Survey of Nitrate Ion Concentrations in Vegetables Cultivated in Plant Factories: Comparison with Open-Culture Vegetables.

A survey of nitrate-ion concentrations in plant-factory-cultured leafy vegetables was conducted. 344 samples of twenty-one varieties of raw leafy vegetables were examined using HPLC. The nitrate-ion concentrations in plant-factory-cultured leafy vegetables were found to be LOD-6,800 mg/kg. Furthermore, the average concentration values varied among different leafy vegetables. The average values for plant-factory-cultured leafy vegetables were higher than those of open-cultured leafy vegetables reported in previous studies, such as the values listed in the Standard Tables of Food Composition in Japan- 2015 - (Seventh revised edition). For some plant-factory-cultured leafy vegetables, such as salad spinach, the average values were above the maximum permissible levels of nitrate concentration in EC No 1258/2011; however, even when these plant-factory-cultured vegetables were routinely eaten, the intake of nitrate ions in humans did not exceed the ADI.

Zinc diethyldithiocarbamate as an inducer of metallothionein in cultured vascular endothelial cells.

Vascular endothelial cells are in direct contact with blood. Inorganic zinc is thought to be incapable of inducing metallothionein, which protects cells from heavy metal toxicity and oxidative stress, in vascular endothelial cells. Here, we aimed to further characterize the induction of metallothionein in vascular endothelial cells. Our results confirmed that inorganic zinc could not induce metallothionein in vascular endothelial cells. Moreover, ZnSO4 could not activate both the metal response element (MRE) transcription factor 1 (MTF-1)/MRE and Nrf2/antioxidant response element (ARE) pathways and was incapable of inducing metallothionein. In addition, bis(L-cysteinato)zincate(II), a zinc complex that activates the MTF-1/MRE pathway, increased MRE promoter activity but failed to induce metallothionein, suggesting that vascular endothelial metallothionein was not induced only by activation of the MTF-1/MRE pathway. Further analysis of a library of zinc complexes showed that zinc(II) bis(diethyldithiocarbamate) activated the MTF-1/MRE pathway but not the Nrf2/ARE pathway, increased MT-1A, MT-1E, and MT-2A mRNA levels, and induced metallothionein proteins. These data indicated that zinc complexes may be excellent tools to analyze metallothionein induction in vascular endothelial cells.

Induction of metallothionein isoforms by copper diethyldithiocarbamate in cultured vascular endothelial cells.

Metallothionein (MT) plays a central role in cellular defense against heavy metals and oxidative stress. Since the induction of MT requires the activation of metal response element (MRE)-binding transcription factor-1 (MTF-1) by binding of zinc ions, inorganic zinc is regarded as a typical MT inducer. However, in a previous report, we showed that inorganic zinc could not induce MT in vascular endothelial cells. While it is suggested that endothelial MT presents mechanisms different from those of other cell types, these remain unclear. In this study, we investigated whether the induction of endothelial MT expression involves the Nrf2-ARE pathway using copper(II) bis(diethyldithiocarbamate), termed Cu10, using a culture system of bovine aortic endothelial cells. Cu10 induced MT-1/2 protein expression and increased the expression of mRNAs for MT-1A, MT-1E, and MT-2, MT isoforms expressed in the cells. Cu10 activated not only the MTF-1-MRE, but also the Nrf2-ARE pathway. MTF-1 knockdown resulted in the repression of Cu10-induced MT-1 and -2 expression. Cu10-induced MT-1 expression was down-regulated by Nrf2 knockdown. However, MT-2 expression was not affected by Nrf2 knockdown. These results suggest that the expression of endothelial MT is up-regulated by the Nrf2-ARE pathway as well as by the MTF-1-MRE pathway. Moreover, MT-1 regulation mechanisms differ from that of MT-2. Specifically, the present data support the hypothesis that MT-1 participates in the biological defense system, while MT-2 mainly regulates intracellular zinc metabolism.