Research progress on molecular mechanism and future perspectives of leonurine

Abstract

Leonurus japonicas Houtt., has been recorded as “light body and long life” properties in the oldest classical medicinal book Shennong Bencao Jing thousands of years ago. Herba leonuri, also named Chinese Motherwort or Siberian Motherwort, has the effects of activating blood circulation, regulating menstruation, diuresis and detumescence, clearing heat and detoxifying, and is known as the “sacred medicine of gynecology.” It has been well known by doctors and usually used in the treatment of common gynecological diseases in clinic. Leonurine is a very important alkaloid in Herba leonuri, which has many biological activities such as anti-oxidation, anti-inflammation, and anti-apoptosis. Diseases of the cardiovascular system and central nervous system are “major health threats” that threaten human life and health worldwide, however, many drugs have certain side effects right now. This paper reviews the potential molecular therapeutic effects of leonurine on cardiovascular system and central nervous system diseases, highlights the current findings of research progress, and focuses on the therapeutic effects of leonurine in various diseases. At present, leonurine is in the stage of clinical experiment, and we hope that our summary can provide guidance for its future molecular mechanism study and clinical application.

Keywords

Leonurus japonicas Houtt. / leonurine / molecular mechanism / research progress / future perspectives

1 Introduction

Herba leonuri, also known as wormwood, motherwort, red flowered motherwort, kuncao, huangwei, triangle flax, growing in temperate areas of Europe and Asia, a few species grow in the Americas and Africa, as the fresh or dry parts above the ground of Labiatae plant Leonurus japonicas Houtt. Herba leonuri is available as either fresh or dried products. The former is harvested from spring seedlings to early summer before flowering, while the latter is collected during or shortly after the summer blooming period. Both forms exhibit similar therapeutic effects. Thousands of years ago, Leonurus japonicas Houtt. was first recorded in Shennong Bencao Jing, one of the most authoritative ancient book of traditional Chinese medicine (Fig.1). Herba leonuri tastes spicy, bitter, slightly cold, has the effect of contracting the uterus, activating blood circulation, diuresis to relieve edema, heat detoxification. It is considered to be an effective drug for the treatment of gynecological diseases and has long been used for the treatment of gynecological and obstetrical diseases such as irregular menstruation, dysmenorrhea, lochia, edema, oliguria and ulcer.

Researchers have isolated and identified about 140 chemical components from Herba leonuri, mainly including alkaloids, flavonoids, and diterpenoids, also contains a large amount of potassium and vitamins. Among these compounds, leonurine is the main medicinal component of Herba leonuri, and its content accounts for 0.02%–0.12% of the fresh weight of the plant [1]. Up to now, four alkaloids have been found in Herba leonuri: leonuridine, leonurine, leonurinine, and stachydrine. Modern medicine has confirmed that Herba leonuri has many functions, such as thrombolysis, anticoagulation, lipid-lowering and blood-lowering, inhibiting red blood cells and platelets aggregation [2], activating blood and regulating menstruation, diuresis and detumification, clearing heat and detoxification, improving microcirculation, anti-free radical activity, and reducing intracellular calcium overload [3]. These functions can prevent cardiovascular and cerebrovascular diseases, including atherosclerosis, acute and chronic myocardial infarction, and ischemic stroke. Studies have shown that the beneficial effects of Herba leonuri are mainly derived from leonurine (4-guanidyl-n-butyl-geranyl butyrate) [4]. Herba leonuri has many pharmacological effects, and has been widely used in food, cosmetics, and pharmaceutical industries, with broad market prospects. This paper reviews the research progress of the pharmacological effects of leonurine to better understand the drug use characteristics of Herba leonuri.

Leonurine is a natural alkaloid mainly extracted from the stems and leaves of Leonurus japonicas Houtt., and a small amount is also contained in the flowers. The scientific name of leonurine is 3, 5-dimethoxy-4-hydroxy-benzoic acid (4-guanidine)-1-butyl ester, the most common form is its hydrochloride hydrate (Fig.1). The molecular formula of leonurine is C₁₄H₂₁N₃O₅, characterized by a guanidino, an n-butyl and a syringate. Unlike other alkaloids, leonurine has a unique guanidino, as well as a hydroxyl group on the benzene ring. Studies have found that leonurine is synthesized by guanbutol and syringoyl glucose together with serine carboxypeptidase-like (SCPL) acyltransferase. The amplification of glucosyltransferase and SCPL gene and novel functionalization of SCPL jointly determine the specific synthesis and accumulation of leonurine in Herba leonuri [5,6]. The high polarity of guanidine and hydroxyl groups brings some difficulties to clinical application, including low bioavailability, weak transmembrane ability, and poor fat solubility.

