Hyperoside: A Review of Its Structure, Synthesis, Pharmacology, Pharmacokinetics and Toxicity

Hyperoside is an active ingredient in plants, such as Hypericum monogynum in Hypericaceae, Crataegus pinnatifida in Rosaceae and Polygonum aviculare in Polygonaceae. Its pharmacologic effects include preventing cancer and protecting the brain, neurons, heart, kidneys, lung, blood vessels, bones, joints and liver, among others. Pharmacokinetic analysis of hyperoside has revealed that it mainly accumulates in the kidney. However, long-term application of high-dose hyperoside should be avoided in clinical practice because of its renal toxicity. This review summarises the structure, synthesis, pharmacology, pharmacokinetics and toxicity of hyperoside.


Introduction
Hyperoside, which has the structure shown in Figure 1, is an active ingredient in plants such as Hypericum monogynum in Hypericaceae, Crataegus pinnatifida in Rosaceae and Polygonum aviculare in Polygonaceae [1][2][3]. These plants are widely distributed worldwide, especially in Southeast Asian countries, such as China, Japan and South Korea. They exhibit various pharmacological effects, such as protecting the blood vessels, regulating the digestive system and protecting against oxidation, aging and cancer [4][5][6].

Introduction
Hyperoside, which has the structure shown in Figure 1, is an active ingredient in plants such as Hypericum monogynum in Hypericaceae, Crataegus pinnatifida in Rosaceae and Polygonum aviculare in Polygonaceae [1][2][3]. These plants are widely distributed worldwide, especially in Southeast Asian countries, such as China, Japan and South Korea. They exhibit various pharmacological effects, such as protecting the blood vessels, regulating the digestive system and protecting against oxidation, aging and cancer [4][5][6].

Chemical Synthesis
Horhammer et al. were the first to synthesise hyperoside. They used quercetin as a raw material for total synthesis and obtained a total yield of only 2.6%. The main synthetic challenge within the Horhammer synthesis of hyperoside was the selective glycosylation of the C3 hydroxyl group of quercetin. The series of highly controlled regioselective protection and deprotection operations resulted in the formation of compound 5. The Koening-Knorr reaction with this compound and acetylated bromoglucose proceeded regioselectivity at the hydroxyl in position C3. Further hydrogenolysis with hydrogen, using palladium on carbon as a catalyst, resulted in the formation of hyperoside [18]. This synthetic route is shown in Scheme 1. Following simple steps, Jiang et al. semi-synthesised hyperoside using rutin as the raw material under mild reaction conditions and obtained a total yield of 6.8% [19]. There are two things to note about this synthesis scheme. First, the team used compound 7 to react with benzoyl chloride and hydrolyse rutinose at the C3 position in the HCl/EtOH system to obtain compound 8. Second, the team also used the same reaction method as the previous team (the Koening-Knorr reaction) to select and further glycosylate the hydroxyl group at the C3, and the 5,7,3 and 4 substituents were converted to hydroxyl groups. Hyperoside was also obtained by hydrolysis of compound 9 [19] and the synthetic route is shown in Scheme 2. In 2002, Zhou integrated and improved the previous two schemes. Since the o-glycoside bond was usually a hemiacetal structure that can be easily hydrolysed, Zhou dissolved compound 10 in hot ethanol solution and hydrolysed it with strong HCl to obtain compound 11. He also used a Koening-Knorr reaction to remove the protective group in a KOH/anhydrous methanol system to obtain the target product. The hydrolysis conditions of benzoylated rutin were improved, and the yield of hyperoside was increased from 6.8% to 11% [12]. This synthetic route is shown in Scheme 3. Table 1. Anti-cancer Activity of Hyperoside.

