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Dihydromyricetin Acts as a Potential Redox Balance Mediator in Cancer Chemoprevention
Dihydromyricetin (DHM) is a flavonoid extracted from the leaves and stems of the edible plant Ampelopsis grossedentata that has been used for Chinese Traditional Medicine. It has attracted considerable attention from consumers due to its beneficial properties including anticancer, antioxidative, and anti-inflammatory activities. Continuous oxidative stress caused by intracellular redox imbalance can lead to chronic inflammation, which is intimately associated with the initiation, promotion, and progression of cancer. DHM is considered a potential redox regulator for chronic disease prevention, and its biological activities are abundantly evaluated by using diverse cell and animal models. However, clinical investigations are still scanty. This review summarizes the current potential chemopreventive effects of DHM, including its properties such as anticancer, antioxidative, and anti-inflammatory activities, and further discusses the underlying molecular mechanisms of DHM in cancer chemoprevention by targeting redox balance and influencing the gut microbiota.
Ampelopsis grossedentata (A. grossedentata) is a medicinal and edible plant widely used in China as a Traditional Chinese Medicine for the treatment of cough, fever, vomiting, hepatitis, colds, chronic nephritis, polyorexia, and sore throat. Tender stems and leaves of A. grossedentata are commonly consumed as vine tea in China for centuries due to its health benefiting effects. Dihydromyricetin (3,5,7,3,4,5-hexahydroxy-2,3-dihydroflavonol (DHM)) (Figure 1), also known as ampelopsin, is a major flavonoid extracted from the leaves and stems of A. grossedentata. The content of DHM in A. grossedentata ranges from 30% to 40% (dry weight), which is considered to have the highest flavonoid content in natural plants . Several scientific investigations reported that DHM possesses various biological activities such as anti-inflammatory [2, 3], antioxidative [4, 5], anticancer [6, 7], antidiabetic [8–10], antiatherosclerosis [11, 12], and cardioprotective effects [13, 14]. The biological properties and the underlying mechanisms of DHM were investigated mostly by in vitro cell cultures and in vivo animal models. In addition, DHM was reported as toxicologically safe and could effectively reverse multidrug resistance [15–19]. Hence, DHM is a promising bioactive compound for developing healthy/functional foods.
Despite these health-promoting effects, DHM has very poor water-solubility and aqueous stability. The solubility characteristics of DHM in cold water, hot water, and ethanol were 0.2-0.32 mg/mL at 25°C, 20 mg/mL at 80°C, and 170 mg/mL at 25°C, respectively . DHM is more stable in acidic conditions (pH range of 1.0-5.0) than in an alkaline environment. Under alkaline conditions, especially at a pH range from 6.0 to 8.0, DHM was prone to oxidation and degraded dramatically . Similarly, the stability of DHM is affected by the pH rather than the digestive enzymes including pepsin and pancreatin under the in vitro digestion system . At a concentration of 20 μg/mL, DHM was stable at room temperature after 12 h and at -20°C for 10 d, but only 45.42% was retained after 3 h in simulated intestinal fluid at 37°C . The plasma DHM concentration reached maximum (159 μg/L) at 1.5 h postadministration when DHM powder was given at a dosage of 115 mg/kg body weight in rabbits, indicating a low bioavailability of DHM . Efflux transporters, multidrug resistance protein 2, and breast cancer resistance protein also played an important role in DHM uptake and transport processes . A research group had investigated the distribution, excretion, and metabolic profile of DHM and found that most unconverted DHM forms were excreted in feces . Eight metabolites of DHM in urine and feces were found to be linked with reduction, methylation, dehydroxylation, glucuronidation, and sulfation metabolic pathways . These problems together resulted in its low membrane permeability () and compromised bioavailability . However, the amount of DHM from the daily intake of Ampelopsis grossedentata that can possibly exert its bioactivity had been investigated in clinical trials. For instance, the administration of DHM at 970 mg/day was reported to effectively ameliorate the glycemic control in type 2 diabetes mellitus in a previous study . In a double-blind clinical trial, daily uptake of 600 mg of DHM exerted anti-inflammatory effects on patients with nonalcoholic fatty liver disease .