2 Absorption, distribution, metabolism, and excretion of leonurine

Previous results have showed the oral administered parent leonurine may undergo intensive first-pass metabolism (primary in intestinal tract and secondary in liver) to form the lead metabolite leonurine-O-glucuronide, which results in the high level of leonurine-O-glucuronide in vivo and the low systemic bioavailability. Interestingly, leonurine-O-glucuronide may have potential cardioprotective effect and its potency is similar to leonurine, which may explain why leonurine still exerts good pharmacological effect with such low bioavailability after oral dosing. The absorption, distribution, metabolism, and excretion profiles of leonurine in rats after intragastric (i.g.) administration is summarized in Fig.2 [7].

Therefore, the current studies still hold that the key issue is to understand the binding situation of leonurine with the action sites. Therefore, many pharmaceutical chemists have tried to modify its structure by using bioisosterism and drug combination principles to make leonurine have a more powerful effect. Scientists have found that combining aspirin with phenolic hydroxyl groups could enhance the pharmacological activity of leonurine, reduce toxicity and side effects, and improve its bioavailability and pharmacokinetic properties. It could significantly improve the cardioprotective effect of leonurine by increasing the activity of antioxidant enzymes, reducing the level of malondialdehyde (MDA), and inhibiting inflammatory mediators [8]. In addition, a series of leonurine analogs were synthesized by replacing the aromatic ring, linker, and guanidine moieties separately for the first time, and the cardioprotective effects of these analogs were also evaluated. These analogs might serve as a potential cardioprotective agent for the treatment of acute myocardial infarction [9].

The study of leonurine began with its unique uterine contractile ability and diuretic effects [10]. There is growing evidence that leonurine can regulate oxidation process [11], inflammatory reaction [12], biological processes such as apoptosis, fibrosis, and lipid metabolism [13]. The diversity of action effects of leonurine indicates its potential to treat many clinical diseases. Of particular interest is leonurine’s potential efficacy in preventing and improving cardiovascular and cerebrovascular diseases [14].

3 Pharmacological effects of leonurine

More than two decades ago, it was reported that Herba leonuri has the effects of strengthening the uterus and promoting diuresis. Later, some researchers discovered that anti-inflammatory, anti-apoptotic, and antioxidant effects, were confirmed. It is believed that leonurine not only has a good therapeutic effect on cardiovascular system diseases, but also has a potential impact on central nervous system diseases such as stroke and brain injury. Although there are many drugs on the market for these diseases, most of them are expensive and have no good therapeutic effect, frequent use can bring many side effects to patients. Currently, the treatment of cardiovascular and central nervous system diseases remains a global issue. Many studies have shown that leonurine has multiple pharmacological effects and good therapeutic effects, and is easy to synthesize industrially, with high yield and good purity. Therefore, the therapeutic ability of leonurine for cardiovascular and central nervous system diseases is becoming increasingly strong, which is a hot topic. Some scientists even predict that leonurine may be a very promising new cardioprotective agent.

3.1 Anti-oxidative stress effect

3.1.1 Leonurine can regulate the balance between reactive oxygen species and antioxidant defense systems

Current studies have shown that leonurine exerts antioxidant properties through its powerful superoxide scavenging ability, which mainly comes from two defense levels: direct scavenging of free radicals, and neutralizing, reducing, or preventing the formation of reactive oxygen species (ROS) chain reactions [15]. Leonurine has been shown to significantly increase levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione peroxidase (GSH), and reduce levels of MDA [4,16]. The effects on SOD, GPx, CAT, GSH, and MDA indicate that leonurine may alleviate oxidative stress and improve clinical prognosis by enhancing endogenous antioxidant capacity during cerebral ischemia and myocardial ischemia [17].

3.1.2 Leonurine can maintain mitochondrial function under oxidative stress

Mitochondria is an important and effective antioxidant machine. Leonurine can significantly reduce the production of mitochondrial ROS and adenosine triphosphate (ATP) in rats with middle cerebral artery occlusion, and restore oxygen consumption and respiratory control ratio, suggesting that leonurine can improve mitochondrial dysfunction. Therefore, enhancing endogenous antioxidant capacity and attenuating mitochondrial dysfunction are two ways in which leonurine exerts anti-oxidative stress activity [18].

