A meta-analysis and a functional study support the influence of mtDNA variant m.16519C on the risk of rapid progression of knee osteoarthritis

OBJECTIVES

To identify mitochondrial DNA (mtDNA) genetic variants associated with the risk of rapid progression of knee osteoarthritis (OA) and to characterise their functional significance using a cellular model of transmitochondrial cybrids.

METHODS

Three prospective cohorts contributed participants. The osteoarthritis initiative (OAI) included 1095 subjects, the Cohort Hip and Cohort Knee included 373 and 326 came from the PROspective Cohort of Osteoarthritis from A Coruña. mtDNA variants were screened in an initial subset of 450 subjects from the OAI by in-depth sequencing of mtDNA. A meta-analysis of the three cohorts was performed. A model of cybrids was constructed to study the functional consequences of harbouring the risk mtDNA variant by assessing: mtDNA copy number, mitochondrial biosynthesis, mitochondrial fission and fusion, mitochondrial reactive oxygen species (ROS), oxidative stress, autophagy and a whole transcriptome analysis by RNA-sequencing.

RESULTS

mtDNA variant m.16519C is over-represented in rapid progressors (combined OR 1.546; 95% CI 1.163 to 2.054; p=0.0027). Cybrids with this variant show increased mtDNA copy number and decreased mitochondrial biosynthesis; they produce higher amounts of mitochondrial ROS, are less resistant to oxidative stress, show a lower expression of the mitochondrial fission-related gene fission mitochondrial 1 and an impairment of autophagic flux. In addition, its presence modulates the transcriptome of cybrids, especially in terms of inflammation, where interleukin 6 emerges as one of the most differentially expressed genes.

CONCLUSIONS

The presence of the mtDNA variant m.16519C increases the risk of rapid progression of knee OA. Among the most modulated biological processes associated with this variant, inflammation and negative regulation of cellular process stand out. The design of therapies based on the maintenance of mitochondrial function is recommended.

Validation of Polymorphisms Associated with the Risk of Radiation-Induced Oesophagitis in an Independent Cohort of Non-Small-Cell Lung Cancer Patients

Simple Summary

Genetic variants identified in association with radiation therapy side effects in non-small-cell lung cancer patients require an independent validation. Therefore, the aim of our study was to replicate, in an independent cohort, the analyses of previously published studies associating single-nucleotide polymorphisms with radiation-induced oesophagitis. Following the original models, 2 of the 18 variants associated with radiation-induced oesophagitis in non-small-cell lung cancer patients were confirmed. Furthermore, we meta-analysed our cohort together with those of the reference studies. Twelve variants located in genes of inflammation and DNA double-strand break repair pathways remained associated with oesophagitis. These variants could be included in models for clinical prediction of radiation-induced oesophagitis to evaluate their performance.

Abstract

Several studies have identified single-nucleotide polymorphisms (SNPs) associated with adverse effects in non-small-cell lung cancer (NSCLC) patients treated with radiation therapy. Here, using an independent cohort, we aimed to validate the reported associations. We selected 23 SNPs in 17 genes previously associated with radiation-induced oesophagitis for validation in a cohort of 178 Spanish NSCLC patients. Of them, 18 SNPs were finally analysed, following the methods described in the original published studies. Two SNPs replicated their association with radiation-induced oesophagitis (rs7165790 located in the BLM gene: odds ratio (OR) = 0.16, 95% CI = 0.04–0.65, p-value = 0.010; rs4772468 at FGF14: OR = 4.36, 95% CI = 1.15–16.46, p-value = 0.029). The SNP rs2868371 at HSPB1 was also validated but displayed an opposite effect to the formerly described (OR = 3.72; 95% CI = 1.49–9.25; p-value = 0.004). Additionally, we tested a meta-analytic approach including our results and the previous datasets reported in the referenced publications. Twelve SNPs (including the two previously validated) retained their statistically significant association with radiation-induced oesophagitis. This study strengthens the role of inflammation and DNA double-strand break repair pathways in the risk prediction of developing radiation-induced oesophagitis in NSCLC patients. The validated variants are good candidates to be evaluated in risk prediction models for patient stratification based on their radiation susceptibility.

