Hepatoprotective and antioxidant effects of dietary Glycyrrhiza polysaccharide against TCDD-induced hepatic injury and RT-PCR quantification of AHR2, ARNT2, CYP1A mRNA in Jian Carp (Cyprinus carpio var. Jian)

The administration of Glycyrrhiza polysaccharides mitigates liver injury in mice caused by mancozeb via the Keap1-Nrf2/NF-κB pathway

The extensive utilization of mancozeb (MCZ) poses environmental pollution risks, threatens human health, particularly hepatotoxicity. Glycyrrhiza polysaccharides (GP) exhibit antioxidant, anti-inflammatory and other biological activities. The aim of this study is to explore the mechanism of liver injury in mice exposed to MCZ and the protective effect of GP on alleviating MCZ induced liver injury. Initially, 70 female mice were divided into 7 groups, and the optimal dose of MCZ induced liver injury in mice was screened by oral administration different doses of MCZ (0, 50, 100, 150, 200, 250 and 300 mg/kg MCZ). The results demonstrated that, compared to the blank control group, as the concentration of MCZ increased, several physiological and biochemical parameters were significantly affected. Specifically, body weight and liver index significantly decreased, while the activities of SOD and CAT also decreased. Additionally, the content of ROS increased, the levels of Keap1 and Nrf2 proteins increased, the mRNA levels of Gpx2 and HO-1decreased, and the mRNA levels of Gstt2, GcLc and NQO1 were upregulated. Based on the test data, select 100 mg/kg MCZ as the optimal modeling dose for experimental animals. Sixty female mice were divided into six groups and orally administered: control group A (0.2 mL deionized water), model group B (100 mg/kg MCZ), positive control group F (100 mg/kg MCZ+100 mg/kg VC), the high-dose GP group C (100mg/kgMCZ+200mg/kgGP), the medium-dose GP group D (100 mg/kg MCZ+150mg/kgGP) and the low-dose GP group E (100 mg/kg MCZ+100mg/kgGP). The results showed that compared to the model group, adding GP alleviated the effects of MCZ on body weight, liver index, CAT and SOD activity, MDA content, HO-1, TNF-α, and IL-1β. Additionally, the addition of GP decreased the expression of Keap1, Nrf2, NF-kB, and NQO1, GcLc, and Gstt2 mRNA. GP ameliorated liver vacuolar degeneration, steatosis and nuclear pyknosis ameliorate by MCZ. The results show that MCZ triggers hepatotoxicity via the activation of the Keap1/Nrf2 signaling pathway, whereas GP has the potential to mitigate liver damage caused by MCZ exposure by inhibiting this pathway.

Pharmacokinetic profiling and network pharmacology of honey-fried Licorice: An Integrative workflow to study traditional Chinese medicines (TCMs)

Licorice, known as the "elder statesman," is commonly used in traditional Chinese medicine (TCM) formulations. This study aims to establish a workflow combining animal and in silico experiments to elucidate the mechanisms of TCMs at both qualitative and quantitative levels. UPLC-Q-TOF-MS/MS was employed to qualitatively characterize the total components of honey-fried licorice and the plasma components after oral administration in Beagle dogs. A UPLC-Q-Trap-MS/MS method was developed for the pharmacokinetic study of honey-fried licorice components in Beagle dog plasma. Network pharmacology and molecular docking were utilized to explore the primary functional targets and pathways. In total, we identified 68 constituents in honey-fried licorice, with 28 detected in Beagle dog plasma, and 18 of them, mainly belong to flavonoids and terpenoids, showing significant exposure. The plasma pharmacokinetic study of these 18 constituents revealed that compounds like liquiritin, glycyrrhizic acid, licoricesaponin G2, and glycyrrhetic acid-3-o-glucuronide had significant exposure. Network pharmacology and molecular docking analyses identified MAPK3, PIK3CB, PIK3CA, RAF1, and EGFR as the main targets of the active constituents of honey-fried licorice, involved in pathways such as the Ras signaling pathway, human cytomegalovirus infection, and the MAPK signaling pathway. This study provides a comprehensive profile and pharmacokinetic characteristics of honey-fried licorice, offering insights into its pharmacological, toxicological, and clinical aspects. The established workflow can serve as a standard for investigating other TCMs.

