The role of proteolytic cellular systems in trabecular meshwork homeostasis

The molecular mechanisms contributing to the progressive malfunction of the trabecular meshwork (TM)/Schlemm's canal (SC) conventional outflow pathway during aging and in Primary Open Angle Glaucoma (POAG) are still poorly understood. Progressive accumulation of damaged and cross-linked proteins is a hallmark of aging tissues and has been proposed to play a major role in the tissue abnormalities associated with organismal aging and many age-related diseases. Such progressive accumulation of damaged proteins with age is believed to result from both, increased oxidative stress that results in faster rates of protein damage, as well as from a functional decline in the cellular proteolytic machinery that eliminates misfolded and damaged proteins. Here, we review the reported data that supports the occurrence of oxidative damage and the alterations in the intracellular proteolytic systems in the TM in aging and POAG. Finally, we discuss how the functional decline of the cellular proteolytic machinery in the TM might lead to the observed physiologic alterations of the outflow pathway in glaucoma.

Resveratrol prevents the expression of glaucoma markers induced by chronic oxidative stress in trabecular meshwork cells

Elevated intraocular pressure (IOP) constitutes the best characterized risk for primary open-angle glaucoma (POAG). Elevated IOP is believed to result from an increase in aqueous humor outflow resistance at the level of the trabecular meshwork (TM)/Schlemm's canal. Malfunction of the TM in POAG is associated with the expression of markers for inflammation, cellular senescence, oxidative damage, and decreased cellularity. Current POAG treatments rely on lowering IOP, but there is no therapeutic approach available to delay the loss of function of the TM in POAG patients. We evaluated the effects of chronic administration of the dietary supplement resveratrol on the expression of markers for inflammation, oxidative damage, and cellular senescence in primary TM cells subjected to chronic oxidative stress (40% O2). Resveratrol treatment effectively prevented increased production of intracellular reactive oxygen species (iROS) and inflammatory markers (IL1alpha, IL6, IL8, and ELAM-1), and reduced expression of the senescence markers sa-beta-gal, lipofuscin, and accumulation of carbonylated proteins. Furthermore, resveratrol exerted antiapoptotic effects that were not associated with a decrease in cell proliferation. These results suggest that resveratrol could potentially have a role in preventing the TM tissue abnormalities observed in POAG.

At environmental doses, dietary methylmercury inhibits mitochondrial energy metabolism in skeletal muscles of the zebra fish (Danio rerio)

The neurotoxic compound methylmercury (MeHg) is a commonly encountered pollutant in the environment, and constitutes a hazard for human health through fish eating. To study the impact of MeHg on mitochondrial structure and function, we contaminated the model fish species Danio rerio with food containing 13 microg of MeHg per gram, an environmentally relevant dose. Mitochondria from contaminated zebrafish muscles presented structural abnormalities under electron microscopy observation. In permeabilized muscle fibers, we observed, a strong inhibition of both state 3 mitochondrial respiration and functionally isolated maximal cytochrome c oxidase (COX) activity after 49 days of MeHg exposure. However, the state 4 respiratory rate remained essentially unchanged. This suggested a defect at the level of ATP synthesis. Accordingly, we measured a dramatic decrease in the rate of ATP release by skinned muscle fibers using either pyruvate and malate or succinate as respiratory substrates. However, the amount and the assembly of the ATP synthase were identical in both control and contaminated muscle mitochondrial fractions. This suggests that MeHg induced a decoupling of mitochondrial oxidative phosphorylation in the skeletal muscle of zebrafish. Western blot analysis showed a 30% decrease of COX subunit IV levels, a 50% increase of ATP synthase subunit alpha, and a 40% increase of the succinate dehydrogenase Fe/S protein subunit in the contaminated muscles. This was confirmed by the analysis of gene expression levels, using RT-PCR. Our study provides a basis for further analysis of the deleterious effect of MeHg on fish health via mitochondrial impairment.