Association of inflammatory mediators with frailty status in older adults: results from a systematic review and meta-analysis

Frailty is a geriatric syndrome defined as a status of extreme vulnerability to stressors, leading to a higher risk of negative health-related outcomes. "Inflammaging", an age-related state of low-grade chronic inflammation, is characterized by an increased concentration of pro-inflammatory cytokines and acute phase proteins. Inflammaging has been postulated as an underlying mechanism of frailty, and several studies tested the relationship between frailty and concentration of inflammatory mediators. The aim of this systematic review and meta-analysis was to test whether inflammatory mediators are overproduced in frail older adults. Among the 758 articles identified in the literature search, 50 were included in the systematic review, and 39 in the three meta-analyses, i.e., C-reactive protein (CRP), interleukin 6 (IL6), and tumor necrosis factor α. To reduce heterogeneity, meta-analyses were restricted to studies identifying frailty by the Fried et al. [1] [J. Gerontol. A. Biol. Sci. Med. Sci. 56, M146-56] phenotypic criteria. Quantitative analyses measuring the association between frailty and biomarker concentrations showed significant differences when frail subjects were compared to non-frail and pre-frail subjects for CRP and IL6. This work established strong association between inflammatory biomarkers and frailty, confirming the role of age-related chronic inflammation in frailty development.

Differential Association of Mitochondrial DNA Haplogroups J and H With the Methylation Status of Articular Cartilage: Potential Role in Apoptosis and Metabolic and Developmental Processes

OBJECTIVE

To analyze the influence of mitochondrial genome variation on the DNA methylome of articular cartilage.

METHODS

DNA methylation profiling was performed using data deposited in the NCBI Gene Expression Omnibus database (accession no. GSE43269). Data were obtained for 14 cartilage samples from subjects with haplogroup J and 20 cartilage samples from subjects with haplogroup H. Subsequent validation was performed in an independent subset of 7 subjects with haplogroup J and 9 with haplogroup H by RNA-seq. Correlated genes were validated by real-time polymerase chain reaction in an independent cohort of 12 subjects with haplogroup J and 12 with haplogroup H. Appropriate analyses were performed using R Bioconductor and qBasePlus software, and gene ontology analysis was conducted using DAVID version 6.8.

RESULTS

DNA methylation profiling revealed 538 differentially methylated loci, while whole-transcriptome profiling identified 2,384 differentially expressed genes, between cartilage samples from subjects with haplogroup H and those with haplogroup J. Seventeen genes showed an inverse correlation between methylation and expression. In terms of gene ontology, differences in correlations between methylation and expression were also detected between cartilage from subjects with haplogroup H and those with haplogroup J, highlighting a significantly enhanced apoptotic process in cartilage from subjects with haplogroup H (P = 0.007 for methylation and P = 0.019 for expression) and repressed apoptotic process in cartilage from subjects with haplogroup J (P = 0.021 for methylation), as well as a significant enrichment of genes related to metabolic processes (P = 1.93 × 10^-4 for methylation and P = 6.79 x 10^-4 for expression) and regulation of gene expression (P = 0.012 for methylation) in cartilage from subjects with haplogroup H, and to developmental processes (P = 0.015 for methylation and P = 8.25 x 10^-12 for expression) in cartilage from subjects with haplogroup J.

CONCLUSION

Mitochondrial DNA variation differentially associates with the methylation status of articular cartilage by acting on key mechanisms involved in osteoarthritis, such as apoptosis and metabolic and developmental processes.

Developing a network view of type 2 diabetes risk pathways through integration of genetic, genomic and functional data

BACKGROUND

Genome-wide association studies (GWAS) have identified several hundred susceptibility loci for type 2 diabetes (T2D). One critical, but unresolved, issue concerns the extent to which the mechanisms through which these diverse signals influencing T2D predisposition converge on a limited set of biological processes. However, the causal variants identified by GWAS mostly fall into a non-coding sequence, complicating the task of defining the effector transcripts through which they operate.