3.1.3 Leonurine can exert protective effect via several crucial signaling pathways

Studies have shown that leonurine reduced NO/NOS production and cell apoptosis, decreased Bax expression and increased Bcl-2 levels in OGD-treated PC12 cells through NO/NOS pathway [19]. Evidence indicated that Nrf2/NRF2 pathway regulates oxidative stress, lipid peroxidation and positively regulates cisplatin-induced acute kidney injury. Leonurine demonstrated the protective effects of Nrf2 activation on cisplatin-induced acute kidney injury via activating the Nrf2 signaling pathway [20]. In addition to antioxidant activity, leonurine could protect endometrial stromal cells (ESCs) from oxidative injury, mainly by inhibiting oxidative stress and reducing apoptosis through Bax/Bcl-2 and ERK signaling pathways [21]. In the further study of the mechanism of antioxidation, leonurine could reduce Aβ1-40 and Aβ1-42 levels which linked to the activation of the Nrf-2 signaling pathway in APP/PS1 mice and promoted Nrf-2 nuclear translocation and expression of HO-1 and NQO-1 [22].

3.2 Anti-inflammation effect

3.2.1 Leonurine can alleviate TNF-α-induced inflammation in human umbilical vein endothelial cells

TNF-α induces oxidative stress and increases ROS production, which triggers several intracellular signaling pathways such as mitogen-activated protein kinase (MAPK) and the IκB kinase pathway, leading to NF-κB activation [23]. Studies have shown that leonurine has a protective effect against TNF-α-mediated inflammation in human umbilical vein endothelial cells (HUVECs) by inhibiting NF-κB activation. Leonurine also inhibits TNF-α-induced monocyte/endothelial cell interactions by downregulating the expression of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), intracellular adhesion molecule-1 (ICAM-1), cyclooxygenase-2 (COX-2) and monocyte chemoattractant protein-1 (MCP-1) and inflammatory factors [24]. In addition, leonurine can also weaken TNF-α-induced phosphorylation of p38, inhibit the degradation of IκBα, and thus inhibit the phosphorylation, nuclear translocation and DNA binding activity of NF-κB p65, and ultimately reduce the downstream inflammatory factors of NF-κB. TNF-α-induced intracellular ROS production was decreased in HUVECs after leonurine treatment [25,26]. In conclusion, these studies suggest that leonurine inhibits TNF-α-induced inflammation in HUVECs by inhibiting the NF-κB pathway, downregulating adhesion molecules and inflammation.

3.2.2 Leonurine can improve lipopolysaccharide-induced inflammation

Toll-like receptor 4 (TLR4) is thought to be a key recognition receptor for lipopolysaccharide (LPS), triggering activation of downstream of NF-κB and MAPK signaling pathways [27]. The results showed that leonurine pretreatment alleviated LPS-induced mastitis in mice induced by E. coli. Leonurine alleviated histopathological changes, upregulated the secretion of anti-inflammatory cytokines, and downregulated the secretion of pro-inflammatory cytokines. In addition, leonurine inhibits TLR4 expression, phosphorylation of p38, extracellular signal-regulated kinase (ERK), Junn-terminal kinase (JNK), and NF-κB activation. These results all suggest that leonurine has a certain alleviating effect on the inflammation of mastitis induced by LPS [28,29].

It has been shown that leonurine has a protective effect on LPS-induced acute kidney injury (AKI) by maintaining redox equilibrium and alleviating renal tissue inflammation, thereby reducing animal mortality, and improving animal survival [30]. Leonurine also downregulates LPS-induced proinflammatory cytokines such as TNF-α, IL-1, IL-6, and IL-8, ROS, also MDA and GSH are restored to control levels, which leads to inhibiting IκBα phosphorylation and p56 translocation. These results suggest that leonurine works by improving LPS-induced inflammatory ROS-mediated NF-κB activation and downstream inflammatory factor inhibition [31]. To sum up, leonurine can ameliorate LPS- and TNF-α-induced inflammation and histopathological changes by downregulating pro-inflammatory effects, while upregulating anti-inflammatory factors and inhibiting NF-κB signaling pathway activation.

3.2.3 Leonurine can reduce inflammatory response via other signaling pathways

Hippo signaling pathway is a classical pathway in the study of inflammation. Recent study has found that leonurine can regulate the Hippo signaling pathway through the miR-21/YOD1/YAP axis to reduce joint inflammation and bone destruction in CIA mice, thereby inhibiting the growth and inflammation of RA-FLSs [32]. In reconstructive and plastic surgery, random skin flaps are commonly utilized to treat skin abnormalities produced by a variety of factors. Through immunohistochemistry and Western blot, studies proved that leonurine treatment can upregulate the level of angiogenesis, and significantly reduced the expression levels of oxidative stress, apoptosis, and inflammation via the PI3K/Akt pathway [33].

