Diallyl sulfide inhibits PhIP-induced cell death via the inhibition of DNA strand breaks in normal human breast epithelial cells

Abstract

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is associated with mammary carcinomas in animals and humans. PhIP is metabolized by CYP 1A1/1A2 and cytochrome b5 reductase, producing free radicals causing DNA strand breaks. Diallyl sulfide (DAS) prevents cancer in animals. We hypothesized that DAS will attenuate PhIP-induced DNA strand breaks and cell death. To test this hypothesis, we treated MCF-10A cells with PhIP, DAS and PhIP/DAS for 24, 48 and 72 h. DAS inhibited the PhIP-induced DNA strand breaks by 22% after 48 h and the strand breaks were completely inhibited at 72 h. PhIP reduced cell viability at each time point. However, DAS only attenuated this reduction in cell viability by 56% at 72 h. N-OH PhIP inhibited cell viability by 26% at 72 h. DAS completely attenuated this reduction in cell viability and may prevent PhIP-induced breast cancer via alterations in DNA damage and cell viability.

Figure 1

Inhibition of the formation of DNA strand breaks in PhIP-treated MCF-10A cells. (A) A cell is shown that was treated with 0.1% DMSO as a control. In this cell, there are no detectable DNA strand breaks as indicated by the absence of a comet tail. (B) A cell that was treated with PhIP (100 µM) is shown. In this cell, the amount of DNA strand breaks was extensive as indicated by the large comet tail. (C) A cell is shown that was treated with PhIP and DAS, 100 µM each. In this cell, DAS inhibited the PhIP-induced DNA strand breaks as indicated by the reduction in the size of the comet tail.

Figure 2

The inhibition of PhIP-induced DNA strand breaks by DAS at 24, 48 and 72 h. MCF-10A cells were treated, harvested and analyzed as described in Materials and methods. Each bar on the graph represents the mean olive tail moment ± S.E.M. of three independent experiments. *Data significantly different from the DMSO treatment group (P<0.05). **Data significantly different from the PhIP treatment group (P<0.05).

Figure 3

The inhibition of N-OH PhIP-induced DNA strand breaks by DAS at 24, 48 and 72 h. MCF-10A cells were treated, harvested and analyzed as described in Materials and methods. Each bar on the graph represents the mean olive tail moment ± S.E.M. of three independent experiments. *Data significantly different from the DMSO treatment group (P<0.05). **Data significantly different from the N-OH PhIP treatment group (P<0.01).

Figure 4

The attenuation of PhIP-induced growth arrest by DAS at 24, 48 and 72 h. Cells were treated, harvested and analyzed as described in Materials and methods. Each bar on the graph represents the mean percentage of viable cells ± S.E.M. of three independent experiments. *Data significantly different from the DMSO treatment group (P<0.05). **Data significantly different from the PhIP treatment group (P<0.01).

Figure 5

The attenuation of N-OH PhIP-induced growth arrest by DAS at 24, 48 and 72 h. Cells were treated, harvested and analyzed as described in Materials and methods. Each bar on the graph represents the mean percentage of viable cells ± S.E.M. of three independent experiments. *Data significantly different from the DMSO treatment group (P<0.05). **Data significantly different from the N-OH PhIP treatment group (P<0.01).