Late-onset major depressive disorder: exploring the therapeutic potential of enhancing cerebral brain-derived neurotrophic factor expression through targeted microRNA delivery.

Major depressive disorder (MDD) is a severe psychiatric condition that significantly impacts the overall quality of life. Although MDD can occur across all age groups, it is notably prevalent among older individuals, with the aggravating circumstance that the clinical condition is frequently overlooked and undertreated. Furthermore, older adults often encounter resistance to standard treatments, experience adverse events, and face challenges associated with polypharmacy. Given that late-life MDD is associated with heightened rates of disability and mortality, as well as imposing a significant economic and logistical burden on healthcare systems, it becomes imperative to explore novel therapeutic approaches. These could serve as either supplements to standard guidelines or alternatives for non-responsive patients, potentially enhancing the management of geriatric MDD patients. This review aims to delve into the potential of microRNAs targeting Brain-Derived Neurotrophic Factor (BDNF). In MDD, a significant decrease in both central and peripheral BDNF has been well-documented, raising implications for therapy response. Notably, BDNF appears to be a key player in the intricate interplay between microRNA-induced neuroplasticity deficits and neuroinflammation, both processes deeply implicated in the onset and progression of the disease. Special emphasis is placed on delivery methods, with a comprehensive comparison of the strengths and weaknesses of each proposed approach. Our hypothesis proposes that employing multiple microRNAs concurrently, with the ability to directly influence BDNF and activate closely associated pathways, may represent the most promising strategy. Regarding vehicles, although the perfect nanoparticle remains elusive, considering the trade-offs, liposomes emerge as the most suitable option.

Marine Compounds and Age-Related Diseases: The Path from Pre-Clinical Research to Approved Drugs for the Treatment of Cardiovascular Diseases and Diabetes.

Ageing represents a main risk factor for several pathologies. Among them, cardiovascular diseases (CVD) and type 2 diabetes mellitus (T2DM) are predominant in the elderly population and often require prolonged use of multiple drugs due to their chronic nature and the high proportion of co-morbidities. Hence, research is constantly looking for novel, effective molecules to treat CVD and T2DM with minimal side effects. Marine active compounds, holding a great diversity of chemical structures and biological properties, represent interesting therapeutic candidates to treat these age-related diseases. This review summarizes the current state of research on marine compounds for the treatment of CVD and T2DM, from pre-clinical studies to clinical investigations and approved drugs, highlighting the potential of marine compounds in the development of new therapies, together with the limitations in translating pre-clinical results into human application.

Subcellular effects and lipid metabolism alterations in the gilthead seabream Sparus aurata fed on ovatoxins-contaminated mussels.

The marine microalgae Ostreopsis cf. ovata are a well-known producer of palytoxin (PlTXs) analogues, i.e. ovatoxins (OVTXs) among others, which arouse concern for animal and human health. Both in field and laboratory studies, presence of OVTXs, detected in species directly feeding on O. cf. ovata, was frequently correlated with impairment on organisms' physiology, development and behaviour, while similar knowledge is still lacking for animals feeding on contaminated preys. In this study, transfer and toxicity of OVTXs were evaluated in an exposure experiment, in which gilthead seabream Sparus aurata was fed with bivalve mussel Mytilus galloprovincialis, contaminated by a toxic strain of O. cf. ovata. Mussels exposed to O. cf. ovata for 21 days accumulated meanly 188 ± 13 µg/kg OVTXs in the whole tissues. Seabreams fed with OVTX-contaminated mussels started to reject the food after 6 days of contaminated diet. Although no detectable levels of OVTXs were measured in muscle, liver, gills and gastro-intestinal tracts, the OVTX-enriched diet induced alterations of lipid metabolism in seabreams livers, displaying a decreased content of total lipid and fatty acid, together with overexpression of fatty acid biosynthetic genes, downregulation of ß-oxidation genes and modulation of several genes related to lipid transport and regulation. Results from this study would suggest the hypothesis that OVTXs produced by O. cf. ovata may not be subject to bioaccumulation in fish fed on contaminated preys, being however responsible of significant biological effects, with important implications for human consumption of seafood products.

Cellular senescence and frailty: a comprehensive insight into the causal links.