3.3 Anti-fibrosis effect

3.3.1 Leonurine can attenuate myocardial fibrosis by inhibiting NADPH oxidase

Cardiac fibroblasts play a significant role in promoting cardiac fibrosis. Under conditions such as myocardial infarction or stimulation by angiotensin II (Ang II), cardiac fibroblasts become abnormally active and invasive by increasing collagen accumulation and secreting matrix metalloproteinases (MMPs) that degrade the extracellular matrix (ECM), both of which directly participate in the process of cardiac remodeling during myocardial infarction [34,35]. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (Nox4) is the primary source of ROS in failing hearts, and its upregulation plays a key role in mediating the activation of cardiac fibroblasts [36]. ROS acts as a second messenger to activate various transcription factors (such as NF-κB) and stimulate the release and activation of inflammatory mediators, leading to cardiac fibroblast activation and myocardial fibrosis. In essence, Nox4 mediates myocardial fibrosis through cardiac fibroblasts [37].

Liu’s study revealed the mechanism by which leonurine alleviates the myocardial fibrotic process, suggesting that leonurine improves the myocardial fibrotic response by inhibiting Nox4 [38]. In vitro experiments of neonatal rat cardiac fibroblasts proved that leonurine pretreatment can improve ROS production, ERK1/2 activation, and MMP-2/9 activity and expression. In the Ang II-induced rat model of myocardial ischemia, leonurine reduces the formation of ischemic myocardial fibrosis, in part via the Nox4-ROS pathway. Leonurine significantly inhibits Nox4 expression, ROS production, and ERK1/2 activation in cardiac fibroblasts, while reducing the expression and activity of MMP-2/9, as well as collagen synthesis [21,38].

3.3.2 Leonurine can improve renal fibrosis via inhibiting TGF-β and NF-κB signaling pathways

The TGF-β/Smad3 pathway plays a crucial part in fibrotic diseases [39]. In response to stimuli such as ROS, TGF-β is released by latency associated peptide (LAP) and latency TGF-β binding protein (LTBP) [40]. TGF-β binding to TGF-β receptors results in phosphorylation and activation of downstream proteins. Receptor-associated Smad, such as Smad3 could bind directly to the promoter region of collagen, triggering the production of collagen I/II and inducing tissue inhibitor of metalloproteinase 1 (TIMP-1) and decrease of MMP-1 activity in fibroblasts, ECM degradation was inhibited, and fiber formation was promoted [41,42]. Other studies have proved that leonurine can attenuate tubulointerstitial fibrosis by inhibiting the ROS-mediated TGF-β/Smad3 pathway. Specifically, leonurine reduces the levels of ROS, TGF-β, and phosphorylated Smad3, as well as fibrosis-related indicators [43].

Advanced glycation end products (AGEs) are believed to accelerate renal fibrosis by triggering TGF-β-related pathways. There are also studies on the inhibitory effect of leonurine on AGE formation [44]. However, whether leonurine exerts its anti-fibrotic activity through AGEs remains to be further studied. At present, the anti-fibrotic action of leonurine is mainly related to the two pathways, including inhibition of Nox4-ROS-ERK1/2 mediated MMP-2/9 and ROS-TGF-β-Smad3 pathways [45].

3.4 Anti-apoptosis effect

3.4.1 Leonurine can exert anti-apoptotic effects by activating Akt signaling and increasing the ratio of Bcl-2/Bax

In the cardiovascular system, activation of the Akt signaling pathway plays a key role in the regulation of myocardial hypertrophy, angiogenesis, and apoptosis, which are essential for survival and regeneration of myocardial cells in myocardial infarction. Hypoxia-inducible factor (HIF-1α), as a downstream effector of Akt, has been shown to benefit MI by enhancing cardiac angiogenesis [46]. HIF-1α mediates transcriptional activation of hypoxic response genes that increase glycolysis, angiogenesis, and survival [47], such as the angiogenic factor VEGF and survival protein [48]. In conclusion, angiogenesis mechanisms may partially explain the protective effect of Akt against ischemic myocardial infarction.

After treatment with leonurine, left ventricular end-diastolic pressure decreased, dp/dt increased, cardiac function was significantly improved, and pulmonary congestion was alleviated in chronic myocardial ischemia rats. At the same time, leonurine increases Akt phosphorylation, induces HIF-1α accumulation, and enhances VEGF and survival protein levels, suggesting that the angiogenesis mechanism is partly responsible for the beneficial effect of leonurine in alleviating cardiomyocyte apoptosis [49,50]. Similarly, leonurine was able to restore HIF-1α and VEGF expression in senescence HUVECs and old ischemic muscle, improving age-dependent impaired angiogenesis. Leonurine significantly increased the anti-apoptotic marker Bcl-2 and decreased the apoptotic marker Bax [51]. This result is consistent with other studies, suggesting that Akt is an effective pathway for anti-apoptotic reaction [52,53].