Detail
Cell Lines/Model Dose Ref.
human gastric cancer MKN-45 50, 75 and 100 µg/mL [31] Inhibits SKOV3 cell proliferation; promotes cell apoptosis; up-regulates cleaved caspase-3 and caspase-9; down-regulates Bcl-2, p65 and p-IκB-α; and decreases cell migration and invasion.  Increases the number of NeuN-positive cells; decreases the number of GFAP-and PECAM-positive cells; up-regulates ZO-1 and claudin5 protein expression; maintains the integrity of the blood-brain barrier; and may protect neural function in CIR-injured mice.
CIR injury induced by MCAO in mice 50 mg/kg [35] Inhibits the activation of microglia and the synthesis of inflammatory factors after SAH; increases the phosphorylation of AKT and GSK-3β; alleviates early brain injury after subarachnoid haemorrhage; and promotes nerve function recovery in rats.
SAH in rats 50 mg/kg [36] Increases cell survival rate; decreases LDH release; reduces cleared ROS level, MDA content and caspase-3 activity; increases SOD and CAT activities and GSH content; increases SIRT1 gene expression; down-regulates NF-κB mRNA and protein expression; and protects against high glucose-induced oxidative damage of human neuroblastoma cells.
SH-SY5Y 50 and 100 µm L/L [37] Significantly shortens the cumulative immobility time of forced swimming and tail suspension mice; can act as an anti-depressant.
Depressive ICR mice 20 mg/kg [38] Targets the PI3K/AKT and MAPK pathways to increase antioxidant levels and decrease the levels of autophagy-related proteins; protects the hippocampal CA3 region from neuronal damage caused by epilepsy.
Neuronal damage in a mouse model 50 mg/kg [39] Decreases TC, TG and LDL-C levels and prevents cognitive dysfunction, neuroinflammation and oxidative stress in diabetic rats.
Rotenone was used to induce Parkinson's disease rat model and SH-SY5Y cell injury model 100   Decreases the levels of AST, CK, CK-MB and c-TnT in rats; the rate of cardiomyocyte apoptosis; and the relative expression of protein and CaMK II protein. Effectively relieves heart failure.
Rat model of myocardial ischaemia-reperfusion injury 50,100 mg/kg [47] Decreases fasting blood glucose, cTnI I and MDA contents and increases SOD activity, the value of ejection fraction and short-axis shortened pitch in diabetic mice; improves glycolipid metabolism; and exerts a protective effect on myocardial injury caused by diabetes.
Type 2 diabetic mice induced by high-fat diet combined with low-dose streptozotocin ND [48] Increases cell survival rate; decreases cell apoptosis rate and ROS and MDA levels; increases SOD level, PI3K relative expression level and AKT and Nrf2 phosphorylation level; and protects cardiac muscle cells from high sugar-induced oxidative stress damage.
High-glucose treatment simulates oxidative stress injury of cardiomyocytes 4, 8 and 20 nmol/L [49] Decreases MDA content and CK-MB activity; increases SOD activity and ATP content; up-regulates Nrf2, PKCε and Kir6.2 expression in cardiomyocytes; and improves cardiac muscle damage.
Myocardial I/R injury in rats 50 mg/kg [50] Decreases CK-MB, TNF-α and IL-1β expression in serum; increases SOD and GSH activities in myocardial tissue; up-regulates SIRT1 protein expression; down-regulates FoxO1 acetylation level and apoptosis protein cleaved caspase-3 expression; alleviates early myocardial injury caused by antioxidative stress and anti-inflammatory effects in severely burned rats.
Early myocardial injury in severely burned rats 30 mg/kg [51] Increases the levels of LVSP, maximum increase rate of left ventricular pressure (+dp/dt max ), maximum decrease rate of left ventricular pressure (−dp/dt max ), HIF-1α and HO-1; decreases the levels of LVEDP, cTnI, BNP, TNF-α and IL-1β; and ameliorates myocardial injury in septic rats.
Myocardial cells of sepsis model in rats 10 and 20 mg/kg [52] Decreases serum oxidative stress; improves thoracic aorta remodelling and endothelial dysfunction to a certain extent; exerts a cardiovascular protective effect on mice with myocardial infarction.
Myocardial infarction model 36 mg/kg [53] Increases the levels of heart rate, mean arterial pressure and heart rate systolic pressure product; decreases the levels of CK-MB and cTnI; and reduces I/R ventricular arrhythmia in rats.
Myocardial I/R model in rats 50 mg/kg [54] Significantly enhances SIRT3 signal expression; alleviates oxidative stress injury of myocardial tissue; inhibits the progression of myocardial fibrosis; and improves pathological myocardial hypertrophy caused by stress load.
Myocardial hypertrophy (mouse) 50 mg/kg/day [55] Increases phosphorylated AMPK, phosphorylated mTOR and P62 proteins; decreases apoptosis index, caspase-3 activity and LC3II and Beclin1 expression; and alleviates I/R injury of H9C2 cells. I/R model 50 µmol/L [56] Decreases cardiac myocyte cross-sectional area and cardiac weight/body weight ratio; inhibits autophagy in TAC rats and AngII-induced H9C2 cells and apoptosis; and effectively alleviates heart failure by inhibiting apoptosis and inducing autophagy.
Myocardial mouse model 18 and 36 mg/kg [60] Decreases cell vitality and aggravates inflammation; down-regulates miR-21 expression in cardiomyocytes; increases cell survival rate; decreases inflammatory response; inhibits miR-21; and regulates cardiomyocyte activity and inflammation.  Decreases ALT, AST and ALP levels; down-regulates α-SMA, type I collagen, fibrotic factor-CTGF, MMP2 and MMP9; inhibits the activation of the transforming growth factor-β-1/Smad pathway and hepatic stellate cells mediated by transforming growth factor-β1; and prevents liver fibrosis. Decreases total cholesterol, triglycerides and low-density lipoprotein cholesterol levels; inhibits the phosphorylation of p65/NF-κB and mitogen-activated protein kinase; activates transcription factor 3 protein expression; and decreases Bax, cytochrome c, caspase-9 and caspase-3 expression. It may be beneficial in the treatment of diabetes.
Middle cerebral artery occlusion/reperfusion rat model 60 and 120 mg/kg [69] Decreases LDH activity and MDA, NSE and S100β contents; relaxes the cerebral basilar artery in a dose-dependent manner; up-regulates IP3, PKC, TRPV4, SKca and IKca expression; reduces Ca 2+ fluorescence intensity; and ameliorates brain injury in rats with ischaemic stroke.
Global CIR model 50 mg/kg [70] Up-regulates BDNF expression in the hippocampus; down-regulates p75NRT; reduces hippocampal neuron and cell damage; improves learning and memory; and protects the hippocampal tissue in rats.
Cerebral I/R injury in rats 50 mg/kg/day [72] Increases SOD, catalase and glutathione peroxidase activities and improves cell apoptosis after nickel administration.
D-gal induces kidney aging and damage model 10 µg/mL 20 mg/kg/day [75] Decreases ROS and H 2 O 2 levels and NADPH oxidase and LD activities and shows potential in the treatment of kidney stones and ROS-related diseases. Human kidney-2 cells 100 and 200 µM [76] Up-regulates Klotho expression; down-regulates p53 expression; and prevents age-related kidney damage. NRK-52E cells 5 and 10 µg/mL [77] Inhibits OPA1 hydrolysis, mitochondrial division, oxidative stress and apoptosis and shows new therapeutic potential in the treatment of acute kidney injury.
Renal ischaemia models 20 mg/kg [78] Decreases ERK pathway activation and downstream transcription factor CREB phosphorylation; down-regulates miRNA-34a expression; and inhibits high glucose-induced proliferation of mesangial cells.  Decreases collagen I and III expression, serum TGF-β1 content and alveolar lavage fluid IL-6 levels and effectively improves bleomycin-induced pulmonary fibrosis in mice.
Pulmonary fibrosis model 100 mg/kg [81] Decreases cytotoxicity and p-AMPK expression; increases p-mTOR expression; inhibits the AMPK/α signalling pathway; down-regulates TNF-α and IL-6 expression in the alveolar lavage fluid; decreases total number of cells in the alveolar lavage fluid; and inhibits autophagy dysregulation and apoptosis by regulating the AMPK/mTOR pathway to prevent lung injury.
Human bronchial epithelial BEAS-2B 50 µM [82] Down-regulates MDA, TNF-α and IL-6 expression; increases SOD activity; inhibits epithelial-mesenchymal transition; and slows the development of pulmonary fibrosis by inhibiting oxidative stress and inflammation in the lung tissues of mice with pulmonary fibrosis.
Lung cancer A549 100, 200 and 400 µg/mL [84]  Reduces LDL-C, MDA and IL-6 levels; increases NO and eNOS levels; decreases plaque area in the aortic lumen of mice; improves lipid deposition; down-regulates PARP1, ARG2 and iNOS expression in mouse aortic tissue; and slows down atherosclerosis.

