Furan and Methylfurans in Foods: An Update on Occurrence, Mitigation, and Risk Assessment.

The acceptance of many foods is related to traditional cooking practices, which create taste and texture and are important to digestibility, preservation, and the reduction of foodborne illnesses. A wide range of compounds are formed during the cooking of foods, a number of these have been shown to lead to adverse effects in classical toxicological models and are known as food processing contaminants (FPC). It is essential that the presence and effects of such compounds alone and in combination within the diet are understood such that proportionate risk management measures can be developed, while taking a holistic view across the whole value chain. Furan and alkylfurans (principally 2- and 3-methylfuran) are highly volatile FPC, which are formed in a wide range of foods at low amounts. The focus of research to-date has been on those foods, which have been identified to be most consequential in terms of being sources of exposure, namely jarred and canned foods for infants and young children (meals and drinks) and coffee (roast and ground, soluble). This report presents (i) new industry data on the occurrence of furan and methylfurans in selected food categories following previous coffee studies, (ii) the most salient parameters that impact furan formation, and (iii) aspects of importance for the risk assessment.

Differential distribution of competence for panplacodal and neural crest induction to non-neural and neural ectoderm.

It is still controversial whether cranial placodes and neural crest cells arise from a common precursor at the neural plate border or whether placodes arise from non-neural ectoderm and neural crest from neural ectoderm. Using tissue grafting in embryos of Xenopus laevis, we show here that the competence for induction of neural plate, neural plate border and neural crest markers is confined to neural ectoderm, whereas competence for induction of panplacodal markers is confined to non-neural ectoderm. This differential distribution of competence is established during gastrulation paralleling the dorsal restriction of neural competence. We further show that Dlx3 and GATA2 are required cell-autonomously for panplacodal and epidermal marker expression in the non-neural ectoderm, while ectopic expression of Dlx3 or GATA2 in the neural plate suppresses neural plate, border and crest markers. Overexpression of Dlx3 (but not GATA2) in the neural plate is sufficient to induce different non-neural markers in a signaling-dependent manner, with epidermal markers being induced in the presence, and panplacodal markers in the absence, of BMP signaling. Taken together, these findings demonstrate a non-neural versus neural origin of placodes and neural crest, respectively, strongly implicate Dlx3 in the regulation of non-neural competence, and show that GATA2 contributes to non-neural competence but is not sufficient to promote it ectopically.

Tissues and signals involved in the induction of placodal Six1 expression in Xenopus laevis.

Ectodermal placodes, from which many cranial sense organs and ganglia develop, arise from a common placodal primordium defined by Six1 expression. Here, we analyse placodal Six1 induction in Xenopus using microinjections and tissue grafts. We show that placodal Six1 induction occurs during neural plate and neural fold stages. Grafts of anterior neural plate but not grafts of cranial dorsolateral endomesoderm induce Six1 ectopically in belly ectoderm, suggesting that only the neural plate is sufficient for inducing Six1 in ectoderm. However, extirpation of either anterior neural plate or of cranial dorsolateral endomesoderm abolishes placodal Six1 expression indicating that both tissues are required for its induction. Elevating BMP-levels blocks placodal Six1 induction, whereas ectopic sources of BMP inhibitors expand placodal Six1 expression without inducing Six1 ectopically. This suggests that BMP inhibition is necessary but needs to cooperate with additional factors for Six1 induction. We show that FGF8, which is expressed in the anterior neural plate, can strongly induce ectopic Six1 in ventral ectoderm when combined with BMP inhibitors. In contrast, FGF8 knockdown abolishes placodal Six1 expression. This suggests that FGF8 is necessary and together with BMP inhibitors sufficient to induce placodal Six1 expression in cranial ectoderm, implicating FGF8 as a central component in generic placode induction.

Effects of azathioprine and its metabolites on repair mechanisms of the intestinal epithelium in vitro.

Erosions and ulcerations of the intestinal epithelium are hallmarks of inflammatory bowel diseases (IBD). Intestinal epithelial cell migration (restitution) and proliferation are pivotal mechanisms for healing of epithelial defects after mucosal injury. In addition, the rate of apoptosis of epithelial cells may modulate intestinal wound healing. The purine antagonists azathioprine (AZA) and 6-mercaptopurine (6-MP) are widely used drugs in the treatment of IBD. In the present study, the hitherto unknown effects of AZA as well as its metabolites 6-MP and 6-thioguanine (6-TG) on repair mechanisms and apoptosis of intestinal epithelia were analysed. Intestinal epithelial cell lines (human Caco-2, T-84 and HT-29 cells, rat IEC-6 cells) were incubated with AZA, 6-MP or 6-TG for 24 h (final concentrations 0.1-10 microM). Migration of Caco-2 and IEC-6 cells was analysed by in vitro restitution assays. Caco-2 and IEC-6 cell proliferation was evaluated by measurement of [3H]thymidine incorporation into DNA. Apoptosis of Caco-2, T-84, HT-29 and IEC-6 cells was assessed by histone ELISA, 4'6'diamidino-2'phenylindole-dihydrochloride staining as well as flow cytometric analysis of Annexin V/propidium iodide (PI)-stained cells. Cell cycle progression was evaluated by PI staining and flow cytometry. Epithelial restitution was not significantly affected by any of the substances tested. However, proliferation of intestinal epithelial cells was inhibited in a dose-dependent manner (maximal effect 92%) by AZA, 6-MP as well as 6-TG. In HT-29 cells, purine antagonist-effected inhibition of cell proliferation was explained by a cell cycle arrest in the G2 phase. In contrast, AZA, 6-MP and 6-TG induced no cell cycle arrest in Caco-2, T-84 and IEC-6 cells. AZA, 6-MP as well as 6-TG induced apoptosis in the non-transformed IEC-6 cell line but not in human Caco-2, T-84 and HT-29 cells. In summary, AZA and its metabolites exert no significant effect on intestinal epithelial restitution. However, they profoundly inhibit intestinal epithelial cell growth via various mechanisms: they cause a G2 cell cycle arrest in HT-29 cells, induce apoptosis in IEC-6 cells and dose-dependently inhibit intestinal epithelial proliferation.