Cultured porcine trabecular meshwork cells display altered lysosomal function when subjected to chronic oxidative stress

PURPOSE

To investigate the effects of chronic oxidative stress on lysosomal function in trabecular meshwork (TM) cells.

METHODS

Confluent cultures of porcine TM cells were grown for 2 weeks in physiological (5% O(2)) or hyperoxic conditions (40% O(2)) in the presence or absence of the protease inhibitor leupeptin (10 microM). The following parameters were quantified using the fluorogenic probes indicated within parentheses: autofluorescence, intracellular reactive oxygen species (ROS; H(2)DCFDA), mitochondrial membrane potential (JC-1), mitochondrial content (Mitotracker Red; Invitrogen-Molecular Probes, Eugene, OR), lysosomal content (acridine orange and Lysotracker Red [Invitrogen-Molecular Probes]), autophagic vacuole content (MDC), SA-beta-galactosidase (FDG), and cathepsin activities (z-FR-AMC). Cathepsin levels were quantified by qPCR and Western blot analysis. Ultrastructural analysis was performed by transmission electron microscopy.

RESULTS

Prolonged exposure of porcine TM cells to a hyperoxic environment led to an increase in ROS production and oxidized material. Electron micrographs revealed the cytoplasmic accumulation of lipofuscin-loaded lysosomes. Augmented lysosomal and autophagic vacuole content was confirmed with specific fluorophores. The mRNA and protein levels of several cathepsins were upregulated with oxidative stress. This upregulated expression did not correlate with increased lysosomal activity.

CONCLUSIONS

The results indicate that chronic exposure of TM cells to oxidative stress causes the accumulation of nondegradable material within the lysosomal compartment, leading to diminished lysosomal activity. Since the lysosomal system is responsible for the continuous turnover of cellular organelles, impaired lysosomal activity may lead to progressive failure of cellular TM function with age.

Occurrence of enterovirus RNA in serum of children with newly diagnosed type 1 diabetes and islet cell autoantibody-positive subjects in a population with a low incidence of type 1 diabetes

BACKGROUND

The penetrance of type 1 diabetes mellitus (T1DM) in a genetically susceptible population is largely determined by environmental influences amongst which the human enteroviruses are prominent putative factors.

AIM/HYPOTHESIS

The aim of this study was to determine the occurrence of enterovirus RNA in serum of children with type 1 diabetes at onset and ICA-positive subjects in a population with low incidence of type 1 diabetes and high circulation of enteroviruses.

SUBJECTS AND METHODS

Serum samples were collected from children with newly diagnosed type 1 diabetes (n = 34); islet autoantibody-positive (n = 32) and -negative (n = 31) first-degree relatives of type 1 diabetic patients; and control subjects (n = 194). Enteroviral RNA was assessed using a highly sensitive reverse transcriptase-polymerase chain reaction method.

RESULTS

The frequency of positive signals corresponding to enteroviral sequence amplifications were higher in newly diagnosed T1DM children (9/34, 26.5%) and islet autoantibody-positive first-degree relatives (5/32, 15.6%) than in their corresponding matched controls (2/68, 2.9%, p = 0.0007 and 0/64, 0.0%, p = 0.0033, respectively). The presence of enteroviral RNA appeared to be associated with severe diabetic ketoacidosis at onset (pH < 7.1, p = 0.0328) and high ICA titres ( > or = 20 JDF units, p < 0.05).

CONCLUSIONS

Despite there is a high circulation of enteroviruses and a low type 1 diabetes incidence in the Cuban population, the presence of enteroviral RNA is associated with type 1 diabetes and beta-cell autoimmunity and is similar to European countries in which this scenario is reversed.

Analysis of LOXL1 polymorphisms in a United States population with pseudoexfoliation glaucoma

PURPOSE

To identify if recently described LOXL1 (lysyl oxidase-like 1) polymorphisms are associated with pseudoexfoliation glaucoma (XFG) in a United States (U.S.) Caucasian patient population.

