(1/3723) Estrogenic potential of certain pyrethroid compounds in the MCF-7 human breast carcinoma cell line.

Estrogens, whether natural or synthetic, clearly influence reproductive development, senescence, and carcinogenesis. Pyrethroid insecticides are now the most widely used agents for indoor pest control, providing potential for human exposure. Using the MCF-7 human breast carcinoma cell line, we studied the estrogenic potential of several synthetic pyrethroid compounds in vitro using pS2 mRNA levels as the end point. We tested sumithrin, fenvalerate, d-trans allethrin, and permethrin. Nanomolar concentrations of either sumithrin or fenvalerate were sufficient to increase pS2 expression slightly above basal levels. At micromolar concentrations, these two pyrethroid compounds induced pS2 expression to levels comparable to those elicited by 10 nM 17ss-estradiol (fivefold). The estrogenic activity of sumithrin was abolished with co-treatment with an antiestrogen (ICI 164,384), whereas estrogenic activity of fenvalerate was not significantly diminished with antiestrogen co-treatment. In addition, both sumithrin and fenvalerate were able to induce cell proliferation of MCF-7 cells in a dose-response fashion. Neither permethrin nor d-trans allethrin affected pS2 expression. Permethrin had a noticeable effect on cell proliferation at 100 microM, whereas d-trans allethrin slightly induced MCF-7 cell proliferation at 10 microM, but was toxic at higher concentrations. Overall, our studies imply that each pyrethroid compound is unique in its ability to influence several cellular pathways. These findings suggest that pyrethroids should be considered to be hormone disruptors, and their potential to affect endocrine function in humans and wildlife should be investigated.  (+info)

(2/3723) Androgen-independent induction of prostate-specific antigen gene expression via cross-talk between the androgen receptor and protein kinase A signal transduction pathways.

Transcription of the prostate-specific antigen (PSA) gene escapes regulation by androgens in advanced prostate cancer. To determine the molecular mechanism(s) of androgen-independent regulation of the PSA gene, the possibility that the androgen receptor (AR) is activated in the absence of androgen by stimulation of protein kinase A (PKA) was investigated. Activation of PKA by forskolin resulted in elevated expression of the PSA gene in androgen-depleted LNCaP cells, an effect that was blocked by the antiandrogen, bicalutamide. Further evidence that induction of PSA gene expression was dependent on AR was obtained from experiments using PC3 cells devoid of AR. Neither PSA, PB, nor ARR3 androgen-responsive reporters could be induced by activation of PKA in the absence of transfected AR. In addition, when nuclear AR from forskolin-treated LNCaP cells was incubated with oligonucleotides encoding an androgen response element of the PSA promoter and examined by electromobility shift assay, an increase in AR-androgen response element complex formation was observed. Lastly, cotransfection of an expression vector for a chimeric protein encoding the amino-terminal domain of the human AR linked to Gal4 and a 5xGal4UAS reporter gene construct resulted in activation of the amino-terminal domain of the AR by stimulation of PKA activity. These results demonstrate androgen-independent induction of PSA gene expression in prostate cancer cells by an AR-dependent pathway.  (+info)

(3/3723) Rational design and synthesis of a novel anti-leukemic agent targeting Bruton's tyrosine kinase (BTK), LFM-A13 [alpha-cyano-beta-hydroxy-beta-methyl-N-(2, 5-dibromophenyl)propenamide].

