ASSESSING HUMAN EXPOSURES WITH BIOLOGICAL MARKERS - PowerPoint PPT Presentation

Loading...

PPT – ASSESSING HUMAN EXPOSURES WITH BIOLOGICAL MARKERS PowerPoint presentation | free to view - id: 227503-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

ASSESSING HUMAN EXPOSURES WITH BIOLOGICAL MARKERS

Description:

Hemoglobin and albumin are two proteins available for use in exposure assessment. ... half-life of lead in bone is approximately 10-40 years (Rabinowitz, 1991) ... – PowerPoint PPT presentation

Number of Views:36
Avg rating:3.0/5.0
Slides: 26
Provided by: dvo8
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: ASSESSING HUMAN EXPOSURES WITH BIOLOGICAL MARKERS


1
ASSESSING HUMAN EXPOSURES WITH BIOLOGICAL MARKERS
  • Conrad D. Volz, DrPH, MPH
  • Department of Environmental and Occupational
    Health, Graduate School of Public Health,
    University of Pittsburgh
  • Co-Director Exposure Assessment, Center for
    Environmental Oncology, University of Pittsburgh
    Cancer Institute
  • Scientific Director, Center for Healthy
    Environments and Communities
  • Lecture 20

2
General
  • Biological markers represent events or changes in
    human biological systems as a result of exposure
    or disease (US NRC, 1991b).
  • They are classified as markers of exposure,
    effect, and susceptibility and are considered to
    represent events along a theoretical continuum
    from causal exposure to resulting health outcome
    (US NRC, 1987 Schulte, 1989). See Hatch papers
    for theoretical description.

Major Text WHO Exposure Assessment
3
General
  • Biological markers represent a means to monitor
    environmental exposure by characterizing an
    individual's total dose of a contaminant from all
    sources of exposure. Remember that dose is mass
    of contaminant over some time.
  • The main advantage of this strategy is in
    evaluation of an individual's total exposure
    using a measure which integrates over all
    exposure sources and is influenced by human
    behavior.
  • Biological markers are believed to be more
    predictive of health effects than external
    measures of exposure.
  • Biological markers address important exposure
    assessment needs
  • characterizing an individual's or a
    population's exposure
  • generating population distributions of dose
  • identifying the environmental and demographic
    determinants of exposure.

4
Disadvantages of Biological Monitoring
  • The main disadvantage of biological markers is
    the difficulty in characterizing the individual
    sources which contribute to the subject's total
    exposure.
  • When developing and utilizing biological markers,
    understanding the toxicokinetics of the
    contaminant in the system is crucial to
    characterize the biological variability and to
    determine whether the biological marker is valid
    for exposure assessment purposes at the
    concentration of interest.
  • There is an ethical concern in relying on
    biomonitoring especially in known occupational
    exposure assessment.

5
What is a Biological Marker of Exposure? A
biological marker of exposure is defined as a
xenobiotic substance or its metabolite(s) or the
product of an interaction between a xenobiotic
agent and some target molecule(s) or cell(s) that
is measured within a compartment of an organism
(US NRC, 1989 IPCS, 1993)-after exposure to the
xenobiotic contaminant or a physical exposure,
such as ionizing radiation.
6
Biological Markers of Effect and Susceptibility
  • Biological markers of effect are measurable
    biochemical, physiological, behavioral or other
    alterations within an organism that, depending
    upon the magnitude, can be recognized as
    associated with an established or possible health
    impairment or disease (IPCS, 1993).
  • Biological markers of susceptibility are
    indicators of inherent or acquired abilities of
    an organism to respond to the challenge of
    exposure to a specific xenobiotic substance
    (IPCS, 1993).
  • Example-Different genotypes of BCHE-K, PON-192,
    and PON-55 may be related to the severity of
    adverse health effects of organophosphorus
    pesticide exposure. (Carboxylic esterase and its
    associations with long-term effects of
    organophosphorus pesticides. Biomed Environ Sci.
    2007 Aug20(4)284-90. )

7
Situations which are bestsuited for biological
monitoring.
  • Ideally, a biological marker of exposure should
    be
  • 1. Chemical-specific.
  • 2. Detectable in trace quantities.
  • 3. Available by non-invasive techniques.
  • Inexpensive to assay.
  • Relate consistently and quantitatively to the
    extent of exposure and ideally also integrate the
    exposure over time (Bond et al., 1992).
  • Currently there are very few biological markers
    that possess all these characteristics.