METHODS

Here, we describe implementation of an analytical pipeline to address this question. First, we integrate multiple sources of genetic, genomic and biological data to assign positional candidacy scores to the genes that map to T2D GWAS signals. Second, we introduce genes with high scores as seeds within a network optimization algorithm (the asymmetric prize-collecting Steiner tree approach) which uses external, experimentally confirmed protein-protein interaction (PPI) data to generate high-confidence sub-networks. Third, we use GWAS data to test the T2D association enrichment of the "non-seed" proteins introduced into the network, as a measure of the overall functional connectivity of the network.

RESULTS

We find (a) non-seed proteins in the T2D protein-interaction network so generated (comprising 705 nodes) are enriched for association to T2D (p = 0.0014) but not control traits, (b) stronger T2D-enrichment for islets than other tissues when we use RNA expression data to generate tissue-specific PPI networks and (c) enhanced enrichment (p = 3.9 × 10^- 5) when we combine the analysis of the islet-specific PPI network with a focus on the subset of T2D GWAS loci which act through defective insulin secretion.

CONCLUSIONS

These analyses reveal a pattern of non-random functional connectivity between candidate causal genes at T2D GWAS loci and highlight the products of genes including YWHAG, SMAD4 or CDK2 as potential contributors to T2D-relevant islet dysfunction. The approach we describe can be applied to other complex genetic and genomic datasets, facilitating integration of diverse data types into disease-associated networks.

Quantitative proteomic profiling of human articular cartilage degradation in osteoarthritis

Osteoarthritis (OA) is the most common rheumatic pathology and is characterized primarily by articular cartilage degradation. Despite its high prevalence, there is no effective therapy to slow disease progression or regenerate the damaged tissue. Therefore, new diagnostic and monitoring tests for OA are urgently needed, which would also promote the development of alternative therapeutic strategies. In the present study, we have performed an iTRAQ-based quantitative proteomic analysis of secretomes from healthy human articular cartilage explants, comparing their protein profile to those from unwounded (early disease) and wounded (advanced disease) zones of osteoarthritic tissue. This strategy allowed us to identify a panel of 76 proteins that are distinctively released by the diseased tissue. Clustering analysis allowed the classification of proteins according to their different profile of release from cartilage. Among these proteins, the altered release of osteoprotegerin (decreased in OA) and periostin (increased in OA), both involved in bone remodelling processes, was verified in further analyses. Moreover, periostin was also increased in the synovial fluid of OA patients. Altogether, the present work provides a novel insight into the mechanisms of human cartilage degradation and a number of new cartilage-characteristic proteins with possible biomarker value for early diagnosis and prognosis of OA.

Analysis of autoantibody profiles in osteoarthritis using comprehensive protein array concepts

Osteoarthritis (OA) is the most common rheumatic disease and one of the most disabling pathologies worldwide. To date, the diagnostic methods of OA are very limited, and there are no available medications capable of halting its characteristic cartilage degeneration. Therefore, there is a significant interest in new biomarkers useful for the early diagnosis, prognosis, and therapeutic monitoring. In the recent years, protein microarrays have emerged as a powerful proteomic tool to search for new biomarkers. In this study, we have used two concepts for generating protein arrays, antigen microarrays, and NAPPA (nucleic acid programmable protein arrays), to characterize differential autoantibody profiles in a set of 62 samples from OA, rheumatoid arthritis (RA), and healthy controls. An untargeted screen was performed on 3840 protein fragments spotted on planar antigen arrays, and 373 antigens were selected for validation on bead-based arrays. In the NAPPA approach, a targeted screening was performed on 80 preselected proteins. The autoantibody targeting CHST14 was validated by ELISA in the same set of patients. Altogether, nine and seven disease related autoantibody target candidates were identified, and this work demonstrates a combination of these two array concepts for biomarker discovery and their usefulness for characterizing disease-specific autoantibody profiles.

Bivalve omics: state of the art and potential applications for the biomonitoring of harmful marine compounds

The extraordinary progress experienced by sequencing technologies and bioinformatics has made the development of omic studies virtually ubiquitous in all fields of life sciences nowadays. However, scientific attention has been quite unevenly distributed throughout the different branches of the tree of life, leaving molluscs, one of the most diverse animal groups, relatively unexplored and without representation within the narrow collection of well established model organisms. Within this Phylum, bivalve molluscs play a fundamental role in the functioning of the marine ecosystem, constitute very valuable commercial resources in aquaculture, and have been widely used as sentinel organisms in the biomonitoring of marine pollution. Yet, it has only been very recently that this complex group of organisms became a preferential subject for omic studies, posing new challenges for their integrative characterization. The present contribution aims to give a detailed insight into the state of the art of the omic studies and functional information analysis of bivalve molluscs, providing a timely perspective on the available data resources and on the current and prospective applications for the biomonitoring of harmful marine compounds.

