Active Components and Pharmacological Effects of Cornus officinalis: Literature Review

Cornus officinalis Sieb. et Zucc. (Shanzhuyu), a herb and food plant in east Asia, has the properties of tonifying the liver and kidney, and nourishing the essence according to the theory of traditional Chinese medicine. C. officinalis has been commonly used to treat asthenia diseases, liver, and kidney diseases, and reproductive system diseases since ancient times. The objectives of this article were to review the pharmacological effects and phytochemistry of C. officinalis. We conducted a literature review of the pharmacological effects of C. officinalis by different systems and compared the effects with the traditional usages, discussed the research status and potential blanks to be filled. The experimental studies showed that C. officinalis extract and its active components had various pharmacological effects such as anti-oxidation, anti-apoptosis, anti-inflammation, anti-diabetes, anti-osteoporosis, immunoregulation, neuroprotection, and cardiovascular protection, but clinical studies are still needed to assess whether the reported pharmacological activities have confirmed efficacy.


INTRODUCTION
Cornus officinalis Sieb. et Zucc. (Shanzhuyu) is a herb and food plant used in traditional Chinese medicine (TCM). C. officinalis has a sour and astringent taste (Liu et al., 2011). In the theory of TCM, C. officinalis belongs to the liver and kidney meridians and has a mild warm nature. It is often used to tonify the liver and kidney, and arrest the loss of essence (Di et al., 2018). Because of its excellent tonic effect, C. officinalis has been commonly used to treat asthenia, liver, and kidney diseases, and reproductive system diseases since ancient times. Pharmacological studies have found that C. officinalis extract has a variety of biological activities such as antiinflammatory, anti-oxidative, anti-apoptotic, anti-diabetic, neuroprotective, and cardiovascular protective activities. There are links and differences between these biological effects and the traditional usages of C. officinalis. (Czerwinska and Melzig, 2018) suggested that different cultural needs resulting from the different geographical distributions of the medicinal herbs could influence the research directions and results. Therefore, a literature review that combines the results of modern pharmacological research with the TCM theories has a certain value. The extract of C. officinalis is a collection of one or several groups of phytochemicals. Unlike single active components, the extract of herbal plant maintains the TCM characteristics of complex components and multiple targets (Liu et al., 2020a). The objectives of this article were to review the pharmacological effects of the extract and active components of C. officinalis separately according to published studies, and discuss the potential blanks to be filled.
Studies on C. officinalis published before December 2020 were gathered by searching the online databases (PubMed, Web of Science and Baidu Scholar) using the keyword "Cornus officinalis" and "Shanzhuyu" (Chinese pinyin of C. officinalis).

