Tangeretin, a citrus pentamethoxyflavone, antagonizes ABCB1-mediated multidrug resistance by inhibiting its transport function

An Update on the Potential of Tangeretin in the Management of Neuroinflammation-Mediated Neurodegenerative Disorders

Neuroinflammation is the major cause of neurodegenerative disorders such as Alzheimer's and Parkinson's disease. Currently available drugs present relatively low efficacy and are not capable of modifying the course of the disease or delaying its progression. Identifying well-tolerated and brain-penetrant agents of plant origin could fulfil the pressing need for novel treatment techniques for neuroinflammation. Attention has been drawn to a large family of flavonoids in citrus fruits, which may function as strong nutraceuticals in slowing down the development and progression of neuroinflammation. This review is aimed at elucidating and summarizing the effects of the flavonoid tangeretin (TAN) in the management of neuroinflammation-mediated neurodegenerative disorders. A literature survey was performed using various resources, including ScienceDirect, PubMed, Google Scholar, Springer, and Web of Science. The data revealed that TAN exhibited immense neuroprotective effects in addition to its anti-oxidant, anti-diabetic, and peroxisome proliferator-activated receptor-γ agonistic effects. The effects of TAN are mainly mediated through the inhibition of oxidative and inflammatory pathways via regulating multiple signaling pathways, including c-Jun N-terminal kinase, phosphoinositide 3-kinase, mitogen-activated protein kinase, nuclear factor erythroid-2-related factor 2, extracellular-signal-regulated kinase, and CRE-dependent transcription. In conclusion, the citrus flavonoid TAN has the potential to prevent neuronal death mediated by neuroinflammatory pathways and can be developed as an auxiliary therapeutic agent in the management of neurodegenerative disorders.

Synergistic effects of flavonoids and paclitaxel in cancer treatment: a systematic review

Paclitaxel is a natural anticancer compound with minimal toxicity, the capacity to stabilize microtubules, and high efficiency that has remained the standard of treatment alongside platinum-based therapy as a remedy for a variety of different malignancies. In contrast, polyphenols such as flavonoids are also efficient antioxidant and anti-inflammatory and have now been shown to possess potent anticancer properties. Therefore, the synergistic effects of paclitaxel and flavonoids against cancer will be of interest. In this review, we use a Boolean query to comprehensively search the well-known Scopus database for literature research taking the advantage of paclitaxel and flavonoids simultaneously while treating various types of cancer. After retrieving and reviewing the intended investigations based on the input keywords, the anticancer mechanisms of flavonoids and paclitaxel and their synergistic effects on different targets raging from cell lines to animal models are discussed in terms of the corresponding involved signaling transduction. Most studies demonstrated that these signaling pathways will induce apoptotic / pro-apoptotic proteins, which in turn may activate several caspases leading to apoptosis. Finally, it can be concluded that the results of this review may be beneficial in serving as a theoretical foundation and reference for future studies of paclitaxel synthesis, anticancer processes, and clinical applications involving different clinical trials.

Connexin43 is associated with the progression of clear cell renal carcinoma and is regulated by tangeretin to sygergize with tyrosine kinase inhibitors

BACKGROUND

The roles of Connexin43 (Cx43) in clear cell renal cell carcinoma (ccRCC) microenviroment remains to be poorly defined.

METHODS

The expression profile, prognosis and immune analysis of Cx43 in various cancers, particularly in ccRCC were performed using TCGA database, and various biological function assays were applied to explore the physiological role of Cx43 and tangeretin in ccRCC. Western blot were applied to examine the protein expression and Kunming mice were used to evaluate preliminary safety or anti-tumor activity of tangeretin and sunitinib.

RESULTS

Compared with the normal group, higher expression levels of Cx43 in ccRCC, and distinct associations between Cx43 expression and ccRCC prognosis or immune infiltration, were found. Notably, the expression of Cx43 was found to be highly correlated with that of receptor tyrosine kinases (RTKs), particularly with VEGFR1, VEGFR2 and VEGFR3. The expression of Cx43 and EGFR was also found to be higher in ccRCC than that in the para-cancerous specimens. Knocking down Cx43 expression decreased RCC cell viability, cell migration, p-EGFR, MMP-9 and survivin expression. Using 14 Chinese medicine monomers, tangeretin was screened and found to inhibit tumor cell viability and Cx43 expression. Tangeretin also enhanced the sensitivity of RCC cells to tyrosine kinase inhibitors (TKIs) sunitinib and sorafenib. However, the same concentration of tangeretin exerted a less prominent effect on normal renal cell viability.

