Quercetin metabolites inhibit MMP-2 expression in A549 lung cancer cells by PPAR-γ associated mechanisms.

Our previous study demonstrated that quercetin-metabolite-enriched plasma (QP) but not quercetin itself upregulates peroxisome proliferator-activated receptor gamma (PPAR-γ) expression to induce G2/M arrest in A549 cells. In the present study, we incubated A549 cells with QP as well as quercetin-3-glucuronide (Q3G) and quercetin-3'-sulfate (Q3'S), two major metabolites of quercetin, to investigate the effects of quercetin metabolites on cell invasion and migration, the possible mechanisms and the role of PPAR-γ. We also compared the effects of QP with those of quercetin and troglitazone (TGZ), a PPAR-γ ligand. The results showed that QP significantly suppressed cell invasion and migration, as well as matrix metalloproteinases (MMPs)-2 activity and expression in a dose-dependent manner. The effects of 10% QP on those parameters were similar to those of 10µM quercetin and 20µM TGZ. However, QP and TGZ rather than quercetin itself increased the expressions of nm23-H1 and tissue inhibitor of metalloproteinase (TIMP-2). Furthermore, we demonstrated that Q3G and Q3'S also inhibited the protein expression of MMP-2. GW9662, a PPAR-γ antagonist, significantly diminished such an effect of Q3G and Q3'S. Silencing PPAR-γ expression in A549 cells also significantly diminished the suppression effect of Q3G and Q3'S on MMP-2 expression. Taken together, our study demonstrated that QP inhibited cell invasion and migration through nm23-H1/TIMP-2/MMP-2 associated mechanisms. The upregulation of PPAR-γ by quercetin metabolites such as Q3G and Q3'S could play an important role in the effects of QP.

Quercetin supplementation suppresses the secretion of pro-inflammatory cytokines in the lungs of Mongolian gerbils and in A549 cells exposed to benzo[a]pyrene alone or in combination with ß-carotene: in vivo and ex vivo studies.

In vitro studies have shown that quercetin modulates the effects of ß-carotene induced by stimulants. Whether these reactions happen in vivo, however, is unclear. Thus, we investigated whether quercetin supplementation suppresses the harmful effects of benzo[a]pyrene (BaP) alone or combined with ß-carotene in the lungs of Mongolian gerbils. The gerbils were given quercetin (100 mg/kg body wt, 3 times/week), ß-carotene (10 mg/kg body wt, 3 times/week), and BaP (8 mmol, 2 times/week) alone or in combination by gavage for 6 months. ß-Carotene supplementation enhanced the pro-inflammatory effects of BaP in the lungs of gerbils. In contrast, quercetin supplementation significantly decreased the infiltration of inflammatory cells as well as the levels of TNF-α and IL-1ß in the bronchoalveolar lavage fluid and plasma of gerbils exposed to BaP or BaP+ß-carotene (P<.05). Such effects of quercetin supplementation were accompanied by a down-regulation of the expression of phospho-c-Jun and phospho-JNK induced by BaP or BaP+ß-carotene in the lungs of gerbils. Furthermore, in the ex vivo study, we found that quercetin-metabolite-enriched plasma (QP) obtained from gerbils acted like a JNK inhibitor to significantly suppress the secretion of pro-inflammatory cytokines induced by BaP or BaP+ß-carotene in A549 cells (P<.05). QP also suppressed the activation of the JNK pathway in the A549 cells. These results suggest that supplemental quercetin suppress the pro-inflammatory effect of ß-carotene induced by BaP in vivo and ex vivo. The regulation of the JNK pathway by the metabolites of quercetin contributes, at least in part, to such effects of quercetin in vivo.

Plasma rich in quercetin metabolites induces G2/M arrest by upregulating PPAR-γ expression in human A549 lung cancer cells.

In this study, we incubated human A549 lung cancer cells with quercetin-metabolite-enriched plasma (QMP) obtained from Mongolian gerbils 2 h after quercetin feeding (100 mg/kg body wt/week). We investigated the effects of QMP on the growth of A549 cells and the possible mechanisms for these effects. We found that QMP but not control plasma (CP) reduced the cell growth in A549 cells. QMP led to cell cycle arrest at the G (2)/M phase by downregulating the expression of cdk1 and cyclin B. QMP but not CP or quercetin itself significantly increased PPAR- γ expression (p < 0.05), which was accompanied by an increase of phosphatase and tensin homologue deleted on the chromosome ten level and a decrease of phosphorylation of Akt. Furthermore, quercetin-3-glucuronide and quercetin-3'-sulfate also significantly increased PPAR- γ expression in A549 cells. GW9662, a PPAR- γ antagonist, significantly suppressed the effects of 10 % QMP on cell proliferation and on the expression of cyclin B and cdk1. Taken together, these data suggest that the activation of PPAR- γ plays an important role, at least in part, in the antiproliferative effects of quercetin metabolites.