PHARMACOLOGICAL EFFECTS OF C. OFFICINALIS EXTRACT Diabetes
In TCM point of view, C. officinalis has the effects of restraining essence loss and reducing urination, and is often used together with Radix Rehmanniae (Dihuang). C. officinalis has been used to treat symptoms such as thirst, frequent urination, and "drink more, urinate more" since ancient times, and these symptoms nowadays are known as some typical symptoms of diabetes mellitus (DM) (Di et al., 2018). Pharmacological studies have found that C. officinalis extract has a significant hypoglycemic effect. (Park et al., 2011a) found that C. officinalis extract had an α-glucosidase inhibitory activity, and that it could improve oral sucrose tolerance and inhibit plasma glucose level increase in normal rats. (He, 2011) suggested that the hypoglycemic effect of C. officinalis was attributable to its total iridoid glycosides. They compared the total iridoid glycosides and the α-glucosidase inhibitory effects of crude and wine-processed C. officinalis. The results showed that the content of total iridoid glycosides of the crude C. officinalis was higher than that of the wineprocessed C. officinalis (75.3 vs. 42.8%), and the α-glucosidase inhibitory effect of the crude C. officinalis was superior to that of the wine-processed C. officinalis, which confirmed their hypothesis.
C. officinalis extract has also been demonstrated to promote glucose uptake of cells. (Lau et al., 2008) found that aqueous extract of C. officinalis could stimulate glucose uptake of human skin fibroblasts Hs68 cells and mice adipose 3T3-L1 cells in vitro, but had no significant effects on glucose absorption of intestinal brush border membrane vesicles (BBMV). (Qian et al., 2001) found that ethanol extract of C. officinalis could increase the protein and mRNA expression of glucose transporter 4 (GLUT4) in skeletal muscle of DM rats induced by streptozotocin (STZ) and promote the transmembrane transport of glucose.
Gluconeogenesis is the major source of glucose output of the liver (Hatting et al., 2018). The effect of C. officinalis extract on hepatic gluconeogenesis remains controversial. Phosphoenolpyruvate carboxykinase (PEPCK) is a gluconeogenic rate-limiting enzyme. (Chen et al., 2008) found that phenolic compounds in the methanol extract of C. officinalis could up-regulate the gene expression of PEPCK and inhibit hepatic gluconeogenesis. However, the research of (Lau et al., 2008) suggested that C. officinalis extract had no significant effect on hepatic gluconeogenesis.
Insulin is the only hypoglycemic hormone in the human body, which can inhibit hepatic gluconeogenesis and glycogen decomposition, promote cell glucose uptake, and is important for maintaining normal glycolipid metabolism (Hatting et al., 2018). Insulin deficiency or insulin resistance is the direct cause of DM. In patients or model animals with type 2 diabetes, insulin resistance abnormally increases serum insulin levels (Jia et al., 2016). The research of (Liu et al., 2012a) showed that total saponins in C. officinalis extract reduced the blood glucose and insulin levels in STZ-induced diabetic rats. C. officinalis has been demonstrated to have islet β-cell protection effect, it can improve the pathological damage of the pancreas, increase the number of insulin releasing β-cells, and increase glucosestimulated insulin secretion . (Sharp-Tawfik et al., 2019) found that C. officinalis extract could inhibit cytokine-mediated β-cell death and improve β-cell function via up-regulating the expression of nuclear factor of activated T cells, cytoplasmic 2 (NFATC2).
As discussed above, the main components of C. officinalis that play a role in reducing blood glucose are iridoid glycosides, polyphenols, and saponins. C. officinalis extract reduces the absorption of glucose by small intestinal chorionic epithelial cells by inhibiting the activity of α-glucosidase; on the other hand, it promotes glucose uptake and utilization by promoting insulin secretion and improving insulin sensitivity of peripheral tissues, and inhibits gluconeogenesis.
In addition, C. officinalis extract can also decrease blood lipid levels, and it showed the effects of reducing the levels of total cholesterol (TC), triglycerides (TG), and low-density lipoprotein (LDL) of STZ-induced diabetic rats, and marginally increasing high-density lipoprotein (HDL) (Gao et al., 2012).

Diabetic Complications
The combination of advanced glycosylation end products (AGEs) and AGE-receptor (RAGE) can cause the activation of endothelin (ET) system (Adamopoulos et al., 2016) and inducible nitric oxide synthase (iNOS) (Tang et al., 2016), and the accumulation of reactive oxygen species (ROS) (Koulis et al., 2015). This will impair vasodilation function and lead to microvascular and macrovascular complications. (Su et al., 2007) found that total triterpene acids isolated from C. officinalis could down-regulate mRNA expression of prepro-endothelin-1 (ppET-1), endothelinconverting enzyme (ECE) and iNOS in thoracic aorta and mRNA expression of ET A receptor and iNOS in retina in diabetic rats. It increased acetyl choline (Ach)-mediated vasodilatation and nitric oxide (NO) bioavailability, and ultimately improved vasodilation function. (Liu et al., 2012b) found that total saponins of C. officinalis could decrease the contractile responsiveness to phenylephrine of the mesenteric artery rings isolated from STZ-induced diabetic rats, increase the diastolic reaction to Ach, and improve the baseline release of NO of the mesenteric artery.
It can be seen from the above that the triterpene acids and saponins from C. officinalis improve the vascular complications of DM mainly by regulating the vasodilation function. Since C. officinalis has specific kidney and liver protective effects, the therapeutic effect on diabetic nephropathy (DN) and DM liver injury are discussed separately in the following sections.