The marine toxin okadaic acid induces alterations in the expression level of cancer-related genes in human neuronal cells

Okadaic acid (OA) is one of the most common and highly distributed marine toxins. It can be accumulated in several molluscs and other marine organisms and cause acute gastrointestinal symptoms after oral consumption by humans, called diarrheic shellfish poisoning. However other toxic effects beyond these gastrointestinal symptoms were also reported. Thus, OA was found to induce important chromosomal abnormalities and other genetic injuries that can lead to severe pathologies, including cancer. Furthermore, the relationship between OA and carcinogenic processes has been previously demonstrated in in vivo studies with rodents, and also suggested in human epidemiological studies. In this context, further research is required to better understand the underlying mechanisms of OA-related tumourigenesis. In a previous study, we identified 247 genes differentially expressed in SHSY5Y neuroblastoma cells exposed to 100nM OA at different times (3, 24 and 48h) by means of suppression subtractive hybridization. These genes were involved in relevant cell functions such as signal transduction, cell cycle, metabolism, and transcription and translation processes. However, due to the high potential percentage of false positives that may be obtained by this approach, results from SSH are recommended to be analyzed by an independent method. In the present study, we selected ten genes related to cancer initiation or progression, directly or indirectly, for further quantitative PCR analysis (ANAPC13, PTTG1, CALM2, CLU, HN1, MALAT1, MAPRE2, MLLT11, SGA-81M and TAX1BP1). Results obtained showed important alterations in the expression patterns of all the genes evaluated at one or more treatment times, providing, for the first time, a possible explanation at the molecular level of the potential relationship between the consumption of OA-contaminated shellfish and the incidence of different cancers in humans. Nevertheless, given the complexity of this process, more exhaustive studies are required before drawing any final conclusion.

Genome-wide DNA methylation analysis of articular chondrocytes reveals a cluster of osteoarthritic patients

OBJECTIVE

Alterations in DNA methylation patterns have been found to correlate with several diseases including osteoarthritis (OA). The aim of this study was to identify, for the first time, the genome-wide DNA methylation profiles of human articular chondrocytes from OA cartilage and healthy control cartilage samples.

METHODS

DNA methylation profiling was performed using Illumina Infinium HumanMethylation27 in 25 patients with OA and 20 healthy controls. Subsequent validation was performed by genome-wide expression analysis using the Affymetrix Human Gene 1.1 ST array in an independent cohort of 24 patients with OA. Finally, the most consistent genes in both assays were amplified by quantitative reverse transcriptase PCR in a validation cohort of 48 patients using microfluidic real-time quantitative PCR. Appropriate bioinformatics analyses were carried out using R bioconductor software packages and qBase plus software from Biogazelle.

RESULTS

We found 91 differentially methylated (DM) probes, which permitted us to separate patients with OA from healthy controls. Among the patients with OA, we detected 1357 DM probes that identified a tight cluster of seven patients who were different from the rest. This cluster was also identified by genome-wide expression in which 450 genes were differentially expressed. Further validation of the most consistent genes in an independent cohort of patients with OA permitted us to identify this cluster, which was characterised by increased inflammatory processes.

CONCLUSIONS

We were able to identify a tight subgroup of patients with OA, characterised by an increased inflammatory response that could be regulated by epigenetics. The identification and isolation of this subgroup may be critical for the development of effective treatment and disease prevention.