CONCLUSIONS

Cx43 is strongly associated with RTK expression and ccRCC progression, while tangeretin can inhibit RCC cell malignancy by inhibiting Cx43 expression and enhance the sensitivity of RCC cells to TKIs.

The mechanism of flavonoids from Cyclocarya paliurus on inhibiting liver cancer based on in vitro experiments and network pharmacology

Introduction: Cyclocarya paliurus (Batal.) Iljinsk., a subtropical tree belonging to the family Juglandaceae, is rich in polysaccharides, flavonoids, and terpenoids. It has important pharmacological effects such as lowering blood lipids, blood sugar, and blood pressure. However, little has been discerned regarding anti tumor effects and their potential mechanisms. Method: In vitro cell culture experiments were used to test the effect of C. paliurus total flavonoids (CTFs) extract on apoptosis mechanisms in HepG2 cells. Network pharmacology was applied to further explore the effects of CTFs on liver cancer as well as the mechanisms through which these effects might be achieved. Both 3 hydroxyflavone and luteolin were randomly selected to verify the effect on inducing apoptosis and inhibiting the proliferation of HepG2 cells. Results and Discussion: Network pharmacological analysis was applied to these 62 compounds and their targets, and 13 flavonoids were further screened for their potential anti liver cancer activity. These 13 flavonoids included: tangeretin, baicalein, 7,3'-dihydroxyflavone, velutin, 3-hydroxyflavone, chrysin, kumatakenin, tricin, luteolin, chrysoeriol, apigenin, pinocembrin, and butin. Together, these flavonoids were predicted to interact with AKT1, MAPK3, PIK3CA, EGFR, MAP2K1, SRC, IGF1R, IKBKB, MET, and MAPK14. It was predicted that the inhibitory effect on hepatocellular carcinoma would be accomplished by regulation of core proteins relating to such KEGG pathways as cancer, PI3K-Akt, proteoglycans in cancer, microRNAs in cancer, and endocrine resistance via core target proteins. Both 3-hydroxyflavone and luteolin were demonstrated to induce apoptosis and inhibit the proliferation of HepG2 cells. Our study provides scientific evidence supporting the use of CTFs for the treatment of liver cancer.

Comparative effects of five polymethoxyflavones purified from Citrus tangerina on inflammation and cancer

Although the Citrus tangerina cultivar “Dahongpao” (CTD) has been established as a rich source of polymethoxyflavones (PMFs) with anti-inflammatory and anti-cancer properties, their individual effects on cellular signaling remain to be elucidated. In this study, five major PMFs from the peel of CTD were isolated, including sinensetin, tetramethyl-O-scutellarin (5,6,7,4′-tetramethoxyflavone), nobiletin (5,6,7,8,3′, 4′-hexamethoxyflavone), tangeretin (5,6,7,8,4′-pentamethoxyflavone), and 5-demethylnobiletin (5-OH-6,7,8,3′,4′-pentamethoxyflavone). These PMFs were found to significantly (p < 0.05) inhibit the production of NO and biomarkers of chronic inflammation (TNF-α and IL-6). Additionally, they effectively suppressed mRNA biomarkers of acute inflammation (Cox-2 and iNOS), and to varying degrees promoted the activation of anti-inflammatory cytokines (IL-4, IL-13, TNF-β, and IL-10). Among the five PMFs, tangeretin was found to have a considerable anti-proliferative effect on tumor cell lines (PC-3 and DU145) and synergistically enhanced the cytotoxicity of mitoxantrone, partially via activation of the PTEN/AKT pathway. The findings of this study provide valuable insights into the activity of different PMF monomers and advance the understanding of the roles of PMFs in promoting apoptotic and anti-cancer effects.

