5.1 TCMs Alleviate Ischemic Stroke and Transient Ischemic Attack via Inhibiting Ferroptosis

Stroke is a leading cause of death and disability worldwide, with the majority of cases resulting from ischemic events due to arterial occlusion. Current treatment strategies focus on rapid reperfusion through intravenous thrombolysis and endovascular thrombectomy. Iron metabolism is tightly regulated in the brain and is crucial for functioning. Imbalance of iron metabolism, including overload and deficiency, has been shown to impact the outcomes of ischemic stroke [8, 9]. Typical characteristics of ferroptosis, including lipid peroxidation and iron accumulation, are observed after ischemic stroke, accompanied by changes in the expression of ferroptosis-related genes such as GPX4, ACSL4 and SLC7A11 [9]. ACSL4 determines sensitivity to ferroptosis and may exacerbate ischemic stroke by increasing brain damage and neuroinflammation, targeting the prevention of neuronal loss [10, 11]. Furthermore, pathways relating to ferroptosis, oxidative stress and endoplasmic reticulum stress may share interactions or overlap [12].

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key target inhibiting ferroptosis following ischemic stroke [13, 14]. Numerous monomers from TCMs have been confirmed to mitigate ischemic brain injury through activating Nrf2. Reports indicated that β-caryophyllene enhances Nrf2 nuclear translocation, reducing ROS production and ferroptosis induced by oxygen–glucose deprivation and reoxygenation (OGD/R) in primary astrocytes [15]. Vitexin has been shown to decrease the rate of Nrf2 translocation from the nucleus to the cytoplasm and regulate the Keap1/Nrf2/heme oxygenase (HO)-1 signalling pathway to suppress ferroptosis [16]. Quercetin can enter the cytoplasm, chelate iron and reduce intracellular unstable iron pools [17], thereby inhibiting oxidative stress and protecting the integrity of the blood–brain barrier (BBB) [18]. A recent study by Peng et al. [19] demonstrated that quercetin improves neurological functions, reduces infarct volume and pathological features, decreases lipid peroxide accumulation and suppresses ferroptosis by regulating the Nrf2/HO-1 signalling pathway in middle cerebral artery occlusion (MCAO) rats. Rhein reduces brain infarct area and BBB damage by mediating the Nrf2/SLC7A11/GPX4 signalling pathway, decreasing oxidative stress and ROS production, and inhibiting ferroptosis [20]. Gastrodin inhibits ferroptosis by regulating the Nrf2/Keap1/GPX4 signalling pathway, thus improving cognitive impairment in vascular dementia rats [21]. Loureirin C, purified from Dracaena cochinchinensis (Lour.) [22] and Icariside II, derived from the herbal medicine Herba Epimedii [23], promote Nrf2 nuclear translocation, activate the Nrf2/HO-1 pathway, upregulate GPX4, and reduce the accumulation of ROS and Fe²⁺ to improve neurological function and suppress ferroptosis in middle cerebral artery occlusion/reperfusion (MCAO/R) mice. Additionally, astragaloside IV inhibits ferroptosis by activating Nrf2 transcription and regulating the P62/Keap1/Nrf2 signalling pathway [24]. Leonurine A has been found to inhibit ferroptosis and exert neuroprotective effects by activating the phosphoinositide 3-kinase (PI3K)/AKT/Nrf2 and SLC7A11/GPX4 signalling pathways [25]. Enhancing GPX4 expression may be another important pathway to inhibit ferroptosis in ischemia-related diseases. Dihydrotanshinone I, a lipophilic danshen ketone extracted from Salvia miltiorrhiza, has been shown to reduce the accumulation of lipid peroxides and upregulate GPX4 protein expression in PC12 cells, thereby inhibiting ferroptosis. It also has been reported to reduce brain infarct area and improve ferroptosis by activating the Nrf2 pathway in MCAO/R rats [26]. Dihydromyricetin can reduce brain infarction in MCAO/R rats, restore neurological function, and inhibit iron metabolism. These effects are believed to be related to a decrease in lipid peroxidation and iron levels, along with an upregulation of GPX4 expression and a downregulation of ACSL4 expression [27]. Moreover, galangin has been shown to improve learning and memory functions in MCAO/R hamsters by mediating the SLC7A11/GPX4 pathway, reducing lipid peroxide accumulation, and inhibiting ferroptosis [28].

