3-Methylthiopropionic acid ethyl ester, isolated from Katsura-uri (Japanese pickling melon, Cucumis melo var. conomon), enhanced differentiation in human colon cancer cells

Metabolomics Analysis for Nitrite Degradation by the Metabolites of Limosilactobacillus fermentum RC4

Nitrite (NIT), a commonly used food additive, especially in pickled and cured vegetables and meat products, might cause acute and chronic diseases. Fermentation with lactic acid bacteria (LAB) is an effective method for degrading NIT and improving the flavor of pickled and cured foods. In this study, Limosilactobacillus fermentum (L. fermentum) RC4 with a high NIT degradation ability was found to degrade NIT in a new manner when compared with reported enzymatic and acid degradation, namely, metabolite degradation during fermentation in MRS broth, which shows a synergistic effect with acid to increase NIT degradation. Liquid chromatography-mass spectrometry analysis identified 134 significantly different metabolites, of which 11 metabolites of L. fermentum RC4, namely, γ-aminobutyric acid (GABA), isocitric acid, D-glucose, 3-methylthiopropionic acid (MTP), N-formyl-L-methionine, dimethyl sulfone (MSM), D-ribose, mesaconate, trans-aconitic acid, L-lysine, and carnosine, showed significant NIT degradation effects compared with the control group (MRS broth). Verification experiments showed that adding the above 11 metabolites to 100 mg/L NIT and incubating for 24 h resulted in NIT degradation rates of 5.07%, 4.41%, 6.08%, 16.93%, 5.28%, 2.41%, 0.93%, 18.93%, 12.25%, 6.42%, and 3.21%, respectively. Among these, three metabolites, namely, mesaconate, MTP, and trans-aconitic acid, showed efficient NIT degradation abilities that might be related to the degradation mechanism involving decarboxylation reactions. This is the first systematic study of NIT degradation by LAB, resulting in the identification of a new metabolite degradation pathway and three efficient NIT degradation metabolites.

Chemical and molecular bases of dome formation in human colorectal cancer cells mediated by sulphur compounds from Cucumis melo var. conomon

Colorectal cancer was the third most commonly diagnosed malignant tumor and the fourth leading cause of cancer deaths worldwide in 2012. A human colorectal cancer cell line, RCM‐1, was established from a colon cancer tissue diagnosed as a well‐differentiated rectum adenocarcinoma. RCM‐1 cells spontaneously form ‘domes’ (formerly designated ‘ducts’) resembling villiform structures. Two sulphur‐containing compounds from Cucumis melo var. conomon (Katsura‐uri, or Japanese pickling melon), referred to as 3‐methylthiopropionic acid ethyl ester (MTPE) and methylthioacetic acid ethyl ester (MTAE), can induce the differentiation of the unorganized cell mass of an RCM‐1 human colorectal cancer cell culture into a dome. However, the underlying molecular mechanisms of such dome formation have not been previously reported. Here, we performed a structure–activity relationship analysis, which indicated that methylthioacetic acid (MTA) was the lowest molecular weight compound with the most potent dome‐inducing activity among 37 MTPE and MTAE analogues, and the methylthio group was essential for this activity. According to our microarray analysis, MTA resulted in down‐regulation of 537 genes and up‐regulation of 117 genes. Furthermore, MTA caused down‐regulation of many genes involved in cell‐cycle control, with the cyclin E2 (CCNE2) and cell division cycle 25A (CDC25A) genes being the most significantly reduced. Pharmacological analysis showed that the administration of two cell‐cycle inhibitors for inactivating CDC25A phosphatase (NSC95397) and the cyclin E2/cyclin‐dependent kinase 2 complex (purvalanol A) increased the dome number independently of MTA. Altogether, our results indicate that MTA is the minimum unit required to induce dome formation, with the down‐regulation of CDC25A and possibly CCNE2 being important steps in this process.

Chemopreventive and biological activities of Helicteres isora L. fruit extracts

Helicteres isora L. (H. isora) has been used in traditional medicine in Asia. This study was aimed to determine biological activities of H. isora fruit extracts. Chemopreventive effect was examined by cell proliferation assay and differentiation-inducing effect. Anti-inflammatory activity of extracts was studied on the levels of nitric oxide (NO), tumor necrosis factor alpha (TNF-α), production of prostaglandin E2 (PGE-2), and cyclooxygenas-2 (COX-2). Cell proliferation assay revealed that H. isora extracts and its major compound, rosmarinic acid, showed no cytotoxicity in THP-1 and RCM-1 cells. Methylthio acetic acid from Cucumis melo var.conomon used as a positive control and 80% ethanol extracts demonstrated significant cell differentiation induction. Hexane extract of H. isora could lower the levels of TNF-α, PGE-2, and NO in THP-1 cells with 51.61 ± 0.79%, 69.68 ± 0.017%, and 69.93 ± 9.41% inhibition, respectively. The highest inhibitory effect on COX-2 was obtained from dichloromethane extract. Dexamethasone inhibited the secretion of TNF-α with 95.82 ± 0.50% while celecoxib showed the inhibitory effect on COX-2 and PGE-2 with 100% and 99.86%, respectively. The ethanol extract showed the best antioxidant activity by DPPH and FRAP assays at IC₅₀ of 5.43 ± 1.01 μg/mL and 22.83 ± 0.13 mmol FeSO₄/g sample, respectively, while the positive control, trolox, showed the antioxidant activity with IC₅₀ and FRAP values at 4.08 ± 0.85 μg/mL and 10.84 ± 0.04 mmol FeSO₄/g sample, respectively. Taken together, H. isora possess chemopreventive and antioxidant activity. Further studies on in vivo activities of this plant are suggested.

Volatile sulphur compounds and pathways of L-methionine catabolism in Williopsis yeasts

Volatile sulphur compounds (VSCs) are important to the food industry due to their high potency and presence in many foods. This study assessed for the first time VSC production and pathways of L: -methionine catabolism in yeasts from the genus Williopsis with a view to understanding VSC formation and their potential flavour impact. Five strains of Williopsis saturnus (var. saturnus, var. subsufficiens, var. suavolens, var. sargentensis and var. mrakii) were screened for VSC production in a synthetic medium supplemented with L: -methionine. A diverse range of VSCs were produced including dimethyl disulphide, dimethyl trisulphide, 3-(methylthio)-1-propanal (methional), 3-(methylthio)-1-propanol (methionol), 3-(methylthio)-1-propene, 3-(methylthio)-1-propyl acetate, 3-(methylthio)-1-propanoic acid (methionic acid) and ethyl 3-(methylthio)-1-propanoate, though the production of these VSCs varied between yeast strains. W. saturnus var. saturnus NCYC22 was selected for further studies due to its relatively high VSC production. VSC production was characterised step-wise with yeast strain NCYC22 in coconut cream at different L: -methionine concentrations (0.00-0.20%) and under various inorganic sulphate (0.00-0.20%) and nitrogen (ammonia) supplementation (0.00-0.20%), respectively. Optimal VSC production was obtained with 0.1% of L: -methionine, while supplementation of sulphate had no significant effect. Nitrogen supplementation showed a dramatic inhibitory effect on VSC production. Based on the production of VSCs, the study suggests that the Ehrlich pathway of L: -methionine catabolism is operative in W. saturnus yeasts and can be manipulated by adjusting certain nutrient parameters to control VSC production.