Through identification and quantification methods, the transport mechanisms and protective effects of DHM in metabolic diseases have recently been reviewed [18, 24]; however, the anti-inflammatory, antioxidative, and anticancer effects and their underlying molecular mechanisms have not been fully documented. This study is aimed at giving an overview of the anti-inflammatory, antioxidative, and anticancer effects of DHM, as well as recent findings regarding its underlying molecular mechanisms including redox balance and the role of gut microbiota.
2. Dihydromyricetin Exerts Its Chemopreventive Potential against Cancer
Cancer is a public health problem and the leading cause of morbidity and mortality worldwide. The redox imbalance involving persistent chronic inflammation and reduced antioxidant capacity are the critical pathological causes of cancer. Presently, chemoprevention is a major approach to prevent the growth of cancer cells. However, high cost and side effects associated with chemotherapy have prompted scientists to search for safe alternative natural compounds for cancer therapy . Flavonoids are plant phytochemicals, and several epidemiological studies have reported that flavonoid intake may prevent a variety of cancers such as lung, breast, prostate, pancreas, and colon cancers .
DHM, a flavonoid from the edible plant Ampelopsis grossedentata, exhibited anticancer activity against a variety of cancer cells in various cultured cancer cells and animal models transplanted with cancer cells, as shown in Table 1. The most widely used cell lines for the determination of anticancer effects of DHM were HepG2 and SK-Hep-1 (human hepatocellular carcinoma), MCF-7 and MDA-MB-231 (human breast cancer), PC-3 (human prostate cancer), A549 and H1975 (human non-small-cell lung cancer), U251 and A172 (human glioma), SKOV3 (human ovarian cancer), SGC7901 and SGC7901/5-FU (human gastric carcinoma), and JAR (human choriocarcinoma) [27–39]. Different cancer cell lines were used by various researchers as each cell line has a different origin, tumor characteristics, and signaling pathways. In addition, animals such as mice and rats with transplanted cancer cells have also been used as in vivo models for investigation of antitumor activity of DHM [31, 37, 40, 41].
DHM effectively showed anticancer activity in a variety of cancers such as breast cancer, hepatocellular carcinoma, melanoma, ovarian cancer, lung cancer, cervical carcinoma, glioma, and osteosarcoma [32, 33, 42–46]. Among the treatments for different cancer cells, DHM has a broad dosage from 1 to 1000 μM with a duration from 6 to 72 h, presenting cell proliferation inhibition and apoptosis-inducing effects (Table 1). The concentration of DHM used in various studies shifts dramatically, which might be due to the differences in cell lines, DHM purity, and cell treatment conditions. The functional mechanisms and major pathways are also listed in Table 1. DHM inhibited the proliferation of HepG2 cells via G2/M phase cell cycle arrest through the Chk1/Chk2/Cdc25C signaling pathway; induced the apoptosis of HepG2 cells that target ROS-related, Akt/Bad, ERK1/2, AMPK, and PI3K/PDK1/Akt signaling pathways; enhanced the levels of DR4, DR5, Bax, Bad, and caspase 3; and reduced the expression of Bcl-2 protein and mTOR [30, 32, 47, 48]. The suppressing effect of DHM on the MDA-MB-231 breast cancer cell line was reported through ROS generation, ER stress pathway, and inhibition of mTOR [28, 31]. DHM treatment dose-dependently inhibited the growth of HeLa cells by inducing apoptosis through activation of caspases 9 and 3 and increasing the ratio of Bax protein to Bcl-2 . In A549 human adenocarcinoma lung epithelial cells, DHM decreased XIAP and survivin expression levels and cleaved poly(ADP-ribose) polymerase. DHM stimulated apoptosis via a p53-mediated pathway in ovarian cancer cells A2780 and SKOV3 . DHM was also reported to inhibit human melanoma SK-MEL-28 cells by inducing apoptosis; arresting cell cycle at the G1/S phases; increasing the production of p53 and p21 proteins; enhancing the expression levels of Bax proteins; and decreasing the protein levels of IKK-α, NF-κB (p65), and P-p38 . In addition, DHM suppressed the glioma cell growth through enhancing apoptosis; arresting the cell cycle at the G1 and S phases; and activating caspase 8, caspase 9, and caspase 3 . DHM exhibited anticancer activity in osteosarcoma cells through G2-M cell cycle arrest, DNA damage prevention, stimulation of the ATM-CHK2-H2AX signaling pathways, and enhancing p21 expression . Zuo et al. reported that DHM suppressed the growth of human choriocarcinoma JAR cells by inducing cell cycle arrest and reducing the expression levels of cyclin A1, cyclin D1, SMAD3, and SMAD4. DHM function on other cancer cells is likely to share similar pathways. However, few studies have investigated the cytotoxic effects of DHM on normal cells. The anticancer effects should selectively inhibit the growth of the cancerous cells without damaging the normal cells. The lack of cytotoxic data on normal cells could potentially limit the use of DHM as an anticancer agent.
