Cytotoxicity of Thioalkaloid-Enriched Nuphar lutea Extract and Purified 6,6'-Dihydroxythiobinupharidine in Acute Myeloid Leukemia Cells: The Role of Oxidative Stress and Intracellular Calcium.

Acute myeloid leukemia (AML) is an aggressive hematological malignancy characterized by uncontrolled proliferation of immature myeloid progenitors. Here, we report the in vitro antileukemic effects of the sesquiterpene thioalkaloid-enriched fraction of the Nuphar lutea leaf extract (NUP) and a purified thioalkaloid 6,6'-dihydroxythiobinupharidine (DTBN). Treatment with 0.3-10 µg/mL NUP caused a dose- and time-dependent reduction in proliferation and viability of human AML cells (KG-1a, HL60 and U937). This was associated with apoptosis induction manifested by annexin-V/propidium iodide binding as well as cleavage of caspases 8, 9, and 3 as well as poly (ADP-ribose) polymerase. Caspase-dependence of the apoptotic effect was confirmed using the pan-caspase inhibitor Q-VD-OPH. NUP induced significant biphasic changes in the cytosolic levels of reactive oxygen species (ROS) compared to untreated cells-a decrease at early time points (2-4 h) and an increase after a longer incubation (24 h). ROS accumulation was accompanied by lowering the cellular glutathione (GSH) levels. In addition, NUP treatment resulted in elevation of the cytosolic Ca2+ (Ca2+cyt) levels. The thiol antioxidant and glutathione precursor N-acetyl cysteine prevented NUP-induced ROS accumulation and markedly inhibited apoptosis. A similar antiapoptotic effect was obtained by Ca2+cyt chelating using BAPTA. These data indicate that NUP-induced cell death is mediated, at least in part, by the induction of oxidative stress and Ca2+cyt accumulation. However, a substantial apoptotic activity of pure DTBN (0.05-0.25 µg/mL), was found to be independent of cytosolic ROS or Ca2+, suggesting that alternative mechanisms are involved in DTBN-induced cytotoxicity. Notably, neither NUP nor DTBN treatment significantly induced cell death of normal human peripheral blood mononuclear cells. Our results provide the basis for further investigation of the antileukemic potential of NUP and its active constituents.

Structure-Activity Relationship of Hydroxycinnamic Acid Derivatives for Cooperating with Carnosic Acid and Calcitriol in Acute Myeloid Leukemia Cells.

Plant phenolic compounds have shown the ability to cooperate with one another at low doses in producing enhanced anticancer effects. This may overcome the limitations (e.g., poor bioavailability and high-dose toxicity) in developing these agents as cancer medicines. We have previously reported that the hydroxycinnamic acid derivative (HCAD) methyl-4-hydroxycinnamate and the phenolic diterpene carnosic acid (CA) can synergistically induce massive calcium-dependent apoptosis in acute myeloid leukemia (AML) at non-cytotoxic concentrations of each agent. Here, we explored the chemical nature of the synergy between HCADs and either CA, in inducing cytotoxicity, or the active metabolite of vitamin D (calcitriol), in enhancing the differentiation of AML cells. This was done by determining the structure-activity relationship of a series of hydroxycinnamic acids and their derivatives (methyl hydroxycinnamates and hydroxybenzylideneacetones) in combination with CA or calcitriol. The HCAD/CA synergy required the following critical structural elements of an HCAD molecule: (a) the para-hydroxyl on the phenolic ring, (b) the carbon C7-C8 double bond, and (c) the methyl-esterified carboxyl. Thus, the only HCADs capable of synergizing with CA were found to be methyl-4-hydroxycinnamate and methyl ferulate, which also most potently enhanced calcitriol-induced cell differentiation. Notably, the C7-C8 double bond was the major requirement for this HCAD/calcitriol cooperation. Our findings may contribute to the rational design of novel synergistically acting AML drugs based on prototype combinations of HCADs with other agents studied here.

Synergistic Cytotoxicity of Methyl 4-Hydroxycinnamate and Carnosic Acid to Acute Myeloid Leukemia Cells via Calcium-Dependent Apoptosis Induction.

Acute myeloid leukemia (AML) is a malignant hematopoietic disease with poor prognosis for most patients. Conventional chemotherapy has been the standard treatment approach for AML in the past 40 years with limited success. Although, several targeted drugs were recently approved, their long-term impact on survival of patients with AML is yet to be determined. Thus, it is still necessary to develop alternative therapeutic approaches for this disease. We have previously shown a marked synergistic anti-leukemic effect of two polyphenols, curcumin (CUR) and carnosic acid (CA), on AML cells in-vitro and in-vivo. In this study, we identified another phenolic compound, methyl 4-hydroxycinnamate (MHC), which among several tested phytochemicals could uniquely cooperate with CA in killing AML cells, but not normal peripheral blood mononuclear cells. Notably, our data revealed striking phenotypical and mechanistic similarities in the apoptotic effects of MHC+CA and CUR+CA on AML cells. Yet, we show that MHC is a non-fluorescent molecule, which is an important technical advantage over CUR that can interfere in various fluorescence-based assays. Collectively, we demonstrated for the first time the antileukemic activity of MHC in combination with another phenolic compound. This type of synergistically acting combinations may represent prototypes for novel antileukemic therapy.

Description of Auricoccus indicus gen. nov., sp. nov., isolated from skin of human ear.

A Gram-stain-positive, non-motile, non-spore-forming, small spherical bacterium, strain S31T, was isolated from skin surface (external ear lobe) of a healthy human subject and characterized using a polyphasic approach. On the basis of 1507 bp 16S rRNA gene sequence comparison, S31T showed highest (92.8 %, AY119686) sequence similarity with Macrococcus brunensis CCUG 47200T followed by Macrococcus caseolyticus DSM 20597T (92.7 % AP009484) and formed a separate clade with 65 % bootstrap support. The DNA G+C content was found to be 34 mol%. Anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0 are the predominant fatty acids in fatty acid methyl ester (FAME) profile of strain S31T. It contained A3α type peptidoglycan with l-Lys-Gly3-l-Ala peptide. Comparative study of morphological and physiological traits indicated that S31T has phenetically diverged from its closest relatives. On the basis of morphological, chemotaxonomic and genotypic data, S31T showed marked distinctions from its closest relatives of the family Staphylococcaceae and is proposed to represent a novel genus Auricoccus with Auricoccus indicus as type species of the genus. S31T (CCUG 69858T=KCTC 33611T=MCC 3027T) is the type strain of the species.

Genome Sequence of Staphylococcus massiliensis Strain S46, Isolated from the Surface of Healthy Human Skin.

Staphylococcus massiliensis strain S46 was isolated from the surface of healthy human skin. Here, we report the draft genome sequence of S. massiliensis S46 (2,447,110 bp, with a G+C content of 36.3%).