In a systematic effort to design potent inhibitors of the anti-apoptotic tyrosine kinase BTK (Bruton's tyrosine kinase) as anti-leukemic agents with apoptosis-promoting and chemosensitizing properties, we have constructed a three-dimensional homology model of the BTK kinase domain. Our modeling studies revealed a distinct rectangular binding pocket near the hinge region of the BTK kinase domain with Leu460, Tyr476, Arg525, and Asp539 residues occupying the corners of the rectangle. The dimensions of this rectangle are approximately 18 x 8 x 9 x 17 A, and the thickness of the pocket is approximately 7 A. Advanced docking procedures were employed for the rational design of leflunomide metabolite (LFM) analogs with a high likelihood to bind favorably to the catalytic site within the kinase domain of BTK. The lead compound LFM-A13, for which we calculated a Ki value of 1.4 microM, inhibited human BTK in vitro with an IC50 value of 17.2 +/- 0.8 microM. Similarly, LFM-A13 inhibited recombinant BTK expressed in a baculovirus expression vector system with an IC50 value of 2.5 microM. The energetically favorable position of LFM-A13 in the binding pocket is such that its aromatic ring is close to Tyr476, and its substituent group is sandwiched between residues Arg525 and Asp539. In addition, LFM-A13 is capable of favorable hydrogen bonding interactions with BTK via Asp539 and Arg525 residues. Besides its remarkable potency in BTK kinase assays, LFM-A13 was also discovered to be a highly specific inhibitor of BTK. Even at concentrations as high as 100 micrograms/ml (approximately 278 microM), this novel inhibitor did not affect the enzymatic activity of other protein tyrosine kinases, including JAK1, JAK3, HCK, epidermal growth factor receptor kinase, and insulin receptor kinase. In accordance with the anti-apoptotic function of BTK, treatment of BTK+ B-lineage leukemic cells with LFM-A13 enhanced their sensitivity to ceramide- or vincristine-induced apoptosis. To our knowledge, LFM-A13 is the first BTK-specific tyrosine kinase inhibitor and the first anti-leukemic agent targeting BTK.  (+info)

(4/3723) Oxidation of low density lipoprotein and plasma by 15-lipoxygenase and free radicals.

It is generally accepted that the oxidation of pentadiene structures of polyunsaturated lipids by lipoxygenase (LOX) is regio- and enantio-specific, while the free radical-mediated lipid peroxidation gives stereo-random racemic products. It was confirmed that the oxidation of human low density lipoprotein (LDL) by 15-LOX from rabbit reticulocytes gave phosphatidylcholine (PC) and cholesteryl ester (CE) hydroperoxides regio-, stereo- and enantio-specifically. 15-LOX also oxidized human plasma to give specific PC and CE hydroperoxides in spite of the presence of high concentrations of antioxidants. More CE hydroperoxides were formed than PC hydroperoxides from LDL, but the reverse order was observed for plasma oxidation. The S/R ratio of the hydroperoxides decreased during long time incubation but remained significantly larger than one, while free radical-mediated oxidation of LDL and plasma gave racemic products.  (+info)

(5/3723) Control of malaria vectors: cost analysis in a province of northern Vietnam.

The cost of permethrin-treated bednets (50% EC; 0.2 g/m2, 2 rounds per year) was compared to the cost of residual spraying with lambdacyhalothrin 10% WP (0.03 g/m2, once yearly) in Hoa Binh, a mountainous province in northern Vietnam. Calculations of the amounts of insecticides needed were based on national guidelines, on data from a cross-sectional survey and on district activity reports. The actual cost of insecticide required per person per year was lower for impregnation (US$ 0.26) than for spraying (US$ 0.36), but the difference was smaller than expected. The total cost for impregnated bednets per person per year amounted to US$ 0.90 compared to USS 0.47 for spraying. The determining factor was the cost of the net, amounting to US$ 0.58 per person per year, assuming a 5-year life of the net. Other material (excluding nets), labour and transport combined, accounted for only 17% of the impregnation cost and 23% of spraying expenses. However, for the National Malaria Control Programme of Vietnam, the cost per person per year for impregnated bednets amounted to US$ 0.32 only, because the vast majority of nets are bought by the population. For spraying, the programme had to bear the entire cost.  (+info)

(6/3723) Molecular characterisation of a novel thermophilic nitrile hydratase.

The thermophilic soil isolate, Bacillus pallidus Dac521, expresses a constitutive nitrile hydratase. The purified enzyme was found to be a 110 kDa tetramer composed of two alpha and two beta subunits with molecular masses of 27 kDa and 29 kDa, respectively. The enzyme electrophoresed as a single protein band on native PAGE but two protein bands with isoelectric points of 4.7 and 5.5 on isoelectric focusing suggested the presence of isozymes. The purified enzyme was moderately thermostable up to 55 degrees C and the enzyme activity was stable over a broad pH range. Comparisons of the N-terminal amino acid sequences of the nitrile hydratase subunits with those of other nitrile hydratases showed up to 90% identity for the beta subunit sequence but no significant identity for the alpha subunit. The enzyme hydrolysed a narrow range of aliphatic substrates and did not hydrolyse any of the cyclic, hydroxy-, di- or aromatic nitriles tested. The activity was irreversibly inhibited by the aromatic nitrile, benzonitrile. The kinetic constants for acetonitrile, acrylonitrile and propionitrile compared favourably with those of mesophilic nitrile hydratases.  (+info)

(7/3723) Role of cytochrome P-450 2E1 in methacrylonitrile metabolism and disposition.

