Cytotoxic effects of the dietary flavones chrysin and apigenin in a normal trout liver cell line

Abstract

Many flavonoids have been shown to possess prooxidant properties, capable of causing oxidative stress, especially at larger doses. Here, we examined the potential cell toxicity caused by exposure to the hydroxylated flavones chrysin, apigenin, luteolin and quercetin in comparison to the methylated flavones 5,7-dimethoxyflavone and 3',4'-dimethoxyflavone in normal Rainbow trout hepatocytes. The hydroxylated flavones, especially chrysin, demonstrated cell toxicity and inhibition of DNA synthesis at very low (2 microM) concentrations. The cytotoxicity of chrysin may partially be due to its metabolism by myeloperoxidase, which was shown to be present in these normal trout liver cells (164pmol/(min mg protein)). In contrast, methylated flavones showed no significant metabolism by myeloperoxidase and no signs of toxicity, even at much higher concentrations. These results may be useful for further investigations of cytotoxicity of dietary flavonoids.

Fig. 1

Chemical structures of the flavonoids studied

Fig. 2

Trout cells after 24-h exposure to medium alone, vehicle control (0.1% DMSO), or 25 μM flavonoids in medium with 0.1% DMSO. Dead or dying cells are indicated by arrows. Magnification = 300x.

Fig. 3

Trout cells treated with various concentrations of chrysin. Cells (96% confluent) were treated for 48 hours. Magnification 300x.

Fig. 4

Quantitative analysis of cell coverage after treatment with 25 μM flavonoids for 24 h. Cell coverage was quantified with Image J software and expressed as percent of DMSO-control. Mean ± SEM of 3−5 cultures are shown. *** and **, significantly different from DMSO-control (p<0.001 & p<0.01, respectively)

Fig. 5

Trout cell proliferation in the presence of varying concentrations of chrysin (squares) and its methylated analogue 5,7-DMF (triangles), as measured by BrdU incorporation into cellular DNA. Means ± SEM are shown (N = 12 from 2 independent experiments).

Fig. 6

Trout liver cells were compared with human leukemia HL-60 cells for myeloperoxidase activity using guaiacol as the substrate. The average catalytic activity in trout hepatocytes was 164 pmol/min/mg protein (N = 4) and in HL-60 cells 131 pmol/min/mg protein (N = 3).

Fig. 7

Human myeloperoxidase (6 U/ml) metabolism of 2.5 μM chrysin (A) or 5,7-DMF (B) with hydrogen peroxide (1.3 mM) as cofactor with and without the presence of 5 mM GSH. (N = 4). *** significantly different from control (p<0.001); ^### significantly different from Chrysin+MPO (p<0.001).