The Toxicologist - Society of Toxicology

three-dimensional structures and biochemical function is gradual, if it occurs at all,
as any sequence changes are balanced by the need to maintain organism survival
and the intrinsic physical properties of the protein for its function. Protein engineering
and evolution studies suggest that changes in sequences of proteins not related
to known toxicological hazards (i.e., toxins or allergens) will not make a protein
potentially hazardous de novo and will likely exert little effect on biological
function, even though some substitutions are deleterious to protein structure and
function.
1730 ENGINEERING PROTEINS TO IMPROVE BIOLOGICAL
FUNCTION.
S. J. Franklin. Protein Technologies, Monsanto Company, Cambridge, MA. Sponsor:
B. Hammond.
Advances in the field of molecular biology over the last 30 years have greatly enabled
our ability to modify the structure, stability and activity of proteins of interest.
The growth of this “protein design” discipline has resulted in the modification
of numerous proteins resulting in beneficial therapeutic agents, biochemical
reagents, and even enhanced agricultural crops. The activities of such engineered
proteins are determined by the details of their three-dimensional structures. The
tools of molecular biology allow us to refine structure as appropriate, under the
control of the laws of physics. When coupled to high-throughput techniques and
computational analyses, protein design can create hundreds of thousands of proteins,
some of which have improved properties. At the same time, screening and
evaluation of products is an integral part of the process, to minimizing creating proteins
with no function or with less desirable activities. The convergence of these
abilities provides great possibilities to create products that positively impact human
health and nutrition in numerous ways. This talk will highlight the underlying biophysical
principles that guide protein behavior, and advances in protein design that
allow the generation of custom proteins with improved, well-characterized functional
properties.
1731 SAFETY ASSESSMENT OF NOVEL PROTEINS.
J. L. Kough. Biopesticides and Pollution Protection Division, Office of Pesticide
Programs, U.S. EPA, Washington, DC. Sponsor: B. Hammond.
The Environmental Protection Agency registers all pesticides sold in the U.S. under
the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and establishes
safe residue levels under the Federal Food Drug and Cosmetic Act (FFDCA). The
advent of plant transformation technology has led to the production of transgenic
plants with new pesticidal properties. These biopesticides are termed Plant-
Incorporated Protectants (PIPs). This category includes plants produced by introduction
of traits that would not normally be available by traditional plant breeding
methods with sexually compatible relatives. An example would be the integration of
bacterial gene sequences into corn for insect resistance. Most PIPs registered to date
have been proteins. Prior to registration, each PIP is examined to decide what data
are needed to insure that a reasonable certainty of no harm to man and the environment
will result from its use. In general, details of the gene construct and expression
levels of the introduced pesticidal substance, as well as information on the
amino acid similarity to toxins and allergens, the digestibility and stability of proteins
produced and toxicity profiles for humans and non-target species are requested
from the registrant.
1732 EFSA’S UPDATED STRATEGY FOR THE RISK
ASSESSMENT OF GM PLANTS AND DERIVED
FOOD/FEED.
H. A. Kuiper. Chair EFSA GMO Panel, European Food Safety Agency (EFSA),
Parma, Italy. Sponsor: B. Hammond.
The EFSA Guidance Document for the risk assessment of genetically modified
plants and derived food and feed provides guidance for the preparation and presentation
of applications submitted within the framework of Regulation (EC)
1829/2003 on GM food and feed, and of Directive 2001/18/EC on the deliberate
release into the environment of genetically modified organisms (GMOs). The
EFSA’s GMO Panel regularly reviews its guidance to take account of scientific developments
and of experience gained through the risk assessment process. In 2008
the Panel updated its guidance document in the light of experience in the risk assessment
of GMO applications and of the outcome of the Panels’ self-tasking activities.
The changes with respect to the risk assessment of food/feed derived from GM
plants will be highlighted in this presentation. Among others the present draft in-
372 SOT 2011 ANNUAL MEETING
cludes updated guidance on: (i) the experimental design of field trials and the statistical
analysis of the collected data, (ii) toxicity testing of newly expressed proteins
and new constituents other than proteins, and (iii) role of animal feeding trials with
whole GM plant material - based on the report of a related EFSA self tasking activity.