3.4.2 Leonurine can induce apoptosis of lung cancer cells through a mitochondria-dependent pathway

Lung cancer is one of the most malignant tumors. Non-small cell lung cancer (NSCLC) is one of the pathological subtypes of lung cancer, and NSCLC metastasis is the leading cause of treatment failure [54]. One study proposed that in human NSCLC H292 cells, leonurine exerts a controversial pro-apoptotic effect through a mitochondria-dependent pathway [55]. Leonurine reduces mitochondrial membrane potential, which leads to oxidative stress and microenvironment disturbances. The breakdown of the mitochondrial outer membrane causes cytochrome C to enter the cytoplasm, leading to caspase3/9 cascade activation and an increase in the Bax/Bcl-2 ratio, which leads to apoptosis [56]. At the same time, leonurine treatment also decreased the phosphorylation level of Akt. Leonurine inhibits proliferation and induces apoptosis of H292 cells, which may provide an effective therapeutic strategy for the future treatment of NSCLC [57].

3.5 Anti-vascular injury and protective effect on glucose metabolism

3.5.1 Leonurine can delay the formation of atherosclerosis

The accumulation of cholesterol causes the transformation of macrophages into foam cells and promotes the formation of atherosclerosis [58]. When intracellular cholesterol levels are very high, liver X receptors (LXRs) act as cholesterol sensors that trigger the transcription of cholesterol efflux genes, including ABCA1 and ABCG1 [59], and mediate the transport of cholesterol from peripheral tissues to the liver for clearance [60]. In addition to early attenuating atherosclerotic lesions in hypercholesterolemic rabbits by modulating inflammatory and oxidative stress pathways [4], leonurine also prevents atherosclerosis by promoting the expression of ABCA1 and ABCG1, inhibiting lipid accumulation through macrophage cholesterol excretion in a PPARγ/LXRα signaling pathway-dependent manner [61].

3.5.2 Leonurine can alleviate aging

Non-enzymatic glycosylation (NEG) refers to the non-enzymatic reaction of the carbonyl group of reducing sugar with the free amino group of protein in vivo to form early glycosylation products, and through oxidation, rearrangement, and crosslinking, these intermediates form irreversible advanced glycosylation end products (AGEs) [62]. AGEs bind to tissue cells in the body, leading to their destruction. It is well known that AGEs accelerate the aging of the human body and lead to the occurrence of many chronic degenerative diseases, such as complications of diabetes [63]. Studies have found that leonurine attenuates carbonyl stress by capturing methyl glyoxal (MGO), one of the dicarbonyl intermediates produced by glycolysis during protein glycation, dose-dependently reducing the production of AGEs [44]. This finding supports the potential anti-glycation activity of leonurine, possibly preventing diabetes and its complications by inhibiting the formation of AGE.

3.5.3 Leonurine can improve impaired angiogenesis

In addition, recent studies have found that leonurine may delay aging by enhancing blood vessel regeneration. The researchers observed more effective neovascularization, blood perfusion, and ischemic limb vitality in older mice taking leonurine compared to younger mice, which is associated with the activation of the HIF-1α-VEGF pathway. Leonurine can reverse this phenomenon by reducing mitochondrial oxidative stress and increasing HIF-1α and VEGF levels [51].

4 Potential clinical applications of leonurine

Due to the protective role of leonurine in a variety of pathological processes, the compound plays a beneficial role in a variety of clinical diseases, such as cardiovascular and cerebrovascular diseases, neurodegenerative diseases, diabetes, kidney damage, rheumatoid arthritis, gynecological and obstetric diseases.

4.1 Protect effect on cardiovascular diseases

Cardiovascular diseases (CVD) are characterized by myocardial ischemia, and lipid metabolism disorders are important risk factors for cardiovascular diseases. Leonurine has been shown to be beneficial in the treatment of CVD through different pharmacological activities, especially for ischemic heart disease.

4.1.1 Leonurine can prevent ischemic heart disease

The most common cause of congestive heart failure is ischemic heart disease. When acute myocardial ischemia occurs in the heart, oxidative stress and inflammatory responses take place in myocardial cells, causing acute damage to them [64]. In addition, persistent myocardial ischemia leads to cardiomyocyte apoptosis and myocardial remodeling characterized by cardiac inflammation and ECM accumulation, reducing ventricular compliance and accelerating the development [65].