Diabetic Nephropathy
The results of experimental studies on DN showed that AGEs/ RAGE signaling pathway in diabetic complications could be regulated by C. officinalis. (Yamabe et al., 2007a;Yamabe et al., 2007b) found that the iridoid glycosides and low molecular weight polyphenols extracted form C. officinalis could reduce the urine protein and serum creatinine (Scr) levels of STZ-induced DM rats by decreasing the levels of AGEs, RAGE, nuclear factor kappa-B (NF-κB), and transforming growth factor-β (TGF-β) in the kidney tissue. The research of (Lv et al., 2016a) showed that the iridoid glycosides and triterpenoid acid in C. officinalis decreased the levels of 24 h urine protein, blood urea nitrogen (BUN), and Scr in db/db mice by down-regulating the activities of AGEs/RAGE/ SphK1 pathway and TGF-β.
The research of (Qi et al., 2014) showed that although total triterpene acids of C. officinalis had no significant effect on blood glucose of DM rats, they could reduce urinary protein, Scr, and BUN levels, and improve renal pathological changes. They found that total triterpene acids of C. officinalis down-regulated malondialdehyde (MDA) level, up-regulated superoxide dismutase (SOD), catalase (CAT), and glutathione peroxide (GSH-px) activities; and decreased TGF-β1 expression in renal tissues of DM rats. The results indicated that total triterpene acids of C. officinalis could improve the diabetic kidney injury by antioxidant effect rather than hypoglycemic effect.
Peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors and plays important roles in the regulation of glycolipid metabolism and insulin sensitivity. PPARγ agonist ligands can down-regulate the expression or activity of nicotinamide adenine dinucleotide (NAD) oxidase. PPARγ activators, such as rosiglitazone, are widely used in the treatment of type 2 DM (Ahsan, 2019). The research of (Gao et al., 2012) found that the ethanol extract of C. officinalis could elevate renal PPARγ expression in DM rats and improve the kidney injury caused by oxidative stress.
C. officinalis extract has protective effects on intrinsic renal cells. (Liu et al., 2012a) found that C. officinalis extract could increase the glomeruli expression of podocyte-specific marker Wilms tumor type 1 (WT1) in STZ-induced DM rats, indicating a capacity to protect the podocytes. The in vitro research of (Ma et al., 2014) showed that C. officinalis extract could inhibit the expressions of collagen IV (Col V), fibronectin (FN), and Interleukin-6 (IL-6) in high glucose induced HBZY-1 mesangial cells, revealing a protective effect of C. officinalis extract on the mesangial cells, and reducing the accumulation of mesangial matrix.
C. officinalis extract can also relieve DN renal fibrosis. The research of (Xu and Hao, 2004) showed that total iridoid glycosides extracted from C. officinalis could decrease serum TGF-β1 level and renal TGF-β1 mRNA expression and suppress the overdeposition of FN and laminin (LN). The research of  showed that C. officinalis extract could inhibit the expression of fibroblast marker protein alphasmooth muscle actin (α-SMA) in the kidney tissues of DN rats.
Our review of the literature showed that iridoid glycosides, low molecular weight polyphenols, and triterpene acids in C. officinalis had anti-inflammatory, anti-oxidative, anti-apoptotic and anti-fibrosis effects by regulating the AGEs/RAGE, NF-κB/ TGF-β, and PPARγ signaling pathways, thereby alleviating the injury of the intrinsic renal cells.
C. officinalis has also been demonstrated to prevent acute liver injury.  pretreated BALB/c mice with the ethanol extract of C. officinalis orally for seven consecutive days before acute liver injury was induced in experimental mice by intraperitoneal (i.p) injection of 200 mg/kg acetaminophen (APAP). The results showed that C. officinalis extract reduced serum AST, ALT, LDH, and MDA levels, elevated the levels of antioxidant enzyme SOD, CAT, and GSH, indicating that C. officinalis improved APAP-induced acute liver injury by preventing or alleviating oxidative stress.