The updated guidance document was also used by the Commission and the
Member States as a basis for the preparation of EC Guidelines.
1733 RISK ASSESSMENT RECOMMENDATIONS FOR
INTRODUCED PROTEINS.
B. G. Hammond. Product Safety Center, Monsanto Company, Saint Louis, MO.
ILSI/IFBiC Task Force 10 was formed to address the role of mammalian toxicology
studies in assessing the safety of the introduced proteins (IP) and the whole foods
from GM crops. This task force is composed of academic, industry and regulatory
agency experts from various world areas. This group addressed in part the history
of safe use (HOSU) concept in food which is a component of the dietary risk assessment
of IP. If a protein has a HOSU in food, this can support the weight of evidence
of its safety for consumption. Some IP will not have a HOSU however, but
that does not necessarily mean that their safety for consumption is uncertain. Some
IP are structurally/ functionally related to proteins that have a HOSU.
Evolutionary divergence of protein families (e.g., enzymes) across different species
has shown that there is considerable variation in amino acid sequence/content, yet
the catalytic site is highly conserved and the enzymes have related functions. Based
on our understanding of protein evolution and learnings from protein engineering,
there is no evidence that changes in amino acid content/sequence impart toxic effects
to proteins that are not known to be toxic. A second aspect of the dietary risk
assessment deals with potential dietary exposure. Crops such as corn and soybeans
are extensively processed into a variety of human foods that often leads to denaturation
and loss of protein function. This has also been demonstrated for IP, such as
enzymes and insect control proteins. IP proteins that have been tested are generally
heat labile and are likely to be denatured by cooking during normal processing
of corn or soy into human food. Thus, toxicology testing of IP without a HOSU
may not be needed if the proteins are structurally/functionally related to those that
have HOSU, and/or there would be negligible dietary exposure to functionally active
IP as they are expected to be denatured during processing of corn or soy into
human foods.
1734 THE SPECTRUM OF SYSTEMS BIOLOGY.
L. Burgoon 1 and W. Mattes 2 . 1 U.S. EPA, Durham, NC and 2 PharmPoint
Consulting, Poolesville, MD.
What is Systems Biology? While being hailed as the most promising approach for
creating breakthroughs in scientific understanding in the wake of the ‘omics crush,
systems biology is a phrase used to describe a multitude of approaches to understanding
and/or predicting biological responses to stimuli. Decades ago systems biology
invoked quantitative metabolic flux modeling, while today it is used to describe
pathway analysis of ‘omic data, quantitative signaling network modeling, the
integration of multiple ‘omic data, and many other approaches. Our panel of experts
are poised to discuss their divergent views of systems biology and will describe
how their research addresses a holistic solution to biologic data. Before concluding
a panel discussion will convene that will provide a more global (i.e., systems) view
of systems biology.
1735 BIOSIMULATION OF DRUG-INDUCED LIVER INJURY.
H. J. Clewell 1 , B. A. Howell 1 , Y. Yang 1 , S. Q. Siler 2 , R. Ho 2 , R. Kumar 2 , A. H.
Harrill 1 , M. E. Andersen 1 and P. B. Watkins 1 . 1 The Hamner Institutes for Health
Sciences, Research Triangle Park, NC and 2 Entelos, Inc., Foster City, CA.
A biosimulation model is being developed to provide a quantitative description of
the key processes involved in drug-induced liver injury: metabolism, reactive
metabolite formation, glutathione depletion and resynthesis, ROS formation, disruption
of energy homeostasis, mitochondrial dysfunction, necrosis, apoptosis, and
tissue regeneration. The initial development of the platform has focused on acetaminophen
(APAP) and includes a whole-body physiologically based pharmacokinetic
(PBPK) model for APAP and its metabolites in the mouse, rat, and human.
The PBPK model is linked to a pharmacodynamic (PD) model describing the reaction
of APAP-derived N-acetyl-p-benzoquinone imine (NAPQI) with glutathione
and the resulting depletion and resynthesis of glutathione. The formation of
NAPQI-adducts with cellular proteins and increased oxidative stress resulting from
glutathione depletion are linked to cellular damage and response. This PBPK/PD