Health effects of quercetin: from antioxidant to nutraceutical.

Tumors contain oxygenated and hypoxic regions, so the tumor cell population is heterogeneous. Hypoxic tumor cells primarily use glucose for glycolytic energy production and release lactic acid, creating a lactate gradient that mirrors the oxygen gradient in the tumor. By contrast, oxygenated tumor cells have been thought to primarily use glucose for oxidative energy production. Although lactate is generally considered a waste product, we now show that it is a prominent substrate that fuels the oxidative metabolism of oxygenated tumor cells. There is therefore a symbiosis in which glycolytic and oxidative tumor cells mutually regulate their access to energy metabolites. We identified monocarboxylate transporter 1 (MCT1) as the prominent path for lactate uptake by a human cervix squamous carcinoma cell line that preferentially utilized lactate for oxidative metabolism. Inhibiting MCT1 with alpha-cyano-4-hydroxycinnamate (CHC) or siRNA in these cells induced a switch from lactate-fueled respiration to glycolysis. A similar switch from lactate-fueled respiration to glycolysis by oxygenated tumor cells in both a mouse model of lung carcinoma and xenotransplanted human colorectal adenocarcinoma cells was observed after administration of CHC. This retarded tumor growth, as the hypoxic/glycolytic tumor cells died from glucose starvation, and rendered the remaining cells sensitive to irradiation. As MCT1 was found to be expressed by an array of primary human tumors, we suggest that MCT1 inhibition has clinical antitumor potential.

/pdf/targeting-lactate-fueled-respiration-selectively-kills-3m61rjbps3.pdf

Targeting lactate-fueled respiration selectively kills hypoxic tumor cells in mice

Given the trillions of microbes that inhabit the mammalian intestines, the host immune system must constantly maintain a balance between tolerance to commensals and immunity against pathogens to avoid unnecessary immune responses against otherwise harmless bacteria. Misregulated responses can lead to inflammatory bowel diseases such as ulcerative colitis or Crohn's disease. The mechanisms by which the immune system maintains this critical balance remain largely undefined. Here, we demonstrate that the short-chain fatty acid n-butyrate, which is secreted in high amounts by commensal bacteria, can modulate the function of intestinal macrophages, the most abundant immune cell type in the lamina propria. Treatment of macrophages with n-butyrate led to the down-regulation of lipopolysaccharide-induced proinflammatory mediators, including nitric oxide, IL-6, and IL-12, but did not affect levels of TNF-α or MCP-1. These effects were independent of toll-like receptor signaling and activation of G-protein-coupled receptors, two pathways that could be affected by short-chain fatty acids. In this study, we provide several lines of evidence that suggest that these effects are due to the inhibition of histone deacetylases by n-butyrate. These findings elucidate a pathway in which the host may maintain tolerance to intestinal microbiota by rendering lamina propria macrophages hyporesponsive to commensal bacteria through the down-regulation of proinflammatory effectors.

https://www.pnas.org/content/pnas/111/6/2247.full.pdf

The microbial metabolite butyrate regulates intestinal macrophage function via histone deacetylase inhibition

Multidrug resistance proteins: role of P-glycoprotein, MRP1, MRP2, and BCRP (ABCG2) in tissue defense

Short-chain fatty acids (SCFAs), the main metabolites produced by bacterial fermentation of dietary fibre in the gastrointestinal tract, are speculated to have a key role in microbiota-gut-brain crosstalk. However, the pathways through which SCFAs might influence psychological functioning, including affective and cognitive processes and their neural basis, have not been fully elucidated. Furthermore, research directly exploring the role of SCFAs as potential mediators of the effects of microbiota-targeted interventions on affective and cognitive functioning is sparse, especially in humans. This Review summarizes existing knowledge on the potential of SCFAs to directly or indirectly mediate microbiota-gut-brain interactions. The effects of SCFAs on cellular systems and their interaction with gut-brain signalling pathways including immune, endocrine, neural and humoral routes are described. The effects of microbiota-targeted interventions such as prebiotics, probiotics and diet on psychological functioning and the putative mediating role of SCFA signalling will also be discussed, as well as the relationship between SCFAs and psychobiological processes. Finally, future directions to facilitate direct investigation of the effect of SCFAs on psychological functioning are outlined.

The role of short-chain fatty acids in microbiota-gut-brain communication.

Dietary flavonoids: effects on xenobiotic and carcinogen metabolism.

Breast cancer resistance protein (BCRP) is a newly identified ATP-binding cassette transporter, shown to confer multidrug resistance (MDR) to a number of important anticancer agents and play an important function in governing drug disposition. Flavonoids are a class of polyphenolic compounds widely present in foods and herbal products. The interactions of flavonoids with P-glycoprotein and multidrug resistance-associated protein 1 have been reported; however, their interaction with BCRP is unknown. Our objective was to evaluate the effects of 20 naturally occurring flavonoids on the cellular accumulation and cytotoxicity of mitoxantrone in both BCRP-overexpressing and BCRP-negative human cell lines. BCRP-overexpressing and BCRP-negative human breast cancer cells (MCF-7) and large cell lung carcinoma cells (NCI-H460) were used in these studies. Many of the tested flavonoids (50 microM) increased mitoxantrone accumulation in BCRP-overexpressing cells, completely reversing mitoxantrone resistance, with no effect on the corresponding BCRP-negative cells, indicating that these flavonoids are BCRP inhibitors. The effects of these flavonoids on the cellular accumulation and cytotoxicity of mitoxantrone were flavonoid concentration dependent, and significant changes were produced at concentrations lower than 10 microM for most of the flavonoids. Chrysin and biochanin A were the most potent BCRP inhibitors, producing significant increases in mitoxantrone accumulation at concentrations of 0.5 or 1.0 microM and in mitoxantrone cytotoxicity at a concentration of 2.5 microM. Flavonoid glycosides had no effects on the BCRP-mediated transport of mitoxantrone. The results obtained in this study could be clinically relevant in terms of both MDR reversal in cancer treatment and drug-flavonoid pharmacokinetic interactions.