Diseases of the Nervous System
According to the theory of TCM, the brain is born from the essence of the kidney. Therefore, the deficiency of kidney essence will lead to insufficiency of the brain and the symptoms of amnesia, dementia, and hemiplegia, which are the manifestations of central nervous system diseases in modern medicine. Experimental studies have confirmed that C. officinalis has therapeutic effects on neurodegenerative diseases such as Alzheimer's disease (AD) and depression. Glutamate can cause neuronal cell death and neurodegenerative diseases through ROS-mediated oxidative glutamate toxicity (Cassano et al., 2016). The study of (Jeong et al., 2012) indicated that the iridoid glycosides of C. officinalis had a significant protective effect against glutamate-induced toxicity in the hippocampal cells. The death of the cholinergic neurons in the basal forebrain area is considered to be one of the main causes of cognitive disorders, including AD. The study of (Lee et al., 2009) found that the methanol extract of C. officinalis and its main component, loganin, alleviated the memory loss in mice with amnesia induced by scopolamine, an anticholinergic drug. (Bhakta et al., 2017) found that several compounds isolated from C. officinalis could interact with both the catalytic active sites and the peripheral anionic sites of cholinesterase (ChEs) and the beta-site of amyloid Frontiers in Pharmacology | www.frontiersin.org April 2021 | Volume 12 | Article 633447 precursor protein cleaving enzyme 1 (BACE1), leading to the inhibition of the activities of ChEs and BACE1. So far, two major pathological lesions have been found in the brains of AD patients, amyloid plaques composed of amyloid-β (Aβ) peptides, and neurofibrillary tangles (NFTs) caused by hyperphosphorylated tau protein. Tau is an important structural protein of neurons, tauopathies are well known to impair the transmission of nerve impulses (Naseri et al., 2019). The study of (Yang et al., 2020) used the APP/PS1/tau triple transgenic(3 × Tg) mice as the rodent model of AD, and they found that the iridoid glycoside extracted from C. officinalis could ameliorate learning and memory impairment of 3 × Tg mice by down-regulating the expressions of Aβ and full-length amyloid precursor protein, as well as decreasing the hyperphosphorylation of tau protein.  got the similar results that the iridoid glycoside of C. officinalis could reduce the hyperphosphorylation and aggregation of tau protein in amygdala and prevent neuronal loss, and suppressed hyperactivity phenotype of AD.
PC12 cells, derived from the pheochromocytoma of the adrenal medulla in rats, have typical neuron characteristics and are widely used in studies of neurological diseases. Corticosterone-induced PC12 injury is considered an in vitro experimental model for depression (Tian et al., 2018). The study of (Ji et al., 2019) indicated that iridoid glycosides of C. officinalis could reduce corticosterone-induced PC12 cell damage in vitro. Oxidative stress plays an important role in neurodegenerative diseases, and stress often lead to excessive accumulation of ROS. Immobilization stress is widely used to induce depressive-like and anxiety-like behaviors and hippocampal neuronal damage in rodents . (Tian et al., 2019) utilized immobilization stress to investigate the protective effect of C. officinalis extract on nerve injury, and the results showed that C. officinalis effectively alleviated the oxidative stress, decreased immobility time in forced swim test (FST), and significantly reduced the levels of corticosterone and β-endorphin, and increased the level of serotonin, which indicated that apart from regulating the cholinergic signaling pathway, C. officinalis could also treat neurodegenerative diseases through antioxidant effects.
In addition, C. officinalis can also reduce the damage caused by cerebral infarction. (Li et al., 2005) found that the area of infarction was reduced in rats fed with C. officinalis extract for 7 days before cerebral infarction was induced, and the effect was related to the decrease in NOS and NF-κB activities.

Male Diseases and Female Menopause Syndrome
In TCM point of view, the functions of the reproductive system (including the gonads and reproductive organs) are regulated by the kidney, and the deficiency of kidney essence can cause spermatorrhea, impotence, irregular menstruation, and infertility. (Jeng et al., 1997) found that some fractions of the aqueous extract of C. officinalis could enhance the motility of human sperm in vitro. The study of (Kam et al., 2012) indicated that C. officinalis extract could improve erectile dysfunction (ED).
They investigated the relaxation effect of C. officinalis extract on the rabbit corpus cavernosum (CC) by an organ bath in vitro, and observed the effects on intracavernous pressure (ICP) and cyclic adenosine monophosphate (cAMP) in rats CC tissues after oral administration of the extract for a month. It was found that C. officinalis extract showed concentration-dependent relaxation effects on the CC in vitro, and significantly elevated the ICP and cAMP concentrations in vivo. (Jin et al., 2019) found that the combination of C. officinalis and Psoralea corylifolia inhibited testosterone-induced benign prostatic hyperplasia (BPH) in rats. (Chen et al., 2016) found that the iridoid glycosides of C. officinalis markedly protected against DM-induced testicular damage, increased the rate of live sperms, and upregulated the levels of testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH), and gonadotropin-releasing hormone (GnRH). Their study also showed that the iridoid glycosides of C. officinalis also had a considerable antioxidative and anti-apoptotic effects, which down-regulated the expressions of ROS and MDA, restored the activities of SOD and CAT, and decreased spermatogenic cell apoptosis and Bax/Bcl-2 ratio by inhibiting the activation of the AGEs/RAGE/p38 MAPK pathway.
In addition, C. officinalis extract has also been demonstratedto inhibit lipid accumulation in adipocytes, promote osteoblastic differentiation, and increase estradiol production and estrogen receptor α (ERα) mRNA expression in granulosa cells, and is used to treat obesity and osteoporosis caused by women's menopausal symptoms (Park et al., 2020a). The above results revealed the therapeutic effect of C. officinalis extract on reproductive system diseases at the functional level.