Several studies evaluated the anticancer effects of DHM in combination with anticancer drugs in order to overcome the drug resistance of cancerous cells. DHM in combination with nedaplatin (anticancer drug) showed a synergistic effect on the inhibition of the growth of hepatocellular carcinoma cells SMMC7721 and QGY7701, and induced apoptosis through the activation of the p53/Bcl-2 signaling pathways . Also, DHM in combination with erlotinib significantly induced the caspase-dependent cell death in NSCLC due to a synergistic effect . More importantly, interactions between DHM and other drugs and their toxicological properties need to be substantially evaluated before use as anticancer drugs since DHM has the potential to show synergy effects with drugs.
Apart from cultured cancer cell lines, many researchers determined the antitumor potential of DHM in various animal models bearing transplanted cancer cells. PC-3 tumor growth was significantly reduced by 49.2% through the administration of DHM at 300 mg/kg BW in mice . It was found that tumor size was significantly reduced in mice treated with DHM compared to the controls in athymic mice xenografted with MDA-MB-231 cells , in a nude mice xenograft model bearing the human osteosarcoma cell line U2OS/MTX, in a mice xenograft model bearing the human osteosarcoma cell line U2OS/MTX , and in xenograft BALB/c-nu mice transplanted with the human glioma cell line U251. Though there are some reports on the antitumor effects of DHM, there are some limitations that could hinder the advancement of DHM as an anticancer agent for human use. On the one hand, the molecular mechanism and major pathways still remain unclear. It is important to reveal the mechanism with consistency among cell models, animal models, and clinical studies. Therefore, more research is needed in animals and humans to generate reliable and consistent scientific evidence regarding the anticancer effects of DHM.
3. Antioxidant Capacity Is the Main Reason for the Anticancer Property of DHM
Aerobic cellular respiration generates free radicals and reactive oxygen species (ROS). The in-built antioxidant defense system protects the body from the harmful effects of free radicals. The imbalance between free radicals and the antioxidant defense system results in oxidative stress. The free radicals and ROS contain unpaired electrons in the outer shell, resulting in their instability. These unstable free radicals are highly reactive; attract electrons from other molecules; and cause oxidative damage to proteins, lipids, carbohydrates, and nucleic acids . The oxidative damage inflicted upon macromolecules results in oxidative stress, which has been found to be highly associated with cancer .
Plant-derived flavonoids have been shown to inhibit free radicals and oxidative stress . Recently, there have been many studies reporting on the antioxidant capacity of DHM. The evaluation methods, antioxidant properties, and mechanisms of DHM are shown in Table 2. Several in vitro, cell culture, and in vivo (animals) models are commonly used for the determination of the antioxidant activity of DHM, of which the most commonly used are the in vitro methods including free radical scavenging methods such as DPPH, ABTS, oxygen radical absorption capacity (ORAC), H2O2 radical scavenging power, and Fe2+ chelating method and ferric reducing antioxidant power (FRAP) [5, 55–58]. Several studies documented the in vitro free radical scavenging activity of DHM. The values measured by DPPH, ABTS, H2O2, and O2 radicals were 3.24-22.6, 3.1-5.32, 7.95, and 7.79 μg/mL, respectively (Table 2) [5, 17, 59, 60].
