Toxicology Research
Mission: To protect and improve the health
of the people of Canada through toxicology Research conducted
to ensure a safe food supply.
Objective: To utilize toxicology research
methods to identify and characterize food based human health
hazards.
The Toxicology Research Division is responsible for the
identification and investigation of potential health hazards
associated with chemical contaminants, including those of
environmental origin, agricultural chemicals, natural food
toxicants and constituents, and food additives. Research is
carried out on the carcinogenic, mutagenic, reproductive,
neurotoxic and other potentially harmful effects of these
chemicals, including alterations to the immune system.
The Toxicology Research Division is located in the Sir
Frederick Banting building, Tunney's Pasture, Ottawa,
Ontario Canada. KlA OL2 (postal Locator 2202Dl). There is a
staff of 37 research scientists, biologists and technicians
and it is part of the Bureau of Chemical Safety, Food
Directorate, Health Protection Branch.
Acting Division Chief: Rekha Mehta, Ph.D.
Tel: (613) 957-0938 / 0987
Rekha_Mehta@hc-sc.gc.ca
Toxicology Research Division Division Chief, Toxicology
Research Division
Frank Iverson Ph.D.
Research Manager
Tel. 613-957-0987
Research Interests:
Toxicology and mechanism of action relating to : cyclic
halogenated hydrocarbon food contaminants inluding PCB,
Dioxins, Furans; natural toxins including shellfish toxins
(domoic acid and okadaic acid); mycotoxins such as vomitoxin
; antioxidants, including synthetic phenols such as BHA,
antioxidant mechanism of action, biologically based risk
assessment, carcinogenicity.
General Toxicology Section
The section undertakes the design, conduct and evaluation of
toxicological studies with food additives, food and
environmental contaminants, and pesticides which find their
way into human food sources. Such studies include a
multi-disciplinary team of researchers who employee a variety
of laboratory animal species in an attempt to find
toxicological endpoints which are relevant to human health
(i.e. reproduction, immunological effects, etc).
Additionally, such studies must conform with the requirements
of Good Laboratory Practices to ensure acceptance by
international regulatory agencies. Expertise in the design
and conduct of acute, sub-chronic and chronic-carcinogenicity
studies using such chemicals as the food additive saccharin,
the pesticide/environmental pollutant hexachlorobenzene, the
mycotoxin commonly known as vomitoxin, the banned pesticide
toxaphene as well as the environmental pollutant PCB
(polychlorinated biphenyls).
Reproduction and Development
Reproductive function - with emphasis on male reproduction.
Endocrine disruption - effects of exposure to organochlorine
food contaminants in utero and during lactation on the
development of the male reproductive system. Mechanism of
action of food contaminants on the male reproductive system -
especially with respect to disruption of androgen
biosynthesis and metabolism and also with sperm function.
Expertise includes Enzymology:- radiometric assays of
steroidogenic enzymes in male and female reproductive tissues
and in male and female liver; Animal handling; Tissue
subcellular fractionation; Isotope handling; Incubations;
Organic extraction; Chromatography; Scintillation
spectrometry; Radioautography; Recrystallization; Kinetic
analysis
Molecular Biology:- Determination of mechanism of action of
food contaminants: RNA extraction. Gel chromatography; RT-PCR
Cell Biology:- to examine the effects of food contaminants on
androgen receptor activation and inactivation. Luminometry
Immunology/Immunotoxicology
Development, maintenance and implementation of the
Immunotoxicology Program within the Food Directorate and the
design of experimental protocols and execution of
immunotoxicity studies to support regulation. The
Immunotoxicology Program includes several internationally
validated techniques. These are applied to the study of
potential adverse effects of chemicals on the immune system
of humans, non-human primates and rodents. The program
provides a novel approach for the evaluation of
chemical-induced immunotoxicity of food additives as well as
environmental chemicals which inadvertetly enter the food
chain. Examples of chemicals which have been investigated to
date include: environmental contaminants such as PCBs,
toxaphene and chlordane; mycotoxins such as deoxynivalenol
and fumonisins; and metals such as lead and mercury. The
Immunotoxicology Program includes techniques for the
quantitative and functional assessment of effects of
chemicals on specific humoral and cellular aspects of the
immune system as well as on non-specific parameters of the
immune system. The program also includes flow cytometry and
tissue culture capabilities. Techniques routinely applied to
research projects include: quantification of T lymphocytes
and their subsets, B lymphocytes, natural killer cells, and
the phagocytic mononuclear cells in peripheral blood-,
spleen- or thymus- derived mononuclear cell preparations
using flow cytometry; evaluation of humoral immunity by
immunizing experimental animals with T- and B- dependent
antigens and by determining antigen-specific antibodies by
the plaque forming cell assay, ELISA, hemagglutination or
complement-dependent lysis techniques; evaluation of
cell-mediated immunity using the mitogen-induced lymphocyte
proliferation technique (tritiated thymidine incorporation)
and the one-way mixed lymphocyte culture technique;
evaluation of the delayed-type hypersensitivity response
using sensitization and challenge with dinitrochlorobenzene
(non-human primates), and sensitization and challenge with
oxazolone in rats and mice; evaluation of non-specific
immunity using flow cytometric analysis of the phagocytic
activity of monocytes (peripheral blood) and macrophages
(peritoneal exudate cells); evaluation of calcium
mobilization using flow cytometric techniques; and evaluation
of resistance to bacteria using the Listeria
monocytogenes infectivity model. The Immunotoxicology
Program is constantly updated and new methods are adapted
and/or developed to adequately serve the needs of the
Program. Standardization and harmonization of
immunotoxicology methods at the National and International
levels are two ongoing processes within the Immunotoxicology
Program.
