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Simple Summary: One of the significant issues of the anti-cancer effects of phytochemicals, bioactive compounds from foods, and other plants, is that the effective dosages of the phytochemicals are too high to be obtained by oral intake, particularly by food intake. The current study aimed to assess if the combination of two phytochemicals, luteolin (LUT) and curcumin (CUR), at low dosages where LUT or CUR alone has no significant effect, synergistically exerts anti-colon cancer. Our results show that combined LUT and CUR synergistically suppressed colon cancer in cultured cells and cell-derived xenograft mice, which may be associated with two possible molecular pathways. This study provides a practical approach to treating or preventing colon cancer in humans by consuming foods having high levels of luteolin and curcumin. This study aimed to select a combination of curcumin and luteolin, two phytochemicals from food, at lower concentrations with a higher inhibitory effect on colon cancer growth and investigate possible molecular mechanisms of this anti-colon cancer effect. By pairwise combination screening, we identified that the combination of curcumin (CUR) at 15 μM and luteolin (LUT) at 30 μM (C15L30) synergistically suppressed the proliferation of human colon cancer CL-188 cells, but the individual chemicals had a little inhibitory effect at the selected concentrations. This result was also confirmed in other colon cancer DLD-1cells, suggesting that this synergistic inhibitory effect of C15L30 applies to different colon cancer cells. The combination C15L30 synergistically suppressed the wound closure (wound healing assay) in CL-188 cells. We also found that the combination of CUR and LUT (at 20 mg/kg/day and 10 mg/kg/day, respectively, IP injection, 5 days for 2 weeks) synergistically suppressed tumor growth in CL-188 cell-derived xenograft mice. Western blot results showed that protein levels of Notch1 and TGF-β were synergistically reduced by the combination, both in CL-188 cells and xenograft tumors. Tumor pathological analysis revealed that combined CUR and LUT synergistically increased necrosis, but the individual treatment with CUR and LUT had no significant effect on tumor necrosis. Therefore, combined curcumin and luteolin synergically inhibit colon cancer development by suppressing cell proliferation, necrosis, and migration associated with Notch1 and TGF-β pathways. This study provides evidence that colon cancer may be prevented/treated by consuming foods having high levels of luteolin and curcumin in humans. [ABSTRACT FROM AUTHOR]

Combining two or more chemicals in chemotherapy is rapidly increasing because of its higher efficacy, lower toxicity, lower dosages, and lower drug resistance. Here, we identified a novel combination of luteolin (LUT) and curcumin (CUR), two bioactive compounds from foods, synergistically suppressed triple-negative breast cancer (TNBC) cell proliferation (LUT 30 µM + CUR 20 µM), colony formation (LUT 1 µM + CUR 2 µM), and tumor growth in xenograft mice (LUT 10 mg/kg body weight/day + CUR 20 mg/kg body weight/day, i.p. injection every other day, 5 weeks), while the individual chemical alone did not show these inhibitory effects significantly at the selected concentrations/dosages. Our total RNA transcriptome analysis in xenograft tumors revealed that combining LUT and CUR synergistically activated type I interferon (IFN) signaling and suppressed transforming growth factor-beta (TGF-β) signaling pathways, which was further confirmed by the expression/activity of several proteins of the pathways in tumors. In addition, this combination of LUT and CUR also synergistically decreased oncoprotein levels of c-Myc and Notch1, the critical molecules required to maintain stem cell properties, tumor clonal evolution, and drug resistance. These results suggest that the combination of LUT and CUR synergistically inhibits TNBC by suppressing multiple cellular mechanisms, such as proliferation, colony formation, and transformation, as well as tumor migration, invasion, and metastasis, via regulating IFN and TGF-β signaling pathways. Therefore, combining LUT and CUR may be an effective therapeutic agent to treat highly aggressive, drug-resistant TNBC patients after clinical trials. [Display omitted] • The first report of combined curcumin and luteolin synergistically inhibit TNBC both in cells and xenograft mice. • This combination of luteolin and curcumin synergistically contains TNBC only, but not ER+ breast cancer. • This combination of LUT and CUR may be a universal approach to treat other diseases, including vascular inflammation and colon cancer. [ABSTRACT FROM AUTHOR]

Simple Summary: Anti-cancer effects of bioactive compounds have been extensively investigated; however, the effective dosages of the bioactive compounds are too high to be obtained by oral intake. Our study aimed to assess if combined two bioactive compounds, luteolin (LUT) and indole-3-carbinol (I3C), at low dosages that LUT or I3C along has no significant effect, synergistically exerts anti-breast cancer. We confirmed that combined LUT and I3C synergistically suppressed estrogen receptor-alpha positive breast cancer in cultured cells and cells-derived xenograft mice. Our results also indicated two possible molecular pathways involving the synergistic effects of the combination of LUT and I3C. Our findings provide a practical approach to treat or prevent breast cancer by combining two bioactive compounds. The high concentrations of individual phytochemicals in vitro studies cannot be physiologically achieved in humans. Our solution for this concentration gap between in vitro and human studies is to combine two or more phytochemicals. We screened 12 phytochemicals by pairwise combining two compounds at a low level to select combinations exerting the synergistic inhibitory effect of breast cancer cell proliferation. A novel combination of luteolin at 30 μM (LUT30) and indole-3-carbinol 40 μM (I3C40) identified that this combination (L30I40) synergistically constrains ERα+ breast cancer cell (MCF7 and T47D) proliferation only, but not triple-negative breast cancer cells. At the same time, the individual LUT30 and I3C40 do not have this anti-proliferative effect in ERα+ breast cancer cells. Moreover, this combination L30I40 does not have toxicity on endothelial cells compared to the current commercial drugs. Similarly, the combination of LUT and I3C (LUT10 mg + I3C10 mg/kg/day) (IP injection) synergistically suppresses tumor growth in MCF7 cells-derived xenograft mice, but the individual LUT (10 mg/kg/day) and I3C (20 mg/kg/day) do not show an inhibitory effect. This combination synergistically downregulates two major therapeutic targets ERα and cyclin dependent kinase (CDK) 4/6/retinoblastoma (Rb) pathway, both in cultured cells and xenograft tumors. These results provide a solid foundation that a combination of LUT and I3C may be a practical approach to treat ERα+ breast cancer cells after clinical trials. [ABSTRACT FROM AUTHOR]