DHM has been shown to protect oxidative stress in various cell culture models with a concentration below 1000 μM, as shown in Table 2. Cell lines such as human hepatoma cells (HepG2), human umbilical vein endothelial cells (HUVECs), human colon cancer (Colo-205) cells, porcine kidney epithelial cells (PK-15), PC12 cells, murine macrophage (RAW264.7) cells, glomerular mesangial cells (MCs), and HEI-OC1 auditory cells have been successfully used to determine the protective effects of DHM in oxidative stress, and oxidative stress is generally created in cell lines by using H2O2 free radicals, LPS, methylglyoxal, and sodium nitroprusside [4, 41, 47, 55, 61–67].
Oxidative stress-induced mice, rat, chicken, and piglet models have also been used by many researchers to investigate the protective role of DHM in oxidative stress. The dose used in animal studies was 25 to 250 mg/kg BW, and the duration was between 2 and 3 months. In animal studies, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione (GSH), and malondialdehyde (MDA) are commonly measured oxidative stress parameters to estimate the antioxidant capacity of DHM [13, 68–70]. The major antioxidant effects of DHM through the Nrf2/HO-1 pathway, the Nrf2/Keap1 pathway, and the ERK and Akt pathways [5, 62, 66, 71], with an increase of DHM, significantly decreased the ROS levels in human umbilical vein endothelial cells (HUVECs) . DHM exhibited an antioxidative power by activating superoxide dismutase (SOD) and the Nrf2/HO-1 signaling pathway or the Nrf2/Keap1 pathway [5, 64]. Recently, Dong et al. found that DHM exhibited antioxidative effects through the inhibition of intracellular ROS production and expression levels of ROS producing the enzymes NADPH oxidase 2 (NOX2) and NOX4, the suppression of MDA levels, the enhancement of SOD, and the activation of the Nrf2/HO-1 signaling pathway . In another study, Zhang et al. determined the protective effects of DHM on HUVECs against sodium nitroprusside- (SNP-) induced oxidative damage and reported that DHM reduced ROS production and MDA levels, and increased SOD activity by activating the PI3K/Akt/FoxO3a signaling pathways in HUVECs . DHM was also reported to inhibit the oxidative stress in HEI-OC1 auditory cells through the suppression of ROS accumulation . DHM inhibited the activity of phase I enzymes, including cytochrome P450 (CYP), and phase II enzymes, including sulfotransferases (SULTs) and N/O-acetyltransferases (NAT1 and NAT2) [72, 73]. Oxidative stress has been involved in several neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease (AD), and Huntington’s disease . Several researchers investigated the neuroprotective effect of DHM in oxidative stress-induced PC12 neuronal-like cells. They also investigated the neuroprotective role of DHM in neuronal-like PC12 cells against H2O2-induced oxidative stress and reported that DHM treatment at 1, 5, and 15 mg/mL for 1 h inhibited the formation of ROS and increased the cellular antioxidant defense through activation of the ERK and Akt signaling pathways in PC12 cells . Jiang et al. found that DHM reduced the oxidative stress in PC12 cells by inhibiting the intracellular ROS production and by modulating the AMPK/GLUT4 signaling pathways .
The oxidative stress protection capacity of DHM was also evaluated in several animal models. DHM showed the highest radical scavenging activity (42.26%) of serum at 4 h after DHM administration in rats . Li et al. induced oxidative stress in the brains of ICR mice by sleep deprivation and found that DHM administration significantly reduced oxidative stress by increasing SOD activity and reducing the MDA level in the hippocampus of sleep-deprived mice . Similarly, for streptozotocin-induced or transverse aortic constriction surgery-induced oxidative stress in mice as well as high-fat diet-induced oxidative stress in rats, DHM decreased MDA and increased SOD, GSH, and GSH-Px [13, 74, 75]. When induced by LPS to cause oxidative stress, DHM increased total antioxidant capacity and reduced the MDA levels in piglets, and increased SOD and GSH-Px activity and GSH in chicken plasma and ileum [55, 70]. The scientific evidence from in vitro, cell culture, and animal studies clearly indicate that DHM could prevent the free radicals, oxidative stress, and related markers. However, scientific data related to the antioxidant capacity of DHM in humans is scanty. Therefore, more clinical investigations are needed to improve the therapeutic applications of DHM as a natural antioxidant.