8
Sampling of Blood
  • Blood is frequently used for biological
    monitoring, especially in clinical settings such
    as occupational medicine.
  • Blood can integrate all sources of exposure,
    including internal sources, and provide an
    indication of current internal dose.
  • Since blood transports all agents throughout the
    organism, it represents an opportunity to sample
    all types of contaminants, such as gases,
    solvents, metals and fat-soluble compounds.

9
Components of Blood Available for Sampling
  • Whole blood consists of all the blood
    components and is preferable when the
    distribution of the analyte between plasma and
    cellular elements is unknown (Que Hee, 1993).
  • Red blood cells make up a large portion of
    blood and their primary role is to transport
    oxygen via hemoglobin throughout the body. Mature
    red blood cells contain no nucleus and therefore
    no DNA, and have a 120-day lifetime. Chemicals
    that interact with hemoglobin, such as carbon
    monoxide, are found in red blood cells.

10
Components of Blood Available for Sampling
Continued
  • Numerous types of white blood cells are present
    in blood. These cells have a half-life ranging
    from 18-20 days to decades (Carrano Natarajan,
    1988).
  • White blood cells are circulating cells that have
  • DNA can itself be altered or its expression can
    be changed as a result of exposure to a genotoxic
    agent, so white blood cell DNA may be used for
    biomarkers of exposure to genotoxic agents
    (Carrano Natarajan, 1988 Kelsey, 1990).
    Interpretation of genotoxic response is
    complicated because DNA damage can result in
    either cell death or removal of the marker by DNA
    repair, or may alter cell functions (Perera,
    1987). Regardless of this, correlations have been
    seen between environmental exposures and DNA
    adducts.
  • A DNA adduct is an abnormal section of DNA which
    is bonded to a contaminant. DNA adducts are used
    as biological markers of exposure. Acetaldehyde
    DNA adducts are common in cigarette smokers.

11
Components of Blood Available for Sampling
Continued
  • Plasma and serum represent the non-cellular
    component of blood.
  • Plasma is a straw-coloured aqueous solution of
    electrolytes, non-electrolytes and macromolecules
    (including clotting factors).
  • Serum is plasma without the clotting factors
    (Que Hee, 1993).
  • Plasma represents a component of whole blood
    (approximately 60), and it may contain the most
    biologically active fraction of blood borne
    contaminants, since plasma is in more immediate
    contact with tissues (Silbergeld, 1993). Plasma
    can be used for analysis of lipophilic chemicals,
    thereby avoiding the need for fat sampling.

12
Components of Blood Available for Sampling
  • Blood proteins can be sensitive monitoring tools
    for chemicals that bind to macromolecules
    including DNA (Osterman-Golkar et al., 1976 Bond
    et al., 1992).
  • Protein adducts, unlike DNA adducts, are not
    repaired and may prove to be a useful dosimeter
    of mutagen exposure (Grassman Haas, 1993 Que
    Hee, 1993).
  • Hemoglobin and albumin are two proteins available
    for use in exposure assessment. Hemoglobin is
    located in red blood cells in high concentration
    and has the half-life of red blood cells
    (120days) albumin is present in serum and has a
    half-life of 21 days.
  • Because of their differing biological half-lives,
    these proteins can be used to investigate the
    timing of exposure.

13
Sampling of Urine
  • The concentrations of compounds found in urine
    usually reflect time-weighted averages in plasma
    during collection and storage in the bladder (Que
    Hee, 1993).
  • The presence of a contaminant or its metabolite
    in urine generally represents recent exposure,
    though in some cases it may represent release
    from storage within the body (Lauwerys, 1983).
    (Release of lipopylic chemicals from adipose
    tissue during weight reduction is an example of
    release from body storage.)
  • Urine can be analysed for metabolites of organic
    chemicals (e.g., benzene and styrene), metals
    (e.g., arsenic and mercury) and pesticides as
    well as for mutagenic potential (Lauwerys, 1983
    Baselt, 1988 Que Hee, 1993).
  • Since collection of urine samples is
    non-invasive, some investigators feel that, when
    validated, urine may be a better sampling medium
    than blood for monitoring (Smith Suk, 1994).

14
Types of Urine Sampling, Advantages and
Disadvantages
  • Spot urine samples are relatively easy to
    collect but there may be significant variability
    with respect to exposure prediction as a result
    of metabolism, liquid consumption and kidney
    function.
  • First morning void samples have less
    variability since they are more concentrated than
    spot samples, but require motivated subjects to
    collect the samples.
  • Twenty-four hour urine samples control much of
    the intraindividual variability but require
    highly motivated subjects in order to collect
    useful samples (Baselt, 1988).
  • To make the results of urine monitoring
    comparable between individuals, analytical
    results are frequently standardized to creatinine
    concentration or specific weight. Standardization
    reduces some of the variability of body size and
    urinary output (Lauwerys).

