High-throughput H295R steroidogenesis assay: utility as an alternative
High-throughput H295R steroidogenesis assay: utility as an alternative and a statistical approach to characterize effects on steroidogenesis Derik E. Haggard ORISE Postdoctoral Fellow National Center for Computational Toxicology Computational Toxicology Communities of Practice Dec. 14th, 2017 The views expressed in this presentation are those of the author and do not necessarily reflect the views or policies of the U.S. EPA Outline
Background Objectives Assay Background Methods and Results 1. Evaluation of the HT-H295R assay 2. Development of a quantitative prioritization metric for the HTH295R assay data Summary and Conclusions 2 Steroid Hormone Biosynthesis & Metabolism Proper steroidogenesis is essential: In utero for fetal development
In adults for reproductive function Disruption can result in congenital adrenal hyperplasia, sterility, prenatal virilization, salt wasting, etc. >90% of steroidogenesis occurs in the gonads Leydig cells (males) or follicular cells (females) Adrenal gland (corticosteroids) 3 https://www.pharmacorama.com/en/Sections/Androgen_steroid_hormones.php US EPA Endocrine Disruptor Screening Program (EDSP) EDSP mandated to screen chemicals for endocrine activity (estrogen, androgen, thyroid)
Initial tiered screen relied on low-throughput assays Modernization of EDSP (EDSP21) to use high-throughput and computational methods Prioritize the universe of EDSP chemicals for endocrine bioactivity Altering hormone levels via disruption of biosynthesis or metabolism can also contribute to endocrine disruption This is difficult to assay in vitro Current Tier 1 Assay: OECD-validated H295R steroidogenesis assay 4 https://www.epa.gov/sites/production/files/2015-04/documents/edsp_dix_ord_communities_of_practice_04_23_15_f.pdf
Objective 1 EPA and OECD test guidelines for the H295R steroidogenesis assay to detect potential perturbation of estradiol (E2) and testosterone (T) synthesis are designed for low-throughput screening Objective 1: Compare the recently developed high-throughput H295R assay (HT-H295R; refer to Karmaus et al., 2016) to the OECD test guideline assay 5 Objective 2 The HT-H295R assay includes measurement of 13 hormones to represent the steroidogenesis pathway Objective 2: Develop a summary measure that integrates these multidimensional data to quantify pathway perturbation and indicate relative priority for further screening and/or evaluation of chemicals for potential
effects on steroidogenesis 6 High-throughput Steroidogenesis Assay in H295R (HT-H295R) Assay contract with Cyprotex (formerly CeeTox) and OpAns Adrenocortical carcinoma cell line All of the major biosynthetic enzymes for steroidogenesis present Characteristics of undifferentiated fetal adrenal cells Change steroid hormone output based on
culturing conditions Measure production of up to 13 hormones/intermediates HPLC-MS/MS 7 HT-H295R Assay Method Concentration-Response Plate Cells (overnight) H295R cells seeded to ~50%
confluency 10 M FSK (48 hrs) pre-treatment: stimulate steroidogenesis Chemical (48 hrs) 6 conc. chemical treatment MTT
Cytotox Media to OpAns Cell viability (70%) HPLC-MS/MS quantification of hormones 8 Objective 1: Evaluation
of the HT-H295R Assay Comparison of results to the reference chemicals used for the OECD interlaboratory validation 9 Does the HT-H295R Assay Replicate Results of the OECD H295R Assay? Comparison to the reference chemicals used in the OECD inter-laboratory validation study (Hecker et al., 2011) Major differences between assays: Primary Difference Number of chemicals (multiple concentrations)
Cell culture Cell viability threshold Number of steroids measured Quantification method OECD H295R 28 HT-H295R 656 24 hr. plating, then 48 hr. exposure (total = 72 hr.)