Detail Cell Lines/Model Dose Ref.
Increases IL-6 and TNF-α levels; decreases Col-I and Col-III levels; up-regulates MMP-3, MMP-9, p-IκB-α and p-p65 expression; prevents IL-1β-induced chondrocyte injury in the sacroiliac joint of mice; improves cell activity; and inhibits inflammatory factors and extracellular matrix disorder.
Ovariectomised mice 40 or 80 mg/kg/day [89] Increases ALP, Col-I and OCN mRNA expression; decreases the rate of apoptosis, expression of apoptosis-related proteins and levels of MC3T3-E1 phosphorylated JNK and p38; and protects osteoblasts by inhibiting MAPK signalling and oxidative damage of cells.
Osteoblastic MC3T3-E1 cells 20 and 40 µmol/L [90] Increases cell viability and proliferation; decreases cell apoptosis and autophagy; and protects osteoblasts from damage induced by Ti particles.
FLS cells 50 and 100 µm/mL [92] Decreases TNF-α and IL-6 contents in the serum; prevents the synovial hyperplasia and inflammatory cell infiltration of the mouse ankle joint; and exerts a certain therapeutic effect on rheumatoid arthritis.
CIA mice 25 and 50 mg/kg [93] Down-regulates MMP3 and TNF-a genes; reduces the loss of cell matrix of rat chondrocytes; maintains cell activity; down-regulates the expression of genes related to cell inflammation; reduces inflammation; and exerts a certain therapeutic effect on osteoarthritis in vitro.
Adult endothelial cells 75 mg/(kg/day) [97] Decreases MDA content; increases SOD, GSH-Px and CAT activities; down-regulates Bax expression; up-regulates Bcl-2, SHH, Gli1 and SMO expression; and protects granular cells from H 2 O 2 -induced apoptosis and oxidative stress by activating the Sonic hedgehog signalling pathway.

Granular cells 40 µM [98]
Increases MiR-499a-5p expression and decreases NRIP1 expression in a dose-dependent manner and mitigates apoptosis and inflammatory response induced by high glucose via the miR-499a-5p/NRIP1 axis.
Human retinal pigmented epithelial ARPE-19 cells and adenocaricinomic human alveolar basal epithelial A549 cells Animals exposed to UVA or blue light 25, 50 and 100 µM 25, 50 and 100 mg/kg [100] Down-regulates caspase-3, caspase-9 and Bax expression; up-regulates Bcl-2 expression; and possibly plays a protective role in diabetic retinopathy by reducing oxidative stress induced by high glucose and inhibiting cell damage and apoptosis.
Rat retinal vascular endothelial cells Rats fed with high-fat rat 10 mg/mL 20, 50 and 100 mg/kg [101] Increases the proliferation of rat bone mesenchymal stem cells and the number of EdU-positive cells; decreases cell cycle distribution; up-regulates Ki67 and PCNA expression; promotes the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells; and exerts potential therapeutic effect on periodontitis.
Diabetic mice induced by high-fat diet and alloxan 200 and 400 mg/kg [105] Inhibits the expression of transcription factors and adipogenic genes and reduces lipid accumulation in adipocytes. Hyperoside at 5 µM inhibits adipogenesis, and hyperoside at 10 µM reduces fat accumulation in mature adipocytes.

Anti-Cancer Activity
The incidence and mortality of cancer have increased with industrialisation [111]. Lung cancer has received increasing attention because of its high incidence rate. Previous studies reported that hyperoside has anti-lung cancer effects and its mechanism is shown in Figure 2.

Anti-Cancer Activity
The incidence and mortality of cancer have increased with industrialisation [111]. Lung cancer has received increasing attention because of its high incidence rate. Previous studies reported that hyperoside has anti-lung cancer effects and its mechanism is shown in Figure 2.

Effect on Lung Cancer
According to the World Health Organization (https://www.who.int/cancer accessed on 10 January 2022), lung cancer deaths have risen significantly in upper-middle-income countries to more than twice that of the three other income groups combined. Clinically, chemotherapy can slightly prolong the survival of patients with advanced cancer but at the cost of significant adverse reactions [112].

Effect on Lung Cancer
According to the World Health Organization (https://www.who.int/cancer accessed on 10 January 2022), lung cancer deaths have risen significantly in upper-middle-income countries to more than twice that of the three other income groups combined. Clinically, chemotherapy can slightly prolong the survival of patients with advanced cancer but at the cost of significant adverse reactions [112]. Recent studies have shown that hyperoside can induce the apoptosis and G1/S phase arrest and inhibit the proliferation of A549 cells by down-regulating the expression of B cell lymphoma-2 (Bcl-2) and B cell lymphoma-extra large (Bcl-xL) and up-regulating the expression of cysteinyl aspartate specific proteinase 3 (caspase-3) [27]. Dong et al. discussed the anti-cancer effects of hyperoside on non-small cell lung cancer (NSCLC) from different aspects. Dong et al. showed that hyperoside inhibits the expression of PD-L1 in NSCLC cells and at the cell membrane surface at the transcriptional level by reducing the protein expression of transcription factor cellularmyelocytomatosis viral oncogene (c-Myc) [24]. Chen et al. investigated the effect of hyperoside on hypoxia-induced NSCLC A549 cells and found that hyperoside increases the phosphorylation and HO-1 expression of A549 AMPK [25]. Furthermore, hyperoside can inhibit the proliferation and induce the apoptosis of T790M-positive NSCLC cells by up-regulating forkhead box protein O1 by colon cancer associated transcript 1. It can also inhibit the proliferation and induce the apoptosis of H1975 cells in a dose-dependent manner [26]. However, the effect of hyperoside on NSCLC remains unclear to date, as is its effect on small cell lung cancer.