Tangeretin Synergizes with 5-Fluorouracil to Induce Autophagy through MicroRNA-21 in Colorectal Cancer Cells

Combining innocuous natural products with cytotoxic agents may enhance the effectiveness of chemotherapy. Tangeretin is a citrus flavonoid that has antineoplastic properties, but its mechanism of action is still unknown. Here, we used a high throughput-screening (HTS) platform to screen for drugs that may synergize with tangeretin and confirmed the top hits against colorectal cancer (CRC) cells in vitro and in vivo. 5-Fluorouracil (5-FU) and PI3K/Akt inhibitors have come out as top hits that show a strong synergy effect with tangeretin by HTS. We further confirmed the synergistic effect of tangeretin with 5-FU against CRC cells in vitro and in vivo. Since 5-FU can increase microRNA-21 (miR-21) expression and activate PI3K/Akt signaling, we addressed if tangeretin acted at this level. In 5-FU treated cells, tangeretin inhibited miR-21 induction, rescued the expression of the target PTEN, reduced Akt activation, and induced autophagy. Together, our data indicated that a natural product, such as tangeretin, can modulate miR-21 expression and that this pathway might be a potential therapeutic target for CRC. Combining tangeretin with 5-FU may be useful in the clinic, since 5-FU is the current first line drug for treating CRC.

Cancer multidrug-resistance reversal by ABCB1 inhibition: A recent update

Chemotherapy is one of the most common treatments for cancer that uses one or more anti-cancer drugs as a part of the standardized chemotherapy regimen. Cytotoxic chemicals delay and prevent cancer cells from multiplying, invading, and metastasizing. However, the significant drawbacks of cancer chemotherapy are the lack of selectivity of the cytotoxic drugs to tumour cells and normal cells and the development of resistance by cells for the particular drug or the combination of drugs. Multidrug resistance (MDR) is the low sensitivity of specific cells against drugs associated with cancer chemotherapy. The most common mechanisms of anticancer drug resistance are: (a) drug-dependent MDR (b) target-dependent MDR, and (c) drug target-independent MDR. In all the factors, the overexpression of multidrug efflux systems contributes significantly to the increased resistance in the cancer cells. Multidrug resistance due to efflux of anticancer drugs by membrane ABC transporters includes ABCB1, ABCC1, and ABCG2. ABCB1 inhibition can restore the sensitivity of the cancerous cells toward chemotherapeutic drugs. In this review, we discussed ABCB1 inhibitors under clinical studies with their mode of action, potency and selectivity. Also, we have highlighted the contribution of repurposing drugs, biologics and nano formulation strategies to combat multidrug resistance by modulating the ABCB1 activity.

The role of dietary flavonoids for modulation of ATP binding cassette transporter mediated multidrug resistance

Flavonoids are widely existing compounds with enormous pharmacological effects from food and medicine. However, the low bioavailability in intestinal absorption and metabolism limits their clinical application. Intestinal efflux ABC (ATP binding cassette) transporters, including P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs), act as "pumping doors" to regulate the efflux of flavonoids from intestinal epithelial cells into the intestinal cavity or the systemic circulation. The present review describes the critical effect of ABC transporters involved in the efflux of flavonoids which depend on its efflux direction. And the role of flavonoids for modulation of intestinal ABC transporters was emphasized and several examples were given. We summarized that the resistance effect of flavonoid-mediated multidrug on ABC transporters may influence the bioavailability of drugs, bioactive ingredients and/or toxic compounds upon dietary uptake. Meanwhile, flavonoids functionalized as reversing agents of the ABC transporter may be an important mechanism for unexpected food-drug, food-toxin or food-food interactions. The overview also indicates that elucidation of the action and mechanism of the intestinal metabolic enzymes-efflux transporters coupling will lay a foundation for improving the bioavailability of flavonoids <i>in vivo</i> and increasing their clinical efficacy.

Structure-activity relationship and mechanism of flavonoids on the inhibitory activity of P-glycoprotein (P-gp)-mediated transport of rhodamine123 and daunorubicin in P-gp overexpressed human mouth epidermal carcinoma (KB/MDR) cells