The systemic xc⁻/GPX4 axis is the key pathway to inhibit ferroptosis. According to the reports, several extractions from TCMs exert their antiferroptosis effects through this axis. Ginsenoside Rb, isolated from Panax ginseng C.A.Mey. or Panax quinquefolium L., was reported to restore system xc activity and inhibit oxidative stress and ferroptosis to exert neuroprotective effects [29]. Moreover, due to the close relationship between ferroptosis and oxidative stress, some researchers also reported that oxidative stress-related signalling pathways including hypoxia-inducible factor (HIF)-1α/ceruloplasmin loop [30], PI3K/Akt/mTOR signalling pathway [31], PI3K-Akt-FoxO signalling [32], and TLR4/p38MAPK pathway [33] may be the target of TCMs to inhibit ferroptosis. In all, the sources and mechanisms of TCM monomers that alleviate cerebral ischemic disease by inhibiting ferroptosis are summarized in Table 1. Additionally, several crude extracts and compound formulas of TCMs that have also been proven to alleviate cerebral ischemic disease by inhibiting ferroptosis are concluded in Table 2.

5.2 TCMs Alleviate Myocardial Ischemic Disease via Inhibiting Ferroptosis

In clinical practice, angina pectoris, myocardial infarct, and ischemic cardiomyopathy are common myocardial ischemic diseases. These diseases were often investigated using myocardial I/R animal model or OGD/R cell model. Myocardial I/R injury occurs when blood supply returns to the tissue after a period of ischemia or lack of oxygen. This jeopardizes the heart muscle, commonly seen in conditions such as myocardial infarction, where blockage of coronary arteries leads to insufficient blood flow, subsequently leading to heart tissue damage. The mortality rate associated with myocardial I/R injury remains significant, contributing substantially to cardiovascular morbidity and mortality worldwide. Current therapeutic approaches to mitigate I/R injury include mechanical reperfusion strategies, such as percutaneous coronary intervention and coronary artery bypass grafting, pharmacological treatments involving antiplatelet and antithrombotic agents, and emerging therapies like ischemic preconditioning and postconditioning.

Several studies have shown that various Chinese herbal formulations exhibit anti-inflammatory and antioxidant properties, which may help reduce oxidative stress, lipid peroxidation, and ferroptosis in ischemic hearts. TCM and its compound formulations offer an integrative approach to alleviating myocardial I/R injury, leveraging centuries of clinical experience and modern scientific validation. Compound preparations or extractions such as Shenmai Injection [64], Zhilong Huoxue Tongyu capsule [65], and HJ11 [52] that can inhibit ferroptosis and alleviate myocardial ischemia are concluded in Table 2.

Recent studies that reported notable candidates of TCMs including ginsenosides from Panax ginseng, curcumin from Curcuma longa L., and Puerarin from Pueraria lobata (Willd.) Ohwi can act as a potent ferroptosis inhibitor and alleviate myocardial ischemia diseases in mice or rat myocardial I/R model or OGD/R-treated H9c2 cells. Structurally, flavonoids, phenolic acids, and terpenoid structures are the most investigated Chinese herbal monomer components, and the mechanisms of these compounds activate Nrf2 and GPX4 signalling pathways, which are concluded in Table 3. Moreover, for the reason that elevated lipid peroxidation and ROS are important features leading to ferroptosis, in these studies, extensive attention was paid to the level of lipid peroxidation products and the expression levels of ferroptosis-related proteins, such as GPX4, ACSL4, Ferritin, and transferrin receptor 1 (TfR1). However, the morphological changes of cells such as decreased mitochondrial size, increased membrane density, decreased or disappeared cristae, and broken outer membrane have not received widespread attention. These agents target various pathways involved in iron metabolism, oxidative stress, and lipid peroxidation, making them promising candidates for therapeutic interventions in ischemic diseases. By alleviating oxidative stress and preventing ferroptosis, these agents may not only mitigate the symptoms of angina pectoris but also improve overall cardiovascular health.