Cardiovascular Diseases
The treatment of cardiovascular diseases is not a traditional usage of C. officinalis, but some experimental studies revealed the cardiovascular protective effects of C. officinalis. (Qi et al., 2008) found that the total triterpene acids of C. officinalis could alleviate diabetic cardiomyopathy by suppressing the ET/ROS pathway. The results showed that the total triterpene acids of C. officinalis alleviated oxidative stress via downregulating ET-1 expression. It elevated the levels of calstabin, sarcoplasmic reticulum Ca 2+ ATPase 2a (SERCA2a), and phospholamban (PLB), and improved cardiac function. The research of (Fang et al., 2012) indicated that C. officinalis extract could alleviate cardiac hypertrophy. They induced vascular hypertension and cardiac hypertrophy in rats using the "two-kidney two-clip" (2K2C) method. The rats were given intragastric administration of C. officinalis extract from the fourth week after the surgery for 4 weeks. The results showed that C. officinalis extract reduced the increase in blood pressure caused by 2K2C, reversed the cardiomyocyte hypertrophy and myocardial fibrosis, and down-regulated the expression of p47 phox and NOX4 in the left ventricular.
Abnormal mitochondrial biogenesis of cardiomyocytes can lead to cardiac dysfunction. (Chen et al., 2015) found that total glycosides and polysaccharides of C. officinalis could improve the cardiac function in rats with acute myocardial infarction (AMI). they reduced the area of myocardial infarction, and promoted the Frontiers in Pharmacology | www.frontiersin.org April 2021 | Volume 12 | Article 633447 mitochondrial biogenesis of cardiomyocytes. Both total glycosides and polysaccharides of C. officinalis could increase the mRNA expressions of mitochondrial biogenesis-related genes in myocardial tissue, including genes encoding the subunits of peroxisome proliferators-activated receptor-γ coactivator (PGC)-1α, PGC-1β and nuclear respiratory factor (NRF-1). The polysaccharides of C. officinalis could also reduce glycogen synthase kinase-3β (GSK-3β) mRNA expression showing a mitochondrial protection effect.

Antiproliferative and Anticancer Activity
Anticancer treatment is not a traditional usage of C. officinalis. But in recent years, some experimental evidences have confirmed the anticancer effect of C. officinalis. The research of (Chang et al., 2004) indicated that the aqueous extract of C. officinalis could inhibit the proliferation of hepatocellular carcinoma cells (HCC) and significantly suppress the activities of free radicals, xanthine oxidase (XO), and lipid peroxidation in vitro.
The combination of selective ER modulators and chemotherapeutic agents is the conventional therapeutic intervention for ER-positive (ER+) breast cancer. The research of (Telang et al., 2012) showed that the aqueous extract of C. officinalis could inhibit the growth of ER+ breast cancer. They found that C. officinalis extract could inhibit 17β-estradiol (E2) -stimulated growth and anchorage-independent colony formation, which indicated an effective reduction of the carcinogenic risk via modulating C2-hydroxylation pathway of E2 metabolism and up-regulating the formation of antiproliferative metabolite 2-OHE 1 . Triple-negative breast cancer (TNBC) lacks the expression of ERα, progesterone receptor, and human epidermal growth factor receptor-2; and is resistant to conventional endocrine or HER-2 targeted therapy. (Telang et al., 2019) found in subsequent research that C. officinalis extract could induce cytostatic growth arrest in MDA-MB-231 cells, an in vitro model of TNBC, by inhibiting the G1 to S phase transition and decreasing the expression of cyclin D1 and phosphorylatedretinoblastoma proteins. Additionally, C. officinalis could promote the apoptosis of tumor cells by up-regulating proapoptotic caspase-3/7 activities.