Senescent cells may have a prominent role in driving inflammation and frailty. The impact of cellular senescence on frailty varies depending on the assessment tool used, as it is influenced by the criteria or items predominantly affected by senescent cells and the varying weights assigned to these items across different health domains. To address this challenge, we undertook a thorough review of all available studies involving gain- or loss-of-function experiments as well as interventions targeting senescent cells, focusing our attention on those studies that examined outcomes based on the individual frailty phenotype criteria or specific items used to calculate two humans (35 and 70 items) and one mouse (31 items) frailty indexes. Based on the calculation of a simple "evidence score," we found that the burden of senescent cells related to musculoskeletal and cerebral health has the strongest causal link to frailty. We deem that insight into these mechanisms may not only contribute to clarifying the role of cellular senescence in frailty but could additionally provide multiple therapeutic opportunities to help the future development of a desirable personalized therapy in these extremely heterogeneous patients.

Spreading Senescent Cells' Burden and Emerging Therapeutic Targets for Frailty.

The spreading of senescent cells' burden holds profound implications for frailty, prompting the exploration of novel therapeutic targets. In this perspective review, we delve into the intricate mechanisms underlying senescent cell spreading, its implications for frailty, and its therapeutic development. We have focused our attention on the emerging age-related biological factors, such as microbiome and virome alterations, elucidating their significant contribution to the loss of control over the accumulation rate of senescent cells, particularly affecting key frailty domains, the musculoskeletal system and cerebral functions. We believe that gaining an understanding of these mechanisms could not only aid in elucidating the involvement of cellular senescence in frailty but also offer diverse therapeutic possibilities, potentially advancing the future development of tailored interventions for these highly diverse patients.

Effects of Human LAV-BPIFB4 Gene Therapy on the Epigenetic Clock and Health of Aged Mice.

The homozygous genotype of the Longevity-Associated Variant (LAV) in Bactericidal/Permeability-Increasing Fold-Containing Family B member 4 (BPIFB4) is enriched in long-living individuals of three independent populations and its genetic transfer in C57BL/6J mice showed a delay in frailty progression and improvement of several biomarkers of aging and multiple aspects of health. The C57BL/6J strain is a suitable model for studying therapies aimed at extending healthy aging and longevity due to its relatively short lifespan and the availability of aging biomarkers. Epigenetic clocks based on DNA methylation profiles are reliable molecular biomarkers of aging, while frailty measurement tools are used to evaluate overall health during aging. In this study, we show that the systemic gene transfer of LAV-BPIFB4 in aged C57BL/6J mice was associated with a significant reduction in the epigenetic clock-based biological age, as measured by a three CpG clock method. Furthermore, LAV-BPIFB4 gene transfer resulted in an improvement of the Vitality Score with a reduction in the Frailty Index. These findings further support the use of LAV-BPIFB4 gene therapy to induce beneficial effects on epigenetic mechanisms associated with aging and frailty in aged mice, with potential implications for future therapies to prevent frailty in humans.

Comprehensive longitudinal non-invasive quantification of healthspan and frailty in a large cohort (n = 546) of geriatric C57BL/6 J mice.

Frailty is an age-related condition characterized by a multisystem functional decline, increased vulnerability to stressors, and adverse health outcomes. Quantifying the degree of frailty in humans and animals is a health measure useful for translational geroscience research. Two frailty measurements, namely the frailty phenotype (FP) and the clinical frailty index (CFI), have been validated in mice and are frequently applied in preclinical research. However, these two tools are based on different concepts and do not necessarily identify the same mice as frail. In particular, the FP is based on a dichotomous classification that suffers from high sample size requirements and misclassification problems. Based on the monthly longitudinal non-invasive assessment of frailty in a large cohort of mice, here we develop an alternative scoring method, which we called physical function score (PFS), proposed as a continuous variable that resumes into a unique function, the five criteria included in the FP. This score would not only reduce misclassification of frailty but it also makes the two tools, PFS and CFI, integrable to provide an overall measurement of health, named vitality score (VS) in aging mice. VS displays a higher association with mortality than PFS or CFI and correlates with biomarkers related to the accumulation of senescent cells and the epigenetic clock. This longitudinal non-invasive assessment strategy and the VS may help to overcome the different sensitivity in frailty identification, reduce the sample size in longitudinal experiments, and establish the effectiveness of therapeutic/preventive interventions for frailty or other age-related diseases in geriatric animals.

Toxicological effects of cigarette butts for marine organisms.

