3--methoxy-4--nitroflavone and alpha-naphthoflavone

A well-balanced activity of the aryl hydrocarbon receptor (AhR) is necessary for normal ovarian function. As known from murine AhR knock-out (KO) models, the AhR is involved in folliculogenesis, gonadotrophin receptor expression, proliferation of granulosa cells and intraovarian estrogen signalling. Highly potent, non-physiological ligands such as the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) lead to a blockade of ovulation, estrogen receptor degradation and reduction of estrogen levels. Estrogen synthesis is a typical function of granulosa cells and essential for normal cyclicity and fertility. We employed the human granulosa cell line KGN to further characterize AhR signalling and AhR function in granulosa cell physiology. Real-time PCR quantification of the target genes Cyp1a1 and Cyp1b1 and reporter gene assays after stimulation with TCDD or beta-naphthoflavone (BNF) or inhibition with alpha-naphthoflavone (ANF) or 3'-methoxy-4'-nitroflavone (3,4-MNF) of the AhR demonstrated constitutive activity and functionality of AhR pathway in KGN granulosa cells. In untreated KGN cells, AhR protein was exclusively detected in the nuclear fraction. TCDD stimulation affected the gonadotrophin receptor but not estrogen receptor β (ERβ) protein expression. Additionally, the constitutively activated AhR suppressed aromatase expression and estrogen synthesis (enzyme-linked immunoassay, ELISA) and enhanced proliferation [Bromodeoxyuridine (BrdU) ELISA] of KGN cells. Activation of the AhR by BNF did not override this inhibitory effect on estrogen synthesis or proliferation. In conclusion, the AhR pathway is constitutively activated and functional in human KGN granulosa cells. It is a potential target for endocrine disruption by exogenous ligands and subsequent dysfunction of granulosa cells.

Topics: Aromatase; Aryl Hydrocarbon Hydroxylases; Benzoflavones; beta-Naphthoflavone; Cell Line; Cell Proliferation; Cytochrome P-450 CYP1A1; Cytochrome P-450 CYP1B1; Enzyme-Linked Immunosorbent Assay; Estrogens; Female; Flavonoids; Granulosa Cells; Humans; Ovary; Polychlorinated Dibenzodioxins; Polymerase Chain Reaction; Receptors, Aryl Hydrocarbon; Receptors, Estrogen; Receptors, Gonadotropin; Signal Transduction

Acute myeloid leukaemia (AML) continues to present demanding treatment challenges, as in general the prognosis for long-term survival remains dire for the patients. Natural plant-derived substances with antileukemic properties offer new treatment possibilities or may act as by-stander therapy. Their molecular mechanisms of action are often not entirely clear, limiting theory-directed screening and application strategies. The plant substance curcumin is a known activator of the transcription factor aryl hydrocarbon receptor (AhR), and has well-documented antileukemic effects. The AhR regulates cell processes, including cell cycle and apoptosis. We ask here whether direct AhR-activation by curcumin contributes to its antileukemic/apoptotic potential.. The induction of caspases 3/7, 8, and 9, the breakdown of mitochondrial transmembrane potential, the BCL-2/BAX ratio, and the DNA content of cells were measured as indicators of apoptosis. In addition, the induction of cell cycle inhibitors p21 and p27 were assessed.. While triggering of AhR signalling by curcumin in HL-60 cells was confirmed, induction of the above apoptosis parameters was not blocked by two AhR antagonists, alpha-naphtoflavone (alphaNF) and 3'-methoxy-4'nitroflavone (MNF). Only a moderate (20%) AhR-dependent induction of caspases 3/7 was detectable. Interestingly, transcriptional changes induced by curcumin and by anticarcinogenic 1,25-dihydroxy vitamin D3 overlapped by one third.. We conclude that AhR is only marginally involved in the antileukemic effects of its ligand curcumin.

Topics: Acute Disease; Apoptosis; Benzoflavones; Caspases; Cell Cycle; Curcumin; Enzyme Activation; Flavonoids; HL-60 Cells; Humans; Isoenzymes; Leukemia, Myeloid; Ligands; Receptors, Aryl Hydrocarbon; Reverse Transcriptase Polymerase Chain Reaction

Some flavonoids are ligands of the aryl hydrocarbon receptor (AHR) and cause cell cycle arrest. The dependency of the cytostatic effects of five flavonoids (flavone, alpha-naphthoflavone, apigenin, 3'-methoxy-4'-nitroflavone and 2'-amino-3'-methoxyflavone) on a functional AHR was examined in AHR-containing rat hepatoma 5L cells and an AHR-deficient cell line (BP8) derived from the 5L line. The potent AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was cytostatic to the 5L line due to the induction of a G(1) arrest and dramatically elevated steady-state levels of CYP1A1 mRNA. TCDD affected neither the proliferation nor CYP1A1 mRNA contents of BP8 cells. With the exception of apigenin, the flavonoids under study induced G(1) arrest in both 5L and BP8 cells when used at concentrations at which they functioned as AHR agonists, but not antagonists. Apigenin-treated 5L and BP8 cultures primarily arrested in G(2)/M. The AHR-containing murine hepatoma cell line 1c1c7 arrested following exposure to AHR agonist concentrations of flavone and alpha-naphthoflavone, but not TCDD. Unlike the G(1) arrest observed in 5L cultures, the latter two flavonoids caused principally G(2)/M arrest in 1c1c7 cells. These studies demonstrate that the cytostatic activities of flavonoids do not require the AHR and the site of checkpoint arrest with a specific flavonoid can vary with cell type.

Topics: Animals; Benzoflavones; Cell Cycle; Cell Division; Chamomile; Cytochrome P-450 CYP1A1; Environmental Pollutants; Flavones; Flavonoids; G1 Phase; Oils, Volatile; Plants, Medicinal; Polychlorinated Dibenzodioxins; Rats; Receptors, Aryl Hydrocarbon; RNA, Messenger; Tumor Cells, Cultured