4. Anti-Inflammatory Capacity Is Fundamental and Is the Immediate Reason for Its Anticancer Efficacy
Inflammation is a complex and normal response of the immune system to external stimuli such as pathogens, toxins, chemical agents, infection, and tissue injury. When inflammatory cells (e.g., macrophages) are activated by stimuli (e.g., LPS and IFN-γ), inflammatory mediators such as IL-1β, IL-6, TNF-α, NO, and PGE2 are excessively produced through the activation of common inflammatory signaling pathways such as the NF-κB, MAPK, and JAK-STAT pathways . The overproduction of inflammatory mediators (IL-1β, IL-6, TNF-α, NO, and PGE2) has been associated with several diseases such as diabetes, cancer, asthma, metabolic syndrome, arthritis, cardiovascular diseases, and inflammatory bowel diseases . Recently, there has been growing interest in nutraceuticals and functional foods derived from plant sources. Flavonoids are polyphenolic compounds largely present in vegetables, fruits, legumes, and tea. Flavonoids such as quercetin, cyanidin, luteolin, anthocyanidin, catechin, and epicatechin have shown to contain anti-inflammatory properties . DHM has been extensively studied by many researchers for its anti-inflammatory activities using various cell cultures, animal models, and human studies. Several researchers used different inflammatory models (neuroinflammation, arthritis inflammation, and lung inflammation) to investigate the anti-inflammatory potential of DHM. Table 3 shows the various models used and the molecular mechanisms of the anti-inflammatory property of DHM.
The most widely used model for the investigation of the anti-inflammatory activity of plant-derived compounds is the macrophage that is stimulated by LPS. Macrophages play an important role in inflammation. The murine RAW264.7 macrophage cell line is the most commonly used cell culture model for the determination of the anti-inflammatory activity of food-derived compounds. Macrophages stimulated by the Toll-like receptor ligand LPS produce various inflammatory markers such as TNF-α, IL-6, IL-1β, NO, transcription factor NF-κB, and prostaglandin-E2 that regulate the inflammatory responses. Numerous studies reported that DHM showed anti-inflammatory activity through different molecular mechanisms such as suppression of proinflammatory cytokines (IL-1β, IL-6, IL-8, and TNF-α), activation of the production of an anti-inflammatory cytokine (IL-10), inhibition of MAPKs, suppression of the production of prostaglandins and nitric oxide, and inhibition of the transcription factor NF-κB [3, 4, 79, 80].
The inflammatory response of the brain or the spinal cord is known as neuroinflammation, and it has an important role in the development of depression by producing cytokines, chemokines, and ROS . Microglial cells are macrophages in the central nervous system and are commonly used as a model to investigate the protective effects of DHM in neuroinflammation. Several researchers evaluated the anti-inflammatory capacity of DHM in neuroinflammation using microglial cells and mice models. Weng et al. investigated the neuroinflammation protection capacity of DHM using murine BV-2 microglial cells activated by LPS and reported that DHM inhibited neuroinflammation by suppressing the IκB/NF-κB inflammation pathway as well as decreasing STAT3 nuclear translocation and the phosphorylation levels of JAK2-STAT3. Additionally, the authors demonstrated that DHM treatment significantly inhibited the production of inflammatory mediators IL-1β, IL-6, TNF-α, nitric oxide (NO), prostaglandin E2 (PGE2), and the enzymes inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-induced microglial cells. DHM treatment at 10 and 20 mg/kg/day for 3 days showed an antidepressant-like activity by significantly inhibiting TNF-α and IL-6 gene expressions and protein levels in a mice model of LPS-induced neuroinflammation . DHM at 1 mg/kg BW for 4 weeks significantly inhibited the neuroinflammation of APP/PS1 double transgenic mice by decreasing IL-1β via reduction of the activation of NLRP3 inflammasomes . In a lead- (Pb-) induced inflammation model in mice, Pb combined with DHM administration at a dose of 125 and 250 mg/kg/BW significantly inhibited TNF-α and IL-1β and the nuclear translocation of NF-κB p65 via regulating the AMPK, Aβ, TLR4, MyD88, p38, and GSK-3β signaling pathways. DHM exhibited an anti-inflammatory effect on LPS-induced BV-2 microglial cells by suppressing the proinflammatory markers IL-6, IL-1β, TNF-α, iNOS, and COX-2 through reducing the activation of the TRL4/NF-κB signaling pathway. These studies proved that DHM possess neuroinflammation protection activity through the inhibition of inflammatory mediators.
