Toxins2014, 6(8), 2256-2269; doi:10.3390/toxins6082256 (doi registration under processing) - published online 31 July 2014 Show/Hide Abstract
Abstract: Maize silage is a widely used feed product for cattle worldwide, which may be contaminated with mycotoxins, pre- and post-harvest. This concerns both farmers and consumers. To assess the exposure of Danish cattle to mycotoxins from maize silage, 99 samples of whole-crop maize (ensiled and un-ensiled) were analyzed for their contents of 27 mycotoxins and other secondary fungal metabolites by liquid chromatography-tandem mass spectrometry. The method specifically targets the majority of common pre- and post-harvest fungi associated with maize silage in Denmark. Sixty-one samples contained one or more of the 27 analytes in detectable concentrations. The most common mycotoxins were zearalenone, enniatin B nivalenol and andrastin A, found in 34%, 28%, 16% and 15% of the samples, respectively. None of the samples contained mycotoxins above the EU recommended maximum concentrations for Fusarium toxins in cereal-based roughage. Thus, the present study does not indicate that Danish maize silage in general is a cause of acute single mycotoxin intoxications in cattle. However, 31 of the samples contained multiple analytes; two samples as much as seven different fungal metabolites. Feed rations with maize silage may therefore contain complex mixtures of fungal secondary metabolites with unknown biological activity. This emphasizes the need for a thorough examination of the effects of chronic exposure and possible synergistic effects.
Toxins2014, 6(8), 2239-2255; doi:10.3390/toxins6082239 (doi registration under processing) - published online 31 July 2014 Show/Hide Abstract
Abstract: Bacterial cell-cell communication or quorum sensing (QS) is a biological process commonly described as allowing bacteria belonging to a same pherotype to coordinate gene expression to cell density. In Gram-positive bacteria, cell-cell communication mainly relies on cytoplasmic sensors regulated by secreted and re-imported signaling peptides. The Bacillus quorum sensors Rap, NprR, and PlcR were previously identified as the first members of a new protein family called RNPP. Except for the Rap proteins, these RNPP regulators are transcription factors that directly regulate gene expression. QS regulates important biological functions in bacteria of the Bacillus cereus group. PlcR was first characterized as the main regulator of virulence in B. thuringiensis and B. cereus. More recently, the PlcR-like regulator PlcRa was characterized for its role in cysteine metabolism and in resistance to oxidative stress. The NprR regulator controls the necrotrophic properties allowing the bacteria to survive in the infected host. The Rap proteins negatively affect sporulation via their interaction with a phosphorelay protein involved in the activation of Spo0A, the master regulator of this differentiation pathway. In this review we aim at providing a complete picture of the QS systems that are sequentially activated during the lifecycle of B. cereus and B. thuringiensis in an insect model of infection.
Toxins2014, 6(8), 2229-2238; doi:10.3390/toxins6082229 - published online 25 July 2014 Show/Hide Abstract
Abstract: Thuringiensin (Thu), also known as β-exotoxin, is a thermostable secondary metabolite secreted by Bacillus thuringiensis. It has insecticidal activity against a wide range of insects, including species belonging to the orders Diptera, Coleoptera, Lepidoptera, Hymenoptera, Orthoptera, and Isoptera, and several nematode species. The chemical formula of Thu is C22H32O19N5P, and it is composed of adenosine, glucose, phosphoric acid, and gluconic diacid. In contrast to the more frequently studied insecticidal crystal protein, Thu is not a protein but a small molecule oligosaccharide. In this review, a detailed and updated description of the characteristics, structure, insecticidal mechanism, separation and purification technology, and genetic determinants of Thu is provided.
Toxins2014, 6(8), 2210-2228; doi:10.3390/toxins6082210 - published online 25 July 2014 Show/Hide Abstract
Abstract: Our previous findings have demonstrated that bee venom (BV) has anti-cancer activity in several cancer cells. However, the effects of BV on lung cancer cell growth have not been reported.Cell viability was determined with trypan blue uptake, soft agar formation as well as DAPI and TUNEL assay. Cell death related protein expression was determined with Western blotting. An EMSA was used for nuclear factor kappaB (NF-κB) activity assay. BV (1–5 μg/mL) inhibited growth of lung cancer cells by induction of apoptosis in a dose dependent manner in lung cancer cell lines A549 and NCI-H460. Consistent with apoptotic cell death, expression of DR3 and DR6 was significantly increased. However, deletion of DRs by small interfering RNA significantly reversed BV induced cell growth inhibitory effects. Expression of pro-apoptotic proteins (caspase-3 and Bax) was concomitantly increased, but the NF-κB activity and expression of Bcl-2 were inhibited. A combination treatment of tumor necrosis factor (TNF)-like weak inducer of apoptosis, TNF-related apoptosis-inducing ligand, docetaxel and cisplatin, with BV synergistically inhibited both A549 and NCI-H460 lung cancer cell growth with further down regulation of NF-κB activity. These results show that BV induces apoptotic cell death in lung cancer cells through the enhancement of DR3 expression and inhibition of NF-κB pathway.
Toxins2014, 6(7), 2194-2209; doi:10.3390/toxins6072194 - published online 23 July 2014 Show/Hide Abstract
Abstract: Bacillus thuringiensis differs from the closely related Bacillus cereus group species by its ability to produce crystalline inclusions. The production of these crystals mainly results from the expression of the cry genes, from the stability of their transcripts and from the synthesis, accumulation and crystallization of large amounts of insecticidal Cry proteins. This process normally coincides with sporulation and is regulated by various factors operating at the transcriptional, post-transcriptional, metabolic and post-translational levels.
Toxins2014, 6(7), 2177-2193; doi:10.3390/toxins6072177 - published online 23 July 2014 Show/Hide Abstract
Abstract: Voltage-gated sodium channels (VGSCs; NaV1.1–NaV1.9) have been proven to be critical in controlling the function of excitable cells, and human genetic evidence shows that aberrant function of these channels causes channelopathies, including epilepsy, arrhythmia, paralytic myotonia, and pain. The effects of peptide toxins, especially those isolated from spider venom, have shed light on the structure–function relationship of these channels. However, most of these toxins have not been analyzed in detail. In particular, the bioactive faces of these toxins have not been determined. Jingzhaotoxin (JZTX)-V (also known as β-theraphotoxin-Cj2a) is a 29-amino acid peptide toxin isolated from the venom of the spider Chilobrachys jingzhao.JZTX-V adopts an inhibitory cysteine knot (ICK) motif and has an inhibitory effect on voltage-gated sodium and potassium channels. Previous experiments have shown that JZTX-V has an inhibitory effect on TTX-S and TTX-R sodium currents on rat DRG cells with IC50 values of 27.6 and 30.2 nM, respectively, and is able to shift the activation and inactivation curves to the depolarizing and the hyperpolarizing direction, respectively. Here, we show that JZTX-V has a much stronger inhibitory effect on NaV1.4, the isoform of voltage-gated sodium channels predominantly expressed in skeletal muscle cells, with an IC50 value of 5.12 nM, compared with IC50 values of 61.7–2700 nM for other heterologously expressed NaV1 subtypes. Furthermore, we investigated the bioactive surface of JZTX-V by alanine-scanning the effect of toxin on NaV1.4 and demonstrate that the bioactive face of JZTX-V is composed of three hydrophobic (W5, M6, and W7) and two cationic (R20 and K22) residues. Our results establish that, consistent with previous assumptions, JZTX-V is a Janus-faced toxin which may be a useful tool for the further investigation of the structure and function of sodium channels.