Osteoporosis
In TCM point of view, the kidney dominates the formation of bone and marrow. The deficiency of the kidney essence can cause diseases of the bones and joints, such as osteoporosis and arthritis. The balance between osteoblasts and osteoclasts helps to maintains the stability of bone mass . The changes in hormone levels or the condition of inflammation can cause imbalance in bone homeostasis, and lead to osteoporosis and fracture.  isolated the bone marrow-derived macrophages (BMMs) from the long bones of male ICR mice, and they found that C. officinalis extract could decrease the mRNA expressions of the osteoclast-specific gene tartrate-resistant acid phosphatase (TRAP) and osteoclast-associated receptor (OSCAR), and inhibit the differentiation of BMMs to osteoclasts. The results of their research showed that C. officinalis extract down-regulated the expressions of c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1), and suppressed the activation of the upstream p38 mitogen-activated protein kinase (p38MAPK), and c-JUN N-terminal kinase (c-JNK) signaling pathways.
The research of (Park et al., 2020b) showed that the mixture of C. officinalis and Achyranthes japonica (Niuxi) significantly promoted osteoblast differentiation of MC3T3-E1 mouse preosteoblasts via up-regulating the expressions of osteoblastic differentiation-associated genes, such as alkaline phosphatase (Alpl), runt-related transcription factor 2 (Runx2), and bone gamma-carboxyglutamic acid-containing protein (Bglap). And on the other hand, the mixed extract also inhibited the differentiation of osteoclasts isolated from primary-cultured mouse monocytes. The above research indicated that C. officinalis has the ability to regulate osteoblasts and osteoclasts at the same time, which reflected the characteristic of two-ways regulation and homeostasis maintenance of TCM.2.10 Other diseases.
Since the anti-oxidative, anti-apoptotic, and other effects of C. officinalis extract have been confirmed (Hwang et al., 2016), some researchers have studied the therapeutic effects of C. officinalis in other diseases based on these functional characteristics in recent years. The skin is one of the largest organs of the human body and the most exposed to outdoor contaminants such as particulate matter <2.5 µm (PM 2.5 ). (Fernando et al., 2020) found that PM 2.5 induced ROS accumulation and oxidative stress, and eventually caused cellular apoptosis of human keratinocytes; while the ethanol extract of C. officinalis could down-regulate the excessively accumulated Ca 2+ in the mitochondria of keratinocytes via anti-oxidative effect and protect the skin against PM 2.5 -induced damage.
C. officinalis extract has been demonstrated to have an immunomodulatory effect. (Quah et al., 2020) found that the ethanol extract of C. officinalis could suppress the IgE-induced degranulation of rat basophilic leukemia cells(RBL-2H3) in vitro and had a potential alleviatory effect on allergic dermatitis. The results of their research also showed that loganin, cornuside, and naringenin 7-O-β-D-glucoside isolated from C. officinalis could potentially disrupt the binding of IgE to human high-affinity IgE receptors (FceRI) by molecular docking analysis. (Du et al., 2008) found that polysaccharides extracted from C. officinalis could notably improve the proliferation and transformation of spleen lymphocytes in cyclophosphamide-induced immunosuppressed mice and enhance non-specific immunity, specific humoral immunity, as well as specific cellular immunity, indicating that C. officinalis could be used as an adjuvant therapy to patients receiving immunosuppressive treatment.

PHARMACOLOGICAL EFFECTS OF C. OFFICINALIS ACTIVE COMPONENTS
The active components with specific pharmacological effects are the medicinal material basis for TCM therapeutic effects. The isolation and identification of the active components is conducive to understanding the mechanism of the TCM. The pharmacological effects of more than 20 phytochemicals isolated from C. officinalis have been confirmed through Frontiers in Pharmacology | www.frontiersin.org April 2021 | Volume 12 | Article 633447 Decrease serum TC; decrease renal lipid peroxidation and ROS levels; down-regulate renal SREBP-1, SREBP-2, NF-κB, COX-2 and iNOS expressions; upregulate GSH/GSSG ratio. (Park et al., 2010b;Yokozawa et al., 2010) Renal tissue In vivo: STZ (50 mg/kg)-induced DM rats. Decrease serum glucose, BUN and urinary protein levels; elevate serum albumin and total protein; reduce glycosylated protein and lipid peroxidation; downregulate RAGE, HO-1. (Yokozawa et al., 2008) Renal tissue In vitro: AGEs treated rat mesangial cells. Inhibit AGE-induced mesangial cells proliferation and cell cycle; down-regulate ROS and MDA; up-regulate SOD and GSH. (Xu et al., 2006)