The anti-inflammatory effects of DHM were investigated with the administration of a DHM dosage from 0.025 to 500 mg/kg BW within 2 weeks to 14 weeks. Xu et al. studied the anti-inflammatory capacity of DHM in an ovalbumin- (OVA-) induced mice C57BL/6 model of asthma and demonstrated that DHM treatment significantly decreased the levels of IL-4, IL-5, and IL-13 in the bronchoalveolar lavage fluid compared to the control group . DHM treatment significantly suppressed IL-1β and IL-18 production by inhibiting the NLRP3 inflammasome through the activation of the SIRT1 signaling pathway in a doxorubicin- (DOX-) induced rat model and in DOX-treated H9C2 cells . DHM was found to reduce the inflammation in CIA rats by attenuating IL-1β production through the suppression of the NF-κB signaling pathway . Chu et al. reported that DHM significantly reduced the inflammation in a rat model of rheumatoid arthritis by inhibiting the levels of inflammatory mediators IL-1β, IL-6, TNF-α, and COX-2 via activating the Nrf2 pathway . Chang et al. investigated the protective role of DHM in ileum inflammation, induced by LPS, in chickens and found that DHM treatment decreased IL-1β and IL-18 expression through the inhibition of the TLR4/NF-κB signaling pathways. DHM significantly decreased the proinflammatory cytokines TNF-α, IL-1β, and IL-6 and the COX-2 gene expressions and increased the production of IL-10 in the liver of piglets injected with LPS . Additionally, the authors demonstrated that DHM supplementation in LPS-treated piglets decreased the activation of AKT and STAT3 phosphorylation and reduced the DNA-binding activity of NF-κB .
More importantly, the anti-inflammatory activity of DHM was also determined in humans. Chen et al. conducted a randomized double-blind controlled clinical trial with sixty adult nonalcoholic fatty liver disease patients, and the DHM was administered (150 mg capsules) twice daily for 12 weeks . The authors found that DHM exhibited an anti-inflammatory activity in humans by decreasing the serum levels of TNF-α, cytokeratin-18 fragment, and fibroblast growth factor 21.
Although sufficient evidence is available from cell culture and animal experiments, the results from clinical studies are meager. Therefore, it is suggested that more studies are needed in humans to further confirm the anti-inflammatory activity of DHM. More results from human studies would provide strong scientific evidence for using DHM as a therapeutic agent to treat inflammation and its related diseases.
5. Gut Microbiota Is a Potential Interface for the Regulation of Redox Balance for Cancer Prevention
The interface of gut microbiota is very important for cancer chemoprevention of DHM, and the interaction between DHM and gut microbiota is the key stage for its mechanism study. DHM is a flavonoid with poor oral bioavailability in vivo because of its rare absorption in the gastrointestinal tract (GI). Due to the low bioavailability, the vast majority of DHM persists in the colon where it is exposed to the gut microbiota, which markedly alters the richness and diversity of the gut microbiota and modulates the gut microbiota composition . Previous studies indicated that DHM could be distributed widely in different organs such as the liver, kidney, lung, brain, and heart, whereas most of them were eliminated in feces, which indicated that DHM is predominantly distributed in the intestinal tract, and closely interacts with the gut microbiota .
