Xanthohumol is the major prenylated flavonoid present in the hop plant
Humulus lupulus L. (Cannabinaceae) and a common ingredient of beer. Recently, xanthohumol has gained considerable interest due ...to its potential cancer chemo-preventive effect. The aim of this study was to reveal the possible anti-genotoxic activity of xanthohumol in metabolically competent human hepatoma HepG2 cells, by use of the comet assay. Xanthohumol by itself was neither cytotoxic nor genotoxic to the cells at concentrations below 10
μM. However, a significant protective effect against the pro-carcinogens benzo(a)pyrene (BaP) and 2-amino-3-methylimidazo4,5-fquinoline (IQ) was observed at concentrations as low as 0.01
μM. In cells treated with xanthohumol in combination with
tert-butyl hydroperoxide (
t-BOOH) – an inducer of reactive oxygen species (ROS) – no protective effect was observed and xanthohumol also showed no significant scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. On the other hand, HepG2 cells pre-treated with xanthohumol showed significantly reduced levels of
t-BOOH-induced DNA strand breaks, indicating that its protective effect is mediated by induction of cellular defence mechanisms against oxidative stress. As xanthohumol is known to be an effective inhibitor of cytochrome P450 enzymes and an inducer of NAD(P)H: quinone reductase (QR), our findings can be explained by an inhibition of metabolic activation of pro-carcinogens and/or by induction of carcinogen-detoxifying and anti-oxidative enzymes by xanthohumol. These results provide evidence that xanthohumol displays anti-genotoxic activity in metabolically competent human cells.
Nastava iz prirodoslovnog područja danas se najčešće temelji na principima konstruktivizma prema kojima djeca trebaju biti aktivni sudionici procesa učenja i izgrađivati svoje znanje na temelju ...iskustva. Metode i sredstva korištena u nastavi prirodoslovnog područja moraju biti prilagođeni perceptivnim potrebama slijepe djece i djece s oštećenjima vida kako bi im se omogućilo aktivno sudjelovanje u procesu učenja. Cilj ovoga rada je opisati posljednje spoznaje o aktivnom i istraživačkom učenju slijepe djece i djece s oštećenjima vida u nastavi prirodoslovnog područja te otkloniti postojeće zablude. Nadalje, rad predstavlja recentna istraživanja koja ukazuju na prilagođene uspješne i visokokvalitetne odgojno-obrazovne pristupe i metode. S obzirom na navedeno, sadržaj rada bit će od koristi nastavnicima iz prirodoslovnog područja, kao i istraživačima inkluzivnih učionica.
Nowadays, science education is based predominantly on the principle of constructivism, according to which children should be active participants in the learning process and construct their knowledge ...based on experience. For blind or visually impaired children, science education methods and educational tools must be adapted according to their perceptual needs, in order for these children to be active participants in the learning process. The aim of the current paper is to describe the latest view on active and inquiry-based learning in science education for blind or visually impaired children while simultaneously minimizing misconceptions. Further, the paper compiles the recent research that enables prosperous and high-quality adaptive educational approaches and tools. Thus, the content of this paper will be useful for both science teachers and researchers of inclusive classrooms.
Nastava iz prirodoslovnog područja danas se najčešće temelji na principima konstruktivizma prema kojima djeca trebaju biti aktivni sudionici procesa učenja i izgrađivati svoje znanje na temelju iskustva. Metode i sredstva korištena u nastavi prirodoslovnog područja moraju biti prilagođeni perceptivnim potrebama slijepe djece i djece s oštećenjima vida kako bi im se omogućilo aktivno sudjelovanje u procesu učenja. Cilj ovoga rada je opisati posljednje spoznaje o aktivnom i istraživačkom učenju slijepe djece i djece s oštećenjima vida u nastavi prirodoslovnog područja te otkloniti postojeće zablude. Nadalje, rad predstavlja recentna istraživanja koja ukazuju na prilagođene uspješne i visokokvalitetne odgojno-obrazovne pristupe i metode. S obzirom na navedeno, sadržaj rada bit će od koristi nastavnicima iz prirodoslovnog područja, kao i istraživačima inkluzivnih učionica.
•An improved method for DNA strand breaks detection.•Comet assay in individual one day zebrafish embryos without prior cell isolation.•A potential tool for monitoring the genotoxic potential of ...chemicals.•A potential tool for monitoring the environmental pollutants.
Zebrafish (Danio rerio) embryos are increasingly used as an experimental model in toxicology for the detection of lethal and sub-lethal effects of diverse chemicals. DNA damage, an early biomarker of long-term effects such as mutagenesis and carcinogenesis, is commonly assessed in vitro and in vivo using the comet assay – single cell gel electrophoresis. Here we describe a new rapid method for the detection of DNA strand breaks in individual, one day old, zebrafish embryos, without the need for prior cell isolation. After the completed spawning, the embryos were exposed to non-toxic concentrations of model genotoxic compounds for 24h. The embryos were then treated with Pronase E, embedded on microscope slides and squashed to release the cells. After alkaline electrophoresis, the nuclei were stained with ethydium bromide and analyzed by fluorescence microscopy. Preparation of slides by the described method resulted in well separated cell nuclei with low background DNA damage. A significant increase in DNA damage was detected after exposure to the model genotoxic compounds, methylmethan sulphonate (MMS) and benzo(a)pyrene (BaP), while no DNA damage was induced by NaCl. Our method proved to be sensitive and suitable for the detection of DNA damage in one day old zebrafish embryos, suggesting it could serve as a useful tool for monitoring the genotoxic potential of chemicals and environmental pollutants.