HT-H295R Data Analyzed Using Methods from OECD Interlaboratory Validation (Hecker et al. 2011) ANOVA and Dunnetts with = 0.05 DMSO control data from the same plate were used for the sample comparison Criteria for positive: 2 consecutive concentrations had to produce results significantly different from control Or, positive at the max concentration that maintained 70% cell viability 1.5-fold change from DMSO control was applied 11
Constructing Confusion Matrices 10/12 core reference chemicals shared Tested in 5 labs for the inter-laboratory validation 15/16 supplemental reference chemicals shared Tested in 2 labs for the inter-laboratory validation OECD inter-laboratory results were equivocal and removed if: 2 of 5 labs failed to report a LOEC (core reference chemicals) or 1 of 2 labs failed to report a LOEC (supplemental reference chemicals) 12 Confusion Matrices Demonstrate
Good Sensitivity, Specificity, and Accuracy for Reference Chemicals. 13 Agreement Among Labs in the Inter-laboratory Validation For any effect on testosterone: Average concordance among labs was 0.88, 0.91, and 0.90 for the 12 core reference chemicals only, the 16 supplemental reference chemicals only, and the entire set. For any effect on estrogen: Average concordance among labs was 0.95, 0.84, and 0.89 for the 12 core reference chemicals only, the 16 supplemental reference chemicals only, and the entire set.
Similar concordance between the HT-H295R and the OECD inter-laboratory validation 14 Objective 2: Development of a Quantitative Prioritization Metric for the HT-H295R Assay Simplifying an 11-dimensional problem to 1-dimension for prioritization 15 HT-H295R Data for Development of a Prioritization Metric 13 hormones measured in HT-H295R
Pregnenolone and DHEA were often measured LLOQ (53.1% and 69.5% of all measurements) and were excluded 16 Example of the 11-dimensional Results for Prochloraz 17 What Can We Learn from the Other Steroid Hormone Data Available in HT-H295R?
Additional evidence for disruption of estrogen or androgen synthesis (e.g., estrone and androstenedione disruption) Putative mechanisms of steroidogenesis disruption Information about effects on other specific steroid hormone classes, namely the corticosteroids and progestagens 18 (Asser et al., 2014; Nielsen et al., 2012; Tinfo et al., 2011; Zhang et al., 2011) Chemicals Screened in HT-H295R Had a Variety of Effects on Steroid Biosynthesis 629 chemical samples
(out of 654 total) affected production 1 steroid hormone class. 19 Developing a Prioritization Metric for HT-H295R Goal: Integrate HT-H295R data into a single value which estimates the overall magnitude of perturbation of steroidogenesis in H295R cells Challenges: Multivariate dataset (11 hormone measures per chemical per concentration)
Hormones are measured from the same experimental well Concentrations of steroid hormones and intermediates are often interdependent 20 A Simple Solution: Euclidean Distance Euclidean distance is a measure that can be used to estimate the distance between two points in multivariate space: = (
1 ) ( 1) Where: yc is the vector of natural log-transformed steroid hormone concentrations at the cth concentration y1 is the vector of natural log-transformed steroid hormone concentrations for the DMSO control 21 http://mccormickml.com/2014/07/21/mahalanobis-distance/ Limitations of Euclidean
Distance Conceptual Example: Hormone A and B show positive covariance conc 2 and conc 3 have the same Euclidean distance from conc 1 Even though conc 3 is more standard deviations, i.e. a more extreme distance from conc 1 than conc 2 22 The Residuals for Some Steroid Hormones in HT-H295R are Correlated Highly correlated residuals:
Estrone and E2 (Pearsons R = 0.75) Androstenedione and T (R = 0.66) Cortisol and 11-deoxycortisol (R = 0.69) Euclidean distance not appropriate for HT-H295R 23 Removing Residual Covariance Using the Mahalanobis Distance The Mahalanobis distance will adjust for covariance among the hormone measures at each concentration Conceptual Example: Scaled and rotated Hormone A and B so
that the error distribution is no longer correlated conc 3 is now ~4 times further away from conc 1 as conc 2 24 Mahalanobis distance To calculate the Mahalanobis distance, the response at each concentration of a test chemical was considered as a point in 11dimensional space Each axis corresponds to the natural logarithm of the measured concentration of one of the hormones included in this analysis Method in brief: 1. Calculate the hormone fold-changes for each test chemical concentration compared