5.3 TCMs Alleviate Peripheral Arterial Ischemia Diseases via Inhibiting Ferroptosis

Peripheral artery ischemia disease is a common circulatory condition characterized by narrowing or blockage of peripheral arteries, often leading to critical complications such as lower limb ischemia and I/R injury. These conditions can result from various factors, including diabetes, atherosclerosis, and other vascular diseases. Recent studies have highlighted the role of ferroptosis in the pathophysiology of peripheral artery ischemic injuries. Syringic acid, a phenolic compound found in various plants, has been shown to suppress ferroptosis in skeletal muscle cells, alleviating lower limb I/R injuries in animal models by modulating the high mobility group box-1 (HMGB1) signalling pathway [95]. Similarly, salidroside, a bioactive glycoside derived from Rhodiola rosea, has demonstrated the ability to promote therapeutic angiogenesis in diabetic hindlimb ischemia by inhibiting ferroptosis [96]. Rutin, a widely studied flavonoid present in many fruits and vegetables, has garnered interest due to its potent antioxidant properties. Research indicates that rutin can prevent pulmonary arterial hypertension by mitigating ferroptosis in both animal models and pulmonary artery smooth muscle cells exposed to hypoxic conditions [97]. These findings offer new avenues for therapeutic intervention.

5.4 TCMs Alleviate Renal Ischemia Diseases via Inhibiting Ferroptosis

Renal ischemic diseases can arise from multiple causes, including renal artery stenosis, acute kidney injury (AKI), and systemic issues such as shock or severe dehydration. The consequences of renal ischemia are severe, with potential progression to chronic kidney disease (CKD), renal fibrosis, and even end-stage renal disease (ESRD). In NRK-52E cells, HK-2 cells as well as I/R mice, quercetin, a natural flavonoid, can act as a ferroptosis inhibitor via activating activation transcription factor 3 (ATF3) [98]. Paeoniflorin, a bioactive monomer extracted from Paeonia lactiflora, has also shown promise in alleviating I/R-induced AKI by inhibiting ferroptosis mediated by SLC7A11 [99]. Furthermore, curcumin, derived from the spice turmeric (Curcuma longa), mitigates ferroptosis in hepatic, pancreatic, and cardiac tissues in I/R models by enhancing ACSL/GPX4 signalling pathways [100]. Jiang et al. [101] proved a similar effect of pachymic acid. Additionally, puerarin, originating from Pueraria lobata, has been reported to reduce oxidative stress and ferroptosis associated with renal fibrosis due to ischemia [102]. Salidroside, a phenylpropanoid glycoside found in Rhodiola rosea, inhibits ferroptosis induced by renal I/R injury through the PI3K/AKT signalling pathway [103]. Furthermore, vitexin, extracted from Crataegus spp., has been demonstrated to alleviate CKD by inhibiting ferroptosis in renal tubular epithelial cells via Nrf2 activation [104]. Loureirin C, a compound from Resina draconis, enhances mitochondrial function by promoting the nuclear translocation of Nrf2, thereby reducing oxidative damage from renal I/R injury [105]. Silibinin, derived from milk thistle (Silybum marianum), has been shown to mitigate ferroptosis in acute kidney injury by targeting ferritin heavy chain (FTH1) [106]. These findings collectively underscore the potential of TCMs and their active components in addressing ferroptosis and promoting renal protection in the context of ischemic-related diseases.