Genotoxicity and Carcinogenesis
Section
The development of cellular and molecular markers for the
early detection of toxicological, genotoxic and carcinogenic
effects of natural and synthetic food additives/contaminants,
and the modulation of such adverse effects by nutrients.
Using animal models, some of these biomarkers are currently
being applied for cancer risk assessment of mycotoxins and
pesticide residues at various organ sites such as the liver,
kidney, mammary gland, esophagus and colon. The ultimate
application of these and other appropriate biomarkers in
molecular epidemiology studies in order to enhance human
cancer risk assessment and primary prevention strategies for
food contaminants. Methodology and techniques employed in the
lab include: Subcellular and macromolecular (DNA, RNA,
protein) tissue fractionation (liver, esophagus, kidney,
stomach, colon, intestine); Hepatocyte isolation; Surgical
procedures (hepatectomy, organ perfusion); HPLC ,Thin layer
chromatography, Gas chromatography; isotope analysis, enzyme
kinetics, fluorimetry spectrophotometry; serum enzymes
Histochemistry - (gamma-glutamyl transpeptidase,
Silver-staining nucleolar organiser
regions)Immunohistochemistry -(glutathione S-transferase
alpha, µ and pi,_Oncogene proteins, Cyclins,
Proliferating cell nuclear antigen, Apoptosis) Flow cytometry
-(cell cycle analysis Glutathione S-transferase alpha, µ
and pi_,Oncogene proteins) Autoradiography -[3 H]-
thymidine to determine cell proliferation; DNA adduct
analysis - (Aflatoxin B1 -DNA adducts,
8-hydroxydeoxyguanosine DNA methylation - (Restriction enzyme
analysis of 5-methylcytosine.) Tissue levels of
S-adenosyl-L-methionine, 5'-methylthioadenosine and
S-adenosylhomocysteine ELISA - Oncogene proteins in serum
Natural Toxins (mycotoxins, shell-fish
toxins)
Design and implementation of short and long term toxicology
studies using rats or mice to investigate the toxicity and
mechanism of action of natural toxins and food contaminants.
expertise in protocol development in the following
subdisciplines: immunotoxicology and immunoassays,
hematology, clinical chemistry, tissue culture and in vitro
toxicity assays. Methodology includes development and
implementation of enzyme-linked immunosorbant assays (ELISAs)
and standard enzyme assays for clinical endpoints measurement
of platelet function and biochemistry; preparation and
culture of lymphocytes for immunotoxicological endpoints;
maintenance and manipulation of continuous cell lines for in
vitro studies; design, validation and application of in vitro
toxicity assays for a range of endpoints, including cell
death, enzyme induction, dye uptake and membrane transport
Molecular Toxicology
Areas of expertise are molecular biology and protein
chemistry. Areas of interest are molecular toxicology and
molecular properties of antigens. Typically, projects involve
the monitoring of transcription and protein expression of
target genes in isolated tissues and organs as a result of a
potential toxicological event or challenge. Some of the
markers of interest are cytochrome P450 1A1, 1A2, 1B1, 2B1/2,
2E1, 2C11, 3A1, and 4A1; GSTa, GSTb, GSTp, PKC's, cyclin
dependent kinases, cell cycle inhibitors p21 and p27; and
cyclin D and cyclin E. The lab is also involved in protein
isolation and characterization of antibodies and proteins of
interest. Commonly used techniques are: DNA and RNA
isolation; Cloning Of DNA and PCR fragments; PCR , RT-PCR and
differential display PCR; DNA sequencing.; Northern blotting
;Southern blotting ; Western blotting ;Relative quantitation
of target mRNA and proteins via densitometry of RT-PCR
products or western blots; Agarose and acrylamide gel
electrophoresis of DNA and RNA. 1D and 2D SDS-poly acrylamide
gel electrophoresis of proteins; FPLC purification of
proteins
Mutagenicity
A focus on in vitro approaches to studying the
toxicology of food associated chemicals and examining the
biological mechanisms involved. The laboratory has been
primarily involved in assessing test chemicals for mutagenic
activity and effects on DNA damage and repair mechanisms.
