Nicole Teller

Coffee constituents as modulators of Nrf2 nuclear translocation and ARE (EpRE)-dependent gene expression

Oxidative cellular stress initiates Nrf2 translocation into the nucleus, thus inducing antioxidant response element (ARE)-mediated expression of Phase II enzymes involved in detoxification and antioxidant defence. We investigated whether coffee extracts (CEs) of different proveniences and selected constituents have an impact on the Nrf2/ARE pathway in human colon carcinoma cells (HT29). Assessed as increased nuclear Nrf2 protein, Nrf2 nuclear translocation was modulated by different CEs as observed by Western blot analysis. In addition to the known Nrf2 activator 5-O-caffeoylquinic acid (CGA), pyridinium derivatives like the N-methylpyridinium ion (NMP) were identified as potent activators of Nrf2 nuclear translocation and ARE-dependent gene expression of selected antioxidative Phase II enzymes in HT29. Thereby, the substitution pattern at the pyridinium core structure determined the impact on Nrf2-signalling. In contrast, trigonelline was found to interfere with Nrf2 activation, effectively suppressing the NMP-mediated induction of Nrf2/ARE-dependent gene expression. In conclusion, several coffee constituents, partly already present in the raw material as well as those generated during the roasting process, contribute to the Nrf2-translocating properties of consumer-relevant coffee. A fine tuning in the degradation/formation of activating and deactivating constituents of the Nrf2/ARE pathway during the roasting process appears to be critical for the chemopreventive properties of the final coffee product.

Do anthocyanins and anthocyanidins, cancer chemopreventive pigments in the diet, merit development as potential drugs?

Anthocyanins, plant pigments in fruits and berries, have been shown to delay cancer development in rodent models of carcinogenesis, especially those of the colorectal tract. Anthocyanins and anthocyanidins, their aglycons, especially cyanidin and delphinidin, have been subjected to extensive mechanistic studies. In cells in vitro, both glycosides and aglycons engage an array of anti-oncogenic mechanisms including anti-proliferation, induction of apoptosis and inhibition of activities of oncogenic transcription factors and protein tyrosine kinases. Anthocyanins and anthocyanidins exist as four isomers, interconversion between which depends on pH, temperature and access to light. Anthocyanidins are much more prone to avid chemical decomposition than the glycosides, and they only survive for minutes in the biophase. These pharmaceutical issues are very important determinants of the suitability of these flavonoids for potential development as cancer chemopreventive drugs, and they have hitherto not received adequate attention. In the light of their robust cancer chemopreventive efficacy in experimental models and their superior stability as compared to that of the aglycons, the anthocyanins seem much more suitable for further drug development than their anthocyanidin counterparts.

Comparison of delphinidin, quercetin and (-)-epigallocatechin-3-gallate as inhibitors of the EGFR and the ErbB2 receptor phosphorylation.

In the present study, delphinidin was found to suppress the phosphorylation of the epidermal growth factor receptor (EGFR) within human tumour cells (human colon carcinoma cell line (HT29), human vulva carcinoma cell line (A431)), albeit less effective than the flavonol quercetin. The higher potency of quercetin was also observed downstream on the level of the mitogen-activated protein kinase (MAPK) cascade. In addition, delphinidin, quercetin and (-)-epigallocatechin-3-gallate (EGCG) were found to suppress the phosphorylation of the ErbB2 receptor, with delphinidin exhibiting the strongest inhibitory properties. Their potency to suppress the ErbB2 receptor phosphorylation can be summarised as delphinidin > EGCG > quercetin. The effectiveness of delphinidin against the EGFR and the ErbB2 receptor was comparable, indicating a broader spectrum of activity against receptor tyrosine kinases. At low micromolar concentrations delphinidin showed some preference towards the ErbB2 receptor. In summary, quercetin and delphinidin appear to differ in their activity profile towards the ErbB receptor family members. Whereas quercetin was most effective against the EGFR, delphinidin exhibited some preference towards the ErbB2 receptor.

Coffees rich in chlorogenic acid or N-methylpyridinium induce chemopreventive phase II-enzymes via the Nrf2/ARE pathway in vitro and in vivo.

Recently, the coffee constituents 5-O-caffeoylquinic acid (CGA) and N-methylpyridinium (NMP) were identified as inducers of the Nrf2/antioxidant-response element (ARE) detoxifying pathway under cell-culture condition. To study the impact of CGA and NMP on the Nrf2-activating properties of a complex coffee beverage, two different model coffees were generated by variation of the roasting conditions: a low-roast coffee rich in CGA and a heavy-roast low in CGA but containing high levels of NMP. Activation of the Nrf2/antioxidant-response element pathway was monitored in vitro and in vivo.