Leonurine can preserve ischemic myocardium by attenuating a variety of pathologic activities, including antioxidant [4], anti-apoptotic [46], and anti-fibrotic effects [38]. First, leonurine improves ischemic myocardial injury through its antioxidant effect. Leonurine reduces myocardial injury and infarct size by decreasing the leakage of myocardial enzymes such as creatine kinase (CK) and lactate dehydrogenase (LDH). Meanwhile, leonurine enhances the antioxidant system, increases the expression level of Mn-SOD and the biological activity of SOD, and reduces the lipid peroxidation index (such as MDA). Also, leonurine improves myocardial injury caused by ischemia through anti-apoptotic effects, among which angiogenesis mechanism plays a crucial role. Leonurine enhances the phosphorylation of Akt and the expression of HIF-1α and downstream cytokines such as survivin and VEGF, which play a key role in angiogenesis. Additionally, leonurine increases the expression of Bcl-2 and reduces the expression of Bax [49,66]. Thirdly, leonurine can improve ventricular remodeling by anti-ischemic myocardial fibrosis. Activation of myocardial fibroblasts is essential for the development of ventricular remodeling in ischemic myocardium [67]. Therefore, in the cardiac fibroblasts directly involved in cardiac progression, the expression and activation of type I/III collagen and MMP-2/9 collagen are inhibited [38].

4.1.2 Leonurine can prevent atherosclerosis through PPARγ/LXRα signaling pathway

Atherosclerosis (AS) is the fundamental pathological basis of cardiovascular diseases such as coronary heart disease. The synergistic effect of inflammation and oxidative stress is involved in the pathological process of AS [68]. Leonurine can delay the progression of early atherosclerotic lesions to advanced plaques by regulating inflammatory and oxidative stress pathways, thereby reducing the levels of ROS, TNF-α, IL-6, and VCAM-1 in atherosclerotic rabbits [4]. In addition, leonurine can reduce LDL cholesterol, total cholesterol, and triglycerides in atherosclerotic rabbits. A recent study has shown that leonurine can inhibit the formation of atherosclerosis by improving lipid metabolism. Leonurine stimulates the expression of ABCA1/G1 in a PPARγ/LXRα signaling pathway dependent manner, thereby inhibiting the formation of atherosclerosis, alleviating lipid accumulation, and promoting cholesterol excretion in human THP-1 macrophage-derived foam cells, and alleviating atherosclerosis in apoE^−/− mice [61] (Fig.3).

4.2 Positive effect on cerebrovascular diseases and neurodegenerative diseases

In addition to its role in protecting the heart, leonurine also has beneficial effects on cerebrovascular diseases, especially ischemic stroke. The immediate cause of ischemic stroke is reduced or completely blocked blood flow, resulting in inadequate glucose and oxygen supply, further inducing oxidative stress and inflammatory responses [69]. Leonurine significantly reduces infarct volume and nerve function deficit score in stroke patients and enhances endogenous antioxidant capacity. In addition, leonurine improved cortical mitochondrial function, decreased ROS production and ATP biosynthesis, and increased RCR (State 3 respiratory rate/State 4 respiratory rate) values, indicating the tight coupling of respiration and phosphorylation [19]. Therefore, the ameliorative effect of leonurine on ischemic stroke occurs in part through antioxidant effects.

Traditionally, multiple sclerosis (MS) has been regarded as an autoimmune-mediated neurodegenerative disease of the central nervous system characterized by inflammatory demyelination with axonal transection [70]. During the pathogenesis of MS, leonurine significantly inhibits the recruitment of brain-derived T cells to the central nervous system, protects MS mice from demyelination, inhibits the trimethylation of histone H3 lysine-27, and promotes the maturation of oligodendrocytes. This may be a promising therapeutic strategy for multiple sclerosis and even other demyelinating diseases [71].

Alzheimer’s disease (AD) is the most common neurodegenerative disease characterized by progressive decline in memory and cognitive abilities. Amyloid beta (Aβ) deposition, neurofibrillary tangles, neuronal loss, and neuroinflammation are its main pathological features [72]. The most convincing hypothesis is the Aβ cascade model; hippocampus-dependent synaptic plasticity is related to the phosphorylation of cAMP response element binding protein (CREB) and its target genes brain-derived neurotrophic factor/tyrosine kinase B (BDNF/TrkB). This pathway plays an important role in neuronal survival and synaptic plasticity. Aβ may inhibit CREB phosphorylation, leading to memory and cognitive impairment in AD models. Therefore, enhancing the CREB/BDNF/TrkB signaling pathway is a viable strategy [73,74]. Leonurine can improve cognitive function and inhibits microglial overactivation and neuronal apoptosis [75]. In the rat model injected with Aβ and a transgenic mouse model of APP/PS1, leonurine exerts anti-neuroinflammatory properties and inhibits microglial overactivation [76]. The latest study also confirmed that leonurine alleviates cognitive dysfunction and oxidative stress in AD mice by activating the Nrf-2 pathway [22].

