Curcumin, but not curcumin-glucuronide, inhibits Smad signaling in TGFβ-dependent bone metastatic breast cancer cells and is enriched in bone compared to other tissues.
Level 5 - mechanism / opinion, no new human data
Mechanistic laboratory and animal tissue study
PubMed 30393127 · doi:10.1016/j.jnutbio.2018.09.021
What was done
Researchers compared the bioactivity of curcumin versus its primary circulating metabolite, curcumin-glucuronide, on Smad-dependent TGFβ signaling in breast cancer cell lines that form bone metastases in rodents (human MDA-SA, MDA-1833, MDA-2287, and murine 4T1 cells). They evaluated TGFβ-receptor-mediated Smad2/3 phosphorylation and TGFβ-stimulated PTHrP secretion in vitro. In addition, they used LC-MS to examine tissue-specific curcumin metabolism and deglucuronidation activity in mice.
What was found
Curcumin inhibited TGFβ-receptor-mediated Smad2/3 phosphorylation in all tested cell lines, whereas curcumin-glucuronide did not. Curcumin, but not curcumin-glucuronide, also blocked TGFβ-stimulated PTHrP secretion from MDA-SA and 4T1 cells. In mice, free curcumin (both absolute amount and percentage of total) was significantly increased in bone compared to serum and other organs, alongside high bone enzymatic deglucuronidation activity. The abstract reported no exact numerical concentrations, effect sizes, or p-values.
Why it matters
These findings suggest that circulating curcumin-glucuronide functions as a prodrug that undergoes site-specific deconjugation and activation within bone tissue. This provides a mechanistic rationale for how dietary polyphenols with low parent bioavailability might still exert bone-targeted effects.
Limits
This study is limited to in vitro cell cultures and mouse tissues, with no human in vivo data. The abstract lacks specific sample sizes (n for animals and replicates), drug dosages, and numerical quantification of tissue concentrations or signaling inhibition.
Cited by
- supports Glucuronidated curcumin is completely biologically inactive.