Experiential learning was introduced to support a child’s concept development towards evolution scientific literacy. This study examined the effect of an experiential learning model (The Mobile ...Natural Science Learning - MNSL) on the knowledge of 4th grade primary school students in Slovenia, during natural science school lessons at the seashore through the use of tablets. Mobile technology provides authentic learning, assisting outdoor lessons providing material and environmental context in learning, which support the experience of a learner. In the experimental group (N = 95), outdoor learning in the seashore included Kolb’s experiential learning cycle with the integration of tablets. In the control group (N=97), the teachers used concrete experience for exploring the seashore, excluding the Kolb’s cycle. The data were collected by using two science knowledge pre and post – tests. The test items were classified into three TIMSS’ cognitive domains: 1) factual knowledge, 2) conceptual understanding, and 3) reasoning and analysis. Differences between groups were analysed through Mann-Whitney U-test and showed that the experimental group had better learning outcomes than the control group. Findings indicate that the MNSL-model had a positive effect on students’ achievement in science, more precisely in knowledge on marine organisms and life at the seashore.
Xanthohumol (XN), the principal prenylated flavonoid in the hop plant,
Humulus lupulus L., is suggested to have cancer chemo-preventive activities. Its mechanisms of protection have been proposed to ...be inhibition of metabolic activation, induction of detoxifying enzymes and antioxidant activity. Our previous study showed that XN efficiently protected human hepatoma HepG2 cells against the genotoxic effects of two pro-carcinogens (2-amino-3-methylimidazo4,5-
fquinoline (IQ) and benzo(a)pyrene (BaP)) that are dependent on cytochrome P450 (CYP) mediated metabolic activation, and against genotoxic effects of the oxidative damage inducing
tert-butyl hydroperoxide (
tBOOH). In the present study, we investigated the antigenotoxic effects of XN in precision-cut rat liver slices. Using the comet assay, we detected that at non-cytotoxic concentrations (0.01–10
μM) XN completely prevented IQ and BaP-induced DNA damage. The protective effects of XN against
tBOOH-induced DNA damage was less efficient; the maximal 50% reduction of DNA damage was observed at 0.1
μM XN. In rat microsomes, XN (0.001–10
μM) inhibited CYP1A activity (7-ethoxycoumarin (7EC) de-ethylation) in a concentration-dependent manner. Surprisingly, no inhibition of 7EC metabolism by XN was observed in rat liver slices. XN also did not have any influence on mRNA expression of the enzymes CYP1A2 and quinone reductase (QR). These results indicate that inhibition of metabolic activation of pro-carcinogens by CYP1A is not likely to be the mechanism of its antigenotoxic action.
In conclusion, XN efficiently protects DNA against genotoxicity of IQ and BaP and against oxidative DNA damage. Although the mechanism of the protective effect of XN is unclear, our results indicate that XN exhibits antigenotoxic effects in fresh liver tissue and provide additional evidence for the cancer preventive potential of XN.
Bioassay-directed fractionation with a
Salmonella/microsomal assay against the food borne mutagen 2-amino-3-methylimidazo4,5-
fquinoline (IQ) was used to identify antimutagenic components of hops. ...Hops pellets extracted with diethylether showed antimutagenic activity against mutations induced by IQ. Fractionation of the diethylether extract (DE) by column chromatography, followed by semi-preparative HPLC yielded two fractions (E4b and E4d) with strong antimutagenic activity against IQ induced mutations. Separation of fraction E4b resulted in inactive fractions, while fraction E4d has been identified to be xanthohumol. In mammalian test system with human hepatoma HepG2 cells fraction E4d at 10
μg/ml completely prevented formation of IQ induced DNA damage. These results indicate that xanthohumol is a very promising potential protective agent against genotoxicity of food borne carcinogens, which warrants further investigation.
The comet assay is a simple and sensitive method for measuring DNA damage at the level of individual cells and is extensively used in genotoxicity studies. It is commonly applied to cultured cells. ...The aim of this study was to apply the comet assay for use in fresh liver tissue, where metabolic activity, all cell types and tissue architecture are preserved.
The response of liver slices to genotoxic agents was tested with the reactive oxygen species generating
tert-butyl hydroperoxide (
tBOOH, 0.1–2
μM), and the pro-carcinogens 2-amino-3-methylimidazo4,5-fquinoline (IQ, 0.5–2
mM) and benzo(a)pyrene (BaP, 10–100
μM). Dose-dependent DNA damage was observed and compared to HepG2 cells. At non-cytotoxic concentrations of carcinogens, human liver slices were more sensitive to
tBOOH than rat liver slices, while no significant difference was found for BaP and IQ. Human liver slices were more sensitive to IQ than HepG2 cells, equally sensitive to BaP and less to
tBOOH. Control slices showed low levels of DNA damage, which did not increase during 24
h preservation (0
°C) or 48
h culturing (37
°C).
In conclusion, the comet assay that we applied for measuring DNA damage in precision-cut liver slices is an useful tool to study genotoxic effects induced by various potential genotoxicants, allowing for detection of species differences in susceptibility to carcinogens.
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