The anti-inflammatory effects of phytochemicals, bioactive components from plants having health benefits, have been heavily investigated in the last several decades. However, the gap between the high dosage demands (μM) of phytochemicals in vitro studies and the low bioavailability (nM) of most phytochemicals after consuming relevant foods/supplements in humans undermines the application of these phytochemicals in the prevention of chronic inflammation and its related chronic diseases in humans. One of the approaches to bridging this gap is to combine two or more phytochemicals/foods to synergistically prevent chronic inflammation. While increasing combinations of phytochemicals on anti-inflammation studies have been reported, there is no report dedicating why combining two or more phytochemicals synergistically attenuates chronic inflammation. In the present review, we summarized different types of combinations exerting synergistic anti-inflammatory effects such as the combination of phytochemicals from the same foods, and the combination of phytochemicals from different foods/plants. Particularly, we proposed five mechanisms including enhancing the bioavailability of phytochemicals, increasing antioxidant capacity, interacting with gut microbiome and targeting same and different signaling pathways, to understand how the combination of phytochemicals exerts synergistic anti-inflammatory effects in cells, animals, and humans. This review provides clues to boost more studies to combine several phytochemicals/foods to reduce chronic inflammation and prevent chronic diseases in humans. [ABSTRACT FROM AUTHOR]

Chronic increased pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) play critical roles in the development of endothelial dysfunction and therefore induce cardiovascular disease. Although phytochemicals have the potential ability to reduce the risk of CVD, the big gap between required high concentration in cells and the low bioavailability in the blood of phytochemicals compromise their therapeutic potentials. This study aims to investigate if combined phytochemicals at low levels exert a synergistic anti-inflammatory effect and to define relevant molecular mechanisms. Our results found that combined curcumin (5 µM) and resveratrol (5 µM) synergistically (combination index is 0.78) inhibited TNF-α-induced monocytes adhesion to human endothelial EA.hy 926 cells while the individual chemicals did not have such effect at the selected concentrations. The concentrations of curcumin (5 µM) and resveratrol (5 µM) are very close to the maximum level of curcumin (3.56 µM) and resveratrol (2 µM) in human blood. Dietary supplementation of combined curcumin (500mg/kg) and resveratrol (200mg/kg) synergistically reduced TNF-α-induced vascular inflammation in C57BL/6 mice with a similar pattern in cells. Moreover, the combination ameliorated the TNF-α-induced protein expressions and circulating levels of vascular cell adhesion molecule 1 and monocyte chemotactic protein-1 in EA.hy 926 cells, mice aorta and serum. Furthermore, combined curcumin and resveratrol significantly inhibited TNF-α-induced nuclear factor-kappaB (NF-κB) p65 nuclear protein expression than that by the individual chemical alone in EA.hy 926 cells, indicating that the synergistic effect of the combination may result from that curcumin reduces the required minimum concentration for resveratrol to inhibit the nuclear translocation of NF-κB. In conclusion, the combination of curcumin and resveratrol protects against TNF-α-induced vascular inflammation by suppressing NF-κB signaling in vitro and in vivo models. This study suggests that dietary intake of a combination of curcumin and resveratrol or its foods may be a practical, safe approach to prevent vascular inflammation and therefore prevent/treat vascular diseases in humans. [ABSTRACT FROM AUTHOR]

Emerging evidence shows that phytochemicals, the secondary plant metabolites present in a large variety of foods, have the potential ability in reducing the risk of cardiovascular diseases. However, the dosages of phytochemicals in the cellular and animal studies are too high to reach in humans by relevant foods or dietary supplement intake. The aims of this study were to investigate whether and how combined curcumin and luteolin synergistically inhibit tumor necrosis factor-alpha (TNF-α)-induced monocytes adhesion endothelium, a crucial step of the development of endothelial dysfunction, both in human vascular cells and mouse aortic endothelium. Our results show that combined curcumin (1 μM) and luteolin (0.5 μM) synergistically (combination index is 0.60) inhibited TNF-α-induced monocytes adhesion to human EA.hy926 endothelial cells while the individual chemicals did not have such effect at the selected concentrations. We also found that TNF-α-enhanced protein expressions of vascular cell adhesion molecule 1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1) and nuclear factor (NF)-κB translocation were synergistically reduced by the combined curcumin and luteolin in EA.hy 926 cells while the individual chemical did not have this inhibitory effect. Consistently, 2 weeks dietary intake of combined curcumin (500 mg/kg) and luteolin (500 mg/kg) in C57BL/6 mice synergistically prevented TNF-α-stimulated adhesion of mouse monocytes to aortic endothelium ex vivo as well as the TNF-α-increased aortic protein expression of MCP-1 and VCAM-1. Therefore, combined curcumin and luteolin at physiological concentrations synergistically inhibits TNF-α-induced monocytes adhesion to endothelial cells and expressions of MCP-1 and VCAM-1 via suppressing NF-κB translocation into the nucleus. [ABSTRACT FROM AUTHOR]