NPC1L1 and ABCG5/8 induction explain synergistic fecal cholesterol excretion in ob/ob mice co-treated with PPAR-α and LXR agonists.

Reverse cholesterol transport (RCT) and transintestinal cholesterol efflux (TICE) are two important pathways for body cholesterol elimination. We studied these pathways in an animal model of diabetes and obesity (ob/ob) where HDL function is compromised as a result of hyperglycemia, low-grade inflammation and oxidative stress. Co-treatment of ob/ob mice with PPAR-α (fenofibrate) and LXR (T0901317) agonists increased fecal cholesterol by 12-fold; PPAR-α and LXR agonists individually showed 2.6- and 4.0-fold fecal cholesterol excretion, respectively. We investigated the mechanism of synergistic efficacy of PPAR-α and LXR agonists in fecal cholesterol excretion. LXR agonist and the combination of PPAR-α and LXR agonists had greater HDL-C elevation. Ex vivo cholesterol efflux showed correlation with the fecal cholesterol excretion but was not sufficient to explain 12-fold increases in the fecal cholesterol in the co-treated mice. Therefore, we examined TICE to explain the 12-fold increases in the fecal cholesterol. A strong positive correlation of fecal cholesterol with ATP binding cassette transporter G5 (ABCG5) and G8 and a negative correlation with NPC1L1 was observed. ABCG5, G8 and NPC1L1 are involved in intestinal cholesterol absorption. The extent of influence of PPAR-α and LXR agonists on RCT and TICE was distinctly different. PPAR-α agonist increased fecal cholesterol primarily by influencing TICE, while LXR agonist influenced fecal cholesterol excretion via both RCT and TICE mechanisms. Synergistic efficacy on fecal cholesterol excretion following co-treatment with PPAR-α and LXR agonists occurred through a combination of RCT, TICE, and the key enzyme in bile synthesis, cholesterol 7-α hydroxylase (cyp7a1). These results suggest that cholesterol efflux, biliary cholesterol excretion, and TICE collectively contributed to the 12-fold increases in the fecal cholesterol excretion in ob/ob mice co-treated with PPAR-α and LXR agonists.

Curcumin and quercetin synergistically inhibit cancer cell proliferation in multiple cancer cells and modulate Wnt/ß-catenin signaling and apoptotic pathways in A375 cells.

BACKGROUND: Traditional therapy using natural products, especially flavonoids and alkaloids have been in practice for a long time. Among flavonoids, curcumin, quercetin, berberine, and epigallocatechin have been studied in greater detail in terms of their anticancer and anti-inflammatory activities. Although many studies focused on the PI3K, MAP kinase and NF-κB pathways, a thorough investigation of modulation of players in the apoptotic and Wnt/ß-catenin signaling pathway by curcumin and quercetin has not been done. Also, only few studies have been carried out on curcumin and quercetin co-treatment studies. HYPOTHESIS/PURPOSE: We hypothesized that the combination of natural products will have synergistic effects and the antiproliferative effect will be attenuated via apoptotic as well as Wnt/ß-catenin signaling pathways. STUDY DESIGN AND METHODS: To test our hypothesis, we compared potency of natural anticancer agents in four cancer cell lines, A549, HCT116, MCF7, and A375 by MTT and colony proliferation assays and investigated mechanism of anticancer activities by analyzing players in apoptotic and Wnt/ß-catenin signaling pathways in A375 cells treated with test agents individually or in combination. RESULTS: Epicatechins, up to 100 µM concentration, did not inhibit cancer cell proliferation, while curcumin inhibited proliferation in A549 and HCT116 cancer cell lines with an IC50 of 3 to 8.5 µM. Quercetin showed stronger inhibition of cell proliferation than berberine. Combination study with two most potent agents, curcumin and quercetin, in 4 cancer cell lines, suggested synergistic effect on cell proliferation with several fold decreases in IC50. Further investigation of the mechanism of action of curcumin and quercetin in melanoma cells, A375, suggested that inhibition of cell proliferation occurred through down-regulation of Wnt/ß-catenin signaling pathway proteins, DVL2, ß-catenin, cyclin D1, Cox2, and Axin2. In addition, both curcumin and quercetin induced apoptosis by down-regulating BCL2 and inducing caspase 3/7 through PARP cleavage. CONCLUSION: These results demonstrate that curcumin and quercetin inhibit cancer cell proliferation synergistically and Wnt/ß-catenin signaling and apoptotic pathways are partly responsible for antiproliferative activities.