Methacrylonitrile (MAN) is a widely used aliphatic nitrile and is structurally similar to the known rat carcinogen and suspected human carcinogen acrylonitrile (AN). There is evidence that AN is metabolized via the cytochrome P-450 (CYP) 2E1. Recently, we identified two biliary conjugates originating from the interaction of MAN and its epoxide with glutathione. Mercapturic acids formed via the degradation of the two conjugates were also identified in rat and mouse urine. Additionally, a significant portion of MAN was eliminated in the expired air as CO2 (formed via the epoxide pathway) and unchanged MAN. The objective of the present work was to determine whether CYP2E1 is involved in the oxidative metabolism of MAN as was suggested for AN. 2-14C-MAN was administered to CYP2E1-null or wild-type mice by gavage at 12 mg/kg. Although total urinary and fecal excretion of MAN-derived radioactivity was slightly different in CYP2E1-null versus wild-type mice, the ratio of mercapturic acids originating from the epoxide-glutathione versus MAN-glutathione conjugates were lower in urine of CYP2E1-null mice than in that of wild-type animals. Exhalation of MAN-derived organic volatiles (primarily parent MAN) was 12- and 42-fold greater in female and male CYP2E1-null mice than in wild-type mice, respectively. Additionally, exhalation of CO2 derived from metabolism of MAN via the CYP2E1 pathway was 3- to 5-fold greater in wild-type than in CYP2E1-null animals. Although these data indicate that CYP2E1 is the principal enzyme responsible for the oxidative metabolism of MAN, other cytochrome P-450 enzymes may be involved. Assessment of MAN metabolism in CYP2E1-null mice pretreated with 1-aminobenzotriazole (CYP inhibitor) resulted in a further decrease in oxidative metabolites of MAN. Comparison of the tissue concentrations of MAN-derived radioactivity in mouse tissues revealed that MAN-derived radioactivity is generally higher in wild-type > CYP2E1-null mice > CYP2E1-null mice pretreated with 1-aminobenzotriazole, suggesting a direct relationship between MAN oxidative metabolism and the half-life of MAN and/or its metabolites in various tissues. It is therefore concluded that MAN oxidative metabolites such as the epoxide intermediate have greater reactivity than parent MAN.  (+info)

(8/3723) A new strategy for treating nets. Part 1: formulation and dosage.

The conventional dosages of pyrethroid insecticides on mosquito nets assume that nets will be retreated at 6-12 month intervals. However, dosage should be related to washing of nets; if nets are only washed once or twice a year, their dosage requirements will be different to those which are washed fortnightly. A 'low-dose, frequent-wash' retreatment system might be technically more appropriate and more affordable where nets are washed frequently, as they are in Dar es Salaam. Moreover, for use as a domestic insecticide, water-based formulations of pyrethroid are preferable to the more commonly used emulsifiable concentrates (ECs). This paper reports laboratory evaluations of three formulations (ECs, Flowable, CS) of three pyrethroids (deltamethrin, lambdacyhalothrin, permethrin). Insecticidal activity was tested using serial bioassays at a range of dosages using Anopheles gambiae. The water-based formulations were no less effective than the ECs, even at the lowest dosages. Nets treated with 3 mg/m2 and then repeatedly washed and retreated after each wash with either 3 mg/m2 or 1 mg/m2 were subjected to gas chromatography analysis. This showed that the amounts of pyrethroid in the nets accumulated rapidly over the first few wash-retreatment cycles and then remained fairly stable over subsequent cycles. These nets gave consistently high bioassay mortalities throughout the experiment, while the mortality declined rapidly after several washes with the nets that were treated at 3 mg/m2 but not retreated. Experimental huts were used to compare the effectiveness of these 2 net retreatment regimes and nets which were not retreated. All nets caused high mortality rates amongst Anopheles females, but had negligible effects on culicines; either in killing them or in preventing feeding. Therefore use of a high 'loading' dose for initial treatment with lower 'maintenance' doses for retreatment may be preferable to ensure that net users promptly perceive the benefits of the insecticide against culicines.  (+info)