Structure-antioxidative and anti-inflammatory activity relationships of purpurin and related anthraquinones in chemical and cell assays

Authors: NAM, WOO - Ajou University Of Korea; KIM, SUNG PHIL - Str Biotech Co Ltd; NAM, SEOK HYUN - Ajou University Of Korea; Friedman, Mendel

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2017
Publication Date: 2/10/2017
Citation: Nam, W., Kim, S., Nam, S., Friedman, M. 2017. Antioxidative and anti-inflammatory activities of the natural food colorant purpurin and related anthraquinones in chemical and cell assays. Molecules. 22(2):265. doi:10.3390/molecules22020265.

Interpretive Summary: The observations in the present study strikingly demonstrate the strong antioxidative potential of the food colorant purpurin of the root madden plant (Rubia tinctorum) as determined using five independent chemical antioxidant assays. The results of the cell assays also presented here reinforce this potential in cellular environments and also demonstrate for the first time strong anti-inflammatory properties of purpurin. Purpurin was not toxic to the cells. The antioxidative properties of purpurin are a result of its ability to destroy free radicals; such free radicals can damage or spoil fat-containing food, for example, soybean oil and meat. Purpurin could therefore have potential as a food additive to provide both antioxidative and anti-inflammatory properties. Indeed, cell data suggest that purpurin also has the potential to destroy reactive oxygen species that damage DNA and essential proteins and to suppress inflammation via immunostimulation in vivo, suggesting its further potential value to protect against chronic and metabolic diseases associated with inflammation, including arthritis, asthma, cancer, and diabetes. The potential of purpurin to improve food quality and safety and human health merits further study.

Technical Abstract: Anthraquinone (9,10-anthraquinone) and its hydroxy derivatives including purpurin (1,2,4-trihydroxyanthraquinone), anthrarufin (1,5-dihydroxyanthraquinone), and chrysazin (1,8-dihydroxy-9,10-anthracenedione) were evaluated for antioxidative and anti-inflammatory activities in chemical assays and mammalian cells (murine macrophage RAW 264.7 cells) Several tests were used to assess their activities: DPPH free radical; ABTS radical cation; hydrogen peroxide (H2O2) scavenging; reduction of potassium ferricyanide; chelation of ferrous ions; inhibition of lipid peroxidation; inhibition of nitric oxide (NO) generation; scavenging of the intracellular hydroxyl radical; expression of NLRP3 polypeptide for inflammasome assembly; and quantitation of proinflammatory cytokine (IL-1ß) for inflammasome activation. The results show that purpurin of the root madden plant (Rubia tinctorum) had exhibited the highest antioxidative activity of those tested in both chemical and cultured cell antioxidant assays. The in vitro assays showed the purpurin antioxidative activity was of same level as or better than that of the synthetic food antioxidant BHA. The antioxidative activities of the other three anthraquinones were several orders of magnitude lower than that of purpurin. In addition, the observed suppression by purpurin of both NLRP3 expression and IL-1ß processing to active forms in murine macrophage RAW 264.7 cells indicated that purpurin could down-regulate NLRP3 inflammasome assembly and activation. The observed antioxidative potential of purpurin in vitro and anti-inflammatory activity in cells suggests that purpurin, used as food colorant, has the potential to protect foods against oxidative damage as well as to prevent in vivo oxidative stress and inflammation. Structure-acivity relationships and the possible significance of the results for food quality and human health are discussed.