This study was aimed to investigate the inhibitory activity of flavonoids on P-glycoprotein (P-gp). Effects of 39 flavonoids on the cellular uptake (CU) of rhodamine123 (Rho) and daunomycin (DNR) were investigated in both parental KB and P-gp overexpressed KB/MDR cells. The inhibition mechanism of selected flavonoids was further investigated by measuring the ATPase activity and expression level of P-gp. Twelve flavonoids improved the uptake of Rho (↑Rho_F) and nineteen flavonoids increased the uptake of DNR (↑DNR_F) in KB/MDR cells with nine flavonoids overlapped. Structure-activity relationship (SAR) indicated that 8-OCH₃, and 2'-OH have a negative effect on Rho and DNR transport. Whereas 5-OH, 5-OCH₃, 6-OH, 7-OCH₃, 3'-OH, and 4'-OH, are essential for inhibition of flavonoids on P-gp and reversing the resistance of Rho and DNR. Eleven selected flavonoids significantly induced the basal P-gp-ATPase activity but much lower than that induced by verapamil. Tangeretin, galangin, kaempferol, quercetin, and morin significantly reversed the ATPase activity stimulated by verapamil. Six of eleven flavonoids significantly decreased P-gp expression, whereas three flavonoids slightly increased P-gp expression. These results provide valuable information that flavonoids can effectively reverse multidrug resistance of P-gp-mediated transport of nutraceutical and drugs by co-administration.

Computer-Aided Drug Design Applied to Secondary Metabolites as Anticancer Agents

Computer-Aided Drug Design (CADD) techniques have garnered a great deal of attention in academia and industry because of their great versatility, low costs, possibilities of cost reduction in in vitro screening and in the development of synthetic steps; these techniques are compared with highthroughput screening, in particular for candidate drugs. The secondary metabolism of plants and other organisms provide substantial amounts of new chemical structures, many of which have numerous biological and pharmacological properties for virtually every existing disease, including cancer. In oncology, compounds such as vimblastine, vincristine, taxol, podophyllotoxin, captothecin and cytarabine are examples of how important natural products enhance the cancer-fighting therapeutic arsenal. In this context, this review presents an update of Ligand-Based Drug Design and Structure-Based Drug Design techniques applied to flavonoids, alkaloids and coumarins in the search of new compounds or fragments that can be used in oncology. A systematical search using various databases was performed. The search was limited to articles published in the last 10 years. The great diversity of chemical structures (coumarin, flavonoids and alkaloids) with cancer properties, associated with infinite synthetic possibilities for obtaining analogous compounds, creates a huge chemical environment with potential to be explored, and creates a major difficulty, for screening studies to select compounds with more promising activity for a selected target. CADD techniques appear to be the least expensive and most efficient alternatives to perform virtual screening studies, aiming to selected compounds with better activity profiles and better "drugability".

Tangeretin as an adjuvant and chemotherapeutic sensitizer against various types of cancers: a comparative overview

OBJECTIVES

Cancer is a leading cause of disabling morbidities and death worldwide. Although there are various strategies for the management of cancer, the severe adverse effects negatively impact the patient's quality of life. In addition, the development of resistance limits the efficacy of many chemotherapeutics. Many natural agents are capable of reducing the adverse effects associated with chemotherapy and improving the therapeutic outcome. Tangeretin, a polymethoxy flavone, is one of the promising natural anticancer agents.

KEY FINDINGS

Tangeretin not only targets various malignancies but also synergizes chemotherapeutic agents and reverses cancer resistance. Hence, the application of tangeretin as an adjuvant in cancer chemotherapy would be a promising strategy.

SUMMARY

This work critically highlighted the proposed anticancer activity of tangeretin and discussed its potential combination with various chemotherapeutic agents. Additionally, it shed light on tangeretin chemical derivatives with improved pharmacokinetic and pharmacodynamic activity. Finally, this review described flavonoid biosynthetic pathways and how bioengineering can be employed to enhance the production yield of tangeretin. Thus, this work paves the way for the rational clinical utilization of tangeretin as a safe and effective adjuvant in chemotherapeutic protocols.

Therapeutic Implications of a Polymethoxylated Flavone, Tangeretin, in the Management of Cancer via Modulation of Different Molecular Pathways