METHODS

Individuals with XFG were identified using standard clinical examination techniques. TaqMan allelic discrimination assays were used to genotype 13 single nucleotide polymorphisms (SNPs) that tag LOXL1 in Caucasian individuals. The coding region of exon 1 that includes the previously associated SNP, rs1048661, was sequenced. Allele and genotype frequencies were compared between cases and unrelated controls.

RESULTS

Fifty affected individuals and 235 control individuals were recruited into this study. We replicated the previously reported association of three SNPs (rs1048661, rs2165241, and rs3825942) in our independent XFG population (single SNP p-values were 0.001-0.02). The risk alleles at these three and several other intragenic SNPs are part of an extended XFG-associated LOXL1 haplotype with a frequency of 32.0% in XFG patients and 21.6% in controls.

CONCLUSIONS

We have performed an analysis of LOXL1 and XFG in a United States patient population and have confirmed the strong association previously reported for Icelandic and Swedish samples. However, due to the high frequency of risk alleles in non-XFG individuals, this association should not form the basis of a diagnostic test for XFG. It is likely that additional genetic or environmental factors modulate the penetrance of LOXL1 susceptibility alleles.

Effects of high salinity wastewater on methanogenic sludge bed systems

The attainable loading potentials of anaerobic sludge bed systems are strongly dependent on the growth of granular biomass with a particular wastewater. Experiments were conducted to determine the effects of high salinity wastewater on the biological and physical properties of methanogenic sludge. Sodium concentration of 5 g/L and 15 g/L were added to the influent of upflow anaerobic sludge bed (UASB) systems. After 100 days of operation, the methanogenic activity, extracellular polymeric substances (EPS), and granular strength were analyzed. The results show a high removal of organic matter but with accumulating propionate concentrations in the effluents. Meanwhile, wash-out of active methanogenic biomass in the effluent of the reactors was observed, likely as a results of the high Na+ concentrations. The rinsed biomass was characterized by a considerable specific methanogenic activity (SMA) on acetate, propionate and hydrogen as the substrates. On the other hand, results show that the SMA evolution was not affected by high salt concentrations. Also the amount and composition of extracellular polymeric substances (EPS) were similar in all sludges. However, results clearly show a sharp drop in the granule strength as a results of high Na+ concentration.

Sustained stress response after oxidative stress in trabecular meshwork cells

PURPOSE

To investigate the mechanisms by which chronic oxidative stress may lead to a sustained stress response similar to that previously observed in the trabecular meshwork (TM) of glaucoma donors.

METHODS

Porcine TM cells were treated with 200 microM H2O2 twice a day for four days and were allowed to recover for three additional days. After the treatment, TM cells were analyzed for generation of intracellular reactive oxygen species (iROS), mitochondrial potential, activation of NF-kappaB, and the expression of inflammatory markers IL-1alpha, IL-6, IL-8, and ELAM-1. Potential sources of iROS were evaluated using inhibitors for nitric oxide, nitric oxide synthetase, cyclooxygenase, xanthine oxidase, NADPH oxidase, mitochondrial ROS, and PKC. The role of NF-kappaB activation in the induction of inflammatory markers was evaluated using the inhibitors Lactacystin and BAY11-7082.

RESULTS

Chronic oxidative stress simulated by H2O2 exposure of porcine TM cells resulted in the sustained production of iROS by the mitochondria. Inhibition of mitochondrial iROS had a significant inhibitory effect on the activation of NF-kappaB and the induction of IL-1alpha, IL-6, IL-8, and ELAM-1 triggered by chronic oxidative stress. Inhibition of NF-kappaB partially prevented the induction of IL-1alpha, IL-8, and ELAM-1, but not IL-6.

CONCLUSIONS

Chronic oxidative stress in TM cells induced iROS production in mitochondria. This increase in iROS may contribute to the pathogenesis of the TM in glaucoma by inducing the expression of inflammatory mediators previously observed in glaucoma donors as well as the levels of oxidative damage in the tissue.