to the DMSO control 2. Estimate the covariance matrix that characterizes both the noise variance and correlation among hormone levels across all of the HT-H295R data 3. Scale the computed Mahalanobis distance at each concentration of chemical screened by the number of hormones measured to give the mean Mahalanobis distance 25 The Mean Mahalanobis Distance (mMD) The mMd for a chemical at each concentration relative to the DMSO control across the steroidogenesis pathway was computed as:
= ( ) ( )/ h Where: yc is the vector of natural log-transformed steroid hormone concentrations at the cth concentration y1 is the vector of natural log-transformed steroid hormone concentrations for the DMSO control Nh is the number of hormones with measurements for this chemical -1 is the estimate of the inverse covariance matrix 26
Covariance Matrix Estimation Fit multivariate linear model (per block) using ln-transformed hormone concentrations Matrix of fit residuals for data from all plates within each block were used to estimate a variance and covariance matrix Unweighted average of the covariance matrices across blocks = full pooled 11 X 11 covariance matrix used for the mMd calculation 27 Ranking Chemicals Using mMd The maximum mMd (maxmMd) is the maximum of the set of mMd values
computed for all concentrations of a test chemical Overall magnitude of effect of a test chemical on the steroidogenesis pathway As mMd generally increases with increasing concentration, a greater maxmMd should indicate: Increasing concentration of chemical Increased potency (i.e., activity at lower concentrations) Critical limit: Derived to distinguish mMd values greater than what would result from noise Accounts for multiple comparisons arising from comparing each concentration to the control 28
Example: Strong effects maxm Md ---- critical limit ---- 1.5-fold vehicle control Mifepristone strongly modulated progestagens with significant effects on progesterone and OH-progesterone and moderate but non-significant trends on corticosteroids and androgens, resulting in a relatively high adjusted maxmMd of 33. 29 Example: Negative
---- critical limit maxm Md ---- 1.5-fold vehicle control Benfluralin provides an example of a chemical with a negative pathway result, with no significant concentration-response for the mMd values, as the maxmMd failed to exceed the critical limit (adjusted maxmMd of -0.14). 30 maxmMd was Reproducible and Quantitatively Distinguished
Chemicals with Larger Effects Bisphenol A Negative maxmMd but variable steroid EDS v. finasteride; same hit count, very different maxmMd 31 Reproducibility of the maxmMd
107 chemicals were replicated in > 1 block, with maxmMd ranging 1-35 for this subset Median maximum difference between maxmMd values across blocks 1.47 units on the arithmetic scale 88% of the maxmMd pathway responses replicated, with failures largely attributable to borderline activity (contrast with 65% recall for OECD ANOVA logic) 32 maxmMd Pathway Responses Matched the OECD Inter-laboratory Reference Chemical Activity
Positive maxmMd pathway response (blue) was observed when signif. effects on E2 and T were observed in LT-H295R MaxmMd value separated strong modulators (e.g., mifepristone, prochloraz, ketoconazole, danazol, letrozole) from moderate (e.g., atrazine, molinate, di(2-ethylhexyl-phthalate) and non-active (e.g., EDS) Reference chemical effects on progestagen and corticosteroid biosynthesis mostly unknown 33 Summary and Conclusions
34 Evaluation of HT-H295R assay This detailed, performance-based comparison highlights good concordance of results, with accuracies that range 0.80 0.95 for effects on E2 and T Agreement among the labs in the inter-laboratory validation generally approached 90% Minor disagreement between the HT-295R and LT-H295R results occurred for chemicals with borderline activity or activity at high concentrations 35 maxmMd May Be Useful for
Prioritization and EDSP Weightof-evidence Applications Calculation of the set of mMd values reduced an 11-dimensional question to a single dimension Selection of the maxmMd appeared to provide a reproducible, quantitative approximation of the magnitude of effect on steroidogenesis Quantitatively distinguished weak, moderate, and strong effects on one or more hormones in the pathway Given an mMd at each concentration, a modeled mMd at the critical limit, or the lowest concentration corresponding to a significant mMd, could be used: As a concentration at which to review effects on specific hormones As a lowest observable effect concentration 36
Acknowledgements Katie Paul Friedman (mentor) Woody Setzer Richard Judson Agnes Karmaus Matt Martin ORISE program
Evaluation of the HT-H295R assay Compare HT-H295R to the OECD interlaboratory results Refer to Karmaus et al. (2016) for assay background and methods Implement staged screening approach (Haggard et al. (accepted) Toxicological Sciences.)