Effect on Cervical Cancer
Cervical cancer is the most common gynaecological cancer in Brazil, second only to breast cancer in women [113]. In Japan, two cases of lung cancer in children (23-month-old and 6-year-old boys) were found to be caused by the mother-to-child transmission of a cervical tumour [114]. Bian  Nampt, NAD and Sirt1 [21]. Wang et al. studied the effects of hyperoside on the apoptosis and antioxidant capacity of HeLa cells by treating and culturing HeLa cells with hyperoside at 0, 25, 50, 100 and 200 µmol/L in vitro for 12, 24 and 48 h, and found that hyperoside decreased the cell survival rate in a dose-and time-dependent manner according to 3-(4,5)dimethylthiahiazo(-z-yl)-3,5-di-phenytetrazoliumromide (MTT) assay, cell morphological observation, cell apoptosis detection and other methods. Their results also showed that hyperoside increases superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) activities; significantly decreases the expression of vascular endothelial growth factor (VEGF) and Bcl-2; and significantly increases the expression of malondialdehyde (MDA), Bax (Bcl2-associated X) and tumour suppressor gene p53 [20]. Guo et al. explained the effect of hyperoside on cervical cancer cells through a protein-protein interaction (PPI) network, PPI module analysis, transcription factor (TF)-target network construction and survival analysis, RT-QPCR and Western blot to detect key genes. They found that hyperoside down-regulates c-Myc gene expression and inhibits HeLa and C-33A cell proliferation [22].

Effect on Liver Cancer
Liver cancer is a high-risk cancer with a high fatality rate. Patients often neglect treatment or misdiagnose this disease at the initial stage because its symptoms are similar to those of other liver diseases. Moreover, liver cancer has become a severe disease affecting the average life expectancy in China [115]. Jiang et al. and Wei et al. studied the protective effect of hyperoside on human liver cancer cells through different pathways. Jiang et al. studied the effects of hyperoside on the apoptosis of human hepatoma HepG2 cells via the P53/caspase pathway, and found that this compound significantly increases (p < 0.05) the expression levels of P53, caspase-9 and caspase-3 proteins in HepG2 cells [23]. Wei et al. studied the effect of hyperoside on the PI3K/AKT pathway in human hepatocellular carcinoma cells. They found that hyperoside down-regulates the expression of bone morphogenetic protein 7 (BMP-7), arrests the cell cycle growth of HepG2 cells in the G1 phase, inhibits the phosphorylation of AKT and significantly down-regulates the expression of PI3K [6]. In addition, Han Jingxia and Hu et al. performed protein-protein interaction experiments, such as fast protein liquid chromatography, co-immunoprecipitation and metabolomics, to illustrate the anti-liver cancer effect of hyperoside. Han Jingxia found that hyperoside inhibits the interaction between YY1 and P65 and P300, reduces the activity of quaking (QKI) promoter and down-regulates the expression of has_circ_0004631 [116]. Hu et al. found that hyperoside at 60 mg/kg can prevent liver damage caused by acetaminophen-induced oxidative stress and regulate glutathione-related metabolites and enzymes by inhibiting cytochrome P450 2E1 [117]. In conclusion, hyperoside exerts its anti-liver cancer effect by inhibiting the proliferation of liver cancer cells, arresting their cell cycle and effectively inhibiting the activity of the YY1 complex, the expression of QKI and the invasion and metastasis of liver cancer cells.

Effect on Breast Cancer
In recent years, the incidence of breast cancer in China has gradually increased, and breast cancer has become the most common malignant tumour in women [118]. Qiu

Effect on Stomach Cancer
The incidence of gastric cancer is decreasing, but its morbidity and mortality remain high  [30,31]. Both studies found that hyperoside increases the apoptosis rate and the G0/G1 phase ratio; up-regulates caspase-3, Bax, nuclear factor B inhibitor (IκBα) expression; decreases M/G2/M phase cell ratio; and down-regulates NF-κB P65 and Bcl-2 protein expression [30,31]. However, in terms of toxicity, a lower dose of hyperoside is safe since it reduces kidney accumulation in vivo. Therefore, given its effectiveness against gastric cancer cells, 25 µg/mL hyperoside should be given priority in the treatment of this disease.