5.5 TCMs Alleviate Intestinal Ischemia Diseases via Inhibiting Ferroptosis

Intestinal ischemic diseases occur primarily during episodes of reduced blood flow to the intestines, often triggered by conditions such as intestinal obstruction, mesenteric artery embolism, or thrombus formation. Commonly used models include the intestinal I/R model, which replicates the hemodynamic changes seen in human patients and can allow researchers to assess both acute and chronic phases of ischemia. Recent studies have focused on the active component found in chilli peppers, capsite, which can protect mice from intestinal ischemia by inhibiting ferroptosis, thereby decreasing oxidative stress and promoting cell survival via activating transient receptor potential vanilloid-1 and increasing GPX4 protein expression [107]. Isoliquiritin apioside, a critical ingredient of Glycyrrhizae radix et rhizoma relieves intestinal I/R-induced acute lung injury by blocking HIF-1α-mediated ferroptosis [108]. A well-known antioxidant, resveratrol, can be isolated from Veratrum album, Polygonum cuspidatum, and many TCMs. It has been reported that resveratrol reduces ROS-induced ferroptosis, the underlying mechanism includes activating SIRT3 and compensating the GSH/GPX4 pathway [109]. Similar effects also have been found by naringenin via targeting YAP/STAT3 signalling axis [110]. Apigenin-7-O-Glucoside (AGL) is a sugar derivative of apigenin, belonging to the flavone compound with poor water solubility. DTPA-N10-10 and mPEG-TK-DA self-assembled to encapsulate AGL through hydrophilic and hydrophobic interactions forming multisite ROS scavenging nanoparticles termed PDN@AGL. PDN@AGL was reported to alleviate intestinal I/R by ATF3/SLC7A11-mediated ferroptosis [111].

5.6 TCMs Alleviate Ischemic Liver Disease via Inhibiting Ferroptosis

Hepatic ischemic diseases result from inadequate blood flow to the liver, leading to significant hepatocyte injury and dysfunction. These conditions frequently occur during scenarios such as hepatic artery embolism, hepatic surgery, and liver transplantation, where blood supply may be temporarily interrupted, leading to high morbidity and mortality rates. Tanshinone functions as a coenzyme that confers the gain of function of NQO1 to suppress ferroptosis, followed by reducing ferroptotic cell death in hepatocytes, thus alleviating acute liver injury [112]. Through enhancing Nrf2/HO-1/GPX4 activity, fucoidan mitigates oxidative stress and inhibits ferroptosis in liver tissues following ischemic events, making them valuable in managing I/R injury in liver transplantation [113]. Normally, due to the high risk of I/R injury, severe hepatic steatosis in the donor liver prohibits transplantation. Oleanolic acid has been reported can alleviate I/R injury and inhibit ferroptosis in severe steatosis liver. Network pharmacology and molecular docking implicated Keap1/NRF2 pathway as a potential target [114].

5.7 TCMs Alleviate Other Ischemic Diseases via Inhibiting Ferroptosis

Recent studies have highlighted some active ingredients and preparations of TCMs, in managing conditions like ocular ischemia and lung I/R injuries. Wolfberry, celebrated for its health benefits, contains polysaccharides known for their antioxidant properties. A recent study reported that Lycium barbarum polysaccharide-derived nanoparticles preserve visual function in response to retinal vascular occlusion by activating the Nrf2 pathway, thus protecting retinal ganglion cells from ferroptosis [115]. Rhodiola rosea has been shown to enhance cellular resilience in hypoxic conditions. Salidroside is a potent active compound of Rhodiola rosea. In models of ischemic brain or eye scenarios, salidroside facilitates metabolic recovery and diminishes iron overload, thus preventing ferroptosis. Moreover, these effects may be due to inhibiting JAK2/STAT3 pathway activation in lung I/R [116]. Ferroptosis has also been proven to play important roles in endometrial injury [117], bone ischemia, including avascular necrosis of the femoral head [118-120]; however, the effects of TCMs remain for further investigation.