Chemotherapeutics can induce oxidative stress, inflammation, apoptosis, mitochondrial dysfunction, and abnormalities in neurotransmitter metabolism leading to toxicity. Because there have been no therapeutic strategies developed to target inflammation and oxidative stress, there is a continuing need for new and improved therapy. As a result, there has been increasing interest in complementary and alternative medicine with anticancer potential. Studies have shown that the antioxidant activities and anti-inflammatory effects of citrus fruits are promising natural phytochemicals in the development of new anticancer agents. Tangeretin is a naturally polymethoxylated flavone compound extracted from the citrus peel that has shown significant intestinal absorption and adequate bioavailability, with the added benefit of promoting longevity. In addition, tangeretin is known to exhibit considerable selective toxicity to many types of cancer cell proliferation such as ovarian, brain, blood, and skin cancer. Evidence indicates that tangeretin acts through several mechanisms including growth inhibition, induction of apoptosis, autophagy, antiangiogenesis, and estrogenic-like effects. Furthermore, tangeretin works through mitigating levels of inflammatory mediators in the immune system. Using tangeretin in combination with clinically applied anticancer drugs could be a good strategy for increasing the efficiency of these agents and protecting noncancerous cells from damage caused by chemotherapy. The purpose of this review is to highlight the protective effects of a novel natural product, tangeretin against chemotherapeutic-induced toxicity. The development of chemoprevention strategies can lead to significant health care improvement in cancer survivors. Thus, study outcomes may attract more investigators to conduct tangeretin-related research and find out potentially significant impacts on health care of cancer patients and decreased health problems associated with chemotherapeutics-induced toxicity.

Tangeretin boosts the anticancer activity of metformin in breast cancer cells via curbing the energy production

BACKGROUND

Breast cancer is the first leading cause of women cancer-related deaths worldwide. While there are many proposed treatments for breast cancer, low efficacy, toxicity, and resistance are still major therapeutic obstacles. Thus, there is a need for safer and more effective therapeutic approaches. Because of the direct link between obesity and carcinogenesis, energy restriction mimetic agents (ERMAs) such as the antidiabetic agent, metformin was proposed as a novel antiproliferative agent. However, the anticancer dose of metformin alone is relatively high and impractical to be implemented safely in patients. The current work aimed to sensitize resistant breast cancer cells to metformin's antiproliferative effect using the natural potential anticancer agent, tangeretin.

METHODS

The possible synergistic combination between metformin and tangeretin was initially evaluated using MTT cell viability assay in different breast cancer cell lines (MCF-7, MDA-MB-231, and their resistant phenotype). The possible mechanisms of synergy were investigated via Western blotting analysis, reactive oxygen species (ROS) measurement, annexin/PI assay, cell cycle analysis, and wound healing assay.

RESULTS

The results indicated the ability of tangeretin to improve the anticancer activity of metformin. Interestingly, the improved activity was almost equally observed in both parental and resistant cancer cells, which underlines the importance of this combination in cases of the emergence of resistance. The synergy was mediated through the enhanced activation of AMPK and ROS generation in addition to the improved inhibition of cell migration, induction of cell cycle arrest, and apoptosis in cancer cells.

CONCLUSION

The current work underscores the importance of metformin as an ERMA in tackling breast cancer and as a novel approach to boost its anticancer activity via a synergistic combination with tangeretin.

Acute regulation of apical ABC transporters in the gut. Potential influence on drug bioavailability

The extensive intestinal surface offers an advantage regarding nutrient, ion and water absorptive capacity but also brings along a high exposition to xenobiotics, including drugs of therapeutic use and food contaminants. After absorption of these compounds by the enterocytes, apical ABC transporters play a key role in secreting them back to the intestinal lumen, hence acting as a transcellular barrier. Rapid and reversible modulation of their activity is a subject of increasing interest for pharmacologists. On the one hand, a decrease in transporter activity may result in increased absorption of therapeutic agents given orally. On the other hand, an increase in transporter activity would decrease their absorption and therapeutic efficacy. Although of less relevance, apical ABC transporters also contribute to disposition of drugs systemically administered. This review article summarizes the present knowledge on the mechanisms aimed to rapidly regulate the activity of the main apical ABC transporters of the gut: multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 2 (MRP2) and breast cancer resistance protein (BCRP). Regulation of these mechanisms by drugs, drug delivery systems, drug excipients and nutritional components are particularly considered. This information could provide the basis for controlled regulation of bioavailability of therapeutic agents and at the same time would help to prevent potential drug-drug interactions.

