroptosis, and its core mechanism lies in the precise regulation of the magnetotherapy/exosome/ferritin signaling axis. This regulatory pathway affects intracellular iron homeostasis and intracellular material transport process, and has a potential regulatory effect on the pathological progress of osteoporosis, confirming the feasibility of physical therapy in intervening in ferroptosis-mediated bone metabolism abnormalities.
As a secondary metabolic bone disease with a high incidence in diabetes, DOP is characterized by bone loss, bone microstructure destruction and high fracture risk, which significantly increase the disability rate and medical burden of patients. However, existing western medical treatments such as calcium supplements and bisphosphonates are difficult to simultaneously improve the dual pathological states of glucose metabolism disorder and bone metabolism imbalance, resulting in an urgent clinical demand.
Recent studies have confirmed that ferroptosis, as a form of programmed cell death regulated by iron-dependent lipid peroxidation, is one of the core mechanisms mediating the pathological progress of DOP. Through three core pathways of iron overload, lipid peroxidation and system Xc-/GSH/GPX4 pathway imbalance, it synergizes with the high-glucose microenvironment and AGEs to respectively inhibit osteoblast differentiation, promote osteoclast activation and damage the osteogenic potential of BMSCs, ultimately breaking the bone formation-resorption homeostasis.
Based on the core pathogenesis of DOP, which is “kidney essence deficiency, spleen dysfunction in transportation, and blood stasis blocking collaterals”, TCM shows the unique advantage of multitarget and multipathway activities in regulating ferroptosis to intervene in DOP. Single TCM herbs and their active components can inhibit ferroptosis by regulating iron metabolism, enhancing the antioxidant system or interfering with key signaling pathways; TCM compound prescriptions achieve “holistic regulation”; external therapies such as electroacupuncture can also inhibit ferroptosis by reducing tissue Fe2+ levels and regulating the activity of antioxidant enzymes, providing a variety of TCM strategies for DOP treatment.