Molecular anatomy of placode development in Xenopus laevis.

We analyzed the spatiotemporal pattern of expression of 15 transcription factors (Six1, Six4, Eya1, Sox3, Sox2, Pax6, Pax3, Pax2, Pax8, Dlx3, Msx1, FoxI1c, Tbx2, Tbx3, Xiro1) during placode development in Xenopus laevis from neural plate to late tail bud stages. Out of all genes investigated, only the expression of Eya1, Six1, and Six4 is maintained in all types of placode (except the lens) throughout embryonic development, suggesting that they may promote generic placodal properties and that their crescent-shaped expression domain surrounding the neural plate defines a panplacodal primordium from which all types of placode originate. Double-labeling procedures were employed to reveal the precise position of this panplacodal primordium relative to neural plate, neural crest, and other placodal markers. Already at neural plate stages, the panplacodal primordium is subdivided into several subregions defined by particular combinations of transcription factors allowing us to identify the approximate regions of origin of various types of placode. Whereas some types of placode were already prefigured by molecularly distinct areas at neural plate stages, the epibranchial, otic, and lateral line placodes arise from a common posterior placodal area (characterized by Pax8 and Pax2 expression) and acquire differential molecular signatures only after neural tube closure. Our findings argue for a multistep mechanism of placode induction, support a combinatorial model of placode specification, and suggest that different placodes evolved from a common placodal primordium by successive recruitment of new inducers and target genes.

Hypothalamic inferior lobe and lateral torus connections in a percomorph teleost, the red cichlid (Hemichromis lifalili).

The neuroanatomic connections of the inferior lobe and the lateral torus of the percomorph Hemichromis lifalili were investigated by 1,1', dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (DiI) tracing. The inferior lobe and the lateral torus both receive afferents from the secondary gustatory nucleus. Additional afferents reach the inferior lobe from the nucleus glomerulosus, nucleus suprachiasmaticus, dorsal and central posterior thalamic nucleus, nucleus lateralis valvulae, magnocellular part of the magnocellular nucleus of the preoptic region, caudal nucleus of the preglomerular region, posterior tuberal nucleus, area dorsalis of the telencephalon, and a tegmental nucleus (T2). Efferents from the inferior lobe and the lateral torus terminate in the dorsal hypothalamic neuropil and corpus mamillare. Furthermore, the inferior lobe projects to the medial nucleus of the lateral tuberal hypothalamus and perhaps makes axo-axonal synapses in the tractus tectobulbaris rectus. The inferior lobe and the torus lateralis have reciprocal connections with the preglomerular tertiary gustatory nucleus and posterior thalamic nucleus and are also mutually interconnected. The inferior lobe is also reciprocally connected with the medial nucleus of the preglomerular region, reticular formation and sparsely with the anterior dorsal thalamic and the ventromedial thalamic nuclei. Thus, whereas the lateral torus is exclusively connected with the gustatory system, the inferior lobe is of a multisensory nature. In comparison with the goldfish (Carassius auratus), the connectivity pattern of the inferior lobe of Hemichromis lifalili reflects its specialization with respect to the visual system, as it receives qualitative (i.e., dorsal posterior, anterior, and ventromedial thalamic nuclei) as well as quantitative (i.e., nucleus glomerulosus) additional visual input.

Targeted disruption of the GAS41 gene encoding a putative transcription factor indicates that GAS41 is essential for cell viability.

The glioma-amplified sequence (GAS) 41 protein has been proposed to be a transcription factor. To investigate its functional role in vivo, we attempted to knock out the GAS41 gene by targeted disruption in the chicken pre-lymphoid cell line DT40. Heterozygous GAS41+/- cell lines generated by the first round of homologous recombination express approximately half the normal level of GAS41 mRNA. However, a homozygous GAS41-/- cell line with both GAS41 alleles disrupted was not obtained following the second round of transfection, indicating that the GAS41 gene is essential for cell viability. Indeed, homozygous GAS41-/- cell lines with two disrupted GAS41 alleles can be generated following substitution of the endogenous gene by stable integration of GAS41 cDNA controlled by a tetracycline-regulated CMV promoter. Inactivation of this promoter by tetracycline withdrawal results in rapid depletion of GAS41, causing a significant decrease in RNA synthesis and subsequently cell death. Thus, our results indicate that GAS41 is required for RNA transcription.