Prospects of tangeretin as a modulator of cancer targets/pathways

To date, cancer is the second leading cause of death worldwide after cardiac arrest. A large number of synthetic drugs are available for the treatment of different types of cancer; however, a major problem associated with these drugs is its toxicity towards the normal cells. To overcome these problems, researchers explore plants derived phytochemicals because of their pleiotropic action and least toxicity towards the normal cells. Tangeretin is a polymethoxylated flavone found extensively in citrus fruits and has shown potent anti-cancer activity in different types of cancer cells. Hence, this review examines the anti-cancer activity of tangeretin via different molecular targets/pathways. Tangeretin induces apoptosis via intrinsic as well as extrinsic pathways and arrest the cell cycle. It also suppresses cell proliferation by modulating PI3K/AKT/mTOR, Notch, and MAPK signalling pathways. Besides, it induces autophagic cell death, suppresses migration, invasion, and angiogenesis. Further, the role of tangeretin in multi-drug resistance and combination therapy, different biological sources of tangeretin, its derivatives, and pharmacokinetics profile and toxicity studies are also discussed. Towards the end, the challenges associated with tangeretin usage as potential anti-cancer phytochemicals have also been discussed. Tangeretin, like a pandora's box, needs to be explored further, and more research is warranted to improve its usefulness for better human health.

Anticancer activities of phytoconstituents and their liposomal targeting strategies against tumor cells and the microenvironment

Various bioactive ingredients have been extracted from Chinese herbal medicines (CHMs) that affect tumor progression and metastasis. To further understand the mechanisms of CHMs in cancer therapy, this article summarizes the effects of five categories of CHMs and their active ingredients on tumor cells and the tumor microenvironment. Despite their treatment potential, the undesirable physicochemical properties (poor permeability, instability, high hydrophilicity or hydrophobicity, toxicity) and unwanted pharmacokinetic profiles (short half-life in blood and low bioavailability) restrict clinical studies of CHMs. Therefore, development of liposomes through relevant surface modifying techniques to achieve targeted CHM delivery for cancer cells, i.e., extracellular and intracellular targets and targets in tumor microenvironment or vasculature, have been reviewed. Current challenges of liposomal targeting of these phytoconstituents and future perspective of CHM applications are discussed to provide an informative reference for interested readers.

Tangeretin: a mechanistic review of its pharmacological and therapeutic effects

To date, a large number of synthetic drugs have been developed for the treatment and prevention of different disorders, such as neurodegenerative diseases, diabetes mellitus, and cancer. However, these drugs suffer from a variety of drawbacks including side effects and low efficacy. In response to this problem, researchers have focused on the plant-derived natural products due to their valuable biological activities and low side effects. Flavonoids consist of a wide range of naturally occurring compounds exclusively found in fruits and vegetables and demonstrate a number of pharmacological and therapeutic effects. Tangeretin (TGN) is a key member of flavonoids that is extensively found in citrus peels. It has different favorable biological activities such as antioxidant, anti-inflammatory, antitumor, hepatoprotective, and neuroprotective effects. In the present review, we discuss the various pharmacological and therapeutic effects of TGN and then, demonstrate how this naturally occurring compound affects signaling pathways to exert its impacts.

Discovery of Novel Multi-target Inhibitor of angiotensin type 1 receptor and neprilysin inhibitors from Traditional Chinese Medicine

Angiotensin II type-1 receptor–neprilysin inhibitor (ARNi) is consisted of Angiotensin II type-1 receptor (AT1) antagonist and neprilysin (NEP) inhibitor, which could simultaneously increase the vasodilators of the natriuretic peptides and antagonize vasoconstrictors of Ang II. ARNi has been proved a superior effect and lower risks of death on chronic heart failure (CHF) and hypertension. In this paper, ARNi from Traditional Chinese Medicines (TCM) was discovered based on target combination of AT1 and NEP by virtual screening, biological assay and molecular dynamics (MD) simulations. Two customized strategies of combinatorial virtual screening were implemented to discover AT1 antagonist and NEP inhibitor based on pharmacophore modeling and docking computation respectively. Gyrophoric acid (PubChem CID: 135728) from Parmelia saxatilis was selected as AT1 antagonist and assayed with IC₅₀ of 29.76 μM by calcium influx assay. And 3,5,3′-triiodothyronine (PubChem CID: 861) from Bos taurus domesticus was screened as NEP inhibitor and has a dose dependent inhibitory activity by biochemistry fluorescence assay. Combined with MD simulations, these compounds can generate interaction with the target, key interactive residues of ARG167, TRP84, and VAL108 in AT1, and HIS711 in NEP were also identified respectively. This study designs the combinatorial strategy to discover novel frames of ARNi from TCM, and gyrophoric acid and 3,5,3′-triiodothyronine could provide the clues and revelations of drug design and therapeutic method of CHF and hypertension for TCM clinical applications.