The CHROMEVALOA database: a resource for the evaluation of Okadaic Acid contamination in the marine environment based on the chromatin-associated transcriptome of the mussel Mytilus galloprovincialis

Okadaic Acid (OA) constitutes the main active principle in Diarrhetic Shellfish Poisoning (DSP) toxins produced during Harmful Algal Blooms (HABs), representing a serious threat for human consumers of edible shellfish. Furthermore, OA conveys critical deleterious effects for marine organisms due to its genotoxic potential. Many efforts have been dedicated to OA biomonitoring during the last three decades. However, it is only now with the current availability of detailed molecular information on DNA organization and the mechanisms involved in the maintenance of genome integrity, that a new arena starts opening up for the study of OA contamination. In the present work we address the links between OA genotoxicity and chromatin by combining Next Generation Sequencing (NGS) technologies and bioinformatics. To this end, we introduce CHROMEVALOAdb, a public database containing the chromatin-associated transcriptome of the mussel Mytilus galloprovincialis (a sentinel model organism) in response to OA exposure. This resource constitutes a leap forward for the development of chromatin-based biomarkers, paving the road towards the generation of powerful and sensitive tests for the detection and evaluation of the genotoxic effects of OA in coastal areas.

Circulating miR-200c as a diagnostic and prognostic biomarker for gastric cancer

Background

MicroRNAs are aberrantly expressed and correlate with tumourigenesis and the progression of solid tumours. The miR-200 family determines the epithelial phenotype of cancer cells and regulates invasiveness and migration. Thus, we hypothesised that the quantitative detection of the miR-200 family as epithelial-specific microRNAs in the blood could be a useful clinical biomarker for gastric cancer (GC).

Methods

We initially validated the expression levels of miR-200a, 200b, 200c and 141 in GC cell lines (n = 2) and blood from healthy controls (n = 19) using real-time quantitative reverse transcription PCR (qRT-PCR). The microarray expression profiles of the miR-200 family in 160 paired samples of non-tumour gastric mucosae and GC were downloaded through ArrayExpress and analysed. MiR-200c was selected for clinical validation. The qRT-PCR prospective assessment of miR-200c was performed using 67 blood samples (52 stage I-IV GC patients and 15 controls); the area under the receiver operating characteristic curve (AUC-ROC) was estimated. The Kaplan-Meier and Breslow-Wilcoxon tests were used to assess the correlation of miR-200c with overall and progression-free survival (OS and PFS). Multivariate analyses were performed using the Cox model.

Results

The miR-200c blood expression levels in GC patients were significantly higher than in normal controls (p = 0.018). The AUC-ROC was 0.715 (p = 0.012). The sensitivity, specificity and accuracy rates of 65.4%, 100% and 73.1%, respectively, were observed. The levels of miR-200c in the blood above the cutoff defined by the ROC curve was found in 17.6% of stage I-II GC patients, 20.6% of stage III patients and 67.7% of stage IV patients (p < 0.001). The miR-200c expression levels were not associated with clinical or pathological characteristics or recent surgical procedures. There was a correlation (p = 0.016) with the number of lymph node metastases and the increased expression levels of miR-200c in blood were significantly associated with a poor OS (median OS, 9 vs 24 months; p = 0.016) and PFS (median PFS, 4 vs 11 months; p = 0.044). Multivariate analyses confirmed that the upregulation of miR-200c in the blood was associated with OS (HR = 2.24; p = 0.028) and PFS (HR = 2.27; p = 0.028), independent of clinical covariates.

Conclusions

These data suggest that increased miR-200c levels are detected in the blood of gastric cancer patients. MiR-200c has the potential to be a predictor of progression and survival.

Identification of Ensis siliqua samples and establishment of the catch area using a species-specific microsatellite marker

European Council Regulation 104/2000 states that fishery products must be labeled to indicate commercial designation of species, the production method, and the catch area. Therefore, traceability of seafood implies knowledge of the species offered to retail and their origin. Ensis siliqua is a bivalve intensively fished in Europe and sold in fresh and canned forms. Although several published methods clearly differentiate Ensis genus species, none of those assess the origin of the commercial samples. In the present study, a microsatellite marker (Esi-UDC3055F) was developed to establish the catch area of E. siliqua samples. Amplification yielded a fragment of 275 or 302 base pairs, depending on whether they were Iberian or Irish populations. The usefulness of this method was also assessed in commercial samples. The results of this study provide a reliable methodology for the identification of catch area in European E. siliqua commercial samples. The coupling of this methodology with existing techniques for razor clam species identification provides a powerful tool for traceability and labeling enforcement.