Effect of cellular senescence on the P2Y-receptor mediated calcium response in trabecular meshwork cells

PURPOSE

The objectives of this study were to evaluate the potential release of ATP that is mediated by mechanical stress on trabecular meshwork (TM) cells, to identify the specific P2Y receptors mediating the ATP response, and to determine whether cellular senescence might interfere with the P2Y receptor-mediated calcium response, thus contributing to the loss of physiologic TM function in aging and primary open angle glaucoma (POAG).

METHODS

Experiments were conducted using primary cultures of porcine TM cells. Cyclic mechanical stretch (10% stretching/second) was generated using the Flexcell system. ATP release and ectoATPase activity induced by mechanical stress were measured using a luciferin/luciferase assay. Replicative senescence was induced by passing the cells 18 times at a 1:2 split ratio and confirmed by the presence of senescence-associated beta-galactosidase (sa-beta-gal) and autofluorescence. For calcium imaging, cells were plated on gelatin-coated coverslips, bathed in calcium Ringer's solution, and loaded with fluo-4 (5 microM) for 1 h. Agonists of P2Y1 (ADP) and P2Y2/P2Y4 (ATP, UTP) receptors at 10 microM or 100 microM concentrations were added to the bathing medium. Relative changes in cytosolic calcium concentration as a function of time were measured by fluorescent microscopy and reported as peak amplitudes of fluo-4 fluorescence normalized to baseline values (deltaF/Fo).

RESULTS

Mechanical stress induced an increase in ATP release from TM cells (258%+/-23% at 15 min, 188%+/-11% at 30 min, and 900%+/-203% at 1 h; p<0.017, n=4) as well as an increase in ectoATPase activity present in the extracellular media during the first 15 min of stress (57%+/-15%, p=0.011, n=4). The P2Y receptor agonists listed above induced a concentration-dependent rise in intracellular calcium in the TM cells. The peak amplitude, deltaF/Fo, was 1.07+/-0.12 (n=3) for 10 microM ADP, 2.59+/-0.33 (n=6) for 100 microM ADP, 1.21+/-0.64 (n=12) for 10 microM UTP, 3.22+/-2.0 (n=12) for 100 microM UTP, 0.88+/-0.40 (n=9) for 10 microM ATP, and 1.37+/-0.61 (n=25) for 100 microM ATP. Cells at passage 18 showed significantly lower levels of intracellular calcium induced by ATP (36%), UTP (34%), and ADP (52%) compared to cells at passage 2, independent from any changes in P2Y receptor changes in expression.

CONCLUSIONS

The ability to release ATP in response to mechanical stress and the presence of functional P2Y receptors in TM cells suggest a novel mechanism by which TM cells could sense and respond to changes in intraocular pressure (IOP). In addition, the decrease in P2Y receptor-mediated calcium responses observed in senescent TM cells suggests that the disregulation of calcium homeostasis in senescence may contribute to the alterations of the TM in aging and POAG.

Economic evaluation of linezolid versus teicoplanin for the treatment of infections caused by gram-positive microorganisms in Spain