Effect on Other Cancers
Ovarian cancer has a very high mortality rate among gynaecological cancers and is a major threat to women's health. Xu et al. showed that hyperoside can up-regulate cleavedcaspase-3 and caspase-9, down-regulate Bcl-2, reduce the protein levels of p65 and p-IκB-α and suppress the migration and invasive abilities of SKOV3 cells. It can also inhibit the activation of the NF-κB signalling pathway and resist ovarian cancer. Pancreatic cancer is a tumour of the digestive system [32]. Xue et al. found that hyperoside exerts a high killing activity on PANCI cells by inducing a high level of perforin in NK cells [33]. Skin cancer is primarily diagnosed visually, but dermatoscopic analysis, biopsy and histopathology are needed for confirmation [119]. Kong et al. studied the effect of hyperoside on skin tumours induced by 7, 12 dimethylbenz(a)anthracene (DMBA)/12-Otetradecanoylphorbol-13-acetate (TPA) and found that hyperoside can reduce the phosphorylation of PI3K, AKT, mammalian target of rapamycin (mTOR) and AMPK [34].
Some animal experimental data are also worthy of our attention. A previous study found that the intragastric administration of hyperoside at 50 mg/kg/day to Sprague-Dawley rats significantly decreases (p < 0.01) the cerebral infarct volume ratio; significantly increases the activities of total antioxidant capacity (T-AOC) (p < 0.01), superoxide dismutase (SOD) (p < 0.01) and glutathione peroxidase (GSH-Px) (p < 0.05); and significantly decreases the content of malondialdehyde (MDA) (p < 0.01) [72]. Intragastric administration of hyperoside at 25 and 12.5 mg/kg to rats also increases cerebral blood flow in the cerebral cortex [120]. These results suggest that hyperoside exerts a protective effect on cerebral infarction in rats. Intraperitoneal injection of 50 and 100 mg/kg hyperoside increases the activity of lactate dehydrogenase in the brain tissues of mice to 147.7 ± 20.4 (p < 0.01) and 163.3 ± 34.2 (p < 0.01), respectively, and improves learning and memory disorders in the platform test [121]. However, the drug doses used in this study are too large and may affect the metabolism and kidney function of mice.  Some animal experimental data are also worthy of our attention. A previous study found that the intragastric administration of hyperoside at 50 mg/kg/day to Sprague-Dawley rats significantly decreases (p < 0.01) the cerebral infarct volume ratio; significantly increases the activities of total antioxidant capacity (T-AOC) (p < 0.01), superoxide dismutase (SOD) (p < 0.01) and glutathione peroxidase (GSH-Px) (p < 0.05); and significantly decreases the content of malondialdehyde (MDA) (p < 0.01) [72]. Intragastric administration of hyperoside at 25 and 12.5 mg/kg to rats also increases cerebral blood flow in the cerebral cortex [120]. These results suggest that hyperoside exerts a protective effect on cerebral infarction in rats. Intraperitoneal injection of 50 and 100 mg/kg hyperoside increases the activity of lactate dehydrogenase in the brain tissues of mice to 147.7 ± 20.4 (p < 0.01) and 163.3 ± 34.2 (p < 0.01), respectively, and improves learning and memory disorders in the platform test [121]. However, the drug doses used in this study are too large and may affect the metabolism and kidney function of mice.

Neuroprotective Effect
Nervous system diseases occur in the central nervous system, peripheral nervous system and vegetative nervous system, with sensory, motor, consciousness and vegetative nervous system dysfunctions as the main manifestations of disease. Nervous system diseases include depression, epilepsy, Huntington's disease, neurodegenerative diseases, and so on. Hyperoside exerts its anti-depressant effects possibly through the serotoninergic system, monoaminergic system and BDNF up-regulation [38,46]. In contrast, it

Neuroprotective Effect
Nervous system diseases occur in the central nervous system, peripheral nervous system and vegetative nervous system, with sensory, motor, consciousness and vegetative nervous system dysfunctions as the main manifestations of disease. Nervous system diseases include depression, epilepsy, Huntington's disease, neurodegenerative diseases, and so on. Hyperoside exerts its anti-depressant effects possibly through the serotoninergic system, monoaminergic system and BDNF up-regulation [38,46]. In contrast, it exerts its anti-epileptic effect by increasing the antioxidant level and reducing the levels of autophagy-related proteins through the PI3K/AKT and MAPK pathways [39]. Systemic degenerative diseases, including Alzheimer's disease and Parkinson's disease (PD), are primary degenerative diseases of the central nervous system caused by the deposition of extracellular β-amyloid protein (amyloid-β, Aβ). Liu et al. showed that hyperoside dose-dependently up-regulates zonula occludens-1 (ZO-1), occludin and claudin-5 and down-regulates MMP (matrix metalloproteinase)-2 and MMP-9 to protect the damaged or weakened blood-brain barrier (BBB) [45]. However, the pathogenesis of Alzheimer's disease is diverse. Damaged or weakened BBB protection is only one mechanism in the pathogenesis of Alzheimer's disease, and the authors only studied the mechanism in vitro. Therefore, more research is required on the specific effects of hyperoside on Alzheimer's disease in vivo and its other pathogenetic pathways to enrich this field. Previous studies found that hyperoside can reduce the expression of caspase3, Cyc and Bcl-2, induce HO-1 activation of Nrf2 and inhibit 6-hydroxydopamine (6-OHDA)-induced oxidative stress to prevent and treat Parkinson's disease [41,44]. Kwon et al. were the first to study the neuroprotective effect of hyperoside on 6-OHDA-induced neurotoxicity and its possible mechanism. This study promotes the application of hyperoside in the treatment of diseases related to Parkinson's disease. Hyperoside can also reduce neuroinflammation, cognitive impairment and oxidative stress in type 2 diabetic rats through the tumour necrosis factor-α (TNF-α)/NF-κB/caspase-3 signalling pathway, activate the SIRT1 gene and inhibit the nuclear factor-kappa-gene binding (NF-κB) gene to protect human neuroblastoma cells (SH-SY5Y) from oxidative damage [37,40]. Furthermore, hyperoside can protect the nerves of mice from cerebral ischemia-reperfusion injury. Intragastric administration of 50 mg/kg hyperoside increases the expression of ZO-1 and Claudin5 protein in mice [35]. In addition, intragastric administration of hyperoside to rats exerts significant anti-depressant-like effects (1.8 mg/kg/day p.o.) (p < 0.05) [122]. For example, intraperitoneal injection of hyperoside 1 mg/kg and 10 mg/kg shortened the immobile time of rats to 78.92 ± 3.32 and 69.33 ± 4.7 s (p < 0.05) and increased sucrose consumption by 103% ± 7.22% and 128% ± 11.1%, respectively (p < 0.01) [123]. Treatment with hyperoside (0.6 mg/kg/day) for 2 weeks significantly reduces plasma adrenocorticotropic hormone and corticosterone levels by 40%-70% [124]. However, current research on hyperoside still faces several problems. For example, the research on the prevention and treatment of neurological diseases by using hyperoside is still in the experimental stage, and few clinical studies have been conducted. A consensus on a safe and effective dose of hyperoside for the human body has yet to be reached, and the clinical efficacy of the treatment is affected by many factors. Therefore, the clinical value and effective concentration of hyperoside needs to be explored and studied further. In addition, Huntington's disease is a neurological disease, but scholars have yet to study whether hyperoside exerts a therapeutic effect on this disease. The mechanisms by which hyperoside exerts nerve protection are shown in Figure 4.

