Working Package 15: Neurodevelopmental and neurodegenerative disorders

Working Package 15: Neurodevelopmental and neurodegenerative disorders

PARTNERS: UPMC, AUTH, USTUTT, JSI, ISS, LMU, NIOM, VTT, UM, TNO, FERA, CSIC, OIKON, URV, KCL, NIPH, SDU
LEADER: ISS
START MONTH: 1
END MONTH: 48

Objectives:

The overall aim of this WP is to quantify the link between  exposures to metals,  pesticides  and chemical compounds  with endocrine  disrupting activity (i.e. polyhalogenated aromatic hydrocarbons,  phthalates and PCB/PBDE) and neurodevelopmental disorders, by applying the HEALS methodological framework. Specific objectives are to:

  • Perform data analysis, harmonisation and identification of major gaps in knowledge using the cohorts available in the HEALS consortium  that focus on environmental exposures and their effects  on neurodevelopment;
  • Assess  the spatial relationships between environmental exposure  and health data from the different cohorts;
  • Assess  internal exposure,  investigate mechanistic  hypotheses  (through omics and other methodologies from Stream 2) and identify robust biomarkers  of exposure,  effect and susceptibility;
  • Apply the HEALS methodology  to validate a model strategy for establishment  of causal links between exposure and health effects as for neurodevelopmental disorders  in general population and twins studies.

 


Description of work and role of partners:

Concern is increasing on the impact that prolonged exposure  to apparently non-toxic doses of neurotoxicants during early development may have on children’s health, possibly representing a major risk factor for neurodevelopmental disorders (NDs). These conditions range from clinical overt cognitive and behavioural abnormalities, such as Autism Spectrum Disorders (ASD) and Attention Deficit Hyperactivity  Disorders (ADHD), to subtle neuropsychological  deficits. The aetiology of most of NDs is unknown,  but there is general agreement that they result from complex  interaction between multiple genes conferring vulnerability (i.e. polymorphisms or defect in genes involved in metabolism of environmental toxins) and adverse environmental factors. Exposures, whether chemical, physical, or microbiological, may act directly upon neural cells, interfering  with critical processes of proliferation, migration, differentiation, synaptogenesis,  programmed apoptosis and myelination, or may affect the expression  of genes that regulate  such embryonic/fetal/infant processes. They operate during sensitive periods of gestation by disrupting endocrine  systems and altering the hormonal milieu necessary for fetal brain development. Moreover,  environmental exposures could contribute to a dysregulated immune system that interacts  at the molecular  level with glial cells and astrocytes, creating a neuroinflammatory condition.

Several epidemiological studies  mainly carried out in the USA have identified a number of chemical compounds that might affect neuropsychological development in exposed infants.They include heavy metals, organophosphate pesticides, organohalogens, and organic compounds  with endocrine  disrupting activity. In vivo and in vitro experimental studies have confirmed that many of these compounds have significant developmental neurotoxicity at low, environmentally relevant doses, but so far experimental data need to be confirmed in focused clinical studies. Large prospective studies beginning before or during early pregnancy are needed  to assess  the relative importance of parental and childhood exposure.  In addition large case-control studies may help to assess  the role of environmental exposure  and their interaction with genetic vulnerability in relatively uncommon outcomes  such as ASD: in the USA, federally-funded trials are currently carried out to evaluate  the genetic and environmental  contributions to ASD etiology taking into account  environmental exposure,  internal exposure,  genetic background and biomarkers  potentially associated to CNS  functioning (beincharge.ucdavis.edu).

The review of existing  literature will help identifying gaps in the knowledge of link between  exposures to metals, pesticides and chemical  compounds  with endocrine  disrupting activity and neurodevelopmental disorders. Additional  inputs that will be of help also in the implementation of WP15 will result  from the European commission-funded  project DENAMIC  “Developmental Neurotoxicity Assessment of Mixtures in Children” that is investigating neurotoxic effects of low-concentration mixtures of pesticides and a number of common environmental pollutants in children on (subclinical) effects on learning (cognitive skills) and developmental disorders in children (e.g. ADHD, autism spectrum disorders and anxiety disorders). Of interest for HEALS will be the results of two distinct DENAMIC  pillars:

– The first pillar involves  hazard characterisation  for neurotoxic chemicals and (environmentally relevant) mixtures thereof. Novel tools, testing methods and procedures  for screening  (mixtures of) chemicals for neurotoxicity are developed,  together with improved assessment methods for exposure  and effects.

– In the second pillar (exposure/epidemiology),  perinatal and early-childhood  exposure  will be studied in maternal urine and cord blood, as well as breast milk and urine of the child. In the epidemiological  part these developed integrated tools are tested in a tailor made cohort of mother/child pairs focusing on learning and developmental disorders,  including the onset of ADHD. In both the experimental  and epidemiological  part of DENAMIC, biomarkers  for developmental  neurotoxicity will be developed and/or validated by using innovative biotechnology tools.

An important aspect of DENAMIC  that will be of utility in HEALS is the development  of biomarkers for (developmental)  neurotoxicity in animal models using (epi-)genomics,  proteomics and metabolomics as HEALS is not going to conduct  ex vivo and in vivo studies in mouse and zebra-fishes. The links with DENAMIC  will be established  through collaborations, exchanges, publications and other initiatives including common  initiatives like a workshop. The fact that two of HEALS partners are also DENAMIC  partners will help in liaising.