Ongoing work includes the development of continuous cell line
based methods to aid in minimizing the use of animal models.
The activities of the laboratory have recently expanded to
include a variety of in vitro assays for evaluating
the neurotoxic and endocrine disruptor activities of test
chemicals. Techniques include cell culture; Chinese hamster
V79/HGPRT mutagenesis assays; Ames
Salmonella mutagenesis assays; assays for DNA adduct
formation, damage removal, strand breakage and DNA repair;
replication; DNA and protein quantification; colony forming
assays; colourimetric and fluorescent viability assays;
radiolabelling uptake assays; molecular biology, construction
of DNA vectors and gene expression techniques; DNA
transfection and reporter gene assays; immunohistochemistry
Biochemical Toxicology,
Pharmacokinetics
Expertise in the field of renal toxicology with an emphasis
on the development and standardization of a program to
evaluate renal function and renal damage following exposure
to nephrotoxicants. In addition, the toxicokinetics of
contaminants may also be evaluated. Interests also include
the study of xenobiotic metabolism with emphasis on a family
of metabolizing enzymes including the cytochrome P450's.
Methodology and techniques include; Determinants of renal
function and/or damage; Urinalysis parameters including
measurement of enzymuria, proteinuria, urinary creatinine and
osmolality; Organic ion transport measurements in renal
cortical slices; Toxicokinetic model of renal clearance;
Cytochrome P450 analysis including assays for specific
isozymes (CYP1A1, CYP2B, CYP3A); Xenobiotic metabolism,
toxicology of chemical mixtures.
Pathology Section
Evaluation of tissue and cellular injury induced by chemical
compounds, natural and/or man made, environmental pollutants,
which enter the food chain or utilized as therapeutic
products. Pathology encompasses the laboratories of
histopathology, neurotoxicologic pathology, haematology and
molecular pathology. A diversified approach is used to
identify the target sites, the nature and extent of
tissue/cellular damage induced by potentially toxic
compounds, their safety margins and potential impact on human
health. The techniques used, are among others:
immunohistochemistry, morphometry, transmission electron
microscopy and molecular biology methodologies. Current
research projects include: sea food toxins, mycotoxins,
dioxins, excitatory amino acids, effects of prenatal exposure
to polyhalogenated aromatic hydrocarbons on brain
development, markers of neural injury and degeneration,
glutamate receptors, application of novel methodology to
toxicologic pathology, circumventricular organs/ autonomic
nervous system and the cardiac conducting system as target
sites for xenobiotic toxicity and cardiotoxicity.
Molecular Pathology
Molecular Toxicology with focus on the heart and brain as
vital target organs for the effect/action of xenobiotics.
Application of molecular biology methodologies to toxicologic
pathology and safety assessment of chemical compounds.
Glutamate receptors in brain and peripheral tissues i.e.
heart, kidney, and testes, as potential mediators of
excitotoxicity. These receptors are differentially localized
to specific cellular types suggesting that they have a
pivotal role in the homeotasis of the organism. Neurotoxicity
of environmental/food toxins using molecular markers for
neural injury. Glutamate, GABA and dopamine receptors in food
safety and toxicity. Developmental neurotoxicology.
Expertise: bacterial genetics, plasmids, DNA sequencing,
construction of genomics banks and species specific probes
for the PGPRs ( plant growth promoting rhizobacteria),
Southerns, extraction of total and mRNA, RT-PCR,
semi-quantitative PCR, Westerns, Northerns, differentially
display of mRNA using RT-PCR, cell culture, immunochemistry,
and in situ hybridization.
Toxicologic Pathology
General Pathology for most animal species, (including Zoo
Animal Diseases, Wildlife- Fish-Diseases.) Comparative
Pathology via collaboration with the Medical School of Ottawa
University; the Ottawa Heart Institute research on
development of ventricular assist devices (artificial Heart
Program); research in conjunction with the University is
carried out in the field of Drug Side Effects, and Drug
Toxicity with emphasis on pathology related to longterm
treatment / exposure. Consulting to the regulatory groups in
the Food Directorate, and in the Therapeutic Products Program
as it pertains to preclinical, and clinical studies.
Current research involves morphometry, histochemistry,
scanning- and transmission electronmicroscopy in a variety of
species of laboratory animals including primates.
Seafood Toxins : Pathologic effects of short, and longterm
exposure, with special emphasis on the study of receptors and
target sites in the nervous- and circulatory system of rats
and monkeys. Light-, and electronmicroscopic studies of
peroxisome proliferation, and phospholipidosis produced by
various classes of chemicals.
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