Inhibition of Escherichia coli nitroreductase by the constituents in Syzygium aromaticum / 中国天然药物

Gut bacterial nitroreductases play an important role in reduction of various nitroaromatic compounds to the corresponding N-nitroso compounds, hydroxylamines or aromatic amines, most of which are carcinogenic and mutagenic agents. Inhibition of gut nitroreductases has been recognized as an attractive approach for reducing mutagen metabolites in the colon, so as to prevent colon diseases. In this study, the inhibitory effects of 55 herbal medicines against Escherichia coli(E. coli) nitroreductase (EcNfsA) were examined. Compared with other herbal extracts, Syzygium aromaticum extract showed superior inhibitory potency toward EcNfsA mediated nitrofurazone reduction. Then, the inhibitory effects of 22 major constituents in Syzygium aromaticum against EcNfsA were evaluted. Compared with other tested natural compounds, ellagic acid, corilagin, betulinic acid, oleanic acid, ursolic acid, urolithin M5 and isorhamnetin were found with strong to moderate inhibitory effect against EcNfsA, with IC50 values ranging from 0.67 to 28.98 mol·L-1. Furthermore, the inhibition kinetic analysis and docking simulation demonstrated that ellagic acid and betulinic acid potently inhibited EcNfsA (Ki < 2 μmol·L -1) in a competitively inhibitory manner, which created strong interactions with the catalytic triad of EcNfsA. In summary, our findings provide new scientific basis for explaining the anti-mutagenic activity of Syzygium aromaticum, where some newly identified EcNfsA inhibitors can be used for developing novel agents to reduce the toxicity induced by bacterial nitroreductase.

Pancreatic lipase inhibitory constituents from Fructus Psoraleae / 中国天然药物

Pancreatic lipase (PL), a crucial enzyme in the digestive system of mammals, has been proven as a therapeutic target to prevent and treat obesity. The purpose of this study is to evaluate and characterize the PL inhibition activities of the major constituents from Fructus Psoraleae (FP), one of the most frequently used Chinese herbs with lipid-lowering activity. To this end, a total of eleven major constituents isolated from Fructus Psoraleae have been obtained and their inhibition potentials against PL have been assayed by a fluorescence-based assay. Among all tested compounds, isobavachalcone, bavachalcone and corylifol A displayed strong inhibition on PL (IC < 10 μmol·L). Inhibition kinetic analyses demonstrated that isobavachalcone, bavachalcone and corylifol A acted as mixed inhibitors against PL-mediated 4-methylumbelliferyl oleate (4-MUO) hydrolysis, with the K values of 1.61, 3.77 and 10.16 μmol·L, respectively. Furthermore, docking simulations indicated that two chalcones (isobavachalcone and bavachalcone) could interact with the key residues located in the catalytic cavity of PL via hydrogen binding and hydrophobic interactions. Collectively, these finding provided solid evidence to support that Fructus Psoraleae contained bioactive compounds with lipid-lowering effects via targeting PL, and also suggested that the chalcones in Fructus Psoraleae could be used as ideal leading compounds to develop novel PL inhibitors.