Cardioprotective Activity
Cardiovascular diseases, including myocardial hypertrophy, atrial fibrillation, heart failure and myocardial ischaemia-reperfusion, are commonly caused by abnormal heart function or structural defects. Hyperoside blocks the AKT pathway, which reduces the protein expression of B-type natriuretic peptide and β-myosin heavy chain by angiotensin II (Ang II) or enhances SIRT3 signal expression to improve cardiac hypertrophy [55,59].

Cardioprotective Activity
Cardiovascular diseases, including myocardial hypertrophy, atrial fibrillation, heart failure and myocardial ischaemia-reperfusion, are commonly caused by abnormal heart function or structural defects. Hyperoside blocks the AKT pathway, which reduces the protein expression of B-type natriuretic peptide and β-myosin heavy chain by angiotensin II (Ang II) or enhances SIRT3 signal expression to improve cardiac hypertrophy [55,59]. Hyperoside also protects against myocardial ischaemia and reperfusion. The activated related pathways are protein kinase 1 (PKC)/mitochondrial ATP channel (mitoKATP) and AMPK/mTOR, and the affected proteins are gap junction protein 43 (Cx43), inwardlyrectifying potassium channel 2.1 (Kir2.1) and calmodulin kinase II (CaMKII), which also affects the activity of myocardial ATPase [47,50,54,56]. In addition, myocardial infarction in mice and heart failure in rats are related to the regulation of autophagy [53,57,60], and myocardial infarction is also related to the nucleotide binding oligomerization domain like receptor 1 (NLRP1) inflammatory pathway [60]. Hyperoside protects the myocardium of severely burned rats by regulating inflammation and oxidative stress and activating the SIRT1 signalling pathway [51]. At the same time, hyperoside can treat sepsis-related cardiac dysfunction by inducing the hypoxia-inducible factor-1α (HIF-1α)/HO-1 signalling pathway or inhibiting microRNA-21 (miR-21) [52,61]. Up-regulation of microRNA-138 (miR-138) can protect cardiomyocytes induced by hypoxia [58]. Hyperoside also protects the myocardial damage caused by diabetes and high glucose [48,49]. The mechanisms of cardioprotective activity are presented in Figure 5. Other research has shown that gavage of hyperoside (20 mg/kg/day) increases the left ventricular ejection fraction to 40.8% ± 5.1%, increases dp/dt max to 8735.4 ± 478.4 mmHg/s and decreases dp/dt min to −7902.3 ± 369.3 mmHg/s. It also decreases heart size and cardiomyocyte cross-sectional area [59]. Intraperitoneal injection of 50 mg/kg hyperoside decreases the infarct size in rats from 48.35 ± 6.74 to 23.61 ± 4.29 (p < 0.01) [125]. Hyperoside can ameliorate heart failure induced by thoracic aortic coarctation in rats and reduce myocardial cell cross-sectional area and heart weight/body weight ratio [57]. These studies suggest that hyperoside prevents stress overload-induced cardiac remodelling, alleviates myocardial ischemia-reperfusion injury and prevents heart failure, among others. However, whether hyperoside affects atrial fibrillation has not been studied. infarct size in rats from 48.35 ± 6.74 to 23.61 ± 4.29 (p < 0.01) [125]. Hyperoside can ameliorate heart failure induced by thoracic aortic coarctation in rats and reduce myocardial cell cross-sectional area and heart weight/body weight ratio [57]. These studies suggest that hyperoside prevents stress overload-induced cardiac remodelling, alleviates myocardial ischemia-reperfusion injury and prevents heart failure, among others. However, whether hyperoside affects atrial fibrillation has not been studied.

Hepatoprotective Activity
Liver-related diseases include fibrosis, non-alcoholic fatty liver disease, and so on. Hyperoside can activate the Nrf2 gene to protect the acute liver injury induced by N-acetyl-para-amino-phenol [64]. Hyperoside also exerts a protective effect on acute liver injury induced by CCl4 via two mechanisms. One is to increase the Nrf2 level by increasing extracellular signal-regulated protein kinase 1/2 (ERK1/2)-chromosomal region maintenance

Hepatoprotective Activity
Liver-related diseases include fibrosis, non-alcoholic fatty liver disease, and so on. Hyperoside can activate the Nrf2 gene to protect the acute liver injury induced by N-acetylpara-amino-phenol [64]. Hyperoside also exerts a protective effect on acute liver injury induced by CCl4 via two mechanisms. One is to increase the Nrf2 level by increasing extracellular signal-regulated protein kinase 1/2 (ERK1/2)-chromosomal region maintenance 1 (Crm1), thereby protecting the liver from injury induced by CCl4 [62]. The other is to regulate the pleckstrin homology domain leucine-rich repeat protein phosphatase 2 (PHLPP2)-AKT-GSK-3β signalling pathway and reverse the decrease in SOD activity in the body [67]. At the same time, the factor member 1 of nuclear receptor subfamily group 4A (Nr4A1) related to Nrf2 is linked to the prevention of non-alcoholic fatty liver disease by hyperoside [66]. Hyperoside exerts a hepatoprotective effect on diabetic mice, rats with liver fibrosis caused by heart failure and rats with hepatic ischaemia-reperfusion injury [63,65,68]. In rats, hyperoside (15 and 60 mg/kg) induces the reversal of serum alanine aminotransferase and aspartate transaminase levels and protects liver tissue from CCl4-induced injury [126]. Intraperitoneal injection of hyperoside (50 mg/kg/day) decreases the Suzuki score of the liver from 6.0 ± 0.9 to 5.0 ± 0.5 (p < 0.05) and histological damage [65]. In addition, gavage of 100 and 200 mg/kg hyperoside improves vacuolar oedema and degeneration of liver cells and inhibits alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase levels in rats [63]. These results reflect the protective effect of hyperoside on the liver, though there is a need for researchers to study the effect of hyperoside on alcoholic fatty liver disease.