The aim of this study was to perform a comparative cost-effectiveness analysis of linezolid vs teicoplanin (i.v., switching to oral/i.m. respectively) in Spain. A decision tree model was used with the results of a randomized, comparative, controlled clinical trial with linezolid vs teicoplanin in the treatment of infections caused by Gram-positive microorganisms, with a timeline of 31 days. The efficacy endpoint was the percentage of patients with clinical healing or improvement in their infection. Direct medical costs were included using Spanish 2005 prices. Average cost per patient, average cost-effectiveness ratio and several sensitivity analyses were carried out. In the intent-to-treat (ITT) analysis linezolid obtained a higher percentage of therapeutic success than teicoplanin (95.5% vs 87.6% respectively, p = 0.005), both with similar tolerability. The average cost per treated patient was euro 8,064.76 for linezolid vs euro 8,727.36 for teicoplanin, with an incremental cost of euro 622.59 (-7,6%). Linezolid yielded a lower average cost-effectiveness ratio, euro 8,444.78 (8,195.90 - 8,709.25) than teicoplanin, euro 9,962.74 (9,465.68 - 10,502.23), with a slight reduction in average cost per successfully treated patient of 15.2% ( euro 1,517.96). The results were robust to the sensitivity analysis. In conclusion, linezolid is a more cost-effective option than teicoplanin in the treatment of infections caused by Gram-positive microorganisms, since it offers superior clinical benefits with a lower use of associated resources.

Comparative evaluation of the toxicity and genotoxicity of cadmium in amphibian larvae (Xenopus laevis and Pleurodeles waltl) using the comet assay and the micronucleus test

The toxic and genotoxic potential of Cadmium (CdCl(2)) were evaluated by the micronucleus test (MNT) and comet assay (CA) using amphibian larvae (Xenopus laevis and Pleurodeles waltl). Acute toxicity results showed that Cd is toxic to Xenopus larvae exposed from 2 to 50 mg/L and to Pleurodeles from 5 to 50 mg/L, depending on the nature of the water (reconstituted water containing mineral salts or mineral water MW (Volvic)). The MNT results obtained in MW showed that Cd (2 mg/L) is genotoxic to Xenopus, whereas it was not genotoxic to Pleurodeles at all concentrations tested. The CA established that the genotoxicity of Cd to Xenopus and Pleurodeles larvae depends on the concentration, the exposure times, and the comet parameters (Tail DNA, ETM, OTM, and TL). The CA and MNT results were compared for their ability to detect genotoxic effects, considering the concentrations of Cd applied and the exposure time. The CA showed Cd to be genotoxic from the first day of exposure. In amphibians, the CA appears to be a sensitive and suitable method for detecting genotoxicity such as that caused by Cd.

Down-regulation of bbc3, flt1 and gstm3 is associated with lymph node metastases in breast carcinoma

21171

Background: Background: Axillary lymph node metastasis is the most significant marker for the pathologic staging of breast cancer. However a proportion of lymph node-negative breast cancer will develop metastatic disease. Therefore, molecular markers of invasion in these patients are needed Methods: We selected 10 primary breast cancer cases, 5 lymph node-negative (T1N0) and 4 lymph node-positive (T1N1). In these cases we searched for gene expression of 8 genes (bbc3, cegp1, fgf18, flt1, cffm4, gstm3, hec, tgfb3) selected from previous studies as a good candidates for metastasis prediction. A quantitative Real-Time PCR was performed using beta-2- microglobulin gene expression to normalized gene expression of each gene. The expression average of beta-2-microglobulin was 303,291 among T1N0 and 342,533 among T1N1 cases (ratio 0.88). The expression average of these 8 genes was 2.11 and 0.002 at T1N0 and T1N1 respectively (ratio 1,055). At least 3 genes were significantly down-regulated in T1N1 (bbc3, flt1, gstm3) in comparison with T1N1 breast carcinomas Results: Computational analysis reveals that these 3 genes (bbc3, flt1, gstm3) contain CpG islands in their promoter regions. Although preliminary data, we found group of genes that are down-regulated in T1N1 tumor Conclusions: The finding that these genes are epigenetically regulated, suggest that could be a good candidates for metastasis prediction, by methylation approach (MethyLight System). Since this down-regulation occurs in primary tumor, the analysis of these genes might be useful to predict metastasis in lymph node-negative breast cancer.

No significant financial relationships to disclose.