Cigarette butts (CBs), one of the most common litter items found on beaches, represent a still unexplored environmental hazard. This study aimed at a multidisciplinary characterization of their toxicological risks on marine organisms integrating chemical analyses of released compounds with a wide panel of biological responses, such as ecotoxicological bioassays on species of different trophic positions, molecular responses in an ex vivo model (Precision-Cut Tissue Slices, PCTS of mussels digestive glands), bioavailability and cellular biomarkers in mussels exposed to CBs in laboratory experiments. Trace metals, aliphatic and polycyclic aromatic hydrocarbons, nicotine and cotinine were released in artificial seawater after 24 h which determined a significant inhibition of bacterial bioluminescence, oyster embryo development and growth in different algal species. Modulation of peroxisomal proliferation and antioxidant gene expression was observed in mussels PCTS, while the in vivo exposure determined accumulation of chemicals and significant alterations of immune system, antioxidant and neurotoxic responses, peroxisomal proliferation and genotoxic damage. Using a quantitative Weight of Evidence model, the risks of CBs to the marine environment were summarized, highlighting the importance of integrating chemical analyses, batteries of ecotoxicological bioassays, molecular and cellular biomarkers to assess the impact of these hazardous materials on marine environment.

Tetrodotoxins (TTXs) and Vibrio alginolyticus in Mussels from Central Adriatic Sea (Italy): Are They Closely Related?

Tetrodotoxins (TTXs), potent neurotoxins, have become an increasing concern in Europe in recent decades, especially because of their presence in mollusks. The European Food Safety Authority published a Scientific Opinion setting a recommended threshold for TTX in mollusks of 44 µg equivalent kg-1 and calling all member states to contribute to an effort to gather data in order to produce a more exhaustive risk assessment. The objective of this work was to assess TTX levels in wild and farmed mussels (Mytilus galloprovincialis) harvested in 2018-2019 along the coastal area of the Marche region in the Central Adriatic Sea (Italy). The presence of Vibrio spp. carrying the non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes, which are suspected to be involved in TTX biosynthesis, was also investigated. Out of 158 mussel samples analyzed by hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry (HILIC-MS/MS), 11 (7%) contained the toxins at detectable levels (8-26 µg kg-1) and 3 (2%) contained levels above the EFSA safety threshold (61-76 µg kg-1). Contaminated mussels were all harvested from natural beds in spring or summer. Of the 2019 samples, 70% of them contained V. alginolyticus strains with the NRPS and/or PKS genes. None of the strains containing NRPS and/or PKS genes showed detectable levels of TTXs. TTXs in mussels are not yet a threat in the Marche region nor in Europe, but further investigations are surely needed.

Transcriptional and Catalytic Responsiveness of the Antarctic Fish Trematomus bernacchii Antioxidant System toward Multiple Stressors.

Ocean-warming and acidification jeopardize Antarctic marine species, adapted to cold and constant conditions and naturally exposed to high pro-oxidant pressures and cadmium (Cd) bioavailability. The aim of this study was to investigate if projected temperature increase and pH reduction may affect the accumulation and the effects of Cd in the rockcod Trematomus bernacchii. Organisms were exposed for 14 days to six scenarios, combining environmental or increased temperature (-1 °C, +1 °C) and control or reduced pH (8.05, 7.60), either with or without Cd (40 µg/L). Responses in liver and gills were analyzed at different levels, including mRNA and functional measurements of metallothioneins and of a wide battery of antioxidants, integrated with the evaluation of the total antioxidant capacity and onset of oxidative damages. In the gills, metallothioneins and mRNA of antioxidant genes (nrf2, keap1, cat, gpx1) increased after Cd exposure, but such effects were softened by warming and acidification. Antioxidants showed slighter variations at the enzymatic level, while Cd caused glutathione increase under warming and acidified scenarios. In the liver, due to higher basal antioxidant protection, limited effects were observed. Genotoxic damage increased under the combined stressors scenario. Overall results highlighted the modulation of the oxidative stress response to Cd by multiple stressors, suggesting the vulnerability of T. bernacchii under predicted ocean change scenarios.

Omics approaches for conservation biology research on the bivalve Chamelea gallina.