Renal Protective Activity
Kidney disease has risen from the 13th to the 10th leading cause of death worldwide. The death rate increased from 813,000 in 2000 to 1.3 million in 2019 (https://www.who. int/cancer) (accessed on 10 January 2022). Hyperoside can improve diabetic nephropathy by targeting the miR-499-5p/APC axis and inhibiting the extracellular regulated kinase (ERK)/cAMP-response element binding protein (CREB)/miRNA-34a signalling pathway [79,80]. It can also treat acute kidney injury by regulating mitochondrial fission mediated by metalloproteinase-associated protein 1 (OMA1)-optic atrophy 1 and inhibiting TLR4 and nucleotide binding oligomerisation domain-like receptorprotein3 (NLRP3) pathways [74,78]. Liu et al. reported that hyperoside can inhibit autophagy through the AMPK-unc-51 like autophagy activated kinase 1 (ULK1) signalling pathway to prevent age-related renal injury, and provided the first opportunity for hyperoside to treat Dgalactose-induced renal aging and damage [77]. In addition to the above three aspects, hyperoside can also improve the endogenous antioxidant and detoxification functions of kidney cells through the Nrf2/HO-1/quinone oxidoreductase 1 (NQO1) pathway [76]. Intragastric administration of hyperoside and quercetin (20 mg/kg/day) at a ratio of 1:1 can reduce the severity of renal crystal deposition (p < 0.05) [127] and reduce urinary citrate excretion to 48.38 ± 22.82 mg/24 h [127]. This finding suggests that hyperoside prevents calculi in rats. A mixture of quercetin and hyperoside (0.1 mg/kg/day) (1:1) was administered intragastrically to rats to reduce the expression of fibrosis-related proteins in obstructed kidneys [128], thereby protecting the kidney. Interestingly, although both experiments proved that hyperoside and quercetin (1:1) exert a protective effect on kidney diseases, the difference in dose gap is very large; thus, the accurate dosage could be explored in the future to provide a preliminary basis for clinical trials.

Others
Firstly, hyperoside can protect blood vessels. Hyperoside can reduce the production rate of ArgII by competing for active sites, changing the surface hydrophobicity of the enzyme, decreasing the vascular tone and inhibiting vascular remodelling, thereby lowering blood pressure [86]. Liu et al. used network pharmacology to elucidate the mechanism of anti-atherosclerosis treatment, which may be mainly related to the PI3K/AKT and MAPK signalling pathways [129]. Other researchers have demonstrated that hyperoside can regulate vascular endothelial cells by reducing low-density lipoprotein-C level, affecting nitric oxide synthase (NOS) activity, regulating NO synthesis, improving vascular endothelial function and reducing p38 MAPK, Jun N-terminal kinase (JNK), ERK, NF-κB and TNF receptor 1 (TNFR1) levels to inhibit vascular inflammation and affect atherosclerosis [85,87]. By contrast, Wang et al. found that hyperoside cannot reduce blood lipids in mice and cannot inhibit the formation of aortic atherosclerotic plaques [130]. Secondly, hyperoside also exhibits lung-protective functions. Hyperoside protects bleomycin-induced pulmonary fibrosis through the AKT/GSK3β pathway and inhibits collagen secretion [81,83]. It also inhibits AMPK/mTOR signalling to reduce particulate-induced lung injury [82], and can be used to treat Mycoplasma pneumoniae pneumonia (MPP) via the interaction of chemokine ligand 5 (CCL5)-CC chemokine receptor 4 (CCR4) [84]. Thirdly, hyperoside has a function in ovarian protection. The protection of hyperoside in ovarian-related diseases is related to SHH signalling pathway, the PI3K/AKT anti-apoptotic pathway and Nrf-2/HO-1 antioxidative stress [97,98]. Fourth, hyperoside has an anti-inflammatory effect [96,102]. This anti-inflammatory effect is related to the miR-499a-5p/nuclear receptor interaction protein 1 (NRIP1) axis, regulation of the p38MAPK/Sirt6/NF-κB signalling pathway and inhibition of the TLR4/NF-κB pathway [99,103,104]. Hyperoside (100 mg/kg, i.p. (p < 0.05) and 200, 500 mg/kg, p.o. (p < 0.01)) significantly inhibits acetic acid-induced vascular permeability in mice [131]. In addition, 100 mg/kg hyperoside significantly decreases serum prostaglandin E2 (PGE2), TNF-α, IL-1β, c-reactive protein (CRP), myeloperoxidase (MPO) and MDA levels (p < 0.01) and significantly increases SOD activity in mice (p < 0.01) [132]. Haematoxylin and eosin results proved the effect of hyperoside on ulcerative colitis, suggesting that hyperoside demonstrates good anti-inflammatory activity. Intragastric administration of 100 mg/kg hyperoside in rats significantly reverses the upregulation of N-methyl-d-aspartic acid (NMDA) receptor containing n-methyl-d-aspartate receptor 2B (NR2B) in the midbrain periaqueductal grey and shows analgesic activity against continuous inflammatory stimulation in mice [133]. Hyperoside can also prevent age-related macular degeneration and protect against diabetic retinopathy [100,101]. It also has antioxidant activity [134][135][136][137]. Wang Mengyu reported that the antioxidant activity of hyperoside is related to the 3-position hydroxyl group of hyperoside [138]. Hyperoside can also protect the pancreas, fight fatigue and enhance NK cell proliferation [105,107,108]. In addition, hyperoside regulates the mTOR/S6K and TLR4/myeloid differentiation factor 88/NF-κB signalling pathways to reduce recurrent pregnancy loss and anterior cruciate ligament injury [109,110]. Pan Shanshan used a multi-omics strategy to demonstrate that hyperoside can regulate the metabolism of high-fat mice by changing the abundance of intestinal flora and down-regulating the expression of Cypla2 and Ugtla6b [137].