Mannitol-enhanced, fluid-phase endocytosis in storage parenchyma cells of celery (Apium graveolens; Apiaceae) petioles

We recently demonstrated the occurrence of a sucrose-enhanced, fluid-phase endocytic (FPE) mechanism of nutrient uptake in heterotrophic cells. In the present work, the possible enhancement/induction of FPE by photoassimilates other than sucrose was investigated by measuring the incorporation of the fluorescent endocytosis marker d-TR (dextran-Texas red, 3000 mw) into celery (Apium graveolens) petiole storage parenchyma (CSP), a tissue that transports and accumulates mannitol. Mannitol uptake in these cells is biphasic, with a hyperbolic phase at concentrations below 20 mM and a linear phase above 20 mM external solute concentration. In the absence of mannitol, or in its presence at concentrations within the hyperbolic phase, CSP cells accumulated low levels of d-TR. Conversely, d-TR accumulation by CSP cells was greatly enhanced in the presence of mannitol at concentrations within the linear phase. At high external mannitol concentration, d-TR accumulation was prevented by the endocytic inhibitors LY294002 and latrunculin B. In addition, d-TR uptake was temperature dependent under high mannitol concentration. Microscopic observations revealed that d-TR accumulated in the vacuole. These data support the occurrence of an FPE mechanism in CSP cells that participates in trapping and transport of photoassimilates to the vacuole. The FPE mechanism is enhanced by high mannitol concentrations.

Cytoprotective effects of proteasome beta5 subunit overexpression in lens epithelial cells

PURPOSE

To determine whether the overexpression of the proteasome catalytic beta5 subunit (PSMB5) can induce the expression of the catalytic subunits beta1 and beta2, enhance proteasome activity, and exert a cytoprotective effect in lens epithelial cells.

METHODS

Cells from the human lens epithelial cell line SRA01/04 (LECs) were stably transfected either with a plasmid expressing the proteasome catalytic subunit beta5 or with an empty plasmid. beta-5-expressing LECs and controls were analyzed for the expression of beta1, beta2, beta5, and alpha6 proteasome subunits; chymotrypsin-like (CT-L) and peptidylglutamyl-peptide hydrolase (PGPH) catalytic activities; as well as for the accumulation of carbonylated proteins, rates of cell viability, and apoptosis after oxidative stress.

RESULTS

Stable expression of the beta5 proteasome subunit resulted in increased expression of the catalytic subunits beta1 and beta2, increased CT-L and PGPH proteasome activities, and increased resistance to accumulation of carbonylated proteins and cell death after oxidative stress.

CONCLUSIONS

The proteasome activity can be genetically "upregulated" in lens cells by overexpression of the beta5 catalytic subunit. The resulting increase in proteasome activity leads to a decrease in the accumulation of oxidized proteins and enhanced cell survival following oxidative stress.

Challenging the model for induction of metallothionein gene expression

Metallothioneins (MTs) are low-molecular-weight, cysteine-rich metal-binding proteins found in a wide variety of organisms including bacteria, fungi and all eukaryotic plant and animal species. MTs bind essential and non-essential heavy metals. In mammalian cells MT genes are highly inducible by many heavy metals including Zn, Cd, Hg, and Cu. Aquatic systems are contaminated by different pollutants, including metals, as a result of man's activities. Bivalve molluscs are known to accumulate high concentrations of heavy metals in their tissue and are widely used as bioindicators for pollution in marine and freshwater environments, with MTs frequently used as a valuable marker of metal contamination. We here describe the MT isoform gene expression patterns of marine and freshwater molluscs and fish species after Cd or Zn contamination. Contamination was carried out at a river site polluted by a zinc ore extraction plant or in the laboratory at low, environmentally relevant metal concentrations. A comparison for each species based on the accumulated MT protein levels often shows discrepancies between gene expression and protein level. In addition, several differences observed in the pattern of MT gene expression between mollusc and mammalian species enable us to discuss and challenge a model for the induction of MT gene expression.

