Metal-ligand coordination and antiradical activity of a trichromium(III) complex with the flavonoid naringenin

<p>The trinuclear chromium(III) complex [Cr₃O(CH₃CO₂)₆(L)(H₂O)₂] (where L is the monoanion of the flavonoid naringenin) was synthesized and characterized. Density functional theory (DFT) calculations and quantum theory of atoms in molecules (QTAIM) analysis show that the flavonoid binds to Cr^III as an <i>O,O</i>-bidentate ligand via the 5-hydroxy and 4-oxo groups. Reactions with 2,2-diphenyl-1-picrylhydrazyl (DPPH) indicate that the antiradical activity of this flavonoid-metal complex is enhanced in comparison with uncoordinated naringenin.</p

Chemical structure of jacaranone isolated from leaves of <i>P. </i><i>desiderabilis</i><i>.</i>

<p>Chemical structure of jacaranone isolated from leaves of <i>P. </i><i>desiderabilis</i><i>.</i></p

ROS generation by jacaranone and loss of mitochondrial transmembrane potential (Δ<i>ψ</i><b>m) in jacaranone-treated cells.</b>

<p>(A) Redox cycling ability of jacaranone detected by NBT/glycinate assay. (B) Untreated melanoma cells (a) or cells treated with jacaranone at 50 µM for 3 h (b), were incubated with the oxidative fluorescent dye DHE (5 µM) for detection of superoxide anion production. Bars = 20 µm. (C) B16F10-Nex2 cells were pre-incubated with NAC at indicated concentrations for 30 min, and then jacaranone at 20 µM was added. Cell viability was assessed using Trypan Blue exclusion test 24 h after jacaranone addition. (D) B16F10-Nex2 cells were treated with 50 µM jacaranone for 24 h and then Δ<i>ψ</i>m was determined using TMRE by flow cytometry.</p

Jacaranone treatment of B16F10-Nex2 cells inhibited Akt pathway activation through ROS generation.

<p>Whole-cell extracts from B16F10-Nex2 exposed to 0 (control), 20 or 50 µM jacaranone (Jac) in the presence (A) or absence (B) of NAC were subjected to Western blotting and probed with phospho-p38, phospho-Akt, total Akt, total p38 and Bax antibodies. Protein levels were normalized to the actin level.</p

Jacaranone increased survival of B16F10-Nex2 tumor-bearing mice.

<p>Animals (5 mice per group) were subcutaneously injected with 5×10⁴ cells and treated with PBS, 0.8 mg/kg or 4 mg/kg of jacaranone on alternate days. Intraperitoneal therapy began one day after inoculation of melanoma cells and was extended for 14 days. Mean survival times were 23.4±2.1 days for untreated tumor control group, 29±4.3 days (<i>p</i> = 0.05) for 0.8 mg/kg of jacaranone-treated group, and 34±3.6 days (*<i>p</i><0.01) for 4 mg/kg jacaranone-treated group.</p

Cytotoxic activity of jacaranone on human cancer cells growing in vitro.

a<p>IC₅₀ is the concentration that kills 50% of viable cells in a dose-dependent survival curve.</p

Jacaranone induced apoptotic morphological alterations on melanoma cells.

<p>(A) 1.0×10⁴ B16F10-Nex2 cells were seeded on coverslips and treated with 20 or 50 µM jacaranone (Jac) for 3 h. State of chromatin was assessed using Hoechst 33342 (2 µM). Positive cells for Hoechst staining were visualized under a fluorescence microscope and expressed as percentage of total cell counts of control cells. Representative images of cells treated without (Control) or with 20 µM jacaranone. (B) Transmission electron micrographs revealed mitochondrial shrinkage (arrows), plasma membrane blebbing (black triangles) and disruption of nuclear membrane (asterisk) after treatment with (b, c, and d) or without (a) 50 µM jacaranone. Original magnification ×10,000 (a, b and c); bar = 2 µm. Original magnification ×20,000 (d); bar = 1µm.</p