Flavonoids Are Inhibitors of Breast Cancer Resistance Protein (ABCG2)-Mediated Transport

Flavonoids are constituents of fruits, vegetables, and plant-derived beverages, as well as components in herbal-containing dietary supplements. The objective of this investigation was to characterize the effect of flavonoids on P-glycoprotein (P-gp)-mediated cellular efflux and to determine the molecular mechanism(s) of the flavonoid-drug interaction. Studies were conducted in the sensitive and multidrug resistant human breast cancer cell lines MCF-7 and MDA435/LCC6 and examined the effects of the flavonoids biochanin A, morin, phloretin, and silymarin on daunomycin (DNM) accumulation and doxorubicin cytotoxicity. The potential mechanism(s) involved in the interaction was evaluated by determining flavonoid effects on 1) P-gp ATPase activity, 2) [ 3 H]azidopine photoaffinity labeling of P-gp, and 3) cellular P-gp levels. The flavonoids increased [ 3 H]DNM accumulation in P-gp positive cells, but not P-gp negative cells, and these effects were both flavonoid concentration- and P-gp expression level-dependent. Biochanin A and silymarin potentiated doxorubicin cytotoxicity in P-gp positive cells. Biochanin A and phloretin stimulated, whereas morin and silymarin inhibited P-gp ATPase activity, confirming that these flavonoids interact with P-gp. Morin and silymarin significantly inhibited [ 3 H]azidopine photoaffinity labeling of P-gp, suggesting a direct interaction with P-gp substrate binding. A 24-h preincubation with all flavonoids, followed by flavonoid removal, did not alter cellular P-gp level in P-gp positive cells. In conclusion, biochanin A, morin, phloretin, and silymarin all inhibited P-gp-mediated cellular efflux and the mechanism of the interaction involved, at least in part, a direct interaction. The findings of this study indicate a potential for significant flavonoid-drug interactions with P-gp substrates.

/pdf/effects-of-the-flavonoids-biochanin-a-morin-phloretin-and-2qh22slfa0.pdf

Effects of the Flavonoids Biochanin A, Morin, Phloretin, and Silymarin on P-Glycoprotein-Mediated Transport

Breast cancer resistance protein (BCRP/ABCG2) is a molecular determinant of pharmacokinetic properties of many drugs in humans. To understand post-transcriptional regulation of ABCG2 and the role of microRNAs (miRNAs) in drug disposition, we found that microRNA-328 (miR-328) might readily target the 3′-untranslated region (3′-UTR) of ABCG2 when considering target-site accessibility. We then noted 1) an inverse relation between the levels of miR-328 and ABCG2 in MCF-7 and MCF-7/MX100 breast cancer cells and 2) that miR-328 levels could be rescued in MCF-7/MX100 cells by transfection with miR-328 plasmid. Luciferase reporter assays showed that ABCG2 3′-UTR-luciferase activity was decreased more than 50% in MCF-7/MX100 cells after transfection with miR-328 plasmid, the activity was increased over 100% in MCF-7 cells transfected with a miR-328 antagomir, and disruption of miR-328 response element within ABCG2 3′-UTR led to a 3-fold increase in luciferase activity. Furthermore, the level of ABCG2 protein was down-regulated when miR-328 was over-expressed, and the level was up-regulated when miR-328 was inhibited by selective antagomir. Altered ABCG2 protein expression was associated with significantly declined or elevated levels of ABCG2 3′-UTR and coding sequence mRNAs, suggesting possible involvement of the mechanism of mRNA cleavage. Finally, miR-328-directed down-regulation of ABCG2 expression in MCF-7/MX100 cells resulted in an increased mitoxantrone sensitivity, as manifested by a significantly lower IC50 value (2.46 ± 1.64 μM) compared with the control (151 ± 32 μM). Together, these findings suggest that miR-328 targets ABCG2 3′-UTR and, consequently, controls ABCG2 protein expression and influences drug disposition in human breast cancer cells.

/pdf/microrna-328-negatively-regulates-the-expression-of-breast-amc24nfvoi.pdf

Marilyn E. Morris

Papers

Dietary flavonoids: effects on xenobiotic and carcinogen metabolism.

Flavonoids Are Inhibitors of Breast Cancer Resistance Protein (ABCG2)-Mediated Transport

Effects of the Flavonoids Biochanin A, Morin, Phloretin, and Silymarin on P-Glycoprotein-Mediated Transport

MicroRNA-328 Negatively Regulates the Expression of Breast Cancer Resistance Protein (BCRP/ABCG2) in Human Cancer Cells

Flavonoid–drug interactions: Effects of flavonoids on ABC transporters