The mechanisms underlying the relaxant effect of methyl and ethyl gallates in the guinea pig trachea in vitro: contribution of potassium channels

The relaxant response and the possible contribution of K+ channels to the relaxation caused by both methyl and ethyl gallates, two compounds isolated from the Brazilian medicinal plant Phyllanthus urinaria, were investigated in the guinea pig trachea in vitro. Both methyl and ethyl gallate (0.01-30 microM) caused graded and complete relaxation of the guinea pig trachea without epithelium, pre-contracted by histamine, with mean EC50 values of 1.8 (1.2-2.2) microM and 0.7 (0.6-0.8) microM, respectively, and Emax of both 100+/-0%. Response to ethyl, but not methyl gallate, was significantly shifted to the right, with no change in the maximum effect when the epithelium was removed. The increase in K+ concentration in the medium to 80 mM completely abolished the relaxant response caused by both methyl and ethyl gallate. In addition, tetraethylammonium (10 mM) reduced by 50+/-6% and 43+/-4% the relaxation caused by methyl and ethyl gallates. In contrast, glibenclamide (3 microM) shifted (by about two- and fourfold) the concentration-response curves for both methyl and ethyl gallates, with no changes in the maximum effect. Charybdotoxin (100 nM), but not apamin (100 nM), significantly blocked by 54+/-5% and 59+/-4% the relaxation of both methyl and ethyl gallates. In contrast, SQ 22536 (10 microM; a selective adenylyl cyclase inhibitor), methylene blue (10 microM) or ODQ (1 microM; a guanylyl cyclase inhibitor) did not significantly affect the relaxant response caused by either of the compounds. These results provide evidence that the relaxation caused by both methyl and ethyl gallates in the guinea pig trachea in vitro may involve the activation of large-conductance Ca2+-activated K+ channels, and, to a lesser extent, ATP-sensitive K+ channels. Such results extend our previous observations and are consistent with the notion that methyl and ethyl gallates are mainly responsible for the relaxant action previously demonstrated in the extract of this plant.     

Effects of Sebastiana schottiana Extracts on Isolated Smooth Muscle Contraction.

Crude aqueous-ethanol, chloroform, and semipurified flavonoid-glycoside extracts of SEBASTIANA SCHOTTIANA (Euphorbiaceae) inhibited contractions of rat uterus to acetylcholine or oxytocin and guinea pig ileum to electric field stimulation. The greatest antispasmodic potency was observed with the chloroform extract. The popular use of this plant in Southern Brazil as a remedy for kidney or bladder calculi may be related to the presence of smooth muscle relaxing compounds.     

Effects of Lanthanum on Human Lymphocytes Viability and DNA Strand Break

Lanthanum (La) is a rare-earth metal with applications in agriculture, industry, and medicine. Since lanthanides show a broad spectrum of applications there is an increased risk of contamination for humans. We examined the effects of lanthanum in Jurkat cells and human peripheral lymphocytes (HPL), and we found that it was cytotoxic and genotoxic on both cell lines. Additionally, HPL were more sensitive to La treatment than Jurkat cells and necrosis was the pathway by which La induced cytotoxicity. Vitamin E was able to diminish the DNA strand breaks induced suggesting that oxidative stress may be involved in the genotoxic process.     

PTEN posttranslational inactivation and hyperactivation of the PI3K/Akt pathway sustain primary T cell leukemia viability

Mutations in the phosphatase and tensin homolog (PTEN) gene leading to PTEN protein deletion and subsequent activation of the PI3K/Akt signaling pathway are common in cancer. Here we show that PTEN inactivation in human T cell acute lymphoblastic leukemia (T-ALL) cells is not always synonymous with PTEN gene lesions and diminished protein expression. Samples taken from patients with T-ALL at the time of diagnosis very frequently showed constitutive hyperactivation of the PI3K/Akt pathway. In contrast to immortalized cell lines, most primary T-ALL cells did not harbor PTEN gene alterations, displayed normal PTEN mRNA levels, and expressed higher PTEN protein levels than normal T cell precursors. However, PTEN overexpression was associated with decreased PTEN lipid phosphatase activity, resulting from casein kinase 2 (CK2) overexpression and hyperactivation. In addition, T-ALL cells had constitutively high levels of ROS, which can also downmodulate PTEN activity. Accordingly, both CK2 inhibitors and ROS scavengers restored PTEN activity and impaired PI3K/Akt signaling in T-ALL cells. Strikingly, inhibition of PI3K and/or CK2 promoted T-ALL cell death without affecting normal T cell precursors. Overall, our data indicate that T-ALL cells inactivate PTEN mostly in a nondeletional, posttranslational manner. Pharmacological manipulation of these mechanisms may open new avenues for T-ALL treatment.     

