18 research outputs found
Refine and Strengthen SAR-Based Read-Across by Considering Bioactivation and Modes of Action
Structure–activity relationship (SAR)-based read-across
is an important and effective method to establish the safety of a
data-poor target chemical (structure of interest (SOI)) using hazard
data from structurally similar source chemicals (analogues). Many
methods use quantitative similarity scores to evaluate the structural
similarity for searching and selecting analogues as well as for evaluating
analogue suitability. However, studies suggest that read-across based
purely on structural similarity cannot accurately predict the toxicity
of an SOI. As mechanistic data become available, we gain a greater
understanding of the mode of action (MOA), the relationship between
structures and metabolism/bioactivation pathways, and the existence
of “activity cliffs” in chemical chain length, which
can improve the analogue rating process. For this purpose, the current
work identifies a series of classes of chemicals where a small change
at a key position can result in a significant change in metabolism
and bioactivation pathways and may eventually result in significant
changes in chemical toxicity that have a big impact on the suitability
of analogues for read-across. Additionally, a series of SAR-based
read-across case studies are presented, which cover a variety of chemical
classes that commonly link to different toxic endpoints. The case
study results indicate that SAR-based read-across can be refined and
strengthened by considering MOAs or proposed reactive metabolite formation
pathways, which can improve the overall accuracy, consistency, transparency,
and confidence in evaluating analogue suitability
Refine and Strengthen SAR-Based Read-Across by Considering Bioactivation and Modes of Action
Structure–activity relationship (SAR)-based read-across
is an important and effective method to establish the safety of a
data-poor target chemical (structure of interest (SOI)) using hazard
data from structurally similar source chemicals (analogues). Many
methods use quantitative similarity scores to evaluate the structural
similarity for searching and selecting analogues as well as for evaluating
analogue suitability. However, studies suggest that read-across based
purely on structural similarity cannot accurately predict the toxicity
of an SOI. As mechanistic data become available, we gain a greater
understanding of the mode of action (MOA), the relationship between
structures and metabolism/bioactivation pathways, and the existence
of “activity cliffs” in chemical chain length, which
can improve the analogue rating process. For this purpose, the current
work identifies a series of classes of chemicals where a small change
at a key position can result in a significant change in metabolism
and bioactivation pathways and may eventually result in significant
changes in chemical toxicity that have a big impact on the suitability
of analogues for read-across. Additionally, a series of SAR-based
read-across case studies are presented, which cover a variety of chemical
classes that commonly link to different toxic endpoints. The case
study results indicate that SAR-based read-across can be refined and
strengthened by considering MOAs or proposed reactive metabolite formation
pathways, which can improve the overall accuracy, consistency, transparency,
and confidence in evaluating analogue suitability
Framework for Identifying Chemicals with Structural Features Associated with the Potential to Act as Developmental or Reproductive Toxicants
Developmental
and reproductive toxicity (DART) end points are important
hazard end points that need to be addressed in the risk assessment
of chemicals to determine whether or not they are the critical effects
in the overall risk assessment. These hazard end points are difficult
to predict using current in silico tools because of the diversity
of mechanisms of action that elicit DART effects and the potential
for narrow windows of vulnerability. DART end points have been projected
to consume the majority of animals used for compliance with REACH;
thus, additional nonanimal predictive tools are urgently needed. This
article presents an empirically based decision tree for determining
whether or not a chemical has receptor-binding properties and structural
features that are consistent with chemical structures known to have
toxicity for DART end points. The decision tree is based on a detailed
review of 716 chemicals (664 positive, 16 negative, and 36 with insufficient
data) that have DART end-point data and are grouped into defined receptor
binding and chemical domains. When tested against a group of chemicals
not included in the training set, the decision tree is shown to identify
a high percentage of chemicals with known DART effects. It is proposed
that this decision tree could be used both as a component of a screening
system to identify chemicals of potential concern and as a component
of weight-of-evidence decisions based on structure–activity
relationships (SAR) to fill data gaps without generating additional
test data. In addition, the chemical groupings generated could be
used as a starting point for the development of hypotheses for in
vitro testing to elucidate mode of action and ultimately in the development
of refined SAR principles for DART that incorporate mode of action
(adverse outcome pathways)
Framework for Identifying Chemicals with Structural Features Associated with the Potential to Act as Developmental or Reproductive Toxicants
Developmental
and reproductive toxicity (DART) end points are important
hazard end points that need to be addressed in the risk assessment
of chemicals to determine whether or not they are the critical effects
in the overall risk assessment. These hazard end points are difficult
to predict using current in silico tools because of the diversity
of mechanisms of action that elicit DART effects and the potential
for narrow windows of vulnerability. DART end points have been projected
to consume the majority of animals used for compliance with REACH;
thus, additional nonanimal predictive tools are urgently needed. This
article presents an empirically based decision tree for determining
whether or not a chemical has receptor-binding properties and structural
features that are consistent with chemical structures known to have
toxicity for DART end points. The decision tree is based on a detailed
review of 716 chemicals (664 positive, 16 negative, and 36 with insufficient
data) that have DART end-point data and are grouped into defined receptor
binding and chemical domains. When tested against a group of chemicals
not included in the training set, the decision tree is shown to identify
a high percentage of chemicals with known DART effects. It is proposed
that this decision tree could be used both as a component of a screening
system to identify chemicals of potential concern and as a component
of weight-of-evidence decisions based on structure–activity
relationships (SAR) to fill data gaps without generating additional
test data. In addition, the chemical groupings generated could be
used as a starting point for the development of hypotheses for in
vitro testing to elucidate mode of action and ultimately in the development
of refined SAR principles for DART that incorporate mode of action
(adverse outcome pathways)
Control group and DEHP experimental group cryptochidism group compared to control group of biological process down regulation of pathway analysis.
<p>Control group and DEHP experimental group cryptochidism group compared to control group of biological process down regulation of pathway analysis.</p
Quantitative real-time PCR Primers for DNA methytransferases and β-actin.
<p>Quantitative real-time PCR Primers for DNA methytransferases and β-actin.</p
Control group and DEHP experimental group offspring (F1-F4) male rat’s DNMT3a expression.
<p>High expression of dnmt1 in the F1 and F2 generation, F3 significantly reduced and F4 generation basic without expression. A:Control;B:F1;C:F2;D:F3 E:F4 (Ă—200)</p
Three kinds of DNA methyltransferase mRNA expression.
<p>* compared with control group, P<0.05</p><p>Three kinds of DNA methyltransferase mRNA expression.</p
Control group and DEHP experimental group offspring (F1-F4) male rat’s testicular histology expression.
<p>A:F1;B:F2;C:F3;D:F4 E: Control (200Ă—).</p