Pharmacokinetics
Hyperoside has a wide range of pharmacological effects and pharmacokinetic characteristics, such as easy accumulation in the viscera and kidneys, low oral bioavailability and compatibility with different drugs that prolong its elimination time in the body. The pharmacokinetics of hyperoside will be discussed in detail below. Ni et al. found that the extraction of hyperoside impurities from dodder seed by using ethyl acetate has minimal interference, high recovery and stability, and that using icariin as an internal standard could reduce errors in sample handling and injection; in addition, the hyperoside curve shows the main and secondary peaks [139]. Another scholar reported that the Cmax in rats intragastrically administered with Qianbai rhinitis capsules was 1.25 times that of rats treated with Senecio extract [140]. This result shows that hyperoside is compatible with other traditional Chinese medicines and they can improve its bioavailability and oral absorption. Chen et al. also found that t 1/2 , T max and AUC 0-∞ are significantly prolonged after hyperoside is combined with other Chinese medicines, indicating that they can slow down the elimination of hyperoside in vivo, prolong the action time, promote its absorption and significantly improve bioavailability. They also found the highest accumulation of hyperoside occurred in the kidney, followed by the liver and lastly in the testes [141]. Chen Shanshan also studied the pharmacokinetics of hyperoside when administered multiple times and showed that this treatment improves C max , T max , AUC Chen Shanshan also studied the pharmacokinetics of hyperoside when administered multiple times and showed that this treatment improves Cmax, Tmax, AUC(0-T), AUC(0ꝏ ) and MRT [142]. Yuan et al. studied the effects of different administration methods in rats and found that the plasma levels from intraperitoneally administered hyperoside are closer to those of intravenously administered hyperoside than to those of intragastrically administered hyperoside; in addition, the bioavailability of hyperoside in rats is particularly low after intragastric administration [143]. These results indicate that intraperitoneal and intravenous injections are effective ways of administration. The pharmacokinetic profile of hyperoside is presented in Table 12. Cuscuta chinensis wa-) and MRT [142]. Yuan et al. studied the effects of different administration methods in rats and found that the plasma levels from intraperitoneally administered hyperoside are closer to those of intravenously administered hyperoside than to those of intragastrically administered hyperoside; in addition, the bioavailability of hyperoside in rats is particularly low after intragastric administration [143]. These results indicate that intraperitoneal and intravenous injections are effective ways of administration. The pharmacokinetic profile of hyperoside is presented in Table 12. nshan also studied the pharmacokinetics of hyperoside when administered muls and showed that this treatment improves Cmax, Tmax, AUC(0-T), AUC(0-ꝏ ) and ]. Yuan et al. studied the effects of different administration methods in rats and t the plasma levels from intraperitoneally administered hyperoside are closer to ntravenously administered hyperoside than to those of intragastrically adminiseroside; in addition, the bioavailability of hyperoside in rats is particularly low gastric administration [143]. These results indicate that intraperitoneal and ininjections are effective ways of administration. The pharmacokinetic profile of e is presented in Table 12. Notes: i.p., intraperitoneal injection; i.g., gavage; i.v., tail intravenous injection; ND, not determined.

Toxicity
Hyperoside has many pharmacological effects, including significant renal protection. Previous pharmacokinetic studies indicated that hyperoside accumulates in the kidney. However, studies on the toxicity of hyperoside are very few. So far, only one team has studied the toxicity of hyperoside, and only animals were used in their studies. Firstly, an acute toxicity test of hyperoside showed that its LD50 > 5000 mg/kg [145]. Secondly, a bacterial reverse mutation assay (Ames test) indicated that hyperoside has no genetic toxicity [145]. An experiment on rat embryo and foetal developmental showed that this compound exerts negligible effects on pregnant rats but slows down the growth of foetal rats [146]. Thirdly, long-term use of hyperoside is toxic to the kidneys, but the damage is reversible [147]. However, research on the toxicity of hyperoside is not comprehensive, and a cellular experiments that verify whether or not hyperoside is cytotoxic remain to be conducted. Therefore, experiments must be conducted in the future to evaluate the biological safety of hyperoside and provide a basis for its future clinical applications.

Conclusions and Perspective
At present, many studies have shown that hyperoside can be found in Hypericaceae, Rosaceae and Polygonaceae plants. However, the plant family with the highest abundance of hyperoside cannot be determined because of the different measurement conditions used. Hyperoside has anti-cancer, brain-protective, neuroprotective, cardioprotective and renal-protective activities, among others. However, most scholars have only studied classic signalling pathways, such as PI3K/AKT and NF-κB, and few scholars have studied other pathways. In the future, scholars could concentrate on different pathways to study the effects of hyperoside on target diseases to promote the advancement of medicine worldwide. At present, few studies have explored the pharmacokinetics, especially the excretion, of hyperoside. However, by consulting the existing literature on the pharmacokinetics of hyperoside, we can conclude that the drug-time curve after oral administration of hyperoside in rats shows bimodal absorption. This phenomenon may be related to hepatoenteric circulation or absorption by dual parts of the intestine, though these conjectures have not been confirmed by researchers. Studies have also shown that the bioavailability of orally administered hyperoside is lower than that of intraperitoneally injected hyperoside, which may be related to the first-pass metabolism of hyperoside and the physical properties of flavonoids (hydrophobicity). In response, researchers have developed hyperosidezein/pectin composite nanoparticles and hyperoside-loaded zein-tea polyphenols-pectin ternary complex nanoparticles to slow the release of hyperoside [14,15]. This system improves the bioavailability of hyperoside. In addition, other scholars have found that combining hyperoside with other drugs can slow down its elimination in the body and prolong its action time, thereby increasing its bioavailability. Hyperoside is also used to treat chronic diseases, such as atherosclerosis, but its safety remains to be verified. As a result, the clinical application of hyperoside is limited. In short, the research on the pharmacology and pharmacokinetics of hyperoside is insufficient, which directly restricts further therapeutic development of hyperoside. This review has summarised the pharmacology and pharmacokinetics of hyperoside and raised some issues worthy of future discussion to promote the application and development of hyperoside in the future.
Author Contributions: H.S. and X.F. reviewed and revised the manuscripts. W.X. participated in the revision of the manuscript. S.X. and S.C. collected the documents and wrote the paper. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest:
The authors declare no potential conflict of interest concerning this article's research, authorship, and publication.