Antimetastatic activity and low systemic toxicity of tetradecyl gallate in a preclinical melanoma mouse model

Gallates with eight or more carbon atoms in the lateral chain show potent anticancer activity against various cell lines. However, studies regarding the in vivo antimelanoma activity of tetradecyl gallate (C₁₄) have not yet been reported. In this study an evaluation of the ability of C₁₄ to inhibit metastasis, using lung metastases as a model, was carried out. The experimental mouse melanoma model was established by intravenous injection of metastatic B16F10 melanoma cells. The systemic toxicity of C₁₄ was evaluated in vivo by monitoring the weight, survival, biochemical and hematological parameters, and through histological analysis. It was observed that C₁₄ decreased lung metastasis in vivo by 80% and increased the survival rate of the animals without toxic effects. Additionally, C₁₄ induced cytotoxic effects on B16F10 cells, inhibited the inter-cellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) expression, and significantly decreased cell adhesion. These results reveal that C₁₄ has potent antimetastatic ability and is a good candidate for further study as a potential therapeutic agent for tumor metastases.     

Lymphotoxin‐β receptor in microenvironmental cells promotes the development of T‐cell acute lymphoblastic leukaemia with cortical/mature immunophenotype

Lymphotoxin‐mediated activation of the lymphotoxin‐β receptor (LTβR; LTBR) has been implicated in cancer, but its role in T‐cell acute lymphoblastic leukaemia (T‐ALL) has remained elusive. Here we show that the genes encoding lymphotoxin (LT)‐α and LTβ (LTA, LTB) are expressed in T‐ALL patient samples, mostly of the TAL/LMO molecular subtype, and in the TEL‐JAK2 transgenic mouse model of cortical/mature T‐ALL (Lta, Ltb). In these mice, expression of Lta and Ltb is elevated in early stage T‐ALL. Surface LTα₁β₂ protein is expressed in primary mouse T‐ALL cells, but only in the absence of microenvironmental LTβR interaction. Indeed, surface LT expression is suppressed in leukaemic cells contacting Ltbr‐expressing but not Ltbr‐deficient stromal cells, both in vitro and in vivo, thus indicating that dynamic surface LT expression in leukaemic cells depends on interaction with its receptor. Supporting the notion that LT signalling plays a role in T‐ALL, inactivation of Ltbr results in a significant delay in TEL‐JAK2‐induced leukaemia onset. Moreover, young asymptomatic TEL‐JAK2;Ltbr^?/? mice present markedly less leukaemic thymocytes than age‐matched TEL‐JAK2;Ltbr^+/+ mice and interference with LTβR function at this early stage delayed T‐ALL development. We conclude that LT expression by T‐ALL cells activates LTβR signalling in thymic stromal cells, thus promoting leukaemogenesis.     

PI3K inhibition synergizes with glucocorticoids but antagonizes with methotrexate in T-cell acute lymphoblastic leukemia

The PI3K pathway is frequently hyperactivated in primary T-cell acute lymphoblastic leukemia (T-ALL) cells. Activation of the PI3K pathway has been suggested as one mechanism of glucocorticoid resistance in T-ALL, and patients harboring mutations in the PI3K negative regulator PTEN may be at increased risk of induction failure and relapse. By gene expression microarray analysis of T-ALL cells treated with the PI3K inhibitor AS605240, we identified Myc as a prominent downstream target of the PI3K pathway. A significant association was found between the AS605240 gene expression signature and that of glucocorticoid resistance and relapse in T-ALL. AS605240 showed anti-leukemic activity and strong synergism with glucocorticoids both in vitro and in a NOD/SCID xenograft model of T-ALL. In contrast, PI3K inhibition showed antagonism with methotrexate and daunorubicin, drugs that preferentially target dividing cells. This antagonistic interaction, however, could be circumvented by the use of correct drug scheduling schemes. Our data indicate the potential benefits and difficulties for the incorporation of PI3K inhibitors in T-ALL therapy.