Delphinidin inhibits a broad spectrum of receptor tyrosine kinases of the ErbB and VEGFR family

Delphinidin has been reported to inhibit EGFR signalling. To determine whether other receptor tyrosine kinases (RTKs) are also influenced by delphinidin, we examined its ability to inhibit the kinase activity of EGFR, ErbB2, VEGFR-2, VEGFR-3 and IGF1R in a cell-free test system. We found that delphinidin strongly inhibited the protein tyrosine kinase activity of all tested RTKs at low micromolar concentrations. In A431 and PAE cells, ligand-induced phosphorylation of the receptors was also potently suppressed, with a preference for the suppression of the activity of ErbB3 (IC(50) approximately 100 nM) and VEGFR-3 (IC(50) < 50 microM). Thus the inhibition of RTKs by delphinidin is not limited to cell-free assays but is also of relevance in the cellular context. The results indicate that delphinidin acts as a broad-spectrum inhibitor of RTKs. Given the crucial role of the receptors in tumour growth and metastasis, we conclude that delphinidin has the potential to act directly against tumour cells as well as to interfere with key tumour-host interactions, although the suitability of delphinidin as a drug in cancer management may be compromised by its limited stability. Nevertheless, delphinidin may represent a novel lead compound for the development of chemopreventative and chemotherapeutic intervention strategies.

Induction of antioxidative Nrf2 gene transcription by coffee in humans: depending on genotype?

The Nrf2/ARE pathway is a major cellular defense mechanism that prevents damage by reactive oxygen species through induction of antioxidative phase II enzymes. However, the activity of the Nrf2/ARE system is not uniform with variability in response presumed to be dependent on the Nrf2 genotype. We recently completed a pilot human coffee intervention trial with healthy humans, where large interindividual differences in the antioxidative response to the study coffee were examined. Here, we address the question whether differences in the modulation of Nrf2 gene transcription, assessed as an induction of Nrf2 gene transcription by Q-PCR, might be correlated with specific Nrf2 genotypes. To date, nine single nucleotide polymorphisms (SNPs) have been identified in the Nrf2 (NFE2L2) gene. Two of these, the −617C/A and −651G/A SNPs are located within the promoter region and have previously been reported to influence the activity of the Nrf2/ARE pathway by reducing Nrf2 transcriptional activity. Sequencing of the critical Nrf2 gene promoter region not only confirmed the existence of these SNPs within the participants of the trial at the expected frequency (33% carrying the −617C/A, 17% the −651G/A and 56% the −653A/G SNP) but also indicated reduced Nrf2 gene transcription associated with a normal diet if the SNPs at position −617, −651 or −653 were present. Of note, the data also indicated the study coffee increased Nrf2 gene transcription even in SNP carriers. This further highlights the relevance of genotype-dependent induction of Nrf2 gene transcription that appears to be largely influenced by dietary factors.

Anthocyanin-rich extracts suppress the DNA-damaging effects of topoisomerase poisons in human colon cancer cells.

SCOPE The effect of two anthocyanin-rich berry extracts (A, bilberry; B, red grape) on topoisomerases was investigated in a cell-free system and in human HT29 colon carcinoma cells. In parallel, their impact on DNA integrity was determined. METHODS AND RESULTS The berry extracts suppressed the activity of topoisomerase I at concentrations ≥50 μg/mL. The activity of the topoisomerase II isoform was preferentially diminished (≥1 μg/mL). Within HT29 cells, the extracts were found to act as catalytic inhibitors without stabilizing the cleavable complex. Although topoisomerase activity was inhibited, none of the extracts induced DNA strand breaks up to 50 μg/mL. Moreover, pre- and coincubation of HT29 cells with A (≥1 μg/mL) significantly suppressed (p-value ≤0.001) the strand-breaking effects of camptothecin, whereas B was found to be less effective (1 μg/mL; p-value ≤0.05). Both extracts were found to significantly diminish doxorubicin-mediated DNA strand breaks at concentrations ≥1 μg/mL (p-value ≤0.001). Consistent with these results, the extracts suppressed doxorubicin-mediated enhancement of levels of topoisomerase II covalently linked to DNA in HT29 cells. CONCLUSION These results raise the possibility that high intake of berry extracts may protect DNA and thus counteract the therapeutic effectiveness of orally applied topoisomerase poisons during chemotherapy.