The Substitution of Fish Meal or Chicken Meal With Yeast Culture in Diets of Bullfrogs (Lithobates catesbeianus): Growth Performance, Serum Biochemical Indices, Intestinal Digestive Enzyme, Hepatic Antioxidant, and Hepatic and Intestinal Histology

The aim of this study was to reveal the effects of yeast culture replacing fish meal (FM) or chicken meal (CM) on the growth performance, serum biochemical indexes, intestinal digestive enzyme activities, hepatic antioxidant, and hepatic and intestinal histology of bullfrog (Lithobates catesbeianus). The basal diet contained 100 g/kg FM and 100 g/kg CM, and then yeast culture was used to decrease FM or CM level to 75 and 50 g/kg with yeast culture inclusion of 32 and 64 g/kg, respectively, resulting in five groups of isonitrogenous diets (control, FM75, FM50, CM75, and CM50). A total of 450 bullfrogs (45.5 ± 0.4 g initial weight) were fed the five diets for 50 days. (1) The FM50 group presented significantly lower weight gain, condition factor, hind leg index, and higher feed conversion ratio than the control group, while the other three groups of FM75, CM75, and CM50 showed no significant difference in growth performance when compared to the control group. (2) The serum triglyceride content of FM50 group was significantly lower, while the alkaline phosphatase activity was significantly higher than those of the control group. The serum total cholesterol levels were significantly lower in the CM50 group compared to the control group. (3) In intestinal digestive enzyme activities, the trypsin and α-amylase activities in the CM75 and CM50 groups, the trypsin activity in the FM75 group, and lipase activity in the CM50 group were all significantly higher than those in the other groups. (4) The replacement of 50% FM with yeast culture (FM50 and CM50 groups) promoted the total antioxidant capacity in the liver, but compared to the control group, the intestinal villi height and muscularis propria thickness in the FM50 group were significantly lower. There was no difference (P > 0.05) in liver histology among all the groups. In conclusion, in a basal diet containing 100 g/kg FM and 100 g/kg CM, 32.0 and 64.0 g/kg yeast cultures could successfully replace 25% of dietary FM and 50% of dietary CM without negative effects on the growth performance, serum biochemical indexes, and hepatic and intestinal health of bullfrogs.

In vivo pharmacokinetics of Glycyrrhiza uralensis polysaccharides

Glycyrrhiza uralensis polysaccharides (GUPS) are widely applied in biomedicine and functional food due to their multiple pharmacological activities and low toxicity. Despite their widespread use, the in vivo metabolic profile of GUPS remains poorly understood. To address this gap, we developed a quantitative analysis method that involves labeling GUPS with visible fluorescein (5-DTAF) and near-infrared (NIR) fluorescein (Cy7), resulting in stable conjugates with substitution degrees of 0.81% for 5-DTAF and 0.39% for Cy7. The pharmacokinetic studies showed a biphasic elimination pattern in the blood concentration-time curve following both intravenous and oral administration, consistent with a two-compartment model. Using fluorescence quantification and NIR imaging, we observed that GUPS was distributed to various tissues, exhibiting higher concentrations particularly in liver, kidney and lung. Excretion studies indicated that feces were the major excretion pathway of GUPS after oral administration (60.98%), whereas urine was the main pathway after intravenous administration (31.16%). Notably, GUPS could be absorbed rapidly by gut (Tmax 1 ± 0.61 h) and showed a biological half-time t1/2 26.4 ± 7.72 h after oral administration. Furthermore, the Caco-2 cells uptake studies illustrated that macropinocytosis and clathrin-mediated endocytosis were participated in the transport of GUPS in intestine epithelium. This comprehensive analysis of the in vivo pharmacokinetics of GUPS not only enhances our understanding of its metabolic pathways but also establishes a foundational basis for its clinical application, optimizing its therapeutic potential and safety profile.

Anti-sepsis effect of Xiaochaihu decoction based on the TLR4/MyD88/NF-κB signalling pathway

The aims of this study were to explore the protective effect of Xiaochaihu decoction in mice with sepsis induced by intraperitoneal injection; to explore its anti-inflammatory effect on the TLR4-MyD88-NF-κB signalling pathway; and to explore the main material basis of the anti-inflammatory effect of Xiaochaihu decoction, with the aim of supplementing and expanding the associated research and providing a scientific foundation for the clinical use of the decoction. The effects of Xiaochaihu decoction on septic mice were analysed by measurements of white blood cells (WBC) and Platelets (PLT); Nitric Oxide (NO) level in serum; IL-6, IL-1β and TNF-α levels in serum; RT-PCR; Haematoxylin-Eosin (HE) immunohistochemistry; western blotting (WB). The results showed the excellent in vivo anti-inflammatory effects of Xiaochaihu decoction in LPS-induced septic mice, through down regulation of the gene and protein expression of TLR4, MYD88, TRAF6, IKK, IKBα and p65 and the subsequent reduction in the release of inflammatory mediators IL-6, IL-1β, TNF-α and NO. Moreover, significant anti-septic effect was observed from high and medium doses of Xiaochaihu decoction, but not from the low dose.