Chromatin specialization in bivalve molluscs: a leap forward for the evaluation of Okadaic Acid genotoxicity in the marine environment

Marine biotoxins synthesized by Harmful Algal Blooms (HABs) represent one of the most important sources of contamination in marine environments as well as a serious threat to fisheries and aquaculture-based industries in coastal areas. Among these biotoxins Okadaic Acid (OA) is of critical interest as it represents the most predominant Diarrhetic Shellfish Poisoning biotoxin in the European coasts. Furthermore, OA is a potent tumor promoter with aneugenic and clastogenic effects on the hereditary material, most notably DNA breaks and alterations in DNA repair mechanisms. Therefore, a great effort has been devoted to the biomonitoring of OA in the marine environment during the last two decades, mainly based on physicochemical and physiological parameters using mussels as sentinel organisms. However, the molecular genotoxic effects of this biotoxin make chromatin structure a good candidate for an alternative strategy for toxicity assessment with faster and more sensitive evaluation. To date, the development of chromatin-based studies to this purpose has been hampered by the complete lack of information on chromatin of invertebrate marine organisms, especially in bivalve molluscs. Our preliminary results have revealed the presence of histone variants involved in DNA repair and chromatin specialization in mussels and clams. In this work we use this information to put forward a proposal focused on the development of chromatin-based tests for OA genotoxicity in the marine environment. The implementation of such tests in natural populations has the potential to provide an important leap in the biomonitoring of this biotoxin. The outcome of such monitoring may have critical implications for the evaluation of DNA damage in these marine organisms. They will provide as well important tools for the optimization of their harvesting and for the elaboration of additional tests designed to evaluate the safety of their consumption and potential implications for consumer's health.

Identification of differentially expressed genes in SHSY5Y cells exposed to okadaic acid by suppression subtractive hybridization

Background

Okadaic acid (OA), a toxin produced by several dinoflagellate species is responsible for frequent food poisonings associated to shellfish consumption. Although several studies have documented the OA effects on different processes such as cell transformation, apoptosis, DNA repair or embryogenesis, the molecular mechanistic basis for these and other effects is not completely understood and the number of controversial data on OA is increasing in the literature.

Results

In this study, we used suppression subtractive hybridization in SHSY5Y cells to identify genes that are differentially expressed after OA exposure for different times (3, 24 and 48 h). A total of 247 subtracted clones which shared high homology with known genes were isolated. Among these, 5 specific genes associated with cytoskeleton and neurotransmission processes (NEFM, TUBB, SEPT7, SYT4 and NPY) were selected to confirm their expression levels by real-time PCR. Significant down-regulation of these genes was obtained at the short term (3 and 24 h OA exposure), excepting for NEFM, but their expression was similar to the controls at 48 h.

Conclusions

From all the obtained genes, 114 genes were up-regulated and 133 were down-regulated. Based on the NCBI GenBank and Gene Ontology databases, most of these genes are involved in relevant cell functions such as metabolism, transport, translation, signal transduction and cell cycle. After quantitative PCR analysis, the observed underexpression of the selected genes could underlie the previously reported OA-induced cytoskeleton disruption, neurotransmission alterations and in vivo neurotoxic effects. The basal expression levels obtained at 48 h suggested that surviving cells were able to recover from OA-caused gene expression alterations.

Sharp decrease of genetic variation in two Spanish localities of razor clam Ensis siliqua: natural fluctuation or Prestige oil spill effects?

Pollution is one of the main concerns in marine ecosystems nowadays. Environmental anthropogenic-mediated toxicants may affect genetic diversity both at the individual and ecosystem levels and may also alter the genetic structure of populations. This study examined the temporal pattern of genetic diversity among populations of the benthic bivalve Ensis siliqua in two locations of Galicia, following the Prestige oil spillage. On November 13, 2002 the oil tanker Prestige sank at 240 km from Galician coast and 63,000 tonnes of heavy fuel were released to the marine environment. E. siliqua samples were sampled between 2001 and 2006. Genetic variation was assessed by means of Random Amplification of Polymorphic DNA (RAPD). A significant decrease in genetic diversity was observed for the 2006 samples. Nei's genetic distance, fixation index (PhiPT), and PCA values also supported differences in the 2006 samples. We hypothesize that the temporal genetic variation observed in E. siliqua populations is due to a strong effect of genetic drift caused by a reduction in population size and that the indirect effects of the Prestige spill possibly caused this reduction.