Anthocyanin-rich red grape extract impedes adenoma development in the ApcMin mouse: Pharmacodynamic changes and anthocyanin levels in the murine biophase

PURPOSE Red grape pomace extract (oenocyanin) is a cheap and rich source of anthocyanins, the agents suggested to possess cancer chemopreventive properties. Here the hypothesis was tested that oenocyanin added to the diet can interfere with intestinal adenoma development in the Apc(Min) mouse, a model of intestinal carcinogenesis linked to an Apc mutation. METHODS Mice received oenocyanin (0.3%) in their diet until week 16, when adenoma number and burden were recorded. Expression of Akt and ERK proteins was studied by Western blot in adenomas to discover effects of anthocyanins on cellular signalling via the PI3 and MAP kinase pathways. Levels of anthocyanins were measured by HPLC with visible spectroscopic or mass spectrometric detection. RESULTS In mice which had consumed oenocyanin, overall adenoma burden was halved and adenoma number was marginally reduced when compared with mice on control diet. The proliferation index in colonic adenomatous crypts, as reflected by Ki-67 staining, was significantly decreased from 88.14% in control mice to 75.6+/-4% in mice on oenocyanin (P=0.014). Expression of Akt in small intestinal adenomas from Apc(Min) mice on oenocyanin was reduced by 54% (P=0.003), when compared to controls. Oenocyanin anthocyanins and glucuronide metabolites were found in the urine and intestine but not in plasma. CONCLUSIONS The results suggest that oenocyanin may be a viable and economical alternative to anthocyanin-rich berry extracts for chemopreventive intervention. Akt and pErk might be suitable biomarkers of anthocyanin target organ efficacy.

Suppression of the Kinase Activity of Receptor Tyrosine Kinases by Anthocyanin-Rich Mixtures Extracted from Bilberries and Grapes

Two standardized anthocyanin-rich mixtures were investigated for their ability to inhibit the receptor tyrosine kinases (RTKs) EGFR, ErbB2, ErbB3, VEGFR-2, and VEGFR-3. Both mixtures reduced the kinase activity of recombinant kinase domains of each RTK at concentrations <or=12.9 microg/mL, with preferential inhibition of VEGFR-2 and EGFR (<or=3.4 microg/mL). Similarly, ligand-induced autophosphorylation of these RTKs in human vulva carcinoma or porcine aortic endothelial cells was suppressed by both mixtures, with ErbB3 and VEGFR-3 being preferentially inhibited. Anthocyanin-rich extracts completely abrogated VEGFR-3 phosphorylation at concentrations of >or=50 microg/mL. These results indicate that anthocyanin-rich mixtures can inhibit RTKs with low specificity. The rank order of inhibitory efficacy against the tested RTKs in intact cells was VEGFR-3 >> VEGFR-2 > ErbB3 > EGFR > ErbB2. Considering the important role of RTKs in carcinogenesis, their inhibition by anthocyanin-rich mixtures suggests that they may serve as biomarkers of the pharmacological efficacy of anthocyanins in future chemoprevention experiments and in clinical intervention studies.

Anthocyanin-rich blackberry extract suppresses the DNA-damaging properties of topoisomerase I and II poisons in colon carcinoma cells.

In the present study, we addressed the question whether cyanidin-3-glucoside (C3G) or complex C3G-rich blackberry extracts affect human topoisomerases with special emphasis on the contribution of the potential degradation products phloroglucinol aldehyde (PGA) and protocatechuic acid (PCA). In HT29 colon carcinoma cells a C3G-rich blackberry extract suppressed camptothecin- (CPT-) or doxorubicin- (DOX-) induced stabilization of the covalent DNA-topoisomerase intermediate, thus antagonizing the effects of these classical topoisomerase poisons on DNA integrity. As a single compound, C3G (100 μM) decreased the DNA-damaging effects of CPT as well, but did not significantly affect those induced by DOX. At the highest applied concentration (100 μM), cyanidin protected DNA from CPT- and DOX-induced damage. Earlier reports on DNA-damaging properties of cyanidin were found to result most likely from the formation of hydrogen peroxide as an artifact in the cell culture medium when the incubation was performed in the absence of catalase. The suppression of hydrogen peroxide accumulation, achieved by the addition of catalase, demonstrated that cyanidin does not exhibit DNA-damaging properties in HT29 cells (up to 100 μM). The observed effects on topoisomerase interference and DNA protection against CPT or DOX were clearly limited to the parent compound and were not observed for the potential cyanidin degradation products PGA and PCA.