Walnut polyphenol metabolites, urolithins A and B, inhibit the expression of the prostate-specific antigen and the androgen receptor in prostate cancer cells

Abstract

Walnuts have been gathering attention for their health-promoting properties. They are rich in polyphenols, mainly ellagitannins (ETs) that after consumption are hydrolyzed to release ellagic acid (EA). EA is further metabolized by microbiota to form urolithins, such as A and B, which are absorbed. ETs, EA and urolithins have shown to slow the proliferation and growth of different types of cancer cells but the mechanisms remain unclear. We investigate the role of urolithins in the regulatory mechanisms in prostate cancer, specifically those related to the androgen receptor (AR), which have been linked to the development of this type of cancer. In our study, urolithins down-regulated the mRNA and protein levels of both prostate specific antigen (PSA) and AR in LNCaP cells. The luciferase assay performed with a construct containing three androgen response elements (AREs) showed that urolithins inhibit AR-mediated PSA expression at the transcriptional level. Electrophoretic mobility shift assays revealed that urolithins decreased AR binding to its consensus response element. Additionally, urolithins induced apoptosis in LNCaP cells, and this effect correlated with a decrease in Bcl-2 protein levels. In summary, urolithins attenuate the function of the AR by repressing its expression, causing a down-regulation of PSA levels and inducing apoptosis. Our results suggest that a diet rich in ET-containing foods, such as walnuts, could contribute to the prevention of prostate cancer.

Urolithin A causes p21 up-regulation in prostate cancer cells

“…However, the decrease in fold change was -1.93 with a p value of less than 0.05; therefore, it was not included in Table 1A, B corresponding to fold changes higher than 2. In the case of AR, its down-regulation, as previously described [22], takes place between 9 and 12 h of treatment with UA, and it does not appear underexpressed in the microarray at 24 h.…”

“…Due to the well-known anti-proliferative role of p21 in tumor cells, we decided to focus on exploring the effects that UA has on the transcriptional regulation of p21 and its role on the cell cycle and apoptosis. The role of ETs in prostate cancer progression has been reported by several authors including ourselves [22,[27][28][29][30]. Using a pomegranate fruit extract, Malik et al [30] determined the increase in Bax and p21, and the decrease in Bcl-2 in PC3 androgen-independent cells.…”

“…We began our approach using a genomic strategy that allowed us to identify p21 as a relevant gene node in the network of differentially expressed genes provoked by UA action. The concentration of 40 µM UA was chosen because it is in the order of low micromolar levels, similar to what can be found in plasma after consumption of ET-rich foods [16,17,32] and was not cytotoxic to LNCaP cells [22]. In addition, most of the biological [18,31,33].…”

“…Different number of cells, depending on the assay, were incubated with 40 µM urolithin A since we have previously used at this concentration [22] which can be found in plasma after consumption of pedunculagin-rich foods [18]. The final concentration of DMSO in the culture medium was always ≤0.2 %.…”

Health benefits of walnut polyphenols: An exploration beyond their lipid profile

“…The anti-proliferative activities of ellagic acid and its metabolites have been evaluated in several human cancer cell lines, some of which have been previously mentioned (Adams et al, 2010;Vicinanza et al, 2013;Sánchez-González et al, 2014. Other studies have also evaluated the anti-proliferative activity of ETs and other byproducts of their hydrolysis in a diverse range of cancer cell lines.…”