Alterations in metabolism-related genes induced in SHSY5Y cells by okadaic acid exposure

Okadaic acid (OA) is a widely distributed marine toxin produced by several phytoplanktonic species and responsible for diarrheic shellfish poisoning in humans. At the molecular level OA is a specific inhibitor of several types of serine/threonine protein phosphatases. Due to this enzymic inhibition, OA was reported to induce numerous alterations in relevant cellular physiological processes, including several metabolic pathways such as glucose uptake, lipolysis and glycolysis, heme metabolism, and glycogen and protein synthesis. In order to further understand the underlying mechanisms involved in OA-induced effects on cellular metabolism, the expression levels of six genes related to different catabolic and anabolic metabolism-related processes were analyzed by real-time polymerase chain reaction. Specifically, the expression patterns of GAPDH, TOMM5, SLC25A4, COII, QARS, and RGS5 genes were determined in SHSY5Y human neuroblastoma cells exposed to OA for 3, 24, or 48 h. All these genes showed alterations in their expression levels after at least one of the OA treatments tested. These alterations provide a basis to understand the mechanisms underlying the previously described OA-induced effects on different metabolic processes, mainly regarding glucose and mitochondrial metabolism. However, other OA-induced affected genes can not be ruled out, and further studies are required to more comprehensively characterize in the mechanisms of OA-induced interaction on cell metabolism.

Two different size classes of 5S rDNA units coexisting in the same tandem array in the razor clam Ensis macha: is this region suitable for phylogeographic studies?

For a study of 5S ribosomal genes (rDNA) in the razor clam Ensis macha, the 5S rDNA region was amplified and sequenced. Two variants, so-called type I or short repeat (approximately 430 bp) and type II or long repeat (approximately 735 bp), appeared to be the main components of the 5S rDNA of this species. Their spacers differed markedly, both in length and nucleotide composition. The organization of the two variants was investigated by amplifying the genomic DNA with primers based on the sequence of the type I and type II spacers. PCR amplification products with primers EMLbF and EMSbR showed that the long and short repeats are associated within the same tandem array, suggesting an intermixed arrangement of both spacers. Nevertheless, amplifications carried out with inverse primers EMSinvF/R and EMLinvF/R revealed that some short and long repeats are contiguous in the same tandem array. This is the first report of the coexistence of two variable spacers in the same tandem array in bivalve mollusks.

Use of three bivalve species for biomonitoring a polluted estuarine environment

Estuaries are marine areas at great contamination risk due to their hydrodynamic features. PAH are wide and ubiquitous contaminants with a high presence in these marine environments. Chemical analysis of sediments can provide information, although it does not give a direct measure of the toxicological effect of such contaminants in the biota. Samples of Venerupis pullastra, Cerastoderma edule, and Mytilus galloprovincialis were collected from two locations in Corcubión estuary (Norhwest of Spain). The level of PAH in sediment and biota, and its possible origin were assessed. A moderate level of contamination was observed with a predominance of PAH of a pyrogenic origin. Genotoxic damage, measured as single-strand DNA breaks with the comet assay, was evaluated in gill tissue and in hemolymph. The values of DNA damage obtained showed a higher sensitivity of clams and cockles to the pollution load level. These differences among species make us suggest the use of some other species coupled with mussels as an optimal tool for biomonitoring estuarine environments.