Parkinson’s disease (PD) is a neurodegenerative disorder associated with α-synuclein aggregation and dopaminergic neuron loss in the midbrain [77]. ALOX15 was upregulated by α-synuclein overexpression and acted as a risk factor in the development of chronic stress-induced parkinsonism and neurodegeneration, leonurine was screened with activities of inhibiting the ALOX15 interaction and thereby attenuating membrane phospholipid peroxidation, and then controlled the process of PD [78]. In addition to AD and PD, studies have also shown that leonurine has an antidepressant-like effect, which is at least partially mediated by improving monoamine neurotransmitters and inhibiting neuroinflammation. This study reveals the potential of leonurine in the treatment of depression [79] (Fig.4).

Depression is a highly prevalent and heterogeneous disorder that requires new strategies to overcome depression. In the latest study, researchers have found that leonurine could modulate hippocampal nerve regeneration in chronic and unpredictable mild stress (CUMS) rats through the SHH/GLI signaling pathway and restoring gut microbiota and microbial metabolic homeostasis [80]. In addition, the treatment of corticosteroid-induced PC12 cells with leonurine was utilized to investigate the effects of glucocorticoid receptor (GR) inhibitors, serum, glucocorticoid-induced kinase 1 (SGK1) on neurite outgrowth and neurotrophic factors, providing a new therapeutic approach for the treatment of depression [81]. In depression, leonurine alleviates depression by inhibiting the activation of NF-κB signal pathway and increasing the levels of 5-HT, NE, and DA. In MS, leonurine reduces inflammation and myelin damage in the central nervous system by inhibiting the recruitment of autoimmune T cells to the central nervous system [14]. To sum up, depression, as a common mental disorder, can lead to slow thinking or movement, poor cognitive ability, and physical symptoms such as sleep disorders, which can be well controlled or alleviated by leonurine [6].

4.3 Anti-effect on diabetes mellitus (DM) and its complications

Diabetes is a chronic metabolic disease characterized by chronic hyperglycemia. Chronic hyperglycemia is thought to be the direct cause of endogenous AGE formation [82]. There is a vicious cycle between DM and AGEs: DM produces large amounts of AGEs, which in turn lead to the worsening of DM and its complications, especially retinopathy, kidney disease, and cardiomyopathy. Therefore, inhibiting the formation of AGEs is considered to be the key to DM treatment [83]. The reaction between the carbonyl group of reducing sugars and the free amino group of proteins is the first and most important step in AGE formation, also known as the non-enzymatic glycosylation reaction (NEG). Methylglyoxal (MGO) is one of the dicarbonyl intermediates produced by glycolysis during protein glycosylation and is thought to significantly promote the formation of AGE in cells. The concentration of MGO in DM patients is significantly increased by 2–4 times [84]. Studies have found that leonurine can trap MGO and inhibit NEG, which in turn inhibits the levels of AGEs [44]. It has also been noted that arginine, one of the targets of protein glycosylation, has similar properties to leonurine. It contains guanidine in its molecular structure, suggesting that leonurine may compete with MGO targets, such as arginine, to eliminate MGO and inhibit the formation of AGEs. Researchers also found that leonurine has a protective effect against dexamethasone-induced pancreatic β cell toxicity via the PI3K/Akt signaling pathway, suggesting that leonurine may be a promising drug for the treatment of steroid diabetes [85]. In addition, diabetic nephropathy (DN) is a common microvascular complication of DM, a recent study has revealed that leonurine can exert anti-DN effects both in vivo and in vitro by suppressing GPX4-mediated endothelial cell ferroptosis, which provides a new perspective on the treatment of diseases using natural medicines and involves a novel form of cell death that could potentially lead to better treatment of DN [86].

4.4 Protective effect against rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes progressive joint destruction, leading to impaired life quality, disability, and even premature mortality [87]. RA fibroblast-like synoviocytes (FLSs) exhibit tumor-like biological characteristics that facilitate pannus generation and are involved in inflammation of the articular cartilage and bone, overexpress fibroblast activation protein (FAP). This is a feature that could be leveraged to improve imaging assessment of disease [88]. Recent studies have found that leonurine regulates the Hippo signaling pathway through the miR-21/YOD1/YAP axis, alleviates joint inflammation and bone destruction in CIA mice, and thereby inhibits the growth and inflammation of RA-FLSs [32]. After loading leonurine and catalase (CAT) to form nanoliposomal system (Leonurine@CAT@nanoliposomal), Wang’s study provided a neutrophil-mimetic and ROS responsive nanoplatform for targeted RA therapy and represented a promising paradigm for the treatment of a variety of inflammation-dominated diseases [89]. Leonurine can also regulate Treg/Th17 balance to attenuate RA by inhibiting TAZ expression [90]. Besides, Lin’ team found that leonurine treatment significantly decreased the production of pro-inflammatory cytokines and MMP-1 and MMP-3 and suppressed the migration and invasion of RA FLSs, suggesting that leonurine has potential as a therapeutic agent for RA [91].