The striped venus (Chamelea gallina) is an important economic resource in the Mediterranean Basin; this species has exhibited a strong quantitative decline in the Adriatic Sea. The aim of this work was to provide a comprehensive view of the biological status of C. gallina to elucidate the bioecological characteristics and genetic diversity of wild populations. To the best of our knowledge, this investigation is the first to perform a multidisciplinary study on C. gallina based on two omics approaches integrated with histological, ecotoxicological, and chemical analyses and with the assessment of environmental parameters. The results obtained through RNA sequencing indicated that the striped venus has a notable ability to adapt to different environmental conditions. Moreover, the stock reduction exhibited by this species in the last 2 decades seems not to have negatively affected its genetic diversity. Indeed, the high level of genetic diversity that emerged from our ddRAD dataset analyses is ascribable to the high larval dispersal rate, which might have played a "compensatory role" on local fluctuations, conferring to this species a good adaptive potential to face the environmental perturbations. These findings may facilitate the efforts of conservation biologists to adopt ad hoc management plans for this fishery resource.

Season specific influence of projected ocean changes on the response to cadmium of stress-related genes in Mytilus galloprovincialis.

Anthropogenic inputs of carbon dioxide in the atmosphere are driving ocean warming and acidification. The potential threat represented by these changes for marine species could be amplified in coastal areas, characterized by higher levels of pollutants. In addition, temperate organisms may exhibit a different seasonal tolerance to stressors influenced by fluctuations of environmental and physiological factors. In this study, Mediterranean mussels Mytilus galloprovincialis collected both in summer and winter were exposed to combinations of two temperatures (SST, seasonal surface temperature and SST+5 °C) and two levels of pH (8.20 and 7.40) in clean or cadmium contaminated seawater (20 µg/L Cd). mRNA levels of genes related to metal-induced stress response were investigated, including metallothionein mt-20, heat-shock protein hsp70, superoxide dismutase Cu/Zn-sod, catalase cat, glutathione peroxidase gpx1 and glutathione S-transferase gst-pi. To further elucidate if tissues with different physiological roles could exhibit different responsiveness, such analyses were carried out in digestive gland and in gills of exposed mussels. mt-20 mRNA increase after Cd-exposure was higher in the digestive gland than in the gills, with few modulations by temperature or pH only in the latter. Acidification, alone or in combination with other stressors, increased hsp70 mRNA, with seasonal- and tissue-specificities (higher in summer and in digestive gland). Among antioxidants, gpx1 mRNA was affected by Cd in both tissues and seasons, with further modulations due to pH and temperature variation tissue- and season-specific; in winter the combination of Cd, warming and acidification affected Cu/Zn-sod both in digestive gland and gills and cat only in gills, while weak seasonal variations were observed for gst-pi transcripts only in digestive gland. The overall results highlighted the importance of considering seasonality and responsiveness of different tissues to predict the effects of sudden changes in environmental parameters on responsiveness to and toxicity of chemicals in marine coastal organisms.

Biological Effects of the Azaspiracid-Producing Dinoflagellate Azadinium dexteroporum in Mytilus galloprovincialis from the Mediterranean Sea.

Azaspiracids (AZAs) are marine biotoxins including a variety of analogues. Recently, novel AZAs produced by the Mediterranean dinoflagellate Azadinium dexteroporum were discovered (AZA-54, AZA-55, 3-epi-AZA-7, AZA-56, AZA-57 and AZA-58) and their biological effects have not been investigated yet. This study aimed to identify the biological responses (biomarkers) induced in mussels Mytilus galloprovincialis after the bioaccumulation of AZAs from A. dexteroporum. Organisms were fed with A. dexteroporum for 21 days and subsequently subjected to a recovery period (normal diet) of 21 days. Exposed organisms accumulated AZA-54, 3-epi-AZA-7 and AZA-55, predominantly in the digestive gland. Mussels' haemocytes showed inhibition of phagocytosis activity, modulation of the composition of haemocytic subpopulation and damage to lysosomal membranes; the digestive tissue displayed thinned tubule walls, consumption of storage lipids and accumulation of lipofuscin. Slight genotoxic damage was also observed. No clear occurrence of oxidative stress and alteration of nervous activity was detected in AZA-accumulating mussels. Most of the altered parameters returned to control levels after the recovery phase. The toxic effects detected in M. galloprovincialis demonstrate a clear biological impact of the AZAs produced by A. dexteroporum, and could be used as early indicators of contamination associated with the ingestion of seafood.

Precision-Cut Tissue Slices (PCTS) from the digestive gland of the Mediterranean mussel Mytilus galloprovincialis: An ex vivo approach for molecular and cellular responses in marine invertebrates.