Quantitative Structure⁻Activity Relationships for the Flavonoid-Mediated Inhibition of P-Glycoprotein in KB/MDR1 Cells

P-glycoprotein (P-gp) serves as a therapeutic target for the development of inhibitors to overcome multidrug resistance (MDR) in cancer cells. In order to enhance the uptake of chemotherapy drugs, larger amounts of P-gp inhibitors are required. Besides several chemically synthesized P-gp inhibitors, flavonoids as P-gp inhibitors are being investigated, with their advantages including abundance in our daily diet and a low toxicity. The cytotoxicity of daunorubicin (as a substrate of P-gp) to KB/MDR1 cells and the parental KB cells was measured in the presence or absence of flavonoids. A two-dimensional quantitative structure–activity relationship (2D-QSAR) model was built with a high cross-validation coefficient (Q²) value of 0.829. Descriptors including vsurf_DW23, E_sol, Dipole and vsurf_G were determined to be related to the inhibitory activity of flavonoids. The lack of 2,3-double bond, 3′-OH, 4′-OH and the increased number of methoxylated substitutions were shown to be beneficial for the inhibition of P-gp. These results are important for the screening of flavonoids for inhibitory activity on P-gp.

Establishment and Use of Human Mouth Epidermal Carcinoma (KB) Cells Overexpressing P-Glycoprotein To Characterize Structure Requirements for Flavonoids Transported by the Efflux Transporter

This study was aimed to determine the mechanism for flavonoid poor absorption related to P-glycoprotein (P-gp). The cellular uptake (CU) of 40 flavonoids was investigated in P-gp overexpressing KB/multidrug-resistant (MDR) cells. A total of 9 flavonoids, including 5,7,3',4'-tetramethoxyflavone, with a significant ( p < 0.05) CU_KBE (2.90 ± 0.146 μmol/g) higher than CU_KBP (1.57 ± 0.129 μmol/g) were identified as P-gp substrates. Besides, 8 substrates, including tangeretin, showed a significant ( p < 0.05) CU_KB (9.72 ± 1.09 μmol/g) higher than its CU_KBP (7.36 ± 0.692 μmol/g). A total of 7 of 17 flavonoid substrates stimulated the P-gp efflux of rhodamine 123, and most substrates increased P-gp expression in KB/MDR cells. Docking analyses showed a good correlation ( R = 0.764; p < 0.01) between efflux fold and S_scoring of flavonoids to the P-gp model, indicating consistency between in silico and in vitro results. A structure-affinity relationship exhibited that 3-OH, 5-OH, 3'-OCH₃, and 4'-OCH₃ are crucial for flavonoids binding to P-gp. These results provide valuable information for finding a solution to improve the absorption of flavonoids.

Citrus Tangeretin Improves Skeletal Muscle Mitochondrial Biogenesis via Activating the AMPK-PGC1-α Pathway In Vitro and In Vivo: A Possible Mechanism for Its Beneficial Effect on Physical Performance

Mitochondrial biogenesis is a key factor, which influences the function of skeletal muscle. Increasingly, flavonoids are reported to have the potential ability of regulating mitochondrial biogenesis. In this study, we investigated the effects of tangeretin, a polymethoxylated flavonoid isolated from mandarin fruits, on mitochondrial biogenesis and its underlying mechanisms. The tangeretin was obtained from the peel of "Dahongpao" tangerine by macroporous adsorptive resins combined with preparative-high performance liquid chromatography. The activity of mitochondrial biogenesis was explored by using mouse-derived C2C12 myoblasts and Kunming mice. Results showed that the purity of tangeretin obtained was 98.64%, and it could effectively activate mitochondrial biogenesis signaling pathway both at gene and at protein levels in C2C12 myoblasts. Animal experiments showed that tangeretin pretreatment could markedly improve exercise performance (the time of hanging wire and run to fatigue was obviously increased 1.6-fold and 2.1-fold in the high-dose tangeretin group, respectively), and the transmission electron microscopy, Western blotting, and immunohistochemistry further indicated that tangeretin increased mitochondria number and activated mitochondrial biogenesis signaling axis. Our findings suggest that tangeretin enhanced mitochondrial biogenesis via activating the AMPK-PGC1-α pathway, resulting in the improvement of exercise performance, and tangeretin may be a potentially novel mitochondria regulator in foods.