4.5 Alleviating effect on acute kidney disease via activating PPARγ

Acute kidney injury (AKI) is a common and serious global health problem with high risks of mortality and the development of chronic kidney diseases, patients either recover or alternatively develop fibrosis and chronic kidney disease. Interactions between injured epithelia, stroma, and inflammatory cells determine whether kidneys repair or undergo fibrosis [92,93]. The latest research has confirmed that leonurine alleviates AKI by regulating the ATF4/CHOP/ASCL4 signaling pathway and inhibiting ER stress-related ferroptosis, providing a new mechanism for AKI treatment [94]. Vancomycin (VCM) is a first-line antibiotic for treating severe infections, but its nephrotoxicity limits the use. Mechanism exploration indicates that leonurine inhibits the renal toxicity of VCM by activating PPARγ and suppressing the TLR4/NF-κB/TNF-α inflammatory pathway, providing a promising therapeutic strategy for treating renal injury [95]. Cisplatin has been widely regarded as an effective chemotherapy drug with various side effects, including nephrotoxicity. A new study has found that leonurine treatment can prevent renal tubular injury and apoptosis by inhibiting the NLRP3 inflammasome, thereby improving renal function [96].

4.6 Significant therapeutic effect on gynecological and obstetric diseases

4.6.1 Leonurine can prevent incomplete miscarriage by enhancing uterine contractility

Incomplete miscarriage is a common obstetric disorder characterized by incomplete discharge of the fetus and placenta, resulting in uterine relaxation and prolonged vaginal bleeding. Leonurine can significantly reduce the bleeding time, bleeding volume, and intrauterine residue of incomplete abortion caused by mifepristone combined with misoprostol in early pregnant rats by enhancing uterine contractions [97]. Uterine contractions are regulated by a variety of factors, such as steroids and peptide hormones, endothelin (ET) and/or nitric oxide (NO). ETs is isolated from endothelial cells and has three isopeptides, ET-1, -2, and -3, that bind to cell surface receptors, ETA, ETB, and ETC, respectively. ET-1 enhances uterine contractions by activating ETA receptors expressed in smooth muscle cells of the uterus. This action correlates with the function of the phospholipase C (PLC)/protein kinase C (PKC)/calcium pathway [98]. It has been reported that leonurine significantly increases ET levels and upregulates ETA expression. In addition, leonurine increased PLC activity, PKC production, and intracellular Ca²⁺ concentration [99]. These results suggest that leonurine increases uterine contractions in incomplete aborted rats by modulating the ET-1 mediated PLC/PKC/Ca²⁺ pathway.

4.6.2 Leonurine can reduce pelvic pain in patients with endometriosis

The pathological feature of adenomyosis is that the endometrial glands and stroma invade the myometrium. It is a common disease among premenopausal women aged 35 to 50 years who have given birth to multiple children [100]. Leonurine reduces hyperalgesia and myoinfiltration in adenomyosis-induced mice, while downregulating the expression of NF-κB phosphorylated p65, COX-2, and oxytocin receptors, all of which are associated with the pathologic progression of dysmenorrhea [101]. For higher infertility and repeated implantation failure in women with endometriosis, leonurine may be a good candidate for pregnancy or prior to embryo transfer [102].

Nowadays clinical effects of leonurine are investigating or are prepared to study in further trials, based on the classical staging of clinical trials. Leonurine has drawn worldwide attention as a potential new drug with significant lipid-lowering effects and therapeutic benefits for stroke. We believe that in the near future, leonurine is highly likely to become one of the five original first-class new drugs following artemisinin, benefiting all mankind.

5 Summary and prospects

Traditional Chinese medicine Herba leonuri is known as the “holy medicine for gynecology” and is often used to treat gynecological diseases. With the development of scientific research technology and the in-depth study of its chemical components, more compounds have attracted the attention of researchers. Herein, we comprehensively summarized the important component of Herba leonuri, leonurine, which has been proven to possess various pharmacological activities, such as antioxidant, cardio-cerebrovascular effects, neuroprotective effects, anti-inflammatory, anti-fibrotic, and anti-infective properties. Despite showing promising pharmacological or therapeutic effects, more precise research is still needed to discover potential biological targets and their mechanisms of action. At the same time, it cannot be ignored that the usage and dosage of leonurine, as well as evidence of its combination with other drugs, are very limited. Over the past few decades, researchers have made tremendous efforts to optimize it from the ground up, including chemical synthesis, pharmacodynamics evaluation in vitro and in vivo, and comprehensive toxicological studies on the final dosage form. All of these will pave the way for its successful entry into the drug counter, making leonurine a modern effective drug and contributing to the treatment of cardiocerebrovascular diseases and other diseases in the future.

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