Components Bioactivities Diseases/Tissues Targets (In vitro and In vivo) Effects References
Ursolic acid Anti-diabetes Liver In vitro: serum-free DMEM with 50mmol/L glucose treated HepG2 cells; in vivo: DM mice model(single intraperitoneal injection of 60 mg/kg STZ).
Inhibit MUC5AC mucin gene expression and mucin protein production. (Cho et al., 2011) Anti-diabetes DM In vivo: intraperitoneal inject into the fasting Wistar rats.
Enhance the release of ACh from nerve terminals, stimulate muscarinic M(3) receptors in the pancreatic β cells and augment the insulin release. (Hsu et al., 2006) Cornuside

Anticholinesterase
Alzheimer's disease In vitro experiments. Inhibit ChEs and BACE1 by interacting with both the catalytic active sites and the peripheral anionic sites. (Bhakta et al., 2017) Vasorelaxant activity In vitro: isometric vascular tone of phenylephrinecontracted thoracic aortae; cGMP production in HUVECs.
Dilates vascular smooth muscle via endotheliumdependent NO/cGMP signaling. (Kang et al., 2007) Polymeric proanthocyanidins Anticholinesterase Alzheimer's disease In vitro experiments. Inhibit ChEs and BACE1 by interacting with both the catalytic active sites and the peripheral anionic sites. (Bhakta et al., 2017) Anti-diabetes DM In vivo: male Wistar rats with normal blood glucose. Inhibit α-glucosidase activity; improve the oral sucrose tolerance, and inhibit the rise in the plasma glucose levels in normal rats. (Park et al., 2011c) 1,2,3-tri-O-galloyl-beta-Dglucose

Anticholinesterase
Alzheimer's disease In vitro experiments. Inhibit ChEs and BACE1 by interacting with both the catalytic active sites and the peripheral anionic sites. (Bhakta et al., 2017) Anti   (Park et al., 2013) Renal tissue In vivo: db/db mice. Decrease serum insulin, Cr and BUN levels; downregulate serum TNF-α, IL-6 and ROS; down-regulate renal ROS, TBARS, NF-κBp65, NOX4, p22 phox , COX-2, iNOS, bax and Cytochrome C; up-regulate GSH/GSSG ratio.  Hepatic and renal tissue In vivo: db/db mice. Down-regulated the expression of SREBP-1; inhibit AGEs formation and RAGE expression in hepatic and renal tissues. (Park et al., 2010a) Malic acid Anti-platelet In vitro: platelet viability assay and platelet adhesion assay.
Inhibit platelet aggregation and prevent platelet adhesion. (Zhang et al., 2013) Succinic acid Anti-platelet In vitro: platelet viability assay and platelet adhesion assay.
Inhibit platelet aggregation and prevent platelet adhesion. (Zhang et al., 2013) Citric acid Anti-platelet In vitro: platelet viability assay and platelet adhesion assay.
Inhibit platelet aggregation and prevent platelet adhesion. (Zhang et al., 2013)  experimental studies. We summarized their pharmacological effects in Table 1. Many of the pharmacological effects of these phytochemicals are consistent with those of the C. officinalis extract, such as anti-oxidation, anti-apoptosis, antiinflammatory, anti-cholinesterase, anti-diabetes, and vasorelaxant activity. In addition, some unique effects are found, such as the mucin secretion inhibitory effect of ursolic acid and oleanolic acid, and the antiplatelet aggregation effect of malic acid, succinic acid, and citric acid.