Development of prioritization metric Compress data from 11 steroid hormone panel Analyze data per the OECD TG to enable comparison Develop prioritization metric
Evaluate the concordance of E2 and T responses Evaluate prioritization metric 41 Staged Screening with HT-H295R Assay Maximized screening resource efficiency # steroid hormones affected in single concentration (along with other considerations) were used to select 656 chemicals for multi-concentration screening.
A maximum testable concentration (MTC) was determined (viability 70%). Single concentration screening at the MTC was conducted for most of the screened 42 space. Karmaus et al. (2016) Toxicological Sciences. PMID 26781511 Brief review of covariance matrix estimation: More information Fit multivariate linear model (per block) using ln-transformed hormone concentrations. Matrix of fit residuals for data from all plates within each block were used to estimate a variance and covariance matrix.
If any data were missing, the hormone measure was dropped from that block prior to linear model fitting (only for 1/8 blocks, i.e. 81 chemicals, proceeded with 9/11 hormones). Unweighted average of the 8 block-specific covariance matrices = full pooled 11 X 11 covariance matrix used for the mMd calculation. The condition for missing data was not reportable flagged by the vendor, likely indicating a lost or dropped sample. During the sample analysis process, samples were flagged as not-detected or not-quantifiable when the sample was available, but the steroid hormone analyte was below the LLOQ; in such cases, a surrogate value of the LLOQ/2 was substituted for analyses herein (CDC, 2009; Hornung and Reed, 1990). Missing data affected only one of the eight blocks, which contained some missing data for estrone and E2, representing 81 unique test chemicals. In this case, the computed covariance matrix for this block included only nine of the 11 steroid hormone analytes. 43
Critical value for positive steroidogenesis pathway results Critical value: Derived to distinguish mMd values greater than what would result from noise. Accounts for multiple comparisons arising from comparing each concentration to the control. Similarity between mMd and Hotelling T2 Hotelling T2 used to compare two groups with multiple measures. In this analysis, within-group variance-covariance matrix is used instead, using method of Nakamura and Imada (2005). Analogous to adjusting for multiple comparisons for univariate tests such as the Dunnetts procedure. Critical value derived for approximate Type I error of 0.01 and is related to
the number of hormones with data for each chemical. 44 Most of the MTC data corresponded to cell viability of 80% 35/671 samples screened in multi-concentration had 70% < viability < 80% - - - 5* baseline median absolute deviation for the Slide 45 of X
The maxmMd distribution for this dataset ---- median = 3.52 Slide 46 of X Concentration at which the Hill fit of the mMd data intersects with the critical value for a given chemical The maxmMd generally indicates potency Spearman-based trend analysis Slide 47 of X
The maxmMd correlates with the AUC AUC was calculated from the mMd vs. concentration for each date-chemicalplate combination. Slide 48 of X Limitations Lack of reference chemical information on the full steroidogenesis pathway No consideration for mitochondrial toxicity Potentially limited metabolic capacity of the assay
H295R do express xenobiotic metabolizing enzymes, but they may not generate all relevant chemical metabolites Current libraries are restricted to DMSO-soluble chemicals Future plans include expanding chemical testing to a water-soluble library 49
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