The preventive effect of Glycyrrhiza polysaccharide on lipopolysaccharide-induced acute colitis in mice by modulating gut microbial communities

Acute colitis is characterised by an unpredictable onset and causes intestinal flora imbalance together with microbial migration, which leads to complex parenteral diseases. Dexamethasone, a classic drug, has side effects, so it is necessary to use natural products without side effects to prevent enteritis. Glycyrrhiza polysaccharide (GPS) is an α-d-pyranoid polysaccharide with anti-inflammatory effects; however, its anti-inflammatory mechanism in the colon remains unknown. This study investigated whether GPS reduces the lipopolysaccharide (LPS)-induced inflammatory response in acute colitis. The results revealed that GPS attenuated the upregulation of tumour necrosis factor-α, interleukin (IL)-1β, and IL-6 in the serum and colon tissues and significantly reduced the malondialdehyde content in colon tissues. In addition, the 400 mg/kg GPS group showed higher relative expressions of occludin, claudin-1, and zona occludens-1 in colon tissues and lower concentrations of diamine oxidase, D-lactate, and endotoxin in the serum than the LPS group did, indicating that GPS improved the physical and chemical barrier functions of colon tissues. GPS increased the abundance of beneficial bacteria, such as Lactobacillus, Bacteroides, and Akkermansia, whereas pathogenic bacteria, such as Oscillospira and Ruminococcus were inhibited. Our findings indicate that GPS can effectively prevent LPS-induced acute colitis and exert beneficial effects on the intestinal health.

The Roles of Polysaccharides in Carp Farming: A Review

Carp is an important aquaculture species globally, and the production is expected to increase with the growing market demands. Despite that, disease outbreaks remain a major challenge, impeding the development of sustainable carp farming. Moreover, the application of antibiotics, a common prophylactic agent, can adversely impact public health and the environment. Therefore, polysaccharide has been recognized as a novel prophylactic agent in the health management of carp farming, as well as gaining consumers' confidence in carp farming products. In this review, the definition, sources, and main roles of polysaccharides in improving growth performance, stimulating the immune system, enhancing disease resistance, and alleviating abiotic stresses in carp farming are discussed and summarized. In addition, the use of polysaccharides in combination with other prophylactic agents to improve carp farming production is also highlighted. This review aims to highlight the roles of polysaccharides and provide valuable information on the benefits of polysaccharides in carp farming.

Immunomodulatory and antioxidant effects of Glycyrrhiza uralensis polysaccharide in Lohmann Brown chickens

Glycyrrhiza polysaccharide extract 1 (GPS-1) is a bioactive component isolated from Glycyrrhiza uralensis, also known as Chinese licorice. It appears to be pharmacologically active as an antibacterial, antiviral, and anti-tumor agent. GPS-1 has also been shown to buffer liver health and regulate the immune system. Moreover, GPS-1 is low cost and easy to extract. More study was needed to elucidate the biochemical pathways underlying the immunomodulatory and antioxidant benefits observed in Glycyrrhiza polysaccharide extract 1 (GPS-1). in vitro experiments on chicken lymphocytes and dendritic cells (DCs) show that GPS-1 significantly promotes the proliferation of immune cells and is linked to lymphocytes' secretion of IL-12, IFN-γ, and TNF-α by. DC secretion of NO, IL-2, IL-1β, IFN-γ, TNF-α, and IL-12p70 was also increased significantly. Additionally, GPS-1 also displayed a significant antioxidant effect in vitro, able to scavenge DPPH, hydrogen peroxide, ABTS, and other free radicals like superoxide anions. Separately, GPS-1 was tested in vivo in combination with the Newcastle disease virus (NDV) - attenuated vaccine. 120 Lohmann Brown chickens were vaccinated, while another 30 became the unvaccinated blank control (BC) group. For three consecutive days 1 mL of GPS-1 was administered at doses of 19.53 μg/mL, 9.77 μg/mL, or 4.88 μg/mL to the ND-vaccinated birds, except for the vaccine control (VC), where n = 30 per group. In vivo results show that GPS-1 combined with Newcastle disease (ND) vaccine had the best efficacy at significantly increasing chickens' body weight and ND serum antibody titer, enhancing their secretion of IL-2 and IFN- γ, and promoting the development of immune organs. The results also indicate that GPS-1 was able increase the proliferation of in vitro immune cells and elevate their cytokine secretion, which enhances the body's immune response. GPS-1 also clearly has the potential to be used as an immune adjuvant alongside ND vaccination.