The precision-cut tissue slices (PCTS) represent a largely used biological model in mammalian research. This ex vivo approach offers the main advantages of in vitro systems, while maintaining the natural architecture of the tissue. The use of PCTS in toxicological research has been proposed for investigating the cellular effects of xenobiotics or bioactive compounds mostly in mammalian models. Their application is increasing also in marine organisms, but still limited to fish. This work validates the use of PCTS in an invertebrate species, the Mediterranean mussel Mytilus galloprovincialis. Intact tissue slices of different thicknesses (300, 350 and 400 µm) were successfully obtained from the digestive gland. The slices maintained the histological integrity and the viability after 6 h and 24 h incubation in culture medium, with some differences depending on the thickness. The enzymatic activities and mRNA levels of catalase and glutathione S-transferase, chosen as model biological endpoints, were measured until 24 h incubation, revealing the functionality of such systems. This work demonstrates the suitability of mussel PCTS for investigating molecular and cellular responses in ecotoxicological research.

Fishing for Targets of Alien Metabolites: A Novel Peroxisome Proliferator-Activated Receptor (PPAR) Agonist from a Marine Pest.

Although the chemical warfare between invasive and native species has become a central problem in invasion biology, the molecular mechanisms by which bioactive metabolites from invasive pests influence local communities remain poorly characterized. This study demonstrates that the alkaloid caulerpin (CAU)-a bioactive component of the green alga Caulerpa cylindracea that has invaded the entire Mediterranean basin-is an agonist of peroxisome proliferator-activated receptors (PPARs). Our interdisciplinary study started with the in silico prediction of the ligand-protein interaction, which was then validated by in vivo, ex vivo and in vitro assays. On the basis of these results, we candidate CAU as a causal factor of the metabolic and behavioural disorders observed in Diplodus sargus, a native edible fish of high ecological and commercial relevance, feeding on C. cylindracea. Moreover, given the considerable interest in PPAR activators for the treatment of relevant human diseases, our findings are also discussed in terms of a possible nutraceutical/pharmacological valorisation of the invasive algal biomasses, supporting an innovative strategy for conserving biodiversity as an alternative to unrealistic campaigns for the eradication of invasive pests.

Nrf2 and regulation of the antioxidant system in the Antarctic silverfish, Pleuragramma antarctica: Adaptation to environmental changes of pro-oxidant pressure.

Despite the key importance of Nrf2-Keap1 in regulating antioxidant system in vertebrates, this system is still poorly investigated in marine species. The present study focused on the Antarctic silverfish Pleuragramma antarctica which, during the final phases of embryo development in platelet ice, is challenged by a sudden enhancement of environmental oxidative conditions associated to ice melting. Partial coding sequences were identified for Nrf2, its repressor Keap1 and for typical Nrf2-target antioxidant genes, like catalase, glutathione peroxidase isoform 1 and Cu/Zn-dependent superoxide dismutase. Compared to temperate homologues, the protein sequences showed an elevated conservation of amino acids essential for catalytic functions, while a few specific substitutions in non-essential regions may represent a molecular adaptation to improve flexibility and accessibility to active site at cold temperatures. The role of the Nrf2-Keap1 pathway in modulating the activation of antioxidant defences was demonstrated at both transcriptional and functional levels with a clear temporal increase of antioxidant protection in embryos before the hatching. Such findings confirm the importance of Nrf2 and highlight regulation of antioxidants as an adaptive strategy in P. antarctica to protect the early life stages toward the environmental changes of pro-oxidant pressure.

Oxidative metabolism of chemical pollutants in marine organisms: molecular and biochemical biomarkers in environmental toxicology.

Oxidative stress biomarkers are widely used in marine ecotoxicology. Environmental pollutants enhance intracellular formation of oxyradicals through several mechanisms, but complex oxidative interactions occur in response to chemical mixtures. Metabolism of individual classes of pollutants can be influenced by a sophisticated network of prooxidant relationships, reciprocal and cascade effects, changes of redox-sensitive signaling proteins, and transcription factors. Chemically mediated pathways can affect antioxidant responses at different levels, including pretranscriptional, transcriptional, protein, and catalytic functions; such mechanisms remain largely unexplored in marine organisms. Molecular responses of antioxidants are frequently not paralleled by expected biochemical changes or cellular effects, and caution is needed when interpreting the effects of environmental pollutants. Results on antioxidant variations can be influenced by mRNA stability and protein turnover, different timing for transcriptional and translational mechanisms, metabolic capability of tissues, posttranscriptional modifications of proteins, biphasic responses of antioxidant enzymes, and adaptation mechanisms to chronic pollution.

Identification of the Nrf2-Keap1 pathway in the European eel Anguilla anguilla: role for a transcriptional regulation of antioxidant genes in aquatic organisms.