CONCLUSION
Previously, (Czerwinska and Melzig, 2018) have compared the similarities and differences in main phytochemical components and corresponding biological effects of two edible plants of the same genus, Cornus mas L. and C. officinalis. The value of their review is to point out that a variety of iridoid glycosides, including morroniside, logmalicids, cornusfurosides, and cornusides, are unique to C. officinalis and are closely related to the corresponding biological activities. In their opinion, the phytochemical composition is the important factor determining the biological activities and justifying the traditional usages. They have distinguished the two closely related species, and emphasized the anti-osteoporotic, immunomodulatory effects of C. officinalis. However, the medicinal value of C. officinalis has not been comprehensively summarized, nor has it been combined with the TCM theories.
According to an authoritative medical book of Ancient China, "Compendium of Materia Medica (Ben Cao Gang Mu)", C. officinalis "warms and nourishes the liver and kidney, eliminates all diseases caused by "pathogenic wind", stops menorrhagia, and treats frequent urination in the elderly" (Li, 1975), indicating the therapeutic effects of C. officinalis on consumptive disease, strokes and other "wind syndromes" in concept of TCM, gynecological diseases and urinary system diseases. The therapeutic effects of C. officinalis on a numbers of diseases have been confirmed by experimental research, but there are still a lot of traditional usages that have not been considered by the modern medical research, such as the treatment of tinnitus and deafness, forgetfulness, hair loss, etc.. At the same time, modern medical research has also found some pharmacological effects beyond the traditional usages of C. officinalis, such as protective effects on cardiovascular system and antiproliferative effects on tumors. These studies have deepened the understanding of the pharmacological effects and expanded the indications of C. officinalis.
The active components are the material basis of the pharmacological effects of C. officinalis. Some of the pharmacological effects of these active components are consistent with those of the C. officinalis extract, including anti-oxidation, antiapoptosis, anti-inflammatory, anti-cholinesterase, anti-diabetes, and vasorelaxant activity, and others are unique, such as the mucin secretion inhibitory effect and the antiplatelet aggregative effect. Iridoid glycosides are the main components with medicinal properties of C. officinalis, among them, morroniside and loganin are the indicators for herb quality control according to the Pharmacopoeia of P.R. of China (2015) (Huang et al., 2018).
Traditionally, herbal combinations are more widely used than single herbs in TCM treatment. The different herbs in TCM formula are considered to have synergistic effects or to reduce side effects, that is, the characteristic of "Jun Chen Zuo Shi" of TCM formulas. Some researchers have suggested that combination therapy of two or more natural products may enhance multiple mechanisms of action and presents synergistic effects with fewer side effects than single natural product treatment (Park et al., 2020b). There have been some studies exploring the pharmacological effects and the corresponding mechanisms of herb pairs containing C. officinalis. For example, studies showed that the mixed extract of C. officinalis and Morus alba root and bark could alleviate Osteoarthritis (OA) symptoms of arthroedema, pain and limping, and suppress the expressions of inflammatory markers TNF-α and MMP-13 in the articular cartilage (Park et al., 2020c); the mixture of C. officinalis and Ribes fasciculatum could ameliorate HFD-induced obesity in C57BL/6J mice, reduce the body fat, decrease the fatty deposition in hepatocytes, and suppress the expressions of adipogenesis-associated genes CCAAT/Cebpa, Fabp4, Pparg, and Srebp1 compared with the model mice (Park et al., 2020d). However, these studies only confirmed that the combination of different herbal medicines could enhance the original pharmacological effects, but did not reflect the synergistic mechanism or the side effects antagonistic mechanism between them. Therefore, new detection technologies are still needed to explain the characteristics of multi-target effects of TCM and the interrelationship between different pharmacological mechanisms more comprehensively.
Finally, C. officinalis has been so intensively studied that it appears almost as a panacea for many major conditions. Clinical trials are clearly needed to assess which of the reported pharmacological activities have confirmed efficacy and practical application in humans. (Park et al., 2020e) conducted a randomized, double-blind, controlled trial in Korea and 76 obese female participants were enrolled. The results showed that 12 weeks of administration of the mixture of C. officinalis and Ribes fasciculatum could significantly decrease the body fat of the participants. However, the clinical studies on the pharmacological effects of single herb of C. officinalis are still needed.

AUTHOR CONTRIBUTIONS
XG and JN concepted and designed the manuscript. XG also drafted the manuscript and acquired the funding. YL and ZA discussed the central ideas of the manuscript, designed the table, and corrected the styles. All authors read and approved the final manuscript.

FUNDING
This research was funded by China Postdoctoral Science Foundation, grant number 2019M650595. The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.