Isolation, Characterization, Pharmacology and Biopolymer Applications of Licorice Polysaccharides: Review

Licorice is known as "Gan-Cao" in traditional Chinese Medicine (TCM), belonging to the genus Glycyrrhiza (Family: Fabaceae/Leguminosae). It has a long medicinal history and wide applications in China. Polysaccharides of licorice (LPs) are one of the key bioactive components. As herbal polysaccharides attracted increasing interest in the past several decades, their extraction, isolation, structural characterization, pharmacological activities, and medicinal application have been explored extensively. It is worth heeding that the method of extraction and purification effects LPs, apart from specie and origin specificity. This review evaluates the method of extraction and purification and demonstrates its performance in gaining specific composition and its structure-activity relationship, which might lead the readers to a fresh horizon for developing advanced treatment strategies. It is recently reported that the conformation of LPs plays a vital role as biopolymers, such as selenized modification, microencapsulation, nanocomposite, liposome formulation, drug/hydrogel combinations, biosensor device, and synergistic effect with a vaccine. In addition, LPs showed a good thermodynamics profile, as these properties enable them to interact with additional supramolecular interaction by chemical modifications or copolymerization. Functional polymers that are responsive to various external stimuli, such as physical, chemical, and biological signals, are a promising study topic. Thus, LPs are emerging as a new biomaterial that can enhance intended formulation along exerting its inherent medicinal effects. It is hoped that this review will provide a basis for the utilization and further developments of licorice polysaccharides in the vast medium.

Coal mine effluent-induced metal bioaccumulation, biochemical, oxidative stress, metallothionein, and histopathological alterations in vital tissues of the catfish, Clarias batrachus

In the present study, a multi-biomarker approach was used to assess the toxicity of the coal mine effluent (CME) generated at the Rajrappa coal mine on the catfish Clarias batrachus. A core of biomarkers indicative of nutritional value, oxidative stress, and histopathology was selected to illustrate the toxic effects of CME-containing different heavy metals and other toxicants. The results of metal bioaccumulation in CME-exposed fish tissues revealed the highest metal concentration in liver (1.34-297.68 mg/kg) while lowest in muscles (1.47-23.26 mg/kg) as compared to other tissues and so was the metallothionein level. The high value of bioaccumulation observed in liver, kidney, and gills reflects their affinity for metals. In addition, the values of metal pollution index (MPI) of different fish tissues further affirmed that liver followed by kidney and gills are at greater risk than brain, skin, and muscles. Significant alterations in the activity of certain enzymes (aspartate amino transferase, alanine amino transferase, alkaline phosphatase) as well as oxidative stress markers (superoxide dismutase, catalase and lipid peroxidation) were detected in the tissues of CME-exposed fish. The tissue-specific metal accumulation and increased metallothionein levels may be associated with the biochemical and physiological activity of an organ and its constitutive antioxidant defenses. The histopathological changes in the various tissues of the CME-exposed fish justify the high metal accumulation and biochemical alterations. Overall results indicate that the Rajrappa coal mine effluent is very toxic having adverse health impact on the fish and might also affect the human health when consumed.