Antioxidant defences play a central role in cell protection against a wide variety of environmental stressors, their variations being thus frequently studied to reveal oxidative stress conditions in fish. The Nrf2-Keap1 pathway is among the main mechanisms of transcriptional regulation in mammalians, but its involvement in modulation of antioxidant system of aquatic organisms is still largely unexplored. The present study focused on the identification of Nrf2 and Keap1 in the European eel Anguilla anguilla using liver slices as an in vitro model during an oxidative challenge. The mRNA levels of Nrf2, Keap1 and typical Nrf2 target genes (catalase, glutathione peroxidase 1 and glutathione S-transferase pi) were analyzed at different H2O2 exposure times to investigate the time course activation of these molecular responses. Obtained results showed a coordinated transcriptional regulation of CAT, GPx1 and GSTpi, also suggesting that Nrf2 de novo synthesis is required for the protracted induction of such antioxidant genes. Further, Keap1 variations would support its role in switching off these molecular responses, providing novel insight on the importance of the Nrf2-Keap1 pathway in the regulation of antioxidant genes in marine species.

Oxidative pathways of chemical toxicity and oxidative stress biomarkers in marine organisms.

The antioxidant system of marine organisms consists of low molecular weight scavengers and antioxidant enzymes which interact in a sophisticated network. Environmental pollutants can unbalance this system through closely related mechanisms, indirect relationships and cascade effects acting from pre-transcriptional to catalytic levels. Chemically-mediated pathways have the potential to greatly enhance intracellular formation of reactive oxygen species (ROS); at the same time, excessive levels of oxyradicals down-regulate xenobiotics metabolism, with important environmental implications for organisms exposed to chemical mixtures. Interactions between different classes of chemicals, generation of ROS and onset of oxidative stress conditions are partly modulated by changes in levels and functions of redox-sensitive signaling proteins and transcription factors. The Nrf2-Keap1 pathway still remains largely unexplored in marine organisms, despite the elevated degree of identity and similarity with homolog transcripts and proteins from different species. Recent evidences on transcriptional up-regulation of this system are consistent with the capability to provide a prolonged expression of ARE-regulated cytoprotective genes, and to efficiently switch off this mechanism when oxidative pressure decreases. Although gene expression and catalytic activities of antioxidants are often measured as alternative biomarkers in monitoring biological effects of contaminants, conflicting results between molecular and biochemical responses are quite frequent. The links between effects occurring at various intracellular levels can be masked by non-genomic processes affecting mRNA stability and protein turnover, different timing for transcriptional and translational mechanisms, metabolic capability of tissues, post-transcriptional modifications of proteins, bi-phasic responses of antioxidant enzymes and interactions occurring in chemical mixtures. In this respect, caution should be taken in monitoring studies where mRNA levels of antioxidants could represent a snapshot of cell activity at a given time, not an effective endpoint of environmental pollutants.

Transcriptional and catalytic responses of antioxidant and biotransformation pathways in mussels, Mytilus galloprovincialis, exposed to chemical mixtures.

Antioxidant and biotransformation pathways are widely studied in marine organisms exposed to environmental stressors. However, mechanisms of responses and links between different intracellular levels are not always easy to elucidate and conflicting results are frequently observed between molecular and enzymatic data. In this study, transcriptional and catalytic responses of antioxidant and biotransformation parameters were analyzed after a 4-week exposure of a marine invertebrate, Mytilus galloprovincialis, to chemical mixtures from low polluted and highly polluted sediments. A significant, dose-dependent bioaccumulation was observed for polycyclic aromatic hydrocarbons, especially low molecular weight compounds. Among antioxidant defences, catalase and glutathione peroxidases did not exhibit variations in enzymatic activity, while the corresponding gene transcriptions were up- and down-regulated, respectively; unchanged mRNA levels of superoxide dismutase confirmed the non-synchronous pathways of variations for such antioxidants. Biotransformation responses also revealed inconsistent trends between transcriptional and catalytic variations of glutathione S-transferases, and a significant increase in mRNA levels for cytochrome P450 3A1. The overall results indicated that transcriptional responses might be sensitive but do not necessarily correspond to functional changes, being more useful as "exposure" rather than "effect" biomarkers. Data on gene transcription and catalytic activities should be carefully interpreted when assessing the impact of chemical pollutants and additional studies are needed on modulation of post-transcriptional mechanisms by environmental stressors.