It is reported that DHM treatment could obviously change the relative abundances of gut microbiota at different levels . DHM is able to dramatically increase the abundance of Bacteroidetes but decrease the abundance of Firmicutes, which was related to obesity intervention in humans. In brief, decreasing the ratio of Firmicutes to Bacteroidetes was demonstrated to control body weight via modulatory glucose and lipid metabolism. Besides, DHM supplement can decrease the abundances of Lachnoclostridium, Alistipes, Ruminococcaceae UCG-010, Allobaculum, Ruminiclostridium 9, Rikenellaceae RC9, Ruminococcaceae UCG-005, Anaerotruncus, Defluviitaleaceae UCG-011, [Eubacterium] ventriosum, Christensenellaceae R-7, and Odoribacter, whereas it can increase the abundances of Parasutterella, Erysipelatoclostridium, and Parabacteroides . Thus, a lot of evidences suggested that DHM supplement could intervene against chronic diseases, such as obesity, diabetes, and cancers, via modulating the gut microbiota composition .
Moreover, the interaction between DHM and gut microbiota is reported to be associated with cancer. DHM was reported to promote the CPT-11 effect both in the mouse model of AOM/DSS cancer; tumors were sensitive to 100 mg/kg DHM chemotherapy under 100 mg/kg or 200 mg/kg CPT-11 (irinotecan). DHM-driven CPT-11 chemotherapy induced enhanced IgG levels and the reduction of Fusobacterium abundance in the gut . Besides, the intestinal tract is the most import target organ for DHM intervention associated with the chemotherapeutic efficacy and reduced risk of the side effects of cancer treatment via the regulation of immune responses and the shaping of gut microbiota .
On the other hand, DHM was reported to be biotransformed into other metabolites by gut microbiota via methylation, reduction, dehydroxylation, glucuronidation, and sulfation pathways which may be closely related to the regulation of redox balance . Therefore, gut microbiota is a potential important interface for regulating the redox balance for providing more therapeutic schedules on various other human diseases.
6. Conclusions and Perspectives
DHM originated from a natural plant in China and has received increasing attention due to its pharmacological activities. In this review, the physicochemical properties of DHM have been mentioned. Its antioxidant, anti-inflammatory, and anticancer activities and related molecular mechanisms have been further reviewed. The molecular mechanism diagram of the inhibitory effect of DHM on cancer has been summarized as shown in Figure 2. In brief, DHM exerts its anticancer activity via direct scavenging of ROS, regulating intestinal microbiota, and indirectly modulating the cellular signaling pathway, including the activation of the Nrf2-ARE pathway, the inhibition of the NF-κB pathway, and the induction of the apoptosis pathway.
Substantial scientific evidence about the functional properties of DHM is available from cell culture and animal studies. DHM exhibited bioactivities by modulating several molecular pathways. However, the mechanism of pharmacological action, distribution, and metabolism are still not well investigated in vivo in animals, and what is more, the evidence from clinical studies is meager. The novel targets of the signaling transduction of DHM still require more work. Furthermore, more studies are needed in humans in order improve the applications of DHM in food and pharmaceutical industries. The future in vivo researches by multiomics technologies are required to understand the safety, bioavailability, and metabolism mechanism of DHM targeting on oxidative stress, inflammation, and cancer, especially to reveal the reciprocal interaction among DHM, cells/organs, and gut microbiota. This could pave ways for the industry applications of DHM as a functional food/healthy food/therapeutic agent.
|AAPH:||2,2-Azobis (2-amidinopropane) dihydrochloride|
|BAD:||Bcl-2-associated death promoter|
|BAX:||BCL-2-associated X protein|
|DPPH:||1,1-Diphenyl-2-picrylhydrazyl radical 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl|
|HUVECs:||Human umbilical vein endothelial cells|
|iNOS:||Inducible nitric oxide synthase|
|:||Half-maximal inhibitory concentration|
|MIC:||Minimum inhibitory concentration|
|MAPKs:||Mitogen-activated protein kinases|
|NF-κB:||Nuclear factor-κ-gene binding|
|Nrf2:||Nuclear factor erythroid 2-related factor 2|
|ORAC:||Oxygen radical absorption capacity|
|ROS:||Reactive oxygen species|
|STAT3:||Transduction and transcription 3|
|TNF-α:||Tumor necrosis factor-alpha|
Conflicts of Interest
The authors declare that they have no conflicts of interest.
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