Effects of dietary yeast culture on shrimp growth, immune response, intestinal health and disease resistance against Vibrio harveyi

The current study was conducted to evaluate the effects of different levels of yeast culture (YC) supplementation at 0% (YC 0%), 1% (YC 1%), and 2% (YC 2%) on growth, feed conversion ratio, body composition, intestinal morphology, microflora, immune response, and resistance to Vibrio harveyi infection in Litopenaeus vannamei. After 8-weeks feeding trial, the results showed significant improvement (p < .05) in the final weight, weight gain rate, specific growth rate, survival rate and low feed conversion ratio in YC groups than the control. Serum total protein, superoxide dismutase, catalase, alkaline phosphatase, acid phosphatase, lysozyme, and phenol oxidase in shrimps fed diet YC (2%) were significantly higher (p < .05), whereas significantly decreased trend in serum cholesterol, triglyceride, aspartate aminotransferase, and alanine aminotransferase (p < .05) were observed in YC (2%) diet. Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes were the core phylum bacteria found in the shrimp intestines. At the genus level, opportunistic pathogenic bacteria, Vibrio was significantly decreased (p < .05) while beneficial bacteria Pseudoalteromonas was increased in YC (2%) group. Intestinal villus height and width in shrimps fed YC diets were significantly improved than the control diet (p < .05). YC groups challenged test significantly showed (p < .05) improved shrimps immune response against V. harveyi infections with YC (2%) recording the highest percentage survival rate (70%). The present study demonstrated that supplementing YC (2%) can improve growth, intestinal microbiota, intestinal morphology, and immune response against V. harveyi infections in L. vannamei.

Resource, chemical structure and activity of natural polysaccharides against alcoholic liver damages

Many natural polysaccharides from bio-resources hold advantages of multi-functions, high efficiency, non-toxicity or low side effect, and have strong potentials in protection against alcoholic liver damages. This review summarized the bio-resources, chemical and structural characteristics of natural polysaccharides with potentials in inhibition against alcoholic liver damages, and also emphasized knowledge on correlations between their chemical structure and function. Approximately 95 species were confirmed in generation of hepatoprotective polysaccharides. Products as crude polysaccharides originated from 17 species were sum up despite the indetermination of their accurate structure. Additional four polysaccharides were described for their known chemical structures. Possible roles of hepatoprotective polysaccharides were provided with evidence on antioxidant promotion, lipids regulation, apoptosis inhibition and anti-inflammation, as well as confirmations in immune enhancement, iron removal and anti-fibrosis when currently treated against the alcoholic liver damages. To sum up, this overview could serve to guide development and utilization of natural hepatoprotective polysaccharides.

Catalpol protects against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cytotoxicity in osteoblastic MC3T3-E1 cells

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental contaminant that produces a wide variety of adverse effects in humans. Catalpol, a major bioactive compound enriched in the dried root of Rehmannia glutinosa, is a major iridoid glycoside that alleviates bone loss. However, the detailed mechanisms underlying the effects of catalpol remain unclear. The present study evaluated the effects of catalpol on TCDD-induced cytotoxicity in osteoblastic MC3T3-E1 cells. Catalpol inhibited TCDD-induced reduction in cell viability and increases in apoptosis and autophagic activity in osteoblastic MC3T3-E1 cells. Additionally, pretreatment with catalpol significantly decreased the nitric oxide and nitrite levels compared with a control in TCDD-treated cells and significantly inhibited TCDD-induced increases in the levels of cytochrome P450 1A1 and extracellular signal-regulated kinase. Pretreatment with catalpol also effectively restored the expression of superoxide dismutase and extracellular signal-regulated kinase 1 and significantly enhanced the expression of glutathione peroxidase 4 and osteoblast differentiation markers, including alkaline phosphatase and osterix. Taken together, these findings demonstrate that catalpol has preventive effects against TCDD-induced damage in MC3T3-E1 osteoblastic cells.

Xiaochaihu Decoction reduces hepatic steatosis and improves D-GalN/LPS-induced liver injury in hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀)