Genome-wide expression profile of human trabecular meshwork cultured cells, nonglaucomatous and primary open angle glaucoma tissue

PURPOSE

To contrast genome-wide gene expression profiles of cultured human trabecular meshwork (HTM) cells to that of control and primary open angle glaucoma (POAG) HTM tissues.

METHODS

Cultured HTM cells, HTM tissue dissected from control donors, and HTM tissue from POAG donors receiving medication for glaucoma were fixed in RNA latertrade mark. Total RNA extracted from these samples was linearly amplified with the Ovation Biotin RNA Amplification and Labeling System and individually hybridized to Affymetrix Human Genome U133 Plus 2.0 high density microarrays. Data analysis was performed using GeneSpring Software 7.0. Selected genes showing significant differential expression were validated by quantitative real-time PCR in nonamplified RNA.

RESULTS

Cultured HTM cells retained the expression of some genes characteristic of HTM tissue, including chitinase 3-like 1 and matrix Gla protein, but demonstrated downregulation of physiologically important genes such as myocilin. POAG HTM tissue showed relatively small changes compared to that of control donors. These changes included the statistically significant upregulation of several genes associated with inflammation and acute-phase response, including selectin-E (ELAM-I), as well as the downregulation of the antioxidants paraoxonase 3 and ceruloplasmin.

CONCLUSIONS

Downregulation in cultured HTM cells of genes potentially relevant for outflow pathway function highlights the importance of developing new conditions for the culture of TM cells capable of preserving the characteristics of TM cells in vivo. Comparative analysis between control and POAG tissues suggests that the upregulation of inflammation-associated genes might be involved in the progression of glaucoma.

Fluid phase endocytic uptake of artificial nano-spheres and fluorescent quantum dots by sycamore cultured cells: evidence for the distribution of solutes to different intracellular compartments

Fluid phase endocytic uptake of external solutes in plant cells was further substantiated using artificial polystyrene nano-spheres (40 nm) and CdSe/ZnS quantum dots (20 nm). Both types of artificial nano-particles were taken up by sycamore-cultured cells. However, whereas polystyrene nano-spheres were delivered to the central vacuole, CdSe/ZnS nano-dots were sequestered into cytoplasmic vesicular structures. Using dextran-Texas Red (m.w. 3,000; d-TR) as additional marker, confocal micrographs confirmed the distinct topographic distribution of CdSe/ZnS quantum dots within the cell. Initially, d-TR and CdSe/ZnS quantum dots colocalized within cytoplasmic vesicles. After 18 h incubation, d-TR was distinctly localized in the vacuole whereas CdSe/ZnS quantum dots remained sequestered in cytoplasmic membranous compartments. The data provide a first evidence for the rapid distribution of solutes taken up by endocytosis to distinct intracellular compartments.

Genotoxic and stress inductive potential of cadmium in Xenopus laevis larvae

The present investigation evaluates the toxic potential of Cd in larvae of the frog Xenopus laevis after 12 days of exposure to environmentally relevant contamination levels, close to those measured in the river Lot (France). Several genotoxic and detoxification mechanisms were analyzed in the larvae: clastogenic and/or aneugenic effects in the circulating blood by micronucleus (MN) induction, metallothionein (MT) production in whole larvae, gene analyses and Cd content in the liver and also in the whole larvae. The results show: (i) micronucleus induction at environmental levels of Cd contamination (2, 10, 30 microgL(-1)); (ii) an increased and concentration-dependent quantity of MT in the whole organism after contamination with 10 and 30 microgCdL(-1) (a three- and six-fold increase, respectively) although no significant difference was observed after contamination with 2 microgCdL(-1); (iii) Cd uptake by the whole organism and by the liver as a response to Cd exposure conditions; (4) up-regulation of the genes involved in detoxification processes and response to oxidative stress, while genes involved in DNA repair and apoptosis were repressed. The results confirm the relevance of the amphibian model and highlight the complementarity between a marker of genotoxicity, MT production, bioaccumulation and genetic analysis in the evaluation of the ecotoxicological impact.