Carnosic acid suppresses colon tumor formation in association with antiadipogenic activity.

This study determined the efficacy of carnosic acid (CA) for suppressing colon carcinogenesis associated with excess adiposity. Cell growth regulation by CA was evaluated in HT-29 colon adenocarcinoma cells cocultured with 3T3-L1 adipocytes. To determine the in vivo efficacies, male A/J mice were divided into four groups and fed one of the following experimental diets for 11 wk: 15% fat, 45% fat, 45% fat + 0.01% CA, or 45% fat + 0.02% CA. Azoxymethane was administered at the beginning of experimental diet and two cycles of dextran sodium sulfate were supplied 1 wk after the azoxymethane injection. The proliferation of HT-29 cells cocultured with 3T3-L1 cells was significantly higher than proliferation of control cells (p < 0.05). CA treatment suppressed the growth of cocultured HT-29 cells through cell cycle arrest and enhanced apoptosis by inhibiting leptin receptor (Ob-R) signaling, including Akt and extracellular signal-regulated kinase (ERK) phosphorylation. CA supplementation in vivo decreased the number of colon tumors and reduced circulating concentrations of leptin, adiponectin, insulin, and insulin-like growth factor 1. Colonic expression of Ob-R, insulin receptor (IR), p-Akt, p-ERK, B-cell lymphoma extra large (Bcl-xL), and cyclinD1 protein was also suppressed in animals fed CA. CA appears to alleviate adipocity-related acceleration of colon tumor formation.