Beneficial Pharmacokinetic Drug Interactions: A Tool to Improve the Bioavailability of Poorly Permeable Drugs

Simultaneous oral intake of herbs, supplements, foods and drugs with other drug(s) may result in pharmacokinetic or pharmacodynamic interactions with the latter. Although these interactions are often associated with unwanted effects such as adverse events or inefficacy, they can also produce effects that are potentially beneficial to the patient. Beneficial pharmacokinetic interactions include the improvement of the bioavailability of a drug (i.e., by enhancing absorption and/or inhibiting metabolism) or prolongation of a drug's plasma level within its therapeutic window (i.e., by decreasing excretion), whereas beneficial pharmacodynamic interactions include additive or synergistic effects. Mechanisms by which pharmacokinetic interactions can cause beneficial effects include enhancement of membrane permeation (e.g., structural changes in the epithelial cell membranes or opening of tight junctions), modulation of carrier proteins (e.g., inhibition of efflux transporters and stimulation of uptake transporters) and inhibition of metabolic enzymes. In the current review, selected pharmacokinetic interactions between drugs and various compounds from different sources including food, herb, dietary supplements and selected drugs are discussed. These interactions may be exploited in the future to the benefit of the patient, for example, by delivering drugs that are poorly bioavailable in therapeutic levels via alternative routes of administration than parenteral injection.

Determination of Tangeretin in Rat Plasma: Assessment of Its Clearance and Absolute Oral Bioavailability

Tangeretin (TAN) is a dietary polymethoxylated flavone that possesses a broad scope of pharmacological activities. A simple high-performance liquid chromatography (HPLC) method was developed and validated in this study to quantify TAN in plasma of Sprague-Dawley rats. The lower limit of quantification (LLOQ) was 15 ng/mL; the intra- and inter-day assay variations expressed in the form of relative standard deviation (RSD) were all less than 10%; and the assay accuracy was within 100 ± 15%. Subsequently, pharmacokinetic profiles of TAN were explored and established. Upon single intravenous administration (10 mg/kg), TAN had rapid clearance (Cl = 94.1 ± 20.2 mL/min/kg) and moderate terminal elimination half-life (t_{1/2 λz} = 166 ± 42 min). When TAN was given as a suspension (50 mg/kg), poor but erratic absolute oral bioavailability (mean value < 3.05%) was observed; however, when TAN was given in a solution prepared with randomly methylated-β-cyclodextrin (50 mg/kg), its plasma exposure was at least doubled (mean bioavailability: 6.02%). It was obvious that aqueous solubility hindered the oral absorption of TAN and acted as a barrier to its oral bioavailability. This study will facilitate further investigations on the medicinal potentials of TAN.

In silico comparisons between natural inhibitors of ABCB1/P-glycoprotein to overcome doxorubicin-resistance in the NCI/ADR-RES cell line

To investigate compound-protein binding mode and molecular dynamic simulation of P-glycoprotein (P-gp), in silico studies were performed to compare 12 naturally occurring compounds using two softwares. The net results showed that piperine (PIP) had the best binding affinity. In vitro studies on doxorubicin (DOX)-resistant NCI/ADR-RES cells, known to express P-gp, showed that, dose-dependently, PIP significantly increased intracellular accumulation of rhodamine-123 and had cytotoxic effects accessed by MTT assay. In addition, PIP at 25 and 50μM significantly potentiated DOX-induced cytotoxicity on the same cell line. P-gp ATPase assay showed that both DOX and PIP had dose-dependent inhibition of orthovandate-sensitive ATPase activity, indicating they are both P-gp inhibitors, with IC₅₀ of 84±1 and 37±2μM, respectively. PIP did not show any activation of ATPase activity, while DOX did, indicating that P-gp does not accept PIP as a substrate. Using DOX at concentration 33.33μM together with PIP (100μM), DOX-mediated P-gp ATPase activity was decreased to levels 4-folds lower than DOX alone. In conclusion, both in silico and in vitro studies confirm that PIP is an inhibitor of P-gp mediated DOX efflux, suggesting PIP as a promising adjuvant to DOX cancer chemotherapy.