In HEALS, the neurodevelopmental  toxicity of metals/metalloids, pesticides and organic compounds with EDC activity  will be studied on mother-child cohorts where both exposure  (fetal and/or neonatal) and neuropsychological outcomes have been measured. They include the EDEN  cohort (France, n= 1,200), the ReproPL cohort (Poland, n = 400), the PHIME cohort (Slovenia and Croatia, n = 675), and the JSI  cohort (Slovenia, n = 600) for a total of 2,875 children in whom exposure  assessments have been or will be performed. Exposure assessment will include biomarkers  of exposure as well as exposure  to environmental pollutants (e.g. flame retardants, plasticizers,  perfluorinated compounds,  metals) or their sources that are known neurotoxicants. As both pesticides  as well as some of these environmental contaminants may very well have a similar mechanism in common, possible mixture effects via human exposure  will also be included in HEALS. Neurodevelopmental disorders and related environmental stressors will be also investigated in pre-existing twins registries  when appropriated data will be available.

We will start with a review of the cohorts,  to identify significant gaps in knowledge with reference  to the framework established in Stream 1 and with methodologies  and criteria developed in Stream 3 and 4. On this basis, we will then select one or more cohorts in order to build a model strategy  to clarify the link between  the chemicals in study and the increased risk of neurodevelopmental disorders in general population. The results of large biomonitoring studies  performed in children  will be also consulted  to obtain EU reference values for the compounds in study. In this work, as previously said, results  from the EU DENAMIC  project  will be taken into account.

Methods perfected in the previous  WPs (-omics; multi-media, pharmacokinetics  and systems biology modelling) will be used to define mechanistic associations  between environmental stressors and adverse effects on neuropsychological functions, as assessed  by validated test batteries (mental and psychomotor scales).

The work in WP15 will be decomposed in the following four tasks:

 


Task 15.1 Data analysis, harmonisation and identification of major gaps in knowledge (ISS, JSI, UPMC, NIOM, FERA, CSIC, URV)

Revision of the data available  in the cohorts, considering strengths and weaknesses of each epidemiological study (sample size, quality of exposure assessment, control of confounders,  methods to evaluate  outcomes, etc.) also according  to the recent  by White et al. that provides  an up-to-date strategy  for the assessment of brain function in longitudinal cohort studies  of children.

Harmonisation in descriptions and formats  will be necessary, while accounting  for the ethical aspects of sample and data sharing according  to informed consent,  local ethical approval and the governance  structures of each HEALS partner. Identification of major gaps in knowledge and acquisition of missing data (i.e. georeferencing of the place of residence if not performed  yet) will be carried  out for all cohort participants.

 


Task 15.2 External exposure assessment (USTUTT, VTT, TNO, FERA, CSIC, OIKON, URV, KCL, NIPH, SDU, AUTH, UPMC)

The spatial relationships between environmental and health data will be analysed. In close connection with Stream 3 partners,  the availability of time-related and cumulative environmental exposures (air, soil, water) to metals/pesticides/EDC will be checked. If necessary (time mismatch, coarse spatial scale, etc.), new modelling will be envisaged.  Wherever  they exist, reference  to national and/or regional registries of neurodevelopmental disorders (autism, ADHD, learning disabilities) may help to establish  a link between prevalence  of specific disorders and exposure data. The organisation (fusion/integration) and easy updating of these complex space/time environmental and health databases will be made possible  through the HEALS database platform developed in Stream 4.

 


Task 15.3 Internal exposure assessment (ISS, AUTH, TNO, KCL, SDU, NIPH, URV, UPMV)

Critical data analysis and -omics analyses in existing samples. With the support of Stream 2 partners, available biological samples will be selected  for omics and biomarker analyses where possible for those cohorts presenting the most robust measures of health outcome (or: for those where testing is still on-going  or has to be replicated, as to obtain the most reliable indication of children’s recent exposure  profile). Attempts will also be made to reconstruct exposure  concentration through pharmacokinetic  modelling (reverse dosimetry), to understand the effects of mixtures in in vitro and possibly in vivo models, and to identify biomarkers  of effects linked to nervous  system dysfunction (DNA methylation, metabolomic, lipidomic). Levels of internal exposure  reported in the examined  cohorts  will be compared  with existing data inventories as well as with the results of previous  biomonitoring studies  performed in EU for the chemicals in study. For each of the chemicals to which mothers  and their children  are exposed, exposure  concentration  will be reconstructed using PBBK  models using the method developed in WP6 for better estimation  of toxicant levels at critical brain sites. Analysis of cohort data should identify exposure  biomarkers  able to capture the temporal dimension  of the exposure (e.g., prenatal versus postnatal and/or acute versus chronic). Biomarkers of effects (clinical parameters, -omics, etc.) indicative of significant neurobehavioural alterations may help to bridge the gap between internal dose and altered structure/function. The problem of co-exposures will be also properly addressed in data re-analysis  and as much information as possible  will be extracted to derive hypothesis  as for co-exposures and synergic/multiple health effects. Finally, cohorts where both measures of gene polymorphisms and environmental factors have been already  obtained for a high proportion of study subjects, such as ReproPl and PHIME (with similar clinical parameters  and outcomes  obtained) will allow assessment of impact of genetic susceptibility in vulnerability to environmental  risk.

 

 


Task 15.4 Application of the HEALS methodology to population studies (ISS, UPMC, KCL, NIPH, SDU, OIKON, CSIC, URV, FERA, UM, NIOM, AUTH, USTUTT)

Multi-level multi-exposure analyses will be carried  out to model the relative influence of internal and external exposures on neuropsychological outcome. Thus, we will draw upon the two exposome  components  (internal and external exposures) to predict biomarker  levels from environmental and domestic exposure sources, and to establish a causal link between biomarkers  and disease risk. The resulting association  will be applied in the pilot EXHES study performed in WP17.