butane] is an isothiocyanate derivative from cruciferous vegetables, with anti-proliferative actions on various cancer and tumor cells. In this paper, we envisaged the effects of sulforaphane on various functions (growth inhibition, cytotoxicity and enhancement of O 2 --generating activity) of human monoblastic leukemia U937 cells. Sulforaphane showed strong cytotoxicity, resulting in inhibition of proliferation in a dose-dependent manner. In addition, cell differentiation induced by 1 μM all-trans retionic acid (RA) remarkably caused the enhanced resistance against cytotoxicity of sulforaphane. Moreover, the RA-induced O 2 --generating activity was also enhanced by sulforaphane in a dose dependent manner. When U937 cells were cultured in the presence of 1 μM RA and 2 μM sulforaphane, the O 2 --generating activity increased more than 2.5-fold compared with that in the absence of the latter. Semiquantitative RT-PCR showed that co-treatment with RA and sulforaphane slightly enhanced transcription of only p47-phox gene among five essential components (p22-phox, gp91-phox, p40-phox, p47-phox and p67-phox) for the O 2 --generating system in phagocytes. On the other hand, immunoblot analysis revealed that co-treatment with RA and sulforaphane caused accumulation of protein levels of p47-phox (upto ~130%) and p67-phox (upto ~240%) compared with those of the RA-treatment alone. These results indicated that sulforaphane may enhance the RA-induced O 2 --generating activity in U937 cells via accumulation of p47-phox and p67-phox proteins. These data suggested that sulforaphane may serve as an effective drug for leukemia treatment.

Flavones are belonging to flavonoids group and show diverse biological functions. Therefore, they have much attention as drugs for maintaining human health via contributing prevention and treatment of various diseases like cancers, diabetes, neurodegenerative diseases, ischemic stroke, inflammation diseases and cardiovascular diseases. On the other hand, human monoblastic leukemia U937 cells have been used as an excellent in vitro model system for macrophage development induced in response to various reagents such as all-trans retinoic acid (RA). Here, we investigated the effects of flavones (flavone and its hydroxy derivatives) on the RA-induced O 2 --generating activity of U937 cells. Very interestingly, at a concentration of 20 μM, 3', 4'-dihydroxyflavone caused up-regulation of the RAinduced O 2 --generating activity (to ~ 170%) although flavone and other hydroxyflavone derivatives tested showed remarkable inhibitory effects on the RA-induced O 2 --generating activity. The promoting effects of 3', 4'-dihydroxyflavone on the RA-induced O 2 --generating activity showed the maximum value at a concentration of 10 μM. Semiquantitative RT-PCR and immunoblotting revealed that 10 μM 3', 4'-dihydroxyflavone up-regulates the RA-induced O 2 --generating activity via enhancing gene expression of gp91-phox (mRNA level: to ~ 160%, protein level: to ~ 200%) while 10 μM 5, 7-dihydroxyflavone and 10 μM 3', 4', 5, 7-tetrahydroxyflavone down-regulate the RA-induced O 2 --generating activity via inhibiting gene expression of gp91-phox and p47-phox. These findings also showed that there may be various risks involved in use of phytochemical mixtures.

l‐Theanine (N‐ethyl‐ l‐glutamine) is an analog of l‐glutamine and l‐glutamic acid, accounts for up to 50% of all free amino acids in green tea, and elicits an umami taste. As l‐theanine also shows various physiological activities including immune response‐modifying activities, it is expected to be an excellent health‐promoting phytochemical agent. To know the influences of l‐theanine on the human innate immune response, we investigated the effect of l‐theanine on the superoxide anion (O2−)‐generating system of leukocytes using U937 cells. The O2−‐generating system in leukocytes consists of membrane cytochrome b558 protein (a complex of p22‐phox and gp91‐phox proteins) and cytosolic p40‐phox, p47‐phox, and p67‐phox proteins. Addition of 500 μM l‐theanine caused remarkable enhancement of the all‐trans retinoic acid (ATRA)‐induced O2−‐generating activity (to ~470% of ATRA‐treated cells), but not l‐glutamine and l‐glutamic acid. Semiquantitative RT‐PCR showed that the transcription level of gp91‐phox is significantly increased in ATRA and l‐theanine‐co‐treated cells. Chromatin immunoprecipitation revealed that l‐theanine enhances acetylations of Lys‐9 and Lys‐14 residues of histone H3 within the chromatin surrounding the promoter region of the gp91‐phox gene. Immunoblotting demonstrated that membrane cytochrome b558 proteins remarkably accumulate in ATRA +  l‐theanine‐treated cells. These results suggested that l‐theanine brings about a remarkable accumulation of cytochrome b558 protein via upregulating the transcription of the gp91‐phox gene during leukocyte differentiation, resulting in marked augmentation of the O2−‐generating ability, which is one of the most important functions of leukocytes responsible for the innate immune system.

Polymethoxyflavones in which all hydroxyl groups are capped by methyl residues show high membrane permeability, metabolic resistance, and diverse biological activities such as cell growth inhibitory effects responsible for their anti-cancer activities. They are expected to be as biotherapeutic drugs for maintaining human health via contributing prevention and treatment of serious illnesses such as cancers, neurodegenerative diseases, inflammatory bowel diseases, lipid metabolism disorders, and so on. Human monoblastic leukemia U937 cell line has been used as an excellent in vitro cell model system for studying macrophage differentiation induced by various cell differentiation inducers such as all-trans retinoic acid (ATRA). In this study, we investigated the influences of two typical polymethoxyflavones, such as nobiletin and tangeretin, on the ATRA-induced superoxide anion (O 2 -)-generating ability of U937 cells. Nobiletin and tangeretin suppressed cell proliferation of U937 cells in a dose-dependent manner. At a concentration of 10 μM, tangeretin drastically brought about down-regulation of the ATRA-induced O 2 --generating ability (to ~15% of ATRA-treated cells) although nobiletin showed moderate inhibitory effects on the ATRA-induced O 2 --generating ability (to ~65% of ATRA-treated cells). Quantitative RT-PCR and immunoblotting revealed that tangeretin down-regulates the ATRA-induced O 2 --generating ability via suppressing gene exprerssion levels of gp91-phox (mRNA: to ~75%, protein: to ~70% of ATRAtreated cells) and p47-phox (mRNA: to ~75%, protein: to ~40% of ATRA-treated cells) genes. These findings demonstrated that tangeretin shows not only the inhibitory effects on cell growth but also the strong suppressing effects on the ATRA-induced O 2 --generating ability of U937 cells.