Excessive lipid accumulation and chemical abuse can induce fatty liver diseases in fish, but the underlying mechanism and therapies are unknown. The present study aims to evaluate the effects of Xiaochaihu Decoction (XCHD) on the growth performance, lipid metabolism and antioxidant function of hybrid grouper in vitro and in vivo, and provide evidence as to whether it can be potentially used as a medicine for liver diseases in aquaculture. In vitro, steatosis model of hybrid grouper primary hepatocytes were incubated for 48 h in control or lipid emulsion (LE)-containing medium with or without 24 h post-treatment with XCHD. XCHD treatment reversed the LE-induced intracellular lipid accumulation, cell viability and hepatocytes morphological structure. In vivo, a total of 300 hybrid grouper with an average initial weight of 25.43 ± 0.18 g were fed diets containing five graded levels of XCHD at 150-1200 mg/kg diet for 8 weeks. After that, a challenge trial was conducted by injection of D-GalN/LPS to induce liver injury. As a result, dietary supplementation with 150-300 mg/kg XCHD diets can significant improve growth performance and feed utilization (P < 0.05). Dietary XCHD down-regulated the expression of lipogenic-related genes (G6PD, DGAT2 and ME1) and up-regulated lipolysis-related genes (ATGL, PPARα and LPL) expression in the liver of hybrid grouper. Livers challenged with D-GalN/LPS exhibited extensive areas of vacuolization with the disappearance of nuclei and the loss of hepatic architecture. These pathological alterations were ameliorated by XCHD treatment. XCHD significantly down-regulated the D-GalN/LPS induced apoptosis-related genes caspase-3, caspase-9 and p53 mRNA expression and up-regulated the antioxidant-related genes CAT and MnSOD mRNA expression in dose dependent manner, respectively. XCHD potently reduced hepatic lipid accumulation and enhanced antioxidant capability in hybrid grouper and may be a potential fish-feed additive to prevent fatty liver diseases onset and progression.

Transcriptomic analysis reveals dose-dependent modes of action of benzo(a)pyrene in polar cod (Boreogadus saida)

Polar cod (Boreogadus saida) has been used as a model Arctic species for hazard assessment of environmental stressors such as polycyclic aromatic hydrocarbons (PAHs). However, most of the PAH studies using polar cod rely on targeted biomarker-based analysis thus may not adequately address the complexity of the toxic mechanisms of the stressors. The present study was performed to develop a broad-content transcriptomic platform for polar cod and apply it for understanding the toxic mechanisms of a model PAH, benzo(a)pyrene (BaP). Hepatic transcriptional analysis using a combination of high-density polar cod oligonucleotide microarray and quantitative real-time RT-PCR was conducted to characterize the stress responses in polar cod after 14d repeated dietary exposure to 0.4 (Low) and 20.3 μg/g fish/feeding (High) BaP doses. Bile metabolic analysis was performed to identify the storage of a key BaP hepatic biotransformation product, 3-hydroxybenzo(a)pyrene (3-OH-BaP). The results clearly showed that 3-OH-BaP was detected in the bile of polar cod after both Low and High BaP exposure. Dose-dependent hepatic stress responses were identified, with Low BaP suppressing genes involved in the defense mechanisms and High BaP inducing genes associated with these pathways. The results suggested that activation of the aryl hydrocarbon receptor signaling, induction of oxidative stress, DNA damage and apoptosis were the common modes of action (MoA) of BaP between polar cod or other vertebrates, whereas induction of protein degradation and disturbance of mitochondrial functions were proposed as novel MoAs. Furthermore, conceptual toxicity pathways were proposed for BaP-mediated effects in Arctic fish. The present study has for the first time reported a transcriptome-wide analysis using a polar cod-specific microarray and suggested novel MoAs of BaP. The analytical tools, bioinformatics solutions and mechanistic knowledge generated by this study may facilitate mechanistically-based hazard assessment of environmental stressors in the Arctic using this important fish as a model species.

Flavonoids as modulators of metabolic enzymes and drug transporters

Flavonoids, natural compounds found in plants and in plant-derived foods and beverages, have been extensively studied with regard to their capacity to modulate metabolic enzymes and drug transporters. In vitro, flavonoids predominantly inhibit the major phase I drug-metabolizing enzyme CYP450 3A4 and the enzymes responsible for the bioactivation of procarcinogens (CYP1 enzymes) and upregulate the enzymes involved in carcinogen detoxification (UDP-glucuronosyltransferases, glutathione S-transferases (GSTs)). Flavonoids have been reported to inhibit ATP-binding cassette (ABC) transporters (multidrug resistance (MDR)-associated proteins, breast cancer-resistance protein) that contribute to the development of MDR. P-glycoprotein, an ABC transporter that limits drug bioavailability and also induces MDR, was differently modulated by flavonoids. Flavonoids and their phase II metabolites (sulfates, glucuronides) inhibit organic anion transporters involved in the tubular uptake of nephrotoxic compounds. In vivo studies have partially confirmed in vitro findings, suggesting that the mechanisms underlying the modulatory effects of flavonoids are complex and difficult to predict in vivo. Data summarized in this review strongly support the view that flavonoids are promising candidates for the enhancement of oral drug bioavailability, chemoprevention, and reversal of MDR.