Evaluation of genotoxicity in gills and hemolymph of clam Ruditapes decussatus fed with the toxic dinoflagellate Prorocentrum lima

Diarrheic shellfish poisoning (DSP) is a gastrointestinal (GIT) disease that appears a few hours after ingesting okadaic acid (OA)-contaminated mollusks; okadaic acid is present in dinoflagellates of the genera Dinophysis and Prorocentrum. Toxic manifestations occur all year round at a higher or lesser intensity, and as a consequence, extractive production factories need to be closed during these periods which affects the economy of aquaculture industries. Although the concentration of harmful algae is usually found at high levels in clam digestive gland, bivalve mortality was not increased. In this study, the genotoxic effects produced by OA in clam Ruditapes decussatus were determined using the comet assay. In vitro (exposing hemocytes to different concentrations of OA) and in vivo (feeding clams with toxic dinoflagellate Prorocentrum lima) experiments were conducted in order to determine the genotoxic effects of OA on bivalve cells. Hemocytes and gill cells were analyzed by in vivo and in vitro approaches. While the in vitro study showed a rapid effect of OA on hemocytes, data obtained in the in vivo experiment reflected contradictory results dependent upon the concentration of OA and cell type evaluated. An increase in DNA damage was observed at the lower concentration and only in gill tissue. The results obtained may contribute to a better understanding of the mechanisms underlying genotoxic effects induced by OA on bivalves.

Monitoring follow up of two areas affected by the Prestige oil four years after the spillage

The sinking of the oil tanker Prestige in November 2002 resulted in the spill of more than 63,000 tonnes of crude oil, and polluted more than 1,000 km of coastline, especially affecting Galicia (northwestern Spain). Four years after the accident, a new biological monitoring study was undertaken of two Galician areas intensely affected by the spill, Lira and Ancoradoiro, previously evaluated in the months following the accident ( Laffon et al. 2006 ). The mussel Mytilus galloprovincialis was employed as bioindicator organism to determine both polycyclic aromatic hydrocarbons (PAH) levels and genotoxic effects. PAH were determined chromatographically in seawater samples and mussel tissues collected from November 2006 to January 2008. The results obtained showed that PAH pollution was still present in these areas, but bioaccumulation of these compounds in mussels was low, compared to reference mussels, and lower than in our previous study. DNA damage assessment was also performed in gills and hemolymph cells by means of the alkaline comet assay. DNA damage levels were higher in mussels from the exposed areas than in reference mussels. DNA damage decreased after a 7-d recovery period in the laboratory, but prolonging the recovery period up to 14 d did not contribute to less DNA damage in gill cells. Hemolymph cells were more sensitive than gill cells to the induction of DNA damage.

Comparison between two bivalve species as tools for the assessment of pollution levels in an estuarian environment

Estuaries are semi-enclosed marine areas with water short residence times. Estuary ecosystems show a higher susceptibility to contamination, as historically these sites are linked to urban and industrial development. Polycyclic aromatic hydrocarbons (PAH) are ubiquitous contaminants present in high quantities in these marine environments. Chemical analyses of sediments provides information regarding PAH pollution levels but not a direct measure of the toxicological effects attributed to these contaminants. Samples of sediments and of two bivalve species, Cerastoderma edule and Mytilus galloprovincialis, were collected from two locations (Corcubión and A Concha) in an estuary from northwestern Spain. The PAH levels in sediment and bivalve species and possible sources were determined. A moderate level and a low level of pyrogenic PAH contamination were observed in Corcubión and in A Concha, respectively. Genotoxic damage was evaluated in gills and hemocytes from mussels and cockles by means of the comet assay. DNA damage measured as DNAt values showed a reliable relationship with pollution load levels of the two sampling sites. The higher sensitivity of C. edule compared to M. galloprovincialis enables one to recommend including another species coupled with mussels for biomonitoring estuarine environments.

Cytogenetics of the razor clam Solen marginatus (Mollusca: Bivalvia: Solenidae)

The razor clam Solen marginatus has a diploid chromosome number of 38. The karyotype consists of one metacentric/submetacentric, three submetacentric/metacentric, five submetacentric, one submetacentric/subtelocentric, one subtelocentric/submetacentric, six subtelocentric and two telocentric chromosome pairs. Staining with chromomycin A3 revealed bright positive bands subcentromerically in the long arms of one medium-sized subtelocentric pair, while DAPI staining showed uniform fluorescence in all chromosomes of the complement. Fluorescence in situ hybridization using an 18S-5.8S-28S rDNA probe locates these loci at the subcentromeric region of one subtelocentric pair and at the subtelomeric region of another subtelocentric pair.