15
Example Atrazine Metabolite from UrineChem Res
Toxicol. 1993 Jan-Feb6(1)107-16.
  • Enzyme-linked immunosorbent assays (ELISAs) are
    reported useful for the detection of atrazine and
    its principle metabolite in human urine. The
    ELISAs can be used with crude urine or following
    extraction and partial purification.
  • GC, MS, and HPLC techniques can be used to
    confirm and complement the ELISA methods for
    qualitative and quantitative detection of urinary
    metabolites.
  • A series of samples from workers applying this
    herbicide confirmed a mercapturic acid conjugate
    of atrazine as a major urinary metabolite. The
    mercapturate was found in concentrations at least
    10 times that of any of the N-dealkylated
    products or the parent compound.
  • Atrazine mercapturic acid was isolated from urine
    using affinity extraction based upon a polyclonal
    antibody for hydroxy-s-triazines and yielded
    products sufficiently pure for structure
    confirmation by MS/MS.
  • In a pilot study monitoring applicators, a
    relationship between cumulative dermal and
    inhalation exposure and total amount of atrazine
    equivalents excreted over a 10-day period was
    observed. On the basis of these data, we propose
    that an ELISA for the mercapturate of atrazine
    could be developed as a useful marker of
    exposure.
  • Lucas AD, Jones AD, Goodrow MH, Saiz SG, Blewett
    C, Seiber JN, Hammock BD., Department of
    Entomology, University of California, Davis 95616.

16
Exhaled Breath
  • Breath analysis is useful for assessing recent
    exposure to gases (e.g., carbon monoxide) and
    organic vapors and solvents (e.g., acetone and
    toluene).

17
Types of Exhaled Breath Samples
  • Exhaled breath can be a mixture of inhaled and
    exhaled air. If the exhaled biological marker is
    not present in inhaled air, then exhaled breath
    analysis is an effective means to measure
    internal exposure. For example, when alcohol has
    an internal source only (i.e., ingestion) a mixed
    breath sample is appropriate.
  • Alveolar air provides a measure of the air that
    is in equilibrium with the blood in the deep lung
    (Bond et al., 1992). For analytes present in
    inhaled air, it is necessary to collect an
    alveolar air sample.

18
Saliva Sampling
  • Glands at four locations in the mouth produce
    saliva the secretion rate varies at each
    location. Chemicals enter saliva via passive
    diffusion from plasma. Therefore, saliva may
    become a useful tool to non-invasively
    characterize plasma levels of contaminants
    (Silbergeld, 1993).
  • Social science research has used saliva sampling
    because of its ease of collection and storage
    (Dabbs, 1991, 1993). Contaminants found in saliva
    include cotinine, drugs, metals, organic
    solvents, pesticides and steroid hormones (Tomita
    Nishimura, 1982 Nigg Wade, 1992 Silbergeld,
    1993).

19
Sampling Keratinized Tissues (hair and nails)
  • Keratinized tissues, primarily hair and toenails,
    are practical sampling media for evaluation of
    past exposure to metals (Bencko et al., 1986
    Bencko, 1991 Subramanian, 1991 Kemper, 1993,
    Bencko, 1995).
  • Toenails are usually the medium of choice because
    these media
  • - integrate exposures over a period of
    months.
  • -contain relatively larger concentrations of
    trace elements than blood or urine and
  • -are easy to collect, store and transport
    (Garland et al., 1993 Kemper, 1993).

20
Sampling of Hair
  • Hair can be used to study exposure to
    environmental tobacco smoke (ETS).
  • The German Environmental Survey (Krause et al.,
    1992) it was concluded that in large population
    studies nicotine and continine in urine as well
    as nicotine in hair are useful indicators of
    exposure for different levels of active and
    passive smoking.
  • Continine and nicotine concentrations in hair
    have also been used to study fetal exposure by
    maternal smoking (Klein et al., 1993).
  • Hair has also successfully been used in studies
    evaluating exposure to organic mercury (Suzuki et
    al., 1989) or PCB (Que Hee, 1993).
  • Hair grows approximately 1 cm/30 days (Que Hee,
    1993) and can be evaluated along the shaft to
    provide a profile of exposure over time. Since
    growth rates of hair differ based on body
    location, standardization of sampling location is
    crucial.

21
Ossified TissueSampling-Teeth and Bones
  • Teeth constitute a unique medium for assessment
    of past exposure. Depending on the tooth type and
    part of the tooth, one can reconstruct early
    childhood exposures to bone-seeking elements,
    such as lead (Rabinowitz MB, Leviton A,
    Bellinger DC (1989) Blood lead tooth lead
    relationship among Boston children. Bull Environ
    Contam Toxicol,43 485-492.).
  • Electron Paramagnetic Resonance (EPR) tooth
    dosimetry has been used to validate dose models
    of acute and chronic radiation exposure.
    (Retrospective assessment of radiation exposure
    using biological dosimetry chromosome painting,
    electron paramagnetic resonance and the
    glycophorin a mutation assay. Kleinerman RA,
    Romanyukha AA, Schauer DA, Tucker JD. Radiat Res.
    2006 Jul166(1 Pt 2)287-302. )

22
Bone Sampling
  • Bone represents both past exposure to
    bone-seeking elements and is a source for future
    internal exposure to these elements. The
    concentrations of elements in bone represent
    long-term exposure and storage of contaminants.
    For example, the half-life of lead in bone is
    approximately 10-40 years (Rabinowitz, 1991).
  • Although numerous elements can be detected in
    bone tissue using destructive analyses such as
    atomic absorption spectroscopy (AAS), in vivo
    measurement of environmental contaminants in bone
    has been limited to lead (e.g., Somervaille et
    al., 1988 Hoppin et al., 1995).
  • Lead concentration in bone can be analyzed
    non-invasively using a technique known as X-ray
    fluorescence (XRF) (Hu et al., 1995).
  • Epidemiological studies have established that
    bone-seeking a-particle-emitting radionuclides
    are effective sarcomagenic agents, increasing
    tumor incidence by up to 1000-fold in exposed
    individuals (H. S. Martland and R. E. Humphries,
    Osteogenic sarcoma in dial painters using
    luminous paint. Arch. Pathol. 7, 406 (1929) and
    C. Mays and H. Spiess, Bone sarcomas in patients
    given 224Ra. In Radiation Carcinogenesis
    Epidemiology and Biological Significance (J. B.
    Fraumeni, Ed.), pp 241252. Raven Press, New
    York, 1982.)

23
Breast Milk Sampling
  • Breast milk sampling represents a non-invasive
    method to estimate body burden of contaminants in
    adipose tissue. The correlation between
    contaminant concentrations in the lipid phase of
    milk and adipose tissue is good (Sim McNeil,
    1992).
  • Environmental studies have used breast milk to
    evaluate past exposure to lipophilic chemicals
    (e.g., pesticides and PCBs) and metals (WHO,
    1996b) and to examine potential exposures for
    breast-feeding infants (Niessen et al., 1984
    Davies Mes, 1987 Sikorski et al., 1990 Sim
    McNeil, 1992).
  • Organic chemicals found in breast milk have high
    lipid solubility, resistance to physical
    degradation or biological metabolism and slow or
    absent excretion rates (Rogan et al., 1980).
    Breast milk represents a major route of excretion
    of lipophilic chemicals for lactating women
    (Rogan et al., 1980 Sim McNeil, 1992).
  • Concentrations of chemicals in breast milk are a
    function of parity, age, body mass, time of
    sampling, nutritional status, lactation period
    and fat content of milk (Rogan et al., 1986 Sim
    McNeil, 1992). Breast milk results are
    generally standardized to milk fat levels.

24
Sampling Adipose Tissue
  • Exposure assessment studies using adipose tissue
    have been limited primarily to ecological studies
    comparing fat from cadavers or surgical specimens
    to general pollution levels.
  • Adipose tissue represents a long-term reservoir
    of lipophilic compounds that the body slowly
    metabolizes and may release into the bloodstream.
  • Unfortunately there is no non-invasive manner to
    sample fat stores directly, and many subjects see
    fat sampling as exceedingly invasive.
  • WHO Human Exposure Assessment

25
Sampling Feces
  • Most often used for bacteriological exposure
    sampling.
  • Feces are a highly fat-soluble medium that
    provides information on compounds of
    high-molecular weight that exit the body via
    biliary excretion (metabolism by liver and
    excretion via bile) and on unabsorbed chemicals
    that enter the body via ingestion.

Main Text for Biomonitoring Material
Extraction-WHO Exposure Assessment
About PowerShow.com